Economist, Jean-Yves Weigel
email: jean-yves.weigel@ird.fr

CANARY CURRENT LARGE MARINE ECOSYSTEM (CCLME) PROJECT

Keywords: Social-ecological system, climate alterations, fishers communities, economic vulnerabilities, capabilities, societal resilience, governance

This presentation is focused on a methodological proposal for adaptation of social-ecological systems governance allowing to reduce vulnerabilities and to increase the capabilities of fishers communities impacted by environmental alterations. A five-step approach is developed: the assessment of environmental alterations on communities, the categorization of social-environmental vulnerabilities of communities, the assessment of capabilities, the pointing out of societal resilience factors, the adaptation of the social ecological systems governance to face up to environmental alterations with the analysis of effects of national or regional public policies, with the analysis of impacts and adaptability of local governance facing environmental alterations, with a special focus on the capacity of protected areas to be an option for a better adaptation of social-ecological systems governance facing environmental alterations. A method is described: the observation units, a compilation of documents relating to livelihoods strategies of selected communities, a compilation of development plans relating to public policies and of institutional and judicial texts on local governance of selected social-ecological systems, a completion of the social-ecological governance analysis framework by defining the problems that governance raises, a completion of village monographs, a carrying out of an household sample-based survey relating to the perception of environmental alterations, the categorization of socioenvironmental vulnerabilities, household functionings and capabilities, societal resilience factors, a mapping of environmental alterations and of communities socio-environmental vulnerabilities. Two possible case studies are presented: the Imraguen social-ecosystem of the Banc d'Arguin National Park, the Bamboung marine protected area social-ecosystem.

Some definitions

A social-ecological system is characterized by dynamic interactions between an ecosystem and human communities. The notion of social-ecological system is highly pertinent when the communities are greatly dependent on environmental conditions and natural resources for their livelihoods [START_REF] Berkes | Linking Social and Ecological Systems. Management Practices and Social Mechanisms for Building Resilience[END_REF][START_REF] Walker | Resilience management in social-ecological systems: a working hypothesis for a participatory approach[END_REF][START_REF] Ostrom | A general framework for analyzing sustainability of social-ecological systems[END_REF]. The governance is the whole of public and private interactions initiated to solve societal problems, to create societal opportunities. The governance includes the formulation and application of principles guiding those interactions. (Kooiman and Chuenpagdee, 2005). Societal includes everything which refers to the structure, the organization or the functioning of a society The functioning is an achievement of a person: what she or he manages to do or be, a functioning refers to the use a person makes of the commodities at his or her command (Sen, 1999) A capability reflects a person's ability to achieve a given functioning (doing or being.) (Sen, 1999) The livelihoods: the whole of capabilities, assets (including both material and social resources) and activities required for a means of living (Carney, 1998).

Utility and objective of this approach

Utility: a concept tool to assess the impacts of environmental alterations on human communities because the use of ecosystem goods and services involves endogenous modifications or modifications resulting from external forcing to which the communities have to adapt. Objective of this approach: a methodological proposal for adaptation of social-ecological systems governance allowing to reduce vulnerabilities and to increase the capabilities of fishers communities impacted by environmental alterations.

A five-step approach

The assessment of environmental alterations on communities

A focus on the modifications of ecosystem goods and services linked to these alterations A retrospective livelihoods strategies analysis (thirty years) taking in count the environmental variations and focused on the evolution of sensibility points This assessment helps to identify and localize the impacted communities, the type and level of this impact for each main livelihood

The categorization of social-environmental vulnerabilities of communities

A description of the chain of causes, and of the hierarchization of causes in distinguishing between distant "root" causes and unsafe conditions [START_REF] Wisner | At risk: natural hazards, people's vulnerability and disasters[END_REF] The drawing of a vulnerability matrix proposed by [START_REF] Cannon | Vulnerability analysis and disasters[END_REF] which points out the components of the vulnerabilities, the variables, the socio-economic and technical determinants.

The assessment of livelihoods vulnerability indexes (Hahne et al, 2009) and economic vulnerability indexes of households (Devereux, 2001;[START_REF] Ch | Are fishers poor or vulnerable ? Assessing economic vulnerability in small-scale fishing communities[END_REF]

The assessment of capabilities

This assessment is linked to the diverse combinations of functionings that an individual or an household can implement [START_REF] Sen | Repenser l'inégalité[END_REF], for example in front of environmental alterations. Two major groups of components have to be taken in count : -the perceptions and general socio-economic consequences of these alterations -the revenue variability, the activity diversification, the level of insertion within social networks, the external help (mutual aid and monetary transfers), the formulation of projects for the future (Gondard-Delacroix et Rousseau, 2005)

The pointing out of societal resilience factors

The drawing of a DROP model (Disaster Relience of Place Model) which helps to have a better understanding of the resilience of a community facing natural disasters including environmental risks or alterations [START_REF] Cutter | A place-based model for understanding community resilience to natural disasters[END_REF]. Societal resilience is defined as the capacity of a social system to react facing to alterations, risks or disasters. We can point out two steps for the research effort: -the identification of resilience factors in distinguishing between inherent resilience (diversification of activities, informal insurance mechanisms, free loans, monetary transfers) and the adaptive resilience (decrease of inputs etc.) -the identification of resilience indicators [START_REF] Schneiderbauer | Social levels and hazard (in)dependence in determining vulnerability[END_REF][START_REF] Paton | Disaster resilience: an integrated approach[END_REF].

The adaptation of the social ecological systems governance to face up to environmental alterations

The analysis of effects of national or regional public policies considered as driving forces. The study of structural effects of national or regional public policies on social-ecological systems governance has to be focused on the consequences of development plans. The analysis of impacts and adaptability of local governance facing environmental alterations. The study of modalities of local governance adaptability has to point out the failures, the various answers depending of the type, the extent and consequences of alterations [START_REF] Ostrom | A general framework for analyzing sustainability of social-ecological systems[END_REF][START_REF] Anderies | A framework to analyse the robustness of socialecological systems from an institutional perspective[END_REF]. A special focus on the capacity of protected areas to be an option for a better adaptation of social-ecological systems governance facing environmental alterations

A method

The observation units are the household and the village community as an aggregation of households having in share the same social-ecological system A compilation of documents relating to livelihoods strategies of selected communities to point out sensibility points as observed during the last thirty years A compilation of development plans relating to public policies A compilation of institutional and judicial texts on local governance of selected socialecological systems, of activity reports from institutions involved in local governance A completion of the social-ecological governance analysis framework by defining the problems that governance raises, classifying the actors of governance, describing the norms which governance complies with, identifying nodal points where the actors' strategies confront, reconstructing the process having led to the governance system A completion of village monographs on the environmental alterations, socio-environmental vulnerabilities, functionings and capabilities, as well as societal resilience factors at the level of the community A carrying out of an household sample-based survey relating to the perception of environmental alterations, the categorization of socio-environmental vulnerabilities, household functionings and capabilities, societal resilience factors Mapping of environmental alterations, and of communities socio-environmental vulnerabilities

Case studies in West Africa

 The Imraguen social-ecosystem and the governance of the Banc d'Arguin National Park

As far as the coastal and maritime domain is concerned, the PNBA is characterized topographically by a continent-ocean interface with little relief, as the Saharan desert disappears into a fairly shallow marine area (5 metres of water at 50 km distance from the coast). From a hydrological point of view, the subsequent rising to the surface of the colder deep waters which are rich in mineral and organic nutritional elements (upwelling), engenders a high level of biological productivity.

As far as the terrestrial domain is concerned, all the different types of desert landscape are represented in the Park: areas of quick dunes (ergs), strings of North-east/south-west facing dunes made up of barkanes, vast groups of stable ogolian dunes, interdunars, former oued beds covered in vegetation and overthrusting zones, sandstone slabs and limestone ridges, evaporation basins in the salty clayey-sandy soil. Despite the prevalent aridity of the area, there is an astonishing variety of flora. Pastoralism has always been the main activity of the populations that inhabit this area from time to time in keeping with the fluctuations of the pasturable areas. However, a small group of multi-ethnic people called Imraguens, who are estimated to number 1 500, have turned towards the exploitation of fishing resources. These people began fishing according to a seasonal rhythm (mullet fishing), then, more recently all through the year as a result of the sedentarization phenomenon begun in the middle of the 20 th century.

In the case of Banc of Arguin, powers regulating access are deferred to the administration of PNBA through a deliberation and decision making process, which is, on the one hand, tribal customary (jama a) and gathers members of different statuses according to codified rules, and on the other hand, relevant to participatory and communal development approach (discussion workshops). A hierarchical model with a predominance of the paradigm of authority characterizes the governance of the Parc National du Banc d'Arguin (PNBA), as the State is placed at the center of decisions, and acts in collusion with the tribal hierarchies, which tends to reduce or exclude the depending populations from the management, even if they take part in the deliberations which remain quite theoretical.

 The Bamboung marine protected area social-ecosystem and its governance

The history of the populating of the Bamboung MPA emphasizes the fact that this region was only relatively recently populated. Thus there was a relatively homogenous population until the XIXth Century, but at the beginning or the XXth Century there was a considerable influx of immigrants and this continued up until the 1950's. This explains the ethnic diversity that is to be found. In contrast to this, the available data shows that the roots of the Seerer identity, and those of the few Socés who see themselves as Nyominka, (agricultural fishermen who live near water) are based either on lifestyle or ethnic belonging.

In view of the diverse lifestyles and ethnic groups there is also the difficulty of the emergence of the identity of resident of this MPA. This may be used to legitimize the regulations concerning the sustainable exploitation and valorization of the natural renewable resources. Some of the means of traditional management of the land can be seen as components in the local governance of this marine and coastal protected area. Firstly, in the oldest Seerer or Socé villages there is the recognition of the traditional mastery of land and sea. This is possessed by the Alcalis (masters of land and sea) and is accompanied by the power to allocate the use of cultivable land and the claim to village rights over part of the sound and some of the bolongs (channels). In almost all the tribal traditions, there is the concession of a right to use land and there are also bans on the use of certain resources. This shows that the natural environment is managed as an integral part of the traditional cosmogony: in certain villages and in the eyes of some inhabitants land trees and animals are still considered to be major divinities or sacred things. Beliefs linked to the natural environment and to indigenous knowledge (naturalistic or other) make up the roots of Seerer or Socé identity. On which are traditionally decreed certain practices or bans which induce the conservation of natural renewable resources either deliberately or by chance. Nevertheless, pressure from the demand for smoked fish, and for wood from the mangrove (for fish smoking, construction and cooking) and the arrival of new immigrants makes the application of these traditional environmental regulations more and more problematic for the MPA.

In the case of Bamboung community-based marine protected area , powers regulating access are exercised both by decentralized services of the State and by rural communities creating an overlapping of responsabilities. The absence of a clear designation of a leader institution in charge of the management of this MPA explains only partially the existing situation. These are rival legitimate interests, which reveal the difficulty to hang together the paradigms of authority and of mutual confidence, that characterize the governance of the Bamboung community-based marine protected area In fact, the numerous bodies producing standards and regulations tend to create problems for the regulation of the access to renewable natural resources.


Y Almadori

L Alvarez

R Le Parc

R Aznar

F Fossard

A Loiseau

B Jousselme

S Campidelli

P Hermet

A Belhboub

A Rahmani

T Saito

J-L Bantignies

Chromophore Ordering by Confinement into Carbon Nanotubes

Keywords: Supramolecular organization, Single wall carbon nanotubes, Dimethyl-quatertiophene, Raman, TEM

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Introduction

Single-walled carbon nanotubes (NTs) have a one-dimensional hollow space varying from 0.4 to 2.0 nm and that can encapsulate various molecules. [START_REF] Khlobystov | Molecules in Carbon Nanotubes[END_REF] In these nanohybrid systems, the physical properties of the molecules are supposed to be strongly influenced by their confinement in the one-dimensional cavity and by their specific interactions. [START_REF] Hornbaker | Mapping the One-Dimensional Electronic States of Nanotube Peapod Structures[END_REF][START_REF] Campestrini | Investigation of the Inner Environment of Carbon Nanotubes with a Fullerene-Nitroxide Probe[END_REF] For example, members of the fullerene family inserted inside nanotubes give rise to π-π interactions which are expected to stabilize the guest-host structures. [START_REF] Smith | Encapsulated C 60 in Carbon Nanotubes[END_REF] Calculations have also suggested that confinement of molecules inside NTs can induce structural phase transitions not seen in the bulk phase. [START_REF] Hummer | Water Conduction through the Hydrophobic Channel of a Carbon Nanotube[END_REF][START_REF] Kim | Encapsulation and Polymerization of Acetylene Molecules inside a Carbon Nanotube[END_REF][START_REF] Guan | Polymorphic Structures of Iodine and Their Phase Transition in Confined Nanospace[END_REF][START_REF] Chorro | 1D-Confinement of Polyiodides inside Single-Wall Carbon Nanotubes[END_REF] Functionalization of nanotubes with organic molecules has attracted significant attention owing to the possibility to modulate NTs properties. [START_REF] Balasubramanian | Chemically Functionalized Carbon Nanotubes[END_REF] These molecules have been envisaged for optoelectronics [START_REF] Yanagi | Light-Harvesting Function of Beta-Carotene inside Carbon Nanotubes[END_REF] or electron-transport devices [START_REF] Shimada | Ambipolar Field-Effect Transistor Behavior of Gd@C-82 Metallofullerene Peapods[END_REF] as they display outstanding photophysical properties. Unfortunately, they often suffer from low stability and poor electrical characteristics. [START_REF] Yanagi | Light-Harvesting Function of Beta-Carotene inside Carbon Nanotubes[END_REF] Thus, endohedral functionalization is an efficient way to overcome these drawbacks. One advantage of the encapsulation is that the nanotube protects the internal organic molecules from photo degradation and attacks by external reactive species, thereby preventing undesirable alteration of the organic molecules. [START_REF] Yanagi | Highly Stabilized Beta-Carotene in Carbon Nanotubes[END_REF] Recently, several experimental works dealt with the encapsulation of oligothiophene derivatives (oTh) into NTs (oTh@NT). [START_REF] Loi | Encapsulation of Conjugated Oligomers in Single-Walled Carbon Nanotubes: Towards Nanohybrids for Photonic Devices[END_REF][START_REF] Kalbac | Sexithiophene Encapsulated in a Single-Walled Carbon Nanotube: An in Situ Raman Spectroelectrochemical Study of a Peapod Structure[END_REF][START_REF] Alvarez | Charge Transfer Evidence between Carbon Nanotubes and Encapsulated Conjugated Oligomers[END_REF] Indeed, these systems are particularly interesting as the π conjugation of the thiophene molecules provides nonlinear optical properties and intrinsic electrical conductivity. [START_REF] Brédas | Bipolarons, and Solitons in Conducting Polymers[END_REF][START_REF] Swager | The Molecular Wire Approach to Sensory Signal Amplification[END_REF][START_REF] Mcquade | Conjugated Polymer-Based Chemical Sensors[END_REF][START_REF] Kertesz | Conjugated Polymers and Aromaticity[END_REF][START_REF] Chen | Nucleus-Independent Chemical Shifts as an Aromaticity Criterion[END_REF] Recent DFT calculations [START_REF] Orellana | Terthiophene in Zigzag Carbon Nanotubes: Density Functional Calculations[END_REF] reported that the electronic states added by the terthiophene molecules inserted into carbon nanotubes would give rise to original optical effects and non radiative relaxation from excited states. Concerning the structure of the nanohybrid material, Yamashita et al. predict that internal thiophene oligomers prefer to be located near the walls of the armchair nanotubes rather than close to the axis. [START_REF] Yamashita | The Role of Weak Bonding in Determining the Structure of Thiophene Oligomers inside Carbon Nanotubes[END_REF][START_REF] Yumura | Modulating the Electronic Properties of Multimeric Thiophene Oligomers by Utilizing Carbon Nanotube Confinement[END_REF] Furthemore, total energy calculations suggest that the van der Waals interaction between the oligothiophene and the tube is stronger than the intermolecular interaction. [START_REF] Loi | Encapsulation of Conjugated Oligomers in Single-Walled Carbon Nanotubes: Towards Nanohybrids for Photonic Devices[END_REF] The different theoretical works suggest a correlation between the structural organization of the guest molecules and the size of the tubes. Nevertheless, up to now, no experimental evidence of such a correlation over a wide range of nanotubes diameter has been reported.

In this work, we investigate experimentally the dependence of the structural properties of NTs filled with methyl-terminated quaterthiophene (4T, figure 1 in supporting information) as a function of the nanotube diameter. We performed a systematic study of hybrid nanotubes in a diameter range from 0.68 to 1.93 nm using Raman spectroscopy and high resolution transmission microscopy. We found out that 4T molecules inside nanotubes form different structures depending on the NT diameters. Different critical diameters are identified, controlled by the interactions between guest thiophene molecules and host nanotube and confined 4T-4T interactions.

EXPERIMENTAL :

Sample preparation: Four sources of nanotubes have been used in this study: commercial electric arc single-walled carbon nanotubes (1.2 nm < d < 1.6 nm), provided by Carbon Solution 24 and called NT14 in the following; carbon nanotubes synthesized by the EDiPS method [START_REF] Saito | Selective Diameter Control of Single-Walled Carbon Nanotubes in the Gas-Phase Synthesis[END_REF] (1.6 nm < d < 2 nm) (NT18 in the following); HiPCO carbon nanotubes (0.6 nm < d < 1.2 nm), [START_REF] Nikolaev | Gas-Phase Catalytic Growth of Single-Walled Carbon Nanotubes from Carbon Monoxide[END_REF] called NT09 in the following and CoMoCAT carbon nanotube enriched in (7,6) nanotubes (0.6 nm < d < 1 nm), 27 NT08 in the following. HiPCO, Carbon Solution and CoMoCAT nanotubes were purified by air oxidation and subsequently treated to remove the catalyst. The eDips nanotubes were purified according to the following protocol: 20 mg of raw SWNT material were sonicated in nitric acid (35 vol. %) (150 mL) with a sonic bath (160 W max) (100% for 5 min and then 40% for 15 min) and then heated at 100°C for 5h. The suspension was then cooled and vacuum filtered through a PTFE membrane (Sartorius, 0.2 µm). While pursuing vacuum filtration, the thick SWNT layer formed on the filtration membrane (buckypaper) was washed by 200 ml of deionized water; pH was monitored during the washing and is about 7 at the end of the process. The nanotubes were redispersed in NaOH 1M (100 mL) using the sonic bath (100% for 10 min) and then filtered through a PTFE membrane and washed with NaOH 1M, deionized water and then HCl 1M followed by deionized water until the filtrate was neutral. Finally, the bucky paper was redispersed in hydrogen peroxide (30 %) (150 mL) using the sonic bath (100% for 5 min and then 40% for 10 min). The suspension was heated at 100°C for 1 h, cooled down at room temperature and then vacuum filtered through a PTFE membrane. The nanotubes were washed by 200 ml of deionized water and then dried at 50°C under high vacuum. The overall yield of the purification process was 60 % (12 mg).

Encapsulation of 4T into carbon nanotubes is performed using the vapour reaction method previously described. [START_REF] Alvarez | Charge Transfer Evidence between Carbon Nanotubes and Encapsulated Conjugated Oligomers[END_REF] Before the encapsulation treatment, carbon nanotubes are outgased at 300°C for 48 hours. Then, NTs are mixed with 4T-CH3 in weight ratio: w NTS /w 4T-CH3 =0.5, in glove box and outgased under 2.10 -6 mbar at ambient temperature for 1 hour. Then, NTs with 4T are sealed in glass tube at 2.10 -6 mbar and heated to 250°C for 72 hours. Sublimation step is then performed. The sample was then washed with organic solvent and stored in the oven at 120°C for 24 hours. The hybrid material is named 4T@NT in the following.

Raman spectroscopy: Micro

Raman experiments have been performed on a triple monochromator spectrometer (Jobin Yvon T64000), equipped with a charge-coupled detector, in a back scattering geometry, using the fixed 457.9, 488.0, 514.5, 568.2 and 647.1 nm excitation wavelengths and a Ti-Sapphire tunable source in the near infrared region. The spot size is around few microns in diameter probing an ensemble of nanotubes.

In order to prevent the heating of the tubes and oligomers, the laser power was adjusted at 100W with a spot diameter of about 3 m using a 50X objective. The resolution is about 2 cm -1 . At least four spatially separated area of each sample were probe to ensure homogeneity.

HR-TEM:

The TEM samples were prepared by dispersing the NTs powders in ethanol. The dispersions were ultrasonicated and subsequently deposited on a holey carbon 3 mm copper grids. TEM images were made using two TEMs: a ZEISS Libra 200 MC operating at 200 kV was used to study different sources of nanotubes. A Cs-corrected JEOL ARM200 CC operating at 80 kV was used to quantify precisely the encapsulation.

Computational details:

DFT calculations were performed with the SIESTA package [START_REF] Sanchez-Portal | Density-Functional Method for Very Large Systems with LCAO Basis Sets[END_REF] on a 4T@(11,0). In this model, we use a (11,0) nanotube of 29.82 Å length (diameter of 8.6 Å) with periodic conditions along its axis. The vacuum size was of 11 Å in the two other directions to avoid interactions between adjacent tubes. The guest molecule is a quaterthiophene oligomer bounded with methyl groups (4T). The first Brillouin zone was sampled using 8 k-points along the nanotube axis. The atomic positions were relaxed at fixed lattice parameters using a conjugate gradient until the maximum residual force on the atoms was smaller than 0.02 eV/Å. Exchangecorrelation effects were handled within the generalized gradient approximation (GGA) as proposed by Perdew, Burke and Ernzerhof. [START_REF] Perdew | Generalized Gradient Approximation Made Simple[END_REF] Core electrons are replaced by nonlocal normconserving pseudopotentials. [START_REF] Troullier | Efficient Pseudopotentials for Plane-Wave Calculations[END_REF] The valence electrons were described by localized pseudoatomic orbitals with a double-ζ singly polarized (DZP) basis set. [START_REF] Artacho | Linear-Scaling Ab-Initio Calculations for Large and Complex Systems[END_REF] The cutoff radii for the s and p orbitals were respectively 4.99 and 6.25 a.u. for the carbon atoms, and 4.97 and 6.22 a.u. for sulfur atoms, whereas it was 6.05 a.u. for the s orbital of hydrogen atoms. A real space integration was performed on a regular grid corresponding to a plane-wave cutoff around 300 Ry. We also use van der Waals corrections (DFT-D) between the tube and the guest molecule according to the Grimme approach. [START_REF] Grimme | Semiempirical GGA-Type Density Functional Constructed with a Long-Range Dispersion Correction[END_REF] This approach consists in adding a semiempirical dispersion potential (a simple pair-wise force field) to the conventional Kohn-Sham DFT energy.

RESULTS AND DISCUSSION :

Raman spectra of carbon nanotubes are very sensitive to charge transfers and/or environmental effects, [START_REF] Dresselhaus | Spectroscopy of Carbon Nanotubes[END_REF][START_REF] Thomsen | Resonant Raman Spectroscopy of Nanotubes[END_REF] making thus possible to investigate very efficiently the interaction between oligothiophene molecules and nanotubes. The G-band undergoes significant modifications after 4T encapsulation associated to a charge transfer, already discussed in reference 15.

Here, we will focus on the low frequency region located between 80 and 350 cm -1 where the Radial Breathing Modes (RBM) related to the tube diameters are observed. The relationship between the frequency  and the tube diameter d is usually given by the following equation: (cm -1 )=A/d(nm)+B where A and B are two constants. [START_REF] Dresselhaus | Spectroscopy of Carbon Nanotubes[END_REF][START_REF] Thomsen | Resonant Raman Spectroscopy of Nanotubes[END_REF][START_REF] Araujo | Resonance Raman Spectroscopy of the Radial Breathing Modes in Carbon Nanotubes[END_REF][START_REF] Machon | Strength of Radial Breathing Mode in Single-Walled Carbon Nanotubes[END_REF][START_REF] Strano | Assignment of (N, M) Raman and Optical Features of Metallic Single-Walled Carbon Nanotubes[END_REF][START_REF] Telg | Chirality Distribution and Transition Energies of Carbon Nanotubes[END_REF][START_REF] Jorio | Resonance Raman Spectroscopy (N,M)-Dependent Effects in Small-Diameter Single-Wall Carbon Nanotubes[END_REF][START_REF] Araujo | Third and Fourth Optical Transitions in Semiconducting Carbon Nanotubes[END_REF][START_REF] Sauvajol | Phonons in Single Wall Carbon Nanotube Bundles[END_REF][START_REF] Rao | Effect of Van Der Waals Interactions on the Raman Modes in Single Walled Carbon Nanotubes[END_REF][START_REF] Alvarez | Excitation Energy Dependence of the Raman Spectrum of Single-Walled Carbon Nanotubes[END_REF] The following relationship

𝑑 = 217,8 𝜔 𝑅𝐵𝑀 -15,7
from the reference [START_REF] Araujo | Third and Fourth Optical Transitions in Semiconducting Carbon Nanotubes[END_REF] is used in this work to determine the carbon nanotube diameters. For small diameter NT, typically between 0.68 and 1.1 nm, the relative up-shifts are almost constant. This trend is well characterized by a plateau around a value of 2 𝑐𝑚 -1 for ∆𝜔 𝑅𝐵𝑀 .

A linear behavior is observed for diameters between 1.1 and 1.4 nm. Another plateau can be also considered between 1.4 and 1.65 nm, suggesting that the RBM shits are independent of the NT diameter in this range. To confirm this assumption, a detailed study of the RBM frequency shifts in this diameter range for the encapsulation into NT14 carbon nanotubes of other kinds of oligothiophenes (quaterthiophene (α-4T), sexithiophene (α-6T) and dimethylquaterthiophene (4T)) is displayed on the inset of figure 2. Those data indicate that the relative RBM up-shift upon encapsulation is rather constant around a value of 7.5 𝑐𝑚 -1 in this diameter range whatever the nature of the confined molecules. Finally, for diameter larger than 1.6 nm the behavior is shown to be linear despite the low number of experimental points.

The RBM behaviors can be associated to the amount of molecules confined into a nanotube section and their supramolecular organization as suggested by experimental work on water encapsulation [START_REF] Cambré | Experimental Observation of Single-File Water Filling of Thin Single-Wall Carbon Nanotubes Down to Chiral Index (5,3)[END_REF] and theoretical studies on sexithiophene into nanotubes. [START_REF] Loi | Encapsulation of Conjugated Oligomers in Single-Walled Carbon Nanotubes: Towards Nanohybrids for Photonic Devices[END_REF] To study the structural organization of the nanohybrid systems, we performed HRTEM measurements on 4T@NT. Figure 3 displays some representative HRTEM micrographs of carbon nanotubes with different diameters filled with 4T (left) and their corresponding contrast profiles (right). Concerning the smallest carbon nanotube, we can distinguish three minima in the contrast profile of figure 3.d. The minima on the sides correspond to the carbon nanotube walls. The minimum in between is reasonably associated to a 4T molecule confined inside the carbon nanotube. The observed configuration is one isolated chain inserted in the carbon nanotube and centered along the nanotube main axis. For the nanotube with a diameter of 1.4 nm, two minima are located in between the NT walls. Thus, the configuration in this case consists in two molecular chains inserted in the same nanotube section.

For the largest carbon nanotube (figure 3c), one can observe three mimima in between the nanotube walls (figure 3f), showing that a third chain is inserted. Thus, to explain the RBM shifts as a function of the nanotube diameter, we propose the model described below. For diameter between 0.68 and 1.1 nm, only one single molecule fit in the tube. Indeed, the oligothiophene width is around 0.48 nm for an isolated molecule in its most stable structure, when adjacent rings are non-parallel to one another thanks to a rotation around the connecting bond. Furthermore, the van der Walls distance to the tube wall is roughly 0.32 nm, [START_REF] Loi | Encapsulation of Conjugated Oligomers in Single-Walled Carbon Nanotubes: Towards Nanohybrids for Photonic Devices[END_REF] so that a 1.1 nm diameter tube can accommodate only one molecule (0.48+20.32=1.12 nm). Below 1.1 nm, we assume that the oligothiophene size is strongly reduced under nano confinement by aligning all the thiophene rings to form a nearly planar structure. This hypothesis is supported by our calculations. Indeed, after relaxation, the 4T molecule inside a (11,0) nanotube displays dihedral angles between thiophene rings smaller than 1.1º and its distance to the nanotubes wall is 4 Å (figure 4.a). Therefore, a planar molecule can incorporate nanotubes with diameter down to 0.68 nm, as experimentally observed. Our calculations also predict that 4T molecules cannot enter a (8,0) nanotube (diameter d=0.63 nm) as no stable configuration is found out. Therefore, the critical NT diameter for 4T encapsulation is around 0.65 nm.

For nanotubes diameter between 1.10 and 1.45 nm, a second chain is inserted (figure 4.b).

DFT calculations for 4T confined into a (17,0) nanotube (diameter =1.35 Å) give the following structural parameters: the distance between the two molecules is 6,5 Å whereas the distance between the molecules and the tube wall is 3.4 Å, close to the inter-sheet distance in graphite (figure 4.b). Around 1.1 nm, the molecules are very close to each other and strongly interact, leading to a slight upshift. When the NT diameter increases, the molecules get further and further away, interacting more and more with the NT wall, giving rise to the linear behavior observed on figure 2. This assumption is consistent with theoretical works since the molecules are calculated to be more and more distant as the nanotube diameter increases as a consequence of a higher affinity of the molecule with the nanotube walls. [START_REF] Yanagi | Light-Harvesting Function of Beta-Carotene inside Carbon Nanotubes[END_REF][START_REF] Loi | Encapsulation of Conjugated Oligomers in Single-Walled Carbon Nanotubes: Towards Nanohybrids for Photonic Devices[END_REF][START_REF] Yanagi | Photosensitive Function of Encapsulated Dye in Carbon Nanotubes[END_REF][START_REF] Gao | Electronic Interactions between "Pea" and "Pod": The Case of Oligothiophenes Encapsulated in Carbon Nanotubes[END_REF][START_REF] Kuwahara | Encapsulation of Carbon Chain Molecules; in Single-Walled Carbon Nanotubes[END_REF][START_REF] Mcintosh | Energetics and Electronic Structure of a Polyacetylene Chain Contained in a Carbon Nanotube[END_REF] Between 1.40 and 1.65 nm, the NT diameter is large enough to accommodate only two molecules close to the wall. Beyond 1.65 nm, the insertion of a third molecule is possible and the distance to the nanotube wall decreases when the tube diameter increases.

The RBM shifts induced by non-covalent endohedral functionalization of nanotubes with different species can have different origins such as dispersive interactions, charge transfer, mechanical strain… For fullerene molecules (C 60 , C 70 , C 76 …), the dispersive interactions (van der Waals), generally lead to a small down-shift (2 or 3 cm -1 ) according to the reference Britz and Khlobystov [START_REF] Britz | Noncovalent Interactions of Molecules with Single Walled Carbon Nanotubes[END_REF] and references therein. However, the shift direction could depend on the nanotube diameter as reported by S. Okada [START_REF] Okada | Radial-Breathing Mode Frequencies for Nanotubes Encapsulating Fullerenes[END_REF] and S. Joung et al. [START_REF] Joung | Effect of Fullerene Encapsulation on Radial Vibrational Breathing-Mode Frequencies of Single-Wall Carbon Nanotubes[END_REF] Indeed, encapsulation into large diameter tubes (above 1.37 nm) leads to a down-shift due to an electronic hybridization between NT and C 60 whereas insertion into smaller diameter tubes leads to a small up-shift caused by a steric hindrance. Charge transfer (positive or negative) onto individual metallic nanotubes has been shown to induce a small RBM up-shift of about 2 cm -1 due to a renormalization effect as observed for the Raman G-band. [START_REF] Farhat | Softening of the Radial Breathing Mode in Metallic Carbon Nanotubes[END_REF] This behavior is observed when electron acceptor molecules are encapsulated into bundles of semiconducting or metallic tubes [START_REF] Britz | Noncovalent Interactions of Molecules with Single Walled Carbon Nanotubes[END_REF] . By contrast, insertion of electron donor species such as alkali metals gives rise to a small down-shift for lithium, [START_REF] Bendiab | Stoichiometry Dependence of the Raman Spectrum of Alkali-Doped Single-Wall Carbon Nanotubes[END_REF] no shift for rubidium [START_REF] Bendiab | Combined in Situ Conductivity and Raman Studies of Rubidium Doping of Single-Wall Carbon Nanotubes[END_REF] and a slight up-shift for cesium. [START_REF] Chen | Anomalous Contraction of the C-C Bond Length in Semiconducting Carbon Nanotubes Observed During Cs Doping[END_REF] As the 4T molecule is an electron donor, the physical interactions with the nanotubes are probably dispersive and combined to a slight charge transfer (as evidenced in ref. 15). It is worth mentioning that the RBM shifts are at most -3 cm -1 for dispersive interactions [START_REF] Britz | Noncovalent Interactions of Molecules with Single Walled Carbon Nanotubes[END_REF][START_REF] Okada | Radial-Breathing Mode Frequencies for Nanotubes Encapsulating Fullerenes[END_REF][START_REF] Joung | Effect of Fullerene Encapsulation on Radial Vibrational Breathing-Mode Frequencies of Single-Wall Carbon Nanotubes[END_REF] and +2 cm -1 for charge transfer. [START_REF] Farhat | Softening of the Radial Breathing Mode in Metallic Carbon Nanotubes[END_REF][START_REF] Chen | Anomalous Contraction of the C-C Bond Length in Semiconducting Carbon Nanotubes Observed During Cs Doping[END_REF] Thus, for 4T confined into NT, one can reasonably expect RBM shifts in this wavenumber range or close to zero if both interactions cancel each other. However, figure 2 displays RBM shifts that reach +8 cm -1 at the second plateau and up to +17 cm -1 for the largest diameter tube. Then, the behavior of the RBM shifts over the large diameter range cannot be simply understood as a superposition of dispersive interactions and charge transfer. H. Kataura et al. interpreted the RBM behavior of nanotubes (shifts of about +5 cm -1 and intensity reduction) after Zn-diphenylporphyrin encapsulation (good electron donor [START_REF] Britz | Noncovalent Interactions of Molecules with Single Walled Carbon Nanotubes[END_REF] ) as a nanotube deformation due to the large size of the molecule (1 nm). [START_REF] Kataura | Optical Properties of Fullerene and Non-Fullerene Peapods[END_REF] We therefore believe that the 4T molecules induce a mechanical strain on the nanotubes whose energy depends on the amount of molecules confined and on the closeness between the 4T and the NT. This closeness depends on the NT diameter as suggested by our DFT calculations.

Thus, according to our Raman investigations, the magnitude of the RBM upshifts as a function of the nanotube diameter is governed by two different parameters: the number of confined molecules lying in a nanotube section and the physical interaction taking place either between the molecules themselves or between the molecules and the nanotubes walls.

Conclusion

In summary, combined Raman and HRTEM measurements allow to determine the supramolecular organization of 4T confined into single-walled carbon nanotubes. We evidence different critical nanotubes diameters. Below 1.1 nm, only one molecule is encapsulated. Between 1.1 and 1.6 nm, two oligothiophenes are confined. Above 1.6 nm, three molecules are inserted. The Raman Radial Breathing Mode frequency displays a nonmonotonic behavior with the NT diameter. It turns out to be monitored by both the number of confined molecules into a nanotube section and the competition between oligothiophene/oligothiophene and oligothiophene/tube walls interactions. Our results allow establishing simple Raman criteria to characterize oligothiophenes supramolecular organization at the nanoscale by investigating carefully the magnitude of the RBM up-shifts.

To go further in our investigations, nanotubes with specific diameters are required. For instance, diameters around 1.3 nm would allow obtaining more experimental points in the linear regime. Diameters larger than 2 nm would allow reaching the third plateau which should correspond to three molecular chains interacting with the nanotubes walls without any interaction between the molecules themselves.

Figure 1

 1 Figure 1 displays the Raman spectra in the RBM frequency range at different laser excitation

Figure 1 :

 1 Figure 1: Raman spectra of NT and 4T@NT in the RBM range recorded at different laser excitation wavelengths

Figure 2 :Figure 3 :Figure 4 :

 234 Figure 2: RBM relative up-shifts after encapsulation of 4T molecules inside NT08 (open circles), NT09 (stars), NT14(triangles) and NT18 (crosses) carbon nanotubes. The colors of the symbols correspond to the laser excitation wavelengths (cyan=458 nm, blue=488 nm, dark green=532 nm, green=514.5 nm, red=647.1 nm, orange=568 nm). The black straight lines are guide for eyes. Inset: RBM relative up-shifts after encapsulation of oligothiophene molecules (4T, α-4T and α-6T) inside NT14 carbon nanotubes.

Acknowledgment :

Authors wish to thank the METSA research foundation for giving access to the Cs-corrected TEM of MPQ-Paris Diderot laboratory.

Supporting Information available:

This information is available free of charge via the Internet at http://pubs.acs.org

Bibliographie


Patrizia Vignolo

Matthieu Bellec

Julian Böhm

Abdoulaye Camara

Jean-Marc Gambaudo

Ulrich Kuhl

Fabrice Mortessagne

Energy landscape in two-dimensional Penrose-tiled quasicrystal

Since their spectacular experimental realisation in the early 80's [START_REF] Shechtman | Metallic phase with long-range orientational order and no translational symmetry[END_REF], quasicrystals [START_REF] Bindi | Natural quasicrystals[END_REF] have been the subject of very active research, whose domains extend far beyond the scope of solid state physics. In optics, for instance, photonic quasicrystals have attracted strong interest [START_REF] Vaderny | Optics of photonic quasicrystals[END_REF] for their specific behaviour, induced by the particular spectral properties, in light transport [START_REF] Hattori | Photonic dispersion relation in a one-dimensional quasicrystal[END_REF][START_REF] Man | Experimental measurement of the photonic properties of icosahedral quasicrystals[END_REF][START_REF] Levi | Disorder-enhanced transport in photonic quasicrystals[END_REF], plasmonic [START_REF] Gopinath | Enhancement of the 1.54 µm Er 3+ emission from quasiperiodic plasmonic arrays[END_REF] and laser action [START_REF] Notomi | Lasing action due to the two-dimensional quasiperiodicity of photonic quasicrystals with a penrose lattice[END_REF]. Very recently, one of the most salient spectral feature of quasicrystals, namely the gap labelling [START_REF] Bellissard | Gap labelling theorems for Schrödinger's operators[END_REF], has been observed for a polariton gas confined in a one dimensional quasi-periodic cavity [START_REF] Tanese | Fractal energy spectrum of a polariton gas in a Fibonacci quasiperiodic potential[END_REF]. This experimental result confirms a theory which is now very complete in dimension one [START_REF] Sütö | Singular continuous spectrum on a Cantor set of zero Lebesgue measure for the Fibonacci hamiltonian[END_REF][START_REF] Luck | Cantor spectra and scaling of gap widths in deterministic aperiodic systems[END_REF]. In dimension greater than one, the theory is very far from being complete. Furthermore, some intriguing phenomena, like the existence of self-similar eigenmodes can occur [START_REF] Sutherland | Self-similar ground-state wave function for electrons on a two-dimensional Penrose lattice[END_REF]. All this makes two dimensional experimental realisations and numerical simulations pertinent and attractive. Here, we report on measurements and energy-scaling analysis of the gap labelling and the spatial intensity distribution of the eigenstates for a microwave Penrose-tiled quasicrystal. Far from being restricted to the microwave system under consideration, our results apply to a more general class of systems.

Quasicrystals are alloys that are ordered but lack translational symmetry. In dimension two, they can be modelled with a collection of polygons (tiles) that cover the whole plane, so that each pattern (a sub-collection of tiles) appears, up to translation, with a given density but the tiling is not periodic. A typical example is given by the Penrose tiling [START_REF] Penrose | The role of aesthetics in pure and applied mathematical research[END_REF]. Here, we implement a microwave realisation of a Penrose-tiled lattice using a set of coupled dielectric resonators [see Fig. 1 (a)]. The microwave setup used has shown its versatility by successfully addressing various physical situations ranging from Anderson localisation [START_REF] Laurent | Localized modes in a finite-size open disordered microwave cavity[END_REF] to topological phase transition in graphene [START_REF] Bellec | Topological transition of Dirac points in a microwave experiment[END_REF], and provided the first experimental realisation of the Dirac oscillator [START_REF] Franco-Villafañe | First experimental realization of the Dirac oscillator[END_REF].

We establish a two-dimensional tight-binding regime [START_REF] Bellec | Tight-binding couplings in microwave artificial graphene[END_REF], where the electromagnetic field is mostly confined within the resonators. For an isolated resonator, only a single mode is important in a broad spectral range around the bare frequency E b ≃ 6.65 GHz. This mode spreads out evanescently, so that the coupling strength t can be controlled by adjusting the separation distance d between the resonators [START_REF] Bellec | Tight-binding couplings in microwave artificial graphene[END_REF]. The resulting system can be described by the following tight-binding Hamiltonian:

H = E b i |i i| + i,j,i =j t ij |i j|, ( 1
)
where |i is the wave function at site i and t ij is the coupling strength between sites i and j. We created a Penrose tiling made of thin and fat diamonds. The lattice is constructed using the inflation rules of the Robinson triangle decomposition [START_REF] Grünbaum | Tilings and Patterns[END_REF] of the Penrose tiling [START_REF] Penrose | The role of aesthetics in pure and applied mathematical research[END_REF]. A microwave resonator is placed at each diamond vertex [Fig. 1 (a)]. The experimentally obtained density of states (DOS), ρ(E) (see Supplementary Information for details), is shown in Fig. 1 (b). The main frequency bands, E i , and gaps, ∆E i , are indicated by the white and grey zones, respectively. The peak at "zero-energy", here the bare frequency E b , predicted when the couplings are restricted to the diamond edges [START_REF] Kohmoto | Electronic states on a Penrose lattice[END_REF], is not observed here. Indeed, as explained below, in our system the spectrum is dominated by the couplings along the short diagonal of thin diamonds.

To visualise the gap labelling, we consider the integrated density of states (IDOS):

N (E) = E -∞ ρ(E ′ ) dE ′ .
As plotted in Fig. 2 (solid blue line), we clearly observe plateaus for specific values of N (E), where the IDOS is approximately constant. In contrast to a periodic crystal, where the number of states in each band is the same and the IDOS is a regular staircase with identical step heights, in a quasicrystal, due to the fractal structure of its spectrum, the IDOS is an irregular staircase. Gap labelling identifies the position of footsteps where N (E) is constant and depends only on the geometry of the quasicrystal and not on the physical nature of the coupling between sites [START_REF] Bellissard | Gap labelling theorems for Schrödinger's operators[END_REF][START_REF] De Prunelé | Penrose structures: Gap labeling and geometry[END_REF][START_REF] Benameur | Gap-labelling for quasi-crystals (proving a conjecture by[END_REF][START_REF] Kaminker | A proof of the gap labeling conjecture[END_REF][START_REF] Bellissard | Finite telescopic approximations and gap-labelling[END_REF]. For instance, for an infinite Fibonacci or Penrose quasicrystal, it was shown that each footstep in the IDOS appears at a precise value given by N (E) = z i1 + λz i2 , where λ = ( √ 5 + 1)/2 is the golden ratio and the z i 's are relative integers. Moreover, the IDOS builds a devil's staircase: each step is divided in smaller steps and each smaller step is divided in steps even smaller, leading to a spectrum with a Cantor set structure [START_REF] Sütö | Singular continuous spectrum on a Cantor set of zero Lebesgue measure for the Fibonacci hamiltonian[END_REF][START_REF] Luck | Cantor spectra and scaling of gap widths in deterministic aperiodic systems[END_REF].

For an infinite Penrose-tiled quasicrystal, as explained in the Supplementary Information, the gap labelling theory establishes the following main hierarchy of the gaps [START_REF] De Prunelé | Penrose structures: Gap labeling and geometry[END_REF]:

N (E) =          5 -3λ, E ∈ ∆E 1 2λ -3, E ∈ ∆E 2 4 -2λ, E ∈ ∆E 3 3λ -4, E ∈ ∆E 4 , (2)
∆E i being the ith frequency gap. As shown in Fig. 2, these values perfectly fit for the IDOS calculated numerically for a large system (dotted red line). The experimental IDOS (solid blue line) is in very good agreement with the predicted hierarchy. The discrepancies between the numerics and the experiments have three main reasons. First, the experimental lattice only possesses a few tens of states in each band; the finite-size effect is particularly visible in the last band, which is the largest. Second, the spatial extension of the resonators is not taken into account in the numerics, thus neglecting screening effects. Third, the microwave resonators are not strictly speaking identical: the relative variation of the bare frequency can reach 0.15%.

For a better understanding of the spectrum, we analyse the wave function spatial distribution band by band (Fig. 3). The data processing from reflexion measure- 1). The dashed blue line is obtained by directly diagonalising the tight-binding Hamiltonian using 2665 sites with the corresponding coupling constants obtained by Eq. ( 9) of Ref. [START_REF] Barkhofen | Disordered graphene and boron nitride in a microwave tight-binding analog[END_REF]). The horizontal dashed lines indicate the gap labelling for an infinite lattice. Isolated and coupled green diamonds are respectively associated with the dimer and trimer structures of closer sites whose couplings generate the five bands Ei in the DOS and give the main structure to the IDOS staircase.

ments to the intensity of wave functions, via LDOS, is reported in the Supplementary Information. We observe that, in the first and last bands (dark grey zones), the energy is mainly distributed in trimers of closer sites, with a maximum of intensity in the central resonator of each trimer [Figs 3 (a) and(f)]. In the second and fourth bands (medium grey zones), the energy is essentially distributed in dimers of closer sites [Figs 3 (d) and(c)]. In the central band (light grey zone), we observe that the energy is distributed more uniformly [Figs 3 (b) and (e)]. Moreover, the dimers and trimers that emerge in the landscape are associated with the two patterns corresponding to isolated or coupled thin diamonds depicted in green in Fig. 2.

Dimer and trimer couplings give the dominant contribution to the spectral structure. This can be understood following a perturbative approach. If there were no coupling among the resonators, the spectrum would be a peak at E b with a degeneracy given by the number of sites in the system. The main Hamiltonian terms which contribute to remove this degeneracy are the ones where the coupling is largest, t ij = t max , i.e. those associated with resonators located at the minimum distance d min . This occurs for the resonators located at the closest vertices of the thin diamonds. Thus, in the isolated thin diamonds we have a dimer structure {|1 d , |2 d }, while in the coupled diamonds we have a trimer struc- ture {|1 t , |2 t , |3 t }. If the other couplings were vanishing, the spectrum would have five peaks located at the energies

E 1 = E b - √ 2t max , E 2 = E b -t max , E 3 = E b , E 4 = E b + t max , E 5 = E b + √ 2t max . (3)
These eigenvalues would correspond to the eigenfunctions

|φ 1 = |1 t - √ 2|2 t + |3 t , |φ 2 = |1 d -|2 d , |φ 3,a = |1 t -|3 t , |φ 3,b = |1 s , |φ 4 = |1 d + |2 d , |φ 5 = |1 t + √ 2|2 t + |3 t . (4)
Eigenvalues E 1 and E 5 result from the trimer structure, while E 2 and E 4 from the dimer one. E 3 results from both the trimer structure and all sites |1 s that are considered uncoupled in this perturbative argument. Thus the degeneracy of the first and the fifth peaks is given by the number of coupled thin diamonds present in the tiling, while the one of the second and fourth by the number of isolated thin diamonds. Finally, the degeneracy of the central peak is given by the number of coupled thin diamonds plus the number of all the remaining resonators that are uncoupled. The other couplings are much smaller than t max since they decrease almost exponentially with distance [START_REF] Bellec | Tight-binding couplings in microwave artificial graphene[END_REF]. Indeed the coupling corresponding to the side of the diamonds is ∼ t max /10 and the others are even smaller. The main effect of these weaker couplings is a broadening of the five peaks into five bands, as observed in the spectrum [see Fig. 1 (c)]. The population of the five bands of the spectrum is just given by the reasoning above. Thus the numbers in Eq. ( 2) are related to the fraction of isolated and coupled thin diamonds in the Penrose tiling as detailed in the Supplementary Information.

The perturbative approach outlined above can also be used to understand the energy landscape shown in Fig. We stress that, for larger systems and with better frequency resolution, it would be possible to observe further hierarchical structure of the bands, namely the fragmentation of each band in sub-bands in connection with the density of larger patterns. This may be possible using ultracold gases [START_REF] Gambaudo | Brillouin zone labelling for quasicrystals[END_REF] trapped in quasicrystal optical lattices [START_REF] Guidoni | Atomic diffusion in an optical quasicrystal with five-fold symmetry[END_REF]. Another important remark is that the gap labelling values in Eq. ( 2) do not depend on the particular values of the hopping energies in Eq. ( 1). For any (non-interacting) classical or quantum system subject to a potential with the same spatial patterns as the ones studied in this work, the first hierarchy of the gaps will be given by the values in Eq. ( 2), the only condition being that the shorter the distance between sites the larger their coupling (the study performed in [START_REF] He | Eigenvalue spectrum, density of states, and eigenfunctions in a two-dimensional quasicrystal[END_REF] does not meet this criterion). Within this condition, different physical systems will exhibit the same energy landscapes as the ones shown in Fig. 3. What will change from one system to another are the widths of the gaps and bands.

The difference between states |φ 1 and |φ 5 (and similarly for |φ 2 and |φ 4 ) is the phase landscape. Because of the positive sign of the coupling in such an experiment [START_REF] Bellec | Tight-binding couplings in microwave artificial graphene[END_REF], the ground state corresponds to trimers with alternating signs (|φ 1 ). Neighbouring trimers are also arranged such that the alternance of signs is fulfilled, thus allowing the minimisation of the energy. The main consequences are twofold: (i) the state is almost localised, as outlined in [START_REF] Kohmoto | Electronic states on a Penrose lattice[END_REF][START_REF] Sutherland | Localization of electronic wave functions due to local topology[END_REF], and indeed the first band is very narrow; (ii) there is a geometrical frustration effect as shown in Fig. 4: where there are patterns with five trimers forming a circular structure, the wave function is vanishing on one of the trimers (the bottom right trimer of the structure, in Fig. 4), because it is not possible for all five trimers to satisfy alternate signs with neighbouring trimers. The wave function is numerically obtained by diagonalising the tight-binding Hamiltonian corresponding to the experimental situation (same number of sites and same couplings). The reflexion measurements only provide the intensity of wave functions, the sign is experimentally accessible via transmission measurements [START_REF] Poli | Selective enhancement of topologically induced interface states[END_REF] which were not implemented in this study.

In conclusion we have measured experimentally the gap labelling and the energy landscape of the eigenstates of a microwave Penrose-tiled quasicrystal. To the best of our knowledge, this is the first measure of these two observables in dimension two. In such a microwave sys- In each trimer the sign alternates between neigbouring sites, and, to minimize the energy, the sign alternates also between neighbouring trimers. The dotted black circle delineates a pattern of five trimers exhibiting a geometrical frustration effect: one of the trimers has to possess a vanishing energy since the complete alternation of signs cannot be fulfilled.

tem, the Hamiltonian terms scale exponentially with the distance. We have shown that this allows to use a perturbative argument to understand and determine both the gap labelling and the energy landscape of the different states. Even though the derivation of our results is related to our particular setup, the gap labelling values and the wave function symmetry in each band that we have found, are general. Indeed, our results concern all systems which share the same quasicrystalline potential energy landscape.

SUPPLEMENTARY INFORMATION

S1. DOS and wavefunctions extractions

The experimental setup and the tight-binding description of the microwave system are detailed in [START_REF] Bellec | Tight-binding couplings in microwave artificial graphene[END_REF]. Here, we describe the procedure used to obtain the density of states (DOS) and the wavefunctions from reflection measurements.

The resonance frequency of an isolated resonator E b is around 6.65 GHz and is associated with the first Mie resonance in the transverse electric polarisation. Due to evanescent coupling, a lattice of such resonators exhibits a discrete spectrum a few hundreds of MHz wide around E b . Figure S1 shows the reflection signal S 11 measured with a vectorial network analyser, via a magnetic antenna positioned above the centre of a given resonator in a Penrose-tiled quasycristal. We have shown in [START_REF] Bellec | Tight-binding couplings in microwave artificial graphene[END_REF] that the local density of states (LDOS), ρ(r 1 , E), measured at position r 1 , is directly related to the amplitude and phase of S 11 . Up to a normalisation factor, the relation reads:

ρ(r 1 , E) ∝ |S 11 (E)| 2 |S 11 | 2 E ϕ ′ 11 (E) (S.1)
where . . . E indicates an averaging over the whole range of the frequency spectrum, ϕ 11 is the phase of the reflected signal: ϕ 11 = Arg(S 11 ), and where ϕ ′ 11 denotes its derivative with respect to the frequency.

In Fig. S2(a), each color (from deep blue to red) corresponds to a given site position. Their respective LDOS are plotted in Fig. S2(b). The density of states (DOS) shown in Fig. S2(c) is obtained by averaging the LDOS over all positions.

Figure S3(a) presents a magnification of the small frequency range indicated by the grey zone in Fig. S2(b). For a given eigenfrequency (grey boxes) and a given position, according to the definition of the local density of states ρ(r 1 , E) = n |Ψ n (r 1 )| 2 δ(E -E n ), the resonance curve exhibits a maximum whose value is related to the intensity of the wavefunction at this specific position. The visualisation of the wavefunction distribution associated with each eigenfrequency thus becomes accessible, see Figs S3(b) and(c). The energy landscapes depicted in Fig. 3 started with a fat diamond and we iterated the inflation procedure 10 times (16 times for the theoretical curves shown in Fig. 2). At the i-th iteration, the number of fat diamonds N i f and thin diamonds N i t is related by the numbers at the preceding iteration by the expression

N i f N i t = A N i-1 f N i-1 t with A = 2 1 1 1 . (S.
2)

The eigenvalues of A are λ + = λ + 1 and λ -= (λ + 1) -1 , and the corresponding eigenvectors u + and u -have components (λ, 1) and (1, -λ). The eigenvector corresponding to the inflation is u + , so that the ratio u +,1 /u +,2 can be identified with the ratio N i f /N i t for large values of i. Thus We remark that, always in the limit of large i, the number of vertices (sites) N i v can be identified with the total number of tiles N i tot = N i f + N i t . Indeed, N i tot -N i r + N i v = 1, where N i r is the number of ribs, that for a diamond tiling is equal to twice the number of tiles, N i r = 2N i tot . This leads to N i v ≃ N i tot . By looking at Fig. ??, one can notice that, after a single inflation, a fat diamond can never give coupled thin diamonds, while the inflation of a thin diamond does. Thus the number N i c of coupled thin diamonds at the i-th iteration is equal at the number N i-1 t of thin diamonds at the preceding iteration. The populations β 2 and β 4 of the second and fourth bands are given by the ratio N i is /N i v , N i is being the number of isolated thin diamonds. Taking into account that N i t = 2N i c + N i is , we get

β 2 = β 4 = N i is N i v = (λ + 1)

FIG. 1 :

 1 FIG. 1: Microwave Penrose-tiled quasicrystal. (a) Diamond-vertex Penrose-tiled quasicrystal, where the tiling is superposed to guide the eye (thin diamonds in green). The sites of the lattice are occupied by dielectric resonators (ceramic cylinders of 5 mm height and 8 mm diameter) with a high index of refraction (n = 6). The lattice is sandwiched between two aluminium plates (the upper one is not shown). The microwaves are excited by a movable loop antenna. (b) Experimentally obtained DOS as a function of frequency, the white and gray zones indicate the main frequency bands, Ei, and the gaps, ∆Ei, respectively. The bare frequency E b is indicated by the white arrow.

FIG. 2 :

 2 FIG. 2: Integrated density of states. Normalised IDOS N (E) for a diamond-vertex Penrose lattice setup. Solid red line corresponds to the experimental Penrose lattice with 164 sites (see Fig.1). The dashed blue line is obtained by directly diagonalising the tight-binding Hamiltonian using 2665 sites with the corresponding coupling constants obtained by Eq. (9) of Ref.[START_REF] Barkhofen | Disordered graphene and boron nitride in a microwave tight-binding analog[END_REF]). The horizontal dashed lines indicate the gap labelling for an infinite lattice. Isolated and coupled green diamonds are respectively associated with the dimer and trimer structures of closer sites whose couplings generate the five bands Ei in the DOS and give the main structure to the IDOS staircase.

FIG. 3 :

 3 FIG. 3: Energy landscape in each band. The central part of the figure shows the DOS for the diamond-vertex tiling. It exhibits five main bands distributed on both sides of the bare frequency E b indicated by the vertical dotted line, the central band showing a point-like dip at E b . For each single resonator we integrate the LDOS band by band and obtain the overall wave function structure within the bands. (a) and (f) Energy localised on trimers of closer sites is associated with the two extreme bands (dark grey zones). (b) and (e) For the two neighbouring bands (medium grey zone) a localisation on dimer structures is observed. (c) and (d) For the central band (light grey zone), integrations from the lower limit to the bare frequency and from the bare frequency to the upper limit give similar uniformly distributed energy landscapes: energy is delocalised over the edge sites of the trimer structures and over the "uncoupled" resonators.

3 .

 3 The trimer structures in the LDOS that appear in the first and in fifth bands [Figs 3 (a) and (f)] correspond to the states |φ 1 and |φ 5 , respectively. The dimerised structures in the LDOS that appear in the second and fourth bands [Figs 3 (b) and (e)] correspond to the states |φ 2 and |φ 4 , respectively. For the central band [Fig. 3 (c) and (d)] the LDOS corresponds to the states |φ 3,a and |φ 3,b and thus it vanishes over the dimers and over the central site of each trimer (|2 t ).

FIG. 4 :

 4 FIG.4: Frustration mechanism. Ground state wave function (numerical calculation) for the Penrose-tiled quasicrystal. In each trimer the sign alternates between neigbouring sites, and, to minimize the energy, the sign alternates also between neighbouring trimers. The dotted black circle delineates a pattern of five trimers exhibiting a geometrical frustration effect: one of the trimers has to possess a vanishing energy since the complete alternation of signs cannot be fulfilled.

  are obtained by superimposing the wavefunction intensities of all the resonances in the same band.

FIG. S1 :

 S1 FIG. S1: From reflexion signal to LDOS. (a) Penrosetiled quasycristal whose sites are occupied by microwave resonators. The coloured site (light blue) indicates the position of the magnetic antenna connected, via a coaxial cable, to a vectorial network analyser. (b) and (c) The corresponding amplitude and phase of the reflexion signal S11. (d) The local density of states deduced from the reflexion measurement according to relation (S.1).

  from which we can deduce the population β 1 and β 5 of the first and last bands in the limit of an infinite system:β 1 = β 5 = N i c N i v = (3λ + 2) -1 = 5 -3λ.(S.5)

- 1 - 2 ( 5 -

 125 3λ) = 5λ -8. (S.6) The population β 3 of the third band will be 1 -2β 1 -2β 2 = 7 -4λ. The 4 values of the gap labelling shown in Fig. 2 correspond to: N 1(E) = β 1 , N 2 (E) = β 1 + β 2 , N 3 (E) = β 1 + β 2 + β 3 and N 4 (E) = β 1 + β 2 + β 3 + β 4 .

Author contributions M.B., U.K. and F.M. designed the experiment; M.B., J.B., A.C. and F.M. performed the experiments and analysed the data; P.V. and A.C. performed the numerical simulations; J-M.G. and P.V. calculated the gap labelling; all the authors participated to the discussion of the results and the writing of the paper.


Shu-Shi Peng

Shilong Piao

Zhenzhong Zeng

Philippe Ciais

Liming Zhou

Laurent Z X Li

Ranga B Myneni

Yi Yin

Hui Zeng

H Z Wrote

Afforestation in China cools local land surface temperature

China has the largest afforested area in the world (∼62 million hectares in 2008), and these forests are carbon sinks. The climatic effect of these new forests depends on how radiant and turbulent energy fluxes over these plantations modify surface temperature. For instance, a lower albedo may cause warming, which negates the climatic benefits of carbon sequestration. Here, we used satellite measurements of land surface temperature (LST) from planted forests and adjacent grasslands or croplands in China to understand how afforestation affects LST. Afforestation is found to decrease daytime LST by about 1.1 ± 0.5 °C (mean ± 1 SD) and to increase nighttime LST by about 0.2 ± 0.5 °C, on average. The observed daytime cooling is a result of increased evapotranspiration. The nighttime warming is found to increase with latitude and decrease with average rainfall. Afforestation in dry regions therefore leads to net warming, as daytime cooling is offset by nighttime warming. Thus, it is necessary to carefully consider where to plant trees to realize potential climatic benefits in future afforestation projects. T he area of planted forest (PF) in China has increased by ∼1.7 million hectares per year (about 41% of the global afforestation rate) during the last 2 decades [START_REF]Global Forest Resources Assessment 2010[END_REF]2). China had the largest PF area in the world in 2008, at ∼62 million hectares (Fig. 1), or ∼23% of global plantation area (264 million hectares) [START_REF]Global Forest Resources Assessment 2010[END_REF]2). The Chinese government launched several projects to convert croplands (CR) and marginal lands into forests, to reduce soil and water quality degradation, in the 1980s and 1990s (2). This afforestation contributed to increased carbon storage [START_REF] Fang | Changes in forest biomass carbon storage in China between 1949 and 1998[END_REF][START_REF] Piao | The carbon balance of terrestrial ecosystems in China[END_REF] but also altered local energy budgets, which has the potential to offer feedback on local and regional climates [START_REF] Bala | Combined climate and carbon-cycle effects of large-scale deforestation[END_REF][START_REF] Betts | Implications of land ecosystem-atmosphere interactions for strategies for climate change adaptation and mitigation[END_REF][START_REF] Rotenberg | Contribution of semi-arid forests to the climate system[END_REF][START_REF] Arora | Small temperature benefits provided by realistic afforestation efforts[END_REF][START_REF] Lee | Observed increase in local cooling effect of deforestation at higher latitudes[END_REF][START_REF] Bonan | Forests and climate change: Forcings, feedbacks, and the climate benefits of forests[END_REF].

Forests generally have a lower albedo than grasslands (GR) and CR. Thus, afforestation increases the amount of absorbed solar radiation at the surface [START_REF] Lee | Observed increase in local cooling effect of deforestation at higher latitudes[END_REF][START_REF] Bonan | Forests and climate change: Forcings, feedbacks, and the climate benefits of forests[END_REF]. Surface cooling will result if this extra energy is dissipated as evapotranspiration (ET) [START_REF] Jackson | Protecting climate with forests[END_REF] or heat convection [START_REF] Rotenberg | Contribution of semi-arid forests to the climate system[END_REF]; otherwise, afforestation will result in surface warming. The biophysical effects of afforestation on local climate can be much larger than the small global cooling effect resulting from uptake of CO 2 by growing forests [START_REF] Arora | Small temperature benefits provided by realistic afforestation efforts[END_REF][START_REF] Georgescu | Direct climate effects of perennial bioenergy crops in the United States[END_REF][START_REF] Loarie | Direct impacts on local climate of sugar-cane expansion in Brazil[END_REF]. However, these biophysical effects are also complex and depend on "background" climate [START_REF] Pitman | Importance of background climate in determining impact of land-cover change on regional climate[END_REF]. Afforestation generally cools the surface in tropical areas but warms it in boreal lands [START_REF] Betts | Implications of land ecosystem-atmosphere interactions for strategies for climate change adaptation and mitigation[END_REF][START_REF] Arora | Small temperature benefits provided by realistic afforestation efforts[END_REF][START_REF] Lee | Observed increase in local cooling effect of deforestation at higher latitudes[END_REF][START_REF] Bonan | Forests and climate change: Forcings, feedbacks, and the climate benefits of forests[END_REF]. The effects of afforestation in temperate regions are not clear. The large area under afforestation in China, the diversity of projects (over former CR, GR, or marginal lands), and the broad range of background climates (most plantations are in temperate regions with varying degrees of annual average rainfall) provide an interesting test bed to assess how afforestation affects local temperature.

In this article, we investigate how plantations affect land surface temperature (LST) across China, using satellite-derived LST data sets from Earth Observing System (EOS)-Terra and EOS-Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) instruments during the period from 2003 to 2010 (Methods). These LST data depend on the radiative properties of the land surface [START_REF] Wan | New refinements and validation of the MODIS Land-Surface Temperature/Emissivity products[END_REF][START_REF] Zhou | Impacts of wind farms on land surface temperature[END_REF] and, therefore, have a larger diurnal amplitude than the standard 2-m air temperature data from meteorological stations [START_REF] Jin | Land surface skin temperature climatology: Benefitting from the strengths of satellite observations[END_REF]. The primary objective of this investigation is to quantify the space-time distribution of differences in LST between PF and adjacent GR or CR (ΔLST), during both daytime and nighttime.

Results and Discussion

We first randomly sampled 1,000 grid cells, 40 × 40 km in size, that have at least 10% fractional cover of PF (Methods). Grid cells in which an elevation difference in the range of -100∼100 m between PF and natural forests (NF), GR, and CR were selected for further analysis to minimize the effect of elevation on ΔLST. This resulted in 787, 163, and 155 sample grid cells for comparison between PF and NF, GR, and CR, respectively (Fig. 1; SI Appendix, Fig. S1). Fig. 1 B-D shows an example of the distribution of land cover types within a grid cell and the annual daytime and nighttime LSTs. There is almost no difference in annual daytime (∼10:30 AM and ∼13:30 PM) and nighttime (∼22:30 PM and ∼01:30 AM) temperatures between PF and NF (ΔLST∼0 °C, Fig. 2). However, annual daytime temperatures of GR and CR were higher than that of PF (Fig. 2), at about 1.1 ± Significance China has the largest afforested area in the world. Afforestation not only contributes to increased carbon storage but also alters local albedo and turbulent energy fluxes, which offers feedback on the local and regional climate. This study presents previously unidentified observational evidence of the effect of large-scale afforestation on land surface temperature (LST) in China. Afforestation decreases daytime LST, because of enhanced evapotranspiration, and increases nighttime LST. This nighttime warming tends to offset daytime cooling in dry regions. These results suggest it is necessary to carefully consider where to plant trees to achieve potential climatic benefits in future afforestation projects. 0.6 °C (mean ± 1 SD) between GR and PF and 1.2 ± 0.5 °C between CR and PF (these differences are statistically significant at P < 0.001). In contrast, the average annual nighttime ΔLSTs between PF and GR and CR were 0.2 ± 0.5 °C and 0.3 ± 0.5 °C, respectively (Fig. 2), indicating that afforestation warms land surface during the night, a signal of opposite sign but smaller magnitude than the daytime cooling.

The average annual daytime and nighttime ΔLST between PF and short vegetation shows an asymmetric diurnal variation, with a larger magnitude in daytime cooling than nighttime warming (Fig. 2). This asymmetric diurnal cycle of ΔLST between PF and short vegetation is observed in more than 93% (PF vs. GR) and 86% (PF vs. CR) of the sampled grid cells, respectively (SI Appendix, Figs. S2 andS3). We conclude that afforestation of former GR and CR decreases the average daily mean LST by 0.5 ± 0.4 °C and 0.4 ± 0.4 °C respectively, because some of the daytime cooling is offset by nighttime warming.

The asymmetric diurnal cycle of LST results from different energy balance processes [START_REF] Dai | Effects of clouds, soil moisture, precipitation, and water vapor on diurnal temperature range[END_REF][START_REF] Zhou | Impact of vegetation removal and soil aridation on diurnal temperature range in a semiarid region: Application to the Sahel[END_REF][START_REF] Zhou | Spatial dependence of diurnal temperature range trends on precipitation from 1950 to 2004[END_REF]. LST during the daytime is controlled by incoming solar radiation, surface properties (such as albedo and emissivity), partitioning of latent and sensible heat fluxes, and mixing in the near-surface atmospheric boundary layer [START_REF] Zhou | Impacts of wind farms on land surface temperature[END_REF]. Incoming solar radiation can be assumed to be similar between adjacent PF and GR or CR pixels. Hence, surface albedo determines the amount of absorbed solar radiation. The expenditure of this energy as latent and sensible heat fluxes is controlled by vegetation activity and soil moisture status [START_REF] Mu | Improvements to a MODIS global terrestrial evapotranspiration algorithm[END_REF]. Our null hypothesis is a lower albedo and higher ET in PF relative to GR or CR (Fig. 3). The albedo of PF is indeed lower than that of short vegetation in 95% (PF vs. GR) and 99% (PF vs. CR) of the grid cells, and ET is higher in 70% (PF vs. GR) and 94% (PF vs. CR) of the grid cells, respectively (SI Appendix, Figs. S4 andS5). This clearly indicates that PF across China absorbs more incoming radiation and dissipates more energy as latent heat [START_REF] Arora | Small temperature benefits provided by realistic afforestation efforts[END_REF][START_REF] Lee | Observed increase in local cooling effect of deforestation at higher latitudes[END_REF][START_REF] Jackson | Protecting climate with forests[END_REF][START_REF] De Noblet-Ducoudre | Climatic impact of global-scale deforestation: Radiative versus nonradiative processes[END_REF]. Thus, afforestation on average induces cooling during the daytime [START_REF] Bonan | Forests and climate change: Forcings, feedbacks, and the climate benefits of forests[END_REF][START_REF] Jackson | Protecting climate with forests[END_REF][START_REF] De Noblet-Ducoudre | Climatic impact of global-scale deforestation: Radiative versus nonradiative processes[END_REF][START_REF] Chapin | Changing feedbacks in the climate-biosphere system[END_REF].

The surface incoming solar radiation under all sky conditions ranges between 3,960 and 6,410 MJ per year in China (Methods). The average annual difference in albedo is -1.37 ± 0.90% between PF and GR and -2.08 ± 1.22% between PF and CR (Fig. 3). Hence, the extra solar energy absorbed by PF is on average about 54-88 MJ per year compared with that of the adjacent GR vegetation (82-133 MJ per year in the case of CR vegetation).

Planted forests transpired 0.22 ± 0.35 mm day -1 more than the adjacent GR vegetation, which equates to extra energy dissipation through latent heat of about 200 ± 310 MJ per year (0.37 ± 0.34 mm day -1 , or about 331 ± 300 MJ per year, in the case of CR). This enhanced energy loss through ET cools the surface because it exceeds the extra energy that is absorbed (Fig. 2; P < 0.001 from variance analysis; SI Appendix, Figs. S6 andS7). The ΔET explains 46% of the variation in daytime ΔLST between PF and GR in the 58 grid cells where ΔAlbedo is -1% or higher, but in grid cells where ΔAlbedo is lower than -1%, it explains less than 5% of the variation in daytime ΔLST (SI Appendix, Fig. S8). Similar results are obtained for PF and CR vegetation types (SI Appendix, Fig. S8). This analysis suggests that if the albedo warming effect is weak, the ET cooling effect controls daytime ΔLST. Otherwise, the ET cooling effect could be masked by the stronger albedo warming effect on daytime ΔLST.

In general, land surfaces absorb and store energy from the atmosphere during the day and release energy during the night. At night, ET is negligible, and thus LST must be closely related to energy stored during the daytime and to the near-surface atmospheric boundary layer [START_REF] Lee | Observed increase in local cooling effect of deforestation at higher latitudes[END_REF][START_REF] Zhou | Impacts of wind farms on land surface temperature[END_REF]. When afforesting GR or CR, it is likely that the increase in surface heat capacity (e.g., as a result of an increase in soil moisture) may result in more daytime heat storage, and thus more nighttime heating, and that the increase in air humidity (e.g., as a result of enhanced daytime evapotranspiration) near the surface and the enhancement of boundary layer cloud formation may result in more downward longwave radiation received from the atmosphere and reduce the outgoing longwave radiation from the planted forests. This longwave radiative imbalance has a stronger effect during nighttime, when the boundary layer is thinner and more stable, than during daytime [START_REF] Dai | Effects of clouds, soil moisture, precipitation, and water vapor on diurnal temperature range[END_REF][START_REF] Zhou | Impact of vegetation removal and soil aridation on diurnal temperature range in a semiarid region: Application to the Sahel[END_REF][START_REF] Zhou | Spatial dependence of diurnal temperature range trends on precipitation from 1950 to 2004[END_REF]. In addition, the nighttime warming effect could be magnified as a result of reduced atmospheric turbulence from a more stable stratification over trees [START_REF] Lee | Observed increase in local cooling effect of deforestation at higher latitudes[END_REF]. This reduces heat dissipation from PF cover types compared with open lands of GR or CR. We found that the nighttime ΔLST between PF and short vegetation is significantly and negatively correlated with ΔET and ΔAlbedo (SI Appendix, Figs. S6 andS7). This suggests that a larger ΔET relative to the excess solar energy absorption by PF during the day results in a smaller warming effect during the nighttime, which confirms the hypothesis that nighttime warming largely reflects the release of daytime heat storage. More daytime heat storage could result in a larger nighttime warming effect in areas where there is not enough soil moisture for transpiration by planted forests to compensate for the excess absorbed solar radiation. Indeed, the nighttime ΔLST is significantly and negatively correlated to mean annual precipitation (MAP) [R, -0.34 (P < 0.001) for PF vs. GR; R, -0.46 (P < 0.001) for PF vs. CR]. The nighttime warming effect almost cancels the daytime cooling effect from afforestation of grasslands in areas with MAP between 400 and 600 mm y -1 (average daily mean ΔLST, ∼-0.1 ± 0.6 °C; SI Appendix, Fig. S9). In the case of afforestation of CR, the average daily mean ΔLST is ∼-0.1 ± 0.3 °C in regions with MAP between 600 and 800 mm y -1 (SI Appendix, Fig. S10). The nighttime ΔLST between PF and GR or CR is close to zero, but the daytime cooling effect is ∼1.3 ± 0.5 °C in wetter regions (i.e., MAP > 800 mm y -1 for PF vs. GR and MAP > 1,000 mm y -1 for PF vs. CR; SI Appendix, Figs. S9 andS10). This is consistent with previous findings of afforestation effects in wet temperate areas [START_REF] Lee | Observed increase in local cooling effect of deforestation at higher latitudes[END_REF]. Furthermore, the fraction of sample grid cells with positive daily mean ΔLST between PF and GR decreases from 43% in areas with MAP between 400 and 600 mm y -1 to 0% in regions with MAP higher than 800 mm y -1 (SI Appendix, Fig. S11). Similar results are obtained for the case of contrasted analysis between PF and CR (SI Appendix, Fig. S11). These results suggest that afforestation will likely lead to warming, rather than cooling, in relatively dry regions.

The cooling effect of afforestation decreases with increasing latitude and even switches to a local warming effect in high-latitude regions (SI Appendix, Figs. S12 andS13). For example, the daytime cooling effect of afforestation is completely offset by the nighttime warming effect in areas north of 45°N (daily mean ΔLST, 0.4 ± 0.4 °C; SI Appendix, Fig. S12). In contrast, afforestation of lands south of 35°N still have a clear cooling effect (ΔLST, -0.6 ± 0.3 °C; SI Appendix, Figs. S12 andS13). Both ΔET and ΔAlbedo between PF and GR or CR significantly decrease with latitude (SI Appendix, Figs. S12 andS13). Thus, going from south to north, PF absorbs more incoming radiation and produces less ET compared with adjacent short vegetation. This surface energy imbalance leads to a larger daytime cooling relative to nighttime warming in the south compared with the north (SI Appendix, Figs. S12 andS13). North of 35°N, the extra ET by PF is smaller than the extra absorbed solar radiation (SI Appendix, Figs. S14 andS15), but daytime ΔLST still shows a cooling effect (SI Appendix, Figs. S12 andS13). This suggests that increased sensible heat flux from PF may increase the efficiency of convective heat transport, which results in daytime cooling and also reduces the explanatory power of ΔET on daytime ΔLST when ΔAlbedo is lower than -1% between PF and GR and ΔAlbedo is lower than -2% between PF and CR (SI Appendix, Fig. S8). The lack of high-resolution gridded data sets of sensible heat transport precludes a detailed investigation of the respective cooling effects of ET and convective heat transfer. In addition, it is difficult to delineate the exact bioclimatic boundary separating the warming versus cooling effects of afforestation because the area of forest plantations north of 45°N is much smaller in China (SI Appendix, Fig. S1).

The warming effect of afforestation at higher latitudes is augmented in winter because of the differences in albedo of tall versus short vegetation, as the latter can be covered by snow [START_REF] Arora | Small temperature benefits provided by realistic afforestation efforts[END_REF]. In line with this argument, the nighttime ΔLST between PF and short vegetation is larger in winter than in summer in areas north of 35°N (Fig. 4). Here, afforestation of CR has a net warming effect during both daytime (0.0 ± 0.6 °C) and nighttime (1.5 ± 0.8 °C) in winter. This is because ΔAlbedo is quite large (-7.1 ± 3.3%) and ΔET is negligible (SI Appendix, Figs. S16 andS17). In summer, however, afforestation enhances ΔET by about 1.0 ± 0.4 mm day -1 , but ΔAlbedo is almost negligible (SI Appendix, Fig. S18). The strong warming effect during winter emphasizes the existence of a significant positive snow-albedo feedback (Fig. 4). The same is not seen in southern parts, as expected (SI Appendix, Fig. S18).

Conclusions

China plans to increase afforested area by about 40 million hectares from 2005 to 2020 to mitigate climate change (2). The challenge is to identify locations where afforestation will create the largest climatic benefits and sustain other ecological services [START_REF] Jackson | Protecting climate with forests[END_REF]. Here we present previously unidentified observational evidence for the effect of large-scale afforestation on temperature in China, using MODIS data products. The cooling/warming effects resulting from sensible heat transport and longwave radiation emission of afforested lands are still poorly understood

Methods

MODIS Data. We use MODIS collection-5 products of LST, land cover map, ET, and surface shortwave albedo at 1 km resolution. These products have been used extensively in a variety of areas and are proven to be of high quality [START_REF] Wan | New refinements and validation of the MODIS Land-Surface Temperature/Emissivity products[END_REF][START_REF] Zhou | Impacts of wind farms on land surface temperature[END_REF]. MODIS Terra and Aqua instruments are sun-synchronous and image the entire Earth every Analyses. First, we randomly sampled 1,000 grid cells, 40 × 40 km in size, that have at least 10% fractional cover of planted forests (see detailed algorithm in SI Appendix). We also applied the same analysis with grid cells with at least 5% fractional cover of planted forest, and the results are similar. Within each 40 × 40 km grid cell, the differences in LST (ΔLST) between PF and NF, GR, and CR are supposed to account for the changes in LST resulting from reforestation or afforestation of NF, GR, and CR. To minimize the effect of elevation on ΔLST, we only selected grid cells in which elevation difference was in the range of -100∼100 m between PF and NF, GR, and CR for further analysis. This resulted in 787, 163, and 155 sample grid cells for comparison between PF and NF, GR, and CR, respectively (Fig. 1; SI Appendix, Fig. S1). As the LST has four measurement times, the Terra and Aqua data are also combined to produce daytime (averages of ∼10:30 AM and ∼1:30 PM) and nighttime (averages of ∼10:30 PM and ∼1:30 AM) LSTs. For each sample area, we averaged 8-d interval ΔLST into monthly means during the period of 2003-2010 to show the seasonal cycle. Similar to ΔLST, we calculated the differences in ET (ΔET) and albedo (ΔAlbedo) between PF and adjacent NF, GR, and CR to gain insights of diurnal cycle, seasonal cycle, and spatial variations of ΔLST. The fractional cover of planted forest in the 40 × 40 km sample grid cells have little effect on ΔLST (R 2 , ∼0; SI Appendix, Fig. S19). The differences in elevation from digital elevation model between PF and GR or CR also have limited effect on ΔLST (R 2 ∼0-0.08; SI Appendix, Fig. S20). We found similar results using bigger sample grid cells (50 × 50 km or 100 × 100 km) (SI Appendix, Figs. S21 andS22). In addition, we also found similar results using a regular grid sample method (i.e., we sampled grid cells every 40 km from 55°N to 15°N and every 40 km from 70°E to 140°E; SI Appendix, Figs. S23 andS24).

  vegetation feedback | climate change mitigation | plantation effects | surface cooling

Fig. 1 .Fig. 2 .

 12 Fig. 1. Spatial distribution of planted forest in China and an example of a 40 × 40 km sample area. (A) Spatial distribution map of PF with mean annual precipitation background. (B) Land cover types; (C) daytime LST; and (D) nighttime LST for the example sample area.

Fig. 3 .

 3 Fig. 3. Differences (mean ± SD) in annual (A) albedo (ΔAlbedo, %) and (B) evapotranspiration (ΔET, mm day -1 ) between PF and the adjacent NF, GR, and CR in China during the period 2003-2010.

Fig. 4 .

 4 Fig. 4. Mean seasonal cycle of differences in (A) daytime and (B) nighttime LST, (C) ΔAlbedo (%), and (D) ΔET (mm day -1 ) between PF and the adjacent GR and CR in northern China (north of 35°N) during the period 2003-2010. The colorful lines and lighted shaded areas represent the mean and SD of all sample grid cells north of 35°N, respectively.

  1-2 d. For LST, we use the 8-d average LST from EOS-Aqua-MODIS (MYD11A2) and EOS-Terra-MODIS (MOD11A2) products during the period from 2003 to 2010. The LST data include daytime (local solar time ∼10:30 AM from Terra and ∼13:30 PM from Aqua) and nighttime (∼22:30 PM from Terra and ∼01:30 AM from Aqua) temperature observations. The retrieval of LST was further improved by correcting noise resulting from cloud contamination, topographic differences, and zenith angle changes; the absolute bias of LST is generally less than 1 K[START_REF] Wan | New refinements and validation of the MODIS Land-Surface Temperature/Emissivity products[END_REF].Planted Forests Map and Climate Data. The spatial distribution of PF map at 1-km resolution was obtained from the report of the Seventh National Forest ResourceInventory (2004Inventory ( -2008)), released by China's State Forestry Administration (2). The mean annual precipitation data during the period of 1980-2009 used in this study are the Climate Research Unit time-series 3.1 climate data set obtained from the University of East Anglia[START_REF] Mitchell | An improved method of constructing a database of monthly climate observations and associated high-resolution grids[END_REF]. Data on the surface incoming solar radiation under all sky conditions, with 1°resolution, during the period of 2003-2010 were obtained from the Clouds and Earth's Radiant Energy System (http://ceres.larc.nasa.gov/).

	We use the
	MODIS ET data (MOD16) at 8-d intervals from 2003 to 2010, which was
	generated using land cover, leaf area index, air temperature, air pressure, air
	humidity, and net radiation as input data (21) independent of the MODIS
	LST product. The mean absolute bias of MODIS ET is about 0.3 mm day -1
	compared with ET observations from eddy flux towers (21). The MODIS al-
	bedo (MCD43B3) products used in this study include black sky albedo and
	white sky albedo over shortwave broadband (0.3-5.0 μm), with 1-km spatial
	resolution and an 8-d interval from 2003 to 2010 (24). We use white sky
	albedo in this study, and the bias of MODIS albedo is mostly less than 5%
	(25). Yearly MODIS land use and land cover map (MCD12Q1) in 2004 was
	used to distinguish forest, GR, and CR pixels (26).

ACKNOWLEDGMENTS. This study was supported by the National Natural Science Foundation of China (41125004), National Basic Research Program of China (2013CB956303), National Youth Top-notch Talent Support Program in China, and Chinese Ministry of Environmental Protection Grant (201209031). R.B.M. acknowledges support from NASA Earth Science Division. L.Z. acknowledges support from the National Science Foundation (NSF AGS-1247137).