Jumana Saleh

Carole Peyssonnaux

Keshav K Singh

Dr Marvin Edeas
email: marvin.edeas@inserm.fr

Mitochondria and Microbiota dysfunction in COVID-19 pathogenesis Running Title: Targeting intra and extracellular mitochondria in Covid-19 pathogenesis

Keywords: Hyper-inflammation, Hypercoagulability, Iron, Oxidative Stress, Extracellular Mitochondria, Platelet Mitochondria, Microbiota

The COVID-19 pandemic caused by the coronavirus (SARS-CoV-2) has taken the world by surprise into a major crisis of overwhelming morbidity and mortality. This highly infectious disease is associated with respiratory failure unusual in other coronavirus infections. Mounting evidence link the accelerated progression of the disease in COVID-19 patients to the hyper-inflammatory state termed as the "cytokine storm" involving major systemic perturbations. These include iron dysregulation manifested as hyperferritinemia associated with disease severity. Iron dysregulation induces reactive oxygen species (ROS) production and promotes oxidative stress. The mitochondria are the hub of cellular oxidative homeostasis. In addition, the mitochondria may circulate "cell-free" in non-nucleated platelets, in extracellular vesicles and mitochondrial DNA is found in the extracellular space. The heightened inflammatory/oxidative state may lead to mitochondrial dysfunction leading to platelet damage and apoptosis. The interaction of dysfunctional platelets with coagulation cascades aggravates clotting events and thrombus formation. Furthermore, mitochondrial oxidative stress may

Introduction

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an enveloped RNA betacoronavirus that emerged in December 2019 in Wuhan, China causing coronavirus disease 2019 . The COVID-19 pandemic is spreading rapidly and to date has led to more than 430,000 deaths worldwide.

Unfortunately, there are no effective antivirals and vaccines to treat or prevent COVID-19 pandemic.

Clinical trials have been launched worldwide including the European study DISCOVERY which shows that the tested antiviral drugs (remdesivir, lopinavir and ritonavir in combination, the latter being administered with or without interferon beta and hydroxychloroquine) are unable to efficiently fight COVID-19 progression [START_REF] Cao | A Trial of Lopinavir-Ritonavir in Adults Hospitalized with Severe Covid-19[END_REF] [START_REF] Mahevas | No evidence of clinical efficacy of hydroxychloroquine in patients hospitalized for COVID-19 infection with oxygen requirement: results of a study using routinely collected data to emulate a target trial[END_REF].

Mainly COVID-19 patients develop a respiratory tract infection; unfortunately, a significant number of patients develop severe fatal consequences attributed to a surge of inflammatory events described as the "cytokine storm". This heightened inflammatory state is reportedly associated with deleterious systemic events including oxidative stress, dysregulation of iron homeostasis, hypercoagulability and thrombus formation [START_REF] Zhou | Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study[END_REF] [START_REF] Phua | Intensive care management of coronavirus disease 2019 (COVID-19): challenges and recommendations[END_REF] [START_REF] Moore | Cytokine release syndrome in severe COVID-19[END_REF] [START_REF] Kernan | Hyperferritinemia and inflammation[END_REF].

Several biomarkers of inflammation and thrombosis are indicated as mortality predictors among critically ill COVID-19 patients. Lymphopenia was reported as a key feature, and was suggested as a potential prognostic marker. In addition, increased D-dimer and Interleukin-6 (IL-6) increased with worsening of the disease [START_REF] Terpos | Hematological findings and complications of COVID-19[END_REF], and correlated with increased mortality [START_REF] Tang | Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia[END_REF].

The largest prospective cohort published in the United States, which focused on patients who required intensive care, reported that 10% increased mortality risk occurred for every 10% increase of IL-6 or Ddimer concentration providing further insight into COVID-19 pathogenesis regarding activation of systemic inflammation and endothelial-vascular damage [START_REF] Cummings | Epidemiology, clinical course, and outcomes of critically ill adults with COVID-19 in New York City: a prospective cohort study[END_REF].

Hyperferritenimia is also highlighted as a predictor of increased mortality of the disease [START_REF] Mehta | COVID-19: consider cytokine storm syndromes and immunosuppression[END_REF]. Also oxidative stress was indicated as a major player in COVID-19 pathogenesis and severity [START_REF] Delgado-Roche | Oxidative Stress as Key Player in Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) Infection[END_REF]. Several lines of evidence have established a link between inflammation and oxidative stress [START_REF] Khomich | Redox biology of respiratory viral infections[END_REF] (Brand et al, 2014). In this context, we have shown that hepcidin, the key iron regulatory molecule, plays a major role during inflammatory processes [START_REF] Bessman | Dendritic cell-derived hepcidin sequesters iron from the microbiota to promote mucosal healing[END_REF]. We also addressed the role and management of a dysregulated iron state in COVID-19 pathogenesis [START_REF] Edeas | Iron: Innocent bystander or vicious culprit in COVID-19 pathogenesis?[END_REF].

Despite its central role in maintaining oxidative homeostasis, and ROS generation, the mitochondrion has received limited attention regarding its role in COVID-19 pathogenesis and management [START_REF] Edeas | Iron: Innocent bystander or vicious culprit in COVID-19 pathogenesis?[END_REF] [START_REF] Keshav | Decoding SARS-CoV-2 Hijacking of Host Mitochondria in Pathogenesis of COVID-19[END_REF]. Many questions remain unanswered about the role of the mitochondria during the inflammatory "cytokine storm" in COVID-19 patients. Here we propose a hypothetical scheme, based on existing evidence, describing the potential role of the inflammatory signals in perpetuating a cycle of events that aggravate mitochondrial oxidative damage and contribute to major systemic alterations including coagulopathy, ferreptosis and microbial dysbiosis. We propose that not only the intracellular mitochondria dysfunction is a consequence of COVID-19 infection, but the less explored extracellular mitochondria (specifically platelets mitochondria) may affect blood coagulation, clot and thrombosis formation [START_REF] Lodigiani | Venous and arterial thromboembolic complications in {COVID}-19 patients admitted to an academic hospital in Milan, Italy[END_REF] (Giannis et al, 2020) (Zhang et al, 2020b) [START_REF] Oxley | Large-Vessel Stroke as a Presenting Feature of Covid-19 in the Young[END_REF]. These extracellular mitochondria may represent critical mediators and may serve as strategic therapeutic targets in COVID-19 pathogenesis.

Interplay between mitochondria, oxidative stress and inflammation

Normally, body tissues and organs require a large number of functional mitochondria to provide energy and regulate cellular functions according to body needs. Increased demand is met by mitochondrial biogenesis while removal of excess mitochondria occurs through mitophagy. Mitochondrial defects have been implicated in numerous pathologies including diabetes, cardiovascular diseases, gastrointestinal disorders, cancer and aging. Mitochondria, is the major source of reactive oxygen species (ROS) that contributes to normal cell function, but also linked to increased intracellular oxidative stress (Anatoly A [START_REF] Starkov | The Role of Mitochondria in Reactive Oxygen Species Metabolism and Signaling[END_REF] [START_REF] Herst | Functional mitochondria in health and disease[END_REF].

Inflammatory cytokines such as TNF-α induces calcium-dependent increase in mitochondrial ROS. Furthermore, interferon-γ was shown to upregulate genes inducing mitochodrial ROS generation. IL-6 and IL-10 were found to modulate mitochondrial ROS generation through mechanisms, independent of its nuclear factor activity, by directly modulating the activity of the electron transport chain. Mitochondrial ROS was found to directly stimulate the production of proinflammatory cytokines as well [START_REF] Li | Targeting mitochondrial reactive oxygen species as novel therapy for inflammatory diseases and cancers[END_REF]. Shao et. al. reported the upregulation of mitochondrial genes and genes responding to oxidative stress in peripheral blood mononuclear cells [START_REF] Shao | Upregulation of mitochondrial gene expression in PBMC from convalescent SARS patients[END_REF] further supporting the interplay between inflammation and oxidative stress.

Recent studies identified a role for the mitochondria in regulating innate immunity and inflammatory responses. It has been implicated that antiviral immunity may arise against viral DNA which could act as danger associated molecular pattern (DAMP), and modulate inflammatory responses via its capacity to generate ROS [START_REF] Mohanty | Mitochondria: the indispensable players in innate immunity and guardians of the inflammatory response[END_REF]. The impact of mitochondrial dysfunction on inflammation happens in both directions. Inflammatory mediators and immune sentinels trigger intracellular cascades that alter mitochondrial metabolism. Cytokines such as TNF-alpha and IL-6, that are found in COVID-19 serum, impede mitochondrial oxidative phosphorylation and associated ATP production and initiate mitochondrial ROS production in the cell [START_REF] Jo | Molecular mechanisms regulating NLRP3 inflammasome activation[END_REF] [START_REF] Naik | Mitochondrial reactive oxygen species drive proinflammatory cytokine production[END_REF]. This may cause mitochondrial membrane permeabilization, altered mitochondrial dynamics, and might ultimately result in cell death (apoptosis).

On the other hand, when severely damaged, the mitochondria contents (spinoffs such as mtDNA) are released into the cytosol and extracellular environment [START_REF] Twig | The interplay between mitochondrial dynamics and mitophagy[END_REF] [START_REF] Mittal | Reactive oxygen species in inflammation and tissue injury[END_REF]. ROS production is accompanied by upregulation of Ca 2+ levels and release of mitochondrial DNA into the cytosol [START_REF] Kozlov | Mitochondria-meditated pathways of organ failure upon inflammation[END_REF] [START_REF] West | Mitochondrial DNA Stress Primes the Antiviral Innate Immune Response[END_REF]. This response drives pro-inflammatory cytokines production such as IL-1β by activating NLRP3 inflammasomes and induces IL-6 production through inflammasome-independent transcriptional regulation [START_REF] Jo | Molecular mechanisms regulating NLRP3 inflammasome activation[END_REF] [START_REF] West | Mitochondrial DNA Stress Primes the Antiviral Innate Immune Response[END_REF] [START_REF] Naik | Mitochondrial reactive oxygen species drive proinflammatory cytokine production[END_REF] [START_REF] Nakahira | Autophagy proteins regulate innate immune response by inhibiting NALP3 inflammasome-mediated mitochondrial DNA release Kiichi[END_REF]. These cytokines are hallmarks of COVID-19 disease severity.

Several studies have shown the impact of dysfunctional mitochondria on the immune response. For example, a recent study revealed that human alveolar epithelial cells with dysfunctional mitochondria displayed increased production of pro-inflammatory cytokines (CXCL-8, IL-6, CCL20, CCL3, CCL4 and IL-12) all of which were found to be increased in COVID-19 (Zhang et al, 2020a) [START_REF] Zhou | Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study[END_REF].

Moreover, these cells presented impaired repair responses and reduced responsiveness to corticosteroids. These findings highlight a potential impact of dysfunctional mitochondria on modulating immune responses by favoring positive feedback loop that cause alveolar tissue damage that is the case in COVID-19 severe form [START_REF] Hoffmann | Prolonged cigarette smoke exposure alters mitochondrial structure and function in airway epithelial cells[END_REF] [START_REF] Hoffmann | Mitochondrial dysfunction increases pro-inflammatory cytokine production and impairs repair and corticosteroid responsiveness in lung epithelium[END_REF] (Zhang et al, 2020a). For instance, upregulation of chemoattractants such as CXCL-8 promotes neutrophil infiltration into the lung, contributing to ROS generation and protease activation that further contribute to the damage of the mitochondria [START_REF] Hoffmann | Prolonged cigarette smoke exposure alters mitochondrial structure and function in airway epithelial cells[END_REF] [START_REF] Hoffmann | Mitochondrial dysfunction increases pro-inflammatory cytokine production and impairs repair and corticosteroid responsiveness in lung epithelium[END_REF]. Noteworthy, the mitochondrial transfer from bone marrow-derived stromal cells to pulmonary alveoli protects against acute lung injury [START_REF] Islam | Mitochondrial transfer from bone marrow-derived stromal cells to pulmonary alveoli protects against acute lung injury[END_REF].

Overall, a vicious inflammatory/oxidation cycle, involving further mitochondrial injury, leads to lung damage. The immune response to COVID-19 is dominated by increased levels of cytokines and chemokines including IL-6 and CXCL-8. The same exacerbated immune response was detected in the Broncho Alveolar Lavage (BAL) with an upregulation of several markers such as CD163, CD226, CCR5, CCR6, CXCR1, CXCR2, CXCR7, etc. (Zhang et al, 2020a) [START_REF] Wang | Characteristics of Peripheral Lymphocyte Subset Alteration in COVID-19 Pneumonia[END_REF].

Together, the proinflammatory cytokines affect diverse physiological processes by driving cellular oxidative stress ROS generation. In turn, increased ROS production stimulates proinflammatory mediator release that contributes to mitochondrial dysfunction (Figure 1).

The role of Iron in mitochondria dysfunction

The extensive studies of COVID-19 biomarkers have confirmed with no doubt the association of systemic hyperferritinemia with increased illness severity and adverse outcomes [START_REF] Huang | Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China[END_REF].

Besides being a marker of inflammation, ferritin is also released by exhausted dying cells.

One of the targets of iron-mediated oxidative stress is the mitochondrion. Appropriate mitochondrial functioning relies on iron uptake that is primarily utilized for three essential activities: heme synthesis, iron-sulfur cluster biogenesis, and storage in mitochondrial ferritin. Briefly, heme and iron-sulfur clusters play an essential role in maintaining a variety of cellular and systemic processes by facilitating oxidationreduction reactions [START_REF] Rouault | Mitochondrial iron overload: Causes and consequences[END_REF]. Hence, disruption of cellular iron levels or mitochondrial iron metabolism can result in cellular stress or death [START_REF] Jouihan | Iron-mediated inhibition of mitochondrial manganese uptake mediates mitochondrial dysfunction in a mouse model of hemochromatosis[END_REF] [START_REF] Aguirre | Battles with iron: Manganese in oxidative stress protection[END_REF].

In line with the importance of these factors, the complication observed in COVID-19 patients may be attributed to high levels of ferritin which in turn, may cause elevated oxidative and cellular stress translated by massive release of inflammatory mediators, free radicals and ROS [START_REF] Lyngsie | Generation of hydroxyl radicals from reactions between a dimethoxyhydroquinone and iron oxide nanoparticles[END_REF]) [START_REF] Edeas | Iron: Innocent bystander or vicious culprit in COVID-19 pathogenesis?[END_REF]. This systemic iron overload phenomenon is also observed in several diseases such as hereditary hemochromatosis (HH) [START_REF] Jouihan | Iron-mediated inhibition of mitochondrial manganese uptake mediates mitochondrial dysfunction in a mouse model of hemochromatosis[END_REF]. It has been described to impair mitochondrial functions by reducing mitochondrial oxygen consumption leading to enhanced oxidative damage, lipid peroxidation and disturbed glucose tolerance [START_REF] Kim | Absorption of Manganese and Iron in a Mouse Model of Hemochromatosis[END_REF] [START_REF] Aguirre | Battles with iron: Manganese in oxidative stress protection[END_REF] [START_REF] Lyngsie | Generation of hydroxyl radicals from reactions between a dimethoxyhydroquinone and iron oxide nanoparticles[END_REF]. Moreover, reduced mitochondrial respiration causes abnormal metal distribution including manganese, copper and zinc [START_REF] Kim | Absorption of Manganese and Iron in a Mouse Model of Hemochromatosis[END_REF] [START_REF] Jouihan | Iron-mediated inhibition of mitochondrial manganese uptake mediates mitochondrial dysfunction in a mouse model of hemochromatosis[END_REF] [START_REF] Skalny | Zinc and respiratory tract infections: Perspectives for COVID-19 (Review)[END_REF]. Subsequently, reduced mitochondrial manganese may result in mitochondrial dysfunctions, likely due to decreased activity of mitochondrial manganese-dependent superoxide dismutase, an enzyme that protects mitochondria from respiration-generated free radicals [START_REF] Kim | Absorption of Manganese and Iron in a Mouse Model of Hemochromatosis[END_REF] [START_REF] Jouihan | Iron-mediated inhibition of mitochondrial manganese uptake mediates mitochondrial dysfunction in a mouse model of hemochromatosis[END_REF] [START_REF] Manes | Mechanisms of HIV-1 Tat-Mediated Regulation of the Manganese-Superoxide Dismutase Promoter[END_REF]. Unquestionably, hyperferritinemia disrupting mitochondrial homeostasis drives mitochondrial respiration from an aerobic into an anaerobic state. Interestingly, anaerobic respiration favors pyruvate reduction into lactate that is ensured by lactate dehydrogenase (LDH), which is highly upregulated marker in COVID-19 illness (Yetkin-Arik et al, 2019) [START_REF] Young | Lactate dehydrogenase supports lactate oxidation in mitochondria isolated from different mouse tissues[END_REF] [START_REF] Huang | Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China[END_REF] [START_REF] Skalny | Zinc and respiratory tract infections: Perspectives for COVID-19 (Review)[END_REF].

In addition, the iron overload may be another major concern due to the susceptibility of loosely bound iron to catalyze production of ROS [START_REF] Torti | Iron and cancer: more ore to be mined[END_REF]. ROS accumulation can damage cellular components including lipids, which interferes with cellular integrity, membrane fluidity, and permeability [START_REF] Dix | Mechanisms and biological relevance of lipid peroxidation initiation[END_REF] [START_REF] Pietrangelo | Iron, oxidative stress and liver fibrogenesis[END_REF] [START_REF] Niemelä | Hepatic lipid peroxidation in hereditary hemochromatosis and alcoholic liver injury[END_REF]. ROS radicles are known to damage the mitochondria as well [START_REF] Pietrangelo | Iron, oxidative stress and liver fibrogenesis[END_REF] [START_REF] Niemelä | Hepatic lipid peroxidation in hereditary hemochromatosis and alcoholic liver injury[END_REF] [START_REF] Gao | Mitochondrial DNA damage in iron overload[END_REF]. Consequently, injured mitochondria can result in diminished cellular respiratory function as was shown in cardiac myocytes with excess iron loading [START_REF] Gao | Mitochondrial DNA damage in iron overload[END_REF]. This result gives solid ground to consider the role of mitochondria in COVID-19 illness, which leads to respiratory failure. These ROS induced mitochondrial impairments could have serious consequences including iron-dependent ferroptosis, leading to tissue damage and eventually organ failure [START_REF] Dixon | Ferroptosis : An Iron-Dependent Form of Nonapoptotic Cell Death[END_REF] [START_REF] Dixon | The role of iron and reactive oxygen species in cell death[END_REF] [START_REF] Edeas | Iron: Innocent bystander or vicious culprit in COVID-19 pathogenesis?[END_REF].

The role of Ferroptosis

Ferroptosis is a newly identified type of programmed cell death that depends on iron accumulation.

Peculiarly, ferroptosis causes irreversible alteration of mitochondrial morphology [START_REF] Twig | The interplay between mitochondrial dynamics and mitophagy[END_REF]. Furthermore, substantial evidence revealed that ferroptosis is involved in bacterial infection induced cell death and tissue damage [START_REF] Zhu | GPx4 in Bacterial Infection and Polymicrobial Sepsis: Involvement of Ferroptosis and Pyroptosis[END_REF]. For instance, Pseudomonas aeruginosa was shown to trigger ferroptosis in host bronchial epithelium through generating lipoxygenase, that is involved in the initiation of lipid peroxidation, by oxidizing host arachidonic acid-phosphatidylethanolamines [START_REF] Dar | Pseudomonas aeruginosa utilizes host polyunsaturated phosphatidylethanolamines to trigger theft-ferroptosis in bronchial epithelium[END_REF]. Moreover, recently Amaral and colleagues demonstrated the capacity of Mycobateruim tuberculosis to trigger ferroptosis of infected macrophages that correlated with iron overload, reduced glutathione and mitochondrial superoxide [START_REF] Amaral | A major role for ferroptosis in Mycobacterium tuberculosis-induced cell death and tissue necrosis[END_REF]. These observations raise an important question about the ability of the SARS-CoV-2 to trigger ferroptosis of bronchial epithelium and macrophages via hyperferritinemia.

Altogether, a dysfunctional mitochondrion would result in iron accumulation due to its incapacity to metabolize iron. This might cause deficient iron sequestration leading to ROS production through Fenton and Haber-Weiss-type reactions (Lane et al, 2015). These reflections are highlighted in figure 1.

Thrombocytopenia and Hypercoagulability in COVID-19

Increasing concerns point out coagulation abnormalities that are associated with COVID-19 substantial mortality rate (Giannis et al, 2020) [START_REF] Tang | Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia[END_REF]. The comparison of coagulation parameters between survivors and non-survivors highlighted an increase of D-dimers, fibrin degradation product (FDP) levels, longer prothrombin time and activated partial thromboplastin time (Giannis et al, 2020) [START_REF] Tang | Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia[END_REF] [START_REF] Levi | Coagulation abnormalities and thrombosis in patients with COVID-19[END_REF]. Unexpectedly, platelet count was relatively decreased in association with increased mortality [START_REF] Tang | Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia[END_REF] [START_REF] Huang | Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China[END_REF] (Giannis et al, 2020) [START_REF] Levi | Coagulation abnormalities and thrombosis in patients with COVID-19[END_REF]. Growing evidence points towards stroke incidents in COVID-19 patients, including younger adults [START_REF] Oxley | Large-Vessel Stroke as a Presenting Feature of Covid-19 in the Young[END_REF]. The inflammation in the blood vessel walls may be driving thrombosis formation [START_REF] Lodigiani | Venous and arterial thromboembolic complications in {COVID}-19 patients admitted to an academic hospital in Milan, Italy[END_REF] (Zhang et al, 2020c) [START_REF] Oxley | Large-Vessel Stroke as a Presenting Feature of Covid-19 in the Young[END_REF].

Thrombocytopenia is the clinical condition describing abnormally low platelet count (van der Meijden & Heemskerk, 2019). In a critical review by Terpos et al., thrombocytopenia was reported to be more prominent in severe versus non severe cases [START_REF] Terpos | Hematological findings and complications of COVID-19[END_REF]. A recent meta-analysis of nine heterogeneous studies suggested that thrombocytopenia is significantly associated with COVID-19 severity mostly in non-survivors, and was suggested among the factors that determined prognosis and identified patients at risk, particularly in association with disseminated intravascular coagulation (DIC) [START_REF] Lippi | Thrombocytopenia Is Associated With Severe Coronavirus Disease 2019 (COVID-19) Infections: A Meta-Analysis[END_REF]. These findings underlined that platelet function should be seriously addressed in association with hypercoagubilty in COVID-19 patients, which may contribute to developing novel therapeutic targets in limiting COVID-19 related mortality.

Extracellular Mitochondria: An intriguing localisation and role

Extracellular mitochondria can be found free, enclosed by a membrane as inside platelets or vesicles.

Mitochondria outside cell can induce paracrine or endocrine responses in an organism. Extracellular mitochondria regulate cell-to-cell communication, regeneration, danger sensing and provoke an immune response [START_REF] Wang | Platelet mitochondrial dysfunction and the correlation with human diseases[END_REF] [START_REF] Miliotis | Forms of extracellular mitochondria and their impact in health[END_REF].In addition to extracellular mitochondria, release of mtDNA outside of the cell during apoptosis has been described [START_REF] Mcarthur | BAK/BAX macropores facilitate mitochondrial herniation and mtDNA efflux during apoptosis[END_REF].

Recently, Dache et al. reported that blood contains intact cell-free full-length mitochondrial DNA in dense and biologically stable structures over 0.22 µm in diameter and that these structures have specific mitochondrial proteins, double membranes and a morphology resembling that of mitochondria (Al Amir Dache et al, 2020). The potential role for circulating free mitochondria or its spinoffs in blood of COVID-19 patients remain to be elucidated.

Platelet Mitochondria and Coagulopathy

The platelet is an anucleated cell with the primary pathophysiological function of hemostasis and wound healing (Holinstat, 2017). In the absence of nuclear control, platelet health is largely determined by the health of their mitochondria. Other critical roles of platelets include thrombosis, injury response, and immunoregulation. In the absence of genomic DNA, platelets preserve organells including mitochondria from megakaryocytes to maintain its structure and function. The, platelet' s lifespan is (7-10 days), is determined by the mitochondria [START_REF] Melchinger | Role of Platelet Mitochondria: Life in a Nucleus-Free Zone[END_REF]. The packaging of 5-8 mitochondria is critical for vital platelet functions including aerobic respiration and metabolism. The role played by mitochondria in platelet function and survival is essential. Mitochondrial dysfunction in disease may also affect platelet survival and apoptosis, and potentially increase the risk for thrombus formation. [START_REF] Hayashi | Role of mitochondria in the maintenance of platelet function during in vitro storage[END_REF]. Importantly, it has been recently shown that apoptotic platelets may induce clotting ≥ 50fold faster than normal platelets [START_REF] Melchinger | Role of Platelet Mitochondria: Life in a Nucleus-Free Zone[END_REF]. In addition, platelets have recently gained attention as important mediators of the of the immune system (van der Meijden & Heemskerk, 2019).

Mitochondria act as the main energy suppliers in platelets during thrombus formation, a process that was shown to be reversed by inhibiting mitochondrial respiration using pharmacological antagonists to the electron transport chain such as nitric oxide and cyanide [START_REF] Wang | Platelet mitochondrial dysfunction and the correlation with human diseases[END_REF].

Further actions for platelet mitochondria include; platelet activation of permeability transition, ROS generation, reduction of mitochondrial membrane potential and platelet apoptosis. It is noteworthy that an increase in mitochondrial ROS production in platelets leads to severe oxidative stress that alters ATP production and mitochondrial membrane potential leading to further platelet activation [START_REF] Ran | Platelets of type 2 diabetic patients are characterized by high ATP content and low mitochondrial membrane potential[END_REF] [START_REF] Tang | Glucose and collagen regulate human platelet activity through aldose reductase induction of thromboxane[END_REF] [START_REF] Wang | Platelet mitochondrial dysfunction and the correlation with human diseases[END_REF] [START_REF] Melchinger | Role of Platelet Mitochondria: Life in a Nucleus-Free Zone[END_REF]. Moreover, the upregulation of ROS drives thrombosis through cytochrome-C release by mitochondria triggers the apoptotic caspase cascade driven by BAX and BAD resulting in mitochondrial damage and apoptosis [START_REF] Wang | Platelet mitochondrial dysfunction and the correlation with human diseases[END_REF] [START_REF] Melchinger | Role of Platelet Mitochondria: Life in a Nucleus-Free Zone[END_REF]. This may explain the reduced number of platelet in COVID-19 sickness despite of thrombosis occurrence. Moreover, COVID-19 patients probably suffer from mitophagy impairment because of environmental stress caused by hyperinflammation. In healthy context, mitophagy protects platelets from oxidative stress and mitochondrial destruction by removing damaged mitochondria to prevent platelet apoptosis [START_REF] Lee | Inducing mitophagy in diabetic platelets protects against severe oxidative stress[END_REF]. When platelet mitophagy is impaired, which is implicated in COVID-19 pathogenesis, increased platelet apoptosis occurs contributing in enhanced thrombosis [START_REF] Lee | Inducing mitophagy in diabetic platelets protects against severe oxidative stress[END_REF] [START_REF] Wang | Platelet mitochondrial dysfunction and the correlation with human diseases[END_REF] [START_REF] Melchinger | Role of Platelet Mitochondria: Life in a Nucleus-Free Zone[END_REF]. Therfore, preserving platelet mitochondrial function may be an additional means of decreasing the risk of potentially fatal thrombotic events in COVID-19 pathogenesis.

On the other hand, increasing evidence suggests that the iron overload is a causative agent of platelet dysfunction. Iron excess alters mitochondrial function and favors oxidative stress. We believe that there is a certain association between iron overloads and high levels of ROS, where ROS represent an important parameter involved in platelet receptor activation that can result in thrombosis [START_REF] García-Yébenes | Iron overload exacerbates the risk of hemorrhagic transformation after TPA (tissue-type plasminogen activator) administration in thromboembolic stroke mice[END_REF]. Further investigations are needed to define the implication of iron in coagulopathy events.

Furthermore, activated platelets may release microvesicle-associated mitochondria to the extracellular medium upon exposure to oxidative stress. Subsequently, secreted phospholipase A2 could hydrolyse the platelet-released mitochondria generating inflammatory mediators such as lysophospholipids, fatty acids, and mitochondrial DNA, and cardiolipin which then promote endothelial inflammation [START_REF] Coly | Extracellular Mitochondria and vesicles new mediators of endothelial inflammation[END_REF].

Thus, extracellular mitochondria and its "spinoffs" may represent critical mediators in progression of the inflammatory setting leading to coagulopathy associated with inflammatory signalling pathways.

Mitochondria and mitochondria embedded in microvesicles constitute a major subset of extracellular vesicles released by activated monocytes, and their proinflammatory activity on endothelial cells is determined by the activation status of their parental cells. Thus, mitochondria may represent critical intercellular mediators in cardiovascular disease and other inflammatory settings associated with type I IFN and TNF signalling [START_REF] Puhm | Mitochondria are a subset of extracellular vesicles released by activated monocytes and induce type I IFN and TNF responses in endothelial cells[END_REF] [START_REF] Coly | Extracellular Mitochondria and vesicles new mediators of endothelial inflammation[END_REF].

Role of Mitochondrial Cardiolipin in COVID-19 infection

Cardiolipin is a mitochondrial phospholipid which participates in the maintenance of the structural integrity of the mitochondrial membrane. The highest concentration of cardiolipin is concentrated in the monolayer of the inner mitochondrial membrane. Interestingly, serological findings of critically ill COVID-19 patients with coagulopathy and thrombocytopenia, showed the presence of anticardiolipin IgA antibodies in serum. Cardiolipin maintains the stability of cytochrome-c of the electron transport chain, however, it is also oxidation sensitive. The presence of anticardiolipin IgA antibodies may signify oxidative mitochondrial impairments associated with COVID-19 pathogenesis. However, not excluding the possibility that this could result from other thrombotic events in the patients (Zhang et al, 2020b).

COVID19 microbiota dysbiosis disturbs mitochondrial homeostasis via metabolites production

It is of great importance to consider mitochondria-microbiota crosstalk in COVID-19 for several reasons. First, some patients had concurrent gastrointestinal symptoms, including diarrhea. Then, SARS-CoV-2 nucleic acid was detected in the stool of patients with COVID-19 pneumonia [START_REF] Wong | Covid-19 and the digestive system[END_REF]. These observations indicate the ability of SARS-CoV-2 to colonize the gastrointestinal tract, which would disturb gut microbiota. Interestingly, fecal metabolomic analysis suggested potential amino acid-related pathways linking gut microbiota to inflammation explaining the predisposition of certain individuals to develop severe COVID-19 [START_REF] Gou | Gut microbiota may underlie the predisposition of healthy individuals to COVID-19[END_REF]. Addressing the impact of COVID-19 microbiota on mitochondrial function would give new avenues for therapeutic strategies.

The interaction between microbiota and mitochondria appears to occur primarily through signaling from the gut microbiota to mitochondria and from mitochondria to the gut microbiota by means of endocrine, immune, and humoral links [START_REF] Mottawea | Altered intestinal microbiota-host mitochondria crosstalk in new onset Crohn's disease[END_REF])(Saint-Georges-Chaumet et al, 2016) [START_REF] Paule | Microbiota and Phage Therapy: Future Challenges in Medicine[END_REF] [START_REF] Durand | Microbiota Quality and Mitochondrial Activity Link with Occurrence of Muscle Cramps in Hemodialysis Patients using Citrate Dialysate: A Pilot Study[END_REF]. Understandings from studies on mitochondrial functions during bacterial infection provide direct evidence on the connection between microbiota and mitochondria. These studies shed the light on the different strategies developed by bacterial pathogens to subvert functions related to calcium homeostasis, maintenance of redox status and mitochondrial morphology (Saint-Georges-Chaumet et al, 2016) [START_REF] Lobet | Mitochondria: A target for bacteria[END_REF]. Pathobionts such as Fusobacterium, Veillonella, and Atopobium parvulum are another microorganisms who were shown to control mitochondrial activity in favor of infection and inflammation via the production of hydrogen sulfide (H2S) and nitrogen oxide (NO) [START_REF] Mottawea | Altered intestinal microbiota-host mitochondria crosstalk in new onset Crohn's disease[END_REF]. These gases are toxic and induce mitochondrial dysfunction.

H2S toxicity is attributed to the inhibition of mitochondrial complex IV of the respiratory chain, which results in shutdown of mitochondrial electron transport and cellular ATP generation [START_REF] Searcy | Metabolic integration during the evolutionary origin of mitochondria[END_REF][START_REF] Duvigneau | Pathological impact of the interaction of NO and CO with mitochondria in critical care diseases[END_REF][START_REF] Saint-Georges-Chaumet | Microbiota-mitochondria inter-talk: Consequence for microbiota-host interaction[END_REF]. NO displays a high affinity to iron in metalloproteins, especially in hemoproteins that requires O2 for their enzymatic activities [START_REF] Radi | Reactions of nitric oxide with metalloproteins[END_REF] [START_REF] Henry | Interactions of nitric oxide with hemoproteins: Roles of nitric oxide in mitochondria[END_REF] [START_REF] Erusalimsky | Nitric oxide and mitochondrial signaling: From physiology to pathophysiology[END_REF].

NO can compete with O2 binding to hemoproteins leading to its inhibition. Hence, NO mediated hematoproteins inhibition plays an important role for the modulation of mitochondrial function and may lead to enhanced generation of ROS and mitochondrial dysfunction [START_REF] Henry | Interactions of nitric oxide with hemoproteins: Roles of nitric oxide in mitochondria[END_REF] [START_REF] Erusalimsky | Nitric oxide and mitochondrial signaling: From physiology to pathophysiology[END_REF]. In addition, NO have a significant role in inflammation via its interaction with O2 and superoxide anion to produce reactive nitrogen species (RNS) that cause cellular stress and promote pro-inflammatory destructive response [START_REF] Korhonen | Nitric oxide production and signaling in inflammation[END_REF] [START_REF] Erusalimsky | Nitric oxide and mitochondrial signaling: From physiology to pathophysiology[END_REF].

Moreover, commensal gut microbiota influence mitochondrial functions related to energy production, mitochondrial biogenesis, redox balance and inflammatory cascades, making it a potential therapeutic target for endurance through metabolites production including the beneficial short chain fatty acids (SCFA) and secondary bile acids [START_REF] Circus | Intestinal redox biology and oxidative stress Magdalena[END_REF] [START_REF] Bär | Mitochondrial gene polymorphisms that protect mice from colitis[END_REF] [START_REF] Besten | The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism[END_REF] [START_REF] Mottawea | Altered intestinal microbiota-host mitochondria crosstalk in new onset Crohn's disease[END_REF] [START_REF] Durand | Microbiota Quality and Mitochondrial Activity Link with Occurrence of Muscle Cramps in Hemodialysis Patients using Citrate Dialysate: A Pilot Study[END_REF]. Interestingly, SCFA such as N-butyrate by gut commensal microbiota reduce oxidative stress and subsequent ROS production [START_REF] Mottawea | Altered intestinal microbiota-host mitochondria crosstalk in new onset Crohn's disease[END_REF][START_REF] Saint-Georges-Chaumet | Microbiota-mitochondria inter-talk: Consequence for microbiota-host interaction[END_REF]. On the contrary, mitochondrial functions could alter gut microbiota composition and activity. Indeed, as described above, under stressful conditions such as bacterial or viral infection conditions, mitochondria can modulate immune responses leading to heightened inflammation [START_REF] Green | Mitochondria and the autophagy-inflammation-cell death axis in organismal aging[END_REF]. This unbalanced immune response can result in microbiota dysbiosis. Moreover, mitochondria was shown to alter microbial community by affecting the activities of intestinal functional effector cells, such as immune cells, epithelial cells and enterochromaffin cells [START_REF] Cunningham | Peroxisome Proliferator-activated Receptor-γ Coactivator 1-α (PGC1α) Protects against Experimental Murine Colitis[END_REF].

Conclusion

COVID-19 disease management is still an ongoing challenge in the absence of available efficient treatments. Strategies to predict, protect and treat billions of people are urgently required. Therefore, it is essential to understand and analyse the complex mechanism of Covid-19 pathogenesis.

Among the fatal events that clinicians try to avoid when treating COVID-19 patients are blood coagulation, clot formation, stroke and thrombus formation [START_REF] Lodigiani | Venous and arterial thromboembolic complications in {COVID}-19 patients admitted to an academic hospital in Milan, Italy[END_REF][START_REF] Giannis | Coagulation disorders in coronavirus infected patients: {COVID}-19, {SARS}-{CoV}-1, {MERS}-{CoV} and lessons from the past[END_REF]Zhang et al, 2020c;[START_REF] Oxley | Large-Vessel Stroke as a Presenting Feature of Covid-19 in the Young[END_REF]. In this context, we highlight two mechanisms; First, the vicious circle where inflammation cytokine storm, oxidative stress, microbiota dysregulation, iron overload and ROS accumulation indefinitely cause intra and extra mitochondrial dysfunction. Second, dysfunctions that affect the platelet mitochondria and its "spinoffs" which represent critical mediators in progression of the inflammatory setting leading to coagulopathy associated with inflammatory signalling pathways (Figure 1). In addition to treatment of the inflammatory state [START_REF] Mehta | COVID-19: consider cytokine storm syndromes and immunosuppression[END_REF], we envisage the application of approved iron chelators, ferroptosis inhibitors, hepcidin modulators and erythropoietin in management of CODID-19 (Eshagh Hossaini & Haeri, 2019) [START_REF] Monti | Does chloroquine really act through oxidative stress?[END_REF]. Iron chelators would be a more adapted option with minimal side effects [START_REF] Edeas | Iron: Innocent bystander or vicious culprit in COVID-19 pathogenesis?[END_REF]. This strategy consists of selectively binding excess of iron and increases its excretion by urinary and fecal routes [START_REF] Wongjaikam | Current and future treatment strategies for iron overload cardiomyopathy[END_REF]. Different chelating substances are available for this clinical purpose such as deferoxamine, deferiprone and deferasirox [START_REF] Taher | Efficacy and safety of ironchelation therapy with deferoxamine, deferiprone, and deferasirox for the treatment of iron-loaded patients with nontransfusion-dependent thalassemia syndromes[END_REF] [START_REF] Botzenhardt | Safety profiles of iron chelators in young patients with haemoglobinopathies[END_REF]. These inhibitors can also inhibit ferroptosis by decreasing intracellular iron levels [START_REF] Dixon | Ferroptosis : An Iron-Dependent Form of Nonapoptotic Cell Death[END_REF] [START_REF] Dixon | The role of iron and reactive oxygen species in cell death[END_REF].

The characterization of COVID-19 microbiota may also be considered to develop strategies to manage COVID-19 pathogenesis. This will encourage doctors to introduce probiotics or prebiotics to reestablish gut homeostasis, which would limit inflammation and the exacerbated immune response as well as preventing mitochondrial stress.

Targeting the mitochondrial metabolic pathways and redox balance may provide useful therapeutic strategies that specifically target extra and intracellular mitochondria dysfunction or even the reactive species interactome production [START_REF] Koning | The Reactive Species Interactome: Evolutionary Emergence, Biological Significance, and Opportunities for Redox Metabolomics and Personalized Medicine[END_REF][START_REF] Kernan | Hyperferritinemia and inflammation[END_REF].

The pathophysiological role played by platelets and their mitochondria in COVID-19 pathogenesis has not been established. It remains unclear whether these organelles provide energy as healing or proinflammatory factors. The complex interplay between platelet mitochondrial dysfunction, oxidative stress and mitophagy requires further investigation regarding their role in COVID-19 pathogenesis. Overall this may also provide promising therapeutic targets for halting the fatal progression of the disease.

Interestingly, blood mitochondria provides a new avenue with promising potential as a biomarker, target for therapies, and a therapeutic agent (Al Amir Dache et al, 2020).

In spite of potential therapeutic and management strategies described in this perspective, several aspects remain to be elucidated mainly; the role of blood and platelet mitochondria, its quality and functionality on the severity of COVID-19 pathogenesis, mortality risk and its clinical applications.

Another point of concern would be convalescent blood and plasma from COVID-19 survivors that may contain extracellular blood mitochondria or its products from platelets or activated monocytes that could raise concerns regarding blood transfusions. In light of this exceptional pandemic, and major systemic disturbances induced by the COVID-19 virus, novel aspects of the disease should be carefully considered for debate and discussion.

Figure 1. Mitochondria dysfunction in pathogenesis of COVID-19

A hypothetical scheme describing events initiated by the COVID-19 pro-inflammatory surge of cytokines and ferritin levels leading to oxidative stress and cellular damage. Excess intracellular iron interacts with molecular oxygen, generating reactive oxygen species (ROS) through Haber-Weiss and Fenton reactions and reactive nitrogen species (RNS) and reactive sulfur species (RSS). The mitochondria is the central organelle of ROS generation. Increased ROS generation leads to intra and extra mitochondrial damage which in turn leads to 1) Microbiota dysbiosis and 2) Platelet dysfunction which plays a major role in blood clotting and coagulopathy events. Mitochondrial damage cause the release of contents including proteins, lipids and DNA "spinoffs" that further aggravate the inflammatory response in a vicious cycle of events contributing to COVID-19 disease progression.

Funding source

KKS is supported by an NIH grant R01 CA204430. JS is supported by College of Medicine, Sultan Qaboos University.

Ethical approval

Approval was not required.

Conflict of interest

No conflict of interest to declare.


Paolo Campo
email: paolo.campo@ird.fr

Olivier Dangles

An overview of games for entomological literacy in support of sustainable development

Insects have a significant role towards achieving sustainable development, but the decline of insect knowledge outreach efforts is dampening their impact. Revisiting the perspective and approach to entomological literacy is required to respond to the evolving human needs for sustainable living in light of the decline of insect biomass and biodiversity, and entomology. This is also an opportunity to reflect on the interests about insects in the age of video games. Using games for learning and education can be a viable strategy to advance entomological literacy and support the sustainable development goals by potentially lowering the barriers to

Introduction

As ecosystem services and disservices provided by insects [1] affect all of the United Nations' sustainable development goals (UN SDGs), research into insect-centric or insect-inspired solutions has great potential to address current global challenges [2]. However this task is under pressure in view of the decline of insect science, which includes the decrease or bias against research funding [3-6], lack of courses being taught at universities [5], the decrease in the number of scientists specializing in entomology [6] and, consequently, entomology outreach efforts. There is a need to reinvigorate insect science from the ground up with entomological literacy at its core if we are to respond to the growing challenges of sustainability. Advancing entomological literacy, in particular, supports the SDG 4 th challenge, which aims for the provision of quality education for all that also incorporates sustainable development concepts and practices. Beyond entomological literacy, studying insects is not only important for the sake of it, but to science in general as it contributes to the understanding of broader scientific concepts and applications [START_REF] Matthews | Insects as teaching tools in primary and secondary education[END_REF][START_REF] Idsardi | Modifying scientific research into introductory science course lessons using a 5E lesson format: an active learning approach[END_REF].

Drawing inspiration from insects as solutions for SDG 4 [START_REF] Matthews | Insects as teaching tools in primary and secondary education[END_REF][START_REF] Weeks | Interest in insects: the role of entomology in environmental education[END_REF][START_REF] Boppré | The butterfly house industry: conservation risks and education opportunities[END_REF][START_REF] Weaver | Community entomology : insects, science and society: part a -community engaged learning[END_REF], however, is far from trivial. The decline of insect biomass and biodiversity across the globe decreases the frequency of contacts between humans and a diverse community of wild insects [3,[START_REF] Sánchez-Bayo | Worldwide decline of the entomofauna: A review of its drivers[END_REF], thus reducing opportunities to learn from them. Moreover, society has adverse perceptions, reactions and behaviours towards insects and other invertebrates [START_REF] Kellert | Values and perceptions of invertebrates[END_REF][START_REF] Matthews | Insects as teaching tools in primary and secondary education[END_REF][START_REF] Weeks | Interest in insects: the role of entomology in environmental education[END_REF], thus there is little interest in learning about what is often referred to as "creepy crawlies". This begs the question, how do we overcome the challenges of entomological literacy when the traditional approaches are no longer enough? Extending this to include the UN SDG perspective, how can we effectively use games to educate people about insects and help them to face key issues in sustainability? We have to revisit our approach to insect education to reflect the pressing need for a sustainable way of life, as well as society's increasing interests in entertainment. To this end, we can turn to games.

In this paper we examine how research is making use of games to promote and advance entomological literacy. We further explore the avenues to which research into games for entomological literacy can advance within and outside the academic setting, thus providing complementary ways for society to respond to the global challenges of sustainability. Using games to pique the interest in insects of sustainable development stakeholders is a strategy worthy of further investigation. A global survey of insect-related topics in Google Trends in the past five years yielded an unexpected result, a topic related to a video game (see Box 1). This challenges our assumption that queries about insects are mainly related to them being problems for humans, either pests or disease vectors. This should make us rethink about the perceptions and valuations of insects in the age of video games, and think about how we may leverage that knowledge to advance entomological literacy. If insects are presented in nonconventional means and in a positive light, it may be possible for people to become interested in insects, and possibly even have more empathy for them [3].

Games for entomological literacy and their relationships with sustainable development

Using games for teaching and learning, while not the only solution, has several advantages, such as effective learning outcomes, personal and social development, and user-centred learning [START_REF] Anastasiadis | Digital game-based learning and serious games in education[END_REF][START_REF] Zhonggen | A meta-analysis of use of serious games in education over a decade[END_REF]. To get an overview of how research has approached the topic of games for entomological literacy, we conducted a search in the Web of Science on all the documents in all of the available databases of the platform for all the years until November 2019, using the following search terms: (game OR serious game OR game science) and (education OR learning OR teaching) and (insect OR entomology). After reading all the abstracts and removing erroneous entries and articles from the same study, we were left with only 12 records [START_REF] Martin | Prevalence of direct and emergent schema and change after play[END_REF][START_REF] Kachergis | Desirable difficulties during the development of active inquiry skills[END_REF][START_REF] Garcia-Barrios | The Azteca Chess experience: learning how to share concepts of ecological complexity with small coffee farmers[END_REF][START_REF] Hong | Gamify garden science knowledge to improve science education[END_REF][START_REF] Bell | Pesticide use and cooperative management of natural enemy habitat in a framed field experiment[END_REF][START_REF] Vontas | Automated innovative diagnostic, data management and communication tool, for improving malaria vector control in endemic settings[END_REF][START_REF] Amelotti | Scientific literacy in the pre-school level: first knowledge as tools for health promotion and prevention of Chagas disease[END_REF][START_REF] Su | A mobile game-based insect learning system for improving the learning achievements[END_REF][START_REF] Westgarth-Smith | A game demonstrating aspects of bumblebee natural history[END_REF][START_REF] Vivas | A game as an educational strategy for the control of Aedes aegypti in Venezuelan schoolchildren[END_REF][START_REF] Neto | Dengue vector control and community participation in Catanduva, São Paulo State, Brazil[END_REF][START_REF] Pieters | Use of computer game Cotgame in teaching entomology[END_REF] (Figure 1). Three of the records were on games focusing on insect biology and ecology, which supports SDG4, with students being the target users of the games [START_REF] Hong | Gamify garden science knowledge to improve science education[END_REF][START_REF] Su | A mobile game-based insect learning system for improving the learning achievements[END_REF][START_REF] Westgarth-Smith | A game demonstrating aspects of bumblebee natural history[END_REF]. Six games for entomological literacy can be linked to other sustainable development goals [START_REF] Garcia-Barrios | The Azteca Chess experience: learning how to share concepts of ecological complexity with small coffee farmers[END_REF][START_REF] Bell | Pesticide use and cooperative management of natural enemy habitat in a framed field experiment[END_REF][START_REF] Vontas | Automated innovative diagnostic, data management and communication tool, for improving malaria vector control in endemic settings[END_REF][START_REF] Amelotti | Scientific literacy in the pre-school level: first knowledge as tools for health promotion and prevention of Chagas disease[END_REF][START_REF] Vivas | A game as an educational strategy for the control of Aedes aegypti in Venezuelan schoolchildren[END_REF][START_REF] Neto | Dengue vector control and community participation in Catanduva, São Paulo State, Brazil[END_REF].

Researchers studied the effectiveness of their games in terms of learning outcomes [START_REF] Hong | Gamify garden science knowledge to improve science education[END_REF][START_REF] Su | A mobile game-based insect learning system for improving the learning achievements[END_REF], engagement of the students to the material [START_REF] Amelotti | Scientific literacy in the pre-school level: first knowledge as tools for health promotion and prevention of Chagas disease[END_REF][START_REF] Westgarth-Smith | A game demonstrating aspects of bumblebee natural history[END_REF], and cognitive abilities [START_REF] Kachergis | Desirable difficulties during the development of active inquiry skills[END_REF]. As examples of studying insects beyond entomological literacy [START_REF] Matthews | Insects as teaching tools in primary and secondary education[END_REF], a live action role-playing game was used to teach about the natural history of a bumblebee, food webs and feeding relationships [START_REF] Westgarth-Smith | A game demonstrating aspects of bumblebee natural history[END_REF] (Figure 2A), and a computer game was used to teach the concept of economic thresholds [START_REF] Pieters | Use of computer game Cotgame in teaching entomology[END_REF]. Also, researchers have been using games to foster collective learning and action, such as in crop pest management. For example, the Azteca Chess board game was used to communicate the complexity of biological pest control to coffee farmers [START_REF] Garcia-Barrios | The Azteca Chess experience: learning how to share concepts of ecological complexity with small coffee farmers[END_REF]. A previous research of one of the co-authors of this article described the use of a tabletop role-playing game to increase the integrated pest management knowledge of farmers in the tropical Andes [START_REF] Rebaudo | Agent-based models and integrated pest management diffusion in small scale farmer communities[END_REF] (Figure 2B). For disease control and in support of SDG 3, the ResistanceSim game (Figure 2C) is being used to train stakeholders involved in malaria control in Africa and Southeast Asia within a comprehensive training program and malaria prevention framework [START_REF] Vontas | Automated innovative diagnostic, data management and communication tool, for improving malaria vector control in endemic settings[END_REF][START_REF] Thomsen | ResistanceSim: development and acceptability study of a serious game to improve understanding of insecticide resistance management in vector control programmes[END_REF]. Linking entomological literacy to practical or real world issues can have direct and knock-on effects on other UN SDGs. Farmers learning about insect-informed agro-ecological practices, for example, may reduce their use of chemical pesticides (SDG 6 and 12), thus improving their livelihoods (SDG 1, 2 and 8) and safeguarding their health (SDG 3). Beyond the games themselves, the deliberate and conscious conservation of insects resulting from improved entomological literacy, together with the creation and strengthening of real-world and virtual communities through individual and collective games, can establish long-lasting partnerships and ensure the sustainability of insects' ecosystem functions and services (SDG 11, 14, and 15). It is worth noting that games are often implemented through non-digital platforms, which is relevant to resource-challenged educational institutions, research projects and outreach efforts.

Advancing research into entomological literacy games to support sustainability

While interest in research into games for learning has been increasing in recent years [START_REF] Zhonggen | A meta-analysis of use of serious games in education over a decade[END_REF], we are interested to know how much of this interest is directed towards insect science. This may reveal the lack of research in this area, and therefore highlight the opportunity for further exploration. To this end, we conducted a search in the Web of Science platform to obtain the number of records on game research related to entomological literacy, and use that as our proxy indicator. Our search was on all the documents in all of the databases for all the years until November 2019 using the following search terms: (game OR serious game OR game science) and (education OR learning OR teaching). The query results yielded 51,448 records across 155 research areas, with 709 unclassified records (Figure 3). Compared with the top research area, computer science, with half of the total volume of games research, entomological-literacy-related research is clearly lagging behind (0.05%). Zoology and environmental sciences hardly fare any better at 1.08% and 2.44%, respectively. We can take stock of the research gaps, particularly in relation to the SDGs (Figure 1). Further research into the effective development and use of games for entomological literacy in support of the SDGs may be enhanced or sustained by advancements in technology and gaming. 3-D digital models providing a detailed view of the morphology and anatomy of insects can be used as a platform to appreciate the beauty of insects [START_REF] Nguyen | Capturing natural-colour 3D models of insects for species discovery and diagnostics[END_REF]. Also, virtual and augmented reality technologies can provide immersive experiences to overcome the phobia or aversion to insects and arthropods [START_REF] Botella | Mixing realities? An application of augmented reality for the treatment of cockroach phobia[END_REF][START_REF] Juan | Using augmented reality to treat phobias[END_REF] (Figure 2D), which can impede the uptake of entomological knowledge. Digital social networks and crowdsourcing can be used to promote [START_REF] Lessard | A guide to public engagement for entomological collections and natural history museums in the age of social media[END_REF], construct and share entomological knowledge, such as the citizen science application iNaturalist developed by the California Academy of Sciences and National Geographic. Incidentally, iNaturalist, is also a gamified application [START_REF] Robson | Is it all a game? Understanding the principles of gamification[END_REF], in which it publicly ranks users based on the number of identifications and observations they have made. We can also look into the popularity of particular games and applications to promote entomological literacy. The augmented reality-based game Pokémon Go (Figure 2E), developed by Niantic and released in 2016, was created by Satoshi Tajiri based on his childhood experience from collecting insects (Time, URL: https://tinyurl.com/jkepqlq).

The entomological community was inspired with its enormous potential to entice people into learning more about insects [35,(J Jackson, Deutsche Welle, URL: https://tinyurl.com/te4h77)].

Another example is Minecraft, in which a customized virtual world could be built and then explored for environmental education, such as pollination [START_REF] Hobbs | Environmental education and engagement using a construction play computer game[END_REF] (Figure 2F). Experiential learning, a pedagogic strategy, can be enhanced by following the principles of the mechanics, dynamics, emotions framework, which outlines the key principles for gamifying an experience [START_REF] Robson | Is it all a game? Understanding the principles of gamification[END_REF]. The recent release of Google Stadia (Google, URL: https://tinyurl.com/y3658j2), a game-streaming platform, opens the floodgates to ubiquitous learning using more complex and highly detailed video games and requires only an internet connection and a display screen (SDG 9). The growing access of women and children to mobile games and devices, such as smartphones, may be an opportunity to increase their participation and inclusion in discussions and actions addressing sustainable development issues (SDG 5 and 9). Using games to promote insectbased food can support the growing industry of insect protein production for animal and human consumption in which the game could be similar to Edible Games (J Sandercock, Game Developers Conference, URL: https://tinyurl.com/tbfrhah) (SDG 2 and 13).

We have to take caution, though, and should not consider the use of games for learning as the silver bullet. Some games have failed to live up to expectations [START_REF] De Freitas | Are games effective learning tools? A review of educational games[END_REF][START_REF] Luz | Using a serious game to promote communitybased awareness and prevention of neglected tropical diseases[END_REF][START_REF] Desmet | A meta-analysis of serious digital games for healthy lifestyle promotion[END_REF], and there is a risk of overloading the end-user with too much information [START_REF] Kalyuga | Evaluating and managing cognitive load in games[END_REF]. Moreover, the cost of developing customized or fit-for-purpose games and the associated equipment, limited access to reliable internet, and the digital literacy required [START_REF] Arnseth | Games as tools for dialogic teaching and learning: outlining a pedagogical model for researching and designing game-based learning environments[END_REF] could perpetuate or even exacerbate societal inequalities (SDG 5 and 10). We have to take steps or make adjustments to minimize these negative effects, such as modifying commercially available games, like Minecraft (A Fleck, Microsoft, URL: https://tinyurl.com/tu5sr8v), to fit the purpose while reducing costs [START_REF] Popescu | Serious games in formal education: discussing some critical aspects[END_REF].

Tabletop and live action role-playing games are also strong options, in which some games may only require pen and paper. Gaming and technological trends and advancements [43,(S Bosman, Newzoo, URL: https://tinyurl.com/rwdrnlf)] are also closing this gap.

Research into systematic approaches for insect literacy that provides opportunities for the target recipients to reflect on and apply the lessons they have learned into practical situations, such as in sustainable development efforts, may prove to be one of the keys to more effective development and use of entomological literacy games. For example, debriefing, a guided analytical process in which the participant is afforded time to reflect, share and give meaning to their experience [START_REF] Lederman | Debriefing: Toward a systematic assessment of theory and practice[END_REF], is often left out in the gaming process [START_REF] Crookall | Serious Games, Debriefing, and Simulation/Gaming as a Discipline[END_REF]. It is argued, however, that learning is mostly concretized through this post-game analysis [START_REF] Lederman | Debriefing: Toward a systematic assessment of theory and practice[END_REF][START_REF] Crookall | Serious Games, Debriefing, and Simulation/Gaming as a Discipline[END_REF]. In addition, systematic approaches to developing game products that can foster collective learning and action are available, such as citizen science (see [START_REF] Irwin | Citizen Science: A Study of People, Expertise and Sustainable Development[END_REF]) and companion modelling (see [START_REF] Barreteau | Our Companion Modelling Approach[END_REF]). Using games in the policy planning and implementation arena may allow equitable participation of different members of communities in the formulation and implementation of these plans [START_REF] Mayer | The Gaming of Policy and the Politics of Gaming: A Review[END_REF][START_REF] Edwards | Tools for adaptive governance for complex social-ecological systems: a review of role[END_REF], which may reduce the injustices that may arise from poorly planned and implemented actions (SDG 16), and allow them to share the risks, rewards and responsibilities for these actions. For example, involving policy designers and decision makers who market or promote harmful pesticides, as well as farmers or communities who use them, in a collective planning environment may socially compel the participants to change their existing practices and policies for food production.

Conclusions

Advancing entomological literacy can help in achieving the UN SDGs. With the increasing popularity of games, as well as games and gaming devices becoming more accessible, games for entomological literacy can be a platform for inclusive and equitable quality education and, as an extension, for supporting sustainable development initiatives. Nonetheless, this requires more exploration and research. For example, a robust and unified method or framework for evaluating the efficacy of games based on their goals for the target (users), as well as in relation to the overall goals of the research linked to these games, is still non-existent. Research in the application and efficacy of more accessible technologies, methods and equipment, such as Google Cardboard© to improve game immersion and learning, as well as game distribution services such as Steam© and Google Stadia© for delivering ubiquitous and accessible learning platforms online, may allow overcoming the boundaries of learning, participation, and action.

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

• of special interest •• In light of the global decline of insects, the authors make a case on the urgency to improve entomological knowledge to conserve insects, and they emphasize the need for public engagement, not only to fill in the data gaps, but also to take active roles in the conservation process. To this end, they outline several approaches to get society interested and involved in insect conservation. We ran a global Google Trend search for the topic of "insect" for the past 5 years and looked at related searched topics. Surprisingly, at the world level, the first topic associated with "insect" search is "glaive" -a weapon in the video game Monster Hunter 4 and Monster Hunter: World. The insect glaive, in conjunction with an insect-like equipment called kinsect, imbues the player's game character with insect-like abilities, which appeals to many players (Reddit, URL: https://tinyurl.com/v3qccax).

We then mapped the countries that had insect-related game topics (not just about Monster Hunter) within their respective top 5 list, with the highest rank shown in the world map below. Countries having no records or no insect-related game topics in the top 5 have a value of 0. North America, Australia, a large section of Europe and portions of South America and South-east Asia have strong games-related interest in insects.

Figure 1. The reviewed research articles and their links to the UN SDGs. We included additional information about the games, namely, the users, the knowledge imparted and the platform of the game.

Figure 2. Examples of insect-related games and game-related inspirations: (A) real-life bumblebee game, in which students and teachers play different roles of bumblebees, cuckoo bees and crab spiders, and they interact based on real behaviors of these animals [START_REF] Westgarth-Smith | A game demonstrating aspects of bumblebee natural history[END_REF]; (B) in this tabletop role-playing board game for community integrated pest management literacy, the player makes management decisions (coloured cards) to control the pests (circular tokens) in their farm plots (grid) [START_REF] Rebaudo | Agent-based models and integrated pest management diffusion in small scale farmer communities[END_REF]; (C) the ResistanceSim game for training on Malaria control takes into account different spatial and management scales, such as at the local or district level shown in this photo [START_REF] Thomsen | ResistanceSim: development and acceptability study of a serious game to improve understanding of insecticide resistance management in vector control programmes[END_REF]; (D) augmented reality allows the patient to control their phobia, in this case cockroaches, without actually being exposed to these insects physically [START_REF] Botella | Mixing realities? An application of augmented reality for the treatment of cockroach phobia[END_REF]; (E) Pokémon Go's augmented reality interface and game design encourages the player to explore the outside world (photo taken by one of the authors); and (F) Minecraft's virtual world for environmental education can be designed to learn about insect pollination processes [START_REF] Hobbs | Environmental education and engagement using a construction play computer game[END_REF].

  Thus, we invite the readers to open their minds to the opportunities that abound in entomological gaming. Let the games begin! Funding: This research received support through the postdoctoral grant of P.C. from the Institut de recherche pour le développement, and from the McKnight Foundation through grant 16-213 (LEGUMIP).

  4. Loxdale HD: Insect science -a vulnerable discipline? Entomologia Experimentalis et Applicata 2016, 159:121-134. 5. Leather SR: Taxonomic chauvinism threatens the future of entomology. 2009, 56:4. 6. Holden C: Entomologists wane as insects wax. Science 1989, 246:754-756. playing-games as serious games at the community-policy interface. Environ Res Lett 2019, 14:113002. Box 1. Interest on insects related to games

Figure 3 .

 3 Figure 3. The distribution of records according to Web of Science research fields in % (log scale),


N Carjan

M Rizea

Acceleration induced neutron emission in heavy nuclei

Keywords: N. Carjan, M. Rizea neutron emission, acceleration, moving potential, time-dependent Schrödinger equation

What if, like a fully-filled water tank, a nucleus will spill its less bound nucleons when accelerated? Most probable this could happen to neutrons since, contrary to protons, they are not protected by a Coulomb barrier.

In case the answer is "yes", we are dealing with a new way of neutron emission from nuclei.

Acceleration of heavy nuclei is an integral part of nuclear fission and reactions induced by heavy-ions. If neutrons are emitted during the acceleration of the fission fragments or when the projectile moves closer to or away from the target, one has to take into account this emission in the analysis of the data.

To give a first answer to this captivating question we choose a simple framework: the independent particle shell model [START_REF] Goeppert-Mayer | Nuclear Shell Structure[END_REF] and a simple scenario borrowed from the operating mode of a linear accelerator [START_REF] Wiedemann | Particle Accelerator Physics[END_REF]. We therefore solve the time-dependent Schrödinger equation with a moving mean-field of Woods-Saxon type and study the change in the neutron eigenstates during 10 -21 sec of constant acceleration followed by 10 -21 sec of constant velocity.

As in the independent particle shell model, we look at one neutron at a time. It moves in a mean field created by all other nucleons. At the same time it contributes to the potential seen by the others. If the nucleons are displaced, the nuclear density is displaced and, by selfconsistency, the potential follows. As for the shell model, our approach is expected to work for weakly bound nucleons.

The motion of a quantum particle in a moving one-dimensional potential well has been already studied in the field of control systems [START_REF] Rouchon | Control of a quantum particle in a moving potential well in[END_REF][START_REF] Beauchard | Controlla-bility of a quantum particle in a moving potential well[END_REF][START_REF] Miyashita | Conveyance of a quantum particle by a moving potential well[END_REF].

In our case, we consider a neutron in a moving nuclear potential that has axial symmetry. It is represented by a wave function solution of the Schrödinger equation

ih ∂Θ(ρ, z, t) ∂t = H(ρ, z, t)Θ(ρ, z, t), (1)
where H is the single-particle Hamiltonian.

H = - h2 2m 1 ρ ∂ ∂ρ + ∂ 2 ∂ρ 2 + ∂ 2 ∂z 2 - Λ 2 ρ 2 +V (ρ, z -α(t)).
To cover nuclei from spherical to strongly deformed, the formalism is developed in cylindrical coordinates. α(t) describes the displacement of the potential in time along the z axis. Λ is the projection of the orbital angular momentum on the symmetry axis. For simplicity the spin-orbit term is neglected. By the Liouville transformation Φ = ρ 1/2 Θ, the first derivative with respect to ρ from H is removed, resulting a simplified Hamiltonian H of the form:

H = - h2 2m ∂ 2 ∂ρ 2 + ∂ 2 ∂z 2 - Λ 2 -1/4 ρ 2
+V (ρ, z -α(t)).

To solve the corresponding equation, a transformation of both the variable and the function from the non-inertial (laboratory) to the inertial (nuclear) system is convenient. It avoids an interpolation of the potential between the grid points at each time step. We will explain this transformation on the 1-D TDSE:

ih ∂Φ(t, z) ∂t = - h2 2m ∂ 2 Φ(t, z) ∂z 2 +V (z-α(t))Φ(t, z) (2)
We go in the nuclear frame by the following changes of the variable z → q and of the function Φ → Ψ [START_REF] Butkovsky | Control of Quantum-Mechanical Processes and Systems[END_REF]:

q = z -α(t), Φ(t, z) = exp(u)Ψ(t, q) (3) where u = ib z α -α α + 1 2 t 0 α2 (t ′ )dt ′ .
By taking b = m h , it can be shown that Eq.(2) will be transformed in ih ∂Ψ(t, q) ∂t = -h2 2m

∂ 2 Ψ(t, q) ∂q 2 + V (q)Ψ(t, q) (4) +mq α(t)Ψ(t, q).
To eliminate the linear term in q (which tends to ∞ as q → ∞), a further function transformation is performed [START_REF] Chou | Time-dependent Schrodinger equation with Markovian outgoing wave boundary conditions: Applications to quantum tunneling dynamics and photoionization[END_REF]

Ψ(t, q) = exp -i λ h χ(t, q) (5)
with

λ(t, q) = qm t 0 α(t ′ )dt ′ = qβ(t).
In our particular case α(t)

= 1 2 At 2 . α = At, α = A, λ = Bqt, B = mA u = ib zAt - 1 3 A 2 t 3
and the equation for χ assumes the form:

ih ∂χ(t, q) ∂t = - h2 2m ∂ 2 χ(t, q) ∂q 2 + 2 hi Bt ∂χ(t, q) ∂q - 1 h2 B 2 t 2 χ(t, q) + V (q)χ(t, q). (6)
The advantage of these transformations is that they lead to equations in which the potential depends on a time-independent variable, the dependence on α(t) being transferred in the coefficients of Eqs.(4), [START_REF] Butkovsky | Control of Quantum-Mechanical Processes and Systems[END_REF].

Since the potential moves along the z-axis, the inclusion of the second coordinate ρ is straightforward. We therefore work with the variables ρ and q on a finite numerical grid: [0,160]x[-256,256], ∆ρ = ∆q =1/8 fm. For the time evolution we use the step ∆t =1/128 ×10 -22 sec. The equations ( 4) and ( 6) are solved numerically by the Crank-Nicolson method. One obtains a linear system which is solved by a routine based on the Strong Implicit Procedure [START_REF] Jesshope | SIPSOL -suite of subprograms for the solution of the linear equations arising from elliptic partial differential equations[END_REF]. As initial so-lutions (at t = 0) we consider eigenfunctions of the original Hamiltonian.

The propagation in time is done in two steps. We consider a quadratic α(t) and use Eq.( 6) for 10 -21 sec. Then we consider a linear α(t) and use Eq.( 4) without the α term for another 10 -21 sec. At any time, by performing the inverse tranformations, we can retrieve the solution Φ(ρ, z, t) of the original equation. For the 1st step we choose the constant acceleration A=0.5[10 44 f m/sec 2 ] resulting a constant velocity v =5[10 22 f m/sec]=0.167c for the 2nd step. c is the speed of light. As first example, we take spherical 236 U and study 3 neutron states with Λ=0 around the Fermi level. The parameters of the Woods-Saxon potential are fitted to single-particle and single-hole states in the 208 Pb region [START_REF] Rost | Proton shell-model potential for lead and the stability of superheavy nuclei[END_REF].

Fig. 1 shows the result for the 14th eigenstate laying at -4.8 MeV. For T > 0, the wave packet exhibits a changing asymmetry with respect to the ρ axis indicative of an oscillation. In fact, we are dealing with an oscillation over the usual vibration of a quasistationary state. A similar vibration causes the barrier asaults in the Gamow picture of α decay [START_REF] Gurwitz | Decay width and shift of a quasistationary state[END_REF]. The presence of the neutron inside the nucleus, measured by N in , decreases from 1.00 (at T=0) to 0.88 (at T=10). A neutron, initially occupying this state, has therefore 12% chance to be emitted during the acceleration phase. For T > 10 the oscillatory motion continues. At T=20 N in reaches an even lower value (0.86) because at T=10 the wave packet has short unbound tails which will inevitably leave the nucleus.

The most probable direction of emission is 180 • with respect to the displacement of the nucleus as in classical mechanics. There is however a weaker branch at ≈ 150 • which has a quantum origin. It is known that the tunneling path of a metastable state is mainly dictated by its quantum numbers [START_REF] Talou | Time-dependent approach to bidimensional quantum tunneling: application to the proton emission from deformed nuclei[END_REF][START_REF] Carjan | Angular distribution of protons emitted from oriented nuclei: toward imaging single-particle wave functions[END_REF]. In other words the emission preserves the spatial distribution of the respective state. Hence we expect a 2nd peak at 125 • in the nuclear system which translates into an emission at 150 • in the laboratory system. Fig. 2 shows the time dependence of a neutron states with energy (-3.4 MeV) above the Fermi level. 49% of this wave function is emitted, in the same interval of time, through strong oscillations. Predictably, the emission starts earlier and is more intense. As for Φ 0 14 , there are also two directions of emission: one intense at 180 • and one weak at an angle between 180 • and 90 • .

A wave function with energy lower than the Fermi level was found to oscillate during both regimes: quadratic and linear α(t). It doesn't however succeed to escape: its presence inside the nucleus doesn't change.

The percentage of the wave packet that leaves the nucleus, N in (0) -N in (T), is a measure of the neutron emission probability. We have plotted this quantity as a function of time for Φ 0 14 and Φ 0 15 in Fig. 3. As expected, neutrons that are less bound have higher emission probability. One can observe the effect of the oscillation of the wave function in the mean-field and the plateau at large times (the emission is gradually reduced when the acceleration is turned off) .

Summing up, we start with an eigenstate that, due to acceleration, becomes wave packet, i.e., it occupies with time dependent probabilities neighbouring states (oscillation) including some in the continuum (emission).

For a better understanding of the physics involved, we divide the total energy in the laboratory system in significant terms:

Φ|H|Φ = - h2 2m Ψ * ∂ 2 Ψ ∂ρ 2 + Ψ * ∂ 2 Ψ ∂q 2 dρdq + h2 2m b 2 α2 |Ψ| 2 dρdq - h2 2m 2ib α Ψ * ∂Ψ ∂q dρdq + h2 2m Λ 2 -1/4 1 ρ 2 |Ψ| 2 dρdq + V (ρ, q)|Ψ| 2 dρdq. (7)
The 1st term is the average kinetic energy in the nuclear frame. The 2nd term reduces to m α2 /2; it is the extra kinetic energy due to the velocity of the potential. The 3rd term reduces to α < p > where < p > is the average momentum in the nuclear frame. It represents the variation of the neutron energy due to the interaction with the moving wall of the potential; equivalent to the "one-body" dissipation [START_REF] Blocki | One-Body Dissipation and the Super-Viscidity of Nuclei[END_REF]. The last two terms are the average centrifugal and nuclear potentials respectively.

The sum E1+E4+E5 i.e., the average neutron energy in the nuclear frame, slightly in- creases up to T=10 and stays constant afterwards. After T=10 the oscillations of E are due only to E3 as clearly seen in Fig. 4.

In the absence of correlations the oscillations last long time. In reality, with increasing excitation energy, the time between collisions decreases and the oscillations are slowly damped due to the onset of correlations.

Finally we study the effect of nuclear deformation on the neutron emission due to acceleration of the nucleus along the deformation axis. For this we describe the nuclear shape by a pure Cassini oval with a prolate deformation parameter ǫ=0.52. It represents the shape isomer of 236 U [START_REF] Pashkevich | On the asymmetric deformation of fissioning nuclei[END_REF]. The results for two neutron states, one below and one above the Fermi level, are presented in Figs. 5 and6 respectively. The emission probability is again larger in the latter case: N in = 0.77 vs 0.39. One can also notice that the emission at angles smaller than 180 • to the z-axis is much intenser than in the previous cases. It is because a quasi-stationary state in a deformed nucleus tunnels most probably pependicularly to the deformation axis [START_REF] Strottman | New Aspects in the Decay of Quasi-Stationary States by Multidimensional Tunneling[END_REF], irrespective if the barrier is lower or higher along this direction. It is what happens here: the emission occurs at 90 The neutron energy in the laboratory system (red), in the nuclear system (blue) and the energy due to the interaction with the moving potential (green).

nuclear system. Due to the displacement of the nucleus however, in the laboratory system, the emission occurs at slightly larger angles (≈ 110 • ). Hence there is a qualitative difference between spherical and strongly deformed nuclei: in the latter case, the direction imposed by quantum mechanics competes in intensity with the classically expected direction of emission. Since in the present calculation the potential moves in the z-direction (Eq. ( 2)), one can study nuclei with the deformation axes aligned with the velocity vector (axial symmetry). In heavy-ion reactions however a deformed projectile approches a target with different orientations of the deformation axes. For a quantitative evaluation, an average over all orientations has to be performed.

This type of neutron emission doesn't occur only during the acceleration of a nucleus but also during the slowing down (A<0) of a projectile when it approaches a target. Among possible effects, an increase of the neutron-transfer cross section is expected.

The chosen value of A (0.5) is two times larger than the acceleration during the Coulomb repulsion of two equal fission fragments from 236 U separated by D cm = 20 fm (A=0.249) but comparable with that for the collision of two 236 U nuclei at the same distance of approach (A=0.498). In conclusion, the excitation of the fission fragments during their acceleration (separation) is improbable. On the other hand, a heavy projectile could become excited (even emit neutrons) when it approaches a heavy target or moves away from it. For a quantitative answer a dedicated study is necessary. The acceleration produced in Coulomb interactions is not constant, it depends on D cm . A high level can be however maintained for 10 -21 sec, a short time at the scale of the above mentioned processes (10 -20 sec).

A heavy-ion of mass m and charge q in an electric field E is accelerated along the field lines; a = qE/m = 0.376

× 10 23 × E[f m/s 2 ] with E in [V /m].
To attain an acceleration comparable with the one used above requires E = 10 21 [V /m] i.e., a much too large value.

A comment on the peculiarity of accelerating a heavy-ion is appropriate. Altough all forces that produce the acceleration of heavy ions (such as the Coulomb force or the force qE exerted by an electric field E on a charge q) act only on protons, the neutrons follow. To decouple the two fields one needs extreme conditions. For instance to excite an isovector giant dipole resonance, a relativistic projectile is necessary [START_REF] Stetcu | Relativistic Coulomb Excitation within the Time Dependent Superfluid Local Density Approximation[END_REF].

The process of acceleration induced neutron emission has similarities with the realease of neutrons at scission i.e., during the last stage of nuclear fission [START_REF] Rizea | Dynamical Scission Model[END_REF][START_REF] Carjan | Similarities between calculated scission-neutron properties and experimental data on prompt[END_REF]. They are both due to a fast change of the poten- tial in which they move that transforms each neutron state into a wave packet with components in the continuum. In the case of scission neutrons however, it is the shape of the potential and not its position that changes.

A more quantitative evaluation of this process requires a time-dependent, selfconsistent microscopic approach [19]. At present it is a difficult task considering the large numerical grid that is necessary.

We are grateful to Gurgen Ter-Akopian and Jorgen Randrup for their interest in this work and illuminating discussions.

Figure 1 :

 1 Figure 1: (Color online) Time evolution of |Φ 0 14 | 2 during (left) and after (right) acceleration for spherical 236 U . N in is the norm inside the dotted circle defined by V 0 /100. T is the time in 10 -22 sec.

Figure 2 :

 2 Figure 2: (Color online) The same as in Fig. 1 but for Φ 0 15 .

Figure 3 : 3 ΣEFigure 4 :

 334 Figure 3: (Color online) The neutron emission probability as a function of time for Φ 0 14 and Φ 0 15 .

Figure 5 :

 5 Figure 5: (Color online) Time evolution of |Φ 0 17 | 2 during (left) and after (right) acceleration for the shape isomer (deformation parameter ǫ=0.52) of 236 U . N in is the norm inside the dotted ellipse defined by V 0 /100. T is the time in 10 -22 sec.

Figure 6 :

 6 Figure 6: (Color online) The same as in Fig.5 but for |Φ 0 19 | 2 .

  fission neutrons , Phys. Lett. B 747, 178 (2015). [19] Simenel C., Umar A. S., Heavy-ion collisions and fission dynamics with the time-dependent Hartree-Fock theory and its extensions, Prog Part Nucl Phys (2018) 103, 19 (2018).