Patrícia Gonçalves
email: patricia@ipma.pt

Vitor Silva
email: vsilva@deetc.isel.ipl.pt

Alberto G Murta

António Melo

Henrique N Cabral

Vitor Vaz Da Silva

António Ávila De Melo

Image Analysis as a Tool to Age Estimations in Fishes: An Approach Using Blue Whiting on ImageJ

Keywords: Otoliths, fish ageing, image analysis, image processing, blue whiting and fisheries science

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Otoliths are constituted by three pairs of calcareous structures, the sagittae, lapilli and asterisci, which are found in the inner ear. At the end of the 1960s and the beginning of the 1970s, sagittae otoliths started to be used for age determination and to study the feeding relationships between fish predators and their prey [START_REF] Tuset | Otolitos de peces del mediterráneo occidental y del atlántico central y nororiental[END_REF]. Since then the modeling of fish species abundance on the majority of fisheries assessment relies on age based models. Accurate and precise age estimates are critical for the effective management and understanding of fisheries resources because dynamic rates of recruitment, growth and mortality depend on these data [2].

Age classification has been based in age readings under stereo-microscopic observation. The interpretation of age reading is a very difficult task and may change among different readers or as a reader becomes more experienced [START_REF] Doering-Arjes | Estimating population age structure using otolith morphometrics: a test with known-age Atlantic cod (Gadus morhua) individuals[END_REF]. Regularly, calibration age reading workshops are conducted aiming the improvement of accuracy and precision of age estimations between the readers of the same species. Quality assurance in the ageing process guarantees the consistency which is uniquely important to this type of research work [START_REF] Morison | An integrated system for production fish aging: image analysis and quality assurance[END_REF]. The criteria used to count the rings and determine age are made to be objective, but the final classifications are always dependent on the reader's experience, which introduces an interpretation error in the process [START_REF] Campana | Accuracy and precision of age and hatch date estimates from otolith microstructure examination[END_REF]. This interpretation error can be either biased or random. In combination, process and interpretation error can result in age estimates that may differ by as much as a factor of three among readers [START_REF] Donald | Evaluation of the scale and operculum methods to determine age of adult goldeyes with special reference to a doyear-class[END_REF].

There is an urgent need to validate and calibrate the currently age reading procedure within more effective automatic classification, in order to avoid subjective, and misinterpretation among readers. The image analysis constitutes a valuable tool applied to otoliths ageing and the recorded images allow performing simultaneously other studies, such as age validation. Several image analysis programs had been adapted in order to allow automatic count of daily increments such as RATOC [7], Image Pro Plus [START_REF]Pro Plus Available: www.mediacy.com/imageproplus 9[END_REF] and TNPC [9] and also annually increments like Image Pro Plus, TNPC, CAF [START_REF] Morison | An integrated system for production fish aging: image analysis and quality assurance[END_REF] and ImageJ [11]. Although, the majority of the programs requires a license and is expensive, ImageJ has the advantage of being free software which allows record macros making simple and plug-ins that add algorithms to improve species ageing classifications.

The aim of this study is to improve ageing classifications through image analysis making the process based in more objective criteria. In order to achieve that goal a plug-in has been written and added to ImageJ. The otoliths used to test this new approach are from the blue whiting (Micromesistius poutassou) and the preliminary results are presented here. This study has been developed in order to know if: ImageJ could be used as an approach to improve the accuracy and precision of blue whiting ageing estimation?

Contribution to Smart Systems

In fisheries, for stock assessment annually a huge number of otoliths are read and the data for different countries combined. As an example, concerning the blue whiting stock, in 2015, around 102,000 fishes were measured and from these around 30,000 otoliths were processed for age reading, comprising data from 16 countries [START_REF]Report of the Working Group on Widely Distributed Stocks (WGWIDE)[END_REF]. The consistent application of the ageing method over years, among readers, and even among laboratories (countries), is a particular requirement of stock assessment studies [2]. The inter-calibration workshops conducted regularly aim to guarantee that these age data can be combined and all the readers, from the different countries, follow the same criteria. The criteria for age estimation, based on ring counts, is defined to be easy to follow and objective. In practice, the accuracy and precision on age classifications is always dependent on the reader experience which reveal some subjectivity on the criteria. The age reading protocols based on images observations, is time consuming and based on decisions which can differ according to the reader experience.

The increasing demand on fisheries science to produce more data, the time involved and the ageing criteria mostly based on human decision, created the require-ments to searching new technologies applied to age reading estimation. These new technologies should be easy to apply and available to a wide range of scientists.

The otolith grows in size as fish grows; ring bands are formed in the otoliths surface registering periods of rapid and slow growth, opaque bands appear alternating with translucent bands. Therefore, the otoliths are constituted by different optically zones according to their structural appearance or light properties, e.g., translucent or opaque and the distinction among them allows to identify and count the rings through stereo-microscope observation [START_REF] Casselman | Age and growth assessment of fish from their calcified structures-techniques and tools[END_REF].

ImageJ is an open source software for image analysis and processing, and allows user java written plug-ins to be added [11]. Thus, new plug-ins are easily spread and become available to a huge number of scientists with the purpose of improving fish age classification. A smart system for otolith age classification could provide input from different expert readers for the same otolith, and then adaptively learn to classify correctly the ring identification providing further information within each ring that may be useful for the expert readers' further research. The best automatic system should use the output of a camera with optical magnification, identify the otolith and determine its age by providing a value, its confidence intervals and precision to help the researchers evaluate and decide in a more objective way the age classification. In this study, the automatic system is still in development aiming to improve the age classification on blue whiting.

Material and Methods

Sample Collection

Fish samples of blue whiting were collected along the Portuguese coast during 2013, from January to December. Total length (cm) and sex of all blue whiting sampled were recorded and the otoliths were removed from each fish. After, the otoliths were washed and stored dry. Sixty seven blue whiting otoliths were considered for this study. Otoliths were submerged in a 0.1% thymol solution (1g of thymol for 1l of filtered and distilled water) for approximately 24h. The whole otolith was immersed in oil and observed under reflected light against a black background in a stereomicroscope. The otoliths images acquisition was performed using the TNPC software (version 7.0) [9]. For age classification only one otolith of the sagittae pair was used. On the current study the left otolith was used. Age classification was made considering the number of translucent rings in the otolith; one translucent ring was equivalent to one year.

Image Analysis

A plug-in was developed in Java for the ImageJ software [11] which allowed counting the age rings in the otolith image files. On the left otolith of each pair a transect line crossing the otolith longer axis is drawn (Figure 1). The automatic reading evaluation is based on the results from the otolith profile plotted along the longer axis (Figure 2). Image Analysis as a Tool to Age Estimations in Fishes 173

Statistical Analysis

A test of symmetry [START_REF] Hoenig | Analysing differences between two age determination methods by tests of symmetry[END_REF] for determining if significant differences existed between the ages by readers and the ages by ImageJ was applied. The test of symmetry uses a chisquare-type statistical test to determine if the age-agreement table is symmetric or not.

If the age-agreement table is determined to be asymmetric then it can be concluded that there is a systematic difference in ages observed between readers and automatic ageing (ImageJ). Two statistical indicators were used to measure the precision: (i) the average percent error (APE) [START_REF] Beamish | A method for comparing the precision of a set of age determinations[END_REF] and (ii) the coefficient of variation (CV). The APE assumes that the standard deviation of the age estimates are proportional to the mean of the age estimates.

All statistical analyses and plots were performed using the packages FSA and ggplot2 from the statistical environment R [START_REF] Team | Available: www.r-project[END_REF].

Results

The length at age by sex was represented taking into account age classifications by readers (Figure 3a) and by ImageJ (Figure 3b). There are differences in the growth curves, namely the range of ages is higher in the Image J between 0 and 7, while the range by readers varied from 1 to 6. The Hoenig test of symmetry (p = 0.094) indicates that there are systematic differences in the assigned ages between readers and ImageJ. The ages estimation based on the automatic procedure are overestimated compared with the ages attributed from the 1 Denomination used when fish gonads show an earlier development stage and is not possible to assign a sex, i.e., to distinguish between female or male. b) a) readers (Figure 4). The same age was attributed by the two procedures in 36 otoliths, in a total of 67. The precision methods reveal a low percentage of agreement (54%) between the two procedures, with CV=21 and APE=16.

Discussion and Conclusions

The results from this study constitute the first application test performed in blue whiting otoliths from the Portuguese coast. In this test fish from a large length range and both sexes have been used, allowing identification of this procedure applicability in otoliths with different growth patterns. Differences were found in the age estimation from readers and using the ImageJ. Ages from readers take into account the time of the year, the type of otolith border and some subjectivity during ring count based on their experience. Ages are also estimated with the use of auxiliary information, such as fish size or sex which may bias the reader's interpretation [START_REF] Morison | An integrated system for production fish aging: image analysis and quality assurance[END_REF]. There is a certain risk on use the fish size as auxiliary information on ageing, which could result in inability to detect changes on fish growth pattern due to the periods of starvation or to the climate changes, since temperature affects growth. The age estimation from Im-ageJ was only based on the ring count on the density profile plot which is an advantage. As an example, of this study results, a fish with length higher than 30cm, was classified as 1 by ImageJ and 2 years by the readers, this underestimation by the program could be due to readers based their classifications on the fish length and this fish could present a different growth pattern which was not detected in readers' classification. Notwithstanding this particular case, ImageJ is overestimating the ages in the majority of this study classifications, which could be due to a higher sensitivity of the software into recognizing patterns in the otolith density across the whole otolith section which could not be so evident through direct image observation or the irregular surface of some otoliths or the software counts is considering the denominated false rings 2 as valid rings. False rings are a common issue in blue whiting and a source of bias amongst the readers [START_REF]Report of the Workshop on the Age Reading of Blue Whiting[END_REF]. Although, since the age's estimations comparison were based on reader's classifications and not in validated ages those hypothesis need to be further evaluated. In order to validate the plug-in ImageJ estimations, it is important to repeat this test using otoliths from fishes in which the absolute age is known. There are also some basic age validations techniques, such as the relations between fish length and otolith length, fish length and otolith weight [2], which could be applied to the samples used on this study as a way to obtain more precision in estimations. This study constitutes a first approach to the blue whiting ageing validation and classification, the facility of incorporate macros on ImageJ will allow improving and calibrating the results until obtaining a good compromise between the automatic procedures and the fish growth.

The future steps, are applying this plug-in and provide the age estimations using the information of the otolith type of border and the time of the year when the fish was collected. Also, applying the ImageJ plug-in to otoliths with ages validated or in which the age estimation does not present any doubts. These tools will also be tested by experiment readers on blue whiting, as an exercise where the auxiliary information (fish length and sex) will not be provided, during the next international calibration workshop which will be held at Lisbon this June. The authors of this study truly believe that this new approach is a valid and useful application to help, the readers from the different countries, producing more precise and accurate fish age estimations on blue whiting.

Fig. 1 .

 1 Fig. 1. Blue whiting left (top) (with the transect line) and right (bottom) otoliths from fishes with: (a) 1 year old and (b) 4 year old.

Fig. 2 .

 2 Fig. 2. Blue whiting left otolith profile along the long axis from fishes with: (a) 1 year old (Fig. 1a) and (b) 4 year old (Fig. 1b). The arrows indicate the rings position in the profile density plot.The results from the automatic reading application were recorded and compared to the reader's age estimation.

Fig. 3 .

 3 Fig. 3. Fish length (cm) by age according to classifications by: a) readers and b) ImageJ application. Symbols correspond to fish's sex: ▲indeterminate 1 ; • females; and ■ males.

Fig. 4 .

 4 Fig. 4. Age-bias plot of estimations by readers and by ImageJ application. The dashed line represents the age-agreement between procedures. The values represent number of otoliths in percentage.

Acknowledgments. We are thankful to the staff from Instituto Português do Mar e da Atmosfera (IPMA) who collected the blue whiting samples from their survey and from their commercial fishery. The samples used on this study were collected under the Portuguese Biological Sampling Programme (PNAB-EC Data Collection Framework) from IPMA. P. Gonçalves was funded by FCT through the fellowship SFRH/BD/88092/2012. This study had the support of Fundação para a Ciência e Tecnologia (FCT), through the strategic project UID/MAR/04292/2013 granted to MARE.


Ondrej Kachman
email: ondrej.kachman@savba.sk

Marcel Balaz
email: marcel.balaz@savba.sk

Configurable Reprogramming Methodology for Embedded Low-Power Devices

Keywords: reprogramming, embedded, low-power, configurable, over-the-air

The embedded low-power devices are very important part of any smart system. With the large amounts of sensors and actuators used, it is a good practice to implement remote reprogramming capabilities into the firmwares of these devices. This paper presents a new configurable reprogramming methodology that can be applied to various platforms. It is built on the best reprogramming practices while giving developers more control over firmware outline, updated functions and modules. It also refers energy efficiency, as the data shared over the network and memory operations on the devices are minimal. The multiplatform capabilities make this scheme ideal for smart systems.

Introduction

The area of remote and efficient reprogramming of the embedded devices has been researched since the introduction of the low-power devices and the wireless sensor networks. Various reprogramming methods have been developed over the past 15 years. The main goal of these methods is to replace the old firmware version with the new one while keeping the procedure energy efficient and secure. Recent progress in the internet of things technologies, cyber-physical systems and smart systems requires these methods to be evaluated and adjusted to the new trends in these areas.

The research topic of this paper is a configurable reprogramming methodology for low-power devices, as these devices are widely used in the modern intelligent systems, including smart systems. The main advantage of the solution that this paper will present is its platform independency. The configurability (see chapter 4.2) of our solution will provide programmers with more control over the outline of the updated firmware and we present experiments that show how it can help to share less update data on the network and spare program memory with less operations executed.

Relationship to Smart Systems

Smart system is a general term for a system that collects information, processes it and acts based on the results of the data analysis. Smart systems evolved from the simpler systems capable of sensing and basic actuation into the systems with perception superior to a human being. The design of a smart system includes cloud services and networking technologies, choices of the appropriate hardware and software components and their implementation [START_REF] Arsan | Smart Systems: From design to implementation of embedded Smart Systems[END_REF]. The sizes of smart systems can be very different depending on their function. They range from nano-scales to meter-scales. Smart systems can be applied in many sectors, for example healthcare, automotive industry, retail, building management, military, etc [START_REF] Moshnyaga | Guidelines for Developers of Smart Systems[END_REF]. Low-power embedded devices are usually used for sensing, actuation a control.

An embedded device used in a smart system is preloaded with a default firmware. Even the thorough testing may not detect all the errors that this initial firmware has. Once the devices are used in the real environment in great numbers, an identified firmware error may cause a long system downtime until the problem is fixed and the system can be considered reliable again. The over-the-air update methods are developed to update the faulty firmware as fast as possible. These methods can be focused on various sub problems, closely analyzed in the chapter 3.1. The new challenge for these methods regarding the smart systems is their adaptability to the devices based on various platforms that form a smart system. Most works in the area of remote reprogramming are focused on the wireless sensor networks (WSNs) and the TinyOS operating system [3][4]. Most WSNs are homogenous, using devices based on the same platform for data collection. Smart systems and may use different devices for sensing, different devices for networking and different devices for presentation of the information to the users of the system.

To create a multiplatform reprogramming method suitable for the smart systems, there should be no alterations to the compilers or the instructions of the linked firmware images, as these alterations are platform specific. Jump, branch and relative call instructions, that are often altered by these methods, may have different operation codes for each platform. Also, not every platform may support the same instruction set and relocation types. The ideal target for a platform independent solution are the object files, the product of compiler, and the executable file, the product of the linker, later transformed into the binary representation of the firmware.

Once a firmware fault is discovered, the developers may estimate if the fix will require one or more updates. In the case of a single update, it is not required for a device to change the outline of its firmware functions, it can just apply a simple update script. If the problem fix requires incremental updates and debugging, it is good to prepare the device for these patches. An example is to put every function that requires an update to its own memory section [START_REF] Koshy | Remote Incremental Linking for Energy-Efficient Reprogramming for Sensor Networks[END_REF]. The amount of the data shared on the system's network must be as small as possible so it will not affect the other parts of system. Different approaches may be the most suitable for the different parts of the smart system.

State of the Art and Related Work

This section analyzes the most important principles and works in the area of the remote reprogramming for embedded devices. Analyzed papers serve as a base for our methodology that we present in the chapter 4 and evaluate in the chapter 5.

Main Challenges for the Remote Reprogramming Methods

The methods for remote reprogramming of the low power devices are mainly focused on the 4 main sub problems [START_REF] Kachman | Effective Over-the-Air Reprogramming for Low-Power Devices in Cyber-Physical Systems[END_REF]:

Improving firmware similarity. Previous works used altered compilers [START_REF] Huang | WUCC: Joint WCET and Update Conscious Compilation for cyber-physical systems[END_REF], object file alterations [START_REF] Shafi | No-reboot and Zero-Flash Over-the-air Programming for Wireless Sensor Networks[END_REF] and custom linker directives [START_REF] Koshy | Remote Incremental Linking for Energy-Efficient Reprogramming for Sensor Networks[END_REF] to make the firmware images as similar as possible.

Generating delta files. Many differencing algorithms have been developed for various networks of embedded devices [9] [10]. These algorithms are designed to generate very small delta files (deltas, patches). Smaller size improves the energy consumption of the wireless interfaces and prevents the network from congestion or desynchronization.

Network dissemination. Network protocols are responsible for the delivery of the delta files to the target devices. In the past, many protocols have been designed specifically for over-the-air updates [START_REF] Hui | The Dynamic Behavior of a Data Dissemination Protocol for Network Programming at Scale[END_REF]. Smart systems may take advantage of the newer and standard protocols used for the low-power devices. The integrity and security are also a concern in this area. Delta files are split into the number of packets protected by CRC codes and error correcting codes [START_REF] Unterschütz | Fail-safe over-the-air programming and error recovery in wireless networks[END_REF]. Network security of the smart systems and the dissemination of the delta files is out of scope of this paper.

Update execution. The last problem deals with the implementation of the update procedure on the target devices. Reprogramming code is often embedded into the bootloader [START_REF] Dong | R3: Optimizing relocatable code for efficient reprogramming in networked embedded systems[END_REF] or resides in its own reserved space [START_REF] Kachman | Optimized differencing algorithm for firmware updates of lowpower devices[END_REF]. The updates of this code are very rare and critical.

Taking Advantage of the Standard ELF File Format and Relocatable Entries

Object files are the product of compilers. Probably the most popular format of these files is the executable and linkable format, ELF [START_REF]Executable and Linking Format (ELF) Specification Version 1[END_REF]. This format is supported by the variety of compilers, including the well-known GCC and its ports for embedded platforms. The file in this format is also the output of the linker and is later used to create a binary image of a firmware. Embedded systems use the following formats:  Relocatable file -created by a compiler, relocatable entries are not resolved  Executable file -created by a linker, all relocations are resolved The process is shown in the Fig. 1. Relocatable files include unresolved relocations, for example calls, jumps, branches, etc., and these entries are resolved during linking. The authors of [START_REF] Dong | R3: Optimizing relocatable code for efficient reprogramming in networked embedded systems[END_REF] managed to reduce the data shared on the network by setting all relocations to the same value for each firmware, making different versions more similar. This allows the differencing algorithm to generate very small deltas. The real relocation values are propagated as a metadata with the delta files and written to their positions by a loader on the target device.

The authors of [START_REF] Shafi | No-reboot and Zero-Flash Over-the-air Programming for Wireless Sensor Networks[END_REF] alter ELF files in various ways. New functions are placed at the end of the program memory and calls to them are edited. This approach also changes the way sections for initialized and uninitialized variables are allocated in the RAM, so there are fewer shifts for these entries. Some instructions are changed directly, so the algorithm understands operation codes for the selected platform. However, it may not work for a completely different microcontroller.

Fig. 1 Linking relocatable ELF files into the executable ELF file

Relaxation. During development of our own solution, we found some problems with the relocations that changed sizes after linking. This is called relaxation. For example, a compiler may allocate 4 bytes for a call instruction to some function. Linker discovers, that it placed the called function within 128 bytes of the relocation and thus reduces the relocation to a 2-byte relative call, shrinking the calling code. It is therefore important to check the resolved relocations in the executable ELF file.

Fragmented Firmware

Linkers can place code segments to any free address in the program memory. These segments are also called .text segments or sections. If there is a .text section generated for each function, linker can provide these functions with the slop region, a free space in which the function can grow or shrink without causing any other functions to shift [START_REF] Koshy | Remote Incremental Linking for Energy-Efficient Reprogramming for Sensor Networks[END_REF]. This approach helps to generate small deltas and prolong the lifespan of the flash memories. Some works criticized this solution for an inefficient use of the program memory [START_REF] Dong | R3: Optimizing relocatable code for efficient reprogramming in networked embedded systems[END_REF]. More jumps between pages in the memory cause more energy to be consumed, as activation of a different page consumes more power than activation of a different block within the same page [START_REF] Pallister | A high-level model of embedded flash energy consumption[END_REF].

Configurable Method for the Remote Reprogramming

This chapter presents our remote reprogramming methodology. It consists of methods that form a complete, platform independent solution capable of learning about the changes in any firmware and generating as small delta files as possible. Our methods are applied in a software tool we developed. Our methodology includes methods responsible for the following tasks:  Analyzing the object files, listing .text sections and relocations 

Tracking changes for each function, detecting new or deleted functions  Assigning addresses to the functions based on their analysis  Invoking linker, checking for relaxed entries in the final files  Generating delta files Our tool includes a wrapper for the GCC compiler and linker. We aim to test our method and tool on the three different platforms -8-bit microcontroller from the AVR family, 16-bit microcontroller from the MSP430 family and a system-on-chip with the 32-bit ARM Cortex-M0 core. Each platform has its version of the GCC available and supports ELF files. We do not alter the instructions generated by the compiler. The flowchart of our method is in the Fig. 2.

Fig. 2 Flowchart of the proposed method

Research Contribution and Innovation

None of the methods used in our methodology alter any ELF sections that hold instructions or relocations. There is no need to specify instruction formats or relocation types for any platform. This makes our solution platform independent.

Our methodology provides developers with various configurable options described in the following subchapter. Produced output files can be reverse analyzed and provide feedback on how the current configuration can be improved. This is a new approach. Various configurations may be the best for different scenarios.

Our methodology generates smaller deltas than basic differencing algorithms. Less data shared on the network improves the energy efficiency of our solution.

Description of the Processes and Configurability Options

This subchapter describes the configurable processes from the Fig. 2. These are the processes within our proposed method that contribute to its good performance.

List text sections, list relocations. Compilers enable developers to generate a .text section for each function, for example .text.function1, .text.function2. However, both will be linked into the .text section in the executable file. To prevent this, programmer must define a target section for each function in the source code. Our method includes two configurations: 1. Split functions into the sections defined explicitly by the developer 2. Edit string tables of the object files, place each function in its own section

The second option will simply iterate through the ELF string tables and add the number to each .text section, putting previously mentioned functions into sections .text1 and .text2. This does not affect any firmware instructions.

Relocation entries can be read at this point, even though they are not resolved. List of these relocations may be later used before the effective delta generation by setting them to zero and making the firmware images more similar -inspired by [START_REF] Dong | R3: Optimizing relocatable code for efficient reprogramming in networked embedded systems[END_REF].

Check with previous versions, assign addresses to the functions. In this step, our method collects information about every function that was present in the previous version. We evaluate its growth, previous positions, free space in its slop region (if present) and memory shifts its change may cause. The results of these evaluations can result in the different outline of the firmware's functions depending on the following possible configurations: 1. Static addresses -developer can assign some functions to a static address 2. No fragmentation -No function will be provided by a slop region 3. Partial fragmentation -Functions that would cause a lot of shifts are copied to a free space where they can be further edited 4. Full fragmentation -Every function is provided with a slop region.

Generate delta. After linking, when the relocations are resolved, there are two possible configurations: 1. Set all the relocations to zero, generate INSERT operations for the delta 2. Do not alter the relocations, run the differencing algorithm directly Differencing algorithm also supports two different modes. These modes are relevant when the firmware is being fragmented or defragmented: 1. Dirty mode -unused sections that previously contained data are not erased 2. Clean mode -unused sections are erased and filled with 0xFF symbols.

Experimental Results and Discussion

This chapter provides experimental results that show, how various configurations of our methodology may be the most suitable for the different scenarios of over-the-air updates. In [START_REF] Kachman | Optimized differencing algorithm for firmware updates of lowpower devices[END_REF], we presented our differencing algorithm that outperforms existing solutions. Therefore, we use it for the following experiments executed on the ATmega32u4 microcontroller. We consider three scenarios: 1. In the first scenario, the devices on the network require one big update of the functions that sense, store and send data -the sensor module 2. The second scenario updates these three sensor module functions incrementally, one after another 3. The third scenario involves 9 incremental updates to various functions in the firmware code -the sensor module (3 functions), the communication module (3 functions), the flash storage module (3 functions) We configure our tool to edit string tables of the ELF files, every function is placed in its own section. We do not set relocations to zero. For each scenario, we evaluate three different configurations: 1. No fragmentation; All deltas are generated in clean mode 2. Partial fragmentation; Changed functions are provided with a slop region (dirty mode), final delta generated in the clean mode defragments the memory 3. Full fragmentation; All functions are provided with slop regions before any update (clean mode), functions are then updated (dirty mode) and finally, the firmware is defragmented (clean mode) Results. The results of our experiments are shown in the Table 1. Column "Delta files" shows, how many delta files were used for the update. Column "Total bytes" shows the sum of the delta file sizes used for reprogramming. Column "Frag. overhead" shows, how many of those bytes were used for memory fragmentation, defragmentation and cleanup. Table 2 shows the sizes of every delta file from the 3rd scenario. The sizes are in bytes. Discussion. The experiment shows, that the single firmware update does not require any memory fragmentation in order to be efficient. With more incremental updates required, configurations with memory fragmentation become more efficientpartial fragmentation performs the best for both 3 and 9 incremental updates. Full fragmentation configuration has the penalty of the big deltas that are used to fragment the memory at the beginning and to defragment it at the end. It is performing significantly better for more updates and it can be expected, that for a great number of incremental updates, this configuration will perform the best. Table 2. shows, that the delta sizes for the full fragmentation approach are mostly the smallest for the single function updates (Δ1-Δ9).

Conclusion

This paper presents a configurable reprogramming methodology that is built on the best practices in the area, and introduces configurations that make remote firmware updates more efficient for the different reprogramming scenarios. Experiments have shown, that various configurations may reduce total amount of the data shared on the network. The solution is multiplatform, which makes it ideal for the smart systems.

Table 1

 1 Experimental results for the three different scenarios and configurations

		Scenario 1 -single update	Scenario 2 -3 updates	Scenario 3 -9 updates
	Config	Delta	Total	Frag.	Delta	Total	Frag.	Delta	Total	Frag.
		files	bytes	overhead	files	bytes	overhead	files	bytes	overhead
	No frag.	1	98 (best)	0	3	216 (+7%)	0	9	1398 (+65%)	0
	Partial frag.	2	164 (+64%)	112	4	202 (best)	102	10	844 (best)	260
	Full frag.	3	680 (+593%)	634	5	638 (+215%)	576	11	1036 (+22%)	568

Table 2

 2 Delta file sizes in bytes for the Scenario 3

	Config	Δfrag Δ1 Δ2 Δ3 Δ4	Δ5	Δ6	Δ7	Δ8	Δ9 Δdefrag Total
	No frag.	-	74 84 58 106 162 150 244 102 418	-	1398
	Partial frag.	-	12 40 48	26 126 50 200 58	24	260	844
	Full. frag.	302 14 14 34	26 126 20 200 20	14	266	1036

Acknowledgement. This work has been supported by Slovak national project VEGA 2/0192/15.


José Teixeira Gonçalves
email: jt.goncalves@campus.fct.unl.pt

Cristina Inês Camus
email: ccamus@deea.isel.pt

Stanimir Stoyanov Valtchev

Solar Thermoelectric System with Biomass Back-up

Keywords: Solar, Thermoelectric, Backup, Biomass and Pellets

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The need to increase the use renewable energy continues in the environmental policy of every country. Climate change keeps being an important issue and all research and investment go into the direction of the Carbon-free technologies.

One of the technologies that has denote an increase in sunny countries is the concentrated solar thermal (CSP) that converts the direct solar irradiation (DNI) into thermal energy through directional mirrors and a receiver. This thermal energy can be stored in molten salt tanks and then converted into electrical energy. The CSP technologies vary with the form of DNI concentration at the receiver. There are four types of CSP: Cylindrical-parabolic collectors, CCP; parabolic dish Stirling; linear Fresnel and central tower receiver [START_REF] García-Segura | Durability studies of solar reflectors: A review[END_REF], [START_REF] Khan | Solar power technologies for sustainable electricity generation-A review[END_REF]. This technology has a high cost, and still needs feed-in tariffs in order to be economically viable.

The central tower solar thermal technology has reached commercial maturity and is expanding. In development since 1980, after the pioneering experience of the Solar I and Solar II in the US and Almeria Platform in Spain during the period 2000-2010 [START_REF] Boudaoud | Solar tower plant implementation in northern algeria: technico economic assessment[END_REF]. Currently, the largest power plant in the world with this type of technology is the Ivanpah with 377 MW (California, U.S.A.) [START_REF]IVANPANH Solar Electric Generating System[END_REF].

The storage technology is very important to able the power plant to generate for longer periods [START_REF] Khan | Solar power technologies for sustainable electricity generation-A review[END_REF], as it is the case of Gemasolar (a solar tower with circular field) that was the first in the world to run 24 hours a day, thanks to the addition of storage and back-up system [5]. The 24 hours a day operation is just possible during a few summer periods with only the energy of the DNI and storage. In winter periods the system needs to add another technology to extend over the period, thereby making a hybrid system, but this addition is often made with oil products or natural gas. This makes the power plant less clean.

With this vision comes the main issue. How to make the CSP system that is completely renewable and clean, work 24 hours a day both in summer and winter periods?

The objective of this work is to study the use of biomass as a back-up for a CSP system central tower with north field and storage to operate 24 hours a day.

Relationship to Smart Systems

This work demonstrates that a hybrid system such as a thermoelectric solar tower with storage and biomass back-up system can operate 24 hours a day, both in summer and in winter and respect the clean and renewable way. Thermoelectric solar systems work automatically, from the solar concentrators drive process (following the sun orientation) [START_REF] Kumar | Analytical and numerical study to assess the solar flux on a heliostat based central receiver[END_REF] thermal fluid process (controlling the valves, the heat transfer fluid, HTF flows, thermal storage, etc.) [START_REF] Tehrani | Off-design simulation and performance of molten salt cavity receivers in solar tower plants under realistic operational modes and control strategies[END_REF] and the electrical system (controlling the power delivered to the grid, the power consumed in the system, etc.), it is noted that the system is fully automatic and intelligent, so it is important that the back-up system the pellets to be implemented is automatic [START_REF] Monteiro | The feasibility of biomass pellets production in Portugal[END_REF]. The implementation of this automatic back-up system with pellets has several advantages:  There is no need of human power to drive the biomass system.  The system works in real time, it allows operation without interruption.  The power supply is 24 hours a day, in winter and in summer.  This allows the two systems to be operated automatically in only an operating room or other type of control. The main contribution to the smart system is that the back-up biomass system works automatically, i.e., from the processing control when the thermoelectric solar system requires thermal power, the system actuates automatically (smart) to inlet the pellet biomass to the boiler which triggers combustion, transferring the thermal energy released from combustion to the overall system. All these processes are automated and help in the system reliability to have a safe and non-stop operation.

State of Art

There are basically four types of CSP, the cylindrical-parabolic collectors, CCP; parabolic dish Stirling; linear Fresnel and central tower receiver.

The elements that differ in each CSP technology are mainly the solar field and receiver. Then they can have heat storage and heat exchanger (depending on the type of CSP and heat transfer fluid, HTF) and finally to convert thermal energy into electric energy a power unit is required.

The system studied in this work was the cavity tower receptor. A remarkable advantage of this technology (central tower solar thermoelectric) compared to other CSP technologies, such as linear Fresnel parabolic or disc is that the receiver operates at a higher thermal efficiency. This is due to the fact that all heliostats concentrate the DNI to a point (surface receptor) [START_REF] Wagner | Simulation and predictive performance modeling of utility-scale central receiver system power plants[END_REF], thereby raising the operating temperature [START_REF] Boudaoud | Thermal performance prediction and sensitivity analysis for future deployment of molten salt cavity receiver solar power plants in Algeria[END_REF] (which aids in hybridization). The rapid growth of this technology is due, in large part, to this advantage. This type of system has also reached the stage of commercial maturity and is expanding.

Description and Operation of the Thermoelectric Solar System with Biomass Backup

The following key elements will be needed for the system to function: heliostats, tower and receiver, storage tank, power block (heat exchanger, turbine steam, electrical generator, condenser, water pumps, etc.) and boiler for pellets. The proper integration of all elements allows the correct operation of the system. Figure 1 shows the proposal of the system to be dimensioned, it shows all the elements already mentioned and we can observe that the structure of the field north the tower, allows to add the system of storage of the biomass to pellets to the south of the tower.

Boiler of Pellets

The pellet boiler is basically a furnace that operates automatically, it is made of tubes that serve as a heat exchanger, the combustion chamber, the pellets storage, the rook wiper carrier, air pump, etc. The boiler operating principle is shown in Figure 2.

Pellets

The fuel pellets are completely natural as they are made primarily from wood chips and sawdust, but can also be made with corn cobs, wheat bran, rice husks, leaves, grasses, and other products.

The pellets are a type of densified biomass and therefore they have better physical and combustion characteristics compared to the raw biomass. Due to the size and shape of the cylinder that the pellets have, it becomes possible to automate the boiler running on this fuel, becoming competitive with gas, Diesel and fuel-oil boilers, since these boilers are also the systems of automatic ignition, automatic transport of the pellets to the combustion chamber, the ash removal mechanism automatic cleaning of the heat exchanger and others. The production of pellets adds the possibility of using different waste biomass into standard fuel systems [START_REF] Monteiro | The feasibility of biomass pellets production in Portugal[END_REF].

In Europe and the United States of America biomass is largely used either on a domestic scale or on an industrial scale such as large thermoelectric power stations [START_REF] Johnston | Economics of co-firing coal and biomass: An application to Western Canada[END_REF].

One can convert a coal plant to function with biomass, thereby reducing carbon dioxide emissions, or to create an original biomass power plant [START_REF] Johnston | Economics of co-firing coal and biomass: An application to Western Canada[END_REF], [12].

The biomass plants can operate only with pellets, such as the Les Awirs plant (Belgium), which was converted from coal to work 100% with wood pellets, and consumes about 350,000 tons of pellets per year at 80MW power level [START_REF] Marchal | Current developments on Belgian pellet market[END_REF], [START_REF]CENTRALE DES AWIRS 100% biomasse[END_REF].

Operating System

The operating principle of this system which occurs automatically, can be described in two periods: The first period consists of the system operation with Direct Normal Irradiation (DNI) and storage and the second period the controlling of biomass combustion to provide the lack of thermal energy to the system (period 2) [START_REF] Boudaoud | Thermal performance prediction and sensitivity analysis for future deployment of molten salt cavity receiver solar power plants in Algeria[END_REF], [START_REF] Gonçalves | Estudo técnico-económico de um sistema solar termoelétrico com back-up a biomassa[END_REF], [START_REF] Hussain | Technological assessment of di erent solar-biomass systems for hybrid power generation in Europe[END_REF], as illustrated in Figure 3.

Period 1: The Direct Normal Irradiation, DNI, reaches the surface of the heliostat, which acts as a mirror, deflecting or reflecting the sun's rays to the receiver. This causes an increased solar concentration which in turn increases the temperature (thermal energy). This temperature is transferred to a heat transfer fluid (in the case molten salt), known as heat transfer fluid, HTF. If the system has two circuits (one primary and one secondary), the molten salt (HTF) only circulates through the primary circuit.

The primary circuit has two storage tanks: A cold and a hot tank, wherein the HTF flows with the aid of hydraulic pumps. The HTF leaving the cold tank, travels through the tube to the top of the tower reaching the receptor where its temperature rises from approximately 290ºC to 575ºC. Then it is transferred to the hot tank, where it can be stored and, subsequently, the fluid leaves the hot tank and passes through a heat exchanger to be conducted again to the cold tank where the same process continues (a cycle).

The heat exchanger has the function to transfer the thermal energy from the primary circuit to the secondary circuit. In the secondary circuit the working fluid (water) rises its temperature changing from a liquid state into a vapor state. The vapor flows through a steam turbine, which converts kinetic energy into mechanical rotary energy. This vapor passes then through a condenser to become saturated liquid and continues its secondary circuit of the cycle. The rotating mechanical energy is converted into electricity by an electric generator coupled to the turbine. The electricity is then directed to a transformer, which increases the voltage lowering the current, so it can be transported by electric cables minimizing transmission losses of energy.

Period 2: In the period when there is neither DNI nor thermal energy stored in the hot tank, comes into operation the biomass back-up system to transfer the needed thermal energy to the HTF of the primary circuit. The stored pellets are transported by an automatic system in the boiler, into the furnace (above a grid), where its ignition is done by an automatic system (an electric resistance). Through this process the biomass is combusted in the combustion chamber (furnace). The heat released by the combustion process is then transferred to the HTF through the walls, which can be called a heat exchanger. Consequently, the HTF exits the boiler with sufficient thermal energy and goes to the system where it is transferred to the secondary circuit through the heat exchanger and then converted to electricity.

Research Contribution and Innovation

Some existing solar systems work with back-up of various forms of energy, such as Gemasolar 20 MW (Spain) that adds a fossil fuel back-up (natural gas) for 15% of the annual energy generated by the plant [START_REF]System Advisor Model (SAM) Case Study. Concentrating Solar Power Systems[END_REF], [START_REF] Amadei | Simulation of GEMASOLARbased solar tower plants for the Chinese energy market: Influence of plant downsizing and location change[END_REF]. There are no CSP plants currently running with biomass back-up. This fact makes this work innovative on the following points:  An automatic pellet boiler biomass (combustion) system works together with a thermoelectric solar system (north field) in a hybrid way ensuring that the system operates 24 hours a day, both in summer and in winter.  A method to simulate with the System Advisor Model (SAM), a hybrid thermoelectric solar system and biomass, as far as the SAM software does not have a specific option for hybridization throughout the year.

Methodology and Simulation

The simulation was performed on System Advisor Model, SAM (the selected version was the "Version 01/14/2014"), with six (6) blocks to enter the parameters for processing, namely the City and climatic resources, Heliostat field, solar tower and receiver, power block (Rankine Cycle thermal dispatch control and electric generator), thermal storage and system costs. The parameters used in these blocks are described in Table 1. Some points should be described in greater detail, such as the location and climatic resort, the thermal dispatch control system and the pellets' system. As a reference, it is possible to analyze some examples of simulations of CSP performed in SAM in [START_REF]System Advisor Model (SAM) Case Study. Concentrating Solar Power Systems[END_REF].

1º-Location and Climatic Resources

In this block, the location where we want to install the plant was set up. The site was near a village in the Alentejo region, with the coordinates described in Table 1. The data from the DNI were extracted from the Photovoltaic platform Geographic Information System (PVGIS), thus having the monthly average data, considered these data as daily for each month and there was thus obtained in an Excel table with 8760 values of annual DNI. It was then possible to create a new database, transferring some values of a model ("Évora database" as stored in the program) in EPW format to Excel and complete with the extracted DNI from PVGIS. Later this database, in Excel, was converted to the executable TMY3 format to enter as an input to the SAM software.

2º-Thermal Dispatch Control System

The thermal clearance control system is an automatic control of thermal energy that is routed to the power block. This control is registered to a table where the lines refer to the months of the year and 24 columns refer to the daily hours (Table 2).

In this paper it is proposed a thermal model order strategy so that only 50% of the rated power is generated when there is no DNI, which means that without DNI the power supply is of only 10MW instead of 20MW. This will cause the stored energy to last during a double period.

When the source is biomass it will also only be supplied 50% of plant capacity, which means that during the back-up period, the power supply is 10MW. This will minimize the cost of biomass and cause the system to work 24 hours a day. Table 2 shows the order made for each month of the year.

Table 2. Strategic model for the control of thermal dispatch system. 100% with DNI 50% with storage 50% with back-up Thus, one can make an assessment of how many hours the biomass will be running for each month (having an average 13.78 hour) and using the pellets in the system calculations.

3º-The Biomass System

It was considered that the boiler has a standardized performance value of =80.6%. The lower heating value (LHV) of the pellets is about 17000 kJ/kg=4060.382kcal/kg. To calculate the amount of pellets consumed by the system it is sufficient to apply the following two steps: 1. Calculate the energy of the biomass pellets, which burns to produce the heat required for the system:

(

Where:

= Boiler performance = Monthly energy, calculated with the following expression.

(

Solar Thermoelectric System with Biomass Back-up 363 = Monthly time given in hours.

= Thermal power in the system.

1. Calculate the amount of pellets burning in the boiler ( ).

(

) 3
6 Results and Discussion

Annual Output of System with Backup of Biomass Pellets

Figure 4 shows several energy conversion processes and system losses that occur. This figure shows the total thermal energy falling on the solar field to power into the grid. The total annual thermal incident energy in the solar field is 436.28 GWh, this energy is thus forwarded to the receiver, causing a loss in the solar field and receiver of 225.95 GWh which corresponds to 51.79%. With this loss the total annual thermal energy output of the receiver is 210.33 GWh, which is directed to the power block. To the thermal energy of 210.33 GWh in the HTF is added a thermal energy from the back-up system of 84 GWh corresponding 39.94%. Therefore, the total annual thermal energy power block is 294.33 GWh. This thermal energy is thus converted (after suffering thermal and electrical losses of 188.57) into electrical energy 105.67 GWh injected into the network. With these data, it can be said that the overall system performance is 19.57%.

The energy injected into the network varies each month of the year (see Figure 5 left), and in July and august it is injected more energy in the network, about 10.77 GWh and 10.04 GWh respectively. The month with less injected energy is the month of January with only 7.27 GWh. This energy generation profile was attained due to the back-up system. Figure 5 (right), shows the amount of pellets each month that the system needs for the production of thermal energy necessary for the system to function in the absence of DNI and storage.

Note that the months with the highest consumption of biomass are January and December and in June, July and August no biomass is consumed, as during these months there is enough DNI to make the system work 24 hours a day.

The total amount of pellets per year that the system will need is about 24 thousand tons, which is less than the amount of pellets each of the three selected producers export (about 180 from 270 thousand tons) per year. These show that only a producer would be enough to power the system.

Validation of the Results

If we analyze the obtained results and compare with the values of central Gemasolar [START_REF]System Advisor Model (SAM) Case Study. Concentrating Solar Power Systems[END_REF], which also have a power of 20MW and back-up system, we verify that many parameters are compatible such as:

The thermal power generated by the receiver of the system under study is 116.505 MWt and Gemasolar is 120.752 MWt, this small difference is due to differences in receptor structure, availability of DNI and because the Gemasolar applies a higher multiplier of 2.5 than 2.4 in the study system.

The storage volume of Gemasolar (3476.76 m3) is greater than the system under study (2514.98 m3), that because the storage time is greater in Gemasolar, and 15 hours after the system under study is 11 hours.

The capacity factor is higher in Gemasolar (70.4%), compared to that of the system under study (69.4%), since the production of the system under study is lower (105 GWh), than that of Gemasolar (about 107.34 GWh).

These differences are reflected in the total system costs: $ 209,003,197.52 for Gemasolar, and $ 155,901,171.55 for the system under study. This difference is understandable if the price of the elements would be taken into account as already mentioned.

To calculate the efficiency of the system under study the example of the central Les Awirs in Belgium was analyzed, which runs on 100% wood pellets. It consumes about 350,000 tons of pellets per year and the output power is 80MW. The analyzed above system in this case should have power of 10 MW and should consume about 43750 tons/year. If we consider the energy of 43750 tons/year and the power of 10 MW, i.e. 24 hours producing 10 MW, and reduce the working time to the average of 13.78 hours a day, in that case the quantity of pellets decreases from the value of 43750 tons/year to 25120 t/year, which is compatible with the pellet consumption in the system under study 24000t / year.

Conclusion

This paper analyses the implementation of an automatic back-up system based in biomass pellets to support a solar thermoelectric system with north field during the less available radiation months. The interconnection of all the elements in order to form a system that converts the DNI and biomass pellets into electricity, was modelled and tested for a 20 MW power plant in Alentejo (Portugal). The design was executed simultaneously by SAM software and in Excel (back-up pellets).

A comparison made of simulated values in the SAM, with the actual values of Gemasolar (obtained from a simulation made in the laboratory of renewable energy in the United States of America, USA), demonstrates a reasonable approximation of these simulated values, both in technical parameters and in economic parameters.

The annual figures were all generated in the SAM and Excel, which demonstrates a certain energy balance, entering thus the system about DNI = 2319.4 kWh / m 2 and 24000 tons of pellets per year, converted to 105,76 GWh of electricity per year, which is a feasible value for this type of system. In terms of back-up, the biomass demonstrates to be viable, increasing the energy produced and thus the capacity factor from that of 49.1% to 69.4%, but the use of biomass also increases the overall yield of 16.99% to 19.57 %.

Fig. 1 .

 1 Fig. 1. Constitution of the complete structure of the proposed thermoelectric solar system with biomass backup.

Fig. 2 .

 2 Fig. 2. Operating principle of the pellets boiler.

Fig. 3 .

 3 Fig. 3. Operating principle of the Solar thermoelectric tower with back-up with biomass.

Fig. 4 .

 4 Fig. 4. Summary of the annual production of the system and loss diagram.

Fig. 5 .

 5 Fig. 5. Energy production per month and monthly consumption of pellets.

Table 1 .

 1 Parameters used in system simulation.

	Block	Parameters	Values
	Location and Resource	DNI (kWh / m2) year	2319,4
		Latitude	38,165
		Longitude	-7,195
	Heliostats Field	Heliostat area (m2)	91
		Number of heliostats	2067
	Tower and Receiver	Receiver type	Cavity
		External pipe diameter (mm)	40
		Pipe Wall Thickness (mm)	1,25
		Tower Height (m)	127,11
		Tube material (stainless steel)	AISI 316
	Power Cycle	Drawing Gross capacity (MW)	20
		Conversion Efficiency (%)	41,2
		Type condensation	Ar
	Thermal storage	Type of storage	2 tanks
		Hours of Storage (hrs)	0-11
		Storage volume (m3)	2514,98
		Initial hot HTF Tem. ( 0 C)	574
		Initial cold HTF Tem. ( 0 C)	290
	Direct Capital Costs	Site improvements ($ / m2)	15
		Heliostats field ($ / m2)	170
		Balance of plant ($ / kW)	350
		Power block ($ / kW)	1200
		Storage ($ / kW ht)	27
		Boiler pellets ($ / kW e)	540
		Fixed tower cost ($)	3000000
		Receiver reference cost ($)	110000000
		Contingencies (%)	7
	Indirect Capital Costs	EPC and ower costs (%)	11
		Total land cost ($ /acre)	10000
		Sales tax of (%)	5
		Direct cost of sales (%)	80
		Cost of O & M ($ / kW)	65


Ridita Ali
email: ridita.ali@shu.ac.uk

Lyuba Alboul
email: l.alboul@shu.ac.uk

Amaka Offiah
email: a.offiah@sheffield.ac.uk

Signal Processing Techniques for Accurate Screening of Wrist Fractures

Keywords: Vibration analysis, Fast Fourier Transform, Wavelet decomposition, Fracture screening

The common way for doctors to differentiate wrist injury in to a sprain or a fracture, is to take radiographs (X-ray), which expose patients to radiation. The purpose of this study is to explore a non-invasive method to screen for potential fractures. A small, computer run, hand-held system has been developed which consists of a vibration induction mechanism and a piezoelectric sensor for capturing the vibration signals. Two analyzing techniques were considered. The first involves extraction of wavelet coefficients from decomposition of data and the second applies Fast Fourier Transform to the data. Results of both techniques were then cluster analyzed to partition between fracture and sprain. The data were acquired from both the injured and uninjured wrists of six adult patients. This study is currently being evaluated on children's wrists.

Introduction

Use of ionizing radiation (x-rays) to produce radiographs is the most common procedure for doctors to differentiate a wrist injury into a sprain or a fracture. Each wrist radiograph costs around £60 in the United Kingdom and almost 60 percent of those radiographs show no fracture. Thus, a non-invasive technique is very desirable to minimize both radiation exposure and cost.

We have used a small, computer run, hand-held system that generates vibration in the bone under examination, and then captures generated vibration signals by a piezoelectric sensor, which then are analyzed by applying signal processing methods. Various technological systems in both industry and medicine apply either Fast Fourier Transform (FFT) or Wavelet Coefficient extraction to process acquired signals. In this study, we have applied both methods on signals obtained from human wrist bones and then compared the results to find out which method is more accurate to screen for fracture.

Vibration analysis is an established method used in industry for monitoring or diagnosing faults in electric machines by means of signal analysis and signal processing. Mechanical vibrations cause one or more inputs and outputs of a system to change over time and the signals produced are then evaluated for type and severity of defect [START_REF] Brandt | Noise and Vibration Analysis: Signal Analysis and Experimental Procedures[END_REF]. Studying the vibration effects, fault detection and capability of this method of machine maintenance, is an on-going process [START_REF] Plante | Faults detection and failures prediction using vibration analysis[END_REF] [START_REF] Plante | Rotating machine fault detection using principal component analysis of vibration signal[END_REF].

By comparison, vibration analysis in the medical field is still in its infancy. In 1932, Lippmann percussed his finger to cause vibration, used his stethoscope to sense it and explained the benefits for using the method in clinical diagnostics. He suggested that analysis of percussion appeared more accurate than x-ray for the diagnosis of fractures [START_REF] Lippmann | The use of Auscultatory Percussion for the Examination of Fractures[END_REF]. Some researchers developed a finite model of a dry tibia for predicting its natural frequencies of vibration [START_REF] Hobatho | Relationship between mechanical properties of the tibia and its natural frequencies[END_REF]. Nokes published a major study where he proposed the idea to monitor various pathological and trauma-induced conditions by applying a stimulus to bone [START_REF] Nokes | The use of low-frequency vibration measurement in orthopaedics[END_REF]. Experiments demonstrated that vibration induced by mechanical means can indicate mechanical properties of bones, such as density, biological state, etc. [START_REF] Alizad | The effects of fracture and fracture repair on the vibrational characteristics of an excised rat femur[END_REF]. The influence and results of low-frequency vibrations in the lower limbs have been accurately determined for the analyses based studies [START_REF] Schneider | Modelization and simulation of the mechanical vibration effect on bones[END_REF]. The effects of skin and muscle on the bone's low frequency vibration signals have been demonstrated [START_REF] Ali | Fuzzy C-Means clustering to analyze bone vibration as a method of screening fracture[END_REF]. We have previously used samples of frequency spectra from adults with and without wrist injuries, to cluster analyze into fractured and sprained bones [START_REF] Razaghi | Spectral analysis of bone low frequency vibration signals[END_REF].

Application of vibration analysis is still developing. Additionally, studies are being conducted to find out if its advantages outweigh the disadvantages. However, in the context of health care, the practical applications of vibration analysis are in the near rather that distant future.

Smart Systems

Smart systems are defined as devices that incorporate the functions of sensing, actuation, control and adaptation. They can describe and analyze situations, and take decisions based on the available data in a predictive or adaptive manner, thereby performing smart (intelligent) actions [START_REF] Wan | Synthesizing Data-to-Wisdom Hierarchy for Developing Smart Systems[END_REF].

Smart systems are found in many applications such as automotive, manufacturing, environment, energy and, health care. These systems have the capability to solve very complex problems, including taking over human cognitive functions [START_REF] Glesner | Embedded Systems Design for Smart System Integration[END_REF].

In the case of health care and medical applications, smart systems are mainly used to improve the quality of diagnosis and treatment. The system described in this paper shows the utilization of miniature smart hardware devices to produce and procure energy through a medium. The first prototype of the device has been tested to find correlation between vibration frequency and bone density, and has been developed by the Medical Electronics Engineering Group at Sheffield Hallam University's Centre for Automation and Robotics Research facility [START_REF] Razaghi | An investigation of relationship between bone vibration frequency and its mass-volume ratio[END_REF]. The device has been then modified and our group now uses it to differentiate between wrist fracture and strain. The data acquired from this method is stored and analyzed using complex programmed routines through specific software.

System

Hardware: The device comprises of the following parts.



Electrical Vibration Inducer -A sample rate of 50000 samples per second makes the inducer move that produces the impact. Squared signals with a duty cycle of 50 percent at maximum, a frequency of 1 Hz, and an offset of 2.5 were selected for generation of the signals during the impacts.



Piezoelectric Sensor -The sensor, used for vibration / impact sensing has broad bandwidth, high sensitivity, light weight and low cost features.  NI myDAQ Assistant -This was used for frequency generation which causes the inducer to initiate and consecutively record the vibration response via the sensor.



12V Battery -This battery removed the portability and electric shocks issues.  Control Circuit -A small Printed Circuit Board (PCB) was built which consists of amplifier, filter, and power divider to control the circuit for minimal battery power consumption. Software: LabVIEW and MATLAB. The fundamental principle behind using LabVIEW is for its Integrated Development Environment (IDE) and the Graphical User Interface (GUI), which were used to develop the data acquisition feature for this device. MATLAB was used to process and analyze the acquired data. LabView was designed in such a way that a NI myDAQ Assistant can generate signals to run the inducer and also acquire the corresponding data; in other words, both the generation and acquisition modes of the DAQ Assistant were utilized. Implementation loops were added to create mechanized applications to reduce manual tasks and enhance repeatability. MATLAB is an efficient tool for signal processing and that had been used to perform both FFT and WD.

Thus the system developed for this research, is undeniably a Smart System.

Fig. 1. Process Flow Chart

Research Methodology and Results

Adult patients, aged between 20 to 70 years old, attending the Emergency Department of a local hospital, following a wrist injury, volunteered to take part in this study. Vibration data were collected from both injured and uninjured wrists of six patients and processed blinded to radiographic findings. This means that at, the time the data were produced and analyzed, it was not known if the injured wrist had a sprain or a fracture. They all sat on a chair during recording. Vibration caused by mechanical excitation, was induced by impacting the most prominent bone in the elbow. The vibration responses were recorded by placing a piezoelectric sensor which has a maximum operating frequency, on a bony prominence at their wrists. The device was intended to induce light vibrations onto the bones for sensing the signals. The vibration inducer had been designed in such a way that its strength can be controlled, if required. All of the volunteers stated after participating in the study that they did not feel any pain due to the vibration induction. 10 vibrations were induced over 10 seconds in total and each response was recorded at a rate of 60000 samples per second. These data were stored in the computer and then processed by Wavelet Decomposition (WD) and Fast Fourier Transform (FFT). I.

The coefficients were extracted, after decomposition of the acquired data by Level 5 filtration. These were derived by a scaling function "Daubechies 5 (db5)" wavelet family. Two degree polynomials were plotted to find the best fitted curve among the number of coefficients derived from the WD. The equation for each of the polynomials was also calculated. II.

The bone vibration recorded from six patients was converted to a magnitude frequency spectrum by application of FFT processing. Figures 2 and3 The frequencies produced by the FFT and the constants derived from the equation produced by the best fitted polynomial curve, were classified using the "dendrogram" (a hierarchical cluster tree diagram) to show which groups are similar. The "dendrogram" was plotted using a linkage of Euclidean distance between each data set. The diagram produced by both FFT and Wavelet Decomposition was similar and is illustrated in Figure 4. These data were then analyzed using Fuzzy C-means to find the membership percentages required for each data set to belong to a particular cluster. Although

Fracture

No Fracture WD produced comparatively similar results to FFT, while using both the dendrogram and Fuzzy C-means. However, there are some disadvantages and unreliable results of using the WD technique:  WD provides both Frequency and Time related information which makes it difficult to use; as the design which induced 10 vibrations must produce vibration responses very similar to each other over the 10 seconds in order to ensure that results can be processed further.  In order to make sure the above reason does not affect the accuracy of the data collected, the first and last few sets of data are left out when doing the analysis.  In addition, there are a sizable number of steps before reaching the concluding stage of Fuzzy C-means cluster. On the other hand, the frequencies produced by the FFT can easily be fed into the Fuzzy C-means code already built, to produce membership values. Fewer steps were involved in building the FFT codes.

Conclusion and Further Works

Both FFT and WD techniques produced almost all correct results. However, the FFT is a hassle free and accurate process with less number of steps for future use. The efficiencies are to be checked by a larger volume of data. The discomfort level experienced by each patient for both wrists was recorded and every participant felt that the vibrations would not be uncomfortable to children aged between 0 and 15 years old. It takes less than 5 minutes to carry out the procedure so it is not a time consuming method. The study is being continued at a local Children's Hospital and aims to recruit a larger number of participants to test the accuracy of the techniques. More signal processing techniques are likely to be assessed once a larger volume of data is available.

  display the results produced by FFT and WD.

Fig. 2 .

 2 Fig. 2. Filtered Vibration Response and Magnitude Spectrum by FFT.

Fig. 3 .

 3 Fig. 3. Best fitting two-degree polynomial among 18 Wavelet Decomposed Coefficients.

Fig. 4 .

 4 Fig. 4. Both FFT and Wavelet Decomposed Coefficients produced the same results by the dendrogram.

similar classes can be observed from the dendrogram, Fuzzy C-means was performed to ascertain the suitable percentage required for each group. The results of cluster analysis are shown in Tables 1 and2.

Discussions

Tables 1 and2 clearly reflect the techniques used in this study.


Gergely Márk Csányi
email: csanyi.gergely@vet.bme.hu

Zoltán Ádám Tamus

Árpád Varga

Impact of Distributed Generation on the Thermal Ageing of Low Voltage Distribution Cables

Keywords: distributed generation, low voltage cables, distribution network, cable ageing, PVC cable, EVR, Extended Voltage Response method, smart

The low voltage (LV) distribution cable networks were installed some decades ago but the new paradigm in electric power engineering generates new requirements from these old assets. The distributed generation, storage and new appliances can cause high variation of load and reverse power flow, nevertheless the LV cable grid was not designed to these new stresses. The aggregate load and generation can surpass the rated capacity of the cable lines causing short term temperature increasing. This temperature stress can decrease the expected lifetime of the cable lines. In this study the short term thermal overload of LV distribution cables was investigated. The experiments were executed on PVC insulated LV cable samples and electrical and mechanical properties of the cable jacket were investigated. The effect of these short-term overloads on the expected lifetime of cables is introduced and non-destructive measurement for tracking the effect of the short term thermal overloads on the cable is suggested.

Introduction

Low voltage underground cables play an important role in electricity distribution all across Europe and are valuable assets. Hence, preventing outages, assessing the cables' condition and optimizing replacement strategies are usually the main goals of an electricity provider [START_REF] Kruizinga | Fault development on water ingress in damaged underground low voltage cables with plastic insulation[END_REF]. Low voltage distribution cables were installed some decades ago, however due to the new paradigm in electric power engineering they have to withstand new stresses. The increasing number of novel appliances connected to the grid (e.g. renewable energy sources, electric vehicles, heat pumps etc.) can easily lead the load to surpass the cable's maximum capacity increasing its temperature [START_REF] Höning | Thermal behaviour of low voltage cables in smart grid-related environments[END_REF]. Higher temperature has harmful effects on cable insulation's expected lifetime. However, overloads can be often remain undetected without blowing the fuses that are responsible for the protection of the given cable section while they have a certain thermal effect on the cable, reducing its lifetime. This kind of overload is more likely to happen in the near future due to the aggregated loads generated by the new appliances. In this study the short term thermal overload of LV distribution cables was investigated. The experiments were executed on new, PVC insulated LV cable samples and short intensive thermal stresses due to the overloads were simulated by laboratory ageing tests. Electrical (tan δ, voltage responses) and mechanical (Shore D hardness) properties of the cable jacket were measured after the ageing cycles and changing of these parameters was evaluated.

Relationship to Smart Systems

As a result of the new paradigm in electric power engineering, low voltage (LV) distribution cables will more often operate in the near future under harmful conditions. The distributed generation, energy storage systems and new appliances can cause high variation of load and reverse power flow, in extreme cases, mostly the photovoltaic systems on hot summer days can cause overloads on low voltage distribution cable lines. These overloads appear when the temperature of the soil is also elevated therefore it can increase the temperature of the core insulation and the jacket over the maximum operation temperature. The increasing temperature decreases the LV distribution cables' expected lifetime. Nevertheless, the LV cable grid was not designed to these new stresses. However, rebuilding the LV cable network would be very expensive therefore the protection of LV assets offers a better solution. Hence, the attention increases on examining how these stresses may affect the LV cables' insulation and how smart solutions can prolong their expected lifetime [START_REF] Höning | Thermal behaviour of low voltage cables in smart grid-related environments[END_REF][START_REF] Armendariz | A method to place meters in active low voltage distribution networks using bpso algorithm[END_REF][START_REF] Ramezani | Fast and revenue-oriented protection of radial lv cables with smart battery operation[END_REF][START_REF] Kadurek | Overloading protection of future low voltage distribution networks[END_REF][START_REF] Trichakis | Predicting the technical impacts of high levels of small-scale embedded generators on low-voltage networks[END_REF]. By means of smart measurements the temperature of the cable sections could be estimated and therefore a more e f f i c i e n t replacement strategy could be developed helping the operators. In order to reach this goal it is essential to examine how LV cable insulations react to the thermal effect of short term overloads.

Experimental

Samples and Thermal Ageing

The samples were prepared from NYCWY 0.6/1 kV 4x10/10 mm 2 low voltage cables. The construction of the cable can be seen in Fig. 1. The cable builds up from a PVC jacket (5), wire and tape screens made of copper [START_REF] Ramezani | Fast and revenue-oriented protection of radial lv cables with smart battery operation[END_REF], filling material between (3) the grounding screen and the PVC core insulations (2) and four copper conductors [START_REF] Kruizinga | Fault development on water ingress in damaged underground low voltage cables with plastic insulation[END_REF].

Each cable sample was half-meter long and the wire and tape screens of the cables were connected to all of the core conductors providing an inner electrode while an outer electrode was created by wrapping an aluminum foil around each cable jacket.

Fig. 1. The construction of the cable

To simulate the thermal effects of short time overloading periods the samples were subjected to accelerated thermal ageing. From the cable specimens two groups were created and were aged for 11 hours at 125°C and 140°C, respectively.

After that a 4-hour-long ageing were carried out at the same temperatures. All in all, the mechanical and electrical properties were measured after 11 and 15 hours of thermal ageing. The correlations between the applied and equivalent ageing durations were calculated by means of Arrhenius equation; the activation energy used for the calculation was 80 kJ/mol [START_REF] Ekelund | Long-term performance of poly(vinyl chloride) cables. part 1: Mechanical and electrical performances[END_REF]. Results can be seen in Table 1.

Table 1. Equivalent ageing duration at different temperatures [hour]

80kJ/mol 11h @ 125°C 15h @ 125°C 11h @ 140°C 15h @ 140°C 80°C 239 326 575 784 100°C 56 76 133 182

Measurement

Both mechanical and electrical properties were measured during the investigation. The mechanical parameters were measured by Shore D hardness tester and the dielectric properties were measured by tan δ measurement and Extended Voltage Response (EVR) measurement [START_REF] Tamus | Characterization of dielectric materials by the extension of voltage response method[END_REF]. The hardness was measured 11 times on each specimen's cable jacket's uncovered part. The measurements can be used only for comparison purposes since the thickness of the jacket is only 2 mm however, the standards (ASTM etc.) require at least 4 mm thickness of the material. The tan δ values were measured 14 times in the 20 Hz...500 kHz range at 5 V. The test equipment was a Wayne-Kerr 6430a impedance analyzer. The EVR method measures the initial slopes of the decay (Sd) and return (Sr) voltages. The decay voltage can be measured after the relatively long duration (100…1000 sec) charging period of the insulation. The return voltage can be measured on the charged insulation after a few seconds of short circuiting [START_REF] Csányi | Investigation of dielectric properties of cable insulation by the extended voltage response method[END_REF]. By changing the shorting times different time constant polarizations can be investigated. During the EVR measurement the inner electrode (inner cores and wire and tape screens) was connected to 1000 V while the outer (aluminum foil) was grounded. The charging time was set to 4000 s the charging voltage to 1000 V DC and return voltages were measured after 20 different discharging times in the 1...2000 s range. During the investigation the specimens were measured at 23.2 ± 0.5°C. Proper connections were examined before each electric measurement.

Results

Shore D hardness measurement, that is used for characterizing polymers, gives a dimensionless value between 0 (soft) and 100 (hard). The Shore D measurement results in Table 2 show that hardness of the jacket is increasing by the thermal ageing and the degradation at 140°C is more intensive than at 125°C. The dielectric parameters were measured by means of Extended Voltage Response method. This measurement provides information about the changing of the conduction by the value of slope of decay voltage (Sd) [START_REF] Németh | Proposed fundamental characteristics describing dielectric processes in dielectrics[END_REF][START_REF] Németh | Measuring voltage response: a non-destructive diagnostic test method of hv insulation[END_REF]. The results can be seen in Table 3. As the data of Table 3 suggest the specific conductivity of the jacket material is decreasing by ageing. This suggests the decreasing of the plasticizer content of the jacket.

Table 3. The slopes of decay voltages (Sd) measured on the jacket [V/s]

Ageing: Ne w 11h @ 125°C 15h @ 125°C 11h @ 140°C 15h @ 140°C Average 76. 1 6 84.42 37.98 50.45 15.60 Deviati on 9.14 4.47 9.17 5.55 0.48

The slopes of return voltages as the function of shorting times are in Fig. 2. The result shows that each curve has a certain cut-off point that shifts to the right by ageing. The order from smaller time constants to the faster: New, 11h @ 125°C, 11h @ 140°C, 15h @ 125°C, 15h @ 140°C. This also suggests the reduction of the plasticizer content of the jacket.

The tan δ as the function of the frequency can be seen in Fig. 3. The curve of 'New' cable suggests that the peak of the tan δ is over 500 kHz. By ageing, the peaks shift to the lower frequency range. This also suggests the changing of the material structure of the jacket. Previous studies have shown that conductivity and the slow polarization processes above 1 s time constant are strongly influenced by the plasticizer content of the PVC [START_REF] Nagy | Effect of dioctyl phthalate (dop) plasticizing agent on the dielectric properties of pvc insulation[END_REF]. The slow polarization processes are related to conduction processes e.g. space charge polarization [START_REF] Raju | Dielectrics in electric fields[END_REF]. The thermal degradation of PVC increases [START_REF] Tamus | Condition assessment of pvc insulated low voltage cables by voltage response method[END_REF], however the loss of plasticizer content reduces the conductivity that is directly proportional to the initial steepness of decay voltage (Sd). The slope of return voltage after short (1...3 s) shorting times is directly proportional to the polarization conductivity of slow polarization processes [START_REF] Németh | Proposed fundamental characteristics describing dielectric processes in dielectrics[END_REF].

All of the measurements indicate that the short term but relatively high temperature ageing cycles initiate deterioration processes in the material structure of the jacket.

The shifting of the cut-off point to longer shorting times (Fig. 2.) suggests that the most intensive polarization processes become slower. In order to prove this assumption, using an iteration algorithm, the polarization spectra have been calculated from the results of the EVR measurements [START_REF] Tamus | Characterization of dielectric materials by the extension of voltage response method[END_REF][START_REF] Csányi | Investigation of dielectric properties of cable insulation by the extended voltage response method[END_REF]. Fig. 4 shows the calculated spectra.

The result shows that in case of new cables the peak of the most intensive polarization process can be found at 12.6 s. By ageing, the peaks shift towards the higher time constants. The highest time constant peak can be observed at 79.4 s on the samples that were exposed to most intensive ageing (15h @ 140°C). Moreover, the shifting of the peaks in the polarization spectrum follows the same order as the changing of the cut-off points in Fig. 2.

Fig. 4. The calculated polarization spectra

The relation between the hardness and the slope of decay voltage is plotted in Fig. 5a. The result shows lower slope of decay voltage (conductivity) correspond to increased hardness values the only exception is the 11h @ 125°C where the slope of decay voltage increased while the hardness also increased. However, the values of different ageing temperatures cannot be fitted to one curve. Similar result can be observed if the slopes of return voltages after 1 s shorting time are plotted as a function of hardness (Fig. 5b).

The general trend of measuring lower slope of decay voltages by increasing degree of thermal ageing indicates that the dominant process is not the dehydrochlorination but the loss of plasticizer from the PVC. In case of the 11h @ 125°C result probably another, faster chemical process (e.g. decomposition of compound) has an effect on the conductivity and later the effect of plasticizer loss becomes dominant, however proving this assumption needs further investigation. Summing up the results of the study, it can be stated that after the ageing the jacket was not in seriously degraded condition, nevertheless both the mechanical and electrical tests prove the evaporation of plasticizer from the jacket. Moreover, the correlation between the mechanical and dielectric measurements proposes the application of non-destructive dielectric measurements for testing both mechanical and electrical condition of the cable jacket. This would be really useful in practice since the cables are laid under the ground therefore determining the mechanical condition is practically impossible, however by means of EVR method both mechanical and electrical degradations could be investigated.

Although the results are promising, to determine a threshold value for increased probability of failure more investigation is required involving the bending test which is generally accepted in nuclear power plant cable testing [START_REF]Ieee standard for qualifying electric cables and splices for nuclear facilities -red-line[END_REF].

Conclusions

The distributed generation in extreme cases, mostly the photovoltaic systems on hot summer days can cause overloads on low voltage distribution cable lines. These overloads appear when the temperature of the soil is also elevated therefore it can increase the temperature of the core insulation and the jacket over the maximum operation temperature. These temperature peaks can initiate degradation processes in these polymeric components of the cable. The effect of the short term thermal overloads on the jacket of PVC insulated low voltage cables was investigated on cable samples. The samples were exposed to periodic thermal ageing test consisting of short but high temperature cycles. After the ageing, the mechanical and dielectric properties of the jacket were tested by Shore D hardness and voltage response measurements, respectively. The results show increasing hardness and decreasing conductive properties of the jacket moreover these properties show high correlation. The relation between these properties enables tracking the effect of the short term thermal overloads by non-destructive dielectric measurements. These results suggest the loss of the plasticizer additive from the jacket material deteriorating the mechanical properties of the jacket. In this condition the jacket is harder and ruptures and cracks can easily appear on it. Therefore, it will not be able to protect the inside of the cable from the environmental stresses e.g. water ingression increasing the probability of the cable failures, which increases the operation risk of low voltage distribution network.

Fig. 2 .

 2 Fig. 2. The slopes of the return voltages (Sr) as the function of shorting times

Fig. 3 .

 3 Fig. 3. Tan δ as the function of frequency

Fig. 5 .

 5 Fig. 5. Slope of decay voltage (Sd) versus Shore D hardness (a,) Slope of return voltage after 1 s shorting time (Sr1) versus Shore D hardness (b,)

Table 2 .

 2 The results of the Shore D hardness measurement of the jacket

	Ageing: Ne	11h @ 125°C 15h @ 125°C 11h @ 140°C 15h	@
	w Average 36.9	39.12	40.04	43.46	140°C 45.67
	Deviati	5	1.49 1.68	1.57	1.69	1.65
	on

Acknowledgement. This research work was supported by the ÚNKP-16-3-II. New National Excellence Program of the Ministry of Human Capacities.