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The demand for cheap and clean energy sources, not based on fossil fuels and having low impact on the environment, is becoming nowadays an urgent matter. In this regard photovoltaic (PV) power generation technology is one of the most promising. A large variety of photovoltaic devices, or most commonly “solar cells”, is currently on market but all of them share an identical research aspect: the need of increase their photovoltaic conversion efficiency in a cost effective way. In addition to improving the electronic properties of the materials used for solar devices construction, there is a very promising approach towards the efficiency enhancement based on the so called Light Management (LM) techniques. LM techniques are based on the introduction of particular photonic nanostructures which depending on the positioning along the cell architecture and depending on their morphological characteristics, can serve for the obtaining of different phenomena including: diffractive effects, modulation of the refractive index, coupling to waveguide modes through surface structuring, and modification of the photonic band structure of the device. Anyway, the goal of LM concept is the enhance of the probability of photons interaction with cell active layer for the generation of an increased quantity of charge carriers involved in the photovoltaic process. Continuous improvement in nanotechnology manufacturing field have led to a great attention for LM techniques applied to photovoltaics and the present work has given a contribute to this interesting field, focusing on a particular type of PV device, Dye Sensitized Solar Cells (DSC). A Bragg grating with defined morphological parameters (theoretically predicted by FEM calculation) has been realized on a high performance photoresist by means of Laser Interference Lithography (LIL) and then replicated on a mesoporous TiO2 layer. Replication process takes place by means of a low-cost Soft Lithographic (SL) process which exploits a PDMS mold for pattern transferring from one layer to the other. The nanostructures good quality replication, over a large area have been demonstrated by microscopic analysis. The nanostructured TiO2 layer was then soaked into a dye and the DSC cell assembled. PV properties of the build-up nanostructured cell and those of a traditional bare one, both realized following identical experimental procedures and differing only for the Bragg grating presence, were compared. Results confirmed an enhanced efficiency, in term of IPCE, of 31% for the nanostructured cell. Therefore, the most important achievement of this study has been the successful easy and low cost TiO2 nanostructuring. The second part of this work concerns on preliminary guidelines for the realization and ordering of different type of nanostructures. In particular a LIL method for 2D Bragg grating structure production has been proposed to be employed for photovoltaic antireflective coating. A transfer method that exploit PDMS mold to align gold nanoparticles (NPs) on a PEDOT:PSS layer of an organic solar cell was applied. The deposition and ordering of such Au NPs along specific patterns, permits to combine the photonic effect, whose effectiveness has been demonstrated in the first part of the work, with the plasmonic one. The presented result demonstrated the great potential of low-cost soft lithographic procedures in LM field.

An extensive experimental investigation was carried out to study the energy absorbing characteristics and progressive deformation behavior of unidirectional pultruded composite tubes subjected to an axial impact load. Pultruded square and circular profiles with glass-polyester and glass-vinylester combinations were used to study the specific energy absorption characteristics. Two types of triggering profiles were incorporated to investigate the effect of triggering on energy absorption. All the above combinations were investigated for three impact velocities. The effects of geometry profile, triggering and strain rate on energy absorption of composite tubes were studied in detail. A numerical simulation using finite element method was carried out to assess the energy absorption capability of composite tubes. To model the delamination between the composite plies, a new approach was adopted using cohesive elements. The progressive failure modes and crushing characteristics of the composite tubes are presented. From these studies, the composite tubes can be considered as energy absorbing members for impact applications.

The chapter gives an introduction to the book "Environmental planning and management : tools for a sustainable development".

A recent addition to the anthropogenic sources of underwater noise is offshore wave energy converters. Underwater noise was recorded from the Wavestar wave energy converter located at Hastholm, Denmark (57°7.73´N, 8°37.23´E). The Wavestar is a full-scale test and demonstration converter of the absorber type. During recordings the converter was operating close to maximum power output (nominal capacity of 110 kW). During operation the independently operating absorbers float semi-submerged in the water and wave-generated up-and-down motion is converted into hydraulic pressure by means of pistons connected to the arms of the absorbers. The hydraulic pressure then in turn drives the generator. A 57 minute sequence of noise from the converter was recorded by a Loggerhead datalogger deployed in 7 m deep water 25 m from the converter. This sequence contained recordings of ambient noise, the converter in full operation and start and stop of the converter. Median broad band (10 Hz – 20 kHz) sound pressure level (Leq) was 123 dB re. 1 Pa, irrespective of status of the wave energy converter (stopped, running or starting/stopping). The most pronounced peak in the third-octave spectrum was in the 160 Hz band during start and stop of the converter, attributed to the hydraulic pump responsible for lifting and lowering the absorbers. Less pronounced, but still statistically significant differences were seen in the bands 125, 160, 200 and 250 Hz when operation and ambient were compared. No statistically significant noise above ambient could be detected above the 250 Hz band. The absolute increase in noise above ambient was very small. L50 third-octave levels in the four bands with the converter running were thus only 1-2 dB above ambient L50 levels.The noise recorded 25 m from the wave energy converter was barely detectable above ambient noise and only in the range 125-250 Hz. Harbour seals have good low frequency hearing and third-octave levels of the converter noise are well above their hearing threshold. Harbour seals are thus expected to be able to hear the converter noise, although the elevation in noise levels is so low (1-2 dB) that it is likely to be close to inaudible even at the close range where recordings were obtained. In contrast to seals, harbour porpoises have poor low frequency hearing and it seems unlikely that the converter noise would have been audible to porpoises. Wave energy converters come in different designs and work according to different principles. Other types of converters could be expected to be noisier, perhaps also to generate noise at other frequencies than those reported from the Wavestar. Therefore the conclusion that noise levels from the Wavestar are unlikely to affect seals and porpoises cannot be generalised. Nevertheless, the results clearly demonstrate that it is possible to harvest wave energy in a way which does not add substantially to the increasing levels of anthropogenic noise in the ocean.

Planktonic organisms are considered good indicators of environmental changes, even more sensitive than abiotic variables per se. In relatively recent years, the importance of pluriannual plankton series has become increasingly important, also for management purposes and in the process of bridging the gap between environmental science and management policy. Plankton studies in Lake Maggiore date back to middle 1900s, although a regular monitoring started in late seventies, in the framework of an agreement between Swiss and Italian Governments. The full long-term data series (1981-2011) entirely covers the lake's recovery, since full mesotrophy of mid-1970s, to present oligotrophy. Response of plankton communities to eutrophication reversal after lake restoration included a gradual increase in the number of phytoplankton taxonomic units and in cell density along with a decrease of average cell size. Changes in taxonomic composition, population density and mean body size were also tracked in the zooplankton. Data we obtained through these studies, however, pertaining to each single level of biological organization, do not allow per se for highlighting quantitative changes in trophic relationships and in ecosystem functioning driven by changes in trophy. Environmental changes, such as those attributable to eutrophication/oligotrophication processes, as well as to climate, are expected to affect not only taxonomic composition of planktonic assemblages, but also the trophic relationships and the ecosystem processes. Moreover, during the lake's oligotrophication the role of climatic constraints became increasingly important in controlling plankton dynamics, affecting phytoplankton nutrient supply, resource ratio, population phenology and the whole life cycles of the organisms involved. Our aim is to track the ecosystem response by analysing the phytoplankton-zooplankton relationship from a functional point of view, trying to find the key driver across different steps of the lake's trophic history, in the attempt to disentangle climate- from trophy-related responses of lake ecosystems.

ÖZET BORU ÇEVRİMİ İLE MEKANİK ENERJİ YUTUMU ÇOLAKO?LU, AH Mürteza Doktora, Makina Mühendisliği Bölümü Tez Yöneticisi: Prof. Dr. R. Orhan YILDIRIM Ortak Tez Yöneticisi: Prof. Dr. Metin AKKÖK Eylül 1996, 139 Sayfa Büyük miktarlardaki kinetik enerjileri kontrol edilebilir şekilde ve önceden belirlenmiş hızlarda yutabilecek metal kabuk yapıların tasarım ve geliştirilmesi son yıllarda mühendislerin dikkatini çekmektedir. İnce et kalınlıklı sünek metal boruların içlerinin dışarı veya dışlarının içeri çevrilmesini içeren boru çevrimi, enerji yutan bu tür yapılardan biridir. Kalıp kullanılmadan yapılan ve bir tarafı uygun biçimde şekillendirilerek halkasal sabitleyici ile tutulan borunun diğer ucunun basılması ile yapılan çevrime serbest çevrim denmektedir. Bu çalışmanın ilk bölümünde, serbest boru çevriminin analitik modeli geliştirilmiştir. Rijit, germimle sertleşen malzeme varsayımı kullanılırken; kalıcı şekil değişikliği sırasında, borudaki et kalınlığı değişiklikleri de hesaba katılmıştır. Tresca akma şartı, Baucshinger etkisi ve ilintili akma koşullan uygulanmıştır. Germim hızının etkisi de incelenerek statik yükleme için çıkarılan model darbe ile boru çevrimi için geliştirilmiştir. Çalışmanın ikinci kısmında, serbest boru çevriminin sonlu elemanlar yöntemi ile modellenmesi yapılmıştır. ModellemedeABAQUS (Versiyon 5.4) kullanılmıştır. Bora çevrimi 3-boyutlu bir metal şekillendirme işlemi olmasına karşın, şekil değişikliğinin eksenel simetrik olması nedeniyle, problem 2-boyuta indirgenebilmektedir. SAX1 (eksenel simetrik, 2-düğümlü lineer kabuk eleman) ve CAX4R (eksenel simetrik, 4-düğümlü bi-lineer katı eleman) elemanlar kullamlarak iki farklı ağ analiz edilmiştir. Elastik, Mises akma şartına uyan ve izotropik sertleşen malzeme varsayımı yapılmıştır. Çalışmanın son kısmında ise deneysel çalışma yapılmıştır. Önceden şekillendirilmiş borular, özel olarak tasarlanıp imal edilmiş bağlama düzeni kullanılarak çevrilmişlerdir. Sabit yük altodaki boru çevrimleri, yer değişim kontrollü universal bir test cihazında yapılmıştır. 10 m/s çarpma hızına kadar olan darbe testleri ise 94 kg kütleli serbest düşme çekici ile yapılmıştır. Testlerde soğuk çekilmiş yumuşak çelikten (BS 3602-CFS 360) imal edilmiş dikişsiz borular kulanılmıştır. Boruların dış çapı 50.8 mm, et kalınlığı 1.6 mm ve uzunluğu 203.2 mm'dir. Sonuç bölümünde, analitik ve sonlu elemanlar yöntemleri kullanılarak elde edilen kuramsal değerlerin deneysel bulgularla karşılaştırılması yapılmış ve mantıksal bir uyum içerisinde oldukları görülmüştür. Anahtar Kelimeler: Boru Çevrimi, Enerji Tutucu VI ABSTRACT MECHANICAL ENERGY ABSORPTION USING TUBE INVERSION ÇOLAKO?LU, Ali Mürteza Ph. D., Department of Mechanical Engineering Supervisor: Prof. Dr. R. Orhan YILDIRIM Co-Supervisor: Prof. Dr. Metin AKKÖK September 1996, 139 Pages The design and development of metal shell structures whichIn the second part of the study, finite element method is employed to investigate the free external tube inversion. The simulation is performed on a using ABAQUS (Version 5.4) finite element program package. Although the inversion is 3-D metal forming process, it is reduced to 2-D problem since the deformation of the tube is axisymmetric. Two different meshes are generated using SAX1 (2-D axisymmetric linear shell element) and CAX4R (2- D axisymmetric bilinear solid element) elements. Both quasi-static and impact loading models are developed. Elastic, Mises yield and isotropic hardening material model is assumed. In the last part of the study an experimental work is done. Pre formed tubes are inverted using a specially designed and manufactured inversion fixture. Quasi-static tests are done using a displacement controlled universal testing machine. The impact tests up to 10 m/s are done on a 94 kg drop weight apparatus. In the tests cold drawn seamless mild steel tubes (BS 3602-CFS 360) with 50.8 mm outside diameter, 1.6 mm wall thickness and 203.2 mm length are used. At the end, the analytical and finite element predictions are compared with the experimental results and the agreement is seen to be a reasonable. Keywords: Tube Inversion, Invertube, Energy Absorber IV 158

The purpose of this thesis is comparison of calculated and in situ measured values of heat transfer coefficient. The heat transfer coefficients are measured on different types of concrete walls considering their thickness, type of wall elements (full concrete wall or hollow concrete block) and thermal isolation. The most important objective while designing energy efficient building, energy retrofitting existing buildings and conducting energy certification is assessment of thermal characteristics of external walls. The heat transfer coefficient is characteristic which describes thermal characteristics of building elements. A method of calculation heat transfer coefficient of opaque structure is given by HRN EN ISO 6946:2008. By applying this procedure it is possible to get reliable results. In some cases it is not possible to apply recommended procedure (unknown layers of construction material, unknown thickness and density of layers), therefore it is necessary to carry out in situ measurements. In this thesis basic concepts related to building physics are described. An overview of the legislative framework for the implementation of energy efficiency in buildings, especially the parts related to heat transfer coefficient, energy audits of building and energy certification is presented in this thesis. In situ measurements described in this thesis were carried out on concrete walls. This thesis also gives historical evolvent of concrete construction in the Republic of Croatia so it is possible to analyse period of time when concrete buildings were constructed and their thermal characteristics. The last part of thesis gives an overview of the procedure and equipment used for in situ measurements. Comparison of results was made, pointing out the possible mistakes which can be made during measurements which could lead to a discrepancy between the calculated and measured values of heat transfer coefficient. Cilj diplomskog rada je usporedba izračunatih i in situ izmjerenih vrijednosti koeficijenta prolaska topline. Koeficijenti prolaska topline mjereni su na različitim vrstama betonskih zidova s obzirom na debljinu, vrstu zidnih elemenata (puni betonski zid ili betonski blok) i toplinsku izolaciju. Određivanje toplinskih karakteristika vanjske ovojnice grijanog dijela zgrade od temeljne je važnosti pri projektiranju energetski efikasnih zgrada, energetskoj obnovi zgrada i izradi energetskih certifikata. Koeficijent prolaska topline karakteristika je građevinskih elemenata kojim se opisuju toplinska svojstva elementa. Metoda proračuna koeficijenta prolaska topline za neprozirne građevne elemente je dana normom HRN EN ISO 6946:2008. Primjenom norme moguće je dobiti pouzdane rezultate. U nekim slučajevima nije moguće primijeniti normu (nepoznati slojevi građevinskog elementa, njihova debljina ili gustoća) te se provode in situ mjerenja. U radu su opisani osnovni pojmovi vezani za fiziku zgrade. Dan je prikaz zakonodavnog okvira za provedbu energetske učinkovitosti u zgradarstvu, posebno dijelovi vezani za koeficijent prolaska topline, energetski pregled građevine i izradu energetskih certifikata. In situ mjerenja provedena su na betonskim zidovima te je prikazan povijesni razvoj gradnje u Republici Hrvatskoj kako bi se vidjelo u kojem razdoblju su najviše građene betonske zgrade i kakva su njihova energetska svojstva. U posljednjem dijelu dan je prikaz opreme i postupka provedenih in situ mjerenja. Napravljena je usporedba rezultata, te je ukazano na pogreške koje mogu nastati pri mjerenju zbog kojih može doći do odstupanja izračunatih i izmjerenih vrijednosti koeficijenta prolaska topline.