170,500 research outputs found
Performance analysis of AlGaAs/GaAs tunnel junctions for ultra-high concentration photovoltaics
No full textAn n(++)-GaAs/p(++)-AlGaAs tunnel junction with a peak current density of 10 100Acm(-2) is developed. This device is a tunnel junction for multijunction solar cells, grown lattice-matched on standard GaAs or Ge substrates, with the highest peak current density ever reported. The voltage drop for a current density equivalent to the operation of the multijunction solar cell up to 10 000 suns is below 5 mV. Trap-assisted tunnelling is proposed to be behind this performance, which cannot be justified by simple band-to-band tunnelling. The metal-organic vapour-phase epitaxy growth conditions, which are in the limits of the transport-limited regime, and the heavy tellurium doping levels are the proposed origins of the defects enabling trap-assisted tunnelling. The hypothesis of trap-assisted tunnelling is supported by the observed annealing behaviour of the tunnel junctions, which cannot be explained in terms of dopant diffusion or passivation. For the integration of these tunnel junctions into a triple-junction solar cell, AlGaAs barrier layers are introduced to suppress the formation of parasitic junctions, but this is found to significantly degrade the performance of the tunnel junctions. However, the annealed tunnel junctions with barrier layers still exhibit a peak current density higher than 2500Acm(-2) and a voltage drop at 10 000 suns of around 20 mV, which are excellent properties for tunnel junctions and mean they can serve as low-loss interconnections in multijunction solar cells working at ultra-high concentrations
Analysis of Chromatic Aberration Effects in Triple-Junction Solar Cells Using Advanced Distributed Models
No full textThe consideration of real operating conditions for the design and optimization of a multijunction solar cell receiver-concentrator assembly is indispensable. Such a requirement involves the need for suitable modeling and simulation tools in order to complement the experimental work and circumvent its well-known burdens and restrictions. Three-dimensional distributed models have been demonstrated in the past to be a powerful choice for the analysis of distributed phenomena in single- and dual-junction solar cells, as well as for the design of strategies to minimize the solar cell losses when operating under high concentrations. In this paper, we present the application of these models for the analysis of triple-junction solar cells under real operating conditions. The impact of different chromatic aberration profiles on the short-circuit current of triple-junction solar cells is analyzed in detail using the developed distributed model. Current spreading conditions the impact of a given chromatic aberration profile on the solar cell I-V curve. The focus is put on determining the role of current spreading in the connection between photocurrent profile, subcell voltage and current, and semiconductor layers sheet resistance
Capacitance Measurements for Subcell Characterization in Multijunction Solar Cells.
No full textOn this paper we present an alternative way to analyze de electronic properties of each subcell from the complete device. By illuminating the cell with light sources which energy is near one of the subcell bandgaps, it is possible to “erase” the presence of such subcell on the CV curve. The main advantages of this technique are that it is not destructive, it can be measured on the complete cell so can be easily implemented as a diagnostic technique for controlling electronic deviations
Nest distribution, habitat selection and nesting success in endangered waders breeding on managed shore meadows
No full textAbstract
European wader populations, particularly species breeding in low-lying shore habitats, are undergoing steep declines due to habitat loss and degradation caused by anthropogenic pressures and climate change. In this thesis, I explore ruff (Calidris pugnax) nesting distribution and the major sources of nest mortality driving their low population growth at managed shore meadows in the Bothnian Bay.
In Chapter 1, I examine which social and environmental cues determine ruff nest distributions in a coastal meadow habitat. I found that ruffs nested closer than expected by chance to the nests of conspecifics and leks, while in some years, they nested further away from the shoreline and meadow edge. This non-random nest distribution in ruffs suggests that females may use social cues and the distance to habitat boundaries when choosing a nest site.
In Chapter 2, I investigate the changing frequency and intensity of wind floods in managed coastal meadows in the northern Baltic Sea. Using long-term breeding (2002–2022) and mareograph data (1970–2023), I assessed the impact of time, water level, and the distance from the shoreline on ruff and southern dunlin (Calidris alpina schinzii) nest survival due to flooding. Nest losses caused by flooding increased over the study periods, with increased nest mortality after a water level rise of 40 cm above theoretical mean sea level in both species. Furthermore, we found that the frequency of such floods has increased during the last 50 years.
Finally, in Chapter 3, I focus on disentangling the drivers of nest failure in ruffs, with a particular focus on nest predation. I assessed the impact of social, spatial, and temporal factors on ruff daily nest survival in three models focusing on distinct sources of mortality. Overall, younger nests and those at an intermediate distance to other nests had the highest daily nest survival, while laying date and distance to paths only affected nest survival in the absence of predation. The use of dummy eggs in vulnerable clutches reduced predation, flooding, and trampling mortality and may provide a valuable management tool to improve nesting success.
This thesis highlights the need for comprehensive studies of nest distributions and mortality sources in waders to ultimately improve their population recovery through informed species and habitat restoration and management. Original papers Algora, H., Tolliver, J. D. M., Pakanen, V., Kupán, K., Belojević, J., Rönkä, N., Küpper, C., & Koivula, K. (2025). Nests, threats, and leks: Nonrandom distributions of nests in ruffs (Calidris pugnax). Ecology and Evolution, 15(3), e70997. https://doi.org/10.1002/ece3.70997 https://doi.org/10.1002/ece3.70997 Self-archived version Koivula, K., Algora, H., Airaksinen, E., Belojević, J., Küpper, C., Oranen, M., Rohr-Bender, V. A., Rönkä, N., Tolliver, J. D. M., & Pakanen, V.-M. (2025). Increased wind flood frequency leads to decreased nest success of endangered waders in managed shore meadows. Biological Conservation, 302, 110970. https://doi.org/10.1016/j.biocon.2025.110970 https://doi.org/10.1016/j.biocon.2025.110970 Self-archived version Algora, H., Kupán, K., Belojević, J., Pakanen, V.-M., Tolliver, J. D. M., Rohr-Bender, V., Koivula, K., & Küpper, C. (2025). Nest survival and failure in ruffs breeding on grazed coastal meadows. https://doi.org/10.22541/au.175268168.89269786/v1 https://doi.org/10.22541/au.175268168.89269786/v1 Tiivistelmä
Eurooppalaiset kahlaajalinnut, erityisesti alavilla ja matalakasvuisilla ranta-alueilla pesivät lajit, ovat vähenemässä nopeasti. Tämä johtuu elinympäristöjen häviämisestä ja niiden laadun heikentymisestä ihmisen aiheuttamien paineiden ja ilmastonmuutoksen vuoksi. Tässä väitöskirjassa tutkin Perämeren hoidetuilla rantaniityillä suokukon (Calidris pugnax) pesien sijoittumista ja siihen liittyviä tärkeimpiä pesäkuolleisuuden syitä, jotka mahdollisesti estävät populaation kasvun.
Luvussa 1 tutkin, mitkä sosiaaliset ja ympäristötekijät vaikuttavat suokukon pesien jakautumisen rantaniityillä. Aineisto on kerätty. Havaitsin, että suokukot pesivät lähempänä toisiaan kuin sattuman kautta odotettiin. Joinakin vuosina ne pesivät satunnaista kauempana rantaviivasta ja pesimäniityn reunasta. Tämä ei-sattumanvarainen pesäpaikkojen jakautuminen viittaa siihen, että suokukkonaaraat käyttävät em. tekijöitä pesimäpaikan valinnassaan.
Luvussa 2 tutkin tuulitulvien yleisyyttä ja voimakkuutta hoidetuilla Perämeren rantaniityillä. Pitkän aikavälin pesimätietojen (2002–2022) ja mareografiaineiston (1970–2023) avulla arvioin ajoittumisen, vedenkorkeuden ja pesän sijoittumisen vaikutusta suokukon ja etelänsuosirrien (Calidris alpina schinzii) pesien selviytymiseen tulvasta. Tulvatuhot lisääntyivät tutkimusjaksojen aikana, ja molemmilla lajeilla ne lisääntyivät selvästi meriveden noustua 40 cm yli teoreettisen keskiveden. Lisäksi havaitsimme, että tämän kriittisen rajan ylittävien tulvien esiintymistiheys on lisääntynyt viimeisten 50 vuoden aikana.
Luvussa 3 keskityn tutkimaan, mitkä tekijät vaikuttavat pesien onnistumiseen ja erityisesti pesäsaalistukseen suokukolla. Tutkin sosiaalisten, tilaan liittyvien ja ajallisten tekijöiden vaikutusta suokukon pesäsäilyvyyteen kolmen mallin avulla erikseen eri kuolleisuussyiden osalta. Haudonnan alkuvaiheen pesillä ja pesillä, jotka sijaitsivat keskimääräisellä etäisyydellä muista pesistä, oli korkein päivittäinen säilyvyys. Pesinnän ajoittuminen ja etäisyys kulku-uriin vaikuttivat pesän eloonjäämiseen mutta vain ilman pesäsaalistusta. Haavoittuvien pesien munien korvaaminen tekomunilla ja munien keinohaudonta vähensi sekä saalistus-, tulva- että tallauskuolleisuutta. Keinohaudonta voi siis joissain erikoistilanteissa olla arvokas pesimämenestystä parantava keino.
Väitöskirjassani korostan tietotarpeita liittyen kahlaajien pesien sijoittumiseen ja säilyvyyteen. Tutkimustieto on elintärkeätä kustannustehokkaan ja vaikuttavan lajien suojelun ja elinympäristöjen ennallistamisen ja hoidon kannalta. Osajulkaisut Algora, H., Tolliver, J. D. M., Pakanen, V., Kupán, K., Belojević, J., Rönkä, N., Küpper, C., & Koivula, K. (2025). Nests, threats, and leks: Nonrandom distributions of nests in ruffs (Calidris pugnax). Ecology and Evolution, 15(3), e70997. https://doi.org/10.1002/ece3.70997 https://doi.org/10.1002/ece3.70997 Rinnakkaistallennettu versio Koivula, K., Algora, H., Airaksinen, E., Belojević, J., Küpper, C., Oranen, M., Rohr-Bender, V. A., Rönkä, N., Tolliver, J. D. M., & Pakanen, V.-M. (2025). Increased wind flood frequency leads to decreased nest success of endangered waders in managed shore meadows. Biological Conservation, 302, 110970. https://doi.org/10.1016/j.biocon.2025.110970 https://doi.org/10.1016/j.biocon.2025.110970 Rinnakkaistallennettu versio Algora, H., Kupán, K., Belojević, J., Pakanen, V.-M., Tolliver, J. D. M., Rohr-Bender, V., Koivula, K., & Küpper, C. (2025). Nest survival and failure in ruffs breeding on grazed coastal meadows. https://doi.org/10.22541/au.175268168.89269786/v1 https://doi.org/10.22541/au.175268168.89269786/v1 Academic dissertation to be presented with the assent of the Doctoral Programme Committee of Technology and Natural Sciences of the University of Oulu for public defence in the OP-Pohjola auditorium (L6), Linnanmaa, on 27 February 2026, at 12 noonAbstract
European wader populations, particularly species breeding in low-lying shore habitats, are undergoing steep declines due to habitat loss and degradation caused by anthropogenic pressures and climate change. In this thesis, I explore ruff (Calidris pugnax) nesting distribution and the major sources of nest mortality driving their low population growth at managed shore meadows in the Bothnian Bay.
In Chapter 1, I examine which social and environmental cues determine ruff nest distributions in a coastal meadow habitat. I found that ruffs nested closer than expected by chance to the nests of conspecifics and leks, while in some years, they nested further away from the shoreline and meadow edge. This non-random nest distribution in ruffs suggests that females may use social cues and the distance to habitat boundaries when choosing a nest site.
In Chapter 2, I investigate the changing frequency and intensity of wind floods in managed coastal meadows in the northern Baltic Sea. Using long-term breeding (2002–2022) and mareograph data (1970–2023), I assessed the impact of time, water level, and the distance from the shoreline on ruff and southern dunlin (Calidris alpina schinzii) nest survival due to flooding. Nest losses caused by flooding increased over the study periods, with increased nest mortality after a water level rise of 40 cm above theoretical mean sea level in both species. Furthermore, we found that the frequency of such floods has increased during the last 50 years.
Finally, in Chapter 3, I focus on disentangling the drivers of nest failure in ruffs, with a particular focus on nest predation. I assessed the impact of social, spatial, and temporal factors on ruff daily nest survival in three models focusing on distinct sources of mortality. Overall, younger nests and those at an intermediate distance to other nests had the highest daily nest survival, while laying date and distance to paths only affected nest survival in the absence of predation. The use of dummy eggs in vulnerable clutches reduced predation, flooding, and trampling mortality and may provide a valuable management tool to improve nesting success.
This thesis highlights the need for comprehensive studies of nest distributions and mortality sources in waders to ultimately improve their population recovery through informed species and habitat restoration and management.Tiivistelmä
Eurooppalaiset kahlaajalinnut, erityisesti alavilla ja matalakasvuisilla ranta-alueilla pesivät lajit, ovat vähenemässä nopeasti. Tämä johtuu elinympäristöjen häviämisestä ja niiden laadun heikentymisestä ihmisen aiheuttamien paineiden ja ilmastonmuutoksen vuoksi. Tässä väitöskirjassa tutkin Perämeren hoidetuilla rantaniityillä suokukon (Calidris pugnax) pesien sijoittumista ja siihen liittyviä tärkeimpiä pesäkuolleisuuden syitä, jotka mahdollisesti estävät populaation kasvun.
Luvussa 1 tutkin, mitkä sosiaaliset ja ympäristötekijät vaikuttavat suokukon pesien jakautumisen rantaniityillä. Aineisto on kerätty. Havaitsin, että suokukot pesivät lähempänä toisiaan kuin sattuman kautta odotettiin. Joinakin vuosina ne pesivät satunnaista kauempana rantaviivasta ja pesimäniityn reunasta. Tämä ei-sattumanvarainen pesäpaikkojen jakautuminen viittaa siihen, että suokukkonaaraat käyttävät em. tekijöitä pesimäpaikan valinnassaan.
Luvussa 2 tutkin tuulitulvien yleisyyttä ja voimakkuutta hoidetuilla Perämeren rantaniityillä. Pitkän aikavälin pesimätietojen (2002–2022) ja mareografiaineiston (1970–2023) avulla arvioin ajoittumisen, vedenkorkeuden ja pesän sijoittumisen vaikutusta suokukon ja etelänsuosirrien (Calidris alpina schinzii) pesien selviytymiseen tulvasta. Tulvatuhot lisääntyivät tutkimusjaksojen aikana, ja molemmilla lajeilla ne lisääntyivät selvästi meriveden noustua 40 cm yli teoreettisen keskiveden. Lisäksi havaitsimme, että tämän kriittisen rajan ylittävien tulvien esiintymistiheys on lisääntynyt viimeisten 50 vuoden aikana.
Luvussa 3 keskityn tutkimaan, mitkä tekijät vaikuttavat pesien onnistumiseen ja erityisesti pesäsaalistukseen suokukolla. Tutkin sosiaalisten, tilaan liittyvien ja ajallisten tekijöiden vaikutusta suokukon pesäsäilyvyyteen kolmen mallin avulla erikseen eri kuolleisuussyiden osalta. Haudonnan alkuvaiheen pesillä ja pesillä, jotka sijaitsivat keskimääräisellä etäisyydellä muista pesistä, oli korkein päivittäinen säilyvyys. Pesinnän ajoittuminen ja etäisyys kulku-uriin vaikuttivat pesän eloonjäämiseen mutta vain ilman pesäsaalistusta. Haavoittuvien pesien munien korvaaminen tekomunilla ja munien keinohaudonta vähensi sekä saalistus-, tulva- että tallauskuolleisuutta. Keinohaudonta voi siis joissain erikoistilanteissa olla arvokas pesimämenestystä parantava keino.
Väitöskirjassani korostan tietotarpeita liittyen kahlaajien pesien sijoittumiseen ja säilyvyyteen. Tutkimustieto on elintärkeätä kustannustehokkaan ja vaikuttavan lajien suojelun ja elinympäristöjen ennallistamisen ja hoidon kannalta
NANOSTRUCTURED CdTe SOLAR CELLS
No full textSilicon photovoltaic cells are preferred in today's market conditions and technological implementations because they are cheap, abundant and the ongoing research has made them more and more efficient. In spite of that, manufacturing of such solar cells is very energy consuming, and silicon cells are very fragile and prone to breaking in the most mildly hostile situations. Hence, there is a lot of potential in the manufacture and use of flexible solar cells. Possible uses for this solar cell technology could be printing on glass, plastics, flexible cloth materials, and theoretically anything you could imagine. This will give endless opportunities for car makers to implement solar cells on their cars, and small gadgets would never have their battery depleted while it is sunny outside.
The aim of this Project is to develop a complete CdTe based thin film flexible as well as based on glass substrates solar cells using nanostructured surfaces as the key point for reaching in a first step the levels of efficiency of standard commercial Si on glass based solar cells. The research and future production in Europe of this innovative approach would give an extraordinary input to build a solid background for the EU industry to further increase the industrial production of CdTe based thin film solar cells devices.
Nanostructured surfaces will be utilized as one of the key technologies for improving the cell efficiency with the goal to reach the same efficiencies as for today’s standard commercial silicon based solar cells. This objective will be completed in three segments stages: the preparation of materials, the complete characterization of the materials, and the characterization of the final solar cells. To prepare the needed pn-junctions, standard processes as closed space sublimation and chemical bath deposition will be used. Further, the nanostructured surfaces will be prepared by modern approaches such as low energy ion and/or laser sputtering. Finally, the electroding will be made using approaches based on transparent conductive oxides (TCOs such as ZnO:Al, ITO, etc). Simulation tools will be required at each step in order to get the optimal geometry and dimensions of the solar cell. In the materials characterization phase, a complete set of classical and modern techniques will be used to characterize the materials: structural, compositional, electrical, optical, etc. Finally, the solar cells will be characterized in order to give feedback to the preparation process for improving their efficiency.
The expected outcomes will be innovative nanostructured solar cells which will have an extraordinary benefit in the expected efficiency, and with a possibility of commercialization as a final step
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The application of Synchrotron X-Ray Tomographic Microscopy to the functional study of the conodont skeleton
No full textMitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Reliability Improvement in III-V Concentrator Solar Cells by Means of Perimeter Protection
No full textThis paper presents the evolution in the strategy to assess the reliability of III-V solar cells and a new thermal ageing test carried out over GaAs single junction solar cells at three different temperatures (130, 150 and 170° C). The perimeter of the solar cells has been protected with silicone, which seems to be an effective way of enhancing the reliability of the solar cells. A preliminary analysis of the results indicates a mean time to failure (MTTF) one order of magnitude larger than the one obtained in a previous thermal test with the perimeter uncoated
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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