Oxidation effects on graded porous silicon anti-reflection coatings

Efficient anti-reflection coatings (ARC) improve the light collection and thereby increase the current output of solar cells. By simple electrochemical etching of the Si wafer, porous silicon (PS) layers with excellent broadband anti-reflection properties can be fabricated. In this work, ageing of graded PS has been studied using Spectroscopic Ellipsometry, Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. During oxidation of PS elements such as pure Si (Si$^0$), Si$_2$O (Si$^+$), SiO (Si$^{2+}$), Si$_2$O$_3$ (Si$^{3+}$), and SiO$_2$ (Si$^{4+}$) are present. In addition both hydrogen and carbon is introduced to the PS in the form of Si$_3$SiH and CO. The oxide grows almost linearly with time when exposed to oxygen, from an average thickness of 0 - 3.8 nm for the surface PS. The oxidation is then correlated to the optical stability of multi-layered PS ARCs. It is found that even after extensive oxidation, the changes in the optical properties of the PS structures are small

Conservation of historic timber structures. An ecological approach

"This text was originally published in 2000 in Butterworth-Heinemann Series in Conservation and Museology.

Electronic Structure and Optical Properties of Silicon Nanocrystals along their Aggregation Stages

The structural control of silicon nanocrystals is an important technological problem. Typically a distribution of nanocrystal sizes and shapes emerges under the uncontrolled aggregation of smaller clusters. The aim of this computational study is to investigate the evolution of the nanocrystal electronic states and their optical properties throughout their aggregation stages. To realistically tackle such systems, an atomistic electronic structure tool is required that can accommodate about tens of thousand nanocrystal and embedding lattice atoms with very irregular shapes. For this purpose, a computationally-efficient pseudopotential-based electronic structure tool is developed that can handle realistic nanostructures based on the expansion of the wavefunction of the aggregate in terms of bulk Bloch bands of the constituent semiconductors. With this tool, the evolution of the electronic states as well as the polarization-dependent absorption spectra correlated with the oscillator strengths over their aggregation stages are traced. The low-lying aggregate nanocrystal states develop binding and anti-binding counterparts of the isolated states. Such information may become instrumental with the maturity of the controlled aggregation of these nanocrystals.Comment: 5 pages, 7 figure

Una nueva arquitectura para la Red de Bibliotecas del CSIC

En esta ponencia, después de un breve repaso al proceso de automatización de las Bibliotecas del CSIC y al desarrollo de la Red de Bibliotecas, se exponen y analizan una serie de cambios importantes que van a tener lugar a medio plazo en la arquitectura de la Red. Por una parte, el paso de una arquitectura distribuida, con cuatro nodos zonales, a una arquitectura centralizada en un solo nodo, y por otra, la introducción de una nueva versión del programa de automatización Aleph, con una estructura y filosofía de funcionamiento totalmente nuevas respecto a la versión actual

Comparison of periodic light-trapping structures in thin crystalline silicon solar cells

Material costs may be reduced and electrical properties improved by utilizing thinner solar cells. Light trapping makes it possible to reduce wafer thickness without compromising optical absorption in a silicon solar cell. In this work we present a comprehensive comparison of the light-trapping properties of various bi-periodic structures with a square lattice. The geometries that we have investigated are cylinders, cones, inverted pyramids, dimples (half-spheres), and three more advanced structures, which we have called the roof mosaic, rose, and zigzag structure. Through simulations performed with a 20 μm thick Si cell, we have optimized the geometry of each structure for light trapping, investigated the performance at oblique angles of incidence, and computed efficiencies for the different diffraction orders for the optimized structures. We find that the lattice periods that give optimal light trapping are comparable for all structures, but that the light-trapping ability varies considerably between the structures. A far-field analysis reveals that the superior light-trapping structures exhibit a lower symmetry in their diffraction patterns. The best result is obtained for the zigzag structure with a simulated photo-generated current Jph of 37.3 mA/cm2, a light-trapping efficiency comparable to that of Lambertian light-trapping. Copyright (2011) AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing

System for forvaltning av digital geografisk informasjon ved Krigsskolen

Fordypningen i Militær Geografi ved Krigsskolen har behov for store mengder digital geografisk informasjon for å kunne gjennomføre sin utdanning. Dette er plasskrevende og det er nødvendig med dedikert maskinvare for å forvalte informasjonen. Ved oppstart av prosjektet var den daværende løsningen basert på flyttbare lagringsmedier og en nettverksdisk uten tilstrekkelig kapasitet. Dette har til en viss grad gått utover undervisningen, da mye tid brukes til å distribuere data som trengs i forbindelse med utdanningen. Derfor er det et behov for en forvaltningsløsning for digital geografisk informasjon. Oppgavens første del tar for seg tre forskjellige forvaltningsløsninger og drøfter disse opp i mot hverandre. På bakgrunn av andre lignende systemer i Forsvaret har gruppen sett på følgende løsninger: 1 Filserver, tjeneste som kjører på Windows Server. 2 Network-attached Storage (NAS). Nettverkstilkoblet harddisk. 3 ArcGIS Server. Forvaltnings og publiseringsverktøy fra Environmental Systems Research Institute (ESRI). Løsningene er blitt drøftet på bakgrunn av kriterier utarbeidet av gruppen. For bruk som forvaltningsløsning på Krigsskolen anbefaler gruppen en filserver. Oppgavens andre del omhandler implementering av den valgte forvaltningsløsningen. Herunder oppsett av løsningen i skolens nettverk og hvilke mekanismer som er tilgjengelig for å kunne dele informasjon over nettverket. Denne delen går ikke i dybden på hvordan hver enkelt mappe er konfigurert, men forklarer de overordnede prinsippene. Oppgavens tredje del forklarer hvordan digital geografisk informasjon bør organiseres. Delen tar for seg hvordan man navngir filer og mapper, samt hvordan nettverksdisker bør struktureres. Det blir også beskrevet hvordan vi har valgt å organisere digital geografisk informasjon på forvaltningsløsningen

3D modelling of geological and anthropogenic deposits at the World Heritage Site of Bryggen in Bergen, Norway

The landscape of many historic cities and the character of their shallow subsurface environments are defined by a legacy of interaction between anthropogenic and geological processes. Anthropogenic deposits and excavations result from processes ranging from archaeological activities to modern urban development. Hence, in heritage cities, any geological investigation should acknowledge the role of past and ongoing human activities, while any archaeological investigation should be conducted with geological processes in mind. In this paper it is shown that 3D geological and anthropogenic models at different scales can provide a holistic system for the management of the subsurface. It provides a framework for the integration of other spatial and processmodels to help assess the preservationpotential for buried heritage. Such an integrated framework model is thus contributing to a decision support system for sustainable urban (re)development and regeneration in cities, while preserving cultural heritage. A collaborative approach is proposed to enhance research and implementation of combined geological and archaeological modelling for sustainable land use planning and heritage preservation, using York and Bryggen as prime examples. This paper presents the status of 3D framework modelling at Bryggen in Norway as an example

The influence of stakeholder groups on organizational decision-making in public hospitals

he thesis presents a contextual analysis that makes an exposition of the structural contingencies of the Norwegian welfare state. A descriptive/ empirical analysis of the public hospital’s decision-making processes provides insight into how stakeholder groups shape the premises of the public hospital’s value creation-process. The thesis’ theoretical propositions are vested in hospitals’ efforts to achieve a stakeholder balance between competing constituent interests. A thesis proposal on descriptive/empirical stakeholder theory is exempt from normative prescriptions on the intrinsic value of all stakeholder groups. The “stakeholder theory of detachment” See thesis section 11.5.3 “Theoretical contributions”. reflects thesis findings that stakeholder management takes place in a departmentalized fashion without an integrated operations perspective. A conceptualization of “stakeholder compliance” See thesis section 11.5.3 “Theoretical contributions”. is introduced and vizualises the embedded nature of stakeholder management in public hospitals. The model is grounded in the empirical accounts on how stakeholder management employs differentiated decision processing techniques at different organizational levels to achieve an optimum balance between competing constituent interests. The thesis summary and conclusions culminate in a set of implications. These address the need for a renewed national discourse on the governance of public hospitals. The thesis empirical findings on the consequences of non-integrated stakeholder management, call for reviews of governance models and managerial practices. Empirical evidence confirms a pattern of decisional sedimentation in which executive-, operational- and ward hospital management work strategically detached on issues of overall strategic importance. The thesis contends that hegemonic and autonomous management make room for staged and manipulative stakeholder behavior. As generalized through this empirical field study, the operational practices of public hospitals exempts authorities from the exercise of rational choice

Two-sided reinforcement of CLT and push-in capacity of fully threaded screws

This thesis aims to complement the study by Rathiens[25] on two-sided reinforcement in CLT through experimental testing. Additionally, it seeks to investigate the push-in capacity of fully threaded screws, also via experimental testing, with a particular focus on the effects of the screw’s tip and head. One part of the experimental work involved plate tests where a reinforced CLT member was subjected to a compressive force through a steel plate. The screw spacing varied and corresponded with different sizes of the steel plates. Another aspect of the laboratory work involved testing of a single screw in various configurations to isolate the effects of the tip and head. Tests were conducted on screws that were 8 and 10 mm in diameter and 120 mm in length. The results from the plate tests were compared with those of Rathiens[25] and the proposed prEN 1995-1-1 model[24]. These results highlighted a significant effect of the enlarged CLT specimens utilized in this thesis, even though the load application area remained the same. Additionally, the results indicated that the prEN 1995-1-1 model[24] underestimates the contribution of the unloaded area to resist compressive forces. From the tests examining the effects of the tip and head, both effects were found to be significant, in contrast to the prEN 1995-1-1 model[24], which assumes identical capacities for withdrawal and push-in for screws. The findings also demonstrated significantly higher results than those predicted by the model, suggesting that it underestimates the push-in capacity of screws