Modelling and Optimisation of Single Junction Strain Balanced Quantum Well Solar Cells

In an attempt to find the optimum number of wells for maximum conversion efficiency a pair of otherwise identical strain balanced samples, one containing 50 wells and the other 65 wells have been characterised. The 65 well sample is found to possess a lower predicted efficiency than the 50 well sample, suggesting that the optimum well number lies between these values. Devices grown using tertiary butyl arsine (TBAs) are found to possess comparable conversion efficiencies to the control cells grown using arsine and slightly superior dark IV characteristics, indicating that TBAs may be substituted for arsine without loss of device efficiency and may even be beneficial to cell performance. Several fundamental refinements to the existing quantum efficiency model of are explored. Firstly, expressions for the strained band gaps are derived. A value for the conduction band offset is . determined using the difference in energy between the heavy and light hole exciton peaks in low temperature photo current scans and found to be 0.55??0.03. The magnitude of the el-hhl exciton binding energy is also estimated from these scans and found to be in excellent agreement with the value obtained from a simple, parameterized expression for the exciton binding energy. Finally, an absolute calculation for the absorption coefficient is incorporated into the quantum efficiency model and values for the heavy and light hole in-planes masses are obtained. The model is found to underestimate the level of absorption in the intrinsic region by an amount consistent with estimates of the magnitude of the reflection from the back surface. The conversion efficiency of a sample predicted using SOL is compared to an independently obtained value. Good agreement is observed between the two results (25.3% and 25.7% for 317 suns AM1.5D). Additionally, an optimum structure for illumination by the AM1.5D spectrum was found to be a 120A well ofIno.lGaAs.Imperial Users onl

Habeas Corpus: Requirement of Exhaustion of State Remedies Before Issuance of Writ Limited to State of Detention

NMR experiments performed under the effect of electric fields, either continuous or pulsed, can provide quantitative parameters related to ion association and ion transport in solution.  Electrophoretic NMR (eNMR) is based on a diffusion pulse-sequence with electric fields applied in the form of pulses. Magnetic field gradients enable the measurement of the electrophoretic mobility of charged species, a parameter that can be related to ionic association. The effective charge of the tetramethylammonium cation ion in water, dimethylsulphoxide (DMSO), acetonitrile, methanol and ethanol was estimated by eNMR and diffusion measurements and compared to the value predicted by the Debye-Hückel-Onsager limiting law. The difference between the predicted and measured effective charge was attributed to ion pairing which was found to be especially significant in ethanol. The association of a large set of cations to polyethylene oxide (PEO) in methanol, through the ion-dipole interaction, was quantified by eNMR. The trends found were in good agreement with the scarce data from other methods. Significant association was found for cations that have a surface charge density below a critical value. For short PEO chains, the charge per monomer was found to be significantly higher than for longer PEO chains when binding to the same cations. This was attributed to the high entropy cost required to rearrange a long chain in order to optimize the ion-dipole interactions with the cations. Moreover, it was suggested that short PEO chains may exhibit distinct binding modes in the presence of different cations, as supported by diffusion measurements, relaxation measurements and chemical shift data. The protonation state of a uranium (VI)-adenosine monophosphate (AMP) complex in aqueous solution was measured by eNMR in the alkaline pH range. The question whether or not specific oxygens in the ligand were protonated was resolved by considering the possible association of other species present in the solution to the complex. The methodology of eNMR was developed through the introduction of a new pulse-sequence which suppresses artifactual flow effects in highly conductive samples. In another experimental setup, using NMR imaging, a constant current was applied to a lithium ion (Li ion) battery model. Here, 7Li spin-echo imaging was used to probe the spin density in the electrolyte and thus visualize the development of Li+ concentration gradients. The Li+ transport number and salt diffusivity were obtained within an electrochemical transport model. The parameters obtained were in good agreement with data for similar electrolytes. The use of an alternative imaging method based on CTI (Constant Time Imaging) was explored and implemented.QC 20140825</p

Markierungsverfahren zur Synthese 4-[18F]Fluorprolyl-haltiger Peptide

The requirement of selective radiopharmaceuticals for PET-diagnostics necessitates the development of new labelling methods taking into account the substantial and structural diversity of the compounds to be labelled . Therefore different concepts for $^{18}$F-fluorination of peptides, which are increasingly important as pharmaceuticals, via proline moieties were explored and evaluated in this work. The direct nucleophilic kryptate based $^{18}$F-fluorination of the model peptide Z-Pro-Leu-Gly-4- (4R)-(TsO)Pro-OMe showed, that the peptide is not stable under the basic labelling conditions, and as a result the $^{18}$F-fluorination is not possible. Perfluorbutane-l-sulfonyl[ $^{18}$F]fluoride is a possible reagent for $^{18}$F-fluorination of sensitive hydroxy groups containing biomolecules due to the mild reaction conditions at which aliphatic alcohols are fluorinated by this reagent. By kryptate catalysed, nucleophilic $^{18}$F-fluorination of N,N-bis(perfluorobutane-l-sulfonyl)aniline and evaporation of the active product no-carrier-added perfluorobutane-l-sulfonyl[ $^{18}$F]fluoride can be achieved either dissolved in toluene (RCY: 83 ± 3 %) or adsorbed an a polystyrole-matrix (LiChrolut$^{®}$ EN) with a total yield of 75 ± 6 %. In the presence of an equimolar amount of perfluorobutane-1-sulfonylfluoride as carrier N-Boc-Hyp- OMe can be $^{18}$F-fluorinated with a radiochemical yield of > 90 % and the two model peptides Z-Pro- Leu-Gly-Hyp-OMe and Z-Gly-Leu-Hyp-Gly-Leu-OMe with 40 - 45 % and 30 - 35 %, while in the case of no-carrier-added synthesis only ca. 1 % of the $^{18}$F-fluoroproduct is obtained . The necessary addition of perfluorobutane-l-sulfonylfluoride carrier allows naturally only the synthesis of radiotracers with low molar activity. For performance of the $^{18}$F-fluorination via perfluorobutane-l-sulfonyl[ $^{18}$F]fluoride of the model peptide N-Boc-Hyp-Leu-OH, which is covalently bound to a Wang resin via the C-terminus, the $^{18}$F-fluorination reagent is prepared in absence of a solvent and adsorbed an the Wang resin with a yield of 31 ± 3 %, based on [$^{18}$F]fluoride. The subsequent $^{18}$F-fluorination of the peptide, which was done in the presence of an equimolar amount of perfluorobutane-1-sulfonylfluoride, proceeds with a radiochemical yield of merely 4 ± 1 %. Altematively, the condensation of 4-[$^{18}$F]fluoroproline-methylester via TBTU at the C-terminus of Z-Pro-Leu-Gly-OH could be carried out under no-carrrier-added conditions with a radiochemical yield of 70 - 80 %. The required 4-[$^{18}$F]fluoroproline-methylester could be achieved with a radiochemical yield of 30 - 40 % by $^{18}$F-substitution of N-Boc-trans-4-(ptoluenesulfonyloxy)- proline-methylester, by which the trans-product is also formed in addition to the cis-product, and the cleavage of the Boc group. As a result of these studies another prosthetic group is available for no-carrier-added labelling of peptides

Zero Field Hall Effect in (2+1)-dimensional QED

In QED of two space dimensions, a quantum Hall effect occurs in the absence of any magnetic field. We give a simple and transparent explanation. In solid state physics, the Hall conductivity for non-degenerate ground state is expected to be given by an integer, the Chern number. In our field-free situation, however, the conductivity is $\pm 1/2$ in natural units. We fit this half-integral result into the topological setting and give a geometric explanation reconciling the points of view of QFT and solid state physics. For quasi-periodic boundary conditions, we calculate the finite size correction to the Hall conductivity. Applications to graphene and similar materials are discussed

Blogs as a Means of Preservation Selection for the World Wide Web

Currently, there is not a strong system of selection in place when looking at preserving content on the Web. This study is an examination of the blogging community for the possibility of utilizing the decentralized and distributed nature of link selection that takes place within the community as a means of preservation selection. The purpose of this study is to compare the blog aggregators, Daypop, Blogdex, and BlogPulse, for their ability to collect content which is of archival quality. This study analyzes the content selected by these aggregators to determine if any content which is linked to most frequently for a given day is of archival quality. Archival quality is determined by comparing the content from the aggregator lists to criteria assembled for the study from a variety of archival policies and principles