Growth and characterisation of titanium sulphide nanostructures by surface-assisted vapour transport methods; from trisulphide ribbons to disulphide nanosheets

Surface Assisted Chemical Vapour Transport (SACVT) methods have been employed to grow nanostructures of titanium disulphide (TiS2) and titanium trisulphide (TiS3). SACVT reactions occur between titanium and sulphur powders to form TiSx species transported in the vapour phase to grow nanometric flower-like structures on titanium-coated silica substrates. The evolution of structure and composition has been followed by powder X-ray diffraction, electron microscopy and Raman spectroscopy. At 1 : 2 Ti : S ratios, the size and shape of the hexagonal 1T-TiS2 titanium disulphide structures formed can be varied from flower-like growths with 'petals' formed from nanosheets 10 nm thick to platelets microns across. Increasing the proportion of sulphur (Ti : S 1 : 4) enables TiS3 flower-like structures composed of radiating nanoribbons to grow at elevated temperatures without decomposition to TiS2. TEM/SAED suggests that individual trisulphide ribbons grow along the [010] direction. Magnetic properties of the disulphide nanomaterials have been determined using SQUID magnetometry and Raman spectra for disulphides suggest that their crystal and electronic structures may be more complex than expected for bulk, stoichiometric, CdI2-structured TiS2

Vitamin E models - The effect of heteroatom substitution in 2-ethyl-2-methyl chroman and 2-ethyl-2-methyl-6-hydroxychroman

The molecular conformations of shortened molecular models of vitamin E (tocopherol and tocotrienol) and their sulfur and selenium congeners were studied computationally at the DFT level of theory [B3LYP/6-31G(d)]. The sequence of stabilization by the various heteroatoms was found to be the following: O similar to Se > S. On the basis of the present structural results it seems that the seleno-congener of vitamin E is a distinct possibility

Mutation of an Arabidopsis Golgi membrane protein ELMO1 reduces cell adhesion

Plant growth, morphogenesis and development involve cellular adhesion, a process dependent on the composition and structure of the extracellular matrix or cell wall. Pectin in the cell wall is thought to play an essential role in adhesion, and its modification and cleavage are suggested to be highly regulated so as to change adhesive properties. To increase our understanding of plant cell adhesion, a population of ethyl methanesulfonate-mutagenized Arabidopsis were screened for hypocotyl adhesion defects using the pectin binding dye Ruthenium Red that penetrates defective but not wild-type (WT) hypocotyl cell walls. Genomic sequencing was used to identify a mutant allele of ELMO1 which encodes a 20 kDa Golgi membrane protein that has no predicted enzymatic domains. ELMO1 colocalizes with several Golgi markers and elmo1-/- plants can be rescued by an ELMO1-GFP fusion. elmo1-/- exhibits reduced mannose content relative to WT but no other cell wall changes and can be rescued to WT phenotype by mutants in ESMERALDA1, which also suppresses other adhesion mutants. elmo1 describes a previously unidentified role for the ELMO1 protein in plant cell adhesion

From binary to multinary copper based nitrides - unlocking the potential of new applications

This review summarizes the current knowledge on the chemistry of binary copper(I) nitride, Cu3N and its multinary derivatives containing either main group or transition metal elements. For many years, research in this area was focused on the development of copper nitride prepared in the form of thin films. Successful deposition of these materials has been achieved mainly by employing physical methods, which have provided materials suitable for potential application in optical data storage. However, for the last decade, attention has also been devoted to expanding the available options by which Cu3N can be synthesized and deposited. Consequently, the focus has switched to the development of chemical synthetic methods towards the fabrication of this semiconductor and to broadening the range of related compounds that might be discovered. Simultaneously, the formulation of novel techniques and the successful preparation of new nanostructured functional materials has resulted in the rapid evolution of new and relevant applications; e.g. catalytic and electrochemical. The overview presented here concentrates on the chemical methods that have been devised to synthesise both bulk samples and thin films of Cu3N. Our article also shows how these approaches have been developed to achieve significant progress in the creation of multinary copper based nitrides and in identifying their potential applications. It provides a concise history of previous copper nitride research and sets the context for the most current advances. These will no doubt provide the springboard for future research areas that will impact both transition metal nitride chemistry and materials science more generally

A scaling law for monocrystalline PV/T modules with CCPC and comparison with triple junction PV cells

Scaling laws serve as a tool to convert the five parameters in a lumped one-diode electrical model of a photovoltaic (PV) cell/module/panel under indoor standard test conditions (STC) into the parameters under any outdoor conditions. By using the transformed parameters, a current-voltage curve can be established under any outdoor conditions to predict the PV cell/module/panel performance. A scaling law is developed for PV modules with and without crossed compound parabolic concentrator (CCPC) based on the experimental current-voltage curves of six flat monocrystalline PV modules collected from literature at variable irradiances and cell temperatures by using nonlinear least squares method. Experiments are performed to validate the model and method on a monocrystalline PV cell at various irradiances and cell temperatures. The proposed scaling law is compared with the existing one, and the former exhibits a much better accuracy when the cell temperature is higher than 40 °C. The scaling law of a triple junction flat PV cell is also compared with that of the monocrystalline cell and the CCPC effects on the scaling law are investigated with the monocrystalline PV cell. It is identified that the CCPCs impose a more significant influence on the scaling law for the monocrystalline PV cell in comparison with the triple junction PV cell. The proposed scaling law is applied to predict the electrical performance of PV/thermal modules with CCPC

Conceptual design and performance evaluation of a hybrid concentrating photovoltaic system in preparation for energy

Concentrating sunlight and focussing it on smaller sized solar cells increases the device's power output per unit active area. However, this process tends to increase the solar cell temperature considerably and has the potential to compromise system reliability. Adding a heat exchanger system to regulate this temperature rise, can improve the electrical performance whilst simultaneously providing an additional source of low temperature heat. In this study the performance of a low concentrator photovoltaic system with thermal (LCPV/T) extraction was conceptualised and evaluated in depth. An experimental analysis was performed using a first-generation prototype consisting of 5 units of Cross Compound Parabolic Concentrators (CCPC) connected to a heat extraction unit. A bespoke rotating table was used as experimental apparatus to effectively evaluate the optical performance of the system, as a function of its angular positions to replicate the motion of actual sun. Key design performance parameters for the LCPV/T collector are presented and discussed. This work also provides a useful technique to effectively calculate system performance, as a function of the orientation-dependant electrical characterisation parameters data. Finally, a Computational Fluid Dynamics (CFD) model was also applied to investigate the efficacy of the heat exchanger and hence estimate the overall co-generation benefit of using such optimisation techniques on realistic CPV systems. It was highlighted through these simulations that the water flow rate had the potential to be a critical power-generation optimisation criterion for LCPV-T systems. The maximum power output at normal incidence with concentrators and no water flow was found to be 78.4 mW. The system was found to perform with an average electrical efficiency ranging between 10 and 16% when evaluated at five different geographic locations. Experimental analysis of the data obtained showed an increase in power of 141% (power ratio 2.41) compared to the analogous non-concentrating counterpart. For example, in the case of London which receives an annual solar radiation of 1300 kWh/m2 the system is expected to generate 210 kWh/m2. This may reduce further to include losses due to temperature, reflectance/glazing losses, and electrical losses in cabling and inverter by up to 36% leading to an annual power output of 134 kWh/m2 of module

A coupled optical-thermal-electrical model to predict the performance of hybrid PV/T-CCPC roof-top systems

A crossed compound parabolic concentrator (CCPC) is applied into a photovoltaic/thermal (PV/T) hybrid solar collector, i.e. concentrating PV/T (CPV/T) collector, to develop new hybrid roof-top CPV/T systems. However, to optimise the system configuration and operational parameters as well as to predict their performances, a coupled optical, thermal and electrical model is essential. We establish this model by integrating a number of submodels sourced from literature as well as from our recent work on incidence-dependent optical efficiency, six-parameter electrical model and scaling law for outdoor conditions. With the model, electrical performance and cell temperature are predicted on specific days for the roof-top systems installed in Glasgow, Penryn and Jaen. Results obtained by the proposed model reasonably agree with monitored data and it is also clarified that the systems operate under off-optimal operating condition. Long-term electric performance of the CPV/T systems is estimated as well. In addition, effects of transient terms in heat transfer and diffuse solar irradiance on electric energy are identified and discussed

Of Bounces, Branes and Bounds

Some recent studies have considered a Randall-Sundrum-like brane world evolving in the background of an anti-de Sitter Reissner-Nordstrom black hole. For this scenario, it has been shown that, when the bulk charge is non-vanishing, a singularity-free ``bounce'' universe will always be obtained. However, for the physically relevant case of a de Sitter brane world, we have recently argued that, from a holographic (c-theorem) perspective, such brane worlds may not be physically viable. In the current paper, we reconsider the validity of such models by appealing to the so-called ``causal entropy bound''. In this framework, a paradoxical outcome is obtained: these brane worlds are indeed holographically viable, provided that the bulk charge is not too small. We go on to argue that this new finding is likely the more reliable one.Comment: 15 pages, Revtex; references added and very minor change

Challenges and Obstacles for a Bouncing Universe in Brane Models

A Brane evolving in the background of a charged AdS black-hole displays in general a bouncing behaviour with a smooth transition from a contracting to an expanding phase. We examine in detail the conditions and consequences of this behaviour in various cases. For a cosmological-constant-dominated Brane, we obtain a singularity-free, inflationary era which is shown to be compatible only with an intermediate-scale fundamental Planck mass. For a radiation-dominated Brane, the bouncing behaviour can occur only for background-charge values exceeding those allowed for non-extremal black holes. For a matter-dominated Brane, the black-hole mass affects the proper volume or the expansion rate of the Brane. We also consider the Brane evolving in an asymmetric background of two distinct charged AdS black hole spacetimes being bounded by the Brane and find that, in the case of an empty critical Brane, bouncing behaviour occurs only if the black-hole mass difference is smaller than a certain value. The effects of a Brane curvature term on the bounce at early and late times are also investigated.Comment: 23 pages, Latex file, comments and references added, version to appear in Phys. Rev.