Spectroscopic study of native defects in the semiconductor to metal phase transition in V2O5 nanostructure

Vanadium is a transition metal with multiple oxidation states and V2O5 is the most stable form among them. Besides catalysis, chemical sensing and photo-chromatic applications, V2O5 is also reported to exhibit a semiconductor to metal transition (SMT) at a temperature range of 530-560K. Even though, there are debates in using the term 'SMT' for V2O5, the metallic behavior above transition temperature and its origin are of great interests in the scientific community. In this study, V2O5 nanostructures were deposited on SiO2/Si substrate by vapour transport method using Au as catalyst. Temperature dependent electrical measurement confirms the SMT in V2O5 without any structural change. Temperature dependent photoluminescence analysis proves the appearance of oxygen vacancy related peaks due to reduction of V2O5 above the transition temperature, as also inferred from temperature dependent Raman spectroscopic studies. The newly evolved defect levels in the V2O5 electronic structure with increasing temperature is also understood from the downward shift of the bottom most split-off conduction bands due to breakdown of pd{\pi} bonds leading to metallic behavior in V2O5 above the transition temperature

Compressibility of electrospun fiber mats

Compressive properties of electrospun fiber mats are reported for the first time. Mats of bisphenol-A polysulfone (PSU) and of poly(trimethyl hexamethylene terephthalamide) [PA 6(3)T] were electrospun and annealed over a range of temperatures spanning the glass transition temperature of each polymer. The data for applied stress versus mat solidity were found to be well-described by a power law of the form σ[subscript zz] = kE(ϕ[superscript n] − ϕ[n over 0]), where σ[subscript zz] is the applied stress and ϕ is solidity, in accord with the analysis of Toll (Polym Eng Sci 38(8):1337, 2004). The values of n range from 3.2 to 6 for PSU and from 8.0 to 20 for PA 6(3)T. The lowest values in each case were exhibited by mats annealed near the glass transition temperature of the fiber material. The values of n are independent of fiber diameter. The higher values of n are attributed to fiber slippage via a mechanism analogous to that of work hardening of metals. The values of kE can vary by an order of magnitude and were difficult to determine precisely, due to the nature of the power law and the inhomogeneity of the mats. The compressibility of electrospun mats in response to an applied stress is sufficiently large that it cannot be neglected in applications where large pressures may be involved, such as filtration or membrane separations. In addition to the initial solidity of the mats, the material compressibility and the operating pressure relevant to the application are important to describe the structure of electrospun mats quantitatively under conditions of use.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R5-CW-08

Revolutionary impact of PET and PET-CT on the day-to-day practice of medicine and its great potential for improving future health care

In this communication, we present an overview of the impact and advantages of PET and PET-CT fusion imaging in the practice of medicine. We also discuss the evolution of this promising molecular imaging technique since its inception and the future prospects of the combined structure-function approach. Superior contrast resolution, accurate quantification and above all optimal image quality aid in improved diagnosis of many serious disorders including cancer. We speculate that this powerful imaging approach will almost completely replace most other conventional methods in the future. Currently, 18[F]-fluorode- -oxyglucose (FDG) is the main radiopharmaceutical employed for PET studies around the globe. With the availability of high quality PET images on a routine basis in most centres around the world and the likelihood that several other useful PET tracers will be approved in the near future for routine clinical applications, this technique will likely become essential in almost any medical disorder