Effect of Piezoelectric Polarization on Phonon group velocity in Wurtzite Nitrides

We have investigated the effect of piezoelectric (PZ) polarization property on group velocity of phonons in binary as well as in ternary wurtzite nitrides. It is found that with the presence of PZ polarization property, the phonon group velocity is modified. The change in phonon group velocity due to PZ polarization effect directly depends on piezoelectric tensor value. Using different piezoelectric tensor values recommended by different workers in the literature, percent change in group velocities of phonons has been estimated. The Debye temperatures and frequencies of binary nitrides GaN, AlN and InN are also calculated using the modified group velocities. For ternary nitrides AlxGa(1-x)N, InxGa(1-x)N and InxAl(1-x)N, the phonon group velocities have been calculated as a functions of composition. A small positive bowing is observed in phonon group velocities of ternary alloys. Percent variations in phonon group velocities are also calculated for a straightforward comparison among ternary nitrides. The results are expected to show a change in phonon relaxation rates and thermal conductivity of III-nitrides when piezoelectric polarization property is taken into account.Comment: 05 figures; Journal of Material science, 201

[18F]2-Fluoro-2-deoxy-D-glucose incorporation by AGS gastric adenocarcinoma cells in vitro during response to epirubicin, cisplatin and 5-fluorouracil

Decreased tumour [18F]2-fluoro-2-deoxy-D-glucose (18FDG) incorporation is related to response however its significance at the cell level in gastro-oesophageal cancer and how it relates to cell death is unknown. Here human gastric adenocarcinoma (AGS) cells were treated with lethal dose 10 and 50 (LD10 and LD50), determined by using the MTT assay, of the three drugs, epirubicin, 5-fluorouracil and cisplatin, commonly used in the treatment of patients with gastro-oesophageal cancer. 18FDG incorporation was determined after 48 and 72 h of treatment with each drug and related to drug-induced changes in glucose transport, hexokinase activity, cell cycle distribution and annexin V-PE binding (a measure of apoptosis). Treatment of cells for 48 and 72 h with LD50 doses of cisplatin resulted in reductions in 18FDG incorporation of 27 and 25% respectively and of 5-fluorouracil reduced 18FDG incorporation by 34 and 33% respectively: epirubicin treatment reduced incorporation by 30 and 69% respectively. Cells that had been treated for 72 h with each drug were incubated in drug-free media for a further 6 days to determine their ability to recover. Comparison of the ability to recover from the chemotherapy agent, with 18FDG incorporation before the recovery period allowed an assessment of the predictive ability of 18FDG incorporation. Cells treated with either 5-fluorouracil or cisplatin demonstrated recovery on removal of the drug. In contrast, cells treated with epirubicin did not recover corresponding with the greatest 72 h treatment decrease in 18FDG incorporation. In contrast to adherent cells treated with cisplatin or 5-fluorouracil, adherent epirubicin-treated cells also exhibited very high levels of apoptosis. Glucose transport was decreased after each treatment whilst hexokinase activity was only decreased after 72 h of treatment with each drug. There was no consistent relationship observed between 18FDG incorporation and cell cycle distribution. Our results show that at the tumour cell level in gastric tumour cells, decreased 18FDG incorporation and glucose transport, accompanies therapeutic growth inhibition. 18FDG incorporation is particularly diminished in cells exhibiting apoptosis

True heterotopic bone in the paralyzed patient

In past years the clinical and radiologic presentation of true heterotopic bone in the paralyzed patient has been confused with osteomyelitis, neoplasm, trauma, and thrombophlebitis. We reviewed 376 paralyzed patients' roentgenographic files and found 78 patients with soft tissue ossification unassociated with infection, neoplasm, or underlying fractures, which we called true heterotopic bone. From this population the usual spectrum of radiologic findings is described, so that the radiologist may separate roentgenographically a group of patients from other types of ectopic ossification.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46816/1/256_2004_Article_BF00347167.pd

Cellular pharmacology studies of anticancer agents: recommendations from the EORTC-PAMM group

An increasing number of manuscripts focus on the in vitro evaluation of established and novel anti-tumour agents in experimental models. Whilst the design of such in vitro assays is inherently flexible, some of these studies lack the minimum information necessary to critically evaluate their relevance or have been carried out under unsuitable conditions. The use of appropriate and robust methods and experimental design has important implications for generating results that are reliable, relevant, and reproducible. The Pharmacology and Molecular Mechanisms (PAMM) group of the European Organization for Research and Treatment of Cancer (EORTC) is the largest group of academic scientists working on drug development and bundle decades of expertise in this field. This position paper addresses all researchers with an interest in the preclinical and cellular pharmacology of anti-tumour agents and aims at generating basic recommendations for the correct use of compounds to be tested for anti-tumour activity using a range of preclinical cellular models of cancer

High-field effects in silicon nitride passivated GaN MODFETs

This paper presents a detailed study of high-field effects in GaN MODFETs. Degradation of de characteristics and change of flicker noise due to hot electron and high-reverse current stresses in Si3N4 passivated GaN MODFETs have been investigated. The authors observe that during hot electron stress, electron trapping in the barrier layer and interface state creation occur. These cause a positive shift of V-t, reduce I-D, skew the transfer characteristics, and degrade g(m). Flicker noise (1/f) measurements show that after hot electron stress, the scaled drain current noise spectrum (SID/ID2) decreases in depletion, but increases Only slightly in strong accumulation, corroborating the creation of interface states but only a small creation of transition-layer tunnel traps that contribute to 1/f noise. During high-reverse current stress, electron trapping dominates for the first 50-60 s and then hole trapping and trap creation begin to manifest. However, there. still is net electron trapping under the gate after one hour of stress. The degradation processes bring about a positive shift of V-t, degrade I-D and g(m), and increase reverse leakage. After high-reverse current stress, S-ID/I-D(2). increases substantially in strong accumulation, indicating the creation of transition layer tunnel traps

Influence of field plate on the transient operation of the AlGaN/GaN HEMT

In this letter, a link between the AlGaN/GaN high-electron-mobility-transistor (HEMT) field plate (FP) and the rate of reoccupation of surface traps is presented. Surface traps are considered to be among the primary factors behind HEMT performance deterioration at high frequencies. Results from simulations using the commercial software package DESSIS are presented, in which the FP is found to reduce trap reoccupation by limiting the tunneling injection of electrons into surface traps in the gate-drain region and thus considerably improve the transient operation of the device. © 2009 IEEE