Electronic properties of SnO2-based ceramics with double function of varistor and humidity sensor

This is the post-print version of the article. The official published version can be obtained from the link below - Copyright @ 2010 AD-Tech.Tin dioxide based varistor ceramics SnO2-Co3O4-Nb2O5-Cr2O3-xCuO (x=0; 0.05; 0.1 and 0.5) were made and their electrical properties were studied. The highest nonlinearity coefficient and electric field (at current density 10-3 A cm-2) were obtained for 0.1 mol.% CuO addition. It was observed that low-field electrical conductivity is increased with relative humidity, therefore, materials obtained exhibit double function of varistor and humidity sensor. The highest humidity sensitivity coefficient is found for SnO2-Co3O4-Nb2O5-Cr2O3 ceramics (without CuO). Observed varistor and humidity-sensitive properties are explained in the frames of grain-boundary double Schottky barrier concept as a decrease of the barrier height with electric field or relative humidity. Using suggested simple theory and data obtained on isothermal capacitance relaxation, the energy of the grain-boundary monoenergetic trapping states were estimated. These values are less than found for activation energy of electrical conduction (as a measure of the barrier height). These observations confirm the barrier concept.This work is funded by the Royal Society, United Kingdom (2007R1/R26999)

Caspase 8 activation independent of Fas (CD95/APO-1) signaling may mediate killing of B-chronic lymphocytic leukemia cells by cytotoxic drugs or gamma radiation.

Ligation of the cell-surface Fas molecule by its ligand (Fas-L) or agonistic anti-Fas monoclonal antibodies results in the cleavage and activation of the cysteine protease procaspase 8 followed by the activation of procaspase 3 and by apoptosis. In some leukemia cell lines, cytotoxic drugs induce expression of Fas-L, which may contribute to cell killing through the ligation of Fas. The involvement of Fas, Fas-L, and caspase 8 was studied in the killing of B-cell chronic lymphocytic leukemia (B-CLL) cells by chlorambucil, fludarabine, or gamma radiation. Spontaneous apoptosis was observed at 24-hour incubation, with additional apoptosis induced by each of the cytotoxic treatments. Although Fas mRNA expression was elevated after exposure to chlorambucil, fludarabine, or gamma radiation, Fas protein levels only increased after irradiation. Therefore, Fas expression may be regulated by multiple mechanisms that allow the translation of Fas mRNA only in response to restricted cytotoxic stimuli. None of the cytotoxic stimuli studied here induced Fas-L expression. An agonistic anti-Fas monoclonal antibody (CH-11) did not significantly augment apoptosis induction by any of the death stimuli. A Fas-blocking antibody (ZB4) did not inhibit spontaneous, chlorambucil-, fludarabine-, or radiation-induced apoptosis. However, procaspase 8 processing was induced by all cytotoxic stimuli. These data suggest that the Fas/Fas-L signaling system does not play a major role in the induction of apoptosis in B-CLL cells treated with cytotoxic drugs or radiation. However, Fas-independent activation of caspase 8 may play a crucial role in the regulation of apoptosis in these cells

Geldanamycin and herbimycin A induce apoptotic killing of B chronic lymphocytic leukemia cells and augment the cells' sensitivity to cytotoxic drugs.

We studied the actions of geldanamycin (GA) and herbimycin A (HMA), inhibitors of the chaperone proteins Hsp90 and GRP94, on B chronic lymphocytic leukemia (CLL) cells in vitro. Both drugs induced apoptosis of the majority of CLL isolates studied. Whereas exposure to 4-hour pulses of 30 to 100 nM GA killed normal B lymphocytes and CLL cells with similar dose responses, T lymphocytes from healthy donors as well as those present in the CLL isolates were relatively resistant. GA, but not HMA, showed a modest cytoprotective effect toward CD34+ hematopoietic progenitors from normal bone marrow. The ability of bone marrow progenitors to form hematopoietic colonies was unaffected by pulse exposures to GA. Both GA and HMA synergized with chlorambucil and fludarabine in killing a subset of CLL isolates. GA- and HMA-induced apoptosis was preceded by the up-regulation of the stress-responsive chaperones Hsp70 and BiP. Both ansamycins also resulted in down-regulation of Akt protein kinase, a modulator of cell survival. The relative resistance of T lymphocytes and of CD34+ bone marrow progenitors to GA coupled with its ability to induce apoptosis following brief exposures and to synergize with cytotoxic drugs warrant further investigation of ansamycins as potential therapeutic agents in CLL

Group synthesis for alternating-time temporal logic

We present an extension of Alternating-time Temporal Logic ATL, called ATLP (Parametric ATL), where parameters are allowed in place of concrete groups of agents. We devise a procedure to nd all instantiations for the parameters in a given formula of ATLP so that is true in a given model. We propose a formalisation of the problem and symbolic algorithms for its solution. We discuss an experimental implementation of the approach on top of the open-source model checker mcmas and demonstrate the bene ts of the technique through experimental results

Swift UVOT grism observations of nearby Type Ia supernovae – II. Probing the progenitor metallicity of SNe Ia with ultraviolet spectra

Ultraviolet (UV) observations of Type Ia supernovae (SNe Ia) are crucial for constraining the properties of their progenitor systems. Theoretical studies predicted that the UV spectra, which probe the outermost layers of an SN, should be sensitive to the metal content of the progenitor. Using the largest SN Ia UV (λ < 2900 Å) spectroscopic sample obtained from Neil Gehrels Swift Observatory, we investigate the dependence of UV spectra on metallicity. For the first time, our results reveal a correlation (∼2σ) between SN Ia UV flux and hostgalaxy metallicities, with SNe in more metal-rich galaxies (which are likely to have higher progenitor metallicities) having lower UV flux level. We find that this metallicity effect is only significant at short wavelengths (λ 2700 Å), which agrees well with the theoretical predictions. We produce UV spectral templates for SNe Ia at peak brightness. With our sample, we could disentangle the effect of light-curve shape and metallicity on the UV spectra. We also examine the correlation between the UV spectra and SN luminosities as parametrized by Hubble residuals. However, we do not see a significant trend with Hubble residuals. This is probably due to the large uncertainties in SN distances, as the majority of our sample members are extremely nearby (redshift z 0.01). Future work with SNe discovered in the Hubble flow will be necessary to constrain a potential metallicity bias on SN Ia cosmology

Use of inert gas jets to measure the forces required for mechanical gene transfection

BACKGROUND: Transferring genes and drugs into cells is central to how we now study, identify and treat diseases. Several non-viral gene therapy methods that rely on the mechanical disruption of the plasma membrane have been proposed, but the success of these methods has been limited due to a lack of understanding of the mechanical parameters that lead to cell membrane permeability. METHODS: We use a simple jet of inert gas to induce local transfection of plasmid DNA both in vitro (HeLa cells) and in vivo (chicken chorioallantoic membrane). Five different capillary tube inner diameters and three different gases were used to treat the cells to understand the dependency of transfection efficiency on the dynamic parameters. RESULTS: The simple setup has the advantage of allowing us to calculate the forces acting on cells during transfection. We found permeabilization efficiency was related to the dynamic pressure of the jet. The range of dynamic pressures that led to transfection in HeLa cells was small (200 ± 20 Pa) above which cell stripping occurred. We determined that the temporary pores allow the passage of dextran up to 40 kDa and reclose in less than 5 seconds after treatment. The optimized parameters were also successfully tested in vivo using the chorioallantoic membrane of the chick embryo. CONCLUSIONS: The results show that the number of cells transfected with the plasmid scales with the dynamic pressure of the jet. Our results show that mechanical methods have a very small window in which cells are permeabilized without injury (200 to 290 Pa). This simple apparatus helps define the forces needed for physical cell transfection methods

Teaching medical students about children with disabilities in a rural setting in a school

Background: To describe and implement a community paediatric placement in a school setting that teaches undergraduate medical students about intellectual disability that provides benefit to the community and is acceptable to both students and teachers. Methods: Twenty six 4th year undergraduate medical students of the University of Newcastle completed their Paediatric studies based in Tamworth in 2004 & 2005 including an 8 week placement at Bullimbal School for Specific Purposes. The placement involved the students being actively involved in assisting with the delivery of a variety of activities aimed at improving the motor skills of a group of disabled children. De-identified data were obtained from completed evaluation surveys from 75% (21 of 26) of the medical students and from 100% (5 of 5) of the teachers. Results: All students and teachers found the placement was acceptable and enjoyed the placement and felt that it gave the medical students a greater understanding of children with disabilities. 80% (4 of 5) of the teachers involved in the program did not feel that its implementation added to their workload and all were enthusiastic to continue with the program. Conclusion: Medical students can be effectively taught and have a valuable clinical experience in a school setting to learn about children with a disability. This educational innovation has provided a mutual benefit for both the medical students and the school children who participated in the program without impacting on the workloads of teachers