Lithium colloids and color center creation in electron-irradiated Li2NH observed by electron-spin resonance

4 pagesInternational audienceWe have irradiated Li2NH powder with MeV electrons at room temperature and investigated the introduced defects with electron spin resonance. CESR indicates the presence of nanosize metallic Li colloids seen as a Lorentzian line with a g = 2.0023 and a line width DeltaH = 50 microT. A second, broader, signal (DeltaH = 3 to 4 mT) appears superimposed upon the Li line at low T (Curie-type behavior) which exhibits complex T-dependence with a break near 180 K for its g-value and DeltaH. We are suggesting for the latter a vacancy-type defect in the NH-sublattice, with freezing of its H-component below 180 K. When heated both the Li colloids and the color centers anneal around 100 C probably due to hydrogen evolution and subsequent chemical degradation

A membrane model for cytosolic calcium oscillations. A study using Xenopus oocytes

Cytosolic calcium oscillations occur in a wide variety of cells and are involved in different cellular functions. We describe these calcium oscillations by a mathematical model based on the putative electrophysiological properties of the endoplasmic reticulum (ER) membrane. The salient features of our membrane model are calcium-dependent calcium channels and calcium pumps in the ER membrane, constant entry of calcium into the cytosol, calcium dependent removal from the cytosol, and buffering by cytoplasmic calcium binding proteins. Numerical integration of the model allows us to study the fluctuations in the cytosolic calcium concentration, the ER membrane potential, and the concentration of free calcium binding sites on a calcium binding protein. The model demonstrates the physiological features necessary for calcium oscillations and suggests that the level of calcium flux into the cytosol controls the frequency and amplitude of oscillations. The model also suggests that the level of buffering affects the frequency and amplitude of the oscillations. The model is supported by experiments indirectly measuring cytosolic calcium by calcium-induced chloride currents in Xenopus oocytes as well as cytosolic calcium oscillations observed in other preparations

The 10Be contents of SNC meteorites

Several authors have explored the possibility that the Shergottites, Nakhlites, and Chassigny (SNC) came from Mars. The spallogenic gas contents of the SNC meteorites have been used to: constrain the sizes of the SNC's during the last few million years; to establish groupings independent of the geochemical ones; and to estimate the likelihood of certain entries in the catalog of all conceivable passages from Mars to Earth. The particular shielding dependence of Be-10 makes the isotope a good probe of the irradiation conditions experienced by the SNC meteorites. The Be-10 contents of nine members of the group were measured using the technique of accelerator mass spectrometry. The Be-10 contents of Nakhla, Governador Valadares, Chassigny, and probably Lafayette, about 20 dpm/kg, exceed the values expected from irradiation of the surface of a large body. The Be-10 data therfore do not support scenario III of Bogard et al., one in which most of the Be-10 in the SNC meteorites would have formed on the Martian surface; they resemble rather the Be-10 contents found in many ordinary chondrites subjected to 4 Pi exposures. The uncertainties of the Be-10 contents lead to appreciable errors in the Be-10 ages, t(1) = -1/lambda ln(1 Be-10/Be-10). Nonetheless, the Be-10 ages are consistent with the Ne-21 ages calculated assuming conventional, small-body production rates and short terrestrial ages for the finds. It is believed that this concordance strengthens the case for at least 3 different irradiation ages for the SNC meteorites. Given the similar half-thicknesses of the Be-10 and Ne-21 production rates, the ratios of the Be-10 and Ne-21 contents do not appear consistent with common ages for any of the groups. In view of the general agreement between the Be-10 and Ne-21 ages it does not seem useful at this time to construct multiple-stage irradiation histories for the SNC meteorites

Encounter complexes and dimensionality reduction in protein-protein association

An outstanding challenge has been to understand the mechanism whereby proteins associate. We report here the results of exhaustively sampling the conformational space in protein–protein association using a physics-based energy function. The agreement between experimental intermolecular paramagnetic relaxation enhancement (PRE) data and the PRE profiles calculated from the docked structures shows that the method captures both specific and non-specific encounter complexes. To explore the energy landscape in the vicinity of the native structure, the nonlinear manifold describing the relative orientation of two solid bodies is projected onto a Euclidean space in which the shape of low energy regions is studied by principal component analysis. Results show that the energy surface is canyon-like, with a smooth funnel within a two dimensional subspace capturing over 75% of the total motion. Thus, proteins tend to associate along preferred pathways, similar to sliding of a protein along DNA in the process of protein-DNA recognition

Sous-vide húsokban előforduló humán patogén baktériumok hőrezisztenciájának vizsgálata = Heat resistance examination of human pathogenic bacteria in sous-vide meat

A sous-vide technológia a kíméletes hőkezelési technológiák közé tartozik, amely során pasztőrözött termékeket állítunk elő. A hőkezelés alacsony hőfoka (55-90 °C) miatt az így készült termékek magasabb tápértékkel és kedvezőbb érzékszervi tulajdonságokkal rendelkeznek a hagyományos technológiákhoz képest. A technológiával szemben támasztott alapvetőkövetelmény az egyensúly megteremtésea mikrobiológiai biztonság és az organoleptikus tulajdonságok között. A mikrobiológiai minőség biztosítása azonban komoly kihívás elé állítja a technológiával foglalkozó szakembereket. A szerzők célja a sous-vide technológiával készült húsok mikrobiológiai minőségének javítása volt. A hús, a legdrágább és a leggyakrabban felhasznált sous-vide nyersanyag, ezért mikroflórájának vizsgálata kiemelt jelentőségű. A húsban előforduló patogén mikrobák közül a spórás Clostridium perfringens és az enterobaktériumokhoz tartozó Salmonella Enteritidis hőrezisztenciáját vizsgáltuk mesterségesen befertőzött csirkehúsban. Kísérleteink során különböző hőfokon és hőntartási idők mellett, légköri nyomáson és vákuum-csomagolásban, a baktériumokkal befertőzött felületileg sterilezett, darált csirkemellet hőkezeltünk. Meghatároztuk a hőkezelési paramétereket, a kezelési hőfokot és a kezelési időt, valamint a hőpusztulási paramétereket: a tizedelési időt (D), a z értéket, a relatív pusztulási sebességet (RPS) és a relatív pusztulási időt (RPI). Vizsgálataink eredménye alapján t-próbával ellenőriztük, hogy a hőkezelés csírapusztító hatásának mértékére milyen hatással van a csomagolás. The sous-vide technology belongs to mild heat treatment technologies in which pasteurized products are prepared. Due to the low temperature (55-90 °C) of the heat treatment, products have higher nutritional values and better organoleptic properties compared to conventional technologies. The basic requirement for this technology is to find the right balance between microbiological safety and organoleptic properties. However, ensuring high microbiological quality poses a serious challenge for professionals dealing with sous-vide technology. The goal of the authors was to improve the microbiological quality of meats made by sous-vide technology. Meat is the most expensive and the most commonly used raw material for sous-vide processes, therefore, testing its microflora is of high priority. The heat resistance of pathogenic bacteria of meat, such as spore-forming Clostridium perfringens and enterobacteria Salmonella Enteritidis was tested in artificially inoculated chicken meat. During our experiments, bacterially inoculated and surface sterilized minced chicken breast was heat treated at various temperatures and hold times, at atmospheric pressure and in vacuum-packaging as well. Effective heat treatment parameters (temperature and hold time) and heat destruction parameters such as decimal reduction time (D), z-value, relative thermal death rate (RTDR) and relative thermal death time (RTDT) were determined. Based on our results, it was investigated, using a t-test, how the magnitude of the germ reducing effect of the heat treatment was influenced by the packaging

X-ray remote sensing and in-situ spectroscopy for planetary exploration missions and gamma-ray remote sensing and in-situ spectroscopy for planetary exploration missions

Detectors that will be used for planetary missions must have their responses calibrated in a reproducible manner. A calibration facility is being constructed at Schlumberger-Doll Research for gamma and x ray detectors. With this facility the detector response can be determined in an invariant and reproducible fashion. Initial use of the facility is expected for the MARS94 detectors. Work is continuing to better understand the rare earth oxyorthosilicates and to define their characteristics. This will allow a better use of these scintillators for planetary missions. In a survey of scintillating materials two scintillators were identified as promising candidates besides GSO, LSO, and YSO. These are CdWO4 and CsI(Tl). It will be investigated if a detector with a better overall performance can be assembled with various photon converters. Considerable progress was achieved in photomultiplier design. The length of an 1 inch diameter PMT could be reduced from 4.2 to 2.5 inches without performance degradation. This technology is being employed in the gamma ray detector for the NEAR project. A further weight and size reduction of the detector package can be achieved with miniaturized integrated power supplies

First Year PIDDP Report on gamma-ray and x-ray spectroscopy: X-ray remote sensing and in situ spectroscopy for planetary exploration missions and gamma-ray remote sensing and in situ spectroscopy for planetary exploration missions

Detectors that will be used for planetary missions must have their responses calibrated in a reproducible manner. In addition, it is important to characterize a detector system at uneven portions of its life cycle, for example after exposure to different amounts of radiation. A calibration and response characterization facility has been constructed at Schlumberger-Doll Research for all types of gamma- and x-ray detectors that may be used for planetary measurement. This facility is currently being tested. Initial use is expected for the MARS 94 detectors. The facility will then also be available for calibrating other detectors as well as arrays of detectors such as the NEAR detector with its central Nal(TI) crystal surrounded with a large BGO crystal. Cadmium telluride detectors are investigated for applications in space explorations. These detectors show an energy resolution of 5 keV for the 122 keV 57Co line. Earlier reported polarization effects are not observed. The detectors can be used at temperatures up to 100 C, although with reduced energy resolution. The thickness of standard detectors is limited to 2 mm. These detectors become fully efficient at bias voltages above 200 V. Initial results for a 1 cm thick detector show that the quality of the material is inferior to the thinner standard detectors and hole trapping affects the pulse height. A detailed characterization of the detector is in progress. Prototypes of photomultipliers based on a Channel Electron Multiplier (CEM) are being built to study their performance. Such photomultipliers promise better timing characteristics and a higher dynamic range while being more compact and of lower in weight

Discovery of macrocyclic inhibitors of apurinic/apyrimidinic endonuclease 1

Apurinic/apyrimidinic endonuclease 1 (APE1) is an essential base excision repair enzyme that is upregulated in a number of cancers, contributes to resistance of tumors treated with DNA-alkylating or -oxidizing agents, and has recently been identified as an important therapeutic target. In this work, we identified hot spots for binding of small organic molecules experimentally in high resolution crystal structures of APE1 and computationally through the use of FTMAP analysis (http://ftmap.bu.edu/). Guided by these hot spots, a library of drug-like macrocycles was docked and then screened for inhibition of APE1 endonuclease activity. In an iterative process, hot-spot-guided docking, characterization of inhibition of APE1 endonuclease, and cytotoxicity of cancer cells were used to design next generation macrocycles. To assess target selectivity in cells, selected macrocycles were analyzed for modulation of DNA damage. Taken together, our studies suggest that macrocycles represent a promising class of compounds for inhibition of APE1 in cancer cells.This work was supported by grants from the National Institutes of Health (Grant R01CA205166 to M.R.K. and M.M.G. and Grant R01CA167291 to M.R.K.) and by the Earl and Betty Herr Professor in Pediatric Oncology Research, Jeff Gordon Children's Foundation, and the Riley Children's Foundation (M.R.K.). Work at the BU-CMD (J.A.P., L.E.B., R.T.) is supported by the National Institutes of Health, Grant R24 GM111625. D.B. and S.V. were supported by the National Institutes of Health, Grant R35 GM118078. (R35 GM118078 - National Institutes of Health; R01CA205166 - National Institutes of Health; R01CA167291 - National Institutes of Health; R24 GM111625 - National Institutes of Health; Earl and Betty Herr Professor in Pediatric Oncology Research; Jeff Gordon Children's Foundation; Riley Children's Foundation)Accepted manuscriptSupporting documentatio