Dose tolerance at helium and nitrogen temperatures for whole cell electron tomography

Interstitial halogen centers in X-irradiated CsBr

Measurements of reflectivity, photoluminescence and cathodoluminescence for various electron beam voltages were performed on p-type single crystals at liquid nitrogen, hydrogen and helium temperatures. By an application of the microreversibility principle and consideration of the reflectivity data, the nature and the energies of the transitions were determined. In addition, we identify the lines due to the annihilation of exciton-neutral defect complexes, in ground or excited state. When the luminescence is modulated by a CO2 laser (hνIR ~ 130 meV) effects are observed at liquid helium temperature. A quenching effect is observed for the free-to-bound and pair recombinations. Quenching of the luminescence due to the annihilation of exciton isoelectronic oxygen complexes is a direct corroboration of the binding-in-two-step theory.

The visualization of macromolecular structures on voxels provides the basis for insights in dynamic events in assembly. Certain macromolecules arise as well organized frameworks. Symmetry or crystalline arrays arise through a strict geometry of subunits. Single asymmetric motifs can be superimposed on themselves taking such geometric constraints into account. Biological molecules are often composed of subunits arranged in a symmetrical manner Such conformations provide an opportunity for signal enhancement originating from the repetition of molecules in a larger configuration. Such repetitions require not only specific interactions among protein motifs, but also a built-in flexibility to accommodate conformational changes. Thus, it is advantageous to analyze critical molecular interactions with detailed protein folding information rooted in the volume density as a whole. Two-dimensional image projections can be collected in electron microscopes at temperatures of liquid nitrogen or helium. Using low-dose electron beams, viral assemblies of large lattices have been studied in vitreous ice to localize function-specific domains identified through difference imaging. Robust algorithms have been implemented based on various grid transformations to allow effective averaging of massive image data sets.

23 - THE CHANGE OF RESISTANCE OF GOLD CRYSTALS AT VERY LOW TEMPERATURES IN A MAGNETIC FIELD AND SUPRA-CONDUCTIVITY: CRITICAL REMARKS REGARDING THE RECENT WORK OF MEISSNER AND SCHEFFERS

Magnetic susceptibility measurements were carried out on octacoordinated uranium(IV) complexes, such as tetrakis(acetylacetonato)uranium (IV), tetrakis(trifluoroacetylacetonato)uranium (IV), tetrakis(benzoylacetonato)uranium(IV), tetrakis(dibenzoylmethanato)uranium(IV), tetrakis(thenoyltrifluoroacetonato)uranium(IV), tetrakis(cupferronato)uranium(IV), and uranium(IV)tetrachloride, in the temperature range from room temperature to the temperature of liquid nitrogen or liquid helium. The Curie-Weiss law holds above the temperature of liquid nitrogen, with a magnetic moment of 3.5–2.92 BM. For the latter two complexes, a temperature-independent paramagnetism was observed in the low temperature range; the other complexes also seemed to show the same trend. We tried to interpret the magnetic behavior on the basis of the crystal-field model of the square antiprism structure or the dodecahedron structure of the complexes.

Many insulating materials and systems for superconducting electrical equipment have been developed in response to the severe demands of safe usage, such as in cryogenic temperature, high mechanical stresses, high radiation, etc. They have been designed to fulfill very extreme service conditions, either at liquid helium or liquid nitrogen temperatures. Whatever the future industrial development, there is already abundant knowledge about insulating materials at cryogenic temperatures, and the feasibility has been proven. Many laboratories in the world continue research to increase this knowledge and to fill in the remaining gaps.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

First Tests of Twisted-Pair HTS 1 kA Range Cables for Use in Superconducting Links

Transient analysis and burnout of high temperature superconducting current leads

The effect of zinc displacement on the luminescence of zinc sulphide

Neutron diffraction studies have been made on a powdered NaUO3 sample. It has been shown that an octahedron composed of six oxygen atoms around pentavalent uranium in this compound is distorted and four of six oxygen atoms are much closer to an uranium atom (U-O distance of 2.15Å) than the other two (U-O distance of 2.24Å). A unit of the UO2 + ion does not exist in the crystal, though the pentavalent uranium has been expected to be in the form of UO2 + as in the case of UO2 2+ of a hexavalent uranium Ion. A neutron diffraction pattern at temperature of liquid helium has shown no appreciable difference from that at temperature of liquid nitrogen.

We have investigated the performance of a few silicon photomultipliers to readout inorganic scintillators operated at cryogenic temperatures. Such detectors, that would need to operate close to liquid helium (LHe) temperatures and in a magnetic field of a few Tesla, have been proposed by our group as a way to build an active polarized target to be used for neutrino physics, for the search of axions and CP violation, as suggested by some theoretical papers. In the present work we investigate in some details the performance of a few different silicon photomultipliers produced by Hamamatsu and Advansid down to liquid helium temperature, to verify the temperature range of usability of these devices and their performance at cryogenic temperatures.

The photoluminescence (PL), optical reflectance, optical transmittance and piezoelectric photothermal spectra were successfully observed between liquid helium and room temperatures for high quality p-type P-doped ZnTe substrates. In the PL spectrum of the ZnTe substrate (1 × 1018 cm—3), three distinct kinds of peaks which were due to the radiative recombination of the exciton bound to a neutral acceptor (I1) and free to a neutral acceptor (FA) with longitudinal optical phonon replicas were present at liquid helium temperature. The bandgap energy was estimated to be 2.394 eV by adding the reflection peak (2.381 eV) to the exciton binding energy. Furthermore, the activation energy of the phosphor acceptor impurity was estimated to be 65 meV. On the other hand, in the higher carrier concentration substrate (8 × 1018 cm—3), the PL intensity was much smaller than in that of the lower carrier concentration substrate. This means that radiative recombination processes decrease with increasing carrier concentrations.

Comments on “size and temperature dependences of the resistivity of thin alkali metal wires at liquid nitrogen, hydrogen and helium temperatures

Excitonic luminescence of cadmium telluride

The polarized absorption and emission spectra of single crystals of LaBr3 doped with nominally 0.15% and 0.75% 237Np have been recorded between 5000 and 25 000 cm−1 at temperatures of liquid helium and nitrogen. Fluorescence excitation spectra and both parallel and perpendicular Zeeman spectra were also recorded. Based on the number, polarization, and magnetic behavior of Stark components appearing in distinct groups, as well as on preliminary 5f-hydrogenic calculations, 14 absorption groups were identified as levels of the ground electronic configuration 5f4 of Np3+. The assumption of a pure 5f4 electronic configuration does not lead to a satisfactory interpretation of the spectrum; however, the inclusion of electrostatic configuration interaction permits a satisfactory fitting of the observed levels with an rms deviation in energy of 86.4 cm−1 using the parameters: E1=3394.3±29.1, E2=14.19±0.22, E3=317.5±1.9, ζ5f=1969.2±10.8, α=35.0±2.2, and β=−802.4±11.3 cm−1. Using 25 crystalline-field-split Stark components of the 5I4,5,6,7 levels of the ground multiplet, a first-order crystal-field perturbation calculation was performed. An rms deviation in energy of 8.0 cm−1 is obtained using the parameters: B20=−22.8±8, B40=−86.7±2.4, B60=−70.8±0.9, B66=+857.1±12.0 cm−1. The negative value obtained for B20 represents a crystal-field shielding in excess of 100% and is discussed in some detail. Parallel and perpendicular Zeeman interactions are also discussed in some detail.