Purcell enhancement of spontaneous emission from quantum cascades inside mirror-grating metal cavities at THz frequencies

Quantum cascade devices processed into double metal cavities with subwavelength thickness and a grating on top are studied at terahertz frequencies. The power extracted from the devices as a function of the device thickness and the grating period is analyzed owing to electrodynamical modeling of dipole emission based on a modal method in multilayer systems. The experimental data thus reveal a strong Purcell enhancement, with Purcell factors up to approximately 50.     

On deformations of cracked anisotropic slabs

The effect of a crack on the bending and shearing of an anisotropic elastic slab is considered. The problems considered are reduced to simultaneous Fredholm equations which may be solved numerically.     

Chromium in biological materials — IAEA intercomparison results

Summary Some reasons for the relatively large confidence intervals for Cr in IAEA Reference Materials are critically evaluated. Possible sources of error in the determination of Cr are mentioned.

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Chrom in biologischen Materialien — Ergebnisse von IAEA-Ringversuchen

     

FS and FS(OH) defect centers at the MgO(1 0 0) surface: cluster and periodic calculations

We present a model of a new paramagnetic defect center which results from the interaction of atomic hydrogen with the MgO(1 0 0) surface. DFT calculations have been performed using periodic supercells and embedded cluster models where long-range polarization effects are included explicitly. The H atom promotes the creation of an oxygen vacancy (F center) by formation of the F_S⁺(OH⁻) defect where an hydroxyl group is adsorbed near an electron trapped in an oxygen vacancy. This new center has some characteristics similar to those of the classical F_S⁺ centers but a smaller formation energy; furthermore, being globally neutral, it can be treated also with supercell methods.     

Survey and evaluation of available biological reference materials for trace element analysis

Summary A database recently prepared by IAEA contains information on 60 internationally available biological reference materials (BRMs) from 9 producers. The data recorded for each material include: name, code No., cost, list of elements, and minimum weight of material recommended for analysis. For each element the concentration and its confidence interval (CI) are recorded, as well as an indication of whether the concentration value is certified or noncertified (e.g. an information value).Large differences among producers are observed in respect of how the concentration values and their CIs are defined, and how other relevant information is reported in the certificates of analysis. International recommendations on how this should be done generally do not seem to be followed.For several elements of biomedical interest there is a serious lack of BRMs namely: Al, F, I, Mo, Si, Sn and V. In addition, the CIs for the following elements are generally excessively large: Al, As, Cd, Cr, Hg, Mo, Ni, Se and V.     

Dynamic mechanical and crystal-strain measurements on ultrahigh modulus oriented polyoxymethylene: A revised value for the true crystal modulus

Dynamic mechanical measurements on ultrahigh modulus polyoxymethylene have been undertaken over the temperature range ?150 to 20°C. Measurements of the longitudinal crystal modulus have also been made by studying changes in the (009) reflection with load, over a similar range of temperatures. The dynamic Young's modulus at 5 Hz reaches a value at low temperatures of 64.5 GPa for the most highly oriented sample. The crystal modulus at low temperatures is 105 GPa, which is almost twice the previously reported room-temperature value.     

Two contact problems in anisotropic thermoelasticity

Some basic equations recently derived by Clements are used to consider two contact problems in anisotropic thermoelasticity. The first problem concerns the determination of the thermal stress in an anisotropic half-space due to a heated load over a section of the boundary. The second problem concerns the indentation of a half-space by a heated rigid punch. In particular, indentation by a cylindrical punch is considered and some numerical results obtained.

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Zusammenfassung Einige Grundgleichungen, die Clements neulich abgeleitet hat, dienen als Grundlage, um zwei Kontaktprobleme in der anisotropischen Thermoelastizität zu betrachten. Im ersten Problem geht es darum, die Wärmespannung in einem anisotropischen Halbraum zu bestimmen, die von einer erhitzten Last über einem Teil der Grenzlinie hervorgebracht wird.Im zweiten Problem geht es darum, einen Halbraum durch eine erhitzte starre Punze auszuzacken. Insbesondere wird das Auszacken durch eine kreisartize Punze betrachtet, und es ergeben sich numerische Angaben.

     

Melting behavior of ultrahigh modulus linear polyethylene

The differential-scanning calorimetry (DSC) behavior of drawn linear polyethylene (LPE) has been investigated as a function of draw ratio and molecular weight. All the samples examined showed a dependence of the melting temperature on heating rate, an effect generally known as superheating. The magnitude of this effect, as well as the maximum melting temperatures, increased markedly at high draw ratio and high molecular weight. The highest melting temperature recorded was 145°C for a tape of draw ratio 25 and weight-average molecular weight of 312,000. The results were first considered in terms of the information which might be provided regarding crystal thickness. It was concluded that the DSC data are consistent with previous wide-angle x-ray diffraction results in confirming that an extended chain morphology similar to that observed in pressure crystallized LPE is not present in these samples. Secondly, the superheating effects were examined in the light of the possible configurational constraints on the amorphous regions of drawn polymers, along the lines proposed by Zachmann. It is possible to understand the effects of draw ratio and molecular weight very well on this basis, in a manner consistent with previous structural results on these materials.