Optical spin injection and spin lifetime in Ge heterostructures

We demonstrate optical orientation in Ge/SiGe quantum wells and study their spin properties. The ultrafast electron transfer from the center of the Brillouin zone to its edge allows us to achieve high spin polarizations and to resolve the spin dynamics of holes and electrons. The circular polarization degree of the direct gap photoluminescence exceeds the theoretical bulk limit, yielding ～37% and ～85% for transitions with heavy and light holes states, respectively. The spin lifetime of holes at the top of the valence band is estimated to be ～0.5 ps and it is governed by transitions between light and heavy hole states. Electrons at the bottom of the conduction band, on the other hand, have a spin lifetime that exceeds 5?ns below 150?K. Theoretical analysis of the spin relaxation indicates that phonon-induced intervalley scattering dictates the spin lifetime of electrons.     

Retention mechanism for ion-pair chromatography with chaotropic reagents

During the last decade, the extensive use of ion-pair chromatography (IPC) in protein, peptides and basic drugs applications prompted chromatographers to evaluate new additives, since traditional ion-pairing reagents (IPRs) are not usually compatible with LC-MS hyphenation and tend to stick very strongly to the stationary phase, thereby impairing the initial column properties. Chaotropic salts received a great share of credit as tentative IPRs, since they proved to be able to mimic the role of classical IPRs, thereby increasing the retention of oppositely charged analytes. Very few quantitative theoretical studies faced the retention modelling when chaotropic additives are made use of in a chromatographic system and, unfortunately, they used a stoichiometric approach. We hereby debate the present state of the theory and illustrate the first attempt to explain the retention mechanism in the presence of chaotropic reagents in RP-HPLC at a thermodynamic level. We quantitatively validate this model for typical positively and negatively charged analytes as well as for ionic liquid, zwitterionic and neutral analytes.     

In plane loaded masonry walls: DEM and FEM/DEM models. A critical review

This work is dedicated to the assessment of the nonlinear behaviour of masonry panels with regular texture and subject to in-plane loads, by means of numerical pushover analysis and an analytical homogenized model. Two numerical models are considered and adopted for performing a set of numerical tests: a discrete model developed by authors and a discrete/finite element model frequently adopted in rock mechanics field and effectively extended to masonry structures. In both models the hypotheses of rigid blocks and elastic–plastic joints following a Mohr–Coulomb yield criterion are adopted. The aim of this work is twofold: (1) a comparison and a calibration of the numerical models, evaluating their effectiveness in determining ultimate loads and collapse mechanisms of masonry panels, by assuming a nonlinear homogenized model for regular masonry as reference solution; (2) the evaluation of sensitivity of masonry behaviour and numerical models to panel dimension ratio and to varying masonry texture. In a first case study, sliding collapse mechanisms changing to overturning collapse mechanisms for increasing panel and block height-to-width ratio are obtained and the results given by the numerical models turn out to be in good agreement. Furthermore, a second case study, dedicated to square panels supported at base ends and vertically loaded, shows different ‘arch mechanisms’ depending on block height-to-width ratio.     

Study of the Light Emitting Diode as a photoreceptor: Spectral and electrical characterization as function of temperature and lighting source

In this study, the temperature influence on the spectral responsivity of a Light Emitting Diode (LED) used as a photoreceptor, combined to light source spectrum is correlated to electrical characteristics in order to propose an alternative method to estimate LED junction temperature, regardless of the absolute illumination intensity and based on the direct correlation between the integral of the product of two optical spectra and the photo-generated currents. A laboratory test bench for experimental optical measurements has been set in order to enable any characterizing of photoelectric devices in terms of spectral behaviour, in a wavelength range placed between 400–1000?nm, and of current-voltage characteristics as function of temperature by using two different illumination sources. The temperature is analysed in a range from 5?°C up to 85?°C, so as to evaluate thermal variation effects on the sensor performance. The photo-generated current of two LEDs with different peak wavelengths has been studied. Research has observed and mathematically analysed what follows: since the photo-generated current strictly depends on the combination between the spectral response of the photoreceptor and the lighting source response, it becomes possible to estimate indirectly the junction temperature of the LEDs by considering the ratio between the photogenerated currents obtained by using two different illumination sources. Such results may for one thing increase knowledge in the fields where LEDs are used as photo-detectors for many applications and for another, they could be extended to generic photodetectors, thus providing useful information in photovoltaic field, for instance.     

The “Arch of equilibration” of Charles Hutton (1772)

This paper is a historical re-visitation of the work of C. Hutton, a mathematician of the XVIII century, who wrote an innovative essay on the shape of arches, whose intrados he identifies with the curve of pressure, that he names “arch of equilibration”. His solution was mostly ignored by his contemporaries and after the middle of the XIX century forgotten. But Hutton’s problem is important, also because it offers the first example of an inverse problem in structural mechanics.     

Solvation and structure of LiAlH(4) in ethereal solvents

The nature of the solute species present in ethereal solutions of LiAlH(4) is of crucial importance for understanding the mechanisms for the reduction of ketones and other functional groups by LiAlH(4). We have employed a combination of theoretical and experimental techniques to investigate the structure of LiAlH(4) in ethereal solutions. Using complexation agents, we measured the IR spectra of LiAlH(4) and AlH(4)(-) in tetrahydrofuran (THF). Hybrid quantum-classical (QM-MM) simulations have also been carried out to compute the IR spectra of associated and dissociated LiAlH(4) species and the free-energy profile for the dissociation process in solution. Our experimental estimate of the dissociation constant in THF is 0.021 +/- 0.002, while the predicted computational value corresponding to a model dimethyl ether solvent is 0.001. The free-energy profile shows only one minimum corresponding to a contact ion pair at a Li-Al separation distance of 3.0 A. These results are consistent with the fact that LiAlH(4) is essentially associated in ethereal solutions forming contact ion pairs.     

Synthesis of 5H-pyrazolo[5,1-c][1,4]benzodiazepine

The reaction of 2-nitrobenzyl bromide with dimethyl pyrazole-3, 5-dicarboxylate gave dimethyl 1-(2-nitrobenzyl)pyrazole-3, 5-dicarboxylate which through a few steps procedure afforded the key intermediate 5, 10-dihydro-11-oxopyrazolo[5, 1-c][l, 4]benzodiazepine. The latter was reduced and dehydrogenated to yield the new tricyclic system 5H-pyrazolo[5, 1-c][1, 4]benzodiazepine.     

Comparison of tungsten and gold radiation from beam-foil excitation and tokamak-produced plasmas

Spectra in the 30–80 Å wavelength region of tungsten and gold ions, with charge states ranging from 20–33, and 25–38, respectively, have been measured in beam-foil excitation and compared with similar spectra from tokamak-produced plasmas.