Temperature-independent lasing wavelength of highly stacked InAs quantum dot laser fabricated on InP(311)B substrate with Bi irradiation.

In this study, the effects of bismuth (Bi) irradiation on InAs quantum dot (QD) lasers operating in the telecommunication wavelength band were investigated. Highly stacked InAs QDs were grown on an InP(311)B substrate under Bi irradiation, and a broad-area laser was fabricated. In the lasing operation, the threshold currents were almost the same, regardless of Bi irradiation at room temperature. These QD lasers were operated at temperatures between 20 and 75°C, indicating the possibility of high-temperature operation. In addition, the temperature dependence of the oscillation wavelength changed from 0.531 nm/K to 0.168 nm/K using Bi in the temperature range 20-75°C.

DFT analysis of nitrogen isotopic reduction partition function ratios in proton exchange equilibria of glutamic acid species in water and its application to the estimation of nitrogen isotope fractionation.

L-Glutamic acid (Glu) plays a pivotal role in amino acid metabolism in living organisms. Theoretical knowledge of how metabolism propagates the nitrogen isotope composition (δ15N) is essential for elucidating the mechanism of amino acid metabolism in vivo. In this paper, to estimate the nitrogen isotope fractionation involving Glu and its protonated/deprotonated species, their nitrogen isotopic reduction partition function ratios (RPFRs) were calculated at the apfd/6-311+G(2d,p) level of theory by the SCRF method. The results show that the RPFR values of the eight possible Glu species at 25 °C are: cation > zwitterion with α-COOH and γ-COO- > zwitterion with α-COO- and γ-COOH > anion with -NH3+ ≫ uncharged molecule > anion with -NH2 and γ-COO- > anion with -NH2 and α-COO- > di-anion. Several correlations between RPFR and bond distances were found. Most importantly, it was found that the shorter the distance of the (C-)N⋯H(-O) hydrogen bond (HB), the greater the RPFR value for that species. This correlation indicates that the tri-coordinate nitrogen atom of the amino group may take on the character of the tetra-coordinate nitrogen atom to some extent by forming a HB of this type. The nitrogen isotope exchange equilibrium between Glu and glycine/serine was evaluated at a typical physiological pH of 7.4. Calculations suggest that the equilibrium constant for the former is an increasing function of temperature from 0 to 100 °C, while the latter is a decreasing function of temperature over the same temperature range.

Nitrogen Isotopic Reduced Partition Function Ratios of Glycine and Serine in Water.

The nitrogen isotopic reduced partition function ratio (RPFR) of glycine (Gly) and serine (Ser) in water has been evaluated by a couple of methods. The experimental fact that those amino acids are present in the zwitterionic form in water has been best reproduced when trihydrated Gly and Ser molecules were treated by the discrete microsolvation method coupled with the self-consistent reaction field (SCRF) approach. The RPFR values of Gly and Ser in water at 25 °C are evaluated as 1.11152 and 1.11070, respectively, and the equilibrium constant of the nitrogen isotope exchange reaction between the two amino acids is calculated as 1.0007 ± 0.0008 at 25 °C. Equivalent results may be obtained by the SCRF method for non- and monohydrated molecules in the zwitterionic form.

Applicability of self-consistent reaction field (SCRF) method to DFT estimation of hydrogen isotope separation factors in reversible processes.

In earlier quantum chemical calculations of isotope effects, chemical species in the liquid phase were generally treated as existing in the gas phase. In recent years, however, advances in computational programs have made it easier for the self-consistent reaction field (SCRF) method to handle chemical species in the liquid phase, and as a result, it has become easier to apply the SCRF method to isotope effect calculations. This paper concerns the scope of application of the DFT-SCRF method to reversible processes for hydrogen isotope enrichment. It is found that the applicability of the method depends on the type of the intermolecular interaction in the liquid phase and the degree of hydrogen isotope effect (separation factor) on which the process is based. When the magnitude of the isotope effect of the separation system is greater than 10-1, the simple SCRF method is fully applicable; when the magnitude is around 10-2, SCRF with a dimer model, in which the monomer is replaced by a dimer, is applicable for the analysis of the liquid phase with relatively strong intermolecular interactions. Anharmonic correction to the separation factor calculated based on harmonic frequencies may be effective to systems with the liquid phase with weak intermolecular interactions.

Focus tuning by liquid crystal lens in imaging system.

A quantitative study of the focus tuning by a liquid crystal lens in an imaging system composed of a camera module and the liquid crystal lens that performs the focusing function is reported. The resolving capability of the imaging system is investigated by analyzing the image of an ISO12233 chart formed by the system. Measurements show that with the focus tuning by the liquid crystal lens, the resolving power of the system can be very close to that of the camera module.

Polarization transformation and destructive interference on subwavelength magnetic domains in magneto-plasmonic systems.

We demonstrate magneto-optical (MO) polarization transformation due to surface plasmons in CoPt perpendicular magnetic films in the polar Kerr geometry. An extraordinary Kerr rotation angle (θK = ± 88.9°) that almost reaches the upper limit of polarization is produced in the attenuated total reflection (Kretschmann) configuration. P-polarized incident radiation is almost transformed upon reflection to s-polarized radiation, which may be out of phase depending on whether the magnetization of CoPt is up or down. Moreover, the reflected intensity may be drastically modulated by applying an external magnetic field. The reflectivity goes almost to zero in the demagnetized state and increases with increasing external magnetic field. This drastic optical response is attributed to the MO destructive interference produced by the subwavelength magnetic domain structure.

A density functional theory (DFT) study on reduced partition function ratios of oxygen species adsorbed on a Pt19 cluster and oxygen isotope effects.

A density functional theory (DFT) computation on oxygen species adsorbed on platinum (Pt) catalyst surfaces has been carried out to elucidate oxygen isotope fractionation observed at the cathode of a polymer electrolyte membrane fuel cell (PEMFC). The Pt(111) catalyst surface was modelled by a Pt19 cluster, and O, OH, OHH, OO, OOH, OHOH and HOHOH were assumed to be the oxygen species adsorbed on the Pt(111) surface. The oxygen isotope reduced partition function ratios (RPFRs) of the adsorbed species were calculated using the vibrational frequencies obtained by normal mode analyses performed on the optimized structures. Various oxygen isotope exchange equilibria among the adsorbed oxygen species and oxygen and water molecules in the gas phase were examined using their RPFRs. Experimental observation that the lighter 16O is enriched in water molecules exhausted from the cathode is explainable in a satisfactory manner by assuming oxygen isotope exchange equilibria of O2 molecule with O, OH, OO and OOH adsorbed on the Pt(111) surface that appear in the first half of the conversion reaction from O2 to H2O and those of H2O molecule with the adsorbed oxygen species, OHH, OHOH and HOHOH, formed in the latter half of the conversion reaction.

Liquid-crystal variable-focus lenses with a spatially-distributed tilt angles.

A pretilt angle controlling method by the density of rubbings using a tiny stylus is proposed. The control of the surface pretilt angle is achieved by rubbing a side-chain type polyimide film for a homeotropic alignment. Smooth liquid crystal (LC) director distribution in the bulk layer is successfully obtained even though the rough surface orientation. This approach is applied to LC cylindrical and rectangular lenses with a variable-focusing function. The distribution profile of the rubbing pitch (the reciprocal of the rubbing density) for small aberration is determined to be quadratic. The variable focusing function is successfully achieved in the LC rectangular lens, and the voltage dependence of the focal length is tried to be explained by the LC molecular reorientation behavior.

Observation of 18O/16O isotope effects at the cathode of a polymer electrolyte membrane fuel cell.

18O/16O isotope effects were observed at the cathode of a polymer electrolyte membrane fuel cell at 25 and 35°C. Results of experiments in which the 18O/16O isotope ratios of the oxygen gases supplied to and exhausted from the cell were measured revealed that the lighter isotope 16O reacted more preferentially to form water molecules at the cathode than the heavier one, 18O. The value of the oxygen isotope separation factor, S1, defined as the ratio of the 18O/16O isotope ratios of the oxygen gases supplied to and exhausted from the cell, ranged from 1.0030 to 1.0139, and tended to decrease with decreasing rate of oxygen utilisation (θ) and with increasing flow rate of the feed oxygen gas (DF). The value of another separation factor, S2, defined as the ratio of the 18O/16O isotope ratios of the exhausted oxygen gas and oxygen having reacted to form water molecules at the cathode, ranged from 1.0049 to 1.0304. The S2 value was much less affected by the change in θ and DF than the S1 value with the majority of the S2 value being in the range of 1.0240-1.0304.