A comparison of algainas and InGaAsP-based 1.3 μm semiconductor lasers using high pressure

Abstract

We have compared the effect of hydrostatic pressure on the threshold current, I_th, and lasing energy, E_lase, of 1.3 pm quantum-well devices based upon AlGaInAs and InGaAsP. Whilst we observe a very similar dependence of E_lase on pressure for the two materials, we measure strikingly different variations of I_th. By applying pressure to 1.3 μm InGaAsP lasers, I_th typically decreases by ～ 10% over 1 GPa consistent with the reduction of Auger recombination, which forms ～ 50% of I_th at room temperature. However, for the 1.3 μm AlGaInAs-based lasers, we observe an increase in I_th by ～ 8% over the same pressure range. From these results we conclude that non-radiative recombination accounts for only ～ 20% of I_th in AlGaInAs-based devices. This is in good agreement with previous temperature dependence measurements and shows why AlGaInAs-based devices exhibit a reduced temperature sensitivity of I_th which is very important for telecommunications applications.     

Influence of high pressure treatment on rheological and other properties of egg white

Abstract

The paper deals with the influence of high pressure treatment of fresh egg white on its properties and protein composition (individual amino-acids predicted as a function of pressure and time levels). The rheological properties are changed by high pressure from Newtonian to non-Newtonian behaviour, with increasing apparent viscosity as the pressure and time increased. The pH, whipping ability, foam stability, gel strength of heat induced gels after treatment and the whole protein content, were also predicted.

The results showed that the foam stability is increased with increasing pressure and time of processing. The foam volume is also increased with pressure. The pH did not change with pressure or time of processing. Composition of proteins as indicated by individual amino-acids did not exhibit statistically important changes. Gel strength of heat induced gels prepared from previously pressured liquid whites showed no important change of values with pressure or time of treatment. The modulus of elasticity showed a decrease for samples pressured to 400 MPa for 5 up to 15 minutes.     

Phase diagram of aqueous solution at high pressure and low temperature

Abstract

This paper presents a constant mass high pressure isothermal calorimeter and describes the range of applications that this type of equipment can deal with. As an example, the thermophysical properties of an aqueous solution of MgSO₄ at low temperature and at high pressure have been investigated. The main results showed that the phase change heat of the solution decreased with increasing pressure and the phase change temperature of the eutectic concentration was depressed under high pressure. Those changes could be related to the MgSO₄ solubility and to water latent heat changes.     

Microorganisms baroinactivation of germinated mung bean (green gram) seeds

It is possible to describe the pressure degradation of microorganisms as being analogous to thermal inactivation. Equation for baroinactivation is derived from thermal death time (TDT) model D _p = D _pref 10^{(pref-p)/z _p} , where D _pref is decimal reduction time at the reference pressure (min), p _ref is the reference pressure (MPa), z _p is the pressure increase (MPa) required to reduce the D _p value by a factor of 10. This method was used for the calculation of baroinactivation model parameters of the total number of microorganisms of pressurized germinated mung bean (green gram) seeds (Vigna radiata (L.) Wilczek). Microbial contamination of germinated mung bean (green gram) seeds can be effectively decreased by treatment at a high pressure of 400 MPa, time of pressurization 5 min.     

High pressure 17O NMR study of solvent exchange on square planar complexes: Water exchange on [Pd(dien)H2O]2+

Abstract

The water exchange reaction of [Pd(dien)H₂O]²⁺ (dien = diethylenetriamine) was studied as function of temperature (268-308 K) and pressure 0.1-197 MPa) using ₁₇O NMR techniques. The rate and activation parameters are: k_cx = 5100 s^?1 at 298 K; ΔH^# =38 kJ mol^?1; ΔS^# = -47 JK^?1 mol^?1; ΔV^# = -2.8 cm³ mol^?1 at 296 K. The results are discussed in reference to solvent exchange data for other Pt(II) and Pd(II) complexes, and are interpreted in terms of an associatively activated substitution process.     

A comparative in vitro study of the digestibility of heat- and high pressure-induced gels prepared from industrial milk whey proteins

We undertook this study to compare the digestibility of heat- and high pressure-induced gels produced from whey protein isolate (WPI). To simulate in vivo gastrointestinal digestion of WPI gels, a pepsin–trypsin digestion system was used. The in vitro protein digestibility of WPI gels induced by high pressure (400 MPa and 30 min; P-gel) and those induced by heat (80°C and 30 min; H-gel) was compared using a protein concentration of 0.14 g mL^?1. The in vitro protein digestibility of P-gels was significantly greater than that of H-gels (p<0.05). The size-exclusion chromatography profiles of the hydrolysates showed that the P-gel generated more and smaller peptides than natural WPI and H-gels. Furthermore, Sodium dodecyl sulfate–polyacrylamide gel electrophoresis analysis showed some soluble disulfide-mediated aggregation in the P-gel, while there was more insoluble aggregation in the H-gel than the P-gel. The P-gel was more sensitive to proteinase than the H-gel, which was related to the content of S–S bonds, and this in turn could be attributed to the differences in the gelation mechanism between the H-gel and P-gel.     

Lattice dynamics and phase diagrams for hydrogen bonded systems

Abstract

A variational correlated ground state wave-function theory is applied to investigate the high-pressure deformation of hydrogen-bond potential described by a double Morse potential functions. The evolution of the hydrogen bond potential with increasing pressure and the effects of deuterium isotope substitution on the quantum-fluctuation-driven phenomena are discussed. The theory was employed for predicting and interpreting the pressure dependence of the phase transition temperatue for KDP-like ferroelectrics and NQR-frequency coefficients for several deuterated and undeuterated crystals.     

Specific heat of liquid hexane up to 500 MPa and from 243 to 473 k from the heat of compression

Abstract

The expansivity of n-hexane was measured through the heat of compression up to 500 MPa in the 243–473 K temperature range. Details about the experiment are given. From the fit to our data, the pressure variation of the specific heat C_p, in the same pressure-temperature domain, is computed; good agreement is obtained with available high pressure data.     

Surface pressure in clusters and small particles—is it real?

Using the methods of statistical mechanics and applying the conditions of thermal equilibrium for an ensemble of interacting molecules, it is proved that there is no excess pressure, nor internal and surface stresses, in clusters and small particles that are not subjected to the action of external forces. With this premise taken into account the thermodynamics of spherical and faceted small particles is developed. In a particle-vapour system surrounded by a rigid impervious shell, Kelvin's and Thomson's formulae and Wulff's rule are derived. For a particle-melt system at a constant external pressure it is expected that the melting points of a particle and a bulk solid should be equal. It is noted that, if a particle is not subjected to the action of external fields or bodies, its molecules occupy their natural equilibrium positions, and it is from them that deformations and internal stresses should be counted off. These equilibrium positions differ from those occupied by the same molecules in a bulk solid, which is what usually gives rise to the illusions of the stressed state of a small particle and its deformation caused by the “uncompensated” surface forces.     

Lattice-dynamical functions of solids at very high pressures

Abstract

Vibrational spectra of face-centered cubical (f.c.c.) solids are investigated at the pressure region, where the quantum-statistical model for the electron energy is applicable. Phonon dispersion curves are obtained for different values of the specific volume. The integration of the phonon spectra over the Brillouin zone yields the zero-point vibrational energy, the Debye temperature, the Gruneisen coefficient, mean-square amplitude of zero-point and thermal vibration, the melting temperature. All quantities under consideration are calculated from the universal functions of the reduced volume, using the scaling relations for given atomic number 2.