Microchip-based CEC of nitroaromatic and nitramine explosives using silica-based sol-gel stationary phases from methyl- and ethyl-trimethoxysilane precursors

Microchip-based CEC of nitroaromatic and nitramine explosives with UV absorbance detection is described. The stationary phase was deposited in the microchip using the sol-gel process. Unique to this work, is the exclusive use of alkylated-trimethoxysilane precursors in the gel solution. Using alkylated precursors allows for the synthesis of a hydrophobic stationary phase in a single step. Three sol-gel formulations of increasing hydrophobicity and suitable for the separation of explosives are established from methyl- and ethyl-trimethoxysilane precursors. Increasing the alkyl-chain length improved the resolution significantly, allowing for the separation of up to seven analytes. Direct injection onto the head of the stationary phase for long injection times, results in sub-mg/L detection limits with little effect on separation efficiency.     

The physics of diamond

The accurate measurement of the thermal conductivity of metals still poses considerable experimental difficulty. The reasons for this, and the main ways in which the problem has been approached, are summarized. A detailed examination of the development in technique and methods of measurement shows that while most of the steady-state methods introduced over 50 years ago are still being improved, the emphasis in the last few years has been on the development of methods which give more rapid results, particularly at high temperatures.     

WDVV Equations for 6d Seiberg–Witten Theory and Bi-Elliptic Curves

We present a generic derivation of the WDVV equations for 6d Seiberg–Witten theory, and extend it to the families of bi-elliptic spectral curves. We find that the elliptization of the naive perturbative and nonperturbative 6d systems roughly “doubles” the number of moduli describing the system.     

Biomedical Application of an Isotope Selective Nondispersive Infrared Spectrometer for 13CO2 and 12CO2 Concentration Measurements in Breath Samples

A newly developed isotope selective nondispersive infrared (NDIR) spectrometer for the measurement of ¹³CO₂ and ¹²CO₂ concentrations in breath samples was applied as a low cost and very simple to operate alternative to isotope ratio mass spectrometry (IRMS). We used this device for several biomedical applications ([¹³C]urea breath test, [¹³C]leucine metabolism, [¹³C]methacetin catabolism of rats) and found that the results agree very well with IRMS.     

Phonon dispersion of ice under pressure

We report measurements of the phonon dispersion of ice Ih under hydrostatic pressure up to 0.5 GPa, at 140 K, using inelastic neutron scattering. They reveal a pronounced softening of various low-energy modes, in particular, those of the transverse acoustic phonon branch in the [100] direction and polarization in the hexagonal plane. We demonstrate with the aid of a lattice dynamical model that these anomalous features in the phonon dispersion are at the origin of the negative thermal expansion (NTE) coefficient in ice below 60 K. Moreover, extrapolation to higher pressures shows that the mode frequencies responsible for the NTE approach zero at approximately 2.5 GPa, which explains the known pressure-induced amorphization (PIA) in ice. These results give the first clear experimental evidence that PIA in ice is due to a lattice instability, i.e., mechanical melting.     

Anisotropy of the incommensurate fluctuations in Sr2RuO4: a study with polarized neutrons

The anisotropy of the magnetic incommensurate fluctuations in Sr2RuO4 has been studied by inelastic neutron scattering with polarized neutrons. We find a sizable enhancement of the out-of-plane component by a factor of 2 for intermediate energy transfer, which appears to decrease for higher energies. Our results qualitatively confirm calculations of the spin-orbit coupling, but the experimental anisotropy and its energy dependence are weaker than predicted.     

Structural aspects of metamagnetism in Ca2-xSrxRuO4: evidence for field tuning of orbital occupation

The crystal structure of Ca(2-x)Sr(x)RuO(4) with 0.2 < or = x < or = 1.0 has been studied by diffraction techniques and by high resolution capacitance dilatometry as a function of temperature and magnetic field. Upon cooling in zero magnetic field, the crystal structure and the octahedra shrink along the c direction and elongate in the a and b planes, whereas the opposite occurs upon cooling at high field (x = 0.2 and 0.5). These findings yield evidence for an orbital rearrangement driven by temperature and magnetic field, which accompanies the metamagnetic transition at low temperature. The temperature and magnetic-field dependencies are found to be governed by the same energy scale.