Hydrogen-Bond Symmetrization of δ-AlOOH

The δ-AIOOH can transport water into the deep mantle along cold subducting slab geothenn. We investigate the hydrogen-bond symmetrization behavior of δ-AIOOH under the relevant pressure-temperature condition of the lower mantle using ab initio molecular dynamics(AID). The static symmetrization pressure of 30.0 GPa can be reduced to 17.0 GPa at 300 K by finite-temperature(T) statistics, closer to the experimental observation of-10.0 GPa. The symmetrization pressure obtained by MD simulation is related to T by P(GPa) = 13.9(GPa) +0.01(GPa/K) × T(K). We conclude that δ-AIOOH in the lower mantle exists with symmetric hydrogen bond from its birthplace, or someplace slightly deeper, to the core-mantle boundary(CATB) along cold subducting slab geotherm. The bulk modulus decreases with T and increases anomalously upon symmetrization: K_o(GPa) =181(GPa)-0.013(GPa/K) × T(K) for δ-AIOOH with asymmetric hydrogen bond, and K_o(GPa) = 216(GPa)-0.013(GPa/K) × T(K) for δ-AIOOH with symmetric hydrogen bond. Our results provide an important insight into the existent form and properties of δ-AIOOH in the lower mantle.     

High-precision measurements of δ2H, δ18O and δ17O in water with the aid of cavity ring-down laser spectroscopy

A thorough evaluation of measurement uncertainty together with control of short-term and long-term precision of measurements should be a basis of any successful quality assurance/quality control (QA/QC) strategy aimed at maintaining a high quality of the analytical process. Here we present the results of a comprehensive assessment of the analytical performance of a Picarro L2140-i CRDS laser spectrometer analysing δ²H, δ¹⁸O and δ¹⁷O in water. The assessment is based on results obtained during 15 months of continuous operation of this instrument (February 2017 to May 2018). The short-term precision of measured and derived quantities was 0.11, 0.036, 0.028, 0.23 ‰ and 11 per meg, for δ²H, δ¹⁸O, δ¹⁷O, d-excess and Δ¹⁷O, respectively, and is comparable to the precision reported by the manufacturer. The long-term precision of the L2140-i, defined as standard uncertainty of the time series of 153 analyses of a laboratory standard conducted throughout 15 months, was roughly two times lower (0.24, 0.053, 0.038, 0.37 ‰ and 21 per meg, for δ²H, δ¹⁸O, δ¹⁷O, d-excess and Δ¹⁷O). In-depth assessment of the measurement uncertainty of a single analysis revealed that assigned uncertainty of the calibration standards is an important component of the uncertainty budget, especially in case of δ²H analysis.     

Screening in a δ-doped semiconductor

The screening of an impurity in the quasi-two-dimensional (2D) electron gas in a δ-doped semiconductor structure is investigated. The screened impurity matrix elements are calculated and compared using three different approaches: the 2D random phase approximation (RPA), the corresponding 2D Thomas–Fermi theory and a quasi-three-dimensional (3D) Yukawa-like screening model. It is found that the 2D Thomas–Fermi theory differs from the RPA result, even in the limit of low q vectors, if more than one subband is occupied. This result is explained analytically by closely examining theq → 0 limit of the dielectric tensor. The 2D Thomas–Fermi theory is shown to represent a poor approximation to the RPA whereas the quasi-3D screening model agrees well with the RPA results for not too smallqvectors. Furthermore, this model reduces computing times by orders of magnitude in comparison with the RPA. Thus, our 3D screening model considerably simplifies the calculation of impurity scattering rates in the investigation of the electron mobility in a δ-doping layer.     

Feynman propagator for the δ-function potential

A new derivation of the Feynman propagator for the Dirac δ-function potential is presented.     

Parity operator and quantization of δ-functions

In the Weyl quantization scheme, the -function at the origin of phase space corresponds to the parity operator. The quantization of a functionf() on phase space is the operator f(/2)W()dM, whereM is the parity andW() the Weyl operator.     

Optical response of a δ-layer capacitor

The fabrication of two δ-layers of opposite polarity in a semiconductor constitutes a capacitor. The charge on each "plate" may be modified by photogenerating carriers to screen the dopant ions, which alters the field between them. This has the effect of changing the transition energies between confined states in the structure, which results in a substantial (60 meV) blue shift, which may be utilised in a modulator structure. These effects have been investigated using steady-state and time-resolved photoluminescence, in conjunction with band modelling.     

Products of distributions and collision of a δ-wave with a δ′-wave in a turbulent model

We study the possibility of collision of a δ-wave with a stationary δ′-wave in a model ruled by equation f (t)u _t+[u²?β(x?γ(t))u]_x = 0, where f, β and γ are given real functions and u = u(x, t) is the state variable. We adopt a solution concept which is a consistent extension of the classical solution concept. This concept is defined in the setting of a distributional product, which is not constructed by approximation processes. By a convenient choice of f, β and γ, we are able to distinguish three distinct dynamics for that collision, to which correspond phenomena of solitonic behaviour, scattering, and merging. Also, as a particular case, taking f = 2 and β = 0 we prove that the referred collision is impossible to arise in the setting of the inviscid Burgers equation. To show how this framework can be applied to other physical models, we included several results already obtained.     

Nonlinear electron transport in Si δ-doped GaAs

In this paper we report abnormal non-ohmic behaviour observed in Si δ-doped GaAs. We have performed measurements in Hall bar and Van der Pauw geometries in which electron transport phenomena can be studiekd by looking into the dependence of the device resistance R_xx on the applied current I or input power per electron, P. Transport of electrons in single Si δ-doped layers in GaAs, grown by MOCVD, in the linear and non-linear response regimes was studied. Our experimental results show that: i) R_xx dramatically decreases with increasingI (P) when sample current (input power) is larger than a critical value I_c (P_c); ii) I_c increases with electron density (Si δ-doping concentration); and iii) the decrease in R_xx with increasing I in the non-linear response regime can be observed both at zero and high magnetic fields over a wide temperature range. When R_xx is plotted as a function of the power loss rate per electron (P) the values of the critical power (P_c) for different samples are roughly the same. We suggest that redistribution of the ionised donors in the sample occurring when I >I_c takes the major responsibility for the observed abnormal phenomena.     

Temperature dependence of elastic constants in δ-Pu

It is shown that the variation of the bulk and shear moduli in δ-Pu in a temperature range of 300–500 K is due to the phonon redistribution between different vibrational modes caused by the dispersion of the Grüneisen coefficients (phonon viscosity). The constants of interaction of the high-frequency acoustic modes with a long-wavelength deformation induced by an ultrasonic wave are estimated.     

Photoluminescence lineshape features of carbon δ-doped GaAs heterostructures

Photoluminescence lineshape properties of quasi-two-dimensional electron systems in setback δ-doped GaAs heterostructures are studied at liquid helium temperature. Contributions from the ground and the first excited two-dimensional subband are clearly observed. A simple fit to the lineshape including broadening demonstrates that there is an exponential low-energy tail associated with the ground subband. No such tail is observed for the first excited subband. The fit precisely reveals the subband bottom energies, the Fermi energy, the electron temperature and the recombination intensities. A self-consistent calculation of subband properties including the potential contribution of the setback δ-doping reproduces well the subband properties and the recombination intensities.     

The self-consistent calculation of Si δ-doped GaAs structures

In this study, we report results of a self-consistent calculation obtained for the sub-band structure of Si δ-doped GaAs material by using a new alternative method. We will discuss the influence of the δ-doping concentration and the δ-layerthickness on the sub-band structure for a non-uniform distribution, which is taken as different from the known Gaussian distribution. The confining potential, the sub-band energies, the sub-band occupations, and the Fermi energy have been calculated by solving the Schr?dinger and Poisson equations by using the Airy functions self-consistently. Received: 4 December 2000 / Accepted: 31 January 2001 / Published online: 26 April 2001     

Field-deployable measurements of free-living individuals to determine energy balance: fuel substrate usage through δ13C in breath CO2 and diet through hair δ13C and δ15N values

Carbon isotopes of breath CO₂ vary depending on diet and fuel substrate used. This study examined if exercise-induced δ¹³C-CO₂ changes in substrate utilization were distinguishable from baseline δ¹³C-CO₂ variations in a population with uncontrolled diet, and compared hair isotope values and food logs to develop an isotope model of diet. Study participants included nine women with diverse Body Mass Index (BMI), age, ancestry, exercise history, and diet. Breath samples were collected prior to and up to 12?h after a 5- or 10?K walk/run. Indirect calorimetry was measured with a smartphone-enabled mobile colorimetric device, and a field-deployable isotope analyzer measured breath δ¹³C-CO₂ values. Diet was assessed by food logs and δ¹³C, δ¹⁵N of hair samples. Post-exercise δ¹³C-CO₂ values increased by 0.54?±?1.09‰ (1 sd, n?=?9), implying enhanced carbohydrate burning, while early morning δ¹³C-CO₂ values were lower than daily averages (p?=?0.0043), indicating lipid burning during overnight fasting. Although diurnal δ¹³C-CO₂ variation (1.90?±?0.77‰) and participant baseline range (3.06‰) exceeded exercise-induced variation, temporal patterns distinguished exercise from dietary isotope effects. Hair δ¹³C and δ¹⁵N values were consistent with a new dietary isotope model. Notwithstanding the small number of participants, this study introduces a novel combination of techniques to directly monitor energy balance in free-living individuals.     

A generalization of the one-dimensional δ-function Bose gas

The one-dimensional boson gas with -function interaction is modified to include arbitrary pseudopotential interaction. The system is shown to be solvable by the Bethe Ansatz for certain classes of pseudopotential.     

Accuracy and precision of a laser-spectroscopy approach to the analysis of δ2H and δ18O in human urine

The isotope ratio analysis of body water often involves large sample numbers and lengthy sample processing. Here we demonstrate the ability of isotope ratio infrared spectroscopy (IRIS) to rapidly and accurately analyse the isotope ratios of water in urine. We analysed water extracted from human urine using traditional isotope ratio mass spectrometry (IRMS) and compared those values with IRIS-analysed extracted water and un-extracted urine. Regression analyses for δ²H and δ¹⁸O values between (1) extracted water analysed via IRMS and IRIS and (2) urine and extracted water analysed via IRIS were significant (R ²=0.99). These results indicate that cryogenic distillation of urine was not required for an accurate estimate of the isotopic composition of urine when using IRIS.     

Wild Rabbit Host and Some Parasites Show Trophic-Level Relationships for δ13C and δ15N: A First Report

Abstract

We report the first isotopic study of an animal host-parasite system. Parasitic, intestinal nematodes, Graphidium strigosum and Passalurus ambiguus, were ¹⁵N-enriched relative to their host, the European rabbit Oryctolagus cuniculus, while parasitic cestodes, Cittataenia denticulata and Mosgovoyia pectinata, were ¹⁵N-depleted, suggesting different trophic relationships. Host embryos were more similar in their δ¹³C and δ¹⁵N values to maternal muscle than were any of the parasites. Coprophagy, the direct recycling of food by the rabbit eating its own faeces, did not lead to isotopic differences between stomach contents and faeces, suggesting that the major point for isotopic discrimination in lagomorph nitrogen metabolism is in the animal rather than in the gut. We conclude that bulk δ¹³C and δ¹⁵N can reveal valuable new information about host-parasite relationships, and these could be explored further at the biochemical level using compound-specific isotopic analyses.     

Accuracy and precision of a laser-spectroscopy approach to the analysis of δ²H and δ¹⁸O in human urine

The isotope ratio analysis of body water often involves large sample numbers and lengthy sample processing. Here we demonstrate the ability of isotope ratio infrared spectroscopy (IRIS) to rapidly and accurately analyse the isotope ratios of water in urine. We analysed water extracted from human urine using traditional isotope ratio mass spectrometry (IRMS) and compared those values with IRIS-analysed extracted water and un-extracted urine. Regression analyses for δ2H and δ1?O values between (1) extracted water analysed via IRMS and IRIS and (2) urine and extracted water analysed via IRIS were significant (R2=0.99). These results indicate that cryogenic distillation of urine was not required for an accurate estimate of the isotopic composition of urine when using IRIS.     

Resonant Multichannel Scattering in a Nanotube with δ-Potentials

The resonant tunneling transmission of an electron through the quantum wire comprising two three-dimensional δ-potentials located along the nanotube axis is considered. Using the formulas obtained recently for amplitudes of multichannel scattering, the condition (equation) of resonance is found for the multichannel scattering, at which the system under consideration becomes completely transparent for motion of the electron. A procedure based on the method of vector diagrams is proposed for simplification of the resonance equation. It is shown that if the initial energy of longitudinal motion is insufficient for excitation of new scattering channels, then the resonance equation coincides with the corresponding equation of one-dimensional problem.     

The Effect of Diet Quality on δ13C and δ15N in the Tissues of Locusts,Locusta migratoria L

Abstract

Locust nymphs were raised from hatching to adult locusts on either seedling wheat (C₃) or maize (C₄), to determine whether relative enrichments/depletions of ¹⁵N and ¹³C within body tissues are influenced by diet. The maize contained less hexose sugars and protein per gram than wheat.

The isotopic spacing between the food and the whole insect was found to differ between the two diets. The lower quality maize diet showed an overall +5.1‰ enrichment in δ¹⁵N compared to + 2.8‰ for wheat, possibly due to increased fractionation due to protein recycling.

The maize diet resulted in increased depletion in lipid and trehalose and depletion in chitin relative to diet. The results for both δ¹⁵N and δ¹³C suggest that substrate recycling was occurring on the low quality maize diet. Therefore diet quality determines the enrichment/depletion in δ¹⁵N and δ¹³C within organisms.