Dependence of a common effective action in a multidimensional R2 gravitation on the metric of the configuration space

A common effective action in a multidimensional R² gravitation on a plane R_d or R_k × T_d–k background is analyzed. The dependence of this effective action on the metric of the configuration space is studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 74–76, July, 1991.     

Gauge dependence of the effective action in multidimensional theories of supergravity

Using the 5-dimensional supergravity as an example, the problem of gauge dependence of the effective action (EA) of multidimensional SUGRA's is discussed. The standard and the Vikovisky-De Witt EA's are computed up to the terms linear in curvature for d=5, N=2, 4, 6, 8 SUGRA's on the R₄,×S₁ background, where R₄, is a 4-dimensional curved space, and S₁ a 1-dimensional sphere. The standard EA obtained in d=5, N= 2 gauge SUGRA on the R ₄ ⁰ ×S₁, where R ₄ ⁰ is a flat 4-dimensional space, depends on three gauge parameters. The gauge-invariant Vilkovsky-De Witt EA is computed for a d=5 SUGRA with broken symmetry on the r ₄ ⁰ ×S₁ background, where R ₄ ⁰ is a 4-dimensional space with nonzero temperature.Translated from Izvestiya Vyssihkh Uchebnykh Zavedenii, Fizika, No. 5, pp. 53–59, May, 1989.I am grateful to I. L. Bukhbinder, I. V. Tyutin, and A. A. Tseitlin for many useful discussions.     

Effective action in higher derivative (Super)gravities

'The one-loop effective action (EA) with an accuracy up to linear curvature terms ind=4R ²-gravity, conformal gravity, andN=1,d=4 conformal supergravity on the backgroundR ₄×T_4–k,k=1, 2, 3 is calculated. (Here,R _k is thek-dimensional curved space, T_n is then-dimensional torus). The one-loop EA in multidimensionalR ²-gravity and ind=10 conformal supergravity on the backgroundR ₄ ×T _d–4 is also obtained. The mechanism of inducing the Einstein gravity from the EA of considered theories of higher derivative (super)gravity is presented.We are grateful to I. L. Bukhbinder for the numerous discussions of considered questions.     

Casimir effect in quantized R2 gravitation

The Casimir energy is calculated in theories of R² gravitation and conformai gravitation in the space R₁ x T₃, where T₃ is a 3D torus. Cosmological applications of the results are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 59–62, June, 1989.I whish to thank I. L. Bukhbinder for useful discussions.     

Spontaneous compactification in A d-dimensional quantum gravity model

It is shown that in a d-dimensional quantum gravity model of special type, AdS₄×S_d–4 compactification is allowed. When d=5, M₄×S₁ compactification is allowed. Here AdS₄, is anti-de Sitter space, M₄, is Minkowski space, and S_d–4 is a (d–4)-dimensional sphere. The Casimir energy is computed in the 5-dimensional quantum gravity model on the M₄×S₁ gravitational background, and in the d-dimensional (odd d) quantum gravity on the M_d–1×S₁ background.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 67–71, October, 1988.In conclusion we have the pleasure of thanking I. L. Bukhbinder for his help in our work.     

Two-photon time-resolved optogalvanic signals of neon

In this work, temporal evolution of two-photon laser optogalvanic signals of neon has been studied. Optogalvanic signals for four transitions from the metastable 2p⁵3s[3/2]₂ state to 2p⁵4d′[3/2]₁, 2p⁵4d′[3/2]₂, 2p⁵4d′[5/2]₃ and 2p⁵4d′[5/2]₂ states were recorded over a range of discharge currents (3.4–9 mA). It was found that the shape of the optogalvanic signal was strongly dependent on the discharge current so that its peak shifted to shorter times and its amplitude increased with the discharge current. The decay rates of the 4d states, calculated from the optogalvanic signals, were found to increase linearly with the discharge current in the range of 6.2–9 mA. However, for the range of 3.4–5.4 mA, the decay rates were observed to slightly decrease with the discharge current.     

The sub-micrometer thickness n-InSb/i-GaAs epilayers for magnetoresistor applications at room temperatures of operation

Magnetotransport at fields up to 500 mT and LF-noise characteristics are reported for miniature magnetoresistors with ferrite concentrators based on Sn-doped n-InSb/i-GaAs heterostructures grown by MBE. The thickness of the InSb epilayers lie in the range 0.55–1.5 μm giving room temperature mobilities of 2.5–5.5 m² V⁻¹ s⁻¹ with carrier densities of (0.5–1.5)×10¹⁷ cm⁻³. The room temperature magnetoresistance (MR) for our two terminal devices could be as high as 115% at 50 mT which is comparable to the extraordinary MR (ExMR) recently reported in microscopic composite van der Pauw disks four terminal devices [Science 289 (2000) 1530]. In addition, a high signal-to-noise ratio and a good temperature stability of R(B)/R₀=0.5–0.83% K⁻¹ was observed for B<60 mT (below the saturation field B_sat for ferrite). Device resistance stability R₀(T) was equal to 0.27–0.66% K⁻¹ in zero field with a nominal device resistance R₀=197–224 Ω for DC currents in the range I=0.01–1.0 mA. The minimum detectable magnetic field is estimated from the reduced differential MR (∂R/∂B)/R=2000% T⁻¹ at B=31 mT and normalised 1/f current noise power spectral density measured at the same field. The resolution limit B_min=2.6 nT at 10² Hz and B_min=0.82 nT at 10³ Hz. These resolution limits are seven times better than those recently reported for the same material n-InSb/i-GaAs and ferrite fabricated Hall sensors [Magnetotransport and Raman characterization of n-InSb/i-GaAs epilayers, for Hall sensors applications over extremely wide ranges of temperature and magnetic field, Proceedings NGS 10, IPAP Conference Series 2, IPAP, Tokyo, 2001, pp. 151–154].     

Photoelectric properties of Pb1−x−y Sn x Ge y Te:In epitaxial films

Pb_1–x–y Sn _x Ge _y Te:In epitaxial films are examined in a wide temperature interval and at various background fluxes. These films have high sensitivity to infrared radiation in the spectral range <20m. The lifetime depends exponentially on temperature and varies from several seconds at T=10 K to 10^–2 s at T=20 K. The two-electron model of Jahn-Teller centers is proposed to explain the results. Multielement photoresistors based on these films are fabricated and D*=1.7×10¹³ cm Hz^1/2 W^–1 at T=25 K is achieved. Noise of the photoresistors is independent of background flux when it varies from 10¹² cm^–2 s^–1 to 10¹⁸ cm^–2 s^–1. As compared with Si:Ga and Ge:Hg photoresistors, the responsitivity is several orders larger at the operating temperature 25–30 K.     

Temperature characteristics of heat exchange due to thermal conductivity of three hollow cylinders in their contact planes

For the case where a system of three hollow cylinders, having contact along their ends, are heated the problem on the determination of the thermal characteristics in the contact planes is solved analytically. Numerical calculations and the construction of plots of the temperature variation, thermal fluxes, and the heating and stabilization times in the contact planes are carried out on the basis of the formulas so obtained.Notation _j = (T_j–T₀)/(T₀–T_c) dimensionless temperature - T₀ initial temperature - T_c temperature of the medium - T_j temperature at an arbitrary point of the j-th cylinder - Fo_j a_jt/R ₁ ² - K_a a₂/a₁ - d R₂/R₁ - b R₁/l - _j, a_j thermal and thermiometric conductivities, respectively - R₂, R₁ respectively, the outer and inner radii of the cylinders - t time - X, Z dimensionless cylindrical coordinates Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 80–84, July, 1972.     

Separation of Anisotropy and Exchange Broadening Using N CSA–N–H Dipole–Dipole Relaxation Cross-Correlation Experiments

Based on the measurement of cross-correlation rates between ¹⁵N CSA and ¹⁵N–¹H dipole–dipole relaxation we propose a procedure for separating exchange contributions to transverse relaxation rates (R₂ = 1/T₂) from effects caused by anisotropic rotational diffusion of the protein molecule. This approach determines the influence of anisotropy and chemical exchange processes independently and therefore circumvents difficulties associated with the currently standard use of T₁/T₂ ratios to determine the rotational diffusion tensor. We find from computer simulations that, in the presence of even small amounts of internal flexibility, fitting T₁/T₂ ratios tends to underestimate the anisotropy of overall tumbling. An additional problem exists when the N–H bond vector directions are not distributed homogeneously over the surface of a unit sphere, such as in helix bundles or β-sheets. Such a case was found in segment 4 of the gelation factor (ABP 120), an F-actin cross-linking protein, in which the diffusion tensor cannot be calculated from T₁/T₂ ratios. The ¹⁵N CSA tensor of the residues for this β-sheet protein was found to vary even within secondary structure elements. The use of a common value for the whole protein molecule therefore might be an oversimplification. Using our approach it is immediately apparent that no exchange broadening exists for segment 4 although strongly reduced T₂ relaxation times for several residues could be mistaken as indications for exchange processes.     

The electro-optic kerr effect in noncentrosymmetric KH2PO4 and KD2PO4 monocrystals

Experimental and theoretical results of the determination of the quadratic electro-optic coefficients in noncentrosymmetric KH₂PO₄(KDP) and KD₂PO₄(DKDP) monocrystals are presented. The coefficientR _c=R ₁₁₂₂-R ₁₁₁₁ for the X-cut crystals has been measured by a dynamic method in the a.c. electric field. The theoretical value of the coefficient has been calculated by the Kurtz-Robinson model. It has been found that the coefficientR _c was less than 10×10^–20m²V^–2.     

Use of radar methods in increasing sensitivity in emission spectral analysis. Part I. Use of correlation

Special scanning methods applied to line and continuous background cause these to build up according to different laws; a line of unvarying intensity is transformed to a train of video pulses (frequency 50 kc), while the background fluctuations remain purely random. Some characteristics are derived for the autocorrelation function; these enable one to use it to reduce the limit of detection in spectral analysis. The autocorrelation function is reported for the arc determination of Cr at concentrations of 5×10^–3, 5×10^–4, 5×10^–5, and 5×10^–6%. Calibration curves are given for these concentrations as determined by photographic and autocorrelation methods. The limit of detection by the photographic method is found to be about two orders of magnitude larger than that for the autocorrelation one.I am indebted to Professor N. A. Prilezhaeva and senior scientist N. G. Preobrazhenskii for valuable advice and discussions, and also to student V. I. Donin for assistance.     

Shallow acceptor population and free hole concentration in Si: In and Si:Ga with IR-photoexcitation

Hall measurements at low temperaturesT<50 K have been performed on Si:In (N _In10¹⁷ cm^–3) and Si:Ga (N _Ga10¹⁸ cm^–3) with infrared photoexcitation of holes into the valence band. It is shown in quantitative agreement with a theoretical model that the population of shallow acceptors, e.g. B and Al, which are present as impurities in concentrations ofN _B,Al10¹²-10¹⁴ cm^–3 strongly affects the photoexcited hole concentration. Photo-Hall measurements can, therefore, serve as a tool for the determination of low impurity acceptor concentrations in the case of high In- or Ga-doping. Hole capture coefficientsB _In=6×10^–4 (T/K)^–1,8 cm³ s^–1 andB _Ga=2×10^–4 (T/K)^–1 cm³ s^–1 have been determined.     

Volume and grain boundary diffusion of implanted 113Sn in aluminium

Volume and grain boundary diffusion of ¹¹³Sn in aluminium was investigated with the radiotracer method. The implantation technique was used for tracer deposition to avoid problems of tracer hold-up caused by the oxide layer always present on aluminium. The diffusion penetration was chosen large enough to permit serial sectioning of samples with the aid of a microtome.The temperature dependence of the volume diffusivity was determined as D(T)=4.54×10^–5×exp[–(114.5±1.2)kJmol^–1/RT] m ² s ^–1. This confirms previous measurements from our group which already showed that Sn is the fastest foreign metal diffusor so far investigated in aluminium.Grain boundary diffusion of ¹¹³Sn in Al polycrystals was measured in the type-B kinetic regime. The grain boundary diffusion product P=sD _gb (s=segregation factor, =grain boundary width, D _gb=grain boundary diffusivity) was found to be strongly affected by the impurity content of aluminium. For Al polycrystals of 99.9992% nominal purity we obtained P _5N(T)=1.08×10^–8exp [–(96.9±7.5) kJ mol^–1/RT] m³ s^–1 and for less pure Al polycrystals of 99.99% nominal purity P _4N(T)=3.0×10^–10 exp [–(90.1±4.2) kJ mol^–1/RT] m³ s^–1 was determined. The grain boundary diffusion product in the purer material is more than one order of magnitude higher than in the less pure material. Very likely this is an effect of co-segregation of non-diffusant impurities into the grain boundaries.     

Cu nuclear spin-spin relaxation in YBa2Cu3O6.98 and YBa2Cu4O8

We have measured the temperature (T) dependence of the transverse relaxation rate (T _G ^–1 ) of the Cu(1) nuclear spin in YBa₂Cu₃O_6.98 (T _c=92 K) and YBa₂Cu₄O₈ (T _c=82 K). From the scaling ratio ofT _G ^–2 (Cu1) toT _G ^–2 (Cu2), we have estimated the strength of a covalent bonding between the CuO₂ plane and the CuO chain to be B0.38×A _zz. The experimentalT _G ^–1 (Cu1) in YBa₂Cu₄O₈ was of the same order of magnitude as the estimated one fromT _G ^–1 (Cu2). These results appear to indicate that the electrons in the CuO₂ plane fairly spread out of the plane in both compounds.     

Surface resistance and far infrared absorptivity at T=7 K of highTc YBaCuO superconductors

A surface resistance as small as R_S=3×10^–2 Ohms has been computed at T=8 K, for v=0.6 Thz (v=20 cm^–1), for an YBaCuO film deposited on an MgO substrate. The calculations are made with the refractive index computed from the Far IR transmission spectra of a 400 Å thick film.Still lower values are obtained with another sample, 300 Å thick of exceptional quality (R_S=1.2×10^–2 Ohms).     

Mössbauer study of magnetic critical behavior of F0.875V0.125

The disordered alloy Fe_1–xV_x has a well defined maximum in T_c at x=0.125. Working at this value to suppress T_c broadening, we have made high precision Mössbauer measurements in the ferromagnetic region. When analyzed in terms of four hyperfine field components our spectra suggest that the sample isannealed. Fitting the hyperfine field over reduced temperatures 1.7×10^–3 < t < 5×10^–1 with corrections to scaling yields p =0.362(8), in agreement with earlier work on pure Fe, and with Fisher's predictions for annealed disordered systems.     

Infrared absorption of silane,ammonia, acetylene and diborane in the range of the CO2 laser emission lines: Measurements and modelling

Absorption spectra of the gases SiH₄, NH₃, C₂H₂ and of SiH₄/Ar and SiH₄/B₂H₆ mixtures have been measured in the spectral range of the CO₂ laser from 9.2 to 10.8 µm. In agreement with literature, silane shows the highest absorption (absorption coefficient = 3.3 × 10^–2 Pa^–1 m^–1). The deviation of the measured absorption behaviour of silane from literature, as far as the pressure dependence is concerned, can be explained by the enhanced spectral energy density in our experiment. This is confirmed by a rate-equation model involving the basic mechanisms of V-V and V-T energy transfer between vibrationally excited silane molecules. In contrast to silane, the absorption coefficient of NH₃ at the 10P(20) laser line is 4.5 × 10^–4 Pa^–1 m^–1 atp = 20 kPa and has its maximum of 4.5 × 10^–3 Pa^–1 m^–1 at the 10R(6) laser line. For C₂H₂ and B₂H₆, is even less ( 2.1 Ò 10^–5 Pa^–1 m^–1 for C₂H₂).     

Wide-band low noise MM-wave SIS mixers with a single tuning element

Several SIS quasiparticle mixers have been designed and tested for the frequency range from 80 to 115 GHz. The sliding backshort is the only adjustable RF tuning element. The RF filter reactance is used as a fixed RF matching element. A mixer which uses a single 2×2 m² Pb-alloy junction in a quarter-height waveguide mount has a coupled conversion gain of G_M(DSB)=2.6±0.5 dB with an associated noise temperature of T_M(DSB)=16.4±1.8 K at the best DSB operation point. The receiver noise temperature T_R(DSB) is 27.5±0.8 K for the mixer test apparatus. This mixer provides a SSB receiver noise temperature below 50 K over the frequency range from 91 to 96 GHz, the minimum being T_R(SSB)=44±4 K. Another mixer with an array of five 5×5 m² junctions in series in a full-height wave-guide mount has much lower noise temperature T_M(DSB)=6.6±1.6 K, but less gain G_M(DSB)=–5.1±0.5 dB.Contribution of the U.S. Government, not subject to copyright     

The hall effect in PdSi-based amorphous alloys containing Co.

The Hall effect in amorphous Pd₈₀Si₂₀ and Pd_80–x Si₂₀Co _x , wherex=2, 4, 6 (at.% are implied throughout) alloys was investigated. Measurements were carried out at r.t. in fields up to 17·5 kG. Also the electrical conductivity was measured. The Hall effect was found negative in all alloys of the above composition. Observedx-dependence of the Hall constantR _H tends to change the sign of the effect and is interpreted on the assumption that an extraordinary Hall effect manifests itself besides the ordinary one in Co-containing alloys. The value ofR _H for the basal alloy should be looked upon as an evidence of electron transfer from glass-former (Si) to transition metal (Pd) empty d-states. The values ofR _H obtained for the alloys withx=0, 2, 4, 6 are respectively, –7·8; –8·7; –8·3; –5·2 (×10^–5 cm³/A. sec throughout).