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.     

On the use of high-Tc superconductors for Perot-Fabry mirrors coatings

In a very rough experiment using two MgO plates, coated with a 200 Å thick YBaCuO film to increase their reflectivity, and facing each other their YBaCuO films to make a Perot-Fabry (PF) interferometer, we have observed a 43% maximum transmission and a finesse around 33 at v=29 cm^–1, in good accordance with a new phenomenological model for YBaCuO. Much higher performances can be expected by optimizing the YBaCuO film thickness.     

Nature of oxygen in the passive film on stainless steels in 0.1 M NaCl solution

Three different oxygen species, O^2–, OH^–, and H₂O, are introduced into the deconvolution of the oxygen peaks measured in the prior study and their true concentrations are investigated in the depth profile. It is found that H₂O exists mainly in the outermost part of the passive film at the interface of solution and the passive film. OH^– and O^2– are found throughout the passive film; they have a maximum concentration in the outer layer at around 10 to 20 Å depth, with a concentration of 40 at.% for the stainless steel 29-4-2 and 50 at.% for 18-12. After the maximum the concentrations are sharply reduced with increasing sputtering time and remain at a constant concentration of about 10 at.% at 35 Å depth. Both species still exist at this concentration even after long time sputtering.     

High Ni2+-mobility in the Chevrel phase Ni2Mo6S8: a quasielastic neutron scattering study

A quasielastic neutron scattering study of Ni₂Mo₆S₈ has established relatively fast long-range motion of the intercalated Ni²⁺ ions, with a diffusion constantD=3×10^–9 cm² s^–1. A model with a jump distance of about 2.1 Å and an activation energy of 24 kJ/mol is favoured. A critical consideration of the information contained in fixed window measurements is given.     

Photoluminescence of aqueous solutions of uranyl nitrate containing sodium tetrametaphosphate

Solutions (10^–5 to 5×10^–2 M) of UO₂(NO₃)₂ have been used in the presence of 2 wt.% Na₄P₄O₁₂, with excitation by a mercury arc over the range 3200–3800 Å. The emission and absorption spectra of the complex are reported; the first is narrow and has peaks at 4910, 5150, and 5400 Å. This spectrum is the same whether the tetrametaphosphate anion has the chair configuration or the boat one.     

Radiant-energy detection by?Ba?Cu?O thin films

High T_c superconducting films offer promise as fast sensitive detectors of microwave and infrared. A high T_c superconducting transition-edge bolometer was fabricated from Y–Ba–Cu–O thin film on a (100) SrTiO₃ substrate, and tested at about the T_c midpoint using a 500 K blackbody source. In this initial work only NEP=5×10^–8W/Hz^1/2 was achieved with a large time constant caused by rather thick substrate. The sensitive element was put in the vacuum chamber of a liquid nitrogen metal cryostat for three weeks and through ten cold-hot cycles (80 K-300 K), the sensitivity of the bolometor kept repeatable. Some future work is also discussed.     

Time and temperature dependent breakdown characteristics of ZnS:Mn films obtained by rf-magnetron sputtering

Breakdown delay times (t_del) for films of managanese-doped zinc sulfide (ZnS:Mn) were measured in the range 10^–6–10^–1 s. The maximum value was t_del=10^–3–10^–2 s. The electrical strength (E_br) was found to increase as the voltage pulse duration was reduced, the more so the thinner the ZnS:Mn film. The temperature dependence of E_br exhibited a weak reduction in E_br as the temperature was raised to roughly 80°C and a sharp reduction in E_br for T>130°C. A maximum in E_br was observed at T130°C which is presumably explained by a structural modification of the ZnS:Mn film. The experimental results obtained are explained in terms of a combined electronic and thermal breakdown mechanism.State Academy of Control Systems and Radioelectronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 3–6, April, 1994.     

Small angle neutron scattering from oxygen precipitates in silicon

The formation of silicon oxide precipitates from Czochralski grown silicon depends on the time and temperature of the heat treatment as well as on the initial content of interstitially dissolved oxygen. Samples containing between 5×10¹⁷ O_i/cm³ and 13×10¹⁷ O_i/cm³ have been heated at 750° C for 96 h. SiO₂ precipitates of various shape and size have been obtained and investigated by means of small angle neutron scattering (SANS) in the Q-range 0.05 Å^–1<Q<0.2 Å^–1. The obtained SANS patterns reveal a typical anisotropy of their intensity distribution, which splits into a central peak at Q<0.1 Å^–1 due to the shape of the individual particles and a number of weak intensities for large Q-values, originating from a correlation between defects, possibly between the precipitates. While these correlation peaks in the SANS patterns are seen best for rather low values of about (5–7)×10¹⁷ O_i/cm³ oxygen content, the central peak anisotropy is most pronounced for higher values of ca 10×10¹⁷ O_i/cm³. The integrated intensity of the central peak increases with increasing initial oxygen content. For comparison, untreated samples of the same initial oxygen content do not reveal any anisotropic SAN scattering or a broadened central peak beam.     

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].     

Isotopic spectral analysis of helium with the aid of an isotope filter

As simple photoelectric method for the isotopic analysis of helium (He³-He⁴) based on measurement of the emission of the He 10830 Å (2³P_0,1,2-2³S₁) line components belonging only to the He³ isotope has been developed. Isolation of these components from the overall line emission was ettected by means ot an isotopic filter in the form of an absorption tube filled with natural helium. A glow discharge was maintained in the tube. The calibration curve in the 0–100% range had a slightly wavy shape. This result was in good agreement with the computed curve.Presented at the 16th Conference on Spectroscopy (Moscow, 28 January–2 February, 1965).     

Properties of the SiO2/SiC interface investigated by angle resolved studies of the Si 2p and Si 1s levels and the Si KLL Auger transitions

Angle resolved photoemission studies of the Si 2p and Si 1s core levels and the Si KL_2,3L_2,3 Auger transitions from SiO₂/SiC samples are reported. Most samples investigated were grown in situ on initially clean and well ordered √3×√3 reconstructed 4H-SiC(0 0 0 1) surfaces but some samples were grown ex situ using a standard dry oxidation procedure. The results presented cover samples with total oxide thicknesses from about 5 to 118 Å. The angle resolved data show that two oxidation states only, Si⁺¹ and Si⁺⁴, are required to explain and model recorded Si 2p, Si 1s and Si KLL spectra.The intensity variations observed in the core level components versus electron emission angle are found to be well described by a layer attenuation model for all samples when assuming a sub-oxide (Si₂O) at the interface with a thickness ranging from 2.5 to 4 Å. We conclude that the sub-oxide is located at the interface and that the thickness of this layer does not increase much when the total oxide thickness is increased from about 5 to 118 Å.The SiO₂ chemical shift is found to be larger in the Si 1s level than in the Si 2p level and to depend on the thickness of the oxide layer. The SiO₂ shift is found to be fairly constant for oxides less than about 10 Å thick, to increase by 0.5 eV when increasing the oxide thickness to around 25 Å and then to be fairly constant for thicker oxides. An even more pronounced dependence is observed in the Si KLL transitions where a relative energy shift of 0.9 eV is determined.The relative final state relaxation energy ΔR(2p) is determined from the modified Auger parameter. This yields a value of ΔR(2p)=−1.7 eV and implies, for SiO₂/SiC, a “true” chemical shift in the Si 2p level of only ≈0.4 eV for oxide layers of up to 10 Å thick.     

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.     

Deep bandtail states picosecond intensity-dependent carrier dynamics of GaN epilayer under high excitation

Picosecond carrier dynamics of deep bandtail states (3.1 eV) in an unintentionally n-doped GaN epilayer at room temperature under high excitation densities (i.e., N ₀ = 1.0× 10¹⁹– 1.1× 10²⁰ cm^–3) have been investigated with nondegenerate femtosecond pump–probe (267/400 nm) reflectance ( R/R ₀). All R/R ₀ traces possess a 2 ps buildup time that represents an overall time for the initial non-thermal carrier population to relax towards the continuum extremes and then into the probed tail states. We observe a saturation of R/R ₀ initial (first 10 ps) recovery rate _i at a density of 5– 6×10¹⁹ cm^–3 close to the Mott transition threshold obtained from time-integrated PL measurements. Such a saturation phenomenon has been identified as the trap-bottleneck due to the bandtail states and deep traps. As N ₀ is further increased, _i accelerates due to the onset of Auger recombination as the trap-bottleneck becomes effective. The best fit by the Auger model for N ₀ in the range of the mid-10¹⁹–10²⁰ cm^–3 yields an Auger coefficient of C _a 5.0× 10^–30 cm⁶ s^–1.     

A Sensitive Fluorimetric Method for the Determination of Epinephrine

A sensitive fluorimetric method for the determination of epinephrine (E) is described in this paper. The experiments indicate that epinephrine can react with formaldehyde (HCHO) in an acid medium to form a condensation product, which can be oxidized by potassium hexacyanoferrate(III) (K₃[Fe(CN)₆]) in borax buffer (pH = 9.5). The reaction product can emit strong fluorescence. Ascorbic acid (AA) is used in order to consume excess potassium hexacyanoferrate and stabilize the fluorescent product. Under optimum conditions, a linear relationship has been obtained between the fluorescence intensity and the concentration of epinephrine in the range of 1.4×10^–9–2.1×10^–6 mol/l, and the detection limit is 2.4×10^–10 mol/l (4.3×10^–11 g/ml, S/N = 3). The method is applied for the determination of E in both actual sample and the synthetic sample with E and norepinephrine (NE) by using the coupling technique of synchronous fluorimetry and H-point standard addition method, and the results obtained are satisfactory.     

Boson peak of AsxS1−x glasses and theoretical calculations of low frequencies clusters vibrations

The results of comparison of spectral position of the LF bands of g-As₂S₃ and g-As₂₂S₇₈ with theoretical calculations of vibrational spectra of different clusters (As₂S₄, As₂S₅, As₂S₆, AsS₃-As₃) in the LF region (10-85 cm⁻¹) are given. The torsion type vibrations of the small chain-like clusters are located in the same spectral region as Boson peak of As-S glasses system. They can make several contributions to the LF spectrum. The cluster lengths by weight distribution functions f(L)*L are from 5.5 to 10.1 Å and from 4.5 to 7.5 Å for g-As₂S₃ and g-As₂₂S₇₈, respectively. The lognormal fittings of the f(L)*L functions give the most probably values about the 7.6 Å (for g-As₂S₃) and 6.2 Å (for g-As₂₂S₇₈).     

Effective Vilcovisky-De witt action in mutidimensional R2 gravitation

The gauge- and parametrization-invariant Vilcovisky-De Witt effective action (EA) in multidimensional R² gravitation against R₄×T_d–4 background, where R₄ is a four-dimensional flat space and T_d is a d-dimensional torus, is calculated in the one-loop approximation. It is shown that with the help of a limiting procedure the Vilcovisky-De Witt EA in multidimensional Einstein gravitation against the background R₄×T_d–4 can be constructed from the EA found. The question of the stability of spontaneous compactification is analyzed taking into account quantum effects in d=5 R² gravitation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 106–111, October, 1989.I thank I. L. Bukhbinder and I. V. Tyutin for useful discussions.     

Decay of tripositronium with spin 3/2 and orbital angular momentum L=1 into an electron and a photon

It is shown that the probability for decay into an electron and a photon of a negative ion of positronium with the quantum numbers S=3/2, L=1, S_z=3/2, and L_z=0 is equal to 0.7·10^–7sec-^–1.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 101–105, October, 1978.The author thanks V. S. Vanyashin for suggesting this problem and for useful discussions.     

Bactericidal effects of Ag nanoparticles immobilized on surface of SiO2 thin film with high concentration

Bactericidal activity of high concentration Ag nanoparticles immobilized on surface of an aqueous sol–gel silica thin film was investigated against Escherichia coli and Staphylococcus aureus bacteria. Size of the surface nanoparticles was estimated in the range of 35–80 nm by using atomic force microscopy. Due to accumulation of the silver nanoparticles at near the surface (at depth of 6 nm and about 40 times greater than the silver concentration in the sol), the synthesized Ag–SiO₂ thin film (with area of 10 mm²) presented strong antibacterial activities against E. coli and S. aureus bacteria with relative rate of reduction of the viable bacteria of 1.05 and 0.73 h⁻¹ for initial concentration of about 10⁵ cfu/ml, respectively. In addition, the dominant mechanism of silver release in long times was determined based on water diffusion in surface pores of the silica film, unlike the usual diffusion of water on the surface of silver-based bulk materials. Therefore, the Ag nanoparticles embedded near the surface of the SiO₂ thin film can be utilized in various antibacterial applications with a strong and long life activity.     

Effect of fine crystalline structure on coercive force of e lectrodeposite d iron films

Iron films 1000 Å thick deposited on sheet copper at pH = 5 at current densities of 0.1–4 A /dm² were investigated. There is a symbatic relationship between H_c and the microstresses.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 14–18, December, 1971.     

Perpendicular anisotropy and magneto-optical Kerr effect of (Ni/Pd) multilayers

Nickel film, with total thickness t_Ni in the range 1000-2000 Å, is known to exhibit perpendicular magnetic anisotropy (PMA), if the film has been deposited at room temperature. This phenomenon is due to the magneto-elastic (ME) effect. The same is also true for the (Ni/Pd)_n multilayers, where n is the period (n≥3). In this paper, we have made two kinds of multilayers: one, which does not have a Pd cap layer, belongs to the A-group, and the other, which has, belongs to the B-group. The polar Kerr rotation θ_k, the polar Kerr ellipticity ε_k, and the figure of merit (θ_k)²R, where R is the reflectance, were measured for the two wavelengths, i.e. λ=633 and 442 nm, respectively. The effective PMA energy K_⊥ was measured from the vibrating sample magnetometer. It was found that the most favorable multilayer for the magneto-optical (MO) application exists among the A-group samples: i.e. the t_Ni=1300 Å, t_Pd=50 Å (seed layer), and n=1 sample. We obtained θ_k=−9.76 min, ε_k=−9.13 min, (θ_k)²R=1.51 (rad)² at λ=442 nm, and K_⊥=3.21×10⁶ erg/cc for this optimal multilayer. Finally, the effects of the Pd seed layer on PMA and MO are also studied.