Classical stability of direct products of spheres in gravitational systems

Classical stability of Einstein spaces S^d₁ ×?×S^d_n(d_j ? 2) against all fluctuations is investigated in euclidean gravity with a cosmological constant. It is shown that S^d is classically stable, while S^d₁ ×?× S^d_n(n ? 2) is classically unstable. As a generalization of this analysis it is proved that a compact Einstein space B₁ ×?× B_n(n ? 2) which is a direct product of each Einstein space is classically unstable. Non-Einstein spaces M² × S⁴ (M² × S² × S²) are also considered in six- dimensional Einstein-Maxwell theory and are shown to be classically stable (unstable).     

The criterion for vacuum stability in Kaluza-Klein supergravity

We prove that in the spectrum of the d = 4 theory obtained by Freund-Rubin compactification of d = 11 superconductivity, only fields of spin 0⁺ can give rise to classical instabilities. The criterion for stability in the 0⁺ sector can be expressed as a certain lower bound on the Lichnerowicz operator Δ_L on the d = 7 compact space. Thus not only are supersymmetric vacua always stable but so are the corresponding non-supersymmetric vacua obtained by reversing the orientation of the compact space, since the 0⁺ spectrum is insensitive to the orientation. Examples are the orientation-reversed spaces with N = 0 obtained from the squashed seven-sphere with N = 1 and from SU(3) ×SU(2) ×U(1) spaces with N = 2 supersymmetry. Product spaces, on the other hand, are always unstable. Finally, we examine the massless sectors of the squashed seven-sphere vacua, and find an additional 135 massless scalars.     

Determination of the piezoelectric constant d14 of trigonal selenium crystals

Using the gain-bandwidth method, the piezoelectric constant d₁₄ of trigonal selenium has been deduced from measurements of the admittance and the electromechanical resonance frequencies of appropriately cut bars. The value was found to be |d₁₄| = (2.54 ± 0.2) × 10^?2C/N.     

Thermal stability and radiation hardness of SiC-based schottky-barrier diodes

Pt/W/Cr/SiC Schottky-barrier diodes that retain good electrophysical parameters up to 450°C are studied. With the Auger electron spectroscopy (AES) method, it is shown that the thermal stability is provided by using a multilayer metal composition that ensures the metal/SiC interface stability. The surface-barrier structures obtained are tested for radiation hardness. They are irradiated by fast neutrons with a fluence of 4.42×10¹⁵ n/cm² and attendant γ radiation with a dose of 8.67×10⁵ R in the concentration range of N _d-N _a=10¹⁶−5×10¹⁷ cm⁻³. Irreversible modifications of the structures at N _d-N _a≤8×10¹⁶ cm⁻³ are found. The degradation of the parameters is inversely proportional to the doping level.     

Lyapunov Exponents for Products of Complex Gaussian Random Matrices

The exact value of the Lyapunov exponents for the random matrix product P _N =A _N A _N?1?A ₁ with each $A_{i} = \varSigma^{1/2} G_{i}^{\mathrm{c}}$ , where Σ is a fixed d×d positive definite matrix and $G_{i}^{\mathrm{c}}$ a d×d complex Gaussian matrix with entries standard complex normals, are calculated. Also obtained is an exact expression for the sum of the Lyapunov exponents in both the complex and real cases, and the Lyapunov exponents for diffusing complex matrices.     

Hamiltonian finite-dimensional models of baroclinic instability

A hierarchy of N-dimensional systems is constructed starting from the standard continuous two-layer quasi-geostrophic model of the geophysical fluid dynamics. These models (“truncations”) preserve the Hamiltonian structure of the parent model and tend to it in the limit N → ∞. The construction is based on the known correspondence SU(N) → SDiff(T²) when N → ∞ between the finite-dimensional group of unitary unimodular N × N matrices and the group of symplectic diffeomorphisms of the torus and the fact that the above-mentioned continuous model has an intrinsic geometric structure related to SDiff(T²) in the case of periodic boundary conditions. A fast symplectic solver for these truncations is proposed and used to study the baroclinic instability. 7     

N = 2, D = 10 non-chiral supergravity and its spontaneous compactification

The non-chiral N = 2, D = 10 supergravity theory is constructed using dimensional reduction from N = 1, D = 11 supergravity. It is shown that this theory may spontaneously compactify, yielding S⁴ × S², CP² × S² and S² × S² × S² spaces for the extra dimensions.     

Non-abelian D = 11 supermembrane

We obtain a U(M) action for super membranes with central charges in the Light Cone Gauge (LCG). The theory realizes all of the symmetries and constraints of the supermembrane together with the invariance under a U(M) gauge group with M arbitrary. The worldvolume action has (LCG) N = 8 supersymmetry arid it corresponds to M parallel supermembranes minimally immersed on the target M g × T ² (MIM2). In order to ensure the invariance under the symmetries and to close the corresponding algebra, a star-product determined by the central charge condition is introduced. It is constructed with a nonconstant symplectic two-form where curvature terms are also present. The theory is in the strongly coupled gauge-gravity regime. At low energies, the theory enters in a decoupling limit and it is described by an ordinary N = 8 SYM in the IR phase for any number of M2-branes.     

Measurement of width and shift of rare gas lines emitted from a stock-tube plasma

In a diaphragm shock-tube, Ar, Kr and Xe plasmas were generated with equilibrium temperatures of 8,000 to 12,000 K. The electron densities were measured with a two-wavelength interferometer and varied from 4×10¹⁶ to 1.4×10¹⁷ cm^-3. Emission profiles of spectral lines were recorded with a polychromator setup in 1 μs intervals using a fast data acquisition system. Width w and shift d turned out to be proportional to electron density N_e for the observed lines. Stark broadening parameters w/N_e and d/N_e are presented for 3 Ar(I), 4 Kr(I) and 5 Xe(I) lines in the visible region of the spectrum.     

N = 3 and N = 1 supersymmetry in a new class of solutions for d = 11 supergravity

We present a new class of compactifying solutions for d = 11 supergravity. The internal 7-spaces are described by coset manifolds N^pqr of the form SU(3) × U(1)/U(1) × U(1). The three integers p, q, r characterize the embedding of the stability subgroup U(1) × U(1) in SU(3) × U(1).Their supersymmetry content is quite remarkable. For a particular choice of p, q, r the isometry of N^pqr is SU(3) × SU(2): in this case we find that N = 3 supersymmetry survives. For all the other values of p, q, r, supersymmetry is broken to N = 1, and the isometry group is SU(3) × U(1).We also find a class of solutions with internal photon curl F_αβγδ ≠ 0, breaking all supersymmetries.     

Gauge dependence of the effective action in multidimensional supergravities

The problem of gauge dependence of the effective action in multidimensional supergravities (SG) is investigated. As an example d=5 SGs are considered. The convenient gauge-dependent effective action (EA) and gauge-invariant Vilkovisky-De Witt EA in d=5, N=2, 4, 6, 8 SGs on the background R₄×S₁ with accuracy to linear curvature terms are obtained. The convenient three-gauge-parameter-dependent EA in d=5, N=2 gauged SG on the background R₄×S₁ is calculated. The Vilkovisky-De Witt EA in d=5 SGs on the background R₄×S₁ at non-zero temperature is also obtained.     

Dark-current relaxation in EuGa2S4 single crystals

The results of the investigation of dark-current relaxation in EuGa₂S₄ single crystals are reported. The depth and concentration of the traps are found to be E_t = 0.79 eV and N_t = 1.64 × 10¹⁴ cm^?3, respectively.The charge accumulation region (d_c = 3.3 × 10^?5 cm) and contact capacitance (C_c = 1.23 × 10^?10 F) are also estimated.     

Neutron study of a displacive phase transition in N-nitrodimethylamine (DMN): High and low frequency vibrational modes; high pressure effect on the transition temperature; principal compressibilities

N-Nitrodimethylamine is known to undergo a displacive structural phase transition at T_t～107 K, (atmospheric pressure) associated with a soft-mode observed in the low temperature phase Raman spectrum.The soft-model has already been assigned to a lattice vibration although crystallographic observations of the symmetry breaking distortion suggest that a coupling with an internal vibration should not be ruled out. To clarify this point neutron inelastic spectra have been recorded. They lead to a better assignment of both the high and low frequency vibrations and to the conclusion that no softening of an intramolecular mode is visible.High pressure (up to 3.5 Kbars) neutron scattering experiments are also described. They give both the directions and magnitudes (k₁=0.33× 10^?2, k_b=1.17 × 10^?2, k₃ = 0.12× 10^?2Kbar^?1) of the isothermal principal compressibilities of DMN and the dependence of T_t on pressure ((dT_t/dP)_P=0 ～ + 4.3 Kbar^?1). Spectroscopic and crystallographic data now available on DMN allow us to discuss the mechanism of the transition. An extension of Samara's rule to molecular crystals is attempted     

Superunification from eleven dimensions

We show how N = 8 supersymmetry can break spontaneously to N = 1 at the Planck scale via a Kaluza-Klein compactification of d = 11 supergravity on the squashed seven-sphere. Features unique to Kaluza-Klein supergravity are (i) the massless gravitino of the N = 1 phase comes from a massiveN = 8 supermultiplet, (ii) the scalars developing nonzero VEVs also belong to massive N = 8 supermultiplets, (iii) parity remains unbroken when N = 8 breaks to N = 1.Next we ask whether the resulting N = 1 theory can provide a realistic SU(3) × SU(2) × U(1) unification and speculate that it might if some of the gauge bosons and fermions are composite as in the EGMZ model. In contrast to their model, however, we avoid unwanted helicities and problems with their non-compact E₇. Moreover, we suggest a scheme in which the electroweak SU(2) × U(1) is a subgroup of the d = 11 general coordinate group but that the strong SU(3) is a subgroup of the d = 11 local Lorentz group and are not, therefore, to be combined into a GUT. The special properties of the seven-sphere also suggest a possible solution of the cosmological constant problem involving fermion condensates.     

Supergravity,the seven-sphere,and spontaneous symmetry breaking

N = 1 supergravity in d = 11 dimensions spontaneously compactifies on S⁷ to an N = 8 supergravity in d = 4 with a local SO(8) × SO(8) invariance, probably enlargeable to SO(8) × SU(8). Apart from group manifolds, S⁷ is the only compact manifold to admit an absolute parallelism. This permits (a) a “squashing” of S⁷ which gives expectation values to the scalar fields and (b) a parallelizing “torsion” which gives expectation values to the pseudoscalars. This correspondence between extrema of the d = 4 effective potential and solutions of the d = 11 field equations provides a Kaluza-Klein origin for the spontaneous breakdown of gauge symmetries, discrete symmetries, and supersymmetries. It also puts a new perspective on the puzzle of the cosmological constant.     

Theoretical modelling of XBn T2SLs InAs/InAsSb/B-AlAsSb mid-wave detector operating below thermoelectrical cooling

The paper reports on the barrier mid-wave infrared InAs/InAsSb (x_Sb = 0.4) type-II superlattice detector operating below thermoelectrical cooling. AlAsSb with Sb composition, x_Sb = 0.97; barrier doping, N_D < 2×10¹⁶ cm^?3 leading to valence band offset below 100 meV in relation to the active layer doping, N_D = 5×10¹⁵ cm^?3 was proved to be proper material not introducing extra barrier in valence band in the analyzed temperature range in XBn architectures. The detectivity of the simulated structure was assessed at the level of ～ 10¹¹ Jones at T ～ 100 K assuming absorber thickness, d = 3 μm. The detector’s architecture for high frequency response operation, τ_s = 420 ps (T ～ 77 K) was presented with a reduced active layer of d = 1 μm.     

Time constants of radiative transitions from the 5<Emphasis Type="Italic">d</Emphasis>[3/2]<Subscript>1</Subscript> level of a xenon atom

Integral yields of spontaneous emission at wavelengths of 1.73, 2.03, and 2.65 μm have been measured upon excitation of pure xenon by a pulsed electron beam. These yields have been analyzed and experimental data have been obtained on time constants of radiative transitions 5d[3/2]₁ → 6p[5/2]₂, 5d[3/2]₁ → 6p[3/2]₁, and 5d[3/2]₁ → 6p[1/2]₀ of XeI, which appeared to be equal to (2300 ± 400) × 10^?9, (300 ± 40) × 10^?9, and (1300 ± 200) × 10^?9 s, respectively. It is shown that the experimental data are in a qualitative agreement with the results of computational and theoretical investigations. The results of averaging the experimental and calculated data are proposed for use as recommended values of the corresponding constants.     

Infrared plasma reflectivity minimum in heavily doped n-Si

This paper presents a numerical analysis of infrared (IR) plasma reflectivity minimum in ultra heavily doped (UHD) n-Si (impurity concentration N up to 6 × 10²¹cm⁻³) by using a self-consistent method (SCM) and a complex physical model. The necessity of taking into account the dependence of effective mass on impurity concentration is shown. The scattering on defects (N_def = 5 × 10¹⁷ cm⁻³) and dislocation (N_dis = 5 × 10¹¹ cm⁻²) is included. The approximate relation for the wavelength λ_m(N) of the reflectivity minimum is given. The results obtained are compared with the experimental results for n-Si and satisfactory agreement is found.     

Polarization of protons in C12(d,p)C13 reaction

The angular distributions of the polarization of protons from C¹²(d,p)C¹³(g.s) reaction were measured at 200 keV intervals for deuteron energies from 1.40 to 2.40 MeV. Elastic scattering on C¹² at 45 ° (lab) was used to analyze the polarization. Positive sign of the polarization corresponds to the vector productK _d ×K _p . The maximum polarization observed is about 30%. The results are not similar to those obtained from the mirror reaction C¹²(d,n)N¹³ in the same deuteron energy range.