Cosmological Density Perturbations from a Quantum Gravitational Model of Inflation

We derive the implications for anisotropies in the cosmic microwave background following from a model of inflation in which a bare cosmological constant is gradually screened by an infrared process in quantum gravity. The model predicts that the amplitude of scalar perturbations is A_S = (2.0 ± 0.2) · 10^—5, that the tensor-to-scalar ratio is r ≈︂ 1.7 · 10^—3, and that the scalar and tensor spectral indices are n ≈︂ 0.97 and n_T ≈︂ —2.8 · 10^—4, respectively. By comparing the model's power spectrum with the COBE 4-year RMS quadrupole, the mass scale of inflation is determined to be M = (0.72 ± 0.03) · 10¹⁶ GeV. At this scale the model produces about 10⁸ e-foldings of inflation, so another prediction is Ω = 1. PACS numbers: 04.60.-m, 98.80.Cq     

Temporal correlations and persistence in the kinetic Ising model: the role of temperature

We study the statistical properties of the sum S _t = dt'σ _t', that is the difference of time spent positive or negative by the spin σ _t, located at a given site of a D-dimensional Ising model evolving under Glauber dynamics from a random initial configuration. We investigate the distribution of S_t and the first-passage statistics (persistence) of this quantity. We discuss successively the three regimes of high temperature ( T > T _c), criticality ( T = T _c), and low temperature ( T < T _c). We discuss in particular the question of the temperature dependence of the persistence exponent , as well as that of the spectrum of exponents (x), in the low temperature phase. The probability that the temporal mean S _t/t was always larger than the equilibrium magnetization is found to decay as t ^{- - ?}. This yields a numerical determination of the persistence exponent in the whole low temperature phase, in two dimensions, and above the roughening transition, in the low-temperature phase of the three-dimensional Ising model. Received 4 December 2000     

Specific features of the BCS-BEC crossover and thermodynamics in the 2D resonant Fermi gas with p-wave pairing

The 2D resonant Fermi gas with p-wave pairing is considered n the BCS-BEC regime. For the 2D analog of the superfluid A1 phase, the Leggett equations [1] for superfluid gap Δ and chemical potential μ are analytically solved at T = 0 and the spectrum of the collective excitations (acoustic waves) is analyzed in the BCS regime (μ > 0), where the triplet Cooper pairs emerge; in the BEC regime (μ < 0), where the triplet local pairs (molecules) emerge; and in the transition region, where μ → 0. At low temperatures, the contribution of the superfluid Fermi quasiparticles of the resonant gas to heat capacity C _v and the density of normal component ρ_n is also calculated. At μ = 0, the fermionic contribution to ρ_n and C _v are represented as power functions of temperature (ρ_n ～ T ³ and C _v ～ T ²). However, similar power contributions to these quantities are related to phonons (bosonic acoustic oscillations). The possibility of the experimental observation of the nontrivial topological term with the charge Q = 1 in the BCS regime of the 2D A1 phase is briefly discussed.     

Electronic states of the c is - and trans - H3ONO molecules: a CASPT2 study

The CASPT2 calculations for the S₀, T₁, S₁, T₂, and S₂ states of the cis- and trans-CH₃ONO molecules predict the energy levels and geometries of the cis- and trans-isomers in the different states. The CASPT2 adiabatic (T ₀) and vertical (T _v) excitation energies are in good agreement with available experimental data (for the S₁ cis- and trans-isomers). The CH₃O-NO dissociation potential energy curves were calculated at the CASPT2//CASSCF level, and the CASPT2 calculations were performed for the transition states along the T₁, S₁, and T₂ dissociation paths. For the repulsive S₂ state the calculations predict the T _v values larger than 5.4 eV and dissociation products of CH₃O (1²A″) + NO (X²Π).     

Deformation behavior of PZN–6%PT single crystal during nanoindentation

The deformation behavior of [001]^T- and [011]^T-cut single crystal solid solution of Pb(Zn_1/3Nb_2/3)O₃–6% PbTiO₃ (PZN–6%PT) in both unpoled and poled states has been investigated by nanoindentation. Nanoindentation experiments reveal that material pile-up and local damage around the indentation impressions are observed at ultra-low loads. These pile-ups and local damage cause a pop-in event (i.e. a sudden increase in displacement at an approximately constant load) in the nanoindentation load–displacement curve (P–h curve). Detailed studies of the relationships between indentation load (P), displacement (h) and harmonic contact stiffness (S) suggest that there is a surface layer, possibly due to crystal fabrication processes, which possesses different mechanical properties from the interior. The thickness of this surface layer is estimated to be approximately 300 nm. Furthermore, it is found that [011]^T-cut crystal is stiffer than [001]^T-cut crystal. On the other hand, both [001]^T- and [011]^T-cut crystals in unpoled state possess lower contact stiffness than poled crystals. This finding suggests that poling improved the mechanical property of the crystal. In summary, poled [001]^T-cut crystals have an elastic modulus of (107 ± 6) GPa and a hardness of (5.1 ± 0.4) GPa. In contrast, the modulus for [011]^T-cut crystals is not constant but increases with indentation depth.     

Electrical conductivity of N-methyl phenazinium tetracyanoquinodimethanide, (NMP) (TCNQ)

New conductivity, σ, vs. temperature, T, measurements on numerous (NMP)-(TCNQ) samples, as well as older data, can all be fit, in the range 65K<T<400K, by the simple expression σ = σ_oT^-αexp(-900/T). σ_o and α(3<α<4) are sample-dependent constants. We interpret this as representing an activated carrier concentration and strongly T-dependent mobility, μ. We can account for the magnitude and T-dependence of μ by a model involving interaction with the molecular vibrations through the known electron-phonon coupling constants of TCNQ^-.     

Plastic-strain localization in barium fluoride single crystals at elevated temperatures

The strain distribution is studied in BaF₂ crystals subjected to compression tests along [110] and [112] at a constant strain rate in the temperature range T = (0.22–0.77)T _m. At T > 0.5T _m, the plastic strain in deformed samples is found to be strongly localized in narrow bands, where the shear strain reaches several hundred percent. The degree of localization increases with temperature. Localized-shear microbands are shown to be oriented along {001}〈110〉 slip systems. The phenomenon of serrated yielding is detected, and stress jumps (serrations) are established to correlate with the formation of shear zones.     

Diffusion Control of Homogeneous Crystallization in Nanoconfined Domains of Block Copolymers

Abstract

Confined crystallization in a poly(oxyethylene)‐b‐poly(oxybutylene)/poly(oxybutylene) blend (E₁₁₅B₁₀₃/B₂₈, φ_E = 0.14) with bcc morphology and in a polystyrene‐b‐poly (oxyethylene)‐b‐polystyrene (S‐E‐S) triblock copolymer (S₄₀E₁₃₆S₄₀, φ_E = 0.407) with lamellar morphology was studied using differential scanning calorimetry (DSC). Two types of confined crystallization with different characteristic Avrami exponents were identified in both systems. At higher crystallization temperature (T _c), the Avrami exponent is 1.0 and the overall crystallization rate is controlled by the homogeneous nucleation rate. At lower T _c, the Avrami exponent is 0.5, which is attributed to diffusion‐controlled confined crystallization. This shows that diffusion has a great influence on the overall crystallization rate when chain mobility is reduced, which can be caused either by lower T _c or by constrained microstructure.     

Three‐photon absorption properties of a novel symmetrical Carbazole derivative having terminal 1,10‐phenanthroline rings via carbon–nitrogen (C = N) double bond

Three‐photon absorption (3PA) properties of symmetric‐type carbazole derivatives show great potential for application in light‐activated therapy and optical limiting. A novel symmetrical carbazole derivative (abbreviated as POCP) with end‐groups of 1,10‐phenanthroline rings as the donor moieties, chained via carbon–nitrogen (C = N) double bond, has been synthetized and its three photon absorption properties has been also determined by using a Q‐switched Nd: YAG laser pumped with 30 ps pulses at 1064 nm in dimethylformamide. The measurement of 3PA cross‐section of this compound is performed by open aperture Z‐scan and σ_3PA is 481 × 10^–78 cm⁶ ? s²/photon² for the transition S₀ → S₁. The influence of the molecular structure of this compound on three‐photon absorption cross‐sections is discussed micromechanically by Austin model 1 and Zerner's Intermediate Neglect of Differential Overlap/S method. Copyright © 2012 John Wiley & Sons, Ltd.     

DC Townsend Discharge in Nitrogen: Temperature‐Dependent Phenomena

Low‐current Townsend discharge in nitrogen has been studied in the temperature range of T = 100–300 K in a semiconductor‐gas‐discharge structure. It was found that the sustaining voltage U_S increases with time when a current is passed through the structure at low T. This effect was not observed at room temperature. A hypothesis is put forward that a film of a neutral phase of nitrogen is formed on the electrodes under cryogenic discharge conditions. The presence of the condensed thin‐film phase leads to a decrease in the secondary electron emission from the electrode and to a corresponding increase in U_S. A possible mechanism of the phenomenon is associated with the formation of large neutral aggregates in the form of [N⁺₂(N₂)_n]^– in the gas discharge volume. The condensation of these aggregates seems to yield a phase that is comparatively stable at cryogenic temperatures (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The synthesis and photolysis mechanisms of 8‐nitroquinoline‐based photolabile caging groups for carboxylic acid

Photolabile protecting groups have been extensively studied and applied for protection of small biological molecules, which make it convenient to detect the biological processes of the caged compounds. In this study, a series of 8‐nitroquinoline‐based photolabile caging groups for carboxylic acid were synthesized with improved photolysis efficiency. Among them, 6‐bromo‐8‐nitro‐1, 2‐dihydroquinolinyl chromophore was proven the best derivative on account of its longest absorption wavelength (345 nm), highest caging ability, and quantum yield (Φ = 0.003). Moreover, density functional theory calculations were performed in order to study the photolysis mechanisms. Theoretical calculations revealed that the reaction was kinetically inert under general mild condition with the high barrier height of 34.3 kcal/mol at carbonyl migration step, while under the photolysis condition, because of the large energy gap (64.5 kcal/mol) between S₀ and S₁ states, the reaction should be accessible in the triplet ground state (T₁) through successive excitation of S₀ → S₁ states, subsequent intersystem crossing of S₁ → T₁ states, and finally returned to the stable S₀ state for product via potential energy surface crossing between T₁ and S₀ states. Copyright © 2014 John Wiley & Sons, Ltd.     

Representations of the coordinate ring of GL q (3)

It is shown that finite-dimensional irreducible representations of the quantum matrix algebraM _q (3) (the coordinate ring of GL _q (3)) exist only whenq is a root of unity (q ^p = 1). The dimensions of these representations can only be one of the following values:p ³,p ³/2,p ³/4, orp ³/8. The topology of the space of states ranges between two extremes, from a three-dimensional torusS ¹ ×S ¹ ×S ¹ (which may be thought of as a generalization of the cyclic representation) to a three-dimensional cube [0, 1] × [0, 1] × [0, 1].     

Dynamic Mechanical Behavior of Ordered Off-Stoichiometric Polyurethane Systems at the Gel Point Threshold

Dynamic mechanical and thermal behavior of ordered off-stoichiometric polyurethane (PU) systems, before and after the gel point, based on the mesogenic diol 6,6′;-[ethylenebis(1,4-phenyleneoxy)]dihexan-1-ol (D),2(4)-methyl-1,3-phenylene diisocyanate (DI), and poly(oxypropylene)triol (T) were studied. Polymer samples were prepared at various initial molar ratios of the reactive groups, r = [OH]_T/[NCO]_DI/[OH]_D, ranging from 1/10/9 to 5/10/9 (the ratio [NCO]_DI/[OH]_D = 10/9 was constant); the total mole ratio of hydroxy (OH) and isocyanate (NCO) groups, rOH = [OH]/[NCO] = ([OH]_D)/[NCO]_DI,changed from 1 to 1.4. Dynamic mechanical measurements during the curing reaction showed that the power law parameters that characterize the critical gel state (gel strength S and relaxation exponent n) are dependent on the initial composition (the ratio r _OH). The gel-point critical ratio of reactive groups r^c _OH, found during curing in the ordered state of the diol (at low curing temperature), has revealed that the critical gel (CG) structure is determined by a contribution of strong physical interactions as well as chemical junctions and does not correspond to pure chemical gelation (CG structure formed at low temperature exhibits flow at elevated temperatures in the isotropic state). This fact suggests that formation of the mesophase enhances the connectivity of the molecular structure at the gel point. Dynamic mechanical behavior of fully cured chemical networks (r _OH < r _OH ^c ) and un-cross-linked (r _OH > r _OH ^c ) samples (and a CG sample) has also been investigated. Decreasing the r_OH ratio (increasing concentration of chemical cross-links in the systems) inhibits conformational rearrangements required for ordering; at the same time, the intensity of the slow relaxation process in the rubbery region decreases.     

Letter: Spherically Symmetric Metrics with Shear Controlling Expansion

An isotropic spatially inhomogeneous spacetime with the stress tensor satisfying the limiting case of the strong energy condition [T₀₀ + 1/2)T] = 0 in the locally inertial coordinates where the observer's four-velocity is u ^a = ₀ ^a satisfying the constraint u ^a u_a = –1 is studied. Special metrics with accelerating expansions of the inhomogeneous spacetime merely controlled by the shear are presented as an alternative model.     

Metal-insulator transition in perovskite oxides: A low-temperature perspective

A review is presented of recent experimental results of low temperature studies of composition driven metal-insulator transition in perovskite oxides of the ABO₃ class. The evolution of physical properties like conductivity, tunnelling, density of states and magnetoconductivity has been studied at low temperatures (T < 10 K) because composition is varied so that the sample goes from the metallic state to the critical region through a weakly localized region. The results show an interesting interplay of disorder and correlation effects. Special attention has been paid to the critical region which is marked by very low conductivity and dσ/dT>0. In this region the following important observations emerge. (1) It is possible to have a metallic state [σ(T = 0) = σ ₀ ≠ 0] with σ ₀/σ _Mott ? 1 and dσ/dT > 0. (2) At T < 2 K the conductivity follows a power law σ ～T^ν , where the exponent can be related to the finite frequency response of a zero temperature phase transition. (3) The Coulomb interaction plays a major role and evidence from tunnelling experiments suggests that a gap in the density of states at the Fermi level opens up continuously as the critical region is approached from the metallic side. (4) The magnetoconductivity is relatively smaller in the metallic and the weakly localized region (except the hole-doped LaMnO₃ and related systems) but becomes very large at the critical region.     

On mechanical stability of molybdenum

Investigations of the strength properties of materials under different loading conditions are of practical importance in many engineering applications. The knowledge of elastic moduli as a function of strain is required for determination of strength properties. In the present work, we have determined the elastic moduli of molybdenum through first principles study of the energy changes under three different loading conditions namely ‘uni-axial tensile deformation’ along [0 0 1] direction, ‘uni-axial tensile loading’ along [0 0 1] direction and ‘hydrostatic tensile loading’. The stability conditions for the system are expressed in terms of the elastic moduli and analyzed along the deformation paths corresponding to these three loading modes. The theoretical spall strength (σ_S), tensile strength (σ_T) along [0 0 1] direction and hydrostatic tensile strength (σ_H), are evaluated as a stress at the first onset of the instability for three loading conditions, respectively. The calculated equilibrium volume and elastic moduli are compared with that reported from experimental and other theoretical works.     

Ru(III), Os(VIII), Pd(II) and Pt(IV) catalysed oxidation of glycyl–glycine by sodium N‐chloro‐p‐toluenesulfonamide: comparative mechanistic aspects and kinetic modelling

The Ru(III)/Os(VIII)/Pd(II)/Pt(IV)‐catalysed kinetics of oxidation of glycyl–glycine (Gly‐Gly) by sodium N‐chloro‐p‐ toluenesulfonamide (chloramine‐T; CAT) in NaOH medium has been investigated at 308 K. The stoichiometry and oxidation products in each case were found to be the same but their kinetic patterns observed are different. Under comparable experimental conditions, the oxidation‐kinetics and mechanistic behaviour of Gly‐Gly with CAT in NaOH medium is different for each catalyst and obeys the underlying rate laws:

• Rate = k [CAT]_t [Gly‐Gly]⁰ [Ru(III)][OH^?]^x
• Rate = k [CAT]_t[Gly‐Gly]^x [Os(VIII)]^y[OH^?]^z
• Rate = k [CAT]_t[Gly‐Gly]^x [Pd(II)][OH^?]^y
• Rate = k [CAT]_t[Gly‐Gly]⁰ [Pt(IV)]^x[OH^?]^y

Here, and x, y, z < 1 in all the cases. The anion of CAT, CH₃C₆H₄SO₂NCl^?, has been postulated as the common reactive oxidising species in all the cases. Under comparable experimental conditions, the relative ability of these catalysts towards oxidation of Gly‐Gly by CAT are in the order: Os(VIII) > Ru(III) > Pt(IV) > Pd(II). This trend may be attributed to the different d‐electronic configuration of the catalysts. Further, the rates of oxidation of all the four catalysed reactions have been compared with uncatalysed reactions, under identical experimental conditions. It was found that the catalysed reaction rates are 7‐ to 24‐fold faster. Based on the observed experimental results, detailed mechanistic interpretation and the related kinetic modelling have been worked out for each catalyst. Copyright © 2008 John Wiley & Sons, Ltd.     

Cubic-tetragonal phase transition in SrTiO3 revisited: Landau theory and transition mechanism

Abstract

Existing experimental data for the antiferroelastic phase transition in strontium titanate are reviewed and analysed using a Landau free energy of the form ΔG = 1/2Aθs (cothθs/ Tc-colb.θ/T)Q² + 1/4BQ ⁴ + 1/6CQ ⁶, with A = 0·6472 J K^?1mol^?1, B = 29·12 Jmol^?1, C = 39·27 Jmol, T _c= 105·6 K, θ _S = 60·8 K. The temperature dependence of the critical exponent is found to be due to the delicate balance between the Q ⁴ and Q ⁶ terms in the free energy expansion, and the saturation of the order parameter at low temperatures.

The spontaneous strains observed in this phase transition are not consistent with simple rotation of the TiO₆ octahedra around [001], An alternative model is proposed, where these octahedra expand in order to preserve the volume of the twelve-fold co-ordinated Sr site and the spacing between SrO₃ pseudo-closepacked layers.