Critical behavior of the aqueous electrolytic system 3-methylpyridine+D2O+NaBr

The system 3-methylpyridine(3MP)+water(H2O)+NaBr has been the subject of an intense scientific debate since the work of Jacob [Phys. Rev. E. 58, 2188 (1988)] and Anisimov [Phys. Rev. Lett. 85, 2336 (2000)]. The crossover critical behavior of this system seemed to show remarkable sensitivity to the weight fraction (X) of the ionic impurity NaBr. In the range X <= 0.10 the system displayed Ising behavior and a pronounced crossover to mean-field behavior in the range 0.10 <= X <= 0.16. A complete mean-field behavior was observed at X=0.17, a result that was later attributed to the existence of long-living nonequilibrium states in this system [Kostko , Phys. Rev. E. 70, 026118 (2004)]. In this paper, we report the near-critical behavior of osmotic susceptibility in the isotopically related ternary system, 3MP+heavy water(D2O)+NaBr. Detailed light-scattering experiments performed at exactly the same NaBr concentrations as investigated by Jacob reveal that the system 3MP+D2O+NaBr shows a simple Ising-type critical behavior with gamma similar or equal to 1.24 and nu similar or equal to 0.63 over the entire NaBr concentration range 0 <= X <= 0.1900. The crossover behavior is predominantly nonmonotonic and is completed well outside the critical domain. An analysis in terms of the effective susceptibility exponent (gamma(eff)) reveals that the crossover behavior is nonmonotonic for 0 <= X <= 0.1793 and tends to become monotonic for X > 0.1793. The correlation length amplitude xi(o), has a value of similar or equal to 2 A for 0.0250 <= X <= 0.1900, whereas for X=0, xi(o)similar or equal to 3.179 A. Since isotopic H -> D substitution is not expected to change the critical behavior of the system, our results support the recent results obtained by Kostko [Phys. Rev. E. 70, 026118 (2004)] that 3MP+H2O+NaBr exhibits universal Ising-type critical behavior typical for other aqueous solutions.

The Tevatron Higgs exclusion limits and theoretical uncertainties: A critical appraisal

We examine the exclusion limits set by the CDF and D0 experiments on the Standard Model Higgs boson mass from their searches at the Tevatron in the light of large theoretical uncertainties on the signal and background cross sections. We show that when these uncertainties are consistently taken into account, the sensitivity of the experiments becomes significantly lower and the currently excluded mass range M-H = 158-175 GeV could be entirely reopened. The necessary luminosity required to recover the current sensitivity is found to be a factor of two higher than the present one. (C) 2011 Elsevier B.V. All rights reserved.

Partial Flow Sensitivity

Compiler optimizations need precise and scalable analyses to discover program properties. We propose a partially flow-sensitive framework that tries to draw on the scalability of flow-insensitive algorithms while providing more precision at some specific program points. Provided with a set of critical nodes — basic blocks at which more precise information is desired — our partially flow-sensitive algorithm computes a reduced control-flow graph by collapsing some sets of non-critical nodes. The algorithm is more scalable than a fully flow-sensitive one as, assuming that the number of critical nodes is small, the reduced flow-graph is much smaller than the original flow-graph. At the same time, a much more precise information is obtained at certain program points than would had been obtained from a flow-insensitive algorithm.

Sensitivity of nucleation phenomena on range of interaction potential

Theoretical and computational investigations of nucleation have been plagued by the sensitivity of the phase diagram to the range of the interaction potential. As the surface tension depends strongly on the range of interaction potential and as the classical nucleation theory (CNT) predicts the free energy barrier to be directly proportional to the cube of the surface tension, one expects a strong sensitivity of nucleation barrier to the range of the potential; however, CNT leaves many aspects unexplored. We find for gas-liquid nucleation in Lennard-Jones system that on increasing the range of interaction the kinetic spinodal (KS) (where the mechanism of nucleation changes from activated to barrierless) shifts deeper into the metastable region. Therefore the system remains metastable for larger value of supersaturation and this allows one to explore the high metastable region without encountering the KS. On increasing the range of interaction, both the critical cluster size and pre-critical minima in the free energy surface of kth largest cluster, at respective kinetic spinodals, shift towards smaller cluster size. In order to separate surface tension contribution to the increase in the barrier from other non-trivial factors, we introduce a new scaling form for surface tension and use it to capture both the temperature and the interaction range dependence of surface tension. Surprisingly, we find only a weak non-trivial contribution from other factors to the free energy barrier of nucleation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3685835]

A critical examination of the paradox of strength and ductility in ultrafine-grained metals

The paradox of strength and ductility is now well established and denotes the difficulty of simultaneously achieving both high strength and high ductility. This paradox was critically examined using a cast Al-7% Si alloy processed by high-pressure torsion (HPT) for up to 10 turns at a temperature of either 298 or 445 K. This processing reduces the grain size to a minimum of similar to 0.4 mu m and also decreases the average size of the Si particles. The results show that samples processed to high numbers of HPT turns exhibit both high strength and high ductility when tested at relatively low strain rates and the strain rate sensitivity under these conditions is similar to 0.14 which suggests that flow occurs by some limited grain boundary sliding and crystallographic slip. The results are also displayed on the traditional diagram for strength and ductility and they demonstrate the potential for achieving high strength and high ductility by increasing the number of turns in HPT.

Notch sensitivity in nanoscale metallic glass specimens: Insights from continuum simulations

Recent experiments have shown that nano-sized metallic glass (MG) specimens subjected to tensile loading exhibit increased ductility and work hardening. Failure occurs by necking as opposed to shear banding which is seen in bulk samples. Also, the necking is generally observed at shallow notches present on the specimen surface. In this work, continuum finite element analysis of tensile loading of nano-sized notched MG specimens is conducted using a thermodynamically consistent non-local plasticity model to clearly understand the deformation behavior from a mechanics perspective. It is found that plastic zone size in front of the notch attains a saturation level at the stage when a dominant shear band forms extending across the specimen. This size scales with an intrinsic material length associated with the interaction stress between flow defects. A transition in deformation behavior from quasi-brittle to ductile becomes possible when this critical plastic zone size is larger than the uncracked ligament length. These observations corroborate with atomistic simulations and experimental results. (C) 2015 Elsevier Ltd. All rights reserved.

Temperature dependent vibrational lifetimes in supercritical fluids near the critical point

Vibrational relaxation measurements on the CO asymmetric stretching mode (similar to 1980 cm(-1)) of tungsten hexacarbonyl (W(CO)(6)) as a function of temperature at constant density in several supercritical solvents in the vicinity of the critical point are presented. In supercritical ethane, at the critical density, there is a region above the critical temperature (Tc) in which the lifetime increases with increasing temperature. When the temperature is raised sufficiently (similar to T-c + 70 degrees C), the lifetime decreases with further increase in temperature. A recent hydrodynamic/thermodynamic theory of vibrational relaxation in supercritical fluids reproduces this behavior semiquantitatively. The temperature dependent data for fixed densities somewhat above and below the critical density is in better agreement with the theory. In fluoroform solvent at the critical density, the vibrational lifetime also initially increases with increasing temperature. However, in supercritical CO2 at the critical density, the temperature dependent vibrational lifetime decreases approximately linearly with temperature beginning almost immediately above T-c. The theory does not reproduce this behavior. A comparison between the absolute lifetimes in the three solvents and the temperature trends is made.

Crossover from Ising to mean-field critical behavior in an aqueous electrolyte solution

The near-critical behavior of the susceptibility deduced from light-scattering measurements in a ternary liquid mixture of 3-methylpyridine, water, and sodium bromide has been determined. The measurements have been performed in the one-phase region near the lower consolute points of samples with different concentrations of sodium bromide. A crossover from Ising asymptotic behavior to mean-field behavior has been observed. As the concentration of sodium bromide increases, the crossover becomes more pronounced, and the crossover temperature shifts closer to the critical temperature. The data are well described by a model that contains two independent crossover parameters. The crossover of the susceptibility critical exponent γ from its Ising value γ=1.24 to the mean-field value γ=1 is sharp and nonmonotonic. We conclude that there exists an additional length scale in the system due to the presence of the electrolyte which competes with the correlation length of the concentration fluctuations. An analogy with crossover phenomena in polymer solutions and a possible connection with multicritical phenomena is discussed.

Enhancement of nonvolatile polarization and pyroelectric sensitivity in lithium tantalate (LT)/poly(vinylidene fluoride) (PVDF) nanocomposite

We report the ferroelectric and pyroelectric properties of the composite films of lithium tantalate (LT) nanoparticle in poly(vinylidene fluoride) PVDF matrix at different volume fractions of LT (f(LT) = 0.047, 0.09 and 0.17). For an applied electric field of 150 kV cm(-1) the nonvolatile polarization of the composite was observed to increase from 0.014 mu C cm(-2) at f(LT) = 0 to 2.06 mu C cm(-2) at f(LT) = 0.17. For f(LT) = 0.17, the composite films exhibit a saturated ferroelectric hysteresis loop with a remanent polarization (2P(r) = 4.13 mu C cm(-2)). Compared with pure poled PVDF the composite films also showed a factor of about five enhancement in the pyroelectric coefficient at f(LT) = 0.17. When used in energy detection mode the pyroelectric voltage sensitivity of the composite films was found to increase from 3.93 to 18.5 VJ(-1) with an increase in f(LT) from 0.0 to 0.17.

Enhanced sensitivity in detection of Kerr rotation by double modulation and time averaging based on Allan variance

Experiments in spintronics necessarily involve the detection of spin polarization. The sensitivity of this detection becomes an important factor to consider when extending the low temperature studies on semiconductor spintronic devices to room temperature, where the spin signal is weaker. In pump-probe experiments, which optically inject and detect spins, the sensitivity is often improved by using a photoelastic modulator (PEM) for lock-in detection. However, spurious signals can arise if diode lasers are used as optical sources in such experiments, along with a PEM. In this work, we eliminated the spurious electromagnetic coupling of the PEM onto the probe diode laser, by the double modulation technique. We also developed a test for spurious modulated interference in the pump-probe signal, due to the PEM. Besides, an order of magnitude enhancement in the sensitivity of detection of spin polarization by Kerr rotation, to 3x10(-8) rad was obtained by using the concept of Allan variance to optimally average the time series data over a period of 416 s. With these improvements, we are able to experimentally demonstrate at room temperature, photoinduced steady-state spin polarization in bulk GaAs. Thus, the advances reported here facilitate the use of diode lasers with a PEM for sensitive pump-probe experiments. They also constitute a step toward detection of spin-injection in Si at room temperature.

On the sensitivity of elastic waves due to structural damages:Time-frequency based indexing method

Time-frequency analysis of various simulated and experimental signals due to elastic wave scattering from damage are performed using wavelet transform (WT) and Hilbert-Huang transform (HHT) and their performances are compared in context of quantifying the damages. Spectral finite element method is employed for numerical simulation of wave scattering. An analytical study is carried out to study the effects of higher-order damage parameters on the reflected wave from a damage. Based on this study, error bounds are computed for the signals in the spectral and also on the time-frequency domains. It is shown how such an error bound can provide all estimate of error in the modelling of wave propagation in structure with damage. Measures of damage based on WT and HHT is derived to quantify the damage information hidden in the signal. The aim of this study is to obtain detailed insights into the problem of (1) identifying localised damages (2) dispersion of multifrequency non-stationary signals after they interact with various types of damage and (3) quantifying the damages. Sensitivity analysis of the signal due to scattered wave based on time-frequency representation helps to correlate the variation of damage index measures with respect to the damage parameters like damage size and material degradation factors.

Inverse Sensitivity Analysis of Singular Solutions of FRF matrix in Structural System Identification

The problem of structural damage detection based on measured frequency response functions of the structure in its damaged and undamaged states is considered. A novel procedure that is based on inverse sensitivity of the singular solutions of the system FRF matrix is proposed. The treatment of possibly ill-conditioned set of equations via regularization scheme and questions on spatial incompleteness of measurements are considered. The application of the method in dealing with systems with repeated natural frequencies and (or) packets of closely spaced modes is demonstrated. The relationship between the proposed method and the methods based on inverse sensitivity of eigensolutions and frequency response functions is noted. The numerical examples on a 5-degree of freedom system, a one span free-free beam and a spatially periodic multi-span beam demonstrate the efficacy of the proposed method and its superior performance vis-a-vis methods based on inverse eigensensitivity.

Dynamic strain ageing in Ni-base superalloy 720Li

An experimental investigation into the dynamic strain ageing (DSA) of a wrought Ni-base superalloy 720Li was conducted. Characteristics of jerky, flow have been studied at intermediate temperatures of 350, 400 and 450 degrees C at strain-rates between 10(-3) and 10(-5) s(-1). Serrations of Type C are predominant within the temperature/strain-rate range explored. The major characteristics of the serrations-i.e. (a) critical plastic strain for onset of serrations, epsilon(c); (b) average stress decrement, Delta sigma(avg); and (c) strain increment between serrations. Delta epsilon(BS)-have been examined at selected temperatures and strain-rates. Negative strain-rate sensitivity was observed in the DSA regime. However. temperature did not influence tensile properties such as yield strength, ultimate strength. elongation, reduction in area, and work hardening rate or fracture features in DSA regime. Analysis of the results Suggests that locking of the mobile dislocations by substitutional alloying elements is responsible for the DSA in alloy 720Li.

Critical Reappraisal Of Plasticity Index Of Soils

A fundamental approach, based on Gouy-Chapman theory of double layer, has been provided to micromechanistically interpret the plasticity index of soils and their relationship with liquid limit. The relationships between plasticity index and liquid limit, developed earlier, through statistical approaches and critical state concepts, have been reexamined. The statistical analysis of extensive published data has resulted in the relationship, IP = 0.74 (wL - 8). On comparison with other relationships in vogue the proposed equation has been found to give better agreement. From the reappraisal of critical state approaches consistent with the micromechanistic interpretation, the possible range of parameters have been computed and compared with those obtained by statistical means to enhance the credibility of the proposed relationship.

Critical Cation Balance In B-]Z Transition - Role Of Li+

The sodium salt of poly(dG-dC) is known to exhibit a B + Z transition in the presence of various cations and 60% alcohol. We here show that the lithium salt of poly(dG-dC) does not undergo B 4 Z transition in the presence of 60% alcohol since Li’ with its large hydration shell cannot stabilize the Z-form. On the other hand, high concentrations of Mg2* or micromolar concentrations of the cobalt hexamine complex which are known to stabilize the Z-form can compete with Li+ for charge neutraIization and hence bring about a B--t Z transition in the same polymer. From the model building studies the mode of action of the cobalt-hexamine complex in stabilizing the Z-form is postulated.