Structure and properties of some glass-forming liquid alloys

Some physical properties (kinematic viscosity, surface tension and magnetic susceptibility) of some Fe-based metallic melts of easily glass-forming alloys have been measured during heating and subsequent cooling. The results indicate that molten liquid metallic alloys undergo a number of structural transformations ranging from the initial microheterogeneous state formed after melting up to the true solution state. Studies by small angle neutron scattering on a eutectic SnPb melt confirm this conclusion in that two families of different sizes have been seen, one in the range 1 to 2 nm and one of size larger than 100 nm. Both kind of particles have relatively sharp interfaces and the size of the smaller particles is found to depend on temperature. Received 25 February 1999 and Received in final form 28 October 1999     

Comparative study on the photocatalytic mineralization of homologous aliphatic acids and alcohols

The photocatalytic mineralization of methanol, ethanol and 1-propanol is compared with those of their homologous carboxylic acids (formic, acetic and propanoic). The presence of S₂O₈²⁻ ions almost does not affect the alcohols mineralization. But, those of the acids are slowed down. In addition to this, adding H₂O₂ inhibits the alcohols mineralization and those of the acids, but to a lesser extent.FT-IR studies have shown that carboxylates generated from the oxidation of the corresponding alcohols adsorb at different centres from those where carboxylates directly generated from formic, acetic and propanoic acids do.From the obtained results, mineralizations of these compounds have been correlated with their proximity and accessibility to photoactive centres.     

Design and charge injection characteristics of an electrostatic dielectric liquid pulsed atomizer

An automotive fuel injector has been retrofitted with novel electrostatic components in order to improve the primary atomization and dispersion characteristics of the device. A specific design variant is presented and discussed outlining how a conventional fuel injector may be modified to house electrostatic components. With 2 bar gauge injection pressure and an electrical power of 2 mW, the injector can successfully supply intermittently charged fuel, containing spray specific charge levels up to ～1.4 C/m³. Root mean square (RMS) spray specific charge and RMS total current vs. voltage curves are presented as a function of voltage pulse and solenoid valve frequencies for both low and high flow-rate operation. The fuel injector was able to operate in a stable manner at pulse train frequencies up to 20 Hz and the charge injection mechanism was identical to previous steady voltage and pulsed voltage steady flow systems. An optimal synchronization between the high voltage (HV) pulse frequency and solenoid valve frequency has been determined, allowing for the prevention of electrical breakdown events within the inter-electrode gap over a negative voltage ranging from 0 to 4.5 kV.     

Structure of some liquid transition metals using integral equation theory

We present the results of calculations of the structure factorS(q) of some liquid 3d transition metals using the self consistent hybridized mean spherical approximation (HMSA) integral equation. The local pseudopotential used is composed of the empty core model and a part that takes care of s-d mixing through an inverse scattering approach to model the interionic pair potential. The results presented are in very good agreement with experiment for most of the systems investigated near freezing, as well as for the noble metals Cu, Ag and Au, thus, confirming the reliability of the pseudopotential in the present integral equation scheme.     

Numerical analysis and design of patterned electrode liquid crystal microlens array with dielectric slab

The phase profile of hole patterned electrode liquid crystal (LC) microlens array (MLA) was studied by a numerical method. It indicated that the formation of inverse domain and tilt wall in the liquid crystal cell limits the optical performance of the microlens array. The physical mechanism that determines the formation of inverse domain and tilt wall was elucidated by analyzing the phase profile and the liquid crystal director distribution. According to our numerical results, a new configuration for hole patterned electrode liquid crystal microlens array was proposed by introducing a dielectric slab between the patterned electrode and the liquid crystal. The physical parameters that influence the optical performance of this new configuration LC MLA were studied, which provide fundamental information for the design. The results indicate that the phase profile and focusing power of the new configuration is greatly improved.     

Investigation of (n,t) reactions at 14.6 MeV and an analysis of some systematic trends in the cross-section data

Cross sections for (n, t) reactions at 14.6 ±0.4 MeV on ⁴⁶Ti, ⁵⁶Fe, ^58,60Ni, ⁸⁸Sr, ⁹⁰Zr, ¹⁴¹Pr and ²⁰⁴Pb have been measured by the activation technique in combination with specific radiochemical methods. Some systematic trends in the cross-section data have been observed. An analysis of the gross trend and isotope effect is given.     

Statistical analysis of floating-car data: an empirical study

We present the results of statistical analysis of the empirical floating-car data. Our investigations are based on analyzing the time series of four basic quantities namely velocity, velocity difference, spatial gap and the acceleration associated to some instrumented cars. We obtain the statistical characteristics, including the mean, variance and relative variance of these time series by taking direct time averages. We also try to identify the moving phases of the instrumented vehicle according to the statistical properties of its velocity time series. Moreover, by exploring the two-point joint probabilities, we propose a new approach for modelling vehicular dynamics based on the floating car data.     

Modeling and design of an optimized patterned electrode liquid crystal microlens array with dielectric slab

To eliminate the occurrence of disclination lines in the hole patterned electrode liquid crystal microlens array (LC MLA), inserting an ultrathin dielectric slab was proved to be an effective method. The thickness of the dielectric slab played an important role in effecting the optical performance of the liquid crystal microlens array device, including the dynamic focal range, focus diameter and symmetry of phase profile. In this paper, we studied the effect of dielectric slab thickness on the optical performance of the liquid crystal microlens array by numerical simulation. It is indicated that the optical performance of the device could be improved by reducing the dielectric slab thickness, assuming that the dielectric slab thickness was larger than the threshold thickness. The dependence of the threshold thickness on some key parameters was investigated and the associated effect on the optical performance by changing these key parameters was also studied. In the end, the approaches to enhance the optical performance, namely the dynamic focal range of the liquid crystal microlens array was proposed and proved to be in effect by numerical simulation results.     

Influence of moieties for the phase stability, spontaneous polarization and dielectric relaxations in an achiral ferroelectric bent liquid crystal, PBUOB

The occurrence of ferroelelectric phases and influence of chemical moieties in the area of supra-molecular achiral Bent core Liquid Crystals (BLCs) are reviewed. Synthesis of an intermediate/higher homolog of PBnOB series (for n=11), PBUOB, viz. 1,3−Phenyline-Bis(4−UndecylOxy Benzoate), is presented. Smectic LC phases exhibited by PBUOB are characterized by Polarized Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and Spontaneous Polarization (P_S) techniques. Observations infer a bi-variant FE LC smectic phase occurrence, viz., isotropic→B₂(FE)→B₅(FE)→solid phases in cooling and solid→B₅→isotropic phases in heating scans. Occurrence of B₂ phase is monotropic (in cooling), while B₅ phase is enantiotropic. I-B₂ and B₂-B₅ phase transitions are found to be of first order nature. The FE phases possess a moderate P_S value of ∼40 nC cm⁻². Transition temperatures from dielectric studies agree with those from TM and DSC. Two modes of relaxations are observed, viz., a slow scissor mode at ∼1 kHz and a fast mode at ∼1 MHz. Anisotropic Dipolar Model is proposed to explain the reorientation mechanism. Arrhenius shifts of Relaxation Frequency (f_R) show differing activation energies for two modes, i.e., 0.11 and 0.98 eV; 0.25 and 1.18 eV in B₂ and B₅ phases, respectively. Temperature variation of dielectric increment Δε and α-parameter LC phases reveals the relative fixture of dipole moment in polar smectic layers. An analytical study for the thermal stability, P_S and f_R in the FE phases is presented with respect to the constitution and configuration of moieties in BLCs.     

Classifier ensembles for fMRI data analysis: an experiment

Functional magnetic resonance imaging (fMRI) is becoming a forefront brain–computer interface tool. To decipher brain patterns, fast, accurate and reliable classifier methods are needed. The support vector machine (SVM) classifier has been traditionally used. Here we argue that state-of-the-art methods from pattern recognition and machine learning, such as classifier ensembles, offer more accurate classification. This study compares 18 classification methods on a publicly available real data set due to Haxby et al. [Science 293 (2001) 2425–2430]. The data comes from a single-subject experiment, organized in 10 runs where eight classes of stimuli were presented in each run. The comparisons were carried out on voxel subsets of different sizes, selected through seven popular voxel selection methods. We found that, while SVM was robust, accurate and scalable, some classifier ensemble methods demonstrated significantly better performance. The best classifiers were found to be the random subspace ensemble of SVM classifiers, rotation forest and ensembles with random linear and random spherical oracle.     

The structure of molten ZnCl2: A new analysis of some old data

Using a recently derived method, based on empirical potential structure refinement (EPSR), the structure of molten zinc chloride (ZnCl₂) is re-analysed. Contrary to the picture given in some early analyses, the results indicate that there are significant uncertainties in the extracted site-site radial distribution functions, particularly the Zn-Zn distribution. These are derived from the small weighting of this partial structure factor in the measured diffraction data and from systematic uncertainties in the original data. The simulated atom distributions are used to discuss the three-dimensional structure of this molten salt.     

Ferroelectric films of deuterated glycine phosphite: Structure and dielectric properties

Polycrystalline textured films of deuterated glycine phosphite consisting of single-crystal blocks with lateral dimensions ～(50–100) μm and a thickness d ～ (1–5) μm have been grown by evaporation on NdGaO₃(100) and α-Al₂O₃ substrates with preliminarily deposited interdigitated electrodes, as well as on Al substrates. The c* (Z) crystallographic axis in the blocks is normal to the film plane, and the a (X) axis and the polar axis b (Y) are oriented in the film plane. The temperature dependences of the capacitance of the structures measured with the interdigitated electrode system reveal a strong dielectric anomaly at the film transition to the ferroelectric state. The phase transition temperature T _c depends on the degree of deuteration D of the glycine phosphite. The maximum value T _c = 275 K obtained in the structures studied corresponds to a degree of deuteration of the glycine phosphite D ～ 50%. The frequency behavior of the dielectric hysteresis loops in glycine phosphite films differs radically from that of the previously studied films of deuterated betaine phosphite, which evidences that polarization switching in these structures proceeds by different mechanisms. It has been that application of a dc bias to the electrodes changes the shape of the dielectric hysteresis loops and shifts them along the electric field axis. The shift of the loops depends on the sign, magnitude, and time of application of the bias. Possible mechanisms underlying the induced unipolarity are discussed.     

Structure, electric and dielectric studies of indium-substituted magnesium copper manganese ferrites

The structure, electric and dielectric properties of In-substituted Mg-Cu-Mn ferrites having the general formula of Mg_0.9Cu_0.1Mn_0.1In_xFe_1.9−xO₄ with 0.0≤x≤0.4 have been studied. X-ray diffraction (XRD) patterns of the samples indicated the formation of single-phase cubic spinel structure up to 0.2 and mixed phase (cubic and tetragonal phase) for samples x≥0.3. The relation of conductivity with temperature revealed a semiconductor to semimetal behavior as In⁺³ concentration increases. Variation in the universal exponent s with temperature indicates the presence of two hopping conduction mechanisms: the correlated barrier hopping (CHB) at low In⁺³ content x≤0.1 and small-polaron (SP) hopping at In⁺³ content x≥0.2. The variation in dielectric permittivity (ε′, ε″) with temperature at different frequencies shows a normal behavior for the studied compounds, while the variation in dielectric loss tangent with frequency at different temperatures shows abnormal behavior with more than relaxation peak. The conduction mechanism used in the present study has been discussed in the light of electron exchange between Fe³⁺ and Fe²⁺ ions and hole hopping between Mn²⁺ and Mn³⁺ ions at the octahedral B-sites.     

Empirical optimization of ASL data analysis using an ASL data processing toolbox: ASLtbx

Arterial spin labeling (ASL) perfusion fMRI data differ in important respects from the more familiar blood oxygen level-dependent (BOLD) fMRI data and require specific processing strategies. In this paper, we examined several factors that may influence ASL data analysis, including data storage bit resolution, motion correction, preprocessing for cerebral blood flow (CBF) calculations and nuisance covariate modeling. Continuous ASL data were collected at 3 T from 10 subjects while they performed a simple sensorimotor task with an epoch length of 48 s. These data were then analyzed using systematic variations of the factors listed above to identify the approach that yielded optimal signal detection for task activation. Improvements in statistical power were found for use of at least 10 bits for data storage at 3 T. No significant difference was found in motor cortex regarding using simple subtraction or sinc subtraction, but the former presented minor but significantly (P<.024) larger peak t value in visual cortex. While artifactual head motion patterns were observed in synthetic data and background-suppressed ASL data when label/control images were realigned to a common target, independent realignment of label and control images did not yield significant improvements in activation in the sensorimotor data. It was also found that CBF calculations should be performed prior to spatial normalization and that modeling of global fluctuations yielded significantly increased peak t value in motor cortex. The implementation of all ASL data processing approaches is easily accomplished within an open-source toolbox, ASLtbx, and is advocated for most perfusion fMRI data sets.     

Lead telluride nanocrystalline thin films: Structure,optical characterization and a broadband dielectric spectroscopy study

Nanocrystalline PbTe thin films were deposited on a glass substrate by thermal evaporation technique with two thicknesses namely, 45 and 250 nm. The structural studies revealed that the films have nanocrystalline cubic structure and the particle size was found to be 11 and 20.7 nm, for low and high thicknesses respectively. The FE-SEM study shows that the surface grains increase for higher thickness film. This indicates that samples lying under the strong regime of confinement for PbTe thin films. The optical properties confirm the occurrence of confinement process as the optical band gap are 1.67 and 0.9 eV for 45 and 250 nm films, respectively. The dielectric results indicated that the conductivity increases by about two orders of magnitude with increasing the thickness from 45 to 250 nm. Moreover, the permittivity shows a higher dispersion step at lower frequencies in both samples due to the hopping conduction mechanism in addition to the interfacial polarization in such heterogeneous structures. Another small dispersion step is noticed in case of the lower thickness. It is attributed to the polarization of the accumulated charge carriers near the grain boundaries interfaces. No indication of any electrode phenomena in both samples is shown here.     

Relativistic analysis of the dielectric Einstein box: Abraham, Minkowski and total energy-momentum tensors

We analyse the “Einstein box” thought experiment and the definition of the momentum of light inside matter. We stress the importance of the total energy-momentum tensor of the closed system (electromagnetic field plus material medium) and derive in detail the relativistic expressions for the Abraham and Minkowski momenta, together with the corresponding balance equations for an isotropic and homogeneous medium. We identify some assumptions hidden in the Einstein box argument, which make it weaker than it is usually recognized. In particular, we show that the Abraham momentum is not uniquely selected as the momentum of light in this case.     

Structure analysis of turbulent mixing patterns in inert and reactive turbulent liquid flows

The paper contains an extended summary of an invited plenary talk given at the Workshop on Active Chaos at the Los Alamos National Laboratory on 29-31 May 2001 by one of us (F.S.R.). (c) 2002 American Institute of Physics.     

Comparison of dielectric and optical responses of chevron ferroelectric liquid crystals

An analysis of consistency of dielectric and optical response methods is carried out for surface stabilized ferroelectric liquid crystals (SSFLC) with chevron geometry. The consistency is found both theoretically and experimentally for weak external electric fields of intermediate frequencies, for which the response of SSFLC is dominated by collective relaxation processes due to azimuthal reorientation of molecules arranging chevron layers. The methods are experimentally shown to lack consistency within very low, relatively low, and high field-frequency ranges. The disagreement appearing at relatively low frequencies is argued to be a consequence of different recording by dielectric and optical techniques the dynamics of zig-zag walls, forming defects in chevron structure.     

Enhanced non-linear optical response in hybrid GSPN crystals: Structural, optical and dielectric analysis

Transparent and well defined crystals of GSPN series have been grown with alpha-glycine in simultaneous presence of two nitrates (NaNO₃ and KNO₃). Transparent and well defined crystals (22 mm × 13 mm × 5 mm) have been obtained in 3-4 weeks time by slow cooling. Addition of a strong acid (0.5% HCl) during growth is seen to enhance solubility, SHG efficiency by 2.78 times, Meyer's hardness index by 1.7 times and M.P by 42 °C of that of GSPN crystals. The SHG efficiency of acid added-GSPN has been found to be more than that of KDP crystal. GSPN is found to crystallize in orthorhombic symmetry and the presence of chemical components/groups has been identified by CHNS, EDAX and NMR analysis. Comparative FTIR and Laser Raman analysis shows the presence of active peaks indicating the molecule with a lack of center of symmetry. The UV spectrum shows existence of wide transparency window suitable for optoelectronic applications with band gap energy of about 5.72 eV. The crystals exhibit linear I-V characteristic followed by switching at 41 V/cm. The dielectric loss was seen to decrease exponentially with applied frequency from 100 Hz to 1 MHz.