Dissipative heat and exchange dispersion on metastability of Gd5Si4

The response of the magnetic and crystal structure of Gd₅Si₄ to both ‘isothermal’ and ‘thermo-mechanical’ process is investigated by the dispersion exchange fluctuation, which can be the cause of the compound's metastability. The X-ray diffraction DTA, SEM and magnetization at room temperature are measured to explore the effect of annealing process (latent heat as isothermal) at different annealing temperatures. The discharge heat (exchange heat) by the annealing process, which is manifested by the thermal loop of DTA, is caused by the reduction in the lattice constant as well as in magnetization behavior measured at room temperature with no observable crystal phase transition. The exchange fluctuation (entropy), which is related to the DTA thermal loop, is increased by the sample's heat absorption (discharge heat) in the direction to lower the free energy of the crystal. The crystallographic slip is investigated by the dissipative heat through the high ball milling energy (HBME) to provide the nature and strength of the exchange. It is shown that the DTA thermal loop and SEM-crystallographic slip should be the character of the “exchange heat” (discharge heat) and “heat exchange” (absorption of heat through the wet environment of ball milling).     

A theory of cosmic rays

We present a theory of non-solar cosmic rays (CRs) in which the bulk of their observed flux is due to a single type of CR source at all energies. The total luminosity of the Galaxy, the broken power-law spectra with their observed slopes, the position of the ‘knee(s)’ and ‘ankle’, and the CR composition and its variation with energy are all predicted in terms of very simple and completely ‘standard’ physics. The source of CRs is extremely ‘economical’: it has only one parameter to be fitted to the ensemble of all of the mentioned data. All other inputs are ‘priors’, that is, theoretical or observational items of information independent of the properties of the source of CRs, and chosen to lie in their pre-established ranges. The theory is part of a ‘unified view of high-energy astrophysics’ — based on the ‘Cannonball’ model of the relativistic ejecta of accreting black holes and neutron stars. The model has been extremely successful in predicting all the novel properties of Gamma Ray Bursts recently observed with the help of the Swift satellite. If correct, this model is only lacking a satisfactory theoretical understanding of the ‘cannon’ that emits the cannonballs in catastrophic processes of accretion.     

Stripe fluctuations, carriers, spectroscopies, transport, and BCS-BEC crossover in the high-Tc cuprates

The quasiparticles of the high-T_c cuprates are found to consist of: polaron-like ‘stripons’ carrying charge, and associated primarily with large-U orbitals in stripe-like inhomogeneities; ‘quasi-electrons’ (QE) carrying charge and spin, and associated with hybridized small-U and large-U orbitals; and ‘svivons’ carrying spin and lattice distortion. It is shown that this electronic structure leads to the systematic behavior of spectroscopic and transport properties of the cuprates. High-T_c pairing results from transitions between pair states of stripons and QEs through the exchange of svivons. The cuprates fall in the regime of crossover between BCS and preformed-pairs Bose-Einstein condensation behaviors.     

Entanglement in a spin-one spin chain

The thermal entanglement in a two-spin-qutrit system with two spins coupled by exchange interaction is investigated in terms of the measure of entanglement called ‘negativity’. We strictly show that for any temperature the entanglement is symmetric with respect to zero magnetic field. The behavior of negativity is presented for four different cases. We find that the entanglement may be enhanced under a nonuniform magnetic field. Because there is not any necessary and sufficient condition for quantum separability in systems of dimension 3⊗3, our results are qualitative, not quantitative.     

Wave packet revivals and the energy eigenvalue spectrum of the quantum pendulum

The rigid pendulum, both as a classical and as a quantum problem, is an interesting system as it has the exactly soluble harmonic oscillator and the rigid rotor systems as limiting cases in the low- and high-energy limits, respectively. The energy variation of the classical periodicity (τ) is also dramatic, having the special limiting case of τ→∞ at the ‘top’ of the classical motion (i.e., the separatrix.) We study the time-dependence of the quantum pendulum problem, focusing on the behavior of both the (approximate) classical periodicity and especially the quantum revival and superrevival times, as encoded in the energy eigenvalue spectrum of the system. We provide approximate expressions for the energy eigenvalues in both the small and large quantum number limits, up to fourth order in perturbation theory, comparing these to existing handbook expansions for the characteristic values of the related Mathieu equation, obtained by other methods. We then use these approximations to probe the classical periodicity, as well as to extract information on the quantum revival and superrevival times. We find that while both the classical and quantum periodicities increase monotonically as one approaches the ‘top’ in energy, from either above or below, the revival times decrease from their low- and high-energy values until very near the separatrix where they increase to a large, but finite value.     

A quantitative criterion validating coupling power proportionality in statistical energy analysis

The response of two general spring-coupled elements is investigated to develop a unifying approach to the weak coupling criterion in Statistical Energy Analysis (SEA). First, the coupled deterministic equations of motion are expressed in the bases given by the uncoupled elements’ eigenmodes. Then, an iterative solution is expressed as a succession of exchanges between elements, where uncoupled motion provides the start approximation, converging if the ‘coupling eigenvalue’ is less than unity, in which case coupling is said to be weak. This definition is related to whether response is ‘local’ or ‘global’, encompassing a number of previously defined coupling strength definitions, applying for deterministically described structures. A stochastic ensemble is defined by that its members are equal to the investigated structure but the elements have random frequencies. It is required that the coupling eigenvalue be less than unity for all members of the ensemble. This requirement generates the title subject of the article: ‘the modal interaction strength’. It is similar to the previously defined coupling strength criterion characterising the ensemble average energy flow in uni-dimensional waveguides. Finally, SEA models are formulated in terms of the uncoupled elements’ modal data.     

Ultimate capabilities of sharp metal tips for plasmon nanofocusing, near-field trapping and sensing

This Letter considers an ‘ultimate’ nanofocusing system with arguably the largest field enhancements achievable in plasmonic nanofocusing structures. These enhancements appear far beyond those required for single molecule detection. The proposed structure is demonstrated to be ∼4 orders of magnitude more efficient for trapping of small nanoparticles and single molecules, than the tip-assisted trapping. It does not require direct irradiation of the tip, and this will enable highly targeted delivery of the optical energy to nanoscale regions as small as a few nanometers (e.g., inside living cells) for trapping, imaging, localized heat discharge, and superior sensing in a new generation of nano-optical detectors.     

Percolation picture for long wavelength phonons in zinc blende alloys: application to GaInAs

We propose a ‘one bond→two modes’ model for the long wavelength optical phonons in random zinc-blende A_xB_1−xC ternary alloys, based on the percolation site theory. Our model takes into account the ‘fractal→normal’ object transition, which goes with the ‘dispersion→continuum’ topology transition at the percolation thresholds of the A-C and B-C bonds. We first introduce the basics of our model in the case of Zn_1−xBe_x(Se,Te) mixed crystals, whose parent binaries display a high contrast in the bond stiffness, which enhances the percolation effects. We then focus our study on standard systems, which display a much weaker contrast in the bond stiffness. The multi-phonon behavior of GaInAs alloys is re-examined in the light of the percolation model, with much success.     

A nanoindentation analysis of the influence of lattice mismatch on some wide band gap semiconductor films

Nanoindentation studies are carried out on epitaxial ZnO and GaN thin films on (0 0 0 1) sapphire and silicon substrates, respectively. A single discontinuity (‘pop-in’) in the load-indentation depth curve is observed for ZnO and GaN films at a specific depths of 13-16 and 23-26 nm, respectively. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the interaction behavior of the indenter tip with the pre-existing threading dislocations present in the films during mechanical deformation. It is observed that the ‘pop-in’ depth is dependent on lattice mismatch of the epitaxial thin film with the substrate, the higher the lattice mismatch the shallower the critical ‘pop-in’ depth.     

The Rayleigh-Plesset equation in terms of volume with explicit shear losses

The most common nonlinear equation of motion for the damped pulsation of a spherical gas bubble in an infinite body of liquid is the Rayleigh-Plesset equation, expressed in terms of the dependency of the bubble radius on the conditions pertaining in the gas and liquid (the so-called ‘radius frame’). However over the past few decades several important analyses have been based on a heuristically derived small-amplitude expansion of the Rayleigh-Plesset equation which considers the bubble volume, instead of the radius, as the parameter of interest, and for which the dissipation term is not derived from first principles. So common is the use of this equation in some fields that the inherent differences between it and the ‘radius frame’ Rayleigh-Plesset equation are not emphasised, and it is important in comparing the results of the two equations to understand that they differ both in terms of damping, and in the extent to which they neglect higher order terms. This paper highlights these differences. Furthermore, it derives a ‘volume frame’ version of the Rayleigh-Plesset equation which contains exactly the same basic physics for dissipation, and retains terms to the same high order, as does the ‘radius frame’ Rayleigh-Plesset equation. Use of this equation will allow like-with-like comparisons between predictions in the two frames.     

Risk evaluation with enhanced covariance matrix

We propose a route for the evaluation of risk based on a transformation of the covariance matrix. The approach uses a ‘potential’ or ‘objective’ function. This allows us to rescale data from different assets (or sources) such that each data set then has similar statistical properties in terms of their probability distributions. The method is tested using historical data from both the New York and Warsaw stock exchanges.     

The distribution of partons in a hadron

The distribution of partons in the dual model of Nielsen and Susskind is derived and some simple explanations of the relation between Regge behavior form factors, pion production and the parton distribution are explained in qualitative terms. A possible modification of this distribution is introduced in order to ‘flatten’ the pomeron.     

‘Superluminal paradox’ in wave packet propagation and its quantum mechanical resolution

We analyse in detail the reshaping mechanism leading to apparently ‘superluminal’ advancement of a wave packet traversing a classically forbidden region. In the coordinate representation, a barrier is shown to act as an effective beamsplitter, recombining envelopes of the freely propagating pulse with various spacial shifts. Causality ensures that none of the constituent envelopes are advanced with respect to free propagation, yet the resulting pulse is advanced due to a peculiar interference effect, similar to the one responsible for ‘anomalous’ values which occur in Aharonov’s ‘weak measurements’. In the momentum space, the effect is understood as a bandwidth phenomenon, where the incident pulse probes local, rather than global, analytical properties of the transmission amplitude T(p)$T\left(p\right)$. The advancement is achieved when T(p)$T\left(p\right)$ mimics locally an exponential behaviour, similar to the one occurring in Berry’s ‘superoscillations’. Seen in a broader quantum mechanical context, the ‘paradox’ is but a consequence of an attempt to obtain ‘which way?’ information without destroying the interference between the pathways of interest. This explains, to a large extent, the failure to adequately describe tunnelling in terms of a single ‘tunnelling time’.     

A study on the heat-treatments of nanocrystalline nickel substituted BaW hexaferrite produced by low combustion synthesis method

The novel low temperature combustion synthesis (LCS) method for the preparation of nanocrystalline W-type BaW hexaferrite i.e. BaNi₂Fe₁₆O₂₇ has been carried out by citrate precursor using the sol-to-gel (S–G) followed by gel-to-nanocrystalline (G–N) conversion. Decomposition behaviors and the phases associated therein are investigated by means of thermal analysis (DTA/DTG/TG) and XRD, respectively. Atomic absorption spectroscopy (AAS) has been used to determine the elemental analysis in different conditions. Surface morphology of the nonporous ultra fine particles have been examined by SEM. The TEM micrographs show that the particles of the size of 10 nm were seemed to be agglomerated in the ‘as synthesized’ condition. Room temperature Fe-57 Mossbauer spectrum, MS has showed doublet of ‘as synthesized’ nanocrystalline powder that indicates the superparamagnetic behavior of the material. This effect is further confirmed by vibrating sample magnetometer (VSM) wherein it was noticed that the magnetic field (10 KG max) did not have any effect on the material. The material was annealed at 400, 700 and 1000 °C in the furnace for 4 h. The grain size is found to increase from 10 to 70 nm after annealing at 1000 °C for 4 h. MS after annealing at 700–1000 °C for 4 h, showed that the doublets of ‘as synthesized’ is further resolved into broad sextets due to the presence of both superparamagnetic and ferrimagnetic particles, in the wide size range from 10 to 70 nm. Only slight increase in particle size (from 10 to 15 nm) is noticed after the heat-treatment for 1–3 and 5 min in microwave oven (2.45 GHz with 760 W) but with predominant phase changes. TEM after the heat treatment revealed the presence of microcrystalline nature of grains of the size ∼70 nm. The transformation of the magnetic properties i.e. from superparamagnetic to ferrimagnetic behaviour after heating in microwave oven has been revealed by hysteresis loops under VSM study. The saturation magnetisation, M_s after heat treatment has been seen to increase from 26.7 to 44.5 emu/gm. Remanence and coercivity have also increased four and seven times, respectively. M_s of the as synthesised hexaferrite nano powder and heat-treated powder in microwave oven for 5 min show doublets, confirming the presence of superparamagnetic relaxation in the nano particles as only slight increase in the particle size is associated with the heat treatment.     

A Lagrangian description of transport associated with a front-eddy interaction: Application to data from the North-Western Mediterranean Sea

We discuss the Lagrangian transport in a time-dependent oceanic system involving a Lagrangian barrier associated with a salinity front which interacts intermittently with a set of Lagrangian eddies — ‘leaky’ coherent structures that entrain and detrain fluid as they move. A theoretical framework, rooted in the dynamical systems theory, is developed in order to describe and analyse this situation. We show that such an analysis can be successfully applied to a realistic ocean model. Here, we use the output of the numerical ocean model DieCAST from Dietrich et al. (2004) [17] and Fernández et al. (2005) [18] studied earlier in Mancho et al. (2008) [15] where a Lagrangian barrier associated with the North Balearic Front in the North-Western Mediterranean Sea was identified. The numerical model provides an Eulerian view of the flow and we employ the dynamical systems approach to identify relevant hyperbolic trajectories and their stable and unstable manifolds. These manifolds are used to understand the Lagrangian geometry of the evolving front-eddy system. Transport in this system is effected by the turnstile mechanism whose spatio-temporal geometry reveals intermittent pathways along which transport occurs. Particular attention is paid to the ‘Lagrangian’ interactions between the front and the eddies, and to transport implications associated with the transition between the one-eddy and two-eddy situation. The analysis of this ‘Lagrangian’ transition is aided by a local kinematic model that provides insight into the nature of the change in hyperbolic trajectories and their stable and unstable manifolds associated with the ‘birth’ and ‘death’ of leaky Lagrangian eddies.     

A way for enhancing second harmonic generation in one-dimensional nonlinear photonic crystals

We investigate one-dimensional nonlinear photonic crystals consisting of ferroelectric domains with the modulated polarization directions. Significant enhancement of second harmonic generation (SHG) is observed from numerical simulations when the frequency of fundamental wave is aimed at the photonic band edge. We devise the model structure with optimal configuration of the polarization directions of the ferroelectric domains in terms of simulated annealing algorithm. The conversion efficiencies of the ‘forward’ and ‘backward’ SHGs can be engineered.     

Towards a novel simulation approach for the transport of atomic states through polarized photons

A novel approach for transferring logic states from one quantum node to other is proposed. Logic states ‘0’ and ‘1’ are represented by two subspaces of the hyperfine states space of rubidium atom (⁸⁷Rb). The atom, placed at the center of a two-mode cavity, is excited by simultaneous application of two laser beams, one for each subspace. Based on the logic state of the atom, it makes a transition to a higher energy level within the corresponding subspace. When the atom relaxes back to a lower state within the subspace, a left- or right-circularly polarized photon is emitted depending on whether the initial state was logic ‘0’ or logic ‘1’. The polarized photon leaks out of the cavity, reaches the receive node and gets detected therein. Simulation results show the efficacy of the approach.     

Particles movement and surface quality in PLD/PR systems

A three-dimensional model based on Monte-Carlo and Finite Elements techniques has been used for simulating plume behavior, ‘micron-sized particles’ movement and interaction with obstacles in a Pulsed Laser Deposition with Plasma Reflection (PLD/PR) system. Have been investigated the influences of mass, surface size and emission time on trajectory and film surface quality as well. Droplet and ‘big-size particles’ deposition statistics are presented and a comparison between theoretical and experimental results upon thin film surface quality as well. One can observe that particles mass and surface size have a strong influence on the particles trajectory by affecting the collisions parameters during the entire propagation process. The emission time should influence the particles trajectory by affecting the probability of interaction with other particles. By making a 10,000 particles statistic for a normal distribution of these investigated parameters, we obtain reasonable good results in modeling ‘big-size particles’ tendency to be deposited at lower reflection angles. These results sustain assumption of ‘big particles’ deflection by plume fine particles during the propagation process.