Virtual Pairs Research Articles

Magnetized effective QCD phase diagram

The QCD phase diagram in the temperature vs quark chemical potential plane is studied in the presence of a magnetic field, using the linear sigma model coupled to quarks. It is shown that the decrease of the couplings with increasing field strength obtained in this model leads to the critical temperature for the phase transition to decrease with increasing field intensity (inverse magnetic catalysis). This happens provided that plasma screening is properly accounted for. It is also found that with increasing field strength the location of the critical end point in the phase diagram moves toward lower values of the critical quark chemical potential and larger values of the critical temperature. In addition, the critical end point approaches the temperature axis for large values of the magnetic field. We argue that a similar behavior is to be expected in QCD, since the physical impact of the magnetic field, regardless of strength, is to produce a spatial dimension reduction, whereby virtual quark-antiquark pairs are closer on average and thus the strength of their interaction decreases due to asymptotic freedom.

Magnetization currents of fluctuating Cooper pairs

Recent experiments show that the Nernst-Ettingshausen effect is orders of magnitude stronger than the thermoelectric Seebeck effect in superconductors above the critical temperature. We explain different magnitudes of the two effects accounting for the magnetization current of virtual Cooper pairs. The method allows for detailed understanding of the surprising non-monotonic dependence of the Nernst-Ettingshausen coefficient on the magnetic field.

Abnormal difference between the mobilities of left- and right-twisted conformations of C6H12N2 roto-symmetrical molecules at very low temperatures.

We report an abnormal difference of low-temperature mobility of left-twisted and right-twisted conformations of roto symmetric molecules C6H12N2 (dabco) located in the same positions in crystal Zn2(C8H4O4)2⋅C6H12N2. The difference between (1)H NMR (Nuclear Magnetic Resonance) spin-relaxation data for left-twisted and right-twisted molecules reaches ∼3 × 10(3) times at 8 K and tends to grow at lower temperatures. We argue that taking into account four-component relativistic Dirac wave functions in the vicinity of the nodal plane of dabco molecules and vacuum fluctuations due to virtual particle-antiparticle pairs can explain the changes which C6H12N2 conformations undergo at low temperatures.

Field signature for apparently superluminal particle motion

In the context of Stueckelberg's covariant symplectic mechanics, Horwitz and Aharonovich [1] have proposed a simple mechanism by which a particle traveling below light speed almost everywhere may exhibit a transit time that suggests superluminal motion. This mechanism, which requires precise measurement of the particle velocity, involves a subtle perturbation affecting the particle's recorded time coordinate caused by virtual pair processes. The Stueckelberg framework is particularly well suited to such problems, because it permits pair creation/annihilation at the classical level. In this paper, we study a trajectory of the type proposed by Horwitz and Aharonovich, and derive the Maxwell 4-vector potential associated with the motion. We show that the resulting fields carry a signature associated with the apparent superluminal motion, providing an independent test for the mechanism that does not require direct observation of the trajectory, except at the detector.

Do parents favor their adoptive or biological children? Predictions from kin selection and compensatory models

Evolutionary reasoning (Kin Selection Theory) predicts less favorable behaviors directed by parents toward their unrelated children, relative to their biologically related children. By extension, it may be argued that parents should also have less favorable perceptions of the intellectual, personality and other behavioral traits of unrelated children, compared with biologically related children. However, recent work has modified this expectation, given the distinction between unrelated adopted children (who are acquired intentionally) and unrelated stepchildren (who are acquired via mating effort). The compensatory model takes into account evolved desires for parenting and the evolutionarily novel availability of unrelated children. It predicts that adopted children may be viewed as favorably, or even more favorably, than biological children due to parents' compensation for the perceived challenges and stigma linked to their exceptional family structure. In the present study, IQ, Adjective Checklist and Child Behavior Checklist scale scores were available for 135 virtual twin pairs (same-age unrelated siblings raised together). Virtual twins included 41 adopted–biological pairs and 94 adopted–adopted pairs, with a mean age of 6.14years (SD=3.51). These unique data allowed tests of hypotheses and predictions concerning parenting perceptions, given the matched age and placement of the biological and adoptive siblings. Consistent with prior research, the IQ scores of the biological children exceeded those of the adopted children, both between and within pairs. A between-pair analysis revealed no difference between biological children and members of adopted–adopted pairs in ratings of favorable or unfavorable traits. However, more telling within-family comparisons of adopted–biological pairs revealed higher scores for adoptees on unfavorable traits, consistent with Kin Selection Theory, but no differences between adoptive and biological children on favorable traits, consistent with the compensatory model. These findings refine our understanding of parenting genetically related and unrelated offspring.

Gravitational correction to vacuum polarization

We consider the gravitational correction to (electronic) vacuum polarization in the presence of a gravitational background field. The Dirac propagators for the virtual fermions are modified to include the leading gravitational correction (potential term) which corresponds to a coordinate-dependent fermion mass. The mass term is assumed to be uniform over a length scale commensurate with the virtual electron-positron pair. The on-mass shell renormalization condition ensures that the gravitational correction vanishes on the mass shell of the photon, i.e., the speed of light is unaffected by the quantum field theoretical loop correction, in full agreement with the equivalence principle. Nontrivial corrections are obtained for off-shell, virtual photons. We compare our findings to other works on generalized Lorentz transformations and combined quantum-electrodynamic gravitational corrections to the speed of light which have recently appeared in the literature.

Performance Evaluation of Virtual MIMO Multi-User System in a Measured Indoor Environment at 5 GHz

Wideband indoor MIMO channel measurements were performed in office building with carrier frequency at 5.25 GHz with 100 MHz radio frequency bandwidth. In this paper nineteen measured indoor propagation data sets are used to study the behavior of virtual MIMO system formed by two users compared to its classical user. A classical user having 4 antenna elements, two spaced antennas from two classical users are brought together to form 4 $$\times $$× 8 virtual MIMO with base station having 8 antennas. Nineteen measured datasets are available from which 171 possible virtual MIMO pairs are formed. The capacity, $$K$$K-factor, rms delay spread and spatial correlation are evaluated for 171 possible pairs of users whose channels were measured while standing. The results show that virtual MIMO in many cases is desirable for capacity improvement. The capacity improvement of virtual MIMO system is found to be 60.2 % over both two constituent users and 31 % over only one constituent user. The result show also that capacity improvement is mostly due to the rms delay spread and special correlation reduction than the $$K$$K-factor reduction.

Conditions for formation of electron pairs in a metal

In an isotropic model of the electron system of metal that is presented by the Fröhlich’s initial Hamiltonian, in the approximation of a weak electron–phonon interaction at T=0, first time, we show that the ground state of the system is the state with pairing correlations of electrons (the pair correlations of occupied electron states). In contrast to the BCS approach, the initial point in our approach is not electron pairing but is the maximum reduction of the energy of the considered system due to virtual processes of the electron–phonon interaction and to the exchange effect for the indirect electron–electron interaction (which is induced by certain phonon modes separately from others). In contrast to the BCS approach, we take into account the portion of the energy of the electron system that is connected with the above exchange effect. In the BCS approach, the corresponding portion is missed, and its role is prescribed to the portion that does not relate to the electron pairing.We show that expectation values of the above Hamiltonian for different wave functions for two interacting electrons above the Fermi sea of the non-interacting system (with interaction between the electrons that is induced by different phonon modes separately from others) are minimum for a certain structure of these functions and simultaneously for phonon modes that can induce the transitions of the interacting electrons between electron states in which they are (without violation of the Pauli exclusion principle and at everything else being equal). On the basis of the above results, the mechanism of the maximum reduction of the energy of the considered electron system is considered. In this mechanism each electron interact with the very different phonons, but in such way that give the maximum-possible negative contribution to the energy of the considered electron system.The theme of the article is conditions for the formation of electron pairs in a metal. This requires our understanding for the mechanism of the formation of electron pairs in a metal. The absence of this understanding is the main drawback of the BCS theory. The considered mechanism gives the solution. If this mechanism is feasible for a metal at T=0, the electron system of this metal can be described by the Hamiltonian that is similar to the BCS reduced Hamiltonian and the ground-state wave function is similar to the BCS ground-state wave function.The considered mechanism combines the simplicity and universality of the BCS model with giving wide opportunities to study conditions for the formation of the state of the electron system in a metal with the pair correlation of conduction electrons near the Fermi surface and with a gap in the spectrum of electronic excitations of this system and to study the dependence of these conditions on crystalline structure and structure of the conduction band of metals. It is so, because the considered mechanism has the universal nature but the above dependence is largely determined by the nature of virtual pairs in a metal.

Superluminal Spot Pair Events in Astronomical Settings: Sweeping Beams

AbstractSweeping beams of light can cast spots moving with superluminal speeds across scattering surfaces. Such faster-than-light speeds are well-known phenomena that do not violate special relativity. It is shown here that under certain circumstances, superluminal spot pair creation and annihilation events can occur that provide unique information to observers. These spot pair events are not particle pair events—they are the sudden creation or annihilation of a pair of relatively illuminated spots on a scattering surface. Real spot pair illumination events occur unambiguously on the scattering surface when spot speeds diverge, while virtual spot pair events are observer dependent and perceived only when real spot radial speeds cross the speed of light. Specifically, a virtual spot pair creation event will be observed when a real spot’s speed toward the observer drops below c, while a virtual spot pair annihilation event will be observed when a real spot’s radial speed away from the observer rises above c. Superluminal spot pair events might be found angularly, photometrically, or polarimetrically, and might carry useful geometry or distance information. Two example scenarios are briefly considered. The first is a beam swept across a scattering spherical object, exemplified by spots of light moving across Earth’s Moon and pulsar companions. The second is a beam swept across a scattering planar wall or linear filament, exemplified by spots of light moving across variable nebulae including Hubble’s Variable Nebula. In local cases where the sweeping beam can be controlled and repeated, a three-dimensional map of a target object can be constructed. Used tomographically, this imaging technique is fundamentally different from lens photography, radar, and conventional lidar.

Effective quantum electrodynamics hamiltonians: A tutorial review

A “with‐pair, no‐retardation” relativistic many‐electron Hamiltonian, that is, effective quantum electrodynamics (eQED) Hamiltonian, can be constructed both algebraically and diagrammatically, in a bottom‐up fashion without recourse to QED itself. It describes all virtual pair effects due to the instantaneous Coulomb/Gaunt/Breit interaction and is compatible with all wave function or density functional based correlation methods. As such, it serves as the basis for “with‐pair relativistic quantum chemistry”, which is an extension of the traditional “no‐pair relativistic quantum chemistry.” Regardless of the numerical significance of the (nonradiative) virtual pair effects, such an extension represents a conceptually important step for going beyond the no‐pair approximation that has been prevailing in relativistic electronic structure calculations of molecular systems. Due to the short range nature, the effective potential Q describing electron vacuum polarization (EVP) and self‐energy (ESE) can be fitted into a model operator, which can be included in variational self‐consistent field calculations. The subsequent treatments of electron correlation and properties can then be simplified greatly. That is, the major QED effects, including EVP and ESE as well as the Coulomb/Gaunt/Breit screenings of them, can be obtained with little overhead over standard no‐pair calculations. It can hence be envisaged that “molecular QED” will soon emerge as a new and exciting field for ultrahigh precision calculations of molecular spectroscopies and dynamics. © 2014 Wiley Periodicals, Inc.

Polarization-dependent heating of the cosmic microwave background radiation by a magnetic field

The changes in the cosmic microwave background (CMB) spectrum seen as an increase of temperature due to a strong magnetic field are determined and their influence on the polarization of the radiation is exhibited. The effect is due to the coupling of the CMB photons to the magnetic field in the QED vacuum via the interaction with virtual pairs. In spite of the fact that the distortion of the CMB spectrum for magnetic fields that exist in the vicinity of magnetars is quite large, this effect is very difficult to detect at present because the required angular resolutions is not yet available.

Long-distance quantum communication over noisy networks without long-time quantum memory

The problem of sharing entanglement over large distances is crucial for implementations of quantum cryptography. A possible scheme for long-distance entanglement sharing and quantum communication exploits networks whose nodes share Einstein-Podolsky-Rosen (EPR) pairs. In Perseguers et al. [Phys. Rev. A 78, 062324 (2008)] the authors put forward an important isomorphism between storing quantum information in a dimension $D$ and transmission of quantum information in a $D+1$-dimensional network. We show that it is possible to obtain long-distance entanglement in a noisy two-dimensional (2D) network, even when taking into account that encoding and decoding of a state is exposed to an error. For 3D networks we propose a simple encoding and decoding scheme based solely on syndrome measurements on 2D Kitaev topological quantum memory. Our procedure constitutes an alternative scheme of state injection that can be used for universal quantum computation on 2D Kitaev code. It is shown that the encoding scheme is equivalent to teleporting the state, from a specific node into a whole two-dimensional network, through some virtual EPR pair existing within the rest of network qubits. We present an analytic lower bound on fidelity of the encoding and decoding procedure, using as our main tool a modified metric on space-time lattice, deviating from a taxicab metric at the first and the last time slices.

Heat recovery networks synthesis of large-scale industrial sites: Heat load distribution problem with virtual process subsystems

This paper presents a targeting strategy to design a heat recovery network for an industrial plant by dividing the system into subsystems while considering the heat transfer opportunities between them. The methodology is based on a sequential approach. The heat recovery opportunity between process units and the optimal flow rates of utilities are first identified using a Mixed Integer Linear Programming (MILP) model. The site is then divided into a number of subsystems where the overall interaction is resumed by a pair of virtual hot and cold stream per subsystem which is reconstructed by solving the heat cascade inside each subsystem. The Heat Load Distribution (HLD) problem is then solved between those packed subsystems in a sequential procedure where each time one of the subsystems is unpacked by switching from the virtual stream pair back into the original ones. The main advantages are to minimize the number of connections between process subsystems, to alleviate the computational complexity of the HLD problem and to generate a feasible network which is compatible with the minimum energy consumption objective. The application of the proposed methodology is illustrated through a number of case studies, discussed and compared with the relevant results from the literature.

Interindividual variation in fornix microstructure and macrostructure is related to visual discrimination accuracy for scenes but not faces.

Transection of the nonhuman primate fornix has been shown to impair learning of configurations of spatial features and object-in-scene memory. Although damage to the human fornix also results in memory impairment, it is not known whether there is a preferential involvement of this white-matter tract in spatial learning, as implied by animal studies. Diffusion-weighted MR images were obtained from healthy participants who had completed versions of a task in which they made rapid same/different discriminations to two categories of highly visually similar stimuli: (1) virtual reality scene pairs; and (2) face pairs. Diffusion-MRI measures of white-matter microstructure [fractional anisotropy (FA) and mean diffusivity (MD)] and macrostructure (tissue volume fraction, f) were then extracted from the fornix of each participant, which had been reconstructed using a deterministic tractography protocol. Fornix MD and f measures correlated with scene, but not face, discrimination accuracy in both discrimination tasks. A complementary voxelwise analysis using tract-based spatial statistics suggested the crus of the fornix as a focus for this relationship. These findings extend previous reports of spatial learning impairments after fornix transection in nonhuman primates, critically highlighting the fornix as a source of interindividual variation in scene discrimination in humans.

Measures of unpaired electrons for large conjugated systems

It is shown that the numerical measure of effectively unpaired electrons Neff, proposed by Head-Gordon in 2003, is a particle-hole index: Neff is reduced to the average occupation of virtual particle-hole pairs. Specific π calculations of the Neff index provide a reasonable interpretation of the radicaloid character of the singlet ground state in complex conjugated systems. The results of the accurate π model (based on the total configuration interaction) and approximate approaches are compared. The coupled cluster method and various Hartree-Fock schemes (UHF and Lowdin EHF scheme) demonstrate an acceptable quantitative description of unpairing effects, UHF being favorable in simplicity of obtaining the measure of unpairing in megamolecules, such as graphene structures. The application of the known Yamaguchi index results in a rougher representation of the radical character of a system.

Mesoscopic capacitor and zero-point energy: Poisson's distribution for virtual charges, pressure, and decoherence control

Mesoscopic capacitor theory, which includes intrinsic inductive effects from quantum tunneling, is applied to conducting spherical shells. The zero-point pressure and the number of virtual charged pairs are determined assuming a Poisson distribution. They are completely defined by a dimensionless mesoscopic parameter (χc) measuring the average number of virtual pairs per solid angle and carrying mesoscopic information. Fluctuations remain finite and well defined. Connections with usual quantum-field-theory limit enables us to evaluate χc ~ 1.007110. Equivalently, for a mesoscopic parallel-plate capacitor, the shot noise distribution becomes operative with χc ~ 0.94705 as well being related to the density of virtual pairs. Temperature decoherence and capacitor control are discussed by considering typical values of quantum dot devices and Coulomb blockade theory.

RVIP: an indistinguishable approach to scalable network simulation at real time

AbstractIn the hybrid simulation research, we investigate a new approach to build software virtual networks (SVNs) that are indistinguishable from their equivalent real live networks (LNs). We define the concept of ‘Network's Interactive Turing Test' based on the similar concept used in the artificial intelligence areas. Our goal is to actualize the interactive and indistinguishable real–virtual interface pair (RVIP) for large‐scale computer network simulations. By RVIP's support, a single SVN is indistinguishable from its equivalent LN. In the entire hybrid system, multiple LNs and multiple SVNs are connected using many RVIPs in an arbitrary topology and at real time. To actualize RVIP, the following necessary conditions must be satisfied: (i) the performance of the underlying simulation platform must be faster than real time; (ii) all needed changes incurred by introducing any SVN into an LN scenario are put on the simulation's side. To interact with an SVN, RVIP requires that no change is made on any live node; (iii) an SVN does not exchange simulation events with LNs, that is, only standard IP protocol interactions between SVN and LN are allowed. (iv) Any LN can be dynamically plugged into the hybrid scenario at real time, just like being plugged into an equivalent purely LN. Compared with existing hybrid simulation efforts on NS‐3, QualNet's EXata and OPNET's system‐in‐the‐loop, in this paper, we use the actual RVIP implementation to show that RVIP is a better candidate to pass the Network's Interactive Turing Test owing to the following two advantages: (i) an interactive network tester can easily distinguish the existing hybrid networks from the LNs by using a live topology that cannot be simulated, for example, by including the entire live Internet. But RVIP is not vulnerable to such tests. RVIP can support hybrid scenarios with multiple SVNs and multiple LNs connected by an arbitrary network topology, and with the LNs on and off at anytime. (ii) Performance‐wise, our studies show that RVIP provides more efficient support in terms of common metrics such as larger throughput limit and smaller extra latency; thus, the simulated SVNs are more indistinguishable from their live counterparts. Copyright © 2014 John Wiley & Sons, Ltd.

New regimes of the stringy (holographic) Pomeron and high-multiplicityppandpAcollisions

Holographic AdS/QCD models of the Pomeron unite a string-based description of hadronic reactions of the pre-QCD era with the perturbative BFKL approach. The specific version we will use due to Stoffers and Zahed, is based on a semiclassical quantization of a "tube" (closed string exchange or open string virtual pair production) in its Euclidean formulation using the scalar Polyakov action. This model has a number of phenomenologically successful results. The periodicity of a coordinate around the tube allows the introduction of a Matsubara time and therefore an effective temperature Teff on the string. We observe that at the LHC energies and for sufficiently small impact parameter, Teff approaches and even exceeds the Hagedorn temperature of the QCD strings. Based on studies of the stringy thermodynamics of pure gauge theories we suggest that there should exist two new regimes of the Pomeron: the "near-critical" and the "post-critical" ones. In the former one, string excitations create a high entropy "string ball", with high energy and entropy but small pressure/free energy. If heavy enough this ball becomes a (dual) black hole (BH). As the intrinsic temperature of the string exceeds the Hagedorn temperature, the ball becomes a post-critical explosive "QGP ball". The hydrodynamical explosion resulting from this scenario was predicted by us to have radial flow exceeding that ever seen even in heavy ion collisions, which was recently confirmed by CMS and ALICE at LHC. We also discuss the elastic scattering profile, finding some hints for new phases in it, as well as two-particle correlations.

Social forces can impact the circadian clocks of cohabiting hamsters

A number of field and laboratory studies have shown that the social environment influences daily rhythms in numerous species. However, underlying mechanisms, including the circadian system's role, are not known. Obstacles to this research have been the inability to track and objectively analyse rhythms of individual animals housed together. Here, we employed temperature dataloggers to track individual body temperature rhythms of pairs of cohabiting male Syrian hamsters (Mesocricetus auratus) in constant darkness and applied a continuous wavelet transform to determine the phase of rhythm onset before, during, and after cohabitation. Cohabitation altered the predicted trajectory of rhythm onsets in 34% of individuals, representing 58% of pairs, compared to 12% of hamsters single-housed as 'virtual pair' controls. Deviation from the predicted trajectory was by a change in circadian period (τ), which tended to be asymmetric-affecting one individual of the pair in nine of 11 affected pairs-with hints that dominance might play a role. These data implicate a change in the speed of the circadian clock as one mechanism whereby social factors can alter daily rhythms. Miniature dataloggers coupled with wavelet analyses should provide powerful tools for future studies investigating the principles and mechanisms mediating social influences on daily timing.

Color difference formulae evaluation by method of adjustment

This experiment was carried out to test color difference formulae by method of adjustment. 6 different color centers (Red, Yellow, Green, Blue-Green, Blue and Violet) were chosen for this psychophysical experiment. 336 virtual sample pairs were prepared. The mean color difference was three CIELAB units. Each pair was assessed by a panel of 15 observers using psychophysical methods called Method of Adjustment. These visual data were used to test color-difference formulae: CIELAB, CMC, CIE94, DIN99d and CIE2000 with the help of simple statistical measures i.e., PF/3 and Stress. It was found that the visual results obtained from psychophysical method of adjustment show that CIE94 as well as DIN99d still perform well for small color differences.