Confinement Mechanism Research Articles

Simulating the Galactic multi-messenger emissions with HERMES

Context. The study of nonthermal processes such as synchrotron emission, inverse Compton scattering, bremsstrahlung, and pion production is crucial to understanding the properties of the Galactic cosmic-ray population, to shed light on their origin and confinement mechanisms, and to assess the significance of exotic signals possibly associated to new physics. Aims. We present a public code called HERMES which is designed generate sky maps associated to a variety of multi-messenger and multi-wavelength radiative processes, spanning from the radio domain all the way up to high-energy gamma-ray and neutrino production. Methods. We describe the physical processes under consideration, the code concept and structure, and the user interface, with particular focus on the python-based interactive mode. In particular, present the modular and flexible design that allows the user to easily extend the numerical package according to their needs. Results. In order to demonstrate the capabilities of the code, we describe the details of a comprehensive set of sky maps and spectra associated to all physical processes included in the code. We comment in particular on the radio, gamma-ray, and neutrino maps, and mention the possibility of studying signals stemming from dark matter annihilation. Conclusions. HERMES can be successfully applied to constrain the properties of the Galactic cosmic-ray population, improve our understanding of the diffuse Galactic radio, gamma-ray, and neutrino emission, and search for signals associated to particle dark matter annihilation or decay.

Topological confinement of vortices in two-flavor dense QCD

We find a novel confinement mechanism in the two-flavor dense quark matter proposed recently, that consists of the 2SC condensates and the P-wave diquark condensates of d-quarks. This quark matter exhibiting color superconductivity as well as superfluidity is classified into two phases; confined and deconfined phases of vortices. We establish that the criterion of the confinement is color neutrality of Aharonov-Bohm (AB) phases: vortices exhibiting color non-singlet AB phases are confined by the so-called AB defects to form color-singlet bound states. In the deconfined phase, the most stable vortices are non-Abelian Alice strings, which are superfluid vortices with fractional circulation and non-Abelian color magnetic fluxes therein, exhibiting color non-singlet AB phases. On the other hand, in the confined phase, these non-Abelian vortices are confined to either a baryonic or mesonic bound state in which constituent vortices are connected by AB defects. The baryonic bound state consists of three non-Abelian Alice strings with different color magnetic fluxes with the total flux canceled out connected by a domain wall junction, while the mesonic bound state consists of two non-Abelian Alice strings with the same color magnetic fluxes connected by a single domain wall. Interestingly, the latter contains a color magnetic flux in its core, but this can exist because of color neutrality of its AB phase.

Autoresonance phenomenon in a long mirror

The paper describes an implementation of a long mirror-based variant of cyclotron autoresonance which permits a local temporary change in the mirror`s induction and provides a mode for filling the trap with primary plasma, and for the generation of plasma bunches with an energetic electron component and their accumulation within a single cavity. The approach does not require injection of external particles into the acceleration zone as particles can be generated directly within the mirror using specialized conditions of electron cyclotron resonance (ECR) as part of the operational mode. A detailed study of the spectral-angular distribution of Bremsstrahlung in various operational modes has been undertaken. The results of this study permit the optimal value of the time sequence between the leading edge of the pulsed magnetic field and the microwave pulse to be determined, which ensures the optimal mode of electron trapping in the cyclotron autoresonance mode. Bremsstrahlung radiation recorded in the transverse direction has a significantly higher intensity of photons and energy compared to the longitudinal direction during the acceleration and subsequent confinement mode of plasma bunches. The observed changes in the intensity and spectral distribution of the Bremsstrahlung, which depend on the values of the operating parameters for acceleration, afford the possibility to define the dependence of the number of initial plasma particles trapped by cyclotron autoresonance for the different operating modes. The results will improve our understanding of the processes taking place at various stages of the operational modes. In general, such studies are important for gaining an improved understanding of the mechanisms of generation and confinement of hot electron plasma bunches with an energetic electron component for autoresonant interaction in a long mirror.

Magic-angle lasers in nanostructured moiré superlattice.

Conventional laser cavities require discontinuity of material property or disorder to localize a light field for feedback. Recently, an emerging class of materials, twisted van der Waals materials, have been explored for applications in electronics and photonics. Here we propose and develop magic-angle lasers, where the localization is realized in periodic twisted photonic graphene superlattices. We reveal that the confinement mechanism of magic-angle lasers does not rely on a full bandgap but on the mode coupling between two twisted layers of photonic graphene lattice. Without any fine-tuning in structure parameters, a simple twist can result in nanocavities with strong field confinement and a high quality factor. Furthermore, the emissions of magic-angle lasers allow direct imaging of the wavefunctions of magic-angle states. Our work provides a robust platform to construct high-quality nanocavities for nanolasers, nano light-emitting diodes, nonlinear optics and cavity quantum electrodynamics at the nanoscale.

Point-Defect-Localized Bound States in the Continuum in Photonic Crystals and Structured Fibers.

We show that point defects in two-dimensional photonic crystals can support bound states in the continuum (BICs). The mechanism of confinement is a symmetry mismatch between the defect mode and the Bloch modes of the photonic crystal. These BICs occur in the absence of band gaps and therefore provide an alternative mechanism to confine light. Furthermore, we show that such BICs can propagate in a fiber geometry and exhibit arbitrarily small group velocity which could serve as a platform for enhancing nonlinear effects and light-matter interactions in structured fibers.

EFT and the SUSY index on the 2nd sheet

The counting of BPS states in four-dimensional \mathcal{N}=1𝒩=1 theories has attracted a lot of attention in recent years. For superconformal theories, these states are in one-to-one correspondence with local operators in various short representations. The generating function for this counting problem has branch cuts and hence several Cardy-like limits, which are analogous to high-temperature limits. Particularly interesting is the second sheet, which has been shown to capture the microstates and phases of supersymmetric black holes in AdS_55. Here we present a 3d Effective Field Theory (EFT) approach to the high-temperature limit on the second sheet. We use the EFT to derive the behavior of the index at orders \beta^{-2},\beta^{-1},\beta^0β−2,β−1,β0. We also make a conjecture for O(\beta)O(β), where we argue that the expansion truncates up to exponentially small corrections. An important point is the existence of vector multiplet zero modes, unaccompanied by massless matter fields. The runaway of Affleck-Harvey-Witten is however avoided by a non-perturbative confinement mechanism. This confinement mechanism guarantees that our results are robust.

BRST symmetry as a mechanism for confinement

The SU(N) QCD in a particular quadratic gauge is shown to contain two phases namely, the deconfined phase and the confined phase. A suitable field dependent parameter in the finite field dependent BRST (FFBRST) transformation interrelates the effective theories in two different gauges. In this paper, we propose a novel application and extension of the FFBRST technique that transforms the effective action in the deconfined phase to that in the confined phase within the quadratic gauge only. The proposed passage becomes interesting as it carries a unique field theoretic meaning and due to the fact that the technique changes the BRST invariant phase to BRST non invariant phase in an unconventional way unlike usual connections where both the theories, before and after application of FFBRST, are BRST invariant. We thus find a new process in field redefinition that executes deconfinement to confinement phase transition other than ghost condensation mechanism.

Assimilation, Removal, Discipline, and Confinement

A full understanding of the roots of child separation must begin with Native children. This Article demonstrates how modern child welfare, delinquency, and education systems are rooted in the social control of indigenous children. It examines the experiences of Native girls in federal and state systems from the late 1800s to the mid1900s to show that, despite their ostensibly benevolent and separate purposes, these institutions were indistinguishable and interchangeable. They were simply differently styled mechanisms of forced assimilation, removal, discipline, and confinement. As the repeating nature of government intervention into the lives of Native children makes clear, renaming a system does not change its effect. The historical roots of these systems must be acknowledged, and the current systems must be abolished and replaced. To answer the question of what a nonpunitive, non-assimilative system would look like, this Article looks to tribal courts and indigenous justice systems. It points to specific examples of how Native communities have reshaped ideas about caring for and disciplining children, including traditional adoption, kinship care, wellness courts, family group conferencing, and a “best interests” standard that emphasizes the link between individual and collective well-being.

Superinsulators: An Emergent Realisation of Confinement

Superinsulators (SI) are a new topological state of matter, predicted by our collaboration and experimentally observed in the critical vicinity of the superconductor-insulator transition (SIT). SI are dual to superconductors and realise electric-magnetic (S)-duality. The effective field theory that describes this topological phase of matter is governed by a compact Chern-Simons in (2+1) dimensions and a compact BF term in (3+1) dimensions. While in a superconductor the condensate of Cooper pairs generates the Meissner effect, which constricts the magnetic field lines penetrating a type II superconductor into Abrikosov vortices, in superinsulators Cooper pairs are linearly bound by electric fields squeezed into strings (dual Meissner effect) by a monopole condensate. Magnetic monopoles, while elusive as elementary particles, exist in certain materials in the form of emergent quasiparticle excitations. We demonstrate that at low temperatures magnetic monopoles can form a quantum Bose condensate (plasma in (2+1) dimensions) dual to the charge condensate in superconductors. The monopole Bose condensate manifests as a superinsulating state with infinite resistance, dual to superconductivity. The monopole supercurrents result in the electric analogue of the Meissner effect and lead to linear confinement of the Cooper pairs by Polyakov electric strings in analogy to quarks in hadrons. Superinsulators realise thus one of the mechanism proposed to explain confinement in QCD. Moreover, the string mechanism of confinement implies asymptotic freedom at the IR fixed point. We predict thus for superinsulators a metallic-like low temperature behaviour when samples are smaller than the string scale. This has been experimentally confirmed. We predict that an oblique version of SI is realised as the pseudogap state of high-TC superconductors.

Confining stress path-based compressive strength model of axially compressed circular concrete-filled double-skin steel tubular short columns

Previous investigations have shown that the confining stress paths (CSPs) of confined concrete significantly affected the compressive behaviour of confined concrete in fibre-reinforced polymer (FRP) confined concrete or concrete-filled steel tube (CFST) columns. Unlike the concrete in FRP-confined concrete or CFST columns, which is only confined by external materials, e.g., FRP sheet or steel tube, the concrete in concrete-filled double-skin steel tubular (CFDST) columns is confined by both the external and internal steel tubes. Due to different confinement mechanisms, the CSPs of confined concrete in CFDST columns may be different from those in FRP-confined concrete or CFST ones, but they have not been investigated so far. In this paper, the CSPs of confined concrete in circular CFDST stub columns were experimentally investigated, and their corresponding influences on the compressive strength were also discussed. It is shown that the CSPs of confined concrete induced by the external tube are considerably influenced by column variables, whereas those generated by the internal tube found no obvious trend. Moreover, the results suggest that the compressive strength of confined concrete in specimens with a confinement coefficient η less than 2.731 is CSP-dependent, based on which, a compressive strength model of confined concrete considering the CSP effect is developed for circular CFDST columns. Based on this model, a CSP-based compressive strength model for estimating the ultimate strength of CFDST columns is proposed, and comparison with existing models against the collected test data indicates a higher accuracy of the predictions for the proposed model.

The role of material fabric in concrete under uniaxial compression

The paper extends the formal structure of the fabric based analysis of cohesion-less granular materials to cemented granular materials such as concrete. The stress-fabric and strain-fabric relationships are derived, and both are seen to be sensitive to particle angularity and maximum particle size. The contributions of the isotropic and anisotropic parts of the micro structural stress and strain are identified and a recently developed discrete element capability used to investigate their separate contributions to the macro behaviour in uniaxial compression. The anisotropic part of the micro-structural stress plays a dominant role in determining the peak strength. However, post peak ductility is largely controlled by the isotropic part. Remarkably fabric anisotropy, which depends strongly on particle angularity, is seen to result in higher hydrostatic pressures. This strengthens the “internal confinement mechanism” and accounts for the superior strength of specimens with angular aggregates observed in experiments.

Research on Battery Technology of Borohydride New Hydrogen Energy Material

Vehicle-mounted hydrogen storage is a “bottleneck” link in promoting the large-scale commercial application of hydrogen fuel vehicles. The development of high-performance vehicle-mounted hydrogen storage material technology has become a hot spot in the current energy and materials field. In recent years, with the continuous expansion of the field of hydrogen storage materials, high-storage coordination metal hydrides represented by lithium borohydride ( LiBH 4 ) have gradually become a new research focus of hydrogen storage materials. This article summarizes the latest modification research and application of metal borohydride hydrogen storage materials from the perspectives of substitution, recombination, doping, nanostructure confinement and corresponding reaction mechanism, and puts forward the existing problems and corresponding countermeasures, and points out the future research direction.

Spatial Confinement of a Carbon Nanocone for an Efficient Oxygen Evolution Reaction.

A major bottleneck of large-scale water splitting for hydrogen production is the lack of catalysts for the oxygen evolution reaction (OER) with low cost and high efficiency. In this work, we proposed an electrocatalyst of a curved carbon nanocone embedded with two TMN4 active sites (TM = transition metal) and used first-principles calculations to investigate their OER mechanisms and catalytic activities. In the particular spatial confinement of a curved nanocone, we found that the distance between intermediates adsorbed on two active sites is shorter than the distance between these two active sites. This finding can be used to enhance OER activity by distance-dependent interaction between intermediates through two different mechanisms. The first mechanism in which an O2 molecule is generated from two neighboring *O intermediates exhibits a linear activity trend, and the lowest overpotential is 0.27 V for the FeN4 system. In the second mechanism, selective stabilization of the *OOH intermediate is realized, leading to a new scaling relationship (ΔG*OOH = ΔG*OH + 3.04 eV) associated with a modified OER activity volcano (theoretical volcano apex at 0.29 V). The studied mechanisms of the spatial confinement of a carbon nanocone provide a new perspective for designing efficient OER catalysts.

Three-dimensional finite element modeling and theoretical analysis of concrete confined with FRP rings

The confinement mechanism of concrete fully confined with fiber-reinforced polymer (FRP) jacket (FRP jacketed concrete) is different from that of concrete partially confined with FRP (i.e., FRP ring-confined concrete and FRP tie-confined concrete) in that the confinement in the latter is non-uniform along the longitudinal direction. In order to build a bridge between FRP jacketed concrete and FRP ring/tie-confined concrete, the current design of concrete confined with FRP rings/ties relies on the “arching action” assumption, which is not necessarily accurate as it was proposed for concrete confined with steel stirrups. Moreover, the arching action assumption usually adopts a hypothesis that the arching action angle equals to 45°, which has not been verified by any theoretical or experimental evidence. To this end, a revised analysis model has been implemented in an advanced finite element (FE) approach to study the axial stress distributions in concrete confined with FRP rings. The stress distribution at the center level of two adjacent FRP rings/ties is obtained, and the relationship between the arching action angle and controlling parameters (i.e., unconfined concrete strength, FRP width, FRP thickness and clear spacing of FRP rings) is established based on a proposed theoretical model of arching action angle. A new confinement effectiveness coefficient is then proposed, leading to a much more reliable prediction of the FRP ring-confined concrete in circular columns. The results presented in the current study can be easily extended to the concrete columns internally reinforced with FRP ties/spiral.

Black holes, stationary clouds and magnetic fields

As the electron in the hydrogen atom, a bosonic field can bind itself to a black hole occupying a discrete infinite set of states. When (i) the spacetime is prone to superradiance and (ii) a confinement mechanism is present, some of such states are infinitely long–lived. These equilibrium configurations, known as stationary clouds, are states “synchronized” with a rotating black hole's event horizon. For most, if not all, stationary clouds studied in the literature so far, the requirements (i)–(ii) are independent of each other. However, this is not always the case. This paper shows that massless neutral scalar fields can form stationary clouds around a Reissner–Nordström black hole when both are subject to a uniform magnetic field. The latter simultaneously enacts both requirements by creating an ergoregion (thereby opening up the possibility of superradiance) and trapping the scalar field in the black hole's vicinity. This leads to some novel features, in particular, that only black holes with a subset of the possible charge to mass ratios can support stationary clouds.

Atomic mechanism of ionic confinement in the thermoelectric Cu2Se based on a low-cost electric-current method

Summary In a fast ion-conductor Cu2Se, phase instability and the loss of Cu under operational conditions are the major impediments to its thermoelectric applications. Herein, a fast and low-cost pulse electric current method is developed to rapidly synthesize Cu2Se-based materials with high thermoelectric performance. The Cu2Se microstructures under an external current and high temperature close to the real working conditions have been investigated by both ex situ and in situ transmission electron microscopy. Due to the presence of Bi interstitials, dynamic Cu-ion fluctuation zones on the nanometer scale have been stabilized through the pinning effect of dislocations and the action of interfacial/boundary phases steric hindrance, both preventing Cu ions from escaping from the lattice. The hierarchical structure spanning from interstitial atoms to nanometer-scale precipitates, created by the pulse electric current method, forms a network of ion-blocking but electrically conducting barriers that greatly improve the stability of Cu2Se-based thermoelectric materials.

Magnetic confinement and instability in partially magnetized plasma

Discharge with an external magnetic field is promising for various applications of low-temperature plasmas from electric propulsion to semiconductor processes owing to high plasma density. It is essential to understand plasma transport across the magnetic field because plasma confinement under the field is based on strong magnetization of light electrons, maintaining quasi-neutrality through the inertial response of unmagnetized ions. In such a partially magnetized plasma, different degrees of magnetization between electrons and ions can create instability and make the confinement and transport mechanisms more complex. Theoretical studies have suggested a link between the instability of various frequency ranges and plasma confinement, whereas experimental work has not been done so far. Here, we experimentally study the magnetic confinement properties of a partially magnetized plasma considering instability. The plasma properties show non-uniform characteristics as the magnetic field increases, indicating enhanced magnetic confinement. However, the strengthened electric field at the edge of the plasma column gives rise to the Simon–Hoh instability, limiting the plasma confinement. The variation of the edge-to-center plasma density ratio (h-factor) with the magnetic field clearly reveals the transition of the transport regime through triggering of the instability. Eventually, the h-factor reaches an asymptotic value, indicating saturation of magnetic confinement.

Simulation of uniaxially compressed square ultra-high-strength concrete-filled steel tubular slender beam-columns

The application of ultra-high-strength concrete in a concrete-filled steel tubular (CFST) column is an emerging topic recognizing the greater member capacities and stiffness of high strength concrete. The current designing codes for composite structures have restricted the use of ultra-high-strength concrete. This is because very little research has been conducted on the structural response of eccentrically loaded square ultra-high-strength CFST slender beam-columns. Set against this limited research, a numerical model implementing the fiber element formulation has been developed in this paper to fill the knowledge gap on the behavior of square ultra-high-strength CFST slender beam-columns under combined compression-bending conditions. The fiber-based model accounts for important features including local and global interaction buckling, triaxial confinement mechanism, member imperfection, and geometric and material nonlinearities. The stress–strain relationships for normal- and high-strength concrete do not reflect completely the brittleness of ultra-high-strength concrete in the post-peak branch. The existing material model is modified for simulating the material response of ultra-high-strength concrete. A comparison is made between the experimental data and the numerical simulation to assess the accuracy of the fiber-based model. The model has shown to provide a good agreement between the test data and the simulation. The parametric investigation indicates that the ultra-high-strength concrete may be effectively and hence more economically used in short and intermediate steel–concrete composite columns subjected to the compression load with a small eccentricity. It is also noted that the steel section with yield stress up to 550 MPa can be utilized with the ultra-high-strength concrete. The design code, Eurocode 4, accurately predicts the bending strength of ultra-high-strength square CFST slender beam-columns subjected to uniaxial bending.

Numerical modeling of rectangular concrete-filled double-skin steel tubular columns with outer stainless-steel skin

Concrete-filled double-skin steel tubular (CFDST) columns composed of outer stainless-steel skin have grown increasingly popular in structural applications on account of their attractive appearance, ductility, resistance to corrosion, fire resistance and easy maintenance. However, only one numerical study of the behavior of rectangular CFDST short columns with outer stainless steel tube has been reported. This paper presents the numerical analysis and design of axially loaded rectangular CFDST short columns where the outer tube is made of stainless-steel. A finite element model is created for analyzing the responses of rectangular CFDST short columns. The numerical analysis accounts for the confinement mechanism of concrete, strain hardening of stainless steel and imperfection of steel tubes. A comparative study of numerically predicted and experimentally observed behavior is presented to gain an appreciation for the accuracy of the developed numerical model. A parametric study is undertaken, investigating the performance of a series of rectangular CFDST columns by varying the concrete strength, load distribution, cross-section shape and tube thickness. The ultimate axial strengths predicted using Australia/New Zealand Standard for composite structures are compared against experimental results. It is demonstrated that the numerical model predicts well the responses of CFDST columns where the outer skin is made of stainless steel. Australia/New Zealand Standard yields the accurate predictions of the ultimate axial strengths of rectangular CFDST columns with outer stainless-steel tube.

Simulating the passive confinement of rectangular concrete prisms allowing for size effect

Tests have shown that providing passive confinement to concrete, either through the use of internal stirrups, external fibre-reinforced polymer (FRP) wraps, FRP tubes or steel tubes, can increase the concrete strength and, in particular, the concrete ductility, thereby allowing greater absorption of energy and consequently ductile failure. The problem of including the benefits of passive confinement in design is in generalising the effect of passive confinement because it varies with the member size, the configuration of the confining reinforcement and material properties. In this paper, all aspects of the complex fundamental mechanics of passive concrete confinement are explained both qualitatively and quantitatively through the use of shear–friction and bond–slip mechanics. The mechanics model was found to have a good correlation with test results. An analysis-oriented procedure is described for quantifying the passive stress–strain of concrete for rectangular sections and it is envisaged that this can be used to develop simplified rules for design, in particular for new types of members and those with new materials.