物理与天体物理最新文献

Ascertaining the morphology and composition of the icy mantles covering dust grains in dense, cold regions of the interstellar medium is essential to developing accurate astrochemical models, determining conditions for ice formation, constraining chemical interactions in and on icy grains and understanding how ices withstand space radiation. The widely observed infrared spectroscopic signature of H₂O ice at ~3 μm discriminates crystalline from amorphous structures in interstellar ices. Weaker bands seen only in laboratory ice spectra at ~2.7 μm, termed ‘dangling OH’ (dOH), are attributed to water molecules not fully bound to neighbouring water molecules and are often considered as tracing the degree of ice compaction. We exploit the high sensitivity of JWST NIRCam to detect two dOH features at 2.703 and 2.753 μm along multiple lines of sight probing the dense cloud Chamaeleon I, attributing these signatures to unbound dOH in cold water ice and dOH in interaction with other molecular species. These detections open a path to using the dOH features as tracers of the formation, composition, morphology and evolution of icy grains during the star and planet formation process.

In this manuscript, we undertake an examination of a classical plasma deployed on two finite co-planar surfaces: a circular regionΩininto an annular regionΩoutwith a gap in between. It is studied both from the point of view of statistical mechanics and the electrostatics of continua media. We employ a dual perspective: the first one is by using molecular dynamics (MD) simulations to find the system's positional correlation functions and velocity distributions. That by modeling the system as a classical two-dimensional Coulomb plasma of point-like charged particlesq₁andq₂on the layersΩinandΩoutrespectively with no background density. The second one corresponds to a finite Surface Electrode (SE) composed of planar metallic layers displayed on the regionsΩin,Ωoutat constant voltagesVin,Voutconsidering axial symmetry. The surface charge density is calculated by the Method of Moments (MoM) under the electrostatic approximation. Point-like and differential charges elements interact via a1/r-electric potential in both cases. The thermodynamic averages of the number density, and electric potential due to the plasma depend on the coupling and the charge ratioξ=q1/q2once the geometry of the layers is fixed. On the other hand, the fields due to the SE depend on the layer's geometry and their voltage. In the document, is defined a protocol to properly compare the systems. We show that there are values of the coupling parameter, where the thermodynamic averages computed via MD agree with the results of MoM for attractiveξ=-1and repulsive layersξ = 1.

The magnetic properties of a circular graphene nanoribbon (carbon belt) in a magnetic field parallel to its central axis is studied using a tight-binding model. Orbital magnetic susceptibility is calculated using an analytical expression of the energy eigenvalues as a function of the magnetic flux density for any size, and its temperature dependence is considered. In the absence of electron hopping parallel to the magnetic field, the orbital magnetic susceptibility diverges at absolute zero if the chemical potential is zero and the number of atoms is a multiple of four. As the temperature increases, the magnitude of susceptibility decreases according to the power law, whose exponent depends on the size. In the presence of electron hopping parallel to the magnetic field, the divergence of the susceptibility near absolute zero disappears, and the sign changes with the transfer integral parallel to the magnetic field and the temperature.

We elaborate on a model of nonassociative and noncommutative Einstein–Dirac–Maxwell, EDM, theory determined by star product R-flux deformations in string theory. Solutions for nonassociative EDM systems and physical properties not studied in modern physics. For modifications of the four-dimensional, 4-d, Einstein gravity, we work on conventional nonassociative 8-d phase spaces modelled as star-deformed co-tangent Lorentz bundles. Generalizing the anholonomic frame and connection deformation method, the nonassociative EDM equations are decoupled and integrated in exact and parametric quasi-stationary forms. Corresponding generic off-diagonal metrics are described by nonlinear symmetries and encode nonassociative effective sources and generating functions depending on space and momentum-like coordinates. For respective nonholonomic parameterizations, such solutions describe nonassociative deformations of the Reissner–Nordström black holes. A variant of nonassociative phase space wormhole solution with fermions possessing anisotropic polarized masses is also analyzed. We conclude that such phase space physical objects can’t be characterized using the concept of Bekenstein–Hawking entropy and show how to compute another type (modified G. Perelman ones) nonassociative geometric and statistical thermodynamic variables.