Numerical Methods for the 3-dimensional 2-body Problem in the Action-at-a-Distance Electrodynamics

We develop two numerical methods to solve the differential equations with deviating arguments for the motion of two charges in the action-at-a-distance electrodynamics. Our first method uses St\"urmer's extrapolation formula and assumes that a step of integration can be taken as a step of light ladder, which limits its use to shallow energies. The second method is an improvement of pre-existing iterative schemes, designed for stronger convergence and can be used at high-energies.Comment: 17 pages, 11 figure

Magnetic superlattice and finite-energy Dirac points in graphene

We study the band structure of graphene's Dirac-Weyl quasi-particles in a one-dimensional magnetic superlattice formed by a periodic sequence of alternating magnetic barriers. The spectrum and the nature of the states strongly depend on the conserved longitudinal momentum and on the barrier width. At the center of the superlattice Brillouin zone we find new Dirac points at finite energies where the dispersion is highly anisotropic, in contrast to the dispersion close to the neutrality point which remains isotropic. This finding suggests the possibility of collimating Dirac-Weyl quasi-particles by tuning the doping

Fractional-Spin Integrals of Motion for the Boundary Sine-Gordon Model at the Free Fermion Point

We construct integrals of motion (IM) for the sine-Gordon model with boundary at the free Fermion point which correctly determine the boundary S matrix. The algebra of these IM (``boundary quantum group'' at q=1) is a one-parameter family of infinite-dimensional subalgebras of twisted affine sl(2). We also propose the structure of the fractional-spin IM away from the free Fermion point.Comment: 19 pages, LaTeX, no figure

Multiple magnetic barriers in graphene

We study the behavior of charge carriers in graphene in inhomogeneous perpendicular magnetic fields. We consider two types of one-dimensional magnetic profiles, uniform in one direction: a sequence of N magnetic barriers, and a sequence of alternating magnetic barriers and wells. In both cases, we compute the transmission coefficient of the magnetic structure by means of the transfer matrix formalism, and the associated conductance. In the first case the structure becomes increasingly transparent upon increasing N at fixed total magnetic flux. In the second case we find strong wave-vector filtering and resonant effects. We also calculate the band structure of a periodic magnetic superlattice, and find a wave-vector-dependent gap around zero-energy.Comment: 9 pages, 18 figure

MicroRNAs: New Players in Multiple Myeloma

MicroRNAs (miRNAs) are short non-coding RNAs that play critical roles in numerous cellular processes through post-transcriptional regulating functions. The aberrant role of miRNAs has been reported in a number of hematopoietic malignancies including multiple myeloma (MM). In this review we summarize the current knowledge on roles of miRNAs in the pathogenesis of MM

Geometrical bounds on irreversibility in open quantum systems

Clausius inequality has deep implications for reversibility and the arrow of time. Quantum theory is able to extend this result for closed systems by inspecting the trajectory of the density matrix on its manifold. Here we show that this approach can provide an upper and lower bound to the irreversible entropy production for open quantum systems as well. These provide insights on the thermodynamics of the information erasure. Limits of the applicability of our bounds are discussed, and demonstrated in a quantum photonic simulator

Mechanism For Copper(II)-Mediated Disaggregation Of A Porphyrin J-Aggregate

J-aggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin form at intermediate pH (2.3–3.1) in the presence of NiSO₄ or ZnSO₄ (ionic strength, I.S. = 3.2 M). These aggregates convert to monomeric porphyrin units via metallation with copper(II) ions. The kinetics for the disassembly process, as monitored by UV/vis spectroscopy, exhibits zeroth-order behavior. The observed zeroth-order rate constants show a two-term dependence on copper(II) ion concentrations: linear and second order. Also observed is an inverse dependence on hydrogen ion concentration. Activation parameters have been determined for the disassembly process leading to ΔH^≠ = (+163 ± 15) kJ·mol⁻¹ and ΔS^≠ = (+136 ± 11) J·K⁻¹. A mechanism is proposed in which copper(II) cation is in pre-equilibrium with a reactive site at the rim of the J-aggregate. An intermediate copper species is thus formed that eventually leads to the final metallated porphyrin either through an assisted attack of a second metal ion or through a direct insertion of the metal cation into the macrocycle core

Phase resolved spectroscopy of the Vela pulsar with XMM-Newton

The ~10^4 y old Vela Pulsar represents the bridge between the young Crab-like and the middle-aged rotation powered pulsars. Its multiwavelength behaviour is due to the superposition of different spectral components. We take advantage of the unprecedented harvest of photons collected by XMM-Newton to assess the Vela Pulsar spectral shape and to study the pulsar spectrum as a function of its rotational phase. As for the middle-aged pulsars Geminga, PSR B0656+14 and PSR B1055-52 (the "Three Musketeers"), the phase-integrated spectrum of Vela is well described by a three-component model, consisting of two blackbodies (T_bb1=(1.06+/-0.03)x10^6 K, R_bb1=5.1+/-0.3 km, T_bb2=(2.16+/-0.06)x10^6 K, R_bb2=0.73+/-0.08 km) plus a power-law (gamma=2.2+/-0.3). The relative contributions of the three components are seen to vary as a function of the pulsar rotational phase. The two blackbodies have a shallow 7-9% modulation. The cooler blackbody, possibly related to the bulk of the neutron star surface, has a complex modulation, with two peaks per period, separated by ~0.35 in phase, the radio pulse occurring exactly in between. The hotter blackbody, possibly originating from a hot polar region, has a nearly sinusoidal modulation, with a single, broad maximum aligned with the second peak of the cooler blackbody, trailing the radio pulse by ~0.15 in phase. The non thermal component, magnetospheric in origin, is present only during 20% of the pulsar phase and appears to be opposite to the radio pulse. XMM-Newton phase-resolved spectroscopy unveils the link between the thermally emitting surface of the neutron star and its charge-filled magnetosphere, probing emission geometry as a function of the pulsar rotation. This is a fundamental piece of information for future 3-dimensional modeling of the pulsar magnetosphere.Comment: 27 pages, 9 figures. Accepted for publication in Ap

Bridging thermodynamics and metrology in non-equilibrium Quantum Thermometry

Single-qubit thermometry presents the simplest tool to measure the temperature of thermal baths with reduced invasivity. At thermal equilibrium, the temperature uncertainty is linked to the heat capacity of the qubit, however the best precision is achieved outside equilibrium condition. Here, we discuss a way to generalize this relation in a non-equilibrium regime, taking into account purely quantum effects such as coherence. We support our findings with an experimental photonic simulation.Comment: 7 pages, 4 figure