380 research outputs found
Atomic levels in superstrong magnetic fields and D=2 QED of massive electrons: screening
The photon polarization operator in superstrong magnetic fields induces the
dynamical photon "mass" which leads to screening of Coulomb potential at small
distances , is the mass of an electron. We demonstrate that this
behaviour is qualitatively different from the case of D=2 QED, where the same
formula for a polarization operator leads to screening at large distances as
well. Because of screening the ground state energy of the hydrogen atom at the
magnetic fields has the finite value .Comment: 12 pages, 2 figure
Cellulosic fiber based hybrid composites: A comparative investigation into their structurally influencing mechanical properties
This paper focuses on hybrid and twisted hybrid Indian mallow/roselle cellulosic fiber yarn mat reinforced polyester composites and effects of their wood sawdust filler. The composite materials were fabricated using compression molding technique. There were four different combinations of hybrid yarn mat composite samples used, while the twisted hybrids were six. An evaluation of the hybrid and twisted hybrid mechanical properties for the single and double layer cases of the yarn mat was done with and without wood sawdust filler effects. The samples were tested at both warp and weft directions. From the results obtained at warp direction, it was observed that for the hybrid double layer case, longitudinal yarn mat with wood sawdust (filler) composite sample exhibited better tensile, impact and flexural strength properties in comparison with other related composites of hybrid type reported in literature. Moreover, the modified twisted hybrid double layer composites with longitudinal yarn mat and wood sawdust filler sample recorded significantly greater improvement on the mechanical properties at warp direction, when compared with the hybrid double layer longitudinal yarn mat composites with wood sawdust filler and other reported similar hybrid composite materials. Scanning electron microscopy (SEM) technique was utilized to evaluate morphological internal damage (cracks) and fractured surfaces of the various tested composite samples. Based on their mechanical performances and for further practical evidence, these two types of eco-composites were used to effectively fabricate tri-wheeler auto-wheel hubs and ceiling fan blades, as applicable to automobile and electronics industries, respectively.Peer reviewedFinal Accepted Versio
Nonadiabatic effects in a generalized Jahn-Teller lattice model: heavy and light polarons, pairing and metal-insulator transition
The ground state polaron potential of 1D lattice of two-level molecules with
spinless electrons and two Einstein phonon modes with quantum phonon-assisted
transitions between the levels is found anharmonic in phonon displacements. The
potential shows a crossover from two nonequivalent broad minima to a single
narrow minimum corresponding to the level positions in the ground state.
Generalized variational approach implies prominent nonadiabatic effects:(i) In
the limit of the symmetric E-e Jahn- Teller situation they cause transition
between the regime of the predominantly one-level "heavy" polaron and a "light"
polaron oscillating between the levels due to phonon assistance with almost
vanishing polaron displacement. It implies enhancement of the electron transfer
due to decrease of the "heavy" polaron mass (undressing) at the point of the
transition. Pairing of "light" polarons due to exchange of virtual phonons
occurs. Continuous transition to new energy ground state close to the
transition from "heavy" polaron phase to "light" (bi)polaron phase occurs. In
the "heavy" phase, there occurs anomalous (anharmonic) enhancements of quantum
fluctuations of the phonon coordinate, momentum and their product as functions
of the effective coupling. (ii) Dependence of the polaron mass on the optical
phonon frequency appears.(iii) Rabi oscillations significantly enhance quantum
shift of the insulator-metal transition line to higher values of the critical
effective e-ph coupling supporting so the metallic phase. In the E-e JT case,
insulator-metal transition coincide with the transition between the "heavy" and
the "light" (bi)polaron phase at certain (strong) effective e-ph interaction.Comment: Paper in LaTex format (file jtseptx.tex) and 9 GIF-figures
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Crystal structure of [meso-5,7,7,12,14,14,-hexamethyl-1,4,8,11-tetraazacyclotetradecane]nickel(II) diperchlorate – dimethylsulphoxide (1/2), C20H48Cl2N4NiO10S2
C20H48Cl2N4NiO10S2, monoclinic, P21/n (no. 14), a = 8.657(2) Å, b = 15.233(4) Å, c = 11.956(3) Å, β = 102.737(2)°, V = 1537.9(7) Å3, Z = 2, R gt (F) = 0.0237, wR ref (F 2) = 0.0655, T = 93(2) K
Decay of Rabi oscillations induced by magnetic dipole interactions in diluted paramagnetic solids
Decay of Rabi oscillations of equivalent spins diluted in diamagnetic solid
matrix and coupled by magnetic dipole interactions is studied. It is shown that
these interactions result in random shifts of spin transient nutation
frequencies and thus lead to the decay of the transient signal. Averaging over
random spatial distribution of spins within the solid and over their spectral
positions within magnetic resonance line, we obtain analytical expressions for
the decay of Rabi oscillations. The rate of the decay in the case when the
half-width of magnetic resonance line exceeds Rabi frequency is found to depend
on the intensity of resonant microwave field and on the spin concentration. The
results are compared with the literature data for E1' centers in glassy silica
and [AlO4] centers in quartz.Comment: 14 pages, 3 figure
Quantum dynamics in strong fluctuating fields
A large number of multifaceted quantum transport processes in molecular
systems and physical nanosystems can be treated in terms of quantum relaxation
processes which couple to one or several fluctuating environments. A thermal
equilibrium environment can conveniently be modelled by a thermal bath of
harmonic oscillators. An archetype situation provides a two-state dissipative
quantum dynamics, commonly known under the label of a spin-boson dynamics. An
interesting and nontrivial physical situation emerges, however, when the
quantum dynamics evolves far away from thermal equilibrium. This occurs, for
example, when a charge transferring medium possesses nonequilibrium degrees of
freedom, or when a strong time-dependent control field is applied externally.
Accordingly, certain parameters of underlying quantum subsystem acquire
stochastic character. Herein, we review the general theoretical framework which
is based on the method of projector operators, yielding the quantum master
equations for systems that are exposed to strong external fields. This allows
one to investigate on a common basis the influence of nonequilibrium
fluctuations and periodic electrical fields on quantum transport processes.
Most importantly, such strong fluctuating fields induce a whole variety of
nonlinear and nonequilibrium phenomena. A characteristic feature of such
dynamics is the absence of thermal (quantum) detailed balance.Comment: review article, Advances in Physics (2005), in pres
2019 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations : summary from the basic life support; advanced life support; pediatric life support; neonatal life support; education, implementation, and teams; and first aid task forces
The International Liaison Committee on Resuscitation has initiated a continuous review of new, peer-reviewed, published cardiopulmonary resuscitation science. This is the third annual summary of the International Liaison Committee on Resuscitation International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. It addresses the most recent published resuscitation evidence reviewed by International Liaison Committee on Resuscitation Task Force science experts. This summary addresses the role of cardiac arrest centers and dispatcher-assisted cardiopulmonary resuscitation, the role of extracorporeal cardiopulmonary resuscitation in adults and children, vasopressors in adults, advanced airway interventions in adults and children, targeted temperature management in children after cardiac arrest, initial oxygen concentration during resuscitation of newborns, and interventions for presyncope by first aid providers. Members from 6 International Liaison Committee on Resuscitation task forces have assessed, discussed, and debated the certainty of the evidence on the basis of the Grading of Recommendations, Assessment, Development, and Evaluation criteria, and their statements include consensus treatment recommendations. Insights into the deliberations of the task forces are provided in the Justification and Evidence to Decision Framework Highlights sections. The task forces also listed priority knowledge gaps for further research
Structure of the Nucleotide Radical Formed during Reaction of CDP/TTP with the E441Q-α2β2 of E. coli Ribonucleotide Reductase
The Escherichia coli ribonucleotide reductase (RNR) catalyzes the conversion of nucleoside diphosphates to deoxynucleotides and requires a diferric-tyrosyl radical cofactor for catalysis. RNR is composed of a 1:1 complex of two homodimeric subunits: α and β. Incubation of the E441Q-α mutant RNR with substrate CDP and allosteric effector TTP results in loss of the tyrosyl radical and formation of two new radicals on the 200 ms to min time scale. The first radical was previously established by stopped flow UV/vis spectroscopy and pulsed high field EPR spectroscopy to be a disulfide radical anion. The second radical was proposed to be a 4′-radical of a 3′-keto-2′-deoxycytidine 5′-diphosphate. To identify the structure of the nucleotide radical [1′-[superscript 2]H], [2′-[superscript 2]H], [4′-[superscript 2]H], [5′-[superscript 2]H], [U−[superscript 13]C, [superscript 15]N], [U−[superscript 15]N], and [5,6 -[superscript 2]H] CDP and [β-[superscript 2]H] cysteine-α were synthesized and incubated with E441Q-α2β2 and TTP. The nucleotide radical was examined by 9 GHz and 140 GHz pulsed EPR spectroscopy and 35 GHz ENDOR spectroscopy. Substitution of [superscript 2]H at C4′ and C1′ altered the observed hyperfine interactions of the nucleotide radical and established that the observed structure was not that predicted. DFT calculations (B3LYP/IGLO-III/B3LYP/TZVP) were carried out in an effort to recapitulate the spectroscopic observations and lead to a new structure consistent with all of the experimental data. The results indicate, unexpectedly, that the radical is a semidione nucleotide radical of cytidine 5′-diphosphate. The relationship of this radical to the disulfide radical anion is discussed.National Institutes of Health (U.S.) (GM29595)(EB002804)(EB002026
Qubit-flip-induced cavity mode squeezing in the strong dispersive regime of the quantum Rabi model
Squeezed states of light are a set of nonclassical states in which the quantum fluctuations of one quadrature component are reduced below the standard quantum limit. With less noise than the best stabilised laser sources, squeezed light is a key resource in the field of quantum technologies and has already improved sensing capabilities in areas ranging from gravitational wave detection to biomedical applications. In this work we propose a novel technique for generating squeezed states of a confined light field strongly coupled to a two-level system, or qubit, in the dispersive regime. Utilising the dispersive energy shift caused by the interaction, control of the qubit state produces a time-dependent change in the frequency of the light field. An appropriately timed sequence of sudden frequency changes reduces the quantum noise fluctuations in one quadrature of the field well below the standard quantum limit. The degree of squeezing and the time of generation are directly controlled by the number of frequency shifts applied. Even in the presence of realistic noise and imperfections, our protocol promises to be capable of generating a useful degree of squeezing with present experimental capabilities
The deuteron: structure and form factors
A brief review of the history of the discovery of the deuteron in provided.
The current status of both experiment and theory for the elastic electron
scattering is then presented.Comment: 80 pages, 33 figures, submited to Advances in Nuclear Physic
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