1,119 research outputs found
The peripheral and central mechanisms of transition of acute to chronic pain and the possible role of cyclooxygenase-2 inhibition in the prevention of pain syndrome chronization
Chronic pain syndromes as a cause of suffering, short-term or persistent disability, and social losses greatly worsen quality of life. The mechanisms leading to the occurrence and maintenance of chronic pain are traditionally of interest for in-depth study since each of them is potentially a target for pharmacotherapy. Peripheral and central sensitizations, as well as disinhibition make different contributions to the development of chronic pain. The fact that cyclooxygenase-2 (COX-2) inhibitors may affect at both the peripheral and central, spinal levels, by modulating such a phenomenon as central sensitization, has been recently discussed. There are theoretical prerequisites for a discussion of this action of COX-2 inhibitors; however, clinical findings supporting this hypothesis have been scarce so far. In this connection, of interest is the clinical trial published in 2016, which may suggest to a high degree of accuracy that some analgesic effect of the selective COX-2 inhibitor etoricoxib is realized through the central mechanisms of pain modulation
Quantum adiabatic polarons by translationally invariant perturbation theory
The translationally invariant diagrammatic quantum perturbation theory (TPT)
is applied to the polaron problem on the 1D lattice, modeled through the
Holstein Hamiltonian with the phonon frequency omega0, the electron hopping t
and the electron-phonon coupling constant g. The self-energy diagrams of the
fourth-order in g are calculated exactly for an intermittently added electron,
in addition to the previously known second-order term. The corresponding
quadratic and quartic corrections to the polaron ground state energy become
comparable at t/omega0>1 for g/omega0~(t/omega0)^{1/4} when the electron
self-trapping and translation become adiabatic. The corresponding non
adiabatic/adiabatic crossover occurs while the polaron width is large, i.e. the
lattice coarsening negligible. This result is extended to the range
(t/omega0)^{1/2}>g/omega0>(t/omega0)^{1/4}>1 by considering the scaling
properties of the high-order self-energy diagrams. It is shown that the polaron
ground state energy, its width and the effective mass agree with the results
found traditionally from the broken symmetry side, kinematic corrections
included. The Landau self trapping of the electron in the classic
self-consistent, localized displacement potential, the restoration of the
translational symmetry by the classic translational Goldstone mode and the
quantization of the polaronic translational coordinate are thus all encompassed
by a quantum theory which is translationally invariant from the outset.Comment: 10 pages, 5 figure
Jahn-Teller systems from a cavity QED perspective
Jahn-Teller systems and the Jahn-Teller effect are discussed in terms of
cavity QED models. By expressing the field modes in a quadrature
representation, it is shown that certain setups of a two-level system
interacting with a bimodal cavity is described by the Jahn-Teller
Hamiltonian. We identify the corresponding adiabatic
potential surfaces and the conical intersection. The effects of a non-zero
geometrical Berry phase, governed by encircling the conical intersection, are
studied in detail both theoretically and numerically. The numerical analysis is
carried out by applying a wave packet propagation method, more commonly used in
molecular or chemical physics, and analytic expressions for the characteristic
time scales are presented. It is found that the collapse-revival structure is
greatly influenced by the geometrical phase and as a consequence, the field
intensities contain direct information about this phase. We also mention the
link between the Jahn-Teller effect and the Dicke phase transition in cavity
QED.Comment: 10 pages, 6 figures. Replaced with final versio
Part of the D - dimensional Spiked harmonic oscillator spectra
The pseudoperturbative shifted - l expansion technique PSLET [5,20] is
generalized for states with arbitrary number of nodal zeros. Interdimensional
degeneracies, emerging from the isomorphism between angular momentum and
dimensionality of the central force Schrodinger equation, are used to construct
part of the D - dimensional spiked harmonic oscillator bound - states. PSLET
results are found to compare excellenly with those from direct numerical
integration and generalized variational methods [1,2].Comment: Latex file, 20 pages, to appear in J. Phys. A: Math. & Ge
Soluble cuticular wax composition and antimicrobial activity of the fruits of Chaenomeles species and an interspecific hybrid
Plants of the genus Chaenomeles Lindl. (Rosaceae) naturally grow in Southeast Asia and represent the richest resource of biologically active compounds with beneficial properties for humans. Plants of C. japonica (Thunb.) Lindl. and C. speciosa (Sweet) Nakai species, and interspecific hybrid C. × superba (Frahm) Rehder (C. japonica × C. speciosa, Superba group) have been successfully introduced in the steppe zone of Ukraine and bear fruits. In this study, we evaluated chemical composition of fruit cuticular waxes and antimicrobial activity of fruit extracts. The soluble waxes were characterized using gas chromatography-mass spectrometry (GC-MS), and 26–36 compounds, representing 91.7–96.6% of the total soluble cuticular waxes, were identified. Waxes of Chaenomeles fruits belonged to six classes, namely fatty acids, alcohols, aldehydes, esters, ethers and alkanes. Aldehydes 7-hexadecenal and heptacosanal, and alkanes hexatriacontane and tetrapentacontane were the main constituents in the soluble cuticular waxes of C. speciosa and C. × superba fruits, accounting for more than half of the total contents. However, alkane tetrapentacontane, alcohol 8,10-hexadecadien-1-ol and heptacosanal prevailed in C. japonica fruit waxes. Isopropanolic fruit extracts exhibited dose-dependent antimicrobial activity against four Gram-negative bacteria, five Gram-positive bacteria and one fungal strain in the disc diffusion assay. In general, extracts from the Chaenomeles fruits demonstrated higher activity against Gram+ bacteria than Gram- strains. The strongest inhibiting activity was shown against Staphylococcus epidermidis (by the fruit extracts of C. × superba and C. speciosa), Micrococcus lysodeikticus and Candida albicans (both by C. × superba fruit extract). Results of the study confirmed accumulation of the bioactive compounds in the fruit waxes of different Chaenomeles species and antimicrobial ability of Chaenomeles fruits as well. These findings revealed the bioactive compounds in fruit cuticular waxes and suggested health-promoting properties of introduced Chaenomeles species
Quantum interference structures in trapped ion dynamics beyond the Lamb-Dicke and rotating wave approximations
We apply wave packet methods to study an ion-trap system in the strong
excitation regime imposing neither the rotating wave nor the Lamb-Dicke
approximations. By this approach we show the existence of states with
restricted phase space evolution, as a genuine consequence of quantum
interference between wave packet fractions. A particular instance of such a
state oscillates between maximal entanglement and pure disentanglement between
the constitute subsystems. The characteristic crossover time is very rapid
making them suitable for state preparations of EPR or Schrodinger cat states.
Over longer time periods the dynamics of these states exhibits collapse-revival
patterns with well resolved fractional revivals in autocorrelation, inversion
and entanglement.Comment: 11 pages, 5 figures. Replaced with revised version. Phys. Rev. A 77,
053808 (2008
Anomalous Thermal Stability of Metastable C_20 Fullerene
The results of computer simulation of the dynamics of fullerene C_20 at
different temperatures are presented. It is shown that, although it is
metastable, this isomer is very stable with respect to the transition to a
lower energy configuration and retains its chemical structure under heating to
very high temperatures, T ~ 3000 K. Its decay activation energy is found to be
E_a ~ 7 eV. Possible decay channels are studied, and the height of the minimum
potential barrier to decay is determined to be U = 5.0 eV. The results obtained
make it possible to understand the reasons for the anomalous stability of
fullerene C_20 under normal conditions.Comment: Slightly corrected version of the paper submitted to Phys. Solid
Stat
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