19,339 research outputs found
Cranked shell model and isospin symmetry near N=Z
A cranked shell model approach for the description of rotational bands in
nuclei is formulated. The isovector neutron-proton pairing is
taken into account explicitly. The concept of spontaneous breaking and
subsequent restoration of the isospin symmetry turns out to be crucial. The
general rules to construct the near yrast-spectra for rotating nuclei are
presented. For the model case of particles in a j-shell, it is shown that
excitation spectra and the alignment processes are well described as compared
to the exact shell model calculation. Realistic cranked shell model
calculations are able to describe the experimental spectra of Kr and
Rb isotopes. \Comment: 23 pages, 5 figure
Observation of coupled plasmon-polariton modes in Au nanoparticle chain waveguides of different lengths: Estimation of waveguide loss
Near-field interactions between closely spaced Au nanoparticles were characterized by studying the spectral position of the extinction bands corresponding to longitudinal (L) and transverse (T) plasmon-polariton modes of Au nanoparticle chains. Far-field spectroscopy and finite-difference time-domain simulations on arrays of 50 nm diameter Au spheres with an interparticle spacing of 75 nm both show a splitting DeltaE between the L and T modes that increases with chain length and saturates at a length of seven particles at DeltaE = 65 meV. We show that the measured splitting will result in a propagation loss of 3 dB/15 nm for energy transport. Calculations indicate that this loss can be reduced by at least one order of magnitude by modifying the shape of the constituent particles
Optical pulse propagation in metal nanoparticle chain waveguides
Finite-difference time-domain simulations show direct evidence of optical pulse propagation below the diffraction limit of light along linear arrays of spherical noble metal nanoparticles with group velocities up to 0.06c. The calculated dispersion relation and group velocities correlate remarkably well with predictions from a simple point-dipole model. A change in particle shape to spheroidal particles shows up to a threefold increase in group velocity. Pulses with transverse polarization are shown to propagate with negative phase velocities antiparallel to the energy flow
Neuroenhancement of exposure therapy in anxiety disorders
Although exposure-based treatments and anxiolytic medications are more effective than placebo for treating anxiety disorders, there is still considerable room for further improvement. Interestingly, combining these two modalities is usually not more effective than the monotherapies. Recent translational research has identified a number of novel approaches for treating anxiety disorders using agents that serve as neuroenhancers (also known as cognitive enhancers). Several of these agents have been studied to determine their efficacy at improving treatment outcome for patients with anxiety and other psychiatric disorders. In this review, we examine d-cycloserine, yohimbine, cortisol, catecholamines, oxytocin, modafinil, and nutrients such as caffeine and amino fatty acids as potential neuroenhancers. Of these agents, d-cycloserine shows the most promise as an effective neuroenhancer for extinction learning and exposure therapy. Yet, the optimal dosing and dose timing for drug administration remains uncertain. There is partial support for cortisol, catecholamines, yohimbine and oxytocin for improving extinction learning and exposure therapy. There is less evidence to indicate that modafinil and nutrients such as caffeine and amino fatty acids are effective neuroenhancers. More research is needed to determine their long term efficacy and clinical utility of these agents.R34 MH086668 - NIMH NIH HHS; R01 AT007257 - NCCIH NIH HHS; R21 MH101567 - NIMH NIH HHS; R34 MH099311 - NIMH NIH HHS; R21 MH102646 - NIMH NIH HHS; K23 MH100259 - NIMH NIH HHS; R01 MH099021 - NIMH NIH HH
Parabolic pulse generation with active or passive dispersion decreasing optical fibers
We experimentally demonstrate the possibility to generate
parabolic pulses via a single dispersion decreasing optical fiber with normal
dispersion. We numerically and experimentally investigate the influence of
the dispersion profile, and we show that a hybrid configuration combining
dispersion decrease and gain has several benefits on the parabolic generated
pulses
Attachment style moderates the effects of oxytocin on social behaviors and cognitions during social rejection: applying an RDoC framework to social anxiety
Whereas the DSM categorizes individuals with similar self-reported symptoms, the Research Domain Criteria (RDoC) offers a new approach for classifying mental disorders based on dimensions of observable behaviors and neurobiological measures. The objective of this proof-of-concept study is to adopt this approach by distinguishing individuals based on disorder-related personality traits during an experimental manipulation that targeted a disorder-related biological mechanism. Specifically, we examined whether attachment style moderated the effect of oxytocin administration on social behaviors and cognitions during a social exclusion test in individuals with social anxiety disorder. When receiving oxytocin compared to placebo, only individuals with low attachment avoidance displayed more social affiliation and cooperation, and only those with high attachment avoidance showed faster detection of disgust and neutral faces. Thus, attachment style moderated oxytocin's effects among individuals who shared the same DSM diagnosis. We conclude that neurobiological tests can inform new classification strategies by adopting an RDoC framework.R01 AT007257 - NCCIH NIH HHS; R01 MH078308 - NIMH NIH HH
Van-der-Waals potentials of paramagnetic atoms
We study single- and two-atom van der Waals interactions of ground-state
atoms which are both polarizable and paramagnetizable in the presence of
magneto-electric bodies within the framework of macroscopic quantum
electrodynamics. Starting from an interaction Hamiltonian that includes
particle spins, we use leading-order perturbation theory for the van der Waals
potentials expressed in terms of the polarizability and magnetizability of the
atom(s). To allow for atoms embedded in media, we also include local-field
corrections via the real-cavity model. The general theory is applied to the
potential of a single atom near a half space and that of two atoms embedded in
a bulk medium or placed near a sphere, respectively.Comment: 18 pages, 3 figures, 1 tabl
Magnetic adatom induced skyrmion-like spin texture in surface electron waves
When a foreign atom is placed on a surface of a metal, the surrounding sea of
electrons responds screening the additional charge leading to oscillations or
ripples. On surfaces, those electrons are sometimes confined to two-dimensional
surface states, whose spin-degeneracy is lifted due to the Rashba effect
arising from the spin-orbit interaction of electrons and the inversion
asymmetric environment. It is believed that at least for a single adatom
scanning tunneling microscopy measurements are insensitive to the Rashba
splitting i.e. no signatures in the charge oscillations will be observed.
Resting on scattering theory, we demonstrate that, if magnetic, one single
adatom is enough to visualize the presence of the Rashba effect in terms of an
induced spin-magnetization of the surrounding electrons exhibiting a twisted
spin texture described as superposition of two skyrmionic waves of opposite
chirality.Comment: 11 pages, 5 figures, accepted in Phys. Rev. Letter
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