10,679 research outputs found
Formation of a condensed state with macroscopic number of phonons in ultracold Bose gases
A mechanism for the formation of a new type of stationary state with
macroscopical number of phonons in condensed atomic gases is proposed. This
mechanism is based on generating longitudinal phonons as a result of parametric
resonance caused by a permanent modulation of the transverse trap frequency in
an elongated trap. The phonon-phonon interaction predetermines the
self-consistent evolution which is completed with macroscopic population of one
from all levels within the energy interval of parametric amplification. This
level proves to be shifted to the edge of this interval. All other levels end
the evolution with zero population.Comment: 9 pages, 8 figure
Probing New Physics From CP Violation in Radiative B Decays
When new CP-violating interactions are dominated by flavor changing neutral
particle exchanges, that may occur in many extensions of the standard model. We
examine a type 3 two Higgs doublet model and find that direct CP asymmetries
can be as large as about 25% . Time-dependent and time-integrated
mixing-induced CP asymmetries up to 85 and 40 %, respectively, are possible
without conflict with other constraints. It mainly requirs an enhanced
chromo-magnetic dipole decay to be close to the present experimental
bound.Comment: 7 pages, latex, no figure
Manifestation of superfluidity in an evolving Bose-condensed gas
We study the generation of excitations due to an ''impurity''(static
perturbation) placed into an oscillating Bose-condensed gas in the
time-dependent trapping field. It is shown that there are two regions for the
position of the local perturbation. In the first region the condensate flows
around the ''impurity'' without generation of excitations demonstrating
superfluid properties. In the second region the creation of excitations occurs,
at least within a limited time interval, revealing destruction of
superfluidity. The phenomenon can be studied by measuring the damping of
condensate oscillations at different positions of the ''impurity''
Small-scale phase separation in doped anisotropic antiferromagnets
We analyze the possibility of the nanoscale phase separation manifesting
itself in the formation of ferromagnetic (FM) polarons (FM droplets) in the
general situation of doped anisotropic three- and two-dimensional
antiferromagnets. In these cases, we calculate the shape of the most
energetically favorable droplets. We show that the binding energy and the
volume of a FM droplet in the three-dimensional (3D) case depend only upon two
universal parameters and , where and are effective
antiferromagnetic (AFM) exchange and hopping integrals, respectively. In the
two-dimensional (2D) case, these parameters have the form and . The most favorable shape of a
ferromagnetic droplet corresponds to an ellipse in the 2D case and to an
ellipsoid in the 3D case.Comment: 6 pages, 1 figure, RevTe
Dynamics of long-range order in an exciton-polariton condensate
We report on time resolved measurements of the first order spatial coherence
in an exciton polariton Bose-Einstein condensate. Long range spatial coherence
is found to set in right at the onset of stimulated scattering, on a picosecond
time scale. The coherence reaches its maximum value after the population and
decays slower, staying up to a few hundreds of picoseconds. This behavior can
be qualitatively reproduced, using a stochastic classical field model
describing interaction between the polariton condensate and the exciton
reservoir within a disordered potential.Comment: 7 pages, 4 figure
Observing the Formation of Long-range Order during Bose-Einstein Condensation
We have experimentally investigated the formation of off-diagonal long-range
order in a gas of ultracold atoms. A magnetically trapped atomic cloud prepared
in a highly nonequilibrium state thermalizes and thereby crosses the
Bose-Einstein condensation phase transition. The evolution of phase coherence
between different regions of the sample is constantly monitored and information
on the spatial first-order correlation function is obtained. We observe the
growth of the spatial coherence and the formation of long-range order in real
time and compare it to the growth of the atomic density. Moreover, we study the
evolution of the momentum distribution during the nonequilibrium formation of
the condensate.Comment: 4 pages, 4 figure
A priori mixing of mesons and the |Delta I|=1/2 rule in K\to\pi\pi
We consider the hypothesis of a priori mixings in the mass eigenstates of
mesons to obtain the |Delta I|=1/2 rule in K\to\pi\pi. The Hamiltonian
responsible for the transition is the strong interacting one. The experimental
data are described using the isospin symmetry relations between the strong
coupling constants
Bound states of three and four resonantly interacting particles
We present an exact diagrammatic approach for the problem of dimer-dimer
scattering in 3D for dimers being a resonant bound state of two fermions in a
spin-singlet state, with corresponding scattering length . Applying this
approach to the calculation of the dimer-dimer scattering length , we
recover exactly the already known result . We use the developed
approach to obtain new results in 2D for fermions as well as for bosons.
Namely, we calculate bound state energies for three and four
resonantly interacting bosons in 2D. For the case of resonant interaction
between fermions and bosons we calculate exactly bound state energies of the
following complexes: two bosons plus one fermion , two bosons plus two
fermions , and three bosons plus one fermion
.Comment: 10 pages, 9 figure
Superconductivity from repulsive interactions in the two dimensional electron gas
We present a well-controlled perturbative renormalization group (RG)
treatment of superconductivity from short-ranged repulsive interactions in a
variety of model two dimensional electronic systems. Our analysis applies in
the limit where the repulsive interactions between the electrons are small
compared to their kinetic energy.Comment: 10 pages 3 figure
Understanding trauma in children and young people in the school setting
Aim: Educational practitioners are increasingly aware of trauma experiences in students as a factor in child disturbance and schooling problems. This discussion paper aims to clarify definitions of trauma and differentiate them from other adverse childhood experiences (ACE), describe trauma impact in terms of clinical outcomes (PTSD, emotional and behavioural disorder) and how attachment factors mediate risk and discuss the challenges and ethics of identifying and enquiring about trauma experience in a school setting.
Rationale: Schools are increasingly required to be 'trauma sensitive' and to intervene where possible, with government requirements of improving mental health in schools. However, this poses a real challenge for educationalists given the barriers due to ethics, stigma/secrecy, referral implications and measurement availability for whole school approaches. Universal screening may provide a framework that helps schools recognise, measure and treat trauma.
Findings: A conceptual model clarifying trauma exposure, trauma impact and mediating factors is identified to aid understanding for teachers. Use of technological screening methods for whole school monitoring of trauma impacts, including mediating risks, are outlined.
Limitations: A full literature review of trauma or school-based interventions is not provided. Nor are biological impacts of trauma at different developmental stages described.
Conclusion: Teachers would benefit from having a psychological understanding of trauma models and their component parts in order to identify what lies within the remit of schools for identification and intervention
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