5,085 research outputs found
Non-equilibrium diagrammatic approach to strongly interacting photons
We develop a non-equilibrium field-theoretical approach based on a systematic
diagrammatic expansion for strongly interacting photons in optically dense
atomic media. We consider the case where the characteristic photon-propagation
range is much larger than the interatomic spacing and where the
density of atomic excitations is low enough to neglect saturation effects. In
the highly polarizable medium the photons experience nonlinearities through the
interactions they inherit from the atoms. If the atom-atom interaction range
is also large compared to , we show that the subclass of diagrams
describing scattering processes with momentum transfer between photons is
suppressed by a factor . We are then able to perform a self-consistent
resummation of a specific (Hartree-like) diagram subclass and obtain
quantitative results in the highly non-perturbative regime of large single-atom
cooperativity. Here we find important, conceptually new collective phenomena
emerging due to the dissipative nature of the interactions, which even give
rise to novel phase transitions. The robustness of these is investigated by
inclusion of the leading corrections in . We consider specific
applications to photons propagating under EIT conditions along waveguides near
atomic arrays as well as within Rydberg ensembles.Comment: 72 pages, 36 figure
Gauss-Codazzi thermodynamics on the timelike screen
It is a known result by Jacobson that the flux of energy-matter through a
local Rindler horizon is related with the expansion of the null generators in a
way that mirrors the first law of thermodynamics. We extend such a result to a
timelike screen of observers with finite acceleration. Since timelike curves
have more freedom than null geodesics, the construction is more involved than
Jacobson's and few geometrical constraints need to be imposed: the observers'
acceleration has to be constant in time and everywhere orthogonal to the
screen. Moreover, at any given time, the extrinsic curvature of the screen has
to be flat. The latter requirement can be weakened by asking that the extrinsic
curvature, if present at the beginning, evolves in time like on a cone and just
rescales proportionally to the expansion.Comment: 8+1 pages, final versio
Discrete Breathers in a Realistic Coarse-Grained Model of Proteins
We report the results of molecular dynamics simulations of an off-lattice
protein model featuring a physical force-field and amino-acid sequence. We show
that localized modes of nonlinear origin (discrete breathers) emerge naturally
as continuations of a subset of high-frequency normal modes residing at
specific sites dictated by the native fold. In the case of the small
-barrel structure that we consider, localization occurs on the turns
connecting the strands. At high energies, discrete breathers stabilize the
structure by concentrating energy on few sites, while their collapse marks the
onset of large-amplitude fluctuations of the protein. Furthermore, we show how
breathers develop as energy-accumulating centres following perturbations even
at distant locations, thus mediating efficient and irreversible energy
transfers. Remarkably, due to the presence of angular potentials, the breather
induces a local static distortion of the native fold. Altogether, the
combination of this two nonlinear effects may provide a ready means for
remotely controlling local conformational changes in proteins.Comment: Submitted to Physical Biolog
Impact of classical forces and decoherence in multi-terminal Aharonov-Bohm networks
Multi-terminal Aharonov-Bohm (AB) rings are ideal building blocks for quantum
networks (QNs) thanks to their ability to map input states into controlled
coherent superpositions of output states. We report on experiments performed on
three-terminal GaAs/Al_(x)Ga_(1-x)As AB devices and compare our results with a
scattering-matrix model including Lorentz forces and decoherence. Our devices
were studied as a function of external magnetic field (B) and gate voltage at
temperatures down to 350 mK. The total output current from two terminals while
applying a small bias to the third lead was found to be symmetric with respect
to B with AB oscillations showing abrupt phase jumps between 0 and pi at
different values of gate voltage and at low magnetic fields, reminiscent of the
phase-rigidity constraint due to Onsager-Casimir relations. Individual outputs
show quasi-linear dependence of the oscillation phase on the external electric
field. We emphasize that a simple scattering-matrix approach can not model the
observed behavior and propose an improved description that can fully describe
the observed phenomena. Furthermore, we shall show that our model can be
successfully exploited to determine the range of experimental parameters that
guarantee a minimum oscillation visibility, given the geometry and coherence
length of a QN.Comment: 7 pages, 8 figure
Effect of a strong laser field on photoproduction by relativistic nuclei
We study the influence of a strong laser field on the Bethe-Heitler
photoproduction process by a relativistic nucleus. The laser field propagates
in the same direction as the incoming high-energy photon and it is taken into
account exactly in the calculations. Two cases are considered in detail. In the
first case, the energy of the incoming photon in the nucleus rest frame is much
larger than the electron's rest energy. The presence of the laser field may
significantly suppress the photoproduction rate at soon available values of
laser parameters. In the second case, the energy of the incoming photon in the
rest frame of the nucleus is less than and close to the electron-positron pair
production threshold. The presence of the laser field allows for the pair
production process and the obtained electron-positron rate is much larger than
in the presence of only the laser and the nuclear field. In both cases we have
observed a strong dependence of the rate on the mutual polarization of the
laser field and of the high-energy photon and the most favorable configuration
is with laser field and high-energy photon linearly polarized in the same
direction. The effects discussed are in principle measurable with presently
available proton accelerators and laser systems.Comment: 21 pages, 4 figure
Intervening Factors in the Impact of Child Maltreatment on Marital Satisfaction in Older Age
The present study investigated the effects of childhood abuse that occurred before the age of 18 on levels of marital satisfaction in older age. The study examined marital satisfaction in a group of Caucasian older married individuals with a mean age of 65.4 years who retrospectively endorsed a history of childhood physical, verbal and/or sexual abuse. Although previous studies examined the relationship of child maltreatment on young and middle-age adult relationship satisfaction, the study addressed a gap in the literature in that it examined the impact of child maltreatment on marital satisfaction in older age. Marital satisfaction in older age is particularly important to understand due to the health and psychological benefits derived from being in a satisfying marriage in older age (Booth & Johnson, 1994; Dush, Taylor, & Kroeger, 2008; Proulx, Helms, & Buehler, 2007), which is a time when health may become fragile. Furthermore, this study expands the current literature by explicating plausible mediators in the association between child maltreatment and late-life marital satisfaction. In particular, based on life course theory, the study examined specific life course risks (i.e., early marriage, early childbirth, and multiple divorces) and adult individual characteristics (i.e., avoidance coping and depression) as plausible mediators in the association between child abuse and later life marital satisfaction. The study examined men and women separately and investigated the effect of the severity of abuse on relationship functioning. The study used Structural Equation Modeling to analyze the data and tested all relationships between abuse, each mediator, and marital satisfaction. Results demonstrate that child maltreatment is negatively associated with late life marital satisfaction and that mid-life depression mediates that association for both men and women. Additionally, modification indices suggested that avoidance coping may influence late life marital satisfaction through a connection with depression and that coping by wishful thinking may be relatively more harmful for martial satisfaction than other forms of cognitive and behavioral avoidance coping. Findings suggest that treating depression in mid-life may be a feasible route to help individuals who have a history of early childhood abuse to have satisfying and protective relationships later in life
Wind sensitivity studies of a non-return wind tunnel with a 216- by 432-mm (8.5- by 17.0-inches) test section, phase 2
The refinement of inlet and exit treatments were studied which would minimize the effect of external wind on the test-section flow quality of a nonreturn wind tunnel. The investigation was conducted in the Ames Research Center 40- by 80-foot Wind Tunnel which served as the wind source. Several inlets and two exits were tested at wind directions ranging from 0 to 180 degrees and at wind-to-test-section velocity ratios from zero to somewhat greater than one. For the best inlet configuration the flow quality was good, with a velocity deviation in each of the three component directions generally less. The loss in total pressure due to the inlet treatment was low: about 0.035 of the test-section dynamic pressure for the no-wind case
Wind sensitivity studies of a non-return wind tunnel, with a 216- by 432-mm (8.5- by 17.0-inch) test section, phase 1
The study to develop inlet and exit treatments which would minimize the effect of external wind on the test-section flow quality of a nonreturn wind tunnel is reported. The investigation was conducted in the Ames Research Center 40- by 80-Foot Wind Tunnel which served as the wind source. Several inlets and two exits were tested at wind directions ranging from 0 to 180 degrees and at wind-to-test-section velocity ratios between zero and one. For the best inlet configuration the flow quality was good, with a velocity deviation in each of the three directions generally less than 1/2 knot (0.26 m/sec) for wind velocities of 15 knots (7.7 m/sec) or less. The loss in total pressure due to the inlet treatment was low: about 0.03 of the test-section dynamic pressure
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