3,221 research outputs found
Effective temperatures of a heated Brownian particle
We investigate various possible definitions of an effective temperature for a
particularly simple nonequilibrium stationary system, namely a heated Brownian
particle suspended in a fluid. The effective temperature based on the
fluctuation dissipation ratio depends on the time scale under consideration, so
that a simple Langevin description of the heated particle is impossible. The
short and long time limits of this effective temperature are shown to be
consistent with the temperatures estimated from the kinetic energy and Einstein
relation, respectively. The fluctuation theorem provides still another
definition of the temperature, which is shown to coincide with the short time
value of the fluctuation dissipation ratio
Exponential decay for the damped wave equation in unbounded domains
We study the decay of the semigroup generated by the damped wave equation in
an unbounded domain. We first prove under the natural geometric control
condition the exponential decay of the semigroup. Then we prove under a weaker
condition the logarithmic decay of the solutions (assuming that the initial
data are smoother). As corollaries, we obtain several extensions of previous
results of stabilisation and control
Derivation of the Zakharov equations
This paper continues the study of the validity of the Zakharov model
describing Langmuir turbulence. We give an existence theorem for a class of
singular quasilinear equations. This theorem is valid for well-prepared initial
data. We apply this result to the Euler-Maxwell equations describing
laser-plasma interactions, to obtain, in a high-frequency limit, an asymptotic
estimate that describes solutions of the Euler-Maxwell equations in terms of
WKB approximate solutions which leading terms are solutions of the Zakharov
equations. Because of transparency properties of the Euler-Maxwell equations,
this study is led in a supercritical (highly nonlinear) regime. In such a
regime, resonances between plasma waves, electromagnetric waves and acoustic
waves could create instabilities in small time. The key of this work is the
control of these resonances. The proof involves the techniques of geometric
optics of Joly, M\'etivier and Rauch, recent results of Lannes on norms of
pseudodifferential operators, and a semiclassical, paradifferential calculus
The Origin of Fe II Emission in AGN
We used a very large set of models of broad emission line (BEL) clouds in AGN
to investigate the formation of the observed Fe II emission lines. We show that
photoionized BEL clouds cannot produce both the observed shape and observed
equivalent width of the 2200-2800A Fe II UV bump unless there is considerable
velocity structure corresponding to a microturbulent velocity parameter v_turb
> 100 km/s for the LOC models used here. This could be either microturbulence
in gas that is confined by some phenomenon such as MHD waves, or a velocity
shear such as in the various models of winds flowing off the surfaces of
accretion disks. The alternative way that we can find to simultaneously match
both the observed shape and equivalent width of the Fe II UV bump is for the Fe
II emission to be the result of collisional excitation in a warm, dense gas.
Such gas would emit very few lines other than Fe II. However, since the
collisionally excited gas would constitute yet another component in an already
complicated picture of the BELR, we prefer the model involving turbulence. In
either model, the strength of Fe II emission relative to the emission lines of
other ions such as Mg II depends as much on other parameters (either v_turb or
the surface area of the collisionally excited gas) as it does on the iron
abundance. Therefore, the measurement of the iron abundance from the FeII
emission in quasars becomes a more difficult problem.Comment: 23 pages. Accepted by Ap
Damage-free single-mode transmission of deep-UV light in hollow-core PCF
Transmission of UV light with high beam quality and pointing stability is
desirable for many experiments in atomic, molecular and optical physics. In
particular, laser cooling and coherent manipulation of trapped ions with
transitions in the UV require stable, single-mode light delivery. Transmitting
even ~2 mW CW light at 280 nm through silica solid-core fibers has previously
been found to cause transmission degradation after just a few hours due to
optical damage. We show that photonic crystal fiber of the kagom\'e type can be
used for effectively single-mode transmission with acceptable loss and bending
sensitivity. No transmission degradation was observed even after >100 hours of
operation with 15 mW CW input power. In addition it is shown that
implementation of the fiber in a trapped ion experiment significantly increases
the coherence times of the internal state transfer due to an increase in beam
pointing stability
Generalised Einstein Relation for Hot Brownian Motion
The Brownian motion of a hot nanoparticle is described by an effective Markov
theory based on fluctuating hydrodynamics. Its predictions are scrutinized over
a wide temperature range using large-scale molecular dynamics simulations of a
hot nanoparticle in a Lennard-Jones fluid. The particle positions and momenta
are found to be Boltzmann distributed according to distinct effective
temperatures and . For we
derive a formally exact theoretical prediction and establish a generalised
Einstein relation that links it to directly measurable quantities
Temperature-mediated transition from Dyakonov-Tamm surface waves to surface-plasmon-polariton waves
The effect of changing the temperature on the propagation of electromagnetic surface waves (ESWs), guided by the planar interface of a homogeneous isotropic temperature-sensitive material (namely, InSb) and a temperature-insensitive structurally chiral material (SCM) was numerically investigated in the terahertz frequency regime. As the temperature rises, InSb transforms from a dissipative dielectric material to a \blue{dissipative} plasmonic material. Correspondingly, the ESWs transmute from Dyakonov--Tamm surface waves into surface--plasmon--polariton waves. The effects of the temperature change are clearly observed in the phase speeds, propagation distances, angular existence domains, multiplicity, and spatial profiles of energy flow of the ESWs. Remarkably large propagation distances can be achieved; in such instances the energy of an ESW is confined almost entirely within the SCM. For certain propagation directions, simultaneous excitation of two ESWs with (i) the same phase speeds but different propagation distances or (ii) the same propagation distances but different phase speeds are also indicated by our results
Long-term quality of life in premenopausal women with node-negative localized breast cancer treated with or without adjuvant chemotherapy
Our purpose was to evaluate the late physical and psychosocial difficulties of premenpausal patients treated for a localized breast cancer and to weigh the impact of chemotherapy on long-term quality of life. Two self-administered questionnaires, the EORTC core QLQ-C30 and the breast module (BR23) were mailed to 179 premenopausal node-negative women continuously disease-free, previously enrolled in a trial testing the efficacy of adjuvant CMF chemotherapy (Espié et al, 1997). The core questionnaire evaluates the physical, role, emotional, cognitive and social functioning and global health status. The breast module includes four functional scales: body image, sexual functioning, sexual enjoyment and future perspective. It also includes symptom scales such as arm or breast symptoms. Some specific professional and social states were added. 119 (68%) patients (mean age 54 years, range 30–69) participated. Mean follow-up time since diagnosis was 9.6 years (4–16). 68% had conservative and 32% radical surgery (with reconstructive surgery in 50%). CMF was given to 77 (65%) patients. Irradiation was administered in 75% of patients irrespective of adjuvant therapy. QLQ-C30 scale scores were similar in patients who had or had not received chemotherapy. Disturbance in body image, sex life and breast symptoms did not differ between patients who had or had not received adjuvant CMF. No major socioprofessional difficulties were reported except problems in borrowing from banks not related to past chemotherapy. With long follow-up, most premenopausal women treated for a localized breast cancer cope with the disease and its treatments. Adjuvant CMF chemotherapy does not appear to impair quality of life nor social and professional life in these patients. © 2000 Cancer Research Campaig
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