42,543 research outputs found
Microwave diode amplifiers with low intermodulation distortion
Distortions can be greatly reduced in narrow-band applications by using the second harmonic. The ac behavior of simplified diode amplifier has negative resistance depending on slope of equivalent I-V curve
Non-equilibrium dynamics in quantum field theory at high density: the tsunami
The dynamics of a dense relativistic quantum fluid out of thermodynamic
equilibrium is studied in the framework of the Phi^4 scalar field theory in the
large N limit. The time evolution of a particle distribution in momentum space
(the tsunami) is computed. The effective mass felt by the particles in such a
high density medium equals the tree level mass plus the expectation value of
the squared field. The case of negative tree level squared mass is particularly
interesting. In such case dynamical symmetry restoration as well as dynamical
symmetry breaking can happen. Furthermore, the symmetry may stay broken with
vanishing asymptotic squared mass showing the presence of out of equilibrium
Goldstone bosons. We study these phenomena and identify the set of initial
conditions that lead to each case. We compute the equation of state which turns
to depend on the initial state. Although the system does not thermalize, the
equation of state for asymptotically broken symmetry is of radiation type. We
compute the correlation functions at equal times. The two point correlator for
late times is the sum of different terms. One stems from the initial particle
distribution. Another term accounts for the out of equilibrium Goldstone bosons
created by spinodal unstabilities when the symmetry is asymptotically
broken.Both terms are of the order of the inverse of the coupling for distances
where causal signals can connect the two points. The contribution of the out of
equilibrium Goldstones exhibits scaling behaviour in a generalized sense.Comment: LaTex, 49 pages, 15 .ps figure
Formulas for Continued Fractions. An Automated Guess and Prove Approach
We describe a simple method that produces automatically closed forms for the
coefficients of continued fractions expansions of a large number of special
functions. The function is specified by a non-linear differential equation and
initial conditions. This is used to generate the first few coefficients and
from there a conjectured formula. This formula is then proved automatically
thanks to a linear recurrence satisfied by some remainder terms. Extensive
experiments show that this simple approach and its straightforward
generalization to difference and -difference equations capture a large part
of the formulas in the literature on continued fractions.Comment: Maple worksheet attache
Microwave resonances of the bubble phases in 1/4 and 3/4 filled higher Landau levels
We have measured the diagonal conductivity in the microwave regime of an
ultrahigh mobility two dimensional electron system. We find a sharp resonance
in Re[sigma_{xx}] versus frequency when nu > 4 and the partial filling of the
highest Landau level, nu^*, is ~ 1/4 or 3/4 and temperatures < 0.1 K. The
resonance appears for a range of nu^* from 0.20 to 0.37 and again from 0.62 to
0.82. the peak frequency, f_{pk} changes from ~ 500 to ~ 150 as nu^* = 1/2 is
approached. This range of f_{pk} shows no dependence on nu where the resonance
is observed. The quality factor, Q, of the resonance is maximum at ~ nu^* =
0.25 and 0.74. We interpret the resonance as due to a pinning mode of the
bubble phase crystal.Comment: revtex 4, 3 figures, minor corrections made. Accepted by pr
Measuring atomic NOON-states and using them to make precision measurements
A scheme for creating NOON-states of the quasi-momentum of ultra-cold atoms
has recently been proposed [New J. Phys. 8, 180 (2006)]. This was achieved by
trapping the atoms in an optical lattice in a ring configuration and rotating
the potential at a rate equal to half a quantum of angular momentum . In this
paper we present a scheme for confirming that a NOON-state has indeed been
created. This is achieved by spectroscopically mapping out the anti-crossing
between the ground and first excited levels by modulating the rate at which the
potential is rotated. Finally we show how the NOON-state can be used to make
precision measurements of rotation.Comment: 14 preprint pages, 7 figure
The Practice of Immigration Health in Complex Emergency Situations - A Case Study of Kosovo from March to July 1999
The need to rapidly transport refugees,
displaced as a result of evolving complex
humanitarian emergencies creates challenges
for those refugee-receiving nations
that require formaI immigration
medical screening of these populations.
Balancing the need to expediently resettle
the refugees with these legislative and
regulatory medical requirements can be
logistically and operationally difficult.
During the 1999 Kosovo crisis, the Humanitarian
Evacuation Programme
from the Former Yugoslav Republic of
Macedonia rapidly moved large numbers
of Kosovar Albanian refugees to nations
with existing formal immigration
medical screening requirements. This
paper describes the successful management and delivery
of immigration health
services during this complicated international
event.La nécessité de transporter rapidement
les réfugiés déplacés à cause d'urgences
humanitaires complexes Ă Ă©volution
rapide représenteun défi pour les nations
receveuses de réfugiés requérant un
tamisage médical routinier de sa population
immigrante. Des points de vue
logistique et opérationnel, il peut
s'avérer fort difficile pour ces états de
concilier la nécessité de relocaliser
rapidement les réfugiés avec les exigences
de leurs lois et règlements en
matière médicale et sanitaire. Lors de la
crise du Kosovo de 1999, le Programme
d'Évacuation Humanitaire de l'ancienne
république yougoslave de Macédoine
déplaça rapidement un grand nombre de
réfugiés albanais kosovars vers des nations
requérant formellement un
tamisage médical de sa population
immigrante. Cet article décrit la gestion
et la distribution réussies de services de
santé à l'immigration au cours de cet
événement international complexe
Gauge Fields Out-Of-Equilibrium: A Gauge Invariant Formulation and the Coulomb Gauge
We study the abelian Higgs model out-of-equilibrium in two different
approaches, a gauge invariant formulation, proposed by Boyanovsky et al.
\cite{Boyanovsky:1996dc} and in the Coulomb gauge. We show that both approaches
become equivalent in a consistent one loop approximation. Furthermore, we carry
out a proper renormalization for the model in order to prepare the equations
for a numerical implementation. The additional degrees of freedom, which arise
in gauge theories, influence the behavior of the system dramatically. A
comparison with results in the 't Hooft-Feynman background gauge found by us
recently, shows very good agreement.Comment: 32 pages, 8 figure
Half-life Limit of 19Mg
A search for 19Mg was performed using projectile fragmentation of a 150
MeV/nucleon 36Ar beam. No events of 19Mg were observed. From the time-of-flight
through the fragment separator an upper limit of 22 ns for the half-life of
19Mg was established
The ICAM-3/LFA-1 interaction is critical for epidermal Langerhans cell alloantigen presentation to CD4 + T cells
Intercellular adhesion molecule (ICAM)-3 is a recently described member of the immunoglobulin superfamily and, as such, is closely related to ICAM-1 and ICAM-2. All three ICAMS are cognate for the counter-receptor lymphocyte function associated antigen-1 (LFA-L CD11a/CD18). Unlike ICAM-1 and ICAM-2. ICAM-3 is constitutively expressed at high levels on resting leucocytes. We investigated the expression and function of ICAM-3 in normal skin ( n = 5), as well as its expression in psoriasis ( n = 4). atopic eczema ( n = 4), allergic (rhus) contact dermatitis ( n =3). and cutaneous T-cell lymphoma (CTCL. n =2). Five-micrometre cryostat sections of skin were stained using monoclonal antibodies to ICAM-3 and A well characterized immunoperoxidase technique. In normal skin. ICAM-3 was expressed by all cutaneous leucocytes hut most striking was the strong expression of ICAM-3 by Langerhans cells within both epidermis and dermis. This observation was confirmed by double-labelling with CD1a and negative staining with an IgG1 isotype control. In psoriasis, atopic eczema, allergic contact dermatitis, and CTCL. ICAM-3 was co-expressed on all CD1a + cells, although, in psoriasis, the intensity of ICAM-3 expression was reduced. Functional blocking experiments were performed to determine whether the observed ICAM-3 expression on Langerhans cells was functionally important in antigen presentation. CD4 + T cells were prepared from peripheral blood and 10 5 CD4 + T cells combined with 10 5 epidermal cells harvested from keratome biopsies of normal skin of an individual allogeneic to the T-cell donor. Addition of 50 Îśg anti-ICAM-3 to the co-culture resulted in a consistent (50%) reduction in degree of alloantigen presentation by Langerhans cells to T cells. Inhibition was 77% of that produced by the addition of anti-LFA-1. These data indicate that ICAM-3 is constitutively expressed by Langerhans cells and is a major ligand for LFA-1 on CD4 + T cells during their response to Langerhans cells. Because fresh Langerhans ceils constitutively express little ICAM-1. whereas ICAM-3 is constitutively expressed at high levels, it would appear that 1CAM-3 is the dominant functional ICAM on in situ Langerhans cells in the normal epidermis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73969/1/j.1365-2133.1995.tb06911.x.pd
Microwave resonance of the reentrant insulating quantum Hall phases in the 1st excited Landau Level
We present measurements of the real diagonal microwave conductivity of the
reentrant insulating quantum Hall phases in the first excited Landau level at
temperatures below 50 mK. A resonance is detected around filling factor
and weaker frequency dependence is seen at and 2.28.
These measurements are consistent with the formation of a bubble phase crystal
centered around these at very low temperatures
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