24,535 research outputs found
A detector of small harmonic displacements based on two coupled microwave cavities
The design and test of a detector of small harmonic displacements is
presented. The detector is based on the principle of the parametric conversion
of power between the resonant modes of two superconducting coupled microwave
cavities. The work is based on the original ideas of Bernard, Pegoraro, Picasso
and Radicati, who, in 1978, suggested that superconducting coupled cavities
could be used as sensitive detectors of gravitational waves, and on the work of
Reece, Reiner and Melissinos, who, {in 1984}, built a detector of this kind.
They showed that an harmonic modulation of the cavity length l produced an
energy transfer between two modes of the cavity, provided that the frequency of
the modulation was equal to the frequency difference of the two modes. They
achieved a sensitivity to fractional deformations of dl/l~10^{-17} Hz^{-1/2}.
We repeated the Reece, Reiner and Melissinos experiment, and with an improved
experimental configuration and better cavity quality, increased the sensitivity
to dl/l~10^{-20} Hz^{-1/2}. In this paper the basic principles of the device
are discussed and the experimental technique is explained in detail. Possible
future developments, aiming at gravitational waves detection, are also
outlined.Comment: 28 pages, 12 eps figures, ReVteX. \tightenlines command added to
reduce number of pages. The following article has been accepted by Review of
Scientific Instruments. After it is published, it will be found at
http://link.aip.org/link/?rs
Comment on "Turbulent heat transport near critical points: Non-Boussinesq effects" (cond-mat/0601398)
In a recent preprint (cond-mat/0601398), D. Funfschilling and G. Ahlers
describe a new effect, that they interpret as non-Boussinesq, in a convection
cell working with ethane, near its critical point. They argue that such an
effect could have spoiled the Chavanne {\it et al.} (Phys. Rev. Lett. {\bf 79}
3648, 1997) results, and not the Niemela {\it et al.} (Nature, {\bf 404}, 837,
2000) ones, which would explain the differences between these two experiments.
We show that:-i)Restricting the Chavanne's data to situations as far from the
critical point than the Niemela's one, the same discrepancy remains.-ii)The
helium data of Chavanne show no indication of the effect observed by D.
Funfschilling and G. Ahlers.Comment: comment on cond-mat/060139
Weak KAM for commuting Hamiltonians
For two commuting Tonelli Hamiltonians, we recover the commutation of the
Lax-Oleinik semi-groups, a result of Barles and Tourin ([BT01]), using a direct
geometrical method (Stoke's theorem). We also obtain a "generalization" of a
theorem of Maderna ([Mad02]). More precisely, we prove that if the phase space
is the cotangent of a compact manifold then the weak KAM solutions (or
viscosity solutions of the critical stationary Hamilton-Jacobi equation) for G
and for H are the same. As a corrolary we obtain the equality of the Aubry
sets, of the Peierls barrier and of flat parts of Mather's functions.
This is also related to works of Sorrentino ([Sor09]) and Bernard ([Ber07b]).Comment: 23 pages, accepted for publication in NonLinearity (january 29th
2010). Minor corrections, fifth part added on Mather's function (or
effective Hamiltonian
The braiding for representations of q-deformed affine
We compute the braiding for the `principal gradation' of for from first principles, starting from the idea of a rigid
braided tensor category. It is not necessary to assume either the crossing or
the unitarity condition from S-matrix theory. We demonstrate the uniqueness of
the normalisation of the braiding under certain analyticity assumptions, and
show that its convergence is critically dependent on the number-theoretic
properties of the number in the deformation parameter . We also examine the convergence using probability, assuming a uniform
distribution for on the unit circle.Comment: LaTeX, 10 pages with 2 figs, uses epsfi
Design of a simulation environment for laboratory management by robot organizations
This paper describes the basic concepts needed for a simulation environment capable of supporting the design of robot organizations for managing chemical, or similar, laboratories on the planned U.S. Space Station. The environment should facilitate a thorough study of the problems to be encountered in assigning the responsibility of managing a non-life-critical, but mission valuable, process to an organized group of robots. In the first phase of the work, we seek to employ the simulation environment to develop robot cognitive systems and strategies for effective multi-robot management of chemical experiments. Later phases will explore human-robot interaction and development of robot autonomy
Aubry sets for weakly coupled systems of Hamilton--Jacobi equations
We introduce a notion of Aubry set for weakly coupled systems of
Hamilton--Jacobi equations on the torus and characterize it as the region where
the obstruction to the existence of globally strict critical subsolutions
concentrates. As in the case of a single equation, we prove the existence of
critical subsolutions which are strict and smooth outside the Aubry set. This
allows us to derive in a simple way a comparison result among critical sub and
supersolutions with respect to their boundary data on the Aubry set, showing in
particular that the latter is a uniqueness set for the critical system. We also
highlight some rigidity phenomena taking place on the Aubry set.Comment: 35 pages v.2 the introduction has been rewritten and shortened. Some
proofs simplified. Corrections and references added. Corollary 5.3 added
stating antisymmetry of the Ma\~n\'e matrix on points of the Aubry set.
Section 6 contains a new example
Threshold Photo/Electro Pion Production - Working Group Summary
We summarize the pertinent experimental and theoretical developments in the
field of pion photo- and electroproduction in the threshold region. We discuss
which experiments and which calculations should be done/performed in the
future.Comment: plain TeX (macro included), 6pp, summary talk presented at the
workshop on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199
Discrete Symmetries on the Light Front and a General Relation Connecting Nucleon Electric Dipole and Anomalous Magnetic Moments
We consider the electric dipole form factor, F_3(q^2), as well as the Dirac
and Pauli form factors, F_1(q^2) and F_2(q^2), of the nucleon in the
light-front formalism. We derive an exact formula for F_3(q^2) to complement
those known for F_1(q^2) and F_2(q^2). We derive the light-front representation
of the discrete symmetry transformations and show that time-reversal- and
parity-odd effects are captured by phases in the light-front wave functions. We
thus determine that the contributions to F_2(q^2) and F_3(q^2), Fock state by
Fock state, are related, independent of the fundamental mechanism through which
CP violation is generated. Our relation is not specific to the nucleon, but,
rather, is true of spin-1/2 systems in general, be they lepton or baryon. The
empirical values of the anomalous magnetic moments, in concert with empirical
bounds on the associated electric dipole moments, can better constrain theories
of CP violation. In particular, we find that the neutron and proton electric
dipole moments echo the isospin structure of the anomalous magnetic moments,
kappa^n ~ - kappa^p.Comment: 25 pages, 1 figure. Published version. Ref. adde
The origin of the LMC stellar bar: clues from the SFH of the bar and inner disk
We discuss the origin of the LMC stellar bar by comparing the star formation
histories (SFH) obtained from deep color-magnitude diagrams (CMDs) in the bar
and in a number of fields in different directions within the inner disk. The
CMDs, reaching the oldest main sequence turnoffs in these very crowded fields,
have been obtained with VIMOS on the VLT in service mode, under very good
seeing conditions. We show that the SFHs of all fields share the same patterns,
with consistent variations of the star formation rate as a function of time in
all of them. We therefore conclude that no specific event of star formation can
be identified with the formation of the LMC bar, which instead likely formed
from a redistribution of disk material that occurred when the LMC disk became
bar unstable, and shared a common SFH with the inner disk thereafter. The
strong similarity between the SFH of the center and edge of the bar rules out
significant spatial variations of the SFH across the bar, which are predicted
by scenarios of classic bar formation through buckling mechanisms.Comment: MNRAS Letters, accepte
Threshold neutral pion photoproduction off the tri-nucleon to O(q^4)
We calculate electromagnetic neutral pion production off tri-nucleon bound
states (3H, 3He) at threshold in chiral nuclear effective field theory to
fourth order in the standard heavy baryon counting. We show that the fourth
order two-nucleon corrections to the S-wave multipoles at threshold are very
small. This implies that a precise measurement of the S-wave cross section for
neutral pion production off 3He allows for a stringent test of the chiral
perturbation theory prediction for the S-wave electric multipole E_{0+}^{pi0
n}.Comment: 17 pages, 5 figures, title changed, final version to appear in EPJA.
arXiv admin note: substantial text overlap with arXiv:1103.340
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