56,586 research outputs found
Growth of heat trace and heat content asymptotic coefficients
We show in the smooth category that the heat trace asymptotics and the heat
content asymptotics can be made to grow arbitrarily rapidly. In the real
analytic context, however, this is not true and we establish universal bounds
on their growth
A Simultaneous Optical and X-ray Variability Study of the Orion Nebula Cluster. II. A Common Origin in Magnetic Activity
We present a statistical analysis of simultaneous optical and X-ray light
curves, spanning 600 ks, for 814 pre-main-sequence (PMS) stars in the Orion
Nebula Cluster. The aim of this study is to establish the relationship, if any,
between the sites of optical and X-ray variability, and thereby to elucidate
the origins of X-ray production in PMS stars. In a previous paper we showed
that optical and X-ray variability in PMS stars are very rarely
time-correlated. Here, using time-averaged variability indicators to examine
the joint occurrences of optical and X-ray variability, we confirm that the two
forms of variability are not directly causally related. However, a strong and
highly statistically significant correlation is found between optical
variability and X-ray luminosity. As this correlation is found to be
independent of accretion activity, we argue that X-ray production in PMS stars
must instead be intimately connected with the presence and strength of
optically variable, magnetically active surface regions (i.e. spots) on these
stars. Moreover, because X-ray variability and optical variability are rarely
time-correlated, we conclude that the sites of X-ray production are not
exclusively co-spatial with these regions. We argue that solar-analog coronae,
heated by topologically complex fields, can explain these findings.Comment: To appear in the Astrophysical Journal. 33 pages, 3 figure
Comment on "Conductance fluctuations in mesoscopic normal-metal/superconductor samples"
Recently, Hecker et al. [Phys. Rev. Lett. 79, 1547 (1997)] experimentally
studied magnetoconductance fluctuations in a mesoscopic Au wire connected to a
superconducting Nb contact. They claimed to have observed an enhancement of the
rms magnitude of these conductance fluctuations in the superconducting state
(rms(Gns)) relative to that in the normal state (rms(Gn)) by a factor of 2.8.
In this comment, we argue that the measured rms(Gns) is NOT significantly
enhanced compared to rms(Gn) when we correct for the presence of an incoherent
series resistance from the contacts, which is different when Nb is in the
superconducting or normal state.Comment: 1 pag
Thruster Allocation for Dynamical Positioning
Positioning a vessel at a fixed position in deep water is of great importance when working offshore. In recent years a Dynamical Positioning (DP) system was developed at Marin [2]. After the measurement of the current position and external forces (like waves, wind etc.), each thruster of the vessel is actively controlled to hold the desired location.
In this paper we focus on the allocation process to determine the settings for each thruster that results in the minimal total power and thus fuel consumption. The mathematical formulation of this situation leads to a nonlinear optimization problem with equality and inequality constraints, which can be solved by applying Lagrange multipliers.
We give three approaches: first of all, the full problem was solved using the MATLAB fmincon routine with the solution from the linearised problem as a starting point. This implementation, with robust handling of the situations where the thrusters are overloaded, lead to promising results: an average reduction in fuel consumption of approximately two percent. However, further analysis proved useful. A second approach changes the set of variables and so reduces the number of equations. The third and last approach solves the Lagrange equations with an iterative method on the linearized Lagrange problem
Binary black hole detection rates in inspiral gravitational wave searches
The signal-to-noise ratios (SNRs) for quasi-circular binary black hole
inspirals computed from restricted post-Newtonian waveforms are compared with
those attained by more complete post-Newtonian signals, which are
superpositions of amplitude-corrected harmonics of the orbital phase. It is
shown that if one were to use the best available amplitude-corrected waveforms
for detection templates, one should expect SNRs in actual searches to be
significantly lower than those suggested by simulations based purely on
restricted waveforms.Comment: 9 pages, 1 figur
Short Report: Association Between Chloroquine and Amodiaquine Resistance and Allelic Variation in the Plasmodium Falciparum Multiple Drug Resistance 1 Gene and the Chloroquine Resistance Transporter Gene in Isolates from the Upper Nile in Southern Sudan.
Amodiaquine, a 4-aminoquinoline compound, is being considered as an alternative to chloroquine and pyrimethamine/sulfadoxine where resistance in Plasmodium falciparum to both drugs has been selected. Although amodiaquine is more potent than chloroquine, its effectiveness is reduced in areas where chloroquine resistance is high. We report an association of the P. falciparum chloroquine resistance transporter (pfcrt) gene and the P. falciparum multiple drug resistance 1 (pfmdr1) gene, two chloroquine resistance markers, with chloroquine and amodiaquine efficacy in vivo in southern Sudan. The data show that the allele of the pfcrt gene with a lysine to threonine change at codon 76 is strongly associated with both chloroquine and amodiaquine resistance. No such association was observed with the pfmdr1 gene
Zeroth Poisson homology of symmetric powers of isolated quasihomogeneous surface singularities
Let X be a surface with an isolated singularity at the origin, given by the
equation Q(x,y,z)=0, where Q is a weighted-homogeneous polynomial. In
particular, this includes the Kleinian surfaces X = C^2/G for G < SL(2,C)
finite. Let Y be the n-th symmetric power of X. We compute the zeroth Poisson
homology of Y, as a graded vector space with respect to the weight grading. In
the Kleinian case, this confirms a conjecture of Alev, that the zeroth Poisson
homology of the n-th symmetric power of C^2/G is isomorphic to the zeroth
Hochschild homology of the n-th symmetric power of the algebra of G-invariant
differential operators on C. That is, the Brylinski spectral sequence
degenerates in this case. In the elliptic case, this yields the zeroth
Hochschild homology of symmetric powers of the elliptic algebras with three
generators modulo their center, for the parameter equal to all but countably
many points of the elliptic curve.Comment: 17 page
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