2,685 research outputs found
Effects of moisture in infrared thermography of resin matrix composites
Several multiply graphite polyimide composite specimens were examined by real-time infrared thermography in order to study the effects of moisture on their thermograms. Heat was injected from one side and IR emission detected on the opposite side using AGA Thermovision System-680. No differences between the thermograms of dry and water containing specimens were detected for defect-free specimens. However, the presence of trapped water in defective specimens modified the thermographic contrast significantly. It is concluded that: (1) IR thermography can be used to detect moisture in defective composites, and (2) because of the possibility of moisture camouflaging defects, IR thermography for subsurface defect detection should be supplemented by other techniques - such as acoustical imaging and X-radiography
Breakdown of Angular Momentum Selection Rules in High Pressure Optical Pumping Experiments
We present measurements, using two complementary methods, of the breakdown of
atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark
states are rendered weakly absorbing due to fine-structure mixing during Rb-He
collisions. The effect substantially increases the photon demand for optical
pumping of dense vapors
Astrometric-spectroscopic determination of the absolute masses of the HgMn binary star Phi Herculis
The Mercury-Manganese star Phi Her is a well known spectroscopic binary that
has been the subject of a recent study by Zavala et al. (2006), in which they
resolved the companion using long-baseline interferometry. The total mass of
the binary is now fairly well established, but the combination of the
spectroscopy with the astrometry has not resulted in individual masses
consistent with the spectral types of the components. The motion of the center
of light of Phi Her was clearly detected by the Hipparcos satellite. Here we
make use of the Hipparcos intermediate data (`abscissa residuals') and show
that by combining them in an optimal fashion with the interferometry the
individual masses can be obtained reliably using only astrometry. We re-examine
and then incorporate existing radial-velocity measurements into the orbital
solution, obtaining improved masses of 3.05 +/- 0.24 M_Sun and 1.614 +/- 0.066
M_Sun that are consistent with the theoretical mass-luminosity relation from
recent stellar evolution models. These mass determinations provide important
information for the understanding of the nature of this peculiar class of
stars.Comment: Total of 18 pages including figures and tables, in emulateapj format.
To appear in The Astronomical Journal, June 2007 issu
Charon's radius and density from the combined data sets of the 2005 July 11 occultation
The 2005 July 11 C313.2 stellar occultation by Charon was observed by three
separate research groups, including our own, at observatories throughout South
America. Here, the published timings from the three data sets have been
combined to more accurately determine the mean radius of Charon: 606.0 +/- 1.5
km. Our analysis indicates that a slight oblateness in the body (0.006 +/-
0.003) best matches the data, with a confidence level of 86%. The oblateness
has a pole position angle of 71.4 deg +/- 10.4 deg and is consistent with
Charon's pole position angle of 67 deg. Charon's mean radius corresponds to a
bulk density of 1.63 +/- 0.07 g/cm3, which is significantly less than Pluto's
(1.92 +/- 0.12 g/cm3). This density differential favors an impact formation
scenario for the system in which at least one of the impactors was
differentiated. Finally, unexplained differences between chord timings measured
at Cerro Pachon and the rest of the data set could be indicative of a
depression as deep as 7 km on Charon's limb.Comment: 25 pages including 4 tables and 2 figures. Submitted to the
Astronomical Journal on 2006 Feb 0
Inelastic Proton‐Proton Scattering at Very High Energy
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87855/2/99_1.pd
Pathogenicity of Fusarium species causing head blight in barley
The pathogenicity of eight Fusarium species causing fusarium head blight (FHB) in barley was studied under controlled conditions. Six barley genotypes varying in resistance to FHB were artificially inoculated with six isolates each of F. acuminatum, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti, F. graminearum, F. poae and F. sporotrichioides 10-14 d after heading. Symptoms of FHB were rated as disease severity using a 0-9 scale, 4, 7, 14, 21 and 28 d after inoculation, and as percentage of infected spikelets (IS) after 21 d. All species tested caused head blight symptoms on the barley genotypes, but only F. crookwellense, F. culmorum and F. graminearum resulted in severe disease development (> 65% IS) and were considered highly pathogenic. Fusarium avenaceum had 48% IS, which was significantly lower than those of the three highly pathogenic species and was moderately pathogenic. The remaining species had 65 %) et ont été considérés comme fortement pathogènes. Avec un PÉI de 48 %, qui était significativement inférieur à ceux des trois espèces les plus pathogènes, le Fusarium avenaceum a été considéré comme moyennement pathogène. Les autres espèces ont eu un PÉI de moins de 15 % et ont été considérées comme faiblement pathogènes. Des différences significatives (P < 0,05) ont été observées entre les espèces pour l'agressivité parmi les isolats et pour la sensibilité parmi les génotypes d'orge, ce qui suggère que le tri pour la résistance à la FÉ doit faire appel à des isolats agressifs ou à un mélange de plusieurs isolats. C'est la première fois que le F. crookwellense est signalé comme fortement pathogène et le F. avenaceum comme moyennement pathogène sur l'orge
Pattern selection as a nonlinear eigenvalue problem
A unique pattern selection in the absolutely unstable regime of driven,
nonlinear, open-flow systems is reviewed. It has recently been found in
numerical simulations of propagating vortex structures occuring in
Taylor-Couette and Rayleigh-Benard systems subject to an externally imposed
through-flow. Unlike the stationary patterns in systems without through-flow
the spatiotemporal structures of propagating vortices are independent of
parameter history, initial conditions, and system length. They do, however,
depend on the boundary conditions in addition to the driving rate and the
through-flow rate. Our analysis of the Ginzburg-Landau amplitude equation
elucidates how the pattern selection can be described by a nonlinear eigenvalue
problem with the frequency being the eigenvalue. Approaching the border between
absolute and convective instability the eigenvalue problem becomes effectively
linear and the selection mechanism approaches that of linear front propagation.
PACS: 47.54.+r,47.20.Ky,47.32.-y,47.20.FtComment: 18 pages in Postsript format including 5 figures, to appear in:
Lecture Notes in Physics, "Nonlinear Physics of Complex Sytems -- Current
Status and Future Trends", Eds. J. Parisi, S. C. Mueller, and W. Zimmermann
(Springer, Berlin, 1996
Coarsening in the q-State Potts Model and the Ising Model with Globally Conserved Magnetization
We study the nonequilibrium dynamics of the -state Potts model following a
quench from the high temperature disordered phase to zero temperature. The time
dependent two-point correlation functions of the order parameter field satisfy
dynamic scaling with a length scale . In particular, the
autocorrelation function decays as . We illustrate these
properties by solving exactly the kinetic Potts model in . We then analyze
a Langevin equation of an appropriate field theory to compute these correlation
functions for general and . We establish a correspondence between the
two-point correlations of the -state Potts model and those of a kinetic
Ising model evolving with a fixed magnetization . The dynamics of this
Ising model is solved exactly in the large q limit, and in the limit of a large
number of components for the order parameter. For general and in any
dimension, we introduce a Gaussian closure approximation and calculate within
this approximation the scaling functions and the exponent . These
are in good agreement with the direct numerical simulations of the Potts model
as well as the kinetic Ising model with fixed magnetization. We also discuss
the existing and possible experimental realizations of these models.Comment: TeX, Vanilla.sty is needed. [Admin note: author contacted regarding
missing figure1 but is unable to supply, see journal version (Nov99)
Experimental Evidence for Simple Relations between Unpolarized and Polarized Parton Distributions
The Pauli exclusion principle is advocated for constructing the proton and
neutron deep inelastic structure functions in terms of Fermi-Dirac
distributions that we parametrize with very few parameters. It allows a fair
description of the recent NMC data on and at
, as well as the CCFR neutrino data at and . We
also make some reasonable and simple assumptions to relate unpolarized and
polarized quark parton distributions and we obtain, with no additional free
parameters, the spin dependent structure functions and
. Using the correct evolution, we have checked that they
are in excellent agreement with the very recent SMC proton data at and the SLAC neutron data at .Comment: 17 pages,CPT-94/P.3032,latex,6 fig available on cpt.univ-mrs.fr
directory pub/preprints/94/fundamental-interactions /94-P.303
Quark Orbital Angular Momentum in the Baryon
Analytical and numerical results, for the orbital and spin content carried by
different quark flavors in the baryons, are given in the chiral quark model
with symmetry breaking. The reduction of the quark spin, due to the spin
dilution in the chiral splitting processes, is transferred into the orbital
motion of quarks and antiquarks. The orbital angular momentum for each quark
flavor in the proton as a function of the partition factor and the
chiral splitting probability is shown. The cancellation between the spin
and orbital contributions in the spin sum rule and in the baryon magnetic
moments is discussed.Comment: 26 pages, 3 figures, revised version with minor eq. no and ref. no.
corrections. Discussion on the spin and a new ref. are adde
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