1,086 research outputs found
On the USCRN Temperature System
In 2004 a new aspirated surface air temperature system was officially deployed nationally in the U.S. Climate Reference Network (USCRN) commissioned by the National Oceanic and Atmospheric Admin- istration. The primary goal of the USCRN is to provide future long-term and high-quality homogeneous observations of surface air temperature and precipitation that can be coupled to past long-term observations for the detection and attribution of present and future climate change. In this paper two precision air temperature systems are included for evaluating the new USCRN air temperature system based on a 1-yr side-by-side field comparison. The measurement errors of the USCRN temperature sensor are systemati- cally analyzed, and the components of error attributable to the datalogger, lead wires, fixed resistors, and the temperature coefficient of the resistors are presented. Although the current configuration is adequate, a more desirable configuration of USCRN temperature sensor coupled with the datalogger is proposed as a means of further reducing the uncertainty for the USCRN temperature measurement
Conditions for the occurrence of mean-motion resonances in a low mass planetary system
The dynamical interactions that occur in newly formed planetary systems may
reflect the conditions occurring in the protoplanetary disk out of which they
formed. With this in mind, we explore the attainment and maintenance of orbital
resonances by migrating planets in the terrestrial mass range. Migration time
scales varying between millions of years and thousands of years are considered.
In the former case, for which the migration time is comparable to the lifetime
of the protoplanetary gas disk, a 2:1 resonance may be formed. In the latter,
relatively rapid migration regime commensurabilities of high degree such as 8:7
or 11:10 may be formed. However, in any one large-scale migration several
different commensurabilities may be formed sequentially, each being associated
with significant orbital evolution. We also use a simple analytic theory to
develop conditions for first order commensurabilities to be formed. These
depend on the degree of the commensurability, the imposed migration and
circularization rates, and the planet mass ratios. These conditions are found
to be consistent with the results of our simulations.Comment: 11 pages with 4 figures, pdflatex, to appear in the proceedings of
the conference "Extra-solar Planets in Multi-body Systems: Theory and
Observations"; eds. K. Gozdziewski, A. Niedzielski and J. Schneider, EAS
Publication Serie
Magnetic Moment of The Pentaquark State
We have calculated the magnetic moment of the recently observed
pentaquark in the framework of the light cone QCD sum rules using the photon
distribution amplitudes. We find that ,
which is quite small. We also compare our result with predictions of other
groups.Comment: 1 eps figure, 13 page
Comet Machholz (C/2004 Q2): morphological structures in the inner coma and rotation parameters
Extensive observations of comet C/2004 Q2 (Machholz) were carried out between
August 2004 and May 2005. The images obtained were used to investigate the
comet's inner coma features at resolutions between 350 and 1500 km/pixel. A
photometric analysis of the dust outflowing from the comet's nucleus and the
study of the motion of the morphological structures in the inner coma indicated
that the rotation period of the nucleus was most likely around 0.74 days. A
thorough investigation of the inner coma morphology allowed us to observe two
main active sources on the comet's nucleus, at a latitude of +85{\deg} \pm
5{\deg} and +45{\deg} \pm 5{\deg}, respectively. Further sources have been
observed, but their activity ran out quite rapidly over time; the most relevant
was at latcom. = 25{\deg} \pm 5{\deg}. Graphic simulations of the geometrical
conditions of observation of the inner coma were compared with the images and
used to determine a pole orientation at RA=95{\deg} \pm 5{\deg}, Dec=+35{\deg}
\pm 5{\deg}. The comet's spin axis was lying nearly on the plane of the sky
during the first decade of December 2004.Comment: 29 pages, 8 figures, 3 table
Effect of membrane character and solution chemistry on microfiltration performance
To help understand and predict the role of natural organic matter (NOM) in the fouling of low-pressure membranes, experiments were carried out with an apparatus that incorporates automatic backwashing and long filtration runs. Three hollow fibre membranes of varying character were included in the study, and the filtration of two different surface waters was compared. The hydrophilic membrane had greater flux recovery after backwashing than the hydrophobic membranes, but the efficiency of backwashing decreased at extended filtration times. NOM concentration of these waters (7.9 and 9.1 mg/L) had little effect on the flux of the membranes at extended filtration times, as backwashing of the membrane restored the flux to similar values regardless of the NOM concentration. The solution pH also had little effect at extended filtration times. The backwashing efficiency of the hydrophilic membrane was dramatically different for the two waters, and the presence of colloid NOM alone could not explain these differences. It is proposed that colloidal NOM forms a filter cake on the surface of the membranes and that small molecular weight organics that have an adsorption peak at 220 nm but not 254 nm were responsible for “gluing” the colloids to the membrane surface. Alum coagulation improved membrane performance in all instances, and this was suggested to be because coagulation reduced the concentration of “glue” that holds the organic colloids to the membrane surface
Closed geodesics in Alexandrov spaces of curvature bounded from above
In this paper, we show a local energy convexity of maps into
spaces. This energy convexity allows us to extend Colding and
Minicozzi's width-sweepout construction to produce closed geodesics in any
closed Alexandrov space of curvature bounded from above, which also provides a
generalized version of the Birkhoff-Lyusternik theorem on the existence of
non-trivial closed geodesics in the Alexandrov setting.Comment: Final version, 22 pages, 2 figures, to appear in the Journal of
Geometric Analysi
Longitudinal broadening of near side jets due to parton cascade
Longitudinal broadening along direction on near side in
two-dimensional () di-hadron correlation
distribution has been studied for central Au+Au collisions at =
200 GeV, within a dynamical multi-phase transport model. It was found that the
longitudinal broadening is generated by a longitudinal flow induced by strong
parton cascade in central Au+Au collisions, in comparison with p+p collisions
at = 200 GeV. The longitudinal broadening may shed light on the
information about strongly interacting partonic matter at RHIC.Comment: 5 pages, 4 figures; accepted by Eur. Phys. J.
Measuring charge fluctuations in high-energy nuclear collisions
Various measures of charge fluctuations in heavy-ion collisions are
discussed. Advantages of the Phi-measure are demonstrated and its relation to
other fluctuation measures is established. To get the relation, Phi is
expressed through the moments of multiplicity distribution. We study how the
measures act in the case of a `background' model which represents the classical
hadron gas in equilibrium. The model assumes statistical particle production
constrained by charge conservation. It also takes into account both the effect
of incomplete experimental apparatus acceptance and that of tracking
inefficiency. The model is shown to approximately agree with the PHENIX and
preliminary STAR data on the electric charge fluctuations. Finally,
`background-free' measures are discussed.Comment: 12 pages, 6 figures, numerous but minor changes, Phys. Rev. C in
prin
Topological and geometrical restrictions, free-boundary problems and self-gravitating fluids
Let (P1) be certain elliptic free-boundary problem on a Riemannian manifold
(M,g). In this paper we study the restrictions on the topology and geometry of
the fibres (the level sets) of the solutions f to (P1). We give a technique
based on certain remarkable property of the fibres (the analytic representation
property) for going from the initial PDE to a global analytical
characterization of the fibres (the equilibrium partition condition). We study
this analytical characterization and obtain several topological and geometrical
properties that the fibres of the solutions must possess, depending on the
topology of M and the metric tensor g. We apply these results to the classical
problem in physics of classifying the equilibrium shapes of both Newtonian and
relativistic static self-gravitating fluids. We also suggest a relationship
with the isometries of a Riemannian manifold.Comment: 36 pages. In this new version the analytic representation hypothesis
is proved. Please address all correspondence to D. Peralta-Sala
Processing of ultrafine-size particulate metal matrix composites by advanced shear technology
Copyright @ 2009 ASM International. This paper was published in Metallurgical & Materials Transactions A 40A(3) and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.Lack of efficient mixing technology to achieve a uniform distribution of fine-size reinforcement within the matrix and the high cost of producing components have hindered the widespread adaptation of particulate metal matrix composites (PMMCs) for engineering applications. A new rheo-processing method, the melt-conditioning high-pressure die-cast (MC-HPDC) process, has been developed for manufacturing near-net-shape components of high integrity. The MC-HPDC process adapts the well-established high shear dispersive mixing action of a twin-screw mechanism to the task of overcoming the cohesive force of the agglomerates under a high shear rate and high intensity of turbulence. This is followed by direct shaping of the slurry into near-net-shape components using an existing cold-chamber die-casting process. The results indicate that the MC-HPDC samples have a uniform distribution of ultrafine-sized SiC particles throughout the entire sample in the as-cast condition. Compared to those produced by conventional high-pressure die casting (HPDC), MC-HPDC samples have a much improved tensile strength and ductility.EP-SR
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