10,567 research outputs found
Shock accelerated vortex ring
The interaction of a shock wave with a spherical density inhomogeneity leads
to the development of a vortex ring through the impulsive deposition of
baroclinic vorticity. The present fluid dynamics videos display this phenomenon
and were experimentally investigated at the Wisconsin Shock Tube Laboratory's
(WiSTL) 9.2 m, downward firing shock tube. The tube has a square internal
cross-section (0.25 m x 0.25 m) with multiple fused silica windows for optical
access. The spherical soap bubble is generated by means of a pneumatically
retracted injector and released into free-fall 200 ms prior to initial shock
acceleration. The downward moving, M = 2.07 shock wave impulsively accelerates
the bubble and reflects off the tube end wall. The reflected shock wave
re-accelerates the bubble (reshock), which has now developed into a vortex
ring, depositing additional vorticity. In the absence of any flow disturbances,
the flow behind the reflected shock wave is stationary. As a result, any
observed motion of the vortex ring is due to circulation. The shocked vortex
ring is imaged at 12,500 fps with planar Mie scattering.Comment: For Gallery of Fluid Motion 200
Containerless high temperature property measurements
Containerless processing in the low gravity environment of space provides the opportunity to increase the temperature at which well controlled processing of and property measurements on materials is possible. This project was directed towards advancing containerless processing and property measurement techniques for application to materials research at high temperatures in space. Containerless high temperature material property studies include measurements of the vapor pressure, melting temperature, optical properties, and spectral emissivities of solid boron. The reaction of boron with nitrogen was also studied by laser polarimetric measurement of boron nitride film growth. The optical properties and spectral emissivities were measured for solid and liquid silicon, niobium, and zirconium; liquid aluminum and titanium; and liquid Ti-Al alloys of 5 to 60 atomic pct. titanium. Alternative means for noncontact temperature measurement in the absence of material emissivity data were evaluated. Also, the application of laser induced fluorescence for component activity measurements in electromagnetic levitated liquids was studied, along with the feasibility of a hybrid aerodynamic electromagnetic levitation technique
Some considerations concerning the challenge of incorporating social variables into epidemiological models of infectious disease transmission
Incorporation of âsocialâ variables into epidemiological models remains a challenge. Too much detail and models cease to be useful; too little and the very notion of infection âa highly social process in human populationsâmay be considered with little reference to the social. The French sociologist Emile Durkheim proposed that the scientific study of society required identification and study of âsocial currents.â Such âcurrentsâ are what we might today describe as âemergent properties,â specifiable variables appertaining to individuals and groups, which represent the perspectives of social actors as they experience the environment in which they live their lives. Here we review the ways in which one particular emergent property, hope, relevant to a range of epidemiological situations, might be used in epidemiological modelling of infectious diseases in human populations. We also indicate how such an approach might be extended to include a range of other potential emergent properties to repre
Novel spin-liquid states in the frustrated Heisenberg antiferromagnet on the honeycomb lattice
Recent experiment on a honeycomb-lattice Heisenberg antiferromagnet (AF)
BiMnO(NO) revealed a novel spin-liquid-like behavior down to
low temperature, which was ascribed to the frustration effect due to the
competition between the AF nearest- and next-nearest-neighbor interactions
and . Motivated by the experiment, we study the ordering of the
- frustrated classical Heisenberg AF on a honeycomb lattice both by
a low-temperature expansion and a Monte Carlo simulation. The model has been
known to possess a massive degeneracy of the ground state, which, however,
might be lifted due to thermal fluctuations leading to a unique ordered state,
the effect known as 'order-by-disorder'. We find that the model exhibits an
intriguing ordering behavior, particularly near the AF phase boundary. The
energy scale of the order-by-disorder is suppressed there down to extremely low
temperatures, giving rise to exotic spin-liquid states like a "ring-liquid" or
a "pancake-liquid" state accompanied by the characteristic spin structure
factor and the field-induced antiferromagnetism. We argue that the recent
experimental data are explicable if the system is in such exotic spin-liquid
states
Analysis of a Large Sample of Neutrino-Induced Muons with the ArgoNeuT Detector
ArgoNeuT, or Argon Neutrino Test, is a 170 liter liquid argon time projection
chamber designed to collect neutrino interactions from the NuMI beam at Fermi
National Accelerator Laboratory. ArgoNeuT operated in the NuMI low-energy beam
line directly upstream of the MINOS Near Detector from September 2009 to
February 2010, during which thousands of neutrino and antineutrino events were
collected. The MINOS Near Detector was used to measure muons downstream of
ArgoNeuT. Though ArgoNeuT is primarily an R&D project, the data collected
provide a unique opportunity to measure neutrino cross sections in the 0.1-10
GeV energy range. Fully reconstructing the muon from these interactions is
imperative for these measurements. This paper focuses on the complete kinematic
reconstruction of neutrino-induced through-going muons tracks. Analysis of this
high statistics sample of minimum ionizing tracks demonstrates the reliability
of the geometric and calorimetric reconstruction in the ArgoNeuT detector
The roots of "Western European societal evolution". A concept of Europe by JenĆ SzƱcs
JenĆ SzƱcs wrote his essay entitled Sketch on the three regions of Europe in the early 1980s in Hungary. During these years, a historically well-argued opinion emphasising a substantial difference between Central European and Eastern European societies was warmly received in various circles of the political opposition. In a wider European perspective SzƱcs used the old âliberty toposâ which claims that the history of Europe is no other than the fulfillment of liberty. In his Sketch, SzƱcs does not only concentrate on questions concerning the Middle Ages in Western Europe. Yet it is this stream of thought which brought a new perspective to explaining European history. His picture of the Middle Ages represents well that there is a way to integrate all typical Western motifs of post-war self-definition into a single theory. Mainly, the âliberty motifâ, as a sign of âEuropeanismâ â in the interpretation of BibĂłâs concept, Anglo-saxon Marxists and Weberâs social theory â, developed from medieval concepts of state and society and from an analysis of economic and social structures. SzƱcsâs historical aspect was a typical intellectual product of the 1980s: this was the time when a few Central European historians started to outline non-Marxist aspects of social theory and categories of modernisation theories, but concealing them with Marxist terminology
Risk factors for development of symptoms after autologous transplantation for multiple myeloma
The ArgoNeuT Detector in the NuMI Low-Energy beam line at Fermilab
The ArgoNeuT liquid argon time projection chamber has collected thousands of
neutrino and antineutrino events during an extended run period in the NuMI
beam-line at Fermilab. This paper focuses on the main aspects of the detector
layout and related technical features, including the cryogenic equipment, time
projection chamber, read-out electronics, and off-line data treatment. The
detector commissioning phase, physics run, and first neutrino event displays
are also reported. The characterization of the main working parameters of the
detector during data-taking, the ionization electron drift velocity and
lifetime in liquid argon, as obtained from through-going muon data complete the
present report.Comment: 43 pages, 27 figures, 5 tables - update referenc
A compactness theorem for complete Ricci shrinkers
We prove precompactness in an orbifold Cheeger-Gromov sense of complete
gradient Ricci shrinkers with a lower bound on their entropy and a local
integral Riemann bound. We do not need any pointwise curvature assumptions,
volume or diameter bounds. In dimension four, under a technical assumption, we
can replace the local integral Riemann bound by an upper bound for the Euler
characteristic. The proof relies on a Gauss-Bonnet with cutoff argument.Comment: 28 pages, final version, to appear in GAF
Resonant two-magnon Raman scattering in antiferromagnetic insulators
We propose a theory of two-magnon {\it resonant\/} Raman scattering from
antiferromagnetic insulators, which contains information both on the magnetism
and the carrier properties in the lighly doped phases. We argue that the
conventional theory does not work in the resonant regime, in which the energy
of the incident photon is close to the gap between the conduction and valence
bands. We identify the diagram which gives the dominant contribution to Raman
intensity in this regime and show that it can explain the unusual features in
the two-magnon profile and in the two-magnon peak intensity dependence on the
incoming photon frequency.Comment: 11 pages (REVTeX) + 3 figures in a single postscript file are
appended in uuencoded format, preprint TCSUH-94:09
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