708 research outputs found
Neutron time-of-flight measurements of charged-particle energy loss in inertial confinement fusion plasmas
Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4 keV and particle densities of n≈(12-2)×10^{24} cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data
The Grizzly, February 10, 1989
Ursinus Seeks Mid-States Reaccreditation • Heck Beats Traffic Blahs • Letter: Doughty Expresses Doubts • U.C. Salutes French Bicentennial • Medieval Fest Needs You • Ginsberg to Give Revolutionary Forum • Casa Maria: Muy Bien • de la Hoya Happy • Ursinus Slays F & M • U.C. Aims for Title • O\u27Malley Leaps to Nationals • Women\u27s Indoor Inspiring • U.C. Fields Strong Squad • A\u27Bears Peaking at Right Time • Scholarships to Scotland • Guess Who\u27s Coming for Dinner? • His Cheating Makes Twice the Test for You • Hallinger Argues for Proposal 42: Academics Before Athlete • Greenstein Grabs Grim \u27Just Right\u27 • Valentine No-No\u27s • From America With Love: Students Flock to U.C.https://digitalcommons.ursinus.edu/grizzlynews/1228/thumbnail.jp
Egg Eviction Imposes a Recoverable Cost of Virulence in Chicks of a Brood Parasite
Background: Chicks of virulent brood parasitic birds eliminate their nestmates and avoid costly competition for foster parental care. Yet, efforts to evict nest contents by the blind and naked common cuckoo Cuculus canorus hatchling are counterintuitive as both adult parasites and large older cuckoo chicks appear to be better suited to tossing the eggs and young of the foster parents. Methodology/Principal Findings: Here we show experimentally that egg tossing imposed a recoverable growth cost of mass gain in common cuckoo chicks during the nestling period in nests of great reed warbler Acrocephalus arundinaceus hosts. Growth rates of skeletal traits and morphological variables involved in the solicitation of foster parental care remained similar between evictor and non-evictor chicks throughout development. We also detected no increase in predation rates for evicting nests, suggesting that egg tossing behavior by common cuckoo hatchlings does not increase the conspicuousness of nests. Conclusion: The temporary growth cost of egg eviction by common cuckoo hatchlings is the result of constraints imposed by rejecter host adults and competitive nestmates on the timing and mechanism of parasite virulence.Michael G. Anderson, Csaba Moskát, Miklós Bán, Tomáš Grim, Phillip Cassey and Mark E. Haube
Loss of Structural Complexity in Staghorn Coral Rubble Habitats Influences the Density of Damselfish in Dry Tortugas National Park, Florida, USA
Different reactions to adverse neighborhoods in games of cooperation
In social dilemmas, cooperation among randomly interacting individuals is
often difficult to achieve. The situation changes if interactions take place in
a network where the network structure jointly evolves with the behavioral
strategies of the interacting individuals. In particular, cooperation can be
stabilized if individuals tend to cut interaction links when facing adverse
neighborhoods. Here we consider two different types of reaction to adverse
neighborhoods, and all possible mixtures between these reactions. When faced
with a gloomy outlook, players can either choose to cut and rewire some of
their links to other individuals, or they can migrate to another location and
establish new links in the new local neighborhood. We find that in general
local rewiring is more favorable for the evolution of cooperation than
emigration from adverse neighborhoods. Rewiring helps to maintain the diversity
in the degree distribution of players and favors the spontaneous emergence of
cooperative clusters. Both properties are known to favor the evolution of
cooperation on networks. Interestingly, a mixture of migration and rewiring is
even more favorable for the evolution of cooperation than rewiring on its own.
While most models only consider a single type of reaction to adverse
neighborhoods, the coexistence of several such reactions may actually be an
optimal setting for the evolution of cooperation.Comment: 12 pages, 5 figures; accepted for publication in PLoS ON
Transverse energy production and charged-particle multiplicity at midrapidity in various systems from to 200 GeV
Measurements of midrapidity charged particle multiplicity distributions,
, and midrapidity transverse-energy distributions,
, are presented for a variety of collision systems and energies.
Included are distributions for AuAu collisions at ,
130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, CuCu collisions at
and 62.4 GeV, CuAu collisions at
GeV, UU collisions at GeV,
Au collisions at GeV, HeAu collisions at
GeV, and collisions at
GeV. Centrality-dependent distributions at midrapidity are presented in terms
of the number of nucleon participants, , and the number of
constituent quark participants, . For all collisions
down to GeV, it is observed that the midrapidity data
are better described by scaling with than scaling with . Also presented are estimates of the Bjorken energy density,
, and the ratio of to ,
the latter of which is seen to be constant as a function of centrality for all
systems.Comment: 706 authors, 32 pages, 20 figures, 34 tables, 2004, 2005, 2008, 2010,
2011, and 2012 data. v2 is version accepted for publication in Phys. Rev.
Measurements of elliptic and triangular flow in high-multiplicity HeAu collisions at GeV
We present the first measurement of elliptic () and triangular ()
flow in high-multiplicity HeAu collisions at
GeV. Two-particle correlations, where the particles have a large separation in
pseudorapidity, are compared in HeAu and in collisions and
indicate that collective effects dominate the second and third Fourier
components for the correlations observed in the HeAu system. The
collective behavior is quantified in terms of elliptic and triangular
anisotropy coefficients measured with respect to their corresponding
event planes. The values are comparable to those previously measured in
Au collisions at the same nucleon-nucleon center-of-mass energy.
Comparison with various theoretical predictions are made, including to models
where the hot spots created by the impact of the three He nucleons on the
Au nucleus expand hydrodynamically to generate the triangular flow. The
agreement of these models with data may indicate the formation of low-viscosity
quark-gluon plasma even in these small collision systems.Comment: 630 authors, 9 pages, 4 figures, 2 tables. v2 is the version accepted
for publication by Physical Review Letters. Plain text data tables for the
points plotted in figures for this and previous PHENIX publications are (or
will be) publicly available at http://www.phenix.bnl.gov/papers.htm
Search for a Fourth Generation Charge -1/3 Quark via Flavor Changing Neutral Current Decay
We report on a search for pair production of a fourth generation charge -1/3
quark (b') in pbar p collisions at sqrt(s) = 1.8 TeV at the Fermilab Tevatron
using an integrated luminosity of 93 pb^-1. Both quarks are assumed to decay
via flavor changing neutral currents (FCNC). The search uses the signatures
gamma + 3 jets + mu-tag and 2 gamma + 2 jets. We see no significant excess of
events over the expected background. We place an upper limit on the production
cross section times branching fraction that is well below theoretical
expectations for a b' quark decaying exclusively via FCNC for b' quark masses
up to m(Z) + m(b).Comment: Eleven pages, two postscript figures, submitted to Physical Review
Letter
Search for Top Squark Pair Production in the Dielectron Channel
This report describes the first search for top squark pair production in the
channel stop_1 stopbar_1 -> b bbar chargino_1 chargino_1 -> ee+jets+MEt using
74.9 +- 8.9 pb^-1 of data collected using the D0 detector. A 95% confidence
level upper limit on sigma*B is presented. The limit is above the theoretical
expectation for sigma*B for this process, but does show the sensitivity of the
current D0 data set to a particular topology for new physics.Comment: Five pages, including three figures, submitted to PRD Brief Report
Direct Measurement of the Top Quark Mass at D0
We determine the top quark mass m_t using t-tbar pairs produced in the D0
detector by \sqrt{s} = 1.8 TeV p-pbar collisions in a 125 pb^-1 exposure at the
Fermilab Tevatron. We make a two constraint fit to m_t in t-tbar -> b W^+bbar
W^- final states with one W boson decaying to q-qbar and the other to e-nu or
mu-nu. Likelihood fits to the data yield m_t(l+jets) = 173.3 +- 5.6 (stat) +-
5.5 (syst) GeV/c^2. When this result is combined with an analysis of events in
which both W bosons decay into leptons, we obtain m_t = 172.1 +- 5.2 (stat) +-
4.9 (syst) GeV/c^2. An alternate analysis, using three constraint fits to fixed
top quark masses, gives m_t(l+jets) = 176.0 +- 7.9 (stat) +- 4.8 (syst)
GeV/C^2, consistent with the above result. Studies of kinematic distributions
of the top quark candidates are also presented.Comment: 43 pages, 53 figures, 33 tables. RevTeX. Submitted to Phys. Rev.
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