9,754 research outputs found
d+Au Collisions at STAR
STAR has measured forward pi^0 production in p+p and d+Au collisions at
sqrt{s_{NN}}=200 GeV. The p+p yield generally agrees with NLO pQCD
calculations. The d+Au yield is strongly suppressed at =4.0, well below
shadowing expectations. Exploratory measurements of azimuthal correlations
between forward pi^0 and mid-rapidity charged hadrons show a recoil peak in p+p
that is suppressed in d+Au at low pion energy. These observations are
qualitatively consistent with a saturation picture of the low-x gluon structure
of heavy nuclei. Future measurements to elucidate the dynamics underlying these
observations are also described.Comment: 4 pages, 3 figures. To appear in proceedings of DIS200
Transverse Spin Studies with STAR at RHIC
STAR has observed sizable transverse single-spin asymmetries for inclusive
pi^0 production at forward rapidity in p+p collisions at sqrt{s}=200 GeV. These
asymmetries may arise from either the Sivers or Collins effect. Studies are
underway during the current RHIC run to elucidate the dynamics that underlie
these single-spin asymmetries. Additional measurements are underway to search
for the Sivers effect in mid-rapidity di-jet production.Comment: 4 pages, 3 figures, to appear in DIS2006 proceeding
Computing Matveev's complexity via crystallization theory: the boundary case
The notion of Gem-Matveev complexity has been introduced within
crystallization theory, as a combinatorial method to estimate Matveev's
complexity of closed 3-manifolds; it yielded upper bounds for interesting
classes of such manifolds. In this paper we extend the definition to the case
of non-empty boundary and prove that for each compact irreducible and
boundary-irreducible 3-manifold it coincides with the modified Heegaard
complexity introduced by Cattabriga, Mulazzani and Vesnin. Moreover, via
Gem-Matveev complexity, we obtain an estimation of Matveev's complexity for all
Seifert 3-manifolds with base and two exceptional fibers and,
therefore, for all torus knot complements.Comment: 27 pages, 14 figure
Feasibility of observer system for determining orientation of balloon borne observational platforms
An observer model for predicting the orientation of balloon borne research platforms was developed. The model was employed in conjunction with data from the LACATE mission in order to determine the platform orientation as a function of time
IETS and quantum interference: propensity rules in the presence of an interference feature
Destructive quantum interference in single molecule electronics is an
intriguing phe- nomenon; however, distinguishing quantum interference effects
from generically low transmission is not trivial. In this paper, we discuss how
quantum interference ef- fects in the transmission lead to either low current
or a particular line shape in current-voltage curves, depending on the position
of the interference feature. Sec- ondly, we consider how inelastic electron
tunneling spectroscopy can be used to probe the presence of an interference
feature by identifying vibrational modes that are se- lectively suppressed when
quantum interference effects dominate. That is, we expand the understanding of
propensity rules in inelastic electron tunneling spectroscopy to molecules with
destructive quantum interference.Comment: 19 pages, 6 figure
Pedestal and Peak Structure in Jet Correlation
We study the characteristics of correlation between particles in jets
produced in heavy-ion collisions. In the framework of parton recombination we
calculate the and distributions of a pion associated with a
trigger particle. The origin of the pedestal in is related to the
longitudinal expansion of the thermal partons that are enhanced by the energy
loss of hard partons traversing the bulk medium. The peaks in and
are related to the same angular spread of the shower partons in a
jet cone. No artificial short- or long-range correlations are put in by hand. A
large part of the correlation between hadrons in jets is due to the correlation
among the shower partons arising from momentum conservation. Recombination
between thermal and shower partons dominates the correlation characterisitics
in the intermediate region.Comment: 14 pages in LaTex and 2 figures in ep
Single-molecule Electronics: Cooling Individual Vibrational Modes by the Tunneling Current
Electronic devices composed of single molecules constitute the ultimate limit
in the continued downscaling of electronic components. A key challenge for
single-molecule electronics is to control the temperature of these junctions.
Controlling heating and cooling effects in individual vibrational modes, can in
principle, be utilized to increase stability of single-molecule junctions under
bias, to pump energy into particular vibrational modes to perform
current-induced reactions or to increase the resolution in inelastic electron
tunneling spectroscopy by controlling the life-times of phonons in a molecule
by suppressing absorption and external dissipation processes. Under bias the
current and the molecule exchange energy, which typically results in heating of
the molecule. However, the opposite process is also possible, where energy is
extracted from the molecule by the tunneling current. Designing a molecular
'heat sink' where a particular vibrational mode funnels heat out of the
molecule and into the leads would be very desirable. It is even possible to
imagine how the vibrational energy of the other vibrational modes could be
funneled into the 'cooling mode', given the right molecular design. Previous
efforts to understand heating and cooling mechanisms in single molecule
junctions, have primarily been concerned with small models, where it is unclear
which molecular systems they correspond to. In this paper, our focus is on
suppressing heating and obtaining current-induced cooling in certain
vibrational modes. Strategies for cooling vibrational modes in single-molecule
junctions are presented, together with atomistic calculations based on those
strategies. Cooling and reduced heating are observed for two different cooling
schemes in calculations of atomistic single-molecule junctions.Comment: 18 pages, 6 figure
Input and Intake in Language Acquisition
This dissertation presents an approach for a productive way forward in the study of language acquisition, sealing the rift between claims of an innate linguistic hypothesis space and powerful domain general statistical inference. This approach breaks language acquisition into its component parts, distinguishing the input in the environment from the intake encoded by the learner, and looking at how a statistical inference mechanism, coupled with a well defined linguistic hypothesis space could lead a learn to infer the native grammar of their native language. This work draws on experimental work, corpus analyses and computational models of Tsez, Norwegian and English children acquiring word meanings, word classes and syntax to highlight the need for an appropriate encoding of the linguistic input in order to solve any given problem in language acquisition
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