3,603 research outputs found
Anisotropic flow at RHIC
We present the first measurement of directed flow () at the Relativistic
Heavy Ion Collider (RHIC). is found to be consistent with zero at
pseudorapidities from -1.2 to 1.2, then rises to the level of a couple
of percent over the range . The latter observation is similar
to that from NA49 if the SPS rapidities are shifted by the difference in beam
rapidity between RHIC and SPS. We studied the evolution of elliptic flow from
p+p collisions through d+Au collision, and onto Au+Au collisions. Measurements
of higher harmonics are presented and discussed.Comment: 6 pages, 3 figures. Proceeding for the 20th Winter Workshop on
Nuclear Dynamics, Jamaic
And you know why: compulsory jailing and racism
Much has been made over the last few months over the mandatory sentencing regime in the Northern Territory and Western Australia. However, the words ‘mandatory sentencing’ obscure what has been perpetrated by the governments of those two jurisdictions. ‘Mandatory sentencing’ is meaningless really: all judges and magistrates sentence those who are found guilty even if, in their judgement, circumstances are such that a conviction might not be recorded. It is a judgement and a discretionary decision on sentence nevertheless. What we are really talking about is not ‘mandatory sentencing’ but ‘compulsory jailing’. We are talking about a legal regime under which, across a large range of property crimes, judges and magistrates have absolutely no choice. They have been left with no discretion; they have been left without powers to take into account any single aspect of the circumstances surrounding the crime such as the mental state of the defendant, or the triviality of the offence. For juveniles, which in the Northern Territory is defined as 15—17 year olds, means compulsory jailing on a second offence of 28 days. Subsequent offences also attract a 28 day compulsory jailing. There is an empty legislative attempt at diversionary schemes. For adults, this means compulsory jailing on a first offence of 14 days; on a second offence of 3 months and a year in jail on a third offence. No second chances. No diversionary schemes
Theory of stripes in quasi two dimensional rare-earth tritellurides
Even though the rare-earth tritellurides are tetragonal materials with a
quasi two dimensional (2D) band structure, they have a "hidden" 1D character.
The resultant near-perfect nesting of the Fermi surface leads to the formation
of a charge density wave (CDW) state. We show that for this band structure,
there are two possible ordered phases: A bidirectional "checkerboard" state
would occur if the CDW transition temperature were sufficiently low, whereas a
unidirectional "striped" state, consistent with what is observed in experiment,
is favored when the transition temperature is higher. This result may also give
some insight into why, in more strongly correlated systems, such as the
cuprates and nickelates, the observed charge ordered states are generally
stripes as opposed to checkerboards.Comment: Added contents and references, changed title and figures. Accepted to
PR
Dynamical layer decoupling in a stripe-ordered, high T_c superconductor
In the stripe-ordered state of a strongly-correlated two-dimensional
electronic system, under a set of special circumstances, the superconducting
condensate, like the magnetic order, can occur at a non-zero wave-vector
corresponding to a spatial period double that of the charge order. In this
case, the Josephson coupling between near neighbor planes, especially in a
crystal with the special structure of La_{2-x}Ba_xCuO_4, vanishes identically.
We propose that this is the underlying cause of the dynamical decoupling of the
layers recently observed in transport measurements at x=1/8.Comment: 4 pages, 3 figures (one with 3 subfigures); ; new edited version; one
new reference (Ref.25); to be published in Physical Review Letters (in press
New Challenges to Hydrodynamics from Azimuthal Anisotropy at RHIC
This paper presents ratio as a function of transverse
momentum (), pseudorapidity () and collision centrality in Au+Au
collisions at GeV using the STAR detector at the
Relativistic Heavy Ion Collider (RHIC). It is found that is
larger than Hydrodynamic calculations, the centrality and transverse dependence
of this ratio can not be fully described by Hydrodynamics, and the
pseudorapidity dependence is opposite to what one expects from Hydrodynamics.
The dependence of is also presented. It is found that
for changes sign, and two possible explanations of
the sign change are discussed.Comment: 4 pages, 3 figures. CIPANP 06 proceedin
Robust artificial neural networks and outlier detection. Technical report
Large outliers break down linear and nonlinear regression models. Robust
regression methods allow one to filter out the outliers when building a model.
By replacing the traditional least squares criterion with the least trimmed
squares criterion, in which half of data is treated as potential outliers, one
can fit accurate regression models to strongly contaminated data.
High-breakdown methods have become very well established in linear regression,
but have started being applied for non-linear regression only recently. In this
work, we examine the problem of fitting artificial neural networks to
contaminated data using least trimmed squares criterion. We introduce a
penalized least trimmed squares criterion which prevents unnecessary removal of
valid data. Training of ANNs leads to a challenging non-smooth global
optimization problem. We compare the efficiency of several derivative-free
optimization methods in solving it, and show that our approach identifies the
outliers correctly when ANNs are used for nonlinear regression
Theory of the nodal nematic quantum phase transition in superconductors
We study the character of an Ising nematic quantum phase transition (QPT)
deep inside a d-wave superconducting state with nodal quasiparticles in a
two-dimensional tetragonal crystal. We find that, within a 1/N expansion, the
transition is continuous. To leading order in 1/N, quantum fluctuations enhance
the dispersion anisotropy of the nodal excitations, and cause strong scattering
which critically broadens the quasiparticle (qp) peaks in the spectral
function, except in a narrow wedge in momentum space near the Fermi surface
where the qp's remain sharp. We also consider the possible existence of a
nematic glass phase in the presence of weak disorder. Some possible
implications for cuprate physics are also discussed.Comment: 9 page, 4 figures, an error in one of expressions corrected and a new
author was added. New references and footnotes are added and this is the
version to appear in PR
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Optical band gap of cross-linked, curved, and radical polyaromatic hydrocarbons.
In this work, the optical band gaps of polycyclic aromatic hydrocarbons (PAHs) crosslinked via an aliphatic bond, curved via pentagon integration and with radical character were computed using density functional theory. A variety of different functionals were benchmarked against optical band gaps (OBGs) measured by ultraviolet-visible spectroscopy with HSE06 being most accurate with a percentage error of 6% for a moderate basis set. Pericondensed aromatics with different symmetries were calculated with this improved functional providing new scaling relationships for the OBG versus size. Further calculations showed crosslinks cause a small decrease in the OBG of the monomers which saturates after 3-4 crosslinks. Curvature in PAHs was shown to increase the optical band gap due to the resulting change in hybridisation of the system, but this increase saturated at larger sizes. The increase in OBG between a flat PAH and a strained curved one was shown to be equivalent to a difference of several rings in size for pericondensed aromatic systems. The effect of σ-radicals on the optical band gap was also shown to be negligible, however, π-radicals were found to decrease the band gap by ∼0.5 eV. These findings have applications in understanding the molecular species involved in soot formation
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