3,953 research outputs found
Measuring The Collective Flow With Jets
In nucleus--nucleus collisions, high-pT partons interact with a dense medium,
which possesses strong collective flow components. Here, we demonstrate that
the resulting medium-induced gluon radiation does not depend solely on the
energy density of the medium, but also on the collective flow. Both components
cannot be disentangled on the basis of leading hadron spectra, but the
measurement of particle production associated to high-pT trigger particles,
jet-like correlations and jets, allows for their independent characterization.
In particular, we show that flow effects lead to a characteristic breaking of
the rotational symmetry of the average jet energy and jet multiplicity
distribution in the -plane. We argue that data on the
medium-induced broadening of jet-like particle correlations in Au+Au collisions
at RHIC provide a first evidence for a significant distortion of parton
fragmentation due to the longitudinal collective flow.Comment: 4 pages, Latex, 3 eps-figure
Algebraic {}-Integration and Fourier Theory on Quantum and Braided Spaces
We introduce an algebraic theory of integration on quantum planes and other
braided spaces. In the one dimensional case we obtain a novel picture of the
Jackson -integral as indefinite integration on the braided group of
functions in one variable . Here is treated with braid statistics
rather than the usual bosonic or Grassmann ones. We show that the definite
integral can also be evaluated algebraically as multiples of the
integral of a -Gaussian, with remaining as a bosonic scaling variable
associated with the -deformation. Further composing our algebraic
integration with a representation then leads to ordinary numbers for the
integral. We also use our integration to develop a full theory of -Fourier
transformation . We use the braided addition and braided-antipode to define a convolution product, and prove a
convolution theorem. We prove also that . We prove the analogous results
on any braided group, including integration and Fourier transformation on
quantum planes associated to general R-matrices, including -Euclidean and
-Minkowski spaces.Comment: 50 pages. Minor changes, added 3 reference
Spin conductivity in almost integrable spin chains
The spin conductivity in the integrable spin-1/2 XXZ-chain is known to be
infinite at finite temperatures T for anisotropies -1 < Delta < 1.
Perturbations which break integrability, e.g. a next-nearest neighbor coupling
J', render the conductivity finite. We construct numerically a non-local
conserved operator J_parallel which is responsible for the finite spin Drude
weight of the integrable model and calculate its decay rate for small J'. This
allows us to obtain a lower bound for the spin conductivity sigma_s >= c(T) /
J'^2, where c(T) is finite for J' to 0. We discuss the implication of our
result for the general question how non-local conservation laws affect
transport properties.Comment: 6 pages, 5 figure
Lower bounds for the conductivities of correlated quantum systems
We show how one can obtain a lower bound for the electrical, spin or heat
conductivity of correlated quantum systems described by Hamiltonians of the
form H = H0 + g H1. Here H0 is an interacting Hamiltonian characterized by
conservation laws which lead to an infinite conductivity for g=0. The small
perturbation g H1, however, renders the conductivity finite at finite
temperatures. For example, H0 could be a continuum field theory, where momentum
is conserved, or an integrable one-dimensional model while H1 might describe
the effects of weak disorder. In the limit g to 0, we derive lower bounds for
the relevant conductivities and show how they can be improved systematically
using the memory matrix formalism. Furthermore, we discuss various applications
and investigate under what conditions our lower bound may become exact.Comment: Title changed; 9 pages, 2 figure
Low-pT Collective Flow Induces High-pT Jet Quenching
Data on low-pT hadronic spectra are widely regarded as evidence of a
hydrodynamic expansion in nucleus-nucleus collisions. In this interpretation,
different hadron species emerge from a common medium that has built up a strong
collective velocity field. Here, we show that the existence of a collective
flow field implies characteristic modifications of high-pT parton
fragmentation. We generalize the formalism of parton energy loss to the case of
flow-induced, oriented momentum transfer. We also discuss how to embed this
calculation in hydrodynamic simulations. Flow effects are found to result
generically in characteristic asymmetries in the eta-phi-plane of jet energy
distributions and of multiplicity distributions associated to high-pT trigger
particles. But collective flow also contributes to the medium-induced
suppression of single inclusive high-pT hadron spectra. In particular, we find
that low-pT elliptic flow can induce a sizeable additional contribution to the
high-pT azimuthal asymmetry by selective elimination of those hard partons
which propagate with significant inclination against the flow field. This
reduces at least partially the recently observed problem that models of parton
energy loss tend to underpredict the large azimuthal asymmetry v2 of high-pT
hadronic spectra in semi-peripheral Au+Au collisions.Comment: 26 pages LaTeX, 11 eps-figure
A translation control reporter system (TCRS) for the analysis of translationally controlled processes in the vertebrate cell
Regulation of translation is critical for the accurate expression of a broad variety of genes that function in cell cycle progression and cell differentiation, as well as in the adaptation to cellular stress. The aetiologies of a number of human diseases, including cancer, have been linked to mutations in genes that control mRNA translation, or in cis-regulatory mRNA-sequences. Therefore, research on translational control and its therapeutic appliance has become most important. However, to date only a limited number of therapeutic drugs are known to affect translational control. Here we describe a novel, straightforward approach for the detection of cellular translational activity. We developed a Translational Control Reporter System (TCRS), which utilizes the cis-regulatory upstream open reading frame (uORF) from the c/ebpα locus to direct the translation of a dual reporter gene into two unique reporter peptides. The peptides contain a pre-pro-trypsin (PPT) signal for secretion into the medium and distinct immunogenic epitopes for detection and quantification purposes. TCRS-peptide expression levels reflect changes of translation initiation induced by serum growth factors, drugs or translation factor mutants. TCRS can be tailored to various research settings and the system may accomplish a broad application to uncover links between translational control and drugs
Shock Waves in Nanomechanical Resonators
The dream of every surfer is an extremely steep wave propagating at the
highest speed possible. The best waves for this would be shock waves, but are
very hard to surf. In the nanoscopic world the same is true: the surfers in
this case are electrons riding through nanomechanical devices on acoustic waves
[1]. Naturally, this has a broad range of applications in sensor technology and
for communication electronics for which the combination of an electronic and a
mechanical degree of freedom is essential. But this is also of interest for
fundamental aspects of nano-electromechanical systems (NEMS), when it comes to
quantum limited displacement detection [2] and the control of phonon number
states [3]. Here, we study the formation of shock waves in a NEMS resonator
with an embedded two-dimensional electron gas using surface acoustic waves. The
mechanical displacement of the nano-resonator is read out via the induced
acoustoelectric current. Applying acoustical standing waves we are able to
determine the anomalous acoustocurrent. This current is only found in the
regime of shock wave formation. We ontain very good agreement with model
calculations.Comment: 14 Pages including 4 figure
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