3,543 research outputs found
Measurement of photons via conversion pairs in \sqrt{s_{NN}} = 200 GeV Au+Au collisions with the PHENIX experiment at RHIC
Thermal photons can provide information on the temperature of the new state
of matter created at RHIC. In the p_T region of 1--3 GeV/c thermal photons are
expected to be the dominant direct photon source. Therefore, a possible excess
compared to a pure decay photon signal due to a thermal photon contribution
should be seen in the double ratio
(\gamma/\gamma(\pi^{0}))_{Measured}/(\gamma/\gamma(\pi^{0}))_{Simulated}, if
sufficient accuracy can be reached. We present a method to reconstruct direct
photons by measuring e^{+}e^{-}--pairs from external photon conversions.Comment: 4 pages, 7 figures. To appear in the proceedings of Hot Quarks 2006:
Workshop for Young Scientists on the Physics of Ultrarelativistic
Nucleus-Nucleus Collisions, Villasimius, Italy, 15-20 May 200
Antifouling activity and microbial diversity of two congeneric sponges Callyspongia spp. from Hong Kong and the Bahamas
Microbial communities of the sponges Callyspongia sp. from Hong Kong and Callyspongia plicifera (Porifera: Demospongia) from the Bahamas were compared with each other and with those from reference substrata using a terminal restriction fragment length polymorphism (T-RFLP) analysis. The least number of bacterial ribotypes and bacterial isolates were retrieved from Bahamas reference and sponge surfaces, while the bacterial communities from Hong Kong Callyspongia sp. and reference surfaces were more diverse. Microbial communities from the 2 sponges were different from each other and from reference substrata. Gas chromatographic–mass spectrometric (GC-MS) analysis of dichloromethane extracts revealed that more than 60% of the compounds were similar in the 2 species Callyspongia sp. and C. plicifera, compared to the compounds of Halichondria spp. At tissue level (TL) concentrations, both sponge extracts predominantly inhibited the growth of bacteria from reference substrata. Multifactor ANOVA revealed that the source of bacteria (sponge surface, interior, or reference substrata), the geographic location of isolates (Hong Kong or the Bahamas), thesponge extract (from Callyspongia sp. or from C. plicifera), and combinations of these factors contributed significant effects in disc diffusion assay experiments. Sponge extracts at both TL concentrations and 10× dilutions were toxic to larvae of the polychaete Hydroides elegans and the barnacle Balanus amphitrite. Our results suggest that the 2 congeneric sponges Callyspongia spp. from different biogeographic regions have different bacterial associates, while producing relatively similar secondary metabolites. It remains to be explored whether differences in sponge-associated bacterial communities will also hold for other congeneric sponge species from different regions
Molecular Basis of Lysosomal Enzyme Recognition: Three-Dimensional Structure of the Cation-Dependent Mannose 6-Phosphate Receptor
AbstractTargeting of newly synthesized lysosomal hydrolases to the lysosome is mediated by the cation-dependent mannose 6-phosphate receptor (CD-MPR) and the insulin-like growth factor II/cation-independent mannose 6-phosphate receptor (IGF-II/CI-MPR). The two receptors, which share sequence similarities, constitute the P-type family of animal lectins. We now report the three-dimensional structure of a glycosylation-deficient, yet fully functional form of the extracytoplasmic domain of the bovine CD-MPR (residues 3–154) complexed with mannose 6-phosphate at 1.8 Å resolution. The extracytoplasmic domain of the CD-MPR crystallizes as a dimer, and each monomer folds into a nine-stranded flattened β barrel, which bears a striking resemblance to avidin. The distance of 40 Å between the two ligand-binding sites of the dimer provides a structural basis for the observed differences in binding affinity exhibited by the CD-MPR toward various lysosomal enzymes
Synchronisation in networks of delay-coupled type-I excitable systems
We use a generic model for type-I excitability (known as the SNIPER or SNIC
model) to describe the local dynamics of nodes within a network in the presence
of non-zero coupling delays. Utilising the method of the Master Stability
Function, we investigate the stability of the zero-lag synchronised dynamics of
the network nodes and its dependence on the two coupling parameters, namely the
coupling strength and delay time. Unlike in the FitzHugh-Nagumo model (a model
for type-II excitability), there are parameter ranges where the stability of
synchronisation depends on the coupling strength and delay time. One important
implication of these results is that there exist complex networks for which the
adding of inhibitory links in a small-world fashion may not only lead to a loss
of stable synchronisation, but may also restabilise synchronisation or
introduce multiple transitions between synchronisation and desynchronisation.
To underline the scope of our results, we show using the Stuart-Landau model
that such multiple transitions do not only occur in excitable systems, but also
in oscillatory ones.Comment: 10 pages, 9 figure
Direct photons ~basis for characterizing heavy ion collisions~
After years of experimental and theoretical efforts, direct photons become a
strong and reliable tool to establish the basic characteristics of a hot and
dense matter produced in heavy ion collisions. The recent direct photon
measurements are reviewed and a future prospect is given.Comment: 8 pages, 8 figures, Invited plenary talk at Quark Matter 200
Loss of synchronization in complex neuronal networks with delay
We investigate the stability of synchronization in networks of delay-coupled
excitable neural oscillators. On the basis of the master stability function
formalism, we demonstrate that synchronization is always stable for excitatory
coupling independently of the delay and coupling strength. Superimposing
inhibitory links randomly on top of a regular ring of excitatory coupling,
which yields a small-world-like network topology, we find a phase transition to
desynchronization as the probability of inhibitory links exceeds a critical
value. We explore the scaling of the critical value in dependence on network
properties. Compared to random networks, we find that small-world topologies
are more susceptible to desynchronization via inhibition.Comment: 6 pages, 4 figure
Dynamics of fully coupled rotators with unimodal and bimodal frequency distribution
We analyze the synchronization transition of a globally coupled network of N
phase oscillators with inertia (rotators) whose natural frequencies are
unimodally or bimodally distributed. In the unimodal case, the system exhibits
a discontinuous hysteretic transition from an incoherent to a partially
synchronized (PS) state. For sufficiently large inertia, the system reveals the
coexistence of a PS state and of a standing wave (SW) solution. In the bimodal
case, the hysteretic synchronization transition involves several states.
Namely, the system becomes coherent passing through traveling waves (TWs), SWs
and finally arriving to a PS regime. The transition to the PS state from the SW
occurs always at the same coupling, independently of the system size, while its
value increases linearly with the inertia. On the other hand the critical
coupling required to observe TWs and SWs increases with N suggesting that in
the thermodynamic limit the transition from incoherence to PS will occur
without any intermediate states. Finally a linear stability analysis reveals
that the system is hysteretic not only at the level of macroscopic indicators,
but also microscopically as verified by measuring the maximal Lyapunov
exponent.Comment: 22 pages, 11 figures, contribution for the book: Control of
Self-Organizing Nonlinear Systems, Springer Series in Energetics, eds E.
Schoell, S.H.L. Klapp, P. Hoeve
Symmetry-breaking transitions in networks of nonlinear circuit elements
We investigate a nonlinear circuit consisting of N tunnel diodes in series,
which shows close similarities to a semiconductor superlattice or to a neural
network. Each tunnel diode is modeled by a three-variable FitzHugh-Nagumo-like
system. The tunnel diodes are coupled globally through a load resistor. We find
complex bifurcation scenarios with symmetry-breaking transitions that generate
multiple fixed points off the synchronization manifold. We show that multiply
degenerate zero-eigenvalue bifurcations occur, which lead to multistable
current branches, and that these bifurcations are also degenerate with a Hopf
bifurcation. These predicted scenarios of multiple branches and degenerate
bifurcations are also found experimentally.Comment: 32 pages, 11 figures, 7 movies available as ancillary file
Heterogeneous Delays in Neural Networks
We investigate heterogeneous coupling delays in complex networks of excitable
elements described by the FitzHugh-Nagumo model. The effects of discrete as
well as of uni- and bimodal continuous distributions are studied with a focus
on different topologies, i.e., regular, small-world, and random networks. In
the case of two discrete delay times resonance effects play a major role:
Depending on the ratio of the delay times, various characteristic spiking
scenarios, such as coherent or asynchronous spiking, arise. For continuous
delay distributions different dynamical patterns emerge depending on the width
of the distribution. For small distribution widths, we find highly synchronized
spiking, while for intermediate widths only spiking with low degree of
synchrony persists, which is associated with traveling disruptions, partial
amplitude death, or subnetwork synchronization, depending sensitively on the
network topology. If the inhomogeneity of the coupling delays becomes too
large, global amplitude death is induced
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