335 research outputs found
Density fluctuations and phase separation in a traffic flow model
Within the Nagel-Schreckenberg traffic flow model we consider the transition
from the free flow regime to the jammed regime. We introduce a method of
analyzing the data which is based on the local density distribution. This
analyzes allows us to determine the phase diagram and to examine the separation
of the system into a coexisting free flow phase and a jammed phase above the
transition. The investigation of the steady state structure factor yields that
the decomposition in this phase coexistence regime is driven by density
fluctuations, provided they exceed a critical wavelength.Comment: in 'Traffic and Granular Flow 97', edited by D.E. Wolf and M.
Schreckenberg, Springer, Singapore (1998
Critical and Near-Critical Branching Processes
Scale-free dynamics in physical and biological systems can arise from a
variety of causes. Here, we explore a branching process which leads to such
dynamics. We find conditions for the appearance of power laws and study
quantitatively what happens to these power laws when such conditions are
violated. From a branching process model, we predict the behavior of two
systems which seem to exhibit near scale-free behavior--rank-frequency
distributions of number of subtaxa in biology, and abundance distributions of
genotypes in an artificial life system. In the light of these, we discuss
distributions of avalanche sizes in the Bak-Tang-Wiesenfeld sandpile model.Comment: 9 pages LaTex with 10 PS figures. v.1 of this paper contains results
from non-critical sandpile simulations that were excised from the published
versio
Nationalism, ethnicity and religion: Fundamental conflicts and the politics of identity in Tanzania
The Impact II, a Very High-Resolution Quadrupole Time-of-Flight Instrument (QTOF) for Deep Shotgun Proteomics
Hybrid quadrupole time-of-flight (QTOF) mass spectrometry is one of the two major principles used in proteomics. Although based on simple fundamentals, it has over the last decades greatly evolved in terms of achievable resolution, mass accuracy, and dynamic range. The Bruker impact platform of QTOF instruments takes advantage of these developments and here we develop and evaluate the impact II for shotgun proteomics applications. Adaption of our heated liquid chromatography system achieved very narrow peptide elution peaks. The impact II is equipped with a new collision cell with both axial and radial ion ejection, more than doubling ion extraction at high tandem MS frequencies. The new reflectron and detector improve resolving power compared with the previous model up to 80%, i.e. to 40,000 at m/z 1222. We analyzed the ion current from the inlet capillary and found very high transmission (>80%) up to the collision cell. Simulation and measurement indicated 60% transfer into the flight tube. We adapted MaxQuant for QTOF data, improving absolute average mass deviations to better than 1.45 ppm. More than 4800 proteins can be identified in a single run of HeLa digest in a 90 min gradient. The workflow achieved high technical reproducibility (R2 > 0.99) and accurate fold change determination in spike-in experiments in complex mixtures. Using label-free quantification we rapidly quantified haploid against diploid yeast and characterized overall proteome differences in mouse cell lines originating from different tissues. Finally, after high pH reversed-phase fractionation we identified 9515 proteins in a triplicate measurement of HeLa peptide mixture and 11,257 proteins in single measurements of cerebellum-the highest proteome coverage reported with a QTOF instrument so far
Dense transcript profiling in single cells by image correlation decoding
Sequential barcoded fluorescent in situ hybridization (seqFISH) allows large numbers of molecular species to be accurately detected in single cells, but multiplexing is limited by the density of barcoded objects. We present correlation FISH (corrFISH), a method to resolve dense temporal barcodes in sequential hybridization experiments. Using corrFISH, we quantified highly expressed ribosomal protein genes in single cultured cells and mouse thymus sections, revealing cell-type-specific gene expression
Universal 1/f Noise from Dissipative SOC Models
We introduce a model able to reproduce the main features of 1/f noise:
hyper-universality (the power-law exponents are independent on the dimension of
the system; we show here results in d=1,2) and apparent lack of a low-frequency
cutoff in the power spectrum. Essential ingredients of this model are an
activation-deactivation process and dissipation.Comment: 3 Latex pages, 2 eps Figure
Meson-Baryon Form Factors in Chiral Colour Dielectric Model
The renormalised form factors for pseudoscalar meson-baryon coupling are
computed in chiral colour dielectric model. This has been done by rearranging
the Lippmann-Schwinger series for the meson baryon scattering matrix so that it
can be expressed as a baryon pole term with renormalized form factors and
baryon masses and the rest of the terms which arise from the crossed diagrams.
Thus we are able to obtain an integral equation for the renormalized
meson-baryon form factors in terms of the bare form factors as well as an
expression for the meson self energy. This integral equation is solved and
renormalized meson baryon form factors and renormalized baryon masses are
computed. The parameters of the model are adjusted to obtain a best fit to the
physical baryon masses. The calculations show that the renormalized form
factors are energy-dependent and differ from the bare form factors primarily at
momentum transfers smaller than 1 GeV. At nucleon mass, the change in the form
factors is about 10% at zero momentum transfer. The computed form factors are
soft with the equivalent monopole cut-off mass of about 500 MeV. The
renormalized coupling constants are obtained by comparing the chiral colour
dielectric model interaction Hamiltonian with the standard form of
meson-nucleon interaction Hamiltonian. The ratio of and
coupling constants is found to be about 2.15. This value is very close to the
experimental value.Comment: 16 pages, 7 postscript figure
Dihyperon in Chiral Colour Dielectric Model
The mass of dihyperon with spin, parity and isospin
is calculated in the framework of Chiral colour dielectric model. The wave
function of the dihyperon is expressed as a product of two colour-singlet
baryon clusters. Thus the quark wave functions within the cluster are
antisymmetric. Appropriate operators are then used to antisymmetrize
inter-cluster quark wave functions. The radial part of the quark wavefunctions
are obtained by solving the the quark and dielectric field equations of motion
obtained in the Colour dielectric model. The mass of the dihyperon is computed
by including the colour magnetic energy as well as the energy due to meson
interaction. The recoil correction to the dihyperon mass is incorporated by
Peierls-Yoccoz technique. We find that the mass of the dihyperon is smaller
than the threshold by over 100 MeV. The implications of our
results on the present day relativistic heavy ion experiments is discussed.Comment: LaTeX, 13 page
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