3,394 research outputs found
Coefficient of restitution for viscoelastic disks
The dissipative collision of two identical viscoelastic disks is studied. By
using a known law for the elastic part of the interaction force and the
viscoelastic damping model an analytical solution for the coefficient of
restitution shall be given. The coefficient of restitution depends
significantly on the impact velocity. It approaches one for small velocities
and decreases for increasing velocities.Comment: 11 pages, 3 figure
Incremental Network Design with Minimum Spanning Trees
Given an edge-weighted graph and a set , the
incremental network design problem with minimum spanning trees asks for a
sequence of edges minimizing
where is the weight of a minimum spanning tree
for the subgraph and . We prove that this problem can be solved by a greedy
algorithm.Comment: 9 pages, minor revision based on reviewer comment
The hadronic interaction model SIBYLL 2.3c and Feynman scaling
The Monte Carlo model Sibyll has been designed for efficient simulation of
hadronic multiparticle production up to the highest energies as needed for
interpreting cosmic ray measurements. For more than 15 years, version 2.1 of
Sibyll has been one of the standard models for air shower simulation. Motivated
by data of LHC and fixed-target experiments and a better understanding of the
phenomenology of hadronic interactions, we have developed an improved version
of this model, version 2.3, which has been released in 2016. In this
contribution we present a revised version of this model, called Sibyll 2.3c,
that is further improved by adjusting particle production spectra to match the
expectation of Feynman scaling in the fragmentation region. After a brief
introduction to the changes implemented in Sibyll 2.3 and 2.3c with respect to
Sibyll 2.1, the current predictions of the model for the depth of shower
maximum, the number of muons at ground, and the energy spectrum of muons in
extensive air showers are presented.Comment: 35th International Cosmic Ray Conferenc
Gene Expression Profiles of Chlamydophila pneumoniae during the Developmental Cycle and Iron Depletion–Mediated Persistence
The obligate intracellular, gram-negative bacterium Chlamydophila pneumoniae (Cpn) has impact as a human pathogen. Little is known about changes in the Cpn transcriptome during its biphasic developmental cycle (the acute infection) and persistence. The latter stage has been linked to chronic diseases. To analyze Cpn CWL029 gene expression, we designed a pathogen-specific oligo microarray and optimized the extraction method for pathogen RNA. Throughout the acute infection, ratio expression profiles for each gene were generated using 48 h post infection as a reference. Based on these profiles, significantly expressed genes were separated into 12 expression clusters using self-organizing map clustering and manual sorting into the “early”, “mid”, “late”, and “tardy” cluster classes. The latter two were differentiated because the “tardy” class showed steadily increasing expression at the end of the cycle. The transcriptome of the Cpn elementary body (EB) and published EB proteomics data were compared to the cluster profile of the acute infection. We found an intriguing association between “late” genes and genes coding for EB proteins, whereas “tardy” genes were mainly associated with genes coding for EB mRNA. It has been published that iron depletion leads to Cpn persistence. We compared the gene expression profiles during iron depletion–mediated persistence with the expression clusters of the acute infection. This led to the finding that establishment of iron depletion–mediated persistence is more likely a mid-cycle arrest in development rather than a completely distinct gene expression pattern. Here, we describe the Cpn transcriptome during the acute infection, differentiating “late” genes, which correlate to EB proteins, and “tardy” genes, which lead to EB mRNA. Expression profiles during iron mediated–persistence led us to propose the hypothesis that the transcriptomic “clock” is arrested during acute mid-cycle
The ReaxFF reactive force-field : development, applications and future directions
The reactive force-field (ReaxFF) interatomic potential is a powerful computational tool for exploring, developing and optimizing material properties. Methods based on the principles of quantum mechanics (QM), while offering valuable theoretical guidance at the electronic level, are often too computationally intense for simulations that consider the full dynamic evolution of a system. Alternatively, empirical interatomic potentials that are based on classical principles require significantly fewer computational resources, which enables simulations to better describe dynamic processes over longer timeframes and on larger scales. Such methods, however, typically require a predefined connectivity between atoms, precluding simulations that involve reactive events. The ReaxFF method was developed to help bridge this gap. Approaching the gap from the classical side, ReaxFF casts the empirical interatomic potential within a bond-order formalism, thus implicitly describing chemical bonding without expensive QM calculations. This article provides an overview of the development, application, and future directions of the ReaxFF method
The Threat of Capital Drain: A Rationale for Public Banks?
This paper yields a rationale for why subsidized public banks may be desirable from a regional perspective in a financially integrated economy. We present a model with credit rationing and heterogeneous regions in which public banks prevent a capital drain from poorer to richer regions by subsidizing local depositors, for example, through a public guarantee. Under some conditions, cooperative banks can perform the same function without any subsidization; however, they may be crowded out by public banks. We also discuss the impact of the political structure on the emergence of public banks in a political-economy setting and the role of interregional mobility
Manganese co-limitation of phytoplankton growth and major nutrient drawdown in the Southern Ocean
Residual macronutrients in the surface Southern Ocean result from restricted biological utilization, caused by low wintertime irradiance, cold temperatures, and insufficient micronutrients. Variability in utilization alters oceanic CO2 sequestration at glacial-interglacial timescales. The role for insufficient iron has been examined in detail, but manganese also has an essential function in photosynthesis and dissolved concentrations in the Southern Ocean can be strongly depleted. However, clear evidence for or against manganese limitation in this system is lacking. Here we present results from ten experiments distributed across Drake Passage. We found manganese (co-)limited phytoplankton growth and macronutrient consumption in central Drake Passage, whilst iron limitation was widespread nearer the South American and Antarctic continental shelves. Spatial patterns were reconciled with the different rates and timescales for removal of each element from seawater. Our results suggest an important role for manganese in modelling Southern Ocean productivity and understanding major nutrient drawdown in glacial periods
An Experimentalist's View of Neutrino Oscillations
Neutrinos, and primarily neutrino oscillations, have undoubtedly been one of
the most exciting topics in the field of high-energy physics over the past few
years. The existence of neutrino oscillations would require an extension of the
currently accepted description of sub-nuclear phenomena beyond the Standard
Model. Compelling evidence of new physics, which seems to be pointing towards
neutrino oscillations, is coming from the solar neutrino deficit and from the
atmospheric neutrino anomaly. More controversial effects have been observed
with artificially produced neutrinos. The present experimental status of
neutrino oscillations is reviewed, as well as the planned future experimental
programme, which, it is hoped, will solve most of the outstanding puzzles.Comment: 64 pages, 29 figures, to be published in Intern. J. Mod. Phys. A
(2001
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