883 research outputs found
Ion holes in the hydrodynamic regime in ultracold neutral plasmas
We describe the creation of localized density perturbations, or ion holes, in an ultracold neutral
plasma in the hydrodynamic regime, and show that the holes propagate at the local ion acoustic wave
speed. We also observe the process of hole splitting, which results from the formation of a density
depletion initially at rest in the plasma. One-dimensional, two-fluid hydrodynamic simulations
describe the results well. Measurements of the ion velocity distribution also show the effects of the
ion hole and confirm the hydrodynamic conditions in the plasma
The Quasar SDSS J105041.35+345631.3: Black Hole Recoil or Extreme Double-Peaked Emitter?
The quasar SDSS J105041.35+345631.3 (z = 0.272) has broad emission lines
blueshifted by 3500 km/s relative to the narrow lines and the host galaxy. Such
an object may be a candidate for a recoiling supermassive black hole, binary
black hole, a superposition of two objects, or an unusual geometry for the
broad emission-line region. The absence of narrow lines at the broad line
redshift argues against superposition. New Keck spectra of J1050+3546 place
tight constraints on the binary model. The combination of large velocity shift
and symmetrical H-beta profile, as well as aspects of the narrow line spectrum,
make J1050+3546 an interesting candidate for black hole recoil. Other aspects
of the spectrum, however, suggest that the object is most likely an extreme
case of a ``double-peaked emitter.'' We discuss possible observational tests to
determine the true nature of this exceptional object.Comment: 5 pages, 2 figures, LaTeX; substantial revision
Turbulent Friction in Rough Pipes and the Energy Spectrum of the Phenomenological Theory
The classical experiments on turbulent friction in rough pipes were performed
by J. Nikuradse in the 1930's. Seventy years later, they continue to defy
theory. Here we model Nikuradse's experiments using the phenomenological theory
of Kolmog\'orov, a theory that is widely thought to be applicable only to
highly idealized flows. Our results include both the empirical scalings of
Blasius and Strickler, and are otherwise in minute qualitative agreement with
the experiments; they suggest that the phenomenological theory may be relevant
to other flows of practical interest; and they unveil the existence of close
ties between two milestones of experimental and theoretical turbulence.Comment: Accepted for publication in PRL; 4 pages, 4 figures; revised versio
Resilience in Virginia: Outlook 2021
VCPC\u27s October webinar included an update on Virginia’s participation in the Regional Greenhouse Gas Initiative and the implementation of Executive Order 24; remarks from the Speaker of the House of Delegates, Eileen Filler -Corn, and a legislative panel discussed resilience issues for the upcoming 2021 Virginia General Assembly session. VCPC was honored to host Governor Ralph Northam for Closing Remarks
Resilience in Virginia: Outlook 2021
VCPC\u27s October webinar included an update on Virginia’s participation in the Regional Greenhouse Gas Initiative and the implementation of Executive Order 24; remarks from the Speaker of the House of Delegates, Eileen Filler -Corn, and a legislative panel discussed resilience issues for the upcoming 2021 Virginia General Assembly session. VCPC was honored to host Governor Ralph Northam for Closing Remarks
X-ray Absorption Studies of Ceria with Trivalent Dopants
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65899/1/j.1151-2916.1991.tb04328.x.pd
The Sol Genomics Network (solgenomics.net): growing tomatoes using Perl
The Sol Genomics Network (SGN; http://solgenomics.net/) is a clade-oriented database (COD) containing biological data for species in the Solanaceae and their close relatives, with data types ranging from chromosomes and genes to phenotypes and accessions. SGN hosts several genome maps and sequences, including a pre-release of the tomato (Solanum lycopersicum cv Heinz 1706) reference genome. A new transcriptome component has been added to store RNA-seq and microarray data. SGN is also an open source software project, continuously developing and improving a complex system for storing, integrating and analyzing data. All code and development work is publicly visible on GitHub (http://github.com). The database architecture combines SGN-specific schemas and the community-developed Chado schema (http://gmod.org/wiki/Chado) for compatibility with other genome databases. The SGN curation model is community-driven, allowing researchers to add and edit information using simple web tools. Currently, over a hundred community annotators help curate the database. SGN can be accessed at http://solgenomics.net/
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
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