3,769 research outputs found
Measurement of light mesons at RHIC by the PHENIX experiment
The PHENIX experiment at RHIC has measured a variety of light neutral mesons
(, K, , , , ) via
multi-particle decay channels over a wide range of transverse momentum. A
review of the recent results on the production rates of light mesons in p+p and
their nuclear modification factors in d+Au, Cu+Cu and Au+Au collisions at
different energies is presented.Comment: 5 pages, 4 figures, talk given at Hard Probes 2008 conference in La
Toja, Spain. submitted to EPJ
Cold Flow Model Study on Interconnected Fluidized Bed Reactors for Multi-generation Systems and Chemical Looping Processes
Interconnected fluidized bed reactors (DCFB) were implemented in multi-generation systems (pyrolysis FB reactor and CFB boiler), chemical looping combustion (CLC) systems (double metal oxides or carbonate oxide reactors) and three reactor chemical looping gasification processes. The presented data focus on the solids circulation rate and on pressure profiles of the DCFB depended on selected operating parameters such as fluidization gas flow rate, loop seal fluidization, and solids inventory. Most work was devoted to studying standpipe and valve operation
The "Horizon-T" Experiment: Extensive Air Showers Detection
Horizon-T is an innovative detector system constructed to study Extensive Air
Showers (EAS) in the energy range above 10^16 eV coming from a wide range of
zenith angles (0 - 85 degrees). The system is located at Tien Shan
high-altitude Science Station of Lebedev Physical Institute of the Russian
Academy of Sciences at approximately 3340 meters above the sea level. It
consists of eight charged particle detection points separated by the distance
up to one kilometer as well as optical detector subsystem to view the
Vavilov-Cerenkov light from the EAS. The time resolution of charged particles
and Vavilov-Cerenkov light photons passage of the detector system is a few ns.
This level of resolution allows conducting research of atmospheric development
of individual EAS.Comment: Initial technical note for Horizon-T experiment, updated with recent
detector upgrades, 11/2016. Updated 12/2017 with minor edits. Large upgrade
will be in another articl
Stability of Nonlinear Normal Modes in the FPU- Chain in the Thermodynamic Limit
All possible symmetry-determined nonlinear normal modes (also called by
simple periodic orbits, one-mode solutions etc.) in both hard and soft
Fermi-Pasta-Ulam- chains are discussed. A general method for studying
their stability in the thermodynamic limit, as well as its application for each
of the above nonlinear normal modes are presented
Cell size as driver and sentinel of phytoplankton community structure and functioning
Body size is a decisive functional trait in many organisms, especially for phytoplankton, which span several orders of magnitude in cell volume. Therefore, the analysis of size as a functional trait driving species’ performance has received wide attention in aquatic ecology, amended in recent decades by studies documenting changes in phytoplankton size in response to abiotic or biotic factors in the environment. We performed a systematic literature review to provide an overarching, partially quantitative synthesis of cell size as a driver and sentinel of phytoplankton ecology. We found consistent and significant allometric relationships between cell sizes and the functional performance of phytoplankton species (cellular rates of carbon fixation, respiration and exudation as well as resource affinities, uptake and content). Size scaling became weaker, absent or even negative when addressing C- or volume-specific rates or growth. C-specific photosynthesis and population growth rate peaked at intermediate cell sizes around 100 µm3. Additionally, we found a rich literature on sizes changing in response to warming, nutrients and pollutants. Whereas small cells tended to dominate under oligotrophic and warm conditions, there are a few notable exceptions, which indicates that other environmental or biotic constraints alter this general trend. Grazing seems a likely explanation, which we reviewed to understand both how size affects edibility and how size structure changes in response to grazing. Cell size also predisposes the strength and outcome of competitive interactions between algal species. Finally, we address size in a community context, where size-abundance scaling describes community composition and thereby the biodiversity in phytoplankton assemblages. We conclude that (a) size is a highly predictive trait for phytoplankton metabolism at the cellular scale, with less strong and nonlinear implications for growth and specific metabolism and (b) size structure is a highly suitable sentinel of phytoplankton responses to changing environments. A free Plain Language Summary can be found within the Supporting Information of this article
Phytoplankton competition in deep biomass maximum
Resource competition in heterogeneous environments is still an unresolved
problem of theoretical ecology. In this article I analyze competition between
two phytoplankton species in a deep water column, where the distributions of
main resources (light and a limiting nutrient) have opposing gradients and
co-limitation by both resources causes a deep biomass maximum. Assuming that
the species have a trade-off in resource requirements and the water column is
weakly mixed, I apply the invasion threshold analysis (Ryabov and Blasius 2011)
to determine relations between environmental conditions and phytoplankton
composition. Although species deplete resources in the interior of the water
column, the resource levels at the bottom and surface remain high. As a result,
the slope of resources gradients becomes a new crucial factor which, rather
than the local resource values, determines the outcome of competition. The
value of resource gradients nonlinearly depend on the density of consumers.
This leads to complex relationships between environmental parameters and
species composition. In particular, it is shown that an increase of both the
incident light intensity or bottom nutrient concentrations favors the best
light competitors, while an increase of the turbulent mixing or background
turbidity favors the best nutrient competitors. These results might be
important for prediction of species composition in deep ocean.Comment: 13 pages, 7 figures; Theoretical Ecology 201
Energetics and performance of a microscopic heat engine based on exact calculations of work and heat distributions
We investigate a microscopic motor based on an externally controlled
two-level system. One cycle of the motor operation consists of two strokes.
Within each stroke, the two-level system is in contact with a given thermal
bath and its energy levels are driven with a constant rate. The time evolution
of the occupation probabilities of the two states are controlled by one rate
equation and represent the system's response with respect to the external
driving. We give the exact solution of the rate equation for the limit cycle
and discuss the emerging thermodynamics: the work done on the environment, the
heat exchanged with the baths, the entropy production, the motor's efficiency,
and the power output. Furthermore we introduce an augmented stochastic process
which reflects, at a given time, both the occupation probabilities for the two
states and the time spent in the individual states during the previous
evolution. The exact calculation of the evolution operator for the augmented
process allows us to discuss in detail the probability density for the
performed work during the limit cycle. In the strongly irreversible regime, the
density exhibits important qualitative differences with respect to the more
common Gaussian shape in the regime of weak irreversibility.Comment: 21 pages, 7 figure
Dynamic evolution in the key honey bee pathogen deformed wing virus: Novel insights into virulence and competition using reverse genetics
The impacts of invertebrate RNA virus population dynamics on virulence and infection out- comes are poorly understood. Deformed wing virus (DWV), the main viral pathogen of honey bees, negatively impacts bee health, which can lead to colony death. Despite previ- ous reports on the reduction of DWV diversity following the arrival of the parasitic mite Var- roa destructor, the key DWV vector, we found high genetic diversity of DWV in infested United States honey bee colonies. Phylogenetic analysis showed that divergent US DWV genotypes are of monophyletic origin and were likely generated as a result of diversification after a genetic bottleneck. To investigate the population dynamics of this divergent DWV, we designed a series of novel infectious cDNA clones corresponding to coexisting DWV genotypes, thereby devising a reverse-genetics system for an invertebrate RNA virus qua- sispecies. Equal replication rates were observed for all clone-derived DWV variants in single infections. Surprisingly, individual clones replicated to the same high levels as their mixtures and even the parental highly diverse natural DWV population, suggesting that complemen- tation between genotypes was not required to replicate to high levels. Mixed clone–derived infections showed a lack of strong competitive exclusion, suggesting that the DWV geno- types were adapted to coexist. Mutational and recombination events were observed across clone progeny, providing new insights into the forces that drive and constrain virus diversifi- cation. Accordingly, our results suggest that Varroa influences DWV dynamics by causing an initial selective sweep, which is followed by virus diversification fueled by negative fre- quency-dependent selection for new genotypes. We suggest that this selection might reflect the ability of rare lineages to evade host defenses, specifically antiviral RNA interference (RNAi). In support of this hypothesis, we show that RNAi induced against one DWV strain is less effective against an alternate strain from the same population
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