68 research outputs found
A model of the effect of collisions on QCD plasma instabilities
We study the effect of including a BGK collisional kernel on the collective
modes of a QCD plasma which has a hard-particle distribution function which is
anisotropic in momentum space. We calculate dispersion relations for both the
stable and unstable modes and show that the addition of hard particle
collisions slows the rate of growth of QCD plasma unstable modes. We also show
that for any anisotropy there is an upper limit on the collisional frequency
beyond which no instabilities exist. Estimating a realistic value for the
collisional frequency for alpha_s ~ 0.2 - 0.4 we find that for the
large-anisotropy case which is relevant for the initial state of matter
generated by free streaming in heavy-ion collisions that the collisional
frequency is below this critical value.Comment: 15 pages, 12 figure
Low Mass Dilepton Rate from the Deconfined Phase
We discuss low mass dilepton rates ( GeV) from the deconfined phase of
QCD using both perturbative and non-perturbative models and compare with those
from lattice gauge theory and in-medium hadron gas. Our analysis suggests that
the rate at very low invariant mass ( MeV) using the nonperturbative
gluon condensate in a semiempirical way within the Green function dominates
over the Born-rate and independent of any uncertainty associated with the
choice of the strong coupling in perturbation theory. On the other hand the
rate from interaction in the deconfined phase is important between 200
MeV M\ge 200M\ge 500$ MeV, constraining on the broad resonance structures
in the dilepton rate at large invariant mass. We also discuss the lattice
constraints on the low mass dilepton rate. Furthermore, we discuss a more
realistic way to advocate the quark-hadron duality hypothesis based on the
dilepton rates from QGP and hadron gas than it is done in the literature.Comment: 24 pages, 9 figures; Discussion added, Accepted in Phys. Rev.
Nitrogen removal processes in lakes of different trophic states from on-site measurements and historic data
Freshwater lakes are essential hotspots for the removal of excessive anthropogenic nitrogen (N) loads transported from the land to coastal oceans. The biogeochemical processes responsible for N removal, the corresponding transformation rates and overall removal efficiencies differ between lakes, however, it is unclear what the main controlling factors are. Here, we investigated the factors that moderate the rates of N removal under contrasting trophic states in two lakes located in central Switzerland. In the eutrophic Lake Baldegg and the oligotrophic Lake Sarnen, we specifically examined seasonal sediment porewater chemistry, organic matter sedimentation rates, as well as 33-year of historic water column data. We find that the eutrophic Lake Baldegg, which contributed to the removal of 20 ± 6.6 gN m; -2; year; -1; , effectively removed two-thirds of the total areal N load. In stark contrast, the more oligotrophic Lake Sarnen contributed to 3.2 ± 4.2 gN m; -2; year; -1; , and had removed only one-third of the areal N load. The historic dataset of the eutrophic lake revealed a close linkage between annual loads of dissolved N (DN) and removal rates (NRR = 0.63 × DN load) and a significant correlation of the concentration of bottom water nitrate and removal rates. We further show that the seasonal increase in N removal rates of the eutrophic lake correlated significantly with seasonal oxygen fluxes measured across the water-sediment interface (R; 2; = 0.75). We suggest that increasing oxygen enhances sediment mineralization and stimulates nitrification, indirectly enhancing denitrification activity.; The online version contains supplementary material available at 10.1007/s00027-021-00795-7
Managing Things and Services with Semantics: A Survey
This paper presents a survey on the usage, opportunities and pitfalls of semantic technologies in the Internet of Things. The survey was conducted in the context of a semantic enterprise integration platform. In total we surveyed sixty-one individuals from industry and academia on their views and current usage of IoT technologies in general, and semantic technologies in particular. Our semantic enterprise integration platform aims for interoperability at a service level, as well as at a protocol level. Therefore, also questions regarding the use of application layer protocols, network layer protocols and management protocols were integrated into the survey. The survey suggests that there is still a lot of heterogeneity in IoT technologies, but first indications of the use of standardized protocols exist. Semantic technologies are being recognized as of potential use, mainly in the management of things and services. Nonetheless, the participants still see many obstacles which hinder the widespread use of semantic technologies: Firstly, a lack of training as traditional embedded programmers are not well aware of semantic technologies. Secondly, a lack of standardization in ontologies, which would enable interoperability and thirdly, a lack of good tooling support
Multi-chord fiber-coupled interferometry of supersonic plasma jets and comparisons with synthetic data
A multi-chord fiber-coupled interferometer [Merritt et al., Rev. Sci.
Instrum. 83, 033506 (2012)] is being used to make time-resolved density
measurements of supersonic argon plasma jets on the Plasma Liner Experiment
[Hsu et al., Bull. Amer. Phys. Soc. 56, 307 (2011)]. The long coherence length
of the laser (>10 m) allows signal and reference path lengths to be mismatched
by many meters without signal degradation, making for a greatly simplified
optical layout. Measured interferometry phase shifts are consistent with a
partially ionized plasma in which an initially positive phase shift becomes
negative when the ionization fraction drops below a certain threshold. In this
case, both free electrons and bound electrons in ions and neutral atoms
contribute to the index of refraction. This paper illustrates how the
interferometry data, aided by numerical modeling, are used to derive total jet
density, jet propagation velocity (~15-50 km/s), jet length (~20-100 cm), and
3D expansion.Comment: 6 pages, 4 figures, invited paper at the 19th High Temperature Plasma
Diagnostics Conference, Monterey, CA, May 6--10, 201
Physical biomarkers for human hematopoietic stem and progenitor cells
Adhesion of hematopoietic stem and progenitor cells (HSPCs) to the bone marrow niche plays critical roles in the maintenance of the most primitive HSPCs. The interactions of HSPC−niche interactions are clinically relevant in acute myeloid leukemia (AML), because (i) leukemia-initiating cells adhered to the marrow niche are protected from the cytotoxic effect by chemotherapy and (ii) mobilization of HSPCs from healthy donors' bone marrow is crucial for the effective stem cell transplantation. However, although many clinical agents have been developed for the HSPC mobilization, the effects caused by the extrinsic molecular cues were traditionally evaluated based on phenomenological observations. This review highlights the recent interdisciplinary challenges of hematologists, biophysicists and cell biologists towards the design of defined in vitro niche models and the development of physical biomarkers for quantitative indexing of differential effects of clinical agents on human HSPCs
Strange quark matter with effective quark masses
The properties of strange quark matter at zero temperature are investigated
including medium effects. The quarks are considered as quasiparticles which
acquire an effective mass generated by the interaction with the other quarks of
the dense system. Within this approach we find that these medium effects reduce
the binding energy of strange quark matter with respect to .Comment: 6 pages, 2 Postscript figures, to be published in Proc. Int. Workshop
"Hirschegg'97: QCD Phase Transitions
Phenomenological model of multiphoto-production of charged pion pairs on the proton
The production of charged pion pairs via multiphoton absorption from an
intense X-ray laser wave colliding with an ultrarelativistic proton beam is
studied. Our calculations include the contributions from both the
electromagnetic and hadronic interactions where the latter are described
approximately by a phenomenological Yukawa potential. Order-of-magnitude
estimates for production on the proton by two- and three-photon
absorption from the high-frequency laser field are obtained and compared with
the corresponding rates for pair creation.Comment: 6 pages, 3 figure
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