940 research outputs found
Polariton condensation and lasing in optical microcavities - the decoherence driven crossover
We explore the behaviour of a system which consists of a photon mode dipole
coupled to a medium of two-level oscillators in a microcavity in the presence
of decoherence. We consider two types of decoherence processes which are
analogous to magnetic and non-magnetic impurities in superconductors. We study
different phases of this system as the decoherence strength and the excitation
density is changed. For a low decoherence we obtain a polariton condensate with
comparable excitonic and photonic parts at low densities and a BCS-like state
with bigger photon component due to the fermionic phase space filling effect at
high densities. In both cases there is a large gap in the density of states. As
the decoherence is increased the gap is broadened and suppressed, resulting in
a gapless condensate and finally a suppression of the coherence in a low
density regime and a laser at high density limit. A crossover between these
regimes is studied in a self-consistent way analogous to the Abrikosov and
Gor'kov theory of gapless superconductivity.Comment: 17 pages, 8 figures, submitted to PR
Multiple fermion scattering in the weakly coupled spin chain compound YbAlO3
The Heisenberg antiferromagnetic spin 1 2 chain, originally introduced almost a century ago, is one of the best studied models in quantum mechanics due to its exact solution, but nevertheless it continues to present new discoveries. Its low energy physics is described by the Tomonaga Luttinger liquid of spinless fermions, similar to the conduction electrons in one dimensional metals. In this work we investigate the Heisenberg spin chain compound YbAlO3 and show that the weak interchain coupling causes Umklapp scattering between the left and right moving fermions and stabilizes an incommensurate spin density wave order at q amp; 8201; amp; 8201;2kF under finite magnetic fields. These Umklapp processes open a route to multiple coherent scattering of fermions, which results in the formation of satellites at integer multiples of the incommensurate fundamental wavevector Q amp; 8201; amp; 8201;nq. Our work provides surprising and profound insight into bandstructure control for emergent fermions in quantum materials, and shows how neutron diffraction can be applied to investigate the phenomenon of coherent multiple scattering in metals through the proxy of quantum magnetic system
Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays
Average charged multiplicities have been measured separately in , and
light quark () events from decays measured in the SLD experiment.
Impact parameters of charged tracks were used to select enriched samples of
and light quark events, and reconstructed charmed mesons were used to select
quark events. We measured the charged multiplicities:
,
, from
which we derived the differences between the total average charged
multiplicities of or quark events and light quark events: and . We compared
these measurements with those at lower center-of-mass energies and with
perturbative QCD predictions. These combined results are in agreement with the
QCD expectations and disfavor the hypothesis of flavor-independent
fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters
Probing quantum gravity using photons from a flare of the active galactic nucleus Markarian 501 observed by the MAGIC telescope
We analyze the timing of photons observed by the MAGIC telescope during a
flare of the active galactic nucleus Mkn 501 for a possible correlation with
energy, as suggested by some models of quantum gravity (QG), which predict a
vacuum refractive index \simeq 1 + (E/M_{QGn})^n, n = 1,2. Parametrizing the
delay between gamma-rays of different energies as \Delta t =\pm\tau_l E or
\Delta t =\pm\tau_q E^2, we find \tau_l=(0.030\pm0.012) s/GeV at the 2.5-sigma
level, and \tau_q=(3.71\pm2.57)x10^{-6} s/GeV^2, respectively. We use these
results to establish lower limits M_{QG1} > 0.21x10^{18} GeV and M_{QG2} >
0.26x10^{11} GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC
sensitivity to propagation effects at these levels. Thermal plasma effects in
the source are negligible, but we cannot exclude the importance of some other
source effect.Comment: 12 pages, 3 figures, Phys. Lett. B, reflects published versio
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Cell-type-specific 3D epigenomes in the developing human cortex
Lineage-specific epigenomic changes during human corticogenesis have been difficult to study owing to challenges with sample availability and tissue heterogeneity. For example, previous studies using single-cell RNA sequencing identified at least 9 major cell types and up to 26 distinct subtypes in the dorsal cortex alone1,2. Here we characterize cell-type-specific cis-regulatory chromatin interactions, open chromatin peaks, and transcriptomes for radial glia, intermediate progenitor cells, excitatory neurons, and interneurons isolated from mid-gestational samples of the human cortex. We show that chromatin interactions underlie several aspects of gene regulation, with transposable elements and disease-associated variants enriched at distal interacting regions in a cell-type-specific manner. In addition, promoters with increased levels of chromatin interactivity—termed super-interactive promoters—are enriched for lineage-specific genes, suggesting that interactions at these loci contribute to the fine-tuning of transcription. Finally, we develop CRISPRview, a technique that integrates immunostaining, CRISPR interference, RNAscope, and image analysis to validate cell-type-specific cis-regulatory elements in heterogeneous populations of primary cells. Our findings provide insights into cell-type-specific gene expression patterns in the developing human cortex and advance our understanding of gene regulation and lineage specification during this crucial developmental window
Prediction of crop coefficients from fraction of ground cover and height. Background and validation using ground and remote sensing data
ReviewThe current study aims at reviewing and providing advances on methods for estimating and applying crop coefficients
from observations of ground cover and vegetation height. The review first focuses on the relationships between single
Kc and basal Kcb and various parameters including the fraction of ground covered by the canopy (fc), the leaf area index
(LAI), the fraction of ground shaded by the canopy (fshad), the fraction of intercepted light (flight) and intercepted
photosynthetic active radiation (fIPAR). These relationships were first studied in the 1970’s, for annual crops, and later,
in the last decennia, for tree and vine perennials. Research has now provided a variety of methods to observe and
measure fc and height (h) using both ground and remote sensing tools, which has favored the further development of Kc
related functions. In the past, these relationships were not used predictively but to support the understanding of
dynamics of Kc and Kcb in relation to the processes of evapotranspiration or transpiration, inclusive of the role of soil
evaporation. Later, the approach proposed by Allen and Pereira (2009), the A&P approach, used fc and height (h) or LAI
data to define a crop density coefficient that was used to directly estimate Kc and Kcb values for a variety of annual and
perennial crops in both research and practice. It is opportune to review the A&P method in the context of a variety of
studies that have derived Kc and Kcb values from field measured data with simultaneously observed ground cover fc and
height. Applications used to test the approach include various tree and vine crops (olive, pear, and lemon orchards and
vineyards), vegetable crops (pea, onion and tomato crops), field crops (barley, wheat, maize, sunflower, canola, cotton
and soybean crops), as well as a grassland and a Bermudagrass pasture. Comparisons of Kcb values computed with the A
&P method produced regression coefficients close to 1.0 and coefficients of determination≥0.90, except for orchards.
Results indicate that the A&P approach can produce estimates of potential Kcb, using vegetation characteristics alone,
within reasonable or acceptable error, and are useful for refining Kcb for conditions of plant spacing, size and density
that differ from standard values. The comparisons provide parameters appropriate to applications for the tested crops.
In addition, the A&P approach was applied with remotely sensed fc data for a variety of crops in California using the
Satellite Irrigation Management Support (SIMS) framework. Daily SIMS crop ET (ETc-SIMS) produced Kcb values using
the FAO56 and A&P approaches. Combination of satellite derived fc and Kcb values with ETo data from Spatial CIMIS
(California Irrigation Management Information System) produced ET estimates that were compared with daily actual
crop ET derived from energy balance calculations from micrometeorological instrumentation (ETc EB).Results produced
coefficients of regression of 1.05 for field crops and 1.08 for woody crops, and R2 values of 0.81 and 0.91, respectively.
These values suggest that daily ETc-SIMS -based ET can be accurately estimated within reasonable error and that the A&P
approach is appropriate to support that estimation. It is likely that accuracy can be improved via progress in remote
sensing determination of fc. Tabulated Kcb results and calculation parameters are presented in a companion paper in this
Special Issueinfo:eu-repo/semantics/publishedVersio
Nucleosomes in gene regulation: theoretical approaches
This work reviews current theoretical approaches of biophysics and
bioinformatics for the description of nucleosome arrangements in chromatin and
transcription factor binding to nucleosomal organized DNA. The role of
nucleosomes in gene regulation is discussed from molecular-mechanistic and
biological point of view. In addition to classical problems of this field,
actual questions of epigenetic regulation are discussed. The authors selected
for discussion what seem to be the most interesting concepts and hypotheses.
Mathematical approaches are described in a simplified language to attract
attention to the most important directions of this field
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