2,236 research outputs found
Dispersion relation of the collective excitations in a resonantly driven polariton fluid
Exciton-polaritons in semiconductor microcavities constitute the archetypal
realization of a quantum fluid of light. Under coherent optical drive,
remarkable effects such as superfluidity, dark solitons or the nucleation of
hydrodynamic vortices have been observed. These phenomena can be all understood
as a specific manifestation of collective excitations forming on top of the
polariton condensate. In this work, we performed a Brillouin scattering
experiment to measure their dispersion relation directly.
The result, such as a speed of sound which is apparently twice too low, cannot
be explained upon considering the polariton condensate alone. In a combined
theoretical and experimental analysis, we demonstrate that the presence of a
reservoir of long-lived excitons interacting with polaritons has a dramatic
influence on the nature and characteristic of the quantum fluid, and that it
explains our measurement quantitatively. This work clarifies the role of such a
reservoir in the different polariton hydrodynamics phenomena occurring under
resonant optical drive. It also provides an unambiguous tool to determine the
condensate-to-reservoir fraction in the quantum fluid, and sets an accurate
framework to approach novel ideas for polariton-based quantum-optical
applications
The role of epidermal growth factor-like module containing mucin-like hormone receptor 2 in human cancers.
G-protein coupled receptors (GPCRs) are among the most diverse and ubiquitous proteins in all of biology. The epidermal growth factor-seven span transmembrane (EGF-TM7) subfamily of adhesion GPCRs is a small subset whose members are mainly expressed on the surface of leukocytes. The EGF domains on the N-terminus add significant size to these receptors and they are considered to be among the largest members of the TM7 family. Although not all of their ligands or downstream targets have been identified, there is evidence implicating the EGF-TM7 family diverse processes such as cell adhesion, migration, inflammation, and autoimmune disease. Recent studies have identified expression of EGF-TM7 family members on human neoplasms including those of the thyroid, stomach, colon, and brain. Their presence on these tissues is not surprising given the ubiquity of GPCRs, but because their functional significance and pathways are not completely understood, they are of tremendous clinical and scientific interest. Current evidence suggests that expression of certain EGF-TM7 receptors is correlated with tumor grade, confers a more invasive phenotype, and increases the likelihood of metastatic disease. In this review, we will discuss the structure, function, and regulation of these receptors. We also describe the expression of these receptors in human cancers and explore their potential mechanistic significance
Immunocompetent murine models for the study of glioblastoma immunotherapy.
Glioblastoma remains a lethal diagnosis with a 5-year survival rate of less than 10%. (NEJM 352:987-96, 2005) Although immunotherapy-based approaches are capable of inducing detectable immune responses against tumor-specific antigens, improvements in clinical outcomes are modest, in no small part due to tumor-induced immunosuppressive mechanisms that promote immune escape and immuno-resistance. Immunotherapeutic strategies aimed at bolstering the immune response while neutralizing immunosuppression will play a critical role in improving treatment outcomes for glioblastoma patients. In vivo murine models of glioma provide an invaluable resource to achieving that end, and their use is an essential part of the preclinical workup for novel therapeutics that need to be tested in animal models prior to testing experimental therapies in patients. In this article, we review five contemporary immunocompetent mouse models, GL261 (C57BL/6), GL26 (C57BL/6) CT-2A (C57BL/6), SMA-560 (VM/Dk), and 4C8 (B6D2F1), each of which offer a suitable platform for testing novel immunotherapeutic approaches
A prospective cohort study about the effect of repeated living high and working higher on cerebral autoregulation in unacclimatized lowlanders
Cerebral autoregulation (CA) is impaired during acute high-altitude (HA) exposure, however, effects of temporarily living high and working higher on CA require further investigation. In 18 healthy lowlanders (11 women), we hypothesized that the cerebral autoregulation index (ARI) assessed by the percentage change in middle cerebral artery peak blood velocity (Δ%MCAv)/percentage change in mean arterial blood pressure (Δ%MAP) induced by a sit-to-stand maneuver, is (i) reduced on Day1 at 5050 m compared to 520 m, (ii) is improved after 6 days at 5050 m, and (iii) is less impaired during re-exposure to 5050 m after 7 days at 520 m compared to Cycle1. Participants spent 4-8 h/day at 5050 m and slept at 2900 m similar to real-life working shifts. High/low ARI indicate impaired/intact CA, respectively. With the sit-to-stand at 520 m, mean (95% CI) in ΔMAP and ΔMCAv were − 26% (− 41 to − 10) and − 13% (− 19 to − 7), P < 0.001 both comparisons; mean ± SD in ARI was 0.58 ± 2.44Δ%/Δ%, respectively. On Day1 at 5050 m, ARI worsened compared to 520 m (3.29 ± 2.42Δ%/Δ%), P = 0.006 but improved with acclimatization (1.44 ± 2.43Δ%/Δ%, P = 0.039). ARI was less affected during re-exposure to 5050 m (1.22 ± 2.52Δ%/Δ%, P = 0.027 altitude-induced change between sojourns). This study showed that CA (i) is impaired during acute HA exposure, (ii) improves with living high, working higher and (iii) is ameliorated during re-exposure to HA
Quantum Phase Transition in a Resonant Level Coupled to Interacting Leads
An interacting one-dimensional electron system, the Luttinger liquid, is
distinct from the "conventional" Fermi liquids formed by interacting electrons
in two and three dimensions. Some of its most spectacular properties are
revealed in the process of electron tunneling: as a function of the applied
bias or temperature the tunneling current demonstrates a non-trivial power-law
suppression. Here, we create a system which emulates tunneling in a Luttinger
liquid, by controlling the interaction of the tunneling electron with its
environment. We further replace a single tunneling barrier with a
double-barrier resonant level structure and investigate resonant tunneling
between Luttinger liquids. For the first time, we observe perfect transparency
of the resonant level embedded in the interacting environment, while the width
of the resonance tends to zero. We argue that this unique behavior results from
many-body physics of interacting electrons and signals the presence of a
quantum phase transition (QPT). In our samples many parameters, including the
interaction strength, can be precisely controlled; thus, we have created an
attractive model system for studying quantum critical phenomena in general. Our
work therefore has broadly reaching implications for understanding QPTs in more
complex systems, such as cold atoms and strongly correlated bulk materials.Comment: 11 pages total (main text + supplementary
Measurement of Rashba and Dresselhaus spin-orbit magnetic fields
Spin-orbit coupling is a manifestation of special relativity. In the
reference frame of a moving electron, electric fields transform into magnetic
fields, which interact with the electron spin and lift the degeneracy of
spin-up and spin-down states. In solid-state systems, the resulting spin-orbit
fields are referred to as Dresselhaus or Rashba fields, depending on whether
the electric fields originate from bulk or structure inversion asymmetry,
respectively. Yet, it remains a challenge to determine the absolute value of
both contributions in a single sample. Here we show that both fields can be
measured by optically monitoring the angular dependence of the electrons' spin
precession on their direction of movement with respect to the crystal lattice.
Furthermore, we demonstrate spin resonance induced by the spin-orbit fields. We
apply our method to GaAs/InGaAs quantum-well electrons, but it can be used
universally to characterise spin-orbit interactions in semiconductors,
facilitating the design of spintronic devices
Tropical metacommunities along elevational gradients: effects of forest type and other environmental factors.
Elevational gradients provide a natural experiment for assessing the extent to which the structure of animal metacommunities is molded by biotic and abiotic characteristics that change gradually, or is molded by aspects of plant community composition and physiognomy that change in a more discrete fashion. We used a metacommunity framework to integrate species-specific responses to environmental gradients as an approach to detect emergent patterns at the mesoscale in the Luquillo Mountains of Puerto Rico. Elements of metacommunity structure (coherence, species turnover and range boundary clumping) formed the basis for distinguishing among random, checkerboard, Gleasonian, Clementsian, evenly spaced and nested patterns. Paired elevational transects (300-1000 m a.s.l.) were sampled at 50 m intervals to decouple underlying environmental mechanisms: a mixed forest transect reflected changes in abiotic and biotic conditions, including forest type (i.e. tabonuco, palo colorado and elfin forests), whereas another transect reflected changes in environmental conditions but not forest type, as its constituent plots were located within palm forest. Based on distributional data (presence versus absence of species), the mixed forest transect exhibited Clementsian structure, whereas the palm forest transect exhibited quasi-Gleasonian structure. In contrast, the distribution of modes in species abundance was random with respect to the latent environmental gradient in the mixed forest transect and clumped with respect to the latent environmental gradient in the palm forest transect. Such contrasts suggest that the environmental factors affecting abundance differed in form or type from those affecting distributional boundaries. Variation among elevational strata with respect to the first axis of correspondence from reciprocal averaging was highly correlated with elevation along each transect, even though axis scores were not correlated between mixed forest and palm forest transects. This suggests that the identity of the environmental characteristics, or the form of response by the fauna to those characteristics, differed between the two elevational transects. Despite the proximity of the transects, the patchy configuration of palm forest, and the pervasive distribution of the dominant palm species, the relative importance of abiotic variables and habitat in structuring gastropod metacommunities differed between transects, which is remarkable and attests to the sensitivity of metacommunity structure to environmental variation
Tropical metacommunities along elevational gradients: effects of forest type and other environmental factors.
Elevational gradients provide a natural experiment for assessing the extent to which the structure of animal metacommunities is molded by biotic and abiotic characteristics that change gradually, or is molded by aspects of plant community composition and physiognomy that change in a more discrete fashion. We used a metacommunity framework to integrate species-specifi c responses to environmental gradients as an approach to detect emergent patterns at the mesoscale in the Luquillo Mountains of Puerto Rico. Elements of metacommunity structure (coherence, species turnover and range boundary clumping) formed the basis for distinguishing among random, checkerboard, Gleasonian, Clementsian, evenly spaced and nested patterns. Paired elevational transects (300 -1000 m a.s.l.) were sampled at 50 m intervals to decouple underlying environmental mechanisms: a mixed forest transect refl ected changes in abiotic and biotic conditions, including forest type (i.e. tabonuco, palo colorado and elfi n forests), whereas another transect refl ected changes in environmental conditions but not forest type, as its constituent plots were located within palm forest. Based on distributional data (presence versus absence of species), the mixed forest transect exhibited Clementsian structure, whereas the palm forest transect exhibited quasi-Gleasonian structure. In contrast, the distribution of modes in species abundance was random with respect to the latent environmental gradient in the mixed forest transect and clumped with respect to the latent environmental gradient in the palm forest transect. Such contrasts suggest that the environmental factors aff ecting abundance diff ered in form or type from those aff ecting distributional boundaries. Variation among elevational strata with respect to the fi rst axis of correspondence from reciprocal averaging was highly correlated with elevation along each transect, even though axis scores were not correlated between mixed forest and palm forest transects. Th is suggests that the identity of the environmental characteristics, or the form of response by the fauna to those characteristics, diff ered between the two elevational transects. Despite the proximity of the transects, the patchy confi guration of palm forest, and the pervasive distribution of the dominant palm species, the relative importance of abiotic variables and habitat in structuring gastropod metacommunities diff ered between transects, which is remarkable and attests to the sensitivity of metacommunity structure to environmental variation
The genomes of two key bumblebee species with primitive eusocial organization
Background: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. Results: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. Conclusions: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation
Search for CP Violation in the Decay Z -> b (b bar) g
About three million hadronic decays of the Z collected by ALEPH in the years
1991-1994 are used to search for anomalous CP violation beyond the Standard
Model in the decay Z -> b \bar{b} g. The study is performed by analyzing
angular correlations between the two quarks and the gluon in three-jet events
and by measuring the differential two-jet rate. No signal of CP violation is
found. For the combinations of anomalous CP violating couplings, and , limits of \hat{h}_b < 0.59h^{\ast}_{b} < 3.02$ are given at 95\% CL.Comment: 8 pages, 1 postscript figure, uses here.sty, epsfig.st
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