60 research outputs found
Size-shrinking of deuterons in very dilute superfluid nuclear matter
It is shown within the strong-coupling BCS approach that, starting from the
zero-density limit of superfluid nuclear matter, with increasing density
deuterons first shrink before they start expanding.Comment: 2 pages, Latex, 1 figure included, submitted to Phys. Rev.
Internal structure of fluctuating Cooper pairs
Abstract.: In order to obtain information about the internal structure of fluctuating Cooper pairs in the pseudogap state and below the transition temperature of high Tc superconductors, we solve the Bethe-Salpeter equation for the two-electron propagator in order to calculate a "pair structure functionâ that depends on the internal distance between the partners and on the center of mass momentum P of the pair. We use an attractive Hubbard model with a local potential for s-wave and a separable potential for d-wave symmetry. The amplitude of gP for small Ï depends on temperature, chemical potential and interaction symmetry, but the Ï dependence itself is rather insensitive to the interaction strength. Asymptotically gP decreases as an inverse power of Ï for weak coupling, but exponentially when a pseudogap develops for stronger interaction. Some possibilities of observing the pair structure experimentally are mentione
The ECAPS Experiment for Solar Cell Characterization in the Stratosphere
The ECAPS project (Experimental Characterization of Advanced Photovoltaics in the Stratosphere) aims at the characterization of performance of a number of different solar cells in the stratospheric environment. ECAPS has been selected to fly as a zero-pressure balloon payload in the frame of the HEMERA H2020 project. Flight is scheduled for August 2022 from CNESâ base in Timmins, Canada.
Testing solar cells in the stratosphere is of great interest for the development of High-Altitude Pseudo Satellite (HAPS) platforms, which will be equipped with high efficiency, flexible solar cells capable to operate at 20-30 km altitude for weeks or months, as well as to perform high-quality calibration of spacecraft solar cells in a near-air mass zero environment. The experiment includes a panel with up to 4 solar cells of different kinds (multi-junction GaAs, CIGS, perovskite, etc.), a dedicated I/V curve recording circuit, temperature and irradiance sensors, and an inertial measurement unit to monitor the instantaneous attitude of the gondola.
During the ascent part of the flight, the I/V characteristic curves of the cells will be continuously recorded so to allow for comparison of performance of the different photovoltaic technologies in identical, real stratospheric flight conditions, as well as to detect performance changes with external temperature, irradiance and altitude. Upon recovery of the experiment, post-flight inspection will also yield useful information on the solar cell compatibility with the high altitude environment
Comparative expression profiling of wild type Drosophila Malpighian tubules and von Hippel-Lindau haploinsufficient mutant
The von-Hippel Lindau (VHL) disease is a hereditary genetic disorder that predisposes to the onset of several highly vascularized benign and malignant tumors, developing with elevate frequency in the central nervous system and kidneys. The most-aggressive VHL tumor is ccRCC, the clear-cell renal cell carcinoma, affecting the kidney. VHL disease etiology can be attributed to the inheritance of a VHL loss-of-function allele, typically a deletion (Gnarra et al., 1994; Herman et al., 1994); this facilitates the somatic inactivation of the other allele (through amorphic mutations or gene silencing through promoter methylation), leading to the onset of the tumorous phenotype (Latif et al., 1993). This reveals the haploinsufficient behavior of the VHL gene.
The high vascularization of VHL tumors can be explained considering that human VHL protein is the substrate-binding subunit of an E3 ubiquitin ligase (Lonergan et al., 1998; Iwai et al., 1999; Kamura et al., 1999) involved in the poly-ubiquitination of HIF-1α transcription factor. This post-translational modification leads HIF-1α to proteosomal degradation (Maxwell et al., 1999). Loss of VHL function causes the stabilization of HIF-1α, triggering cellular response and adaptation to hypoxic conditions (expression of genes involved in glycolysis, angiogenesis and erythropoiesis) (Bader and Hsu, 2012). While this represents the canonical function of VHL, other HIF-1α-independent function of VHL have been identified, thanks to the contribution of model organisms (Hsu, 2012). Indeed, VHL gene function is conserved and also Drosophila has a VHL homolog, the dVHL gene (Adryan et al., 2000; Aso et al., 2000). dVHL is involved in the development of Drosophila vascular system (Adryan et al., 2000; Hsouna et al., 2010) and in morphogenesis of follicular epithelium of the egg chamber (Duchi et al., 2010). Interestingly, some VHL functions are mediated by Awd, an endocytic mediator whose human orthologs are NME1/2 metastasis suppressors (Rosengard et al., 1989). Awd is broadly required during Drosophila development since it is involved in epithelial morphogenesis (Nallamothu et al., 2008; Woolworth et al., 2009; Ignesti et al., 2014) and required for maintaining genomic stability (Romani et al., 2017). Moreover, Awd is also present into the extracellular fluids of Drosophila larvae (Romani et al., 2016, 2018).
In Drosophila, two pairs of monolayered epithelial Malpighian tubules, each composed of 100-150 cells, absolve to osmoregulation and excretion functions (Denholm and Skaer, 2009). Transcriptomic analysis of Malpighian tubules revealed that among genes that are here enriched there are homologs of human genes implicated into renal pathologies (Wang et al., 2004). This justifies the use of Drosophila Malpighian tubules as model system to gain insights into pathophysiology of human kidneys (Dow and Romero, 2010; Miller et al., 2013).
The dVHL1.1 allele is a loss of function mutation of the dVHL locus (Duchi et al., 2010; Hsouna et al., 2010). dVHL1.1/+ flies mimic the genetic condition of VHL patients. We carried out a genome-wide gene expression profiling of whole Malpighian tubules dissected from Drosophila females both heterozygous for the dVHL1.1 mutation and with two wild type copies of the dVHL gene. The comparison of differentially expressed genes in the two genetic backgrounds potentially allows to identify genes that are sensible to dVHL functional copy number. Quality control assessments of the data were performed and results obtained from the differential expression analysis were confirmed by qRT-PCR. With this approach we aimed to provide a well-controlled dataset for a better understanding of the VHL disease. Indeed, even if further molecular and functional characterization are needed, human homologs of the differentially expressed genes, if existing, could have a role in the somatic inactivation of the wild type copy of VHL and/or into the very first phase of cancer onset
Phase ordering induced by defects in chaotic bistable media
The phase ordering dynamics of coupled chaotic bistable maps on lattices with
defects is investigated. The statistical properties of the system are
characterized by means of the average normalized size of spatial domains of
equivalent spin variables that define the phases. It is found that spatial
defects can induce the formation of domains in bistable spatiotemporal systems.
The minimum distance between defects acts as parameter for a transition from a
homogeneous state to a heterogeneous regime where two phases coexist The
critical exponent of this transition also exhibits a transition when the
coupling is increased, indicating the presence of a new class of domain where
both phases coexist forming a chessboard pattern.Comment: 3 pages, 3 figures, Accepted in European Physics Journa
Comment on ``BCS to Bose-Einstein crossover phase diagram at zero temperature for a d_{x^2-y^2} order parameter superconductor: Dependence on the tight-binding structure''
The work by Soares et al. [Phys. Rev. B 65, 174506 (2002)] investigates the
BCS-BE crossover for d-wave pairing in the 2-dimensional attractive Hubbard
model. Contrary to their claims, we found that a non-pairing region does not
exist in the density vs coupling phase diagram. The gap parameter at T=0, as
obtained by solving analytically as well as numerically the BCS equations, is
in fact finite for any non-zero density and coupling, even in the weak-coupling
regime.Comment: 7 pages, 1 figur
Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites
Satellite Communication systems are a promising solution to extend and
complement terrestrial networks in unserved or under-served areas. This aspect
is reflected by recent commercial and standardisation endeavours. In
particular, 3GPP recently initiated a Study Item for New Radio-based, i.e., 5G,
Non-Terrestrial Networks aimed at deploying satellite systems either as a
stand-alone solution or as an integration to terrestrial networks in mobile
broadband and machine-type communication scenarios. However, typical satellite
channel impairments, as large path losses, delays, and Doppler shifts, pose
severe challenges to the realisation of a satellite-based NR network. In this
paper, based on the architecture options currently being discussed in the
standardisation fora, we discuss and assess the impact of the satellite channel
characteristics on the physical and Medium Access Control layers, both in terms
of transmitted waveforms and procedures for enhanced Mobile BroadBand (eMBB)
and NarrowBand-Internet of Things (NB-IoT) applications. The proposed analysis
shows that the main technical challenges are related to the PHY/MAC procedures,
in particular Random Access (RA), Timing Advance (TA), and Hybrid Automatic
Repeat reQuest (HARQ) and, depending on the considered service and
architecture, different solutions are proposed.Comment: Submitted to Transactions on Vehicular Technologies, April 201
Critical Temperature and Energy Gap for the BCS Equation
We derive upper and lower bounds on the critical temperature and the
energy gap (at zero temperature) for the BCS gap equation, describing
spin 1/2 fermions interacting via a local two-body interaction potential
. At weak coupling and under appropriate
assumptions on , our bounds show that and
for some explicit coefficients , and
depending on the interaction and the chemical potential . The ratio
turns out to be a universal constant, independent of both and
. Our analysis is valid for any ; for small , or low density,
our formulas reduce to well-known expressions involving the scattering length
of .Comment: RevTeX4, 23 pages. Revised version, to appear in Phys. Rev.
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