7,730 research outputs found
Quantum phase transitions of atom-molecule Bose mixtures in a double-well potential
The ground state and spectral properties of Bose gases in double-well
potentials are studied in two different scenarios: i) an interacting atomic
Bose gas, and ii) a mixture of an atomic gas interacting with diatomic
molecules. A ground state second-order quantum phase transition (QPT) is
observed in both scenarios. For large attractive values of the atom-atom
interaction, the ground-state is degenerate. For repulsive and small attractive
interaction, the ground-state is not degenerate and is well approximated by a
boson coherent state. Both systems depict an excited state quantum phase
transition (ESQPT). For the mixed atom-molecule system the critical point of
the ESQPT displays a discontinuity in the first derivative of the density of
states.Comment: 25 pages, 18 figures. RevTex 4.1 (version to appear in Phys. Rev. E
Aerostack2: A Software Framework for Developing Multi-robot Aerial Systems
In recent years, the robotics community has witnessed the development of
several software stacks for ground and articulated robots, such as Navigation2
and MoveIt. However, the same level of collaboration and standardization is yet
to be achieved in the field of aerial robotics, where each research group has
developed their own frameworks. This work presents Aerostack2, a framework for
the development of autonomous aerial robotics systems that aims to address the
lack of standardization and fragmentation of efforts in the field. Built on ROS
2 middleware and featuring an efficient modular software architecture and
multi-robot orientation, Aerostack2 is a versatile and platform-independent
environment that covers a wide range of robot capabilities for autonomous
operation. Its major contributions include providing a logical level for
specifying missions, reusing components and sub-systems for aerial robotics,
and enabling the development of complete control architectures. All major
contributions have been tested in simulation and real flights with multiple
heterogeneous swarms. Aerostack2 is open source and community oriented,
democratizing the access to its technology by autonomous drone systems
developers
Adding feasibility constraints to a ranking rule under a monotonicity constraint
We propose a new point of view in the long-standing problem where several voters have expressed a linear order relation (or ranking) over a set of candidates. For a ranking a > b > c to represent a group's opinion, it would be logical that the strength with which a > c is supported should not be less than the strength with which either a > b or b > c is supported. This intuitive property can be considered a monotonicity constraint, and has been addressed before. We extend previous approaches in the following way: as the voters are expressing linear orders, we can take the number of candidates between two candidates to be a measure of the degree to which one candidate is preferred to the other. In this way, intensity of support is both counted as the number of voters who indicate a > c is true, as well as the distance between a and c in these voters' rankings. The resulting distributions serve as input for a natural ranking rule that is based on stochastic monotonicity and stochastic dominance. Adapting the previous methodology turns out to be non-trivial once we add some natural feasibility constraints
Colorless devices and reception techniques for polarization multiplexed communications
Future optical networks call for flexible, high performance and low cost coherent optical receivers. We present here several advances towards such receivers, including integrated optical couplers with ultra-broad bandwidth,
as well as novel reception techniques and architectures that will enable high performance coherent reception without filtering and polarization splitting elements.Universidad de Málaga - Campus de Excelencia Internacional Andalucía Tech. Spanish Ministry of Science under project TEC2013-46917-C2-1-
The physics potential of a reactor neutrino experiment with Skipper CCDs: Measuring the weak mixing angle
We analyze in detail the physics potential of an experiment like the one
recently proposed by the vIOLETA collaboration: a kilogram-scale Skipper CCD
detector deployed 12 meters away from a commercial nuclear reactor core. This
experiment would be able to detect coherent elastic neutrino nucleus scattering
from reactor neutrinos, capitalizing on the exceptionally low ionization energy
threshold of Skipper CCDs. To estimate the physics reach, we elect the
measurement of the weak mixing angle as a case study. We choose a realistic
benchmark experimental setup and perform variations on this benchmark to
understand the role of quenching factor and its systematic
uncertainties,background rate and spectral shape, total exposure, and reactor
antineutrino flux uncertainty. We take full advantage of the reactor flux
measurement of the Daya Bay collaboration to perform a data driven analysis
which is, up to a certain extent, independent of the theoretical uncertainties
on the reactor antineutrino flux. We show that, under reasonable assumptions,
this experimental setup may provide a competitive measurement of the weak
mixing angle at few MeV scale with neutrino-nucleus scattering.Comment: 11 pages, 6 figure
Agreement and clinical comparison between a new swept-source optical coherence tomography-based optical biometer and an optical low-coherence reflectometry biometer
Purpose
To compare measurements taken using a swept-source optical coherence tomography-based optical biometer (IOLmaster 700) and an optical low-coherence reflectometry biometer (Lenstar 900), and to determine the clinical impacts of differences in their measurements on intraocular lens (IOL) power predictions.
Methods
Eighty eyes of 80 patients scheduled to undergo cataract surgery were examined with both biometers. The measurements made using each device were axial length (AL), central corneal thickness (CCT), aqueous depth (AQD), lens thickness (LT), mean keratometry (MK), white-to-white distance (WTW), and pupil diameter (PD). Holladay 2 and SRK/T formulas were used to calculate IOL power. Differences in measurement between the two biometers were determined using the paired t-test. Agreement was assessed through intraclass correlation coefficients (ICC) and Bland–Altman plots.
Results
Mean patient age was 76.3±6.8 years (range 59–89). Using the Lenstar, AL and PD could not be measured in 12.5 and 5.25% of eyes, respectively, while IOLMaster 700 took all measurements in all eyes. The variables CCT, AQD, LT, and MK varied significantly between the two biometers. According to ICCs, correlation between measurements made with both devices was excellent except for WTW and PD. Using the SRK/T formula, IOL power prediction based on the data from the two devices were statistically different, but differences were not clinically significant.
Conclusions
No clinically relevant differences were detected between the biometers in terms of their measurements and IOL power predictions. Using the IOLMaster 700, it was easier to obtain biometric measurements in eyes with less transparent ocular media or longer AL
Lipoic acid inhibits leptin secretion and Sp1 activity in adipocytes
Lipoic acid (LA) is an antioxidant with therapeutic potential on several diseases such as diabetes and obesity. Hyperleptinemia and oxidative stress play a major role in the development of obesity-linked diseases. The aim of this study was to examine in vivo and in vitro the effects of LA on leptin production, as well as to elucidate the mechanisms and signalling pathways involved in LA actions. Methods and results: Dietary supplementation with LA decreased both circulating leptin, and adipose tissue leptin mRNA in rats. Treatment of 3T3-L1 adipocytes with LA caused a concentration-dependent inhibition of leptin secretion and gene expression. Moreover, LA stimulated the anaerobic utilization of glucose to lactate, which negatively correlated with leptin secretion. Furthermore, LA enhanced phosphorylation of Sp1 and inhibited Sp1 transcriptional activity in 3T3-L1 adipocytes. Moreover, LA inhibited Akt phosphorylation, a downstream target of phosphatidylinositol 3-kinase (PI3K). Treatment with the PI3K inhibitor LY294002 mimicked LA actions, dramatically inhibiting both leptin secretion and gene expression and stimulating Sp1 phosphorylation. Conclusion: All of these data suggest that the phosphorylation of Sp1 and the accompanying reduced DNA-binding activity are likely to be involved in the inhibition of leptin induced by LA, which could be mediated in part by the abrogation of the PI3K/Akt pathway
Polarization independent 2×2 multimode interference coupler with bricked subwavelength metamaterial
The silicon-on-insulator (SOI) platform enables high integration density in photonic integrated circuits while maintaining compatibility with CMOS fabrication processes. Nevertheless, its inherently high modal birefringence hinders the development of polarization-insensitive devices. The dispersion and anisotropy engineering leveraging subwavelength grating (SWG) metamaterials makes possible the development of polarization agnostic waveguide components. In this work we build upon the bricked SWG metamaterial nanostructures to design a polarization independent 2×2 multimode interference (MMI) coupler for the 220 nm SOI platform, operating in the telecom O-band. The designed device exhibits a 160 nm bandwidth with excess loss, polarization dependent loss and imbalance below 1 dB and phase error lower than 5°.Ministerio de Economía y Competitividad (PID2019-106747RB-I00), Junta de Andalucía (P18-RT-1453, UMA20-FEDERJA-158), Ministerio de Ciencia Innovación y Universidades (FPU16/06762, FPU19/02408) and Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech
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