1,551 research outputs found
Nematic Fermi Fluids in Condensed Matter Physics
Correlated electron fluids can exhibit a startling array of complex phases,
among which one of the more surprising is the electron nematic, a
translationally invariant metallic phase with a spontaneously generated spatial
anisotropy. Classical nematics generally occur in liquids of rod-like
molecules; given that electrons are point-like, the initial theoretical
motivation for contemplating electron nematics came from thinking of the
electron fluid as a quantum melted electron crystal, rather than a strongly
interacting descendent of a Fermi gas. That such phases exist in nature was
established by dramatic transport experiments in ultra-clean quantum Hall
systems in 1999 and in Sr3Ru2O7 in a strong magnetic field in 2007.
In this paper, we briefly review the theoretical considerations governing
nematic order, summarize the quantum Hall and Sr3Ru2O7 experiments that
unambiguously establish the existence of this phase, and survey some of the
current evidence for such a phase in the cuprate and Fe-based high temperature
superconductors.Comment: 30 pages, 7 figures (some in color); to appear in Annual Reviews of
Condensed Matter Physics. Edited version
Entropy-based Guidance of Deep Neural Networks for Accelerated Convergence and Improved Performance
Neural networks have dramatically increased our capacity to learn from large,
high-dimensional datasets across innumerable disciplines. However, their
decisions are not easily interpretable, their computational costs are high, and
building and training them are uncertain processes. To add structure to these
efforts, we derive new mathematical results to efficiently measure the changes
in entropy as fully-connected and convolutional neural networks process data,
and introduce entropy-based loss terms. Experiments in image compression and
image classification on benchmark datasets demonstrate these losses guide
neural networks to learn rich latent data representations in fewer dimensions,
converge in fewer training epochs, and achieve better test metrics.Comment: 13 pages, 4 figure
Optical Absorption by Indirect Excitons in a Transition Metal Dichalcogenide Double Layer
We calculate the binding energy, transition energies, oscillator strength,
and absorption coefficient of indirect excitons in transition metal
dichalcogenide (TMDC) double layers separated by an integer number of hexagonal
boron nitride (h-BN) monolayers. The absorption factor, a dimensionless
quantity which gives the fraction of incoming photons absorbed by the indirect
excitons in the double layer, is evaluated. The aforementioned optical
quantities are obtained for transitions from the ground state to the first two
excited states. All quantities are studied as a function of the interlayer
separation, which may be experimentally controlled by varying the number of
h-BN monolayers between the TMDC layers. Calculations are performed by using
the exciton wave function and eigenenergies obtained for the Keldysh potential.
For each material, we choose a combination of the exciton reduced mass and the
dielectric screening length from the existing literature which give the largest
and the smallest indirect exciton binding energy. These combinations of
material parameters provide upper and lower bounds on all quantities presented.
Our findings can be examined experimentally via two-photon spectroscopy.Comment: 13 pages, 3 figure
How does iron interact with sporopollenin exine capsules? An X-ray absorption study including microfocus XANES and XRF imaging
Sporopollenin exine capsules (SECs) derived from plant spores and pollen grains have been proposed as adsorption, remediation and drug delivery agents. Despite many studies there is scant structural data available. This X-ray absorption investigation represents the first direct structural data on the interaction of metals with SECs and allows elucidation of their structure–property relationships. Fe K-edge XANES and EXAFS data have shown that the iron local environment in SECs (derived from Lycopodium clavatum) reacted with aqueous ferric chloride solutions is similar to that of ferrihydrite (FeOOH) and by implication ferritin. Fe Kα XRF micro-focus experiments show that there is a poor correlation between the iron distribution and the underlying SEC structure indicating that the SEC is coated in the FeOOH material. In contrast, the Fe Kα XRF micro-focus experiments on SECs reacted with aqueous ferrous chloride solutions show that there is a very high correlation between the iron distribution and the SEC structure, indicating a much more specific form of interaction of the iron with the SEC surface functional groups. Fe K-edge XANES and EXAFS data show that the FeII can be easily oxidised to give a structure similar to, but not identical to that in the FeIII case, and that even if anaerobic conditions are used there is still partial oxidation to FeIII
The spatial pattern of atrial cardiomyocyte calcium signalling modulates contraction
We examined the regulation of calcium signalling in atrial cardiomyocytes during excitation-contraction coupling, and how changes in the distribution of calcium impacts on contractility. Under control conditions, calcium transients originated in subsarcolemmal locations and showed local regeneration through activation of calcium-induced calcium release from ryanodine receptors. Despite functional ryanodine receptors being expressed at regular (~2 μm) intervals throughout atrial myocytes, the subsarcolemmal calcium signal did not spread in a fully regenerative manner through the interior of a cell. Rather, there was a diminishing centripetal propagation of calcium. The lack of regeneration was due to mitochondria and SERCA pumps preventing the inward movement of calcium. Inhibiting these calcium buffering mechanisms allowed the globalisation of action potential-evoked responses. In addition, physiological positive inotropic agents, such as endothelin-1 and β-adrenergic agonists, as well as enhanced calcium current, calcium store loading and inositol 1,4,5-trisphosphate infusion also led to regenerative global responses. The consequence of globalising calcium signals was a significant increase in cellular contraction. These data indicate how calcium signals and their consequences are determined by the interplay of multiple subcellular calcium management systems
The risk of miscarriage following COVID-19 vaccination: a systematic review and meta-analysis
STUDY QUESTION: What is the risk of miscarriage among pregnant women who received any of the COVID-19 vaccines? SUMMARY ANSWER: There is no evidence that COVID-19 vaccines are associated with an increased risk of miscarriage. WHAT IS KNOWN ALREADY: In response to the COVID-19 pandemic, the mass roll-out of vaccines helped to boost herd immunity and reduced hospital admissions, morbidity and mortality. Still, many were concerned about the safety of vaccinesfor pregnancy, which may have limited their uptake among pregnant women and those planning a pregnancy. STUDY DESIGN, SIZE, DURATION: For this systematic review and meta-analysis, we searched MEDLINE, EMBASE and Cochrane CENTRAL from inception until June 2022 using a combination of keywords and MeSH terms. PARTICIPANTS/MATERIALS, SETTING, METHODS: We included observational and interventional studies that enrolled pregnant women and evaluated any of the available COVID-19 vaccines compared to placebo or no vaccination. We primarily reported on miscarriage in addition to ongoing pregnancy and/or live birth. MAIN RESULTS AND THE ROLE OF CHANCE: We included data from 21 studies (5 randomised trials and 16 observational studies) reporting on 149,685 women. The pooled rate of miscarriage among women who received a COVID-19 vaccine was 9% (n = 147,49/123,185, 95%CI 0.05-0.14). Compared to those who received a placebo or no vaccination, women who received a COVID-19 vaccine did not have a higher risk of miscarriage (RR 1.07, 95%CI 0.89-1.28, I2 35.8%) and had comparable rates for ongoing pregnancy or live birth (RR 1.00, 95%CI 0.97-1.03, I2 10.72%). LIMITATIONS, REASONS FOR CAUTION: Our analysis was limited to observational evidence with varied reporting, high heterogeneity and risk of bias across included studies, which may limit the generalisability and confidence in our findings. WIDER IMPLICATIONS OF THE FINDINGS: COVID-19 vaccines are not associated with an increase in the risk of miscarriage or reduced rates of ongoing pregnancy or live birth among women of reproductive age. The current evidence remains limited and larger population studies are needed to further evaluate the effectiveness and safety of COVID-19 in pregnancy. STUDY FUNDING/COMPETING INTEREST: No direct funding was provided to support this work. MPR is funded by the Medical Research Council Centre for Reproductive Heath Grant No: MR/N022556/1. BHA hold a personal development award from the National Institute of Health Research in the UK. All authors declare no conflict of interest. REGISTRATION NUMBER: CRD42021289098
Influence of anticipated and actual grades on studying
This study explores two questions regarding differences between students’ anticipated and actual grades in university courses: what factors contribute to those differences arising, and which of those differences influence students’ subsequent studying? The research surveyed 278 students in a first-year undergraduate business course. Students with stronger academic abilities tended to have smaller (less negative) gaps between their grades and goals, while students with higher personal control scores tended to have wider (more negative) gaps. These gaps narrowed later in the course as students’ goals decreased to match their actual grades more closely. Students increased their studying if their actual grades were lower than their original goals, and/or lower than their updated goals. By contrast, the difference between students’ subjective grade goals and their objectively forecast final grades did not influence their studying intentions.Brock University Chancellor's Chair for Teaching Excellence, 2012-201
The Push and Pull of Nostalgia: Sentimental Longing in a Fundamental Component of the Behavior Change Process
Abstract: Behavior change is hard, and the recovery process is equally as challenging. Yet a paucity of research has been conducted on factors that motivated and undermine sustained behavior change. In this talk, we will discuss a growing body of work that suggests nostalgic reverie (i.e., sentimental longing) is a critical factor in both the behavior change and recovery process among people living with a gambling disorder. First, we will report the results of research (Study 1) that demonstrates nostalgic reverie for life before one’s problematic gambling behaviour facilitates behaviour change. We will then report the results of new research (three studies) that demonstrates the potential dark side of nostalgia among people in recovery from a gambling disorder (as well as those living with an eating disorder). Specifically, we show that among people in recovery from an eating disorder (Study 2) and disordered gambling (Study 3) who are nostalgic for the perceived benefits of their disorder (e.g., the excitement of winning) felt they were less (subjective) advanced in their recovery process. Among those living with a gambling disorder, we also showed that optimism about their recovery process interacted with nostalgia to create ambivalence about their recovery.
Implications: This program of research suggests there are both basic and applied implications of nostalgic reverie (and its content) that both researchers and treatment providers need to take into consideration when trying to understand and facilitate sustained behavior change
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