1,122 research outputs found
Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A comparative study
New classes two-dimensional (2D) materials beyond graphene, including layered
and non-layered, and their heterostructures, are currently attracting
increasing interest due to their promising applications in nanoelectronics,
optoelectronics and clean energy, where thermal transport property is one of
the fundamental physical parameters. In this paper, we systematically
investigated the phonon transport properties of 2D orthorhombic group IV-VI
compounds of , , and by solving the Boltzmann transport
equation (BTE) based on first-principles calculations. Despite the similar
puckered (hinge-like) structure along the armchair direction as phosphorene,
the four monolayer compounds possess diverse anisotropic properties in many
aspects, such as phonon group velocity, Young's modulus and lattice thermal
conductivity (), etc. Especially, the along the zigzag and
armchair directions of monolayer shows the strongest anisotropy while
monolayer and shows an almost isotropy in phonon transport. The
origin of the diverse anisotropy is fully studied and the underlying mechanism
is discussed in detail. With limited size, the could be effectively
lowered, and the anisotropy could be effectively modulated by nanostructuring,
which would extend the applications in nanoscale thermoelectrics and thermal
management. Our study offers fundamental understanding of the anisotropic
phonon transport properties of 2D materials, and would be of significance for
further study, modulation and aplications in emerging technologies.Comment: 14 pages, 8 figures, 2 table
On the measurement of the Hubble constant in a local low-density universe
Astrophysical observations indicate that the ``Local Universe" has a
relatively lower matter density () than the predictions of the
standard inflation cosmology and the large-scale motions of galaxies which
provide a mean mass density to be very close to unity. In such a local
underdense region the Hubble expansion may not be representative of the global
behaviour. Utilizing an underdense sphere embedded in a flat universe as the
model of our ``Local Universe", we show that the local Hubble constant would be
1.2 -- 1.4 times larger than the global value on scale of Mpc,
depending on the variation of . This may account for the recent
measurements of the unpleasantly large Hubble constant of 80 km/s/Mpc
using the Cepheid variables in the Virgo cluster and the relative distance
between Virgo and Coma cluster and removes the resulted apparent paradox of the
age of our universe.Comment: 9 pages, Latex file, 3 figures available by reques
Health status prediction for the elderly based on machine learning
Health and social care services are crucial to old people. The provision of services to the elderly with care needs requires more accurate predictions of the health status of the elderly to rationalize the allocation of the limited social care resources. The traditional analytical methods have proved incapable of predicting the demands of today's society, compared to which machine learning methods can more accurately capture the nonlinear relationships between the variables. To ascertain visually the performance of these machine learning methods regarding the prediction of the elderly's care needs, we designed and verified the experiment
Discrimination, Perceived Social Inequity, and Mental Health Among Rural-to-Urban Migrants in China
Status-based discrimination and inequity have been associated with the process of migration, especially with economics-driven internal migration. However, their association with mental health among economy-driven internal migrants in developing countries is rarely assessed. This study examines discriminatory experiences and perceived social inequity in relation to mental health status among rural-to-urban migrants in China. Cross-sectional data were collected from 1,006 rural-to-urban migrants in 2004-2005 in Beijing, China. Participants reported their perceptions and experiences of being discriminated in daily life in urban destination and perceived social inequity. Mental health was measured using the symptom checklist-90 (SCL-90). Multivariate analyses using general linear model were performed to test the effect of discriminatory experience and perceived social inequity on mental health. Experience of discrimination was positively associated with male gender, being married at least once, poorer health status, shorter duration of migration, and middle range of personal income. Likewise, perceived social inequity was associated with poorer health status, higher education attainment, and lower personal income. Multivariate analyses indicate that both experience of discrimination and perceived social inequity were strongly associated with mental health problems of rural-to-urban migrants. Experience of discrimination in daily life and perceived social inequity have a significant influence on mental health among rural-to-urban migrants. The findings underscore the needs to reduce public or societal discrimination against rural-to-urban migrants, to eliminate structural barriers (i.e., dual household registrations) for migrants to fully benefit from the urban economic development, and to create a positive atmosphere to improve migrant\u27s psychological well-being
DNA methylation-mediated Rbpjk suppression protects against fracture nonunion caused by systemic inflammation
Challenging skeletal repairs are frequently seen in patients experiencing systemic inflammation. To tackle the complexity and heterogeneity of the skeletal repair process, we performed single-cell RNA sequencing and revealed that progenitor cells were one of the major lineages responsive to elevated inflammation and this response adversely affected progenitor differentiation by upregulation of Rbpjk in fracture nonunion. We then validated the interplay between inflammation (via constitutive activation of Ikk2, Ikk2ca) and Rbpjk specifically in progenitors by using genetic animal models. Focusing on epigenetic regulation, we identified Rbpjk as a direct target of Dnmt3b. Mechanistically, inflammation decreased Dnmt3b expression in progenitor cells, consequently leading to Rbpjk upregulation via hypomethylation within its promoter region. We also showed that Dnmt3b loss-of-function mice phenotypically recapitulated the fracture repair defects observed in Ikk2ca-transgenic mice, whereas Dnmt3b-transgenic mice alleviated fracture repair defects induced by Ikk2ca. Moreover, Rbpjk ablation restored fracture repair in both Ikk2ca mice and Dnmt3b loss-of-function mice. Altogether, this work elucidates a common mechanism involving a NF-κB/Dnmt3b/Rbpjk axis within the context of inflamed bone regeneration. Building on this mechanistic insight, we applied local treatment with epigenetically modified progenitor cells in a previously established mouse model of inflammation-mediated fracture nonunion and showed a functional restoration of bone regeneration under inflammatory conditions through an increase in progenitor differentiation potential
SARS-associated Coronavirus Transmitted from Human to Pig
Severe acute respiratory syndrome–associatedcoronavirus (SARS-CoV) was isolated from a pig during a survey for possible routes of viral transmission after a SARS epidemic. Sequence and epidemiology analyses suggested that the pig was infected by a SARS-CoV of human origin
The Collapse of Neutron Stars in High-Mass Binaries as the Energy Source for the Gamma-Ray Bursts
The energy source has remained to be the great mystery in understanding of
the gamma-ray bursts (GRBs) if the events are placed at cosmological distances
as indicated by a number of recent observations. The currently popular models
include (1)the merger of two neutron stars or a neutron star and a black hole
binary and (2)the hypernova scenario of the collapse of a massive member in a
close binary. Since a neutron star will inevitably collapse into a black hole
if its mass exceeds the limit , releasing a total
binding gravitational energy of erg, we explore semi-empirically
the possibility of attributing the energy source of GRB to the accretion-
induced collapse of a neutron star (AICNS) in a massive X-ray binary system
consisting of a neutron star and a type O/B companion. This happens because a
significant mass flow of -- yr may be
transferred onto the neutron star through the Roche-lobe overflow and primarily
during the spiral-in phase when it plunges into the envelope of the companion,
which may eventually lead to the AICNS before the neutron star merges with the
core of the companion. In this scenario, a ``dirty'' fireball with a moderate
amount of beaming is naturally expected because of the nonuniformity of the
stellar matter surrounding the explosion inside the companion, and a small
fraction () of the energy is sufficient to create the observed GRBs.
In addition, the bulk of the ejecting matter of the companion star with a
relatively slow expansion rate may act as the afterglow. Assuming a
non-evolutionary model for galaxies, we estimate that the birthrate of the
AICNS events is about 2 per day within a volume to redshift for an
universe, consistent with the reported GRB rate.Comment: 4 pages, no figures, emulateapj.sty, to appear in ApJ Letters,
several paragraphs added, references added and update
Incremental value of non-invasive myocardial work for the evaluation and prediction of coronary microvascular dysfunction in angina with no obstructive coronary artery disease
BackgroundEvidence suggests that patients suffering from angina with no obstructive coronary artery disease (ANOCA) experience coronary microvascular dysfunction (CMD). We aimed to understand the diagnosis value of noninvasive myocardial work indices (MWIs) with left ventricular pressure-strain loop (LV PSL) by echocardiography in ANOCA patients with CMD.Methods97 patients with ANOCA were recruited. All subjects underwent standard echocardiography with traditional ultrasound parameters, two-dimensional speckle-tracking echocardiography with global longitudinal strain (GLS), LV PSL with MWIs include global work index (GWI), global constructive work (GCW), global waste work (GWW) and global work efficiency (GWE). In addition, all enrolled cases underwent high-dose adenosine stress echocardiography (SE) with coronary flow velocity reserve (CFVR). CMD was defined as CFVR <2.0.ResultsOf the 97 patients with ANOCA, 52 were placed in the CMD group and 45 in the control group. GWI and GCW were decreased significantly in the CMD group compared with the control group (P < 0.001 for both). GWI and GCW were moderately correlated with CFVR (r = 0.430, P < 0.001 and r = 0.538, P < 0.001, respectively). In the multiple logistic regression analyses, GCW was identified as the only independent echocardiography parameter associated with CMD after adjusting for age and baseline APV [OR (95%CI) 1.009 (1.005–1.013); P < 0.001]. Moreover, the best predictor of CMD in patients with ANOCA using receiver operating characteristic (ROC) curve was GWI and GCW, with an area under the curve (AUC) of 0.800 and 0.832, sensitivity of 67.3% and 78.8%, specificity of 80.0% and 75.6%, respectively.ConclusionMWIs with LV PSL is a new method to detect LV systolic function noninvasively in ANOCA patients with CMD
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