90 research outputs found
Ab-initio calculations of spin tunneling through an indirect barrier
We use a fully relativistic layer Green's functions approach to investigate
spin-dependent tunneling through a symmetric indirect band gap barrier like
GaAs/AlAs/GaAs heterostructure along [100] direction. The method is based on
Linear Muffin Tin Orbitals and it is within the Density Functional Theory (DFT)
in the Local Density Approximation (LDA). We find that the results of our {\it
ab-initio} calculations are in good agreement with the predictions of our
previous empirical tight binding model [Phys. Rev. {\bf B}, 075313 (2006)]. In
addition we show the -dependence of the spin polarization which we did
not previously include in the model. The {\it ab-initio} calculations indicate
a strong -dependence of the transmission and the spin polarization due
to band non-parabolicity. A large window of 25-50 % spin polarization was found
for a barrier of 8 AlAs monolayers at = 0.03 . Our
calculations show clearly that the appearance of energy windows with
significant spin polarization depends mostly on the location of transmission
resonances and their corresponding zeros and not on the magnitude of the spin
splitting in the barrier.Comment: 10 pages, 3 figure
Deep Generative Imputation Model for Missing Not At Random Data
Data analysis usually suffers from the Missing Not At Random (MNAR) problem,
where the cause of the value missing is not fully observed. Compared to the
naive Missing Completely At Random (MCAR) problem, it is more in line with the
realistic scenario whereas more complex and challenging. Existing statistical
methods model the MNAR mechanism by different decomposition of the joint
distribution of the complete data and the missing mask. But we empirically find
that directly incorporating these statistical methods into deep generative
models is sub-optimal. Specifically, it would neglect the confidence of the
reconstructed mask during the MNAR imputation process, which leads to
insufficient information extraction and less-guaranteed imputation quality. In
this paper, we revisit the MNAR problem from a novel perspective that the
complete data and missing mask are two modalities of incomplete data on an
equal footing. Along with this line, we put forward a generative-model-specific
joint probability decomposition method, conjunction model, to represent the
distributions of two modalities in parallel and extract sufficient information
from both complete data and missing mask. Taking a step further, we exploit a
deep generative imputation model, namely GNR, to process the real-world missing
mechanism in the latent space and concurrently impute the incomplete data and
reconstruct the missing mask. The experimental results show that our GNR
surpasses state-of-the-art MNAR baselines with significant margins (averagely
improved from 9.9% to 18.8% in RMSE) and always gives a better mask
reconstruction accuracy which makes the imputation more principle
On -dimensional neither pointed nor semisimple Hopf algebras and the associated weak Hopf algebras
For a class of neither pointed nor semisimple Hopf algebras of
dimension , it is shown that they are quasi-triangular, which universal
-matrices are described. The corresponding weak Hopf algebras
and their representations are constructed. Finally, their
duality and their Green rings are established by generators and relations
explicitly. It turns out that the Green rings of the associated weak Hopf
algebras are not commutative even if the Green rings of are
commutative.Comment: 18 page
Fabrication of three-dimensional microdisk resonators in calcium fluoride by femtosecond laser micromachining
We report on fabrication of on-chip calcium fluoride (CaF2) microdisk
resonators using water-assisted femtosecond laser micromachining. Focused ion
beam (FIB) milling is used to create ultra-smooth sidewalls. The quality
(Q)-factors of the fabricated microresonators are measured to be 4.2x10^4 at
wavelengths near 1550 nm. The Q factor is mainly limited by the scattering from
the bottom surface of the disk whose roughness remains high due to the
femtosecond laser micromachining process. This technique facilitates formation
of on-chip microresonators on various kinds of bulk crystalline materials,
which can benefit a wide range of applications such as nonlinear optics,
quantum optics, and chip-level integration of photonic devices.Comment: 7 pages, 3 figure
No genetic causal association between iron status and osteoporosis: A two-sample Mendelian randomization
ObjectiveTo explore the genetic causal association between osteoporosis (OP) and iron status through Mendelian randomization (MR).MethodsPublicly available genome-wide association study (GWAS) summary data were used for MR analysis with four iron status-related indicators (ferritin, iron, total iron binding capacity, and transferrin saturation) as exposures and three different types of OP (OP, OP with pathological fracture, and postmenopausal OP with pathological fracture) as outcomes. The inverse-variance weighted (IVW) method was used to analyze the genetic causal association between the four indicators of iron status and OP. The heterogeneity of MR results was determined using IVW and MR–Egger methods. The pleiotropy of MR results was determined using MR–Egger regression. A leave-one-SNP-out test was performed to determine whether the MR results were affected by a single nucleotide polymorphism (SNP). The weighted median method was conducted to further validate our results.ResultsBased on IVW, MR–Egger and weighted median models, we found no causal association between iron status (ferritin, iron, total iron binding capacity, or transferrin saturation) and OP (Pbeta > 0.05 in all models). IVW and MR–Egger analysis of OP with pathological fracture and iron status indicators showed no potential genetic causal association (Pbeta> 0.05 in the two analyses). The results of the weighted median were consistent with those of IVW (Pbeta> 0.05 in all analyses). There was no potential genetic causal association between iron status and postmenopausal OP with pathological fracture based on serum iron (Pbeta>0.05 in all models). No heterogeneity or horizontal pleiotropy was found in any of the analyses. None of the leave-one-out tests in the analyses found any SNP that could affect the results of MR.ConclusionOur results demonstrate that there is no genetic causal association between OP and iron status, but the effects of other factors were not excluded
Impact of biogenic SOA loading on the molecular composition of wintertime PM2.5 in urban Tianjin: an insight from Fourier transform ion cyclotron resonance mass spectrometry
Biomass burning is one of the key sources of urban aerosols in the North China Plain, especially in winter when the impact of secondary organic aerosols (SOA) formed from biogenic volatile organic compounds (BVOCs) is generally considered to be minor. However, little is known about the influence of biogenic SOA loading on the molecular composition of wintertime organic aerosols. Here, we investigated the water-soluble organic compounds in fine particles (PM2.5) from urban Tianjin by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Our results show that most of the CHO and CHON compounds were derived from biomass burning; they contain O-poor and highly unsaturated compounds with aromatic rings, which are sensitive to photochemical reactions, and some of which probably contribute to light-absorbing chromophores. Under moderate to high SOA loading conditions, the nocturnal chemistry is more efficient than photooxidation to generate secondary CHO and CHON compounds with high oxygen content. Under low SOA-loading, secondary CHO and CHON compounds with low oxygen content are mainly formed by photochemistry. Secondary CHO compounds are mainly derived from oxidation of monoterpenes. But nocturnal chemistry may be more productive to sesquiterpene-derived CHON compounds. In contrast, the number- and intensity-weight of S-containing groups (CHOS and CHONS) increased significantly with the increase of biogenic SOA-loading, which agrees with the fact that a majority of the S-containing groups are identified as organosulfates and nitrooxy-organosulfates that are derived from the oxidation of BVOCs. Terpenes may be potential major contributors to the chemical diversity of organosulfates and nitrooxy-organosulfates under photo-oxidation. While the nocturnal chemistry is more beneficial to the formation of organosulfates and nitrooxy-organosulfates under low SOA-loading. The SOA-loading is an important factor associating with the oxidation degree, nitrate group content and chemodiversity of nitrooxy-organosulfates. Furthermore, our study suggests that the hydrolysis of nitrooxy-organosulfates is a possible pathway for the formation of organosulfates.</p
Platelet-rich plasma treatment for talar cartilage repair: a systematic review and meta-analysis
Abstract Purpose To systematically review the studies regarding to the safety, efficacy and application methods of PRP in promoting the talar cartilage repair. Methods A systematic review was performed by searching PubMed, Web of Science, OVID and EMBASE to identify studies that compared the clinical efficacy of PRP for talar cartilage repair. Main outcome was the American Orthopedic Foot and Ankle Society (AOFAS) score for function and Visual Analog Scale (VAS) for pain was the second outcome. Results A total of 10 studies were included in this systematic review, including 4 randomized controlled trials, 1 controlled trial, 3 case series and 2 cohort studies. Four RCTs were analyzed using meta-analysis. For all outcomes, statistical results favored PRP group (AOFAS: MD = 7.84; 95% CI= [-0.13, 15.80], I2 = 83%, P < 0.01; VAS: MD = 1.86; 95% CI= [0.68, 3.04], I2 = 85%, P < 0.01). There were almost no reports of adverse events related to PRP intervention. Subgroup analysis showed that whether PRP was used alone or combined with other treatments could result in high heterogeneity but no more specific factors were identified to contribute to this. Conclusion PRP is safe and effective for talar cartilage repair. In addition to the standardization of PRP preparation and application, it is necessary to distinguish the effects of PRP used alone or in combination with other treatments. In PRP studies, surgical treatment of talar cartilage repair remains the mainstream. The regulation of PRP in surgical applications are worth exploring. The most relative component is the mesenchymal stem cell because it is the only exposed chondrocyte precursor in the articular cavity whether it is microfracture or cell transplantation. Trial registration The study was registered in the PROSPERO International prospective register of systematic reviews (CRD42022360183)
Numerical Simulation of Environmental Characteristics of Containment in Severe Accident of Marine Nuclear Power Plant
With the reliance on ocean resources, the nuclear power powers have set their sights on marine nuclear power plants to break through the bottleneck of energy supply for the development of ocean resources. In this paper, the computational fluid dynamics software ANSYS CFX 2021 is used to simulate the TOSQAN benchmark experiment. Three different turbulence models, the k−ε model, RNG k−ε model, and SST model, are selected to analyze the adaptability of the turbulence model. The simulation results are compared with the benchmark experimental results, and the selected numerical calculation model is used to analyze the influence of vapor on the pressure, temperature, hydrogen distribution, and hydrogen risk in the containment space when a hypothetical serious accident occurs in a marine nuclear power plant. The results show that the results simulated with the k−ε turbulence model are closer to the benchmark experimental results. Vapor has no obvious effect on the response speed of pressure balance at each position in the closed containment space, and the condensation of the vapor wall can effectively reduce the pressure peak in the closed containment space. The existence of vapor and the increase in vapor concentration will increase the temperature in the closed containment space. The condensation of vapor on the wall surface will cause the temperature in the containment space to have a peak value, which can effectively reduce the temperature in the containment space. Vapor will promote the mixing of gas in the containment space and make the hydrogen distribution tend to be uniform. The presence of vapor and the increase in vapor concentration can reduce the hydrogen risk in the containment space, but the condensation of vapor may increase the hydrogen risk in the containment space
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