431 research outputs found
On-the-fly machine learning for parametrization of the effective Hamiltonian
The first-principles-based effective Hamiltonian is widely used to predict
and simulate the properties of ferroelectrics and relaxor ferroelectrics.
However, the parametrization method of the effective Hamiltonian is complicated
and hardly can resolve the systems with complex interactions and/or complex
components. Here, we developed an on-the-fly machine learning approach to
parametrize the effective Hamiltonian based on Bayesian linear regression. The
parametrization is completed in molecular dynamics simulations, with the
energy, forces and stress predicted at each step along with their
uncertainties. First-principles calculations are executed when the
uncertainties are large to retrain the parameters. This approach provides a
universal and automatic way to compute the effective Hamiltonian parameters for
any considered systems including complex systems which previous methods can not
handle. BaTiO3 and Pb(Sc,Ta)O3 are taken as examples to show the accurateness
of this approach comparing with conventional first-principles parametrization
method.Comment: 11 pages, 2 figure
Experimental demonstrations of high-Q superconducting coplanar waveguide resonators
We designed and successfully fabricated an absorption-type of superconducting
coplanar waveguide (CPW) resonators. The resonators are made from a Niobium
film (about 160 nm thick) on a high-resistance Si substrate, and each resonator
is fabricated as a meandered quarter-wavelength transmission line (one end
shorts to the ground and another end is capacitively coupled to a through
feedline). With a vector network analyzer we measured the transmissions of the
applied microwave through the resonators at ultra-low temperature (e.g., at 20
mK), and found that their loaded quality factors are significantly high, i.e.,
up to 10^6. With the temperature increases slowly from the base temperature
(i.e., 20 mK), we observed the resonance frequencies of the resonators are blue
shifted and the quality factors are lowered slightly. In principle, this type
of CPW-device can integrate a series of resonators with a common feedline,
making it a promising candidate of either the data bus for coupling the distant
solid-state qubits or the sensitive detector of single photons.Comment: Accepted by Chinese Science Bulleti
Spectrum of malignancies among the population of adults living with HIV infection in China: A nationwide follow-up study, 2008-2011.
BackgroundAlthough increasingly studied in high-income countries, there is a paucity of data from the Chinese population on the patterns of cancer among people living with HIV (PLHIV).MethodsWe conducted a nationwide follow-up study using routinely collected data for adult PLHIV diagnosed on or before 31 December 2011 and alive and in care as of 1 January 2008. Participants were observed from 1 January 2008 (study start) to 30 June 2012 (study end). Main outcome measures were gender-stratified age-standardized incidence rates for China (ASIRC) and standardized incidence ratios (SIR) for all malignancy types/sites observed.ResultsAmong 399,451 subjects, a majority was aged 30-44 years (49.3%), male (69.8%), and Han Chinese (67.9%). A total of 3,819 reports of cancer were identified. Overall, ASIRC was 776.4 per 100,000 for males and 486.5 per 100,000 for females. Malignancy sites/types with highest ASIRC among males were lung (226.0 per 100,000), liver (145.7 per 100,000), and lymphoma (63.1 per 100,000), and among females were lung (66.8 per 100,000), lymphoma (48.0 per 100,000), stomach (47.8 per 100,000), and cervix (47.6 per 100,000). Overall SIR for males was 3.4 and for females was 2.6. Highest SIR was observed for Kaposi sarcoma (2,639.8 for males, 1,593.5 for females) and lymphoma (13.9 for males, 16.0 for females).ConclusionsThese results provide evidence of substantial AIDS-defining and non-AIDS-defining cancer burden among adult Chinese PLHIV between 2008 and 2011. Although further study is warranted, China should take action to improve cancer screening, diagnosis, and treatment for this vulnerable population
Toxicological responses in alfalfa (Medicago sativa) under joint stress of cadmium and napropamide
Joint effects of Cd2+ and napropamide in seeds, roots or leaves of alfalfa were investigated under different treatments. It was shown that single stress of Cd2+ or napropamide decreased chlorophyll content after 30 days of treatment in different concentrations. The decrease in chlorophyll content became insignificant under joint stress of Cd2+ and napropamide. It can be concluded that the interaction of Cd2+ and napropamide would aggravate the toxic effects on chlorophyll synthesis in leaves of alfalfa. The joint effect of Cd2+ and napropamide was markedly significant (p < 0.05) on the change of SP content in leaves in all treatment. Moreover, Cd2+ and napropamide mixture exposure can increase lignin content and present synergistic effect. In a mixture treated with Cd2+ and napropamide, 52% decrease in β-carotene content contrasted with the control in young leaves. The contents of protein thiols and non-protein thiols in the roots of alfalfa were significantly increased by Cd2+ treatment in all treatment levels. In contrast, increasing napropamide supply did not have any significant effect on the protein thiols and non-protein thiols content. The Cd2+ induced accumulation of O2•- in seeds could be increased by treatment with different Cd2+ concentration. Production of H2O2 and O2•- was also higher in the napropamide treatments than in the control. The addition of napropamide significantly increased the H2O2 and O2•- level in the seeds of alfalfa.Key words: Alfalfa, joint stress, cadmium, napropamide
Negative electrocaloric effect in nonpolar phases of perovskite over wide range of temperature
The electrocaloric effect (ECE) offers a promising alternative to the
traditional gas compressing refrigeration due to its high efficiency and
environmental friendliness. The unusual negative electrocaloric effect refers
to the adiabatic temperature drops due to application of electric field, in
contrast with the normal (positive) ECE, and provides ways to improve the
electrocaloric efficiency in refrigeration cycles. However, negative ECE is
unusual and requires a clear understanding of microscopic mechanisms. Here, we
found unexpected and extensive negative ECE in nonpolar orthorhombic,
tetragonal, and cubic phases of halide and oxide perovskite at wide range of
temperature by means of first-principle-based large scale Monte Carlo methods.
Such unexpected negative ECE originates from the octahedral tilting related
entropy change rather than the polarization entropy change under the
application of electric field. Furthermore, a giant negative ECE with
temperature change of 8.6 K is found at room temperature. This giant and
extensive negative ECE in perovskite opens up new horizon in the research of
caloric effects and broadens the electrocaloric refrigeration ways with high
efficiency.Comment: 11 pages, 7 figure
Validation of internal control for gene expression study in soybean by quantitative real-time PCR
<p>Abstract</p> <p>Background</p> <p>Normalizing to housekeeping gene (HKG) can make results from quantitative real-time PCR (qRT-PCR) more reliable. Recent studies have shown that no single HKG is universal for all experiments. Thus, a suitable HKG should be selected before its use. Only a few studies on HKGs have been done in plants, and none in soybean, an economically important crop. Therefore, the present study was conducted to identify suitable HKG(s) for normalization of gene expression in soybean.</p> <p>Results</p> <p>All ten HKGs displayed a wide range of Ct values in 21 sample pools, confirming that they were variably expressed. GeNorm was used to determine the expression stability of the HGKs in seven series sets. For all the sample pools analyzed, the stability rank was <it>ELF1B</it>, <it>CYP2 </it>> <it>ACT11 </it>> <it>TUA </it>> <it>ELF1A </it>> <it>UBC2 </it>> <it>ACT2/7 </it>> <it>TUB </it>> <it>G6PD </it>> <it>UBQ10</it>. For different tissues under the same developmental stage, the rank was <it>ELF1B</it>, <it>CYP2 </it>> <it>ACT2/7 </it>> <it>UBC2 </it>> <it>TUA </it>> <it>ELF1A </it>> <it>ACT11 </it>> <it>TUB </it>> <it>G6PD </it>> <it>UBQ10</it>. For the developmental stage series, the stability rank was <it>ACT2/7</it>, <it>TUA </it>> <it>ELF1A </it>> <it>UBC2 </it>> <it>ELF1B </it>> <it>TUB </it>> <it>CYP2 </it>> <it>ACT11 </it>> <it>G6PD </it>> <it>UBQ10</it>. For photoperiodic treatments, the rank was <it>ACT11</it>, <it>ELF1B </it>> <it>CYP2 </it>> <it>TUA </it>> <it>ELF1A </it>> <it>UBC2 </it>> <it>ACT2/7 </it>> <it>TUB </it>> <it>G6PD </it>> <it>UBQ10</it>. For different times of the day, the rank was <it>ELF1A</it>, <it>TUA </it>> <it>ELF1B </it>> <it>G6PD </it>> <it>CYP2 </it>> <it>ACT11 </it>> <it>ACT2/7 </it>> <it>TUB </it>> <it>UBC2 </it>> <it>UBQ10</it>. For different cultivars and leaves on different nodes of the main stem, the ten HKGs' stability did not differ significantly. ΔCt approach and 'Stability index' were also used to analyze the expression stability in all 21 sample pools. Results from ΔCt approach and geNorm indicated that <it>ELF1B </it>and <it>CYP2 </it>were the most stable HKGs, and <it>UBQ10 </it>and <it>G6PD </it>the most variable ones. Results from 'Stability index' analysis were different, with <it>ACT11 </it>and <it>CYP2 </it>being the most stable HKGs, and <it>ELF1A </it>and <it>TUA </it>the most variable ones.</p> <p>Conclusion</p> <p>Our data suggests that HKGs are expressed variably in soybean. Based on the results from geNorm and ΔCt analysis, <it>ELF1B </it>and <it>CYP2 </it>could be used as internal controls to normalize gene expression in soybean, while <it>UBQ10 </it>and <it>G6PD </it>should be avoided. To achieve accurate results, some conditions may require more than one HKG to be used for normalization.</p
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Overrepresentation of Injection Drug Use Route of Infection Among Human Immunodeficiency Virus Long-term Nonprogressors: A Nationwide, Retrospective Cohort Study in China, 1989-2016.
BackgroundWhy some persons living with human immunodeficiency virus (HIV) (PLWH) progress quickly and others remain "healthy" for a decade or more without treatment remains a fundamental question of HIV pathology. We aimed to assess the epidemiological characteristics of HIV long-term nonprogressors (LTNPs) based on a cohort of PLWH in China observed between 1989 and 2016.MethodsWe conducted a nationwide, retrospective cohort study among Chinese PLWH with HIV diagnosed before 1 January 2008. Records were extracted from China's national HIV/AIDS database on 30 June 2016. LTNPs were defined as those with AIDS-free, antiretroviral therapy-naive survival, with CD4 cell counts consistently ≥500/μL for ≥8 years after diagnosis. Prevalence was calculated, characteristics were described, and determinants were assessed by means of logistic regression. Potential sources of bias were also investigated.ResultsOur cohort included 89 201 participants, of whom 1749 (2.0%) were categorized as LTNPs. The injection drug use (IDU) route of infection was reported by 70.7% of LTNPs, compared with only 37.1% of non-LTNPs. The odds of LTNP status were greater among those infected via IDU (adjusted odds ratio [95% confidence interval], 2.28 [1.94-2.68]) and with HIV diagnosed in settings with large populations of persons who inject drugs (1.75 [1.51-2.02] for detention centers, 1.61 [1.39-1.87] for Yunnan, 1.94 [1.62-2.31] for Guangdong, and 2.90 [2.09-4.02] for Xinjiang).ConclusionsOverrepresentation of the IDU route of infection among LTNPs is a surprising finding worthy of further study, and this newly defined cohort may be particularly well suited to exploration of the molecular biological mechanisms underlying HIV long-term nonprogression
Influence of EOM sideband modulation noise on space-borne gravitational wave detection
Clock noise is one of the dominant noises in the space-borne gravitational
wave (GW) detection. To suppress this noise, the clock noise-calibrated
time-delay-interferometry (TDI) technique is proposed. In this technique, an
inter-spacecraft clock tone transfer chain is necessary to obtain the
comparison information of the clock noises in two spacecraft, during which an
electro-optic-modulator (EOM) is critical and used to modulate the clock noise
to the laser phase. Since the EOM sideband modulation process introduces
modulation noise, it is significant to put forward the corresponding
requirements and assess whether the commercial EOM meets. In this work, based
on the typical Michelson TDI algorithm and the fundamental noise requirement of
GW detectors, the analytic expression of the modulation noise requirement is
strictly derived, which relax the component indicator need compared to the
existing commonly used rough assessments. Furthermore, a commercial EOM
(iXblue-NIR-10 GHz) is tested, and the experimental results show that it can
meet the requirement of the typical GW detection mission LISA in whole
scientific bandwidth by taking the optimal combination of the data stream. Even
when the displacement measurement accuracy of LISA is improved to 1 pm/
in the future, it still meets the demand
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