Ultrafast Electron Correlations and Memory Effects at Work: Femtosecond Demagnetization in Ni.

Experimental observations of the ultrafast (less than 50 fs) demagnetization of Ni have so far defied theoretical explanations particularly since its spin-flipping time is much less than that resulting from spin-orbit and electron-lattice interactions. Through the application of an approach that benefits from spin-flip time-dependent density-functional theory and dynamical mean-field theory, we show that proper inclusion of electron correlations and memory (time dependence of electron-electron interaction) effects leads to demagnetization at the femtosecond scale, in good agreement with experimental observations. Furthermore, our calculations reveal that this ultrafast demagnetization results mainly from spin-flip transitions from occupied to unoccupied orbitals implying a dynamical reduction of exchange splitting. These conclusions are found to be valid for a wide range of laser pulse amplitudes. They also pave the way for ab initio investigations of ultrafast charge and spin dynamics in a variety of quantum materials in which electron correlations may play a definitive role.

[Seroepidemiological survey and influencing factors of hepatitis E virus infection among key occupational population in Tianjin].

Objective: To evaluate the infection rate and influencing factors of hepatitis E virus (HEV) among key occupational population in Tianjin, so as to help occupational population to carry out HEV prevention and control. Methods: A combination of stratified random sampling and convenience sampling was carried out for the study in Tianjin in June 2019. The livestock and poultry-related farming workers, slaughtering workers, selling workers, doctors, farmers, seafood sellers, sewage pipeline workers as the key occupational population groups (1036 person) , and non key occupational population as the control group (200 person) , cross-sectional surveys were conducted in the groups. Enzyme-linked immunosorbent assay (ELISA) was used to detect the serum IgG and IgM antibodies to HEV, and logistic regression model was used to analyze the influencing factors of HEV infection. Results: The positive rate of anti-HEV IgG in key occupational group was 26.45% (274/1036) , which was higher than that in control group of 14.50% (29/200) (χ(2)=13.41, P<0.01) . The occupations with the highest positive rate of anti-HEV IgG were livestock (swine) , breeding and slaughtering workers, all of which reached 33.96% (18/53) . The difference in infection rates between different occupations was statistically significant (χ(2)=22.57, P<0.01) . Multivariate logistic regression analysis showed that the longer working years, high frequency of eating out (3-5, ≥6 times/week) , drinking raw water, eating under-cooked pork or pig liver, and low frequency of washing hands were risk factors for HEV infection in occupational population (P<0.05) . But the high education is a protective factor for HEV infection (P<0.05) . Conclusion: There is a high positive rate of anti-HEV IgG in key occupational population in Tianjin. It is necessary to strengthen the monitoring, publicity and education of the high-risk population, pay attention to personal and dietary hygiene.

Association of tumor necrosis factor-α gene polymorphism with osteoarticular tuberculosis prognosis in a Hebei population.

This study investigated the association of tumor necrosis factor-α (TNF-α)-308, -238, and -863 polymorphisms with osteoarticular tuberculosis (OA-TB) prognosis in a Hebei population. Genomic DNA was extracted from venous blood samples of 120 OA-TB patients and 100 healthy volunteers. TNF-α-308, -238, and -863 were analyzed by PCR-restriction fragment length polymorphism; genotype and allele frequencies were calculated. Serum TNF-α level was significantly higher in OA-TB patients (283.16 ± 51.68 ng/L) than in control (122.54 ± 54.65 ng/L; P < 0.05). Higher frequency of TNF-α-308 GG genotype in healthy volunteers (91.0%) than in OA-TB patients (79.2%) indicated that it was a protective factor against OA-TB (OR = 0.405, 95%CI = 0.147-0.657, P = 0.007). Higher frequencies of TNF-α-308 GA genotype and TNF-α-308 allele (A) in OA-TB patients (20.8 and 10.4%, respectively) than in healthy volunteers (8.0 and 5.0%, respectively) indicated an association with increased risk of OA-TB (OR = 3.112, 95%CI = 1.520-6.343, P = 0.003; OR = 3.109, 95%CI = 1.676-6.538, P = 0.006; respectively). Haplotype association analysis of TNF-α polymorphisms (-308/-238/-863) showed a higher frequency of TNF-α AGA in OA-TB patients (12.1%) than in healthy volunteers (3.5%), indicating that it was a risk factor for OA-TB (OR = 4.201, 95%CI = 1.80-9.91, P = 0.010). TNF-α-308 G/A and TNF-α AGA (-308/-238/-863) were associated with a predisposition to OA-TB, which could aid clinical detection, prevention, and prognosis of OA-TB.

Intrinsic ferromagnetism in hexagonal boron nitride nanosheets.

Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstrate such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.

Analysis of the linear epitope for Fc-binding on the mouse IgG Fc receptor (moFcγRI) by synthetic peptide.

To identify the linear epitope for Fc-binding to the mouse immunoglobulin G (IgG) Fc receptor (moFcγRI), peptides derived from the membrane-distal extracellular domain (EC2) of moFcγRI, corresponding to the homologous region of human FcγRI (huFcγRI) and huFcγRII, were synthesized. Using a dot-blot assay, six peptides were tested. The results showed that the moRI3 peptide (CVFYRNGKSFQFS) could combine with mouse IgG efficiently. A competitive enzyme-linked immunosorbent assay (ELISA) showed that the IC50 value of the moRI3 peptide was 38.03 mM. The moRI3 peptide could inhibit the combination of mouse IgG to the transfected COS 7 cells significantly with an IC50 value of 72.68 mM. The IgG-binding region of moFcγRI was also localized in the C'-E loop of the EC2 domain as predicted according to huFcγRI and huFcγRII. We predicted that the minimum effective IgG-binding region of moFcγRI may be the peptide 153SFQFSS158. The linear epitope for immunoglobulin-binding to mouse FcγR is also described. Thus, we generated a peptide that targets a fundamental aspect of ligand recognition by this receptor class.

All-optical spin switching on an ultrafast time scale.

Information technology revolution demands bigger and faster magnetic storage. All-optical spin switching (AOS) may offer a solution, where an ultrafast laser pulse alone can switch magnetization from one direction to another faithfully within 1-10 ps, free of a magnetic field. There are two types of switching: One is the helicity-dependent all-optical spin switching (HD-AOS) and the other the helicity-independent all-optical spin switching (HID-AOS). In a few alloys, one single laser pulse, with sufficient fluence, can switch spin, but the majority of magnetic materials requires multiple pulses. Both material-specific and laser-specific properties strongly affect the switching process. However, the underlying mechanism is still under debate. As the entire research field moves toward applications, it is very appropriate to review what has been achieved in the last decade. This review covers some of the major experimental and theoretical developments within the last decade, and serves as an introduction to the uninitiated reader in this field and a summary for the seasoned researchers.

Shear stress-driven refreshing capability of plastic deformation in nanolayered metals.

Severely localized deformation within shear bands can occur much more easily in a metal with nanoscale microstructures, such as nanograined and nanolayered materials. Based on atomic-scale observations, here we show that such locally large deformation (the continuous thinning of the layers) within the indentation-induced shear bands of the Cu/Au nanolayers is essentially attributed to the large shear stress component along the interface, which can refresh the capability of the interface to absorb incoming dislocations through unlocking the product of the dislocation-interface reaction. The results have implications for understanding the interface-mediated mechanisms of plastic deformation and for the engineering application of severe plastic deformation processing of metals at nanoscales.

Strong ultrafast demagnetization due to the intraband transitions.

Demagnetization in ferromagnetic transition metals driven by a femtosecond laser pulse is a fundamental problem in solid state physics, and its understanding is essential to the development of spintronic devices.Ab initiocalculation of time-dependent magnetic moment in the velocity gauge so far has not been successful in reproducing the large amount of demagnetization observed in experiments. In this work, we propose a method to incorporate intraband transitions within the velocity gauge through a convective derivative in the crystal momentum space. Our results for transition-element bulk crystals (bcc Fe, hcp Co and fcc Ni) based on the time-dependent quantum Liouville equation show a dramatic enhancement in the amount of demagnetization after the inclusion of an intraband term, in agreement with experiments. We also find that the effect of intraband transitions on each ferromagnetic material is distinctly different because of their band structure and spin property differences. Our finding has a far-reaching impact on understanding of ultrafast demagnetization.

New approaches in the diagnosis and prognosis of gestational diabetes mellitus.

Gestational diabetes mellitus (GDM) is the most common pregnancy metabolic disorder in which a person with no history of hyperglycemia exhibits any degree of impaired glucose tolerance during gestation. GDM can be resolved on its own after birth, but mothers with GDM are more at risk for future problems, such as type 2 diabetes, obesity, and cardiovascular disease. In addition, GDM can cause macrosomia in infants and obesity or even the risk of diabetes in childhood. Standard diagnostic tests for GDM are the oral glucose tolerance test (OGTT) and glucose challenge test (GCT), which is a mandatory test at 28-28 weeks of pregnancy in most countries. Disorders in various molecular mechanisms, such as hepatocyte growth factor (HGF), mechanistic target of rapamycin (mTOR), and nuclear factor-kappaB (NF-κB) signaling pathways are involved in GDM. Therefore, a better understanding of these mechanisms can help find new therapeutic and diagnostic strategies accordingly. In this review, we first deal with molecular mechanisms involved in GDM occurrence and then summarized the studies that hired this knowledge for early diagnosis and prognosis of GDM. Finally, we present the latest achievements in the diagnosis of GDM based on exosomes, microRNAs, glycosylated hemoglobin, and inflammatory factors detection in maternal circulation.

Proposed coherent trapping of a population of electrons in a C60 molecule induced by laser excitation.

This Letter demonstrates the possibility of generating coherent population trapping in C(60). Similar to a three-level Λ system, C(60) has a forbidden transition between the highest occupied molecular orbital (HOMO) (|a}) and the lowest unoccupied molecular orbital (LUMO) (|c}), but a dipole-allowed transition between HOMO and LUMO+1 (|b}) and between |b} and |c}. We employ two cw laser fields, one coupling and one probe. The strong coupling field is switched on first to resonantly excite the transition between |b} and |c}. After a delay, the probe is switched on; the coherent interaction between the coupling and probe fields traps the population in |a} and |c}. This forms a partially dark state in C(60), analogous to that in atomic vapors. Turning off the coupling field restores C(60)'s absorption. Pulsed lasers work as well. We use two pulses to steer the system into a dark state; when we send in a cw probe field, the electric polarization of C(60) plunges by five times, in comparison with the noncontrol case. This should be detectable experimentally.

Magnetic ordering and structural phase transitions in a strained ultrathin SrRuO3/SrTiO3 superlattice.

Ruthenium-based perovskite systems are attractive because their structural, electronic, and magnetic properties can be systematically engineered. The SrRuO3/SrTiO3 superlattice, with its period consisting of one unit cell each, is very sensitive to strain change. Our first-principles simulations reveal that, in the high tensile strain region, it transits from a ferromagnetic metal to an antiferromagnetic insulator with clear tilted octahedra, while in the low strain region, it is a ferromagnetic metal without octahedra tilting. Detailed analyses of three spin-down Ru-t(2g) orbitals just below the Fermi level reveal that the splitting of these orbitals underlies these dramatic phase transitions, with the rotational force constant of RuO(6) octahedron high up to 16 meV/Deg(2), 4 times larger than that of TiO(6). Differently from nearly all the previous studies, these transitions can be probed optically through the diagonal and off-diagonal dielectric tensor elements. For a 1% change in strain, our experimental spin moment change is -0.14±0.06 µ(B), quantitatively consistent with our theoretical value of -0.1 µ(B).

Spin-phonon dispersion in magnetic materials.

Microscopic coupling between the electron spin and the lattice vibration is responsible for an array of exotic properties from morphic effects in simple non magnets to magnetodielectric coupling in multiferroic spinels and hematites. Traditionally, a single spin-phonon coupling constant is used to characterize how effectively the lattice can affect the spin, but it is hardly enough to capture novel electromagnetic behaviors to the full extent. Here, we introduce a concept of spin-phonon dispersion to project the spin moment change along the phonon crystal momentum direction, so the entire spin change can be mapped out. Different from the phonon dispersion, the spin-phonon dispersion has both positive and negative frequency branches even in the equilibrium ground state, which correspond to the spin enhancement and spin reduction, respectively. Our study of bcc Fe and hcp Co reveals that the spin force matrix, that is, the second-order spatial derivative of spin moment, is similar to the vibrational force matrix, but its diagonal elements are smaller than the off-diagonal ones. This leads to the distinctive spin-phonon dispersion. The concept of spin-phonon dispersion expands the traditional Elliott-Yafet theory in nonmagnetic materials to the entire Brillouin zone in magnetic materials, thus opening the door to excited states in systems such as CoF2and NiO, where a strong spin-lattice coupling is detected in the THz regime.

[Transmission characteristics and risk factors of household COVID-19 clusters caused by 2019-nCoV Omicron variant in Tianjin].

Objective: To understand the transmission characteristics and risk factors of household COVID-19 clusters caused by 2019-nCoV Omicron variant in Tianjin and provide evidence for COVID-19 prevention and control. Methods: Field epidemiological method was used to investigate the epidemiological characteristics of COVID-19 cases, and descriptive analysis was used to describe the epidemiological information. Results: A total of 430 cases were reported in this epidemic in Tianjin, in which 409 cases were included in this study. Among these cases, 70.90% (290/409) occurred in families. The family secondary attack rate was 33.64% The family secondary attack rate in age group 12-17 years (13.79%) was significantly lower than that in age group 18-49 years (36.48%), the OR was 0.378 (95%CI: 0.170-0.840). The logistic regression analysis showed that compared with centralized quarantine, the OR of the index cases found in closed-off/controlled areas and in home quarantine were 2.951 (95%CI:1.322-6.586) and 2.287 (95%CI:1.164-4.495), respectively, compared with the cases without sore throat, the OR of the index cases with sore throat was 3.003 (95%CI: 1.576-5.720), and compared with cases in families without completed COVID-19 vaccinations in all members, the OR of the cases in families with completed COVID-19 vaccinations in all members was 0.268 (95%CI: 0.132-0.552). Conclusions: The risk of household transmission of infection with Omicron variant was high. Detecting the index case in closed-off/controlled areas or in home quarantine and sore throat in index cases were the risk factors of the household transmission, completed COVID-19 vaccination was the protective factor.

Rapid screening of monoclonal antibodies against porcine circovirus type 2 using colloidal gold-based paper test.

A proof of concept for using paper test as a suitable method in the production of monoclonal antibodies (MAbs) is reported. The paper test which detects antibodies against porcine circovirus type 2 (PCV2) using colloidal gold-labelled capsid protein as the antigen probe was applied exclusively in the screening of anti-PCV2 MAbs. It allowed the detection of 118 single cell clones within 30 min using naked eyes. MAbs with specific binding to authentic epitopes on the virus were selected using a blocking strategy in which the antibody was pre-incubated with PCV2 viral sample before applying to the test paper. Five hybridomas secreting MAbs against the capsid protein were obtained, with only three of them capable of binding to PCV2. The results were validated and confirmed using enzyme-linked immunosorbent assay and immunofluorescence assay. The paper test is simple, rapid, and independent on professional technicians and proves to be an excellent approach for the screening of MAbs against specific targets.

Electronic structure and transport of a carbon chain between graphene nanoribbon leads.

The electronic structure and transport property of a carbon chain between two graphene nanoribbon leads are studied using an ab initio tight-binding (TB) model and Landauer's formalism combined with a non-equilibrium Green's function. The TB Hamiltonian and overlap matrices are extracted from first-principles density functional calculations through the quasi-atomic minimal basis orbital scheme. The accuracy of the TB model is demonstrated by comparing the electronic structure from the TB model with that from first-principles density functional theory. The results of electronic transport on a carbon atomic chain connected to armchair and zigzag graphene ribbon leads, such as different transport characters near the Fermi level and at most one quantized conductance, reveal the effect of the electronic structure of the leads and the scattering from the atomic chain. In addition, bond length alternation and an interesting transmission resonance are observed in the atomic chain connected to zigzag graphene ribbon leads. Our approach provides a promising route to quantitative investigation of both the electronic structure and transport property of large systems.

Change of psychotropic drug prescription for schizophrenia in a psychiatric institution in Beijing, China between 1999 and 2008.

BACKGROUND: To date, no study has investigated how prescription patterns change over time in Chinese patients with schizophrenia. This study aimed to determine psychotropic drug prescription patterns and the use of electroconvulsive therapy (ECT) for schizophrenia and their changes over time in a large psychiatric institution in Beijing, China. METHODS: The case notes of inpatients with schizophrenia were scrutinized to identify psychotropic drug prescription patterns and the use of ECT on November 10, 1999 and the same calendar day in 2008 and to compare the two surveys. RESULTS: In 1999, 45.1% of inpatients with schizophrenia were on first-generation antipsychotic drugs (FGA), while 52.9% were on second-generation antipsychotic drugs (SGA). In 2008, the percentage of patients on FGAs decreased to 15.1%, while those on SGAs increased to 77.2%. The proportion of schizophrenia patients on mood stabilizers and antidepressants rose from 3.3% and 4.3% in 1999 to 18% and 9.5% by 2008, respectively. Use of ECT grew from 0.5% in 1999 to 5.6% by 2008. The proportion of schizophrenia patients not prescribed antipsychotic drugs changed from 5.6% in 1999 to 13.7% in 2008. CONCLUSIONS: The prescription pattern of psychotropic drugs changes considerably over time, even in the same clinical setting. Mental health professionals need to keep up with changes in the prescription patterns of psychotropic drugs in order to serve their patients at the best possible level. The socio-economic reasons for not prescribing antipsychotic drugs to schizophrenia patients should be further explored.

Identification and characterization of Japanese encephalitis virus envelope protein gene from swine.

AIMS: Identification and characterization of Japanese encephalitis virus (JEV) envelope protein gene from swine. METHODS AND RESULTS: Genomic RNA was separated from JEV isolated strain Henan-09-03, and used as templates for cDNA synthesis of E gene. The cDNA of E gene was amplified by RT-PCR and cloned into the pMD19-T-Vector and confirmed by sequencing. The cloned gene was then subcloned into the pET-32a and was introduced into Escherichia coli BL21 (DE3) for expression. The E protein was purified by Ni chelating column-based affinity chromatography. The molecular weight of expressed protein was about 50 kDa. Compared with the published sequence of SA14 (AF495589), the homology of the nucleotide sequence was 98% and the seven mutations resulting in amino acid substitutions at Leu 36 Ser, Leu107 Val, Ala167 Thr, Asn 230 Ser, Leu 340 Pro, Asn 430 Ile, Phe 448 Leu. Phylogenetic analysis of the E sequence of isolated strain classified it within genotype III of the JEV. The result of Western blotting indicated that the antigenicity of the protein was specific. CONCLUSIONS: The stable expression of the protein and the analysis of its antigenic specificity provide the foundation for developing the ELISA early stage diagnosis kit. SIGNIFICANCE AND IMPACT OF THE STUDY: As coating antigen, the recombinant E protein served a good source in the indirect ELISA method for the detection of JEV antibody.

Modulating the electronic and optical properties for SrTiO3/LaAlO3 bilayers treated as the 2D materials by biaxial strains.

The emerging two-dimensional (2D) materials such as graphene have opened the door to industrial applications. Here, we consider the oxide perovskite monolayer of SrTiO3 (STO), LaAlO3 (LAO) and their heterostructures as the 2D transitional metal system. Results show that a band-gap transition from indirect to direct occurs when the separated monolayer STO (indirect band gap of 3.210 eV), and LAO (indirect band gap of 4.024 eV), form the heterostructures (direct band gap of 2.976 eV). The obtained bandgap for the stable bilayers may effectively be modulated by biaxial strains from -12% to 8%. With 12% compressive biaxial strain, the band gap reduces to be 0.23 eV. The optical properties for the stable bilayers are also tuned by the biaxial strain. When the strain increases from compressive strain to tensile strain, the strongest peak of the imaginary part of dielectric function red shifts to lower energy. In comparing with the monolayer STO and LAO, the elastic property enhances obviously for the stable heterostructure, suggesting the heterostructure can be more stable freestanding or may be applied in device fabrications.

[Investigation and analysis on characteristics of a cluster of COVID-19 associated with exposure in a department store in Tianjin].

Objective: To describe the epidemiological characteristics of a cluster of COVID-19 cases reported in Baodi district of Tianjin as of 18 February, 2020, which might be associated with the exposure in a local department store, and provide suggestions for prevention and control strategy development. Methods: The basic characteristics, time and area distributions, clinical manifestations, epidemiological history and transmission mode of the COVID-19 cases associated with the department store exposure were analyzed. Results: A total of 40 COVID-19 cases were associated with the department store exposure, accounting for 75.47% of the total confirmed cases (53 cases) reported in Baodi district. The cases were mainly at the age of 60 years or older (35.00%) and farmers (40.00%). The main clinical manifestations included fever (95.00%), cough (35.00%), and diarrhea (15.00%). The proportion of confirmed severe cases was 32.50%. The incidence curve showed that the incidence peak occurred on 31 January, 2020. Among the 40 cases, 6(15.00%) were department store employees, 19 (47.50%) were customers and 15 (37.50%) were close contacts (secondary cases). The first case occurred on 21 January, 2020, this case was a department store employee who had a purchasing history at whole sale markets in other provinces and cities before the onset, and 3 employees were still on duty after symptom onsets. The median of the incubation period of customer cases was 6 days, and the median of the interval between onset and medical treatment of customer cases was 7 days. Conclusion: This was a cluster epidemic of COVID-19, which might be associated with the exposure in the department store. By now, the current prevention and control measures have achieved satisfied effects.

Angular momentum conservation for coherently manipulated spin polarization in photoexcited NiO: an ab initio calculation.

In an ultrafast laser-induced magnetization-dynamics scenario we demonstrate for the first time an exact microscopic spin-switch mechanism. Combining ab initio electronic many-body theory and quantum optics analysis we show in detail how the coherently induced material polarization for every elementary process leads to angular-momentum exchange between the light and the irradiated antiferromagnetic NiO. Thus we answer the long-standing question where the angular momentum goes. The calculation also predicts a dynamic Kerr effect, which provides a signature for monitoring spin dynamics, by simply measuring the transient rotation and ellipticity of the reflected light.