Stationary states and quantum quench dynamics of Bose-Einstein condensates in a double-well potential

We consider the properties of stationary states and the dynamics of Bose-Einstein condensates (BECs) in a double-well (DW) potential with pair tunneling by using a full quantum-mechanical treatment. Furthermore, we study the quantum quench dynamics of the DW system subjected to a sudden change of the Peierls phase. It is shown that strong pair tunneling evidently influences the energy spectrum structure of the stationary states. For relatively weak repulsive interatomic interactions, the dynamics of the DW system with a maximal initial population difference evolves from Josephson oscillations to quantum self-trapping as one increases the pair tunneling strength, while for large repulsion the strong pair tunneling inhibits the quantum self-trapping. In the case of attractive interatomic interactions, strong pair tunneling tends to destroy the Josephson oscillations and quantum self-trapping, and the system eventually enters a symmetric regime of zero population difference. Finally, the effect of the Peierls phase on the quantum quench dynamics of the system is analyzed and discussed. These new features are remarkably different from the usual dynamical behaviors of a BEC in a DW potential.Comment: 9 pages,7 figures,accepted for publication in Journal of Physics

Controlling the Si/C ratio in SiC matrix based on the modified polymethysilane for C/C–SiC composites with enhanced mechanical properties

Fabricating SiC matrix with controllable Si/C ratio for C/C–SiC composites via precursor infiltration and pyrolysis is difficult to realize due to the absence of suitable precursors. Here, SiC precursors with Si-rich (Si/C = 1.23), near-stoichiometric (Si/C = 1.01), and C-rich (Si/C = 0.88) pyrolyzed ceramics at 1200 ℃ were successfully synthesized by the novel modification of polymethysilane. The structure and ceramization of synthesized SiC precursors were studied, and C/C–SiC composites with similar Si/C ratio in SiC matrix were also fabricated. The results revealed that the defects and Young’s modulus of SiC matrix and the thermal residual stress on pyrolytic carbon coated carbon fiber were determined by the Si/C ratio. As a result, the Si/C ratio exerted significant effects on the crack deflection behavior and the mechanical properties of the composites. The composites with near-stoichiometric SiC matrix showed excellent mechanical properties because of the effective crack deflection and the moderate Young’s modulus of their SiC matrix. The flexural strength, flexural modulus, and compressive strength were 423±27 MPa, 33.41±4.52 GPa, and 393±8 MPa, respectively. Meanwhile, after a heat treatment at 1600 ℃, the role of carbon fiber toughening was improved and accompanied by a decrease in mechanical properties for all composites, which was attributed to the increased defects in SiC matrix and the damaged interfaces by the thermal residual stress

Topological mosaics in moiré superlattices of van der Waals heterobilayers

Van der Waals (vdW) heterostructures formed by 2D atomic crystals provide a powerful approach towards designer condensed matter systems. Incommensurate heterobilayers with small twisting and/or lattice mismatch lead to the interesting concept of Moir\'e superlattice, where the atomic registry is locally indistinguishable from commensurate bilayers but has local-to-local variation over long range. Here we show that such Moir\'e superlattice can lead to periodic modulation of local topological order in vdW heterobilayers formed by two massive Dirac materials. By tuning the vdW heterojunction from normal to the inverted type-II regime via an interlayer bias, the commensurate heterobilayer can become a topological insulator (TI), depending on the interlayer hybridization controlled by the atomic registry between the vdW layers. This results in mosaic pattern of TI regions and normal insulator (NI) regions in Moir\'e superlattices, where topologically protected helical modes exist at the TI/NI phase boundaries. By using symmetry based k.p and tight-binding models, we predict that this topological phenomenon can be present in inverted transition metal dichalcogenides heterobilayers. Our work points to a new means of realizing programmable and electrically switchable topological superstructures from 2D arrays of TI nano-dots to 1D arrays of TI nano-stripes.Comment: 17 pages,5 figure

Genome-wide association analysis identifies 30 new susceptibility loci for schizophrenia

We conducted a genome-wide association study (GWAS) with replication in 36,180 Chinese individuals and performed further transancestry meta-analyses with data from the Psychiatry Genomics Consortium (PGC2). Approximately 95% of the genome-wide significant (GWS) index alleles (or their proxies) from the PGC2 study were overrepresented in Chinese schizophrenia cases, including ∼50% that achieved nominal significance and ∼75% that continued to be GWS in the transancestry analysis. The Chinese-only analysis identified seven GWS loci; three of these also were GWS in the transancestry analyses, which identified 109 GWS loci, thus yielding a total of 113 GWS loci (30 novel) in at least one of these analyses. We observed improvements in the fine-mapping resolution at many susceptibility loci. Our results provide several lines of evidence supporting candidate genes at many loci and highlight some pathways for further research. Together, our findings provide novel insight into the genetic architecture and biological etiology of schizophrenia

In conditions of over-expression, WblI, a WhiB-like transcriptional regulator, has a positive impact on the weak antibiotic production of Streptomyces lividans TK24

Regulators of the WhiB-like (wbl) family are playing important role in the complex regulation of metabolic and morphological differentiation in Streptomyces. In this study, we investigated the role of wblI, a member of this family, in the regulation of secondary metabolite production in Streptomyces lividans. The over-expression of wblI was correlated with an enhanced biosynthesis of undecylprodigiosin and actinorhodin and with a reduction of the biosynthesis of yCPK and of the grey spore pigment encoded by the whiE locus. Five regulatory targets of WblI were identified using in vitro formaldehyde crosslinking and confirmed by EMSA and qRT-PCR. These included the promoter regions of wblI itself, two genes of the ACT cluster (actVA3 and the intergenic region between the divergently orientated genes actII-1 and actII-2) and that of wblA, another member of the Wbl family. Quantitative RTPCR analysis indicated that the expression of actVA3 encoding a protein of unknown function as well as that of actII-1, a TetR regulator repressing the expression of actII-2, encoding the ACT transporter, were down regulated in the WblI over-expressing strain. Consistently the expression of the transporter actII-2 was up-regulated. The expression of WblA, that is known to have a negative impact on ACT biosynthesis, was strongly down regulated in the WblI over-expressing strain. These data are consistent with the positive impact that WblI over-expression has on ACT biosynthesis. The latter might result from direct activation of ACT biosynthesis and export and from repression of the expression of WblA, a likely indirect, repressor of ACT biosynthesis

Preparation of HfC_xN_1−x Nanoparticles Derived from a Multifunction Precursor with Hf-O and Hf-N Bonds

HfCxN1−x nanoparticles were synthesized using the urea-glass route, employing hafnium chloride, urea, and methanol as raw materials. The synthesis process, polymer-to-ceramic conversion, microstructure, and phase evolution of HfCxN1−x/C nanoparticles were thoroughly investigated across a wide range of molar ratios between the nitrogen source and the hafnium source. Upon annealing at 1600 °C, all precursors demonstrated remarkable translatability to HfCxN1−x ceramics. Under high nitrogen source ratios, the precursor exhibited complete transformation into HfCxN1−x nanoparticles at 1200 °C, with no observed presence of oxidation phases. In comparison to HfO2, the carbothermal reaction of HfN with C significantly reduced the preparation temperature required for HfC. By increasing the urea content in the precursor, the carbon content of the pyrolyzed products increased, leading to a substantial decrease in the electrical conductivity of HfCxN1−x/C nanoparticle powders. Notably, as the urea content in the precursor increased, a significant decrease in average electrical conductivity values was observed for the R4-1600, R8-1600, R12-1600, and R16-1600 nanoparticles measured at a pressure of 18 MPa, yielding values of 225.5, 59.1, 44.8, and 46.0 S·cm−1, respectively

In conditions of over-expression, WblI, a WhiB-like transcriptional regulator, has a positive impact on the weak antibiotic production of <i>Streptomyces lividans</i> TK24 - Fig 2

<p><b>Effects of <i>wblI</i> overexpression and deletion on the production of yCPK (A) and spore grey pigment (B).</b> Strains were cultivated on GYM medium for 36 h (A) and 72 h (B), respectively.</p