2,973 research outputs found
Correlated metallic state in honeycomb lattice: Orthogonal Dirac semimetal
A novel gapped metallic state coined orthogonal Dirac semimetal is proposed
in the honeycomb lattice in terms of slave-spin representation of
Hubbard model. This state corresponds to the disordered phase of slave-spin and
has the same thermaldynamical and transport properties as usual Dirac semimetal
but its singe-particle excitation is gapped and has nontrivial topological
order due to the gauge structure. The quantum phase transition from
this orthogonal Dirac semimetal to usual Dirac semimetal is described by a
mean-field decoupling with complementary fluctuation analysis and its
criticality falls into the universality class of 2+1D Ising model while a large
anomalous dimension for the physical electron is found at quantum critical
point (QCP), which could be considered as a fingerprint of our fractionalized
theory when compared to other non-fractionalized approaches. As byproducts, a
path integral formalism for the slave-spin representation of Hubbard
model is constructed and possible relations to other approaches and the
sublattice pairing states, which has been argued to be a promising candidate
for gapped spin liquid state found in the numerical simulation, are briefly
discussed. Additionally, when spin-orbit coupling is considered, the
instability of orthogonal Dirac semimetal to the fractionalized quantum spin
Hall insulator (fractionalized topological insulator) is also expected. We hope
the present work may be helpful for future studies in slave-spin theory
and related non-Fermi liquid phases in honeycomb lattice.Comment: 12 pages,no figures, more discussions added. arXiv admin note: text
overlap with arXiv:1203.063
Determining Singularity-Free Inner Workspace through Offline Conversion of Assembly Modes for a 3-RRR PPM
The existing singularity avoidance methods have deficiencies, such as the conditionality of the online conversion of the assembly modes (AMs) and the kinematically redundant manipulator with the predicament of the prototype design and added complexity of the mechanism. To address these issues, a method to determine a singularity-free inner workspace through offline conversion of the AMs of the 3-RRR planar parallel manipulator (PPM) is presented. Based on the geometric relations among rods of the manipulator during the occurrence of singularity, and the singular points at or near the boundary of the workspace are permitted, the AMs and ranges of the orientation angle of the moving platform corresponding to the inner singularity-free workspace are determined through a three-dimensional search method. The simulation and experimental comparisons indicate that singular-free paths related to the constant or variable orientation angle of the moving platform can be planned on the singularity-free inner workspace
Prevalence of insomnia symptoms and their associated factors in patients treated in outpatient clinics of four general hospitals in Guangzhou, China
Background: Data on the prevalence of insomnia symptoms in medical outpatient clinics in China are lacking. This study examined the prevalence of insomnia symptoms and their socio-demographic correlates in patients treated at medical outpatient clinics affiliated with four general hospitals in Guangzhou, a large metropolis in southern China.
Method: A total of 4399 patients were consecutively invited to participate in the study. Data on insomnia and its socio-demographic correlates were collected with standardized questionnaires.
Results: The prevalence of any type of insomnia symptoms was 22.1% (95% confidence interval (CI): 20.9–23.3%); the prevalence of difficulty initiating sleep was 14.3%, difficulty maintaining sleep was 16.2%, and early morning awakening was 12.4%. Only 17.5% of the patients suffering from insomnia received sleeping pills. Multiple logistic regression analysis revealed that male gender, education level, rural residence, and being unemployed or retired were negatively associated with insomnia symptoms, while lacking health insurance, older age and more severe depressive symptoms were positively associated with insomnia symptoms.
Conclusions: Insomnia symptoms are common in patients attending medical outpatient clinics in Guangzhou. Increasing awareness of sleep hygiene measures, regular screening and psychosocial and pharmacological interventions for insomnia are needed in China.
Trial registration: ChiCTR-INR-16008066. Registered 8 March 2016
Non-collinear magnetic structure and anisotropic magnetoelastic coupling in cobalt pyrovanadate Co2V2O7
The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced
magnetization plateaus and ferroelectricity, but its magnetic ground state
remains ambiguous due to its structural complexity. Magnetometry measurements,
and time-of-flight neutron powder diffraction (NPD) have been employed to study
the structural and magnetic properties of Co2V2O7, which consists of two
non-equivalent Co sites. Upon cooling below the Ne\'el temperature TN = 6.3 K,
we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of
long range magnetic order of Co2+ moments. After symmetry analysis and magnetic
structure refinement, we demonstrate that Co2V2O7 possesses a complicated
non-collinear magnetic ground state with Co moments mainly located in b-c plane
and forming a non-collinear spin-chain-like structure along the c-axis. The ab
initio calculations demonstrate that the non-collinear magnetic structure is
more stable than various ferromagnetic states at low temperature. The
non-collinear magnetic structure with canted up-up-down-down spin configuration
is considered as the origin of magnetoelectric coupling in Co2V2O7 because the
inequivalent exchange striction induced by the spin-exchange interaction
between the neighboring spins is the driving force of ferroelectricity.
Besides, it is found that the deviation of lattice parameters a and b is
opposite below TN, while the lattice parameter c and stay almost constant below
TN, evidencing the anisotropic magnetoelastic coupling in Co2V2O7.Comment: 9 pages, 8 figure
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