6,489 research outputs found
Magnetic Bose glass phases of coupled antiferromagnetic dimers with site dilution
We numerically investigate the phase diagram of two-dimensional site-diluted
coupled dimer systems in an external magnetic field. We show that this phase
diagram is characterized by the presence of an extended Bose glass, not
accessible to mean-field approximation, and stemming from the localization of
two distinct species of bosonic quasiparticles appearing in the ground state.
On the one hand, non-magnetic impurities doped into the dimer-singlet phase of
a weakly coupled dimer system are known to free up local magnetic moments. The
deviations of these local moments from full polarization along the field can be
mapped onto a gas of bosonic quasiparticles, which undergo condensation in zero
and very weak magnetic fields, corresponding to transverse long-range
antiferromagnetic order. An increasing magnetic field lowers the density of
such quasiparticles to a critical value at which a quantum phase transition
occurs, corresponding to the quasiparticle localization on clusters of local
magnets (dimers, trimers, etc.) and to the onset of a Bose glass. Strong
finite-size quantum fluctuations hinder further depletion of quasiparticles
from such clusters, and thus lead to the appearance of pseudo-plateaus in the
magnetization curve of the system. On the other hand, site dilution hinders the
field-induced Bose-Einstein condensation of triplet quasiparticles on the
intact dimers, and it introduces instead a Bose glass of triplets. A thorough
numerical investigation of the phase diagram for a planar system of coupled
dimers shows that the two above-mentioned Bose glass phases are continuously
connected, and they overlap in a finite region of parameter space, thus
featuring a two-species Bose glass. The quantum phase transition from Bose
glass to magnetic order in two dimensions is marked by novel universal
exponents.Comment: 15 pages, 16 figure
Quantum disorder and Griffiths singularities in bond-diluted two-dimensional Heisenberg antiferromagnets
We investigate quantum phase transitions in the spin-1/2 Heisenberg
antiferromagnet on square lattices with inhomogeneous bond dilution. It is
shown that quantum fluctuations can be continuously tuned by inhomogeneous bond
dilution, eventually leading to the destruction of long-range magnetic order on
the percolating cluster. Two multicritical points are identified at which the
magnetic transition separates from the percolation transition, introducing a
novel quantum phase transition. Beyond these multicritical points a
quantum-disordered phase appears, characterized by an infinite percolating
cluster with short ranged antiferromagnetic order. In this phase, the
low-temperature uniform susceptibility diverges algebraically with
non-universal exponents. This is a signature that the novel quantum-disordered
phase is a quantum Griffiths phase, as also directly confirmed by the
statistical distribution of local gaps. This study thus presents evidence of a
genuine quantum Griffiths phenomenon in a two-dimensional Heisenberg
antiferromagnet.Comment: 14 pages, 17 figures; published versio
The disordered-free-moment phase: a low-field disordered state in spin-gap antiferromagnets with site dilution
Site dilution of spin-gapped antiferromagnets leads to localized free
moments, which can order antiferromagnetically in two and higher dimensions.
Here we show how a weak magnetic field drives this order-by-disorder state into
a novel disordered-free-moment phase, characterized by the formation of local
singlets between neighboring moments and by localized moments aligned
antiparallel to the field. This disordered phase is characterized by the
absence of a gap, as it is the case in a Bose glass. The associated
field-driven quantum phase transition is consistent with the universality of a
superfluid-to-Bose-glass transition. The robustness of the
disordered-free-moment phase and its prominent features, in particular a series
of pseudo-plateaus in the magnetization curve, makes it accessible and relevant
to experiments.Comment: 4 pages, 4 figure
Dark-bright gap solitons in coupled-mode one-dimensional saturable waveguide arrays
In the present work, we consider the dynamics of dark solitons as one mode of
a defocusing photorefractive lattice coupled with bright solitons as a second
mode of the lattice. Our investigation is motivated by an experiment which
illustrates that such coupled states can exist with both components in the
first gap of the linear band spectrum. This finding is further extended by the
examination of different possibilities from a theoretical perspective, such as
symbiotic ones where the bright component is supported by states of the dark
component in the first or second gap, or non-symbiotic ones where the bright
soliton is also a first-gap state coupled to a first or second gap state of the
dark component. While the obtained states are generally unstable, these
instabilities typically bear fairly small growth rates which enable their
observation for experimentally relevant propagation distances
Duration of untreated bipolar disorder: A multicenter study
Little is known about the demographic and clinical differences between short and long duration of untreated bipolar disorder (DUB) in Chinese patients. This study examined the demographic and clinical features of short (≤2 years) and long DUB (\u3e2 years) in China. A consecutively recruited sample of 555 patients with bipolar disorder (BD) was examined in 7 psychiatric hospitals and general hospital psychiatric units across China. Patients’ demographic and clinical characteristics were collected using a standardized protocol and data collection procedure. The mean DUB was 3.2 ± 6.0 years; long DUB accounted for 31.0% of the sample. Multivariate analyses revealed that longer duration of illness, diagnosis of BD type II, and earlier misdiagnosis of BD for major depressive disorder or schizophrenia were independently associated with long DUB. The mean DUB in Chinese BD patients was shorter than the reported figures from Western countries. The long-term impact of DUB on the outcome of BD is warranted
Dual Actions for Born-Infeld and Dp-Brane Theories
Dual actions with respect to U(1) gauge fields for Born-Infeld and -brane
theories are reexamined. Taking into account an additional condition, i.e. a
corollary to the field equation of the auxiliary metric, one obtains an
alternative dual action that does not involve the infinite power series in the
auxiliary metric given by ref. \cite{s14}, but just picks out the first term
from the series formally. New effective interactions of the theories are
revealed. That is, the new dual action gives rise to an effective interaction
in terms of one interaction term rather than infinite terms of different
(higher) orders of interactions physically. However, the price paid for
eliminating the infinite power series is that the new action is not quadratic
but highly nonlinear in the Hodge dual of a -form field strength. This
non-linearity is inevitable to the requirement the two dual actions are
equivalent.Comment: v1: 11 pages, no figures; v2: explanation of effective interactions
added; v3: concision made; v4: minor modification mad
New Spinor Field Realizations of the Non-Critical String
We investigate the new spinor field realizations of the algebra,
making use of the fact that the algebra can be linearized by the
addition of a spin-1 current. We then use these new realizations to build the
nilpotent Becchi-Rouet-Stora--Tyutin (BRST) charges of the spinor non-critical
string.Comment: 8 pages, no figures, revtex4 style, accepted by Chin. Phys. Let
Single-nucleotide polymorphism-based genetic risk score and patient age at prostate cancer diagnosis
Importance: Few studies have evaluated the association between a single-nucleotide polymorphism-based genetic risk score (GRS) and patient age at prostate cancer (PCa) diagnosis.
Objectives: To test the association between a GRS and patient age at PCa diagnosis and to compare the performance of a GRS with that of family history (FH) in PCa risk stratification.
Design, Setting, and Participants: A cohort study of 3225 white men was conducted as a secondary analysis of the Reduction by Dutasteride of Prostate Cancer Events (REDUCE) chemoprevention trial, a 4-year, randomized, double-blind, placebo-controlled multicenter study conducted from March 2003 to April 2009 to evaluate the safety and efficacy of dutasteride in reducing PCa events. Participants were confirmed to be cancer free by prostate biopsy (6-12 cores) within 6 months prior to the study and underwent 10 core biopsies every 2 years per protocol. The dates for performing data analysis were from July 2016 to October 2019.
Interventions: A well-established, population-standardized GRS was calculated for each participant based on 110 known PCa risk-associated single-nucleotide polymorphisms, which is a relative risk compared with the general population. Men were classified into 3 GRS risk groups based on predetermined cutoff values: low (\u3c0.50), average (0.50-1.49), and high (≥1.50).
Main Outcomes and Measures: Prostate cancer diagnosis-free survival among men of different risk groups.
Results: Among 3225 men (median age, 63 years [interquartile range, 58-67 years]) in the study, 683 (21%) were classified as low risk, 1937 (60%) as average risk, and 605 (19%) as high risk based on GRS alone. In comparison, 2789 (86%) were classified as low or average risk and 436 (14%) as high risk based on FH alone. Men in higher GRS risk groups had a PCa diagnosis-free survival rate that was worse than that of those in the lower GRS risk group (χ2 = 53.3; P \u3c .001 for trend) and in participants with a negative FH of PCa (χ2 = 45.5; P \u3c .001 for trend). Combining GRS and FH further stratified overall genetic risk, indicating that 957 men (30%) were at high genetic risk (either high GRS or positive FH), 1667 men (52%) were at average genetic risk (average GRS and negative FH), and 601 men (19%) were at low genetic risk (low GRS and negative FH). The median PCa diagnosis-free survival was 74 years (95% CI, 73-75 years) for men at high genetic risk, 77 years (95% CI, 75 to \u3e80 years) for men at average genetic risk, and more than 80 years (95% CI, \u3e80 to \u3e80 years) for men at low genetic risk. In contrast, the median PCa diagnosis-free survival was 73 years (95% CI, 71-76 years) for men with a positive FH and 77 years (95% CI, 76-79 years) for men with a negative FH.
Conclusions and Relevance: This study suggests that a GRS is significantly associated with patient age at PCa diagnosis. Combining FH and GRS may better stratify inherited risk than FH alone for developing personalized PCa screening strategies
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