2,204 research outputs found
Phase diagram and magnetic excitations of - Heisenberg model on the square lattice
We study the phase diagram and the dynamical spin structure factor of the
spin-1/2 J1-J3 Heisenberg model on the square lattice using density matrix
renormalization group, exact diagonalization (ED), and cluster perturbation
theory (CPT). By extrapolating the order parameters and studying the level
crossings of the low-lying energy and entanglement spectra, we obtain the phase
diagram of this model and identify a narrow region of quantum spin liquid (QSL)
phase followed by a plaquette valence-bond solid (PVBS) state in the
intermediate region, whose nature has been controversial for many years. More
importantly, we use CPT and ED to study the dynamical spin structure factor in
the QSL and the PVBS phase. In the QSL phase, the high-energy magnon mode
completely turns into some dispersive weak excitations around the X and M
points. For the PVBS phase, the low-energy spectrum is characterized by a
gapped triplet excitation, and at the high energy, we find another branch of
dispersive excitation with broad continua, which is unlike the plaquette phase
in the 2x2 checkerboard model. In the latter case, the second branch of
excitation is nearly flat due to the weak effective interactions between the
local excitations of the plaquettes. And in the J1-J3 Heisenberg model, the
uniform interactions and the spontaneously translational symmetry breaking of
the PVBS phase make the difference in the excitation spectra.Comment: 14 pages, 14 figure
Haldane phases and phase diagrams of the S = 3/2, 1 bilinear-biquadratic Heisenberg model on the orthogonal dimer chain
We systematically study the effects of higher-order interactions on the S =
3/2, 1 orthogonal dimer chains using exact diagonalization and density matrix
renormalization group. Due to frustration and higher spin, there are rich
quantum phases, including three Haldane phases, two gapless phases and several
magnetically ordered phases. To characterize these phases and their phase
transitions, we study various physical quantities such as energy gap, energy
level crossing, fidelity susceptibility, spin correlation, entanglement
spectrum and central charge. According to our calculations, the biquadratic
term can enhance the Haldane phase regions. In particular, we numerically
identify that a Haldane phase in S = 3/2 case is adiabatically connected to the
exact AKLT point when adding bicubic term. Our study on the orthogonal dimer
model, which is a 1D version of Shastry-Sutherland model, provides insights
into understanding the possible S = 3/2, 1 Haldane phases in quasi-1D and 2D
frustrated magnetic materials.Comment: 14 pages, 17 figure
Salvia miltiorrhiza aqueous root extract plays an important role in improving locomotor activity in rats with spinal cord injury
Purpose: To investigate the activity of the aqueous root extract of Salvia miltiorrhiza (S. miltiorrhiza) (Lamiaceae), collected from Anhui Province, China, for the treatment of spinal cord injury (SCI) in Sprague-Dawley (SD) rats.Methods: In total, 30 adult rats were selected and divided into three groups; normal control, untreated and treated. Aqueous root extract of S. miltiorrhiza was introduced intraperitoneally to the treated group. Basso, Beattie and Bresnahan rating scale (BBB) was used to evaluate improvement in locomotor activity after SCI. Total RNA was extracted from tissue sections using Sepasol (NacalaiTesque) and RNA samples were reverse-transcribed using M-MLV reverse transcriptase. BioSense SC-810 Gel Documentation System and Gel-Pro 3.1 software were employed for the analysis of band intensity.Results: A significant reduction in SCI cavity area was observed in the S. miltiorrhiza extract-treated group, relative to the untreated group, after 11 days (0.10 ± 0.05 mm2 treated vs. 0.30 ± 0.01 mm2 untreated). Treatment with root extract also improved the BBB scores; the treated group scored 15, compared to a score of 8 for the untreated group. In addition, the degradation of neurons at the site of injury in the spinal cord was reduced in the treated group compared to the untreated group. Treatment with S. miltiorrhiza aqueous root extract also significantly increased the expression of platelet-derived growth factor-B (PDGF-B) mRNA (p < 0.01).Conclusion: These data suggest that, in addition to other pharmacological activities, S. miltiorrhiza extract has therapeutic potential for the treatment of neuronal degeneration following SCI.Keywords: Salvia Miltiorrhiza, Neurons, Spinal cord injury, Locomotor capacity, Platelet-derived growth factor-B, Basso, Beattie and Bresnahan rating scal
Discovery of six high-redshift quasars with the Lijiang 2.4m telescope and the Multiple Mirror Telescope
Quasars with redshifts greater than 4 are rare, and can be used to probe the
structure and evolution of the early universe. Here we report the discovery of
six new quasars with -band magnitudes brighter than 19.5 and redshifts
between 2.4 and 4.6 from the YFOSC spectroscopy of the Lijiang 2.4m telescope
in February, 2012. These quasars are in the list of quasar candidates
selected by using our proposed criterion and the photometric redshift
estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine
candidates were observed by YFOSC, and five among six new quasars were
identified as quasars. One of the other three objects was identified as
a star and the other two were unidentified due to the lower signal-to-noise
ratio of their spectra. This is the first time that quasars have been
discovered using a telescope in China. Thanks to the Chinese Telescope Access
Program (TAP), the redshift of 4.6 for one of these quasars was confirmed by
the Multiple Mirror Telescope (MMT) Red Channel spectroscopy. The continuum and
emission line properties of these six quasars, as well as their central black
hole masses and Eddington ratios, were obtained.Comment: 7 pages, 2 figures, published in Research in Astronomy and
Astrophysics (RAA) as a lette
Whole-transcriptome sequencing identifies key differentially expressed circRNAs/lncRNAs/miRNAs/mRNAs and linked ceRNA networks in adult degenerative scoliosis
BackgroundAdult degenerative scoliosis (ADS) is forecast to be a prevalent disabling condition in an aging society. Universally, its pathogenesis is perceived as intervertebral disc degeneration (IDD), however, a thought-provoking issue is why precisely a subset of patients with disc degeneration develop ADS. Exploring the diversities between common IDD and ADS would contribute to unraveling the etiological mechanisms of ADS. Therefore, we aimed to integrate the circRNA, lncRNA, miRNA, and mRNA expression profiles from normal adults (Normal), patients with lumbar disc herniation (LDH), and ADS by whole transcriptome sequencing, which identifies critical functional ncRNA and ceRNA networks and crosstalk between the various transcripts.MethodsThe fresh whole blood samples (n =â3/group) were collected from ADS patients, LDH patients, and healthy volunteers (Normal group), which were examined for mRNA, miRNA, lncRNA, and circRNA expression and screened for differentially expressed (DE) ncRNAs. Then, Gene Ontology (GO) and KEGG analyses were performed for gene annotation and enrichment pathways on the DE RNAs, which were constructed as a lncRNA-miRNA-mRNA network. Eventually, DE RNAs were validated by qRT-PCR targeting disc nucleus pulposus (NP) tissue in ADS and LDH group (n =â10/group).ResultsCompared to the LDH group, we identified 3322 DE mRNAs, 221 DE lncRNAs, 20 DE miRNAs, and 15 DE circRNAs in the ADS. In contrast to Normal, 21 miRNAs and 19 circRNAs were differentially expressed in the ADS. The expression of multiple differentially expressed ncRNAs was confirmed by qRT-PCR analysis to be consistent with the sequencing results. In addition, GO, and KEGG analysis demonstrated that most DE mRNAs and ncRNAs target genes are involved in various biological processes, including Endocytosis, Apoptosis, Rap1 signaling pathway, Notch signaling pathway, and others. The constructed lncRNA-miRNA-mRNA co-expression network was primarily related to angiogenesis and regulation.ConclusionBy focusing on comparing asymmetric and symmetric disc degeneration, whole-transcriptome sequencing and bioinformatics analysis systematically screened for key ncRNAs in the development of ADS, which provided an abundance of valuable candidates for the elucidation of regulatory mechanisms. The DE ncRNAs and the lncRNA-miRNA-mRNA network are intrinsically involved in the regulation of mediator and angiogenesis, which may contribute to the insight into the pathogenesis of ADS
Totally thoracoscopic closure of ventricular septal defect without a robotically assisted surgical system: A summary of 119 cases
ObjectivesTo summarize the clinical outcomes of totally thoracoscopic closure of a ventricular septal defect (VSD).MethodsTotally thoracoscopic VSD closure was performed in 119 patients (66 boys; mean age, 7.1 ± 3.6 years). An additional 35 patients undergoing open-chest VSD closure were selected as a control group. Using 3 port incisions in the right chest, pericardiotomy, bicaval occlusion, atriotomy, and VSD closure were performed by thoracoscopy without the aid of a robotically assisted surgical system.ResultsCardiopulmonary bypass and aortic crossclamp times were 42.2 ± 9.8 and 32.5 ± 7.3 minutes, respectively. There were no deaths but 1 patient required insertion of a permanent pacemaker as a result of postoperative atrioventricular conduction block. The length of stay in the intensive care unit (11.0 ± 2.6 vs 22.9 ± 4.9 hours, P < .01) or postoperative hospital stay (4.2 ± 1.1 vs 6.6 ± 2.1 days, P < .03) in the thoracoscopic group were shorter than in the control group. The percentage of patients who required postoperative opioid analgesics in the thoracoscopic group was lower than in the control group (31.9% vs 74.2%, P < .001). Rate of blood transfusion during the operation (17.6% vs 65.7%, P = .001) and the postoperative use of opioid analgesics (31.9% vs 74.3%, P = .003) in the thoracoscopic group was lower than in the control group. Transesophageal echocardiographic analysis 4.6 ± 2.3 months after the operation showed complete closure of the defect.ConclusionsTotally thoracoscopic closure of VSD through a 3-port entry was safe and effective
Deep Reinforcement Learning for Image-to-Image Translation
Most existing Image-to-Image Translation (I2IT) methods generate images in a
single run of a deep learning (DL) model. However, designing such a single-step
model is always challenging, requiring a huge number of parameters and easily
falling into bad global minimums and overfitting. In this work, we reformulate
I2IT as a step-wise decision-making problem via deep reinforcement learning
(DRL) and propose a novel framework that performs RL-based I2IT (RL-I2IT). The
key feature in the RL-I2IT framework is to decompose a monolithic learning
process into small steps with a lightweight model to progressively transform a
source image successively to a target image. Considering that it is challenging
to handle high dimensional continuous state and action spaces in the
conventional RL framework, we introduce meta policy with a new concept Plan to
the standard Actor-Critic model, which is of a lower dimension than the
original image and can facilitate the actor to generate a tractable high
dimensional action. In the RL-I2IT framework, we also employ a task-specific
auxiliary learning strategy to stabilize the training process and improve the
performance of the corresponding task. Experiments on several I2IT tasks
demonstrate the effectiveness and robustness of the proposed method when facing
high-dimensional continuous action space problems
Joint Optimization for RIS-Assisted Wireless Communications: From Physical and Electromagnetic Perspectives
Reconfigurable intelligent surfaces (RISs) are envisioned to be a disruptive
wireless communication technique that is capable of reconfiguring the wireless
propagation environment. In this paper, we study a free-space RIS-assisted
multiple-input single-output (MISO) communication system in far-field
operation. To maximize the received power from the physical and electromagnetic
nature point of view, a comprehensive optimization, including beamforming of
the transmitter, phase shifts of the RIS, orientation and position of the RIS
is formulated and addressed. After exploiting the property of line-of-sight
(LoS) links, we derive closed-form solutions of beamforming and phase shifts.
For the non-trivial RIS position optimization problem in arbitrary
three-dimensional space, a dimensional-reducing theory is proved. The
simulation results show that the proposed closed-form beamforming and phase
shifts approach the upper bound of the received power. The robustness of our
proposed solutions in terms of the perturbation is also verified. Moreover, the
RIS significantly enhances the performance of the mmWave/THz communication
system
- âŠ