Publications by authors named "Liwei Duan"

18 Publications

  • Page 1 of 1

Ulinastatin Ameliorates IL-1-Induced Cell Dysfunction in Human Nucleus Pulposus Cells via Nrf2/NF-B Pathway.

Oxid Med Cell Longev 2021 21;2021:5558687. Epub 2021 Apr 21.

Department of Orthopedic Surgery, Changzheng Hospital, Navy Medical University (Second Military Medical University), No. 415 Fengyang Road, Shanghai 200003, China.

Low back pain (LBP) has been a wide public health concern worldwide. Among the pathogenic factors, intervertebral disc degeneration (IDD) has been one of the primary contributors to LBP. IDD correlates closely with inflammatory response and oxidative stress, involving a variety of inflammation-related cytokines, such as interleukin 1 beta (IL-1), which could result in local inflammatory environment. Ulinastatin (UTI) is a kind of acidic protein extracted from human urine, which inhibits the release of tumor necrosis factor alpha (TNF-) and other inflammatory factors to protect organs from inflammatory damage. However, whether this protective effect of UTI on human nucleus pulposus (NP) exists, and how UTI affects the biological behaviors of human NP cells during IDD remain elusive. In this current study, we revealed that UTI could improve the viability of NP cells and promote the proliferation of NP cells. Additionally, UTI could protect human NP cells via ameliorating IL-1-induced apoptosis, inflammatory response, oxidative stress, and extracellular matrix (ECM) degradation. Molecular mechanism analysis suggested that the protective effect from UTI on IL-1-treated NP cells were through activating nuclear factor- (erythroid-derived 2-) like 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway and the suppression of NF-B signaling pathway. Therefore, UTI may be a promising therapeutic medicine to ameliorate IDD.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1155/2021/5558687DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8084647PMC
May 2021

Respiratory Variations in Peak Peripheral Artery Velocities and Waveforms for Rapid Assessment of Fluid Responsiveness in Traumatic Shock Patients.

Med Sci Monit 2021 Jan 8;27:e928804. Epub 2021 Jan 8.

Department of Biotechnology and Pathology, Shanghai University of Medicine and Health Sciences, Shanghai, China (mainland).

BACKGROUND This study aimed to assess the correlation between the variability of the end-inspiratory and end-expiratory blood flow waveform and fluid responsiveness (FR) in traumatic shock patients who underwent mechanical ventilation by evaluating peripheral arterial blood flow parameters. MATERIAL AND METHODS A cohort of 60 patients with traumatic shock requiring mechanical ventilation-controlled breathing received ultrasound examinations to assess the velocity of carotid artery (CA), femoral artery (FA) and brachial artery (BA). A rehydration test was performed in which of 250 mL of 0.9% saline was administered within 30 min between the first and second measurement of cardiac output by echocardiography. Then, all patients were divided into 2 groups, a responsive group (FR+) and a non-responsive group (FR-). The velocity of end-inspiratory and end-expiratory peripheral arterial blood flow of all patients was ultrasonically measured, and the variability were measured between end-inspiratory and end-expiratory. RESULTS The changes in the end-inspiratory and end-expiratory carotid artery blood flow velocity waveforms of the FR+ groups were significantly different from those of the FR- group (P<0.001). A statistically significant difference in ΔVmax (CA), ΔVmax (BA), and ΔVmax (FA) between these 2 groups was found (all P<0.001). The ROC curve showed that DVmax (CA) and ΔVmax (BA) were more sensitive values to predict FR compared to ΔVmax (FA). The sensitivity of ΔVmax (CA), ΔVmax (FA), and ΔVmax (BA) was 70.0%, 86.7%, and 93.3%, respectively. CONCLUSIONS The study showed that periodic velocity waveform changes in the end-inspiratory and end-expiratory peripheral arterial blood flow can be used for quick assessment of fluid responsiveness.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.12659/MSM.928804DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7802376PMC
January 2021

Analysis of Endoscopy Findings to Identify Early Gastric Cancers with Tumor Budding: A Retrospective Study.

J Gastrointest Surg 2020 Nov 9. Epub 2020 Nov 9.

Department of Endoscopy, The Second Hospital of Jilin University, Changchun, 130041, Jilin, China.

Background: No reliable method has been reported for determining tumor budding with frozen sections during surgical procedures. This study investigated endoscopic features predictive of tumor budding in early gastric cancers (EGC).

Methods: This retrospective study evaluated data from 137 patients diagnosed with EGC who underwent endoscopy, followed by endoscopic submucosal dissection (ESD); 71 patients underwent a second gastrectomy. Based on pathological analyses, lesions were categorized as being positive (n = 80) or negative for tumor budding (n = 57). Endoscopic features were analyzed using multivariable logistic regression. Patient survival rates were analyzed with Kaplan-Meier method and log-rank test.

Results: Mean age of our study population was 66 years (range, 31-86 years). The tumor budding-positive cohort (73.3 ± 5.9 years) was significantly older than the tumor budding-negative cohort (56.7 ± 7.6 years) (p < 0.001). Endoscopic features significantly different between tumor budding-positive and budding-negative groups included tumor size (p = 0.003), remarkable redness (p = 0.015), and margin elevation (p < 0.001). Tumor size (odds ratio (OR): 1.561; 95% confidence interval (CI): 0.984, 2.285; p = 0.047) and margin elevation (OR: 2.141; 95% CI: 1.147, 5.117; p = 0.003) were independent predictors of tumor budding. Margin elevation was found in 19.3% of tumor budding-negative and 53.8% of budding-positive cases. In the tumor budding-positive group, ESD and second gastrectomy were associated with disease-free survival.

Conclusions: Margin elevation and large tumor size (> 29 mm) of EGCs on endoscopy are promising imaging biomarkers for predicting tumor budding in EGCs. ESD and a second gastrectomy can be better for tumor budding-positive patients with EGCs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11605-020-04862-6DOI Listing
November 2020

The novel coronavirus (SARS-CoV-2) infections in China: prevention, control and challenges.

Intensive Care Med 2020 04 2;46(4):591-593. Epub 2020 Mar 2.

Department of Critical Care Medicine, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, China.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00134-020-05977-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7079863PMC
April 2020

A modified procedure of single-level transforaminal lumbar interbody fusion reduces immediate post-operative symptoms: a prospective case-controlled study based on two hundred and four cases.

Int Orthop 2020 05 21;44(5):935-945. Epub 2020 Feb 21.

Department of Orthopedic Surgery, Spine Center, Changzheng Hospital, Second Military Medical University, No. 415 Fengyang Road, Shanghai, 200003, People's Republic of China.

Study Design: This is a prospective case-controlled study.

Purpose: The purpose of this study is to investigate the effect of a modified transforaminal lumbar interbody fusion (TLIF) on the immediate post-operative symptoms in patients with lumbar disc herniation (LDH) accompanied with stenosis.

Methods: A total of 204 LDH patients with single-level TLIF were enrolled. According to the sequence of the placement of rods and cage, patients were divided into group R (rod-prior-to-cage) and group C (cage-prior-to-rod). Neurological function was evaluated by the Japanese Orthopedic Association (JOA) score. Radiological assessment includes height of intervertebral space (HIS), foraminal height (FH), foraminal area (FA), and segmental lordosis (SL). Change of original symptoms (pain/numb) and new-onset symptoms (pain/numb) after surgery were also recorded.

Results: Patients in group R had less change of HIS at L3/4, L4/5, and L5/S1 levels compared with pre-operation (all p > 0.05), whereas group C had larger change (all p < 0.05). No statistical difference was found in FH between the two groups before and after surgery at L3/4, L4/5, and L5/S1, respectively (all p > 0.05). In terms of FA, patients in group R had better improvement after surgery than those in group C at L3/4 and L4/5 (both p < 0.05). Patients in both groups acquired good improvement of neurological function. However, there were fewer patients in group R who experienced post-operative leg pain or numb compared with those in group C (p < 0.05).

Conclusion: The modified open TLIF can significantly reduce the incidence of immediate post-operative symptoms for patients with single-level lumbar disc herniation via installation of rods prior to insertion of cage and the "neural standard" should serve as the goal of decompression for spine surgeons to restore disc/foraminal height and to minimize nerve distraction.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00264-020-04508-xDOI Listing
May 2020

The mixed quantum Rabi model.

Sci Rep 2019 Dec 4;9(1):18353. Epub 2019 Dec 4.

Department of Physics and Zhejiang Province Key Laboratory of Quantum Technology and Device, Zhejiang University, Hangzhou, 310027, China.

The analytical exact solutions to the mixed quantum Rabi model (QRM) including both one- and two-photon terms are found by using Bogoliubov operators. Transcendental functions in terms of 4 × 4 determinants responsible for the exact solutions are derived. These so-called G-functions with pole structures can be reduced to the previous ones in the unmixed QRMs. The zeros of G-functions reproduce completely the regular spectra. The exceptional eigenvalues can also be obtained by another transcendental function. From the pole structure, we can derive two energy limits when the two-photon coupling strength tends to the collapse point. All energy levels only collapse to the lower one, which diverges negatively. The level crossings in the unmixed QRMs are relaxed to avoided crossings in the present mixed QRM due to absence of parity symmetry. In the weak two-photon coupling regime, the mixed QRM is equivalent to an one-photon QRM with an effective positive bias, suppressed photon frequency and enhanced one-photon coupling, which may pave a highly efficient and economic way to access the deep-strong one-photon coupling regime.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-019-54756-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6892885PMC
December 2019

Long noncoding RNA/circular noncoding RNA-miRNA-mRNA axes in cardiovascular diseases.

Life Sci 2019 Sep 30;233:116440. Epub 2019 Apr 30.

Department of Cardiology, The Second Hospital of Jilin University, 218 Ziqiang Road, Changchun 130041, China. Electronic address:

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. Non-coding RNAs including long non-coding RNAs (lncRNAs), circular RNAs (circRNAs) and microRNAs (miRNAs) have been reported to participate in pathological developments of CVDs through various mechanisms. Among them, the networks among lncRNAs/circRNAs, miRNAs, and mRNAs have recently attracted attention. Understanding the molecular mechanism could aid the discovery of therapeutic targets or strategies in CVDs including atherosclerosis, myocardial infarction (MI), hypertrophy, heart failure (HF) and cardiomyopathy. In this review, we summarize the latest research involving the lncRNA/circRNA-miRNA-mRNA axis in CVDs, with emphasis on the molecular mechanism.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.lfs.2019.04.066DOI Listing
September 2019

Management of a Steel Bar Injury Penetrating the Head and Neck: A Case Report and Review of the Literature.

World Neurosurg 2019 Mar 14;123:168-173. Epub 2018 Nov 14.

Department of Neurosurgery, Changzheng Hospital, Second Military Medical University, Shanghai, China. Electronic address:

Background: Nonmissile penetrating injuries to the head and neck caused by a steel bar are rare, and a standard management strategy is lacking.

Case Description: A 42-year-old woman sustained a steel bar injury with penetration of the head and neck. Computed tomography and three-dimensional reconstruction were performed for preoperative evaluation. Digital subtraction angiography was performed to confirm potential vascular injury. The steel bar was successfully removed through an open surgical procedure by a multidisciplinary team.

Conclusions: Relevant literature regarding nonmissile penetrating injuries involving a steel bar was reviewed to propose appropriate management strategies. Comprehensive imaging evaluation and prompt surgery by a multidisciplinary team contributed to the successful removal of the steel bar.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.wneu.2018.11.029DOI Listing
March 2019

Interleukin-32: its role in asthma and potential as a therapeutic agent.

Respir Res 2018 06 25;19(1):124. Epub 2018 Jun 25.

Department of Respiratory Medicine, the Second Hospital of Jilin University, Changchun, Jilin, China.

Interleukin (IL)-32, also named natural killer cell transcript 4 (NK4), has increasingly been described as an immunoregulator that controls cell differentiation and cell death and is involved in the stimulation of anti-/pro-inflammatory cytokines. Abnormal presence of IL-32 has been repeatedly noticed during the pathogenesis of allergic, infectious, cancerous, and inflammatory diseases. Of particular note was the observation of the anti-inflammatory property of IL-32 in a murine ovalbumin model of allergic asthma. Compared to wild-type mice, IL-32γ transgenic mice show decreased levels of inflammatory cells, recruited eosinophils, and lymphocytes in bronchoalveolar lavage fluid in a mouse model of acute asthma. To date, the molecular mechanism underlying the role of IL-32 in asthma remains to be elucidated. This review aims to summarize recent advances in the pathophysiology of asthma and describe the links to IL-32. The possibilities of using IL-32 as an airway inflammation biomarker and an asthma therapeutic agent are also evaluated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s12931-018-0832-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6019726PMC
June 2018

Oridonin increases anticancer effects of lentinan in HepG2 human hepatoblastoma cells.

Oncol Lett 2018 Feb 24;15(2):1999-2005. Epub 2017 Nov 24.

Department of Interventional Center, Jilin Provincial Cancer Hospital, Changchun, Jilin 130012, P.R. China.

The aim of the present study was to investigate whether oridonin is able to increase the effects of lentinan (LNT) in HepG2 human hepatoblastoma cells by MTT, flow cytometry, reverse transcription-quantitative polymerase chain reaction and western blot analysis. The results demonstrated that 20 µg/ml of oridonin was a nontoxic concentration for L02 normal liver cells and HepG2 liver cancer cells. Furthermore, treatment with 0-200 µg/ml LNT was only able to decrease the viability of HepG2 liver cancer cells. The growth inhibitory rate of the LNT-L (100 µg/ml) treatment group was 20.7% and the rate of the LNT-H (200 µg/ml) treatment group was 54.8%. Notably, the growth inhibitory rate of the oridonin + LNT-H group was 84.3%. The highest percentage of apoptotic cells was observed in the oridonin + LNT-H group (20 µg/ml oridonin and 200 µg/ml LNT). The percentage of apoptotic cells in the oridonin + LNT-H group was significantly different from the percentage of apoptotic cells in the LNT-H (26.1%) and the LNT-L (16.8%) groups. Treatment with LNT produced an increase in caspase-3, caspase-9, Bcl-2-like protein 4, p53, p21, nuclear factor κB inhibitor-α mRNA and protein expression and a decrease in B-cell lymphoma 2 and nuclear factor-κB expression in HepG2 cells compared with untreated control cells. Treatment with a combination of oridonin and LNT-H induced a further increase in expression with the biggest differences in expression observed between the oridonin + LNT-H group and control. It was observed that treatment with oridonin was able to increase the anticancer effects of LNT in HepG2 cells. Therefore, oridonin may be used to sensitize cells to LNT.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3892/ol.2017.7485DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5774387PMC
February 2018

[Formulation of combined predictive indicators using logistic regression model in predicting sepsis and prognosis].

Zhonghua Wei Zhong Bing Ji Jiu Yi Xue 2017 Feb;29(2):139-144

Department of Emergency and Critical Care Unit, Changzheng Hospital, Second Military Medical University, Shanghai 200003, China. Corresponding author: Lin Zhaofen, Email:

Objective: To explore the method and performance of using multiple indices to diagnose sepsis and to predict the prognosis of severe ill patients.

Methods: Critically ill patients at first admission to intensive care unit (ICU) of Changzheng Hospital, Second Military Medical University, from January 2014 to September 2015 were enrolled if the following conditions were satisfied: (1) patients were 18-75 years old; (2) the length of ICU stay was more than 24 hours; (3) All records of the patients were available. Data of the patients was collected by searching the electronic medical record system. Logistic regression model was formulated to create the new combined predictive indicator and the receiver operating characteristic (ROC) curve for the new predictive indicator was built. The area under the ROC curve (AUC) for both the new indicator and original ones were compared. The optimal cut-off point was obtained where the Youden index reached the maximum value. Diagnostic parameters such as sensitivity, specificity and predictive accuracy were also calculated for comparison. Finally, individual values were substituted into the equation to test the performance in predicting clinical outcomes.

Results: A total of 362 patients (218 males and 144 females) were enrolled in our study and 66 patients died. The average age was (48.3±19.3) years old. (1) For the predictive model only containing categorical covariants [including procalcitonin (PCT), lipopolysaccharide (LPS), infection, white blood cells count (WBC) and fever], increased PCT, increased WBC and fever were demonstrated to be independent risk factors for sepsis in the logistic equation. The AUC for the new combined predictive indicator was higher than that of any other indictor, including PCT, LPS, infection, WBC and fever (0.930 vs. 0.661, 0.503, 0.570, 0.837, 0.800). The optimal cut-off value for the new combined predictive indicator was 0.518. Using the new indicator to diagnose sepsis, the sensitivity, specificity and diagnostic accuracy rate were 78.00%, 93.36% and 87.47%, respectively. One patient was randomly selected, and the clinical data was substituted into the probability equation for prediction. The calculated value was 0.015, which was less than the cut-off value (0.518), indicating that the prognosis was non-sepsis at an accuracy of 87.47%. (2) For the predictive model only containing continuous covariants, the logistic model which combined acute physiology and chronic health evaluation II (APACHE II) score and sequential organ failure assessment (SOFA) score to predict in-hospital death events, both APACHE II score and SOFA score were independent risk factors for death. The AUC for the new predictive indicator was higher than that of APACHE II score and SOFA score (0.834 vs. 0.812, 0.813). The optimal cut-off value for the new combined predictive indicator in predicting in-hospital death events was 0.236, and the corresponding sensitivity, specificity and diagnostic accuracy for the combined predictive indicator were 73.12%, 76.51% and 75.70%, respectively. One patient was randomly selected, and the APACHE II score and SOFA score was substituted into the probability equation for prediction. The calculated value was 0.570, which was higher than the cut-off value (0.236), indicating that the death prognosis at an accuracy of 75.70%.

Conclusions: The combined predictive indicator, which is formulated by logistic regression models, is superior to any single indicator in predicting sepsis or in-hospital death events.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3760/cma.j.issn.2095-4352.2017.02.009DOI Listing
February 2017

miR-206 is an independent prognostic factor and inhibits tumor invasion and migration in colorectal cancer.

Cancer Biomark 2015 ;15(4):391-6

Department of Gastroenterology, 2nd Affiliated Hospital of Jilin University, Changchun, Jilin, China.

microRNAs (miRNAs) are small non-coding RNAs that play important role in a variety of biological processes, and aberrant expression of miRNA is always associated with tumor progression and invasion. However, the role of miR-206 in colorectal cancer (CRC) is still unclear. In this study, the expression of miR-206 in CRC tissue was compared to paired normal adjacent tissue, and results indicate that miRNA-206 levels are significantly lower in CRC tissue compared to control tissue. Kaplan-Meier analysis showed that patients with low miR-206 expression had significantly poorer overall survival. In addition, we found that over-expression of miR-206 can inhibit CRC cell migration and invasion. In conclusion, our results suggest that miR-206 functions as a tumor suppressor by inhibiting CRC migration and invasion. These findings suggest that miR-206 may be useful as a new potential therapeutic target for CRC.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3233/CBM-150489DOI Listing
June 2016

Sub-Ohmic spin-boson model with off-diagonal coupling: ground state properties.

J Chem Phys 2013 Oct;139(16):164103

Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore.

We have carried out analytical and numerical studies of the spin-boson model in the sub-ohmic regime with the influence of both the diagonal and the off-diagonal coupling accounted for, via the Davydov D1 variational ansatz. While a second-order phase transition is known to be exhibited by this model in the presence of diagonal coupling only, we demonstrate the emergence of a discontinuous first order phase transition upon incorporation of the off-diagonal coupling. A plot of the ground state energy versus magnetization highlights the discontinuous nature of the transition between the isotropic (zero magnetization) state and nematic (finite magnetization) phases. We have also calculated the entanglement entropy and a discontinuity found at a critical coupling strength further supports the discontinuous crossover in the spin-boson model in the presence of off-diagonal coupling. It is further revealed via a canonical transformation approach that for the special case of identical exponents for the spectral densities of the diagonal and the off-diagonal coupling, there exists a continuous crossover from a single localized phase to doubly degenerate localized phase with differing magnetizations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4825205DOI Listing
October 2013

Dynamics of the sub-Ohmic spin-boson model: a comparison of three numerical approaches.

Phys Rev E Stat Nonlin Soft Matter Phys 2013 Aug 16;88(2):023303. Epub 2013 Aug 16.

Division of Materials Science, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 and State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China.

Dynamics of the sub-Ohmic spin-boson model is examined using three numerical approaches, namely the Dirac-Frenkel time-dependent variation with the Davydov D(1) ansatz, the adaptive time-dependent density matrix renormalization group method within the representation of orthogonal polynomials, and a perturbative approach based on a unitary transformation. In order to probe the validity regimes of the three approaches, we study the dynamics of a qubit coupled to a bosonic bath with and without a local field. Comparison of the up-state population evolution shows that the three approaches are in agreement in the weak-coupling regime but exhibit marked differences when the coupling strength is large. The Davydov D(1) ansatz and the time-dependent density matrix renormalization group can both be reliably employed in the weak-coupling regime, while the former is also valid in the strong-coupling regime as judged by how faithfully the trial state follows the Schrödinger equation. We further explore the bipartite entanglement dynamics between two qubits coupled with individual bosonic baths which reveals entanglement sudden death and revival.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1103/PhysRevE.88.023303DOI Listing
August 2013

Entanglement dynamics of two qubits coupled individually to Ohmic baths.

J Chem Phys 2013 Jul;139(4):044115

Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore.

Developed originally for the Holstein polaron, the Davydov D1 ansatz is an efficient, yet extremely accurate trial state for time-dependent variation of the spin-boson model [N. Wu, L. Duan, X. Li, and Y. Zhao, J. Chem. Phys. 138, 084111 (2013)]. In this work, the Dirac-Frenkel time-dependent variational procedure utilizing the Davydov D1 ansatz is implemented to study entanglement dynamics of two qubits under the influence of two independent baths. The Ohmic spectral density is used without the Born-Markov approximation or the rotating-wave approximation. In the strong coupling regime finite-time disentanglement is always found to exist, while at the intermediate coupling regime, the entanglement dynamics calculated by Davydov D1 ansatz displays oscillatory behavior in addition to entanglement disappearance and revival.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4816122DOI Listing
July 2013

Delocalized Davydov D1 Ansatz for the Holstein polaron.

J Chem Phys 2013 May;138(17):174116

School of Physics and Materials Science, Anhui University, Heifei 230601, China.

An efficient, yet very accurate trial wave function, constructed from projecting the well-known Davydov D1 Ansatz onto momentum eigenstates, is employed to study the ground state properties of the generalized Holstein Hamiltonian with simultaneous diagonal and off-diagonal coupling. Ground-state energies have been obtained with a precision matching that of the computationally much more demanding density-matrix renormalization group method. The delocalized D1 Ansatz lowers the ground-state energies at the Brillouin zone boundary significantly compared with the Toyozawa and Global-Local Ansätze in the weak coupling regime, while considerable improvement is demonstrated to have been achieved over the entire Brillouin zone in the strong coupling regime. Unique solutions are obtained with the delocalized D1 for different initial conditions when the transfer integral is 20 times the phonon frequency at the zone center, implying the absence of any self-trapping discontinuity. The scaled correlation variance is found to fit satisfactorily well with the predictions of the perturbation theories.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4802961DOI Listing
May 2013

Dynamics of the sub-Ohmic spin-boson model: a time-dependent variational study.

J Chem Phys 2013 Feb;138(8):084111

School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.

The Dirac-Frenkel time-dependent variation is employed to probe the dynamics of the zero temperature sub-Ohmic spin-boson model with strong friction utilizing the Davydov D1 ansatz. It is shown that initial conditions of the phonon bath have considerable influence on the dynamics. Counterintuitively, even in the very strong coupling regime, quantum coherence features still manage to survive under the polarized bath initial condition, while such features are absent under the factorized bath initial condition. In addition, a coherent-incoherent transition is found at a critical coupling strength α ≈ 0.1 for s = 0.25 under the factorized bath initial condition. We quantify how faithfully our ansatz follows the Schrödinger equation, finding that the time-dependent variational approach is robust for strong dissipation and deep sub-Ohmic baths (s ≪ 1).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4792502DOI Listing
February 2013

Polaronic discontinuities induced by off-diagonal coupling.

J Chem Phys 2012 Jul;137(3):034108

Division of Materials Science, Nanyang Technological University, Singapore 639798, Singapore.

In this paper, we study a form of the Holstein molecular crystal model in which the influence of lattice vibrations on the transfers of electronic excitations between neighboring sites (off-diagonal coupling) is taken into account. Using the Toyozawa Ansatz and the Lanczos algorithm, the Holstein Hamiltonian with two types of off-diagonal coupling is studied focusing on a number of analyticity issues in the ground state. For finite-sized lattices and antisymmetric coupling, a sequence of discontinuities are found in the polaron energy dispersion, the size of the ground-state phonon cloud, and the linearized von Neumann entropy used to quantify the quantum entanglement between the exciton and the phonons in the ground state. Such behavior is accompanied by a shift of the ground-state crystal momentum from zero to nonzero values as the coupling strength is increased. In the thermodynamic limit, all discontinuities associated with antisymmetric coupling vanish except the one corresponding to the initial departure of the ground-state wavevector from the Brillouin zone center. For the case of symmetric off-diagonal coupling, a smooth crossover is found to exist in all parameters regimes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1063/1.4733986DOI Listing
July 2012