Unraveling the binding mechanisms of SARS-CoV-2 variants through molecular simulations.

The emergence of SARS-CoV-2 variants like Delta (AY.29) and Omicron (EG.5) poses continued challenges for vaccines and therapeutics. Mutations in the viral spike protein are key in altering infectivity and immune evasion. This study uses computational modeling to investigate the molecular binding mechanisms between spike protein variants and the ACE2 host receptor. Using the MARTNI force field, coarse-grained molecular dynamics (CGMD) simulations and nudged elastic band (NEB) calculations explore spike-ACE2 interactions for the wild type, Delta variant, and Omicron variant. The simulations reveal Omicron has the strongest binding affinity at -128.35 ± 10.91 kcal/mol, followed by Delta and wild type. Key mutations in Delta and Omicron, like Q493R and Q498R, optimize electrostatic contacts, enhancing ACE2 interactions. The wild-type spike has the highest transition state energy barrier at 17.87 kcal/mol, while Delta has the lowest barrier at 9.21 kcal/mol. Despite slightly higher dual barriers, Omicron's increased binding energy lowers its overall barrier to rapidly bind ACE2. These findings provide residue-level insights into mutation effects on SARS-CoV-2 infectivity. The computational modeling elucidates mechanisms underlying spike-ACE2 binding kinetics, aiding the development of vaccines and therapies targeting emerging viral strains.

AI-Driven Design System for Fabrication of Inhalable Nanocatchers for Virus Capture and Neutralization.

The global pandemic presents a critical threat to humanity, with no effective rapid-response solutions for early-stage virus dissemination. This study aims to create an AI-driven entry-blocker design system (AIEB) to fabricate inhalable virus-like nanocatchers (VLNCs) fused with entry-blocking peptides (EBPs) to counter pandemic viruses and explore therapeutic applications. This work focuses on developing angiotensin-converting enzyme 2 (ACE2)-mimic domain-fused VLNCs (ACE2@VLNCs) using AIEB and analyzing their interaction with the SARS-CoV-2 receptor binding domain (RBD), demonstrating their potential to hinder SARS-CoV-2 infection. Aerosol-based tests show ACE2@VLNCs persist over 70 min in the air and neutralize pseudoviruses within 30 min, indicating their utility in reducing airborne virus transmission. In vivo results reveal ACE2@VLNCs mitigate over 67% of SARS-CoV-2 infections. Biosafety studies confirm their safety, causing no damage to eyes, skin, lungs, or trachea, and not eliciting significant immune responses. These findings offer crucial insights into pandemic virus prevention and treatment, highlighting the potential of the ACE2@VLNCs system as a promising strategy against future pandemics.

Myocardial Flow Assessment After Heart Transplantation Using Dynamic Cadmium-Zinc-Telluride Single-Photon Emission Computed Tomography With 201Tl and 99mTc Tracers and Validated by 13N-NH3 Positron Emission Tomography.

BACKGROUND: Cardiac allograft vasculopathy (CAV) is an obliterative and diffuse form of vasculopathy and is the most common cause of long-term cardiovascular mortality in heart transplant patients. This study aimed to investigate the diagnostic performance of 99mTc and 201Tl tracers in the assessment of CAV using cadmium-zinc-telluride (CZT) single-photon emission computed tomography (SPECT) for myocardial blood flow (MBF) and myocardial flow reserve (MFR) quantification, which was further validated using 13 N-NH3 positron emission tomography (PET). METHODS: Thirty-eight patients with prior heart transplantation who underwent CZT SPECT and 13 N-NH3 PET dynamic scans were included in this study. CZT SPECT with 99mTc-sestamibi was used in the first 19 patients and 201Tl-chloride for the remaining patients. To determine the diagnostic accuracy of angiographically defined moderate-to-severe CAV, the analysis included patients who underwent angiographic examinations within 1 year of their second scan. RESULTS: There were no significant differences in the patient characteristics between the 201Tl and 99mTc tracer groups. Both 201Tl and 99mTc CZT SPECT-derived stress MBF and MFR values globally and in 3 coronary territories showed good correlations with 13 N-NH3 PET. The 201Tl and 99mTc cohorts did not differ significantly in the correlation coefficients of CZT SPECT versus PET for MBF and MFR, except for stress MBF (201Tl:0.95 versus 99mTc:0.80, P=0.03). 201Tl and 99mTc CZT SPECT were satisfactory for detecting PET MFR <2.0 (201Tl area under the curve, 0.92 [0.71-0.99], 99mTc area under the curve, 0.87 [0.64-0.97]) and angiographically defined moderate-to-severe CAV, and CZT SPECT results were comparable to that of 13 N-NH3 PET (CZT area under the curve, 0.90 [0.70-0.99], PET area under the curve, 0.86 [0.64-0.97]). CONCLUSIONS: This small study suggests that CZT SPECT using 201Tl and 99mTc tracers showed comparable MBF and MFR, and the results correlated well with those of 13 N-NH3 PET. Hence, CZT SPECT with 201Tl or 99mTc tracers can be used to detect moderate-to-severe CAV in patients with prior heart transplantation. However, validation using larger studies is warranted.

Design single-stranded DNA aptamer of cluster of differentiation 47 protein by stochastic tunnelling-basin hopping-discrete molecular dynamics method.

The formation of the Cluster of Differentiation 47 (CD47, PDB code: 2JJT)/signal regulatory protein α (SIRPα) complex is very important as it protects healthy cells from immune clearance while promoting macrophage phagocytosis for tumour elimination. Although several antibodies have been developed for cancer therapy, new function-blocking aptamers are still under development. This study aims to design the aptamer AptCD47, which can block the formation of the CD47/SIRPα complex. This study employs the MARTINI coarse-grained (CG) force field and the stochastic tunnelling-basin hopping-discrete molecular dynamics (STUN-BH-DMD) method to identify the most stable AptCD47/CD47 complexes. Coarse-grained molecular dynamics (CGMD) simulations were used to obtain root-mean-square deviation (RMSD) and root-mean-square fluctuation (RMSF) analyses. The results demonstrate that the formation of AptCD47/CD47 complexes renders the CD47 structure more stable than the single CD47 molecule in a water environment. The minimum energy pathway (MEP) obtained by the nudged elastic band (NEB) method indicates that the binding processes of 5'-ATTCAATTCC-3' and 5'-AGTGCAATCT-3' to CD47 are barrierless, which is much lower than the binding barrier of SIRPα to CD47 of about 14.23 kcal/mol. Therefore, these two AptCD47/CD47 complexes can create a high spatial binding barrier for SIRPα, preventing the formation of a stable CD47/SIRPα complex. The proposed numerical process with the MARTINI CG force field can be used to design CD47 aptamers that efficiently block SIRPα from binding to CD47.Communicated by Ramaswamy H. Sarma.

Synergistic Functionality of Dopants and Defects in Co-Phthalocyanine/B-CN Z-Scheme Photocatalysts for Promoting Photocatalytic CO2 Reduction Reactions.

The realization of solar-light-driven CO2  reduction reactions (CO2 RR) is essential for the commercial development of renewable energy modules and the reduction of global CO2 emissions. Combining experimental measurements and theoretical calculations, to introduce boron dopants and nitrogen defects in graphitic carbon nitride (g-C3 N4 ), sodium borohydride is simply calcined with the mixture of g-C3 N4 (CN), followed by the introduction of ultrathin Co phthalocyanine through phosphate groups. By strengthening H-bonding interactions, the resultant CoPc/P-BNDCN nanocomposite showed excellent photocatalytic CO2 reduction activity, releasing 197.76 and 130.32 µmol h-1  g-1 CO and CH4 , respectively, and conveying an unprecedented 10-26-time improvement under visible-light irradiation. The substantial tuning is performed towards the conduction and valance band locations by B-dopants and N-defects to modulate the band structure for significantly accelerated CO2 RR. Through the use of ultrathin metal phthalocyanine assemblies that have a lot of single-atom sites, this work demonstrates a sustainable approach for achieving effective photocatalytic CO2 activation. More importantly, the excellent photoactivity is attributed to the fast charge separation via Z-scheme transfer mechanism formed by the universally facile strategy of dimension-matched ultrathin (≈4 nm) metal phthalocyanine-assisted nanocomposites.

Assessment of the Suitability of the Fleischner Society Imaging Guidelines in Evaluating Chest Radiographs of COVID-19 Patients

Background@#The Fleischner Society established consensus guidelines for imaging in patients with coronavirus disease 2019 (COVID-19). We investigated the prevalence of pneumonia and the adverse outcomes by dividing groups according to the symptoms and risk factors of patients and assessed the suitability of the Fleischner society imaging guidelines in evaluating chest radiographs of COVID-19 patients. @*Methods@#From February 2020 to May 2020, 685 patients (204 males, mean 58 ± 17.9 years) who were diagnosed with COVID-19 and hospitalized were included. We divided patients into four groups according to the severity of symptoms and presence of risk factors (age > 65 years and presence of comorbidities). The patient groups were defined as follows: group 1 (asymptomatic patients), group 2 (patients with mild symptoms without risk factors), group 3 (patients with mild symptoms and risk factors), and group 4 (patients with moderate to severe symptoms). According to the Fleischner society, chest imaging is not indicated for groups 1–2 but is indicated for groups 3–4. We compared the prevalence and score of pneumonia on chest radiographs and compare the adverse outcomes (progress to severe pneumonia, intensive care unit admission, and death) between groups. @*Results@#Among the 685 COVID-19 patients, 138 (20.1%), 396 (57.8%), 102 (14.9%), and 49 (7.1%) patients corresponded to groups 1 to 4, respectively. Patients in groups 3–4 were significantly older and showed significantly higher prevalence rates of pneumonia (group 1–4: 37.7%, 51.3%, 71.6%, and 98%, respectively, P < 0.001) than those in groups 1-2. Adverse outcomes were also higher in groups 3–4 than in groups 1–2 (group 1–4: 8.0%, 3.5%, 6.9%, and 51%, respectively, P < 0.001). Patients with adverse outcomes in group 1 were initially asymptomatic but symptoms developed during follow-up. They were older (mean age, 80 years) and most of them had comorbidities (81.8%). Consistently asymptomatic patients had no adverse events. @*Conclusion@#The prevalence of pneumonia and adverse outcomes were different according to the symptoms and risk factors in COVID-19 patients. Therefore, as the Fleischner Society recommended, evaluation and monitoring of COVID-19 pneumonia using chest radiographs is necessary for old symptomatic patients with comorbidities.

Effect of a Patient Blood Management Program on the Appropriateness of Red Blood Cell Transfusion and Clinical Outcomes in Elderly Patients Undergoing Hip Fracture Surgery

Background@#Elderly patients with hip fractures frequently receive perioperative transfusions, which are associated with increased morbidity and mortality. This study aimed to evaluate the impact of a patient blood management (PBM) program on the appropriateness of red blood cell (RBC) transfusion and clinical outcomes in geriatric patients undergoing hip fracture surgery. @*Methods@#In 2018, the revised PBM program was implemented at the Korea University Anam Hospital, Seoul, Republic of Korea. Elderly patients aged ≥ 65 years who underwent hip fracture surgery from 2017 to 2020 were evaluated. Clinical characteristics and outcomes were analyzed according to the timing of PBM implementation (pre-PBM, early-PBM, and late-PBM). Multiveriate regression analysis was used to evaluate the risk factors of the adverse outcomes, such as in-hospital mortality or 30-day readmission. @*Results@#A total of 884 elderly patients were included in this study. The proportion of patients who received perioperative RBC transfusions decreased significantly (43.5%, 40.1%, and 33.2% for pre-PBM, early-PBM, and late-PBM, respectively; P = 0.013). However, the appropriateness of RBC transfusion significantly increased (54.0%, 60.1%, and 94.7%, respectively; P < 0.001). The duration of in-hospital stay and 30-day readmission rates significantly decreased. Multivariable regression analysis revealed that RBC transfusion (odds ratio, 1.815; 95% confidence interval, 1.137–2.899; P = 0.013) was significantly associated with adverse outcomes. @*Conclusion@#Implementing the PBM program increased the appropriateness of RBC transfusion without compromising transfusion quality and clinical outcomes. Therefore, adopting the PBM program may improve the clinical management of elderly patients following hip fracture surgery.

The Novel Hooked Kirschner Wire Technique for Ulna Coronoid Process Fractures

Background@#The aim of this study was to introduce a novel technique to improve the ease of fixing of even small fragments of the coronoid process and report the clinical outcomes of this method. @*Methods@#Forty-nine patients with ulnar coronoid process fractures fixed using the hooked Kirschner wire (K-wire) technique at our hospital from 2007 to 2019 were reviewed. Radiological features and fracture union were assessed using simple radiographs.Functional outcomes of the treated elbows were evaluated at the final follow-up visit using the Mayo Elbow Performance Score (MEPS). @*Results@#All patients were examined at a mean follow-up of 17.7 months (range, 6–62 months). We observed bony union in patients at a mean of 10.9 weeks (range, 6–22 weeks). The mean flexion and extension ranges of the elbow were 132.0° (range, 106° –151°) and 4.5° (range, –20° to 30°), respectively. The mean pronation and supination ranges of the forearm were 81.1° (range, 60°–90°) and 88.3° (range, 60°–120°), respectively. The mean arc of the elbow was 127.4° (range, 78°–160°). All patients were evaluated using the MEPS at the final follow-up visit, with a mean score of 96.9 points (range, 80–100 points). One case of coronoid nonunion was observed and re-fixation was performed. One case of infection was observed and also treated with additional surgery. Three patients complained of ulnar nerve symptoms and 1 patient underwent surgical release for tardy ulnar nerve palsy. @*Conclusions@#Despite its limitations, the hooked K-wire technique was a useful method for even smaller coronoid process fractures. K-wires were also a useful temporary intraoperative fixation method and could provide permanent fixation.

How atoms of polycrystalline Nb20.6Mo21.7Ta15.6W21.1V21.0 refractory high-entropy alloys rearrange during the melting process.

The melting mechanism of single crystal and polycrystalline Nb20.6Mo21.7Ta15.6W21.1V21.0 refractory high entropy alloys (RHEAs) were investigated by the molecular dynamics (MD) simulation using the second-nearest neighbor modified embedded-atom method (2NN MEAM) potential. For the single crystal RHEA, the density profile displays an abrupt drop from 11.25 to 11.00 g/cm3 at temperatures from 2910 to 2940 K, indicating all atoms begin significant local structural rearrangement. For polycrystalline RHEAs, a two-stage melting process is found. In the first melting stage, the melting of the grain boundary (GB) regions firstly occurs at the pre-melting temperature, which is relatively lower than the corresponding system-melting point. At the pre-melting temperature, most GB atoms have enough kinetic energies to leave their equilibrium positions, and then gradually induce the rearrangement of grain atoms close to GB. In the second melting stage at the melting point, most grain atoms have enough kinetic energies to rearrange, resulting in the chemical short-ranged order changes of all pairs.

Design the RNA aptamer of PCA3 long non-coding ribonucleic acid by the coarse-grained molecular mechanics.

The stochastic tunneling-basin hopping-discrete molecular dynamics (STUN-BH-DMD) method was applied to predict the tertiary structure of the prostate cancer marker PCA3 using two respective secondary structures predicted by the Vienna RNA package and Mathews lab package. The RNA CG force field with the geometrical restraints for maintaining PCA3 secondary structures is used. For each secondary structure, 5000 PCA3 structures were predicted by using 5000 independent initial structures. These structures were then evaluated by a scoring function, considering the contributions from the radius of gyration, contact energy, and surface fraction of complementary nucleotides to ASO683 and ASO735 used in the related experiment. For each secondary structure, the PCA3 structures with the highest three scores were selected for aptamer design and further adsorption simulation. The ASOs complementary to PCA3 surface segments possessing relatively higher RMSF values are selected to be the potential PCA3 aptamers. After the adsorption simulation, the adsorption energies of ASO961, ASO3181, ASO3533, and ASO3595 are higher than or comparable to those of ASO683 and ASO735 used in the experiment. The NEB method was used to obtain MEPs for the adsorption process of all predicted ASOs onto PCA3. The adsorption barriers range between 29 ∼ 39 kcal/mol, while the desorption barriers range between 112 ∼ 352 kcal/mol, indicating these aptamer/PCA3 complexes are very stable. Using PCA3 surface segments with relatively higher RMSF values, longer ASOs can be also obtained and most longer ASOs possess lower binding energy, ranging between -486.1 and -618.2 kcal/mol.Communicated by Ramaswamy H. Sarma.

Pericardial Versus Porcine Valves for Surgical Aortic Valve Replacement

Background and Objectives@#There still are controversies on which type between bovine pericardial and porcine valves is superior in the setting of aortic valve replacement (AVR). This study aims to compare clinical outcomes of AVR using between pericardial or porcine valves. @*Methods@#The study involved consecutive 636 patients underwent isolated AVR using stented bioprosthetic valves between January 2000 and May 2016. Of these, pericardial and porcine valves were implanted in 410 (pericardial group) and 226 patients (porcine group), respectively. Clinical outcomes including survival, structural valve deterioration (SVD) and trans-valvular pressure gradient were compared between the groups. To adjust for potential selection bias, inverse probability treatment weighting (IPTW) was conducted. @*Results@#The mean follow-up duration was 60.1±50.2 months. There were no significant differences in the rates of early mortality (3.1% vs. 3.1%; p=0.81) and SVD (0.3%/patient-year [PY] vs. 0.5%/PY; p=0.33) between groups. After adjustment using IPTW, however, landmark mortality analyses showed a significantly lower late (>8 years) mortality risk in pericardial group over porcine group (hazard ratio [HR], 0.61; 95% confidence interval, [CI] 0.41–0.90; p=0.01) while the risks of SVD were not significantly difference between groups (HR, 0.45; 95% CI, 0.12–1.70; p=0.24). Mean pressure gradient across prosthetic AV was lower in the Pericardial group than the Porcine group at both immediate postoperative point and latest follow-up (p values <0.001). @*Conclusions@#In patients undergoing bioprosthetic surgical AVR, bovine pericardial valves showed superior results in terms of postoperative hemodynamic profiles and late survival rates over porcine valves.

Exploring the most stable aptamer/target molecule complex by the stochastic tunnelling-basin hopping-discrete molecular dynamics method.

The stochastic tunnelling-basin hopping-discrete molecular dynamics (STUN-BH-DMD) method was applied to the search for the most stable biomolecular complexes in water by using the MARTINI coarse-grained (CG) model. The epithelial cell adhesion molecule (EpCAM, PDB code: 4MZV) was used as an EpCAM adaptor for an EpA (AptEpA) benchmark target molecule. The effects of two adsorption positions on the EpCAM were analysed, and it is found that the AptEpA adsorption configuration located within the EpCAM pocket-like structure is more stable and the energy barrier is lower due to the interaction with water. By the root mean square deviation (RMSD), the configuration of EpCAM in water is more conservative when the AptEpA binds to EpCAM by attaching to the pocket space of the EpCAM dimer. For AptEpA, the root mean square fluctuation (RMSF) analysis result indicates Nucleobase 1 and Nucleobase 2 display higher flexibility during the CGMD simulation. Finally, from the binding energy contour maps and histogram plots of EpCAM and each AptEpA nucleobase, it is clear that the binding energy adsorbed to the pocket-like structure is more continuous than that energy not adsorbed to the pocket-like structure. This study has proposed a new numerical process for applying the STUN-BH-DMD with the CG model, which can reduce computational details and directly find a more stable AptEpA/EpCAM complex in water.

Treatment of Traumatic Sternoclavicular Joint Anterior Dislocation with a Sternal Fracture / 대한정형외과학회잡지

A traumatic dislocation of the sternoclavicular joint is a rare injury, and among them, anterior dislocation is more common than a posterior dislocation. Posterior dislocation is a potential risk by compressing the mediastinal structures, but an anterior dislocation has not been considered a risk. Traumatic sternoclavicular joint anterior dislocation associated with anterior angulation of a sternal fracture can develop mediastinal compression and have a risk in the same way as a posterior dislocation. This case report is about a traumatic sternoclavicular joint anterior dislocation with a sternal fracture accompanied by mediastinal compression that was treated surgically using a plate and showed relatively good clinical results. This rare case is reported along with a review of the relevant literature.

Effect of Pulmonary Valve Replacement in the Repaired Tetralogy of Fallot Patients with Trans-annular Incision:More than 20 Years of Follow-up

Background and Objectives@#We reviewed the long-term outcomes after tetralogy of Fallot (TOF) repair with trans-annular incision; and evaluated the effectiveness of pulmonary valve replacement (PVR) on outcomes. @*Methods@#This was a retrospective review of clinical outcomes of 180 of 196 TOF patients who underwent total correction with trans-annular incision from 1991 to 1997 (PVR group: 81; non-PVR group: 99). @*Results@#The median age of the patients was 14.0 months (interquartile range [IQR], 10.7–19.8 months) at TOF repair. Ten in-hospital deaths (5.1%) occurred. During the followup, 81 patients underwent PVR at the median age of 13.5 years (IQR, 11.2–17.1 years). The patients in PVR group showed better outcomes than non-PVR group in overall survival rate (100% in PVR vs. 88.7% in non-PVR, p=0.007), in all adverse events (arrhythmia, neurologic complications, 95.5% in PVR vs. 74.6% in non-PVR, p=0.024) at 20 years. Age at TOF repair younger than 1 year (hazard ratio [HR], 2.265; p=0.01) and previous shunt history (HR, 2.195; p=0.008) were predictive for requiring PVR. During follow-up, 10 late deaths (5 sudden deaths) occurred in the non-PVR group, mainly due to ventricular arrhythmia and right ventricular failure; there was 1 late death (not a sudden death) in the PVR group. @*Conclusions@#Long-term survival after repair of TOF with trans-annular incision were acceptable. However, arrhythmias were frequently observed during 20 years of follow-up. The patient age <1 year at the time of TOF repair and shunt implantation prior to TOF repair were predictive factors for requiring PVR.

Effect of Pulmonary Valve Replacement in the Repaired Tetralogy of Fallot Patients with Trans-annular Incision:More than 20 Years of Follow-up

Background and Objectives@#We reviewed the long-term outcomes after tetralogy of Fallot (TOF) repair with trans-annular incision; and evaluated the effectiveness of pulmonary valve replacement (PVR) on outcomes. @*Methods@#This was a retrospective review of clinical outcomes of 180 of 196 TOF patients who underwent total correction with trans-annular incision from 1991 to 1997 (PVR group: 81; non-PVR group: 99). @*Results@#The median age of the patients was 14.0 months (interquartile range [IQR], 10.7–19.8 months) at TOF repair. Ten in-hospital deaths (5.1%) occurred. During the followup, 81 patients underwent PVR at the median age of 13.5 years (IQR, 11.2–17.1 years). The patients in PVR group showed better outcomes than non-PVR group in overall survival rate (100% in PVR vs. 88.7% in non-PVR, p=0.007), in all adverse events (arrhythmia, neurologic complications, 95.5% in PVR vs. 74.6% in non-PVR, p=0.024) at 20 years. Age at TOF repair younger than 1 year (hazard ratio [HR], 2.265; p=0.01) and previous shunt history (HR, 2.195; p=0.008) were predictive for requiring PVR. During follow-up, 10 late deaths (5 sudden deaths) occurred in the non-PVR group, mainly due to ventricular arrhythmia and right ventricular failure; there was 1 late death (not a sudden death) in the PVR group. @*Conclusions@#Long-term survival after repair of TOF with trans-annular incision were acceptable. However, arrhythmias were frequently observed during 20 years of follow-up. The patient age <1 year at the time of TOF repair and shunt implantation prior to TOF repair were predictive factors for requiring PVR.

Improvement of Model Predictive Current Control Sensing Strategy for a Developed Small Flux-Switching Permanent Magnet Motor.

This paper presents an improved control system for a small flux-switching permanent magnet motor (FSPM) to enhance its performance and torque sensing. The analytical magnetic circuit design was used to determine the related motor parameters, such as the air gap flux density, permeance coefficient (Pc), torque, winding turns, pole number, width, length, magnet geometry, and the current density of FSPM. The electromagnetic analysis of this motor was performed by software (ANSYS Maxwell) to optimize the motor performance. In this study, the performance of FSPM was investigated by the uniform design experimentation (UDE). For the control system, the model predictive current control (MPCC) is currently recognized as a high-performance control strategy, due to its quick response and simple principle. This model contained the nonlinear part of the system, to improve the torque ripple of FSPM. A modified MPCC strategy was proposed to improve the distortion of the current waveform and decrease the computational burden. The new modified control architecture was mainly composed of three parts, such as the estimation of electromotive force (EMF), current prediction, and optimal vector selection/vector duration. When the reference voltage vector was obtained, the three-phase duties were easily determined by the principle of space vector modulation (SVM). The results show the different strategy methods between the newly proposed modified MPCC and traditional proportional integral (PI) controller. In the control of FSPM, a modified MPCC strategy was able to achieve a better performance response and decrease the computational burden. At a low speed of 350 rpm, the proposed modified MPCC can achieve a better dynamic response. The nonlinear problem of the startup speed was also effectively resolved. The torque sensing performance of the simulation and the experimental test value were compared. The torque sensing performance of the simulation and the actual test value were also examined. In this study, the optimization focused not only on the motor design and fabrication, but also on an improved motor control strategy and torque sensing, in order to achieve the integrity of the FSPM system.

The Mechanical Behaviors of Polyethylene/Silver Nanoparticle Composites: an Insight from Molecular Dynamics study.

This research uses molecular dynamics simulation (MD) to study the mechanical properties of pristine polyethylene (PE) and its composites which include silver nanoparticles (PE/AgNPs) at two AgNP weight fractions of 1.05 wt% and 3.10 wt%. The stress-strain distribution of the tensile process shows that the embedded AgNPs can significantly improve the Young's modulus and tensile strength of the pristine PE, due to improvements in the local density and strength of the PE near the AgNP surface in the range of 12 Å. Regarding the effect of temperature on the mechanical properties of pristine PE and PE/AgNP composites, the Young's modulus and the strength of the pristine PE and PE/AgNP composites decreased significantly at 350 K and 450 K, respectively, consistent with predicted melting temperature of pristine PE, which lies at around 360 K. At such temperatures as these, PE material has stronger ductility and a higher mobility of AgNPs in the PE matrix than those at 300 K. With the increase of tensile strain, AgNPs tend to be close, and the fracture of PE leads to a similarity between both the Young's modulus and ultimate strength found for the pristine PE and those found for the PE/AgNP composites at 350 K and 450 K, respectively.

Effects of Strontium incorporation to Mg-Zn-Ca biodegradable bulk metallic glass investigated by molecular dynamics simulation and density functional theory calculation.

Molecular dynamics (MD) simulation and density functional theory (DFT) calculations were used to predict the material properties and explore the improvement on the surface corrosion resistance for the Mg66Zn30Ca3Sr1 bulk metallic glass (BMG). The Mg66Zn30Ca4 BMG was also investigated to realize the influence of the addition of Sr element on the material behaviors of Mg66Zn30Ca4. The Mg-Zn-Ca-Sr parameters of the next nearest-neighbor modified embedded atom method (2NN MEAM) potential were first determined by the guaranteed convergence particle swarm optimization (GCPSO) method based on the reference data from the density functional theory (DFT) calculation. Besides, using the 2NN MEAM parameters of the Mg-Zn-Ca-Sr system, the structures of Mg66Zn30Ca4 and Mg66Zn30Ca3Sr1 were predicted by the simulated-annealing basin-hopping (SABH) method. The local atomic arrangements of the predicted BMG structures are almost the same as those measured in some related experiments from a comparison with the calculated and experimental X-ray diffraction (XRD) profiles. Furthermore, the HA index analysis shows that the fractions of icosahedra-like local structures are about 72.20% and 72.73% for Mg66Zn30Ca4 and Mg66Zn30Ca3Sr1, respectively, indicating that these two BMG structures are entirely amorphous. The uniaxial tensile MD simulation was conducted to obtain the stress-strain relationship as well as the related mechanical properties of Mg66Zn30Ca4 and Mg66Zn30Ca3Sr1. Consequently, the predicted Young's moduli of both BMGs are about 46.4 GPa, which are very close to the experimental values of 48.8 ± 0.2 and 49.1 ± 0.1 GPa for Mg66Zn30Ca4 and Mg66Zn30Ca3Sr1, respectively. However, the predicted strengths of Mg66Zn30Ca4 and Mg66Zn30Ca3Sr1 are about 850 and 900 MPa, both are slightly higher than the measured experimental values about 747 ± 22 and 848 ± 21 MPa for Mg66Zn30Ca4 and Mg66Zn30Ca3Sr1. Regarding the thermal properties, the predicted melting temperature of Mg66Zn30Ca3Sr1 by the square displacement (SD) profile is about 620 K, which is very close to the experimental melting temperature of about 613 K. The self-diffusion coefficients of Mg, Zn, Ca, and Sr elements were also calculated for temperatures near their melting points by means of the Einstein equation. The methodology can determine the diffusion barriers for different elements by utilizing these diffusion coefficients resulting in a fact that the diffusion barriers of Ca and Sr elements of Mg66Zn30Ca3Sr1 are relatively high. For the electronic properties predicted by the DFT calculation, the projected density of states (PDOS) profiles of surface Mg, Zn, Ca, and Sr elements clearly show that the addition of Sr into Mg66Zn30Ca4 effectively reduces the s and p orbital states of surface Mg and Zn elements near the Fermi level, particularly the p orbits, which suppresses the electron transfer as well as increases the surface corrosion resistance of Mg66Zn30Ca4. Consequently, this study has provided excellent 2NN MEAM parameters for the Mg, Zn, Ca, and Sr system by the GCPSO method to predict real BMG structures as well as by means of the DFT calculation to explore the electronic properties. Eventually, through our developed numerical processes the material properties of BMGs with different compositions can be predicted accurately for the new BMG design.

Peptide Capping Agent Design for Gold (111) Facet by Molecular Simulation and Experimental Approaches.

The stochastic tunneling-basin hopping method (STUN-BH) was utilized to obtain the most stable peptide S7 configuration (Ac-Ser-Ser-Phe-Pro-Gln-Pro-Asn-CONH2) adsorbed on Au(111) facet. After the most stable S7 configuration was found, molecular dynamics (MD) simulation was conducted to investigate the thermal stability between S7 and Au facet at 300 K in both vacuum and water environment. Moreover, further design sets of peptide sequences on Au(111) facet were used to compare with S7. All molecular simulations were carried out by the large-scale atomic/molecular massively parallel simulator (LAMMPS). The Amber99sb-ILDN force field was employed for modeling the interatomic interaction of peptides, and the TIP3P water was used for the water environment. The CHARMM-METAL force field was introduced to model the S7, PF8 (Ac-Pro-Phe-Ser-Pro-Phe-Ser-Pro-Phe-CONH2) and FS8 (Ac-Phe-Ser-Phe-Ser-Phe-Ser-Phe-Ser-CONH2) interactions with Au(111). The MD simulation results demonstrate that the morphology of Pro affects the adsorption stability of Phe. Therefore, we designed two sequences, PF8 and FS8, to confirm our simulation result through experiment. The present study also develops a novel low-temperature plasma synthesis method to evaluate the facet selecting performance of the designed peptide sequences of S7, PF8, and FS8. The experimental results suggest that the reduced Au atom seed is captured with the designed peptide sequences and slowing growing under room temperature for 72 hours. The experimental results are in the excellent agreement with the simulation finding that the Pro in the designed peptide sequences plays a critical role in the facet selection for Au atom stacking.

Observing the three-dimensional terephthalic acid supramolecular growth mechanism on a stearic acid buffer layer by molecular simulation methods.

The terephthalic acid (TPA) supramolecular growth mechanisms on the stearic acid (STA) buffer layer, such as the phase separation and layer-by-layer (LBL) mechanisms, were considered by molecular simulations. The electrostatic surface potential (ESP) charges obtained by the semi-empirical ab initio package VAMP with PM6 were used with the Dreiding force field. The stochastic tunneling-basin hopping-discrete molecular dynamics method (STUN-BH-DMD) was first used to construct the most stable STA buffer layers (STA100, STA120, and STA140) on graphene. At STA100 and STA120, the STA molecule stacking along their long axis is the major mechanism to obtain the stable STA buffer layer. At STA140, the hydrogen bond network between the terminal COOH groups of STA molecules makes the STA buffer layer the most stable, leading to a higher disintegration temperature among all STA coverages. In the early growth of the TPA supramolecule, TPA molecules were first adsorbed by the holes between STA piles. At STA100 and STA120, the subsequent TPA molecules were adsorbed by the TPA molecules within the holes, leading to the phase separation growth. At STA140, the TPA supramolecule tends to grow by the LBL mechanism.