Study on the Melt Rheological Characterization of Micro-Tube Gas-Assisted Extrusion Based on the Cross-Scale Viscoelastic Model.

In the micro-tube gas-assisted extrusion process, flow theories ignoring cross-scale viscoelastic variations fail to effectively characterize the rheological state of the melt. To investigate the impact of cross-scale viscoelastic variation on the quality of the micro-tube gas-assisted extrusion, a 3D multiphase flow extrusion model incorporating a double gas-assisted layer was developed. Subsequently, we modified the DCPP constitutive equations based on the cross-scale factor model. Both the traditional and gas-assisted extrusions were simulated under macroscale and cross-scale models using the Ansys Polyflow. Finally, using the established gas-assisted extrusion platform, extrusion experiments were conducted. The results indicate that, owing to the reduced melt viscosity under the cross-scale model, the deformation behavior of the melt is more pronounced than in the macroscale model. The cross-scale model's numerical results more closely match the experimental outcomes under the same parameters, thereby confirming the feasibility of the theoretical analysis and numerical simulation. Moreover, the predictive capability of the cross-scale model for the micro-tube gas-assisted extrusion is further validated through numerical and experimental analyses with varying parameters. It is demonstrated that the cross-scale viscoelastic variation is a critical factor that cannot be overlooked in the gas-assisted extrusion.

Complex principal component analysis-based complex-valued fully connected NN equalizer for optical fibre communications.

An increasing number of scholars have proposed many schemes to mitigate the Kerr nonlinearity effect restricting the transmission capacity of optical fibres. In this paper, we proposed a complex principal component analysis-based complex-valued fully connected neural network (P-CFNN) model aided by perturbation theory and demonstrated it experimentally on a dual-polarization 64-quadrature-amplitude modulation coherent optical communication system. What we believe to be a novel complex principal component analysis (CPCA) algorithm applied to complex-valued fully connected neural network (CFNN) is designed to further reduce the computational complexity of the model. Meanwhile, an equivalent real-valued fully connected neural network (RFNN) with the same time complexity as a CFNN is proposed for fair performance comparison. Under all launched optical powers, the performance of the P-CFNN equalizer is the best among all comparison algorithms, and the maximum ΔQ-factor compared to without employing the nonlinear compensation algorithm reaches 3.94 dB. In addition, under the constraint of the same Q-factor, we confirmed that the proposed P-CFNN obtained a 40% reduction in time complexity and a 70% reduction in space complexity compared with the PCA-based RFNN, which also proved the very large application prospect of the P-CFNN equalizer in optical fibre communication systems.

Predictive Value of Fibrin Fibrinogen Degradation Products-to-Potassium Ratio for Poor Functional Outcome in Patients with Aneurysmal Subarachnoid Hemorrhage: A Retrospective Case-Control Study.

BACKGROUND: The relationship of fibrin(ogen) degradation products (FDPs) and potassium with the functional outcomes of patients with aneurysmal subarachnoid hemorrhage (aSAH) is still uncertain. This study aims to evaluate the predictive value of a novel combination biomarker, the FDP-to-potassium ratio (FPR), for poor functional outcomes in patients with aSAH. METHODS: A total of 425 consecutive patients with aSAH at a single center were retrospectively enrolled in our study. An unfavorable outcome was defined as a modified Rankin Scale (mRS) score of 3-6 at 3 months after discharge. Univariate analysis and multivariable logistic regression were performed for baseline information and laboratory parameters recorded at admission. In addition, the receiver operating characteristic curve was plotted, and propensity score matching was performed based on the FPR. RESULTS: On the basis of mRS grade, 301 patients were classified as having favorable outcomes, and 124 patients were assessed as having unfavorable outcomes. FPR levels were significantly correlated with mRS grade (r[Spearman] = 0.410; P < 0.001). Multivariate logistic regression analysis showed that age (odds ratio [OR] 1.043, 95% confidence interval [CI] 1.016-1.071; P = 0.002), white blood cell count (OR 1.150, 95% CI 1.044-1.267; P = 0.005), potassium (OR 0.526, 95% CI 0.291-0.949; P = 0.033), World Federation of Neurosurgical Societies grade (OR 1.276, 95% CI 1.055-1.544; P = 0.012), and FPR (OR 1.219, 95% CI 1.102-1.349; P < 0.001) at admission were independently associated with poor functional outcomes. The DeLong test showed that the area under the receiver operating characteristic curve of FPR was higher than that of age, white blood cell count, potassium, World Federation of Neurosurgical Societies grade, or FDP alone, indicating that FPR had better predictive potential than these other variables. After 1:1 propensity score matching (FPR ≥ 1.45 vs. FPR < 1.45), the rate of poor prognosis was still significantly increased in the high-FPR group (48/121 [39.7%] vs. 16/121 [13.2%], P < 0.001). CONCLUSIONS: Fibrin(ogen) degradation product-to-potassium ratio is an independent predictor of poor outcomes for patients with aSAH and may be a promising tool for clinicians to evaluate patients' functional prognosis.

Ultra-low complexity random forest for optical fiber communications.

In this paper, we present an efficient equalizer based on random forest for channel equalization in optical fiber communication systems. The results are experimentally demonstrated in a 120 Gb/s, 375 km, dual-polarization 64-quadrature magnitude modulation (QAM) optical fiber communication platform. Based on the optimal parameters, we choose a series of deep learning algorithms for comparison. We find that random forest has the same level of equalization performance as deep neural networks as well as lower computational complexity. Moreover, we propose a two-step classification mechanism. We first divide the constellation points into two regions and then use different random forest equalizers to compensate the points in different regions. Based on this strategy, the system complexity and performance can be further reduced and improved. Furthermore, due to the plurality voting mechanism and two-stage classification strategy, the random forest-based equalizer can be applied to actual optical fiber communication systems.

Quaternion Wavelet Transform and a Feedforward Neural Network-Aided Intelligent Distributed Optical Fiber Sensing System.

In this paper, aiming at a large infrastructure structural health monitoring network, a quaternion wavelet transform (QWT) image denoising algorithm is proposed to process original data, and a depth feedforward neural network (FNN) is introduced to extract physical information from the denoised data. A Brillouin optical time domain analysis (BOTDA)-distributed sensor system is established, and a QWT denoising algorithm and a temperature extraction scheme using FNN are demonstrated. The results indicate that when the frequency interval is less than 4 MHz, the temperature error is kept within ±0.11 °C, but is ±0.15 °C at 6 MHz. It takes less than 17 s to extract the temperature distribution from the FNN. Moreover, input vectors for the Brillouin gain spectrum with a frequency interval of no more than 6 MHZ are unified into 200 input elements by linear interpolation. We hope that with the progress in technology and algorithm optimization, the FNN information extraction and QWT denoising technology will play an important role in distributed optical fiber sensor networks for real-time monitoring of large-scale infrastructure.

Study on chest injury and bulletproof vest protection under the combined action of blast wave and fragments.

Using a simulation based method, this paper analysis the damage effect of blast wave and fragments on human body and the protective effect of bulletproof vest. The results show that compared with the single blast shock wave, the chest injury is more serious under the combined action of blast shock wave and fragments. The peak stress of sternum, costal cartilage and rib increases by 334.34%, 170.23% and 39.72%, respectively. The peak stress on the side of the lung decreases by 3.95%, with little change. The peak stress on the front and back of the lung increases by 83.58% and 409.09% respectively. Overall, the lung injury is aggravated. With the addition of the bulletproof vest, the damage caused by fragments is reduced, and the peak stress of the sternum and the costal cartilage decreases by 48.77% and 69.78%, respectively. Due to the interaction of the blast wave with the vest and the chest, the damage caused by blast wave is aggravated. The peak stress of rib increases by 13.55%, and the peak stress of lung front, side and back increases by 1.22%, 6.51% and 3.57%, respectively.

Numerical and Experimental Studies on the Improvement of Gas Chamber Structure during Gas-Assisted Extrusion.

In the gas-assisted extrusion process, the melt inside the die is in a low-viscosity molten state, so the flow field of the gas cushion layer has a great effect on the cross-sectional shape of the micro-tube. Therefore, this study establishes the gas distribution chamber model of the gas-assisted die. Ansys Fluent software was used to simulate the gas flow field of the gas distribution chamber. The effect of the gas chamber structure on the size of the micro-tube was analyzed by the extrusion experiment. The research shows that the velocity unevenness coefficient of the gas outlet of the single gas chamber die is 11.8%, which is higher than that of the double gas chamber die. The use of a double gas chamber die can improve the stability of the gas cushion layer and the wall thickness non-uniformity of the micro-tube, which verifies the simulation results.

Effect of antiplatelet treatment on aneurysmal subarachnoid hemorrhage patients after endovascular treatment: a systematic review with meta-analysis.

Antiplatelet treatment (APT) has been reported to be used in some patients with aneurysmal subarachnoid hemorrhage (aSAH) after endovascular treatment, but there is controversy among different studies regarding its clinical effects. This study intends to conduct a meta-analysis to evaluate the impact of APT on aSAH patients after endovascular treatment. The PubMed, EMBASE, and Cochrane Library databases were systematically searched up to January 2022 for eligible English publications. Quality assessment was conducted for the included studies. Publication bias and heterogeneity were assessed by Egger's test and the I2 statistic, respectively. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated by meta-analysis. Robustness was checked by subgroup and sensitivity analyses. In total, 597 and 522 patients with and without APT, respectively, in 5 retrospective studies were retained for the meta-analysis. Pooled analyses showed that the APT group had a lower mortality (41/499 [8%] versus 56/402 [14%]; OR = 0.533; 95% CI, 0.347-0.820; P = 0.004) and a higher proportion of favorable clinical outcomes (400/532 [75%] versus 266/421 [63%]; OR = 1.801; 95% CI, 1.359-2.414; P = 0.000) than the control group. There was no significant difference in the incidence of hemorrhagic complications (39/564 [7%] versus 26/503 [5%]; OR = 1.386; 95% CI, 0.825-2.329; P = 0.218) between groups. Although the incidence of delayed cerebral ischemia (DCI) was significantly lower in the APT group (65/512 [13%] versus 105/447 [23%]; OR = 0.325; 95% CI, 0.107-0.988; P = 0.048), it showed substantial heterogeneity (I2 = 64.7%). Subsequent sensitivity analysis suggested that the meta-analysis was robust. Subgroup analyses revealed that long-term (> 2 weeks) APT (60/479 [13%] versus 103/428 [24%]; OR = 0.212; 95% CI, 0.056-0.806; P = 0.023) significantly reduced the DCI rate and that different grouping methods in the included studies may be a source of heterogeneity. In the absence of randomized controlled trials, a meta-analysis of retrospective studies suggested that APT was associated with reduced mortality and better functional outcomes in aSAH patients after endovascular treatment without an increased incidence of hemorrhagic complications. Long-term APT was also associated with a decrease in the incidence of DCI. Well-designed randomized controlled trials are warranted and updated meta-analyses are needed to verify our findings.

Study on protective performance and gradient optimization of helmet foam liner under bullet impact.

Protective equipment in war plays a vital role in the safety of soldiers, the threat to soldiers from brain damage caused by deformation at the back of the helmet cannot be ignored, so research on reduce blunt post-cranial injury has great significance and value. This study first conducted gunshot experiments, used rifle bullets impact bulletproof plate and different density liner foam to record the incident process and internal response of craniocerebral model. After verifying the accuracy of finite element model through experimental data, optimization model is established based on response surface method to optimize the structure of gradient foam, analyze the cranial strain and energy absorption to select the best density and thickness distribution of each foam layer. Optimization results show that liner foam which designed to have lower density and thicker thickness for impact and brace layers, higher density and thinner thickness for middle layer can significantly improve the energy absorption efficiency. Compared to the 40.65 J of energy absorption before optimization, the optimized gradient foam can absorb 109.3 J of energy, with a 169% increase in the absorption ratio. The skull strain in the craniocerebral model was reduced from 1.260 × 10-2 to 1.034 × 10-2, with a reduction of about 22%. This study provides references for the design and development of protective equipment and plays an important role in ensuring the safety of soldiers in the battlefield environment.

Effect of Pressure Difference between Inner and Outer Gas Layer on Micro-Tube Deformation during Gas-Assisted Extrusion.

In the process of double-layer gas-assiste extrusion of a plastic micro-tube, the tugging effect caused by the pressure difference of the gas cushion layer inside the die has a great influence on the external dimensions of the micro-tube. Therefore, this study establishes a two-phase extrusion model based on compressible gas and incompressible melt. Ansys Polyflow finite element software was used to numerically simulate the extrusion process of the melt to analyze the effect of the gas cushion layer pressure difference on the micro-tube deformation. The research shows that the shrinkage rate of the micro-tube increases with increasing pressure of the outer cushion layer, and the degree of tube wall migration increases, too. In the process of extrusion, the first normal stress difference at the entrance of the gas cushion layer shows a significant effect on the melt velocity field distribution and the extruded micro-tube cross-sectional deformation.

Experimental Study on Intracranial Pressure and Biomechanical Response in Rats under the Blast Wave.

Explosion overpressure propagates extracranially and causes craniocerebral injury after being transmitted into the brain. Studies on the extent of skull to reduce impact overpressure are still lacking. Therefore, it is necessary to study the relationship between intracranial pressure (ICP) and external field pressure and the situation of craniocerebral injury under the blast wave. Pressure sensor of ϕ 1.2 mm was disposed 3 mm posterior to the bregma of rat skull, and type I biological shock tube (BST-I) was used as the source of injury while a side-on air pressure sensor was installed at the horizontal position of the ICP sensor. Eleven groups of blast experiments with peak air overpressure ranging from 167 kPa to 482 kPa were performed to obtain the variation law of ICP and injury of rats. Data measured by sensors show that the peak pressure formed in the rat brain are lower than the external air overpressure; the differential pressure between the inside and outside of the brain is 27-231 kPa. When side-on air overpressure is ≤363 kPa, ICP is ≤132 kPa, and the hemorrhage area of the rat's brain is <15%, the injury is minor. When side-on air overpressure is 363 kPa-401 kPa, ICP range is from 132 kPa to 248 kPa, hemorrhage area is about 15%-20%, and the injury increases. When side-on air overpressure is 401 kPa-435 kPa, ICP range from 248 kPa to 348 kPa, the hemorrhage area is about 20%-24%, and the injury is serious. When side-on air overpressure ≥482 kPa, the peak ICP surged to 455 kPa and the peak negative ICP reached -84 kPa, the hemorrhage area exceeded 26%. When the external blast wave is weak, skull can absorb the blast wave better, reducing the pressure by 81.4%, when the external shockwave is strong, skull only reduces the pressure by 5.6%, but both can play certain protective role. The fitting curve of air overpressure and ICP can be used to predict the changes of ICP under different external blast overpressure. Analysis of cranial injury showed that the area of cranial hemorrhage with extremely severe injury increased by 107.9% compared with mild injury, increased by 53.3% compared with moderate injury, and increased by 21.6% compared with severe injury. This work may provide references for the dynamic response of biological cranial and brain injury mechanism under the effect of blast wave.

RQC helical hairpin in Bloom's syndrome helicase regulates DNA unwinding by dynamically intercepting nascent nucleotides.

The RecQ family of helicases are important for maintenance of genomic integrity. Although functions of constructive subdomains of this family of helicases have been extensively studied, the helical hairpin (HH) in the RecQ-C-terminal domain (RQC) has been underappreciated and remains poorly understood. Here by using single-molecule fluorescence resonance energy transfer, we found that HH in the human BLM transiently intercepts different numbers of nucleotides when it is unwinding a double-stranded DNA. Single-site mutations in HH that disrupt hydrogen bonds and/or salt bridges between DNA and HH change the DNA binding conformations and the unwinding features significantly. Our results, together with recent clinical tests that correlate single-site mutations in HH of human BLM with the phenotype of cancer-predisposing syndrome or Bloom's syndrome, implicate pivotal roles of HH in BLM's DNA unwinding activity. Similar mechanisms might also apply to other RecQ family helicases, calling for more attention to the RQC helical hairpin.

Postoperative red blood cell distribution width predicts functional outcome in aneurysmal subarachnoid hemorrhage after surgical clipping: A single-center retrospective study.

Objective: Red blood cell (RBC) parameters are associated with outcomes following aneurysmal subarachnoid hemorrhage (aSAH), but their predictive value remains uncertain. This study aimed to detect the association between RBC parameters and functional outcome in aSAH patients undergoing surgical clipping. Methods: This retrospective observational study included aSAH patients who underwent surgical clipping at Affiliated Hospital of North Sichuan Medical College between August 2016 and September 2019. The functional outcome following aSAH was assessed by modified Rankin Scale (mRS), and mRS 3-6 was defined as poor functional outcome. Results: Out of 187 aSAH patients included (62% female, 51-66 years old), 73 patients had poor functional outcome. Multivariate logistic regression of admission parameters showed that World Federation of Neurosurgical Societies (WFNS) grade (odds ratio [95% CI]: 1.322 [1.023-1.707], p = 0.033) and white blood cell (WBC) (odds ratio [95% CI]: 1.136 [1.044-1.236], p = 0.003) were independently associated with poor functional outcome. In postoperative parameters, RBC distribution width (RDW) (odds ratio [95% CI]: 1.411 [1.095-1.818], p = 0.008), mean platelet volume (MPV, odds ratio [95% CI]: 1.253 [1.012-1.552], p = 0.039) and admission WFNS grade (odds ratio [95% CI]: 1.439 [1.119-1.850], p = 0.005) were independently associated with poor functional outcome. The predictive model including WFNS grade, admission WBC, and postoperative RDW and MPV had significantly higher predictive power compared to WFNS grade alone (0.787 [0.722-0.852] vs. 0.707 [0.630-0.784], p = 0.024). The combination of WFNS grade and WBC on admission showed the highest positive predictive value (75.5%) and postoperative RDW and MPV combined with admission WFNS grade and WBC showed the highest negative predictive value (83.7%). Conclusion: Postoperative RDW is independently associated with poor functional outcome in aSAH patients undergoing surgical clipping. A combined model containing postoperative RDW may help predict good outcome in patients with aSAH after timely aneurysm clipping.

Craniocerebral Dynamic Response and Cumulative Effect of Damage Under Repetitive Blast.

Soldiers suffer from multiple explosions in complex battlefield environment resulting in aggravated brain injuries. At present, researches mostly focus on the damage to human body caused by single explosion. In the repetitive impact study, small animals are mainly used for related experiments to study brain nerve damage. No in-depth research has been conducted on the dynamic response and damage of human brain under repetitive explosion shock waves. Therefore, this study use the Euler-Lagrange coupling method to construct an explosion shock wave-head fluid-structure coupling model, and numerically simulated the brain dynamic response subjected to single and repetitive blast waves, obtained flow field pressure, skull stress, skull displacement, intracranial pressure to analyze the brain damage. The simulation results of 100 g equivalent of TNT exploding at 1 m in front of the craniocerebral show that repetitive blast increase skull stress, intracranial pressure, skull displacement, and the damage of brain tissue changes from moderate to severe. Repetitive blasts show a certain cumulative damage effect, the severity of damage caused by double blast is 122.5% of single shock, and the severity of damage caused by triple blast is 105.9% of double blast and 131.5% of single blast. The data above shows that it is necessary to reduce soldiers' exposure from repetitive blast waves.

Study on the Dissolution and Diffusion of Supercritical Carbon Dioxide in Polystyrene Melts Based on Adsorption and Diffusion Mechanism.

In order to reveal the dissolution process, the adsorption kinetics and diffusion theory are combined and used to describe the adsorption-diffusion mechanism. This can not only predict the solubility of supercritical CO2 in polymer melts but also describe two important parameters of supercritical CO2 in the dissolution process: dissolution amount and dissolution rate, which can provide a good theoretical basis for microcellular foaming. To verify the feasibility and accuracy of the theoretical calculation method, an experimental device for the volume-changing method under static condition was established. The results showed that the theoretical calculation value was in good agreement with the experimental value. In addition, the dissolution amount and dissolution rate of supercritical CO2 in three polystyrene melts with different molecular weights under different temperature and pressure conditions were measured. The results showed that the difference of polystyrene molecular weight can cause the change of dissolution rate during the dissolution process, that is, the larger the molecular weight, the slower the dissolution rate.

Mismatch sensing by nucleofilament deciphers mechanism of RecA-mediated homologous recombination.

Recombinases polymerize along single-stranded DNA (ssDNA) at the end of a broken DNA to form a helical nucleofilament with a periodicity of ∼18 bases. The filament catalyzes the search and checking for homologous sequences and promotes strand exchange with a donor duplex during homologous recombination (HR), the mechanism of which has remained mysterious since its discovery. Here, by inserting mismatched segments into donor duplexes and using single-molecule techniques to catch transient intermediates in HR, we found that, even though 3 base pairs (bp) is still the basic unit, both the homology checking and the strand exchange may proceed in multiple steps at a time, resulting in ∼9-bp large steps on average. More interestingly, the strand exchange is blocked remotely by the mismatched segment, terminating at positions ∼9 bp before the match-mismatch joint. The homology checking and the strand exchange are thus separated in space, with the strand exchange lagging behind. Our data suggest that the strand exchange progresses like a traveling wave in which the donor DNA is incorporated successively into the ssDNA-RecA filament to check homology in ∼9-bp steps in the frontier, followed by a hypothetical transitional segment and then the post-strand-exchanged duplex.

Research on Inner Gas Inflation Improvements in Double-layer Gas-assisted Extrusion of Micro-tubes.

Micro-tubes have small diameters and thin wall thicknesses. When using double-layer gas-assisted extrusion (DGAE) technology to process micro-tubes, due to the influence of flow resistance, airflow from the inner gas-assisted layer cannot flow into the atmosphere through the lumen. Over time, it will inflate or even fracture the micro-tubes intermittently and periodically. To solve this problem, a new double-layer micro-tube gas-assisted extrusion die was designed in this study. Its mandrel has an independent airway leading to the lumen of the extrudate, with which the gas flow into the lumen of the extrudate can be regulated by employing forced exhaust. Using the new die, we carried out extrusion experiments and numerical calculations. The results show a significant positive correlation between micro-tube deformation and gas flow rate in the lumen of a micro-tube. Without considering the refrigerant distortion of the microtube, the flow rate of forced exhaust should be set equal to that of the gas from the inner gas-assisted layer flow into the micro-tube lumen. By doing this, the problem of the micro-tube being inflated can be eliminated without causing other problems.

Study on Behind Helmet Blunt Trauma Caused by High-Speed Bullet.

The mechanism of Behind Helmet Blunt Trauma (BHBT) caused by a high-speed bullet is difficult to understand. At present, there is still a lack of corresponding parameters and test methods to evaluate this damage effectively. The purpose of the current study is therefore to investigate the response of the human skull and brain tissue under the loading of a bullet impacting a bullet-proof helmet, with the effects of impact direction, impact speed, and impactor structure being considered. A human brain finite element model which can accurately reconstruct the anatomical structures of the scalp, skull, brain tissue, etc., and can realistically reflect the biomechanical response of the brain under high impact speed was employed in this study. The responses of Back Face Deformation (BFD), brain displacement, skull stress, and dura mater pressure were extracted from simulations as the parameters reflecting BHBT risk, and the relationships between BHBT and bullet-proof equipment structure and performance were also investigated. The simulation results show that the frontal impact of the skull produces the largest amount of BFD, and when the impact directions are from the side, the skull stress is about twice higher than other directions. As the impact velocity increases, BFD, brain displacement, skull stress, and dura mater pressure increase. The brain damage caused by different structural bullet bodies is different under the condition of the same kinetic energy. The skull stress caused by the handgun bullet is the largest. The findings indicate that when a bullet impacts on the bullet-proof helmet, it has a higher probability of causing brain displacement and intracranial high pressure. The research results can provide a reference value for helmet optimization design and antielasticity evaluation and provide the theoretical basis for protection and rescue.

The Formation Mechanism of the Double Gas Layer in Gas-Assisted Extrusion and Its Influence on Plastic Micro-Tube Formation.

The diameter of a micro-tube is very small and its wall thickness is very thin. Thus, when applying double-layer gas-assisted extrusion technology to process a micro-tube, it is necessary to find the suitable inlet gas pressure and a method for forming a stable double gas layer. In this study, a double-layer gas-assisted extrusion experiment is conducted and combined with a numerical simulation made by POLYFLOW to analyze the effect of inlet gas pressure on micro-tube extrusion molding and the rheological properties of the melt under different inlet gas pressures. A method of forming a stable double gas layer is proposed, and its formation mechanism is analyzed. The research shows that when the inlet gas pressure is large, the viscosity on the inner and outer wall surfaces of the melt is very low due to the effects of shear thinning, viscous dissipation, and the compression effect of the melt, so the melt does not easily adhere to the wall surface of the die, and a double gas layer can be formed. When the inlet gas pressure slowly decreases, the effects of shear thinning and viscous dissipation are weakened, but the gas and the melt were constantly displacing each other and reaching a new balanced state and the gas and melt changed rapidly and steadily in the process without sudden changes, so the melt still does not easily adhere to the wall of the die. Thus, in this experiment, we adjusted the inlet gas pressure to 5000 Pa first to ensure that the melt do not adhere to the wall surface and then slowly increased the inlet gas pressure to 10,000 Pa to reduce the viscosity of the melt. Lastly, we slowly decreased the inlet gas pressure to 1000 Pa to form a stable double gas layer. Using this method will not only facilitate the formation of a stable double gas layer, but can also accurately control the diameter of the micro-tube.

Dynamic structural insights into the molecular mechanism of DNA unwinding by the bacteriophage T7 helicase.

The hexametric T7 helicase (gp4) adopts a spiral lock-washer form and encircles a coil-like DNA (tracking) strand with two nucleotides bound to each subunit. However, the chemo-mechanical coupling mechanism in unwinding has yet to be elucidated. Here, we utilized nanotensioner-enhanced Förster resonance energy transfer with one nucleotide precision to investigate gp4-induced unwinding of DNA that contains an abasic lesion. We observed that the DNA unwinding activity of gp4 is hindered but not completely blocked by abasic lesions. Gp4 moves back and forth repeatedly when it encounters an abasic lesion, whereas it steps back only occasionally when it unwinds normal DNA. We further observed that gp4 translocates on the tracking strand in step sizes of one to four nucleotides. We propose that a hypothetical intermediate conformation of the gp4-DNA complex during DNA unwinding can help explain how gp4 molecules pass lesions, providing insights into the unwinding dynamics of gp4.