Abrupt Contraction Research Articles

Lower limb acute onset muscle pain: what do we have to look for? A case of isolated rupture of the rectus femoris.

Acute muscle pain is muscle soreness that occurs during or within 24 hours of strenuous activity. Possible causes of acute muscle pain include localized muscle trauma, muscle tear, contusion with acute hemorrhage, or acute compartment syndrome. Isolated ruptures of the rectus femoris muscle are rare clinical conditions that result from excessive muscle strain following an abrupt contraction, incorrect movement, or sudden snap that exceeds the physiological limit of strain that the muscle can withstand. To date, there are few published reports evaluating the results of non-invasive treatment of such injuries. Herein, we report an unusual case of isolated distal rectus femoris tear in a 46-year-old female patient with no risk factors, who initially presented with extensor muscle weakness and pain and was treated conservatively with functional rest, physiotherapy, and cryotherapy.

Molecular dynamics simulation of slit rheometer for predicting shear thinning of short polyethylene chains

Understanding the molecular basis of rheological properties is crucial from both experimental and theoretical perspectives. Slit rheometry is commonly employed to measure the viscosity of fluids. This study utilized molecular dynamics simulations to investigate isothermal contraction flow at the nanoscale. Short linear polyethylene chains were uniformly extruded by a constant-speed piston from a reservoir through an abrupt contraction slit into the surrounding vacuum. Overall, die swelling and die wetting phenomena were observed. Molecular chains were stretched within the slit, while those outside the slit shrunk. Notably, the velocity profile within the slit varied with wall slip at different extrusion velocities. The relationship between the apparent shear viscosity and shear rate exhibited two primary characteristics: the first-Newtonian plateau and the shear thinning slope. Therefore, this molecular simulation method effectively demonstrates the general non-Newtonian behavior of macroscopic polymer fluids.

On more insightful dimensionless numbers for computational viscoelastic rheology

Abrupt contraction flows involving viscoelastic fluids represent a longstanding computational challenge within the field of non-Newtonian fluid mechanics. Despite the apparent simplicity of the geometry, these flows have given rise to intricate discussions in the study of viscoelastic phenomena. This study aims to re-examine the numerical solutions for flows through abrupt contractions, offering a fresh interpretation through the lens of reformulated dimensionless numbers. These numbers are designed to consider the characteristic shear rate of the problem, providing a more comprehensive understanding of the underlying dynamics.When investigating models with intermediate levels of complexity, such as the Giesekus and Phan-Thien-Tanner constitutive equations, the usual comparison with the corresponding Oldroyd-B model becomes inadequate because it tends to rely on the nominal relaxation time (λ) and the nominal total viscosity (η) instead of their effective counterparts when defining the Reynolds number (Re), the Weissenberg number (Wi) and the ratio of solvent to total viscosities (β) (β plays a role only in rheological models involving a solvent contribution). If these dimensionless numbers are tailored to account for the characteristic shear rate specific to the problem under investigation, the choice of the corresponding Oldroyd-B flow, at the adequate values of Re, Wi, and β allows for significantly better quantification of the correct effects of nonlinear viscoelasticity of the original model.We show the conventional approach tends to overemphasize the role of the nonlinear parameter in nonlinear constitutive equations, like the Giesekus and PTT models, when examining standard abrupt contraction flow outputs such as the Couette correction and vortex size. This overestimation occurs because the conventional method does not allow the Reynolds and Weissenberg numbers (and possibly β) to carry the portion of the nonlinear effect that can potentially be captured by the linear Oldroyd-B model through the use of characteristic shear rate-based values. We believe the present approach provides a better perspective of the role played by the nonlinear parameter and its extension to more general flows is also discussed.

Memory and scission effects of polymers on the flow regime of polyethylene oxide solutions in continuous abrupt contraction–expansion microchannels with different cavity lengths

This study experimentally observes the flow regimes of polyethylene oxide solutions in continuous, abrupt contraction–expansion microchannels. In dilute solutions (0.5 × 10−3–1.5 × 10−3 wt. %), the effects of flow rate, concentration, and cavity length on flow characteristics in the contraction and expansion parts of each cavity are analyzed, including quantified calculations of normalized vortex lengths and extension rates. The results indicate that polymer memory and scission affect the flow transitions. Memory effects enhance vortex growth and scission weakens flow, and these effects occur continuously within the channel. Increased flow rates and cavity lengths intensify polymer scission, accelerating the transitions from elastic instability to corner vortex, lip vortex, and then to steady vortex-free flows in the contraction parts and from steady vortex-free flows to lip and corner vortices in the expansion parts. The flow-regime transitions for concentrations from 0.01 to 0.4 wt. % for dilute and unentangled semi-dilute solutions at various flow rates are summarized in the Reynolds and Weissenberg number spaces. Polymer chains tend to become entangled in higher-concentration solutions, rendering the solution rigid and inducing complex flow regimes.

Chemical modification of nickel-rich layered cathode materials to improve battery life

Mechanical integrity issues of Ni-rich cathode materials are major bottlenecks for their commercial application, stemming from the abrupt anisotropic lattice contraction during H2 ↔ H3 phase transitions. Herein, zirconium is used to modify LiNi0.9Co0.05Mn0.05O2 to solve the mechanical integrity issues. The relationship between the mechanical integrity issues and electrochemical performance is systematically examined to gain insights into the Zr activity-governing mechanisms. Results find that the addition of zirconium not only improves the diffusion ability of lithium ions by providing a rapid channel for diffusion of lithium ions, but also enhances mechanical properties by inhibiting cation mixing. As a result, the optimal LiNi0.9Co0.05Mn0.05O2 achieves superiority capacity retention of 84.12 % after 200 cycles at 5C, higher than that of unmodified LiNi0.9Co0.05Mn0.05O2 74.32 %. This work deeply investigates the information on the bulk structure and interaction mechanism between substitution cations and Ni-rich layered oxides, which provides a new insight to design and construct of advanced high-capacity cathode materials.

Some experimental results for converging flow of dilute polymer solution

This paper presents the results of experimental studies of the flow of a dilute polymer solution in a converging pipe. Three geometries with restriction rates are considered: 2.41, 3.92, and 5.65. A water–glycerin solution of 0.1% polyacrylamide was used as a working fluid. Point velocity measurements are made by using the smoke image velocimetry technique, which previously was proved by the construction of velocity profiles corresponding to the laminar viscoelastic flow in a straight pipe. The influence of the Weissenberg number and the restriction rate of the channel on the velocity profiles are established for both transverse and longitudinal directions. For small Weissenberg numbers, the experimental results are compared with the numerical results obtained using the Giesekus and exponential form of Phan-Thien–Tanner rheological models. Three flow regimes are identified: flow without vortex, vortex enhancement, and divergent flow, which is consistent with published results on the abrupt contraction and converging flows. Vortex length for a wide range of Weissenberg numbers is well predicted by a logarithm function. Modified expression of stretch rate with location of detachment plane can predict the flow regimes and the onset of unsteady flow in converging channels.

Effects of Stepped Chute Slope and Slit Location on a Jet from Abrupt Contraction Aerator

Effects of Stepped Chute Slope and Slit Location on a Jet from Abrupt Contraction Aerator

Simulation of the effect of pulsatile flow on flow features dynamics during abrupt contraction into two parallel rectangular jets

The analysis of the converging region of two parallel jets under unsteady flow conditions is important in its design and safety. Numerical simulation was used to investigate the flow features before the contraction plane. Pulsatile flows with a fixed flow period of 5 s, mean flow velocities between 0.033–0.045 m/s, and flow amplitudes of 0.2–0.4 were simulated in this study. The changes at the contraction were characterized by repeated changes in the velocity profile, recirculation area, and corner vortices. The velocity profile in the contraction region remains axisymmetric throughout the cycle of pulsation. The corner vortices increased with a decrease in the mean velocity when the vortex length was longer than the length from the corner to the stagnation point but began to reduce when the mean velocity started increasing in the pulsation cycle. The results provide more explanation of flow feature characteristics at channel corners and abrupt contraction planes.

The effect of pipeline sudden contraction structure on the deflagration characteristics of hydrogen-methane-air

Based on the visualized gas cloud explosion pipeline test platform, the influence of the sudden contraction structure on the deflagration characteristics of the hydrogen-methane-air gas cloud is investigated. The results show that the changes of flame propagation velocity, explosion overpressure, and flame temperature after deflagration of the premixed gas cloud all present three stages: rapid increase, rapid decline, and secondary acceleration caused by the sudden contraction of pipeline structure. The equivalence ratio significantly affects the hydrogen-methane-air detonation process in the sudden contraction of the pipe structure. As the hydrogen content increases, the flame propagation becomes faster and the explosion impact becomes greater. The formation of “Tulip” flame is closely related to the flame propagation speed. During the process of flame propagation, inertia dominates, causing the flame propagation speed to reach its first peak at the abrupt contraction structure.

Effect of ground tire rubber media's viscoelasticity and flow passage geometry on the abrasive flow finishing of helical gear

This work aims to elucidate the behavior of viscoelastic ground tire rubber media (GTRM) under abrupt contraction and expansion of the media at the entry and exit of the gear flow channel and its influence on polishing results. Due to the inherent nature of the abrasive flow finishing (AFF) process, the media flow converges at the entrance of the gear tooth as it flows from a larger fixture cross-section to a narrower volumetric space between gear teeth. The material removal and subsequent surface roughness rely heavily on the flow's pressure and velocity. A numerical simulation was performed to obtain the pressure and velocity along the gear flank face width (FFW). To investigate the effect of variation in the media deformation rate along the gear flow channel on AFF results, the material removal height and improvement in average surface roughness at different locations along the tooth flank face width were measured. AFF results reveal that the material removal near the two edges of the gear tooth is higher and has an inferior surface finish compared to the tooth's center. Due to the abrupt compression of the media at the flow channel entrance, the media act elastically dominant, resulting in high pressure and flow velocity near the tooth edge (flow channel's entry). Additionally, the effect of the helix angle on the AFF of various helical gear (HG) was investigated. Among the three HGs chosen, the 30° HG produces the lowest surface roughness under moderate pressure and high velocity. The microhardness and fretting wear analyses further confirm that the AFF polishing increases the microhardness and wear resistance of the gear tooth surface as a result of work hardening and minimizing surface defects.

Effect of Covid-19 on Eye Banks and Corneal Transplantations: Current Perspectives.

The coronavirus disease 2019 (COVID-19) pandemic exerted a great impact on medical practice, which was reframed according to the actual needs. Ophthalmological services and procedures including corneal transplantation did not represent an exception. The adoption and implementation of new standard operating procedures as well as of new technologies for remote consultation and smart-working reshaped daily activities of both eye bankers, physicians, researchers, and patients. Regulatory restrictions were issued redefining corneal donor eligibility criteria, as well as handling and harvesting procedures of donor ocular tissues. Surgical schedules underwent an abrupt contraction with prioritization of urgent procedures. Local lockdowns and confinement strategies resulted in both a reduction and redirection of research activities. The evaluation of SARS-CoV-2 colonization of ocular tissues, long-term corneal storage techniques, new disinfection strategies, split corneal transplants and cell-based therapies for the treatment of corneal disease peaked in the pipeline. Aim of this article is to summarizes the overall impact of the pandemic on the corneal transplantation machinery, and the current and future perspectives for the corneal transplant community.

Abrupt Contraction of the Indo‐East Asian Monsoons Ended the Holocene Humid Period

AbstractRain‐belt migration, and in particular monsoon migration, are a cardinal, yet under‐constrained aspect of climate change. Here, we present a new lake‐level record from a closed‐basin lake in northern China and a compilation of available lake level records from closed‐basin lakes located at the northern margins of East Asian and Indian monsoon regions. These data show that ca. 6 ka ago, changes in water availability, as recorded by the surface areas of the closed‐basin lakes, shrunk dramatically, within a few decades, and have not been restored to their pre‐6 ka sizes since. These data imply that the Indo‐East Asian monsoon systems underwent a large coeval southward contraction, which preceded the gradual decline in insolation forcing, and abruptly ended the Holocene Humid Period (HHP). This new compilation enables to constrain potential feedback mechanisms involved in the early termination of the HHP at the monsoon fringes.

How Do I Find Clues About Where Myoclonus Is Originating?

Myoclonus is defined as a brief and jerky shock‐like involuntary movement caused by abrupt muscle contraction or sudden cessation of ongoing muscular activity. Myoclonus can be generated by abnormal activity in different parts of the nervous system, both peripheral and central, including cortical and subcortical structures. According to the presumed neural generator, myoclonus is classified as cortical, subcortical (including myoclonus‐dystonia and brainstem/reticular myoclonus), spinal (including segmental spinal and propriospinal myoclonus), and peripheral. The identification of myoclonus subtypes, and therefore its potential source, is clinically important because it can guide diagnosis and treatment. In this video lecture (Video), we reviewed how to determine myoclonus origin. We first reviewed the clinical features typical of each myoclonus subtype. We, then, explored the electrophysiological techniques that can aid in the differential diagnosis of myoclonus, based on its origin. In conclusion, we provided a clinical and electrophysiological overview on how to find clues about neural generators of myoclonus.

3D simulation of the hierarchical multi-mode molecular stress function constitutive model in an abrupt contraction flow

• First simulation of the hierarchical multi-mode molecular stress function model. • The model is compared to experiment for a 3D contraction flow of Lupolen LDPE. • Striking agreement shown for vortex opening angles over a large range of flow rates. • Simulated and experimental birefringence show very good correspondence. • Variation of apparent stress optical coefficient with flow rate shown to be low. A recent development of the Molecular Stress Function constitutive model, the Hierarchical Multi-Mode Molecular Stress Function (HMMSF) model has been shown to fit a large range of rheometrical data with accuracy, for a large range of polymer melts. We develop a 3D simulation of the HMMSF model and compare it to experimental data for the flow of Lupolen 1840H LDPE through an abrupt 3D contraction flow. We believe this to be the first finite element implementation of the HMMSF model. It is shown that the model gives a striking agreement with experimental vortex opening angles, with very good agreement to full-field birefringence measurements, over a wide range of flow rates. A method to give fully-developed inlet boundary conditions is implemented (in place of using parabolic inlet boundary conditions), which gives a significantly improved match to birefringence measurements in the inlet area, and in low stress areas downstream from the inlet. Alternative constitutive model parameters are assessed following the principle that extensional rheometer data actually provides a ‘lower bound’ for peak extensional viscosity. It is shown that the model robustly maintains an accurate fit to vortex opening angle and full-field birefringence data, provided that both adjustable parameters are kept such that both shear and extensional data are well fitted.

Viscoplastic corner eddies

When viscous fluid in a corner is disturbed, eddies can form in the absence of inertia. Examples of flow configurations in which this motion occurs include flow through an abrupt contraction and over a cavity. Six decades ago, Moffatt (J. Fluid Mech., vol. 18, 1964, pp. 1–18) calculated the slow viscous flow of Newtonian fluids in sharp corners, detailing his eponymous ‘Moffatt eddies’. In this study we examine corner flows of viscoplastic materials, a class of non-Newtonian fluids which exhibit solid-like behaviour for stresses below a yield stress. Specifically, we consider a Bingham fluid, for which the material is perfectly rigid at stresses below the yield stress. While a static unyielded plug forms at the tip of the corner, eddies analogous to those found by Moffatt can also form. We examine these viscoplastic eddies numerically, by computing finite element solutions using the augmented-Lagrangian method, and analytically, by employing a viscoplastic boundary layer formulation and scaling arguments. We measure the depth of the static plug as a function of the Bingham number (dimensionless yield stress), show that the process of a new eddy forming as the Bingham number is decreased is driven by the pressure in the yielded fluid adjacent to the static plug, and provide a heuristic argument for the critical Bingham number at which this occurs.

Study of propofol for control of nausea and vomiting during caesarian delivery under spinal anaesthesia

Introduction: The incidence of nausea-vomiting during and immediately after caesarean delivery with spinal anesthesia is common occurrence and annoying problems to all concerned. The abrupt diaphragmatic contractions, present in emesis are uncomfortable to the patient and may cause protrusion of the abdominal viscera, rendering surgery more difficult and increasing the risk of visceral injuries. If the stomach is full, aspiration is an additional hazard. Therefore, it seems to be advisable to prevent it during spinal anesthesia for caesarean section. Aim & Objective: To assess the magnitude of intraoperative and post operative nausea, retching and vomiting in parturients, Evaluate the efficacy of propofol at subhypnotic doses for reducing emetic episodes in parturients. Observation: The result of study indicates the incidence of intraoperative emetic episodes in caesarean delivery is very high. In the study 6% of patients in propofol group experienced intra-operative vomiting, while in placebo group it was 30%(p=0.004). Conclusion: Propofol at 1mg/kg/hr infusion, administered immediately after clamping the umbilical cord, significantly decreased the incidence and severity of nausea, retching and vomiting and the need for rescue antiemetic therapy compared with placebo.

Deformation Behavior of Droplets When Flowing in a Channel with an Abrupt Contraction

Deformation Behavior of Droplets When Flowing in a Channel with an Abrupt Contraction

Mechanical scission of a flexible polymer (polyethylene oxide) under highly turbulent flows through abrupt contractions

We analyze the polymer scission of a flexible polymer (polyethylene oxide) in a turbulent flow in pipelines, including abrupt contractions. The role played by these local occurrences is studied for an extensive range of concentrations and molecular weight over time (passes through our system). We pointed that the final value of the drag reduction parameter (DR) is independent of the initial value of molecular weight. This behavior is different for flows in straight tubes in the absence of local occurrences. We propose a model for DR as a function of concentration, molecular weight, contraction rate, and the number of passes through the system. We also showed that the fall of DR is linearly dependent on the molecular weight decrease.

Flow-induced structure change of rod-like micellar solutions in an abrupt contraction and expansion flow

Owing to investigation of generation for flow-induced structure (FIS) of micellar solutions in an abrupt contraction and expansion flow, we observed the FIS of a rod-like micellar solution passing through a rectangular channel with a symmetric or asymmetric slit. Furthermore, liquid-temperature was changed as experimental conditions (relatively high-, room-, and low-temperature). For relatively high-temperature, a weak FIS exhibited in a symmetric slit-flow. For roomtemperature, agreement between the resultant FIS and the reported FIS was obtained. For relatively low-temperature, drastic FIS in upstream and slit section. In case of an asymmetric slit flow, the same tendency was obtained. However, profile of retardation was asymmetric in slit section. Moreover, degree of spatial constraint was discussed.

Effect of nozzle inlet swirl and air column shape in nozzle on water jet occurring periodic droplets splashing

Water with free surface inside the water tank was pressurized and ejected as a water jet from nozzle with abrupt contraction flow path attached to the bottom of the tank. When the height of the free surface of water makes low into some height from the bottom of the tank, a peculiar air column is generated in the nozzle, a phenomenon occurs in which the droplets are periodically aligned outward in the radial direction and are rapidly splashed from the jet due to the pressure difference from the atmospheric pressure. In order to investigate how water swirling near the nozzle inlet affects this droplet splashing phenomenon, The bottom of the tank was designed to affect the flow of water, and the flow of water was analyzed using visualization photography. As a result, it was found that the circumferential velocity has a great influence on the droplet splashing phenomenon under low pressure. When the circumferential velocity increases, it affects the shape of the air column in the large tube of nozzle, and the shape makes it easier for air bubbles to be generated in the small tube of nozzle. It was found that these processes facilitated the occurrence of the droplet splashing phenomenon.