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Abstract Background Rape, as an adverse incidence, leads to irreparable complications and consequences in women. Provision of health services to women survivors of rape requires catering for their real needs and identifying current deficits as well as barriers. The present study aimed to explore health system-related needs in women survivors of rape. Methods In the present qualitative study, the participants consisted of 39 individuals, including 19 women survivors of rape and 20 individuals with work experience in providing services to women survivors of rape. The participants were selected using the purposive sampling method with a maximum variation in Isfahan, Iran. Data were collected through in-depth interviews as well as field notes and were concurrently analyzed via conventional qualitative content analysis method. Results After analyzing the interviews, the health system-related needs of women survivors of rape were classified into two main categories: 1- The need for efficient medical care services with three sub-categories, namely “receiving services with respect for privacy and confidentiality”, “non-judgmental behavior and approach”, and “the need to receive empathy and the feeling of not being alone”, and 2- The need for desirable conditions and structure to provide services with two sub-categories, namely “the need to receive comprehensive and integrated services”, and “establishing specialized centers for providing services to survivors”. Conclusions Overall, explaining and highlighting the health system-related needs of women survivors of rape could provide a suitable basis for policy-making and planning according to their real needs. Receiving continuous services in separate centers with confidentiality and empathy could reduce the worries and concerns of women survivors of rape and help improve their health.

Abstract Background Rape is one of the principal forms of sexual violence leading to numerous psychological consequences for women. Providing effective psychological services to women survivors of rape requires identifying and considering their real needs. This study aimed to explore the psychological needs of women survivors of rape. Methods In this exploratory-descriptive qualitative study, the participants consisted of 19 women survivors of rape and 20 people with experience in providing services to survivors of rape, selected via purposive sampling method in Isfahan, Iran. In-depth individual semi-structured interviews and field notes were used to collect data, which were then analyzed using the conventional content analysis method. Results Based on the analysis of the interviews, the psychological needs of women survivors of rape were classified into three main categories: facing psychological problems, attention to emotional reactions, and the need to accept and adapt to reality. Conclusions The results revealed that women survivors of rape have different psychological needs. Thus, to meet these needs, supportive and psychological interventions can be considered at both individual and environmental levels. Also, eliminating gender stereotypes affecting the occurrence of rape in the dimensions of Iranian culture can lead to the liberation of the society from the culture of rape.

Background: Rape is a serious global problem linked to long-term physical health complications in women. Women survivors of rape have different needs, the identification of which ensures optimal services and improves their health conditions. This study aimed to explore the needs of women survivors of rape through a narrative review. Materials and Methods: This review was conducted by searching databases of ISI Web of Science, Scopus, Science Direct, Cochrane, PubMed, Scientific Information Database (SID), the Iranian Magazine Database (Magiran), Iranian Research Institute for Information Science and Technology (IranDoc), Iranian Medical Articles Database (IranMedex), and the Google Scholar engine.All English and Persian articles published from January 2000 to August 2022 were searched using the keywords rape, sexual assault, sexual violence, victim, survivor, demands, and needs. Two independent researchers conducted all steps of article extraction and review to avoid possible bias, and a third person reviewed the articles in the case of disagreement between the two researchers. The final related articles were selected and evaluated using a pre-prepared checklist. Results: Out of 112 articles, 26 articles were selected for final evaluation. The needs of women survivors of rape were divided into six categories, including sociocultural, educational, legal and judicial, psychological, spiritual and religious, and healthcare. Conclusions: Women survivors of rape need survivor-centered, culturally appropriate services, necessitating careful planning and policymaking to address health and judicial issues from different dimensions considering their real-world needs.

Abstract Short QT-interval is a condition that bear the suspicion of short QT syndrome (SQTS). SQTS is known to increase risk of life-threatening arrythmias and sudden cardiac death (SCD). Due to the insufficient population-based studies and use of various QT cut-off values, it accounts for as an undiagnosed condition. In this study, we sought for prevalence of short QT interval in Kherameh cohort study, one of the southern branches of the Prospective Epidemiological Research Studies in Iran (PERSIAN). Data of 4363 adult subjects were analyzed from phase 1 of the cohort during 2014–2017. The corrected QT (QTc) intervals were calculated and electrocardiograms (ECGs) with QTc of less than 370 ms (msec) were reanalyzed for bradycardia, early repolarization, atrial fibrillation (AF), arrhythmias, and other electrical conduction abnormalities. Seventy-two subjects (1.65%) had a QTc of less than 370 ms (mean QTc of 360.72 ± 11.72). A male predominance and a lower mean heart rate observed in SQTS susceptible group (M/F of 1/0.26 vs. 1/1.145, p-value

Objective: The purpose of this study is to test the use of visual financial ratios to predict the bankruptcy of companies using a convolutional neural network and compare it with traditional models. Methods: The research period was 2009 to 2018. The sample companies have been selected from the ones which were listed on the Tehran Stock Exchange in two groups of bankrupt companies (66) and non-bankrupt companies (66). Since the work of convolution neural network is to recognize images from existing images, first the financial ratios were converted into images as research data through MATLAB 2019 software, then, the situation of the sample companies were predicted and diagnosed with the help of convolution neural network and under Google net architecture. Results: Convolutional neural network models performed accurate images and predictions with 50% accuracy. On the one hand, in order to strengthen the results and determine the effectiveness of the first hypothesis, three other hypotheses were proposed to be compared to Altman, Spring-gate and Zimski models. The results of all three indicated that the convolution model was not confirmed as accurate compared to these three models. Conclusion: Advances in computers and the use of deep learning, which is a kind of improvement in artificial intelligence, affect the prediction of bankruptcy through visual financial ratios. However, to consolidate the test results of the first hypothesis, three practical models of bankruptcy prediction including Altman (1983), Springgate (1978) and Zimski (1984) were tested, the results of which did not confirm the accuracy of the convolution model compared to these three models.

Subject and Purpose of the Article: Accounting knowledge has entered the field of research through research training. In this study, the commercialization factors of doctoral dissertations in accounting have been modeled. The main purpose of this research is to identify the effective factors and to present an appropriate model for commercialization of doctoral dissertations in accounting. Research Method: This research is qualitative in terms of approach and exploratory in terms of purpose. Data were designed through a questionnaire and distributed electronically among 300 accounting professors and collected comments. On the other hand, doctoral dissertations in accounting from 1993 to 2021, including 116 relevant dissertations on the subject of commercialization were reviewed. Research Findings: Individual, cultural, organizational, environmental, political and economic factors are effective in providing a conceptual model for the commercialization of accounting doctoral dissertations. level of public sector audit quality proposition. Conclusion, Originality and its Contribution to the Knowledge: The results showed that the economic factor with a weight of 5.89 in the first rank and the individual factor with a weight of 4.74 in the second rank and the environmental factor with a weight of 3.36 in the third rank and the cultural factor with a weight of 3.06 in the fourth rank and the organizational factor and Politics with an average rank of 2.83 and 1.12 are in the fifth and sixth ranks, respectively. In this research, for the first time, the commercialization of doctoral dissertations in accounting has been investigated.

BACKGROUND: Rape can lead to various physical and psychological consequences. Thus, survivors should receive immediate interventions and need-based care. The present study aims to design and psychometric evaluation of needs in women survivors of rape. MATERIALS AND METHODS: This mixed methods study is conducted using a sequential exploratory approach. In the first phase, the participants (women survivors of rape and healthcare providers) are selected through purposive sampling in Isfahan. Data are collected through in-depth semi-structured interviews and field notes and are analyzed using conventional qualitative content analysis. The draft of the questionnaire is prepared based on the findings of the qualitative phase and literature review. Then, the face validity, content validity, and reliability of the questionnaire are assessed. Construct validity is assessed using the exploratory factor analysis through a descriptive cross-sectional study on women survivors of rape in the quantitative phase. Using a convenience sampling method, the data are collected in the research environment and analyzed via descriptive and inferential statistical methods. Cronbach's alpha coefficient is used to assess the internal correlation of the questionnaire. CONCLUSION: The valid and reliable questionnaire that is developed in this study can be used by planners to provide services and care according to the needs of women survivors of rape.

In the recent years, many companies in the Tehran Stock Exchange, TSE, revaluated their non-current assets and increased their capital value to do reforms in their financial structure and to exit from the inclusion of Article 141 of the Commercial Code. This, with regard to the inflation condition in the community, often increases firms’ capital values and changes financial statements that may cause auditors revalue their audit fees. This study aims at investigating the effects of revaluating non-current assets on audit costs of firms. In this study, a sample of 127 companies listed in the TSE was selected, in which 62 companies revaluated their non-current assets and 65 companies held their own historical value of non-current assets unchanged, all in the period 2010 to 2016, and then, the data was collected from financial statements of these companies. Findings showed that revaluation of assets leads to increase in audit costs. Also, the companies that reevaluate their own assets, compared to other companies, experience more audit costs.

Background: Medical errors are the main concerns in health systems, which considering their ascending rate in the recent years, especially in the field of midwifery, have caused a medical crisis. Considering the importance of evidence-based health services as a way to improve health systems, the aim of this study was to suggest a guideline for preventing malpractice in midwifery services. Materials and Methods: In this cross-sectional study that was conducted in 2013, we investigated 206 cases that were referred to the Isfahan Legal Medicine Organization and Medical Council of Forensic Medicine from 2006–2011. Data were collected by a checklist and were analyzed using SPSS-16 software. Descriptive statistical tests (mean, maximum, minimum, standard deviation, frequency, and percentage agreement) were used to describe the data. Then, we used the Delphi technique with the participation from 17 experts in midwifery, gynecology, and legal medicine to provide an evidence-based draft guideline for prevention of midwifery errors. Results: A total of 206 cases were reviewed. In 66 cases (32%) the verdict for malpractice in midwifery services was approved. A practical draft guideline for preventing clinical errors for midwifery in the fields of pregnancy, delivery, and postpartum period was developed. Conclusions: This evidence-based draft guideline can improve the attention of all the healthcare providers, especially midwives and physicians to prevent urgent problems and offer effective health services for mothers and infants.

Background: Medical errors almost have been the most common causes of proceedings against physicians, and a significant amount of complaints is related to inevitable issues. This study aimed to investigate the causes of complaints related to skin and cosmetics to give over preventive solutions. Methods: In this descriptive study, the medical malpractice cases related to skin and cosmetics were studied in general offices of legal medicine of Isfahan Province, Iran, during 2002-2013. As the instrument was a checklist, the formal validity was approved by the relevant experts. Mean and standard deviation for quantitative variables and frequency for qualitative variables were calculated using SPSS software. The chi-square test was used to evaluate the correlation of variables. Findings: Most of the complaints were from specialists (62.7%). The issued votes included 41.9% failure, 55.8% acquittal and 2.3% were closed with no vote. The blood money was less than 25% in 55.6% of cases, 25-50% in 22.2% of cases and more than 50% in the 22.2% of cases. The chi-square test showed no significant relationship between the issued judgments and physicians’ educational certifications (P > 0.05). Conclusion: In general, we can say that the medical malpractices were related to specialists and the complaints mainly were from specialists in other fields. For this reason, making sure that the diagnosis is based on appropriate expertise and avoiding the interference in other fields are recommended.

Mechanics studies the relationships between space, time, and matter. These relationships can be expressed in terms of the dimensions of length , time , and mass . Each dimension broadens the scope of mechanics. Historically, mechanics emerged from geometry, which considers quantities like lengths or areas, with dimensions of the form . With the Renaissance, quantities combining space and time were considered, like speed, acceleration and later diffusivity, all of the form . Eventually, mechanics reached its full potential by including "mass-carrying" quantities such as mass, force, momentum, energy, action, power, viscosity, etc. These standard mechanical quantities have dimensions of the form where x and y are integers. In this contribution, we show that, thanks to this dimensional structure, these mass-carrying quantities can be readil y arranged into a table such that x and y increase along the row and column, respectively. Ratios of quantities in the same rows provide characteristic lengths, while those in the same columns yield characteristic times, encompassing a great variety of physical phenomena from atomic to astronomical scales. Most generally, we show that selecting duos of mechanical quantities that are neither on the same row nor column of the table yields dynamics, where one mechanical quantity is understood as impelling motion, while the other impedes it. The force and the mass are the prototypes of impelling and impeding factors, but many other duos are possible. We present examples from the physical and biological realms, including planetary motion, sedimentation, explosions, fluid flows, turbulence, diffusion, cell mechanics, capillary and gravity waves, and spreading, pinching, and coalescence of drops and bubbles. This review provides a novel synthesis revealing the power of scaling or dimensional analysis, to understand processes governed by the interplay of two mechanical quantities. This elementary decomposition of space, time and motion into pairs of mechanical factors is the foundation of "dimensional mechanics", a method that this review wishes to promote and advance. Pairs are the fundamental building blocks, but they are only a starting point. Beyond this simple world of mechanical duos, we envision a richer universe that beckons with an interplay of three, four, or more quantities, yielding multiple characteristic lengths, times, and kinematics. This review is complemented by online video lectures, which initiate a discussion on the elaborate interplay of two or more mechanical quantities.

Planar spindle orientation is critical for epithelial tissue organization and is generally instructed by the long cell-shape axis or cortical polarity domains. We introduced mouse intestinal organoids in order to study spindle orientation in a monolayered mammalian epithelium. Although spindles were planar, mitotic cells remained elongated along the apico-basal (A-B) axis, and polarity complexes were segregated to basal poles, so that spindles oriented in an unconventional manner, orthogonal to both polarity and geometric cues. Using high-resolution 3D imaging, simulations, and cell-shape and cytoskeleton manipulations, we show that planar divisions resulted from a length limitation in astral microtubules (MTs) which precludes them from interacting with basal polarity, and orient spindles from the local geometry of apical domains. Accordingly, lengthening MTs affected spindle planarity, cell positioning, and crypt arrangement. We conclude that MT length regulation may serve as a key mechanism for spindles to sense local cell shapes and tissue forces to preserve mammalian epithelial architecture., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Understanding the kinematics and dynamics of spreading, pinching, and coalescence of drops is critically important for a diverse range of applications involving spraying, printing, coating, dispensing, emulsification, and atomization. Hence experimental studies visualize and characterize the increase in size over time for drops spreading over substrates, or liquid bridges between coalescing drops, or the decrease in the radius of pinching necks during drop formation. Even for Newtonian fluids, the interplay of inertial, viscous, and capillary stresses can lead to a number of scaling laws, with three limiting self-similar cases: visco-inertial (VI), visco-capillary (VC) and inertio-capillary (IC). Though experiments are presented as examples of the methods of dimensional analysis, the lack of precise values or estimates for pre-factors, transitions, and scaling exponents presents difficulties for quantitative analysis and material characterization. In this tutorial review, we reanalyze and summarize an elaborate set of landmark published experimental studies on a wide range of Newtonian fluids. We show that moving beyond VI, VC, and IC units in favor of intrinsic timescale and lengthscale determined by all three material properties (viscosity, surface tension and density), creates a complementary system that we call the Ohnesorge units. We find that in spite of large differences in topological features, timescales, and material properties, the analysis of spreading, pinching and coalescing drops in the Ohnesorge units results in a remarkable collapse of the experimental datasets, highlighting the shared and universal features displayed in such flows.

The novel Coronavirus-2019 (COVID-19) was declared a pandemic by the World Health Organization (WHO) in March 2020, impacting the lifestyles, economy, physical and mental health of individuals globally. This study aimed to test the model triggered by physical symptoms resembling COVID-19 infection, in which the need for health information and perceived impact of the pandemic mediated the path sequentially, leading to adverse mental health outcomes. A cross-sectional research design with chain mediation model involving 4612 participants from participating 8 countries selected via a respondent-driven sampling strategy was used. Participants completed online questionnaires on physical symptoms, the need for health information, the Impact of Event Scale-Revised (IES-R) questionnaire and Depression, Anxiety and Stress Scale (DASS-21). The results showed that Poland and the Philippines were the two countries with the highest levels of anxiety, depression and stress; conversely, Vietnam had the lowest mean scores in these areas. Chain mediation model showed the need for health information, and the perceived impact of the pandemic were sequential mediators between physical symptoms resembling COVID-19 infection (predictor) and consequent mental health status (outcome). Excessive and contradictory health information might increase the perceived impact of the pandemic. Rapid COVID-19 testing should be implemented to minimize the psychological burden associated with physical symptoms, whilst public mental health interventions could target adverse mental outcomes associated with the pandemic.

The coronavirus disease (COVID-19) pandemic has impacted the economy, livelihood, and physical and mental well-being of people worldwide. This study aimed to compare the mental health status during the pandemic in the general population of seven middle income countries (MICs) in Asia (China, Iran, Malaysia, Pakistan, Philippines, Thailand, and Vietnam). All the countries used the Impact of Event Scale-Revised (IES-R) and Depression, Anxiety and Stress Scale (DASS-21) to measure mental health. There were 4479 Asians completed the questionnaire with demographic characteristics, physical symptoms and health service utilization, contact history, knowledge and concern, precautionary measure, and rated their mental health with the IES-R and DASS-21. Descriptive statistics, One-Way analysis of variance (ANOVA), and linear regression were used to identify protective and risk factors associated with mental health parameters. There were significant differences in IES-R and DASS-21 scores between 7 MICs (p<0.05). Thailand had all the highest scores of IES-R, DASS-21 stress, anxiety, and depression scores whereas Vietnam had all the lowest scores. The risk factors for adverse mental health during the COVID-19 pandemic include age <30 years, high education background, single and separated status, discrimination by other countries and contact with people with COVID-19 (p<0.05). The protective factors for mental health include male gender, staying with children or more than 6 people in the same household, employment, confidence in doctors, high perceived likelihood of survival, and spending less time on health information (p<0.05). This comparative study among 7 MICs enhanced the understanding of metal health in the general population during the COVID-19 pandemic., Competing Interests: The authors have declared that no competing interests exist.

The spectrin-based membrane skeleton is a major component of the cell cortex. While expressed by all metazoans, its dynamic interactions with the other cortex components, including the plasma membrane or the acto-myosin cytoskeleton, are poorly understood. Here, we investigate how spectrin re-organizes spatially and dynamically under the membrane during changes in cell mechanics. We find spectrin and acto-myosin to be spatially distinct but cooperating during mechanical challenges, such as cell adhesion and contraction, or compression, stretch and osmolarity fluctuations, creating a cohesive cortex supporting the plasma membrane. Actin territories control protrusions and contractile structures while spectrin territories concentrate in retractile zones and low-actin density/inter-contractile regions, acting as a fence that organize membrane trafficking events. We unveil here the existence of a dynamic interplay between acto-myosin and spectrin necessary to support a mesoscale organization of the lipid bilayer into spatially-confined cortical territories during cell mechanoresponse.

The physical cues from the extracellular environment mediates cell signaling spatially and temporally. Cells respond to physical cues from their environment in a non-monotonic fashion. Despite our understanding of the role of substrate rigidity on single cell migration, how cells respond collectively to increasing extracellular matrix stiffness is not well established. Here we patterned multicellular epithelial Madin-Darby canine kidney (MDCK) islands on polyacrylamide gels of varying stiffness and studied their expansion. Our findings show that the MDCK islands expanded faster with increasing stiffness only up to an optimum stiffness, over which the expansion plateaued. We then focused on the expansion of the front of the assemblies and the formation of leader cells. We observed cell front destabilization only above substrate stiffness of a few kPa. The extension of multicellular finger-like structures at the edges of the colonies for intermediate and high stiffnesses from 6 to 60 kPa responded to higher substrate stiffness by increasing focal adhesion areas and actin cable assembly. Additionally, the number of leader cells at the finger-like protrusions increased with stiffness in correlation with an increase of the area of these multicellular protrusions. Consequently, the force profile along the epithelial fingers in the parallel and transverse directions of migration showed an unexpected relationship leading to a global force decrease with the increase of stiffness. Taken together, our findings show that epithelial cell colonies respond to substrate stiffness but in a non-trivial manner that may be of importance to understand morphogenesis and collective cell invasion during tumour progression.

Biological systems integrate dynamics at many scales, from molecules, protein complexes and genes, to cells, tissues and organisms. At every step of the way, mechanics, biochemistry and genetics offer complementary approaches to understand these dynamics. At the tissue scale, in vitro monolayers of epithelial cells provide a model to capture the influence of various factors on the motions of the tissue, in order to understand in vivo processes from morphogenesis, cancer progression and tissue remodelling. Ongoing efforts include research aimed at deciphering the roles of the cytoskeleton, of cell-substrate and cell-cell adhesions, and of cell proliferation-the point we investigate here. We show that confined to adherent strips, and on the time scale of a day or two, monolayers move with a characteristic front speed independent of proliferation, but that the motion is accompanied by persistent velocity waves, only in the absence of cell divisions. Here we show that the long-range transmission of physical signals is strongly coupled to cell density and proliferation. We interpret our results from a kinematic and mechanical perspective. Our study provides a framework to understand density-driven mechanisms of collective cell migration.

Morphogenesis requires dynamic coordination between cell-cell adhesion and the cytoskeleton to allow cells to change shape and move without losing tissue integrity. We used genetic tools and superresolution microscopy in a simple model epithelial cell line to define how the molecular architecture of cell-cell zonula adherens (ZA) is modified in response to elevated contractility, and how these cells maintain tissue integrity. We previously found that depleting zonula occludens 1 (ZO-1) family proteins in MDCK cells induces a highly organized contractile actomyosin array at the ZA. We find that ZO knockdown elevates contractility via a Shroom3/Rho-associated, coiled-coil containing protein kinase (ROCK) pathway. Our data suggest that each bicellular border is an independent contractile unit, with actin cables anchored end-on to cadherin complexes at tricellular junctions. Cells respond to elevated contractility by increasing junctional afadin. Although ZO/afadin knockdown did not prevent contractile array assembly, it dramatically altered cell shape and barrier function in response to elevated contractility. We propose that afadin acts as a robust protein scaffold that maintains ZA architecture at tricellular junctions., (© 2016 Choi et al.)

The rheology of NFC suspensions that exhibited different microstructures and colloidal stability, namely TEMPO and enzymatic NFC suspensions, was investigated at the macro and mesoscales using a transparent Couette rheometer combined with optical observations and ultrasonic speckle velocimetry (USV). Both NFC suspensions showed a complex rheology, which was typical of yield stress, non-linear and thixotropic fluids. Hysteresis loops and erratic evolutions of the macroscale shear stress were also observed, thereby suggesting important mesostructural changes and/or inhomogeneous flow conditions. The in situ optical observations revealed drastic mesostructural changes for the enzymatic NFC suspensions, whereas the TEMPO NFC suspensions did not exhibit mesoscale heterogeneities. However, for both suspensions, USV measurements showed that the flow was heterogeneous and exhibited complex situations with the coexistence of multiple flow bands, wall slippage and possibly multidimensional effects. Using USV measurements, we also showed that the fluidization of these suspensions could presumably be attributed to a progressive and spatially heterogeneous transition from a solid-like to a liquid-like behavior. As the shear rate was increased, the multiple coexisting shear bands progressively enlarged and nearly completely spanned over the rheometer gap, whereas the plug-like flow bands were eroded.

We report on the recent progress made on flows of living polymer fluids. Such fluids have been model systems for rheological research for more than twenty years and they continue to be fascinating. Like most if not all soft matter systems, living polymers under flow show a strong feedback between the structure of the fluid and that of the flow, the first influencing the second and vice versa. In our opinion, such interplay between microscopic kinetics and macroscopic kinematics has historically been mostly understood from a "structural perspective", in the tradition of physical chemistry. Nevertheless, in recent years, a more "hydrodynamical perspective" has emerged by making fruitful analogies with elastic and inertio-elastic instabilities known in solutions of regular polymers. We also underline how this new perspective constrains theoretical modelling and calls for the use of new tools of investigation.

The flow between concentric cylinders is routinely used in soft matter studies. In many cases, the purpose of the setup is rheometric: the idea is to relate macroscopic changes in material properties to microscopic changes in the structure of the material. The correspondence between the modifications of the microscopic structure and the macroscopic flow often relies on viscometric assumptions, which require the flow to be at least laminar. Flow instabilities are usually neglected because the viscosities of the materials are high and the geometries are small, such that the creeping flow approximation can be used. Nonetheless, the phenomenology of viscoelastic instabilities that emerged in the last twenty years warns us that flows can become turbulent without inertia, in particular flows between concentric cylinders. Given the strong similarities between inertial hydrodynamic instabilities and viscoelastic instabilities, a general knowledge of the former is advised for any researcher working on complex fluids. In this tutorial review, we focus on the inertial instability of isothermal and incompressible Newtonian fluids flowing between concentric cylinders. We highlight important aspects that can guide the study and control of instabilities in complex fluids in general.

Complex fluids such as emulsions, colloidal gels, polymer or surfactant solutions are all characterized by the existence of a "microstructure" which may couple to an external flow on time scales that are easily probed in experiments. Such a coupling between flow and microstructure usually leads to instabilities under relatively weak shear flows that correspond to vanishingly small Reynolds numbers. Wormlike micellar surfactant solutions appear as model systems to study two examples of such instabilities, namely shear banding and elastic instabilities. Focusing on a semidilute sample we show that two-dimensional ultrafast ultrasonic imaging allows for a thorough investigation of unstable shear-banded micellar flows. In steady state, radial and azimuthal velocity components are recovered and unveil the original structure of the vortical flow within an elastically unstable high shear rate band. Furthermore thanks to an unprecedented frame rate of up to 20,000 fps, transients and fast dynamics can be resolved, which paves the way for a better understanding of elastic turbulence.

Homogeneous polymer solutions are well known to exhibit viscoelastic flow instabilities: purely elastic when inertia is negligible and inertio-elastic otherwise. Recently, shear-banding wormlike micelle solutions were also discovered to follow a similar phenomenology. In the shear-banding regime, inertia is usually negligible so only purely elastic flows have been reported. Here, we investigate a non-shear-banding solution where inertia becomes significant, leading to flow patterns akin to the inertio-elastic regime of dilute polymer solutions. We show that the instability follows a supercritical bifurcation and we investigate the structure of the inertio-elastic vortices that develop above the onset.

The Taylor-Couette flow of a dilute micellar system known to generate shear-induced structures is investigated through simultaneous rheometry and ultrasonic imaging. We show that flow instabilities must be taken into account since both Reynolds and Weissenberg numbers may be large. Before nucleation of shear-induced structures, the flow can be inertially unstable, but once shear-induced structures are nucleated, the kinematics of the flow become chaotic, in a pattern reminiscent of the elastically dominated turbulence known in dilute polymer solutions. We outline a general framework for the interplay between flow instabilities and flow-induced structures.

We describe a technique coupling standard rheology and ultrasonic imaging with promising applications to characterization of soft materials under shear. Plane wave imaging using an ultrafast scanner allows to follow the local dynamics of fluids sheared between two concentric cylinders with frame rates as high as 10 000 images per second, while simultaneously monitoring the shear rate, shear stress, and viscosity as a function of time. The capacities of this "rheo-ultrasound" instrument are illustrated on two examples: (i) the classical case of the Taylor-Couette instability in a simple viscous fluid and (ii) the unstable shear-banded flow of a non-Newtonian wormlike micellar solution.

Shear-banding is ubiquitous in complex fluids. It is related to the organization of the flow into macroscopic bands bearing different viscosities and local shear rates and stacked along the velocity gradient direction. This flow-induced transition towards a heterogeneous flow state has been reported in a variety of systems, including wormlike micellar solutions, telechelic polymers, emulsions, clay suspensions, colloidal gels, star polymers, granular materials, or foams. In the past twenty years, shear-banding flows have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. In wormlike micelle solutions, many of the data collected exhibit unexplained spatio-temporal fluctuations. Different candidates have been identified, the main ones being wall slip, interfacial instability between bands or bulk instability of one of the bands. In this review, we present experimental evidence for a purely elastic instability of the high shear rate band as the main origin for fluctuating shear-banding flows.

Cell migration and spreading involve the coordination of membrane trafficking, actomyosin contraction, and modifications to plasma membrane tension and area. The biochemical or biophysical basis for this coordination is however unknown. In this study, we show that during cell spreading, lamellipodia protrusion flattens plasma membrane folds and blebs and, once the plasma membrane area is depleted, there is a temporary increase in membrane tension by over twofold that is followed by activation of exocytosis and myosin contraction. Further, an artificial increase in plasma membrane tension stopped lamellipodia protrusion and activated an exocytotic burst. Subsequent decrease in tension restored spreading with activation of contraction. Conversely, blebbistatin inhibition of actomyosin contraction resulted in an even greater increase in plasma membrane tension and exocytosis activation. This spatiotemporal synchronization indicates that membrane tension is the signal that coordinates membrane trafficking, actomyosin contraction, and plasma membrane area change. We suggest that cells use plasma membrane tension as a global physical parameter to control cell motility.

Cell spreading is regulated by signaling from the integrin receptors that activate intracellular signaling pathways to control actin filament regulatory proteins. We developed a hybrid model of whole-cell spreading in which we modeled the integrin signaling network as ordinary differential equations in multiple compartments, and cell spreading as a three-dimensional stochastic model. The computed activity of the signaling network, represented as time-dependent activity levels of the actin filament regulatory proteins, is used to drive the filament dynamics. We analyzed the hybrid model to understand the role of signaling during the isotropic phase of fibroblasts spreading on fibronectin-coated surfaces. Simulations showed that the isotropic phase of spreading depends on integrin signaling to initiate spreading but not to maintain the spreading dynamics. Simulations predicted that signal flow in the absence of Cdc42 or WASP would reduce the spreading rate but would not affect the shape evolution of the spreading cell. These predictions were verified experimentally. Computational analyses showed that the rate of spreading and the evolution of cell shape are largely controlled by the membrane surface load and membrane bending rigidity, and changing information flow through the integrin signaling network has little effect. Overall, the plasma membrane acts as a damper such that only ∼5% of the actin dynamics capability is needed for isotropic spreading. Thus, the biophysical properties of the plasma membrane can condense varying levels of signaling network activities into a single cohesive macroscopic cellular behavior., (Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

Many cell types have the ability to move themselves by crawling on extra-cellular matrices. Although cell motility is governed by actin and myosin filament assembly, the pattern of the movement follows the physical properties of the network ensemble average. The first step of motility, cell spreading on matrix substrates, involves a transition from round cells in suspension to polarized cells on substrates. Here we show that the spreading dynamics on 2D surfaces can be described as a hydrodynamic process. In particular, we show that the transition from isotropic spreading at early time to anisotropic spreading is reminiscent of the fingering instability observed in many spreading fluids. During cell spreading, the main driving force is the polymerization of actin filaments that push the membrane forward. From the equilibrium between the membrane force and the cytoskeleton, we derive a first order expression of the polymerization stress that reproduces the observed behavior. Our model also allows an interpretation of the effects of pharmacological agents altering the polymerization of actin. In particular we describe the influence of Cytochalasin D on the nucleation of the fingering instability.

Cell motility is important for many developmental and physiological processes. Motility arises from interactions between physical forces at the cell surface membrane and the biochemical reactions that control the actin cytoskeleton. To computationally analyze how these factors interact, we built a three-dimensional stochastic model of the experimentally observed isotropic spreading phase of mammalian fibroblasts. The multiscale model is composed at the microscopic levels of three actin filament remodeling reactions that occur stochastically in space and time, and these reactions are regulated by the membrane forces due to membrane surface resistance (load) and bending energy. The macroscopic output of the model (isotropic spreading of the whole cell) occurs due to the movement of the leading edge, resulting solely from membrane force-constrained biochemical reactions. Numerical simulations indicate that our model qualitatively captures the experimentally observed isotropic cell-spreading behavior. The model predicts that increasing the capping protein concentration will lead to a proportional decrease in the spread radius of the cell. This prediction was experimentally confirmed with the use of Cytochalasin D, which caps growing actin filaments. Similarly, the predicted effect of actin monomer concentration was experimentally verified by using Latrunculin A. Parameter variation analyses indicate that membrane physical forces control cell shape during spreading, whereas the biochemical reactions underlying actin cytoskeleton dynamics control cell size (i.e., the rate of spreading). Thus, during cell spreading, a balance between the biochemical and biophysical properties determines the cell size and shape. These mechanistic insights can provide a format for understanding how force and chemical signals together modulate cellular regulatory networks to control cell motility., (Copyright 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

We study the dynamics of the Taylor-Couette flow of shear banding wormlike micelles. We focus on the high shear rate branch of the flow curve and show that for sufficiently high Weissenberg numbers, this branch becomes unstable. This instability is strongly subcritical and is associated with a shear stress jump. We find that this increase of the flow resistance is related to the nucleation of turbulence. The flow pattern shows similarities with the elastic turbulence, so far only observed for polymer solutions. The unstable character of this branch led us to propose a scenario that could account for the recent observations of Taylor-like vortices during the shear banding flow of wormlike micelles.

Extracellular matrices in vivo are heterogeneous structures containing gaps that cells bridge with an actomyosin network. To understand the basis of bridging, we plated cells on surfaces patterned with fibronectin (FN)-coated stripes separated by non-adhesive regions. Bridges developed large tensions where concave cell edges were anchored to FN by adhesion sites. Actomyosin complexes assembled near those sites (both actin and myosin filaments) and moved towards the centre of the non-adhesive regions in a treadmilling network. Inhibition of myosin-II (MII) or Rho-kinase collapsed bridges, whereas extension continued over adhesive areas. Inhibition of actin polymerization (latrunculin-A, jasplakinolide) also collapsed the actomyosin network. We suggest that MII has distinct functions at different bridge regions: (1) at the concave edges of bridges, MIIA force stimulates actin filament assembly at adhesions and (2) in the body of bridges, myosin cross-links actin filaments and stimulates actomyosin network healing when breaks occur. Both activities ensure turnover of actin networks needed to maintain stable bridges from one adhesive region to another.

Maintaining a physical connection across cytoplasm is crucial for many biological processes such as matrix force generation, cell motility, cell shape and tissue development. However, in the absence of stress fibers, the coherent structure that transmits force across the cytoplasm is not understood. We find that nonmuscle myosin-II (NMII) contraction of cytoplasmic actin filaments establishes a coherent cytoskeletal network irrespective of the nature of adhesive contacts. When NMII activity is inhibited during cell spreading by Rho kinase inhibition, blebbistatin, caldesmon overexpression or NMIIA RNAi, the symmetric traction forces are lost and cell spreading persists, causing cytoplasm fragmentation by membrane tension that results in 'C' or dendritic shapes. Moreover, local inactivation of NMII by chromophore-assisted laser inactivation causes local loss of coherence. Actin filament polymerization is also required for cytoplasmic coherence, but microtubules and intermediate filaments are dispensable. Loss of cytoplasmic coherence is accompanied by loss of circumferential actin bundles. We suggest that NMIIA creates a coherent actin network through the formation of circumferential actin bundles that mechanically link elements of the peripheral actin cytoskeleton where much of the force is generated during spreading.

Using flow visualizations in Couette geometry, we demonstrate the existence of Taylor-like vortices in the shear-banding flow of a giant micelles system. We show that vortices stacked along the vorticity direction develop concomitantly with interfacial undulations. These cellular structures are mainly localized in the induced band and their dynamics is fully correlated with that of the interface. As the control parameter increases, we observe a transition from a steady vortex flow to a state where pairs of vortices are continuously created and destroyed. Normal stress effects are discussed as potential mechanisms driving the three-dimensional flow.