Active and passive microrheology with large tracers in hard colloids.

The dynamics of a tracer particle in a bath of quasi-hard colloidal spheres is studied by Langevin dynamics simulations and mode coupling theory (MCT); the tracer radius is varied from equal to up to seven times larger than the bath particles radius. In the simulations, two cases are considered: freely diffusing tracer (passive microrheology) and tracer pulled with a constant force (active microrheology). Both cases are connected by linear response theory for all tracer sizes. It links both the stationary and transient regimes of the pulled tracer (for low forces) with the equilibrium correlation functions; the velocity of the pulled tracer and its displacement are obtained from the velocity auto-correlation function and the mean squared displacement, respectively. The MCT calculations give insight into the physical mechanisms: At short times, the tracer rattles in its cage of neighbours, with the frequency increasing linearly with the tracer radius asymptotically. The long-time tracer diffusion coefficient from passive microrheology, which agrees with the inverse friction coefficient from the active case, arises from the transport of transverse momentum around the tracer. It can be described with the Brinkman equation for the transverse flow field obtained in extension of MCT, but cannot be recovered from the MCT kernel coupling to densities only. The dynamics of the bath particles is also studied; for the unforced tracer the dynamics is unaffected. When the tracer is pulled, the velocity field in the bath follows the prediction of the Brinkman model, but different from the case of a Newtonian fluid.

Actualización en el manejo de la hipertensión intracraneal tras un traumatismo craneoencefálico / Update in management of intracraneial hypertensión after traumatic brain injury

El traumatismo craneoencefálico es una entidad heterogénea y dinámica cuya característica común, cualquiera que sea su etiología, es la disminución de la perfusión cerebral en las horas siguientes al impacto. Dado que las lesiones cerebrales por hipoxia,pueden producirse en momentos variables tras el traumatismo, la monitorización de la hipoxia, la disfunción metabólica, la hipertensión intracraneal y la actividad comicial deben detectarse de forma precoz para evitar secuelas. La neuromonitorización va a permitir detectar esas posibles anomalías que pueda comprometer el adecuado aporte de oxígeno y sustrato metabólico a las células cerebrales. A pesar de que, en los últimos años, se han incrementado las herramientas de medición de oximetría cerebral, en nuestro país su uso sigue siendo todavía muy limitado y la monitorización se basa, fundamentalmente, en la observación de la presión intracraneal y la presión de perfusión cerebral, insuficiente para garantizar una adecuada oxigenación cerebral. El objetivo de esta revisión pretende integrar la fisiopatología del traumatismo craneoencefálico con las distintas técnicas de neuromonitorización, proporcionando así un manejo actualizado y más individualizado que mejore el pronóstico del enfermo neurocrítico. (AU)

Trauma brain injury is a heterogeneous and dynamic entity characterized, whatever its etiology, by a decrease in cerebral perfusion the first hours after the impact. Brain injury due to hypoxia can occur after trauma, so monitoring brain hypoxia, metabolic dysfunction, intracranial hypertension and seizure activity must be detected early to prevent brain sequelae. Neuromonitoring will detect those anomalies that could compromise the adequate oxygen supply and substrates of cerebral metabolism. Despite cerebral oximetry monitoring has increased in recent years, unfortunately very limited in our country, neuromonitoring is often based on intracranial pressure and cerebral perfusion pressure, insufficient to measure cerebral oxygenation. The objective of this review is to integrate the pathophysiology of trauma brain injury with the different neuromonitoring techniques to provide an updated and more individualized management that improves the prognosis of neurocritical patients. (AU)

Quantitative analysis of p16 methylation in Barrett's carcinogenesis.

p16 hypermethylation in Barrett's carcinogenesis has been evaluated in studies which did not take into account sample heterogeneity and yielded qualitative (methylated/unmethylated) instead of accurate quantitative (percentage of CpG methylation) data. We aimed to measure the degree of p16 methylation in pure samples representing all the steps of Barrett's tumorogenesis and to evaluate the influence of sample heterogeneity in methylation analysis. METHODS: 77 paraffin-embedded human esophageal samples were analyzed. Histological grading was established by two pathologists in: negative for dysplasia, indefinite for dysplasia, low-grade dysplasia, high-grade dysplasia and adenocarcinoma. Areas of interest were selected by laser-capture microdissection. p16 methylation was quantified by pyrosequencing. An adjacent section of the whole sample was also analyzed to compare methylation data. RESULTS: After microdissection, we obtained 15 samples of squamous epithelium, 36 non-dysplastic Barrett's esophagus, 3 indefinite for dysplasia, 24 low-grade dysplasia, 4 high-grade dysplasia and 12 adenocarcinoma. Squamous epithelium showed the lowest methylation rates: 6% (IQR 5-11) vs. 11%(7-39.50) in negative/indefinite for dysplasia, p<0.01; 10.60%(6-24) in low-grade dysplasia, p<0.05; and 44.50%(9-66.75) in high-grade dysplasia/adenocarcinoma, p<0.01. This latter group also exhibited higher methylation rates than Barrett's epithelium with and without low-grade dysplasia (p<0.05). p16 methylation rates of microdissected and non-microdissected samples did not correlate unless the considered histological alteration comprised >71% of the sample. CONCLUSIONS: p16 methylation is an early event in Barrett's carcinogenesis which increases with the severity of histological alteration. p16 methylation rates are profoundly influenced by sample heterogeneity, so selection of samples is crucial in order to detect differences.

Dynamics and friction of a large colloidal particle in a bath of hard spheres: Langevin dynamics simulations and hydrodynamic description.

The analysis of the dynamics of tracer particles in a complex bath can provide valuable information about the microscopic behavior of the bath. In this work, we study the dynamics of a forced tracer in a colloidal bath by means of Langevin dynamics simulations and a theory model within continuum mechanics. In the simulations, the bath is comprised of quasihard spheres with a volume fraction of 50% immersed in a featureless quiescent solvent, and the tracer is pulled with a constant small force (within the linear regime). The theoretical analysis is based on the Navier-Stokes equation, where a term proportional to the velocity arises from coarse-graining the friction of the colloidal particles with the solvent. As a result, the final equation is similar to the Brinkman model, although the interpretation is different. A length scale appears in the model, k_{0}^{-1}, where the transverse momentum transport crosses over to friction with the solvent. The effective friction coefficient experienced by the tracer grows with the tracer size faster than the prediction from Stokes's law. Additionally, the velocity profiles in the bath decay faster than in a Newtonian fluid. The comparison between simulations and theory points to a boundary condition of effective partial slip at the tracer surface. We also study the fluctuations in the tracer position, showing that it reaches diffusion at long times, with a subdiffusive regime at intermediate times. The diffusion coefficient, obtained from the long-time slope of the mean-squared displacement, fulfills the Stokes-Einstein relation with the friction coefficient calculated from the steady tracer velocity, confirming the validity of the linear response formalism.

Critical force in active microrheology.

Soft solids like colloidal glasses exhibit a yield stress, above which the system starts to flow. The microscopic analogon in microrheology is the untrapping or depinning of a tracer particle subject to an external force exceeding a threshold value in a glassy host. We characterize this delocalization transition based on a bifurcation analysis of the corresponding mode-coupling theory equations. A schematic model that allows analytical progress is presented first, and the full physical model is studied numerically next. This analysis yields a continuous dynamic transition with a critical power-law decay of the probe correlation functions with exponent -1/2. To compare with simulations with a limited duration, a finite-time analysis is performed, which yields reasonable results for not-too-small wave vectors. The theoretically predicted findings are verified by Langevin dynamics simulations. For small wave vectors we find anomalous behavior for the probe position correlation function, which can be traced back to a wave-vector divergence of the critical amplitude. In addition, we propose and test three methods to extract the critical force from experimental data, which provide the same value of the critical force when applied to the finite-time theory or simulations.

A model for foreign exchange markets based on glassy Brownian systems.

In this work we extend a well-known model from arrested physical systems, and employ it in order to efficiently depict different currency pairs of foreign exchange market price fluctuation distributions. We consider the exchange rate price in the time range between 2010 and 2016 at yearly time intervals and resolved at one minute frequency. We then fit the experimental datasets with this model, and find significant qualitative symmetry between price fluctuation distributions from the currency market, and the ones belonging to colloidal particles position in arrested states. The main contribution of this paper is a well-known physical model that does not necessarily assume the independent and identically distributed (i.i.d.) restrictive condition.

Lactobacillus plantarum CIDCA 8327: An α-glucan producing-strain isolated from kefir grains.

Lactobacillus plantarum CIDCA 8327 is an exopolysaccharide (EPS)-producer strain isolated from kefir with promising properties for the development of functional foods. The aim of the present study was to characterize the structure of the EPS synthesized by this strain grown in skim milk or semidefined medium (SDM). Additionally, genes involved in EPS synthesis were detected by PCR. L. plantarum produces an EPS with a molecular weight of 104Da in both media. When grown in SDM produce an heteropolysaccharide composed mainly of glucose, glucosamine and rhamnose meanwhile the EPS produced in milk was composed exclusively of glucose indicating the influence of the sugar source. FTIR spectra of this EPS showed signals attributable to an α-glucan. Both by 1H NMR and methylation analysis it was possible to determine that this polysaccharide is a branched α-(1→4)-d-glucan composed of 80% linear α-(1→4)-d-glucopyranosyl units and 19% (1→4)-d-glucopyranosyl units substituted at O-3 by single α-d-glucopyranosil residues.

Diffusive and Arrestedlike Dynamics in Currency Exchange Markets.

This work studies the symmetry between colloidal dynamics and the dynamics of the Euro-U.S. dollar currency exchange market (EURUSD). We consider the EURUSD price in the time range between 2001 and 2015, where we find significant qualitative symmetry between fluctuation distributions from this market and the ones belonging to colloidal particles in supercooled or arrested states. In particular, we find that models used for arrested physical systems are suitable for describing the EURUSD fluctuation distributions. Whereas the corresponding mean-squared price displacement (MSPD) to the EURUSD is diffusive for all years, when focusing in selected time frames within a day, we find a two-step MSPD when the New York Stock Exchange market closes, comparable to the dynamics in supercooled systems. This is corroborated by looking at the price correlation functions and non-Gaussian parameters and can be described by the theoretical model. We discuss the origin and implications of this analogy.

Active microrheology in a colloidal glass.

We study the dynamics of a probe particle driven by a constant force through a colloidal glass of hard spheres. This nonequilibrium and anisotropic problem is investigated using a new implementation of the mode-coupling approximation with multiple relaxation channels and Langevin dynamics simulations. A force threshold is found, below which the probe remains localized, while above it the probe acquires a finite velocity. We focus on the localized regime, comparing theory and simulations concerning the dynamics in the length scale of the cage and the properties of the transition to the delocalized regime, such as the critical power-law decay of the probe correlation function. Probe van Hove functions predicted by the theory show exponential tails reminiscent of an intermittent dynamics of the probe. This scenario is microscopically supported by simulations.

Oral bacteria in placental tissues: increased molecular detection in pregnant periodontitis patients.

OBJECTIVES: The objective of this study was to identify the DNA of oral bacteria in placental samples from women with and without periodontitis who had or had not had preterm births and/or low birthweight (PB/LBW) neonates. METHODS: Data were gathered from 57 puerperal women in relation to socio-demographic, gynaecological, and periodontal variables and to placental histomorphology. Fifty-seven biopsies, 28 from mothers with periodontitis, were taken aseptically from preterm placentas (n = 36) and from full-term placentas (n = 21). Total DNA was extracted, and the presence of 15 oral bacteria was assessed using Nested-PCR. RESULTS: The placentas from women with periodontitis showed a higher prevalence of periodontopathogens compared to those from women without periodontitis (P = 0.009). Samples showed low prevalences of Actinomyces israelii, Parvimonas micra and Tannerella forsythia. An association was found between Eikenella corrodens in placenta and periodontitis (P = 0.002). The most ubiquitous bacterium, Fusobacterium nucleatum, was more prevalent in mothers with periodontitis and PB/LBW (P = 0.033). Porphyromonas gingivalis, Treponema denticola, Prevotella intermedia and Aggregatibacter actinomycetemcomitans were not detected. CONCLUSIONS: These results, along with previous findings, show that oral bacteria may be normally present in the placenta, however, the levels of certain oral pathogens in the placenta would highly depend on the mother's periodontal state.

Microrheology of colloidal systems.

Microrheology was proposed almost twenty years ago as a technique to obtain rheological properties in soft matter from the microscopic motion of colloidal tracers used as probes, either freely diffusing in the host medium, or subjected to external forces. The former case is known as passive microrheology, and is based on generalizations of the Stokes-Einstein relation between the friction experienced by the probe and the host-fluid viscosity. The latter is termed active microrheology, and extends the measurement of the friction coefficient to the nonlinear-response regime of strongly driven probes. In this review article, we discuss theoretical models available in the literature for both passive and active microrheology, focusing on the case of single-probe motion in model colloidal host media. A brief overview of the theory of passive microrheology is given, starting from the work of Mason and Weitz. Further developments include refined models of the host suspension beyond that of a Newtonian-fluid continuum, and the investigation of probe-size effects. Active microrheology is described starting from microscopic equations of motion for the whole system including both the host-fluid particles and the tracer; the many-body Smoluchowski equation for the case of colloidal suspensions. At low fluid densities, this can be simplified to a two-particle equation that allows the calculation of the friction coefficient with the input of the density distribution around the tracer, as shown by Brady and coworkers. The results need to be upscaled to agree with simulations at moderate density, in both the case of pulling the tracer with a constant force or dragging it at a constant velocity. The full many-particle equation has been tackled by Fuchs and coworkers, using a mode-coupling approximation and the scheme of integration through transients, valid at high densities. A localization transition is predicted for a probe embedded in a glass-forming host suspension. The nonlinear probe-friction coefficient is calculated from the tracer's position correlation function. Computer simulations show qualitative agreement with the theory, but also some unexpected features, such as superdiffusive motion of the probe related to the breaking of nearest-neighbor cages. We conclude with some perspectives and future directions of theoretical models of microrheology.

Improving patient safety by detecting obstetric care-related adverse events: application of a new screening guide.

PURPOSE: Determining the magnitude and importance of patient safety-related incidents and the effectiveness of measures to improve patient safety (PS) are high-priority goals in efforts to improve the quality of obstetric care. The aim of this study was to evaluate the usefulness of the MRF1-OBST screening guide in detecting adverse events in women who received obstetric care. METHODS: This retrospective cohort study included 244 women who were hospitalized for delivery. All medical records were reviewed with the MRF1-OBST screening guide to identify adverse events and incidents. This tool is a modified form of the MRF1 screening guide regularly used in epidemiological studies of PS, to which we added items developed specifically for obstetric care. We calculated the positive predictive value and compared the ability of the MRF1 and MRF1-OBST guides to detect incidents related to PS in Obstetrics. RESULTS: The MRF1-OBST guide did not identify any additional complications during hospitalization or incidents related to PS that were not also identified by the MRF1 guide. CONCLUSIONS: The MRF1-OBST guide did not improve the detection of obstetric AE. The modified version of the guide required more work to use as a screening aid than the original MRF1 instrument. Efforts to improve the detection of incidents related to PS in obstetrics require complementary tools to be developed for information analysis.

Prevention of group B streptococcal neonatal disease revisited. The DEVANI European project.

The purpose of this paper was to present the current knowledge on the prevention of group B streptococcus (GBS) neonatal infections and the status of prevention policies in European countries and to present the DEVANI pan-European program, launched in 2008. The aim of this program was to assess the GBS neonatal infection burden in Europe, to design a new vaccine to immunize neonates against GBS infections, to improve the laboratory performance for the diagnosis of GBS colonization and infection, and to improve the methods for the typing of GBS strains. The current guidelines for GBS prevention in different countries were ascertained and a picture of the burden before and after the instauration of prevention policies has been drawn. After the issue of the Centers for Disease Control and Prevention (CDC) guidelines, many European countries have adopted universal screening for the GBS colonization of pregnant women and intrapartum prophylaxis to colonized mothers. Nevertheless, some European countries continue advocating the risk factor approach to GBS prevention. Most European countries have implemented policies to prevent GBS neonatal infections and the burden of the disease has decreased during the last several years. Nevertheless, further steps are necessary in order to develop new strategies of prevention, to improve microbiological techniques to detect GBS colonization and infection, and to coordinate the prevention policies in the EU.

Duodenal metastasis of alveolar soft part sarcoma.

Aveolar soft part sarcoma is a rare tumor responsible for about 1% of all soft tissue sarcomas, affecting mostly adolescents and young adults. ASPS has curious patterns of metastatic spread, with seldom lymph node involvement. Lung, bone and brain are the most common metastatic places. Small bowel metastasis are infrequent, having found reported only one case of duodenal metastasis with polypous appearance. We describe a case of duodenal metastasis presenting as abdominal mass five years after initial diagnosis of alveolar soft part sarcoma.

Human umbilical cord stromal stem cell express CD10 and exert contractile properties.

BACKGROUND: It has been demonstrated that human umbilical cord stromal stem cells (UCSSCs) are bio-equivalent to bone marrow mesenchymal stem cells. However, little is known about their tissue origin or in vivo functions, and data on their expansion properties are limited due to early senescence in the culture methods described to date. METHODS: UC sections and cultured UCSSCs were analyzed with a panel of 12 antibodies. UCSSCs were grown in low-FCS containing medium at 5% or 21% oxygen and were assayed for their clonogenic properties, karyotype stability, expression of specific cellular markers, and multi-lineage potential. UCSSC contractile properties were evaluated by using collagen gel contraction assays under cytokine stimulus. RESULTS: Immunohistochemistry studies showed that the UCSSCs were derived from the Wharton's jelly and not from the vascular smooth muscle sheath of the blood vessels. UCSSC growth properties were increased in a 5% oxygen atmosphere in comparison to normoxic culture conditions. In both culture conditions, UCSSCs were CD14-, CD34-, and CD45-negative while expressing high levels of CD73, CD90 and CD105 and maintaining their differentiation potentialities. UCSSCs expressed alpha smooth muscle actin and behaved as functional myofibroblasts when cellular contraction was challenged with appropriate stimuli. CONCLUSIONS: UCSCs are mesenchymal stem cells that reside in the perivascular area of Wharton's jelly and are phenotypically and functionally related to myofibroblasts.

Structural relaxation of polydisperse hard spheres: comparison of the mode-coupling theory to a Langevin dynamics simulation.

We analyze the slow glassy structural relaxation as measured through collective and tagged-particle density correlation functions obtained from Brownian dynamics simulations for a polydisperse system of quasi-hard spheres in the framework of the mode-coupling theory (MCT) of the glass transition. Asymptotic analyses show good agreement for the collective dynamics when polydispersity effects are taken into account in a multicomponent calculation, but qualitative disagreement at small q when the system is treated as effectively monodisperse. The origin of the different small-q behavior is attributed to the interplay between interdiffusion processes and structural relaxation. Numerical solutions of the MCT equations are obtained taking properly binned partial static structure factors from the simulations as input. Accounting for a shift in the critical density, the collective density correlation functions are well described by the theory at all densities investigated in the simulations, with quantitative agreement best around the maxima of the static structure factor and worst around its minima. A parameter-free comparison of the tagged-particle dynamics however reveals large quantitative errors for small wave numbers that are connected to the well-known decoupling of self-diffusion from structural relaxation and to dynamical heterogeneities. While deviations from MCT behavior are clearly seen in the tagged-particle quantities for densities close to and on the liquid side of the MCT glass transition, no such deviations are seen in the collective dynamics.

What is the most reliable ultrasound parameter for assessment of fetal head descent?

OBJECTIVES: The aims of this study were, first, to establish the agreement between digital and ultrasound assessment of occipital position and, second, to evaluate the repeatability of the measurements of head direction, angle of the middle line, progression distance and angle of progression in women in the second stage of labor. METHODS: Digital examination and then transabdominal ultrasound examination was performed on 50 women in the second stage of labor to determine the fetal occipital position. We also obtained three-dimensional (3D) blocks of the fetal head by transperineal sonography, and two experts in 3D ultrasound measured head direction, angle of the middle line, progression distance and angle of progression. Intraclass correlation coefficients with 95% CIs, and Bland-Altman analysis, were used to evaluate intraobserver and interobserver repeatability of measurements. RESULTS: The fetal head position, determined by ultrasound examination, was occiput anterior in 33 (66%) cases and occiput lateral in 17 (34%) cases. Vaginal digital examination failed to identify the correct fetal head position by more than 45° in 33 (66%) cases. All four 3D ultrasound measurements were reproducible but the progression angle had the highest intraclass correlation coefficient for the same observer (0.94; 95% CI, 0.90-0.97) and for two different operators (0.84; 95% CI, 0.73-0.91). The progression angle was also the measurement for which smaller limits of agreement (LOA) were found in the Bland-Altman test, performed to calculate the intraobserver (bias 0.9; LOA, - 9.2 to 11.1%) and interobserver (bias 1.5; LOA, - 15.4 to 18.3%) variability. CONCLUSIONS: Digital pelvic examination for determining the fetal head position during labor is not accurate. The most reproducible of the 3D measurements for progression of the fetal head in labor is the progression angle.

Active and nonlinear microrheology in dense colloidal suspensions.

We present a first-principles theory for the active nonlinear microrheology of colloidal model system; for a constant external force on a spherical probe particle embedded in a dense host dispersion, neglecting hydrodynamic interactions, we derive an exact expression for the friction. Within mode-coupling theory, we discuss the threshold external force needed to delocalize the probe from a host glass, and its relation to strong nonlinear velocity-force curves in a host fluid. Experimental microrheology data and simulations, which we performed, are explained with a simplified model.