Approximate Analytical Model for the Squeeze-Film Lubrication of the Human Ankle Joint with Synovial Fluid Filtrated by Articular Cartilage

The aim of this article is to propose an analytical approximate squeeze-film lubrication model of the human ankle joint for a quick assessment of the synovial pressure field and the load carrying due to the squeeze motion. The model starts from the theory of boosted lubrication for the human articular joints lubrication (Walker et al., Rheum Dis 27:512–520, 1968; Maroudas, Lubrication and wear in joints. Sector, London, 1969) and takes into account the fluid transport across the articular cartilage using Darcy’s equation to depict the synovial fluid motion through a porous cartilage matrix. The human ankle joint is assumed to be cylindrical enabling motion in the sagittal plane only. The proposed model is based on a modified Reynolds equation; its integration allows to obtain a quick assessment on the synovial pressure field showing a good agreement with those obtained numerically (Hlavacek, J Biomech 33:1415–1422, 2000). The analytical integration allows the closed form description of the synovial fluid film force and the calculation of the unsteady gap thickness

Studying the effects of thalamic interneurons in a thalamocortical neural mass model

Neural mass models of the thalamocortical circuitry are often used to mimic brain activity during sleep and wakefulness as observed in scalp electroencephalogram (EEG) signals [1]. It is understood that alpha rhythms (8-13 Hz) dominate the EEG power-spectra in the resting-state [2] as well as the period immediately before sleep [3]. Literature review shows that the thalamic interneurons (IN) are often ignored in thalamocortical population models; the emphasis is on the connections between the thalamo cortical relay (TCR) and the thalamic reticular nucleus (TRN). In this work, we look into the effects of the IN cell population on the behaviour of an existing thalamocortical model containing the TCR and TRN cell populations [4]. A schematic of the extended model used in this work is shown in Fig.1. The model equations are solved in Matlab using the Runge-Kutta method of the 4th/5th order. The model shows high sensitivity to the forward and reverse rates of reactions during synaptic transmission as well as on the membrane conductance of the cell populations. The input to the model is a white noise signal simulating conditions of resting state with eyes closed, a condition well known to be associated with dominant alpha band oscillations in EEG e.g. [5]. Thus, the model parameters are calibrated to obtain a set of basal parameter values when the model oscillates with a dominant frequency within the alpha band. The time series plots and the power spectra of the model output are compared with those when the IN cell population is disconnected from the circuit (by setting the inhibitory connectivity parameter from the IN to the TCR to zero). We observe (Fig. 2 inset) a significant difference in time series output of the TRN cell population with and without the IN cell population in the model; this in spite of the IN having no direct connectivity to and from the TRN cell population (Fig. 1). A comparison of the power spectra behaviour of the model output within the delta (1-3.5Hz), theta (3.75-7.5Hz), alpha (7.75-13.5Hz) and beta (13.75-30.5Hz) bands is shown in Fig. 2. Disconnecting the IN cell population shows a significant drop in the alpha band power and the dominant frequency of oscillation now lies within the theta band. An overall ‘slowing’ (left-side shift) of the power spectra is observed with an increase within the delta and theta bands and a decrease in the alpha and beta bands. Such a slowing of EEG is a signature of slow wave sleep in healthy individuals, and this suggests that the IN cell population may be centrally involved in the phase transition to slow wave sleep [6]. It is also characteristic of the waking EEG in Alzheimer’s disease, and may help us to understand the role of the IN cell population in modulating TCR and TRN cell behaviour in pathological brain conditions

Experimental investigations of ambiguity: the case of most

In the study of natural language quantification, much recent attention has been devoted to the investigation of verification procedures associated with the proportional quantifier most. The aim of these studies is to go beyond the traditional characterization of the semantics of most, which is confined to explicating its truth-functional and presuppositional content as well as its combinatorial properties, as these aspects underdetermine the correct analysis of most. The present paper contributes to this effort by presenting new experimental evidence in support of a decompositional analysis of most according to which it is a superlative construction built from a gradable predicate many or much and the superlative operator -est (Hackl, in Nat Lang Semant 17:63–98, 2009). Our evidence comes in the form of verification profiles for sentences like Most of the dots are blue which, we argue, reflect the existence of a superlative reading of most. This notably contrasts with Lidz et al.’s (Nat Lang Semant 19:227–256, 2011) results. To reconcile the two sets of data, we argue, it is necessary to take important differences in task demands into account, which impose limits on the conclusions that can be drawn from these studies

Must . . . stay . . . strong!

This is the fourth installment in our trilogy of papers on epistemic modality.It is a recurring matra that epistemic must creates a statement that is weaker than the corresponding flat-footed assertion: It must be raining vs. It’s raining. Contrary to classic discussions of the phenomenon such as by Karttunen, Kratzer, and Veltman, we argue that instead of having a weak semantics, must presupposes the presence of an indirect inference or deduction rather than of a direct observation. This is independent of the strength of the claim being made. Epistemic must is therefore quite similar to evidential markers of indirect evidence known from languages with rich evidential systems. We work towards a formalization of the evidential component, relying on a structured model of information states (analogous to some models used in the belief dynamics literature). We explain why in many contexts, one can perceive a lack of confidence on the part of the speaker who uses must

Activation energy and entropy of dynamic fatigue of pristine silica optical fibers

ABSTRACT Subcritical crack growth in fused silica can be modeled as a stress assisted chemical reaction between water and strained bonds at the crack tip. The stress influences the crack growth rate by reducing the free energy of the activated complex. In principal, the stress changes both the activation enthalpy (energy) and entropy; however, the influence of stress on entropy has generally been ignored. The dynamic fatigue behavior of "pristine" optical fiber can be used to determine the fatigue kinetics parameters with unprecedented precision. It is shown that the entropy contribution is at least as significant as the enthalpy and therefore should not be ignored

Multi-level selection and the issue of environmental homogeneity

In this paper, I identify two general positions with respect to the relationship between environment and natural selection. These positions consist in claiming that selective claims need and, respectively, need not be relativized to homogenous environments. I then show that adopting one or the other position makes a difference with respect to the way in which the effects of selection are to be measured in certain cases in which the focal population is distributed over heterogeneous environments. Moreover, I show that these two positions lead to two different interpretations – the Pricean and contextualist ones – of a type of selection scenarios in which multiple groups varying in properties affect the change in the metapopulation mean of individual-level traits. Showing that these two interpretations stem from different attitudes towards environmental homogeneity allows me to argue: a) that, unlike the Pricean interpretation, the contextualist interpretation can only claim that drift or selection is responsible for the change in frequency of the focal trait in a given metapopulation if details about whether or not group formation is random are specified; b) that the traditional main objection against the Pricean interpretation – consisting in arguing that the latter takes certain side-effects of individual selection to be effects of group selection – is unconvincing. This leads me to suggest that the ongoing debate about which of the two interpretations is preferable should concentrate on different issues than previously thought

Partial Thickness Rotator Cuff Tears: Current Concepts

Partial thickness rotator cuff tears are a common cause of pain in the adult shoulder. Despite their high prevalence, the diagnosis and treatment of partial thickness rotator cuff tears remains controversial. While recent studies have helped to elucidate the anatomy and natural history of disease progression, the optimal treatment, both nonoperative and operative, is unclear. Although the advent of arthroscopy has improved the accuracy of the diagnosis of partial thickness rotator cuff tears, the number of surgical techniques used to repair these tears has also increased. While multiple repair techniques have been described, there is currently no significant clinical evidence supporting more complex surgical techniques over standard rotator cuff repair. Further research is required to determine the clinical indications for surgical and nonsurgical management, when formal rotator cuff repair is specifically indicated and when biologic adjunctive therapy may be utilized

At Sea Test 2 recovery cruise : Cruise 206 on board R/V Knorr April 10 - 15, 2012 Woods Hole - Woods Hole, MA

The R/V Knorr, on Cruise 206, carried out the recovery of three moorings for the Coastal and Global Scale Nodes (CGSN) Implementing Organization of the NSF Ocean Observatories Initiative. These three moorings are prototypes of the moorings to be used by CGSN at the Pioneer, Endurance, and Global Arrays. Knorr departed from Woods Hole, Massachusetts on April 10, 2012 and steamed south to the location of the mooring deployments on the shelf break. Over five days, April 10-15, Knorr surveyed the bottom at the planned mooring sites, recovered the moorings, and carried out preliminary investigations of mechanical and electrical functionality on the recovered moorings and mooring hardware, including observations of biofouling and corrosion. Knorr returned to Woods Hole on April 15, 2012.Funding was provided by the National Science Foundation contract #SA9-10 through the Consortium for Ocean Leadershi