The Efficacy of Fibrinogen Concentrates in Relation to Cryoprecipitate in Restoring Clot Integrity and Stability against Lysis

Loss of fibrinogen is a feature of trauma-induced coagulopathy (TIC), and restoring this clotting factor is protective against hemorrhages. We compared the efficacy of cryoprecipitate, and of the fibrinogen concentrates RiaSTAP^® and FibCLOT^® in restoring the clot integrity in models of TIC. Cryoprecipitate and FibCLOT^® produced clots with higher maximal absorbance and enhanced resistance to lysis relative to RiaSTAP^®. The fibrin structure of clots, comprising cryoprecipitate and FibCLOT^®, mirrored those of normal plasma, whereas those with RiaSTAP^® showed stunted fibers and reduced porosity. The hemodilution of whole blood reduced the maximum clot firmness (MCF) as assessed by thromboelastography. MCF could be restored with the inclusion of 1 mg/mL of fibrinogen, but only FibCLOT^® was effective at stabilizing against lysis. The overall clot strength, measured using the Quantra^® hemostasis analyzer, was restored with both fibrinogen concentrates but not cryoprecipitate. α₂antiplasmin and plasminogen activator inhibitor-1 (PAI-1) were constituents of cryoprecipitate but were negligible in RiaSTAP^® and FibCLOT^®. Interestingly, cryoprecipitate and FibCLOT^® contained significantly higher factor XIII (FXIII) levels, approximately three-fold higher than RiaSTAP^®. Our data show that 1 mg/mL fibrinogen, a clinically achievable concentration, can restore adequate clot integrity. However, FibCLOT^®, which contained more FXIII, was superior in normalizing the clot structure and in stabilizing hemodiluted clots against mechanical and fibrinolytic degradation.     

Optimal movement in the prey strikes of weakly electric fish: a case study of the interplay of body plan and movement capability

Animal behaviour arises through a complex mixture of biomechanical, neuronal, sensory and control constraints. By focusing on a simple, stereotyped movement, the prey capture strike of a weakly electric fish, we show that the trajectory of a strike is one which minimizes effort. Specifically, we model the fish as a rigid ellipsoid moving through a fluid with no viscosity, governed by Kirchhoff's equations. This formulation allows us to exploit methods of discrete mechanics and optimal control to compute idealized fish trajectories that minimize a cost function. We compare these with the measured prey capture strikes of weakly electric fish from a previous study. The fish has certain movement limitations that are not incorporated in the mathematical model, such as not being able to move sideways. Nonetheless, we show quantitatively that the computed least-cost trajectories are remarkably similar to the measured trajectories. Since, in this simplified model, the basic geometry of the idealized fish determines the favourable modes of movement, this suggests a high degree of influence between body shape and movement capability. Simplified minimal models and optimization methods can give significant insight into how body morphology and movement capability are closely attuned in fish locomotion.     

Grain Size Distributions after Single Hit Deformation of a Segregated, Commercial Nb-Containing Steel: Prediction and Experiment

The present investigation examines the applicability of the Dutta–Sellars equations in predicting the recrystallized grain sizes following deformation for a 0.046 wt pct Nb-bearing, commercially produced steel with a segregated solute content (from continuous casting). The investigation considered initial unimodal and bimodal grain size distributions before deformation that were generated by reheating the steel to 1498 K and 1423 K (1225 °C and 1150 °C), respectively. It was found that the reheated grain size distribution (separated into grain size classes) could be related to the solute-rich (smaller grain size classes) and solute-depleted (larger grain size classes) regions. The use of these relationships and a simple halving of the grain size within the distribution on recrystallization (used previously for homogenized samples of this steel) were found to be appropriate in the grain size class-based use of the Dutta–Sellars equations with respect to mode and maximum grain sizes after hot deformation and holding. This approach successfully predicted (confirmed by experiment) the grain size distribution after deformation in the presence of Nb segregation from continuous casting.     

Motion detectors in the locust visual system: From biology to robot sensors

Motion detectors in the locust optic lobe and brain fall into two categories: neurones that respond selectively to approaching vs. receding objects and neurones that respond selectively to a particular pattern of image motion over a substantial part of the eye, generated by the locust's own movements through its environment. Neurones from the two categories can be differentiated on the basis of their response to motion at a constant velocity at a fixed distance from the locust: neurones of the first category respond equally well to motion in any direction whereas neurones in the second category respond selectively to one preferred direction of motion. Several of the motion detectors of the first category, responding to approaching objects, share the same input organisation, suggesting that it is important in generating a tuning for approaching objects. Anatomical, physiological, and modelling studies have revealed how the selectivity of the response is generated. The selectivity arises as a result of a critical race between excitation, generated when image edges move out over the eye and delayed inhibition, generated by the same edge movements. For excitation to build up, the velocity and extent of edge motion over the eye must increase rapidly. The ultrastructure of the afferent inputs onto the dendrites of collision sensitive neurones reveals a possible substrate for the interaction between excitation and inhibition. This interpretation is supported by both physiological and immunocytochemical evidence. The input organisation of these neurones has been incorporated into the control structure of a small mobile robot, which successfully avoids collisions with looming objects. The ecological role of motion detectors of the second category that respond to image motion over a substantial part of the visual field, is discussed as is the input organisation that generates this selective response. The broad tuning of these neurones, particularly at low velocities (<0.02 degree/s), suggests they may have a role in navigation during migratory flights at altitude. By contrast, their optimum tuning to high-image velocities suggests these motion detectors are adapted for use in a fast flying insect, which does not spend significant time hovering.     

Effects of aerosol scattering phase function formulation on point-spread-function calculations

The quality of the image produced by an outdoor optical system is affected by the presence of atmospheric aerosols between object and receiver. The properties of the point-spread function that result from aerosol particles were calculated by a new Monte Carlo code called MEDIA (an acronym for Modélisation des Effets de Diffusion Inhérents à l'Atmosphère). The influence of the scattering phase function's angular dependence on the irradiance of the focal plane of a detector was studied. Calculations were performed by use of Mie theory and of the Henyey-Greenstein formulation for the same asymmetry parameter and various detector optical characteristics and atmospheric conditions. Major variations were observed for strong forward-peaked scattering phase functions and a large detector field of view.     

Satellite-derived parameters for biological modelling in coastal waters: Illustration over the eastern continental shelf of the Bay of Biscay

In biological modelling of the coastal phytoplankton dynamics, the light attenuation coefficient is often expressed as a function of the concentrations of chlorophyll and mineral suspended particulate matter (SPM). In order to estimate the relationship between these parameters over the continental shelf of the northern Bay of Biscay, a set of in situ data has been gathered for the period 1998-2003 when SeaWiFS imagery is available. These data comprise surface measurements of the concentrations of total SPM, chlorophyll, and irradiance profiles from which is derived the attenuation coefficient of the photosynthetically available radiation, K_PAR. The performance of the IFREMER look-up table used to retrieve the chlorophyll concentration from the SeaWiFS radiance is evaluated on this new set of data. The quality of the estimated chlorophyll concentration is assessed from a comparison of the variograms of the in situ and satellite-derived chlorophyll concentrations. Once the chlorophyll concentration is determined, the non living SPM, which is defined as the SPM not related to the dead or alive endogenous phytoplankton, is estimated from the radiance at 555 nm by inverting a semi-analytic model. This method provides realistic estimations of concentrations of chlorophyll and SPM over the continental shelf all over the year. Finally, a relationship, based on non living SPM and chlorophyll, is proposed to estimate K_PAR on the continental shelf of the Bay of Biscay. The same formula is applied to non living SPM and chlorophyll concentrations, observed in situ or derived from SeaWiFS radiance.     

Possibilistic uncertainty handling for answer set programming

In this work, we introduce a new framework able to deal with a reasoning that is at the same time non monotonic and uncertain. In order to take into account a certainty level associated to each piece of knowledge, we use possibility theory to extend the non monotonic semantics of stable models for logic programs with default negation. By means of a possibility distribution we define a clear semantics of such programs by introducing what is a possibilistic stable model. We also propose a syntactic process based on a fix-point operator to compute these particular models representing the deductions of the program and their certainty. Then, we show how this introduction of a certainty level on each rule of a program can be used in order to restore its consistency in case of the program has no model at all. Furthermore, we explain how we can compute possibilistic stable models by using available softwares for Answer Set Programming and we describe the main lines of the system that we have developed to achieve this goal.     

Towards a one‐pot synthesis of a polystyrene–PMMA block copolymer via atom‐transfer radical polymerization

The solution atom‐transfer radical copolymerization of styrene and methyl methacrylate in butyl acetate at 110 °C in the presence of Cu(II) bromide and 2,2′‐bipyride was investigated. Polystyrene was polymerized by atom‐transfer radical polymerization using benzyl bromide as initiator and MMA was then added to the system. Block copolymers were formed when MMA was added at ≤90% styrene conversion. Molecular weight distributions (M_w/M_n) of the block copolymers were ≤1.5. The possibility of end‐capping the polystyrene precursor as a means of improving its initiating efficiency towards MMA was also investigated but did not improve the system. © 2002 Society of Chemical Industry     

Solute diffusion in dilute alloys

Expressions are written for diffusion properties in terms of solute and solvent jump frequencies and solute defect interaction energies. These are used in reviewing the general experimental features of dilute alloy diffusion and in showing how, through their interrelations, one may confirm or refute proposed mechanisms of diffusion and extract information on jump frequencies and defect properties. Impurities diffuse by the vacancy mechanism when their diffusion rates are comparable with the host self-diffusion rate (“normal diffusion”). When the impurity diffusion rate greatly exceeds that of self-diffusion (“anomalous diffusion”) the vacancy mechanism is untenable and diffusion is believed to be dominated by some form of interstitial migration. Evidence supporting these beliefs is described. While normal diffusion is now fairly well understood in some detail, this is not the case for anomalous diffusion because of the present lack of knowledge of the properties of the interstitial defects responsible for it.