Strain Rate Contribution due to Dynamic Recovery of Ultrafine-Grained Cu–Zr as Evidenced by Load Reductions during Quasi-Stationary Deformation at 0.5 Tm

During quasi-stationary tensile deformation of ultrafine-grained Cu-0.2 mass%Zr at 673 K and a deformation rate of about e - 4 / s load changes were performed. Reductions of relative load by more than about 25% initiate anelastic back flow. Subsequently, the creep rate turns positive again and goes through a relative maximum. This is interpreted by a strain rate component ϵ ˙ - associated with dynamic recovery of dislocations. Back extrapolation indicates that ϵ ˙ - contributes the same fraction of ( 20 ± 10 ) % to the quasi-stationary strain rate that has been reported for coarse-grained materials with high fraction of low-angle boundaries; this suggests that dynamic recovery of dislocations is generally mediated by boundaries. The influence of anelastic back flow on ϵ ˙ - is discussed. Comparison of ϵ ˙ - to the quasi-stationary rate points to enhancement of dynamic recovery by internal stresses. Subtraction of ϵ ˙ - from the total rate yields the rate component ϵ ˙ + related with generation and storage of dislocations; its activation volume is in the order expected from the classical theory of thermal glide.

Influence of temperature on spatial fibrin clot formation process in thrombodynamics

In this study we have investigated the process of spatial fibrin clot formation in non-steered platelet-free plasma at the temperatures from 20°C to 43°C using thrombodynamics – the novel in vitro hemostasis assay, which imitates the process of hemostatic clot growth in vivo. During data processing the following parameters were calculated: initial (V i ) and stationary (V st ) rates of clot growth which characterize initiation and propagation phases of clotting process, and clot size on the 30 th minute. The temperature dependence of extrinsic and intrinsic tenase activities, which determine values of the initial and stationary clot growth rates, respectively, have been also measured. It was established that the temperature lowering from 37°C to 24°C extends mainly on the initiation phase of clot growth, while the stationary rate of clot growth changes insignificantly. Meanwhile none of the thrombodynamics parameters shows the dramatic change of plasma coagulation system condition at the temperature of 24°C (acute hypothermia). Using the thrombodynamics assay an assumption, that the temperature lowering does not change the state of plasma hemostasis system significantly has been confirmed.

Effect of Pre-Analytical Conditions On the Results of Thrombodynamics Assay

Abstract 4393 Introduction Thrombodynamics is a novel global coagulation assay based on spatial separation of clotting activation and propagation. In this assay fibrin clot grows from the TF-coated surface in a thin layer of non-stirred plasma. Clot formation is monitored via light scattering (Fig.1). The main parameters measured in the assay are: lag-time (Tlag), time between bringing plasma in contact with TF and actual start of clot growth: initial rate of clot growth (Vin), rate of clot growth during first 5 minutes; stationary rate of clot growth (Vst), rate of clot formation in 20 minutes after the beginning. (Fig.2) In this study we analyzed effect of the pre-analytic conditions (blood collection and plasma preparation) on the results of Thrombodynamics assay. Materials and Methods Blood was collected into sodium citrate tubes with 9:1 volume ratio. It was usually processed by two centrifugations to obtain PPP (1 600g, 15 min) and then PFP (10 000g, 5 min). 20 μg/ml of Corn Tripsin Inhibitor (CTI) was used to prevent contact activation. 20 mM of CaCl2 was added to plasma prior to the experiment. Coagulation was activated by tissue factor immobilized to plastic surface (100 pmol/m2). Results Sodium citrate venous blood collection tubes of three major manufacturers (BD Vacutainer, Greiner Vacuette and Sarstedt Monovette) and citrate concentrations 3.2% and 3.8% for Greiner Vacuette tubes were compared. Blood from 12 healthy volunteers was used for that purpose. All experiments were performed in duplicates. BD Vacutainer tubes showed significant hypercoagulation compared to the other tubes tested. Stationary rate was significantly higher (Mann-Whitney test p=0.05) in these tubes while three other types of tubes showed similar results (Table 1). There was no significant difference between 3.2% and 3.8% of sodium citrate for Vacuette tubes in all parameters measured. Sarstedt Monovette and BD Vacutainer tubes revealed an increased initial rate of clot growth compared to both Vacuette tubes (p=0.05). Lag times were similar for all the tubes tested. To estimate the possible error introduced by blood collection procedure, 3 independent collections from different veins were performed for 3 healthy volunteers. Standard deviation for the Thrombodynamics parameters were 12% for Tlag, 7% for Vin, 8% for Vst. Two centrifugation protocols were studied: PPP was centrifuged for 5 min at 10 000 g or for 20 min at 1600 g. No significant difference was observed for these methods (n=7, p=0.05). PPP can potentially be used in the Thrombodynamics assay as well as PFP with adjusted range of normal values. Clot growth rates increase in PPP compared to PFP (n=50, Vin =48.8±7.4μm/min and 45.6±12.8 μm/min for PPP and PFP respectively; Vin= 28.6±4.2 μm/min and 24.1±3.0 μm/min for PPP and PFP respectively). Inhibition of contact activation is important as thin layer of plasma is used and surface to volume ratio in experimental chamber is high. Addition of CTI to PPP with subsequent centrifugation induced significant decrease in initial rate (44.8±6.7 μm/min) compared to 51.1±7.6 μm/min when CTI was added to PFP directly, n=12, p=0.05. Stationary rate did not change significantly (25.8±3.6 μm/min and 28.2±4 μm/min respectively, p=0.05). Finally we studied the effects of sample storage. For healthy donors no significant change in Thrombodynamics parameters was observed during 3 hours (n=8) and 24 hours (n=3) of storage of PFP at RT. 50 samples of fresh and frozen plasma from healthy volunteers were compared. Clot growth rates increased for frozen plasma (Vst = 28.4±4.0μm/min) compared to non-frozen samples (24.1±3.0μm/min). Therefore frozen plasma can be used in the assay but normal ranges for frozen and non-frozen samples should be defined separately. These data represent a first step for standardization of Thrombodynamics assay and decrease of variability due to pre-analytic conditions. Disclosures: Dashkevich: HemaCore LLC: Employment. Vuimo:HemaCore LLC: Employment. Balandina:HemaCore LLC: Employment. Ovsepyan:HemaCore LLC: Employment. Soshitova:HemaCore LLC: Employment. Seregina:HemaCore LLC: Employment. Surov:HemaCore LLC: Employment. Lipets:HemaCore LLC: Employment. Panteleev:HemaCore LLC: Employment. Ataullakhanov:HemaCore LLC: Employment, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties.

Plastic Flow Establishment in Circular Pipes Under the Effect of a Magnetic Field

In many biological, chemical and industrial applications the time for discharging a pipe in a process is very important in order to obtain optimal mixing. Particulary in the case of stationary rate processes it may mean lower cost and improved optimization. In this paper a new method to compute the velocity profile in established plastic flow in circular pipes under the effect of a magnetic field is presented. Results are presented for a variety of pressure gradients and yield stresses for different values of the Hartmann number.

AN INTERMITTENTLY USED SYSTEM WITH PREPARATION TIME FOR THE REPAIR FACILITY

Two models of an intermittently used system with preparation time for the repair facility are considered. Mean stationary rate of the disappointments, the joint probability that disappointments do not occur at specified intervals are obtained for both the models.

Computation of posterior distribution in Bayesian analysis – application in an intermittently used reliability system

Bayesian estimation is presented for the stationary rate of disappointments, D∞, for two models (with different specifications) of intermittently used systems. The random variables in the system are considered to be independently exponentially distributed. Jeffreys’ prior is assumed for the unknown parameters in the system. Inference about D∞ is being restrained in both models by the complex and non-linear definition of D∞. Monte Carlo simulation is used to derive the posterior distribution of D∞ and subsequently the highest posterior density (HPD) intervals. A numerical example where Bayes estimates and the HPD intervals are determined illustrates these results. This illustration is extended to determine the frequentistical properties of this Bayes procedure, by calculating covering proportions for each of these HPD intervals, assuming fixed values for the parameters.