411 research outputs found

    Structure, Thermodynamics and Kinetics of Chemically Heterogeneous Interfaces

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    In this work we have used atomistic computer simulations to examine the structure, thermodynamics and transport properties, for two models of chemically heterogeneous interfaces: an ideal model (repulsive soft spheres against a potential wall), and a metal alloy interface (Cu-Pb). In both systems, interfacial prefreezing (crystal formation above the melting point of the fluid) was observed and this prefreezing was seen to promote heterogeneous nucleation, when the systems were cooled below the melting temperature. In our study of inverse-power repulsive soft spheres, we found that the soft-sphere fluid exhibited prefreezing at the wall surface. Similar behavior was previously observed in hard-sphere fluids at hard wall [17, 18, 20], however, to our knowledge, this the first time that prefreezing is reported for soft spheres. The prediction of prefreezing is based on the calculation of interfacial free energies wall-crystal (g_wc) and wall-fluid (g_wf ) using a variant of the cleaving wall method. With the calculated, g_wc and g_wf together with g_cf , previously computed [79], the tendency to prefreeze was quantified by the wetting angle formed between the metastable crystal phase on the wall and the soft-sphere fluid. We found that all the closest packing orientations [(111) FCC and (110) BCC] developed prefreezing (complete wetting). A detailed atomic-level characterization of the structure, energetics and transport properties of the planar Cu/Pb solid-liquid interface in equilibrium was performed at a several temperatures (625K and 750K) above the melting point of Pb and for two Cu crystal orientations [(111) and (100)]. Among the most relevant findings are that the Cu(100)/Pb interfaces presents surfaces alloying and the Cu(111)/Pb exhibits a prefreezing layer of Pb crystal. It was also observed that both interfaces have a nucleation barrier that prevents heterogeneous nucleation and that the mechanisms by which each structure promotes heterogeneous nucleation are different. Both models, the inverse-power soft spheres and the EAM Cu-Pb, showed the connection between atomistic behavior and prefreezing. The crystalline layer formed above the melting point of the fluids showed to be influential in heterogeneous nucleation in both cases. In this way, the study of basic properties shed new light on the atomistic underlying nature of macroscopic events, such as wetting and nucleatio

    The Effects of Weathered Crude Oil from the M/T Alvenus Spill on Eggs and Yolk-Sac Larvae of Red Drum (Sciaenops ocellatus)

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    The Biitish tanker M/T ALVENUS ran aground 16.1 km south of Cameron, Louisiana, on 30 July 1984. An estimated 10,157 MT of Venezuelan crude oil were spilled into the Gulf of Mexico. Approximately 2,700 MT of the heavy viscous oil impacted beaches and an additional 1,360 MT remained in the subtidal areas of west Galveston Island, about 160 km southwest of the accident site. Red drum, which spawn in the Gulf of Mexico in the fall, could have been seriously impacted by oil concentrations potentially lethal to eggs or larvae. The impact of weathered crude oil on the survival, growth, and morphological development of red drum eggs and larvae was assessed in the laboratory. Equal numbers of eggs were randomly assigned to one of six treatments of weathered crude oil (control, 50, 100, 500, 1,000 and 2,000 mg/l) and observed through the yolk-sac stage. There were no differences in mean survival, length of surviving larvae, and frequency of morphological abnormalities among treatments (α \u3c 0.05). In addition, the frequency of spinal deformity and abnormal mouth development was low in all treatments. The initial chemical composition of the fresh crude oil and the seasonally warm weather contributed to the natural degradation of the soluble toxic components

    Effects of lattice mismatch on interfacial structures of liquid and solidified Al in contact with hetero-phase substrates: MD simulations

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    Published under licence in IOP Conference Series: Material Science and Engineering by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.In this study, the effects of the misfit on in-plane structures of liquid Al and interfacial structure of solidified Al in contact with the heterophase substrates have been investigated, using molecular dynamics (MD) simulations. The MD simulations were conducted for Al/fcc (111) substrates with varied misfits. The order parameter and atomic arrangement indicated that the in-plane ordering of the liquid at the interface decreases significantly with an increase of the misfit, i.e., solid-like for small misfit and liquid-like for large misfit. Further, our MD simulation results revealed that a perfect orientation relationship forms at the interface between the substrate and the solidified Al for a misfit of less than -3% and the boundary is coherent. With an increase in the misfit, Shockley partial and extended dislocations form at the interface, and the boundary becomes a semi-coherent or low-angle twist boundary.EPSR

    Detecting affective states in virtual rehabilitation

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    Virtual rehabilitation supports motor training following stroke by means of tailored virtual environments. To optimize therapy outcome, virtual rehabilitation systems automatically adapt to the different patients' changing needs. Adaptation decisions should ideally be guided by both the observable performance and the hidden mind state of the user. We hypothesize that some affective aspects can be inferred from observable metrics. Here we present preliminary results of a classification exercise to decide on 4 states; tiredness, tension, pain and satisfaction. Descriptors of 3D hand movement and finger pressure were collected from 2 post-stroke participants while they practice on a virtual rehabilitation platform. Linear Support Vector Machine models were learnt to unfold a predictive relation between observation and the affective states considered. Initial results are promising (ROC Area under the curve (mean±std): 0.713 ± 0.137). Confirmation of these opens the door to incorporate surrogates of mind state into the algorithm deciding on therapy adaptation

    Surgical treatment of type-II choledochal cyst: a case report

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    Choledochal cyst is a pathology conditioned by a complex congenital malformation that involves different degrees of dilation of both the common bile duct and the pancreatic duct with a malignant tendency, these are reported more frequently in children, representing 1% of benign diseases of the biliary. Babbitt 's theory is the most frequently proposed theory and states that CCs (choledochal cysts) result from an anomalous pancreatobiliary junction (APBJ) where the pancreatic duct and bile duct connect 1-2 cm proximal to the sphincter of Oddi. In adults, the presentation is usually nonspecific and vague, with abdominal pain being the most common symptom. Surgical resection of cysts can significantly decrease the risk of malignancy and reduce associated complications. However, less attention has been paid to CC in adults, and its surgical parameters have been reported to be frequently controversial. This manuscript describes the clinical case of a Todani II choledochal cyst managed with surgical resection by laparotomy with Roux-en-Y biliodigestive reconstruction, obtaining satisfactory results

    Unobtrusive inference of affective states in virtual rehabilitation from upper limb motions: a feasibility study

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    Virtual rehabilitation environments may afford greater patient personalization if they could harness the patient's affective state. Four states: anxiety, pain, engagement and tiredness (either physical or psychological), were hypothesized to be inferable from observable metrics of hand location and gripping strength -relevant for rehabilitation-. Contributions are; (a) multiresolution classifier built from Semi-Naïve Bayesian classifiers, and (b) establishing predictive relations for the considered states from the motor proxies capitalizing on the proposed classifier with recognition levels sufficient for exploitation. 3D hand locations and gripping strength streams were recorded from 5 post-stroke patients whilst undergoing motor rehabilitation therapy administered through virtual rehabilitation along 10 sessions over 4 weeks. Features from the streams characterized the motor dynamics, while spontaneous manifestations of the states were labelled from concomitant videos by experts for supervised classification. The new classifier was compared against baseline support vector machine (SVM) and random forest (RF) with all three exhibiting comparable performances. Inference of the aforementioned states departing from chosen motor surrogates appears feasible, expediting increased personalization of virtual motor neurorehabilitation therapies
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