关键词： ultrasound   piezosurgery   dacryocystorhinostomy   DCR   time   mechanical   drill  

摘要： BackgroundThe purpose of this study is to report the time taken for superior osteotomy and complications during this step in primary powered endoscopic dacryocystorhinostomy (PEnDCR) using the piezoelectric system and mechanical burr. MethodsThis prospective interventional comparative series was performed on all consecutive patients who underwent a primary PEnDCR over a 4-month period. The surgery was performed as per standard protocols and all patients were operated on by a single surgeon (M.J.A.). Parameters documented were demographic data, type of powered instrument used, time taken for superior osteotomy, exposure of the agger nasi, exposure of entire sac, and complications such as excess bleeding, soft tissue injury, or mucosal burns. Statistical analyses were performed using the linear mixed-effect model and 2-sample t tests. ResultsA total of 55 PEnDCRs were studied, 29 in the mechanical burr group and 26 in the piezoelectric or ultrasonic group. The mean time for superior osteotomy in the mechanical burr group was 3.71 minutes (range, 1.75 to 6.58 minutes);in the ultrasonic group it was 4.12 minutes (range, 1.33 to 6.25 minutes). There was no significant difference (p = 0.17) between the 2 groups. Subcategory analyses of time taken by age (p = 0.057) and sex (p = 0.56) did not show any difference between the groups. Two patients in the mechanical burr group had an insignificant superficial sac injury and 1 patient in the ultrasonic group suffered epithelial burns away from the site of osteotomy, which resolved spontaneously without any sequelae. There was no excess bleeding in any of the groups. ConclusionThe time taken by mechanical burr and piezoelectric system are comparable for superior osteotomy in PEnDCR. If anatomical boundaries are respected, their use appears to be safe without major complications.

关键词： Structural force   Mechanical dynamics   Motor proteins   Mechanosensors   Fluorescence-based force sensors  

摘要： Three signaling systems play the fundamental roles in modulating cell activities: chemical, electrical, and mechanical. While the former two are well studied, the mechanical signaling system is still elusive because of the lack of methods to measure structural forces in real time at cellular and subcellular levels. Indeed, almost all biological processes are responsive to modulation by mechanical forces that trigger dispersive downstream electrical and biochemical pathways. Communication among the three systems is essential to make cells and tissues receptive to environmental changes. Cells have evolved many sophisticated mechanisms for the generation, perception and transduction of mechanical forces, including motor proteins and mechanosensors. In this review, we introduce some background information about mechanical dynamics in live cells, including the ubiquitous mechanical activity, various types of mechanical stimuli exerted on cells and the different mechanosensors. We also summarize recent results obtained using genetically encoded FRET (fluorescence resonance energy transfer)-based force/tension sensors;a new technique used to measure mechanical forces in structural proteins. The sensors have been incorporated into many specific structural proteins and have measured the force gradients in real time within live cells, tissues, and animals. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Incubation time   Diffusion model   Activation energy   Growth kinetics   Adherence   Tribology  

摘要： In this work, American Iron and Steel Institute (AISI) O1 steel was pack borided in the temperature range of 1123-1273 K for treatment times between 2 and 8 hours. A kinetic model was proposed for estimating the boron diffusion coefficients through the Fe2B layers. As a result, the boron activation energy for the AISI O1 steel was estimated as 197.2 kJ mol(-1). This value of energy was compared to the literature data. In addtion, to extend the validity of the present model, two additional boriding conditions were done. The Fe2B layers grown on AISI O1 steel were characterised by use of the following experimental techniques: scanning electron microscopy, X-ray diffraction analysis and Daimler-Benz Rockwell-C indentation technique. Finally, the scratch and pin on disc tests for wear resistance were respectively performed using an LG Motion Ltd and a CSM tribometer under dry sliding conditions.

关键词： Broiler house   Computational fluid dynamics   Corrected Archimedes number   Jet-drop-distance   Ventilation  

摘要： Controlling airflow trajectory through slot-openings is important to induce an efficient thermal exchange in a broiler house, particularly in winter. A jet-drop-distance model was proposed to establish a plan for the control and management of a cold jet trajectory by Zhang & Strom (1999), Transactions of the ASAE, 42(4), 1121-1126. Jet-drop-distance is defined as the horizontal distance from a wall to an animal occupied zone where the incoming cold air first reaches at. Regression models employing jet-drop-factor and corrected Archimedes number variables were calculated based on experimental data. However, this approach was restricted, because of the small-scale model, the small number of slot-openings and difficulties in measuring invisible airflows being observed. Here, computational fluid dynamics (CFD) was adopted to overcome the experimental limitations and to analyse jet-drop-distances qualitatively and quantitatively in a commercial broiler house with multiple slot-openings. Predictions of jet-drop-distances were computed using the experimental conditions used by Zhang & Strom (1999) and compared with their regression models to validate the accuracy of developed method. In the validation test, the regression model using the corrected Archimedes number more accurately predicted the jet-drop-distance in the simulation model (R-2 = 0.90). The validated method was subsequently applied to the analysis of the jet-drop-distance in a mechanically ventilated broiler house with multiple slot-openings. Trends of the CFD computed jet-drop-distance were analysed according to such variables as ventilation rate, initial angle of slot-openings and outdoor air temperature. (C) 2015 IAgrE. Published by Elsevier Ltd. All rights reserved.

关键词： molecular dynamics   electric field   electrophoresis   nanorod  

摘要： Non-equilibrium molecular dynamics (MD) of small, charged cadmium selenide nanorods have been carried out in the absence and presence of static applied electric fields. In the absence of applied fields, it was found that opposite dipolar alignment (antiferromagnetic) was achieved, along with self-assembly of the nanorods. However, in the case of induced electrophoresis in applied fields, the rods approached each other less readily, while at and above a field intensity of 0.05 V/angstrom, preferential alignment with the field was achieved for all rods, in contrast to the zero-field case. These results have implications for electric field-mediated control of nanorod assembly in solution, of key importance in a wide range of areas from photovoltaics to energy storage.

关键词： Two-photon microscopy   Somatosensory cortex   Voluntary locomotion   Tissue mechanics  

摘要： Understanding the spatial dynamics of dilation in the cerebral vasculature is essential for deciphering the vascular basis of hemodynamic signals in the brain. We used two-photon microscopy to image neural activity and vascular dynamics in the somatosensory cortex of awake behaving mice during voluntary locomotion. Arterial dilations within the histologically-defined forelimb/hindlimb (FL/HL) representation were larger than arterial dilations in the somatosensory cortex immediately outside the FL/HL representation, demonstrating that the vascular response during natural behaviors was spatially localized. Surprisingly, we found that locomotion drove dilations in surface vessels that were nearly three times the amplitude of intracortical vessel dilations. The smaller dilations of the intracortical arterioles were not due to saturation of dilation. Anatomical imaging revealed that, unlike surface vessels, intracortical vessels were tightly enclosed by brain tissue. A mathematical model showed that mechanical restriction by the brain tissue surrounding intracortical vessels could account for the reduced amplitude of intracortical vessel dilation relative to surface vessels. Thus, under normal conditions, the mechanical properties of the brain may play an important role in sculpting the laminar differences of hemodynamic responses. (C) 2015 Elsevier Inc. All rights reserved.

关键词： Molecular dynamics   Silica glass   Nanoscratch   Scratched surface   Nanoindentation  

摘要： In order to study the mechanical properties of the processed surface for silica glass, a nanoscratch of the silica glass is built based on molecular dynamics method and a nanoindentation is performed on the scratched surface subsequently. The model of silica glass is established by using the approach of melting-quenching and the forming mechanism of the microscopic voids in the process of preparation is analyzed. During nanoindentation, the mechanical properties of the machined surface and the original surface are compared. The results show that the microscopic cavity in the silica glass will form in the cooling process due to the accumulation of large rings generating by the restructuring of the Si-O bonds. The hardness and plastic of the scratched surface will improve after the abrasive sweeps away. The deformation mechanism of the model during nanoscratch is densification rather than plastic flow, which is the reason of the increasing of the surface hardness. According to the further analysis of the atomic concentration areas in the scratched surface, it is found that the fivefold defect is responsible for the change of the plastic behavior. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Shear deformation   Molecular dynamics   Stress strain relations   Monolayers   Ab initio calculations  

摘要： The temperature-dependent stress-strain relations of monolayer black phosphorus (BP) under biaxial and uniaxial tension as well as shear deformation are investigated using molecular dynamics (MD) simulations. The predicted strength and moduli are in good agreement with the available results from the first-principle method. In particular, the amplitude to wavelength ratio of wrinkles under shear deformation using MD simulations also agrees well with that from the existing theory. This study provides physical insights into the origins of the temperature-dependent mechanical properties of the monolayer BP. (C) 2015 AIP Publishing LLC.

关键词： Shape memory alloys   Phase-field   Thermo-mechanical   Isogeometic analysis  

摘要： The paper focuses on numerical simulation of the 3D phase-field (PF) equations for modeling cubic-to-tetragonal martensitic transformations in shape memory alloys (SMAs), their complex microstructures and thermo-mechanical behavior. The straightforward solution to the fourth-order diffuse interface 3D PF equations, based on the Landau-Ginzburg potential, is numerically solved using an isogeometric analysis. We present microstructure evolution in different geometries of SMA nanostructures under temperature-induced phase transformations to illustrate the geometrical flexibility, accuracy and robustness of our approach. The simulations successfully capture the dynamic thermo-mechanical behavior of SMAs observed experimentally. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： cohesion energy   conjugated polymers   mechanical properties   molecular dynamics   polymer entanglement   P3HT  

摘要： Due to their inherent mechanical flexibility and stretchability, organic-based electronic devices have garnered a great deal of academic and industrial interest. Here, molecular-dynamics simulations are used to examine the molecular-scale details that govern the relationships among molecular weight, chain entanglement, persistence length, and the elastic characteristics of the widely studied -conjugated polymer poly-(3-hexyl thiophene), P3HT. Oligomers containing at least 50 monomer units are required in the simulations to observe elastic behavior in P3HT, while much longer chains are required to ensure description of appropriate levels of entanglement: only when the molecular weight is greater than 50 kDa, that is, oligomers with approximately 400 monomer units, is truly entangled behavior observed. Interestingly, results from primitive path analysis of amorphous P3HT matches well with the observed onsets of inter-chain excitonic coherence with increased molecular weight. The simulations also indicate that the P3HT modulus saturates at 1.6 GPa for chain lengths of 50-100 monomers, a result that compares well with experimental results. This work highlights the care that needs to be taken to accurately model P3HT morphologies in relation to experimental measurements. (c) 2015 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 934-942