Piezoelectricity in Monolayer Hexagonal Boron Nitride

2D hexagonal boron nitride (hBN) is a wide-bandgap van der Waals crystal with a unique combination of properties, including exceptional strength, large oxidation resistance at high temperatures, and optical functionalities. Furthermore, in recent years hBN crystals have become the material of choice for encapsulating other 2D crystals in a variety of technological applications, from optoelectronic and tunneling devices to composites. Monolayer hBN, which has no center of symmetry, is predicted to exhibit piezoelectric properties, yet experimental evidence is lacking. Here, by using electrostatic force microscopy, this effect is observed as a strain-induced change in the local electric field around bubbles and creases, in agreement with theoretical calculations. No piezoelectricity is found in bilayer and bulk hBN, where the center of symmetry is restored. These results add piezoelectricity to the known properties of monolayer hBN, which makes it a desirable candidate for novel electromechanical and stretchable optoelectronic devices, and pave a way to control the local electric field and carrier concentration in van der Waals heterostructures via strain. The experimental approach used here also shows a way to investigate the piezoelectric properties of other materials on the nanoscale by using electrostatic scanning probe techniques.     

Control of the permeability of a porous media using a thermally sensitive polymer

Experiments explore the reduction in permeability of a porous bead pack when a suspension of thermally responsive polymer is injected and the temperature then increased above the thermal activation temperature. The change in permeability is greater with higher polymer concentration, provided that the ionic concentration of the solution is sufficient for floc formation. The time for activation of the blocking effect is within tens of seconds to minutes of when the polymer solution is heated. This is consistent with the timescale for diffusion‐limited aggregation, although the detailed value depends on the geometry and polymer concentration. Dynamical experiments demonstrate that once the porous media is blocked, adding additional polymer has no effect. The mechanism for permeability reduction may be modeled in the context of a pore‐network model, and we build a simple model to illustrate the permeability reduction as a function of the fraction of pores links which are blocked. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1193–1201, 2014     

Oligosaccharide model of the vascular endothelial glycocalyx in physiological flow

Experiments have consistently revealed the pivotal role of the endothelial glycocalyx layer in vasoregulation and the layer’s contribution to mechanotransduction pathways. However, the exact mechanism by which the glycocalyx mediates fluid shear stress remains elusive. This study employs atomic-scale molecular simulations with the aim of investigating the conformational and orientation properties of highly flexible oligosaccharide components of the glycocalyx and their suitability as transduction molecules under hydrodynamic loading. Fluid flow was shown to have nearly no effect on the conformation populations explored by the oligosaccharide, in comparison with static (diffusion) conditions. However, the glycan exhibited a significant orientation change, when compared to simple diffusion, aligning itself with the flow direction. It is the tethered end of the glycan, an asparagine amino acid, which experienced conformational changes as a result of this flow-induced bias. Our results suggest that shear flow through the layer can have an impact on the conformational properties of saccharide-decorated transmembrane proteins, thus acting as a mechanosensor.     

中美两国相互学习，共同促进制造经济

今天能与大家交流,我感到既高兴又荣幸。2009年,我被任命为AMT即美国机械制造技术协会的会长,在此之前,我曾在企业做过,自己也曾办过企业。上任两年以来,只要有人愿意听。我就一直在宣传制造业在建设可持续经济中的重要性,一直在宣传合作对我们行业未来发展的重要性。     

Purity Assessment of Commercial Zein Products After Purification

Successful utilization of commercial zein products for certain food, pharmaceutical, cosmetic and medical applications requires a decolorized/deodorized zein of high purity that can be achieved by column filtration of commercial yellow zein solutions through Zeolite 5A and activated carbon. The objective of this investigation was to devise a combination of methodologies to assess purity and degree of deodorization and decolorization. Off-odor removal is defined by a UV spectroscopic ratio of 280:325 nm where diferuloylputrescine is the major contributor. Removal of yellow color, attributed to xanthophylls in zein, was followed by visible spectroscopic assays of a series of dilutions at 448 nm. SDS-PAGE analysis demonstrated removal of β-zein in combination with diminished sulfur content by sulfur analysis. Zein purity was assessed by Dumas nitrogen and FTIR of commercial zein before and after column filtration. Spectral differences were observed in the amide I (1,650 cm⁻¹) peak, amide II region (1,530 and 1,550 cm⁻¹) and the amide III peak at 1,240 cm⁻¹, where ratio of the dominant peaks were strongly dependent on purity of sample. Circular dichroism (CD) analyses validated the FTIR results by showing increased α-helical content for the column purified zeins. Combinations of these methodologies can be used to define zein products as a quality control measure for a commercial operation.     

Synthesis and characterization of polyaniline/carbon nanotube composites

The synthesis of polyaniline (PANI) containing different carbon nanotubes (CNTs) by in situ polymerization is reported in this study. The samples were characterized by X‐ray diffraction and scanning electron microscopy. Fourier transform infrared and ultraviolet–visible spectroscopy were used to determine the change in structure of the polymer/CNT composites. Thermogravimetric analysis showed that the composites had better thermal stability than the pure PANI. Photoluminescence spectra showed a blueshift in the PANI–single‐walled nanotube (SWNT) composite. Low‐temperature (77–300 K) electrical transport properties were measured in the absence and presence of a magnetic field up to 1 T. Direct‐current conductivity exhibited a nonohmic, three‐dimensional variable range hopping mechanism. The room‐temperature magnetoconductivity of all of the investigated samples except the PANI–SWNT composite were negative; however, it was positive for the PANI–SWNT composite, and its magnitude decreased with increasing temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A Quasiparticle Detector for Imaging Quantum Turbulence in Superfluid ^3He-B

We describe the development of a two-dimensional quasiparticle detector for use in visualising quantum turbulence in superfluid $^3$ He-B at ultra-low temperatures. The detector consists of a $5 \times 5$ matrix of pixels, each a 1 mm diameter hole in a copper block containing a miniature quartz tuning fork. The damping on each fork provides a measure of the local quasiparticle flux. The detector is illuminated by a beam of ballistic quasiparticles generated from a nearby black-body radiator. A comparison of the damping on the different forks provides a measure of the cross-sectional profile of the beam. Further, we generate a tangle of vortices (quantum turbulence) in the path of the beam using a vibrating wire resonator. The vortices cast a shadow onto the face of the detector due to the Andreev reflection of quasiparticles in the beam. This allows us to image the vortices and to investigate their dynamics. Here we give details of the design and construction of the detector and show some preliminary results for one row of pixels which demonstrates its successful application to measuring quasiparticle beams and quantum turbulence.     

Behavior therapy for Tourette's disorder: Utilization in a community sample and an emerging area of practice for psychologists.

The current article describes the phenomenology and empirically supported treatments for Tourette's disorder (TD) and presents data on treatment utilization from two separate national surveys of adults with TD (N = 672) and parents of children with TD (N = 740). Despite a wealth of empirical evidence demonstrating its effectiveness, results suggest that most people with TD do not receive behavior therapy for the condition. Reasons for this include a lack of information about the disorder among consumers and providers, a shortage of providers trained in the treatment, and concern about possible negative effects of behavioral treatment. The article concludes with a discussion about dissemination efforts aimed at making behavior therapy more widely available to children and adults with chronic tics and a review of beliefs about the negative effects of behavior therapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Copper Fixed-Point Measurements for Radiation Thermometry at National Research Council

Due to its high transition temperature relative to other fixed points defined in the International Temperature Scale of 1990 (ITS-90) and its relatively low cost compared to silver and gold, copper is often chosen as the fixed point used to define the ITS-90 above 1235 K at national measurement institutes. Measurement of the copper freezing point can be done in a variety of furnaces. Although there are a large number of copper fixed-point designs, we expect the freezing temperatures to be the same. The difference between realizing different sized fixed points and the use of different furnaces in which to realize them is explored here. A traditional, large aperture fixed-point containing over 600 g of copper is compared to a hybrid-type fixed point containing only 15 g of copper and a commercial fixed point. Three types of furnaces including a heat-pipe furnace, a compact furnace, and a high-temperature blackbody were used to realize the copper freezing point. Between the fixed-point types, only the length of the plateau differed. However, a significant difference was found between the freezing temperatures determined in the different furnaces, and this difference was independent of cell type.