Anisotropy of Silica Aerogels Induced by Small Strain

We have performed optical birefringence measurements on isotropic aerogel samples grown with varying amounts of ammonia catalyst to determine the relationship between stress, strain, and transmitted light intensity, focusing on the regime of relatively small axial strain. We find that our samples exhibit a delayed onset of birefringence at ～3 % strain, beyond which the transmitted intensity increases linearly, with a faster rate of increase for samples prepared with larger catalyst concentrations. We have also calculated the sound velocity from the slope of the stress-strain curve, and found an approximately linear increase with catalyst solution pH for samples of similar density. Samples of similar density also appear to exhibit a universal relationship between applied stress and transmitted intensity. We are not able to identify the mechanism for this unique behavior.     

<Emphasis Type=Italic>In-Situ</Emphasis> X-Ray Diffraction Observations of Low-Temperature Ag-Nanoink Sintering and High-Temperature Eutectic Reaction with Copper

Nanoinks, which contain nanometer-sized metallic particles suspended in an organic dispersant fluid, are finding numerous microelectronic applications. One characteristic of nanoinks is that they sinter at much lower temperatures than bulk metals due to their high surface area to volume ratio and small radius of curvature, which reduces their melting points significantly below their bulk values. The unusually low sintering temperatures have unique potential for materials joining, since their melting points increase dramatically afterward. In this article, the sintering kinetics of Ag nanoink is studied using in-situ synchrotron methods to determine diffraction peak characteristics during the sintering cycle, and to subsequently calculate particle size and growth during sintering. Ag nanoink is further explored as a eutectic bonding medium by tracking phase transformations between sintered Ag nanoink and a Cu substrate to high temperatures, where melting occurs at the Ag-Cu eutectic, demonstrating nanoinks as a viable eutectic bonding medium.     

具有世界一流水平的LEIPA#4纸机--以100%的废纸生产轻量涂布纸

德国LEIPA Georg Leinfelder集团的#4纸机,以100%的废纸为原料,年产50万吨优质轻量涂布纸.这条世界一流生产线,配有创新的TwinDrum双鼓碎浆机、EcoCell浮选系统、两套具有新分散概念的热分散系统、同一平台概念纸机、EcoSoft与Janus MK2软压光机、SpeedSizer涂布机、Sirus卷纸系统、VariTop复卷机、Twister 2纸卷包卷站、双层PrintFlex O毛毯等.     

New photoremovable protecting groups for carboxylic acids with high photolytic efficiencies at near-UV irradiation. Application to the photocontrolled release of L-glutamate

We report here the syntheses and the photolytic properties of 3-(4,5-dimethoxy-2-nitrophenyl)-2-butyl (DMNPB) esters as new photoremovable groups for carboxylic acids, and their use for the caging of L-glutamate. A high-yielding synthesis of the DMNPB esters led to a 4:1 threo/erythro diastereomeric mixture, which could be separated by HPLC. While these esters were stable in neutral buffer, photolysis at 364 nm induced a > or =95 % release of the carboxylic acid, with a 0.26 quantum yield for L-glutamate formation. L-Glutamate release was also possible by two-photon photolysis with an action cross section of 0.17 GM at 720 nm. Laser photolysis at 350 nm generated a transient species at around 410 nm, attributed to a quinonoid aci-nitro intermediate that decayed in the submillisecond time range (t(1/2)=0.53 ms) for the faster gamma-L-glutamyl threo-esters. Given the absorbance of these esters (lambda(max)=350 nm; epsilon=4500), the threo DMNPB esters represent new caging groups that can be efficiently photolyzed at near-UV wavelengths. An efficient and rapid photolytic release of L-glutamate has been demonstrated on hippocampal neurons in primary culture.     

Amorphous Ge‐Sb‐Se thin films fabricated by co‐sputtering: Properties and photosensitivity

Amorphous Ge–Sb–Se thin films were fabricated by a rf‐magnetron co‐sputtering technique employing the following cathodes: GeSe₂, Sb₂Se₃, and Ge₂₈Sb₁₂Se₆₀. The influence of the composition, determined by energy‐dispersive X‐ray spectroscopy, on the optical properties was studied. Optical properties were analyzed based on variable angle spectroscopic ellipsometry and UV‐Vis‐NIR spectrophotometry. The results show that the optical bandgap range 1.35‐2.08 eV with corresponding refractive index ranging from 3.33 to 2.36 can be reliably covered. Furthermore, morphological and topographical properties of selenide‐sputtered films studied by scanning electron microscopy and atomic force microscopy showed a good quality of fabricated films. In addition, structure of the films was controlled using Raman scattering spectroscopy. Finally, irreversible photoinduced changes by means of change in optical bandgap energy and refractive index of co‐sputtered films were studied revealing the photobleaching effect in Ge‐rich films when irradiated by near‐bandgap light under Ar atmosphere. The photobleaching effect tends to decrease with increasing antimony content.     

Slumping-rolling transition of granular solids in rotary kilns

Recent research work on the slumping-rolling transition of granular solids in rotary kilns is reviewed. A mathematical model is presented for the calculation of critical Froude number. It is supposed that the transition occurs when the time needed by the propagating avalanche to leave the shear wedge becomes comparable to the time of the shear wedge to be refilled with new particles transported by the rotating wall. It is found that the critical Froude number is proportional to the size ratio d/D (particle to cylinder diameter) and inversely proportional to , where ε is the fill angle of the solid bed. Besides the particle diameter, the influence of the bed material needs to be described by only one measurable parameter—the upper angle of repose. To validate the model, the transition behaviour of different bed materials was measured in cylinders of three different sizes. The model is found to predict our measurements as well as those reported in the literature. It is also compared with models from other authors.     

Targeted biodegradable nanoparticles for drug delivery to smooth muscle cells

Targeted delivery of therapeutic agents to prevent smooth muscle cell (SMC) proliferation is important in averting restenosis (a narrowing of blood vessels). Since platelet derived growth factor (PDGF) receptors are over-expressed in proliferating SMCs after injury from cardiovascular interventions, such as angioplasty and stent implantation, our hypothesis is that conjugation of PDGF-BB (platelet-derived growth factor BB (homodimer)) peptides to biodegradable poly (D,L-lactic-co-glycolide) (PLGA) nanoparticles (NPs) would exhibit an increased uptake of these NPs by proliferating SMCs. In this study, poly (D,L-lactide-co-glycolide) (PLGA) nanoparticles containing dexamethasone were formulated and conjugated with PDGF-BB peptides. These NPs were stable, biocompatible, and exhibited a sustained drug release over 14 days. Various particle uptake studies using HASMCs (human aortic smooth muscle cells) demonstrated that PDGF-BB peptide-conjugated nanoparticles significantly increased cellular uptake and decreased proliferation of HASMCs compared to control nanoparticles (without conjugation of PDGF-BB peptides). These NPs were internalized primarily by clathrin-mediated endocytosis and macropinocytosis. Our in vitro results suggest that PDGF-BB peptide-conjugated NPs could represent as an effective targeted, sustained therapeutic delivery system to reduce restenosis and neointimal hyperplasia.     

Feasibility Study of Continuous Casting of Steel Billets in Twin-Belt Caster

Metallurgical and Materials Transactions B - Integrated casting and rolling in a series production line is well established for the non-ferrous metals through the use of twin-belt casting...     

Thumbnail galleries for procedural models

Procedural modeling allows for the generation of innumerable variations of models from a parameterized, conditional or stochastic rule set. Due to the abstractness, complexity and stochastic nature of rule sets, it is often very difficult to have an understanding of the diversity of models that a given rule set defines. We address this problem by presenting a novel system to automatically generate, cluster, rank, and select a series of representative thumbnail images out of a rule set. We introduce a set of ‘view attributes’ that can be used to measure the suitability of an image to represent a model, and allow for comparison of different models derived from the same rule set. To find the best thumbnails, we exploit these view attributes on images of models obtained by stochastically sampling the parameter space of the rule set. The resulting thumbnail gallery gives a representative visual impression of the procedural modeling potential of the rule set. Performance is discussed by means of a number of distinct examples and compared to state‐of‐the‐art approaches.     

Thermomechanical analysis of direct chill casting using finite element method

The transient nature of the start-up phase is the most critical phase in the direct chill (DC) casting during which the quality of the ingot is questioned. The hot crack and cold crack are the two major problems in the DC casting which originate during and after the solidification. In this work, the thermal, metallurgical, and the mechanical fields of DC casting are modeled. The attention is focused on the mushy state of alloy where the chances are high for the hot tearing. The heat conduction and metallurgical phase-change phenomenon are modeled together in a strongly coupled manner. An isothermal staggered approach is followed to couple the thermal and mechanical parts within a time step. Finite element method is used to discretize the thermal and mechanical field equations. A temperature-based fixed grid method is followed to incorporate the latent heat. The mushy state of alloy is characterized through the Norton-Hoff viscoplastic law and the solid phase is modeled through the Garafalo law. An axisymmetric round billet is simulated. The casting material is considered as AA1201 aluminum alloy. It is found that all the components of stress and viscoplastic strain are maximum at the billet center. Further, the start-up phase stresses and strains are always higher than the steady state phase. Therefore, the chances of hot crack formation are higher during the start-up phase and specifically at the billet center. It is proved that through the ramping procedure, the vulnerability of start-up phase can be lowered.