Analytic solution for planar indeterminate impact problems using an energy constraint

This work proposes an analytic method for resolving planar multi-point indeterminate impact problems for rigid-body systems. An event-based approach is used to detect impact events, and constraints consistent with the rigid-body assumption are used to resolve the indeterminacy associated with multi-point impact analysis. The work-energy relation is utilized to determine post-impact velocities based on an energetic coefficient of restitution to model energy dissipation, thereby yielding an energetically consistent set of post-impact velocities based on Stronge’s energetic coefficient of restitution for the treatment of rigid impacts. The effect of stick–slip transition is analyzed based on Coulomb friction. This paper also discusses the transition from impact to contact. This analysis is essential for considering the rocking block problem that is used as an example herein. The predictions of the model for the rocking block problem are compared to experimental results published in the literature. An example of a planar ball undergoing two-point impact is also presented.     

Effects of normal mode loss in dielectric waveguide directional couplers and interferometers

Theoretical arguments and experimental evidence are presented to show that the two fundamental normal modes of a coupled waveguide structure have different attenuations in traversing such a structure. The effects of this phenomenon on evanescent wave directional couplers and interferometers are derived. Parasitic effects in Mach-Zehnder and Sagnac interferometers utilizing directional couplers are described. An asymmetric output for the recently demonstrated all-single-mode fiber resonator is predicted and compared to experimental results. Some qualitative results are presented for integrated optic directional coupler switches.     

Effects of a Rough Boundary Surface on Polarization of the Scattered Field from an Inhomogeneous Medium

The effect of surface roughness on the polarization of the scattered field is studied by combining the standard Kirchhoff method for rough surface scattering with the radiative transfer method for volume scattering using the Rayleigh phase function. Corresponding cases of pure surface scattering from a homogeneous layer and volume scattering from a plane inhomogeneous layer are also computed to serve as points of reference. In each case the degree of polarization DP, polarization ratio PR, locations on the Poincaré sphere of copolarization nulls CN, and cross-polarization nulls XN are computed. It is found that for pure surface scattering PR between 0-20° incidence angles is quite sensitive to change in surface roughness. However, when both surface and volume scattering are present, CN by colatitude or DP between 0-15° incidence angles and CN or XN by longitude at large incidence angles (>60°) are better indicators of change in surface roughness. Since XN changes insignificantly in pure surface scattering, it appears that a significant change in it can serve as an indicator for the presence of volume scattering. Also, in pure surface or volume scattering, the variations of DP and CN by colatitude are monotone with the incidence angle, while in the combined surface and volume scattering DP has a minimum and CN by colatitude has a maximum. This character offers the possibility of separating combined surface and volume scattering from pure surface or volume scattering.     

Semantic memory in Alzheimer's disease and the frontotemporal dementias: A longitudinal study of 236 patients.

Using semantic dementia (SD) as a reference point, the authors assessed semantic memory in four other neurodegenerative disorders: progressive nonfluent aphasia (PNFA), frontal variant frontotemporal dementia (fvFTD), Alzheimer's disease (AD), and posterior cortical atrophy (PCA). Individuals with SD were more impaired than other groups on semantic measures and showed a characteristic pattern across tasks: category fluency (CF) worse than letter fluency (LF), naming worse than comprehension, and visual and verbal comprehension equally affected, suggesting disruption to an amodal semantic system. Individuals with AD demonstrated a similar pattern to a milder degree. Although PNFA, fvFTD, and PCA groups had abnormal scores (relative to controls) on most semantic measures, their differing patterns across measures indicate that the apparent semantic impairment in these conditions is largely secondary to other factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cannabidiol Downregulates Myocardial de Novo Ceramide Synthesis Pathway in a Rat Model of High-Fat Diet-Induced Obesity

It is known that metabolic disturbances, including obesity, predispose to an increased incidence of cardiovascular diseases. Elevated consumption of dietary fat results in intramyocardial accumulation of lipids and their biologically active derivatives, which can disrupt the contractile function of the heart, its metabolism, and intracellular signaling pathways. Therefore, alternative methods, such as phytocannabinoids, are being sought for the treatment of obesity-related effects. In a model of rodent obesity (seven weeks of high-fat-diet (HFD) regime), we used cannabidiol—CBD therapy (intraperitoneal injections for 14 days; 10 mg/kg). High-performance and gas-liquid chromatographies were applied in order to determine sphingolipids in the heart and plasma as well as Western blotting for protein expression. Two-week CBD administration significantly inhibited the de novo ceramide synthesis pathway in the heart of HFD fed rats by lowering sphinganine and sphinganine-1-phosphate contents. The above reductions were accompanied by markedly diminished expressions of myocardial serine palmitoyltransferase 1 and 2 as well as ceramide synthase 5 and 6 in the HFD group with 2-week CBD treatment. To our knowledge, this research is the first that reveals unknown effects of CBD treatment on the heart, i.e., amelioration of de novo ceramide synthesis pathway in obese rats.     

Solidification of thermoviscoelastic melts. Part 3: Effects of mold surface temperature differences on warpage and residual stresses

The solidification of a molten layer of amorphous thermoplastic between cooled parallel plates is used to model the mechanics of part warpage in the injection-molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification so that this model can be used to assess packing-pressure effects in injection molding. Parametric results are presented on the effects of the mold temperatures and the packing pressure—the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic—on the in-plane and through-thickness shrinkages, on warpage, and on residual stresses in plaque-like geometries. The packing pressure is shown to have a significant effect on part warpage. While the results are presented in terms of normalized variables based on the properties of bisphenol-A polycarbonate, they can be interpreted for other amorphous thermoplastics, such as modified polyphenylene oxide, polyetherimide, and acrylonitrile-butadiene-styrene.     

A phenomenological study of the mechanical properties of long‐fiber filled injection‐molded thermoplastic composites

Tensile and flexural tests on specimens cut from rectangular injection‐molded plaques show that long‐fiber filled thermoplastic composites are complex, non‐homogeneous, anistropic material systems. Like all fiber‐filled materials, they exhibit through‐thickness nonhomogeneity as indicated by differences between tensile and flexural properties. The in‐plane orientation of fibers in through‐thickness layers causes the material to have in‐plane anisotropic properties. However, these long‐fiber filled materials exhibit an unexpectedly large level of in‐plane nonhomogeneity. Also, the effective mechanical properties of these materials are strongly thickness dependent. The thinnest plaques exhibit the largest differences between the flow and cross‐flow tensile properties. These differences decrease with increasing thickness. A methodology for part design with this class of materials is discussed.