On the geometric character of stress in continuum mechanics

This paper shows that the stress field in the classical theory of continuum mechanics may be taken to be a covector-valued differential two-form. The balance laws and other fundamental laws of continuum mechanics may be neatly rewritten in terms of this geometric stress. A geometrically attractive and covariant derivation of the balance laws from the principle of energy balance in terms of this stress is presented. Jerrold G. Marsden: Research partially supported by the California Institute of Technology and NSF-ITR Grant ACI-0204932.     

Dynamic optical correlation using localized holography

A new technique for optical correlation using gated holographic recording is demonstrated. Several persistent holograms are localized within separate slices as close as 33 microm apart along the crystal. Individual holograms can be dynamically erased and rerecorded with no need to refresh all other recorded holograms. Experimental results showing the correlation capability, cross talk, shift invariance, and dynamicity of the localized holographic correlator demonstrate unique performance and capabilities for these correlators.     

碳基固体酸催化剂上溶剂上条件下酮和芳香醛交叉羟醛缩合反应

Aromatic aldehydes undergo cross-aldol condensation with ketones in the presence of carbon-based solid acid under solvent-free conditions to afford the corresponding α,β-unsaturated aldol products in excellent yields. The catalyst is reusable several times without any decrease in the yield of the reactions.     

An Assessment of the Utility of Tissue Smears in Rapid Cancer Profiling with Desorption Electrospray Ionization Mass Spectrometry (DESI-MS)

Mass spectrometry imaging with desorption electrospray ionization mass spectrometry (DESI-MS) is used to characterize cancer from ex vivo slices of tissues. The process is time-consuming. The use of tissue smears for DESI-MS analysis has been proposed as it eliminates the time required to snap-freeze and section the tissue. To assess the utility of tissue smears for rapid cancer characterization, principal component analysis (PCA) was performed to evaluate the concordance between DESI-MS profiles of breast cancer from tissue slices and smears prepared on various surfaces. PCA suggested no statistical discrimination between DESI-MS profiles of tissue sections and tissue smears prepared on glass, polytetrafluoroethylene (PTFE), and porous PTFE. However, the abundances of cancer biomarker ions varied between sections and smears, with DESI-MS analysis of tissue sections yielding higher ion abundances of cancer biomarkers compared with smears. Coefficient of variance (CV) analysis suggests DESI-MS profiles from tissue smears are as reproducible as the ones from tissue sections. The limit of detection with smear samples from single pixel analysis is comparable to tissue sections that average the signal from a tissue area of 0.01 mm². The smears prepared on the PTFE surface possessed a higher degree of homogeneity compared with the smears prepared on the glass surface. This allowed single MS scans (~1 s) from random positions across the surface of the smear to be used in rapid cancer typing with good reproducibility, providing pathologic information for cancer typing at speeds suitable for clinical utility.

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Closing the Nanographene Gap: Surface‐Assisted Synthesis of Peripentacene from 6,6′‐Bipentacene Precursors

The thermally induced cyclodehydrogenation reaction of 6,6′‐bipentacene precursors on Au(111) yields peripentacene stabilized by surface interactions with the underlying metallic substrate. STM and atomic‐resolution non‐contact AFM imaging reveal rectangular flakes of nanographene featuring parallel pairs of zig‐zag and armchair edges resulting from the lateral fusion of two pentacene subunits. The synthesis of a novel molecular precursor 6,6′‐bipentacene, itself a synthetic target of interest for optical and electronic applications, is also reported. The scalable synthetic strategy promises to afford access to a structurally diverse class of extended periacenes and related polycyclic aromatic hydrocarbons as advanced materials for electronic, spintronic, optical, and magnetic devices.     

Calculation of Half-Metal,Debye and Curie Temperatures of Co_2 VAl Compound: First Principles Study

By FP-LAPW calculations, the structural, elastic, Debye and Curie temperatures, electronic and magnetic properties of Co2 VAl are investigated. The results indicate that Ferromagnetic(FM) phase is more stable than AntiFerromagnetic(AFM) and Non-magnetic(NM) ones. In addition, C11–C12 0, C44 0, and B 0 so Co2 VAl is an elastically stable material with high Debye temperature. Also, the B/G ratio exhibits a ductility behavior. The relatively high Curie temperature provides it as a favorable material for spintronic application. It's electronic and magnetic properties are studied by GGA+U approach leading to a 100% spin polarization at Fermi level.     

Coupled thermo-mechanical analysis of shape memory alloy circular bars in pure torsion

Pure torsion of shape memory alloy (SMA) bars with circular cross section is studied by considering the effect of temperature gradient in the cross sections as a result of latent heat generation and absorption during forward and reverse phase transformations. The local form of energy balance for SMAs by taking into account the heat flux effect is coupled to a closed-form solution of SMA bars subjected to pure torsion. The resulting coupled thermo-mechanical equations are solved for SMA bars with circular cross sections. Several numerical case studies are presented and the necessity of considering the coupled thermo-mechanical formulation is demonstrated by comparing the results of the proposed model with those obtained by assuming an isothermal process during loading–unloading. Pure torsion of SMA bars in various ambient conditions (free and forced convection of air, and forced convection of water flow) subjected to different loading–unloading rates are studied and it is shown that the isothermal solution is valid only for specific combinations of ambient conditions and loading rates.     

Structure of defective crystals at finite temperatures: A quasi-harmonic lattice dynamics approach

In this paper we extend the classical method of lattice dynamics to defective crystals with partial symmetries. We start by a nominal defect configuration and first relax it statically. Having the static equilibrium configuration, we use a quasi-harmonic lattice dynamics approach to approximate the free energy. Finally, the defect structure at a finite temperature is obtained by minimizing the approximate Helmholtz free energy. For higher temperatures we take the relaxed configuration at a lower temperature as the reference configuration. This method can be used to semi-analytically study the structure of defects at low but non-zero temperatures, where molecular dynamics cannot be used. As an example, we obtain the finite temperature structure of two 180° domain walls in a 2D lattice of interacting dipoles. We dynamically relax both the position and polarization vectors. In particular, we show that increasing temperature the domain wall thicknesses increase.     

Polyvinyl alcohol-acid redox active gel electrolytes for electrical double-layer capacitor devices

Journal of Solid State Electrochemistry - Since the mechanism of charge storage in electrical double-layer capacitors (EDLCs) relies on diffusion of ions into the pores of the electrodes, in...