Strength of metals at the Fermi length scale

Using silver and gold, we have measured the size‐dependence of the yield strength of atomic‐sized samples as small as a single‐atom bridge, with pico‐level resolution in the applied force and displacement. The strength approaches theoretical values as the diameter of the sample becomes comparable to the Fermi wavelength of electrons (～0.5 nm); in the limit of a single‐atom bridge, the strength is over four orders of magnitude higher than in bulk single crystals. Results provide direct evidence for Pauling's prediction of bond stiffening with reduced atomic coordination. Beginning with a single‐atom bridge, strength evolves in a staircase manner in Ag, instead of the intuitively assumed continuous approach to a saturating bulk value.

     

Effects of 5-aminolaevulinic acid on human ovarian cancer cells and human vascular endothelial cells in vitro.

Results are reported on the cellular effects and the sensitivity of cultured tumor epithelial cells (TEC) derived from human ovarian cystadenocarcinoma and human umbilical vein-derived endothelial cells (HUVEC) to exogenous 5-aminolaevulinic acid (ALA) and ALA-induced photodynamic therapy (PDT). Cellular alterations and PDT efficiency were evaluated using colorimetric thiazolyl blue (MTT) assay, trypan blue exclusion assay, electron microscopy, and gel electrophoresis. ALA-induced protoporphyrin IX (PpIX) accumulation in TEC was associated with a concentration and time-dependent significant decrease in mitochondrial activity, increase in cell membrane permeability, and dark toxicity. Maximum PpIX loaded TEC demonstrated a high sensitivity to PDT. Neither cellular alterations nor PDT effects were observed in HUVEC under identical experimental conditions. These results indicate a potential clinical value for the use of ALA-mediated PDT to treat minimal residual disease in mucinous ovarian carcinoma. In addition, the ALA-induced PpIX cytotoxicity may be exported to a new chemotherapeutic regimen via a conventionally viewed photochemotherapeutic agent.     

Systems theoretic questions in coding theory

A central theme of current research in coding theory are low density parity-check (LDPC) codes and more generally codes defined via graphs. There exist various decoding algorithms which work in a decentralized manner and which can be viewed as discrete dynamical systems. In this talk, we explain these algorithms from a systems theoretic point of view. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

One pot,three component synthesis of spiroindenoquinoxaline pyrrolidine fused nitrochromene derivatives following 1,3-dipolar cycloaddition

An expedient one-pot sequential three-component synthesis of a series of diverse spiroindenoquinoxaline pyrrolidine fused nitrochromene derivatives following 1,3-dipolar cycloaddition of azomethine ylides generated in situ by the condensation of indenoquinoxalone and α-amino acids (L-proline and L-phenyl alanine) with 3-nitrochromenes as dipolarophile under classical as well as microwave irradiation is described. The protocol provides a mild reaction condition, high yield of the products, high regioselectivity, and operational simplicity to assemble complex structural entity in a single operation with good to excellent yield. The regio and stereochemical outcome of the cycloaddition reaction is ascertained by spectroscopic and single crystal X-ray analysis.     

Alternative fiber-optic backreflectance sensor for measurement of the effective focal lengths of optical elements and distances

An alternative and simple fiber-optic backreflectance sensor method for accurate measurement of either effective focal lengths of optical elements and short distances using a single-mode optical fiber and cw laser is presented. The method is based on the intensity sensing of focused backreflectance laser emission and the spatial location of three specific points: the focal point of the focusing optical element and two object points. The single-mode fiber is a key optical element and serves simultaneously as a point laser source for testing, an object for projecting and a highly sensitive point receiver of the focused backreflectance emission. The experimental and analytical results demonstrate the potential of the method for locating the spatial points and determining the effective focal length with accuracies exceeding 1 μm and 0.5%, respectively, as well as for short distance measurement with submicron accuracy.     

An anisotropic magnetized viscous fluid cosmological model in general relativity

We investigate the behavior of a magnetic field in a viscous fluid cosmological model where the free gravitational field is of Petrov type D and the coefficient of shear viscosity is proportional to the rate of expansion in the model. Also discussed are the behavior of the model when the magnetic field tends to zero and some other physical properties.     

Influence of oxygen deficiency on the thermoelectric power of Y1Ba2Cu3O7-x

In this paper we report measurements of the thermoelectric power on a series of Y₁Ba₂Cu₃O_7-x specimens with varying amounts of oxygen deficiency obtained by changing the cooling rate of the sintered specimens. The specimens have been characterized by X-ray diffraction measurements, electric resistivity and oxygen contents. The temperature variation of the thermopower reveals a peak just before the onset of superconducting transition. We examine possible theoretical explanations of this anomaly. In particular we argue that this anomaly is associated with the pairing fluctuations in the normal state close toT _c . We present some theoretical results in support of this conclusion.     

On ternary problems

We consider ternary matrices, i.e., integer matrices having all entries 0, 1 or 2. Three associated problems—the group problem, covering, and packing—are studied. General classes of vertices and facets are discussed in each case. Certain lifting procedures are also described. For all three problems techniques used are natural extensions of those used in the binary case.     

Transport and structural properties of polymerized AC60 (A = K, Rb) under zero and high pressure conditions

60 display transport properties vastly different from their unpolymerized counterparts. We here describe structural (X-ray diffraction and transmission electron microscopy) and dc resistivity measurements of polymerized AC₆₀ (A = K, Rb) at zero and high pressures. The structural and electronic properties are rich, and evidence is found for unusual phase transitions in both materials. Received: 28 October 1996/Accepted: 13 December 1996