Observation of a strongly nested Fermi surface in the shape-memory alloy Ni0.62Al0.38

The Fermi surface topology of the shape-memory alloy Ni0.62Al0.38 has been determined using Compton scattering. A large area of this Fermi surface can be made to nest with other areas by translation through a vector of approximately 0.18[1,1,0](2pi/a), which corresponds to the wave vector associated with martensitic precursor phenomena such as phonon softening and diffuse streaking in electron diffraction patterns. This observation is compelling evidence that these phenomena are driven by the enhanced electron-lattice coupling due to the Fermi surface nesting.     

Competitive binding exchange between alkali metal ions (K+, Rb+, and Cs+) and Na+ ions bound to the dimeric quadruplex [d(G4T4G4)]2: a 23Na and 1H NMR study

A comparative study of the competitive cation exchange between the alkali metal ions K⁺, Rb⁺, and Cs⁺ and the Na⁺ ions bound to the dimeric quadruplex [d(G₄T₄G₄)]₂ was performed in aqueous solution by a combined use of the ²³Na and ¹H NMR spectroscopy. The titration data confirm the different binding affinities of these ions for the G‐quadruplex and, in particular, major differences in the behavior of Cs⁺ as compared to the other ions were found. Accordingly, Cs⁺ competes with Na⁺ only for the binding sites at the quadruplex surface (primarily phosphate groups), while K⁺ and Rb⁺ are also able to replace sodium ions located inside the quadruplex. Furthermore, the ¹H NMR results relative to the CsCl titration evidence a close approach of Cs⁺ ions to the phosphate groups in the narrow groove of [d(G₄T₄G₄)]₂. Based on a three‐site exchange model, the ²³Na NMR relaxation data lead to an estimate of the relative binding affinity of Cs⁺ versus Na⁺ for the quadruplex surface of 0.5 at 298 K. Comparing this value to those reported in the literature for the surface of the G‐quadruplex formed by 5′‐guanosinemonophosphate and for the surface of double‐helical DNA suggests that topology factors may have an important influence on the cation affinity for the phosphate groups on DNA. Copyright © 2009 John Wiley & Sons, Ltd.     

Scatter Search for Network Design Problem

A fixed charge capacitated multicommodity network design problem on undirected networks is addressed. At the present time, there exists no algorithm that can solve large instances, common in several applications, in a reasonable period of time. This paper presents an efficient procedure using a scatter search framework. Computational experiments on a large set of randomly generated problems show that this procedure is capable of finding good solutions to large-scale problems within a reasonable amount of time.     

Diagnostics of mixed van der Waals clusters

We present two complementary techniques that provide detailed diagnostics of supersonic beams involving several species. First, surface scattering, together with quadrupole mass spectrometer detection, yields the monomer percentage for each species within the beam. Second, analyses of beam profiles for different masses after scattering by a buffer gas permit determination of mixed cluster presence and, if any, of cluster sizes and compositions. The two techniques are applied to supersonic expansions of an argon-nitrogen mixture. We discuss the results that provide new insight in binary nucleation processes. Received: 6 October 1997 / Revised: 4 November 1997 / Accepted: 13 November 1997     

Indirect determination of pepsin activity in human seric protein samples by polyphenol oxidase electrodes

We present a new chronoamperometric methodology for the indirect determination of pepsin activity in proteic solutions. The high-sensitive polyphenol oxidase (PPO) carbon paste bioelectrodes, prepared with 150–200 U of PPO adsorbed on the carbon paste surface and trapped behind a dialysis membrane were able to detect free -tyrosine ( -Tyr) as well as -Tyr-containing peptides, the product of pepsin hydrolysis on haemoglobin samples. The electroactive enzymatic products were determined by their reduction current at −0.050 V, a working potential low enough for preventing electrochemical interferences. The external diffusional barrier posed by the dialysis membrane and the high PPO-superficial concentrations allowed us to prevent electrode surface fouling and to reach stationary diffusional currents after 3 min. The electrochemical -Tyr concentrations measured with proper internal standards, were correlated to those determined by the spectrophotometric reference method (Folin–Ciocalteu), reaching a linear relationship with a slope of 1.05±0.04 and a linear regression coefficient of 0.9951. These results as well as a recovery assay of 98% and the detection limit lower than that of the spectrophotometric method indicate that the proposed methodology is very satisfactory and potentially useful for indirect determination of pepsin in biological samples. The technique was also applied for the determination of pepsin activity in hydrolysed immuno globulin solutions of different composition.     

Grasp Embedded Scatter Search for the Multicommodity Capacitated Network Design Problem

A GRASP embedded Scatter Search is developed for the multicommodity capacitated network design problem. Difficulty for this problem arises from the fact that selection of the optimal network design is an NP-complete combinatorial problem. There exist no polynomial exact algorithms which can solve this problem in a reasonable period of time for realistically sized instances. In such cases, heuristic procedures are commonly used. Two strategies were designed for GRASP: a traditional approach and a memory based technique. As for Scatter Search, 5 different strategies were used to update the reference set. Computational results on a large set of randomly generated instances show the convenience of the proposed procedures.     

Diffraction of a Bose-Einstein condensate from a magnetic lattice on a microchip

We experimentally study the diffraction of a Bose-Einstein condensate from a magnetic lattice, realized by a set of 372 parallel gold conductors which are microfabricated on a silicon substrate. The conductors generate a periodic potential for the atoms with a lattice constant of 4 microm. After exposing the condensate to the lattice for several milliseconds we observe diffraction up to fifth order by standard time of flight imaging techniques. The experimental data can be quantitatively interpreted with a simple phase imprinting model. The demonstrated diffraction grating offers promising perspectives for the construction of an integrated atom interferometer.