Profiting from nature: macroporous copper with superior mechanical properties

Macroporous copper with a complex hyperbolic morphology and superior mechanical properties was produced by replicating the remarkable form of a sea urchin skeletal plate using templated electrochemical deposition.     

Generation of complex concentration profiles in microchannels in a logarithmically small number of steps

We describe the principles of design and the architecture of planar microfluidic networks producing concentration gradients with the shape of any given monotonic function. Each microfluidic network is fed by two separate source solutions and delivers to its outlet a set of N solutions that all differ in concentration. Inside the network, the source solutions flow through a series of k = log(2)(N-1) stages, where they are repeatedly split and mixed. Streams of the solutions emerging from the network are combined to create a single stream with the desired shape of the concentration profile across the direction of flow. To demonstrate the functionality of the proposed architecture, we have built and tested three networks with k = 4 and N = 17 that generate an exponential concentration profile, a linear profile, and a profile with a shape of two fused branches of a parabola.     

Rapid mass spectrometric identification of human genomic polymorphisms using multiplexed photocleavable mass-tagged probes and solid phase capture

A mass spectrometric approach for rapid and simultaneous detection of several single nucleotide polymorphisms (SNPs) is reported. Oligonucleotide single base extension (SBE) primers, labelled at the 5'-end with photocleavable, quaternised and brominated peptidic mass tags, are extended by a mixture of the four dideoxynucleotides of which one is biotinylated. The 3'-biotinylated extension products are captured by streptavidin-coated solid phase magnetic beads, whilst non-biotinylated extension products and unreacted primers are washed away. Quaternised and brominated mass tags, cleaved from captured extension products during analysis by matrix-assisted laser desorption/ionisation-time-of-flight (MALDI-TOF) MS, are detected at pmol levels. This method is applied to the analysis of mitochondrial DNA polymorphisms for the purpose of human identification.     

Boronic acid–lectin affinity chromatography. 1. Simultaneous glycoprotein binding with selective or combined elution

We introduce a novel combination of boronic acid affinity chromatography with lectin affinity chromatography, dubbed as boronic acid–lectin affinity chromatography (BLAC). Concanavalin A and wheat germ agglutinin lectins were mixed with the pesudo-lectin boronic acid to form the BLAC affinity column and their performance was evaluated with standard glycoproteins. Optimization of the binding and elution buffers for the BLAC system is described. The BLAC columns were employed to isolate glycoproteins of interest using both selective and/or combined elution.     

Probing nanoscale solids at thermal extremes

We report a novel nanoscale thermal platform compatible with extreme temperature operation and real-time high-resolution transmission electron microscopy. Applied to multiwall carbon nanotubes, we find atomic-scale stability to 3200 K, demonstrating that carbon nanotubes are more robust than graphite or diamond. Even at these thermal extremes, nanotubes maintain 10% of their peak thermal conductivity and support electrical current densities approximately 2 x 10{8} A/cm{2}. We also apply this platform to determine the diameter dependence of the melting temperature of gold nanocrystals down to three nanometers.     

Impurity clustering and ferromagnetic interactions that are not carrier induced in dilute magnetic semiconductors: the case of Cu2O:Co

Current models for ferromagnetism in diluted magnetic semiconductors, such as "p-d exchange" or "double-exchange", rely on the presence of partially filled gap states. We point out a new mechanism, not requiring partially filled states, in which ferromagnetic coupling arises from the occupation of previously unoccupied levels when two transition metal impurities form a close pair. We find from first-principles calculations that this mechanism explains strong ferromagnetic coupling between Co impurities in Cu2O, and at the same time gives rise to Co clustering.     

Stochastic perturbation theory: a low-scaling approach to correlated electronic energies

We discuss a stochastic implementation of M?ller-Plesset (MP) theory based upon the concept of a "graph," a set of connected Slater determinants. We show how contributions from an arbitrary level, MPn, of perturbation theory can be expressed diagrammatically in terms of graphs, and that these may be stochastically sampled to give a good estimate of the energy. We show this to be the case for Ne, Ar, N2, and H2O molecules. N-molecule chains of He atoms and H2 molecules at equilibrium and stretched geometries show an effective scaling of O[N(2.6)] and O[N(5.6)] for MP2 and MP3 theories.     

Nature of perpendicular-to-parallel spin reorientation in a Mn-doped GaAs quantum well: canting or phase separation?

It is well known that the magnetic anisotropy in a compressively strained Mn-doped GaAs film changes from perpendicular to parallel with increasing hole concentration p. We study this reorientation transition at T=0 in a quantum well with delta-doped Mn impurities. With increasing p, the angle theta that minimizes the energy E increases continuously from 0 (perpendicular anisotropy) to pi/2 (parallel anisotropy) within some range of p. The shape of E(min)(p) suggests that the quantum well becomes phase separated with regions containing low hole concentrations and perpendicular moments interspersed with other regions containing high hole concentrations and parallel moments. However, because of the Coulomb energy cost associated with phase separation, the true magnetic state in the transition region is canted with 0相似文献   

Quantum mushroom billiards

We report the first large-scale statistical study of very high-lying eigenmodes (quantum states) of the mushroom billiard proposed by L. A. Bunimovich [Chaos 11, 802 (2001)]. The phase space of this mixed system is unusual in that it has a single regular region and a single chaotic region, and no KAM hierarchy. We verify Percival's conjecture to high accuracy (1.7%). We propose a model for dynamical tunneling and show that it predicts well the chaotic components of predominantly regular modes. Our model explains our observed density of such superpositions dying as E(-1/3) (E is the eigenvalue). We compare eigenvalue spacing distributions against Random Matrix Theory expectations, using 16,000 odd modes (an order of magnitude more than any existing study). We outline new variants of mesh-free boundary collocation methods which enable us to achieve high accuracy and high mode numbers (approximately 10(5)) orders of magnitude faster than with competing methods.