An OpenMP/MPI approach to the parallelization of iterative four-atom quantum mechanics

We present an approach to parallel iterative four-atom quantum mechanics calculations in a computing environment of distributed memory nodes, each node consisting of a group of processors with a shared memory. We parallelize the action of the Hamiltonian matrix on a vector, which is the main computational bottleneck in both iterative calculations of eigenvalues and eigenvectors and the iterative determination of quantum dynamics information via, e.g., wavepacket methods. OpenMP is used to facilitate the parallel work within each node, and MPI is used to communicate information between nodes. For a realistic problem the approach is shown to scale very well up to 512 processors at the NERSC computing facility, working at up to 20% of the theoretical peak performance rate. The highest total floating point rate we achieve is 0.16 Tflops, using 768 processors. Our approach should also be applicable to quantum dynamics problems with more than four atoms.     

The Lyapunov–Malkin theorem and stabilization of the unicycle with rider

This paper analyzes stabilization of a nonholonomic system consisting of a unicycle with rider. It is shown that one can achieve stability of slow steady vertical motions by imposing a feedback control force on the rider's limb.     

Locked phase conjugation for two-beam coupling of pulse repetitionrate solid-state lasers

Theoretical and experimental results obtained in the study of phase-locked conjugation of two light beams using a phase synchronizer demonstrate how phase conjugation of depolarized radiation can be used to compensate aberration and depolarization distortions in solid-state media. Two-beam phase conjugation via mutual scattering of orthogonally polarized pump waves under four-wave mixing is discussed. A novel analog operation-orthogonal phase conjugation (OPC)-involving an electromagnetic field was realized with a phase synchronizer     

Force control of robotic manipulators with structured uncertainties using variable structure control

A discrete variable structure tracking controller is developed for a wide class of linear and nonlinear systems with structured uncertainties. The proposed controller uses a pole placement controller as a kernel and compensates for the errors associated with uncertainties. The algorithm is computationally efficient and can be easily used as a robust backup controller for the higher performance, but sensitive, adaptive algorithms.     

Isotopic variations of Zn in biological materials

Variations in the isotopic composition of Zn present in various biological materials were determined using high-resolution multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), following digestion and purification by anion exchange chromatography. To correct for differences in instrumental mass discrimination effects between samples and standards, Cu was employed as an elemental spike. Complementary analyses of Zn separates by sector field ICPMS instruments revealed that the concentrations of the majority of potentially interfering elements were reduced to negligible levels. Residual spectral interferences resulting from (35)Cl(16)O(2)(+), (40)Ar(14)N(2)(+), and (40)Ar(14)N(16)O(+) could be instrumentally resolved from the (67)Zn, (68)Zn, and (70)Zn ion beams, respectively, during measurement by MC-ICPMS. The only other observed interference in the Cu and Zn mass range that could not be effectively eliminated by high-resolution multicollection resulted from (35)Cl(2)(+), necessitating modification of the sample preparation procedure to allow accurate (70)Zn detection. Complete duplication of the entire analytical procedure for human whole blood and hair, as well as bovine liver and muscle, provided an external reproducibility of 0.05-0.12 per thousand (2sigma) for measured delta(66/64)Zn, delta(67/64)Zn, and delta(68/64)Zn values, demonstrating the utility of the method for the precise isotopic analysis of Zn in biological materials. Relative to the selected Zn isotopic standard, delta(66/64)Zn values for biological samples varied from -0.60 per thousand in human hair to +0.56 per thousand in human whole blood, identifying the former material as the isotopically lightest Zn source found in nature to date.     

MALDI matrices for biomolecular analysis based on functionalized carbon nanomaterials

When used in small molar ratios of matrix to analyte, derivatized fullerenes and single wall nanotubes are shown to be efficient matrices for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The mixing of an acidic functionalized fullerene with a solution of bioanalyte, depositing a dried droplet, and irradiating with a pulsed nitrogen laser yields protonated or cationized molecular ions. Derivatized fullerenes could offer several advantages over conventional MALDI matrices: a high analyte ionization efficiency, a small molar ratios (less than 1) of matrix/analyte, and a broader optical absorption spectrum, which should obviate specific wavelength lasers for MALDI acquisitions. The major disadvantage to the use of fullerenes is the isobaric interference between matrix and analyte ions; however, it is overcome by using MALDI-ion mobility time-of-flight (IM-oTOF) mass spectrometry to preseparate carbon cluster ions from bioanalyte ions prior to TOF mass analysis. However, an alternative to the dried droplet preparation of fullerene MALDI samples is the aerosolization of matrix-analyte solutions (or slurries) followed by impacting the aerosol onto a stainless surface. We also demonstrate that the fullerene matrices can be used to acquire spectra from rat brain tissue.     

Isotopic fractionation during diffusion of transition metal ions in solution

Isotope ratios and elemental concentrations were measured in aqueous solutions sampled at varying distances from sources of Fe or Zn ions. The measurements reveal fractionation of isotopes resulting from pure diffusion in solution. Our data demonstrate that diffusion alone can cause changes in (56)Fe/(54)Fe and (66)Zn/(64)Zn isotope ratios in excess of -0.3 per thousand. These findings thus confirm previous suspicions that transport processes contribute to observed variations in isotopic compositions. Diffusion must therefore be considered when attempting to make inferences from isotope measurements on samples originating from aqueous systems where concentration gradients may develop.     

Apertureless tip-enhanced Raman microscopy with confocal epi-illumination/collection optics

It is demonstrated that confocal epi-illumination/collection optics can be effectively used to generate surface-enhanced Raman scattering at the near-field region of a gold-coated tip for an atomic force microscope operated in semi-contact tapping mode. When the tip, with a 50-nm apex radius, was illuminated by a highly focused laser beam at 532 nm and approached the isolated diamond particle, with a size of approximately 1 microm, the Raman signal was enhanced by approximately 10(3). This result is in good agreement with numerical simulations performed by the finite difference time-domain method. Since our apertureless microscope is based on readily available conventional components, there is wide room for improvements and modifications by common users in various applications of micro-Raman analysis.     

LMI-based H ∞-optimal control with transients

In this article, the worst-case norm of the regulated output over all exogenous signals and initial states as a performance measure of the system is characterised in terms of linear matrix inequalities (LMIs). Optimal time-invariant state- and output-feedback controllers are synthesised as minimising this performance measure. The essential role in this synthesis plays a weighting matrix reflecting the relative importance of the uncertainty in the initial state contrary to the uncertainty in the exogenous signal. H _∞-optimal control with transients is shown to be actually a trade-off between H _∞-control, being optimal under unknown exogenous disturbances and zero initial state, and γ-control, being optimal under zero exogenous signal and unknown initial conditions, if and only if the weighting matrix satisfies a fundamental inequality. If this inequality is met, the performance measure is achieved and the explicit formulae for the worst-case disturbance and initial state are provided. If this inequality fails, the performance measure coincides with the H _∞-norm and the trade-off gets broken.     

Survey on hierarchical routing schemes in?��flat�� distributed hash tables

The first generation of DHT designs offered a completely flat structure of the key space that is randomly partitioned among participating DHT nodes. That has certain advantages, for example, even distribution of workload among nodes. On the other hand, grouping keys under a single authority or achieving latency guarantees for queries is difficult. To address these shortcomings, various kinds of hierarchy have been proposed over recent years. The last generation is hierarchical DHTs (HDHTs) where nodes are organized onto layers; each next layer consists of supernodes for the previous layer. In this survey paper, we thoroughly go over the evolution of DHTs from pure flat to pre-hierarchical. Our focus is on hierarchical schemes in DHT routing. We argue that their application is not restricted within HDHT designs. We sequentially built a set of design principles; each provides a base for hierarchical routing schemes. In the extreme case, application these principles leads to HDHT designs.