Mass Spectrometric Analysis of Water-soluble Gold Nanoclusters

Batches of water-soluble gold nanoclusters of nominal 2.0 or 3.5-nm diameter were prepared to evaluate particle size determinations by a number of techniques such as transmission electron microscopy or atomic force microscopy and to validate estimates derived by mass spectrometric analysis using matrix-assisted laser desorption ionization (MALDI). Good agreement was found and MALDI lends itself to analyses even in the presence of aggregates.     

Precision measurements of the diffusion of reactive atoms

Resonance ionization spectroscopy is described for precision measurements of the diffusion of reactive atoms in gaseous media. Results are given for Cs atoms in an Ar-CH₄ mixture and are used to test a rigorous solution of the diffusion equation.     

Crystal structure and solid-state31P CP-MAS NMR spectrum of the bis(trifluoroacetato) (triphenylphosphine)mercury(II) dimer [Hg(CF3CO2)2PPh3]2

The title compound belongs to the monoclinic space groupP2₁/c,a=20.29(1),b=12.644(8),c=18.25(1), Å,=95.76(5)°. The unit cell contains two dimeric [Hg(CF₃CO₂)₂PPh₃]₂ molecules in which each Hg atom forms strong primary bonds to a PPh₃ molecule and an oxygen of a monodentate trifluoroacetate ligand. These two Hg atoms are bridged by two extra trifluoroacetate ligands, one providing a single oxygen to a Hg-O-Hg bridge, the other including both carboxylate oxygens in a Hg-O-C-O-Hg bridging moiety. This unusual type of bridging makes the two halves of the molecule symmetry independent, leading to distinct signals at 31.5 and 29.9 ppm for the phosphines in the³¹P CP-MAS NMR spectrum of the solid complex.     

Division Algebras with PSL(2, q)-Galois Maximal Subfields

If G is a finite group and k is a field, then G is k-admissible if there exists a G-Galois extension L/k such that L is a maximal subfield of a k-division algebra. We prove that PSL(2, 7) is k-admissible for any number field which either fails to contain or which has two primes lying over the dyadic prime. In addition, PSL(2, 11) is shown to be admissible over or any number field k with at least two extensions of the dyadic prime. Indeed, there exist infinitely many linearly disjoint admissible extensions for these groups.     

Echolocation signals of free-ranging killer whales (Orcinus orca) and modeling of foraging for chinook salmon (Oncorhynchus tshawytscha)

Fish-eating "resident"-type killer whales (Orcinus orca) that frequent the coastal waters off northeastern Vancouver Island, Canada have a strong preference for chinook salmon (Oncorhynchus tshawytscha). The whales in this region often forage along steep cliffs that extend into the water, echolocating their prey. Echolocation signals of resident killer whales were measured with a four-hydrophone symmetrical star array and the signals were simultaneously digitized at a sample rate of 500 kHz using a lunch-box PC. A portable VCR recorded the images from an underwater camera located adjacent to the array center. Only signals emanating from close to the beam axis (1185 total) were chosen for a detailed analysis. Killer whales project very broadband echolocation signals (Q equal 0.9 to 1.4) that tend to have bimodal frequency structure. Ninety-seven percent of the signals had center frequencies between 45 and 80 kHz with bandwidths between 35 and 50 kHz. The peak-to-peak source level of the echolocation signals decreased as a function of the one-way transmission loss to the array. Source levels varied between 195 and 224 dB re: 1 microPa. Using a model of target strength for chinook salmon, the echo levels from the echolocation signals are estimated for different horizontal ranges between a whale and a salmon. At a horizontal range of 100 m, the echo level should exceed an Orcinus hearing threshold at 50 kHz by over 29 dB and should be greater than sea state 4 noise by at least 9 dB. In moderately heavy rain conditions, the detection range will be reduced substantially and the echo level at a horizontal range of 40 m would be close to the level of the rain noise.     

Quantitative phase radiography with polychromatic neutrons

We develop and experimentally demonstrate a formalism that allows accurate phase imaging using neutron sources producing highly polychromatic beams. The results of measurements from a rectangular block of silicon compare favorably with theoretical simulations based upon the known composition and geometry of the block. The increased flux and reduced exposure times will permit a simple extension of the technique to tomographic phase imaging.     

Functional MRI involving painful stimulation of the ankle and the effect of physiotherapy joint mobilization

We examined whether cerebral activation due to secondary hyperalgesia resulting from intrajoint capsaicin injection could be detected using functional magnetic resonance imaging (fMRI) in alpha-chloralose anesthetized rats. We also examined whether we could detect analgesic changes in the central nervous system response to pain as a result of physiotherapy joint manipulation. Robust activation of areas of the brain known to be associated with the processing of pain, namely the anterior cingulate (bilateral), frontal cortex (bilateral) and sensory motor cortex (contralateral), was found in all animals following injection of 25 microl of capsaicin (128 microg/ml in 7.5% DMSO) into the plantar surface of the rat hindpaw (n = 7) and 75 microL into the ankle joint (n = 13). Significantly greater activation was observed when capsaicin was injected into the plantar surface of the hindpaw compared to the ankle joint. Mechanical allodynia and secondary hyperalgesia following capsaicin injection into the ankle joint also resulted in activation of the same brain regions. Trends toward decreased areas of activation in brain regions associated with pain in animals following physiotherapy joint mobilization were observed.     

Preparation and characterization of cholic acid-derived antimicrobial agents with controlled stabilities

[reaction: see text] Novel cholic acid-derived antimicrobial agents that decompose under mildly basic conditions have been prepared. These compounds range in biological properties from potent antibacterial activity to effective permeabilization of the outer membranes of Gram-negative bacteria.     

Quantum Phase Shift Caused by Spatial Confinement

This paper presents the results of optical interferometry experiments in which the phase of photons in one arm of a Mach-Zehnder interferometer is modified by applying a transverse constriction. An equivalent quantum interferometry experiment using neutron de Broglie waves is discussed in which the observed phase shift is in the spirit of the force-free phase shift of the Aharonov-Bohm effects. In the optical experiments the experimental results are in excellent agreement with predictions.     

Branch-and-price for a class of nonconvex mixed-integer nonlinear programs

This work attempts to combine the strengths of two major technologies that have matured over the last three decades: global mixed-integer nonlinear optimization and branch-and-price. We consider a class of generally nonconvex mixed-integer nonlinear programs (MINLPs) with linear complicating constraints and integer linking variables. If the complicating constraints are removed, the problem becomes easy to solve, e.g. due to decomposable structure. Integrality of the linking variables allows us to apply a discretization approach to derive a Dantzig-Wolfe reformulation and solve the problem to global optimality using branch-andprice. It is a remarkably simple idea; but to our surprise, it has barely found any application in the literature. In this work, we show that many relevant problems directly fall or can be reformulated into this class of MINLPs. We present the branch-and-price algorithm and demonstrate its effectiveness (and sometimes ineffectiveness) in an extensive computational study considering multiple large-scale problems of practical relevance, showing that, in many cases, orders-of-magnitude reductions in solution time can be achieved.