Aspects of the chemistry of some phosphorus halides and pseudohalides

The preparation of pseudohalogeno derivatives of the simple phosphorus(V) species PC1(_4)(^+), PC1(_5) and PC1(_6)(^-) has been attempted. In the case of the tetrachlorophosphonium ion only azido-derivatives are observable in normal organic solvents, cyano and thiocyanato derivatives being more stable in liquid halogen media. Isolation of these compounds was not possible. Molecular derivatives based on PC1(_5) seem to be particularly unstable and are only readily observable under forcing conditions for cyanide. The derivatives of the hexachlorophosphate ion are all observable, PX(_6)(^-) being readily formed for X = N(_3), NCS, NCO and OCN although these and the intermediate species are all unstable. The series of cyanides PC1(_6-n)(CN)(_n)(^-) (0 < n < 3) have been isolated as solids and fully characterised, and the presence of isomers for n = 2 and 3 has been clearly established. The six-coordinate fluorochlorophosphates PF(_3)Cl(_3)(^-), PF(_2)C1(_4)(^-) and PFC1(_5)(^-) have been isolated as pure tetraalkylammonium salts and the reactions of these anions studied with respect to substitution by pseudohalides. The observation of PF(_6-n)X(_n)(^-) (X = pseudohalogen) has been carried out by ligand exchange between PF(_6)(^-) and PX(_6)(^-) (where known) or PX(_3) and attempts have been made to isolate compounds, where feasible, by other reactions such as the addition of pseudohalide ions to PF(_5).The use of pairwise interactions has proved invaluable in assigning formulae in the tetrahedral systems, and in both assigning formulae and identifying specific isomers in many of the six-coordinate systems. The substitution patterns in the six-coordinate systems can be rationalised in terms of a simple steric model, or on the basis of ligand field theory for the cyanides. Other six-coordinate systems have been studied with respect to substitution by azide and several new species have been identified

Food Habits of Juvenile American Alligators in the Upper Lake Pontchartrain Estuary

Food habits of juvenile (0.49-1.21 m total length) American alligators (Alligator mississippiensis) from an area in southeastern Louisiana were investigated. One-hundred and one stomach samples were obtained by stomach-pumping. Crustaceans (crayfish; blue crabs, Callinectes sapidus; grass shrimp, Palaemonetes sp.), insects (hemipterans, coleopterans), and small fish (least killifish, Heterandria formosa; mosquitofish, Gambusia affinis) constituted the majority of prey items taken. Fish consumption was significantly more frequent during April and May than during June through September (P\u3c0.025). This differential use of prey species may be due to seasonally fluctuating water levels in the study area. Comparisons of juvenile alligator food habits revealed dietary differences between Louisiana and Florida (P\u3c0.001), possibly due to the different prey available at the two areas. Prey utilization was not significantly different between larger alligators (0.9-1.2 m total length) and smaller alligators (0.3·0.9 m total length) (P\u3e0.25)

Remote Sensing of Ocean Color in the High Arctic

With four years of NASA SeaWiFS funding I established a completely new capability and expertise for in-water optical measurements nearly from scratch and with very little optical background. My first-year budget included only capital for a profiling spectral radiometer. Over the next 30 months we conducted six cruises and collected almost 300 optical profiles in challenging environments; many were collected from 21' launches. I also changed institutions during this period: it is very disruptive to move, set up a new lab, and hire and train new people, etc. We also did not have access to NASA funds for almost a year during the move because of difficulties in subcontracting and/or transferring funds. Nevertheless, we delivered data sets from six bio-optical cruises from three high latitude regions, although only two or three cruises from two areas were promised for our SeaWiFS research. The three Canadian Arctic field programs comprise the most comprehensive high latitude bio-optical and biogeochemical data sets in existence. Optical and pigment data from all six cruises have been submitted to NASA and are being included in the algorithm development test set. Additional data are still being submitted

Photoinhibition of photosynthesis in natural assemblages of marine phytoplankton

A new empirical equation is introduced that describes the photosynthesis by phytoplankton as a single, continuous function of available light from the initial linear response through the photoinhibited range at the highest light levels liable to be encountered under any natural conditions. The properties of the curve are derived, and a procedure is given for fitting it to the results of light-saturation experiments for phytoplankton...

Complexes of triphenylphosphine oxide with lanthanide bromides

The reaction between hydrated lanthanide bromides and triphenylphosphine oxide in 1:3 and 1:4 ratios in ethanol gave a series of complexes [LnBr2(Ph3PO)4]Br (Ln = Pr, Nd, Gd, Tb, Er, Yb, Lu) which contain ethanol and water in the lattice, regardless of the ratio of reactants used. The single crystal x-ray structures of [NdBr2(Ph3PO)4]Br, [GdBr2(Ph3PO)4]Br and [YbBr2(Ph3PO)4]Br have been determined and have an octahedral geometry about the metal ion. Analysis of the bond distances shows that the Ln-O and Ln-Br distance change in accord with the lanthanide contraction, but the non bonded Ln....P distances and the Ln-O-P angles differ significantly for the Yb complex. Conductivity and variable temperature 31P NMR measurements in dichloromethane indicate that the complexes dissolve as [LnBr2(Ph3PO)4]+ for the lighter lanthanides with further ionisation becoming progressively more important for the heavier metals. In methanol more extensive dissociation is apparent. The electrospray mass spectra obtained from methanol solution show [LnBr2(Ph3PO)4]+ is present in high abundance in the gas phase with other species formed due to ligand redistribution, ionisation and solvolysis

Competition between Intramolecular and Intermolecular Interactions in an Amyloid-Forming Protein

Despite much progress in understanding the folding and the aggregation processes of proteins, the rules defining their interplay have yet to be fully defined. This problem is of particular importance since many diseases are initiated by protein unfolding and hence the propensity to aggregate competes with intramolecular collapse and other folding events. Here, we describe the roles of intramolecular and intermolecular interactions in defining the length of the lag time and the apparent rate of elongation of the 100-residue protein human β2-microglobulin at pH&nbsp;2.5, commencing from an acid-denatured state that lacks persistent structure but contains significant non-random hydrophobic interactions. Using a combination of site-directed mutagenesis, quantitative kinetic analysis and computational methods, we show that only a single region of about 10 residues in length, determines the rate of fibril formation, despite the fact that other regions exhibit a significant intrinsic propensity for aggregation. We rationalise these results by analysing the effect of incorporating the conformational properties of acid-unfolded β2-microglobulin and its variants at pH&nbsp;2.5 as measured by NMR spectroscopy into the Zyggregator aggregation prediction algorithm. These results demonstrate that residual structure in the precursor state modulates the intrinsic propensity of the polypeptide chain to aggregate and that the algorithm developed here allows the key regions for aggregation to be more clearly identified and the rates of their self-association to be predicted. Given the common propensity of unfolded chains to form non-random intramolecular interactions as monomers and to self-assemble subsequently into amyloid fibrils, the approach developed should find widespread utility for the prediction of regions important in amyloid formation and their rates of self-assembly. © 2009 Elsevier Ltd. All rights reserved

Anisotropy in the Cosmic Microwave Background at Degree Angular Scales: Python V Results

Observations of the microwave sky using the Python telescope in its fifth season of operation at the Amundsen-Scott South Pole Station in Antarctica are presented. The system consists of a 0.75 m off-axis telescope instrumented with a HEMT amplifier-based radiometer having continuum sensitivity from 37-45 GHz in two frequency bands. With a 0.91 deg x 1.02 deg beam the instrument fully sampled 598 deg^2 of sky, including fields measured during the previous four seasons of Python observations. Interpreting the observed fluctuations as anisotropy in the cosmic microwave background, we place constraints on the angular power spectrum of fluctuations in eight multipole bands up to l ~ 260. The observed spectrum is consistent with both the COBE experiment and previous Python results. There is no significant contamination from known foregrounds. The results show a discernible rise in the angular power spectrum from large (l ~ 40) to small (l ~ 200) angular scales. The shape of the observed power spectrum is not a simple linear rise but has a sharply increasing slope starting at l ~ 150.Comment: 5 page

The Cryogenic Refractive Indices of S-FTM16, a Unique Optical Glass for Near-Infrared Instruments

The Ohara glass S-FTM16 is of considerable interest for near-infrared optical designs because it transmits well through the K band and because negative S-FTM16 elements can be used to accurately achromatize positive calcium fluoride elements in refractive collimators and cameras. Glass manufacturers have sophisticated equipment to measure the refractive index at room temperature, but cannot typically measure the refractive index at cryogenic temperatures. Near-infrared optics, however, are operated at cryogenic temperatures to reduce thermal background. Thus we need to know the temperature dependence of S-FTM16's refractive index. We report here our measurements of the thermal dependence of S-FTM16's refractive index between room temperature and ~77 K. Within our measurement errors we find no evidence for a wavelength dependence or a nonlinear temperature term so our series of measurements can be reduced to a single number. We find that Delta n_{abs} / Delta T = -2.4x10^{-6} K^{-1} between 298 K and ~77 K and in the wavelength range 0.6 micron to 2.6 micron. We estimate that the systematic error (which dominates the measurement error) in our measurement is 10%, sufficiently low for most purposes. We also find the integrated linear thermal expansion of S-FTM16 between 298 K and 77 K is -0.00167 m m^{-1}.Comment: 8 pages, including 9 figures. Uses emulateapj.cls. Accepted for publication in PAS

Inhibition in multiclass classification

The role of inhibition is investigated in a multiclass support vector machine formalism inspired by the brain structure of insects. The so-called mushroom bodies have a set of output neurons, or classification functions, that compete with each other to encode a particular input. Strongly active output neurons depress or inhibit the remaining outputs without knowing which is correct or incorrect. Accordingly, we propose to use a classification function that embodies unselective inhibition and train it in the large margin classifier framework. Inhibition leads to more robust classifiers in the sense that they perform better on larger areas of appropriate hyperparameters when assessed with leave-one-out strategies. We also show that the classifier with inhibition is a tight bound to probabilistic exponential models and is Bayes consistent for 3-class problems. These properties make this approach useful for data sets with a limited number of labeled examples. For larger data sets, there is no significant comparative advantage to other multiclass SVM approaches