trans‐Dichloro(dimethyl sulfide‐κS)(pyridine‐κN)platinum(II)

The structure of the title compound, [PtCl₂(C₅H₅N)(C₂H₆S)], consists of discrete mol­ecules in which the Pt‐atom coordination is slightly distorted square planar. The Cl atoms are trans to each other, with a Cl—Pt—Cl angle of 176.60 (7)°. The pyridine ligand is rotated 64.5 (2)° from the Pt square plane and one of the Pt—Cl bonds essentially bisects the C—S—C angle of the di­methyl sulfide ligand. In the crystal structure, there are extensive weak C—H⋯Cl interactions, the shortest of which connects mol­ecules into centrosymmetric dimers. A comparison of the structural trans influence on Pt—S and Pt—­N distances for PtS(CH₃)₂ and Pt(pyridine) fragments, respectively, in square‐planar Pt^II complexes is presented.     

Measurement of the absolute Raman cross section of the optical phonon in silicon

The absolute Raman cross section σ_RS of the first-order 519 cm⁻¹ optical phonon in silicon was measured using a small temperature-controlled blackbody for the signal calibration of the Raman system. Measurements were made with a 25-mil thick (001) silicon sample located in the focal plane of a 20-mm effective focal length (EFL) lens using 785-, 1064-, and 1535-nm CW pump lasers for the excitation of Raman scattering. The pump beam was polarized along the [100] axis of the silicon sample. Values of 1.0±0.2×10⁻²⁷, 3.6±0.7×10⁻²⁸, and 1.1±0.2×10⁻²⁹ cm² were determined for for 785-, 1064-, and 1535-nm excitation, respectively. The corresponding values of the Raman scattering efficiency S are 4.0±0.8×10⁻⁶, 1.4±0.3×10⁻⁶, and 4.4±0.8×10⁻⁸ cm⁻¹ sr⁻¹.The values of the Raman polarizability |d| for 785-, 1064-, and 1535-nm excitation are 4.4±0.4×10⁻¹⁵, 5.1±0.5×10⁻¹⁵, and 1.9±0.2×10⁻¹⁵ cm², respectively. The values of 4.4±0.4×10⁻¹⁵ and 5.1±0.5×10⁻¹⁵ cm² for |d| for 785- and 1064-nm excitation, respectively, are 1.3 and 2.0 times larger than the values of 3.5×10⁻¹⁵ and 2.5×10⁻¹⁵ cm² calculated by Wendel. The Raman polarizability |d| computed using the density functional theory in the long-wavelength limit is consistent with the general trend of the measured data and Wendel’s model.     

A Stable H-Dibaryon: Dark Matter, Candidate Within QCD?

Particle physics arguments suggest that the H-dibaryon—a state consisting of two u, two d, and two s quarks—may have a mass 1.5 ± 0.2 MeV, and that r _H r _N. Remarkably, the observed stability of nuclei and other experimental limits do not exclude this scenario at present, as discussed here. If they are present in sufficient abundance, relic H's would be the cold dark matter. Tests of this scenario are discussed.     

High-frequency dynamic nuclear polarization in the nuclear rotating frame

A proton dynamic nuclear polarization (DNP) NMR signal enhancement (epsilon) close to thermal equilibrium, epsilon = 0.89, has been obtained at high field (B(0) = 5 T, nu(epr) = 139.5 GHz) using 15 mM trityl radical in a 40:60 water/glycerol frozen solution at 11 K. The electron-nuclear polarization transfer is performed in the nuclear rotating frame with microwave irradiation during a nuclear spin-lock pulse. The growth of the signal enhancement is governed by the rotating frame nuclear spin-lattice relaxation time (T(1rho)), which is four orders of magnitude shorter than the nuclear spin-lattice relaxation time (T(1n)). Due to the rapid polarization transfer in the nuclear rotating frame the experiment can be recycled at a rate of 1/T(1rho) and is not limited by the much slower lab frame nuclear spin-lattice relaxation rate (1/T(1n)). The increased repetition rate allowed in the nuclear rotating frame provides an effective enhancement per unit time(1/2) of epsilon(t) = 197. The nuclear rotating frame-DNP experiment does not require high microwave power; significant signal enhancements were obtained with a low-power (20 mW) Gunn diode microwave source and no microwave resonant structure. The symmetric trityl radical used as the polarization source is water-soluble and has a narrow EPR linewidth of 10 G at 139.5 GHz making it an ideal polarization source for high-field DNP/NMR studies of biological systems.     

An assessment of the sharpness of carotid artery tissue boundaries with acquisition voxel size and field strength

A measure of the sharpness of vessel wall interfaces in carotid artery MRI may be useful for assessing the conspicuity of the wall's features. An edge detection technique was used to measure the signal intensity gradients in 2D time-of-flight (2D-TOF) and double-inversion recovery black-blood (DIR-BB) carotid artery images of normal subjects that were acquired at 1.5 T with 0.55 x 0.55 x 2.0-mm (0.6 mm3) acquisition voxels and zero filled to reduce the in-plane reconstructed voxel size by one half in each dimension as well as with 0.27 x 0.27 x 2.0-mm (0.15 mm3) acquisition voxels and at 3.0 T with 0.27 x 0.27 x 2.0-mm (0.15 mm3) acquisition voxels using surface coils. The gradient intensities of the lumen-to-background interface varied closely with the contrast-to-noise ratio of the 2D-TOF imaging. For the DIR-BB imaging, in which higher spatial frequency artery structures are visible, the gradient intensities at the interfaces were higher than theoretically predicted at both field strengths with smaller acquisition voxels. The use of acquisition voxels smaller than those previously used at 1.5 T can improve the visualization of carotid artery structures at 1.5 and 3.0 T with surface coil reception.     

Measurement of the absolute Raman scattering cross section of the 1584‐cm−1 band of benzenethiol and the surface‐enhanced Raman scattering cross section enhancement factor for femtosecond laser‐nanostructured substrates

The absolute Raman scattering cross section (σ_RS) for the 1584‐cm⁻¹ band of benzenethiol at 897 nm (1.383 eV) has been measured to be 8.9 ± 1.8 × 10⁻³⁰ cm² using a 785‐nm pump laser. A temperature‐controlled, small‐cavity blackbody source was used to calibrate the signal output of the Raman spectrometer. We also measured the absolute surface‐enhanced Raman scattering cross section (σ_SERS) of benzenethiol adsorbed onto a silver‐coated, femtosecond laser‐nanostructured substrate. Using the measured values of 8.9 ± 1.8 × 10⁻³⁰ and 6.6 ± 1.3 × 10⁻²⁴ cm² for σ_RS and σ_SERS respectively, we calculate an average cross‐section enhancement factor (EF) of 0.8 ± 0.3 × 10⁶. Copyright © 2009 John Wiley & Sons, Ltd.     

Violation of the Greisen-Zatsepin-Kuzmin cutoff: a tempest in a (magnetic) Teapot? Why cosmic ray energies above 10(20) eV may not require new physics

The apparent lack of suitable astrophysical sources for the observed highest energy cosmic rays within approximately 20 Mpc is the "Greisen-Zatsepin-Kuzmin (GZK) paradox." We constrain representative models of the extragalactic magnetic field structure by Faraday rotation measurements; limits are at the microG level rather than the nG level usually assumed. In such fields, even the highest energy cosmic rays experience large deflections. This allows nearby active galactic nuclei (possibly quiet today) or gamma ray bursts to be the source of ultrahigh energy cosmic rays without contradicting the GZK distance limit.     

Tripyrrolylphosphine as a unique bridging ligand in the Rh6CO14(mu2-P(NC4H4)3) cluster: structure,bonding, fluxionality,thermodynamics, and kinetics studies

Tripyrrolylphosphine reacts with the cluster Rh6CO15(NCMe) to afford the disubstituted Rh6CO14(mu2)-P(NC4H4)3) derivative (2) via the Rh6CO15P(NC4H4)3 intermediate (1) with eta(1)-P coordination. In the solid state, 2 has the phosphine occupying a bridging position where it is bonded to two neighboring Rh atoms in the Rh(6) octahedron through the P-atom and an approximately tetrahedral alpha-carbon atom of one of the pyrrolyl rings. This can be described by the interaction of an electron pair, associated with a negative charge on one of the canonical forms of the NC(4)H(4) ring, with the adjacent Rh center. (1)H NMR spectra show that the solid-state structure is retained in solution, but the phosphine is not rigid, and three distinctive dynamic processes are observed. Each of these represents independent hindered rotation of inequivalent pyrrolyl rings about P-N bonds, the ring involved in the interaction with the Rh(6) skeleton displaying the highest activation barrier with deltaH = 15.8 +/- 0.1 kcal mol(-1) and deltaS = 1.4 +/- 0.3 cal K(-1) mol(-1). The assignment has been confirmed by 1H TOCSY and EXSY experiments, and a mechanism is proposed. The formation of 2 from 1 is reversible in the presence of CO, which is highly unusual for bridged clusters. The kinetics of the forward and reverse reactions have been studied, and the values of DeltaH degrees and DeltaS degrees for formation of 2 (+1.3 +/- 0.5 kcal mol(-1) and -9 +/- 2 cal K(-1) mol (-1), respectively) show that the Rh-C bond in the bridge is comparable in strength with the Rh-CO bond it replaces. The intrinsic entropy of 2 is exceptionally unfavorable, overcoming the favorable entropy caused by CO release, and this allows the reversibility of bridge formation. The reactions proceed via a reactive intermediate that may involve agostic bonding of the ring. The reverse reaction has an exceedingly unfavorable activation entropy that emphasizes the unique nature of 2.     

Errors as Multistable Response Options

Five simulations mimicked benchmark phenomena of intact and dyslexic word naming. Initially, an iterative map was tuned to simulate the frequency × consistency interaction in skilled naming. Subsequently, two model parameters were changed, in turn, to produce the regularization error of surface dyslexia (PINT pronounced to rhyme with /mint/), absent pseudoword (BINT) naming of phonological dyslexia (words are named correctly; pseudowords are not), the semantic error of deep dyslexia (BUSH named as /tree/), and a dissociation in picture naming of spoken versus written responses (the spoken response to a picture of a bush is /tree/, but the written response is BUSH). All errors, except absent pseudoword naming, were simulated as transcritical bifurcations.