Exact scalar field cosmologies in a higher derivative theory

We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR ² in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity. Some new and interesting potentials are noted in the presence of R ² term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover approximation.     

φ meson production fromp\bar p collisions at\sqrt s = 1.8 TeV

Fermilab experiment E735 located at the CO intersection region of the $\sqrt s = 1.8$ TeV $p\bar p$ collider analysed over 900 Φ→K ⁺ K ^? events. Measured were the transverse momentum spectrum, the correlation between the average transverse momentum <pt> and the charged particle multiphcityN _c , as well as the probability of Φ production per charged track,N _Φ /N _c , versusN _c . We have also made an estinate of the total inclusive cross section for Φ mesons, $\sigma (p\bar p \to \phi X) = 7.3 \pm 2.2 mb$ .     

Conversion of aryl azides to O-alkyl imidates via modified Staudinger ligation

[reaction: see text] o-Carboalkoxy triarylphosphines are shown to react with aryl azides to provide Staudinger ligation products bearing O-alkyl imidate linkages. This is in contrast to alkyl azides whose ligation to o-carboalkoxy triarylphosphines has been reported to yield amide-linked materials. This extension of the Staudinger ligation for coupling of abiotic reagents under biocompatible conditions highlights the utility of commercially available triarylphosphines through which suitable linkers can be attached via an ester moiety.     

Structure and chemistry of 1-silafluorenyl dianion, its derivatives, and an organosilicon diradical dianion.

1-Silafluorene dianion was synthesized by potassium reduction of 1,1-dichloro-1-silafluorene in refluxing THF. The X-ray structure of 1,1-dipotassio-1-silafluorene (3b) shows C-C bond length equalization in the five-membered silole ring and C-C bond length alternation in the six-membered benzene rings, indicating aromatic delocalization of electrons in the silole ring. The downfield (29)Si chemical shift at 29.0 ppm and theoretical calculations also support electron delocalization in the silole ring of 3b. Dianion salt 3b underwent nucleophilic reactions with Me(3)SiCl and EtBr to form the corresponding disubstituted products. Benzaldehyde underwent reductive coupling in the presence of 3b. Slow oxidation of 3b yielded 1,1'-dipotassio-1,1'-bis(silafluorene) (16). The X-ray structure and (29)Si chemical shift (-38.0 ppm) of 16 indicate localized negative charges at the silicon atoms and no aromatic character. Heating a DME/hexane solution of 3b in the presence of 18-crown-6 led to a novel diradical dianion salt.     

Glycine exists mainly as monomers, not dimers, in supersaturated aqueous solutions: implications for understanding its crystallization and polymorphism

Glycine, the simplest amino acid, is described as existing as hydrogen-bonded cyclic dimers in supersaturated aqueous solutions and, as a result, crystallizing in a centrosymmetric polymorph (polymorph alpha) for which the dimer can be viewed as the building unit, in favor of other polymorphs of polar structures. In exhibiting this relation between polymorphic selectivity and self-association in solution, glycine is thought to illustrate a general principle. We measured the freezing-point depression of glycine-water up to 30% supersaturation and found that glycine exists mainly as monomers, not dimers, and that the dimer stability constant K D is smaller than 0.1 kg of H 2O/mol if the observed osmotic abnormality is attributed to dimerization. We also revisited a report cited as evidence for glycine dimerization: the slowdown of glycine diffusion with solution age. Pulsed gradient spin-echo NMR spectroscopy was used in place of the previous method of Gouy interferometry to avoid perturbations to sloution structure caused by the interdiffusion between two solutions of different concentrations. No aging effect was observed on glycine diffusion up to 24% supersaturation after five days. The solute size calculated from diffusivity, viscosity, and the Stokes-Einstein relation showed no increase with concentration or solution age. We conclude that glycine exists in supersaturated aqueous solutions mainly as monomers, not dimers, and remains so upon aging. This result does not invalidate the theories of how pH and additives affect glycine's polymorphic preference, because they begin with the assumption that alpha glycine is the preferred polymorph under normal conditions, but requires a new explanation for that assumption itself.     

Orbital Angular Momentum in Scalar Diquark Model and QED

We compare the orbital angular momentum of the ‘quark’ in the scalar diquark model as well as that of the electron in QED (to order α) obtained from the Jaffe–Manohar decomposition to that obtained from the Ji relation. We estimate the importance of the vector potential in the definition of orbital angular momentum.     

High contrast images of uterine tissue derived using Raman microspectroscopy with the empty modelling approach of multivariate curve resolution-alternating least squares

Approaches that allow one to rapidly understand tissue structure and functionality in situ remain to be developed. Such techniques are required in many instances, including where there is a need to remove with a high degree of confidence positive tumour margins during surgical excision. As biological tissue has little contrast, gold standard confirmation of surgical margins is conventionally undertaken by histopathological diagnosis of tissue architecture via optical microscopy. Vibrational spectroscopy techniques, when coupled to sophisticated computational analyses, are capable of constructing bio-molecular contrast images of unstained tissue. To assess the relative applicability of a range of candidate algorithms to distinguish the in situ bio-molecular structures of a complex tissue, the empty modelling approach of multivariate curve resolution-alternating least squares (MCR-ALS) was compared to hierarchical cluster analysis (HCA) or principal component analysis (PCA). Such chemometric analyses were applied to Raman images of benign (tumour-adjacent) endometrium, stage I and stage II endometrioid cancer. Re-constructed images from the in situ bio-molecular tissue architectures highlighted features associated with glandular epithelium, stroma, glandular lumen and myometrium. Of the tested chemometric analyses, MCR-ALS provided the best bio-molecular contrast images, superior to those derived following HCA or PCA, with clear and defined margins of histological features. Iteratively-resolved spectra identified wavenumbers responsible for the contrast image. Wavenumbers 1234 cm(-1) (Amide III), 1390 cm(-1) (CH(3) bend), 1675 cm(-1) (Amide I/lipid), 1275 cm(-1) (Amide III), 918 cm(-1) (proline) and 936 cm(-1) (proline, valine and proteins) were responsible for generating the majority of the contrast within MCR-ALS-generated images. Applications of sophisticated computational analyses coupled with vibrational spectroscopy techniques have the potential to lend novel functionality insights into bio-molecular structures in vivo.     

Effects of dimethylhydrazine on Zn, C, and H doping of GaP

Surfactants are beginning to be used during vapor-phase growth to provide control of the materials characteristics of epitaxial layers. This paper reports the effects of utilizing N, from pyrolysis of dimethylhydrazine (DMHy), as a surfactant during the organometallic vapor-phase epitaxial growth of GaP. Nitrogen is isoelectronic with the group V host element; thus, it generates no free carriers. Additionally, due to its small size, N is strongly rejected from the solid, so little incorporation is expected. This is confirmed by the determination of the very low N distribution coefficient (3.2×10⁻⁵). Using secondary ion mass spectroscopy analysis, we observe an increase in the distribution coefficient of the acceptor Zn when DMHy is added during growth, resulting in an increase in the doping efficiency by nearly an order of magnitude. Furthermore, the Zn doping efficiency increases linearly with the amount of DMHy added during growth over the range of partial pressures from 2.83×10⁻⁴ to 2.20×10⁻³ atm. The increase of doping for Zn is believed to be mainly a N surfactant effect. The addition of DMHy also leads to increases in both H and C incorporation. The concentrations of both are linear functions of DMHy concentration. Both H and C incorporation most likely arise mainly from pyrolysis of the DMHy. We propose a simple mechanism for the surfactant effect due to an increase in the Zn incorporation coefficients at the step edge induced by the presence of N (and probably H) on the surface.