Phenomenology of flow disappearance in intermediate-energy heavy ion collisions

The disappearance of collective flow effects in heavy ion collisions is investigated using a microscopic optical model formalism for estimating collision momentum transfers. Phenomenological expressions for the balance energy are obtained which agree very well with measurements for various experimental collision pairs and with results obtained from Boltzmann-Uehling-Uhlenbeck simulations.     

Phase matching considerations in second harmonic generation from tissues: Effects on emission directionality, conversion efficiency and observed morphology

We present a heuristic treatment which relates SHG image intensities, signal directionality, and observed morphology to the physical structure of collagen and cellulose fibrillar tissues. The SHG creation model is based upon relaxed phase matching conditions which account for dispersion, randomness, and axial momentum contributions from the media, and includes a mathematical treatment which relates SHG conversion efficiency to fibril diameter and packing through the inclusion of potential intensity amplification resultant from quasi-phase matching (QPM). A direct consequence of this theory is that SHG in biological tissues is not strictly a coherent process, and that the forward directed SHG has a longer coherence length than the backward component, Through this treatment, we show that the emission directionality and also conversion efficiency do not arise solely from the fibril size but also depend on packing density and order of the inter-fibril structure. We demonstrate these principles in comparing the SHG response in normal and Osteogenesis Imperfecta (OI) skin. We show that the observed directionality and decreased relative intensity in the diseased state is consistent with phase matching conditions arising from the decreased fibril size and more random assembly. We further use this theory to explain the differences in morphology seen in forward and backward collected SHG in fibrillar tissues (e.g., collagenous and cellulosic). Specifically, we attribute segmented appearance to destructive interference between small fibrils separated by less than the coherence length. We suggest the approach based on relaxed phasematching conditions is general in predicting the SHG response in tissues and may be broadly applicable in interpreting the SHG contrast for diagnostic applications.     

Anyons from strings

The Nambu-Goto string in a three-dimensional (3D) Minkowski spacetime is quantized preserving Lorentz invariance and parity. The spectrum of massive states contains anyons. An ambiguity in the ground state energy is resolved by the 3D N=1 Green-Schwarz superstring, which has massless ground states describing a dilaton and dilatino, and first-excited states of spin 1/4.     

Invariance of actions,rheonomy, and the new minimal N = 1 supergravity in the group manifold approach

A new definition of rheonomy is proposed based on Bianchi identities instead of field equation. For theories with auxiliary fields, the transformation rules are obtained in a completely geometrical way and invariance of the action is equivalent to d$\text{P}$ = 0, which means surface-independence of the action integral. For theories without auxiliary fields, the transformation rules are found by requiring that the action be invariant, just as in the component approach. Previous methods of obtaining the transformation rules which start from rheonomy of field equations and use certain recipes to find the off-shell extensions of the rules are abandoned. New minimal supergravity is worked out in detail; it is the gauge theory based on a free differential algebra which includes the auxiliary fields.     

Nuclear data for space radiation

Human space flight requires protecting astronauts from the harmful effects of space radiation. The availability of measured nuclear cross-section data needed for these studies is reviewed in the present paper. The energy range of interest for radiation protection is approximately 100 MeV/n–10 GeV/n. The majority of data are for projectile fragmentation partial and total cross-sections, including both charge changing and isotopic cross-sections. The cross-section data are organized into categories which include charge changing, elemental, isotopic for total, single and double differential with respect to momentum, energy and angle. Gaps in the data relevant to space radiation protection are discussed and recommendations for future experiments are made.     

Landau levels and Riemann zeros

The number N(E) of complex zeros of the Riemann zeta function with positive imaginary part less than E is the sum of a "smooth" function N[over ](E) and a "fluctuation." Berry and Keating have shown that the asymptotic expansion of N[over ](E) counts states of positive energy less than E in a "regularized" semiclassical model with classical Hamiltonian H=xp. For a different regularization, Connes has shown that it counts states "missing" from a continuum. Here we show how the "absorption spectrum" model of Connes emerges as the lowest Landau level limit of a specific quantum-mechanical model for a charged particle on a planar surface in an electric potential and uniform magnetic field. We suggest a role for the higher Landau levels in the fluctuation part of N(E).     

Performance of a quarter-wavelength particle concentrator

A series of devices have been investigated which use acoustic radiation forces to concentrate micron sized particles. These multi-layered resonators use a quarter-wavelength resonance in order to position an acoustic pressure node close to the top surface of a fluid layer such that particles migrate towards this surface. As flow-through devices, it is then possible to collect a concentrate of particulates by drawing off the particle stream and separating it from the clarified fluid and so can operate continuously as opposed to batch processes such as centrifugation. The methods of construction are described which include a micro-fabricated, wet-etched device and a modular device fabricated using a micro-mill. These use silicon and macor, a machinable glass ceramic, as a carrier layer between the transducer and fluid channel, respectively. Simulations using an acoustic impedance transfer model are used to determine the influence of various design parameters on the acoustic energy density within the fluid layer and the nodal position. Concentration tests have shown up to 4.4-, 6.0- and 3.2-fold increases in concentration for 9, 3 and 1 microm diameter polystyrene particles, respectively. The effect of voltage and fluid flow rates on concentration performance is investigated and helps demonstrate the various factors which determine the increase in concentration possible.     

A reinvestigation of the structures for 5-diazouracil, 5-diazouridine, 5-diazo-2′-deoxyuridine and certain related derivatives by proton magnetic resonance spectroscopy

The structure of 5-diazouracil and several closely related derivatives have been revised on the basis of pmr spectroscopy. 5-Diazouracil, 5-diazouracil hydrate, 5-diazouracil methanol adduct, 5-diazouridine and 5-diazo-2′-deoxyuridine have been reassigned the structures 5-diazopyrimidin-2,4(3H)dione (XI), 5-diazo-6-hydroxy-1,6-dihydropyrimidin-2,4(1H,3H,6H)dione (XIII), 5-diazo-6-methoxy-1,6-dihydropyrimidin-2,4(1H,3H,6H)dione (XII), 1 -(β-D-ribofuranosyl)-O^5′ -6(S)cyclo-5-diazo-1,6-dihydropyrimidin-2,4(3H,6H)dione (XVII) and 1-(2-deoxy-β-D-ribofuranosyl)-O^5′ -6(S)cyclo-5-diazo-1,6-dihydropyrimidin-2,4(3H,6H)dione (XIX), respectively. Treatment of XII with dimethylamine resulted in a coupling of the 5-diazo group with dimethylamine and a concomitant rearomatization of the heterocyclic ring by expulsion of the 6-methoxy group to furnish 5-(3,3-dimethyl-1-triazeno)uracil (XIV). A similar reaction of XIX and XVII with dimethylamine furnished the corresponding 5-(3,3-dimethyl-1-triazeno)derivatives. The effect which certain resonance hybrids of the diazo moiety may exert in reactions of the above hetero-cycles and the assignment of S configuration at C-6 for the nucleoside derivatives is also discussed.     

Pyrazolopyrimidine nucleosides. Part VII. The synthesis of certain pyrazolo [3,4-d] pyrimidine nucleosides related to the nucleoside antibiotics toyocamycin and sangivamycin

The condensation of 4-acetamido-3-cyanopyrazolo[3,4-d]pyrimidine ( 5 ) with crystalline 2,3,5-tri-O-acetyl-β- D -ribofuranosyl chloride ( 6 ) has furnished a good yield of nucleoside material ( 7 ) which on treatment with sodium methoxide in methanol provided a high yield of nucleoside which was subsequently established as methyl 4-amino-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]-pyrimidine-3-formimidate monohydrate ( 11 ). The formimidate function of 11 was found to be highly reactive and 11 was readily converted into the corresponding carhoxamidine ( 8 ), carboxamidoxime ( 14 ) and carboxamidrazone ( 15 ) when treated with the appropriate nucleophiles. Treatment of the imidate ( 11 ) with sodium hydrogen sulfide gave a high yield of the thiocarboxamide ( 12 ) which was then readily converted into 4-amino-3-cyano-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]pyrimidine ( 16 ). Aqueous base transformed 11 into 4-amino-1-(β- D -ribofuranosyl)-pyrazolo[3,4-d]pyrimidine-3-carboxamide ( 10 ) while more vigorous basic hydrolysis provided the corresponding carboxylic acid ( 9 ) in nearly quantitative yield. Decarboxylation of 9 proceeded smoothly in hot sulfolane to provide the known 4-amino-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]pyrimidine ( 13 ) in 68% yield which unequivocally established the site of ribosylation and anomeric configuration for all nucleosides reported in this investigation.