Nuclear stopping from 0.09A to 1.93A GeV and its correlation to flow

We present a complete systematics (excitation functions and system-size dependences) of global stopping and side flow for heavy ion reactions in the energy range between 0.09A and 1.93A GeV. For the heaviest system, Au+Au, we observe a plateau of maximal stopping extending from about 0.2A to 0.8A GeV with a fast drop on both sides. The degree of stopping, which is shown to remain significantly below the expectations of a full stopping scenario, is found to be highly correlated to the amount of side flow.     

The structure and stability of biological metaphosphate, phosphate, and phosphorane compounds in the gas phase and in solution

Density functional calculations of a series of metaphosphates, acyclic and cyclic phosphates and phosphoranes relevant to RNA catalysis are presented. Solvent effects calculated with three well-established solvation models are analyzed and compared. The structure and stability of the compounds are characterized in terms of thermodynamic quantities for isomerization and ligand substitution reactions, gas-phase proton affinities, and microscopic solution pK(a)() values. The large dataset of compounds allows the estimation of bond energies to determine the relative strengths of axial and equatorial P-O phosphorane single bonds and P-O single and double bonds in metaphosphates and phosphates. The relative apicophilicty of hydroxyl and methoxy ligands in phosphoranes are characterized. The results presented here provide quantitative insight into RNA catalysis and serve as a first step toward the construction of a high-level quantum database for development of new semiempirical Hamiltonian models for biological reactions     

Real and Rational Forms of Certain O<Subscript>2</Subscript>(ℂ)-actions,and a Solution to the Weak Complexification Problem

The main result of this paper is that there is a non-linearizable real algebraic action of the circle S¹ on ⁴, an action which becomes linearizable over . This solves the Weak Complexification Problem. We also show that for any field k of characteristic zero, there are non-linearizable algebraic actions of the group O₂(k) on four-dimensional affine k-space, and if k contains a square root of 3, then this action restricts to a non-linearizable action of the symmetric group S₃ on four-dimensional affine k-space.     

Comparison of the (17)O NMR spectra of zeolites LTA and LSX

¹⁷O NMR studies of various cation-exchanged LTA and LSX zeolites have shown similarities between the two systems. LSX samples containing divalent cations contain resonances with similar chemical shifts to those previously assigned to ‘bare’ framework oxygen atoms in Ca-LTA and Sr-LTA. The assignments are consistent with the trends seen in the spectra of monovalent cation-containing LSX and LTA zeolites, which show an increase in the average chemical shift with increasing cationic radius. The spectrum of Li-LSX, like Na-LSX, can be assigned based on the T–O–T bond angles. Gas sorption studies on Li-LSX are used to help identify the framework oxygen atoms that form the β-cages and demonstrate the sensitivity of the ¹⁷O shifts to gas loading.     

Sensitised near-infrared emission from lanthanides using a covalently-attached Pt(II) fragment as an antenna group

In a series of heterodinuclear complexes in which a Pt(PPh3)2(catecholate) chromophore is covalently linked to a lanthanide tris(diketonate) unit, sensitised near-IR emission from Yb(III), Nd(III) and Er(III) occurs on excitation of the Pt(II) chromophore at 520 nm.     

A transient N-O-linked Pauson-Khand strategy for the synthesis of the deschloro carbocyclic core of the palau'amines and styloguanidines

A stereocontrolled route to the deschloro cyclopentyl core of the palau'amines and styloguanidines has been developed. This strategy makes use of the intramolecular Pauson-Khand cyclization of an enyne with a "transient N-O tether" to construct a five-membered carbocycle in a diastereoselective fashion. [reaction: see text]     

Charge density: A probe for the nuclear interaction in microscopic transport models

The transport properties of the ³⁶Ar +⁵⁸Ni system at measured with the INDRA array, are studied within the BNV kinetic equation. A general protocol of comparison between the N-body experimental fragment information and the one-body distribution function is developed using global variables, with a special focus on charge density. This procedure avoids any definition of sources and any use of an afterburner in the simulation. We shall discuss the feasibility of such an approach and the distortions induced by the finite detection efficiency and the completeness requirements of the data selection. The sensitivity of the different global observables to the macroscopic parameters of the effective nuclear interaction will be studied in detail.Received: 21 January 2003, Published online: 5 August 2003PACS: 25.70.-z Low and intermediate energy heavy-ion reactions - 24.10.-i Nuclear reaction models and methodsN. Le Neindre: Permanent address: Institut de Physique Nuclaire, IN2P3-CNRS, F-91406 Orsay cedex, France.     

Embeddings of Danielewski surfaces

A Danielewski surface is defined by a polynomial of the form P=x ^nz –p(y). Define also the polynomial P =x ^nz –r(x)p(y) where r(x) is a non-constant polynomial of degree n–1 and r(0)=1. We show that, when n2 and deg p(y)2, the general fibers of P and P are not isomorphic as algebraic surfaces, but that the zero fibers are isomorphic. Consequently, for every non-special Danielewski surface S, there exist non-equivalent algebraic embeddings of S in ³. Using different methods, we also give non-equivalent embeddings of the surfaces xz=(y ^d _n >–1) for an infinite sequence of integers d _n . We then consider a certain algebraic action of the orthogonal group on ⁴ which was first considered by Schwarz and then studied by Masuda and Petrie, who proved that this action could not be linearized. This was done by comparing the strata of this action to those of the induced tangent space action. Inequivalent embeddings of a certain singular Danielewski surface S in ³ are found. We generalize their result and show how this leads to an example of two smooth algebraic hypersurfaces in ³ which are algebraically non-isomorphic but holomorphically isomorphic. Partially supported by NSF Grant DMS 0101836.     

Halo structure of (14)Be

The two-neutron halo nucleus (14)Be has been investigated in a kinematically complete measurement of the fragments ((12)Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation.