Effects of nuclear deformation on neutron total cross sections

Neutron total cross section differences have been determined for ^150,152,154Sm from 0.8 to 15 MeV by measuring transmission ratios. Significant differences were observed for ^152,150Sm and for ^154,150Sm. Evidence is presented that these results can be attributed to nuclear deformation.     

Elastic scattering of deuterons by 14C from Ed = 4 to 10 MeV

Angular distributions for the elastic scattering of deuterons by ¹⁴C were measured at nine energies between E_d = 4.2 and 10 MeV. Excitation functions were taken in 50 keV steps from E_d = 4 to 10 MeV. A resonance was observed at E_d = 4.5 MeV, which corresponds to an excitation energy of 14.41 MeV in ¹⁶N. An analysis using an optical model plus a single-level formula derived from the R-matrix formalism yields an l-value assignment of l = 4 for this resonance. Of the three J^π values allowed for l = 4 (J^π = 3⁺, 4⁺, 5⁺), the value of J_π = 3⁺ is found to be slightly preferred. Possible identification of this resonance with an analog in ¹⁶O is discussed. The angular distributions measured at off-resonance energies were analyzed with an optical-model potential which has a surface-peaked imaginary well. The energy dependence of the real and imaginary well depths are explicitly determined in the present work for E_d = 4 to 10 MeV. The best-fit optical-model parameters obtained from the present study are compared to those from the ¹⁴N(d, d)¹⁴N work.     

Study of the decay D0 --> K+pi-

Using a large sample of photoproduced charm mesons from the FOCUS experiment at Fermilab (FNAL-E831), we observe the decay D0-->K+pi- with a signal yield of 149+/-31 events compared to a similarly cut sample consisting of 36 760+/-195 D0-->K-pi+ events. We use the observed ratio of D0-->K+pi- to D0-->K-pi+ (0.404+/-0.085+/-0.025)% to obtain a relationship between the D0 mixing and doubly Cabibbo suppressed decay parameters.     

Ab initio study of cubyl chains and networks

The spatial arrangements and physical properties of one- and two-dimensional structures, based on the amazing cubane (C(8)H(8)) molecule, are investigated in detail. In particular, we compute the electronic structure, both by first principle calculations and by semiempirical methods. The elastic and vibrational properties are evaluated as well. All these results are compared with those of the single cubane molecule, in order to elucidate the influence of dimensionality.     

Competing magnetic phases on a kagomé staircase

We present thermodynamic and neutron data on Ni3V2O8, a spin-1 system on a kagomé staircase. The extreme degeneracy of the kagomé antiferromagnet is lifted to produce two incommensurate phases at finite T--one amplitude modulated, the other helical--plus a commensurate canted antiferromagnet for T-->0. The H-T phase diagram is described by a model of competing first and second neighbor interactions with smaller anisotropic terms. Ni3V2O8 thus provides an elegant example of order from subleading interactions in a highly frustrated system.     

Multiple field-induced phase transitions in the geometrically frustrated dipolar magnet: Gd(2) Ti(2)O(7)

Field-driven phase transitions generally arise from competition between Zeeman energy and exchange or crystal-field anisotropy. Here we present the phase diagram of a frustrated pyrochlore magnet Gd(2)Ti(2)O(7), where crystal-field splitting is small compared to the dipolar energy. We find good agreement between zero-temperature critical fields and those obtained from a mean-field model. Here, dipolar interactions couple real space and spin space, so the transitions in Gd(2)Ti(2)O(7) arise from field-induced "cooperative anisotropy," reflecting the broken spatial symmetries of the pyrochlore lattice.     

X-Ray fluorescence analysis of dry deposit samples in Mexico City

The American National Standard "Calibration and Use of Germanium Spectrometers for the Measurement of Gamma-Ray Emission Rates of Radionuclides" has been reissued as N42.14-1999. The performance tests in it can be used to make sure that a gamma-spectroscopy program is set up correctly. The same tests can also be used to verify the improvements made by program developers. However, sometimes the tests in this ANSI standard are not enough. To satisfy certain quality assurance requirements, it is necessary to demonstrate that the results are correct either by hand calculations or by comparing the results to known values.     

Factors contributing to peak broadening and mass accuracy in the characterization of intact spores using matrix-assisted laser desorption/ionization coupled with time-of-flight mass spectrometry

Factors contributing to peak broadening, accuracy and precision in mass assignment in the matrix-assisted laser desorption/ionization characterization of a lipopeptide desorbed from intact Bacillus spores were investigated. These spores were studied as an example of a thick, topologically irregular sample, which present a more difficult target than a pure peptide or protein. The type of matrix, matrix:sample ratio, laser fluence, and localized repetitive laser irradiation were all found to affect the full-width at half maximum of the biomarker. Both in-source and post-source phenomena were shown to contribute. Sample thickness had less effect. Precision and accuracy of mass assignment were also affected by matrix:sample ratio and laser fluence. In general, this sample was responsive to the same experimental variables as pure peptides, and the use of an internal standard produced significant improvements in precision and accuracy.     

Nanoconfinement Inside Molecular Metal Oxide Clusters: Dynamics and Modified Encapsulation Behavior

Encapsulation behavior, as well as the presence of internal catalytically active sites, has been spurring the applications of a 3 nm hollow spherical metal oxide cluster {Mo₁₃₂} as an encapsulation host and a nanoreactor. Due to its well‐defined and tunable cluster structures, and nanoscaled internal void space comparable to the volumes of small molecules, this cluster provides a good model to study the dynamics of materials under nanoconfinement. Neutron scattering studies suggest that bulky internal ligands inside the cluster show slower and limited dynamics compared to their counterparts in the bulk state, revealing the rigid nature of the skeleton of the internal ligands. NMR studies indicate that the rigid internal ligands that partially cover the interfacial pore on the molybdenum oxide shells are able to block some large guest molecules from going inside the capsule cluster, which provides a convincing protocol for size‐selective encapsulation and separation.     

Synthesis and optical characterization of photoactive poly(2‐phenoxyethyl acrylate) copolymers containing azobenzene units,prepared by frontal polymerization using novel ionic liquids as initiators

2‐Phenoxyethyl acrylate (2‐PEA) was polymerized alone and in the presence of an azobenzene comonomer derived from Disperse Red‐1, N‐ethyl‐N‐(2‐hydroxyethyl)‐4‐(4‐nitrophenylazo)aniline (MDR‐1), by using the frontal polymerization technique. Two novel ionic liquids, recently synthesized by us, were used as initiators: tetrabutylphosphonium persulfate (TBPPS) and trihexyltetradecylphosphonium persulfate (TETDPPS). Even if their concentrations were smaller than those found when benzoyl peroxide and terbutylperoxy neodecanoate were used, these compounds gave rise to stable propagating polymerization fronts characterized by relatively low maximum temperatures and good velocities. Moreover, at variance to these latter, TBPPS and TETDPPS prevent bubble formation, thus allowing the use of the obtained materials in optical applications. The obtained polymers were characterized by infrared spectroscopy (FTIR), their thermal properties were determined by differential scanning calorimetry, and their optical properties were studied by absorption spectroscopy in the UV–vis region. Finally, the nonlinear optical (NLO) properties of the 2‐PEA/MDR‐1 copolymers obtained with TBPPS and TETDPPS were performed according to the Z‐Scan technique with prepared film samples. It has been proven that samples with higher MDR‐1 content (0.05 mol %) exhibited outstanding cubic NLO activity with negative NLO refractive coefficients around n₂ = ?1.7 × 10^?3 esu. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012