Directional correlations of γ-rays in 143Pr

Directional correlation measurements have been made for γ-transitions in ¹⁴³Pr following the decay of 33.0 h ¹⁴³Ce using two Ge(Li) detectors. Correlation coefficients are reported for twelve cascades, of which coefficients for five cascades are previously unreported. Deduced are mixing ratios for thirteen transitions and spins and parities for the following levels: $\text{57 (}\text{5}\text{2}{}^{\mathrm{+}}\text{), 351 (}\text{3}\text{2}{}^{\mathrm{+}}\text{), 490 (}\text{5}\text{2}{}^{\mathrm{+}}\text{), 722 (}\text{3}\text{2}{}^{\mathrm{+}}\text{), 739 (}\text{1}\text{2}{}^{\mathrm{?}}\text{), 938 (}\text{3}\text{2}{}^{\mathrm{+}}\text{),}\text{and}\text{1160 (}\text{3}\text{2}{}^{\mathrm{+}}\text{)}\text{keV}$.     

Temperature-dependent structure of methyltributylammonium bis(trifluoromethylsulfonyl)amide: X ray scattering and simulations

We report the combined results of computational and x ray scattering studies of amorphous methyltributylammonium bis(trifluoromethylsulfonyl)amide as a function of temperature. These studies included the temperature range for the normal isotropic liquid, a deeply supercooled liquid and the glass. The low q peaks in the range from 0.3 to 1.5 A(-1) in the structure function of this liquid can be properly accounted for by correlations between first and second nearest neighbors. The lowest q peak can be assigned to real space correlations between ions of the same charge, while the second peak arises mostly from nearest neighbors of opposite charge. Peaks at larger q values are mostly intramolecular in nature. While our simulated structure functions provide an excellent match to our experimental results and our experimental findings agree with previous studies reported for this liquid, the prior interpretation of the experimental data in terms of an interdigitated smectic A phase is not supported by our simulations. In this work, we introduce a set of general theoretical partitions of real and reciprocal space correlations that allow for unambiguous analysis of all intra- and interionic contributions to the structure function and coherent scattering intensity. We find that the intermolecular contributions to the x ray scattering intensity are dominated by the anions and cross terms between cations and anions for this ionic liquid.     

Focusing of longitudinal ultrasonic waves in air with an aperiodic flat lens

Modeling and experimental results of an ultrasonic aperiodic flat lens for use in air are presented. Predictive modeling of the lens is performed using a hybrid genetic-greedy algorithm constrained to a linear structure. The optimized design parameters are used to fabricate a lens. A method combining a fiber-disk arrangement and scanning laser vibrometer measurements is developed to characterize the acoustic field distribution generated by the lens. The focal spot size is determined to be 0.88 of the incident wavelength of 80-90 kHz at a distance of 2.5 mm from the lens. Theoretically computed field distributions, optimized frequency of operation, and spatial resolution focal length are compared with experimental measurements. The differences between experimental measurements and the theoretical computations are analyzed. The theoretical calculation of the focal spot diameter is 1.7 mm which is 48% of the experimental measurement at a frequency of 80-90 kHz. This work illustrates the capabilities of a hybrid algorithm approach to design of flat acoustic lenses to operate in air with a resolution of greater than the incident wavelength and the challenges of characterizing acoustic field distribution in air.     

Surface chemistry of room-temperature ionic liquids

In many applications of room-temperature ionic liquids, it has been recognized that the interface is a vital component. In electrochemistry, for instance, the electron transfer is significant to the efficiency of the solar cell and is very much dependent on the behavior of a given interface. This review presents the current state of knowledge of room-temperature ionic liquids in contact with solids, liquids, and gas phases. Experimental and molecular modeling studies have been conducted to investigate the surface structure and composition of ions in pure ionic liquids. However, surface studies on these liquids are still in its infancy and as the range of the available surface techniques and systematic investigations are increased, our understanding will improve which will lead to advances on this field.     

Calculations of the EPR g-tensor using unrestricted two- and four-component relativistic approaches within the HF and DFT frameworks

ABSTRACT

Approaches and programs for calculations of the EPR g-tensor in the framework of the two- and four-component methods are still very rare. There are three main reasons for this: the wider community's unawareness of the importance of second- and higher order spin–orbit effects on the g-tensor, the methodological problems associated with performing such calculations and the lack of understanding of these problems. This paper reports on the implementation of a method for calculation of the g-tensor in the framework of the relativistic unrestricted two- and four-component Hartree–Fock and density functional theory approaches based on the Kramers pair formalism. This implementation allows us to analyse problems which arise when the g-tensor is calculated via Kramers pairs in the unrestricted framework.     

Correlations between electron and positron workfunctions on copper surfaces

We have performed contact potential difference measurements on low-index faces of copper in ultrahigh vacuum using positrons as positive test particles in a retarding field analyzer. For negative positron affinity surfaces bombarded with keV positrons we also measured energy distributions of reemitted slow positrons and found them to sharply peaked in energy about a value which we label ?φ⁺. Both adsorbing sulfur on a Cu(111) sample and raising its temperature cause changes in φ⁺ which are equal and opposite to the contact potential change of the sample, i.e. the electron workfunction change. This result is in complete accordance with φ⁺ being a measure of the negative positron workfunction of the sample and high temperature or adsorbates inducing a change only in the electrostatic surface dipole layer.     

Interactions of 10.6 GeV/n gold nuclei with light and heavy target nuclei in nuclear emulsion

Zeitschrift für Physik C Particles and Fields - We have investigated the particle production and fragmentation of nuclei participating in the interactions of 10.6 GeV/n gold nuclei in nuclear...     

Modeling wave propagation in realistic heart geometries using the phase-field method

We present a novel algorithm for modeling electrical wave propagation in anatomical models of the heart. The algorithm uses a phase-field approach that represents the boundaries between the heart muscle and the surrounding medium as a spatially diffuse interface of finite thickness. The chief advantage of this method is to automatically handle the boundary conditions of the voltage in complex geometries without the need to track the location of these boundaries explicitly. The algorithm is shown to converge accurately in nontrivial test geometries with no-flux (zero normal current) boundary conditions as the width of the diffuse interface becomes small compared to the width of the cardiac action potential wavefront. Moreover, the method is illustrated for anatomically realistic models of isolated rabbit and canine ventricles as well as human atria.