Shallow Potential Research Articles

Constraints on the threshold [formula omitted] nuclear potential from FINUDA [formula omitted] spectra

1sΛ hypernuclear formation rates in stopped K− reactions on several p-shell targets are derived from hypernuclear formation spectra measured recently by the FINUDA Collaboration and are compared with calculated 1sΛ formation rates based on a chirally motivated coupled channel model. The calculated rates are about 15% of the derived rates, and in contrast with previous calculations depend weakly on the depth of the threshold K− nuclear potential. The A dependence of the calculated 1sΛ rates is in fair agreement with that of the derived 1sΛ rates, showing a slight preference for a deep density dependent potential, ReVK−(ρ0)∼−(150–200) MeV, over a shallow potential, ReVK−(ρ0)∼−50 MeV. These new features originate from a substantial energy and density dependence found for the in-medium subthreshold K−n→π−Λ branching ratio that enters the hypernuclear formation rate calculations.

Rattling-Induced Heavy Fermion State in the Anharmonic Holstein Model

We investigate the heavy fermion states in the half-filled anharmonic Holstein model by using the dynamical mean-field theory combined with the exact diagonalization method at low temperatures down to 1/10 4 of the conduction bandwidth. For the weak anharmonic cases with single-well or shallow double-well potentials, the bipolaronic first order phase transition takes place at a critical value of the electron–phonon coupling below a critical temperature as recently observed in the harmonic Holstein model. On the other hand, for the strong anharmonic case with deep double-well potential, the bipolaronic transition is suppressed and changes to a crossover where the heavy fermion state with a large effective mass is realized due to the effect of largely anharmonic local oscillations called rattling.

Paracyclophanes as model compounds for strongly interacting π-systems. Part 2: mono-hydroxy[2.2]paracyclophane

The structure of the electronic ground- and first excited state of mono-hydroxy [2.2]paracyclophane (MHPC) and the S(1)← S(0) electronic transition have been investigated by resonance-enhanced multiphoton ionisation (REMPI) and by quantum chemical spin-component-scaled-approximate coupled cluster second order (SCS-CC2) computations. The origin of the S(1)← S(0) transition was located at 30,772 cm(-1) (3.815 eV) in the REMPI spectrum. The value has to be compared with a computed excitation energy of 3.79 eV. The vibrational structure of the spectrum confirms a significant geometry change upon excitation along the coordinates corresponding to twist- and shift-motions in the molecule. It gives rise to an experimentally observed progression with a fundamental of +30 cm(-1) and an inverse anharmonicity. From the experimental data a shallow potential along the twist coordinate was derived for the S(1) state. For the shift vibration a wavenumber of +91 cm(-1) was observed, while +85 cm(-1) was computed. The ionisation energy of MHPC was determined to be 7.63 ± 0.05 eV using synchrotron radiation. When compared to earlier results on the parent compound [2.2]paracyclophane and pseudo-ortho-dihydroxy[2.2]paracyclophane it can be seen that already small variations in the substitution pattern have a significant impact on the shapes of the involved potential energy surfaces leading to strong variations in ground and excited state geometries and opto-electronic properties governing the exciton transfer processes.

The entropy core in galaxy clusters: numerical and physical effects in cosmological grid simulations

We investigated the numerical and physical reasons leading to a flat distribution of low gas entropy in the core region of galaxy clusters, as commonly found in grid cosmological simulations. To this end, we run a set of 30 high resolution re-simulations of a 3 x 10^14 M_sol/h cluster of galaxies with the AMR code ENZO, exploring and investigating the details involved in the production of entropy in simulated galaxy clusters. The occurrence of the flat entropy core is found to be mainly due to hydro-dynamical processes resolved in the code and that additional spurious effects of numerical origin (e.g. artificial heating due to softening effects or N-body noise) can affect the size and level of the entropy core only in a minor way. We show that the entropy profile of non-radiative simulations is produced by a mechanism of "sorting in entropy" which takes place with regularity during the cluster evolution. Using gas tracers we prove that the flat entropy core is caused by physical mixing of gravity-driven subsonic motions within the shallow inner cluster potential. Re-simulations were also produced for the same cluster object with the addition of radiative cooling, uniform pre-heating at high redshift (z=10) and late (z<1) thermal energy feedback from AGN activity in the cluster, in order to assess the effects of such mechanisms on the final entropy profile of the cluster. We report on the infeasibility of balancing the catastrophic cooling and recovering a flat entropy profile with the investigated trials for AGN activity alone, while for a sub-set of pre-heating models, or AGN feedback plus pre-heating models, a flat entropy distribution similar to non-radiative runs can be obtained with a viable energy requirement, and in good consistency with X-ray observations.

COMPETITIVE ACCRETION IN A SHEET GEOMETRY AND THE STELLAR IMF

We report a set of numerical experiments aimed at addressing the applicability of competitive accretion to explain the high-mass end of the stellar initial mass function in a sheet geometry with shallow gravitational potential, in contrast to most previous simulations which have assumed formation in a cluster gravitational potential. Our flat cloud geometry is motivated by models of molecular cloud formation due to large-scale flows in the interstellar medium. The experiments consisted of SPH simulations of gas accretion onto sink particles formed rapidly from Jeans-unstable dense clumps placed randomly in the finite sheet. These simplifications allow us to study accretion with a minimum of free parameters, and to develop better statistics on the resulting mass spectra. We considered both clumps of equal mass and gaussian distributions of masses, and either uniform or spatially-varying gas densities. In all cases, the sink mass function develops a power law tail at high masses, with $dN/dlog M \propto M^{-\Gamma}$. The accretion rates of individual sinks follow $\dot{M} \propto M^2$ at high masses; this results in a continual flattening of the slope of the mass function towards an asymptotic form $\Gamma \sim 1$ (where the Salpeter slope is $\Gamma = 1.35$). The asymptotic limit is most rapidly reached when starting from a relatively broad distribution of initial sink masses. In general the resulting upper mass slope is correlated with the maximum sink mass; higher sink masses are found in simulations with flatter upper mass slopes. Although these simulations are of a highly idealized situation, the results suggest that competitive accretion may be relevant in a wider variety of environments than previously considered, and in particular that the upper mass distribution may generally evolve towards a limiting value of $\Gamma \sim 1$.

ChemInform Abstract: First‐Principles Study of the Crystal and Electronic Structures of α‐Tetragonal Boron.

The crystal and electronic structures of α-tetragonal (α-t) boron were investigated by first-principles calculation. Application of a simple model assuming 50 atoms in the unit cell indicated that α-t boron had a metallic density of state, thus contradicting the experimental fact that it is a p-type semiconductor. The presence of an additional two interstitial boron atoms at the 4c site made α-t boron semiconductive and the most stable. The cohesive energy per atom was as high as those of α- and β-rhombohedral boron, suggesting that α-t boron is produced more easily than was previously thought. The experimentally obtained α-t boron in nanobelt form had about two interstitial atoms at the 8i sites. We consider that the shallow potential at 8i sites generates low-energy phonon modes, which increase the entropy and consequently decrease the free energy at high temperatures. Calculation of the electronic band structure showed that the highest valence band had a larger dispersion from Γ to Z than from Γ to X; this indicated a strong anisotropy in hole conduction.

Two-photon, two-gluon and radiative decays of heavy flavoured mesons

Here we present the two-photon and two-gluon decay widths of the S-wave ( η Q ∈ c , b ) and P-wave ( χ Q ∈ c , b J ) charmonium and bottonium states and the radiative transition decay widths of c c ¯ , b b ¯ and c b ¯ systems based on Coulomb plus power form of the inter-quark potential ( CPP ν ) with exponent ν. The Schrödinger equation is solved numerically for different choices of the exponent ν. We employ the masses of different states and their radial wave functions obtained from the study to compute the two-photon and two-gluon decay widths and the E1 and M1 radiative transitions. It is found that the quarkonia mass spectra and the E1 transition can be described by the same interquark model potential of the CPP ν with ν = 1.0 for c c ¯ and ν = 0.7 for b b ¯ systems, while the M1 transition (at which the spin of the system changes) and the decay rates in the annihilation channel of quarkonia are better estimated by a shallow potential with ν < 1.0 .

3D model of magnetic fields evolution in dwarf irregular galaxies

AbstractRadio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.

Dissipation-Managed Bright Soliton in a 1D Bose–Einstein Condensate in an Optical-Lattice Potential

We study the formation of a dynamically-stabilized dissipation-managed bright soliton in a quasi-one-dimensional Bose–Einstein condensate by including an imaginary three-body recombination loss term and an imaginary linear feeding one in the Gross–Pitaevskii equation, trapped in a shallow optical-lattice potential. Based on the direct approach of perturbation theory for the nonlinear Schrödinger equation, we demonstrate that the height (as well as width) of bright soliton may have little change through selecting experimental parameters.

Evaluation of radiation force acting on macromolecules by combination of Brownian dynamics simulation with fluorescence correlation spectroscopy

The effect of optical gradient force from a focused laser beam on the fluorescence correlation spectroscopy (FCS) was investigated by a computing method based on Brownian dynamics simulation. A series of calculations revealed that, in relatively shallow optical force potential up to 1.0kTR (TR=298.15 K), the conventional theoretical model of FCS without consideration of the optical gradient force could evaluate the increase in the average number of molecules and the diffusion time in the potential. On the other hand, large deviation between the simulated fluorescence correlation curve and the theoretical model was observed under the potential depth >1.0kTR. In addition, by integrating the optical force potential with the temperature elevation under optical trapping condition, it was deduced that the temperature rise does not seriously affect the average number of particles in the sampling area, but the average residence time is more sensitively affected by the temperature elevation. The present study using the simulation also provides a method to experimentally estimate molecular polarizabilities from FCS measurements.

STAR FORMATION AND FEEDBACK IN SMOOTHED PARTICLE HYDRODYNAMIC SIMULATIONS. II. RESOLUTION EFFECTS

We examine the effect of mass and force resolution on a specific star formation (SF) recipe using a set of N-body/Smooth Particle Hydrodynamic simulations of isolated galaxies. Our simulations span halo masses from 10^9 to 10^13 solar masses, more than four orders of magnitude in mass resolution, and two orders of magnitude in the gravitational softening length, epsilon, representing the force resolution. We examine the total global star formation rate, the star formation history, and the quantity of stellar feedback and compare the disk structure of the galaxies. Based on our analysis, we recommend using at least 10^4 particles each for the dark matter and gas component and a force resolution of epsilon approximately equal to 10^-3 R_vir when studying global SF and feedback. When the spatial distribution of stars is important, the number of gas and dark matter particles must be increased to at least 10^5 of each. Low mass resolution simulations with fixed softening lengths show particularly weak stellar disks due to two-body heating. While decreasing spatial resolution in low mass resolution simulations limits two-body effects, density and potential gradients cannot be sustained. Regardless of the softening, low-mass resolution simulations contain fewer high density regions where SF may occur. Galaxies of approximately 10^10 solar masses display unique sensitivity to both mass and force resolution. This mass of galaxy has a shallow potential and is on the verge of forming a disk. The combination of these factors give this galaxy the potential for strong gas outflows driven by supernova feedback and make it particularly sensitive to any changes to the simulation parameters.

First-principles study of the crystal and electronic structures of α-tetragonal boron

The crystal and electronic structures of α-tetragonal (α-t) boron were investigated by first-principles calculation. Application of a simple model assuming 50 atoms in the unit cell indicated that α-t boron had a metallic density of state, thus contradicting the experimental fact that it is a p-type semiconductor. The presence of an additional two interstitial boron atoms at the 4 c site made α-t boron semiconductive and the most stable. The cohesive energy per atom was as high as those of α- and β-rhombohedral boron, suggesting that α-t boron is produced more easily than was previously thought. The experimentally obtained α-t boron in nanobelt form had about two interstitial atoms at the 8 i sites. We consider that the shallow potential at 8 i sites generates low-energy phonon modes, which increase the entropy and consequently decrease the free energy at high temperatures. Calculation of the electronic band structure showed that the highest valence band had a larger dispersion from Γ to Z than from Γ to X; this indicated a strong anisotropy in hole conduction.

Three-α continuum states

We investigate three-α continuum states in the hyperspherical formalism for J = 0+ and J = 2+. Two different types of α + α interactions are used: the shallow Ali–Bodmer potential and the deep potential of Buck et al. We determine the 3α phase shifts up to E = 6 MeV, in parallel with an analysis of resonances in the framework of the complex scaling method. We show that shallow potentials provide additional narrow resonances, in contrast with experimental data. Deep potentials, however, only give rise to broad resonances, and are more consistent with the data.

Stable periodic regime in a scalar field cosmology

AbstractWe describe three different regimes in the cosmological dynamics of a Universe filled with a scalar field. In particular, we claim the existence of a stable periodic solution, which has been found numerically for the case of a shallow scalar field potential.

Effects ofα-cluster potentials for theO16+O16fusion reaction andSfactor

A joint analysis of the elastic-scattering angular distributions and fusion cross sections together with the $S$ factor for the $^{16}\mathrm{O}+^{16}\mathrm{O}$ system near and below the Coulomb barrier is reported. To describe these observables within the framework of the optical model, a comparative study of microscopic $\ensuremath{\alpha}$-$\ensuremath{\alpha}$ double-folding clusters and phenomenological shallow potentials with surface-transparent imaginary parts is performed. Although the phenomenological Woods-Saxon type of shallow real potentials is unable to provide a consistent explanation of these data, the $\ensuremath{\alpha}$-$\ensuremath{\alpha}$ double-folding cluster potential obtained by considering the $\ensuremath{\alpha}$-cluster structure of $^{16}\mathrm{O}$ provides a considerable improvement. The $\ensuremath{\alpha}$-$\ensuremath{\alpha}$ double-folding cluster potential also reproduces the normalized resonant energy states of $^{32}\mathrm{S}$ for the $N=24$ cluster band.

Recognition of shallow karst water resources and cave potentials using thermal infrared image and terrain characteristics in semi-arid regions of Iran

Shallow karst water resources and caves may influence land surface temperatures due to cold transfer property of rocks and evaporation from buried karst. The objective of this research was to develop a method for recognition of karst areas based on evaluating the surface characteristics that manifest itself by low land surface temperature in the satellite images. Investigation of thermal ETM+ image of the study region in Iran showed that parts of carbonate rocks that bear karst water are relatively cooler compared to areas with similar terrain conditions. Relational modeling provided useful information on spatial distribution of areas that have the potential to hold karst water resources and/or caves. Further inspection of ASTER images, along with geotechnical, geophysical and geological field surveys verified the approach. Significant correlation was found between electrical resistivity and thermal band values. The method may be used as a primary exploratory tool for shallow karst water explorations in similar areas.

Use of supersymmetric isospectral formalism to realistic quantum many-body problems

We propose a novel mathematical approach for the calculation of resonances in weakly bound systems. For any potential, families of strictly isospectral potentials (with very different shape) having desirable and adjustable features can be generated. For systems having no bound ground state, an isospectral potential with a bound state in the continuum is possible. The quasi-bound state in the original shallow potential will be effectively trapped in the deep well of the isospectral family, facilitating more accurate calculation of resonance energy. Application to 6He, 6Li and 6Be yield excellent results. Another application is the calculation of Efimov states in weakly bound threebody system. We present the result of 4He trimer, where the first excited state is claimed to be an Efimov state.

Raman scattering of rare earth hexaborides

Raman scattering spectra were measured for the rare-earth hexaborides RB6 (R = Ce, Gd, or Dy). All Raman-active phonons due to B6 vibrations were observed in the range 600 – 1400 cm-1. Anomalous peaks were detected below 200 cm-1, which correspond to vibrations of rare-earth ion excited by second-order Raman scattering process. The intensity and energy of the rare-earth mode decrease with decreasing temperature. This suggests that the rare-earth ion vibrates in a shallow and anharmonic potential due to the boron cage. Using the reported values of mean square displacement of rare-earth ion, we estimated the anharmonic contribution for the rare-earth vibrations.

Toward Accurate Microscopic Calculation of Solvation Entropies: Extending the Restraint Release Approach to Studies of Solvation Effects

The evaluation of the solvation entropies is a major conceptual and practical challenge. On the one hand, it is interesting to quantify the factors that are responsible for the solvation entropies in solutions, whereas on the other, it is essential to be able to assess the contributions of the solvation entropies to the binding free energies and related properties. In fact, the solvation entropies are neglected in almost all of the studies of the binding entropies. The main problem is that widely used approaches, such as the quasiharmonic (QH) approximation, do not provide reliable results particularly in cases of shallow potential and multidimensional surfaces while brute force evaluations of the entropic effects by simulating temperature dependence of the free energy converges very slowly. This paper addresses the above issue by starting with an analysis of the factors that are responsible for the negative solvation entropy of ions, showing that it is not due to the change in the solvent vibration modes or to the solvent force constant but to the changes in the solvent configurational space upon change in the solute charges. We begin by clarifying that when one deals with aqueous solutions, it is easy to evaluate the corresponding entropic effect by the Langevin dipole (LD) treatment. However, in this work we are interested in developing a general microscopic tool that can be used to study similar effects in the proteins. To this end, we explore the ability of our restraint release (RR) approach to evaluate the solvation entropy. We start this analysis by reviewing the foundation of this approach and in particular, the requirements of minimizing the enthalpy contribution to the RR free energy. We then establish that our approach is not a specialized harmonic treatment but a rather powerful general approach. Moving to the main topic of this work, we demonstrate that the RR approach provides quantitative results for the solvation entropies of monovalent and divalent ions and effectively captures the physics of these entropic effects. The success of the current approach indicates that it should be applicable to the studies of the solvation entropies in the proteins and also, in examining hydrophobic effects. Thus, we believe that the RR approach provides a powerful tool for evaluating the corresponding contributions to the binding entropies and, eventually, to the binding free energies. This holds promise for extending the information theory modeling to proteins and protein-ligand complexes in aqueous solutions and consequently, facilitating computer-aided drug design.

Designed Workfunction Engineering of Double-Stacked Metal Nanocrystals for Nonvolatile Memory Application

A double-stacked nanocrystal (DSNC) flash memory is presented for improvement of both program/erase (P/E) speed and data retention time. Four combinations of nickel (Ni) and gold (Au) (Ni/Ni, Au/Au, Ni/Au, and Au/Ni) are used as charge storage DSNC materials and are compared from the perspective of memory performance. Through experimental results for P/E efficiency and retention time, the optimized energy band lineup for faster P/E and longer charge retention is presented. A combination of a deep potential well at the top and a shallow potential well at the bottom exhibits optimized performance in P/E, and this combination also shows the longest data retention characteristics.