Search results for "Charge density"
showing 10 items of 206 documents
Quark transverse charge densities in the from lattice QCD
2009
Abstract We extend the formalism relating electromagnetic form factors to transverse quark charge densities in the light-front frame to the case of a spin-3/2 baryon and calculate these transverse densities for the Δ ( 1232 ) isobar using lattice QCD. The transverse charge densities for a transversely polarized spin-3/2 particle are characterized by monopole, dipole, quadrupole, and octupole patterns representing the structure beyond that of a pure point-like spin-3/2 particle. We present lattice QCD results for the Δ-isobar electromagnetic form factors for pion masses down to approximatively 350 MeV for three cases: quenched QCD, two-degenerate flavors of dynamical Wilson quarks, and three…
Isotopic Differences in the Charge Distribution of Even Molybdenum Isotopes from Elastic Electron Scattering
1975
Elastic-electron-scattering cross sections for $^{92,94,96,98,100}\mathrm{Mo}$ in an effective momentum transfer range of 0.6-2.1 ${\mathrm{fm}}^{\ensuremath{-}1}$ are analyzed in a practically model-independent way, using a Fourier-Bessel expansion for the charge distribution. The ratios of cross sections of neighboring isotopes yield differences of charge distributions, which exhibit pronounced shell effects.
Charge Distribution ofPb208and the Difference inρ(r)for Pb and Tl Investigated by by Elastic Electron Scattering
1976
Elastic electron-scattering cross sections from $^{208}\mathrm{Pb}$ have been measured for $0.5 {\mathrm{fm}}^{\ensuremath{-}1}lql2.24 {\mathrm{fm}}^{\ensuremath{-}1}$. The charge distribution for this nucleus is determined by a "model-independent" method; it exhibits a bump in the center of the nucleus which is also a characteristic feature of Hartree-Fock calculations. The influence of the $3s$ protons on $\ensuremath{\rho}(r)$ has been investigated by a difference measurement between lead and thallium isotones.
Investigations of Superheavy Quasiatoms via Spectroscopy of δ Rays and Positrons
1984
There exists a long-standing and very interesting problem in atomic physics, namely, the question: What is the binding energy of an electron if the strength of the Coulomb potential exceeds Zα = 1? According to the Dirac-Sommerfeld fine-structure formula for a point charge $$E = {m_e}{c^2}{[1 - {(Z\alpha )^2}]^{1/2}}$$ (1) the total energy of the lowest bound Is-state becomes imaginary for Zα > 1. But even as early as 1945 it was realized(59) that this property of Eq. (1) is caused by the singularity of the Coulomb potential at the origin. Assuming a realistic charge distribution of the nucleus there is no restriction suc as Zα < 1 for the binding energy. Recent calculations show (cf., e.g.…
Analysis of Cylindrical Dielectric Resonators in Rectangular Cavities Using a State-Space Integral-Equation Method
2006
In this letter, a state-space integral-equation method in the s-domain has been employed for the accurate analysis of rectangular cavities loaded with cylindrical dielectric resonators. The dielectric obstacles have been treated in terms of their polarization equivalent charge and current densities. The dielectric resonator can be placed at any arbitrary position inside the cavity. The presented technique allows to calculate in a very efficient way a large number of solenoidal modes. The resonant frequencies of dielectric-loaded cavities are calculated and compared with data from literature and a commercial finite element method software, showing a good agreement
On the odd-even staggering of mean-square charge radii in the light krypton and strontium region
1995
Recently isotope shifts of $^{72,74-96}$Kr and $^{77-100}$Sr have been measured at the ISOLDE/ CERN mass separator facility by collinear laser spectroscopy. The deduced changes in mean square charge radii reveal sharp transitions in nuclear shape from spherical near the magic neutron number N=50 towards strongly deformed for both the neutron deficient and neutron rich isotopes far from stability. The mean square charge radii of the neutron deficient isotopes exhibit a sign change of the odd-even staggering (OES), i.e. below the neutron number N=46 the radius is systematically larger for the odd-N nuclei than for their even-N neighbours. This is in contrast to the situation of normal OES whi…
Pressure-Induced Collapse of the Charge Density Wave and Higgs Mode Visibility in 2H−TaS2
2019
The pressure evolution of the Raman active electronic excitations of the transition metal dichalcogenides $2H\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ is followed through the pressure phase diagram embedding incommensurate charge-density-wave and superconducting states. At high pressure, the charge-density wave is found to collapse at 8.5 GPa. In the coexisting charge-density-wave and superconducting orders, we unravel a strong in-gap superconducting mode, attributed to a Higgs mode, coexisting with the expected incoherent Cooper-pair breaking signature. The latter remains in the pure superconducting state reached above 8.5 GPa. Our report constitutes a new observation of such Raman active H…
Quantifying Artifacts in Ewald Simulations of Inhomogeneous Systems with a Net Charge
2014
Ewald summation, which has become the de facto standard for computing electrostatic interactions in biomolecular simulations, formally requires that the simulation box is neutral. For non-neutral systems the Ewald algorithm implicitly introduces a uniform background charge distribution that e ectively neutralizes the simulation box. Because a uniform distribution of counter charges typically deviates from the spatial distribution of counterions in real systems, artifacts may arise, in particular in systems with an inhomogeneous dielectric constant. Here we derive an analytical expression for the e ect of using an implicit background charge instead of explicit counterions, on the chemical po…
Strong enhancement of superconductivity at high pressures within the charge-density-wave states of2H−TaS2and2H−TaSe2
2016
We present measurements of the superconducting and charge density wave critical temperatures (Tc and TCDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that Tc increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of TCDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases coexisting with superconductivity within our full pressure range.
Valence Topological Charge-Transfer Indices for Dipole Moments
2003
Valence topological charge-transfer (CT) indices are applied to the calculation of dipole moments. The dipole moments calculated by algebraic and vector semisums of the CT indices are defined. The combination of the CT indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them with the dipole moment of the valence-isoelectronic series of benzene and styrene. Two CT indices, μ v e c (vector semisum of vertex-pair dipole moments) and μ V v e c (valence μ v e c ) are proposed. μ v e c and μ V v e c are important for the predicti…