Direct determination of vibrational density of states change on ligand binding to a protein

The change in the vibrational density of states of a protein (dihydrofolate reductase) on binding a ligand (methotrexate) is determined using inelastic neutron scattering. The vibrations of the complex soften significantly relative to the unbound protein. The resulting free-energy change, which is directly determined by the density of states change, is found to contribute significantly to the binding equilibrium.     

Semi-microscopic calculation of the level density in spherical nuclei

The level density at the neutron binding energy for 90 spherical nuclei in the interval 50 < A < 205 is calculated by a method of direct counting of the number of states taking into account collective vibrational excitations. The results of calculations are in satisfactory agreement with the experimental data. The difference in the level density of doubly even and odd-A nuclei is correctly described. The effect of nuclear vibrations on the level density is studied, and it is shown that the account of them leads to an increase in the density by a factor of 1.5–10 and to a decrease in the density fluctuations. It is also studied how the level density depends on excitation energy. With increasing excitation energy, our results come nearer the corresponding values obtained by the statistical model. It is found that the density fluctuations decrease with increasing excitation energy but remain still strong at the neutron binding energy for nuclei with A = 50–70 and for nuclei around closed shells. The density ρ(I^π) is studied as a function of spin and parity. It is shown that at the neutron binding energy the ratio $\text{ρ(I}{}^{\mathrm{+}}\text{)}\text{ρ(I}{}^{\mathrm{?}}\text{)}$ is different from unity for the majority of nuclei. This difference is especially striking for ⁵⁷Fe and ⁵⁸Fe nuclei.     

Temperature-induced deformation — A possible mechanism for washing out spherical shell effects in the nuclear level density

The interplay of shell structure and rotational motion in the nuclear level density is discussed. The result of a schematic calculation reveals a washing out of spherical shell effects at much lower excitation energies than expected if only the intrinsic level density in the independent particle model is considered.     

Experimental determination of spherical resonator diffraction losses

To obtain single transversal mode oscillation of a laser oscillator a pinhole has to be inserted into the resonator. This causes diffraction losses, comparable with the internal losses of the laser system. For a pulsed Nd-YAG-laser, the total losses and the diffraction losses are determined experimentally as a function of the Fresnel number for TEM₀₀ and TEM₀₁ mode. The agreement between the experimental values and numerical data from diffraction theory is satisfying.     

Increasing the cold atom density in an integrating spherical cavity

A novel method of angled incidence for diffuse laser cooling of ⁸⁷Rb is presented to improve the distribution of cold atom density in an integrating sphere. The angled injection scheme could cool more atoms in the middle of the sphere compared to the previous normal injection scheme. The loading time of the cold atoms for the angled injection scheme is twice as that of the normal injection scheme. The SNR and the contrast of the detected signal would be improved in the angled injection scheme.     

Contact condition for the density profiles in spherical and cylindrical double layers

Exact sum rules involving the contact values of the density profiles and bulk osmotic pressure in spherical and cylindrical electric double layers are formulated. When the radius of curvature in these systems tends to infinity, the contact conditions reduce to the well-known contact condition in planar double layer due to Henderson, Blum, and Lebowitz (1979). However, unlike the latter relation, the contact conditions in the non-planar geometries are non-local, and require for their implementation full knowledge of the electrode–ion singlet distribution functions.     

Opto-acoustic sensing of fluids and bioparticles with optomechanofluidic resonators

Opto-mechano-fluidic resonators (OMFRs) are a unique optofluidics platform that can measure the acoustic properties of fluids and bioanalytes in a fully-contained microfluidic system. By confining light in ultra-high-Q whispering gallery modes of OMFRs, optical forces such as radiation pressure and electrostriction can be used to actuate and sense structural mechanical vibrations spanning MHz to GHz frequencies. These vibrations are hybrid fluid-shell modes that entrain any bioanalyte present inside. As a result, bioanalytes can now reflect their acoustic properties on the optomechanical vibrational spectrum of the device, in addition to optical property measurements with existing optofluidics techniques. In this work, we investigate acoustic sensing capabilities of OMFRs using computational eigenfrequency analysis. We analyze the OMFR eigenfrequency sensitivity to bulk fluid-phase materials as well as nanoparticles, and propose methods to extract multiple acoustic parameters from multiple vibrational modes. The new informational degrees-of-freedom provided by such opto-acoustic measurements could lead to surprising new sensor applications in the near future.     

Trace formula for level density of a spherical billiard

A trace formula for the oscillating part of the level density for a spherical billiard has been obtained in spherical polar coordinates. The Jacobian of stability and the length of the orbits are obtained from the classical mechanics of the problem. The same formula is applicable to both the planar and the diametric orbits. Numerical results have been obtained with this formula and compared with the results from exact quantum theory, EBK quantization, and Balian and Bloch.     

Electric field effects on Nano-Scale bio-membrane of spherical cells

Various properties of Nano-Scale cell bio-membranes or vesicle membranes in an external electric field and free salt environment are studied and reviewed in a theoretical and computational framework. This is done by calculating the radial forces acting on cells generated as the result of an applied electric field and the ensuing charge re-distribution. Our results could help to shed light on mechanisms responsible for the observed deformation and fusion of cells which can be designed by biotechnological devices.     

On the role of density inhomogeneity and local anisotropy in the fate of spherical collapse

We obtain an expression for the active gravitational mass of a collapsing fluid distribution, which brings out the role of density inhomogeneity and local anisotropy in the fate of spherical collapse.     

Effects of compression and stretch on the determination of laminar flame speeds using propagating spherical flames

The effects of flow compression and flame stretch on the accurate determination of laminar flame speeds at normal and elevated pressures using propagating spherical flames at constant pressure or constant volume are studied theoretically and numerically. The results show that both the compression-induced flow motion and flame stretch have significant impacts on the accuracy of flame speed determination. For the constant pressure method, a new method to obtain a compression-corrected flame speed (CCFS) for nearly constant pressure spherical bomb experiments is presented. Likewise, for the constant volume method, a technique to obtain a stretch-corrected flame speed (SCFS) at elevated pressures and temperatures is developed. The validity of theoretical results for both constant pressure and constant volume methods is demonstrated by numerical simulations using detailed chemistry for hydrogen/air, methane/air, and propane/air mixtures. It is shown that the present CCFS and SCFS methods not only improve the accuracy of the flame speed measurements significantly but also extend the parameter range of experimental conditions. The results can be used directly in experimental measurements of laminar flame speeds.     

Simultaneous determination of the temperature and density of rubidium vapor

We propose a new method for the simultaneous determination of the temperature and atom number density in rubidium vapor. The method is based on the comparison of theoretical simulations of the self-broadened absorption profiles of rubidium resonance lines with the measured profiles. Absorption measurements performed in rubidium vapor indicate that in the spectral region around resonance lines (760–835 nm), excellent agreement between theoretical and experimental absorption profiles can be achieved. In the temperature interval 500–700 K, the simultaneous determination of the atom number density and temperature of rubidium vapor is possible. We have applied the present method to nearly homogeneous and inhomogeneous rubidium vapors generated in a sapphire cell. PACS 31.15.Gy; 32.30.Jc; 32.70.-n     

A quantum mechanical determination of the superfluid density

The constituting conservation laws for a superfluid are quantum mechanically derived. Using thermodynamic relations the superfluid density is model-independently expressed in terms of reduced-density matrices. The general relation is illustrated for the Bogolubov model, and for two other approximations for the two-particle reduced-density matrix. The resulting relations between the densities of the super component and of the condensate are discussed.     

The virial,boundary kinetic-energy density and electron density,in one dimension and in spherical symmetry

The virial is expressed in terms of the actual forces appearing in Schrödinger's equation and a term involving the kinetic-energy density at the boundary, and the derivatives of the electron density on the boundary.     

E0 transitional density for nuclei between spherical and deformed shapes

The Generator Coordinate Method (GCM) is used to construct the effective nuclear density operator suitable for calculations of E0 transitional densities with collective eigenfunctions of the phenomenological Bohr Hamiltonian. For example, the 0⁺ _gs \( \rightarrow\) 0⁺ ₂ transitional density is calculated for the shape-phase transitional nucleus ¹⁵⁰Nd using the eigenfunctions of the approximate X(5) solution of the Bohr Hamiltonian.     

Isovector coupling channel and central properties of the charge density distribution in heavy spherical nuclei

The influence of the isovector coupling channel on the central depression parameter and the central value of the charge density distribution in heavy spherical nuclei was studied. The isovector coupling channel leads to about 50% increase of the central depression parameter, and weakens the dependency of both central depression parameter and central density on the asymmetry, impressively contributing to the semibubble form of the charge density distribution in heavy nuclei, and increasing the probability of larger nuclei with higher proton numbers and higher neutron-to-proton ratios stable.     

On the determination of laminar flame speed from low-pressure and super-adiabatic propagating spherical flames

The outwardly propagating spherical flame (OPF) method is popularly used to measure the laminar flame speed (LFS). Recently, great efforts have been devoted to improving the accuracy of the LFS measurement from OPF. In the OPF method, several assumptions are made. For examples, the burned gas is assumed to be static and in chemical equilibrium. However, these assumptions may not be satisfied under certain conditions. Here we consider low-pressure and super-adiabatic propagating spherical flames, for which chemical non-equilibrium exists and the burned gas may not be static. The objective is to assess the chemical non-equilibrium effects on the accuracy of LFS measurement from the OPF method. Numerical simulations considering detailed chemistry and transport are conducted. Stoichiometric methane/air flames at sub-atmospheric pressures and methane/oxygen flames at different equivalence ratios are considered. At low pressures, broad heat release zone is observed and the burned gas cannot quickly reach the adiabatic flame temperature, indicating the existence of chemical non-equilibrium of burned gas. Positive flow in the burned gas is identified and it is shown to become stronger at lower initial pressure. Consequently, the LFS measurement from OPF at low pressures is not accurate if the burned gas is assumed to be static and at chemical equilibrium. For super-adiabatic spherical flames, the burned gas speed is found to be negative due to the local temperature overshoot at the flame front. Such negative speed of burned gas can also reduce the accuracy of LFS measurement. It is recommended that the direct method measuring both flame propagation speed and flow speed of unburned gas should be used to determine the LFS at low pressures or for mixtures with super-adiabatic flame temperature.     

Substituent effects on the geometry of some trigonal radicals

A simple level of ab initio molecular orbital theory with a split-valence shell basis with d-type polarization functions (6–31G*) is used to predict equilibrium geometries for the ground and some low-lying excited states of AH_n molecules and cations where A is carbon, nitrogen, oxygen or fluorine. The results are shown to be close to the limit for single determinant wave functions in cases where corresponding computations with more extensive bases are available. Comparison with experimental results also shows good agreement although a systematic underestimation of bond lengths up to 3 per cent is evident. For systems where no experimental data are available, the results provide predictions of equilibrium geometry.