Critical threshold of noise-induced energy transduction in molecular machinery system

Responses of energy transduction of molecular machinery to random perturbation were investigated at the conditions where the system stayed near the bifurcation point. It was found that noise-induced oscillation (NIO) could occur. But how far from bifurcation point could one get the admissible region of NIO? We proposed and demonstrated numerically that there existed a critical threshold of NIO for each fixed noise intensity. Furthermore, it was found that noise intensity was a key factor for the determination of critical threshold. Finally, the detailed bifurcation diagram depending on noise intensity was replotted.     

Effect of electron correlation on the Pa atom energy levels and electron coupling

The lower energy levels of the protactinium (Pa) atom are unusually difficult to treat theoretically. Pa is located where the 6d and 5f energies cross; simple calculations consistently put the electron configurations $5f^16d^27s^2$ and $5f^26d^17s^2$ in the incorrect order. We have used multireference spin?Corbit configuration interaction to compute the energies of these states to determine which additional interactions need to be included. We also discuss the less common J ₁ j coupling scheme suggested for these atomic states with applications also to the $5f^16d^2$ and $5f^26d^1$ states of $\hbox{Pa}^{2+}$ .     

On the collision density in recoil hot atom systems. Effect of reactive events

Characteristics of the collisional distribution function for reactive hot atoms in nuclear recoil systems are examined and illustrated for the T + H₂ system both unmoderated and moderated with argon. Reaction induced extrema are evident in the collision density of the unmoderated case. For this system depletion of hot atoms from the collisional distribution function due to reactive events is reflected significantly in the product yields even at high moderation.     

Effect of pressure on transfer annealing in51Cr/III/-doped potassium chromate

The effect of compression on⁵¹Cr/III/-doped potassium chromate, pre-irradiated, or not, with -radiation, has been studied. Compression appeared to have no effect on the initial⁵¹Cr/VI/ yield, while it was found to retard considerably the transfer annealing process.     

Specific radiation and recoil energy effects in recoil implantation reaction of51Cr in metal acetylacetonates

In recoil implantation reaction of⁵¹Cr in Cr/acac/₃ a polymer component which was sensitive to radiation dose was found. However, a retention type component⁵¹Cr/acac/₃ was not so sensitive to radiation dose. A remarkable dependence of the yield of⁵¹Cr/acac/₃ on recoil energy was found in the range 10²–10⁶ eV in recoil implantation using a thin film technique. This suggests a special role of implantation reaction in solids.     

Effect of residual copper on stability of molecular brushes prepared by atom transfer radical polymerization

Effect of residual copper on stability of molecular brushes with poly(n-butyl acrylate) (PBA) side chains was studied. The brushes were prepared by atom transfer radical polymerization (ATRP) using the grafting-from approach. Although the copper concentration was decreased down to below ten ppm levels by passing through alumina column, further removal was required to prevent crosslinking reactions. Further removal was performed by dialysis or precipitation.     

The effect of donor atom and ligand size on the molecular and solid state structure of selected tin (IV) compounds

The arrangement of bonded and nonbonded atoms surrounding the central tin atom in several methyltin halide and pseudohalide compounds has been calculated using a stereochemical model that takes into account the spatial requirements of atoms. Inherent in the analytical procedure is a parameter which provides a measure of the validity of the calculations when applied to a particular compound. The technique calculates an optimum ligand arrangement based upon a balancing of nonbonded intramolecular interactions; the procedure is then completed by calculating the distances of the Sn…X intermolecular interactions that occur when the approach of the associating atom is restricted only by the van der Waals contacts of the ligands on the central tin atom. In general, the calculations reproduce or account for the structural features of the methyltin compounds of known structure. The calculations show that the (CH₃)₃SnX, (CH₃)₂SnX₂, and CH₃SnX₃ molecules have ligand arrangements that may accommodate, 1, 2, or 3 strong intermolecular interactions, respectively. This agrees with the known tendency of (CH₃)₃SnX compounds to possess five-coordination and (CH₃)₂SnX₂ compounds to exhibit six-coordination. The calculated strengths of the intermolecular interactions vary in the order Sn…F > Sn…Cl > Sn…Br > Sn…I. Also, the strength of a particular type of Sn…X intermolecular interaction in a series of (CH₃)_nSnX_4?n compounds varies in the order (CH₃)₃SnX > (CH₃)₂SnX₂ > CH₃SnX₃. These calculations correlate with the observed variations in the discretely molecular or polymeric character of the solid states.     

Effect of molecular size on the parity-non-conserving contributions to the nuclear magnetic resonance shielding constant

We present density-functional theory studies on the effects of molecular size on the parity-violating contribution to the nuclear magnetic shielding constant. We focus on models with different backbone and side chain lengths, as well as the details of geometry optimization for certain helical polysilylenes and investigate the parity-violating contribution to the shielding constant of the ²⁹Si nucleus of the backbone. Our calculations show that the molecular geometry has a large influence on the magnitude of the parity-violating shielding contribution, a result that is in line with the previous studies on much smaller molecules. In addition, we find convergence in the magnitude of the PV effect with respect to system size, when using geometries that preserve the helical Si backbone structure optimized for the largest of the present systems. This can be interpreted in terms of the non-size-extensive nature of the parity-violating operator influencing the leading-order effect on nuclear magnetic shielding, as opposed to the size-extensive interaction affecting the energy difference between enantiomers. Our molecules are truncated models of large polysilylene systems, for which a difference in the ²⁹Si chemical shift between enantiomers has been observed to be 0.06 ppm (Fujiki in Macromol Rapid Commun 22, 669–674, 2001). As expected based on earlier first principles studies of small molecules, we do not find support for the difference to be of the parity-violating origin. Instead, the predicted parity-violation-induced splitting of the ²⁹Si resonance is found to converge at values around 10^?8 ppm with increasingly large Si backbone.     

Conversion of kinetic energy to internal energy in the 2-pentanone molecular ion at threshold in low-energy collisions with helium target atoms

Values of the threshold kinetic energy for formation of m/z 58 and m/z 43 from 2-pentanone molecular ion after collisional activation (CA) with He were studied in a hybrid tandem quadrupole system. These values indicate that the fraction of kinetic energy converted to internal energy and available for fragmentation is 0.14–0.25. Onset of conversion to internal energy through an electronically excited state was observed at 2.0 eV. Uses of He and heavier gases as collision gases in low-energy CA are projected to differ, He being used to screen classes of compounds and heavier gases to provide more complete structural information for ions.     

A new energy level of the neutral tantalum atom

Investigating the hyperfine structure (hfs) of the not yet classified line λ=4160.99 Å we succeeded in the determination of the electronic angular momenta of the combining levels and in the identification of the lower level using the hfs constants of all known levels as a finger-print card-index. In this way the lower level turned out to be thea ² G _9/2 level, which has even parity. Using the energy of this level and the wavenumber of the transition it was possible to determine the energy of the (odd parity) upper level to 34716.23 ± 0.02 cm^?1. The total angular momentum quantum number amounts toJ=11/2. Additionally, it was possible to identify the line λ=3436.00 Å as a further combination with this new level.     

Effect of surfactant conformation on the structures of small size nonionic reverse micelles: a molecular dynamics simulation study

We used constant pressure (P=0.1 MPa) and temperature (T=298 K) molecular dynamics simulations to study the structures and dynamics of small size reverse micelles (RMs) with poly(ethylene glycol) alkyl ether (CmEn) surfactants. The water-to-surfactant molar ratio was 3, with decane as the apolar solvent. We focused on the effect of the two possible imposed conformations (trans vs gauche) for the surfactant headgroups on RMs structures and water dynamics. For this purpose, we built up two RMs, which only differ by their surfactant headgroup conformations. The results obtained for the two RMs were compared to what is known in the literature. Here, we show that the surfactant headgroup conformation affects mainly the water-related properties such as the water core size, the area per surfactant headgroup, the headgroup hydration, and the water core translational diffusion. The properties computed for the RM with the surfactant in trans conformation fit better with the experimental data than the gauche conformation. We further show that the surfactant hydrophilic headgroup plays a crucial role in the micellar structures, favors the entrapment of the micellar water, and reduces strongly their diffusion compared to the bulk water.     

Radioanalytical methods in the hot atom chemistry of sulfur in inorganic systems

The paper presents a comprehensive review of radioanalytical methods for chemical identification of radioactive sulfur atoms recoiling in neutron irradiated (or implanted) inorganic systems.     

Effect of the molecular weight and architecture on the size and glass transition of arborescent polyisobutylenes

This article discusses the characterization of arborescent (hyperbranched) polyisobutylenes (arb‐PIBs) by size exclusion chromatography and differential scanning calorimetry, in comparison with linear PIB standards. The radius of gyration (〈r〉^1/2 = R_z), measured from the angle dependence of light scattering of high‐molecular‐weight arb‐PIBs, was significantly larger than the hydrodynamic radius (R_h) from size exclusion chromatography/viscometry, and the R_h values were significantly smaller than R_h of linear PIBs. The glass‐transition temperature of arb‐PIBs having a branch molecular weight higher than the critical entanglement molecular weight was dependent on both the total number‐average molecular weight and BR up to BR ～ 15. A modified Fox–Flory equation is proposed to describe the effect of architecture on the thermal transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1770–1776, 2006     

Interaction energy contours of molecules as probed by a test atom

Potential energy contour curves for some simple molecules interacting with a test atom (a Li atom in the ground state) are calculated by theab initio method. Relative hardness of the repulsive molecular surface is found to be anisotropic. This indicates that the outer boundary surface of a molecule changes its form depending on the extent of applied external forces. The attractive nature of the molecular surface is demonstrated to be local. Surroundings of electronegative atoms having nonbonded electron pairs are found to be attractieve to the test atom having both electron-donating and electron-accepting abilities.     

Lower bounds for the energy levels of the lithium atom

A recent modification of the intermediate hamiltonian method, intended to circumvent the problem associated with a low-lying continuum in the operator H⁰, has been applied to the lithium atom with a basis of discrete hydrogenic functions. The intended raising of the continuum occurs, but not to the extent that the beginning of the continuum is raised above the ground state of the atom; indications are that no basis of discrete hydrogenic eigenfunctions can accomplish this. Since these calculations were performed on the full lithium atom hamiltonian, they are not strictly comparable to those of Fox and Siglillito, in which a simplified hamiltonian was used.     

Effect of non-central interactions on energy and lattice dynamics of molecular crystals

Atom-atom, multipole-multipole and three-body potentials have been used to calculate the energy and lattice dynamics of β-paradichlorobenzene, phenanthrene and m-chloronitrobenzene. Non-central interactions are shown to give a significant contribution to the intermolecular interaction energy but have little effect on the phonon spectrum of the crystals.