A computational study of the linear and nonlinear complexes of FArCCH···N2

Linear and nonlinear weakly bound complexes of the metastable argon-containing compound FArCCH and N₂ were predicted to be stable from ab initio computations at the MP2/6-311++G(2d,2p) level of theory. Both complexes were found to have similar interaction energies and they exhibit red shifts of the C–H stretch, blue shifts of the Ar–C stretch and red shifts of the F–Ar stretch, in the same order as the stabilities. These effects are rationalized by considering changes in orbital occupancies on complexation, which are brought about by a combination of the intermolecular electrostatic interaction and charge density transferred from the N₂ molecule to the argon-containing molecule.     

A QM/QTAIM microstructural analysis of the tautomerisation via the DPT of the hypoxanthine·adenine nucleobase pair

We provide a pathway for the tautomerisation of the biologically important hypoxanthine·adenine (Hyp·Ade) nucleobase pair (C_s) formed by the keto tautomer of the Hyp and the amino tautomer of the Ade into the Hyp*·Ade* base pair (C_s) formed by the enol tautomer of the Hyp and the imino tautomer of the Ade by applying quantum-mechanical calculations and Bader's Quantum Theory of Atoms in Molecules analysis. It was found out that the dipole active Hyp·Ade?Hyp*·Ade* tautomerisation occurs via the asynchronous concerted double proton transfer (DPT) through the TS_{Hyp·Ade?Hyp*·Ade*} (C_s). Based on the sweeps of the energies of the intermolecular H-bonds along the intrinsic reaction coordinate, it was established that the N6H···O6 H-bond (5.40) is cooperative with the N1H···N1 H-bond (6.99) in the Hyp·Ade base pair, as well as the O6H···N6 H-bond (11.50) is cooperative with the N1H···N1 H-bond (7.28 kcal·mol^?1) in the Hyp*·Ade* base pair, mutually strengthening each other. The Hyp*·Ade* base pair possesses an extremely short lifetime 2.68·10^?14 s, which is predetermined by the negative value of the Gibbs free energy of the reverse barrier of its tautomerisation, and all of the six low-frequency intermolecular vibrations cannot develop during this period of time. Consequently, the Hyp·Ade→Hyp*·Ade* DPT tautomerisation cannot serve as a source of the rare tautomers of the bases.     

A theoretical study of N–H ··· π H-bond interaction of pyrrole: from clusters to the liquid

The N–H?···?π H-bond interactions of clusters and liquid formed by pyrrole molecules were investigated by Quantum Mechanics (QM) and classical Molecular Dynamics (MD), respectively. Based on the optimized geometry at the B97-D/aug-cc-pVTZ level of theory including dispersion correction, the nature and the origin of N–H?···?π H-bond interactions were unveiled by atoms in molecules (AIM), natural bond orbital (NBO), and energy decomposition analysis (EDA). Among them, the AIM analysis gives evidence to the presence of N–H?···?π H-bond interactions, the NBO examination reveals that π?→?σ* donor-acceptor orbital interaction is of great importance. EDA study indicates that N–H?···?π interactions are governed by the electrostatic and dispersion term. Meanwhile, MD simulation with OPLS-AA (optimized potentials for liquid simulations all-atom) was applied to study the pure liquid pyrrole at different temperature. The results confirm the existence of the N–H?···?π H-bond in the pure liquid pyrrole, and further characterized the structures of this H-bond which is somewhat different to the clusters.     

Pulse ENDOR studies on the radical pair P 700 +· A 1 ·− and the photoaccumulated quinone acceptor A 1 ·− of photosystem I

The secondary acceptor A₁ of the electron transport chain(s) of photosystem (PS) I is a phylloquinone (vitamin K₁, VK₁). Pulse electron paramagnetic resonance and electron nuclear double resonance (ENDOR) experiments at X-band frequencies were performed on the photoaccumulated acceptor radical A ₁ ^·? and the radical pair state P ₇₀₀ ^·+ A ₁ ^·? in PS I ofThermosynechococcus elongatus. The data obtained were compared with data from the respective radical anion of VK₁ in organic solvents. The unusualg tensor magnitude of A ₁ ^·? is explained by the hydrophobic binding pocket of this radical. The hyperfine couplings and the spin (and charge) density distribution is very different for A ₁ ^.? in PS I and VK ₁ ^·? in frozen alcoholic solution. This is attributed to a rather strong one-sided hydrogen bond to A ₁ ^·? . The presence of a hydrogen bond to A ₁ ^·? has only a minor effect ong. The hyperfine coupling constants of A ₁ ^·? determined from the radical pair spectra deviate only slightly from those derived from photoaccumulated A ₁ ^·? in PS I treated with dithionite at high pH. ENDOR resonances of the proton in a H bond were detected and an estimate of the strength and geometry of this bond to A ₁ ^·? was obtained. The significance of the hydrogen bond and other (hydrophobic) interactions of A₁ with the surrounding are briefly discussed.     

A comparison of the reproducibility of the parameters of the ¹³C-aminopyrine breath test for the assessment of hepatic function

This study determined the within-subject and between-subject variability of different ways of expressing the results of the (13)C-aminopyrine breath test ((13)C-ABT) and the effect of shortening the test duration. The (13)C-ABT was conducted on three separate occasions in 10 healthy volunteers and on a single occasion in 22 patients with established liver cirrhosis. The within-subject variability of cumulative percentage dose recovered (cPDR), using measured CO(2) production rate (VCO(2)), in the reference group over three trials was 15% over 120 min. Higher within-subject variability in cPDR would have been evident if the test was terminated at either 30 or 60 min. Substitution of predicted VCO(2) to calculate cPDR yielded comparable values at all time points. Significant differences between cirrhotics and reference group were evident after just 10 min using PDR/h, cPDR or enrichment (all P<0.05). The ABT demonstrates clinically acceptable reproducibility. Shortening of the duration may make the test more acceptable clinically, but it is associated with increasing imprecision.     

A comparison of two models of theρ-meson

A renormalization of the-propagator is presented. It is shown that if the-wave, isovector - amplitude is assumed to be dominated by this renormalized, many scattering parameters are predicted that agree well with experimental data. The model is compared with one presented by Tschang and Parkinson. It is shown that the predictions of the two models are the same, but that the renormalization model does not contain some of the theoretical problems of the Tschang and Parkinson scheme.Research partially supported by NSF Institutional Grant No. GU3220 and a grant from the Research Corporation.     

A Study of Antiferromagnetic Ordering in β-FeF3·3H2O by the Use of the NMR Method

The present work cites the investigation results of local magnetic fields on ¹H and ¹⁹F nuclei and spin ordering in β-FeF₃·3H₂O. In the structure of this compound (space group P4₂/n, a=7.846 Å, c=7.754 Å, z=4^1,2) Fe atoms are bonded via bridged F atoms (1) in infinite chains along the /001/ axis. With such positioning, in which two paramagnetic atoms are separated by a diamagnetic atom (F, O, C1 and others) there is a possibility for indirect (superexchange) interaction. Linear chains … Fe - F - Fe - F - Fe - F … are separated from each other by F(2) atoms and water molecules H₂O (1) and H₂O (2), so that exchange between neighboring Fe atoms from various chains is ostensibly much encumbered.     

Construction of the HL-2A Tokamak

HL-2A is the first tokamak with divertor in China. The objectives of HL-2A are to produce more adaptable divertor configurations to study energy exhaust and impurity control, and to study enhanced core plasma confinement by profile control and moderate plasma shaping. HL-2A has well optimized operational flexibility and excellent accessi-bility for the diagnostic systems to facilitate various plasma experiments.     

Proton-proton correlations in central collisions of Ni+Ni at 1.93 A·GeV and the space-time extent of the emission source

Small-angle correlations of proton pairs produced in central Ni+Ni collisions at a beam energy of 1.93 A·GeV are investigated with the FOPI detector system at GSI Darmstadt. Simultaneous comparison of longitudinal and transverse correlation functions with the predictions of the Koonin model allows to unravel the space-time ambiguity of the source extension. The determination of the source rest frame is found essential for the identification of this effect. For the present system, the selection of central events comprising about 8 % of the total cross section allows for the isolation of a compact source in momentum space which is centered around the c.m. velocity of the colliding nuclei. Taking into account the strong collective expansion of the participant zone, which introduces a reduction of the extracted source radius of more than 30 %, r.m.s. radius and emission time parameters of R _rms = (4.2 ± 1.2) fm and t _trms = (11 _? ⁺⁷ ) fm/c are extracted, respectively. In contrast, the analysis of the angle-integrated correlation function mixes the spatial and temporal size of the source and gives an upper limit R _trms = (7.0 ± 0.8) fm of the source radius.     

A Precise Formulation of the Third Law of Thermodynamics

The third law of thermodynamics is formulated precisely: all points of the state space of zero temperature  Γ₀  are physically adiabatically inaccessible from the state space of a simple system. In addition to implying the unattainability of absolute zero in finite time (or “by a finite number of operations”), it admits as corollary, under a continuity assumption, that all points of  Γ₀  are adiabatically equivalent. We argue that the third law is universally valid for all macroscopic systems which obey the laws of quantum mechanics and/or quantum field theory. We also briefly discuss why a precise formulation of the third law for black holes remains an open problem.     

A new type of the evolution of the bubble front in the Richtmyer–Meshkov instability

We study the coherent motion of bubbles and spikes in the Richtmyer–Meshkov instability. The theoretical solutions capturing the interplay of harmonics in the nonlinear dynamics are found, and a new type of the evolution of the bubble front is predicted.     

Effective orientation of water in 1,4-dioxane···water: the rotational spectrum of the H2 17O isotopologue

The measurements of the rotational spectrum of 1,4-dioxane-water complex, performed by pulsed jet Fourier transform microwave spectroscopy, have been extended to the 7–18.5 GHz frequency region and to two additional isotopologues, 1,4-dioxane···H₂ ¹⁷O and 1,4-dioxane···HOD. The effective orientation of water in the complex has been obtained from the ¹⁷O quadrupole coupling constants.     

A test of the Lorentz structure of semi-hadronic τ decays

A method is proposed for the determination of the Lorentz structure of the electroweak interaction in semi-hadronic τ decays. Spin correlations in the process $$e^ + e^ - \to \tau ^ + \tau ^ - \to \bar v_\tau \pi ^ + \pi ^0 v_\tau \pi ^ - \pi ^0 $$ are exploited for a measurement of the normalized product, γ_AV = 2Re{g_Ag _V ^* }/(|g_V|² + |g_V|²), of the vector (g _V ) and axial vector (g _A ) coupling of the τ lepton. The contribution of scalar (g _S ) or pseudo-scalar (g _P ) couplings is also investigated. Since in the above process the direction of flight of the τ leptons can be reconstructed up to a twofold ambiguity a likelihood method using the whole kinematic information can be employed. The matrix element entering the likelihood function has been evaluated in terms of the momenta and angles of the observed pions. The sensitivity of the derived method in ane ⁺ e ^? energy region around 10 GeV has been investigated for the ARGUS experiment using Monte Carlo simulations.     

A Re-interpretation of the Concept of Mass and of the Relativistic Mass-Energy Relation

For over a century the definitions of mass and derivations of its relation with energy continue to be elaborated, demonstrating that the concept of mass is still not satisfactorily understood. The aim of this study is to show that, starting from the properties of Minkowski spacetime and from the principle of least action, energy expresses the property of inertia of a body. This implies that inertial mass can only be the object of a definition—the so called mass-energy relation—aimed at measuring energy in different units, more suitable to describe the huge amount of it enclosed in what we call the “rest-energy” of a body. Likewise, the concept of gravitational mass becomes unnecessary, being replaceable by energy, thus making the weak equivalence principle intrinsically verified. In dealing with mass, a new unit of measurement is foretold for it, which relies on the de Broglie frequency of atoms, the value of which can today be measured with an accuracy of a few parts in 10⁹.     

Description of the Superdeformed Bands of the Odd-Odd Nuclei in A ～ 150 Region

With the supersymmetry scheme including many-body interactions, the global property and the △I ＝ 4bifurcation in the superdeformed (SD) bands of odd-odd nuclei in A ～ 150 mass region are investigated systematically.Good results for the γ-ray energies, the dynamical moments of inertia, and energy differences △ Eγ - △ Erefγ are obtained.It shows that this approach is quite powerful in describing not only the SD bands in even-even and odd-A nuclei butalso those in odd-odd nuclei in the mass region.     

Description of the Superdeformed Bands of the Odd-Odd Nuclei in A～150 Region

With the supersymmetry scheme including many-body interactions, the global property and the ΔI=4 bifurcation in the superdeformed (SD) bands of odd-odd nuclei in A～150 mass region are investigated systematically. Good results for the γ-ray energies, the dynamical moments of inertia, and energy differences ΔE_γ-ΔE_γ^ref are obtained. It shows that this approach is quite powerful in describing not only the SD bands in even-even and odd-A nuclei but also those in odd-odd nuclei in the mass region.     

Determination of the Avogadro constant – A contribution to the new definition of the mass unit kilogram

An improved attempt of several national metrology institutes to replace the present definition of the kilogram with the mass of a certain number of ¹²C atoms is described. This requires the determination of the Avogadro constant, N _A, via the silicon route with a relative uncertainty better than 2 ⋅ 10^-8. Previously, the limiting factor is the measurement of the average molar mass. Consequently, a world-wide collaboration has been set up, to produce, approximately, 5 kg of ²⁸Si single-crystal with an enrichment factor greater than 99.985% to be used for an improved determination of N _A. The first successful tests of all technological steps (enrichment of SiF₄, purification and synthesis of silane, deposition of polycrystalline ²⁸Si, single crystal growth) for the production of high-purity ²⁸Si are described.     

A New Approach to the Justification of the Wolkenstein–Ptitsyn Formula for the Parameter of the Vitrification Equation

Technical Physics - An extended interpretation of the Wolkenstein–Ptitsyn formula for temperature band δTg, characterizing a range of transition from liquid to glass, is considered using...