Geometry of the internal dynamics of the 12C13CH 3 + carbocation

The internal dynamics of the ¹²C¹³CH₃⁺ isotopomer of the simplest carbocation is considered to be a distorted dynamics of its symmetric C₂H₃⁺ isotopomer. By using the group-chain methods and assuming quite naturally that the carbocation equilibrium structures continue to be planar and the nonrigid motion occurring between them is retained upon this isotopic substitution, a simple algebraic model is constructed to describe the spectrum of the ¹²C¹³CH₃⁺ isotopomer. The correctness of the model is limited only by that of the adopted geometrical symmetry of internal dynamics of the C₂H₃⁺ isotopomer.     

Description of the torsional motion in the isotopically asymmetric ionic complexes ArH<Subscript>2</Subscript>D<Superscript>+</Superscript> and ArD<Subscript>2</Subscript>H<Superscript>+</Superscript>

The internal dynamics of the isotopically asymmetric ionic complexes ArH₂D⁺ and ArD₂H⁺ is considered to be a distorted dynamics of the isotopically symmetric ArH₃⁺ complex. By using the group chain methods, a rigorous algebraic model is constructed to describe the spectrum of the asymmetric complexes with an allowance for the torsional motion of the structure of hydrogen nuclei. The model is based on the geometrical group of symmetry of internal dynamics of the isotopically symmetric ionic complex, which is used here as a noninvariant group.     

Multinuclear NMR Study of Structure and Mobility in Cyclic Model Lithium Conducting Systems

The transport of the lithium ions is the basis of lithium ion conductivity of currently used electrolytes. Understanding how the transport of lithium ions within the matrix is influenced by the interactions with solvating moieties is needed to improve their performance. Along these lines well-defined model compounds based on cyclotriphosphazene (CTP) and hexaphenylbenzene (HPB) cores, bearing side groups of ethylene carbonate, a common solvent for lithium salts used as electrolytes in Li-ion batteries (Thielen et al. Chem. Mater, 23, 2120, 2011) and blended with different amounts of Lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) have been studied by multinuclear nuclear magnetic resonance (NMR) spectroscopy. The local dynamics of the matrix was probed by ¹H and ³¹P NMR, while the local dynamics of the Li⁺ cations was unraveled by ⁷Li and ¹³C NMR. Transport of both ions was studied by pulsed-field gradient (PFG) NMR. Based on the different temperature dependences of the dynamics the bulk ion transport is not attributed to local dynamics, but to translational diffusion best characterized by PFG NMR. Although the glass transition temperatures of the blends are low, their conductivities are only in the range of typical polymer electrolytes. The results of NMR spectroscopy are in accord with the conjecture that the coordination between the cyclic carbonate functionality and the Li⁺-ion is too tight to allow for fast ion dynamics.     

Interpretation of 1H and 2H spin–lattice relaxation dispersions: Insights from molecular dynamics simulations of polymer melts

We demonstrate that molecular dynamics simulations are a versatile tool to ascertain the interpretation of spin–lattice relaxation data. For ¹H, our simulation approach allows us to separate and to compare intra- and inter-molecular contributions to spin–lattice relaxation dispersions. Dealing with the important example of polymer melts, we show that the intramolecular parts of ¹H spectral densities and correlation functions are governed by rotational motion, while their inter-molecular counterparts provide access to translational motion, in particular, to mean-squared displacements and self-diffusion coefficients. Exploiting that the full microscopic information is available from molecular dynamics simulations, we determine the range of validity of experimental approaches, which often assume Gaussian dynamics, and we provide guidelines for the determination of free parameters required in experimental analyses. For ²H, we examine the traditional methodology to extract correlation times of complex dynamics from relaxation data. Furthermore, based on knowledge from our computational study, it is shown that measurement of ²H spin–lattice relaxation dispersions allows one to disentangle the intra- and inter-molecular contributions to the corresponding ¹H data in experimental work. Altogether, our simulation results yield a solid basis for future ¹H and ²H spin–lattice relaxation analysis.     

Newtonian versus Langevin dynamics: Example of ϕ4-model with infinite range interactions

The functional integral representation for the generating functional (GF) of the canonically averaged ensemble with an underlying Newtonian dynamics is obtained. It is shown that for this representation the non-linear fluctuation-dissipation theorem (NFDT) has the same form as for the Langevin dynamics case. This GF-representation is used for the investigation of the dynamics of the ϕ⁴-model with infinite range interactions at T > T_c. It is shown that the kinetic equation for the complete correlation function has the same form as for the Langevin dynamics case, which was considered before. All peculiarities of Newtonian dynamics are absorbed by one-particle (2-point and 4-point) correlator and response functions. The analysis of this equation shows that the 1/N-fluctuations (where N is the number of particles) restore the ergodicity of the system with the characteristicsrate τ⁻¹ ∼ μ²/N, where μ is a coupling constant.     

Reading the patterns in living cells —the physics of ca2+ signaling

Ca²⁺ is one of the most important messengers. It transmits signals inside living cells and takes part in intercellular coordination. The dynamics of the Ca²⁺ concentration shows a transition from elemental, stochastic events to global events like waves and oscillations. This transition renders it an ideal tool for studying basic concepts of pattern formation, especially since access to the most important experimental parameters is given. Ca²⁺ dynamics in living cells has been a major topic of biophysical modelling in the last 15 years. Modelling has reached the level of predictive power. The theoretical analysis of waves provided new insight into the mechanisms of Ca²⁺ signaling and led to new concepts of analysis of wave equations with concentration dependent diffusion and novel wave bifurcations. Modelling of oscillations provided understanding especially of complex oscillations and allowed to extract information about the underlying cellular parameters and mechanisms. The investigation of the stochastic aspects of intracellular Ca²⁺ dynamics demonstrated the fundamental role of fluctuations arising from the control of the release channel by Ca²⁺ and IP₃. This review presents an overview of current theoretical research on Ca²⁺ dynamics in living cells driven by the inositol 1,4,5-trisphosphate receptor channel.     

Nelsonian mechanics revisited

In de Broglie and Bohm’s pilot-wave theory, as is well known, it is possible to consider alternative particle dynamics while still preserving the |ψ|² distribution. I present the analogous result for Nelson’s stochastic theory, thus characterising the most general diffusion processes that preserve the quantum equilibrium distribution, and discuss the analogy with the construction of the dynamics for Bell’s beable theories. I briefly comment on the problem of convergence to |ψ|² and on possible experimental constraints on the alternative dynamics.     

13C NMR of tunnelling methyl groups

The dipolar interactions between the protons and the central ¹³C nucleus of a ¹³CH₃ group are used to study rotational tunnelling and incoherent dynamics of such groups in molecular solids. Single-crystal ¹³C NMR spectra are derived for arbitrary values of the tunnel frequency ν_t. Similarities to ESR and ²H NMR are pointed out. The method is applied to three different materials. In the hydroquinone/acetonitrile clathrate, the unique features in the ¹³C NMR spectra which arise from tunnelling with a tunnel frequency that is much larger than the dipolar coupling between the methyl protons and the ¹³C nucleus are demonstrated, and the effects of incoherent dynamics are studied. The broadening of the ¹³C resonances is related to the width of the quasi-elastic line in neutron scattering. Selective magnetization transfer experiments for studying slow incoherent dynamics are proposed. For the strongly hindered methyl groups of L-alanine, an upper limit for ν_t is derived from the ¹³C NMR spectrum. In aspirin? (acetylsalicylic acid), incoherent reorientations dominate the spectra down to the lowest temperatures studied; their rate apparently increases with decreasing temperature below 25 K.     

Does confined water exhibit a fragile-to-strong transition?

The dynamics of supercooled confined water has recently been shown to have a pronounced, apparent fragile-to-strong transition (FST). Here we use broadband dielectric spectroscopy (10^-2–10⁹ Hz) to study the dynamics of water confined in silica matrices MCM-41 C10 and C18, with pore diameter of 21.4 and 36.1 ?, respectively. The local dynamics of water molecules and the dynamics of the hydroxyl groups on the inner wall of the pores are followed up to over 240 K. We argue that the reported FST for confined water is due to the vanishing of the cooperative α relaxation, which implies that it should not be interpreted as a true FST.     

中能重离子碰撞中晕核反应动力学

基于同位旋相关量子分子动力学研究了中子晕核和质子晕核的核反应动力学，着重研究了松散的晕结构对于重离子碰撞中的碎裂和动量耗散中的特殊作用. 为了突出晕核松散结构在反应动力学中的特殊作用. 同时计算了在完全相同入射道条件下相等质量稳定弹核引起核反应. 通过对晕核和稳定核核反应动力学结果的对比分析，发现晕核的松散结构对核反应动力学的作用和影响是重要的. 如这种松散结构明显的增加了碎裂多重性；相反, 减小了原子核阻止(动量耗散). 关键词： 中子晕核 质子晕核 重离子碰撞 核反应动力学     

Software package for modeling spin–orbit motion in storage rings

A software package providing a graphical user interface for computer experiments on the motion of charged particle beams in accelerators, as well as analysis of obtained data, is presented. The software package was tested in the framework of the international project on electric dipole moment measurement JEDI (Jülich Electric Dipole moment Investigations). The specific features of particle spin motion imply the requirement to use a cyclic accelerator (storage ring) consisting of electrostatic elements, which makes it possible to preserve horizontal polarization for a long time. Computer experiments study the dynamics of 10⁶–10⁹ particles in a beam during 10⁹ turns in an accelerator (about 10¹²–10¹⁵ integration steps for the equations of motion). For designing an optimal accelerator structure, a large number of computer experiments on polarized beam dynamics are required. The numerical core of the package is COSY Infinity, a program for modeling spin–orbit dynamics.     

New Dynamics in the Anti-de Sitter Universe AdS 5

This paper deals with the propagation of the gravitational waves in the Poincaré patch of the 5-dimensional Anti-de Sitter universe. We construct a large family of unitary dynamics with respect to some high order energies that are conserved and positive. These dynamics are associated with asymptotic conditions on the conformal time-like boundary of the universe. This result does not contradict the statement of Breitenlohner-Freedman that the hamiltonian is essentially self-adjoint in L ² and thus accordingly the dynamics is uniquely determined. The key point is the introduction of a new Hilbert functional framework that contains the massless graviton which is not normalizable in L ². Then the hamiltonian is not essentially self-adjoint in this new space and possesses a lot of different positive self-adjoint extensions. These dynamics satisfy a holographic principle: there exists a renormalized boundary value which completely characterizes the whole field in the bulk.     

Description of torsional motion in ionic complexes ArH<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> and ArD<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack>

An algebraic model that describes the internal dynamics of the ionic complexes ArH₃⁺ and ArD₃⁺ in the ground electronic-vibrational state taking into account the torsional motion of the structure of identical hydrogen nuclei is constructed by symmetry-group chain methods. It is important that the correctness of this model is only limited by the correctness of the choice of geometric symmetry of the internal dynamics of the ionic complex.     

Protein dynamics studied on myoglobin

Two methods of inelastic scattering of synchrotron radiation were used to measure the dynamics of myoglobin in the temperature range from T = 60 K to 300 K. The inelastic Rayleigh scattering of metmyoglobin was analyzed by delayed elastic nuclear forward scattering of an iron foil. This yields averaged information on all phonons within the sample. The mean square displacement of the atoms due to this dynamics is 〈x〉 ²/T = 2.1 · 10^—4 Ų K^—1 on average. Complementary information was obtained by phonon assisted nuclear scattering on deoxymyoglobin. This method selects the phonons coupling to the iron atom in the active center of the protein. The mean square displacement of the iron was measured to be 〈x〉 ²/T = 0.6· 10^—4 Ų K^—1. The results are in agreement with Mössbauer absorption experiments in the low temperature range. Above 200 K the results allow one to distinguish between harmonic and quasidiffusive dynamics within the protein. A comparison with Raman spectroscopy is made.

     

Out-of-equilibrium quantum field dynamics in external fields

The quantum dynamics of the symmetry-broken λ(Φ ²)² scalar-field theory in the presence of an homogeneous external field is investigated in the large-N limit. We consider an initial thermal state of temperature T for a constant external field J. A subsequent sign flip of the external field, J→ - J, gives rise to an out-of-equilibrium nonperturbative quantum field dynamics. We review here the dynamics for the symmetry-broken λ(Φ ²)² scalar N component field theory in the large-N limit, with particular stress in the comparison between the results when the initial temperature is zero and when it is finite. The presence of a finite temperature modifies the dynamical effective potential for the expectation value, and also makes that the transition between the two regimes of the early dynamics occurs for lower values of the external field. The two regimes are characterized by the presence or absence of a temporal trapping close to the metastable equilibrium position of the potential. In the cases when the trapping occurs it is shorter for larger initial temperatures.     

Boson-like quantum dynamics of association in ultracold Fermi gases

We study the collective association dynamics of a cold Fermi gas of 2N atoms in M atomic modes into a single molecular bosonic mode. When the atomic translational motion is slow compared to the atom-molecule conversion rate, the many-body fermionic problem for 2^M amplitudes is effectively reduced to a dynamical system of min{N, M} + 1 amplitudes, making the solution no more complex than the solution of a two-mode Bose-Einstein condensate and allowing realistic calculations with up to 10⁴ particles. The many-body dynamics is shown to be formally similar to the dynamics of the bosonic system under the mapping of boson particles to fermion holes, producing collective enhancement effects due to many-particle constructive interference.     

Dynamics of the Up-Conversion Emission in Holmium Doped Zblan Fiber

The dynamics of up-conversion, green emission under excitation at different infra-red wavelength in Ho^3? doped ZBLAN fiber is reported. Under infrared, 890 nm quasi cw pumping the complicated temporal behavior of the up-conversion signal is strongly influenced by the intermediate ⁵I₅ state cross relaxation. The mechanisms of the observed up-conversion processes are proposed and the time evolution of the ⁵S₂ population is described by the rate equation model. Parameters of the model are determined and numerical simulations of the excited state dynamics are performed.     

Investigation of the structural and dynamical properties of the (0 0 1) surface of LiCu2O2

We report on studies of the structure and dynamics of the (0 0 1) surface of single crystal LiCu₂O₂, investigated by He beam scattering at room temperature, and with lattice-dynamical models. The best fit surface corrugation to measured diffraction patterns shows that the surface termination is exclusively a Li¹⁺Cu²⁺O^2? plane. Lattice dynamics fits to inelastic He scattering spectra reveal the presence of two low-lying surface phonon modes, identified with the motion of Cu²⁺, Li¹⁺ surface ions normal to the surface.