Wavelength-dependent rotation of dye molecules in a polar solution

Investigation of rotation movement of 3-amino-N-methylphthalimide in glycerol was carried out, taking into consideration the fluctuation of solvate structure. It was shown theoretically and experimentally that structural relaxation of the solvate shell, which follows excitation of the dye molecule, causes not only shift of the fluorescence spectrum in time but also additional rotation of the dye molecule. This effect, which may be called wavelength-dependent rotation, depends on the light frequency of both excitation and fluorescence. In particular, at excitation near the maximum of the absorption band, when the relaxation process is followed with the red shift of the fluorescence maximum, the anisotropy of fluorescence decreases faster in the red part of the fluorescence band than in the blue part. On the contrary, in the case of far anti-Stokes excitation, when the temporal shift of fluorescence is going to the blue, the anisotropy in the red part of the spectrum drops more slowly than in the blue part. Finally, there is a special excitation frequency which causes neither change of the fluorescence maximum nor acceleration of the rotational movement of the dye molecule. It is also shown that the temporal evolution of the spectrum and anisotropy of fluorescence in a polar dye solution may be quantitatively described using the socalled inhomogeneous broadening function (IBF). This function gives the distribution of dye molecules in a solution over frequencies of pure electronic transition due to fluctuations of the surrounding shell structure. Measurements of IBF changes in time carried out for 3-amino-N-methylphthalimide showed that during first 3 ns after excitation, the half-width of the IBF grows, and at the same time its maximum quickly shifts to the red. At the later time period there are only small changes of IBF position but considerable exponential decrease in its half-width. The IBF during this period preserves the Gaussian shape.     

Dielectric properties of a strongly polar nematic liquid crystal compound doped with gold nanoparticles

This study focuses on the electrical characteristics of a strongly polar nematic liquid crystal, Hexyloxy-cyanobiphenyl (6OCB), doped with a low concentration (2% by weight) of citrate buffer stabilised gold nanoparticles (GNPs) at low frequencies between 20 Hz and 35 MHz. The doped samples have lower values of nematic–isotropic transition temperature, permittivity (both parallel and perpendicular to the field direction) and dielectric anisotropy; however, relaxation time and activation energy were increased. The observed results could be explained on the basis of weakly anisotropic nature of GNPs and a local rearrangement of liquid crystal molecules surrounding the nanoparticles. Moreover, a complimentary suggestion on a possible change in the dipole–dipole correlation is made to explain the difference in changes (qualitative and quantitative) observed for permittivity of the host nematic liquid crystal doped with GNP. Temperature dependent dielectric relaxation studies indicate an increase in viscosity and potential barrier; and hence a change in strength of inter-molecular and intra-molecular interactions is suggested.     

Dynamics of a bilayer membrane with membrane-solvent partial slip boundary conditions

We discuss the dynamics of a bilayer membrane with partial slip boundary conditions between the monolayers and the bulk fluid. Using Onsager’s variational principle to account for the associated dissipations, we derive the coupled dynamic equations for the membrane height and the excess lipid density. The newly introduced friction coe?cients appear in the renormalized fluid viscosities. For ordinary lipid bilayer membranes, we find that it is generally justified to ignore the e?ects of permeation and parallel slip at the membrane surface.     

Rational Design of [13C,D14]Tert‐butylbenzene as a Scaffold Structure for Designing Long‐lived Hyperpolarized 13C Probes

Dynamic nuclear polarization (DNP) is a technique to polarize the nuclear spin population. As a result of the hyperpolarization, the NMR sensitivity of the nuclei in molecules can be dramatically enhanced. Recent application of the hyperpolarization technique has led to advances in biochemical and molecular studies. A major problem is the short lifetime of the polarized nuclear spin state. Generally, in solution, the polarized nuclear spin state decays to a thermal spin equilibrium, resulting in loss of the enhanced NMR signal. This decay is correlated directly with the spin‐lattice relaxation time T₁. Here we report [¹³C,D₁₄]tert‐butylbenzene as a new scaffold structure for designing hyperpolarized ¹³C probes. Thanks to the minimized spin‐lattice relaxation (T₁) pathways, its water‐soluble derivative showed a remarkably long ¹³C T₁ value and long retention of the hyperpolarized spin state.     

组稀疏优化问题精确连续Capped-L_(1)松弛北大核心CSCD

本文主要研究损失函数为凸函数且带有约束的组稀疏正则回归问题及组稀疏正则项的精确连续Capped-L_(1)松弛问题.首先对组Capped-L_(1)松弛问题定义了三类稳定点:D(irectional)-稳定点、C(ritical)-稳定点、L(ifted)-稳定点,然后刻画了这三类稳定点之间的关系.进一步,给出了组Capped-L_(1)松弛问题和原始组稀疏正则问题的最优性条件,并从全局解和局部解角度讨论了松弛问题和原问题解的等价关系.     

A system of conservation laws including a stiff relaxation term; the 2D case

We analyze a system of conservation laws in two space dimensions with a stiff relaxation term. A semi-implicit finite difference method approximating the system is studied and an error bound of order measured inL ¹ is derived. This error bound is independent of the relaxation time > 0. Furthermore, it is proved that the solutions of the system converge towards the solution of an equilibrium model as the relaxation time tends to zero, and that the rate of convergence measured inL ¹ is of order . Finally, we present some numerical illustrations.This research has been supported by the Norwegian Research Council (NFR), program no. STP 110673/420, at the Department of Applied Mathematics, SINTEF, Oslo, Norway     

Some new results on the two-dimensional kinetic Ising model in the phase coexistence region

We consider a Glauber dynamics reversible with respect to the two-dimensional Ising model in a finite square of sideL with open boundary conditions, in the absence of an external field and at large inverse temperature . We prove that the gap in the spectrum of the generator restricted to the invariant subspace of functions which are even under global spin flip is much larger than the true gap. As a consequence we are able to show that there exists a new time scalet _even, much smaller than the global relaxation timet _rel, such that, with large probability, any initial configuration first relaxes to one of the two phases in a time scale of ordert _even and only after a time scale of the order oft _rel does it reach the final equilibrium by jumping, via a large deviation, to the opposite phase. It also follows that, with large probability, the time spent by the system during the first jump from one phase to the opposite one is much shorter than the relaxation time.     

On the layering transition of an SOS surface interacting with a wall. I. Equilibrium results

We consider the model of a 2D surface above a fixed wall and attracted toward it by means of a positive magnetic fieldh in the solid-on-solid (SOS) approximation when the inverse temperature is very large and the external fieldh is exponentially small in . We improve considerably previous results by Dinaburg and Mazel on the competition between the external field and the entropic repulsion with the wall, leading, in this case, to the phenomenon of layering phase transitions. In particular, we show, using the Pirogov-Sinai scheme as given by Zahradník, that there exists a unique critical valueh _k ^* () in the interval (1/4e ^–4k , 4e ^–4k ) such that, for allh(h _k+1 ^* ,h _k ^* ) and large enough, there exists a unique infinite-volume Gibbs state. The typical configurations are small perturbation of the ground state represented by a surface at heightk+1 above the wall. Moreover, for the same choice of the thermodynamic parameters, the influence of the boundary conditions of the Gibbs measure in a finite cube decays exponentially fast with the distance from the boundary. Whenh=h _k ^* () we prove instead the convergence of the cluster expansion for bothk andk+1 boundary conditions. This fact signals the presence of a phase transition. In the second paper of this series we will consider a Glauber dynamics for the above model and we will study the rate of approach to equilibrium in a large finite cube with arbitrary boundary conditions as a function of the external fieldh. Using the results proven in this paper, we will show that there is a dramatic slowing down in the approach to equilibrium when the magnetic field takes one of the critical values and the boundary conditions are free (absent).     

溴仿在冲击压缩下的光辐射及化学反应

 利用多通道光学高温计测量了溴仿在37 GPa到85 GPa压力范围内的温度,并观察了溴仿/单晶氯化钠界面的热驰豫过程。结果发现,当冲击波压力升高到46 GPa时,溴仿的光辐射强度随时间的变化呈现出“双阶梯”或“双台阶”形状的剖面结构,且台阶之间的时间间隔随冲击压力的增高而减小。当压力达到85 GPa时,上述“双台阶”结构消失,呈现为普通的单台阶剖面结构。冲击波温度测量表明,当压力低于50 GPa时,实测温度与Gokulya报道的数据一致;当压力增至76 GPa以上时,冲击波温度出现突跃性增加。结合对溴仿/氯化钠界面上的热驰豫过程的分析,文中提出,溴仿在上述冲击压力区间内发生了一次带有时间驰豫（或化学诱导期）的化学放热反应。     

Structure and properties of TentaGel resin beads: Implications for combinatorial library chemistry

Summary In view of the widespread use of TentaGel resin beads for the synthesis of combinatorial libraries, the properties of TentaGel resin have been examined using a combination of confocal laser microscopy and NMR spectroscopy. Evidence is presented that trypsin, a 23.5-kDa enzyme, can penetrate to the core of 90-m TentaGel beads, and that the matrix of such beads permits molecular motion at a similar rate to that in solution. The beads act as a separate gel phase rather than as a porous solid. These conclusions have important implications for the bioassay of on-bead combinatorial chemical libraries.