Order of the phase transition in models of DNA thermal denaturation

We examine the behavior of a model which describes the melting of double-stranded DNA chains. The model, with displacement-dependent stiffness constants and a Morse on-site potential, is analyzed numerically; depending on the stiffness parameter, it is shown to have either (i) a second-order transition with nu( perpendicular) = -beta = 1,nu(||) = gamma/2 = 2 (characteristic of short-range attractive part of the Morse potential) or (ii) a first-order transition with finite melting entropy, discontinuous fraction of bound pairs, divergent correlation lengths, and critical exponents nu( perpendicular) = -beta = 1/2,nu(||) = gamma/2 = 1.     

Fractal dimension and localization of DNA knots

The scaling properties of DNA knots of different complexities were studied by atomic force microscope. Following two different protocols DNA knots are adsorbed onto a mica surface in regimes of (i) strong binding, that induces a kinetic trapping of the three-dimensional (3D) configuration, and of (ii) weak binding, that permits (partial) relaxation on the surface. In (i) the radius of gyration of the adsorbed DNA knot scales with the 3D Flory exponent nu approximately 0.60 within error. In (ii), we find nu approximately 0.66, a value between the 3D and 2D (nu=3/4) exponents. Evidence is also presented for the localization of knot crossings in 2D under weak adsorption conditions.     

Translocation of a confined polymer through a hole

Based on an analogy between polymer translocation across a free energy barrier associated with polymer worming through a hole and classical nucleation and growth process, the escape time tau is predicted asymptotically to be N(N/rho)(1/3nu). N is the polymer length, rho is the monomer density prior to escape, and nu is the radius of gyration exponent. Monte Carlo simulation data collected in the high salt limit (nu approximately 3/5) are in agreement with the asymptotic law and provide vivid details of the escape.     

Stretching and collapse of neutral polymer layers under association with ionic surfactants

We provide experimental evidence for stretching and collapse of neutral polymer layers, already adsorbed at an oil-in-water interface, due to its interaction with surfactants. Upon stretching, the first interaction length (2L(0)) follows a power law dependence on surfactant concentration ( proportional, variant C(x)(s), where x approximately 0.5 for cationic surfactants) and collapses in the presence of salt, as a relatively weak power law (C(-y)(s), where y=0.17), in good agreement with brush length decay for polyelectrolyte brushes.     

Critical exponents for random knots

The size of a zero-thickness (no excluded volume) nonphantom polymer ring is shown to scale with chain length N in the same way as the size of the excluded-volume (self-avoiding) linear polymer, that is, as Nnu, where nu approximately 0.588. The consequences of this fact are examined, including the sizes of trivial and nontrivial knots.     

Ground-state phase diagram of 2D electrons in a high Landau level: a density-matrix renormalization group study.

The ground-state phase diagram of 2D electrons in a high Landau level (index N = 2) is studied by the density-matrix renormalization group method. Pair correlation functions are systematically calculated for various filling factors from nu = 1/8 to 1/2. It is shown that the ground-state phase diagram consists of three different charge density wave states called stripe phase, bubble phase, and Wigner crystal. The boundary between the stripe and the bubble phases is determined to be nu(s-b)c approximately 0.38, and that for the bubble phase and Wigner crystal is nu(b-W)c approximately 0.24. Each transition is of first order.     

Conformation of circular DNA in two dimensions

The conformation of circular DNA molecules of various lengths adsorbed in a 2D conformation on a mica surface is studied. The results confirm the conjecture that the critical exponent nu is topologically invariant and equal to the self-avoiding walk value (in the present case nu=3/4), and that the topology and dimensionality of the system strongly influence the crossover between the rigid regime and the self-avoiding regime at a scale L approximately 7l{p}. Additionally, the bond correlation function scales with the molecular length L as predicted. For molecular lengths L相似文献   

Cold collision frequency shift in two-dimensional atomic hydrogen

We report a measurement of the cold collision frequency shift in atomic hydrogen gas adsorbed on the surface of superfluid (4)He at T approximately < 90 mK. Using two-photon electron and nuclear magnetic resonance in 4.6 T field we separate the resonance line shifts due to the dipolar and exchange interactions, both proportional to surface density sigma. We find the clock shift Delta nu(c) = -1.0(1) x 10(-7) Hz cm(-2) x sigma, which is about 100 times smaller than the value predicted by the mean field theory and known scattering lengths in the three-dimensional case.     

Potential energy in a three-dimensional vibrated granular medium measured by NMR imaging

We use molecular dynamics simulations to study the swelling of randomly end-cross-linked polymer networks in good solvent conditions. We find that the equilibrium degree of swelling saturates at Q(eq) approximately N(3/5)(e) for mean strand lengths &Nmacr;(s) exceeding the melt entanglement length N(e). The internal structure of the network strands in the swollen state is characterized by a new exponent nu = 0.72+/-0.02. Our findings can be rationalized by a Flory argument for a self-similar structure of mutually interpenetrating network strands, agree partially with the classical Flory-Rehner theory, and are in contradiction to de Gennes' c(*)-theorem.     

Scaling laws of single polymer dynamics near attractive surfaces

We present a molecular dynamics study of a generic model for single polymer diffusion on surfaces, which have variable atomic-scale corrugation but no artificial, impenetrable obstacles. The diffusion coefficient D scales as D is proportional to (-3/2) with the degree of polymerization N for strongly adsorbed, linear polymers on solid substrates in good solvents. Weaker scaling, i.e., D is proportional to (-1), is found if (i) the substrate is a fluid, e.g., a membrane, (ii) the polymer is a ring polymer, and (iii) the polymer is commensurate with the substrate. In poor solvents, diffusion on solids slows exponentially fast with N. Reptation is not observed in any of the simulations presented here.     

Theoretical Study of Collision-Induced Double Transitions in CO(2)-X(2) (X(2) = H(2), N(2), and O(2)) Pairs

The double vibrational collision-induced absorptions CO(2) (nu(3) = 1) + X(2) (nu(1) = 1) <-- CO(2) (nu(3) = 0) + X(2) (nu(1) = 0), for X(2) = H(2), N(2), and O(2) are studied on the basis of quantum lineshapes computed using isotropic potentials and dipole-induced dipole functions. The linestrengths and energies of the vibration-rotation transitions are treated explicitly for X(2) and utilizing the HITRAN database for CO(2). From the frequency-dependent absorption profiles, the integrated absorption intensities are determined to be 7.2 +/- 1.2, 1.2 +/- 0.1, and 1.1 +/- 0.2 (10(-4) cm(-2) amagat(-2)) for the H(2), N(2), and O(2) collision partners, respectively. The integrated intensities for H(2) and N(2) agree well with previously measured and calculated results, while the value for O(2), which represents the first theoretical determination for this absorption, is approximately four times greater than the only experimental measurement (0.29 x 10(-4) cm(-2) amagat(-2)). Copyright 2001 Academic Press.     

Full current statistics of incoherent "cold electrons"

We evaluate the full current statistics (FCS) in the low-dimensional (1D and 2D) diffusive conductors in the incoherent regime eV>E(Th)=D/L(2), E(Th) being the Thouless energy. It is shown that the Coulomb interaction substantially enhances the probability of big current fluctuations for short conductors with E(Th)>1/tau(E), tau(E) being the energy relaxation time, leading to the exponential tails in the current distribution. The current fluctuations are most strong for low temperatures, provided E(Th) approximately [(eV)(2)/Dnu(2)(1)](1/3) for 1D and E(Th) approximately (eV/g)ln(g for 2D, where g is a dimensionless conductance and nu(1) is a 1D density of states. The FCS in the "hot electron" regime is also discussed.     

Mean-field theory for polymer adsorption on curved surfaces

We discuss the influence of polymer adsorption on the curvature energy of an interface. Following an article by Clement and Joanny (J. Phys. II 7, 973 (1997)), a mean-field theory is used to calculate the surface tension, rigidity constants and spontaneous curvature associated with both reversible and irreversible polymer adsorption. In the case of irreversible polymer adsorption it is assumed that the amount of adsorbed polymer remains constant upon curving the interface. Unfortunately, constraining the amount of polymer by adding a Lagrange multiplier affects the thermodynamic state of the (free) polymer far away from the interface. Clement and Joanny solve this problem by removing the polymers in the bulk. We allow for the presence of free polymers, but to achieve this we have to apply a local external field to keep the adsorbed amount fixed. The results of the two approaches are compared and a physical interpretation is given. Received 25 July 2001 and Received in final form 5 December 2001     

2-噻吩乙醛酸-邻菲罗啉-铕配合物的合成、结构表征及荧光性能的研究

合成了铕与 2 噻吩乙醛酸 (HL)和邻菲罗啉 (phen)的配合物 ,用元素分析、电导率、红外光谱和核磁共振谱测定了配合物的分子式为 [EuL2 phen·(H2 O) 3 ]NO3 ;配合物中的Eu(Ⅲ )离子与 2 噻吩乙醛酸和水分子中的O原子以及邻菲罗啉中的N原子配位。在室温下测定了配合物的激发和发射光谱 ,配合物中Eu(Ⅲ )离子的5D0 7F1和5D0 7F2 跃迁分别位于 5 92和 6 18nm。该固体配合物于室温下被紫外光激发可以发出强的特征红色荧光。IR光谱中 ,2 噻吩乙醛酸的特征吸收峰νCO (1719cm-1) ,νC—O(12 32cm-1) ,δO—H(90 9cm-1)在形成配合物后消失。在配合物中出现—COO-的反对称νas(16 4 2cm-1)和对称νs(14 0 8cm-1)伸缩振动吸收峰。在1HNMR谱图中 ,2 噻吩乙醛酸环上的 3个氢原子的化学位移形成配合物后移向高场 ,邻菲罗啉环上 4种不同环境的质子峰的化学位移形成配合物后向低场移动。从TG曲线可以看出 ,此配合物在常温至 2 5 0℃以下是稳定的。     

Rovibrational Analysis of the nu(2) Band of Diazirine-d(2)

The gas-phase IR spectrum of the nu(2) (A(1), 1610.33 cm(-1)) band of the deuterated isotopomer of diazirine, D(2)CN(2), a three-membered ring compound which belongs to the molecular symmetry point group C(2v), has been studied at a resolution of about 0.005 cm(-1). This vibrational mode which can be approximately described as N&dbond;N stretching is widely perturbed. This is due to various interactions with the tetrad consisting of the binary combinations nu(6) + nu(7) (A(1)), nu(7) + nu(9) (A(2)), nu(5) + nu(6) (B(2)), and nu(5) + nu(9) (B(1)), which form a relatively isolated pentad together with nu(2) in the wavenumber region 1560-1610 cm(-1). A simultaneous upper state analysis of nu(2) from a pentad model including these resonances has been performed and a set of spectroscopic parameters has been obtained. Since the four combination bands of the pentad are dark states, only band centers could be determined; in addition for nu(5) + nu(9) and nu(7) + nu(9) also the term (B - C)/2 has been obtained. A number of Coriolis interaction constants and the vibrational resonance (with nu(6) + nu(7)) parameter have been calculated as well. Copyright 2001 Academic Press.     

Observable N-N oscillation in high scale seesaw models

We discuss a realistic high scale (nu(B-L) approximately 10(12) GeV) supersymmetric seesaw model based on the gauge group SU(2)L x SU(2)R x SU(4)c where neutron-antineutron oscillation can be in the observable range. This is contrary to the naive dimensional arguments which say that tau(N-N) is proportional to nu(B-L)5 and should therefore be unobservable for seesaw scale nu(B-L) > or = 10(5) GeV. Two reasons for this enhancement are (i) accidental symmetries which keep some of the diquark Higgs masses at the weak scale and (ii) a new supersymmetric contribution from a lower dimensional operator. The net result is that tau(N-N) is proportional to nu(B-L)2 nu(wk)3 rather than nu(B-L)5. The model also can explain the origin of matter via the leptogenesis mechanism and predicts light diquark states which can be produced at LHC.     

The multidimensional filter diagonalization method

The theory and numerical aspects of the recently developed multidimensional version of the filter diagonalization method (FDM) are described in detail. FDM can construct various "ersatz" or "hybrid" spectra from multidimensional time signals. Spectral resolution is not limited by the time-frequency uncertainty principle in each separate frequency dimension, but rather by the total joint information content of the signal, i.e., N(total) = N(1) x N(2) x vertical ellipsis x N(D), where some of the interferometric dimensions do not have to be represented by more than a few (e.g., two) time increments. It is shown that FDM can be used to compute various reduced-dimensionality projections of a high-dimensional spectrum directly, i.e., avoiding construction of the latter. A subsequent paper (J. Magn. Reson. 144, 357-366 (2000)) is concerned with applications of the method to 2D, 3D, and 4D NMR experiments.     

Nusselt number measurements for turbulent Rayleigh-Bénard convection

We present high-precision measurements of the Nusselt number N as a function of the Rayleigh number R for a cylindrical sample of water (Prandtl number sigma=4.4) of height L approximately equal to 50 cm and aspect ratio Gamma identical with D/L approximately equal to 1 (D is the diameter) for 3 x 10(9)< or =R< or =6 x 10(10). For R approximately 3 x 10(9) the data are consistent with existing results for acetone (sigma=4.0, R< or =3 x 10(9)). There the measurements are also consistent with a model by Grossmann and Lohse (GL). As R increases, the measurements fall below the GL prediction. Near R=6 x 10(10) the prediction is 8% above the data.     

Spectroscopic evidence for the localization of Skyrmions near nu = 1 as T --> 0

Optically pumped nuclear magnetic resonance measurements of 71Ga spectra were carried out in an n-doped GaAs/Al(0.1)Ga0.9As multiple quantum well sample near the integer quantum Hall ground state nu = 1. As the temperature is lowered (down to T approximately 0.3 K), a "tilted plateau" emerges in the Knight shift data, which is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional Skyrmions.     

Quadratic lagrangians in a space with torsion and the theory of the spinor gauge field

The linear approximation of the theory of the spinor gauge field (TSGF), introduced in the localization of the group of tetrad Lorentz transformations, is discussed. In constructing the TSGF, use is made of the principle of correspondence with the tetrad theory of gravitation in a space of absolute parallelism. It is shown that the imposing of additional conditions of the Lorentz-Hilbert type in the linearized TSGF leads to a unique definition of the Lagrangian of the A-field, quadratic in the field intensity, of the form RR. which is usually postulated from considerations of simplicity and by analogy with other gauge fields. Two new identities in a space with torsion are proved.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 74–79, September, 1979.