Experimental evidence of the ferroelectric nature of the λ-point transition in liquid water

We studied the dielectric properties of nano-sized liquid water samples confined in polymerized silicates MCM-41 characterized by pore sizes 3–10 nm. Freezing temperature suppression in nanopores helps keep the water samples in liquid form at temperatures well below 0°C and thus effectively study the properties of supercooled liquid water. We report the first direct measurements of the dielectric constant by the dielectric spectroscopy method and demonstrate very clear signatures of the second-order phase transition of ferroelectric nature at temperatures next to the λ-point in the supercooled bulk water in full agreement with the recently developed model of the polar liquid.     

Finite-size effects in plane layers of liquid 4He near the λ point

Quantitative measurements of the liquid ⁴He density temperature dependence are taken near the λ point in a thin plane-parallel gap of thickness d=3.3×10⁻⁵ cm with a well controlled geometry. Evidence is obtained that there are three effects contributing to the average helium density in the gap: (i) the shift of the λ transition temperature in the gap as compared to the bulk helium, (ii) the contribution to the average density from the inhomogeneity of the equilibrium order parameter distribution across the gap below T_λ, (iii) the rounding of the logarithmic anomaly of the helium thermal expansion coefficient in the gap due to changes in the spectrum of the order parameter fluctuation in the direction across the gap. A comparison is given with predictions of the phenomenological Ψ-theory of superfluidity near the λ point as well as with those of scaling theory.     

Investigation of the dynamical behaviour of the FH(CN−) centre in KCl with temperature dependent endor spectroscopy

Abstract

The temperature dependence of the electron nuclear double resonance (ENDOR) spectra of F_H(CN^?) centres in KCl was investigated in the temperature range between 10–220 K. At the lowest temperature of 10 K only one CN^? orientation with respect to the F centre electron is present, in which the nitrogen is thought to be nearer to the F-electron than the carbon. With the very small thermal activation energy of 2.9 meV the opposite orientation is occupied. The superhyperfine interactions of those first shell K nuclei nearest to CN^? and of the ¹³C interaction of the CN^? molecule are strongly temperature dependent between 10 and 60 K, following an exponential law with a thermal activation energy of 4.2 meV. It is assumed that a soft local mode involving those two nearest K nuclei and the CN^? is causing the strong temperature dependence. The shf interactions of ¹⁴N nuclei have not been seen, probably because of the dynamical effects.     

X-ray studies of the smectic B phase of the 4-bromobenzylidene-4′-alkoxyanilines

The results of X-ray studies of the nine members (4?÷?12) of the 4-bromobenzylidene-4′-alkyloxyaniline homologous series (nBBAA) in smectic B (SmB) and smectic A (SmA) phases are presented. Interestingly, no SmC phase was identified. The thickness of smectic layers in the SmA and SmB phases was estimated showing unexpectedly that in SmA it is bigger than in the SmB. For the SmB phase, orthorhombic unit cell parameters were determined as a function of temperature. The obtained data are discussed in relation to rotational dynamics.     

Pressure-induced solidifications of liquid sulfur below and above λ-transition

Two kinds of glassy sulfurs are synthesized by the rapid compression method from liquid sulfur at temperatures below and above the λ-transition point. The glassy sulfur has different colors and transparencies, depending on temperature, which may inherit some structural information from the λ-transition. Raman spectrum studies of these samples show that a large fraction of polymeric chains exist in the glassy sulfur, even in the one solidified from T T_λ. We find that a higher compression rate instead of a higher temperature of the parent liquid captures more polymeric chains. Pressure-induced glassy sulfur presents high thermal stability compared with temperature quenched glassy sulfur and could transform into liquid sulfur directly without crystallization through an abnormal exothermic melting course. High energy x-ray diffraction is utilized to study the local order of the pressure-induced glassy sulfur.     

Nonlinear renormalization-group analysis applied to the hydrodynamic light scattering spectrum of4He belowT λ

We calculate the observable critical temperature dependence of the transport coefficients entering the hydrodynamic form of the dynamic structure factor of⁴He belowT . Application of our recently introduced nonlinear renormalization-group analysis yields quantitative agreement with previous light scattering experiments in the hydrodynamic region. This resolves a long-standing problem in the critical dynamics below the superfluid transition of⁴He.Supported in part by the Fonds zur Förderung der wissenschaftlichen Forschung     

Interpretation of experimental data near λ-transition point in liquid helium

The recently published experimental data for specific heat C_p of liquid helium in zero gravity conditions very close to the λ–transition have been discussed. We have shown that these data allow different interpretations. They can be well interpreted within the perturbative RG approach and within our recently developed theory, as well. Allowing the logarithmic correction, the corresponding fits lie almost on top of each other over the whole range of the reduced temperatures t (for bin averaged data) 6.3 ×10^-10 < t < 8.8 ×10^-3. However, the plot of the effective exponent α _eff(t) suggests that the behaviour of C_p, probably, changes very close to T_λ. To clarify this question, we need more accurate data for t<10^-7. In addition, we show that the experimental data for superfluid fraction of liquid helium close to T_λ within t ∈[3 ×10^-7;10^-4] can be better fit by our exponents ν=9/13 ≃0.6923, Δ=5/13 ≃0.3846 than by the RG exponents ν≃0.6705 and Δ≃0.5. The latter ones are preferable to fit the whole measured range t ∈[3 ×10^-7;10^-2] where, however, remarkable systematic deviations appear. Our estimated value 0.694 ±0.017 of the asymptotic exponent ν well agrees with the theoretical prediction ν=9/13.     

Influence of high-order optical parameters of tissue on spatially resolved reflectance in the region close to the source

Influences of the scattering phase functions on spatially resolved diffuse reflectance from a homogenous semi-infinite medium close to source are studied with Monte Carlo simulation. It is shown that the influences of optical parameters higher than the second order on the diffuse reflectance are quite weak in the region from 0.3 to several transport mean free pathes when Henyey-Greenstein phase function or a combined phase function of two parameters are used. But this influence may be substantial if the double Henyey-Greenstein function is used to describe the scattering property of tissue.     

Bounds on the decay of correlations for λ(∇φ)4 models

We consider models, with an abelian continuous group of symmetry, of the type: $$H = \sum\limits_x {\left[ {\frac{1}{2}(\nabla _x \phi )^2 + \frac{\lambda }{4}(\nabla _x \phi )^4 } \right].}$$ We generalize Brascamp-Lieb inequalities to get (λ-independent) bounds on the low momentum behaviour of general correlation functions when these are truncated into two clusters. We then use this result to derive an asymptotic expansion (up the second order in λ) of the dielectric constant of this system.     

Comparison of frequency stabilities of the Rb standard and of the He−Ne/CH4 laser stabilized to theE line in methane

The paper reports on the production of an optical time standard on the basis of the He?Ne laser stabilized to theE line in methane and on a comparison of its frequency stability with that of the rubidium standard. It is shown that the stability of the optical standard is better than that of the rubidium one. Frequency measurements of theE line gavev _E=88373149031.2±1.2 kHz. We have also made new measurements on the frequency of the He?Ne laser stabilized to theF ₂ ⁽²⁾ methane line: $$v_F = 88376181602.9 \pm 1.2kHz.$$      

Effects of nanoparticle doping on the phase transitional behaviour of ferroelectric liquid crystal Langmuir–Blodgett composite films

Langmuir–Blodgett films of ferroelectric liquid crystals (FLCs) doped with a low concentration of functionalized Al: ZnO (AZO) nanoparticles were prepared and characterized. Pressure–area isotherms show that the nanoparticles as well as FLC composite systems have the capability to form stable monolayers at the air–water interface. The molecular interaction between nanoparticles and FLC molecules increased during barrier compression, which resulted in increased surface pressure. We observed various phases in isotherms with increasing concentration of nanoparticles in the FLC matrix. An X-ray diffraction profile at a low angle confirmed that FLCs retain their layer structure at a low concentration doping of AZO nanoparticles in the FLC matrix. Atomic force microscopy images indicate that low wt% composites are uniformly deposited without disturbing the translation behaviour of SmC* liquid crystals.     

Photoemission of protons from4He in theΔ-resonance region

High resolution proton energy spectra from the⁴He(γ,p) reaction have been measured with tagged photons in the range E_γ = 130?525 MeV using the large Mainz NaI(T1) spectrometer atΘ _p ^lab =37.1°. Three separate reaction channels were identified, viz.⁴He(γ,p)t two-body breakup,⁴He photodisintegration via two-nucleon photon absorption processes and the quasifree pion production channel. Differential cross sections are presented for each of these channels as a function of photon energy. The sum of the two-nucleon photon absorption and the quasifree pion production differential cross sections, in the CM system, resembles that of the corresponding free-nucleon differential cross section when Fermi motion is taken into account.     

Determination of the nuclear vertex constants for the 7Be ↔ 3He4He vertex using theN/D equations and calculation of the astrophysical S factor for the 4He(3He, γ)7Be reaction

N/D equations taking into account the Coulomb interaction effects are used to consider the phase analysis data on ³He⁴He scattering and determine the nuclear vertex constants for the ⁷Be ? ³He⁴He vertex, where the beryllium nucleus is in the ground (3/2^?) or first excited (1/2^?) states. Information about the asymptotic normalization coefficients of the wave functions of the ⁷Be nucleus in the noted states is derived. The data obtained are used to calculate the astrophysical S factor for the ⁴He(³He, γ)⁷Be reaction.     

Current investigations in theoretical studies of nanostructure–liquid interfaces

Wettability of surfaces is a significant factor affecting properties like water dispersion, spreading, evaporation, dissociation and etc. Surface wettability and wetting behavior of a surface are a subject of broad interest, there is then a great interest to understand better liquid–solid interfaces and water contact angle, in addition to the potential applications in micro- and nano fluidics. This subject is interesting as the growing attractions on the wetting and dynamical properties of water on 2D materials. Also, two clearly defined rigid water layers on solid surfaces are a well-known phenomenon and have been described on several surfaces. Detailed molecular dynamic simulation studies on the origin of this phenomenon are also of general interest. In this current review, recent attempts concerning to the wettability of graphene, graphene oxide and also some metal surfaces obtained by theoretical are presented. Their result contents, therefore, is of interest in order to understand the behavior of water nano-droplets when physisorbed on different substrates. The information is relevant for experimental teams working in this subject, with application in areas as catalysis, friction, surface chemistry, adsorption, etc.     

What is the physics behind the 3He–4He anomaly?

We show that coalescence of nucleons emitted prior to thermalization in highly excited nuclei can explain the anomaly of kinetic energies of helium clusters. A new coalescence algorithm has been included in the statistical approach to nuclear reactions formerly used to describe intermediate mass fragment production. Received: 24 September 1999 / Revised version: 22 November 1999     

Variational Calculation of 4He Tetramer Ground and Excited States Using Realistic 4He–4He Potentials

We calculated binding energies and wave functions of the ⁴He tetramer ground and excited states employing various realistic ⁴He?⁴He potentials which includes the currently most accurate one with the adiabatic, relativistic, QED and residual retardation corrections. We used our Gaussian expansion method (GEM) for ab initio variational calculations of few-body systems. We found that precisely the same shape of the short-range correlation (r _ij < 4Å) in the dimer appear in the ground and excited states of trimer and tetramer. The four kinds of the binding energies of the trimer and tetramer ground and excited states, ${B_3^{(0)}, B_3^{(1)}, B_4^{(0)}}$ and ${B_4^{(1)}}$ , for the different potentials exhibit perfect linear correlations over the range of binding energies relevant for ⁴He atoms; namely, six types of the generalized atomic Tjon lines were observed.     

μSR studies of YFeMnO4

Muon spin relaxation (SR) studies were carried out on YFeMnO₄. Two interesting phenomena were found in measurements of longitudinal relaxation time spectra atT>T _cusp for a single crystal: (1) difference of the relaxation rates between the directions parallel with and perpendicular to thec-axis, and (2) suppression of local field fluctuations in a longitudinal external field. The spectra atT >T _cusp were reproduced with the function exp[-(₀ t)]. The results are discussed under a picture of the magnetic spin fluctuations of triangular antiferromagnets.     

Generalized Ginzburg-Landau equation and the properties of superconductors with Ginzburg-Landau parameter κ close to 1

An expression is derived for the free energy of a superconductor near the critical temperature, taking account of the terms of next highest order in the parameter 1−T/T _c. These terms become important for Ginzburg-Landau parameter values |κ−1|≪1, and in this case, in an external magnetic field H ₀ close to H _c2, the structure of the order parameter is determined by the relative values of the three small parameters |κ−1|, 1−T/T _c, and (H _c2−H ₀)/H _c2. Three types of lattices are investigated: triangular with one and two flux quanta per cell and square with one flux quantum per cell. Zh. éksp. Teor. Fiz. 115, 726–739 (February 1999)