Dispersive viscosity coefficient of nuclear matter

By application of Landau's kinetic theory of a Fermi liquid in non-equilibrium, we have deduced a dispersive, momentum and frequency dependent shear viscosity coefficient η(q, ω) for symmetric nuclear matter. The resulting formula for η is found to be complicated for arbitrary q, ω; however, simple interpretation is possible in the limit of small momentum q → 0. In the static limit, ω → 0, η reduces to the well known kinetic formula for the hydrodynamic viscosity coefficient η_o, while in the high frequency (zero sound) limit, ωτ ? 1, η(ω) is found proportional to (?iω)^? indicating elastic behaviour of nuclear matter. As is discussed shortly, application of these results to finite nuclei unfortunately does not seem justified.     

On the theory of rheological properties of magnetic suspensions

The paper deals with a theoretical study of influence of magnetic field on effective viscosity of suspension of non-Brownian magnetizable particles. It is supposed that experimentally observed magnetorheological effects are provided by chain-like aggregates, consisting of the particles. Unlike previous works on this subject, we take into account that the chains cannot be identical and estimate their size distribution. The following power law (η-η₀)/η₀∼Mn^-Δ, detected in many experiments, is obtained theoretically (η and η₀ are the suspension effective viscosity and the carrier liquid viscosity, respectively, Mn is the so-called Mason number, proportional to the shear rate and inversely proportional to the square of magnetic field). The calculated magnitude of the exponent Δ increases with the applied magnetic field from approximately 0.66 to 0.8-0.9 and slowly increases with the volume concentration ? of the particles. These results are in agreement with known experiments.     

Shear viscosity of superfluid He-A1 at low temperatures

The shear viscosity tensor of the A₁-phase of superfluid ³He is calculated at low temperatures and melting pressure, by using the Boltzmann equation approach. The two normal and superfluid components take part in elements of the shear viscosity tensor differently. The interaction between normal and Bogoliubov quasiparticles in the collision integrals is considered in the binary, decay, and coalescence processes. We show that the elements of the shear viscosities η_xy, η_xz, and η_zz are proportional to (T/T_c)⁻². The constant of proportionality is in nearly good agreement with the experimental results of Roobol et al.     

Study of molecular motions in liquids by electron spin-lattice relaxation measurements,I: Semiquinone ions in hydrogen bonding solvents

The electron spin-lattice relaxation times (T ₁) of a variety of semiquinone ions in hydrogen bonding solvents have been measured by the pulsed saturation recovery technique as a function of temperature (T) and viscosity (η) of the solvent. Also linewidths (ΔH) have been measured in suitable cases in such solvents at low radical concentrations (～10^?4 M). It is observed that (i) the temperature and viscosity dependence ofT ₁ can be fitted to an equation of the form 1/T ₁=A(T/η)+Bexp(-ΔE/RT) whereA andB are constants and ΔE is an activation energy of the order of 1 kcal mole^?1 for these systems; (ii)T ₁ is essentially independent of the radical concentration within the range 10^?3 to 5×10^?2 M; (iii) the concentration independent part of the linewidth (ΔH) increases linearly with (η/T) at sufficiently low temperatures, and (iv) the (η/T) dependent part ofT ₁ is sensitive to the size of the semiquinone as well as that of the solvent molecule, whereas the linewidth which is proportional to (η/T) at high viscosity, low temperature region is not sensitive to the size of the semiquinone and that of the solvent. Based on these observations, it is postulated that in hydrogen bonding solvents, three types of motion contribute significantly to electron spin relaxation:

1. A restricted small step diffusional motion, not involving large changes in the orientation of the molecule, leading to the dominant viscosity dependent contributions toT ₁ and ΔH, due to spin rotation interaction;
2. a large amplitude reorientation of the semiquinone, coupled to translational diffusion, resulting in viscosity dependent contributions toT ₁ and ΔH, throughg-modulation;
3. a hindred rotation of the semiquinone within the solvent cage, contributing toT ₁ due to spin rotation interaction.

The fact thatT ₁ is not sensitive to the concentration of the radicals, is ascribed to the formation of the solvent cage that prevents the close approach of radicals, thereby rendering radical-radical interactions to be weak mechanisms for relaxation, even at relatively high radical concentrations.     

Shear viscosity of the Quark–Gluon Plasma from a virial expansion

We calculate the shear viscosity η in the quark–gluon plasma (QGP) phase within a virial expansion approach with particular interest in the ratio of η to the entropy density s, i.e. η/s. The virial expansion approach allows us to include the interactions between the partons in the deconfined phase and to evaluate the corrections to a single-particle partition function. In the latter approach we start with an effective interaction with parameters fixed to reproduce thermodynamical quantities of QCD such as energy and/or entropy density. We also directly extract the effective coupling α _V for the determination of η. Our numerical results give a ratio η/s≈0.097 at the critical temperature T _c, which is very close to the theoretical bound of 1/(4π). Furthermore, for temperatures T≤1.8T _c the ratio η/s is in the range of the present experimental estimates 0.1–0.3 at RHIC. When combining our results for η/s in the deconfined phase with those from chiral perturbation theory or the resonance-gas model in the confined phase we observe a pronounced minimum of η/s close to the critical temperature T _c.     

Viscometric Studies of Interactions between Hydrophobically Modified Acrylamide Copolymer and Poly(N-isopropylacrylamide) in Dilute Solutions

The viscosity behavior of the dilute aqueous solutions of hydrophobically modified acrylamide copolymer (HMPAM) and poly(N-isopropylacrylamide) (PNIPAM) was investigated. A negative deviation of reduced viscosity of HMPAM + PNIPAM from the theoretical values was observed. Both a conventional viscometry method and a method using an aqueous solution of one polymer as the solvent for the other polymer were used to clarify the mechanism behind the observed viscosity behavior. With the conventional method, the theoretical predictions obtained by the Δb (or α) criterion are contradictory to the experimental results and cannot be applied to describe the interaction between HMPAM and PNIPAM, where Δb is the difference of experimental interspecific interaction coefficient b_m and theoretical b_m,i and α is the difference of experimental Huggins coefficient k_m and theoretical k_m,i. The change of Δ[η]/[η]_i suggests that there is only an attractive interaction between HMPAM and PNIPAM, where Δ[η] is the difference of experimental intrinsic viscosity [η]_m and theoretical [η]_i. Results from the method using an aqueous solution of one polymer as the solvent for the other polymer confirmed the attractive interaction between HMPAM and PNIPAM and indicated that the attachment of the PNIPAM molecules to the hydrophobic groups in HMPAM can disrupt both the initial intra- and intermolecular associations between HMPAM chains simultaneously. The disruption of the original intramolecular association of HMPAM leads to an increase in the intrinsic viscosity [η], while the disruption of the original intermolecular association of HMPAM yields a negative deviation of the reduced viscosity.     

Electron resonance spectra of NCS and vibronically-excited NCO in the gas phase

Near 25 °C, ab initio calculations of the zero-density viscosity of helium gas η _He have an uncertainty of approximately 0.001%, which is 1/40th of the uncertainty of the best measurements. The uncertainties of the published calculations for neon and argon are probably much larger. This paper presents new measurements of the viscosities of neon, argon, and krypton at 25 °C made with a capillary viscometer that was calibrated with helium. The resulting viscosity ratios are η _Ne/η _He?=?1.59836?±?0.00037, η _Ar/η _He?=?1.13763?±?0.00030, and η _Kr/η _He?=?1.27520?±?0.00040. The argon ratio agrees with a recent, unpublished calculation to within the combined uncertainty (measurement plus calculation) of 0.032%. The neon ratio is smaller than the calculated value by 0.13%.     

The phase shifts leading to the broadening and shift of spectral lines

The classical theory of collisional broadening and shift parameters (β, δ) of an isolated spectral line was used to obtain simple analytical formulas for calculating both β and δ. These formulas were obtained on the assumption that the short range interaction is effective only in the broadening while the long range is effective in the shift of the spectral line. These parameters β and δ depend on the limiting phase shifts responsible for broadening η_b and shift ηδ. It was found that the values of η_b and η_δ are not equal to each other as was proposed by Weisskopf η_b=η_δ=1. The maximum and average values of η_b (η_b max, η_b av) and η_δ (η_δ max, η_δ av) were obtained by numerical evaluation, using different inverse power potentials. By introducing these parameters into the approximated formulas for β and δ using Van der Waals and Lennard-Jones potential, it was found that the results of calculations for (β and δ) with different atomic transitions perturbed by different inert gases are in close agreement with earlier results. Those results, obtained earlier, were based on the Lindholm-Foley theory especially with the average values of η_b [η_b av=0.6057] and the maximum values of η_δ [η_δ max=1.57625]. The impact parameters ρ_b and ρ_δ leading to the broadening and shift of the spectral line were also obtained for different interactions. It was found that the end parameter for the broadening ρ_b is not equal to the starting parameter for the shift ρ_δ.     

The parity of regge cuts

The exchange of two reggeons of naturalities η_a and η_b will in general produce a J plane cut in amplitudes of both naturalities ± η_aη_b. We show that the amplitudes of naturality ? η_aη_b are suppressed, and this suppression grows with the energy, regardless of the particular model used for the vertices coupling the reggeons to the external particles. In consequence, for cuts where the two reggeons are any of ?, A₂, f, ω, or the pomeron, the natural-parity cut (if it is present) will dominate over the unnatural parity. We also show that cut vertices which contribute to both naturalities satisfy the conspiracy condition at t = 0 by suppressing both contributions equally. Away from t = 0, the η = + η_aη_b contribution can recover from this suppression. This behaviour is of importance in, for example, the pion-pomeron cut.We compare these conclusions with experiment.     

Nuclear quadrupole resonance in C-nitro compounds

The nitrogen-14 nuclear quadrupole resonance spectra of CH₃NO₂ and of C₆H₅NO₂ were measured at 77°K. The results are: CH₃NO₂: e²qQ/h = 1694.6 kHz, η = 0.4240 and C₆H₅NO₂: e²qQ/h = 1424.9 kHz, η = 0.4039.     

Temperature effect on the molecular interactions between two ammonium ionic liquids and dimethylsulfoxide

To understand the molecular interactions between newly synthesized ammonium ionic liquids (ILs) and highly polar solvent dimethylsulfoxide (DMSO), precise measurements such as densities (ρ), ultrasonic sound velocities (u) and viscosities (η) have been performed over the whole composition range at temperature ranging from 298.15 to 308.15 K and at atmospheric pressure. The ILs investigated in the present study included diethyl ammonium acetate ([Et₂NH][CH₃COO], DEAA) and triethyl ammonium acetate ([Et₃NH][CH₃COO], TEAA). Further, to gain some insight into the nature of molecular interactions in these mixed solvents, we predicted the excess molar volume (V^E), the deviation in isentropic compressibilities (ΔK_s) and deviation in viscosity (Δη) as a function of the concentration of IL using the measured properties of ρ, u and η, respectively. Redlich-Kister polynomial was used to correlate the results. The intermolecular interactions and structural effects were analyzed on the basis of the measured and the derived properties. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding between ILs and DMSO molecules and their structural factors.     

Anisotropies in momentum space at finite shear viscosity in ultrarelativistic heavy-ion collisions

Within a parton cascade we investigate the dependence of anisotropies in momentum space, namely the elliptic flow v₂=〈cos(2?)〉 and the v₄=〈cos(4?)〉, on both the finite shear viscosity η and the freeze-out (f.o.) dynamics at the RHIC energy of 200 GeV. In particular the impact of the f.o. dynamics is discussed looking at two different procedures: switching-off the collisions when the energy density goes below a fixed value or reducing the cross section according to the increase in η/s from a QGP phase to a hadronic one. We address the relation between the scaling of v₂(p_T) with the eccentricity ?_x and with the integrated elliptic flow. We show that the breaking of the v₂(p_T)/?_x scaling is not coming mainly from the finite η/s but from the f.o. dynamics and that the v₂(p_T) is weakly dependent on the f.o. scheme. On the other hand the v₄(p_T) is found to be much more sensitive to both the η/s and the f.o. dynamics and hence is indicated to put better constraints on the properties of the QGP. A first semi-quantitative analysis shows that both v₂ and v₄ (with the smooth f.o.) consistently indicate a plasma with 4πη/s∼1−2.     

High-resolution mapping of the energy conversion efficiency of solar cells and silicon photodiodes in photovoltaic mode

We demonstrate an optical technique to derive the two-dimensional energy conversion efficiency (η_CE), fill factor (FF) and external quantum efficiency (η_QE) distributions across the surface of photovoltaic devices. A compact, inexpensive optical-feedback laser diode microscope is constructed to acquire the confocal reflectance and efficiency maps enabling the observation of the local parametric behavior in silicon photodiodes in photovoltaic mode and single-junction solar cells. The η_CE and η_QE distributions are greatly influenced by local parasitic resistances that depend on laser irradiance. These parasitic resistances decrease the η_CE and η_QE values with distance from the contact electrode at high laser irradiance. The optical technique enables microscopic comparison of η_CE and η_QE within the pn-overlay region of the photodiode sample, revealing its optimization for photodetection rather than power generation. The technique also elucidates the decreasing local η_CE of the solar cell under intense irradiation.     

Spectroscopy of η′ Mesic Nuclei with (p, d) Reaction

We are going to perform an inclusive spectroscopy experiment of η′ mesic nuclei with the ¹²C(p,d) reaction to study in-medium properties of the η′ meson. In nuclear medium, the η′ meson mass may be reduced due to partial restoration of chiral symmetry. In case of sufficiently large mass reduction and small absorption width of η′ at normal nuclear density, peak structures of η′ mesic states in ¹¹C will be observed near the η′ emission threshold even in an inclusive spectrum. The experiment will be carried out at GSI with proton beam supplied by SIS using FRS as a spectrometer. The detail of the experiment is described.     

Rapid viscous flow of a nematic liquid crystal in the vicinity of the nematic-smectic <Emphasis Type="Italic">A</Emphasis> transition

The resistance to shear flow is investigated theoretically for polar liquid crystals, such as 4-n-octyl-4′-and 4-n-octyloxy-4′-cyanobiphenyls. It is established that the lowest resistance to shear flow at temperatures in the vicinity of the nematic-smectic A phase transition point T _NA is observed when the nematic director is oriented perpendicular to both the flow velocity vector and the flow velocity gradient. The three Miesowicz shear viscosity coefficients η_i (i=1–3) at temperatures close to the phase transition temperature (tens of millikelvins from T _NA ) and far from this transition are calculated in the framework of the Ericksen-Leslie theory. The decrease in the viscosity coefficients in the order η₂>η₁>η ₃ is explained by the fact that fluctuations of the local smectic order in the nematic phase lead to a singular behavior of the viscosity coefficient η₂, whereas the other two viscosity coefficients η₁ and η₃ are not affected by order parameter fluctuations.     

Nuclear effects in 800 GeV proton interactions

We discuss here the nuclear effects in multiparticle production processes in 800 GeV proton-emulsion nuclei interactions. The multiplicity of medium energy particles (N _g ) was used as a measure of the average number of projectile collisions (<v(N _g )>). To study nuclear effects, we determined <v(N _g )> and ratio of normalized rapidity density of all produced charged particles in hadron-nucleus to hadron-hadron interaction,R(N _η ). It was found that the average multiplicity of shower particles increases with <v(N _g )>. From theR(N _η ) distribution, we find; a strong maxima in the target fragmentation region, a plateau in the central region and depletion of particle density in the projectile fragmentation region.     

Constraints on distribution amplitudes of the η and η′ mesons in the light of new experimental results

Constraints on the distribution amplitudes of the SU _f (3) singlet η ₁ and octet η ₈ states are obtained from a comparison of the theoretical predictions for the η γ and η′γ electromagnetic transition form factors with experimental data of the CLEO and BaBar Collaborations. In calculations of the form factors F _η(η′)γ (Q ²) the power-suppressed corrections arising from the end-point integration regions x→0,1 are taken into account by employing the infrared renormalon approach. It is demonstrated that the power-suppressed corrections allow one to describe the data on the η γ and η′γ transitions within a framework of the SU _f (3) octet–singlet basis using one mixing angle for both the physical states and decay constants.     

Pseudoscalar mesons in the c-c and b-b systems

It is shown that the pseudoscalar η_c and “η_c” (η_b and “η_b”) with M ≈ 2.80 and 3.51 GeV (9.17 and 9.88 GeV) can be predicted by using the radial mixing model, where the “η_c” and “η_b” are the excited 0^- states in the $\text{c-}\text{c}$ and $\text{b-}\text{b}$ systems, respectively, and the former would correspond to the observed 0^- meson with M ≈ 3.45 GeV in charmonium.