Commentary on “Mechanical properties of monodomain side-chain nematic elastomers” by P. Martinoty,P. Stein,H. Finkelmann,H. Pleiner and H.R. Brand

We discuss the background to static and dynamic soft elasticity. The evidence in the static case and the symmetry basis for soft and semi-soft elasticity is well understood. By contrast the dynamic analogy is less clear. Lack of clean time scale separation clouds the interpretation of director relaxation keeping up, or not, with imposed strains. However, the reduction in modulus between geometries obtaining at low frequencies and being lost at high frequencies confirms that director reaction indeed determines dynamical semi-softness.Received: 13 April 2004, Published online: 17 August 2004PACS: 83.80.Va Elastomeric polymers - 61.30.-v Liquid crystals - 83.60.Bc Linear viscoelasticity     

E.P.R. study of γ-irradiated single crystals of K2C2O4.H2O and (NH4)2C2O4.H2O

The electron paramagnetic resonance of γ-irradiated single crystals of K₂C₂O₄.H₂O and (NH₄)₂C₂O₄.H₂O has been studied. The spectra show interesting microwave power saturation effects. The singlet spectrum is attributed to the C₂O₄ ^- radical derived from the C₂O₄ ^-- ion. The principal g-values are determined to be 1·998, 2·0028 and 2·0004. Certain weak lines are observed with different power saturation and interpreted as due to OH radicals derived from water molecules in the crystal lattice.     

Implications of axion-like particles from the Fermi-LAT and H.E.S.S.observations of PG 1553+113 and PKS 2155−304

We investigate the axion-like particle(ALP)-photon oscillation effect in the high-energy y-ray spectra of PG 1553+113 and PK.S 2155-304 measured by Fermi-LAT and H.E.S.S.The choice of extragalactic background light(EBL)model,which induces the attenuation effect in observed y-ray spectra,affects the ALP implications.For the ordinary EBL model that prefers a null hypothesis,we set constraints on the ALP-photon coupling constant at 95% C.L.as gay 5×10^-11 GeV^-1 for the ALP mass 〜10 neV.We also consider the CIBER observation of the cosmic infrared radiation,which shows an excess at wavelengths of -1μm after the substraction of foregrounds.High-energy gamma-rays from extragalactic sources at high redshifts would suffer from a more significant attenuation effect caused by this excess.In this case,we find that the ALP-photon oscillation would improve the fit to the observed spectra of PKS 2155-304 and PG 1553+113 and find a favored parameter region at 95%CL..     

Alignment of non-polar molecules—electric field effects in the 2H N.M.R. spectrum of perdeuterobenzene in solutions with nitrobenzene

Electric field experiments on the ²H N.M.R. spectrum of perdeuterobenzene, dissolved in nitrobenzene, are reported. The alignment of the polar molecules, induced by a strong electric field, is transferred to the non-polar ones and as a result their N.M.R. spectrum is modified.

Local field models, e.g. those of Lorentz and Onsager, treat the environment of a molecule as a continuum and are unable to explain the alignment of the non-polar molecules. Intermolecular interactions are essential. In an expression for the alignment these interactions are described in terms of correlation functions for the mixture.

N.M.R. and Kerr data of nitrobenzene-benzene solutions have been compared. The Kerr constant of a binary mixture is shown to depend on the alignments of both the polar and non-polar component. N.M.R. electric field experiments may be useful to separate these two contributions.     

Nachruf Prof. Hübner

Abstract

Representative water samples were collected from different oases in the western desert of Egypt to examine characteristics of Egyptian groundwater. Chemical data recognized two basic groundwater types; alkali bicarbonate and alkali chloride, where sodium has the highest concentration. For each region the median SD, δ¹⁸ 0 and ionic strength of water calculated from their chemical analyses are recorded and plotted.

Generally, the results of isotopic content measurements of the groundwaters from the different oases in the western desert indicate the fossile origin of these waters. The values of δD and δ¹⁸ 0 of the western desert oases' waters are characteristic of old paleowaters from the Nubian sand aquifer. Modern sparse rainfall data suggest that any precipitation will exhibit moderate to large positive isotopic content enrichments and cannot be a source for these waters. They have been in no connection with the Nile water, moreover the change in isotopic composition is due to evaporation which is now ineffective at deeper levels.     

The low-temperature 13C and 2H spectra and relaxation rates of methyl groups depend on the azimuth of B0 in the molecular frame. Those of 1H do not. Why?

It is shown that the answer to the question asked in the title is: Because the axial symmetry axes of the H-H dipolar coupling tensors in a -CH3 group are perpendicular to the (assumed) threefold axis of the group. By contrast, those of the 13C-H dipolar and 2H quadrupolar coupling tensors are not. The use of "symmetry adapted" spin functions and of a symmetry adapted form of the (dipolar) coupling Hamiltonian greatly simplifies the analysis.     

Another calculation of the Higgs mass and the top mass from the principles of H. B. Nielsen: m H ≅ 163GeV for M t ≅ 190GeV

We calculate the Higgs mass and the top mass starting from the principle that there are two, essentially degenerate minima in the Higgs effective potential; the second is at about the Planck energy scale M _P = 1.2 × 10¹⁹ GeV. Thus the parameter of the quartic self-coupling λ _h vanishes, as does β _λH at M _P. The new element is the addition of a quantum interaction term which couples the square of the Higgs field to the square of a pseudoscalar field, in the domain of the energy scale between about 10¹⁴ GeV and M _P. We modify β _λH at one loop. The pseudoscalar field which is introduced may be the field which is responsible for a spontaneous breakdown of discrete symmetry — for CP noninvariance at an energy scale of (10¹⁵–10¹⁶) GeV. The result is then a closer value for m _H ? 163 GeV for the top pole-mass M _t ? 190 GeV; both values are now close to the electroweak scale parameter $\langle {\phi _H}\rangle /\sqrt 2 = 175{\text{ GeV}}$ . In terms of dimensionless running coupling parameters, which determine the masses near to the electroweak scale, we get $\sqrt {{\lambda _H}} \cong 0.06$ and $gt/\sqrt 2 \cong 0.72$ , values that are close to each other and close to unity.     

Transport and relaxation properties of isotopomeric hydrogen–helium binary mixtures. I. H2–He mixtures

An extensive comparison has been carried out between calculated and measured bulk properties of H₂–helium mixtures. Detailed comparisons are presented for the interaction second virial coefficient, binary diffusion, mixture shear viscosity and thermal conductivity, rotational relaxation, thermal diffusion field-effects, collision broadening of the depolarized Rayleigh light scattering spectrum, and flow birefringence. Scattering calculations have been carried out for the ab initio potential energy surfaces obtained by Tao (1994, J. chem. Phys., 100, 4947) and Schaefer and Köhler (1985, Physica A, 129, 469). The values for the various bulk gas properties calculated from these two potential surfaces are generally found to lie within or near the experimental uncertainties.     

On the measurement of ¹⁵N-{¹H} nuclear Overhauser effects. 2. Effects of the saturation scheme and water signal suppression

Measurement of steady-state (15)N-{(1)H} nuclear Overhauser effects forms a cornerstone of most methods to determine protein backbone dynamics from spin-relaxation data, since it is the most reliable probe of very fast motions on the ps-ns timescale. We have, in two previous publications (J. Magn. Reson. 192 (2008) 302-313; J. Am. Chem. Soc. 131 (2009) 6048-6049) reevaluated spin-dynamics during steady-state (or "saturated") and reference experiments, both of which are required to determine the NOE ratio. Here we assess the performance of several windowed and windowless sequences to achieve effective saturation of protons in steady-state experiments. We also evaluate the influence of the residual water signal due to radiation damping on the NOE ratio. We suggest a recipe that allows one to determine steady-state (15)N-{(1)H} NOE's without artifacts and with the highest possible accuracy.     

W.H.布拉格的科学生涯与科学贡献

W．H．布拉格是20世纪伟大的英国科学家,但长期以来物理学界对他的了解不够全面．本文回顾了W．H．布拉格的人生轨迹,较系统地介绍了他的科学贡献,揭示了一些令人深思的问题,对他在科学界的深远影响也作了充分肯定     

Comment on “The growth of Fe overlayers on Ag(100)” by G.C. Smith,H.A. Padmore and C. Norris

Smith, Padmore and Norris have claimed that the first three monolayers of Fe grown at room temperature on Ag(100) form a strained fcc γ-Fe layer for which the mismatch to the substrate is 11%. We point out a simple error in their calculations of mismatch, and suggest instead that such growth produces a bcc α-Fe(100) film, for which the mismatch to the substrate is only 0.8%.     

Comment on “Foam imbibition in microgravity. An experimental study” by H. Caps,H. Decauwer,M.-L. Chevalier,G. Soyez,M. Ausloos and N. Vandewalle

In a recent paper, [1] described parabolic flight experiments showing the movement of liquid into the foam during the microgravity phase. In this comment, we present a detailed theory of this process, supported by numerical calculations, confirming their conclusion that the wetting front moves with the square root of time. We further show that this diffusion process is similar for different surfactant systems, which allows us to provide bounds on the value of the diffusion coefficient.Received: 28 April 2004, Published online: 3 August 2004PACS: 82.70.Rr Aerosols and foams - 83.80.Iz Emulsions and foams     

‘Factors of ignorance’ and the rationalized M.K.S.A. system of units

An attempt is made, by means of an allusive (rather than a systematic) historical account of the development of the subject, to exhibit the essentially unique character of the rationalized M.K.S.A. system of units. The establishment of this system involved one arbitrary decision—the determination to retain unaltered the size of the previously accepted unit of current. Thereafter, any choice of derived units, other than the choice actually made, would have destroyed the basic symmetry of the formulation.