Measurement of the generalized polarizabilities of the proton in virtual Compton scattering at Q2=0.92 and 1.76 GeV2

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states.     

Ultrafast laser excitation of CO/Pt(111) probed by sum frequency generation: coverage dependent desorption efficiency

CO photodesorption from Pt(111) induced by femtosecond laser pulses is probed by IR+visible sum frequency generation (SFG). Steady state analysis of SFG spectra at varying CO pressure and laser fluence allows one to measure a approximately 5 orders of magnitude decrease of the photodesorption rate constant when CO coverage decreases from 0.37 to 0.07 monolayer. We ascribe this effect in the framework of the Menzel-Gomer-Redhead mechanism to electron delocalization in the CO layer. The lifetime of electronic excitation decreases when coverage decreases.     

Functionalization of polyoxometalates: from Lindqvist to Keggin derivatives. 1. synthesis, solution studies, and spectroscopic and ESI mass spectrometry characterization of the rhenium phenylimido tungstophosphate [PW11O39(ReNC6H5)]4-

Reaction of [Bu(4)N](4)[H(3)PW(11)O(39)] with [Re(NPh)Cl(3)(PPh(3))(2)], in acetonitrile and in the presence of NEt(3), provided the first Keggin-type organoimido derivative [Bu(4)N](4)[PW(11)O(39)(ReNPh)] (Ph = C(6)H(5)) (1). The functionalization was clearly demonstrated by various techniques including (1)H and (14)N NMR, electrochemistry, and ESI mass spectrometry. Conditions for the formation of 1 are also discussed.     

Determination of the charge state distribution of a highly ionized coronal Au plasma

We present the first definitive measurement of the charge state distribution of a highly ionized gold plasma in coronal equilibrium. The experiment utilized the Livermore electron beam ion trap EBIT-II in a novel configuration to create a plasma with a Maxwellian temperature of 2.5 keV. The charge balance in the plasma was inferred from spectral line emission measurements which accounted for charge exchange effects. The measured average ionization state was 46.8+/-0.75. This differs from the predictions of two modeling codes by up to four charge states.     

Molecular tectonics. Use of the hydrogen bonding of boronic acids to direct supramolecular construction

Tetraboronic acids 1 and 2 have four -B(OH)(2) groups oriented tetrahedrally by cores derived from tetraphenylmethane and tetraphenylsilane. Crystallization produces isostructural diamondoid networks held together by hydrogen bonding of the -B(OH)(2) groups, in accord with the tendency of simple arylboronic acids to form cyclic hydrogen-bonded dimers in the solid state. Five-fold interpenetration of the networks is observed, but 60% and 64% of the volumes of crystals of tetraboronic acids 1 and 2, respectively, remain available for the inclusion of disordered guests. Guests occupy two types of interconnected channels aligned with the a and b axes; those in crystals of tetraphenylmethane 1 measure approximately 5.9 x 5.9 A(2) and 5.2 x 8.6 A(2) in cross section at the narrowest points, whereas those in crystals of tetraphenylsilane 2 are approximately 6.4 x 6.4 A(2) and 6.4 x 9.0 A(2). These channels provide access to the interior and permit guests to be exchanged quantitatively without loss of crystallinity. Because the Si-C bonds at the core of tetraboronic acid 2 are longer (1.889(3) A) than the C-C bonds at the core of tetraboronic acid 1 (1.519(6) A), the resulting network is expanded rationally. By associating to form robust isostructural networks with predictable architectures and properties of porosity, compounds 1 and 2 underscore the usefulness of molecular tectonics as a strategy for making ordered materials.     

Do superconductors have zero resistance in a magnetic field?

We show that dc voltage versus current measurements of a YBa(2)Cu(3)O(7-delta) film in a magnetic field can be collapsed onto scaling functions proposed by Fisher et al. [Phys. Rev. B 43, 130 (1991)] as is widely reported in the literature. We find, however, that good data collapse is achieved for a wide range of critical exponents and temperatures. These results strongly suggest that agreement with scaling alone does not prove the existence of a phase transition. We propose a criterion to determine if the data collapse is valid, and thus if a phase transition occurs. To our knowledge, none of the data reported in the literature meet our criterion.     

Nematic-wetted colloids in the isotropic phase: pairwise interaction, biaxiality, and defects

We calculate the interaction between two spherical colloidal particles embedded in the isotropic phase of a nematogenic liquid. The surface of the particles induces wetting nematic coronas that mediate an elastic interaction. In the weak wetting regime, we obtain exact results for the interaction energy and the texture, showing that defects and biaxiality arise, although they are not topologically required. We evidence rich behaviors, including the possibility of reversible colloidal aggregation and dispersion. Complex anisotropic self-assembled phases might be formed in dense suspensions.     

Phonon screening in high-temperature superconductors

In good conductors optical phonons are usually screened, and therefore not observed. However, sharp features due to infrared-active modes in the copper-oxygen planes are observed in the optical conductivity of Pr1.85Ce0.15CuO4 and YBa2Cu3O6.95. Oscillator strengths indicate that the screening of these modes is poor or totally absent. These materials are compared with eta-Mo4O11, in which lattice modes appear suddenly below the charge-density wave transition. It is proposed that poor screening in the cuprates originates from fluctuating charge inhomogeneities in the copper-oxygen planes.     

Contribution of Russian chemists to foundation of the French chemical society (La Société Chimique de France) (1857–1860)

A little-known history of the contribution of Russian chemists to the foundation of the French Chemical Society (La Société Chimique de France) was discussed in the context of the original proceedings of the earliest meetings of the Society and some other materials of that time (1857–1860). It was shown that prominent Russian chemists, such as A.M. Butlerov, L.N. Shishkov, and some others, were among the founders of the Society and its most active members during the formative years of this scientific organization. Published in Russian in Rossiiskii Khimicheskii Zhurnal, 2007, Vol. 51, No. 6, pp. 5–11. The text was submitted by authors in French.     

Asymptotics of the Bohr radius for polynomials of fixed degree

We obtain a characterization and conjecture asymptotics of the Bohr radius for the class of complex polynomials in one variable. Our work is based on the notion of bound-preserving operators.