Fission fragment γ-ray anisotropies

The anisotropy of fission fragment γ-rays in the reactions ²³⁹Pu(n_th, f) and ²³³U(n_th, f) have been measured. In this work, two γ energy bands were used to confirm the energy independence of the anisotropy. For the γ energy band of 0.49–0.65 MeV and the γ energy band of 0.83–0.92 MeV the anisotropies were found to be 0.18 ± 0.03, 0.13 ± 0.03 and 0.19 ± 0.03, 0.11 ± 0.03 for the ²³⁹Pu and ²³³U targets respectively. The data are corrected for the Doppler effect and the time of flight was large enough to eliminate the counting of neutrons. Comparisons with the theories of Nix and Swiatecki, and Strutinsky have been made and approximate correction for fragment rotation along fission axis made.     

Gauge-invariant temperature anisotropies and primordial non-Gaussianity

We provide the gauge-invariant expression for large-scale cosmic microwave background temperature fluctuations at second-order perturbation theory. This enables us to define unambiguously the nonlinearity parameter f(NL), which is used by experimental collaborations to pin down the level of non-Gaussianity in the temperature fluctuations. Furthermore, it contains a primordial term encoding all the information about the non-Gaussianity generated at primordial epochs and about the mechanism which gave rise to cosmological perturbations, thus neatly disentangling the primordial contribution to non-Gaussianity from the one caused by the postinflationary evolution.     

A coercivity model with competing anisotropies

In standard coercivity theory, formulae derived for homogeneous material are applied to inhomogeneous situations. The model considered here contains inherent inhomogeneity in the form of competing volume and surface anisotropies. Its coercivity never exceeds half the Stoner-Wohlfarth value, decreases with particle size, and vanishes at a finite critical size.     

Magnetic anisotropies in FeCo fine particles

 The single-domain particles, especially FeCo fine particles have many applications in magnetic information technology. We have prepared Fe_1−xCo_x fine particles for different x by borohydride method and measured the magnetic and structural properties of the samples. We have then determined the variations of coercivity and anisotropy energy versus x in Fe_1−xCo_x fine particles. The obtained results have been analyzed on the basis of various magnetic anisotropies. Magnetic anisotropies affect the coercivity of the medium for each x   as follows: shape and crystal anisotropies for x=0$x=0$, surface and crystal anisotropies for x=1$x=1$, shape, induced and crystal anisotropies for x=0.3$x=0.3$ and 0.5, and shape and induced anisotropies for x=0.45$x=0.45$.     

Magnetic anisotropies of some aromatic molecules

A common method for the estimation of uncertainties introduced by surface and impurity effects into experimental measurements of virial coefficients is described. The sign and the amplitude of the second virial coefficient response to perturbation caused by adsorption of molecules on the internal surface of the vessel have been determined. It has been shown that the magnitude of the second virial coefficient distortion depends on such competing factors as adsorption-impurity perturbation parameter, mixture composition which has been corrected taking into account this perturbation, and the nature of the impurity expressed in terms of its second virial coefficient and of the solvent-impurity cross second virial coefficient. The character of the Lennard-Jones 12–6 potential parameters perturbation, caused by the adsorption-impurity effects, is determined using second virial coefficient data inversion technique. Numerical estimates are made for nitrogen, helium, argon, xenon, their binary mixtures, and also for krypton-sulphur hexafluoride gaseous mixtures.     

Probing hadronic polarizations with dilepton anisotropies

We investigate the production of e ⁺ e ^? pairs from p + Be and nucleus-nucleus collisions from 2 GeV/A to 200 GeV/A within a covariant transport approach and focus on the dilepton angular anisotropies as a function of the dilepton invariant mass. Whereas the low mass regime yields information about the Dalitz decays of the Δ, η and ω, above M ≈ 0.5 GeV the angular anisotropies provide additional information about the π ⁺ π ^? → ρ ⁰ → e ⁺ e ^? channel in the medium. The anisotropy coefficient is found to change its sign for M > 0.5 GeV in case of nucleus-nucleus reactions when increasing the bombarding energy from 2 GeV/A to 200 GeV/A which sheds some light on the ππ → ρ dynamics.     

Collisional polarizability anisotropies of the noble gases

We present a simple approximate calculation of the pair polarizability anisotropy β(R) of interacting inert gas atoms, including overlap effects. The overlap contribution to β(R) is found to be relatively long-range and to have an exponential form. We compare our results with recent ab initio Hartree-Fock calculations and experimental low density depolarized scattering spectra; agreement is excellent.     

CMB polarization as complementary information to anisotropies

The origin of CMB polarization is reviewed. Special emphasis is placed on the cosmological information encoded in it: the nature of primordial fluctuations, the connection with the inflation paradigm. Insights into more recent epochs are also discussed: early reionization and high redshift matter distribution from CMB lensing. To cite this article: J. Kaplan et al., C. R. Physique 4 (2003).     

CMB anisotropies and inflation from non-standard spinors

The apparent alignment of the cosmic microwave background multipoles on large scales challenges the standard cosmological model. Scalar field inflation is isotropic and cannot account for the observed alignment. We explore the imprints, a non-standard spinor driven inflation would leave on the cosmic microwave background anisotropies. We show it is natural to expect an anisotropic inflationary expansion of the Universe which has the effect of suppressing the low multipole amplitude of the primordial power spectrum, while at the same time to provide the usual inflationary features.     

Hydrogen-deuterium exchange on iron: Kinetic anisotropies

The equilibration and replacement reactions between H₂ and D₂ have been studied, at 294 K and at pressures comprised between 10^?6 and 10^?2 Torr, on defined surfaces of iron. Preparation of the samples has been done under UHV conditions using argon ion bombardment and annealing y rf induction currents as well as electron bombardment. The reactivity for the equilibration reaction follows the pattern (poly) #62; (110) #62; (100) #62; (111) with a five fold difference between the most reactive, (poly), and the less reactive (111) surfaces. The equilibration rate shows a pressure dependence with a fractional order of about 0.85 for each of the four samples considered within the experimental pressure range used. Replacement experiments indicate the presence of two definite and different processes on these materials: an initial, extremely fast exchange (stage I) associated to a surface reaction, and a second slower exchange (stage II) which we attribute to dissolved species. The amount of dissolved hydrogen (or deuterium) increases regularly with exposure time prior to replacement. Material balances and thermodynamic onsiderations allow the calculation of the adsorbed and dissolved amounts. The fast exchange proceeds via one-atom exchanges only on the oriented crystal surfaces whereas twoatom exchanges are also present, although in small proportion, on the polycrystalline samples.     

Magnetic anisotropies of late transition metal atomic clusters

We analyze the impact of the magnetic anisotropy on the geometric structure and magnetic ordering of small atomic clusters of palladium, iridium, platinum, and gold. We have employed a noncollinear implementation of density functional theory where the spin-orbit interaction has been included self-consistently. The size of the clusters ranges from two to five, six, or seven atoms, depending on the element. Our results highlight the relevance of the spin-orbit interaction in the magnetic properties of small atomic clusters made of fourth- and fifth-row elements.