[en] Uranium is the only element know so far to exhibit a charge-density wave instability. The structure below the transition (T₀∼43 K) is complex consisting of small displacements of the atoms away from their α-phase equilibrium structure position. It is usually assumed that this transition involves a soft-phonon condensing at (or near) the charge density wave position in the Brillouin zone. New high-resolution neutron scattering experiments at low temperature show that the principal softening occurs exactly at the charge-density wave positions, as expected for a pure Fermi-surface instability. This result is in disagreement with a model of Yamada (1993), but in agreement with a recent theory which suggests that the charge-density wave vector components are related to the Fermi-surface nesting topology. (authors)

[en] PkFit - a user friendly software for the Macintosh, Open VMS and UNIX workstations - is intended for the data processing of neutron three-axis spectrometers. Inelastic, quasi-elastic or elastic spectra are fitted by a linear background plus a series of peak functions. The program offers several built-in peak functions but the user may add its own peak shapes through stand-alone code resources. The model can include the Bose factor, the k_f or k_i correction, the neutron absorption and the convolution of the signal with a one-dimensional or a four-dimensional resolution function. The latter is calculated from the configuration parameters of the spectrometer through the help of the Cooper-Nathans method or the Popovici method. Fast 4D integration is performed by means of new methods, one based on a Monte-Carlo integration technique and the other based on a Gaussian approximation. (orig.)

[en] Complete text of publication follows. The alpha phase of uranium is known to exhibit a charge-density wave (CDW) transition at T₀ = 43K. The main component of the displacement pattern associated with the CDW has the symmetry of the Σ₄ phonon mode, and earlier experiments have shown that the transition may be regarded as driven by a softening of this phonon mode at, or at least near, the point (1/2, 0, 0) inside the Brillouin zone (1). Recently, this phonon softening has been examined just above T₀ in more detail with neutron inelastic scattering, it was found that the minimum position of the phonon frequency is at an incommensurate position (q_x ∼0.5, q_y, q_z) (2). It is at this point that elastic scattering is seen just below T₀. These experiments support the recent theoretical treatment (3) which proposes that all three components of the CDW wavevector are determined by the nesting properties of the Fermi surface. (author)

[en] The experimental data on incommensurate phase versus temperature, as they have been obtained by high resolution inelastic neutron scattering, are compared to theoretical models. In the experiments reported we have set out to examine the phonon dispersion surface to verify that the charge-density wave (CDW) state is present continuously at temperature even above T_CDW. The position of the phonon minimum (q_min = q_CDW), as well as the detailed shape of the dispersion surface of phonon modes over an extended areas in the (E, q) space, is important in view of the debate on the origin of the CDW at the Peierls transition (2nd_order phase) and gives rise to a further modulation of the structure. This work confirms that the CDW state has precursor effects before the phase transition, there is a strong coupling between phonon and electronic states and that a 'soft-mode transition' occurs at T_CDW. This result is compared to theories discussing the origin of the CDW state

[en] Harvested wood products are not included yet as a sink in the national greenhouse gas inventories. Following the current IPCC guidelines for the agriculture, forest and land use sectors (AFOLU), carbon is considered as being released as the tree is harvested. Nevertheless, products are manufactured from harvested trees and can store carbon over long periods of time. Negotiations are under way to include carbon storage in harvested wood products in the national inventories for the post-2012 period of the Kyoto Protocol. IPCC guidelines exist already for such a reporting which is for now done only on a voluntary basis. The French Ministry for Agriculture and Fisheries has commissioned FCBA, assisted by Ernst and Young consulting firm, to calculate the harvested wood product (HWP) contribution to France's greenhouse gas inventory provided to the United Nation Convention on Climate Change (UNFCCC) for the year 2005. The methodology used is to show strong guaranties of transparency and reliability to promote the eligibility of harvested wood products as a sink. Three methods are described in the guidelines to calculate the variables: TIER 1, TIER 2 and TIER 3. TIER 1 corresponds to a calculation based on default equations and data provided by IPCC, TIER 2 to a calculation based on default equations but country specific data and TIER 3 to a calculation based on country specific equations and data. The method used for products in use corresponds to TIER 3 which corresponds to the best level of precision and specificity. For products places in solid waste disposal site, the method used is TIER 2. The study analyses five stocks or pools of carbon downstream of the forest in the wood chain and the paper sector: wood construction, wood furniture, wood packaging, wood energy, pulp and paper. For each sector, the stocks are identified (intermediate technical stocks and final in service stocks), and then quantified. Depending on the lifetime of the products considered, different methods have been used to calculate the stocks. For short lived products, the accumulation rate method has been used (wood energy except firewood, intermediate stocks, paper and board, light packaging). For products having a lifetime longer than one year, the demographic method has been used (firewood, construction products, heavy packaging, furniture). The furniture and construction products have much longer lifetime than the other products: up to 25 years for furniture and up to 75 years for construction products such as wood frames. In the study, a development is also done on the question of the acceptability of imported forest products. Indeed it is important to account for carbon stored in wood from legal cutting or grown in a forest managed in a sustainable way. Considering the stock change approach, the construction sector is the main contributor to the variation of carbon stock (55% of total) along with the variation of carbon stored in landfills (32% of total). As far as the construction sector is concerned, the stock increase comes from wood panels and wood frames. The packaging sector represents 10% of the stock variation. This contribution could be circumstantial due to an increase in pallet consumption in 2005 following a decrease in 2004. In the same way, the small negative contribution of paper and board products is also circumstantial. The wood energy sector is a small part of the stock variation whereas it represents the biggest volume of wood consumed. Results are sensitive to assumptions made on lifetimes. If the lifetime of structural element is reduced from 75 years to 40 years (47% decrease), the stock variation of the construction sector decreases by 30% and the total stock variation decreases by 20%. For products with short lifetime, stock variation is proportional to the lifetime variation. As far as the production approach is concerned, the contribution of harvested wood product to carbon stock variation is smaller by 25% as compared with the stock change approach. This smaller value is mainly linked with a smaller contribution of the stock variation in landfill. This is explained by the fact that for the calculation of stock change in landfills, IPCC allows that only domestic landfills may be accounted for as it is difficult to estimate the fate of exported products. Wood product exported and then landfilled abroad are not included in the calculation of stock variation in landfills although exported products are included in the calculation of the variation of products in use. The construction sector is also responsible for a smaller value for the production approach. Indeed, wood used for industrial light wood frames and glulam are mainly imported and the exports of such products are small. This is partially compensated by the panels for the export rate is high. Wood panel production in France is more important than the French wood panel consumption; as a result the production approach gives a better result than the stock change approach for the panels

[en] Neutron scattering measurements have been performed with time-of-flight spectrometers on an YbB₁₂ polycrystal. The spectra show clearly the presence of magnetic excitations and a gap at around 14 meV. At low temperature, two broad signals (FWHM ∼ 7 meV), one asymmetric, the other one of Lorentzian shape, are well defined. After subtracting the phonon contribution, the former signal is further decomposed into a sharp 15.5 meV peak and a broader 20 meV peak. The 15.5 meV peak behaves similarly to that of the exciton at 14.5 meV for SmB₆ as regards both the Q- and T-dependencies. The 20 meV peak was identified as manifesting a transition from a localized Kondo singlet with a gap to a magnetic state. With decreasing temperature, the gap disappears and the scattering becomes quasi-elastic, like for the metallic Kondo system. The second signal, centred at 37 meV, was assigned previously to a crystal-field excitation. However, the observed behaviour is anomalous, indicating a shift of the intensity from the lower peaks to the higher peak, suggesting a change in the T_K-value due to lattice distortion. (author)