Formalism for obtaining nuclear momentum distributions by the Deep Inelastic Neutron Scattering technique

We present a new formalism to obtain momentum distributions in condensed matter from Neutron Compton Profiles measured by the Deep Inelastic Neutron Scattering technique. The formalism describes exactly the Neutron Compton Profiles as an integral in the momentum variable $y$. As a result we obtain a Volterra equation of the first kind that relates the experimentally measured magnitude with the momentum distributions of the nuclei in the sample. The integration kernel is related with the incident neutron spectrum, the total cross section of the filter analyzer and the detectors efficiency function. A comparison of the present formalism with the customarily employed approximation based on a convolution of the momentum distribution with a resolution function is presented. We describe the inaccuracies that the use of this approximation produces, and propose a new data treatment procedure based on the present formalism.Comment: 11 pages, 8 figure

Raman-like scattering using high energy neutrons: applications to hydrogen and hydrogen-containing materials

The extensive use of Raman spectroscopy in the investigation of the internal molecular motions has been one the most relevant achievements of the last century. Thanks to this experimental technique, thousands of molecular structures have been determined and refined. Nonetheless, the use of photons, mostly in the visible region, has been soon recognized to represent a limiting factor for optically dense materials. The availability of dense beams of high energy neutrons, together with the construction of dedicated spectroscopic instrumentation, has allowed to get rid of this restriction and to take full advantage of the high neutron penetration power in dense matter. Today, the resolving power of neutron instrumentation is not too much dissimilar from that of the corresponding photon instrumentation and the available energy range extends well beyond the eV limit. Thus, allowing to cover the whole vibrational spectrum available to any molecular system. In this contribution, I will show how a dedicated instrument (TOSCA at ISIS) can be effectively used in neutron spectroscopy applications for the investigation of rotovibrational motions in condensed matter systems. Thus becoming an effective aquivalent of a Raman spectrometer, with the invaluable advantage of the neutron penetration power in dense systems. A further advantage of a dedicated high energy neutron spectrometer is represented by the possibility of exploring the application of the Impulse Approximation limit to the center of mass dynamics of molecular systems. By this technique, taking into account the high incoherent neutron scattering cross section of the proton and the extensive energy range available on TOSCA, a wide research area can be exploited allowing to obtain a direct experimental information on the quantum dynamics of liquid and solid bulk hydrogen. Also, it will be shown how the peculiar characteristics of a dedicated neutron Raman instrument can be exploited in the investigation of the quantum dynamics of molecular hydrogen in the nanoconfined geometry of clathrate hydrates, or in detecting its rotational motion on the surface of a carbon nanotube. Last, but not least, important applications of this spectroscopic tool to the investigation of hydrogen-storage materials, including simple and complex light metal hydrides, will be outlined

Monetary Policy and Large Crises in a Financial Accelerator Agent-Based Model

An accommodating monetary policy followed by a sudden increase of the short term interest rate often leads to a bubble burst and to an economic slowdown. Two examples are the Great Depression of 1929 and the Great Recession of 2008. Through the implementation of an Agent Based Model with a financial accelerator mechanism we are able to study the relationship between monetary policy and large scale crisis events. The main results can be summarized as follow: a) sudden and sharp increases of the policy rate can generate recessions; b) after a crisis, returning too soon and too quickly to a normal monetary policy regime can generate a "double dip" recession, while c) keeping the short term interest rate anchored to the zero lower bound in the short run can successfully avoid a further slowdown

The New Sorgentina Fusion Source-NSFS: 14 MeV neutrons for fusion and beyond

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Trophic Activity of Human P2X7 Receptor Isoforms A and B in Osteosarcoma

The P2X7 receptor (P2X7R) is attracting increasing attention for its involvement in cancer. Several recent studies have shown a crucial role of P2X7R in tumour cell growth, angiogenesis and invasiveness. In this study, we investigated the role of the two known human P2X7R functional splice variants, the full length P2X7RA and the truncated P2X7RB, in osteosarcoma cell growth. Immunohistochemical analysis of a tissue array of human osteosarcomas showed that forty-four, of a total fifty-four tumours (81.4%), stained positive for both P2X7RA and B, thirty-one (57.4%) were positive using an anti-P2X7RA antibody, whereas fifteen of the total number (27.7%) expressed only P2X7RB. P2X7RB positive tumours showed increased cell density, at the expense of extracellular matrix. The human osteosarcoma cell line Te85, which lacks endogenous P2X7R expression, was stably transfected with either P2X7RA, P2X7RB, or both. Receptor expression was a powerful stimulus for cell growth, the most efficient growth-promoting isoform being P2X7RB alone. Growth stimulation was matched by increased Ca2+ mobilization and enhanced NFATc1 activity. Te85 P2X7RA+B cells presented pore formation as well as spontaneous extracellular ATP release. The ATP release was sustained in all clones by P2X7R agonist (BzATP) and reduced following P2X7R antagonist (A740003) application. BzATP also increased cell growth and activated NFATc1 levels. On the other hand cyclosporin A (CSA) affected both NFATc1 activation and cell growth, definitively linking P2X7R stimulation to NFATc1 and cell proliferation. All transfected clones also showed reduced RANK-L expression, and an overall decreased RANK-L/OPG ratio. Mineralization was increased in Te85 P2X7RA+B cells while it was significantly diminished in Te85 P2X7RB clones, in agreement with immunohistochemical results. In summary, our data show that the majority of human osteosarcomas express P2X7RA and B and suggest that expression of either isoform is differently coupled to cell growth or activity

The instrument suite of the European Spallation Source

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact o

The experimental determination of the translational kinetic energy of liquid and solid hydrogen

TOSCA is a novel inelastic spectrometer operating on the pulsed neutron source ISIS (UK). It covers a wide momentum and energy range, even though its kinematic region is close to a line in the (k, E) plane. Its use is mainly intended for vibrational spectroscopy. However, taking advantage of its good resolving power, we have carried out a test experiment aimed to use this instrument to measure the centre of mass kinetic energy of molecular hydrogen. The experiment was successful and we have obtained the translational kinetic energy of liquid and solid para-hydrogen improving the overall accuracy by almost an order of magnitude with respect to previous determinations. The data are compared with the results of a Path Integral Monte-Carlo simulations with almost perfect agreement. We have demonstrated that TOSCA can be used for measuring the translational kinetic energy of small molecular systems, taking advantage of the intrinsic incoherence that is introduced in the scattering process by the intra-molecular transitions