3,880 research outputs found
Neutron electric dipole moment from gauge/string duality
We compute the electric dipole moment of nucleons in the large QCD
model by Witten, Sakai and Sugimoto with degenerate massive flavors.
Baryons in the model are instantonic solitons of an effective five-dimensional
action describing the whole tower of mesonic fields. We find that the dipole
electromagnetic form factor of the nucleons, induced by a finite topological
angle, exhibits complete vector meson dominance. We are able to
evaluate the contribution of each vector meson to the final result - a small
number of modes are relevant to obtain an accurate estimate. Extrapolating the
model parameters to real QCD data, the neutron electric dipole moment is
evaluated to be . The
electric dipole moment of the proton is exactly the opposite.Comment: Latex, 4 pages; v2: minor corrections, few comments adde
Assessing the effect of the CAP on farm innovation adoption. An analysis in two French regions
Literature on innovation adoption mechanism has emphasised the positive effect of Single Farm Payments (SFP) and Rural Development Payments on adoption of new technologies. In this context, the expected process of CAP reforming after 2013 is likely to strengthen the role of innovation in the European Union (EU). The objective of this paper is to identify the determinants of the adoption of future innovation, in particular in connection to past innovation, and to assess the role of agricultural policy in the promotion of innovation adoption. The analysis is applied to two regions (Centre and Midi-Pyrénées) in France. Two separate Count models are developed in order to explain famers’ stated intention concerning different intensities of innovation adoption under two different policy scenarios. Preliminary results highlight that the CAP strongly affects the decision to innovate and the innovation intensity, even if there is no statistical significance for the variable connected to the amount of payments or the level of payment per hectare
Multi-Pulse Laser Wakefield Acceleration: A New Route to Efficient, High-Repetition-Rate Plasma Accelerators and High Flux Radiation Sources
Laser-driven plasma accelerators can generate accelerating gradients three
orders of magnitude larger than radio-frequency accelerators and have achieved
beam energies above 1 GeV in centimetre long stages. However, the pulse
repetition rate and wall-plug efficiency of plasma accelerators is limited by
the driving laser to less than approximately 1 Hz and 0.1% respectively. Here
we investigate the prospects for exciting the plasma wave with trains of
low-energy laser pulses rather than a single high-energy pulse. Resonantly
exciting the wakefield in this way would enable the use of different
technologies, such as fibre or thin-disc lasers, which are able to operate at
multi-kilohertz pulse repetition rates and with wall-plug efficiencies two
orders of magnitude higher than current laser systems. We outline the
parameters of efficient, GeV-scale, 10-kHz plasma accelerators and show that
they could drive compact X-ray sources with average photon fluxes comparable to
those of third-generation light source but with significantly improved temporal
resolution. Likewise FEL operation could be driven with comparable peak power
but with significantly larger repetition rates than extant FELs
Dynamic Effects of Wind Loads on a Gravity Damper
AbstractThe gravity damper is safety device used for the air treatment that prevent overpressure inside the unit through the opening. It is a normally closed valve under the effect of the gravity force, which, under the action of the incident air flow, allows to manage any excess mass. Clearly, although the device is rather simple and therefore reliable, the operating conditions may prove burdensome, especially if the gravity dampers are applied to installations of energy transformation, such as the gas turbines; this is mainly due to the need to develop large masses of air at speeds rather incurred. This article describes an experiment carried out on a gravity damper designed to be installed in a gas turbine. The characterization has been performed in numerical (CFD-FEM), considering both the mode shapes and the natural frequencies of the device in working condition as well as any phenomenon of detachment of the fluid that can trigger vortex shedding and subsequently validated in the wind tunnel facilities of the University of Perugia. In particular, what is wanted to be highlighted is the fact that, after a preliminary analysis, it has been clearly evident that, under the operating conditions, the structure would be affected by phenomena of vortex shedding. The shedding frequency is next to some natural frequencies of the structure, with obvious repercussions on the integrity of the structure. An experimental vibration analysis performed in the wind tunnel at flow regime has in fact allowed to identify the phenomenon of lock-in
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