1,721,082 research outputs found
Inverse Compton constraints on the Dark Matter e± excesses
Full text linkRecent results from experiments like PAMELA have pointed to excesses of e± in cosmic rays. If interpreted in terms of Dark Matter annihilations, they imply the existence of an abundant population of e± in the galactic halo at large. We consider the high energy gamma ray fluxes produced by Inverse Compton Scattering of interstellar photons on such e±, and compare them with the available data from EGRET and some preliminary data from FERMI. We consider different observation regions of the sky and a range of DM masses, annihilation channels and DM profiles. We find that large portions of the parameter space are excluded, in particular for DM masses larger than 1 TeV, for leptonic annihilation channels and for benchmark Einasto or NFW profiles. © 2009 Elsevier B.V. All rights reserved
Erratum to: Wino-like Minimal Dark Matter and future colliders[JHEP10(2014), DOI: 10.1007/JHEP10(2014)033]
No full textSecond-order approximation pseudo-rigid model of flexure hinge with parabolic variable thickness
No full textThe paper deals with a study to determine an accurate pseudo-rigid model of flexure hinges with parabolic variable thickness subjected to pure applied moment. The work can be considered an extension of previous investigations on constant-thickness flexure hinges. Starting from the observation on second-order kinematic invariants of the relative motion between two bodies connected by such a flexure hinge, a pseudo-rigid model comprised of two circles rolling without slipping (planetary arrangement) is conceived. Thanks to parametric investigations, closed formulas for the computation of the radii of the two rolling circles and for the assessment of the concentrated spring are deduced in terms of main geometrical and elastic parameters. The proposed pseudo-rigid model is able to reproduce the elasto-kinematic behaviour of conic flexure hinges with accuracy, using a single degree of freedom surrogate mechanism. Finite element simulations confirm the accuracy of the closed form expressions. An example of application of the proposed methodology dealing with a vibration problem is presented in details
Henry Léauté: the forgotten kinematician and discoverer of the cubic of stationary curvature equation
No full textHenry Leaute (1847-1916) was a French kinematician who taught at the ecole polytechnique. In 1878, Leaute derived the cubic of stationary curvature (CSC) equation in its modern form which is widely applied as a tool for synthesizing path generator mechanisms. The deduction of CSC equation by Leaute is based on an earlier work from the French school due to A. Mannheim in 1872. According to historical bibliographical evidence, Leaute and Mannheim are recognized as the true discoverers of CSC equation. However, the subsequent literature on CSC equation does not acknowledge the aforementioned French contributions, by not giving them credit. In the present work, early investigations on CSC is reviewed by quoting excerpts from original works and the precedence of discovery to Leaute is clarified. Then, the mathematical treatment of Leaute is elaborated, followed by the discussion of a graphical procedure for tracing the CSC through an example. A brief review of other scientific works of Leaute is also included. At the end, it is recommended to consider terming the CSC equation alternatively as "Mannheim-Leaute equation"
Cosmology and astrophysics of minimal dark matter
No full textWe consider DM that only couples to SM gauge bosons and fills one gauge multiplet, e.g., a fermion 5-plet (which is automatically stable), or a wino-like 3-plet. We revisit the computation of the cosmological relic abundance including non-perturbative corrections. The predicted mass of, e.g., the 5-plet increases from 4.4 to 10 TeV, and indirect detection rates are enhanced by 7 orders of magnitude. Next, we show that due to the quasi-degeneracy among neutral and charged components of the DM multiplet, a significant fraction of DM with energy E greater than or similar to 10(17) eV (possibly present among ultra-high energy cosmic rays) can cross the Earth exiting in the charged state and may in principle be detected in neutrino telescopes. (C) 2007 Elsevier B.V. All rights reserved
L'esame ecocardiografico nella stenosi aortica congenita valvolare
No full textEchocardiographic studies were performed in 15 patients, aged 8 months to 20 years, with congenital valvular aortic stenosis confirmed by hemodynamic findings. Seven patients showed an anomalous pattern of the valvular echo in diastole (multiple valve echoes), seven exhibited an eccentric closure, and only in two patients the area was significantly reduced in systole. Therefore aortic valve diastolic pattern was more important than systolic appearance in the echocardiografic diagnosis of congenital valvular aortic stenosis. In all cases a correlation was found between the left ventricular pressure obtained with this non invasive method and the pressure measured in the left ventricle at the cardiac catheterization (p less than 0.001
On the paper Kinematic properties of planar and spherical logarithmic spirals: Applications to thesynthesis of involute tooth profiles, Mechanism and Machine Theory Volume 136 (June 2019), pp. 14–26
No full textComparison of flexibility models for the multibody simulation of compliant mechanisms
Full text linkThis paper presents a comparison among different flexibility models of elastic elements to be implemented in multibody simulations of compliant mechanisms. In addition to finite-element analysis and a pseudo-rigid body model, a novel matrix-based approach, called the Displaced Compliance Matrix Method, is proposed as a further flexibility model to take into account geometric nonlinearities. According to the proposed formulation, the representation of the elastic elements is obtained by resorting to the ellipse of elasticity theory, which guarantees the definition of the compliance matrices in diagonal form. The ellipse of elasticity is also implemented to predict the linear response of the compliant mechanism. Multibody simulations are performed on compliant systems with open-loop and closed-loop kinematic chains, subject to different load conditions. Beams with uniform cross-section and initially curved axis are considered as flexible elements. For each flexibility model, accuracies of displacements and rotations, and computational time, are evaluated and compared. The numerical results have been also compared to the data obtained through a set of experimental tests
Power-flow and mechanical efficiency computation in two-degrees-of-freedom planetary gear units: new compact formulas
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