380 research outputs found
Graviweak Unification
The coupling of chiral fermions to gravity makes use only of the selfdual
SU(2) subalgebra of the (complexified) SO(3,1) algebra. It is possible to
identify the antiselfdual subalgebra with the SU(2)_L isospin group that
appears in the Standard Model, or with its right-handed counterpart SU(2)_R
that appears in some extensions. Based on this observation, we describe a form
of unification of the gravitational and weak interactions. We also discuss
models with fermions of both chiralities, the inclusion strong interactions,
and the way in which these unified models of gravitational and gauge
interactions avoid conflict with the Coleman-Mandula theorem.Comment: 18 pages, typos corrected and improved wordin
Chirality in unified theories of gravity
We show how to obtain a single chiral family of an SO(10) GUT, starting from
a Majorana-Weyl representation of a unifying ("GraviGUT") group SO(3,11), which
contains the gravitational Lorentz group SO(3,1). An action is proposed, which
reduces to the correct fermionic GUT action in the broken phase.Comment: 7 pages. Discussion clarified. Version matching the published on
Gravity-Yang-Mills-Higgs unification by enlarging the gauge group
We revisit an old idea that gravity can be unified with Yang-Mills theory by
enlarging the gauge group of gravity formulated as gauge theory. Our starting
point is an action that describes a generally covariant gauge theory for a
group G. The Minkowski background breaks the gauge group by selecting in it a
preferred gravitational SU(2) subgroup. We expand the action around this
background and find the spectrum of linearized theory to consist of the usual
gravitons plus Yang-Mills fields charged under the centralizer of the SU(2) in
G. In addition, there is a set of Higgs fields that are charged both under the
gravitational and Yang-Mills subgroups. These fields are generically massive
and interact with both gravity and Yang-Mills sector in the standard way. The
arising interaction of the Yang-Mills sector with gravity is also standard.
Parameters such as the Yang-Mills coupling constant and Higgs mass arise from
the potential function defining the theory. Both are realistic in the sense
explained in the paper.Comment: 61 pages, no figures (v2) some typos correcte
Type 2 diabetes and reduced exercise tolerance: A review of the literature through an integrated physiology approach
The association between type 2 diabetes mellitus (T2DM) and heart failure (HF) is well established. Early in the course of the diabetic disease, some degree of impaired exercise capacity (a powerful marker of health status with prognostic value) can be frequently highlighted in otherwise asymptomatic T2DM subjects. However, the literature is quite heterogeneous, and the underlying pathophysiologic mechanisms are far from clear. Imaging-cardiopulmonary exercise testing (CPET) is a non-invasive, provocative test providing a multi-variable assessment of pulmonary, cardiovascular, muscular, and cellular oxidative systems during exercise, capable of offering unique integrated pathophysiological information. With this review we aimed at defying the cardiorespiratory alterations revealed through imaging-CPET that appear specific of T2DM subjects without overt cardiovascular or pulmonary disease. In synthesis, there is compelling evidence indicating a reduction of peak workload, peak oxygen assumption, oxygen pulse, as well as ventilatory efficiency. On the contrary, evidence remains inconclusive about reduced peripheral oxygen extraction, impaired heart rate adjustment, and lower anaerobic threshold, compared to non-diabetic subjects. Based on the multiparametric evaluation provided by imaging-CPET, a dissection and a hierarchy of the underlying mechanisms can be obtained. Here we propose four possible integrated pathophysiological mechanisms, namely myocardiogenic, myogenic, vasculogenic and neurogenic. While each hypothesis alone can potentially explain the majority of the CPET alterations observed, seemingly different combinations exist in any given subject. Finally, a discussion on the effects -and on the physiological mechanisms-of physical activity and exercise training on oxygen uptake in T2DM subjects is also offered. The understanding of the early alterations in the cardiopulmonary response that are specific of T2DM would allow the early identification of those at a higher risk of developing HF and possibly help to understand the pathophysiological link between T2DM and HF
High Performances Corrugated Feed Horns for Space Applications at Millimetre Wavelengths
We report on the design, fabrication and testing of a set of high performance
corrugated feed horns at 30 GHz, 70 GHz and 100 GHz, built as advanced
prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission.
The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70
GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz, and
by electro-formation at higher frequencies. The measured performances on side
lobes and return loss meet the stringent Planck requirements over the large
(20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape
and side lobes levels of the dual profiled designs has been demonstrated.Comment: 16 pages, 7 figures, accepted for publication in Experimental
Astronom
A comparison between standard and crossfeed monopulse radars in presence of rough sea scattering and ship movements
Monopulse radars are widely used in tracking systems, due to their relative
simplicity and theoretical precision, but the presence of multipath
impairs the tracking capabilities of these radars, especially when multipath
signals are strong, as in a naval environment. A special monopulse
setup, the crossfeed, has been proposed in the past to provide an automatic
cancellation from smooth sea multipath. In this contribution,
the performances of such a system are analyzed in presence of rough sea
scattering and compared with those of a standard monopulse setup. Particular
attention is devoted to performance degradations due to possible
phase errors in the passive network implementing the comparator and
due to ship rolling and pitching. This latter requires a full 3D monopulse
simulator for its correct evaluation
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