143,033 research outputs found
Hybrid Passive Control Strategies for Reducing the Displacements at the Base of Seismic Isolated Structures
In this paper, the use of hybrid passive control strategies to mitigate the seismic response of a base-isolated structure is examined. The control performance of three different types of devices used for reducing base displacements of isolated buildings is investigated. Specifically, the Tuned Mass Damper (TMD), the New Tuned Mass Damper (New TMD) and the Tuned Liquid Column Damper (TLCD), each one associated to a Base Isolated structure (BI), have been considered. The seismic induced vibration control of base-isolated structures equipped with the TMD, New TMD or the TLCD is examined and compared with that of the base-isolated system without devices, using real recorded seismic signals as external input. Data show that the New TMD is the most effective in controlling the response of base-isolated structures so that it can be considered as a practical and appealing means to mitigate the dynamic response of base-isolated structures
Anti-transpirant effects on vine physiology, berry and wine composition of cv. Aglianico (Vitis vinifera L.) Grown in South Italy
In viticulture, global warming requires reconsideration of current production models. At the base of this need there are some emerging phenomena: modification of phenological phases; acceleration of the maturation process of grapes, with significant increases in the concentration of sugar musts; decoupling between technological grape maturity and phenolic maturity. The aim of our study was to evaluate the effect of a natural anti-transpirant on grapevine physiology, berry, and wine composition of Aglianico cultivar. For two years, Aglianico vines were treated at veraison with the anti-transpirant Vapor Gard and compared with a control sprayed with only water. A bunch thinning was also applied to both treatments. The effectiveness of Vapor Gard were assessed through measurements of net photosynthesis and transpiration and analyzing the vegetative, productive and qualitative parameters. The results demonstrate that the application of antitranspirant reduced assimilation and transpiration rate, stomatal conductance, berry sugar accumulation, and wine alcohol content. No significant differences between treatments were observed for other berry and wine compositional parameters. This method may be a useful tool to reduce berry sugar content and to produce wines with a lower alcohol content
Ion-supported tori: a thermal bremsstrahlung model for the X-ray Background
We discuss the possibility that a significant contribution of the hard X-ray
Background is the integrated emission from a population of galaxies undergoing
advection-dominated accretion in their nuclei. Owing to poor coupling between
ions and electrons and to efficient radiative cooling of the electrons, the
accreting plasma is two-temperature, with the ions being generally much hotter
than the electrons and forming an ion-supported torus. We show that the
electron te mperature then saturates at approximately 100keV independent of
model parameters. At this temperature the hard X-ray emission is dominated by
bremsstrahlung radiation. We find that this physical model gives an excellent
fit to the spectrum of the XRB in the 3-60 keV range, provided that there is
some evolution associated with the spectral emissivity which must peak at a
redshift of about 2. We estimate that such galaxies contribute only to a small
fraction of the local X-ray volume emissivity. The model implies a higher mean
black hole mass than is obtained from the evolution of quasars alone.Comment: 7 pages, 7 ps figures, uses mn.sty (included). Submitted for
publication to MNRA
Magnetic flares in accretion disc coronae and the Spectral States of black hole candidates: the case of GX 339-4
We present a model for the different X-ray spectral states displayed by
Galactic Black Hole Candidates (GBHC). We discuss the physical and spectral
implications for a magnetically structured corona in which magnetic flares
result from reconnection of flux tubes rising from the accretion disk by the
magnetic buoyancy instability. Using observations of one of the best studied
examples, GX339-4, we identify the geometry and the physical conditions
characterizing each of these states. We find that, in the Soft state, flaring
occurs at small scale heights above the accretion disk. The soft thermal-like
spectrum is the result of heating and consequent re-radiation of the hard
X-rays produced by such flares. The hard tail is produced by Comptonization of
the soft field radiation. Conversely, the hard state is the result of flares
triggered high above the underlying accretion disk which produce X-rays via
Comptonization of either internal synchrotron radiation or soft disk photons.
The spectral characteristics of the different states are naturally accounted
for by the choice of geometry: when flares are triggered high above the disk
the system is photon-starved, hence the hard Comptonized spectrum of the hard
state. Intense flaring close to the disk greatly enhances the soft-photon field
with the result that the spectrum softens. We interpret the two states as being
related to two different phases of magnetic energy dissipation. In the Soft
state, Parker instability in the disk favours the emergence of large numbers of
relatively low magnetic field flux tubes. In the hard state, only intense
magnetic fields become buoyant. The model can also qualitatively account for
the observed short timescale variability and the characteristics of the X-ray
reflected component of the hard state.Comment: submitted to MNRAS, Feb. 1998, 10 pages, 3 figures in MNRAS LaTex
styl
Order, Disorder and Confinement
Studying the order of the chiral transition for is of fundamental
importance to understand the mechanism of color confinement. We present results
of a numerical investigation on the order of the transition by use of a novel
strategy in finite size scaling analysis. The specific heat and a number of
susceptibilities are compared with the possible critical behaviours. A second
order transition in the O(4) and O(2) universality classes are excluded.
Substantial evidence emerges for a first order transition. Results are in
agreement with those found by studying the scaling properties of a disorder
parameter related to the dual superconductivity mechanism of color confinement.Comment: 7 pages, 11 figures. Talk given at the International Workshop on
Quantum Chromodynamics: QCD@Work 2005, Conversano, Italy, 16-20 June 200
The chiral transition in two-flavor QCD
QCD with N_f=2 is a specially interesting system to investigate the chiral
transition. The order of the transition has still not been established. We
report the results of an in-depth numerical investigation performed with
staggered fermions on lattices with L_t=4 and L_s=12,16,20,24,32 and quark
masses am_q ranging from 0.01335 to 0.307036. Using finite-size techniques we
compare the scaling behavior of a number of thermodynamical susceptibilities
with the expectations of O(4) and O(2) universality classes. Clear disagreement
is observed. Indications of a first order transition are found.Comment: 6 pages, 4 figures, PoS style. Talk presented at Lattice 2005
(Nonzero temperature and density), Dublin, Ireland, July 25-3
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