3,356 research outputs found
Damaging micromechanisms in an as cast ferritic and a ferritized ductile cast iron
Mechanical behavior and damaging micromechanisms in Ductile Cast Irons (DCIs) are strongly effected by matrix microstructure (e.g., phases volume fraction, grains size and grain distribution) and graphite nodules morphology peculiarities (e.g., nodularity level, nodule size, nodule count, etc.). The influence of the graphite nodules depends on both the matrix microstructure and the loading conditions (e.g., quasi-static, dynamic or cyclic loadings). According to the most recent results, these graphite nodules show a mechanical properties gradient inside the graphite nodules, with the graphite elements – matrix debonding as only one of the possible damaging micromechanisms. In this work, two different ferritic DCIs were investigated (a ferritic matrix obtained from as-cast condition and a ferritized matrix) focusing on the damaging micromechanisms in graphite nodules due to tensile stress. Specimens lateral surfaces were observed using a Scanning Electron Microscope (SEM) during the tests following a step by step procedure.Fil: D' Agostino, Laura. UniversitĂ di Cassino e del Lazio Meridionale; ItaliaFil: Di Cocco, Vittorio. UniversitĂ di Cassino e del Lazio Meridionale; ItaliaFil: Fernandino, Diego Omar. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales. Universidad Nacional de Mar del Plata. Facultad de IngenierĂa. Instituto de Investigaciones en Ciencia y TecnologĂa de Materiales; ArgentinaFil: Lacoviello, Francesco. UniversitĂ di Cassino e del Lazio Meridionale; Itali
Stretching and relaxation dynamics in double stranded DNA
We study numerically the mechanical stability and elasticity properties of
duplex DNA molecules within the frame of a network model incorporating
microscopic degrees of freedom related with the arrangement of the base pairs.
We pay special attention to the opening-closing dynamics of double-stranded DNA
molecules which are forced into non-equilibrium conformations. Mechanical
stress imposed at one terminal end of the DNA molecule brings it into a
partially opened configuration. We examine the subsequent relaxation dynamics
connected with energy exchange processes between the various degrees of freedom
and structural rearrangements leading to complete recombination to the
double-stranded conformation. The similarities and differences between the
relaxation dynamics for a planar ladder-like DNA molecule and a twisted one are
discussed in detail. In this way we show that the attainment of a
quasi-equilibrium regime proceeds faster in the case of the twisted DNA form
than for its thus less flexible ladder counterpart. Furthermore we find that
the velocity of the complete recombination of the DNA molecule is lower than
the velocity imposed by the forcing unit which is in compliance with the
experimental observations for the opening-closing cycle of DNA molecules.Comment: 21 pages, 9 figure
Inferring DNA sequences from mechanical unzipping data: the large-bandwidth case
The complementary strands of DNA molecules can be separated when stretched
apart by a force; the unzipping signal is correlated to the base content of the
sequence but is affected by thermal and instrumental noise. We consider here
the ideal case where opening events are known to a very good time resolution
(very large bandwidth), and study how the sequence can be reconstructed from
the unzipping data. Our approach relies on the use of statistical Bayesian
inference and of Viterbi decoding algorithm. Performances are studied
numerically on Monte Carlo generated data, and analytically. We show how
multiple unzippings of the same molecule may be exploited to improve the
quality of the prediction, and calculate analytically the number of required
unzippings as a function of the bandwidth, the sequence content, the elasticity
parameters of the unzipped strands
GRB Observed by IBIS/PICsIT in the MeV Energy Range
We present the preliminary results of a systematic search for GRB and other
transients in the publicly available data for the IBIS/PICsIT (0.2-10 MeV)
detector on board INTEGRAL. Lightcurves in 2-8 energy bands with time
resolution from 1 to 62.5 ms have been collected and an analysis of spectral
and temporal characteristics has been performed. This is the nucleus of a
forthcoming first catalog of GRB observed by PICsIT.Comment: 6 pages, 3 figures. Poster presented at COSPAR 2008. Advaces in Space
Research, accepted for publicatio
The dynamics of proving uncolourability of large random graphs I. Symmetric Colouring Heuristic
We study the dynamics of a backtracking procedure capable of proving
uncolourability of graphs, and calculate its average running time T for sparse
random graphs, as a function of the average degree c and the number of vertices
N. The analysis is carried out by mapping the history of the search process
onto an out-of-equilibrium (multi-dimensional) surface growth problem. The
growth exponent of the average running time is quantitatively predicted, in
agreement with simulations.Comment: 5 figure
Modelling and performance analysis of a Low Temperature A-CAES system coupled with renewable energy power plants
The ever-increasing electricity production from non-programmable Renewable Energy Sources (RES) requires flexible and sustainable solutions for energy storage. In this paper, the design, and the performance of a Low Temperature Adiabatic Compressed Air Energy Storage (LTA-CAES) system are presented. The design of this system is optimised to better utilise the energy produced by either a photovoltaic (PV) power plant and an onshore wind farm in order to meet the energy demand of a small town of about 10,000 inhabitants, considered as the case study. To ensure efficient operation of the turbomachines, the mass flow rate during both the charge and discharge phases was fixed, allowing most of the compressors and turbines to operate at design conditions. Two packed-bed Thermal Energy Storage (TES) systems are used to store the thermal energy produced during the compression phase: the first exchanges heat directly with the compressed air, while the second uses Therminol-66 as a heat transfer fluid. A mathematical model of the LTA-CAES system was developed using MATLAB/Simulink to simulate its performance, considering the off-design behaviour of the turbomachines and the TES systems over a year. The results demonstrate that the LTA-CAES system increases the share of the yearly energy demand covered by renewable energy, from 41.8% to 60.7% when coupled with the PV plant, and from 48.0% to 56.5% when coupled with the wind farm
Relaxation and Metastability in the RandomWalkSAT search procedure
An analysis of the average properties of a local search resolution procedure
for the satisfaction of random Boolean constraints is presented. Depending on
the ratio alpha of constraints per variable, resolution takes a time T_res
growing linearly (T_res \sim tau(alpha) N, alpha < alpha_d) or exponentially
(T_res \sim exp(N zeta(alpha)), alpha > alpha_d) with the size N of the
instance. The relaxation time tau(alpha) in the linear phase is calculated
through a systematic expansion scheme based on a quantum formulation of the
evolution operator. For alpha > alpha_d, the system is trapped in some
metastable state, and resolution occurs from escape from this state through
crossing of a large barrier. An annealed calculation of the height zeta(alpha)
of this barrier is proposed. The polynomial/exponentiel cross-over alpha_d is
not related to the onset of clustering among solutions.Comment: 23 pages, 11 figures. A mistake in sec. IV.B has been correcte
Spectral Properties of Stochastic Processes Possessing Finite Propagation Velocity.
This article investigates the spectral structure of the evolution operators associated with the statistical description of stochastic processes possessing finite propagation velocity. Generalized Poisson-Kac processes and LĂ©vy walks are explicitly considered as paradigmatic examples of regular and anomalous dynamics. A generic spectral feature of these processes is the lower boundedness of the real part of the eigenvalue spectrum that corresponds to an upper limit of the spectral dispersion curve, physically expressing the relaxation rate of a disturbance as a function of the wave vector. We also analyze Generalized Poisson-Kac processes possessing a continuum of stochastic states parametrized with respect to the velocity. In this case, there is a critical value for the wave vector, above which the point spectrum ceases to exist, and the relaxation dynamics becomes controlled by the essential part of the spectrum. This model can be extended to the quantum case, and in fact, it represents a simple and clear example of a sub-quantum dynamics with hidden variables
Antiarrhythmic effect of the calcium antagonist tiapamil (ro 11–1781) by intravenous administration in patients with coronary heart disease
Twenty coronary patients with a median age of 76 years were treated in the coronary care unit with tiapamil, a new Ca2+ antagonist, by intravenous infusion (until December, 1979, the generic name was dimeditiapramine). The following arrhythmias were identified: atrial fibrillation with ventricular rate greater than 95 beats/min (5 patients); supraventricular premature complexes (SVPC) (4 patients); and ventricular premature complexes (VPC), Lown grades 2-4 (15 patients). Electrocardiograms and hemodynamic parameters were continuously monitored prior to, during, and after the therapy. In patients with atrial fibrillation, sinus rhythm was not restored, but tiapamil decreased the ventricular rate by 54%. In patients with VPC, the median frequency of VPC decreased from 310.5 before tiapamil to 32.5 beats/h at the fourth hour of therapy (p less than 0.01). The median ectopic/sinus beat ratio decreased from 0.083 (pretreatment) to 0.008 at the fourth hour of infusion (p less than 0.10). In one of the patient with an insufficient decrease in the number of VPC, the VPOC changed from class 4a (pretreatment) to class 2 (during the therapy), returning to class 4a after the infusion was stopped. Tiapamil reduced the median systolic and diastolic blood pressures by 8.3 and 7.1%, respectively (p less than 0.05), the third hour. Hypotension and bradycardia were observed in 5/20 patients. The results show that tiapamil is effective against both supraventricular and ventricular arrhythmias, and thus its spectrum of action differs from that of other calcium antagonists
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