103,482 research outputs found
Global weak solutions for systems of balance laws
No full textAbstractWe are concerned with global, weak solutions to the Cauchy problem for a (strictly hyperbolic) system of balance laws, ut+[F(u)]x=g(u), u(0, x)=u0(x).Assume that the initial data has small total variation. We give a sufficient condition for global existence of solutions in BV. Such a condition generalizes the one required by Dafermos and Hsiao in their paper [1]
A note on positive solutions for conservation law with singular source
No full textWe consider the Cauchy problem for the scalar conservation law
∂tu+∂xf(u)= 1/g(u), t>0, x∈R,
with g ∈ C^1(R), g(0) = 0, g(u) > 0 for u > 0, and assume that the initial datum u0 is nonnegative. We show the existence of entropy solutions that are positive a.e., by means of an approximation of the equation that preserves positive solutions, and by passing to the limit using a monotonicity argument. The difficulty lies in handling the singularity of the right hand side (the source term) as
u possibly vanishes at the initial time. The source term is shown to be locally integrable. Moreover, we prove an uniqueness and stability result for the above equation
Amadori-Compounds as Cocoa Aroma Precursors
No full textS.142-145Several Amadori-compounds (fructose-amino acids), important intermediates of Maillard reaction, have been found in unroasted cocoa beans some years ago. Now, in cocoa additional fructose-phenylalanine (fru-phe) could be detected by means of a modified extraction procedure. For studying the contribution of Amadori-compounds fru-phe and fru-leu (fructose-leucine) were roasted at 145 centigrades. The roasted flavours contained a lot of key compounds of cocoa flavour. If cocoa was moist-thermally treated and dried the level of Amadori-compounds could be raised and the roasted aroma intensified. Amadori-compounds obviously contribute the flavour formation in cocoa. This effect may be used technologically to increase flavour yield. Mehrere Amadori-Verbindungen (Fructose-Aminosäuren), wichtige Zwischenprodukte der Maillard-Reaktion, wurden 1991 erstmals in rohen Kakaobohnen nachgewiesen. Durch ein modifiziertes Extraktionsverfahren konnte jetzt auch Fructose-Phenylalanin (Fru-Phe) in Rohkakao gefunden werden. Um den Beitrag der Amadori-Verbindungen als Aromavorstufen zu verfolgen, wurden Fru-Phe und Fru-Leu (Fructose-Leucin) bei 145 Grad Celsius geröstet und die Röstaromen analysiert. Sie enthielten Schlüsselverbindungen des Kakaoaromas. Durch feucht-thermische Behandlung und Trocknung ließ sich die Konzentration an Amadori-Verbindungen in Kakaokernbruch erhöhen und die Aromaausbeute nach Röstung steigern. Der Beitrag von Amadori-Verbindungen in Kakao scheint erwiesen und könnte technologisch genutzt werden.41Nr.
EXPERIMENTAL IDENTIFICATION OF THE DYNAMICAL MODEL OF VISCOELASTIC HOMOGENEOUS ISOTROPIC MATERIALS.
No full textThe standard dynamical model of a viscoelastic homogeneous isotropic material [1] only
depends on two parameters, e.g. the E tension-compression and the G shear moduli, the value
of these parameters being expected to vary with respect to f frequency.
E(ω=2‧pi‧f) and G(ω) estimates can typically be obtained from measurements made on slender beam specimens under uniaxial harmonic stress experimental conditions, e.g. tension compression for E and torsion-shear for G [1]. An extensive number of works is also known for E(ω), G(ω) modeling in the frequency domain [2] under the material linear viscoelastic behavior assumption. In previous works the authors of this paper proposed some techniques to identify the E(ω) model from forced harmonic flexural vibration measurements on a beam specimen made of the material under study [3], and such approach could be adopted to the G(ω) identification as well. Nevertheless, it can be found that for a linear viscoelastic material E(ω) and G(ω) real and imaginary parts are bounded [4]. Some more general constraining relations between E(ω) with respect to G(ω) are shown in this work, so that an experimentally identified material model is expected to satisfy such relations to be consistent. A E(ω), G(ω) model identification procedure from measurements with different experimental set-ups on beam specimens made of the same material may be uneffective, errors arising from measurement and model (boundary conditions and other model-based assumptions) lack of accuracy, so that locally identified E(ω) and G(ω) values are not expected to satisfy the previously cited consistency conditions.
In this work E-1(ωk) and G-1(ωk), k=1...Nω, estimates are simultaneously obtained by means of an algebraic iterative robust algorithm, adopting a set of H(ωk)= v(ωk)/F(ωk) estimates, where (~) is the Fourier transform operator, v(ωk) is the measured displacement
and F(ωk) is the measured force at one end of the beam specimen end. The H(ωk) set
contains measurements made on Nm beam specimens, same material but different geometry.
A flexural experimental set-up is adopted, and the choice of the geometrical dimensions of
each measured specimen beam is made in order to differentiate the beam shear contributions, mainly dependent on G(ω), with respect to the beam axial contributions, mainly dependent
on E(ω).
Model behavior of many highly-damped polymeric materials at low frequency values is
expected to be fully different from the same behavior in the medium to high frequency range,
E(ωk) and G(ωk) estimates from H(ωk). in the low frequency range should be experimentally
identified and cannot be extrapolated from measurements in the medium frequency range.
Forced harmonic flexural vibration v(ωk), F(ωk) measurements are used to obtain H(ωk),
but low frequency H(ωk) estimates, e.g. ω/2‧ᴨ‧<0.01 Hz , cannot be performed since the
required experimental time is too high. Some algorithms were proposed in the past [5] to
estimate E(ω) or G(ω) at low frequency values by processing creep-relaxation measurements
under ideal assumptions, i.e. an ideal time step applied stress. An algorithm for the H(ωk)
numerical estimate from ν(t) and force F(t) measurements under general relaxation conditions is proposed. A material E(ω) and G(ω) identification procedure from the H(ωk) experimentally estimated values is then discussed and some results are also shown
Oncologia medica veterinaria e comparata (a cura di Laura Marconato e Dino Amadori)
No full textQuesto nuovo testo di oncologia condensa lo stato dell'arte in oncologia, preservando unitarietà concettuale e fornendo un impianto didattico semplice e immediato. Questo manuale ha ambizione di completezza e praticità: gli autori si augurano che ciò sia di aiuto a chi di oncologia già si occupa e possa avvicinare alla materia chi invece è ancora soltanto curioso ... Si è voluto il confronto con l'oncologia umana (si ricorda che in campo oncologico ci si aiuta a vicenda); il professor Amadori e i suoi collaboratori hanno partecipato con entusiasmo alla stesura di questo testo: i lettori apprezzeranno la parte di oncologia comparata che completa ogni capitolo ..
Damping contributions of coatings to the viscoelastic behaviour of mechanical components
No full textCoating layer technology is known in literature as an effective tool for modifying the viscoelastic behaviour of materials. In this work various coating solutions are investigated in order to estimate their contribution to the dissipative behaviour of mechanical components. Different production processes are used to apply single-layer and dual-layer coatings of Al oxide, Ti and TiO2 , Cr and CrN to uncoated specimens made of Al, stainless steel and harmonic steel. Force and displacement experimental data obtained from forced excitation dynamic mechanical measurements are used to find the specimen constitutive equation estimated parameters. A high order generalized Kelvin model is adopted to model the constitutive equivalent material relationship of coated specimens in the form of the ratio of two polynomials expressed as a function of frequency. The model parameters are numerically identified and the model reduced and optimized by means of a robust identification technique
Experimental identification of the material standard linear solid model parameters by means of dynamical measurements
No full textA procedure for the experimental identification of the material standard linear solid model parameters by means of dynamic mechanical analysis test instrument measurements is presented. Since the standard linear solid material stress–strain functional D(ω) relationship in the frequency domain formally depends on the standard linear solid material parameters, a procedure able to identify these parameters from test measurement estimates is proposed in this work. Nevertheless, a critical, nonlinear and non-parametric approach is to be followed since the number of the material standard linear solid block components is generally unknown, and the material D(ω) shows a highly nonlinear dependency on the unknown standard linear solid material parameters. For these reasons, measurement and test model noise is expected to strongly influence the accuracy of the identification results. A multi-step procedure is presented, consisting first in the non-parametric identification of a frequency dependent, two degrees of freedom model instrument frame by means of a polynomial rational function, where polynomial order and parameters, such as polynomial coefficients and pole-residue couples, are optimally identified by means of an algebraic numerical technique and of an iterative stabilization procedure. Another procedure able to identify the material D(ω) polynomial rational functional relationship in the frequency domain is also proposed, taking into account the dynamic contribution of the instrument frame, of the inertial contribution of the distributed mass of the beam and of the lumped mass of the instrument force measuring system. An effective procedure, able to identify the standard linear solid material model parameters in the time domain from the identified material physical poles, is finally proposed. Some application examples, concerning the identification of the standard linear solid model of a known material and of an unknown composite material, are shown and discussed as well
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