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A piezoelectric micropump based on micromachining of silicon

The design and realization of two pumps based on micromachining of silicon are described. The pumps, which are of the reciprocating displacement type, comprise one or two pump chambers, a thin glass pump membrane actuated by a piezoelectric disc and passive silicon check valves to direct the flow. Chambers, channels and valves are realized in a silicon wafer by wet chemical etching. The results of mechanical calculations and simulations show good agreement with the actual behaviour of the pumps. It is possible to design pumps having a specific yield and pressure dependence, and which are fail-safe (the flow is blocked while the pump is switched off)

Softness dependence of the Anomalies for the Continuous Shouldered Well potential

By molecular dynamic simulations we study a system of particles interacting through a continuous isotropic pairwise core-softened potential consisting of a repulsive shoulder and an attractive well. The model displays a phase diagram with three fluid phases, a gas-liquid critical point, a liquid-liquid critical point, and anomalies in density, diffusion and structure. The hierarchy of the anomalies is the same as for water. We study the effect on the anomalies of varying the softness of the potential. We find that, making the soft-core steeper, the regions of density and diffusion anomalies contract in the T - {\rho} plane, while the region of structural anomaly is weakly affected. Therefore, a liquid can have anomalous structural behavior without density or diffusion anomalies. We show that, by considering as effective distances those corresponding to the maxima of the first two peaks of the radial distribution function g(r) in the high-density liquid, we can generalize to continuous two-scales potentials a criterion for the occurrence of the anomalies of density and diffusion, originally proposed for discontinuous potentials. We observe that the knowledge of the structural behavior within the first two coordination shells of the liquid is not enough to establish the occurrence of the anomalies. By introducing the density derivative of the the cumulative order integral of the excess entropy we show that the anomalous behavior is regulated by the structural order at distances as large as the fourth coordination shell. By comparing the results for different softness of the potential, we conclude that the disappearing of the density and diffusion anomalies for the steeper potentials is due to a more structured short-range order. All these results increase our understanding on how, knowing the interaction potential, we can evaluate the possible presence of anomalies for a liquid

Energy loss of a heavy quark produced in a finite-size quark-gluon plasma

We study the energy loss of an energetic heavy quark produced in a high temperature quark-gluon plasma and travelling a finite distance before emerging in the vacuum. While the retardation time of purely collisional energy loss is found to be of the order of the Debye screening length, we find that the contributions from transition radiation and the Ter-Mikayelian effect do not compensate, leading to a reduction of the zeroth order (in an opacity expansion) energy loss.Comment: QM2006 Proceedings; caption of fig 1 and ref [7] modified in v

Biaxial nematic phases in fluids of hard board-like particles

We use density-functional theory, of the fundamental-measure type, to study the relative stability of the biaxial nematic phase, with respect to non-uniform phases such as smectic and columnar, in fluids made of hard board-like particles with sizes $\sigma_1>\sigma_2>\sigma_3$. A restricted-orientation (Zwanzig) approximation is adopted. Varying the ratio $\kappa_1=\sigma_1/\sigma_2$ while keeping $\kappa_2=\sigma_2/\sigma_3$, we predict phase diagrams for various values of $\kappa_2$ which include all the uniform phases: isotropic, uniaxial rod- and plate-like nematics, and biaxial nematic. In addition, spinodal instabilities of the uniform phases with respect to fluctuations of the smectic, columnar and plastic-solid type, are obtained. In agreement with recent experiments, we find that the biaxial nematic phase begins to be stable for $\kappa_2\simeq 2.5$. Also, as predicted by previous theories and simulations on biaxial hard particles, we obtain a region of biaxility centred on $\kappa_1\approx\kappa_2$ which widens as $\kappa_2$ increases. For \kappa_2\agt 5 the region $\kappa_2\approx\kappa_1$ of the packing-fraction vs. $\kappa_1$ phase diagrams exhibits interesting topologies which change qualitatively with $\kappa_2$. We have found that an increasing biaxial shape anisotropy favours the formation of the biaxial nematic phase. Our study is the first to apply FMT theory to biaxial particles and, therefore, it goes beyond the second-order virial approximation. Our prediction that the phase diagram must be asymmetric is a genuine result of the present approach, which is not accounted for by previous studies based on second-order theories.Comment: Preprint format. 18 pages, 5 figure

Charmonia enhancement in quark-gluon plasma with improved description of c-quarks phase-distribution

We present a dynamical model of heavy quark evolution in the quark-gluon plasma (QGP) based on the Fokker-Planck equation. We then apply this model to the case of central ultra-relativistic nucleus-nucleus collisions performed at RHIC and estimate the component of $J/\psi$ production (integrated and differential) stemming from c-$\bar{c}$ pairs that are initially uncorrelated.Comment: contribution presented at SQM0

Energy Loss of a Heavy Quark Produced in a Finite Size Medium

We study the medium-induced energy loss $-\Delta E_0(L_p)$ suffered by a heavy quark produced at initial time in a quark-gluon plasma, and escaping the plasma after travelling the distance $L_p$. The heavy quark is treated classically, and within the same framework $-\Delta E_0(L_p)$ consistently includes: the loss from standard collisional processes, initial bremsstrahlung due to the sudden acceleration of the quark, and transition radiation. The radiative loss {\it induced by rescatterings} $-\Delta E_{rad}(L_p)$ is not included in our study. For a ultrarelativistic heavy quark with momentum p \gsim 10 {\rm GeV}, and for a finite plasma with L_p \lsim 5 {\rm fm}, the loss $-\Delta E_0(L_p)$ is strongly suppressed compared to the stationary collisional contribution $-\Delta E_{coll}(L_p) \propto L_p$. Our results support that $-\Delta E_{rad}$ is the dominant contribution to the heavy quark energy loss (at least for L_p \lsim 5 {\rm fm}), as indeed assumed in most of jet-quenching analyses. However they might raise some question concerning the RHIC data on large $p_{\perp}$ electron spectra.Comment: 18 pages, 3 figures. New version clarified and simplified. A critical discussion added in section 2, and previous sections 3 and 4 have been merged together. Main results are unchange