Fluorescence intermittency in blinking quantum dots: renewal or slow modulation?

We study time series produced by the blinking quantum dots, by means of an aging experiment, and we examine the results of this experiment in the light of two distinct approaches to complexity, renewal and slow modulation. We find that the renewal approach fits the result of the aging experiment, while the slow modulation perspective does not. We make also an attempt at establishing the existence of an intermediate condition.Comment: 27 pages, 8 figures. Accepted for pubblication on Journal of Chemical Physic

Performance evaluation of a pulsatile ventricular assist device under non physiologic pumping frequencies by means FEM and 2D approach

A ventricular assist device (VAD) is a blood pump that works in parallel with heart. It is used as a mechanical assistance for patients that suffer cardiac insufficiency: as a therapy, as a bridge to transplant or to extend life. The blood flow simulation into VAD is of great interest for the design and evaluation, mainly before building the prototypes. In previous works, by means of blood flow simulation, was evaluated a new concept of implantable VAD consisting on a pump with a double effect piston, driven without contact and four active valves. In this work, the flow into VAD is analyzed for four frequencies values: 1.05, 2.10, 3.15 and 4.20 Hz. The former is the physiologic frequency, the second allows the basal flow rate (5 l/min), while the others are higher in order to assure an increase in flow rates. The analysis is carried out comparing variables as velocity and pressure distribution into VAD and evaluating blood damage due to acting shear stress over cells. The blood flow simulation is performed on a 2D simplified geometry using COMSOL Multiphysics software to resolve NavierStokes and continuity equations, assuming blood as a Newtonian incompressible fluid. The blood damage is evaluated by means of platelet activation state index and a cumulative damage model. The global variables as flow rate, force and power to impel fluid, are shown in agreement with theoretical predictions. The risk of blood damage raises for higher frequencies, however, the predictions shown that the VAD analyzed is comparable and best to other VAD and mechanical heart valves

Assessing the need for neutralizing KCl filter testing aerosol

American Association for Aerosol Research 28th Annual Conference, Minneapolis (MN), 26-30 October 2009, Abstract #81

Disorder regimes and equivalence of disorder types in artificial spin ice

The field-induced dynamics of artificial spin ice are determined in part by interactions between magnetic islands, and the switching characteristics of each island. Disorder in either of these affects the response to applied fields. Numerical simulations are used to show that disorder effects are determined primarily by the strength of disorder relative to inter-island interactions, rather than by the type of disorder. Weak and strong disorder regimes exist and can be defined in a quantitative way.Comment: The following article has been submitted to J. Appl. Phys. After it is published, it will be found at http://link.aip.org/link/?ja

Diversity enabling equilibration: disorder and the ground state in artificial spin ice

We report a novel approach to the question of whether and how the ground state can be achieved in square artificial spin ices where frustration is incomplete. We identify two types of disorder: quenched disorder in the island response to fields and disorder in the sequence of driving fields. Numerical simulations show that quenched disorder can lead to final states with lower energy, and disorder in the driving fields always lowers the final energy attained by the system. We use a network picture to understand these two effects: disorder in island responses creates new dynamical pathways, and disorder in driving fields allows more pathways to be followed.Comment: 5 pages, 5 figure

Vertex dynamics in finite two dimensional square spin ices

Local magnetic ordering in artificial spin ices is discussed from the point of view of how geometrical frustration controls dynamics and the approach to steady state. We discuss the possibility of using a particle picture based on vertex configurations to interpret time evolution of magnetic configurations. Analysis of possible vertex processes allows us to anticipate different behaviors for open and closed edges and the existence of different field regimes. Numerical simulations confirm these results and also demonstrate the importance of correlations and long range interactions in understanding particle population evolution. We also show that a mean field model of vertex dynamics gives important insights into finite size effects.Comment: 4 pages, 4 figures; v2: minor changes to text and figures. Accepted to Phys. Rev. Let

Impact of the motor magnetic model on direct flux vector control of interior PM motors

The stator-field-oriented, direct-flux vector control has been proven to be effective in terms of linear torque control and model independent performance at limited voltage and current (i.e. in flux weakening) for AC drives of various types. The performance of the direct-flux vector control relies on the accuracy of the flux estimation, as for any field oriented control. The knowledge of the motor magnetic model is critical for flux estimation when the operating at low speed. This paper addresses the effects of a limited knowledge of the motor model on the performance of the control at low speed, for an Interior Permanent Magnet motor drive. Experimental results are give

Application of Taylor models to the worst-case analysis of stripline interconnects

This paper outlines a preliminary application of Taylor models to the worst-case analysis of transmission lines with bounded uncertain parameters. Taylor models are an algebraic technique that represents uncertain quantities in terms of a Taylor expansion complemented by an interval remainder encompassing approximation and truncation errors. The Taylor model formulation is propagated from input uncertainties to output responses through a suitable redef nition of the algebraic operations involved in their calculation. While the Taylor expansion def nes an analytical and parametric model of the response, the remainder provides a conservative bound inside which the true value is guaranteed to lie. The approach is validated against the SPICE simulation of a coupled stripline and shows promising accuracy and eff ciency

Model of tunneling transistors based on graphene on SiC

Recent experiments shown that graphene epitaxially grown on Silicon Carbide (SiC) can exhibit a energy gap of 0.26 eV, making it a promising material for electronics. With an accurate model, we explore the design parameter space for a fully ballistic graphene-on-SiC Tunnel Field-Effect Transistors (TFETs), and assess the DC and high frequency figures of merit. The steep subthreshold behavior can enable I_{ON}/I_{OFF} ratios exceeding 10^4 even with a low supply voltage of 0.15 V, for devices with gatelength down to 30 nm. Intrinsic transistor delays smaller than 1 ps are obtained. These factors make the device an interesting candidate for low-power nanoelectronics beyond CMOS