Probing for electrical inclusions with complex spherical waves

Let a physical body Ω in ?² or ?³ be given. Assume that the electric conductivity distribution inside Ω consists of conductive inclusions in a known smooth background. Further, assume that a subset Γ ? ?Ω is available for boundary measurements. It is proved using hyperbolic geometry that certain information about the location of the inclusions can be exactly recovered from static electric measurements on Γ. More precisely: given a ball B with center outside the convex hull of Ω and satisfying (B? ∩ ?Ω) ? Γ, boundary measurements on Γ with explicitly given Dirichlet data are enough to determine whether B intersects the inclusion. An approximate detection algorithm is introduced based on the theory. Numerical experiments in dimension two with simulated noisy data suggest that the algorithm finds the inclusion‐free domain near Γ and is robust against measurement noise. © 2007 Wiley Periodicals, Inc.     

Atomic layer deposition of PbZrO3 thin films

In this paper, we report on the preparation of lead zirconate films for the first time using atomic layer deposition in an attempt to investigate some of the film properties and also to evaluate possible use of the precursor combination to prepare more complex lead titanate zirconate. In the depositions tetraphenyl lead (Ph₄Pb) was used as the lead and zirconium 2,2,6,6-tetramethyl-3,5-heptadionato (Zr(thd)₄) as the zirconium precursor, while ozone was used as the oxygen source. Film growth, stoichiometry and quality were studied using different pulsing ratios at deposition temperatures of 275 and 300 °C. According to X-ray diffraction, the crystalline perovskite phase was observed when films deposited on SrTiO₃(1 0 0) were annealed at 600 °C. Surface roughness was reduced for lead deficient films as well as in annealed samples.     

Kinematic analysis of Bricard’s mechanism

We show how the tools of computational algebra can be used to analyze the configuration space of multibody systems. One advantage of this approach is that the mobility can be computed without using the Jacobian of the system. As an example, we treat thoroughly the well-known Bricard’s mechanism, but the same methods can be applied to a wide class of rigid multibody systems. It turns out that the configuration space of Bricard’s system is a smooth closed curve, which can be explicitly parametrized. Our computations also yield a new formulation of constraints which is better than the original one from the point of view of numerical simulations.     

The discrete maximal operator in metric spaces

We study the action of the so-called discrete maximal operator on Newtonian, Hölder and BMO spaces on metric measure spaces equipped with a doubling measure and a Poincaré inequality. The discrete maximal operator has better regularity properties than the standard Hardy-Littlewood maximal operator and hence is a more flexible tool in this context.     

Size- and state-aware dispatching problem with queue-specific job sizes

We consider the dispatching problem in a size- and state-aware multi-queue system with Poisson arrivals and queue-specific job sizes. By size- and state-awareness, we mean that the dispatcher knows the size of an arriving job and the remaining service times of the jobs in each queue. By queue-specific job sizes, we mean that the time to process a job may depend on the chosen server. We focus on minimizing the mean sojourn time (i.e., response time) by an MDP approach. First we derive the so-called size-aware relative values of states with respect to the sojourn time in an M/G/1 queue operating under FIFO, LIFO, SPT or SRPT disciplines. For FIFO and LIFO, the size-aware relative values turn out to be insensitive to the form of the job size distribution. The relative values are then exploited in developing efficient dispatching rules in the spirit of the first policy iteration.     

Accelerated beam tracing algorithm

Determining early specular reflection paths is essential for room acoustics modeling. Beam tracing algorithms have been used to calculate these paths efficiently, thus allowing modeling of acoustics in real-time with a moving listener in simple, or complex but densely occluded, environments with a stationary sound source. In this paper, it is shown that beam tracing algorithms can still be optimized by utilizing the spatial coherence in path validation with a moving listener. Since the precalculations required for the presented technique are relatively fast, the acoustic reflection paths can be calculated even for a moving source in simple cases. Simulations were performed to show how the accelerated algorithm compares with the basic algorithm with varying scene complexity and occlusion. Up to two-orders of magnitude speed-up was achieved.     

Layer-by-layer polyelectrolyte coating of low molecular weight poly(lactic acid) nanoparticles

Low molecular weight (M(w)) poly(L-lactic acid) (PLA) nanoparticles were coated with polyelectrolytes (PEs) by layer-by-layer (LbL) technique using a filtration approach. Poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) were applied as PEs in coating. LbL coating is aimed to use in producing (nano)particulate drug delivery systems with improved biocompatibility and sustained or targeted release of drug substances. Nanoparticles of rapidly biodegradable polymers, like the low M(w) PLA, open up a possibility to control the release of the encapsulated substance by the coating, but set challenges to the coating process due to increased aggregation tendency and degradation rate of the polymer. When the core PLA nanoparticles were prepared by nanoprecipitation, surface properties of the nanoparticles were affected by solvent selection. Successful LbL coating of the PLA nanoparticles was obtained only with chloroform, but not with dichloromethane as the solvent during nanoprecipitation. Reason for this was found to be the more charged surface of the nanoparticles prepared with chloroform compared to the nanoparticles prepared with dichloromethane.     

A stochastic model for a vehicle in a dial-a-ride system

We consider a stochastic model for a system which can serve n customers concurrently, and each accepted and departing customer generates a service interruption. The proposed model describes a single vehicle in a dial-a-ride transport system and is closely related to Erlang’s loss system. We give closed-form expressions for the blocking probability, the acceptance rate, and the mean sojourn time, which are all shown to be insensitive with respect to the forms of the distributions defining the workload and interruption durations.     

A Portable Liquid Scintillation Counter for General LSC and High Sensitivity Alpha-Counting Applications

Applicability of a new portable, single tube liquid scintillation (LS) spectrometer was demonstrated for general LS applications, such as wipe tests and low level alpha counting, especially radon (²²²Rn) measurements in water. Wipe tests were performed with wad sticks. They were counted conventionally in a small volume in Eppendorf tubes with less than 200µl of LS cocktail, thus minimizing costs and waste. Small volume is specially recommended because low background can be achieved without heavy lead shielding, thus maintaining portability. Typical NRC recommended LLD's were reached for ³H and other typical LS isotopes. For ²²²Rn in water a biphasic extraction system was adopted where radon is extracted from water into a water-immiscible LS cocktail. The method is sensitive because radon can be extracted from a large water volume. It was observed that common non-evaporating "safe" cocktails with di-isopropyl naphtalene solvent are convenient to use and quite suitable for extraction. Also the isotope ²²⁶Ra can be reliably measured via production of its daughter ²²²Rn. The instrument includes pulse shape electronics to perform alpha/beta separation. This is based on the fact that in LS cocktails alphas generate pulses with longer duration than betas. The alpha/beta separation can be visualized with a two dimensional graph where the x-axis represents pulse amplitude (MCA channels) and the y-axis its length. The graphical operations are all done in standard Excel/Windows environment. Due to their longer pulses, alphas have greater y-coordinates than betas with the same x-coordinate (amplitude). With this graph, one can select a region occupied only by alphas and exclude betas. The above mentioned "safe" cocktails posses good alpha/beta separation properties. Because natural background (cosmic-rays and environmental gammas) produces beta-like pulses, they can be stripped away giving low background for alpha counting, typically a few counts per hour for the extraction samples. The LLD for ²²²Rn was 0.1 Bq/I.     

Influence of ethanol on lipid membranes: from lateral pressure profiles to dynamics and partitioning

We have combined experiments with atomic-scale molecular dynamics simulations to consider the influence of ethanol on a variety of lipid membrane properties. We first employed isothermal titration calorimetry together with the solvent-null method to study the partitioning of ethanol molecules into saturated and unsaturated membrane systems. The results show that ethanol partitioning is considerably more favorable in unsaturated bilayers, which are characterized by their more disordered nature compared to their saturated counterparts. Simulation studies at varying ethanol concentrations propose that the partitioning of ethanol depends on its concentration, implying that the partitioning is a nonideal process. To gain further insight into the permeation of alcohols and their influence on lipid dynamics, we also employed molecular dynamics simulations to quantify kinetic events associated with the permeation of alcohols across a membrane, and to characterize the rotational and lateral diffusion of lipids and alcohols in these systems. The simulation results are in agreement with available experimental data and further show that alcohols have a small but non-vanishing effect on the dynamics of lipids in a membrane. The influence of ethanol on the lateral pressure profile of a lipid bilayer is found to be prominent: ethanol reduces the tension at the membrane-water interface and reduces the peaks in the lateral pressure profile close to the membrane-water interface. The changes in the lateral pressure profile are several hundred atmospheres. This supports the hypothesis that anesthetics may act by changing the lateral pressure profile exerted on proteins embedded in membranes.