823 research outputs found
Vector field electron tomography of magnetic materials: Theoretical development
No full textThe theory of vector field electron tomography, the reconstruction of the three-dimensional magnetic induction around a magnetized object, is derived within the framework of Lorentz transmission electron microscopy. The tomographic reconstruction method uses as input two orthogonal tilt series of magnetic phase maps and is based on the vector slice theorem. An analytical reconstruction of the magnetic induction of a single magnetic dipole is presented as a proof-of-concept. The method is compared to two previously reported approaches: a reconstruction starting from the gradient of the magnetic phase maps, and a direct reconstruction of the magnetic vector potential. Numerical examples as well as estimates of the reconstruction errors for a range of magnetic particle shapes are reported. (c) 2007 Elsevier B.V. All rights reserved
On the magnetostatics of chains of magnetic nanoparticles
No full textA novel approach is presented for the computation of the magnetostatic energy of straight and bent chains of identical, uniformly magnetized particles of arbitrary shape. The formalism relies on the concept of the magnetometric tensor field, and allows for closed form expressions for the magnetostatic energy, demagnetization factor, Young's modulus, and bending modulus of chains in terms of the shape amplitude of the particles. Analytical solutions are presented for straight chains of spheres, cubes, and cylinders, and for bent chains of spheres. Numerical results include chains of octahedra, tetrahedra, cuboctahedra, and bi-cones. The axial demagnetization factor for the bi-cone shape is derived in analytical form. An approximate energy expression, using the full shape-dependent interaction formalism for short separation distances, and the standard dipolar interaction expression for larger distances, is introduced
Theoretical study of ferroelectric nanoparticles using phase reconstructed electron microscopy
No full textFerroelectric nanostructures are important for a variety of applications in electronic and electro-optical devices, including nonvolatile memories and thin-film capacitors. These applications involve stability and switching of polarization using external stimuli, such as electric fields. We present a theoretical model describing how the shape of a nanoparticle affects its polarization in the absence of screening charges, and quantify the electron-optical phase shift for detecting ferroelectric signals with phase-sensitive techniques in a transmission electron microscope. We provide an example phase shift computation for a uniformly polarized prolate ellipsoid with varying aspect ratio in the absence of screening charges
High-temperature thermal expansion and stability of V2AlC up to 950 degrees C
No full textHerein, we report on the thermal expansion and stability of
V2AlC in the 25–950 C temperature range. The sample was
heated in an Argon atmosphere in a quartz capillary and the
thermal expansion was measured using a X-ray synchrotron radiation
source. Up to the maximum temperature explored, there
were no signs of decomposition or phase transitions. The temperature
variation of volumetric thermal expansion is given
by a=2.53(5)x10-5 +5.75(3)x10-9 T C-1. At 9.40x10-6 C-1, the thermal expansions along both the a and c
lattice directions are quite comparable; in other words, there is
little thermal expansion anisotropy in V2AlC
Thermal expansion and stability of Ti2SC in air and inert atmospheres
No full textThe thermal expansion and stability of predominantly single-phase Ti2SC powders in argon and air was investigated by Rietveld analysis of
synchrotron X–ray diffraction spectra. When the sample was heated in an Ar atmosphere, it started to dissociate into TiS2 (see footnote 1) at
≈400 ◦C. At 8.5 (5)×10−6 ◦C−1 and 8.8 (2)×10−6 ◦C−1 the thermal expansion coefficients along the a and c-directions, respectively, are quite
similar. The volumetric thermal expansion is 25.2 (5)×10−6 ◦C−1. When Ti2SC was heated in air, it started to oxidize, at 400 ◦C, first to anatase,
which converts, at higher temperatures, to rutile. The sulfur and carbon atoms presumably diffuse outward and escape as gases
An Architecture for Mobile Databases
No full textThe use of mobile computers is gaining popularity. The number of users with laptops and notebooks is increasing and this trend is likely to continue in the future where the number of mobile clients will far exceed the number of traditional xed clients. Applications running on mobile clients download information by periodically connecting to repositories of data. Mobile clients constitute a new and different kind of workload and exhibit different access patterns than those seen in traditional client server systems. Though le systems have been modified to handle clients that are capable of downloading information, updating the information while disconnected, and later reintegrating the updates, databases have not been redesigned to accommodate mobile clients. Thus, there is a need to support mobile clients in the context of client server databases. In this paper, we present a new architecture for database systems which takes mobile environments into consideration. This architecture allows us to address issues of concurrency control, disconnection, replica control in mobile databases. We also propose the concept of hoard keys which facilitates hoarding. We present simulation results that illustrate the performance of an example database system with both disconnected and traditional clients.Technical report DCS-TR-35
Biocidal Efficacies of Contact Lens Disinfecting Solutions Against International Organization for Standardization (ISO) Compendial Organisms
No full textJennifer Corwin-Buell, Denise Callahan, Deborah McGrath, Kimberly Millard, Gary Mosehauer, Nitasha R Phatak Vision Care, Bausch & Lomb Incorporated, Rochester, NY, USACorrespondence: Nitasha R Phatak, Vision Care, Bausch & Lomb Incorporated, Rochester, NY, USA, Tel +1 585-413-6397, Email [email protected]: This study was conducted to evaluate and compare the in vitro disinfection efficacies of six commercial lens cleaning and disinfecting products for planned replacement soft contact lenses.Methods: Disinfection efficacies of five multi-purpose solutions (MPSs) and one hydrogen peroxide solution (HPS) as control were evaluated in the presence of organic soil according to the International Organization for Standardization (ISO, Geneva, Switzerland) ISO 14729 stand-alone test protocol. The five specified compendial organisms, three bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, and Serratia marcescens) and two fungi (Candida albicans and Fusarium solani) were incubated with each solution under standard conditions, after which microbes were recovered and quantified.Results: Each of the solutions evaluated met or exceeded the standard’s primary criteria (3-log reduction of bacteria and 1-log reduction of fungi) after incubation for the manufacturer-recommended soaking time, except for COMPLETE MPS, which achieved only 0.4 ± 0.1 average log reduction for C. albicans. However, differences in efficacy between the solutions were noted. Average log reduction across all microbes for Biotrue Hydration Plus (4.6 ± 0.1) was comparable to that for CLEAR CARE PLUS HPS (4.3 ± 0.1) and greater than those for OPTI-FREE puremoist (3.6 ± 0.1), OPTI-FREE Replenish (4.0 ± 0.2), ACUVUE RevitaLens (3.9 ± 0.03), and COMPLETE MPS (3.6 ± 0.1). Biotrue Hydration Plus was especially effective at reducing the population of C. albicans (4.2 ± 0.7-log reduction).Conclusion: Products marketed for planned replacement soft CL disinfection generally meet the ISO 14729 standard’s primary criteria for reducing populations of compendial organisms, with larger differences between solutions noted with C. albicans.Keywords: multi-purpose solution, MPS, hydrogen peroxide solution, HPS, disinfection, myristamidopropyl dimethylamine, MAPD, polyhexamethylene biguanide, PHMB, ISO 1472
Database Server Organization for Handling Mobile Clients
No full textThe use of mobile computers is gaining popularity. The number of users with laptops, notebooks is increasing and this trend is likely to continue in to the future where the number of mobile clients will far exceed the number of traditional fixed" clients. Applications running on the mobile clients download information by periodically connecting to repositories of data stored in either databases or file systems. Such mobile clients constitute a new and different kind of work load and exhibit a different access pattern than seen in traditional client server systems. Though file systems have been modified to handle clients that can download information, disconnect, and later reintegrate, databases have not been redesigned to accommodate mobile clients. There is a need to support mobile clients in the context of client server databases This paper is about organizing the database server to take into consideration the access patterns of mobile clients. We propose a concept of hoard key which captures these access patterns. Three different techniques for organizing data at the server based on the hoard key are presented. We argue that each technique is suited for a particular workload. The workload is a combination of requests from mobile clients and traditional clients. This reorganization also allows us to address issues of concurrency control, disconnection, replica control in mobile databases.
We present simulation results that show the performance of server reorganization using hoard keys. We also provide an elaborate discussion of issues resulting from this new reorganization in this new paradigm that includes mobile clients and traditional clients.Technical report DCS-TR-32
Bounded locking for optimistic concurrency control
No full textOptimistic methods of concurrency control are gaining popularity. This is especially true with the resurgence of mobile and distributed databases, which inherently rely on optimistic techniques to improve availability and performance of the database system. A key problem with optimistic techniques is that they do not perform well in highly conflict prone environments. Pessimistic techniques, especially locking, perform much better under these circumstances.
In this paper we explore a hybrid technique that provides locking for high conflict data items and optimistic access for the rest. While hybrid techniques have been proposed in earlier literature, our technique is unique in that it is self tuning and does not require the transaction manager, the transaction or the user to incorporate any additional knowledge or to specify which data items or transactions are optimistic. Rather, the system uses an LRU data structure called lock buffer to maintain an optimal level of locks in the system. This data structure enhances the performance of the basic optimistic model by automatically providing locking for highly conflict prone data. A unique feature of our algorithm is that locks may be evicted from the lock buffer in an LRU fashion, if the number of data items for which locks are requested exceeds the size of the lock buffer. All transactions affected by such an eviction of locks automatically “become” optimistic with respect to the evicted data items.Technical report DCS-TR-38
Mechanism study of reversible resistivity change in oxide thin film
No full textHere we present our findings related to the mechanism of reversible resistivity in Pt/Ti
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