Development of an electrostatic positioner for space material processing

This paper describes an electrostatic positioning instrument which was developed at the Jet Propulsion Laboratory to enable experimenters to conduct containerless material science experiments in space. Samples that are to be studied are electrically charged and controlled by the electrostatic force produced by a set of properly arranged electrodes. Three different types of positioners are described, i.e., the dish type, the ring type, and the tetrahedral type. In all these systems, the positioning and the damping of the sample is accomplished by a feedback control system. The advantage of this electrostatic positioning method, in comparison to the other methods, such as acoustic and electromagnetic, lies in the fact that it can operate in a high vacuum and does not require the material to be electrically conductive as long as the material can carry a certain amount of charge

Lead-associated endocarditis: the important role of methicillin-resistant Staphylococcus aureus.

BACKGROUND: Infection is a potentially life-threatening complication of cardiac device implantation. Lead-associated endocarditis (LAE) may be the most serious complication since it is associated with a high mortality. METHODS: The medical records of patients referred to our institution for the treatment of LAE between 1999 and 2007 were reviewed. RESULTS: A total of 51 of 107 patients referred for device-related infections met the criteria for LAE. Of these, 19 occurred within 6 months of their most recent procedure (early), while the remaining 32 occurred more than 6 months later (mean = 31.9 months post procedure). Devices included pacemakers in 33 patients and ICDs in 18 patients. The most common organism responsible for infection was Staphylococcus aureus (S. aureus) followed by coagulase-negative staphylocci (22%) and streptococci (12%). Methicillin-resistant S. aureus (MRSA) accounted for 67% of the S. aureus infections. Coagulase-negative staphylococci were responsible for only 26% of early and 19% of late cases. A distant site of infection was common (26/51 = 51%), particularly in patients with MRSA LAE. The device and leads were removed percutaneously in all patients. Only one patient failed to respond to intravenous antibiotics. CONCLUSIONS: Our data suggest that methicillin-resistant S. aureus is an important pathogen in LAE. Since many infections occur months after the last device procedure, hematogenous spread of organisms from a distant site may be an important contributing factor. These data suggest that strategies to prevent hematogenous infection, particularly with S. aureus, are critical in patients with implantable cardiac devices

Monodisperse, polymeric microspheres produced by irradiation of slowly thawing frozen drops

Monodisperse, polymeric microspheres are formed by injecting uniformly shaped droplets of radiation polymerizable monomers, preferably a biocompatible monomer, having covalent binding sites such as hydroxyethylmethacrylate, into a zone, impressing a like charge on the droplet so that they mutually repel each other, spheroidizing the droplets within the zone and collecting the droplets in a pool of cryogenic liquid. As the droplets enter the liquid, they freeze into solid, glassy microspheres, which vaporizes a portion of the cryogenic liquid to form a layer. The like-charged microspheres, suspended within the layer, move to the edge of the vessel holding the pool, are discharged, fall and are collected. The collected microspheres are irradiated while frozen in the cryogenic liquid to form latent free radicals. The frozen microspheres are then slowly thawed to activate the free radicals which polymerize the monomer to form evenly-sized, evenly-shaped, monodisperse polymeric microspheres

Demagnetization of Quantum Dot Nuclear Spins: Breakdown of the Nuclear Spin Temperature Approach

The physics of interacting nuclear spins arranged in a crystalline lattice is typically described using a thermodynamic framework: a variety of experimental studies in bulk solid-state systems have proven the concept of a spin temperature to be not only correct but also vital for the understanding of experimental observations. Using demagnetization experiments we demonstrate that the mesoscopic nuclear spin ensemble of a quantum dot (QD) can in general not be described by a spin temperature. We associate the observed deviations from a thermal spin state with the presence of strong quadrupolar interactions within the QD that cause significant anharmonicity in the spectrum of the nuclear spins. Strain-induced, inhomogeneous quadrupolar shifts also lead to a complete suppression of angular momentum exchange between the nuclear spin ensemble and its environment, resulting in nuclear spin relaxation times exceeding an hour. Remarkably, the position dependent axes of quadrupolar interactions render magnetic field sweeps inherently non-adiabatic, thereby causing an irreversible loss of nuclear spin polarization.Comment: 15 pages, 3 figure

Physical properties and biocompatibility of Chitosan/soy blended membranes

Blends of polysaccharides and proteins are a source for the development of novel materials with interesting and tailorable properties, with potential to be used in a range of biomedical applications. in this work a series of blended membranes composed by chitosan and soy protein isolate was prepared by solvent casting methodology. in addition, cross-linking was performed in situ with glutaraldehyde solutions in the range 5 × 10–3 – 0.1 M. Furthermore, the influence of the composition and cross-linking on the degradation behaviour, water uptake and cell adhesion was investigated. The obtained results showed that the incorporation of chitosan, associated to network formation by cross linking, promoted a slight decrease of water absorption and a slower degradability of the membranes. Moreover, direct contact biocompatibility studies, with L929 cells, indicate that the cross-linking enhances the capability of the material to support cell growth.Fundação para a Ciência e a Tecnologia (FCT