An arbitrary waveform stimulus circuit for visual prostheses using a low-area multibias DAC

Attempts are underway to construct a retinal prosthesis to recover limited vision for blind patients with retinitis pigmentosa using implantable electronic devices. These microchips provide electrical stimulation to damaged retinal tissues using an array of stimulus circuits. This paper describes improvements to conventional circuit designs with significantly decreased implementation area and the ability to support arbitrary stimulus waveforms where an array of such stimulus circuits is required. This yields greater spatial resolution in stimulation owing to more stimulus circuits per chip area. Also introduced are digital-to-analog converter gain prescalar and dc-offset circuits which tune the stimulus circuits to an optimally effective range due to variation in retinal degradation. The prototype chip was fabricated by MOSIS in 1.2-/spl mu/m CMOS technology.     

Dynamic current density of the disk electrode double-layer

With applied potential, the current distribution at the surface of a disk electrode is spatially nonuniform and time dependent. This distribution is important to control in applications that desire a uniform current density profile or minimal corrosion. We examine the current density profile of a capacitive disk electrode subjected to a voltage-step using finite element analysis software to solve the system of partial differential equations. In detailed analyses we show quantitatively that the current density shifts from peripheral enhancement to near-uniformity following 1/2 of the lumped element time constant. As charging continues, the current density is slightly enhanced in the central region. We present curves for the evolution of local "time constants" as time progresses and calculate their effective values. The model is intended to be the basis of future work to control the corrosion profile of biologically implantable electrodes of arbitrary shape. Data suggest a means to control corrosion by retarding the edges of a stimulus pulse. Additionally, smaller electrodes may be more effective in fully utilizing surface area for charge transfer due to their shorter time constants.     

Characterization of porcine sclera using instrumented nanoindentation

Sclera tissue is the outermost protective layer of the eye and often involved in mechanical interactions during ocular medical procedures. In this study, instrumented nanoindentation is evaluated as a methodology for characterizing porcine sclera submerged in phosphate-buffered saline (PBS). Variances within a single sample and between samples are compared. Reduced modulus measurements are used to determine the effects of hydration, mounting conditions, and maximum applied load. Extended in vitro exposure beyond four hours to PBS is determined to decrease sample integrity. The use of glue to secure samples improved data consistency and had no negative effects on measurements. The data suggest that nanoindentation is a high precision method for measuring the reduced modulus of ultra low modulus soft tissue such as sclera (E_r ~ 30 kPa) and illustrates the importance of environmental factors upon material properties.     

The Microcalorimeter for Industrial Applications

To achieve the dramatic increases in x-ray spectral resolution (<20 eV at 1.5k eV) desired by market segments such as the semiconductor industry, NIST developed a transition-edge sensor (TES) microcalorimeter. To bring this exciting, yet demanding, new technology to the industrial users, certain criteria must be addressed. Aspects of resolution, cooling and hold time, count rates as well as vibrations are considered. Data is presented to the present efforts to handle these issues as well as discussing development plans for the future.     

Limited humoral immunity in hepatitis C virus infection

BACKGROUND & AIMS: The extremely high rate of chronicity to hepatitis C virus (HVC) infection suggests an inefficient immune response. The humoral immune response to HCV was evaluated in 60 patients with chronic HCV infection and in 12 patients acutely infected with HCV. METHODS: A number of recombinant HCV antigens including the core, envelope 2 (E2), nonstructural (NS) 3, NS4, and NS5 proteins, and NS4a and E2-HVR-1 peptides were used in enzyme-linked immunoassays. RESULTS: Immunoglobulin (Ig) G antibody responses to these viral antigens, except for the HCV core, were highly restricted to the IgG1 isotype. The prevalence of antibodies of the IgG1 isotype specific for the HCV core, E2, E2-HVR1, NS3 (helicase domain), NS4, and NS5 antigens was 97%, 98%, 28%, 88%, 33%, and 68%, respectively. Antibodies of the IgG3 isotype specific for E2, E2-HVR-1, NS3, NS4, and NS5 were detected in a minority of serum samples. The IgG2 and IgG4 isotypes were rarely if ever detected. Furthermore, antibody responses to HCV viral antigens were of relatively low titer and, with the exception of anti-HCV core, were delayed in appearance until the chronic phase of infection. CONCLUSIONS: The IgG1 restriction, low titer, and delayed appearance of antibody responses elicited during HCV infection suggest that the immunogenicity of HCV proteins is limited in the context of natural infection. Inasmuch as recombinant HCV viral antigens perform as relatively normal immunogens in small animals, we suggest that the defective humoral immune responses during HCV infection may be attributable to an "immune avoidance" strategy.     

Elevated mortality from nonalcohol-related chronic liver disease among female rubber workers: is it associated with exposure to nitrosamines?

BACKGROUND: Despite several case reports describing liver toxicity of nitrosamines and the fact that some N-nitroso compounds are used to induce cirrhosis of the liver in animal models, this association has not been investigated in epidemiological studies. METHODS: A cohort of 2,875 female rubber workers who were active on January 1, 1976, or hired thereafter, and who had been employed for at least 1 year in one of five plants producing tires or technical rubber goods was followed for mortality from January, 1976, through December, 1991. Work histories were reconstructed using routinely documented "cost center codes" and classified into six work areas. Age and calendar year standardized mortality ratios (SMR) and 95% confidence intervals (95% CI) were calculated and stratified by plant, work area, year of hire, and years of employment in the respective work area. RESULTS: The excess mortality from cirrhosis of the liver was most pronounced for nonalcohol-related cirrhosis of the liver (ICD-9 571.4-571.9: 10 deaths, SMR 202; 95% CI 97-372). Mortality from alcohol-related cirrhosis of the liver (ICD-9 571.0-571.3: 3 deaths, SMR 153; 95% CI 31-446) and from other alcohol-related diseases (organic psychoses, injury, and poisoning) was not statistically significantly elevated. All 10 cases of nonalcohol-related cirrhosis had worked in production of technical rubber goods (SMR 279; 95% CI 134-514) and risks increased with earlier years of hire and with longer duration of employment in this work area. DISCUSSION: Although our results must be interpreted with caution, they suggest that the observed excess deaths from cirrhosis of the liver are associated with occupational risk factors. In light of additional evidence from case reports and animal data, exposure to nitrosamines may be a plausible risk factor for the observed excess mortality.     

Usage Scenarios for Byte-Addressable Persistent Memory in High-Performance and Data Intensive Computing

Byte-addressable persistent memory(B-APM)presents a new opportunity to bridge the performance gap between main memory and storage.In this paper,we present the usage scenarios for this new technology,based on the capabilities of Intel's DCPMM.We outline some of the basic performance characteristics of DCPMM,and explain how it can be configured and used to address the needs of memory and I/O intensive applications in the HPC(high-performance computing)and data intensive domains.Two decision trees are presented to advise on the configuration options for B-APM;their use is illustrated with two examples.We show that the flexibility of the technology has the potential to be truly disruptive,not only because of the performance improvements it can deliver,but also because it allows systems to cater for wider range of applications on homogeneous hardware.     

Applying texture analysis to materials engineering problems

Textures in materials have been studied extensively since the 1930s following the pioneering work of Wassermann.^1,2 The modern era of texture measurement started in 1949 with the development of the x-ray pole figure technique for texture measurement by Schultz.³ Finally, modern texture analysis was initiated with the publication by Bunge⁴ and Roe⁵ of a mathematical method of pole figure inversion, which is now used to calculate the orientation distribution function (ODF). This article cannot summarize such an extensive body of work, but it does endeavor to provide the background necessary to understand texture analysis; it also illustrates several applications of texture.