Quantitation of Cefaclor in Pharmaceutical Dosage Forms Using High Performance Liquid Chromatography

A stability-indicating high-performance liquid chromatography for the quantitation of cefaclor in pharmaceutical dosage forms has been developed. The method is accurate and precise with a percent relative standard deviation of 1.2 based on 5 readings. A number of inactive ingredients present in the capsules and suspensions did not interfere with the assay procedure. The extraction procedure from the dosage forms is very simple. The recovery from the synthetic mixtures was quantitative. The capsules which had expired 3 years ago lost only 3% of the potency. The drug appears to be very sensitive to strong acids or bases since a 5 minute boiling caused 100% degradation of drug in both the solutions.     

Interconnection of Subsystem Reduced-Order Models in the Electrothermal Analysis of Large Systems

Heat conduction in an electronic device is commonly modeled as a discretized thermal system (e.g., finite element or finite difference models) that typically uses large matrices for solving complex problems. The large size of electronic-system heat transfer models can be reduced using model reduction methods and the resulting reduced-order models can yield accurate results with far less computational costs. Electronic devices are typically composed of components, like chips, printed circuit boards, and heat sinks that are coupled together. There are two ways of creating reduced-order models for devices that have many coupled components. The first way is to create a single reduced-order model of the entire device. The second way is to interconnect reduced-order models of the components that constitute the device. The second choice (which we call the "reduce then interconnect" approach) allows the heat transfer specialist to perform quick simulations of different architectures of the device by using a library of reduced-order models of the different components that make up the device. However, interconnecting reduced-order models in a straightforward manner can result in unstable behavior. The purpose of this paper is two-fold: creating reduced-order models of the components using a Krylov subspace algorithm and interconnecting the reduced-order models in a stable manner using concepts from control theory. In this paper, we explain the logic behind the "reduce then interconnect" approach, formulate a control-theoretic method for it, and finally exhibit the whole process numerically, by applying it to an example heat conduction problem     

A new binary accelerator system for the sulfur vulcanization of natural rubber latex

Vulcanization of latex products are usually carried out at lower temperatures compared to dry rubber products. It has been suggested that, in latex vulcanization systems where thiourea is used as a secondary accelerator, it acts as a nucleophilic reagent facilitating the cleavage of the sulfur bonds in the primary accelerator like TMTD or CBS at lower temperature. But no conclusive proof is given to such a postulate. In the present study 1-phenyl-2,4-thiobiuret (DTB II) and 1,5-diphenyl-2,4-dithiobiuret (DTB III), which are more nucleophilic than thiourea and which vary in their nucleophilic reactivity, were studied as secondary accelerators along with tetramethyl thiuram disulphide (TMTD) and N-cyclohexylbenzothiazyl sulphenamide (CBS) in the vulcanization of natural rubber latex. These binary systems were found to be very effective in reducing the optimum vulcanization time. Also it was noted that 1-phenyl-2,4-dithiobiuret, which is more nucleophilic, is more reactive (as observed from the reduction in optimum cure time) as a secondary accelerator, indicating a nucleophilic reaction mechanism in the vulcanization reactions under review. The optimum dosages of the secondary accelerators required were derived. Physical properties like tensile strength, 300% modulus, and elongation at break of the latex vulcanizates were also studied. There is a definite advantage with respect to many of these properties for dithiobiuret systems compared to the systems containing TMTD alone or TMTD/thiourea. DTB III gives higher values in many of these physical properties than DTB II. Chemical characterization of the vulcanizates was also carried out to correlate the physical properties with the type of chemical crosslinks formed. © 1993 John Wiley & Sons, Inc.     

ESTIMATION FOR NONNEGATIVE AUTOREGRESSIVE PROCESSES WITH AN UNKNOWN LOCATION PARAMETER

Abstract. Consider an AR(1) process given by X ^t=γ+ø X _t+ Z _t≥ 1. where 0 ≤γ, 0 ≤ø 1 are unknown parameters and the innovations Z _t, ≥ 1, are independently and identically distributed positive random variables. We propose estimates of (γø) which are obtained as the solution to a linear programming problem and establish their strong consistency. When the Z _ts have the exponential distribution. our estimate becomes the conditional maximum likelihood estimate given X ₀. Under the assumption of regular variation of the innovation distribution at its left and right endpoints (assumed to be 0 and ∝ respectively), we establish asymptotic limit laws for the estimates. Consistent estimators for a class of moving-average processes with heavy-tailed innovation distribution are also presented.     

Evaluation of Nd:YAG-pumped Raman shifter as a broad-spectrum light source

We have examined the utility of a gas-filled, Nd:YAG-laser-pumped Raman shifter as a possible broad-spectrum light source. Six to nine new output frequencies with pulse energies above 1 μJ are produced when a pure-hydrogen or pure-methane Raman shifter is pumped with 40 mJ of secondharmonic, 20 mJ of third-harmonic, or 11 mJ of fourth-harmonic pump pulse energy. Optimum output occurs at pressures of approximately 10 atm for the pure-gas experiments. We also report the output frequencies and pulse energies of a mixed hydrogen-methane Raman shifter pumped by 20 mJ of the third harmonic of the laser for various proportions of the two gases at pressures up to nearly 20 atm. Depending on composition and pressure, over a dozen new output lines with pulse energies over 1 μJ can be produced. We discuss the nonlinear processes involved, the optimum operating conditions, and the suitability of the source for our application of groundwater monitoring.     

A High-Precision Quasi-optical Polarizer for Zeeman Splitting Observations

A series of grooved dielectric quarter-wave plates was made for radio astronomical Zeeman splitting observations at millimeter wavelengths. To meet the stringent requirements on reflection and polarization purity, a design method was formulated based on optimization of multiple reflections. The method solves the problem of achieving low reflections for both polarization components while attaining high purity of circular polarization. Several plates have been manufactured, tested, and used successfully for astronomical observations.     

Characterization and profile optimization of SiGe pFETs onsilicon-on-sapphire

We present the details of the fabrication, electrical characterization, and profile optimization of a SiGe pFET on silicon-on-sapphire (SOS) technology. The results show that the SiGe pFETs have higher low-field mobility (μ_eff), transconductance (g_m), and cutoff frequency (f_T) than a comparable Si pFET. At low temperature (85 K), a secondary peak is observed in the linear g_m of the SiGe pFETs and is attributed to hole confinement in the SiGe channel. The effect of reducing the SOS film thickness on the mobility and short-channel performance is studied. A low-frequency noise study shows significant improvement in the SiGe pPETs over comparable Si pFETs, and is attributed to a lower sampling of interface trap density caused by the band offset at the oxide interface due to SiGe. Drain Induced Back Channel Inversion (DIBCI) is shown to occur in short gate length devices, resulting in high off-state leakage current through conduction at the back silicon-sapphire interface. The paper also discusses important optimization issues in the design of 0.25-μm gate length SiGe pFETs. A novel structure is proposed which optimizes the threshold voltage, maximizes hole confinement gate voltage range and cutoff frequency, while at the same time minimizing DIBCI to make the design usable to gate lengths as short as 0.25 μm     

5-GHz 32-bit integer execution core in 130-nm dual-V/sub T/ CMOS

A 32-bit integer execution core containing a Han-Carlson arithmetic-logic unit (ALU), an 8-entry /spl times/ 2 ALU instruction scheduler loop and a 32-entry /spl times/ 32-bit register file is described. In a 130 nm six-metal, dual-V/sub T/ CMOS technology, the 2.3 mm/sup 2/ prototype contains 160 K transistors. Measurements demonstrate capability for 5-GHz single-cycle integer execution at 25/spl deg/C. The single-ended, leakage-tolerant dynamic scheme used in the ALU and scheduler enables up to 9-wide ORs with 23% critical path speed improvement and 40% active leakage power reduction when compared to a conventional Kogge-Stone implementation. On-chip body-bias circuits provide additional performance improvement or leakage tolerance. Stack node preconditioning improves ALU performance by 10%. At 5 GHz, ALU power is 95 mW at 0.95 V and the register file consumes 172 mW at 1.37 V. The ALU performance is scalable to 6.5 GHz at 1.1 V and to 10 GHz at 1.7 V, 25/spl deg/C.     

Frequency tunable metallo-dielectric structure for backscattering reduction

Electromagnetic scattering behaviour of a superstrate loaded metallo-dielectric structure based on Sierpinski carpet fractal geometry is reported. The results indicate that the frequency at which backscattering is minimum can be tuned by varying the thickness of the superstrate. A reduction in backscattered power of /spl sim/44 dB is obtained simultaneously for both TE and TM polarisations of the incident field.