Frequency multiplier measurements on heterostructure barriervaractors on a copper substrate

We have fabricated heterostructure barrier varactors (HBV) on a copper substrate, which offers reduced spreading resistance, and improved thermal conductivity compared to an InP substrate. The devices are fabricated without degrading the electrical characteristics. The three-barrier HBV material grown by MOVPE has a leakage current of only 0.1 μA/μm² at 19 V. The maximum capacitance is 0.54 fF/μm². In a frequency tripler experiment a maximum output power of 7.1 mW was generated at 221 GHz with a flange-to-flange efficiency of 7.9%     

Three dimensional write model for magnetic recording

A three dimensional self-consistent write model is developed. Transitions are computed for infinite and finite pole tip narrow track heads on oriented and in-plane isotropic horizontal media. Magnetization patterns and readback on- and off-track are discussed.     

Optimization of guanidination procedures for MALDI mass mapping

Improved procedures for guanidination of lysine-containing peptides, a derivatization that results in increased MALDI mass spectral signal intensities are presented. The complete conversion of lysines to homoarginines can be accomplished in as little as 5 min. The method is demonstrated on a model peptide and on tryptic digests of three proteins. To demonstrate the applicability to proteomics samples, it is successfully applied to the digest of 50 fmol of a protein. Approaches for concentrating and purifying low-quantity protein digests following guanidination are evaluated. Experiments with the model peptide GRGDSPK enable investigation of the specificity of the guanidination reaction.     

Imaging effects in contact recording on particulate media

Contact recording on longitudinal particulate media is modeled self-consistently, including the proper image for the finite gapped head. For moderate ratios of deep gap field to remanent coercivity, the major effect of the proper image occurs in readback, where the reciprocity integral must be performed self-consistently, convolving the head field with the magnetization at each head position. In contact recording the use of proper imaging has a significant effect which predominates in readback and is due to the reversible permeability of the medium. Utilization of proper imaging largely removes the vertical contribution from the readback pulse. However, for higher deep gap fields, the first readback causes irreversible erasure of the high-frequency components of the transition.     

Declining seroprevalence in a very large HIV epidemic: injecting drug users in New York City, 1991 to 1996

OBJECTIVES: This study assessed recent trends in HIV seroprevalence among injecting drug users in New York City. METHODS: We analyzed temporal trends in HIV seroprevalence from 1991 through 1996 in 5 studies of injecting drug users recruited from a detoxification program, a methadone maintenance program, research storefronts in the Lower East Side and Harlem areas, and a citywide network of sexually transmitted disease clinics. A total of 11,334 serum samples were tested. RESULTS: From 1991 through 1996, HIV seroprevalence declined substantially among subjects in all 5 studies: from 53% to 36% in the detoxification program, from 45% to 29% in the methadone program, from 44% to 22% at the Lower East Side storefront, from 48% to 21% at the Harlem storefront, and from 30% to 21% in the sexually transmitted disease clinics (all P < .002 by chi 2 tests for trend). CONCLUSIONS: The reductions in HIV seroprevalence seen among injecting drug users in New York City from 1991 through 1996 indicate a new phase in this large HIV epidemic. Potential explanatory factors include the loss of HIV-seropositive individuals through disability and death and lower rates of risk behavior leading to low HIV incidence.     

Instrument for measurement of tap radial relief

An instrument has been developed to measure the radial relief of all types of taps to a high degree of accuracy. It provides a visual record of geometrical irregularities and of surface texture. The radial profile of a variety of centred rotary cutting tools can also be displayed and measured     

Chemical composition of urea-treated corn silage containing added dried whey or whey products

Dried whole whey, partially delactosed whey, or lactose were added at two percents (1 and 2% dried whole whey equivalent) to corn silage and .5% urea-treated corn silage and .5% urea-treated corn silage in laboratory silos. Additions of whey products reduced nonprotein nitrogen and ammonia nitrogen in urea-treated corn silage. Dried whey was most effective in reducing ammonia nitrogen while lactose was least effective. This reduction in ammonia nitrogen with no change in total nitrogen indicated that additions of whey products to urea-treated corn silage may have added to the corn silage. Amount of addition of whey products did not influence results. Acid detergent fiber was slightly reduced by all additions and was lowest in corn silages with added lactose. Lactic acid, acetic acid, and pH were higher in corn silages containing urea but were not affected by additions of whey products.