Integral equations applied to wave propagation in two dimensions: modeling the tip of a near-field scanning optical microscope.

We present a Green's-function/Green's-theorem integral equation approach to numerically modeling two-dimensional, s-polarized, wave propagation problems effectively for a variety of geometries. The model accurately calculates both near fields and far fields because of the minimal assumptions made on the behavior of the scattered radiation. The method was applied to modeling light emission from a near-field scanning optical microscope fiber tip. Several convergence and energy tests were used to give confidence in the results. The behavior of intensity and power near the tip was investigated. The effects of changing the dielectric constant of a sample material located below the tip were also examined.

Localization of catheter-induced urinary tract infections: interpretation of bladder washout and antibody-coated bacteria tests.

Accurate differentiation of upper from lower urinary tract infection (UTI) has been reported based on the presence or absence of antibody-coated bacteria (ACB) in the urinary sediment. The specificity of ACB localization in adults has been reported to be high based on a strong correlation with localization results obtained with the bladder washout technique. The present study examines the efficacy of ACB testing with respect to accurate anatomic localization of UTI in 20 studies in 14 patients exhibiting bacteriuria as a result of chronic urethral catheterization. 17 studies (85%) demonstrated significant ACB. Localization of UTI was assessed in each study by the bladder washout technique. Following instillation of a washout solution, a normal decrease in colony counts was observed in only 3 studies (15%), a frequency significantly lower than the value of 90% previously reported in noncatheterized bacteriuric patients (p less than 0.001). Each of these 3 patients was ACB-positive, yet anatomic localization indicated lower tract UTI. The observed characteristics of the 14 patients included the absence of upper tract signs and symptoms, and spontaneous clearing of ACB and bacteriuria following catheter removal. These findings suggest that in chronically catheterized patients, both (1) the observed abnormal resistance of bacteria to bladder washout and (2) the high frequency of positive ACB tests are indices of severe chronic tissue invasion and intense antibody production in the lower urinary tract in this condition and thus not of value in localizing infection to the upper tract. Neither ACB nor washout testing with current techniques can reliably localize UTI in chronically catheterized patients.

Comparison of three cryoprotective solutions for human semen.

Three media for human semen were tested--(1) HAMS F10 supplemented with fructose, glycine and glycerol (MHAMS), (2) another chemically defined medium, but specifically designed for human semen (HSPM) and (3) medium containing egg yolk (EYCM). Twenty ejaculates of donor quality were divided into three aliquots, each aliquot was mixed with a different medium, the solutions were vapour frozen, and stored at -196 degrees C. Motility and quality of motility were measured 0.5 h and 3 h after thawing. Average cryosurvivals 0.5 h after thawing for MHAMS, HSPM and EYCM were 44.1 (s.d. = 17.0)%, 56.0 (s.d. = 15.3)% and 66.0 (s.d. = 10.8)%, respectively; the proportions of ejaculates with cryosurvival below 50% were 11/20, 5/20 and 1/20 respectively. The results indicated that the EYCM medium had clear advantages over other cryoprotective solutions for use in a spermatozoa freezing programme.