Effect of poor control of film processors on mammographic image quality

With the increasingly stringent standards of image quality in mammography, film processor quality control is especially important. Current methods are not sufficient for ensuring good processing. The authors used a sensitometer and densitometer system to evaluate the performance of 22 processors at 16 mammographic facilities. Standard sensitometric values of two films were established, and processor performance was assessed for variations from these standards. Developer chemistry of each processor was analyzed and correlated with its sensitometric values. Ten processors were retested, and nine were found to be out of calibration. The developer components of hydroquinone, sulfites, bromide, and alkalinity varied the most, and low concentrations of hydroquinone were associated with lower average gradients at two facilities. Use of the sensitometer and densitometer system helps identify out-of-calibration processors, but further study is needed to correlate sensitometric values with developer component values. The authors believe that present quality control would be improved if sensitometric or other tests could be used to identify developer components that are out of calibration.

Simplification of antibiotic dose adjustments in renal insufficiency: the DREM system

Many clinicians, unassisted by reference books, are unable to make the required dose adjustment of antibiotics needed when a patient has renal insufficiency. We describe the DREM (dosing in renopathy by easy-to-use multipliers) system, which simplifies the understanding and the process of dose adjustment. DREM is a two-step process: Cockcroft and Gault estimation of creatinine clearance (CLcr) from age, sex, and serum creatinine and calculation of the adjusted dose or dosing interval by multipliers. If the normal dose is multiplied by the dose multiplier (CLcr/100) and the dosing interval by the interval multiplier (100/CLcr), the adjusted dose and interval, respectively, are obtained. Theoretical trough concentrations calculated with the DREM system correlated closely (r = 0.9) with actual concentrations obtained from doses calculated by the Hull and Sarubbi method in 23 patients. With DREM, gentamicin or tobramycin trough concentrations above 2 micrograms/ml were less likely to occur. The DREM system is a simple and easily remembered method for dose adjustments of certain anti-infective agents in renal insufficiency. Dose estimates with this method are reasonably accurate and compare favourably with other standard methods of correction.

Stability analysis for grating-tuned strong-external-feedback semiconductor lasers

We give a simple stability analysis within the scope of steady-state solution for the grating-tuned strong-external-feedback semiconductor lasers. In our model, a fluctuation in the refractive index of an active medium through the coupling of carrier density will cause another fluctuation in the refractive index. If the latter is always smaller than the former, the fluctuation will be damped, and therefore the corresponding operating point of the laser is stable. Our analysis indicates that there are various stable and unstable operating-frequency ranges for various reflectivities of the internal facet of the laser diode. In addition, it agrees well with the experimental results and explains the bistability of threshold gain versus operating frequency.

Analysis of polarization dynamics by singularity decomposition method

The driving point immittance (impedance or admittance) function is commonly used in electrical characterization of polarized materials and interfaces. The immittance function typically attenuates following a power function dependence on frequency. This fact has been recognized as a macroscopic dynamical property manifested by strongly interacting dielectric, viscoelastic and magnetic materials and interfaces between different conducting substances. Linear interfacial polarization processes which occur at metal electrode-electrolyte interfaces have been represented by the Fractional Power Pole [FPP] function in single or multiple stages. The FPP function is referred to as the Davidson-Cole function in the dielectrics literature. A related function widely used in mathematical modeling of dielectric and viscoelastic polarization dynamics is the Cole-Cole function. The fractional power factor which parametrizes the FPP or the Davidson-Cole function has been shown earlier to equal the logarithmic ratio of the locations of the pole-zero singularities. In this paper we first review a modified form of the singularity decomposition of the FPP function accomplished within a prescribed error range. The distribution spectrum and the corresponding simulation by a cascade R-C network, as opposed to the synthesis by a ladder R-C network, are readily obtained as the next step in the simulation. The method is then applied to decompose the Cole-Cole function; the pole-zero placement of the singularity function is determined and the equivalent cascade R-C network is synthesized.

[Effects of McAbs HIP2, APT4 and HI117 on the human platelet cytoskeleton]

The effects of monoclonal antibodies HIP2, APT4 and HI117 on the platelet cytoskeleton were investigated. The results showed that HIP2, APT4 and HI117 could induce an increase of platelet cytoskeleton materials in PRP. The action of HIP2 and APT4 could be obviously inhibited by the calmodulin inhibitor EBB. The inhibition rates of EBB were 76.3% and 48.95%, respectively. But EBB couldn't inhibit the HI117-induced an increase of platelet cytoskeleton materials. EBB could completely inhibit APT4-induced platelet aggregation(100%) and partially inhibit HIP2-induced platelet aggregation (14.26%). It couldn't inhibit HI117-induced platelet aggregation. These McAbs couldn't induce aggregation and actin mobilization in washed platelets in the presence of EDTA. The results indicate that platelet aggregation and the increase of actin induced by these McAbs, in addition to Ca2+, could be related to a factor or factors in the plasma. The Ca(2+)-CM system might play an important role in platelet aggregation and actin mobilization induced by HIP2 and APT4.

Genetic and physical analyses of sister chromatid exchange in yeast meiosis

We have used nonessential circular minichromosomes to monitor sister chromatid exchange during yeast meiosis. Genetic analysis shows that a 64-kb circular minichromosome undergoes sister chromatid exchange during 40% of meioses. This frequency is not reduced by the presence of a homologous linear minichromosome. Furthermore, sister chromatid exchange can be stimulated by the presence of a 12-kb ARG4 DNA fragment, which contains initiation sites for meiotic gene conversion. Using physical analysis, we have directly identified a product of sister chromatid exchange: a head-to-tail dimer form of a circular minichromosome. This dimer form is absent in a rad50S mutant strain, which is deficient in processing of the ends of meiosis-specific double-stranded breaks into single-stranded DNA tails. Our studies suggest that meiotic sister chromatid exchange is stimulated by the same mechanism as meiotic homolog exchange.

Stereoselective degradation of the fenoprofen acyl glucuronide enantiomers and irreversible binding to plasma protein

Stereoselective degradation of fenoprofen (FEN) glucuronides and irreversible binding of FEN enantiomers to human serum albumin via their glucuronides were studied. At different pH values, 37 degrees C, and in the absence of albumin, degradation half-lives were diastereomeric, resulting mainly from a combination of hydrolysis and acyl migration. Lower pH enhanced FEN glucuronide stability and reduced the extent of irreversible binding. The degradation rate of R-FEN glucuronide was greater than that of the S-glucuronide (S-FEN). When human serum albumin was added to the medium, stability was decreased as compared to protein-free buffer. FEN glucuronides were readily hydrolyzed to parent drug, indicating an esterase-like activity of the albumin molecule. In vitro irreversible binding was higher for R-FEN (1.22% +/- 0.36) than for S-FEN glucuronide (0.76% +/- 0.12), when a 0.1 mM concentration of each conjugate enantiomer was incubated under physiological conditions (pH 7.4, 37 degrees C). Incubation with unconjugated FEN did not lead to measurable irreversible binding. Analysis of plasma samples from a clinical study showed that enantioselective irreversible binding of FEN to plasma proteins also occurs in vivo. After administration of a single 600-mg dose of racemic FEN to six healthy volunteers, covalent binding of R- and S-FEN to plasma proteins was measured in all subjects. The percentage of S-FEN protein adduct was greater than that of its R-enantiomer adduct. Total amounts of FEN irreversibly bound to plasma protein in vivo were also very low (1.02 +/- 0.32 and 3.23 +/- 0.85 mol/mol protein x 10(-4) for R- and S-FEN, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of ceftriaxone binding to immunoglobulin G and potential clinical significance

The interaction between immunoglobulin G (IgG) and ceftriaxone was studied. Using an ultrafiltration method, we performed dose ranging studies at a ceftriaxone concentration range of 1 to 720 micrograms/ml in the presence of various concentrations of human IgG, human serum albumin (HSA), and combinations of IgG and HSA at pH 7.4 and 37 degrees C. The results showed that ceftriaxone binding to IgG was nonlinear and was consistent with the presence of two binding sites that possess different binding capacities and affinities. Except for increased peak percent binding as the IgG concentration increased, the binding characteristics did not change with IgG concentration. Binding to HSA was consistent, with the presence of only one high-affinity binding site. A mathematical model based on the observed data was constructed; this model was used to predict protein binding at various concentrations of drug, IgG, HSA, or combinations of IgG and HSA in buffer and in plasma medium. Correlations between the observed versus the predicted values were excellent in both media. Simulations with the model indicated that patients with hypergammaglobulinemia have an increased potential of being exposed to prolonged subinhibitory concentrations of ceftriaxone if the drug is given once every 24 h.

Extensive 3'-overhanging, single-stranded DNA associated with the meiosis-specific double-strand breaks at the ARG4 recombination initiation site

Meiosis-specific double-strand breaks occur at the initiation site for meiotic gene conversion in the yeast ARG4 gene. Here we show that the break fragments end in extensive 3'-overhanging, single-stranded tails. The single-stranded tails very in length, generating a gradient of single-strandedness that parallels the gradient of gene conversion frequencies in ARG4. In strains carrying a rad50S mutation, which blocks meiotic recombination, the extensive single-stranded tails do not form, suggesting that their generation is an obligatory step in meiotic recombination. Using the rad50S mutant, we have mapped the site of the ARG4 break to a small region within the genetically defined recombination initiation site. These results strongly support the double-strand break model of meiotic recombination.

Early events in liver allograft rejection. Delineation of sites of simultaneous intragraft and recipient lymphoid tissue sensitization

The early events of liver allograft rejection in untreated rats were studied in the DA to BN rejection strain combination and compared with DA and BN liver isograft recipients. In the liver allografts, T-cell infiltration first occurred at 2 days after transplantation and localized to the portal triads and subjacent to the terminal hepatic venules (THV), regions rich in intensely Ia + spindle and dendritic-shaped interstitial cells. Double staining showed distinct 'clustering' between donor Ia-positive dendritic-shaped cells and W3/25+ infiltrating lymphocytes, or to a lesser extent, OX8+ cells. The infiltrating mononuclear cells underwent blastogenesis and proliferated in both the triads and THV regions at 3 and 4 days. Donor Ia-positive cells were also noted in the W3/25+ periarterial lymphatic sheath and marginal zone of the recipient spleen 1 day after transplantation. The number of these cells in the spleen peaked at 3 to 4 days, but were no longer detectable by 10 to 12 days. Mitotic activity became evident in these same regions by days 3 and 4. Paracortical blastogenesis (day 2) and proliferation (days 3 and 4) were also noted in the regional lymph nodes of liver allograft recipients, but no donor Ia+ cells were found in the mesenteric nodes or thymus of the allograft recipients. These results demonstrate that sensitization of the recipient lymphoid tissue to liver allografts can occur both peripherally (intragraft) and centrally (spleen and lymph nodes). Passenger leukocytes (donor dendritic cells) are likely the primary stimulators of the rejection reaction. Still, it is probable that other pathways of sensitization exist.

Stereoselective analysis of fenoprofen and its metabolites

Reversed-phase high-performance liquid chromatographic assays have been developed to quantitate simultaneously fenoprofen and its major metabolites as well as to distinguish between their R- and S- enantiomers following a single oral dose of 600 mg racemic fenoprofen to healthy volunteers. The compounds are extracted from plasma (after precipitation of plasma protein) or assayed directly in diluted urine samples employing a gradient solution on a C18 column and ultraviolet detection. Two internal standards, ketoprofen and flunoxaprofen, are used to allow measurement of very low (0.05 microgram/ml) and high (70 microgram/ml) concentrations in each sample. R- and S-fenoprofen glucuronides can be separated directly; the 4'-hydroxyfenoprofen conjugates are measured via an indirect method by comparing the concentration of 4'-hydroxyfenoprofen before and after hydrolysis. The R- and S-enantiomers of both parent and 4'-hydroxy metabolite are derivatized with L-leucinamide via an ethyl chloroformate intermediate and subsequently analyzed on a C18 column. Concentrations of metabolites found in plasma were low when compared to parent drug. The S/R ratio of fenoprofen in plasma always exceeds 1 and increases with time after dosage while the S/R ratio of its 4'-hydroxy metabolite remains almost unchanged at 1.1. R-Fenoprofen glucuronide disappears rapidly from plasma as compared to its S-antipode; a less pronounced difference is noted between R- and S-4'-hydroxyfenoprofen conjugates. Fenoprofen is almost completely excreted as its S-acyl glucuronides; the renal clearance of unchanged drug is very low.

Pattern formation in an immobilized bienzyme system. A morphogenetic model

Experimental and theoretical studies of a reaction-diffusion model of two immobilized enzymes participating in the cellular acid-base metabolism, namely glutaminase and urease, are presented. The system shows an unstable steady state at pH 6.0, where any perturbation will drive the system towards a more alkaline or more acidic pH, owing to the autocatalytic behaviour with respect to pH exhibited by both enzymes. When diffusion is coupled to reaction by means of immobilization, different patterns of the internal pH profile appear across the membrane. If the bienzymic membrane is subjected to a perturbation at its boundaries, of the same amplitude but in opposite directions, the internal pH evolves through an asymmetric pattern to attain a nearly symmetric distribution of pH. The pH value at the final steady state is more acidic or more alkaline than the initial state according to the initial and boundary conditions. The final nearly symmetric state is attained more rapidly when less enzyme is immobilized (1.8 x 10(-4) M.s-1 as against 3.3 x 10(-4) M.s-1 of total enzyme activity in the membrane volume). The experimental results agree rather well qualitatively with numerical predictions of the model equations.

Tomography for reconstructing continuous fields from ill-posed multidirectional interferometric data

A computational tomographic technique has been developed to accurately reconstruct continuous flow fields of a simple shape from severely limited interferometric data. The algorithm is based on iterative reconstruction of the complementary field, the difference between the field to be reconstructed and its estimate. Its advantages lie in the treatment of various ill-posed problems in a unified manner and ease of incorporation of a priori information, even an approximate field shape. In principle it can utilize only available data. Test results demonstrated stable convergence and potential for substantial error reduction with a proper field estimate.