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J W Choi

Publications and source records attributed to J W Choi.

100 records · Page 6Linked to original sources
PubMed1989

Effects of fixation on cell volume of marine planktonic protozoa.

The effects of fixation on the cell volume of marine heterotrophic nanoflagellates and planktonic ciliates were investigated. Decreases in cell volume depended on the combination of the protozoan taxa and the particular fixative. For a particular fixative and protozoan species, degree of shrinkage was independent of physiological state. The volume of fixed cells was found to be approximately 20 to 55% lower than the cell volume of live organisms. For the heterotrophic microflagellates, the fixatives ranked, in order of decreasing effect on cell volume, as glutaraldehyde, formaldehyde, acid Lugol's solution, and modified van der Veer solution. With oligotrichous ciliates and a tintinnid ciliate, formaldehyde caused less shrinkage than glutaraldehyde or acid Lugol's solution. With the aldehyde fixatives, the microflagellates were found to shrink more than the ciliates. Differential effects of fixation on cell volumes may result in an underestimation of the biomass of certain protozoan taxa in natural samples.

Journal Article↗
PubMed1989

A reduction factor in goodness-of-fit and independence tests for clustered and weighted observations.

Situations often arise in a large-scale household survey where a complex probability sample of clusters rather than of individuals is drawn from a large population. Typically, the clusters of such complex samples include a number of correlated members. The responses of these members are then weighted to obtain estimates for the population. Such weighted data are commonly published by the National Center for Health Statistics and other U.S. federal agencies. Frequently, problems arise when such data are tested by usual chi-square test statistics for goodness of fit or independence. Researchers have discovered that the usual chi-square tests provide spuriously inflated results when applied to cluster samples and that new methods are required to correct such problems. This paper proposes a strategy for a goodness-of-fit or independence test based on correlated and weighted data arising in cluster samples, and provides a factor that validly reduces the inflation of the usual chi-square statistics. This method is applied to the chronic condition data collected from the St Paul-Minneapolis, Minnesota, primary sampling unit (PSU) during the 1975 National Health Interview Survey (NHIS). This analysis, together with simulation studies presented elsewhere, provides evidence that the usual chi-square statistics from such data can be corrected for the impacts of clustering and weighting by use of the proposed reduction factor.

Analysis of Variance↗
PubMedDate not supplied

Unusual renal cell carcinomas: a pictorial essay.

Renal cell carcinoma (RCC) is the most common solid renal neoplasm. Clear cell (conventional) carcinoma is the most common pathologic subtype of RCC. Usually RCC is a hypervascular, solid, solitary mass with contour bulging. However, RCC can manifest different features according to the pathologic tumor subtypes. Preoperative diagnosis of cyst-associated RCC is very difficult, especially in cases of RCC originating in a cyst. Multiple or bilateral presentation of RCC occurs in fewer than 5% of cases. In addition, RCCs may demonstrate unusual findings such as infiltrative growth mimicking transitional cell carcinoma, fatty component mimicking angiomyolipoma, severe perinephric infiltration, and extensive calcifications mimicking inflammation or other tumor. RCCs can be associated with hereditary diseases such as von Hippel-Lindau disease. Familiarity with these radiologic features of unusual RCCs can help ensure correct diagnosis and proper management.

Adult↗
PubMedDate not supplied

A tether-free, moving actuator total artificial heart.

An electromechanical moving-actuator TAH was developed and implanted for 5 days in a calf experiment. The efficiency and durability were further improved using pendulous motion of the actuator. This new pendulum pump has a circular motion produced by gear mechanisms connected to the motor. It has a height (from valves to housing bottom) of 7 cm and centrally directed inlets and outlets for good fittability. Active filling (-10 mmHg) inside inner blood sacs was produced by the suction effects of the outer sacs attached to a moving actuator. Two acute animal experiments were performed using the pendulum pump with a Coridale sheep (50 kg weight), and a male calf (70 kg weight). A test was made of 30 minutes of tether-free operation of the implanted pendulum pump inside the small chest of the calf. The pump shows the engineering feasibility of the implantable electrical TAH inside a human chest cavity.

Animals↗
PubMedDate not supplied

The fluid dynamic effect on protein adsorption in left ventricular assist devices.

Plasma protein adsorption onto an artificial surface is strongly influenced by not only the surface characteristics of materials, but also by the fluid dynamics inside the blood pump, and it would influence subsequent platelet adhesion or activation, which plays a major role in the initiation of thrombus formation at the blood-material interface in vivo. In vitro flow visualization of an electrohydraulic LVAD was performed by a video camera (CCD, Hitachi) and an image processor (PC VISION PLUS) with an IBM PC. The electrohydraulic LVADs were implanted in mongrel dogs of approximately 20 kg. The authors sectioned the blood contacted ventricle after animal death according to the level of shear rate. Because analysis of adsorbed protein might be influenced by the size of the ventricle segment, the number of segments was limited to eight per ventricle. Platelet adhesion and its morphology were observed by scanning electron microscopy (SEM). Adsorbed plasma proteins (fibrinogen, albumin, and IgG) on each segment were quantified by enzyme linked immunosorbent assay (ELISA). The specimens were soaked in 2% (wt/vol) SDS/PBS for 2 days and the released protein concentration assessed. A well developed large vortex was observed at the center of the artificial ventricle. Polyurethane blood pumps displayed different degrees of protein adsorption and subsequent platelet adhesion on each segment.

Adsorption↗