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Biomedical subjects

A Engel

Publications and source records attributed to A Engel.

At least 289 records · Page 16Linked to original sources
PubMed1987

Pseudocyst in splenic hilus with splenic vein thrombosis. Case presentation and review.

Pseudocyst of the pancreas involving the spleen is a rare event; occlusion of splenic vein is even rarer. The mortality rate of these complications is high and therefore necessitates early diagnosis. Nuclear medicine, ultrasound and computed tomography are helpful, but definitive diagnosis is done by selective celiac or splenic artery arteriography. A case of splenic vein thrombosis due to pancreatic pseudocyst is presented and the literature on splenic involvement by pseudocyst is reviewed.

Adult↗
PubMed1986

Modeling of selection processes with age-dependent birth and death rates.

Two simple models for the competition and selection in age-dependent populations are developed and analyzed mathematically. Following Eigen, competition is introduced by the condition of constant overall-number of the population. In the first model this condition is satisfied by regulation of a dilution flux and in the second case by regulation of a food density. The calculation of maximal fitness is given explicitly for both situations. It is shown that fitness depends in a complicated way on the age-dependence of the birth and death rates. Therefore species have to develop special aging strategies in order to survive in a population under selection pressure. In general, early reproduction is of advantage and increases fitness.

Age Factors↗
PubMed1986

Contrast and resolution of scanning transmission electron microscope imaging modes.

Image blurring due to delocalization of inelastic events was studied for scanning transmission electron microscopy (STEM) of unstained thin sections. The delocalization probability was obtained from the angular distribution of inelastic scattering, which was calculated from experimental electron loss spectra of organic samples. This probability was implemented in a Monte Carlo program to simulate the effects of multiple scattering and delocalization for STEM images collected by either the annular detector or the spectrometer, and images generated by a combination of these two signals. Depending on the illumination, the detector geometry and the energy-loss range selected for imaging the annular detector image is blurred by a non-negligible fraction of inelastically scattered electrons. Simultaneous acquisition of an inelastic image using a spectrometer allows the blurring to be reduced by calculation of either the ratio or the difference of the two darkfield signals. While inherent nonlinearities reduce the interpretability of ratio-contrast images, difference-contrast improves the visibility of details submerged in a diffuse background without introducing artifacts.

Data Display↗
PubMed1986

Stoichiometric model of the photosynthetic unit of Ectothiorhodospira halochloris.

A stoichiometric model of the photosynthetic unit of Ectothiorhodospira halochloris has been obtained by means of scanning transmission electron microscope mass determination and mass mapping in conjunction with polyacrylamide gel electrophoresis. One reaction center, consisting of four single polypeptides, including one cytochrome, is surrounded by six identical light-harvesting complexes, each containing three polypeptides with 2:2:2 stoichiometry. This stoichiometric model was incorporated into the three-dimensional structure of the photosynthetic unit as derived from surface relief reconstructions of the two surfaces of shadowed membranes. The reaction center protrudes substantially from both membrane surfaces and has the cytochrome attached to the periplasmic face in a noncentrosymmetric fashion. The reaction center may assume various orientations within the photosynthetic complexes.

Journal Article↗
PubMed1986

Radiology in war.

Explore the source record for details and available documents.

Abdominal Injuries↗
PubMed1986

Defining family in family medicine: perceived family vs household structure in an urban black population.

This paper explores two hypotheses: first, that household structure, the people who live in one's household, and perceived family, the people one considers members of one's family, are different entities among urban black pregnant women; and second, that the perceived family is a stronger predictor of social, psychological, and health outcomes than is household structure. The study data are from the first interview of a prospective study of a consecutive sample of 140 black pregnant women patients of a Cleveland, Ohio, university hospital family practice center. The study hypotheses are supported: household structure and perceived family differ in their size and the inclusion or exclusion of members of the family of origin and the father of the baby. Household structure is strongly correlated with demographic variables such as age, socioeconomic status, and household income, whereas perceived family is less strongly associated with these measures. Perceived family, but not household structure, is associated with family functioning, measures of psychological status, worries about household change, and better family and parental relationships during the woman's childhood.

Adolescent↗
PubMed1985

Serum sialic acid in malignant tumors, bacterial infections, and chronic liver diseases.

The total serum sialic acid concentration was determined in 2,264 persons with various malignant tumors, bacterial infections, rheumatic diseases, and chronic liver diseases, and in a control group. The thiobarbiturate method according to Warren was used. The upper limit (95% percentile) in the control group was 2.23 mumol/ml. Higher values were found in the groups with neoplasms (mean: 3.04 mumol/ml), inflammatory diseases (e.g., pneumonia: 3.02 mumol/ml), and active rheumatoid arthritis (3.05 mumol/ml). In the group with malignant diseases, the sialic acid concentration at the time of diagnosis was highest for bronchial carcinoma (3.29 mumol/ml) and lowest for breast cancer (2.58 mumol/ml). In chronic liver diseases the mean sialic acid level was lower than in a heterogeneous group of noninflammatory and nonneoplastic diseases. The estimation of the serum sialic acid concentration could be useful in the detection of tumor burden and metastases, and in the evaluation of the later course and prognosis of malignant neoplasms if bacterial/inflammatory and active rheumatoid processes can be excluded.

Adolescent↗
PubMed1985

Polymorphism of reconstituted human epidermal keratin filaments: determination of their mass-per-length and width by scanning transmission electron microscopy (STEM).

We have determined the mass-per-length (MPL) and the width of unstained freeze-dried reconstituted human epidermal keratin filaments by scanning transmission electron microscopy (STEM). Filaments were reassembled from keratins extracted from four different sources: cultured human epidermal cells (CHEC), human callus (CAL), and the living layers (LL) and stratum corneum (SC) of normal human epidermis. MPL histograms of all four keratin filament types could be fitted by a superposition of two or three Gaussians, with their respective major peaks located between 17 and 20 kDa/nm. We interpreted the multiple MPL peaks to represent different polymorphic forms of the reconstituted filaments. The number of subunits per filament cross section calculated from MPL peak positions, average subunit molecular weight, and an axial repeat of the subunits within the filament of 46.5 nm revealed an average difference between polymorphic variants of 7.5 +/- 0.9 subunits. These data suggest that reconstituted human epidermal keratin filaments are made of two to four 8-stranded "protofibrils" (i.e., made of two laterally aggregated 4-stranded protofilaments), in agreement with earlier observations. The average widths of unstained freeze-dried keratin filaments were larger than those of negatively stained filaments: 12.6 nm (9.6 nm) for CHEC, 12.3 nm (9.7 nm) for CAL, 11.6 nm (8.3 nm) for LL, and 11.3 nm (7.9 nm) for SC keratin filaments, with the values in brackets corresponding to negatively stained samples. Assuming the MPL to be proportional to the square of the filament width, there is a good correlation between the MPL and width measurements both for filaments within a given type as well as among those reconstituted from different types of keratin extracts.

Cytoskeleton↗
PubMed1984

Molecular weight of poly(C9). 12 to 18 C9 molecules form the transmembrane channel of complement.

Poly(C9), the tubular 27 S complex forming the transmembrane channel of the membrane attack complex of complement, was purified to homogeneity by gel filtration and sucrose density gradient ultracentrifugation. The molecular weight of poly(C9) was determined by two independent methods in addition to sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. First, sedimentation equilibrium analysis using 0.2% SDS or 1% deoxycholate containing buffer as solvents yielded a point weight average molecular weight exclusive of bound detergent of 0.9 to 1.3 X 10(6) and a weight average molecular weight of all poly(C9) complexes of 1,050,000 +/- 40,000 (S.D.). SDS and deoxycholate binding to poly(C9) was measured in an air-driven ultracentrifuge and was determined to be 0.53 +/- 0.065 (S.D.) g of SDS and 0.26 +/- 0.015 (S.D.) g of deoxycholate/g of poly(C9), respectively. Second, the mass of 27 S poly(C9) devoid of bound detergent was determined by electron scattering of unstained specimens in the scanning transmission electron microscope. The molecular weight obtained by this method was 1,078,000 +/- 194,000. The inner diameter of poly(C9) tubules imaged in top view projections by negative staining electron microscopy varied between 9 and 12 mm. The accumulated data suggest a true heterogeneity of the molecular weight of poly(C9) due to polymers with varying protomer numbers. Using a mean value of 73,500 for the molecular weight of monomeric C9, the protomer number of poly(C9) tubules appear to vary between 12 and 18 C9 subunits. Approximately 50-75% of the tubules have 14 to 16 subunits as deduced from the mass distribution determined by electron scattering and from ring size measurements. It is suggested that poly(C9) tubules with various protomer numbers may arise due to limited flexibility in the C9-C9 interaction.

Complement C9↗
PubMed1984

Unshadowed myosin molecules: STEM mass-maps of myosin heads.

Myosin molecules were directly visualized without heavy metal shadowing by scanning transmission electron microscopy (STEM) under low dose conditions. The general appearance and dimensions of heavy metal-free molecules were similar to those of shadowed myosin, either after freeze-drying without or air-drying with glycerol. Two characteristic configurations of myosin head regions were found, a first type showing two pear-shaped heads with narrow necks and a second type showing two heads connected by an extra mass in the central regulatory domain where the light chains are located. The mass of the latter type (mol. wt. = 265 +/- 39 kd) is in excellent accordance with biochemical data whereas the mass of the first type is somewhat lower (mol. wt. 219 +/- 44 kd).

Animals↗
PubMed1984

3D reconstruction from electron micrographs: its potential and practical limitations.

The 3D structure of stain-penetrated transmembrane channels of E. coli outer membrane porin has been reconstructed from electron microscopic projections. The averaged unit cells of the projected hexagonal porin lattices were calculated by correlation averaging. Amplitude and phase values along the continuous lattice lines were obtained from the unit cell transforms, and continuous curves were fitted using either a cubic spline-fit or by convolution with an appropriate sinc function. The reconstructed model shows that the three channels of a porin triplet merge to a single channel while traversing the membrane. This is in excellent agreement with results of functional studies. Some technical difficulties and limitations as well as the potential of the reconstruction process are discussed.

Bacterial Proteins↗
PubMed1984

Imaging of biological structures with the scanning transmission electron microscope.

The scanning transmission electron microscope (STEM) is discussed in view of biological applications. Theoretical considerations are given, but the emphasis is directed to practical examples from a range of biological projects. The STEM is most efficiently used in elastic and inelastic dark-field modes providing information on the scattering power of the irradiated sample. Thus, the STEM is an ideal tool for quantitative measurements such as mass-mapping or element-mapping at high resolution. Limitations of such methods due to multiple scattering and quantum noise are briefly reviewed.

Animals↗