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Biomedical subjects

C Haber

Publications and source records attributed to C Haber.

14 recordsLinked to original sources
PubMed2000

Shape anisotropy of a single random-walk polymer.

Random walks have been used to describe a wide variety of systems ranging from cell colonies to polymers. Sixty-five years ago, Kuhn [Kuhn, W. (1934) Kolloid-Z. 68, 2-11] made the prediction, backed later by computer simulations, that the overall shape of a random-walk polymer is aspherical, yet no experimental work has directly tested Kuhn's general idea and subsequent computer simulations. By using fluorescence microscopy, we monitored the conformation of individual, long, random-walk polymers (fluorescently labeled DNA molecules) at equilibrium. We found that a polymer most frequently adopts highly extended, nonfractal structures with a strongly anisotropic shape. The ensemble-average ratio of the lengths of the long and short axes of the best-fit ellipse of the polymer was much larger than unity.

Anisotropy↗
PubMed2000

Shear-induced assembly of lambda-phage DNA.

Recombinant DNA technology, which is based on the assembly of DNA fragments, forms the backbone of biological and biomedical research. Here we demonstrate that a uniform shear flow can induce and control the assembly of lambda-phage DNA molecules: increasing shear rates form integral DNA multimers of increasing molecular weight. Spontaneous assembly and grouping of end-blunted lambda-phage DNA molecules are negligible. It is suggested that shear-induced DNA assembly is caused by increasing the probability of contact between molecules and by stretching the molecules, which exposes the cohesive ends of the otherwise undeformed lambda-phage DNA molecules. We apply this principle to enhance the kinetics and extent of DNA concatenation in the presence of ligase. This novel approach to controlled DNA assembly could form the basis for improved approaches to gene-chip and recombinant DNA technologies and provide new insight into the rheology of associating polymers.

Bacteriophage lambda↗
PubMed1999

Dynamics of individual flexible polymers in a shear flow.

Polymer dynamics are of central importance in materials science, mechanical engineering, biology and medicine. The dynamics of macromolecular solutions and melts in shear flow are typically studied using bulk experimental methods such as light and neutron scattering and birefringence. But the effect of shear on the conformation and dynamics of individual polymers is still not well understood. Here we describe observations of the real-time dynamics of individual, flexible polymers (fluorescently labelled DNA molecules) under a shear flow. The sheared polymers exhibit many types of extended conformation with an overall orientation ranging from parallel to perpendicular with respect to the flow direction. For shear rates much smaller than the inverse of the relaxation time of the molecule, the relative populations of these two main types of conformation are controlled by the rate of the shear flow. These results question the adequacy of assumptions made in standard models of polymer dynamics.

Biopolymers↗
PubMed1995

Antioxidants attenuate endotoxin-gentamicin induced acute renal failure in rats.

The synergistic mechanism by which endotoxin enhances the nephrotoxic potential of gentamicin is unknown. In this study, we attempted to shed light on this mechanism by injecting rats with endotoxin plus gentamicin. Renal injury was assessed by measuring creatinine, inulin and PAH clearance, NADH levels and electrolyte reabsorption, for 24 hr following this injection. Gentamicin alone (20 mg/100 g) induced no renal injury, while endotoxin without gentamicin (0.075 mg/100 g) induced mild injury. However, endotoxin plus gentamicin resulted in acute renal failure. In an attempt to halt the progressive renal dysfunction, the antioxidants NAO (5 mg/100 g), Vitamin E (0.2 mg/100 g per day) and dimethylthiourea (DMTU-50 mg/100 g) were administered, or early endotoxin tolerance was induced before injecting the rats with endotoxin plus gentamicin. The reduction in renal function was markedly slower in rats administered with antioxidants compared with untreated rats. Similar results were obtained with endotoxin tolerance. These data suggest that NAO, vitamin E, DMTU and endotoxin tolerance are potentially beneficial in arresting progressive renal damage associated with endotoxin plus gentamicin.

Animals↗
PubMed1984

Dyslipoproteinemia and xanthomatosis.

The cutaneous markers associated with dyslipoproteinemia are reviewed in the context of the current view of lipid and lipoprotein metabolism. The utility of determining the plasma levels of lipoproteins and certain apoproteins in children or adults with xanthomas or xanthelasma is discussed. We hope that early identification and appropriate treatment of such patients will reduce the morbidity and mortality from the two major complications of dyslipoproteinemia--atherosclerotic cardiovascular disease and pancreatitis.

Adolescent↗
PubMedDate not supplied

Geriatrics: a specialty in search of specialists.

This paper explores the historical reasons why geriatrics has failed to become a popular specialty in America. Focusing upon the nineteenth and early twentieth centuries, it examines the medical theories and ideas that led to the creation of a specialty in the diseases of old age. According to Haber, these beliefs caused many would-be geriatricians to be extremely reluctant to devote themselves to the new field. While such physicians were often convinced that a separate practice for the old was both theoretically valid and necessary, they were far less sure of the ultimate usefulness of their work. The prevailing model of senescence portrayed old age as a progressive, incurable disease, and the elderly as the most difficult and trying of patients. Medically, as well as economically, geriatrics seemed to have little appeal. The author concludes that these beliefs still influence many physicians' conception of geriatrics; it remains a specialty in search of specialists.

Aged↗
PubMedDate not supplied

Conductivity detection in capillary electrophoresis--a powerful tool in ion analysis.

Conductivity detection in CE has recently become available in a commercial CE instrument. The new conductivity cell is based on an end-capillary concept. The conductivity sensor and the detection end of the fused-silica capillary are permanently encapsulated in two individually modified coupling connectors (ConTip, ConCap [both from Orion Research, Boston, MA, U.S.A.]). This open-architecture cell permits interchangeability of sensors and capillaries, while maintaining a precisely defined detection volume between those two components when inserted into the detector cell block. The detector's performance is evaluated for sensitivity, linearity, and reproducibility using low-mobility electrolytes. Electropherograms comprising a variety of ionic class separations including inorganic and organic anions, organic surfactants, alkali metals, alkaline earths, transition metals, and organic amines are shown along with separations of actual samples.

Cations↗