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Biomedical subjects

J Feder

Publications and source records attributed to J Feder.

At least 19 recordsLinked to original sources
PubMed2001

Coupling particles and fields in a diffusive hybrid model.

A general scheme to patch together discrete and continuous descriptions of diffusion within the same physical space is studied. In the discrete description, diffusion is described by microscopic random walkers on a lattice; in the continuous description, diffusion is described through the macroscopic diffusion equation. The coupling scheme is based on the mutual exchange of mass flux across the discrete-continuous interface. Detailed tests of the scheme, coupling particle, and field descriptions are particularly illustrative for the diffusion problem. Both the nonequilibrium transport behavior and the equilibrium fluctuations of the combined discrete-continuous system are in agreement with theoretical predictions.

Journal Article↗
PubMed2000

Differential HFE allele expression in hemochromatosis heterozygotes.

BACKGROUND & AIMS: Hereditary hemochromatosis is associated with C282Y homozygosity. Some heterozygotes may also present with abnormal iron parameters. However, the precise role of H63D and C282Y mutations in iron overload is poorly understood. We investigated the level of expression of the mutated and unmutated HFE alleles in these heterozygous patients. METHODS: We studied the expression of HFE messenger RNAs in peripheral blood mononuclear cells from 34 heterozygotes using reverse-transcription polymerase chain reaction (PCR) followed by enzymatic digestion or sequence analysis of the PCR products, which allows relative quantification of mutated and unmutated transcripts. HFE proteins were quantified by Western blotting in Epstein-Barr virus-immortalized lymphocyte extracts from 2 C282Y and H63D homozygotes and a compound heterozygote. RESULTS: (187C > G; H63D) mutated transcripts predominated in H63D and compound heterozygotes and the normal transcripts in C282Y heterozygotes. The amount of HFE protein was increased in the H63D homozygotes and the compound heterozygote compared with the C282Y homozygotes. In addition, we found a new mutation at codon 282 (C282S) associated with severe iron overload. CONCLUSIONS: We demonstrate the existence of differential allelic expression of the HFE alleles, suggesting that the (187C > G; H63D) mutation plays a role in the disease expression in H63D heterozygotes, in particular when associated with environmental or host factors.

Adult↗
PubMed2000

Children's health insurance: the difference policy choices make.

This paper provides estimates of the cost and coverage impacts of the new State Children's Health Insurance Program (SCHIP). The estimates reflect the many choices the states are given by the legislation: whether to use traditional Medicaid or establish separate state-run programs; how far to extend eligibility up the income distribution; and how much to use premiums. We estimate the impacts of these choices on participation by the uninsured as well as by the insured--that is, the crowd-out effect--and on public expenditures. We also estimate the savings to families and firms that substitute SCHIP for private coverage. We conclude with estimates of the cost and coverage impacts of the actual initial choices that states have made.

Child↗
PubMed1999

Cell adhesion force microscopy.

The adhesion forces of cervical carcinoma cells in tissue culture were measured by using the manipulation force microscope, a novel atomic force microscope. The forces were studied as a function of time and temperature for cells cultured on hydrophilic and hydrophobic polystyrene substrates with preadsorbed proteins. The cells attached faster and stronger at 37 degreesC than at 23 degreesC and better on hydrophilic than on hydrophobic substrates, even though proteins adsorb much better to the hydrophobic substrates. Because cell adhesion serves to control several stages in the cell cycle, we anticipate that the manipulation force microscope can help clarify some cell-adhesion related issues.

Adsorption↗
PubMed1999

Dynamics of water coning.

Water beneath a layer of oil in a producing reservoir may rise and form a bell-shaped cone in the vicinity of the well. We discuss how the dynamics of cone formation in two dimensions depends on the gravitational contrast, the interfacial tension, and the flow rate of oil. For a constant flow rate below a critical rate Q(c), stable cones are formed. At rates above Q(c), two dynamical regimes are expected. These are slow initial formation and fast breakthrough to the well. Quasi-two-dimensional transparent porous models were used to perform cone formation experiments. Effective acceleration due to gravity was systematically varied. The experiments were simulated using a stochastic model based on invasion percolation in which capillary forces were explicitly taken into account. We find agreement between experiments and simulations, and consistency with the theoretical predictions.

Journal Article↗
PubMed1999

Can Medicare survive its saviors?

It is now an open question whether Medicare will provide adequate health coverage to the baby-boom generation as it begins turning 65 just over a decade from now. The source of uncertainty is not whether America has the resources to sustain the program; we do. The real challenge comes instead from proposals to save Medicare. Far from preserving its benefits, the major restructuring proposals under discussion would radically alter the principles on which Medicare rests and erode the protection it affords.

Aged↗
PubMed1997

Low density lipoprotein receptor-related protein modulates the expression of tissue-type plasminogen activator in human colon fibroblasts.

Human colon fibroblasts (HCF) produce tissue-type plasminogen activator (t-PA) in culture, but after 24-48 h, t-PA ceases to accumulate in the medium. Here, we report negative feedback regulation of t-PA expression, exerted by t-PA or complexes of t-PA with its physiological inhibitor, plasminogen activator inhibitor type 1 (PAI-1). Inhibition of t-PA expression could be induced by addition of exogenous t-PA or t-PA.PAI-1 complexes and reversed by monoclonal antibody directed against the active site of t-PA. Analysis of metabolically radiolabeled protein and cellular mRNA showed that both t-PA protein and mRNA levels declined considerably after 24 h. When 125I-labeled t-PA or t-PA.PAI-1 complexes were incubated with HCF, monensin-inhibitable endocytosis and catabolism were observed. The low density lipoprotein receptor-related protein (LRP) was found to be expressed by HCF and to mediate these events. Addition of the 39-kDa receptor-associated protein (RAP), an antagonist for ligand interactions with LRP, removed the block to t-PA expression and restored its accumulation in the medium. Moreover, RAP completely prevented the degradation of exogenous 125I-labeled t-PA by HCF, suggesting that LRP is the endocytic receptor for t-PA in these cells. These results demonstrate that cellular modulation of t-PA expression in HCF involves LRP receptor-mediated clearance of t-PA. This LRP receptor-mediated event results in down-regulation of t-PA expression at the mRNA level.

Cells, Cultured↗
PubMed1997

Pes planus in patients with posterior tibial tendon insufficiency: asymptomatic versus symptomatic foot.

Bilateral weightbearing anteroposterior and lateral radiographs were analyzed in 43 patients with a clinical diagnosis of posterior tibial tendon insufficiency by two independent observers. The radiographs of each patient's asymptomatic foot was considered to serve as the control for the preexistance of pes planus. The radiographs were assessed for the severity of flatfoot deformity, the degree of talonavicular coverage, the talometatarsal angle, the calcaneometatarsal angle, the cuneiform to ground height and the cuneiform to fifth metatarsal height. Interobserver correlations were assessed. Results indicated that there was a high interobserver correlation for the values measured, making these angles reproducible among observers. Strong correlations were found in the degree of severity of flatfoot deformity between the asymptomatic and symptomatic feet as well as the values used to assess pes planus (i.e., similar radiographic measurements on the opposite side). The data suggest that patients with posterior tibial tendon insufficiency often have a preexisting flatfoot. This substantiates our belief that a preexisting flexible flatfoot, although far from the determining factor, is one of several etiological factors in the development of posterior tibial tendon insufficiency.

Adult↗