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Biomedical subjects

J Eggers

Publications and source records attributed to J Eggers.

At least 19 recordsLinked to original sources
PubMed2006

Sink flow deforms the interface between a viscous liquid and air into a tip singularity.

In our experiment, an interface between a viscous liquid and air is deformed by a sink flow of constant flow rate to form a sharp tip. Using a microscope, the interface shape is recorded down to a tip size of 1 microm. The curvature at the tip is controlled by the distance h between the tip and the sink. As a critical distance h*is approached, the curvature diverges like 1/(h-h*)3and the tip becomes cone shaped. As the distance to the sink is decreased further, the opening angle of the cone vanishes like h2. No evidence for air entrainment was found, except when the tip was inside the orifice.

Journal Article↗
PubMed2005

Droplet detachment and satellite bead formation in viscoelastic fluids.

The presence of a very small amount of high molecular weight polymer significantly delays the pinch-off singularity of a drop of water falling from a faucet and leads to the formation of a long-lived cylindrical filament. In this Letter, we present experiments, numerical simulations, and theory which examines the pinch-off process in the presence of polymers. The numerical simulations are found to be in good agreement with experiment. As a test case, we establish the conditions under which a small bead remains on the filament; we find that the presence of a bead is due to the asymmetry induced by the self-similar pinch off of the droplet.

Journal Article↗
PubMed2005

Time-dependent strength of colloidal gels.

Colloidal silica gels are shown to stiffen with time, as demonstrated by both dynamic light scattering and bulk rheological measurements. Their elastic moduli increase as a power law with time, independent of particle volume fraction; however, static light scattering indicates that there are no large-scale structural changes. We propose that increases in local elasticity arising from bonding between neighboring colloidal particles can account for the strengthening of the network, while preserving network structure.

Journal Article↗
PubMed2005

Serotonergic effects of smoking are independent from the human serotonin transporter gene promoter polymorphism: evidence from auditory cortical stimulus processing.

BACKGROUND: Cigarette smoking has been associated with mood enhancing properties and modulating effects on serotonin activity. The loudness dependence (LD) of the auditory-evoked N1/P2-component has been related to serotonergic neurotransmission, i. e. the allelic variants in the promoter of the 5-hydroxytryptamine-transporter (5-HTT) gene (SCL6A4). Moreover, smoking behavior has been associated to the 5-HTT-genotype. It was hypothesized that cigarette smoking modulates the LD and this effect was expected to interact with the 5-HTT-genotype. METHODS: 5-HTT-genotype and LD were determined in 63 healthy smokers and 114 nonsmokers. RESULTS: LD was significantly affected by smoking status (p = 0.008) and 5-HTT-genotype (p = 0.045) but not by smoking*genotype-interaction or daily cigarette consumption. Current smokers exhibited a significantly weaker LD compared to nonsmokers. 5-HTT-genotype showed no significant effect on smoking behavior. DISCUSSION: The results indicate a higher serotonergic activity in smokers as compared to nonsmokers independent of 5-HTT-genotype. Since former smokers and never smokers showed similar LDs, the serotonin enhancing effect of smoking seems to be a characteristic state, which may contribute to the maintenance of smoking behavior.

Acoustic Stimulation↗
PubMed2005

Creatine has no beneficial effect on skeletal muscle energy metabolism in patients with single mitochondrial DNA deletions: a placebo-controlled, double-blind 31P-MRS crossover study.

The purpose of our randomized, double-blind, placebo-controlled crossover study in 15 patients with chronic progressive external ophthalmoplegia (CPEO) or Kearns-Sayre syndrome (KSS) because of single large-scale mitochondrial (mt) DNA deletions was to determine whether oral creatine (Cr) monohydrate can improve skeletal muscle energy metabolism in vivo. Each treatment phase with Cr in a dosage of 150 mg/kg body weight/day or placebo lasted 6 weeks. The effect of Cr was estimated by phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS), clinical and laboratory tests. (31)P-MRS analysis prior to treatment showed clear evidence of severe mitochondrial dysfunction. However, there were no relevant changes in (31)P-MRS parameters under Cr. In particular, phosphocreatine (PCr)/ATP at rest did not increase, and there was no facilitation of post-exercise PCr recovery. Clinical scores and laboratory tests did not alter significantly under Cr, which was tolerated without major side-effects in all patients. Cr supplementation did not improve skeletal muscle oxidative phosphorylation in our series of patients. However, one explanation for our negative findings may be the short study duration or the limited number of patients included.

Adult↗
PubMed2004

Limits to gelation in colloidal aggregation.

We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstrates that cluster growth is limited by gravity-induced restructuring. In the absence of gravity, thermal fluctuations ultimately inhibit fractal growth and set the fundamental limitation to the lowest volume fraction which will gel.

Colloids↗
PubMed2002

Circulating microemboli after composite replacement or valve-sparing aortic root surgery.

BACKGROUND: The purpose of this study was to determine whether microembolic signals (MES) occur after valve-sparing operations on the aortic root. One of the advantages of these procedures relates to the freedom of macroemboli without anticoagulation. Whether this holds true for circulating microemboli has not yet been verified. METHODS: For comparison, 8 male patients (mean age: 51.8 +/- 12.8 years) were investigated 20.5 +/- 8.4 months after implantation of a mechanical composite graft (group I) and 9 female and 7 male patients (mean age 55.0 +/- 13.4 years) 23.5 +/- 20.0 months after valve-sparing replacement of the aortic root (group II). The middle cerebral artery was insonated for 2 periods of 30 min, breathing room air or O 2 at 9 l/min. RESULT: Breathing room air, the amount of MES was considerably smaller in group II (0.94 +/- 1.95 vs. 56.1 +/- 58.9 per 30 min, p = 0.006). The difference was less pronounced (0.5 +/- 1.3 vs. 28.9 +/- 42.6 per 30 min, p = 0.009) breathing oxygen. Breathing oxygen reduced MES significantly in group I (p < 0.05) but not in group II (p > 0.05). CONCLUSIONS: Aortic valve-sparing operations induce MES at a significantly lower rate than composite aortic valve replacement using a mechanical valve.

Aorta↗
PubMed2001

Air entrainment through free-surface cusps.

In many industrial processes, such as pouring a liquid or coating a rotating cylinder, air bubbles are entrapped inside the liquid. We propose that this is due to air being drawn into the narrow channel of a cusp singularity that generically forms on free surfaces. Since the width of the cusp is exponentially small in the driving strength, even the minute viscosity of air is enough to destroy the stationary solution, and a sheet emanates from the cusp's tip, through which air is entrained. Our analytical theory is confirmed by quantitative comparison with numerical simulations of the flow equations, and is found to be in qualitative agreement with experimental observation.

Journal Article↗
PubMed1999

Repeated exposure of rats to JP-4 vapor induces changes in neurobehavioral capacity and 5-HT/5-HIAA levels.

Thirty-two Sprague-Dawley rats were exposed for 6 h/d for 14 consecutive days to JP-4 jet fuel vapor (2 mg/L) or room air control conditions. Following a 14- or 60-d recovery period, rats completed a battery of 8 tests selected from the Navy Neurobehavioral Toxicity Assessment Battery (NTAB) to evaluate changes in performance capacity. Exposure to JP-4 vapor resulted in significant changes in neurobehavioral capacity on several tests that varied as a function of the duration of the recovery period. Rats were evaluated for major neurotransmitter and metabolite levels in five brain regions and in the blood serum. Levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were shown to be significantly elevated in several brain regions as well as in the blood serum in the vapor-exposed groups. Results of the rat study are compared to previously reported neurobehavioral evaluations of European manufacturing personnel exposed chronically to jet fuel vapor.

Adaptation, Ocular↗
PubMed1999

Use of hematoxylin stain to enhance evaluation of heart malformations in the fetal rat.

Fresh and formalin-fixed visceral microdissection techniques are valuable tools for studying cardiac teratology in the fetal rat, but are limited by the difficulty experienced in visualizing the minute structures needing to be evaluated. This paper describes a simple and quick staining technique used to enhance the examination procedure. A hematoxylin-saline mixture applied directly on endothelial-lined surfaces of the heart at different stages during microdissection greatly improved visualization of membrane-thin structures such as the pulmonary and aortic semilunar valves, right- and left-side atrioventricular valves, and atrial and ventricular septa. Hematoxylin staining of endocardial surfaces is a useful adjunct to the standard visceral microdissection technique.

Animals↗
PubMed1998

Differential mucin MUC7 gene expression in invasive bladder carcinoma in contrast to uniform MUC1 and MUC2 gene expression in both normal urothelium and bladder carcinoma.

Mucins (MUCs) are high molecular weight membrane glycoproteins. The gene expression of MUCs (MUC1-MUC8) may change characteristically during malignant transformation of epithelial tissues. Total RNA was isolated from the four bladder cancer cell lines RT4, 647V, HT1376, and 486P (pathological gradings between G1 and G4) and 17 samples of transitional cell carcinomas, as well as 16 samples of normal human urothelium of the bladder from surgically removed specimens. The RNA samples were studied with MUC1-, MUC2- and MUC7-specific nested reverse transcription-PCRs. Gene expression of MUC1 and MUC2 was found positive in all normal, as well as in malignant, tissue samples and in the tumor cell lines. In contrast, gene expression of MUC7 was only detected in bladder cancer cell lines and samples of invasive transitional cell carcinomas, but neither in superficial, noninvasive bladder tumors nor normal bladder urothelium. Only one of the samples of normal urothelium obtained from 16 different tumor-bearing bladders was positive for MUC7 gene expression. These results suggest a differential MUC7 gene expression with the onset of malignant transformation of the bladder urothelium.

Carcinoma, Transitional Cell↗