Biomedical subjects

M Sperl

Publications and source records attributed to M Sperl.

At least 19 recordsLinked to original sources

PubMed2005

Nearly logarithmic decay in the colloidal hard-sphere system.

Nearly logarithmic decay is identified in the data for the mean-squared displacement of the colloidal hard-sphere system at the liquid-glass transition [W. van Megen, Phys. Rev. E 58, 6073 (1998)]. The solutions of the mode-coupling theory for the microscopic equations of motion fit the experimental data well. Based on these equations, the nearly logarithmic decay is explained as the equivalent of a beta-peak phenomenon, a manifestation of the critical relaxation when the coupling between of the probe variable and the density fluctuations is strong. In an asymptotic expansion, a Cole-Cole formula including corrections is derived from the microscopic equations of motion, which describes the experimental data for three decades in time.

Journal Article↗

PubMed2004

Nearly logarithmic decay of correlations in glass-forming liquids.

Nearly logarithmic decay of correlations, which was observed for several supercooled liquids in optical-Kerr-effect experiments [Phys. Rev. Lett. 84, 2437 (2000)]; Phys. Rev. Lett. 90, 197401 (2003)]], is explained within the mode-coupling theory for ideal glass transitions as a manifestation of the beta-peak phenomenon. A schematic model, which describes the dynamics by only two correlators, one referring to density fluctuations and the other to the reorientational fluctuations of the molecules, yields for strong rotation-translation coupling response functions in agreement with those measured for benzophenone and Salol for the time interval extending from 2 ps to about 20 and 200 ns, respectively.

Journal Article↗

PubMed2004

Dynamics in colloidal liquids near a crossing of glass- and gel-transition lines.

Within the mode-coupling theory for ideal glass transitions, the mean-squared displacement and the correlation function for density fluctuations are evaluated for a colloidal liquid of particles interacting with a square-well potential for states near the crossing of the line for transitions to a gel with the line for transitions to a glass. It is demonstrated how the dynamics is ruled by the interplay of the mechanisms of arrest due to hard-core repulsion and due to attraction-induced bond formation as well as by a nearby higher-order glass-transition singularity. Application of the universal relaxation laws for the slow dynamics near glass-transition singularities explains the qualitative features of the calculated time dependence of the mean-squared displacement, which are in accord with the findings obtained in molecular-dynamics simulation studies by Zaccarelli et al. [Phys. Rev. E 66, 041402 (2002)]. Correlation functions found by photon-correlation spectroscopy in a micellar system by Mallamace et al. [Phys. Rev. Lett. 84, 5431 (2000)] can be interpreted qualitatively as a crossover from gel to glass dynamics.

Journal Article↗

PubMed2003

Logarithmic relaxation in a colloidal system.

The slow dynamics for a colloidal suspension of particles interacting with a hard-core repulsion complemented by a short-ranged attraction is discussed within the frame of mode-coupling theory for ideal glass transitions for parameter points near a higher-order glass-transition singularity. The solutions of the equations of motion for the density correlation functions are solved for the square-well system in quantitative detail by asymptotic expansion using the distance of the three control parameters-packing fraction, attraction strength and attraction range-from their critical values as small parameters. For given wave vectors, distinguished surfaces in parameter space are identified where the next-to-leading-order contributions for the expansion vanish so that the decay functions exhibit a logarithmic decay over large time intervals. For both coherent and tagged particle dynamics the leading-order logarithmic decay is accessible in the liquid regime for wave vectors of several times the principal peak in the structure factor. The logarithmic decay in the correlation function is manifested in the mean-squared displacement as a subdiffusive power law with an exponent varying sensitively with the control parameters. Shifting parameters through the distinguished surfaces, the correlation functions and the logarithm of the mean-squared displacement considered as functions of the logarithm of the time exhibit a crossover from concave to convex behavior, and a similar scenario is obtained when varying the wave vector.

Journal Article↗

PubMed2002

Logarithmic relaxation in glass-forming systems.

Within the mode-coupling theory for ideal glass transitions, an analysis of the correlation functions of glass-forming systems for states near higher-order glass-transition singularities is presented. It is shown that the solutions of the equations of motion can be asymptotically expanded in polynomials of the logarithm of time t. In leading order, a ln(t) law is obtained, and the leading corrections are given by a fourth-order polynomial. The correlators interpolate between three scenarios. First, there are surfaces in parameter space where the dominant corrections to the ln(t) law vanish, so that the logarithmic decay governs the structural relaxation process. Second, the dynamics due to the higher-order singularity can describe the initial and intermediate part of the alpha process thereby reducing the range of validity of von Schweidler's law and leading to strong alpha relaxation stretching. Third, the ln(t) law can replace the critical decay law of the beta process, leading to a particularly large crossover interval between the end of the transient and the beginning of the alpha process. This may lead to susceptibility spectra below the band of microscopic excitations exhibiting two peaks. Typical results of the theory are demonstrated for models dealing with one and two correlation functions.

Journal Article↗

PubMed2002

[Carotid sonography and measurement of intima-medial thickness as indicators for risk of systemic atherosclerosis].

Ultrasound of carotid arteries belongs to non-invasive, safe, and comparatively inexpensive methods of the subclinical phase arteriosclerosis detection. It allows identification of atherosclerosis plaques, which can be found in higher numbers in elderly persons. Measurement of intima-media thickness (IMT) belongs to the time-proven methods and it represents an independent indicator of the risk of the cerebro-vascular event, coronary event including the myocardial infarction, and lower limbs ischaemic disease. In asymptomatic forms in persons over 45 years, the meticulous IMT examination can bring an additional information on the traditional risk factors, specify further the risks of cardio-vascular events, and help to elaborate the extent of preventive measures.

Aged↗

PubMed2000

Higher-order glass-transition singularities in colloidal systems with attractive interactions.

The transition from a liquid to a glass in colloidal suspensions of particles interacting through a hard core plus an attractive square-well potential is studied within the mode-coupling-theory framework. When the width of the attractive potential is much shorter than the hard-core diameter, a reentrant behavior of the liquid-glass line and a glass-glass-transition line are found in the temperature-density plane of the model. For small well-width values, the glass-glass-transition line terminates in a third-order bifurcation point, i.e., in a A3 (cusp) singularity. On increasing the square-well width, the glass-glass line disappears, giving rise to a fourth-order A4 (swallow-tail) singularity at a critical well width. Close to the A3 and A4 singularities the decay of the density correlators shows stretching of huge dynamical windows, in particular logarithmic time dependence.

Journal Article↗

PubMed1998

[Treatment of hypopituitarism in adults with growth hormone improves improves the thickness of the arterial intima].

BACKGROUND: Increased mortality of hypopituitary adults with atherosclerotic vascular disease is commonly explained by growth hormone deficiency and forms the main argument for the growth hormone replacement. At the same time it is known that the growth hormone-IGF-I axis stimulates the vessel wall proliferation as an initial step of atherosclerosis. Investigation of the arterial intima thickness in hypopituitary adults with duplex ultrasound system and its follow up during the growth hormone therapy may clarify these effects of growth hormone on the vessel wall. METHODS AND RESULTS: Luminal diameter, maximal blood flow velocity and arterial intima thickness of common carotid arteries was measured with colour duplex ultrasound system in 15 adults with hypopituitarism before and after one year therapy with recombinant growth hormone. The results were compared with healthy controls matched for gender, age, blood pressure and weight. The luminal diameter did not changed during the therapy with growth hormone and was the same in patients and controls. Maximal blood velocity in hypopituitary patients before the therapy was lower than in control subjects (74.8 +/- 13.9 cm/s vs. 94.0 +/- 21.0 cm/s), but the statistical difference was only borderline. Arterial intima thickness was significantly thinner in hypopituitary patients when compared with controls (0.56 +/- 0.1 mm vs. 0.71 +/- 0.12 mm, p < 0.001) but became thicker after the treatment and was not any more different from the controls (0.56 +/- 0.1 mm vs. 0.66 +/- 0.1 mm, p < 0.001). CONCLUSIONS: In hypopituitary adults the arterial intima thickness of common carotid arteries is less than in healthy controls. The reduced thickness was normalised after one year treatment with growth hormone. Atheromatous plaques were not found either before or after the treatment. Duplex ultrasound measurement may be one of the means of checking of the effects of growth hormone therapy.

Adult↗

PubMed1994

Early changes of serum N-acetyl-beta-glucosaminidase, tissue plasminogen activator and erythrocyte superoxide dismutase in relation to retinopathy in type 1 diabetes mellitus.

Biochemical markers of early changes that are characteristic for diabetic microangiopathy are not completely understood. We investigated activities of serum N-acetyl-beta-glucosaminidase (NAG), tissue plasminogen activator and erythrocyte superoxide dismutase in well defined groups of type 1 diabetic patients. Patients were selected on the basis of 4 year follow-up observation. Forty-two type 1 diabetic patients were subdivided into those without retinopathy (n = 13) throughout the study, those with newly developed or worsened retinopathy (n = 12) during 4 years and those with retinopathy already established at the beginning of the study and without evidence of its progression (n = 17). All diabetic patients had albustix-negative urine. A significant increase of the mean serum NAG activity during 4 years was found only in patients without retinopathy (P < 0.01) whereas no changes of the altered enzyme activities were present in patients with developing and established retinopathy. The mean activity of tissue plasminogen activator was elevated in all groups of diabetic patients compared with healthy subjects (P < 0.001). A significant positive correlation was found between plasminogen activator and serum NAG (r = 0.51, P < 0.01). Erythrocyte superoxide dismutase was higher in diabetic patients than in healthy persons (P < 0.01) but no differences were observed between the patients with or without retinopathy. Superoxide dismutase positively correlated with NAG (r = 0.57, P < 0.01). We conclude that early functional changes precede a morphological development of diabetic retinopathy as was evident from the altered enzyme activities.

Acetylglucosaminidase↗

PubMed1993

[Albuminuria and N-acetyl-beta-glucosaminidase activity in a prospective study of type I diabetics].

The authors investigated a group of 47 type I diabetics in a prospective study extending over 8 years. Every year they evaluated the albuminuria and the N-acetyl-beta-glucosaminidase (NAG) activity in serum and urine and the results were compared with the state of compensation of diabetes and with the clinical finding on the ocular fundus. During the eight-year period newly manifested microalbuminuria developed in 8 of 32 patients (25%) who at the onset had a normal finding. In patients with newly manifested microalbuminuria the authors found a significant rise of the fructosamine serum concentration (p < 0.05) and at the same time a rise of serum NAG activity (p < 0.05). A positive correlation was proved between the serum NAG activity and glycated haemoglobin (r = 0.67, p < 0.01). In 13 patients (28%) in the course of the eight-year period the finding on the ocular fundus deteriorated. In these patients the NAG serum activity was elevated already at the onset of the investigation, while albuminuria rose in the course of the mentioned period. Dynamic changes of the NAG serum activity along with albuminuria can serve as bio-chemical markers of developing microangiopathy the manifestation of which is hastened by deteriorated compensation of diabetes.

Acetylglucosaminidase↗

PubMed1991

A six-year follow-up of the relationship between N-acetyl-beta-glucosaminidase and albuminuria in relation to retinopathy.

Fifty patients with Type 1 diabetes mellitus were observed over 6 years. Serum and urinary N-acetyl-beta-glucosaminidase (NAG) activity, and albuminuria were measured in groups of patients subdivided according to ophthalmological findings. Significantly higher mean serum NAG activity was found at the beginning of the study in patients who later developed diabetic retinopathy in comparison with those who did not (geometric mean (2SD range) 19.7 (12.4-31.2) vs 14.4 (9.5-22.7) U l-1, p less than 0.01). Urinary NAG activity was significantly higher in all groups of diabetic patients than in healthy control subjects (p less than 0.05). A significant increase in albumin:creatinine ratio during the study was found in patients with newly developed diabetic retinopathy compared with patients who did not (at 6 years 1.33 (0.40-4.43) vs 0.75 (0.24-2.31) g mol-1, p less than 0.01). No differences in either biochemical variable were found between hypertensive and normotensive diabetic patients at the end of the study. The results suggest that both serum NAG activity and albuminuria may serve as early functional indicators of diabetic retinopathy.

Acetylglucosaminidase↗

PubMed1991

[Pregnancy and obesity. II. Hormonal and metabolic changes].

28 obese women were investigated in the course of the 21st (A) and 30th (B) week of pregnancy. Increased serum levels of GH, T4 and T3 were found in both samples of blood (A and B), while serum insulin, cholesterol and triacylglycerols were increased only at time B. It was suggested that the similar increase of GH, T4 and T3 at time A and B was due to pregnancy because the level of these hormones is usually not increased in non-pregnant obese women, while hyperinsulinemia and often increased values of cholesterol and triacylglycerols are a common finding in non-pregnant obesity. This presumption was confirmed only partially--body weight and the skin folds correlated only with insulin and T3, while GH, cortisol, T4, cholesterol and triacylglycerols correlated only exceptionally. High levels of insulin and T3 may be due to overeating.

Adult↗

PubMed1989

N-acetyl-beta-glucosaminidase and albuminuria in normal and diabetic pregnancies.

Fourteen diabetic women without signs of nephropathy were examined during pregnancy. Serum fructosamine concentration indicating short-term metabolic control of diabetes was normalized at the beginning of the second trimester and was within the normal limits till the delivery. A gradual increase of N-acetyl-beta-glucosaminidase activity in serum and urine has been found during pregnancy in diabetic and healthy women. No significant differences of N-acetyl-beta-glucosaminidase activities were observed between the above groups. A successive increase of albuminuria during pregnancy was present in diabetic and healthy women with about 10-times higher values at delivery. A significant positive correlation was observed between albuminuria and urinary NAG activity in both groups of pregnant women (r = 0.77). We did not find any deterioration in N-acetyl-beta-glucosaminidase activities and albuminuria in seven diabetic women one year after delivery.

Acetylglucosaminidase↗

PubMed1987

Directional selectivities of visual afferents to the pretectal neuropil in the fire salamander.

Single-unit recordings from visual afferents in the pretectal neuropil of Salamandra salamandra were performed to characterize the properties of direction specific units which are probably involved in the optokinetic reflex. It was shown that afferents from the contralateral eye were more sharply tuned than those from the ipsilateral eye. However, the majority of both were selective for temporonasal movements.

Animals↗

PubMed1986