50 research outputs found
Rescaling Relations between Two- and Three-dimensional Local Porosity Distributions for Natural and Artificial Porous Media
Local porosity distributions for a three-dimensional porous medium and local
porosity distributions for a two-dimensional plane-section through the medium
are generally different. However, for homogeneous and isotropic media having
finite correlation-lengths, a good degree of correspondence between the two
sets of local porosity distributions can be obtained by rescaling lengths, and
the mapping associating corresponding distributions can be found from
two-dimensional observations alone. The agreement between associated
distributions is good as long as the linear extent of the measurement cells
involved is somewhat larger than the correlation length, and it improves as the
linear extent increases. A simple application of the central limit theorem
shows that there must be a correspondence in the limit of very large
measurement cells, because the distributions from both sets approach normal
distributions. A normal distribution has two independent parameters: the mean
and the variance. If the sample is large enough, LPDs from both sets will have
the same mean. Therefore corresponding distributions are found by matching
variances of two- and three-dimensional local porosity distributions. The
variance can be independently determined from correlation functions. Equating
variances leads to a scaling relation for lengths in this limit. Three
particular systems are examined in order to show that this scaling behavior
persists at smaller length-scales.Comment: 15 PostScript figures, LaTeX, To be published in Physica
Local Entropy Characterization of Correlated Random Microstructures
A rigorous connection is established between the local porosity entropy
introduced by Boger et al. (Physica A 187, 55 (1992)) and the configurational
entropy of Andraud et al. (Physica A 207, 208 (1994)). These entropies were
introduced as morphological descriptors derived from local volume fluctuations
in arbitrary correlated microstructures occuring in porous media, composites or
other heterogeneous systems. It is found that the entropy lengths at which the
entropies assume an extremum become identical for high enough resolution of the
underlying configurations. Several examples of porous and heterogeneous media
are given which demonstrate the usefulness and importance of this morphological
local entropy concept.Comment: 15 pages. please contact [email protected] and have a look
at http://www.ica1.uni-stuttgart.de/ . To appear in Physica
Local Percolation Probabilities for a Natural Sandstone
Local percolation probabilities are used to characterize the connectivity in
porous and heterogeneous media. Together with local porosity distributions they
allow to predict transport properties \cite{hil91d}. While local porosity
distributions are readily obtained, measurements of the local percolation
probabilities are more difficult and have not been attempted previously. First
measurements of three dimensional local porosity distributions and percolation
probabilities from a pore space reconstruction for a natural sandstone show
that theoretical expectations and experimental results are consistent.Comment: 9 pages, see also http://www.ica1.uni-stuttgart.de , Physica
Porous structure of thick fiber webs
The bulk properties and stochastic pore geometry of finite-thickness fiber webs are studied using a realistic model for the sedimentation of flexible fibers [K. J. Niskanen and M. J. Alava, Phys. Rev. Lett. 73, 3475 (1994)]. The resulting web structure is controlled by a dimensionless number F=Tfwf/tf, where Tf is fiber flexibility, wf fiber width, and tf fiber thickness. The fiber length (≫wf,tf) is irrelevant. With increasing coverage c̄, a crossover occurs at c̄=c0≈1+2F from a vacancy-controlled two-dimensional (2D) structure to a pore-controlled 3D structure. The 3D structures are isomorphic in that the pore dimensions are exponentially distributed, with the decay rate dependent only on F.Peer reviewe
Increased Prevalence of Metabolic Syndrome in Patients with Acne Inversa
BACKGROUND: Acne inversa (AI; also designated as Hidradenitis suppurativa) is a common chronic inflammatory skin disease, localized in the axillary, inguinal and perianal skin areas that causes painful, fistulating sinuses with malodorous purulence and scars. Several chronic inflammatory diseases are associated with the metabolic syndrome and its consequences including arteriosclerosis, coronary heart disease, myocardial infraction, and stroke. So far, the association of AI with systemic metabolic alterations is largely unexplored. METHODS AND FINDINGS: A hospital-based case-control study in 80 AI patients and 100 age- and sex-matched control participants was carried out. The prevalence of central obesity (odds ratio 5.88), hypertriglyceridemia (odds ratio 2.24), hypo-HDL-cholesterolemia (odds ratio 4.56), and hyperglycemia (odds ratio 4.09) in AI patients was significantly higher than in controls. Furthermore, the metabolic syndrome, previously defined as the presence of at least three of the five alterations listed above, was more common in those patients compared to controls (40.0% versus 13.0%; odds ratio 4.46, 95% confidence interval 2.02 to 9.96; P<0.001). AI patients with metabolic syndrome also had more pronounced metabolic alterations than controls with metabolic syndrome. Interestingly, there was no correlation between the severity or duration of the disease and the levels of respective parameters or the number of criteria defining the metabolic syndrome. Rather, the metabolic syndrome was observed in a disproportionately high percentage of young AI patients. CONCLUSIONS: This study shows for the first time that AI patients have a high prevalence of the metabolic syndrome and all of its criteria. It further suggests that the inflammation present in AI patients does not have a major impact on the development of metabolic alterations. Instead, evidence is given for a role of metabolic alterations in the development of AI. We recommend monitoring of AI patients in order to correct their modifiable cardiovascular risk factors
Mechanisms Underlying Interferon-γ-Induced Priming of Microglial Reactive Oxygen Species Production.
Microglial priming and enhanced reactivity to secondary insults cause substantial neuronal damage and are hallmarks of brain aging, traumatic brain injury and neurodegenerative diseases. It is, thus, of particular interest to identify mechanisms involved in microglial priming. Here, we demonstrate that priming of microglia with interferon-γ (IFN γ) substantially enhanced production of reactive oxygen species (ROS) following stimulation of microglia with ATP. Priming of microglial ROS production was substantially reduced by inhibition of p38 MAPK activity with SB203580, by increases in intracellular glutathione levels with N-Acetyl-L-cysteine, by blockade of NADPH oxidase subunit NOX2 activity with gp91ds-tat or by inhibition of nitric oxide production with L-NAME. Together, our data indicate that priming of microglial ROS production involves reduction of intracellular glutathione levels, upregulation of NADPH oxidase subunit NOX2 and increases in nitric oxide production, and suggest that these simultaneously occurring processes result in enhanced production of neurotoxic peroxynitrite. Furthermore, IFNγ-induced priming of microglial ROS production was reduced upon blockade of Kir2.1 inward rectifier K+ channels with ML133. Inhibitory effects of ML133 on microglial priming were mediated via regulation of intracellular glutathione levels and nitric oxide production. These data suggest that microglial Kir2.1 channels may represent novel therapeutic targets to inhibit excessive ROS production by primed microglia in brain pathology
Skeletal Muscle Myofibrillar and Sarcoplasmic Protein Synthesis Rates Are Affected Differently by Altitude-Induced Hypoxia in Native Lowlanders
As a consequence to hypobaric hypoxic exposure skeletal muscle atrophy is often reported. The underlying mechanism has been suggested to involve a decrease in protein synthesis in order to conserve O2. With the aim to challenge this hypothesis, we applied a primed, constant infusion of 1-13C-leucine in nine healthy male subjects at sea level and subsequently at high-altitude (4559 m) after 7–9 days of acclimatization. Physical activity levels and food and energy intake were controlled prior to the two experimental conditions with the aim to standardize these confounding factors. Blood samples and expired breath samples were collected hourly during the 4 hour trial and vastus lateralis muscle biopsies obtained at 1 and 4 hours after tracer priming in the overnight fasted state. Myofibrillar protein synthesis rate was doubled; 0.041±0.018 at sea-level to 0.080±0.018%⋅hr−1 (p<0.05) when acclimatized to high altitude. The sarcoplasmic protein synthesis rate was in contrast unaffected by altitude exposure; 0.052±0.019 at sea-level to 0.059±0.010%⋅hr−1 (p>0.05). Trends to increments in whole body protein kinetics were seen: Degradation rate elevated from 2.51±0.21 at sea level to 2.73±0.13 µmol⋅kg−1⋅min−1 (p = 0.05) at high altitude and synthesis rate similar; 2.24±0.20 at sea level and 2.43±0.13 µmol⋅kg−1⋅min−1 (p>0.05) at altitude. We conclude that whole body amino acid flux is increased due to an elevated protein turnover rate. Resting skeletal muscle myocontractile protein synthesis rate was concomitantly elevated by high-altitude induced hypoxia, whereas the sarcoplasmic protein synthesis rate was unaffected by hypoxia. These changed responses may lead to divergent adaptation over the course of prolonged exposure
Psoriasis Carries an Increased Risk of Venous Thromboembolism: A Danish Nationwide Cohort Study
Psoriasis is an immunoinflammatory disease associated with cardiovascular risk factors, atherothrombotic events, and hypercoagulability. Venous thromboembolism (VTE) is potentially lethal and shares risk factors with psoriasis, but the risk of VTE associated with psoriasis is unknown. The present study investigated the potential association between psoriasis and VTE.Information from nationwide prospectively recorded registers of hospitalization, drug dispensing from pharmacies, socio-economic data, and causes of death was linked on an individual level. In an unselected nationwide cohort, we used multivariate Poisson regression models controlling for age, gender, comorbidity, concomitant medication, socio-economic data, and calendar year, to assess the risk of VTE associated with psoriasis. A total of 35,138 patients with mild and 3,526 patients with severe psoriasis were identified and compared with 4,126,075 controls. Patients with psoriasis had higher incidence rates per 1000 person-years of VTE than controls (1.29, 1.92, and 3.20 for controls, mild psoriasis, and severe psoriasis, respectively). The rate ratio (RR) of VTE was elevated in all patients with psoriasis with RR 1.35 (95% confidence interval [CI] 1.21–1.49) and RR 2.06 (CI 1.63–2.61) for mild and severe psoriasis, respectively. Exclusion of patients with malignancies, and censoring of patients undergoing surgery did not alter the results.This nationwide cohort study indicates that patients with psoriasis are at increased risk of VTE. The risk was highest in young patients with severe psoriasis. Physicians should be aware that patients with psoriasis may be at increased risk of both venous and arterial thromboembolic events