82 research outputs found
Multidimensional simple waves in fully relativistic fluids
A special version of multi--dimensional simple waves given in [G. Boillat,
{\it J. Math. Phys.} {\bf 11}, 1482-3 (1970)] and [G.M. Webb, R. Ratkiewicz, M.
Brio and G.P. Zank, {\it J. Plasma Phys.} {\bf 59}, 417-460 (1998)] is employed
for fully relativistic fluid and plasma flows. Three essential modes: vortex,
entropy and sound modes are derived where each of them is different from its
nonrelativistic analogue. Vortex and entropy modes are formally solved in both
the laboratory frame and the wave frame (co-moving with the wave front) while
the sound mode is formally solved only in the wave frame at ultra-relativistic
temperatures. In addition, the surface which is the boundary between the
permitted and forbidden regions of the solution is introduced and determined.
Finally a symmetry analysis is performed for the vortex mode equation up to
both point and contact transformations. Fundamental invariants and a form of
general solutions of point transformations along with some specific examples
are also derived.Comment: 21 page
The Influence of Chemical Surface Treatment on the Corrosion Resistance of Titanium Castings Used in Dental Prosthetics
Abstract Air abrasion process is used for cleaning casting surface of prosthetic components, and to prepare the surface of these elements for the application of veneering items. Its side effect, however, is that abrasive particles are embedded in the treated surface, which can be up to 30% of the surface and it constitutes the side effect of this procedure. Such a significant participation of foreign material can not be indifferent to the properties of the surface. Embedded particles can be the place of stress concentration causing cracking of ceramics, and may deteriorate corrosion resistance by forming corrosive microlinks. In the latter cases, it would be advisable to remove elements embedded into the surface. The simplest method is chemical etching or electrochemical one. Nevertheless, these procedures should not significantly change the parameters of the surface. Among many possible reagents only a few fulfills all the above conditions. In addition, processing should not impair corrosion resistance of titanium, which is one of the most important factors determining its use as a prosthetic restoration in the mouth. The study presented results of corrosion resistance of titanium used to make prosthetic components by means of casting method, which were subjected to chemical processing designed to remove the embedded abrasive particles. The aim of the study was to investigate whether etching with selected reagents affects the corrosion resistance of titanium castings. For etching the following reagents were used: 30% HNO 3 + 3% HF + H 2 O, HNO 3 + HF+ glycerol (1:2:3), 4% HF in H 2 O 2 , 4% HF in H 2 O, with a control sandblasted sample, not subjected to etching. Tests demonstrated that the etching affected corrosion properties of test samples, in each case the reduction of the corrosion potential occurred -possibly due to the removal of particles of Al 2 O 3 from the surface and activation of the surface. None of the samples underwent pitting corrosion as a result of polarization to 9 V. Values of the polarization resistance, and potentiodynamic characteristics indicated that the best corrosion resistance exhibited the samples after etching in a mixture of 4% solution of HF in H 2 O 2 . They showed very good passivation of the surface
Classification of integrable two-component Hamiltonian systems of hydrodynamic type in 2+1 dimensions
Hamiltonian systems of hydrodynamic type occur in a wide range of
applications including fluid dynamics, the Whitham averaging procedure and the
theory of Frobenius manifolds. In 1+1 dimensions, the requirement of the
integrability of such systems by the generalised hodograph transform implies
that integrable Hamiltonians depend on a certain number of arbitrary functions
of two variables. On the contrary, in 2+1 dimensions the requirement of the
integrability by the method of hydrodynamic reductions, which is a natural
analogue of the generalised hodograph transform in higher dimensions, leads to
finite-dimensional moduli spaces of integrable Hamiltonians. In this paper we
classify integrable two-component Hamiltonian systems of hydrodynamic type for
all existing classes of differential-geometric Poisson brackets in 2D,
establishing a parametrisation of integrable Hamiltonians via
elliptic/hypergeometric functions. Our approach is based on the Godunov-type
representation of Hamiltonian systems, and utilises a novel construction of
Godunov's systems in terms of generalised hypergeometric functions.Comment: Latex, 34 page
The characterization of two-component (2+1)-dimensional integrable systems of hydrodynamic type
We obtain the necessary and sufficient conditions for a two-component
(2+1)-dimensional system of hydrodynamic type to possess infinitely many
hydrodynamic reductions. These conditions are in involution, implying that the
systems in question are locally parametrized by 15 arbitrary constants. It is
proved that all such systems possess three conservation laws of hydrodynamic
type and, therefore, are symmetrizable in Godunov's sense. Moreover, all such
systems are proved to possess a scalar pseudopotential which plays the role of
the `dispersionless Lax pair'. We demonstrate that the class of two-component
systems possessing a scalar pseudopotential is in fact identical with the class
of systems possessing infinitely many hydrodynamic reductions, thus
establishing the equivalence of the two possible definitions of the
integrability. Explicit linearly degenerate examples are constructed.Comment: 15 page
Riemann Invariants and Rank-k Solutions of Hyperbolic Systems
In this paper we employ a "direct method" in order to obtain rank-k solutions
of any hyperbolic system of first order quasilinear differential equations in
many dimensions. We discuss in detail the necessary and sufficient conditions
for existence of these type of solutions written in terms of Riemann
invariants. The most important characteristic of this approach is the
introduction of specific first order side conditions consistent with the
original system of PDEs, leading to a generalization of the Riemann invariant
method of solving multi-dimensional systems of PDEs. We have demonstrated the
usefulness of our approach through several examples of hydrodynamic type
systems; new classes of solutions have been obtained in a closed form.Comment: 30 page
Effects of serum proteins on corrosion behavior of ISO 5832–9 alloy modified by titania coatings
Stainless steel ISO 5832–9 type is often used to
perform implants which operate in protein-containing physiological
environments. The interaction between proteins and
surface of the implant may affect its corrosive properties. The
aim of this work was to study the effect of selected serum
proteins (albumin and γ-globulins) on the corrosion of ISO
5832–9 alloy (trade name M30NW) which surface was modified
by titania coatings. These coatings were obtained by sol–
gel method and heated at temperatures of 400 and 800 °C. To
evaluate the effect of the proteins, the corrosion tests were
performed with and without the addition of proteins with
concentration of 1 g L−1 to the physiological saline solution
(0.9 % NaCl, pH 7.4) at 37 °C. The tests were carried out
within 7 days. The following electrochemical methods were
used: open circuit potential, linear polarization resistance, and
electrochemical impedance spectroscopy. In addition, surface
analysis by optical microscopy and X-ray photoelectron spectroscopy
(XPS) method was done at the end of weekly corrosion
tests. The results of corrosion tests showed that M30NW
alloy both uncoated and modified with titania coatings exhibits
a very good corrosion resistance during weekly exposition
to corrosion medium. The best corrosion resistance in
0.9 % NaCl solution is shown by alloy samples modified by
titania coating annealed at 400 °C. The serumproteins have no
significant effect onto corrosion of investigated biomedical
steel. The XPS results confirmed the presence of proteins on
the alloy surface after 7 days of immersion in proteincontaining
solutions.The investigations were supported by the National Science Centre project No. N N507 501339. The authors gratefully acknowledge Dr. Janusz
Sobczak and Dr. hab. Wojciech Lisowski from Institute of Physical
Chemistry of PAS for XPS surface analyses
Structural analysis and corrosion studies on an ISO 5832-9 biomedical alloy with TiO2 sol–gel layers
The aim of this study was to demonstrate the
relationship between the structural and corrosion properties
of an ISO 5832-9 biomedical alloy modified with titanium
dioxide (TiO2) layers. These layers were obtained via the
sol–gel method by acid-catalyzed hydrolysis of titanium
isopropoxide in isopropanol solution. To obtain TiO2 layers
with different structural properties, the coated samples
were annealed at temperatures of 200, 300, 400, 450, 500,
600 and 800 C for 2 h. For all the prepared samples,
accelerated corrosion measurements were performed in
Tyrode’s physiological solution using electrochemical
methods. The most important corrosion parameters were
determined: corrosion potential, polarization resistance,
corrosion rate, breakdown and repassivation potentials.
Corrosion damage was analyzed using scanning electron
microscopy. Structural analysis was carried out for selected
TiO2 coatings annealed at 200, 400, 600 and 800 C. In
addition, the morphology, chemical composition, crystallinity,
thickness and density of the deposited TiO2 layers
were determined using suitable electron and X-ray measurement
methods. It was shown that the structure and
character of interactions between substrate and deposited
TiO2 layers depended on annealing temperature. All the
obtained TiO2 coatings exhibit anticorrosion properties, but
these properties are related to the crystalline structure and
character of substrate–layer interaction. From the point of
view of corrosion, the best TiO2 sol–gel coatings for stainless steel intended for biomedical applications seem to
be those obtained at 400 C.This study was supported by Grant No. N N507
501339 of the National Science Centre. The authors wish to express
their thanks to J. Borowski (MEDGAL, Poland) for the Rex 734 alloy
High‐throughput sequencing approach in analysis of microbial communities colonizing natural gas pipelines
This study provides a deep modern insight into the phylogenetic diversity among bacterial consortia found in working and nonworking high‐methane natural gas pipelines located in Poland. The working pipeline was characterized by lower biodiversity (140–154 bacterial genera from 22 to 23 classes, depending on the source of the debris) in comparison to the off‐gas pipeline (169 bacterial genera from 23 classes). The sediment recovered from the working pipeline contained mostly DNA identified as belonging to the phylum Firmicutes (66.4%–45.9% operational taxonomic units [OTUs]), predominantly Bacillus (41.4%–31.1% OTUs) followed by Lysinibacillus (2.6%–1.5% OTUs) and Clostridium (2.4%–1.8% OTUs). In the nonworking pipeline, Proteobacteria (46.8% OTUs) and Cyanobacteria (27.8% OTUs) were dominant. Over 30% of the Proteobacteria sequences showed homologies to Gammaproteobacteria, with Pseudomonas (7.1%), Enhydrobacter (2.1%), Stenotrophomonas (0.5%), and Haempohilus (0.4%) among the others. Differences were noted in terms of the chemical compositions of deposits originating from the working and nonworking gas pipelines. The deposits from the nonworking gas pipeline contained iron, as well as carbon (42.58%), sulphur (15.27%), and oxygen (15.32%). This composition can be linked to both the quantity and type of the resident microorganisms. The presence of a considerable amount of silicon (17.42%), and of aluminum, potassium, calcium, and magnesium at detectable levels, may likewise affect the metabolic activity of the resident consortia in the working gas pipeline. All the analyzed sediments included both bacteria known for causing and intensifying corrosion (e.g., Pseudomonas, Desulfovibrio, Shewanella, Serratia) and bacteria that can protect the surface of pipelines against deterioration (e.g., Bacillus). Biocorrosion is not related to a single mechanism or one species of microorganism, but results from the multidirectional activity of multiple microbial communities. The analysis presented here of the state of the microbiome in a gas pipeline during the real gas transport is a particularly valuable element of this work
Childhood sarcoidosis: A rare but fascinating disorder
Childhood sarcoidosis is a rare multisystemic granulomatous disorder of unknown etiology. In the pediatric series reported from the southeastern United States, sarcoidosis had a higher incidence among African Americans. Most reported childhood cases have occurred in patients aged 13–15 years. Macrophages bearing an increased expression of major histocompatibility class (MHC) II molecules most likely initiate the inflammatory response of sarcoidosis by presenting an unidentified antigen to CD4+ Th (helper-inducer) lymphocytes. A persistent, poorly degradable antigen driven cell-mediated immune response leads to a cytokine cascade, to granuloma formation, and eventually to fibrosis. Frequently observed immunologic features include depression of cutaneous delayed-type hypersensitivity and a heightened helper T cell type 1 (Th1) immune response at sites of disease. Circulating immune complexes, along with signs of B cell hyperactivity, may also be found. The clinical presentation can vary greatly depending upon the organs involved and age of the patient. Two distinct forms of sarcoidosis exist in children. Older children usually present with a multisystem disease similar to the adult manifestations, with frequent hilar lymphadenopathy and pulmonary infiltrations. Early-onset sarcoidosis is a unique form of the disease characterized by the triad of rash, uveitis, and arthritis in children presenting before four years of age. The diagnosis of sarcoidosis is confirmed by demonstrating a typical noncaseating granuloma on a biopsy specimen. Other granulmatous diseases should be reasonably excluded. The current therapy of choice for sarcoidosis in children with multisystem involvement is oral corticosteroids. Methotrexate given orally in low doses has been effective, safe and steroid sparing in some patients. Alternative immunosuppressive agents, such as azathioprine, cyclophosphamide, chlorambucil, and cyclosporine, have been tried in adult cases of sarcoidosis with questionable efficacy. The high toxicity profile of these agents, including an increased risk of lymphoproliferative disorders and carcinomas, has limited their use to patients with severe disease refractory to other agents. Successful steroid sparing treatment with mycophenolate mofetil was described in an adolescent with renal-limited sarcoidosis complicated by renal failure. Novel treatment strategies for sarcoidosis have been developed including the use of TNF-alpha inhibitors, such as infliximab. The long-term course and prognosis is not well established in childhood sarcoidosis, but it appears to be poorer in early-onset disease
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