1,181 research outputs found
Magnesium deficiency and cerium promote fibrogenesis in rat heart
No full textCerium is a biologically active lanthanide and a major constituent of monazite. The observation that inhalation of particles of cerium causes pneumoconiosis had generated considerable interest in the toxicology of the element (Venugopal and Luckey 1978; Vocatura et al 1983). Cerium tartrate was found to produce cardiac injury and polycythaemia in small animals (Venugopal and Luckey 1978). More recently, tropical endomyocardial fibrosis (EMF), a restrictive cardiomyopathy, was postulated to be the cardiac expression of cerium toxicity in combination with magnesium deficiency (Valiathan et al 1989; Valiathan and Kartha 1990). The postulation was based upon the observation of elevated levels of cerium and depressed levels of magnesium in the cardiac tissue of patients with EMF (Valiathan et al 1989; Valiathan and Kartha 1990). Studies carried out in pursuance of the hypothesis showed that tissue levels of cerium are enhanced in magnesium deficiency (Eapen et al 1996) and that cerium and magnesium deficiency have a synergistic effect on cardiac metabolism (Gunther 1990; Shivakumar and Renuka Nair 1991). Importantly, recent observations on the mode of action of cerium at the molecular level suggested that the element may influence expression of matrix proteins like collagen in the heart and produce fibrosis (Prakash et al 1995; Shivakumar et al 1992). A sequel to these earlier investigations, the present study examined whether chronic ingestion of low doses of cerium would produce cardiac fibrosis in experimental animals. This communication presents evidence that cerium per se or in combination with magnesium deficiency produces subendocardial fibrosis and increase in interstitial cellularity and collagen content in rat heart. It also confirms the earlier observation from this laboratory that magnesium deficiency promotes accumulation of cerium in the cardiac tissue (Eapen el al 1996)
Krein's method in inverse scattering
No full textA detailed discussion of the Krein’s results (applicable for solving the inverse scattering problem) is given with complete proofs. It is shown that the S-function S(k) used in Krein’s work is the S-matrix used in physics. The basic new results of the paper include the detailed description and analysis of an inversion algorithm based on Krein’s results and a proof of its consistency, that is the proof that the reconstructed potential generates the same scattering data from which it was reconstructed. Numerical advantages of using Krein’s method are discussed
Analysis and evaluation of mechanical performance of reinforced sandwich structures: X-CorTM and K-CorTM
No full textX-CorTM and K-CorTM are foam based lightweight structural cores reinforced with ZFiber
® rods oriented in a truss pattern. They can generate sandwich structures which
possess strength- and stiffness-to-weight ratios such to compete with aerospace grade
honeycomb constructions. The enhanced tailoring ability to specific design needs, the
flexibility in reinforcement type and arrangement, the variety between closed cell foamfilled
or hollow core configurations for ultimate weight savings or structural
multifunctionality, while utilising manufacturing procedures similar to traditional
honeycomb sandwich structures (low cost out-of-autoclave manufacturing techniques
included) make these novel materials an attractive alternative. The process of their
implementation into current engineering practice requires a parallel comparison with
existing competitor cores and a critical evaluation of their performance, identifying
advantages and disadvantages.
This study represents one of the first attempts to create a rigorous methodology for the
analysis and evaluation of their mechanical behaviour and manufacturing sensitivities.
The balance of out-of-plane properties (shear and compression), fundamental for a
sandwich core material, has been investigated. The material energy absorption capacity
for the aforementioned loading cases, as well as for in-plane crushing was evaluated.
For this purpose, a new quasi-static test for progressive crushing of flat sandwich
laminates was designed successfully. The experimental data gathered validate proposed
analytical models which allowed further deductions on core parameters influence to be
made. Those parameters were the pin insertion angle, pin lay-out, pin density and the
role of the foam. A local-global FE modelling approach for Z-pinned sandwich cores is
also provided and validated for X-CorTM structures. Structural differences between XCorTM
and K-CorTM are at the base of a diverse mechanical response; their performance
is sensitive to the manufacturing process, as it determines the quality of the pin-skin and
pin-adhesive film interfaces. An ‘improved’ manufacturing technique designed for XCorTM
resulted in a sandwich panel able to offer the same mechanical performance of a
Nomex® honeycomb structure for a 25% of weight saving
Pro-fibrogenic effects of magnesium deficiency in the cardiovascular system
No full textMagnesium deficiency is known to produce cardiovascular injury. A large body of experimental evidence supports the postulation that an immuno-inflammatory reaction and increased oxidative stress may damage the myocardium and vasculature in magnesium deficiency. Reparative/reactive fibrosis in response to the injury has, however, received little attention. Recent evidence from a rodent model of acute magnesium deficiency suggests that humoral factors may activate cardiac fibroblasts by a free radical-mediated mechanism and contribute to cardiac fibrogenesis. A similar mechanism may also promote cellular hyperplasia and increased matrix synthesis in the vasculature
Dental caries vaccine
No full textDental caries is one of the most common diseases in humans. In modern times, it has reached epidemic proportions. Dental caries is an infectious microbiologic disease of the teeth that results in localized dissolution and destruction of the calcified tissue. Dental caries is a mulitifactorial disease, which is caused by host, agent, and environmental factors. The time factor is important for the development and progression of dental caries. A wide group of microorganisms are identified from carious lesions of which S. mutans , Lactobacillus acidophilus , and Actinomyces viscosus are the main pathogenic species involved in the initiation and development of dental caries. In India, surveys done on school children showed caries prevalence of approximately 58%. Surveys among the U.S. population showed an incidence of 45.3% in children and 93.8% in adults with either past or present coronal caries. Huge amounts of money and time are spent in treating dental caries. Hence, the prevention and control of dental caries is the main aim of public health, eventually the ultimate objective of public health is the elimination of the disease itself. Recently, dental caries vaccines have been developed for the prevention of dental caries. These dental caries vaccines are still in the early stages
Peregrination of endodontic tools-past to present
No full textThe clinical practice of yesterday′s endodontics becomes the heresy of today, and today′s endodontic practice becomes the heresy of tomorrow. The history of endodontics begins in the 17 th century. Since then, there have been numerous advances and developments, and research has proceeded continuously without pause. The manufacture of the first instruments for endodontic use dates back to 1875. These early instruments were made by hand from thin steel wires, and they performed the function of modern barbed broaches. In 1955, Ingle was the first to express the need for standardization of canal instruments. In 1965, the American Association of Endodontists adopted the terminology and nomenclature of the proposed standardized system. For many years, the standard cutting instruments have been the reamer, the K-type file, and the Hedstroem file. Recent changes in both metallurgy and endodontic concepts have led to the introduction of a wide range of new instruments. An effort has been made here to present the journey of endodontic instruments from the past to the present
Model of cardiovascular injury in magnesium deficiency
No full textMagnesium deficiency is known to produce cardiovascular lesions. It is, however, not clear as to what constitutes magnesium deficiency - reduced serum levels, reduced tissue levels or reduced intracellular levels of the ionic form of the element. This article cites evidence in support of a hypothesis that a fall in serum magnesium levels may trigger a temporal sequence of events involving vasoconstriction, hemodynamic alterations and vascular endothelial injury to produce pro-inflammatory, pro-oxidant and pro-fibrogenic effects, resulting in initial perivascular myocardial fibrosis which, in turn, would cause myocardial damage and replacement fibrosis. Further, angiotensin II may be the prime mover of the pathogenetic cascade in magnesium deficiency. Importantly, such a mechanism of cardiovascular injury would be independent of a reduction in myocardial or vascular tissue levels of magnesium. (C) 2001 Harcourt Publishers Ltd
Hypoxia and antioxidants enhance soluble ICAM-1 release from cardiac fibroblasts
No full textIntercellular adhesion molecule-1 plays a key role in mediating inflammatory and immune responses. There is also increasing appreciation of the role of its soluble form, sICAM-1, in regulating inflammation. This study evaluated the effects of hypoxia and N-acetyl-L-cysteine on sICAM-1 production by adult rat cardiac fibroblasts. By ELISA, hypoxia was found to cause a 61% increase in sICAM-1 in cardiac fibroblast culture supernates. However, RT-PCR did not reveal a concomitant increase in cell surface ICAM-1 transcript levels, suggesting that the increase in sICAM-1 may involve post-transcriptional and/or post-translational mechanisms. Using pharmacological inhibitors, it was observed that p42/44 MAPK and PKC mediate the stimulatory effect of hypoxia on sICAM-1 production. Remarkably, N-acetyl-L-cysteine caused a 3-fold increase in sICAM-1 by p42/44 MAPK-, p38 MAPK- and PKC-independent mechanisms. Pyrrolidine dithiocarbamate, another potent antioxidant, also augmented sICAM-1. The findings presented in this communication underscore the link between redox status and sICAM-1 release from cardiac fibroblasts. Further, because hypoxia is a major component of myocardial ischemia and is pro-inflammatory, and both N-acetylcysteine and pyrrolidine dithiocarbamate are clinically used antioxidants, the observations may have clinical significance
- …
