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Search Results: 1 - 10 of 462152 matches for " A. Petkov "
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Investigation of possibilities for high heavy metal content sludges utilization by incorporating them in concrete products
Simeonova A.,Petkov A.,Delchev N.,Balgaranova J.
Journal of Mining and Metallurgy, Section B : Metallurgy , 2006, DOI: 10.2298/jmmb0601025s
Abstract: The safe removal of sludge, obtained during the surface treatment of different metal products, is a serious environmental problem. These sludges are usually characterized by a high content of heavy metals (Pb, Cu, Ni, Zn, Cr, Cd, Mn), low quality and are obtained in many small industrial units in the whole country, which makes their centralized treatment difficult. In world practice, different methods are used for component fixation of such sludge, in the aim to prevent leaching of the metals causing pollution of the soil and underground water. The aim of the recent work is to prepare the sludge in a form of light (keramzit) fillers by preliminary treatment with binding substances and to introduce them in non supporting concrete products - curbs, stakes and similar products. The investigation was made with two types of sludge - from a production line for thermal treatment and hardening of different parts used in machine building and from a production line for surface decoration treatment (nickel-plating and chromium-plating) of consumer products. The sludge were dried and ground and then granulated with a solution of water glass. After their solidifying the air dried granules with a size of 5 to 15 mm were treated with cement milk and air dried again. With the obtained granules, standard percolation test for leaching metals like Pb, Cu, Zn, Ni and Cr was carried out. After a preliminary calculation of concrete mixtures, these granules were mixed with Portland cement and concrete sample products were made. These molded concrete samples were characterized by their density, water absorption, and mechanical strength for defined standard periods of time. The samples were subjected to a modified percolation test for leaching metals. The metal concentration in eluates was determined by Atomic Spectral Analysis.
Alcohol, metabolic risk and elevated serum gamma-glutamyl transferase (GGT) in Indigenous Australians
Matthew T Haren, Ming Li, John Petkov, Robyn A McDermott
BMC Public Health , 2010, DOI: 10.1186/1471-2458-10-454
Abstract: Data were from N = 2609 Indigenous Australians who participated in a health screening program in rural far north Queensland in 1999-2000 (44.5% response rate). The individual and interactive effects of metabolic risk and alcohol drinking on elevated serum GGT concentrations (≥50 U/L) were analyzed using logistic regression.Overall, 26% of the population had GGT≥50 U/L. Elevated GGT was associated with alcohol drinking (moderate drinking: OR 2.3 [95%CI 1.6 - 3.2]; risky drinking: OR 6.0 [4.4 - 8.2]), and with abdominal obesity (OR 3.7 [2.5 - 5.6]), adverse metabolic risk cluster profile (OR 3.4 [2.6 - 4.3]) and metabolic syndrome (OR 2.7 [2.1 - 3.5]) after adjustment for age, sex, ethnicity, smoking, physical activity and BMI. The associations of obesity and metabolic syndrome with elevated GGT were similar across alcohol drinking strata, but the association of an adverse metabolic risk cluster profile with elevated GGT was larger in risky drinkers (OR 4.9 [3.7 - 6.7]) than in moderate drinkers (OR 2.8 [1.6 - 4.9]) and abstainers (OR 1.6 [0.9 - 2.8]).In this Indigenous population, an adverse metabolic profile conferred three times the risk of elevated GGT in risky drinkers compared with abstainers, independent of sex and ethnicity. Community interventions need to target both determinants of the population's metabolic status and alcohol consumption to reduce the risk of elevated GGT.Non-alcoholic fatty liver disease (NAFLD) has become the most common cause of chronic liver disease and cryptogenic cirrhosis in developed countries. The increasing prevalence of obesity, type 2 diabetes, and metabolic syndrome may be important drivers of increasing rates of NAFLD diagnoses [1]. An elevated serum gamma-glutamyl transferase (GGT) has been demonstrated as a biomarker of NAFLD [2] and, although it is not the only marker of chronic liver disease, it does predict future diabetes, coronary heart disease and stroke [3,4].The Australian indigenous population has an excess of metab
Molecular Expression and Pharmacological Evidence for a Functional Role of Kv7 Channel Subtypes in Guinea Pig Urinary Bladder Smooth Muscle
Serge A. Y. Afeli, John Malysz, Georgi V. Petkov
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0075875
Abstract: Voltage-gated Kv7 (KCNQ) channels are emerging as essential regulators of smooth muscle excitability and contractility. However, their physiological role in detrusor smooth muscle (DSM) remains to be elucidated. Here, we explored the molecular expression and function of Kv7 channel subtypes in guinea pig DSM by RT-PCR, qRT-PCR, immunohistochemistry, electrophysiology, and isometric tension recordings. In whole DSM tissue, mRNAs for all Kv7 channel subtypes were detected in a rank order: Kv7.1~Kv7.2Kv7.3~Kv7.5Kv7.4. In contrast, freshly-isolated DSM cells showed mRNA expression of: Kv7.1~Kv7.2Kv7.5Kv7.3~Kv7.4. Immunohistochemical confocal microscopy analyses of DSM, conducted by using co-labeling of Kv7 channel subtype-specific antibodies and α-smooth muscle actin, detected protein expression for all Kv7 channel subtypes, except for the Kv7.4, in DSM cells. L-364373 (R-L3), a Kv7.1 channel activator, and retigabine, a Kv7.2-7.5 channel activator, inhibited spontaneous phasic contractions and the 10-Hz electrical field stimulation (EFS)-induced contractions of DSM isolated strips. Linopiridine and XE991, two pan-Kv7 (effective at Kv7.1-Kv7.5 subtypes) channel inhibitors, had opposite effects increasing DSM spontaneous phasic and 10 Hz EFS-induced contractions. EFS-induced DSM contractions generated by a wide range of stimulation frequencies were decreased by L-364373 (10 μM) or retigabine (10 μM), and increased by XE991 (10 μM). Retigabine (10 μM) induced hyperpolarization and inhibited spontaneous action potentials in freshly-isolated DSM cells. In summary, Kv7 channel subtypes are expressed at mRNA and protein levels in guinea pig DSM cells. Their pharmacological modulation can control DSM contractility and excitability; therefore, Kv7 channel subtypes provide potential novel therapeutic targets for urinary bladder dysfunction.
Scientific Annals of the Alexandru Ioan Cuza University of Iasi : Economic Sciences Series , 2010,
Abstract: This paper argues that a disclosure-only approach provides a better means of incorporating human capital information into the financial statements. The express purpose of the financial notes is to allow an informed assessment of the company’s operations, financial position and future business strategies and prospects. We show that the current accounting framework under IFRS, specifically IAS 1, could accustom the disclosure of human capital into the notes of the financial statements. In addition, we identify the key compulsory indicators that organizations need to disclose into the notes to the financial statements. These indicators include the short and long term strategies related to human capital, information on acquisition and retention, learning and development. In addition, organizations need to provide details on the effectiveness and performance of their human capital management policies and practices. The reporting is to be accomplished with the use of a mix of quantitative and qualitative data.
In Situ Real-Time TEM Reveals Growth, Transformation and Function in One-Dimensional Nanoscale Materials: From a Nanotechnology Perspective
Nikolay Petkov
ISRN Nanotechnology , 2013, DOI: 10.1155/2013/893060
Abstract: This paper summarises recent developments in in situ TEM instrumentation and operation conditions. The focus of the discussion is on demonstrating how improved understanding of fundamental physical phenomena associated with nanowire or nanotube materials, revealed by following transformations in real time and high resolution, can assist the engineering of emerging electronic and optoelectronic devices. Special attention is given to Si, Ge, and compound semiconductor nanowires and carbon nanotubes (CNTs) as one of the most promising building blocks for devices inspired by nanotechnology. 1. Introduction Every aspect of basic nanoscale science as well as commercial production of nanotechnologies is dependent upon the capacity of instruments and methodologies to measure, sense, fabricate, and manipulate matter at the nanoscale. Microscopy has the advantage over other characterisation techniques (e.g., bulk spectroscopy or electrical testing) in that it is descriptive, producing images of objects that are directly related to their structure, morphology, and composition, and hence it directly uncovers spatial heterogeneities. Nowadays, lattice resolution images of crystalline materials are acquired routinely by high resolution transmission electron microscopy (TEM) using conventional TEM optics. In the last few years, the state-of-the-art has become the sub-Angstroms resolution imaging and analysis, achieved through the use of image or probe aberration-corrected TEM instruments [1]. Using the ability of forming an extremely small and intense electron probe within aberration-corrected scanning transmission electron microscope (STEM), quantifiable images of atomic columns and indeed atom-by-atom visualisation have been demonstrated [2]. Observing processes “on site” as they are occurring and under changing external stimuli is the paramount goal of in situ time resolved techniques. Various in situ and operandi techniques have emerged and are gaining importance in different areas of science and engineering. In the field of nanoscience and nanotechnology, there are only a handful of techniques that can merge extreme spatial resolution with the possibility of in situ real-time detection. Among them, in situ electron microscopy is probably the most versatile and mature technique, and it has been a topic of separate workshops, dedicated books, and extended reviews [3–12]. It emerged in the 1960s, driven by the technology needs to examine stability and radiation damage of materials for aviation, nuclear reactors, and space exploration. In the past, it was not rare
Time and Reality of Worldtubes
Vesselin Petkov
Physics , 2008,
Abstract: In this essay, dedicated to the one hundredth anniversary of Hermann Minkowski's talk "Space and Time", I argue that physicists should face the issue of the reality of spacetime and worldtubes of physical objects for two reasons. First, this issue is not a philosophical question, as some appear to think, since the kinematical special relativistic effects would be impossible, as will be demonstrated, if the physical objects involved in these effects did not exist as four-dimensional worldtubes. Second, taking into account that worldtubes are real four-dimensional objects provides an unexpected insight into the origin of inertia, the nature of the force acting on a body supported in a gravitational field, and possibly even the nature of quantum objects.
On the gravitational redshift
Vesselin Petkov
Physics , 1998,
Abstract: The purpose of this paper is twofold - to demonstrate that in the gravitational redshift it is the frequency a photon that is constant, and to describe the mechanism responsible for the change of its wavelength.
Lessons from failures to achieve what was possible in the twentieth century physics
Vesselin Petkov
Physics , 2010,
Abstract: For several decades there has been no breakthrough in fundamental physics as revolutionary as relativity and quantum physics despite the amazing advancement of applied physics and technology. By discussing several examples of what physics could have achieved by now, but failed, I will argue that the present state of fundamental physics is not caused by the lack of talented physicists, but rather by problematic general views on how one should do physics. Although it appears to be widely believed that such general views cannot affect the advancement of physics I would like to draw the attention of the younger generation of physicists to three reasons that might have been responsible for failures in the past and might cause problems in the future: (i) misconceptions on the nature of physical theories, (ii) underestimation of the role of conceptual analyses so successfully employed by Galileo and Einstein, and (iii) overestimation of the predictive power of mathematics in physics.
Acceleration-dependent self-interaction effects as a possible mechanism of inertia
Vesselin Petkov
Physics , 1999,
Abstract: The paper pursues two aims. First, to revisit the classical electromagnetic mass theory and develop it further by making use of a corollary of general relativity - that the propagation of light in non-inertial reference frames is anisotropic. Second, to show that the same type of acceleration-dependent self-interaction effects that give rise to the inertia and mass of the classical electron appear in quantum field theory as well when the general relativistic frequency shift of the virtual quanta, mediating the electromagnetic, weak, and strong interactions between non-inertial particles, is taken into account. Those effects may account for the origin of inertia and mass of macroscopic objects.
Propagation of light in non-inertial reference frames
Vesselin Petkov
Physics , 1999,
Abstract: It is shown that the complete description of the propagation of light in a gravitational field and in non-inertial reference frames in general requires an average coordinate and an average proper velocity of light. The need for an average coordinate velocity of light in non-inertial frames is demonstrated by considering the propagation of two vertical light rays in the Einstein elevator (in addition to the horizontal ray originally discussed by Einstein). As an average proper velocity of light is implicitly used in the Shapiro time delay (as shown in the Appendix) it is explicitly derived and it is shown that for a round trip of a light signal between two points in a gravitational field the Shapiro time delay not only depends on which point it is measured at, but in the case of a parallel gravitational field it is not always a delay effect. The propagation of light in rotating frames (the Sagnac effect) is also discussed and an expression for the coordinate velocity of light is derived. The use of this coordinate velocity naturally explains why an observer on a rotating disk finds that two light signals emitted from a point on the rim of the disk and propagating in opposite directions along the rim do not arrive simultaneously at the same point.
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