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Search Results: 1 - 10 of 200641 matches for " P. Kharb "
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Pc-scale study of Radio galaxies & BL Lacs
P. Kharb,P. Shastri,D. C. Gabuzda
Physics , 2003, DOI: 10.1016/S1387-6473(03)00065-4
Abstract: We study two aspects of the differences between Active Galactic Nuclei (AGN) of the two Fanaroff-Riley types in order to investigate the causes of the F-R divide. We (a) contrast the properties of the optical cores in beamed and unbeamed AGN of the two types, incorporating Hubble Space Telescope measurements of the unbeamed objects, and (b) contrast the nuclear magnetic field geometry of the beamed AGN of the two types using Very Long Baseline Polarimetry.
Magnetic Field Geometry in "Red" and "Blue" BL Lacs
P. Kharb,D. C. Gabuzda,P. Shastri
Physics , 2003, DOI: 10.1023/B:ASTR.0000004993.84117.d4
Abstract: We compare the systematics of the magnetic field geometry in the "red" low-energy peaked BL Lacs (LBLs) and "blue" high-energy peaked BL Lacs (HBLs) using VLBI polarimetric images. The LBLs are primarily "radio--selected" BL Lacs and the HBLs are primarily "X-ray selected". In contrast to the LBLs, which show predominantly transverse jet magnetic fields, the HBLs show predominantly longitudinal fields. Thus, while the SED peaks of core-dominated quasars, LBLs and HBLs form a sequence of increasing frequency, the magnetic field geometry does not follow an analogous sequence. We briefly investigate possible connections between the observed parsec-scale magnetic field structures and circular polarization measurements in the literature on various spatial scales.
Magnetic Field Geometry of the Broad Line Radio Galaxy 3C111
P. Kharb,D. Gabuzda,W. Alef,E. Preuss,P. Shastri
Physics , 2003, DOI: 10.1016/S1387-6473(03)00107-6
Abstract: Very Long Baseline Polarimetric observations of the Broad Line Radio galaxy 3C111 performed in July and September of 1996 at 8 and 43 GHz reveal rapidly evolving parsec-scale radio structure after a large millimetre outburst. The B-field geometry is not simple. We present a first analysis of possible Faraday and optical depth effects based on a comparison of the polarization images for the two frequencies.
Extended radio emission in MOJAVE Blazars: Challenges to Unification
P. Kharb,M. L. Lister,N. J. Cooper
Physics , 2010, DOI: 10.1088/0004-637X/710/1/764
Abstract: We present the results of a study on the 1.4 GHz kpc-scale radio emission in the complete flux density limited MOJAVE sample, comprising 135 radio-loud AGNs. While extended emission is detected in the majority of the sources, about 7% of the sources exhibit only radio core emission. Many BL Lacs exhibit extended radio power and kpc-scale morphology typical of powerful FRII jets, while a substantial number of quasars possess radio powers intermediate between FRIs and FRIIs. This poses challenges to the simple radio-loud unified scheme, which links BL Lacs to FRIs and quasars to FRIIs. We find a significant correlation between extended radio emission and pc-scale jet speeds: the more radio powerful sources possess faster jets. This indicates that the 1.4 GHz (or low frequency) radio emission is indeed related to jet kinetic power. Various properties such as extended radio power and apparent pc-scale jet speeds vary smoothly between different blazar subclasses, suggesting that, at least in terms of radio jet properties, the distinction between quasars and BL Lac objects, at an emission-line equivalent width of 5 Angstrom is essentially an arbitrary one. Based on the assumption that the extended radio luminosity is affected by the kpc-scale environment, we define the ratio of extended radio power to absolute optical magnitude as a proxy for environmental effects. Trends with this parameter suggest that the pc-scale jet speeds and the pc-to-kpc jet misalignments are not affected by the large-scale environment, but are more likely to depend upon factors intrinsic to the AGN, or its local pc-scale environment. We suggest that some of the extremely misaligned MOJAVE blazar jets could be "hybrid" morphology sources, with an FRI jet on one side and an FRII jet on the other. (Abridged)
The Search for Binary Black holes in Seyferts with Double Peaked Emission Lines
P. Kharb,M. Das,S. Subramanian,Z. Paragi
Physics , 2015,
Abstract: We discuss results from very long baseline interferometry (VLBI) observations of two Seyfert galaxies with double peaked emission lines in their SDSS optical spectra. Such AGN are potential candidates for the presence of binary black holes, which can be resolved on parsec-scales with VLBI. Our observations do not detect twin radio cores but rather nuclear outflows in these Seyferts. These outflows could be interacting with the emission line clouds producing the double peaks in the emission lines.
Low blood glutathione levels in acute myocardial infarction.
Kharb Simmi
Indian Journal of Medical Sciences , 2003,
Abstract: BACKGROUND: Although experimental studies have demonstrated that reduced glutathione (GSH) is involved in cellular protection from deleterious effects of oxygen free radicals in ischaemia and reperfusion, there are controversial data on the correlation between levels of GSH and the ischaemic process. AIM: The present study was planned to evaluate erythrocyte GSH levels in patients with acute myocardial infarction (AMI). SETTING & DESIGN: Erythrocyte GSH levels were determined in 22 patients with AMI and 15 age matched healthy volunteers served as control. MATERIAL & METHODS: Erythrocyte GSH levels were measured by using Bentler in AMI and control patients. Also lipid profile was analyzed enzymatically in these subject. STATISTICS: The values were expressed as means +/- standard deviation (SD) and data from patients and controls was compared using student′s ′t′-test. Results and CONCLUSION: GSH levels were significantly decreased in AMI as compared to control (p<0.001). Also, total cholesterol and triglycerides were higher is AMI subjects (p<0.05). These finding suggest that depressed GSH levels may be associated with enhanced protective mechanism to oxidative stress in AMI.
Activity of Extracellular Superoxide Dismutase in Gestational Diabetes
Simmi Kharb
Research Journal of Obstetrics and Gynecology , 2010,
Abstract: Recent studies indicate that Extracellular Superoxide (EC-SOD) may not be as scarce in some tissues as was initially believed. The EC-SOD is the major isoenzyme of SOD in the umbilical cord and is a major source of SOD activity in the uterus. The possible role of EC-SOD in gestational diabetes has not been reported. Hence, the present study was planned to study EC-SOD in healthy non-pregnant, healthy normotensive pregnant women and women with gestational diabetes. The present study was carried out in twenty healthy Non-Pregnant (NPW) controls (in age group 18-35 years), twenty healthy age-matched normotensive pregnant women (28-36 weeks gestation) and twenty (age-and parity-matched) women with gestational diabetes. Serum Extracellular Superoxide Dismutase Activity (EC-SOD) and superoxide generation was analyzed in these women. The EC-SOD levels were significantly decreased in G-DM as compared to HPW, NPW controls (p<0.001) and superoxide generation was raised in G-DM as compared to HPW (p<0.001). A significant negative correlation was observed between EC-SOD levels and superoxide generation (r = -0.175, p<0.05) in G-DM. These findings indicate that radical scavenging antioxidants are consumed by enhanced levels of free radicals produced during glucose induced oxidative stress.
Association Between Rheology and Lipoproteins in Menopausal Womens
Simmi Kharb
JK Science : Journal of Medical Education & Research , 2008,
Abstract: Lipid profile, haematocrit, fibrinogen, and blood viscosity were studied in 26 healthy volunteers (15premenopausal, 11 post menopausal). Menopausal women had significantly higher total cholesterol,fibrinogen, hematocrit and blood viscosity levels as compared to premenopausal women. Also, triglyceride,LDL-cholesterol and HDL-cholesterol levels were higher in menopausal women, but the difference wasstatistically insignificant. Since these parameters are considered to be risk factor for the development ofcoronary artery disease (CAD), menopausal women are at an increased risk of developing CAD.
Rotation-Measures across Parsec-scale Jets of FRI radio galaxies
P. Kharb,D. C. Gabuzda,C. P. O'Dea,P. Shastri,S. A. Baum
Physics , 2009, DOI: 10.1088/0004-637X/694/2/1485
Abstract: We present the results of a parsec-scale polarization study of three FRI radio galaxies - 3C66B, 3C78 and 3C264 - obtained with the Very Long Baseline Array at 5, 8 and 15 GHz. Parsec-scale polarization has been detected in a large number of beamed radio-loud active galactic nuclei, but in only a handful of the relatively unbeamed radio galaxies. We report here the detection of parsec-scale polarization at one or more frequencies in all three FRI galaxies studied. We detect Faraday rotation measures of the order of a few hundred rad/m^2 in the nuclear jet regions of 3C78 and 3C264. In 3C66B polarization was detected at 8 GHz only. A transverse rotation measure gradient is observed across the jet of 3C78. The inner-jet magnetic field, corrected for Faraday rotation, is found to be aligned along the jet in both 3C78 and 3C264, although the field becomes orthogonal further from the core in 3C78. The RM values in 3C78 and 3C264 are similar to those previously observed in nearby radio galaxies. The transverse RM gradient in 3C78, the increase in the degree of polarization at the jet edge, the large rotation in the polarization angles due to Faraday rotation and the low depolarization between frequencies, suggests that a layer surrounding the jet with a sufficient number of thermal electrons and threaded by a toroidal or helical magnetic field is a good candidate for the Faraday rotating medium. This suggestion is tentatively supported by Hubble Space Telescope optical polarimetry but needs to be examined in a greater number of sources.
Probing the Active Massive Black Hole Candidate in the Center of NGC 404 with VLBI
Z. Paragi,S. Frey,P. Kaaret,D. Cseh,R. Overzier,P. Kharb
Physics , 2014, DOI: 10.1088/0004-637X/791/1/2
Abstract: Recently Nyland et al. (2012) argued that the radio emission observed in the center of the dwarf galaxy NGC 404 originates in a low-luminosity active galactic nucleus (LLAGN) powered by a massive black hole ($M\sim<10^6$ M$_{\odot}$). High-resolution radio detections of MBHs are rare. Here we present sensitive, contemporaneous Chandra X-ray, and very long baseline interferometry (VLBI) radio observations with the European VLBI Network (EVN). The source is detected in the X-rays, and shows no long-term variability. If the hard X-ray source is powered by accretion, the apparent low accretion efficiency would be consistent with a black hole in the hard state. Hard state black holes are known to show radio emission compact on the milliarcsecond scales. However, the central region of NGC 404 is resolved out on 10 milliarcsecond (0.15-1.5 pc) scales. Our VLBI non-detection of a compact, partially self-absorbed radio core in NGC 404 implies that either the black hole mass is smaller than $3^{+5}_{-2}\times10^5$ M$_{\odot}$, or the source does not follow the fundamental plane of black hole activity relation. An alternative explanation is that the central black hole is not in the hard state. The radio emission observed on arcsecond (tens of pc) scales may originate in nuclear star formation or extended emission due to AGN activity, although the latter would not be typical considering the structural properties of low-ionization nuclear emission-line region galaxies (LINERs) with confirmed nuclear activity.
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