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Whole Body Vibration Impact Assessment on Dumper Operator Using Computational Learning Technique
Kaviraj Ramar,L. A. Kumaraswamidhas,P. S. Balaji,A. Agasthian 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.2
In the mining industry, the dumper vehicle plays a vital role in material handling tasks. During the various operations, the dumper operators are subjected to whole-body vibrations (WBV) which also affects their physiological factors. The present study investigates the dumper operator discomfort during various dumper operations such as material-loading (ML), loaded-travel (LT), material-unloading (MU) and unloaded-travel (UT). As per ISO 2631:1 specified, limit during the ML and MU task, the measured crest factor value is greater than the recommended values. However, the measured aw(8) and VDV(8) magnitude are within the specified limit. In the LT, it is observed that the VDV is within the limit, although the measured value is 1.39 times greater than MU task. The maximum WBV is observed during the UT, and the measured value of VDV falls above the specified limit, and experience a greater amplification of source vibration at 1.6 Hz. Moreover, the demand for high number of operation cycle increases the risk of neck pain and back pain among the study population. Operator physiological stress under WBV exposure showed a significant increase in heart rate by 2.04 bpm. Whereas, no significant influence on the increase in blood pressure (SYS/DIA: 1.56/0.76 mmHg) and a decrease in oxygen saturation level (SpO2) by 1% was observed. Therefore, to optimize the performance of seat design under different operation cycle using computational learning technique support vector machine classifier with quadratic preset model provides a best accuracy of 98.5% over the other machine learning algorithm. The study reveals that the prolonged sitting and constant experience of WBV could increase the job work stress, the computational learning technique warranted to prevent the operator from high WBV exposures.
UV bright globular clusters in M87: more evidence for super-He-rich stellar populations?
Kaviraj, S.,Sohn, S. T.,O'Connell, R. W.,Yoon, S.-J.,Lee, Y. W.,Yi, S. K. Blackwell Publishing Ltd 2007 Monthly notices of the Royal Astronomical Society Vol.377 No.3
<P>ABSTRACT</P><P>We study the ultraviolet (UV) and optical properties of 38 massive globular clusters (GCs) in the Virgo elliptical, M87, imaged using the STIS and WFPC2 instruments onboard the <I>Hubble Space Telescope</I>. The majority of these GCs appear extremely bright in the far-UV (FUV) – roughly a magnitude brighter than their Galactic counterparts with similar metallicities. The observed FUV flux is several times larger than predictions of canonical old stellar population models. These canonical models, which assume a fiducial helium enrichment parameter, Δ<I>Y</I>/Δ<I>Z</I>= 2, are able to reproduce the observed FUV fluxes only if ages ∼3–5 Gyr larger than the <I>Wilkinson Microwave Anisotropy Probe</I> (<I>WMAP</I>) age of the Universe are invoked, although the same models fit the UV photometry of Galactic and M31 GCs for ages less than the ‘<I>WMAP</I> age’. A similar discrepancy (∼3 Gyr) is found between the mass-weighted and UV-luminosity-weighted ages of the massive Galactic GC ω Cen, whose colour–magnitude diagram (including peculiar features on its well-populated horizontal branch) can be accurately reproduced by invoking a small super-He-rich (Δ<I>Y</I>/Δ<I>Z</I>≳ 90) stellar component. By comparison to ω Cen, we propose that the majority of M87 GCs in our sample contain strong signatures of similarly minor super-He-rich subcomponents. This hypothesis is supported by simulations which suggest that, based on the UV detection limit of this survey, the number of GCs detected is several times that predicted by canonical models. Although we cannot prove or disprove the extreme helium scenario at the moment, we show that the same phenomenon that causes the extended horizontal branch of ω Cen explains the UV brightness of our sample. If this is indeed due to the extreme helium, this study would be the first to find its signatures in extragalactic objects.</P>
A WFC3 study of globular clusters in NGC 4150: an early‐type minor merger
Kaviraj, Sugata,Crockett, R. Mark,Whitmore, Bradley C.,Silk, Joseph,O’Connell, Robert W.,Windhorst, Rogier A.,Mutchler, Max,Rejkuba, Marina,Yi, Sukyoung,Frogel, Jay A.,Calzetti, Daniela Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society. Vol.422 No.1
<P><B>ABSTRACT</B></P><P>We combine near‐ultraviolet (NUV; 2250 Å) and optical (<I>U</I>, <I>B</I>, <I>V</I>, <I>I</I>) imaging from the Wide Field Camera 3 (WFC3), on‐board the <I>Hubble Space Telescope</I> (<I>HST</I>), to study the globular cluster (GC) population in NGC 4150, a sub‐L* (<I>M</I><SUB><I>B</I></SUB>∼−18.48 mag) early‐type minor‐merger remnant in the Coma I cloud. We use broad‐band NUV–optical photometry from the WFC3 to estimate individual ages, metallicities, masses and line‐of‐sight extinctions [<I>E</I>(<I>B</I>−<I>V</I>)] for 63 bright (<I>M</I><SUB><I>V</I></SUB> < −5 mag) GCs in this galaxy. In addition to a small GC population with ages greater than 10 Gyr, we find a dominant population of clusters with ages centred around 6 Gyr, consistent with the expected peak of stellar mass assembly in faint early types residing in low‐density environments. The old and intermediate‐age GCs in NGC 4150 are metal poor, with metallicities less than 0.1 Z<SUB>⊙</SUB>, and reside in regions of low extinction [<I>E</I>(<I>B</I>−<I>V</I>) < 0.05 mag]. We also find a population of young, metal‐rich (<I>Z</I> > 0.3 Z<SUB>⊙</SUB>) clusters that have formed within the last Gyr and reside in relatively dusty [<I>E</I>(<I>B</I>−<I>V</I>) > 0.3 mag] regions that are coincident with the part of the galaxy core that hosts significant recent star formation. Cluster disruption models (in which ∼80–90 per cent of objects younger than a few ×10<SUP>8</SUP> yr dissolve every dex in time) suggest that the bulk of these young clusters are a transient population.</P>
Martin, G,Kaviraj, S,Volonteri, M,Simmons, B D,Devriendt, J E G,Lintott, C J,Smethurst, R J,Dubois, Y,Pichon, C Oxford University Press 2018 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.476 No.2
<P>Understanding the processes that drive the formation of black holes (BHs) is a key topic in observational cosmology. While the observed M-BH-M-Bulge correlation in bulge-dominated galaxies is thought to be produced by major mergers, the existence of an M-BH-M star relation, across all galaxy morphological types, suggests that BHs may be largely built by secular processes. Recent evidence that bulge-less galaxies, which are unlikely to have had significant mergers, are offset from the M-BH-M-Bulge relation, but lie on the MBH-M star relation, has strengthened this hypothesis. Nevertheless, the small size and heterogeneity of current data sets, coupled with the difficulty in measuring precise BH masses, make it challenging to address this issue using empirical studies alone. Here, we use Horizon-AGN, a cosmological hydrodynamical simulation to probe the role of mergers in BH growth over cosmic time. We show that (1) as suggested by observations, simulated bulge-less galaxies lie offset from the main MBH-MBulge relation, but on the M-BH-M star relation, (2) the positions of galaxies on the M-BH-M star relation are not affected by their merger histories, and (3) only similar to 35 per cent of the BH mass in today's massive galaxies is directly attributable to merging - the majority (similar to 65 per cent) of BH growth, therefore, takes place gradually, via secular processes, over cosmic time.</P>
Suppression of star formation in early-type galaxies by feedback from supermassive black holes
Schawinski, Kevin,Khochfar, Sadegh,Kaviraj, Sugata,Yi, Sukyoung K.,Boselli, Alessandro,Barlow, Tom,Conrow, Tim,Forster, Karl,Friedman, Peter G.,Martin, D. Chris,Morrissey, Patrick,Neff, Susan,Schimino Nature Publishing Group 2006 Nature Vol.442 No.7105
Detailed high-resolution observations of the innermost regions of nearby galaxies have revealed the presence of supermassive black holes. These black holes may interact with their host galaxies by means of ‘feedback’ in the form of energy and material jets; this feedback affects the evolution of the host and gives rise to observed relations between the black hole and the host. Here we report observations of the ultraviolet emissions of massive early-type galaxies. We derive an empirical relation for a critical black-hole mass (as a function of velocity dispersion) above which the outflows from these black holes suppress star formation in their hosts by heating and expelling all available cold gas. Supermassive black holes are negligible in mass compared to their hosts but nevertheless seem to play a critical role in the star formation history of galaxies.