190 research outputs found

    A Study of the Effect of Bulges on Bar Formation in Disk galaxies

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    We use N-body simulations of bar formation in isolated galaxies to study the effect of bulge mass and bulge concentration on bar formation. Bars are global disk instabilities that evolve by transferring angular momentum from the inner to outer disks and to the dark matter halo. It is well known that a massive spherical component such as halo in a disk galaxy can make it bar stable. In this study we explore the effect of another spherical component, the bulge, on bar formation in disk galaxies. In our models we vary both the bulge mass and concentration. We have used two sets of models, one that has a dense bulge and high surface density disk. The second model has a less concentrated bulge and a lighter disk. In both models we vary the bulge to disk mass fraction from 0 to 0.7. Simulations of both the models show that there is an upper cutoff in bulge to disk mass ratio M b /M d above which bars cannot form; the cutoff is smaller for denser bulges( M b /M d = 0.2) compared to less denser ones (M b /M d = 0.5). We define a new criteria for bar formation in terms of bulge to disk radial force ratio (F b /F d ) at the disk scale lengths above which bars cannot form. We find that if F b /F d > 0.35, a disk is stable and a bar cannot form. Our results indicate that early type disk galaxies can still form strong bars in spite of having massive bulges.Comment: Accepted at MNRAS,12 pages, 19 figure

    How Shakespeares Dramas Help to Acquire Knowledge for the Students of all Levels

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    This paper presents how Shakespeare through his writing always juxtaposes the philosophy of our own life He is the best to portray human character which outdoes even the portrayal of Christopher Marlowe He has written with a great charm of artistic beauty filled with moral vision His supremacy lies in the fact that he can pierce very deeply the heart of so many passions accepting the respect of life His writing combines so many unique phrases exquisite metaphors and inverted sentences So students of all levels must gain some knowledge from Shakespeare s writing

    A Cost Shared Quantization Algorithm and its Implementation for Multi-Standard Video CODECS

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    The current trend of digital convergence creates the need for the video encoder and decoder system, known as codec in short, that should support multiple video standards on a single platform. In a modern video codec, quantization is a key unit used for video compression. In this thesis, a generalized quantization algorithm and hardware implementation is presented to compute quantized coefficient for six different video codecs including the new developing codec High Efficiency Video Coding (HEVC). HEVC, successor to H.264/MPEG-4 AVC, aims to substantially improve coding efficiency compared to AVC High Profile. The thesis presents a high performance circuit shared architecture that can perform the quantization operation for HEVC, H.264/AVC, AVS, VC-1, MPEG- 2/4 and Motion JPEG (MJPEG). Since HEVC is still in drafting stage, the architecture was designed in such a way that any final changes can be accommodated into the design. The proposed quantizer architecture is completely division free as the division operation is replaced by multiplication, shift and addition operations. The design was implemented on FPGA and later synthesized in CMOS 0.18 μm technology. The results show that the proposed design satisfies the requirement of all codecs with a maximum decoding capability of 60 fps at 187.3 MHz for Xilinx Virtex4 LX60 FPGA of a 1080p HD video. The scheme is also suitable for low-cost implementation in modern multi-codec systems

    The stellar bar - dark matter halo connection in the TNG50 simulations

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    Stellar bars in disk galaxies grow by losing angular momentum to their environments, including the Dark Matter (DM) halo, stellar and gas disks, and interacting satellite galaxies. This exchange of angular momentum during galaxy evolution hints at a connection between bar properties and the DM halo spin λ\lambda -- the dimensionless form of DM angular momentum. We investigate the connection of halo spin λ\lambda and galaxy properties in the presence/absence of stellar bars, using the cosmological magneto-hydrodynamic TNG50 simulations at three redshifts zr=0,0.1z_r=0, 0.1 and 1. We estimate the halo spin for barred and unbarred galaxies (bar strength: 0<A2/A0<0.70<A_2/A_0<0.7) at the central regions of the DM halo close to the galaxy disk and far from the disk, close to halo virial radius. At zr=0z_r=0, strongly barred galaxies (A2/A0>0.4A_2/A_0>0.4) reside in DM halos having low spin and low specific angular momentum, while unbarred and weakly barred galaxies (A2/A0<0.2A_2/A_0<0.2) are hosted in high spin and high specific angular momentum halos. The inverse correlation between bar strength and halo spin is surprising since previous studies show that bars transfer angular momentum to DM halos. However, the bar strength-halo spin connection is more complex at higher redshift (zr=1z_r=1) with higher halo spin for all galaxies than that at zr=0z_r=0. Using galaxy samples across various DM halo mass ranges, we highlight the importance of sample selection in obtaining meaningful results. Investigating the bar--halo connection in further detail is crucial for understanding the impact of bars on galaxy evolution models.Comment: 20 pages (including Appendix), 12 figures; submitted to AAS Journals; comments are welcome

    Starbursts triggered by central overpressure. ii. A parameter study

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    A parameter study is made of the radiative shock compression of a disk molecular cloud due to the high pressure of the central molecular intercloud medium, after the cloud has fallen into the central region of a galaxy following a galaxy interaction. The dependence of the compression on the disk cloud and central gas parameters has been studied. We show that fshell, the fraction of cloud mass compressed in the outer shell that becomes unstable, is a function of only the external pressure, the cloud radius, and the cloud density. We find that for a wide range of values for the input parameters, fshell is high and lies between 0.75 to 0.90. The fraction fshell is not sensitively dependent on the value of the central gas pressure because the initial inward shock velocity is proportional to the square root of the central pressure, and at later stages it is determined mainly by the self-gravity of the shocked shell. Thus, star formation triggered in disk clouds by compression by the central overpressure, as proposed by Jog &amp; Das, is a general triggering mechanism and is valid as long as the central gas has an overpressure of even a factor of a few higher than that of the incoming disk molecular clouds.We apply the mechanism to the galaxies for which the central gas parameters are known; for example, IC 342 and NGC 1808. We find that in both cases a large fraction of the cloud mass will be compressed. Hence, these galaxies should show a central starburst, provided that there is a substantial gas infall rate from the disk to the central region. This agrees with observations, in that NGC 1808 with gas infall due to galaxy interaction has a central starburst, while IC 342 does not

    Spontaneous uterine rupture in primigravida at 15 weeks

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    This is a very rare and interesting case of primigravida with sonographic evidence of intrauterine pregnancy presenting with acute abdomen at 15 weeks. With the diagnosis of uterine rupture, emergency laparotomy was done. The defect was repaired and post-operative recovery was good. This shows that spontaneous uterine rupture can occur in primigravida and should be kept in mind during diagnosis of acute abdomen