9,228 research outputs found
The National Virtual Observatory
As a scientific discipline, Astronomy is rather unique. We only have one
laboratory, the Universe, and we cannot, of course, change the initial
conditions and study the resulting effects. On top of this, acquiring
Astronomical data has historically been a very labor-intensive effort. As a
result, data has traditionally been preserved for posterity. With recent
technological advances, however, the rate at which we acquire new data has
grown exponentially, which has generated a Data Tsunami, whose wave train
threatens to overwhelm the field. In this conference proceedings, we present
and define the concept of virtual observatories, which we feel is the only
logical answer to this dilemma.Comment: 5 pages, uses newpasp.sty (included), to appear in "Extragalactic Gas
at Low Redshfit", ASP Conf. Series, J. S. Mulchaey and J. T. Stocke (eds.
Radio Pulse Properties of the Millisecond Pulsar PSR J0437-4715. I. Observations at 20cm
We present a total of 48 minutes of observations of the nearby, bright
millisecond pulsar PSR J0437-4715 taken at the Parkes radio observatory in
Australia. The data were obtained at a central radio frequency of 1380 MHz
using a high-speed tape recorder that permitted coherent Nyquist sampling of 50
MHz of bandwidth in each of two polarizations. Using the high time resolution
available from this voltage recording technique, we have studied a variety of
single-pulse properties, most for the first time in a millisecond pulsar. We
find no evidence for "diffractive" quantization effects in the individual pulse
arrival times or amplitudes as have been reported for this pulsar at lower
radio frequency using coarser time resolution (Ables et al. 1997). Overall, we
find that the single pulse properties of PSR J0437-4715 are similar to those of
the common slow-rotating pulsars, even though this pulsar's magnetosphere and
surface magnetic field are several orders of magnitude smaller than those of
the general population. The pulsar radio emission mechanism must therefore be
insensitive to these fundamental neutron star properties.Comment: 24 Postscript pages, 11 eps figures. Accepted for publication in the
Astrophysical Journal. Abbreviated abstract follow
Expected characteristics of the subclass of Supernova Gamma-ray Bursts (S-GRBs)
The spatial and temporal coincidence between the gamma-ray burst (GRB) 980425
and supernova (SN) 1998bw has prompted speculation that there exists a class of
GRBs produced by SNe (``S-GRBs''). Robust arguments for the existence of a
relativistic shock have been presented on the basis of radio observations. A
physical model based on the radio observations lead us to propose the following
characteristics of supernovae GRBs (S-GRBs): 1) prompt radio emission and
implied brightness temperature near or below the inverse Compton limit, 2) high
expansion velocity of the optical photosphere as derived from lines widths and
energy release larger than usual, 3) no long-lived X-ray afterglow, and 4) a
single pulse (SP) GRB profile. Radio studies of previous SNe show that only
type Ib and Ic potentially satisfy the first condition. Accordingly we have
investigated proposed associations of GRBs and SNe finding no convincing
evidence (mainly to paucity of data) to confirm any single connection of a SN
with a GRB. If there is a more constraining physical basis for the burst
time-history of S-GRBs beyond that of the SP requirement, we suggest the 1% of
light curves in the BATSE catalogue similar to that of GRB 980425 may
constitute the subclass. Future optical follow-up of bursts with similar
profiles should confirm if such GRBs originate from some fraction of SN type
Ib/Ic.Comment: 11 pages of LaTeX with 1 figure. Submitted to the Astrophysical
Journal Letter
Gurulinga Sangama Worship
Saiva metaphysics, guru worship, Linga worship, confluence worship, and the goal of the soul is to attain godliness. Thirumanthiram, the eighth sutra of Sivagnanabodha refers to the Saarala (Single Point) system. The perfection of the soul, the word Guru is also referred to as the remover of darkness. God will appear as a Guru. Arrogance, karma, and illusion lead to birth. It is God who prevents them. The word Shiva means purity. It is God who purifies the three unclean things. According to perfection in the souls, he will manifest himself as form, incorporeity, and corporeal. Devoted service, godly deeds, meditation, and knowledge are the paths to reaching God. The highest point of spirituality is knowledge. Gurulinga Sangama worship is the simplest way to attain enlightenment. The clergy regarded God as their guru. Gurulinga Sangama worship is a simple means for the soul to be liberated. The Lord himself has come as the Guru of Manickavasagar. He gave knowledge to the Apparadi through his sister. Guru worship is the first way for the soul to reach the end. Guru worship removes the misery of births. Linga worship is the worship of the embodied form of Linga (Here, Linga that is visible to the eyes is invisible to the mind). Confluence worship is the practice of performing worship together with the devotees. Confluence worship is the simplest way to receive god's grace. The confluence worship is explained in the 12 sutras of Thirugnanabodhar. Gurulinga Sangama worship is a state of interconnection with the Lord. When arrogance reduces, the strength of Karma and illusion also diminish. This is the basis of Gurulinga Sangama worship
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Selective dispersal of avian rhombomere cells in orthotopic and heterotopic grafts
During hindbrain development, cells become segregated into segmental groups, rhombomeres, by mechanisms that are presently unknown. One contributory factor early in development may be an alternating periodicity in cell surface properties down the neuraxis. This possibility was previously suggested by experiments in which tissue from different segmental levels was apposed in the absence of a boundary. New boundaries were regenerated only when rhombomeres from adjacent positions or positions three rhombomeres distant from one another were apposed. Combinations of two odd-numbered or two even-numbered rhombomeres usually failed to generate a boundary. In order to pursue this phenomenon to the cellular level, we have used two approaches, both involving donor-to-host transplantation. First, quail rhombomeres were grafted at various hindbrain levels of a chick host. Apposition of rhombomere 4 (r4) with r3 was concomitant with negligible cell mixing across the interface. By contrast, combinations of r3 with r5 or with r3 tissue led to cell mixing that was more extensive in combinations of identical rhombomeres (r3 with r3) than between two alternate ones (r3 with r5). Secondly, we grafted small pieces of fluorescently prelabelled chick rhombomere tissue at various hindbrain levels of chick hosts. In most cases, cells dispersed widely when transplanted orthopically or two segments distant from that of their origin. Cells transplanted into an adjacent segment, however, showed a tendency to remain undispersed. Among the different graft combinations, furthermore, there was a variation in the extent of dispersal that showed an additional level of complexity not revealed in boundary regeneration experiments. The possibility is raised that the early partitioning of rhombomeres involves a hierarchy in the adhesive preferences of cell-cell interactions along the neuraxis
A Group Theoretical Identification of Integrable Equations in the Li\'enard Type Equation : Part II: Equations having Maximal Lie Point Symmetries
In this second of the set of two papers on Lie symmetry analysis of a class
of Li\'enard type equation of the form ,
where over dot denotes differentiation with respect to time and and
are smooth functions of their variables, we isolate the equations which
possess maximal Lie point symmetries. It is well known that any second order
nonlinear ordinary differential equation which admits eight parameter Lie point
symmetries is linearizable to free particle equation through point
transformation. As a consequence all the identified equations turn out to be
linearizable. We also show that one can get maximal Lie point symmetries for
the above Li\'enard equation only when (subscript denotes
differentiation). In addition, we discuss the linearising transformations and
solutions for all the nonlinear equations identified in this paper.Comment: Accepted for publication in Journal of Mathematical Physic
Single Pulse Characteristics of the Millisecond Radio Pulsar PSR B1937+21 at 430 MHz
The single-pulse characteristics of the millisecond pulsar PSR B1937+21 are studied using the recently installed Caltech baseband recorder at the Arecibo Radio Observatory in Puerto Rico. This is the first such analysis of this object that includes both average intensity pulses as well as "giant pulses." Pulse ensemble-averaging techniques are developed in order to study the characteristics of PSR B1937+21's single pulses since the high time resolution signal-to-noise ratio is less than unity. This analysis reveals that the non-giant pulse radio emission is extremely stable. All observed fluctuations are consistent with diffractive interstellar scattering. Such intrinsic stability has yet to be observed in other radio pulsars
Observations of Two Millisecond Pulsars in the Globular Cluster NGC 5904
We report on 5 yr of pulsar observations of the globular cluster NGC 5904 (M5). A timing model has been obtained for the two known pulsars, and a deep search for additional faint isolated pulsars has lowered the detection Ăux limit to 40 ”Jy without further detection. We discuss the details and implications of the phase coherent timing models for PSR B1516+02A and PSR B1516+02B. Of particular interest for the binary PSR B1516+02B are the observed negative period derivative due to acceleration in the gravitational field of M5 and a detection of orbital precession
Inverse scattering approach to multiwavelength Fabry-PĂ©rot laser design
A class of multiwavelength Fabry-Pérot lasers is introduced where the spectrum is tailored through a patterning of the cavity effective index. The cavity geometry is obtained using an inverse scattering approach and can be designed such that the spacing of discrete Fabry-Pérot lasing modes is limited only by the bandwidth of the inverted gain medium. A specific two-color semiconductor laser with a mode spacing in the THz region is designed, and measurements are presented demonstrating the simultaneous oscillation of the two wavelengths. The nonperiodic effective index profile of the particular two-color device considered is shown to be related to a Moiré or superstructure grating
The first detection of coherent emission from radio pulsars
The statistical properties of the radio emission from the pulsars B0823+26, B0950+08, B1133+16, and B1937+21 are studied using high time resolution observations taken at the Arecibo Observatory in Puerto Rico. Temporally coherent non-Gaussian emission has been detected in three of the four observed objects. This is the first time such a phenomenon has been observed. The results have been interpreted using a generalized shot noise model, and various basic physical quantities pertaining to the magnetospheric plasma have been estimated
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