703 research outputs found
Revisit of non-linear Landau damping for electrostatic instability driven by blazar-induced pair beams
We revisit the effect of non-linear Landau (NL) damping on the electrostatic
instability of blazar-induced pair beams, using a realistic pair-beam
distribution. We employ a simplified 2D model in -space to study the
evolution of the electric-field spectrum and to calculate the relaxation time
of the beam. We demonstrate that the 2D model is an adequate representation of
the 3D physics. We find that non-linear Landau damping, once it operates
efficiently, transports essentially the entire wave energy to small wavenumbers
where wave driving is weak or absent. The relaxation time also strongly depends
on the IGM temperature, , and for eV, and
in the absence of any other damping mechanism, the relaxation time of the pair
beam is longer than the inverse Compton (IC) scattering time. The weak
late-time beam energy losses arise from the accumulation of wave energy at
small , that non-linearly drains the wave energy at the resonant
of the pair-beam instability. Any other dissipation process
operating at small would reduce that wave-energy drain and hence lead to
stronger pair-beam energy losses. As an example, collisions reduce the
relaxation time by an order of magnitude, although their rate is very small.
Other non-linear processes, such as the modulation instability, could provide
additional damping of the non-resonant waves and dramatically reduce the
relaxation time of the pair beam. An accurate description of the spectral
evolution of the electrostatic waves is crucial for calculating the relaxation
time of the pair beam
Effects of organic nutrient management on aromatic rice (Oryza sativa)-linseed (Linum usitatissimum) sequence
The experiment was conducted during 2019 and 2020 at the Instructional-cum Research (ICR) Farm, Assam Agricultural University, Jorhat, Assam to study the impact of different combinations of organic nutrient sources on aromatic rice (Oryza sativa L.) (rainy-kharif) and their residual effect on linseed (Linum usitatissimum L.) (winter- rabi) crop for developing a double cropping sequence for rice growers of Assam with organic management. The experiment comprised three aromatic rice cultivars, viz. Kola joha, Keteki joha and Chakhao poireiton and five combinations of organic nutrient sources. Out of the organic nutrient sources, application of N @30 kg/ha through vermicompost along with pre-season green manuring of Sesbania bispinosa and root dip treatment of rice seedlings with Azospirillium and phosphorus solubilising bacteria @3.5 kg/ha each (N3) resulted the highest number of panicles/ m2 (216.72 in 2019 and 223.96 in 2020), highest yield of rice (30.26 q/ha in 2019, 32.58 q/ha in 2020 grain yield and 65.99 q/ha in 2019, 68.98 q/ha in 2020 straw yield). The highest seed yield (394.52 kg/ha in 2019, 416.97 kg/ha in 2020) and stover yield (890.09 kg/ha in 2019, 896.63 kg/ha in 2020) of succeeding relay sown linseed were recorded with the N3 treatment. The highest available N (250.10 kg/ha), P2O5 (20.40 kg/ha) and K2O (140.06 kg/ha), organic C (0.65%), soil organic carbon (SOC) stock (13.29 t/ha), soil microbial biomass carbon (SMBC) (183.43 µg/g of soil) in soil were recorded with the N3 treatment after harvest of linseed in 2020. The study affirmed the suitability of rice-linseed cropping sequence for efficient utilization and conservation of resources
MALS SALT-NOT survey of MIR-selected powerful radio-bright AGN at 0<z<3.5
We present results of an optical spectroscopic survey using SALT and NOT to
build a WISE mid-infrared color-based, dust-unbiased sample of powerful
radio-bright (200 mJy at 1.4 GHz) AGN for the MeerKAT Absorption Line Survey
(MALS). Our sample has 250 AGN (median ) showing emission lines, 26 with
no emission lines, and 27 without optical counterparts. Overall, our sample is
fainter (=0.6 mag) and redder (=0.2 mag) than
radio-selected quasars, and representative of fainter quasar population
detected in optical surveys. About 20% of the sources are narrow line AGN
(NLAGN) 65% of these, at are galaxies without strong nuclear
emission, and 10% at , have emission line ratios similar to radio
galaxies. The farthest NLAGN in our sample is M15132524 (),
and the largest (size330 kpc) is M09093133 (). We
discuss in detail 110 AGN at . Despite representing the radio
loudest quasars (median =3685), their Eddington ratios are similar to the
SDSS quasars having lower . We detect 4 CIV BALQSOs, all among AGN with
least , and highest black hole masses and Eddington ratios. The BAL
detection rate (%) is consistent with that seen in extremely
powerful ( WHz) quasars. Using optical light-curves,
radio polarization and -ray detections, we identify 7 high-probability
BL Lacs. We also summarize the full MALS footprint to search for HI 21-cm and
OH 18-cm lines at .Comment: 62 pages, 15 figures and 3 tables; accepted in ApJ (updated the
redshift of M1312-2026 to z=0.977
Discovery of Hydrogen Radio Recombination Lines at z = 0.89 toward PKS 1830-211
We report the detection of stimulated hydrogen radio recombination line (RRL) emission from ionized gas in a z = 0.89 galaxy using 580-1670 MHz observations from the MeerKAT Absorption Line Survey. The RRL emission originates in a galaxy that intercepts and strongly lenses the radio blazar PKS 1830−211 (z = 2.5). This is the second detection of RRLs outside of the local Universe and the first clearly associated with hydrogen. We detect effective H144α (and H163α) transitions at observed frequencies of 1156 (798) MHz by stacking 17 (27) RRLs with 21σ (14σ) significance. The RRL emission contains two main velocity components and is coincident in velocity with H i 21 cm and OH 18 cm absorption. We use the RRL spectral line energy distribution and a Bayesian analysis to constrain the density (n e ) and the volume-averaged path length (ℓ) of the ionized gas. We determine log ( n e ) = 2.0 − 0.7 + 1.0 cm−3 and log ( ℓ ) = − 0.7 − 1.1 + 1.1 pc toward the northeast (NE) lensed image, likely tracing the diffuse thermal phase of the ionized ISM in a thin disk. Toward the southwest (SW) lensed image, we determine log ( n e ) = 3.2 − 1.0 + 0.4 cm−3 and log ( ℓ ) = − 2.7 − 0.2 + 1.8 pc, tracing gas that is more reminiscent of H scii regions. We estimate a star formation (surface density) rate of ΣSFR ∼ 0.6 M ⊙ yr−1 kpc−2 or SFR ∼ 50 M ⊙ yr−1, consistent with a star-forming main-sequence galaxy of M ⋆ ∼ 1011 M ⊙. The discovery presented here opens up the possibility of studying ionized gas at high redshifts using RRL observations from current and future (e.g., SKA and ngVLA) radio facilities
The MeerKAT Absorption Line Survey (MALS) data release I: Stokes I image catalogs at 1-1.4 GHz
The MeerKAT Absorption Line Survey (MALS) has observed 391 telescope
pointings at L-band (900 - 1670 MHz) at . We present
radio continuum images and a catalog of 495,325 (240,321) radio sources
detected at a signal-to-noise ratio (SNR) 5 over an area of 2289 deg
(1132 deg) at 1006 MHz (1381 MHz). Every MALS pointing contains a central
bright radio source ( Jy). The median spatial
resolution is (). The median rms noise
away from the pointing center is 25 Jy beam (22 Jy
beam) and is within 15% of the achievable theoretical
sensitivity. The flux density scale ratio and astrometric accuracy deduced from
multiply observed sources in MALS are less than 1% (8% scatter) and
, respectively. Through comparisons with NVSS and FIRST at
1.4 GHz, we establish the catalog's accuracy in the flux density scale and
astrometry to be better than 6% (15% scatter) and ,
respectively. The median flux density offset is higher (9%) for an alternate
beam model based on holographic measurements. The MALS radio source counts at
1.4 GHz are in agreement with literature. We estimate spectral indices
() of a subset of 125,621 sources (SNR8), confirm the flattening of
spectral indices with decreasing flux density and identify 140 ultra
steep-spectrum () sources as prospective high- radio galaxies
(). We have identified 1308 variable and 122 transient radio sources
comprising primarily of AGN that demonstrate long-term (26 years) variability
in their observed flux densities. The MALS catalogs and images are publicly
available at https://mals.iucaa.in.Comment: 64 pages, 25 figures, accepted for publication in the ApJS (full
version of the paper with complete tables is available at DR1 release notes
Effect of Freezing Rate on Quality of Cryopreserved Goat Spermatozoa Using a Programmable Freezer
Abstract: A total of 45 ejaculates from nine Beetal bucks collected by artificial vagina, washed and extended i
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