arXiv subjects

M. Singh

Publications and source records attributed to M. Singh.

66 records · Page 4Linked to original sources

arXiv2015

Silicon Quantum Dots with Counted Antimony Donor Implants

Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors close to quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants.

cond-mat.mes-hall↗

arXiv2014

Discovery of a red quasar with recurrent activity

We report a new double-double radio quasar, DDRQ, J0746$+$4526 which exhibits two cycles of episodic activity. From radio continuum observations at 607 MHz using the GMRT and 1400 MHz from the FIRST survey we confirm its episodic nature. We examine the SDSS optical spectrum and estimate the black hole mass to be (8.2$\pm$0.3)$\times$10$^7$M$_\odot$ from its observed MgII emission line, and the Eddington ratio to be 0.03. The black hole mass is significantly smaller than for the other reported DDRQ, J0935+0204, while the Eddington ratios are comparable. The SDSS spectrum is significantly red continuum dominated suggesting that it is highly obscured with ${E(B-V)}_{host}=0.70\pm0.16$ mag. This high obscuration further indicates the existence of a large quantity of dust and gas along the line of sight, which may have a key role in triggering the recurrent jet activity in such objects.

astro-ph.GA↗

arXiv2013

Influence of solar and cosmic-ray variability on climate

We analyze solar, geomagnetic and cosmic ray flux data along with rainfall and temperature data for almost five solar cycles. We provide evidence of significant influence of solar variability on climate. Specifically, we demonstrate association between lower (higher) rainfall and higher (lower) temperatures with increasing (decreasing) solar activity and decreasing (increasing) cosmic ray intensities. We propose a plausible scenario that accounts the results of our analysis.

physics.ao-ph↗

arXiv2013

Further refinements of the Heinz inequality

The celebrated Heinz inequality asserts that $ 2|||A^{1/2}XB^{1/2}|||\leq |||A^νXB^{1-ν}+A^{1-ν}XB^ν|||\leq |||AX+XB|||$ for $X \in \mathbb{B}(\mathscr{H})$, $A,B\in \+$, every unitarily invariant norm $|||\cdot|||$ and $ν\in [0,1]$. In this paper, we present several improvement of the Heinz inequality by using the convexity of the function $F(ν)=|||A^νXB^{1-ν}+A^{1-ν}XB^ν|||$, some integration techniques and various refinements of the Hermite--Hadamard inequality. In the setting of matrices we prove that \begin{eqnarray*} &&\hspace{-0.5cm}\left|\left|\left|A^{\frac{α+β}{2}}XB^{1-\frac{α+β}{2}}+A^{1-\frac{α+β}{2}}XB^{\frac{α+β}{2}}\right|\right|\right|\leq\frac{1}{|β-α|} \left|\left|\left|\int_α^β\left(A^νXB^{1-ν}+A^{1-ν}XB^ν\right)dν\right|\right|\right|\nonumber\\ &&\qquad\qquad\leq \frac{1}{2}\left|\left|\left|A^αXB^{1-α}+A^{1-α}XB^α+A^βXB^{1-β}+A^{1-β}XB^β\right|\right|\right|\,, \end{eqnarray*} for real numbers $α, β$.

math.FA↗

arXiv2012

A study of the environments of large radio galaxies using SDSS

The distributions of galaxies in the environments of 16 large radio sources have been examined using the Sloan Digital Sky Survey. In the giant radio galaxy J1552+2005 (3C326) which has the highest arm-length ratio, the shorter arm is found to interact with a group of galaxies which forms part of a filamentary structure. Although most large sources occur in regions of low galaxy density, the shorter arm is brighter in most cases suggesting asymmetries in the intergalactic medium which may not be apparent in the distribution of galaxies. In two cases with strong and variable cores, J0313+4120 and J1147+3501, the large flux density asymmetries are possibly also caused by the effects of relativistic motion.

astro-ph.CO↗

arXiv2012

A General Double Inequality Related to Operator Means and Positive Linear Maps

Let $A,B\in \mathbb{B}(\mathscr{H})$ be such that $0<b_{1}I \leq A \leq a_{1}I$ and $0<b_{2}I \leq B \leq a_{2}I$ for some scalars $0<b_{i}< a_{i},\;\; i=1,2$ and $Φ:\mathbb{B}(\mathscr{H})\rightarrow\mathbb{B}(\mathscr{K})$ be a positive linear map. We show that for any operator mean $σ$ with the representing function $f$, the double inequality $$ ω^{1-α}(Φ(A)#_αΦ(B))\le (ωΦ(A))\nabla_αΦ(B)\leq \fracαμΦ(AσB) $$ holds, where $μ=\frac{a_{1}b_{1}(f(b_{2}a_{1}^{-1})-f(a_{2}b_{1}^{-1}))}{b_{1}b_{2}-a_{1}a_{2}}, $ $ν=\frac{a_{1}a_{2}f(b_{2}a_{1}^{-1})-b_{1}b_{2}f(a_{2}b_{1}^{-1})}{a_{1}a_{2}-b_{1}b_{2}}, $ $ω=\frac{αν}{(1-α)μ}$ and $#_α$ ($\nabla_α$, resp.) is the weighted geometric (arithmetic, resp.) mean for $α\in (0,1)$. As applications, we present several generalized operator inequalities including Diaz--Metcalf and reverse Ando type inequalities. We also give some related inequalities involving Hadamard product and operator means.

math.FA↗

arXiv2012

A low-frequency study of two asymmetric large radio galaxies

We present the results of multifrequency observations of two asymmetric, Mpc-scale radio sources with the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). The radio luminosity of these two sources, J1211+743 and J1918+742, are in the Fanaroff-Riley class II (FRII) range, but have diffuse radio components on one side of the galaxy while the opposite component appears edge-brightened with a prominent hot-spot. Although the absence of a hot-spot is reminiscent of FRI radio galaxies, suggesting a hybrid morphology, the radio jet facing the diffuse lobe in J1211+743 is similar to those in FRII radio sources, and it is important to consider these aspects as well while classifying these sources in the FR scheme. The observed asymmetries in these Mpc-scale sources are likely to be largely intrinsic rather than being due to the effects of orientation and relativistic motion. The formation of a diffuse lobe facing the radio jet in J1211+743 is possibly due to the jet being highly dissipative. The low-frequency spectral indices of the lobes are in the range of approximately -0.8 to -1, while at the outer edges these vary from approximately -0.65 to -1.05 suggesting steep injection spectral indices, which need to be examined further from observations at even lower frequencies by telescopes such as the LOw Frequency ARray (LOFAR).

astro-ph.CO↗

arXiv2011

A study of giant radio galaxies at RATAN-600

We report the results of flux density measurements in the extended components of thirteen giant radio galaxies, made with the RATAN-600 in the centimeter range. Supplementing them with the WENSS, NVSS and GB6 survey data we constructed the spectra of the studied galaxy components. We computed the spectral indices in the studied frequency range and demonstrate the need for a detailed account of the integral contribution of such objects into the background radiation.

astro-ph.CO↗

arXiv2011

A Second Set of RATAN-600 Observations of Giant Radio Galaxies

Results of RATAN-600 centimeter-wavelength flux-density measurements of the extended components in five giant radio galaxies are reported. The spectra of the components of these radio galaxies have been constructed using the data of the WENSS, NVSS, and GB6 surveys together with new RATAN-600 data. Spectral indices in the studied frequency range have been calculated.

astro-ph.CO↗

arXiv2010

Radio Spectra of Giant Radio Galaxies from RATAN-600 Data

Measurements of the flux densities of the extended components of seven giant radio galaxies obtained using the RATAN-600 radio telescope at wavelengths of 6.25 and 13 cm ar e presented. The spectra of components of these radio galaxies are constructed using these new RA TAN-600 data together with data from the WENSS, NVSS, and GB6 surveys. The spectral indices in the stu died frequency range are calculated, and the need for detailed estimates of the integrated contributi on of such objects to the background emission is demonstrated.

astro-ph.CO↗

arXiv2010

A multifrequency study of the large radio galaxies 3C46 and 3C452

We present low-frequency observations starting from ~150 MHz with the Giant Metrewave Radio Telescope (GMRT), and high-frequency observations with the Very Large Array (VLA) of two large radio galaxies 3C46 and 3C452. These observations were made with the objectives of estimating their spectral ages and examining any evidence of diffuse extended emission at low radio frequencies due to an earlier cycle of activity. While no evidence of extended emission due to an earlier cycle of activity has been found, the spectral ages have been estimated to be ~15 and 27 Myr for the oldest relativistic plasma seen in the regions close to the cores for 3C46 and 3C452 respectively. The spectra in the vicinity of the hotspots are consistent with a straight spectrum with injection spectral indices of ~1.0 and 0.78 respectively, somewhat steeper than theoretical expectations.

astro-ph.CO↗

arXiv2002

Evidence for Shock Acceleration and Intergalactic Magnetic Fields in a Large-Scale Filament of Galaxies ZwCl 2341.1+0000

We report the discovery of large-scale diffuse radio emission from what appears to be a large-scale filamentary network of galaxies in the region of cluster ZwCl 2341.1+0000, and stretching over an area of at least $6 h^{-1}_{50}$ Mpc in diameter. Multicolour CCD observations yield photometric redshifts indicating that a significant fraction of the optical galaxies in this region is at a redshift of z=0.3. This is supported by spectroscopic measurements of 4 galaxies in the SDSS survey at a mean z=0.27. We present VLA images at 20 cm (NVSS) and 90 cm wavelengths, showing the detailed radio structure of the filaments. Comparison with the VLA high resolution FIRST radio survey shows that the diffuse emission is not due to known individual point sources. The diffuse radio-emission has a spectral index $α\lesssim -0.5$, and is most likely synchrotron emission from relativistic charged particles in an inter-galactic magnetic field. Furthermore, this optical/radio structure is detected in X-rays by the ROSAT all-sky survey. It has a 0.1--2.4 keV luminosity of about $10^{44}$ erg s$^{-1}$ and shows an extended highly non-relaxed morphology. These observations suggest that ZwCl 2341.1+0000 is possibly a proto-cluster of galaxies in which we are witnessing the process of structure formation. We show (both analytically and by numerical simulations) that the energetics of accretion shocks generated in forming large-scale structures are sufficient to produce enough high energy cosmic-ray (CR) electrons required to explain the observed radio emission, provided a magnetic field of strength of about 1 micro Gauss is present there.Thus it is the first evidence of cosmic-ray particle acceleration and magnetic fields occuring on a super-cluster scale. (Abridged)

astro-ph↗