Rm GHz Research Articles

Hilbert–Schmidt Measure of Pairwise Quantum Discord for Three-Qubit X States

The Hilbert-Schmidt distance between a mixed three-qubit state and its closest state is used to quantify the amount of pairwise quantum correlations in a tripartite system. Analytical expressions of geometric quantum discord are derived. A particular attention is devoted to two special classes of three-qubit $X$ states. They include three-qubit states of ${\rm W}$, ${\rm GHZ}$ and Bell type. We also discuss the monogamy property of geometric quantum discord in some mixed three-qubit systems.

CONSTRAINING THE RADIO-LOUD FRACTION OF QUASARS ATz> 5.5

Radio-loud Active Galactic Nuclei at z~2-4 are typically located in dense environments and their host galaxies are among the most massive systems at those redshifts, providing key insights for galaxy evolution. Finding radio-loud quasars at the highest accessible redshifts (z~6) is important to study their properties and environments at even earlier cosmic time. They would also serve as background sources for radio surveys intended to study the intergalactic medium beyond the epoch of reionization in HI 21 cm absorption. Currently, only five radio-loud ($R=f_{\nu,5{\rm GHz}}/f_{\nu,4400\AA}>10$) quasars are known at z~6. In this paper we search for 5.5 < z < 7.2 quasars by cross-matching the optical Pan-STARRS1 and radio FIRST surveys. The radio information allows identification of quasars missed by typical color-based selections. While we find no good 6.4 < z <7.2 quasar candidates at the sensitivities of these surveys, we discover two new radio-loud quasars at z~6. Furthermore, we identify two additional z~6 radio-loud quasars which were not previously known to be radio-loud, nearly doubling the current z~6 sample. We show the importance of having infrared photometry for z>5.5 quasars to robustly classify them as radio-quiet or radio-loud. Based on this, we reclassify the quasar J0203+0012 (z=5.72), previously considered radio-loud, to be radio-quiet. Using the available data in the literature, we constrain the radio-loud fraction of quasars at z~6, using the Kaplan--Meier estimator, to be $8.1^{+5.0}_{-3.2}\%$. This result is consistent with there being no evolution of the radio-loud fraction with redshift, in contrast to what has been suggested by some studies at lower redshifts.

Effects of Rayleigh scattering on the CMB and cosmic structure

During and after recombination, in addition to Thomson scattering with free electrons, photons also coupled to neutral hydrogen and helium atoms through Rayleigh scattering. This coupling influences both CMB anisotropies and the distribution of matter in the Universe. The frequency-dependence of the Rayleigh cross section breaks the thermal nature of CMB temperature and polarization anisotropies and effectively doubles the number of variables needed to describe CMB intensity and polarization statistics, while the additional atomic coupling changes the matter distribution and the lensing of the CMB. We introduce a new method to capture the effects of Rayleigh scattering on cosmological power spectra. Rayleigh scattering modifies CMB temperature and polarization anisotropies at the $\sim\!1 \%$ level at $353 {\rm GHz}$ (scaling $\propto \nu^4$), and modifies matter correlations by as much as $\sim\!0.3\%$. We show the Rayleigh signal, especially the cross-spectra between the thermal (Rayleigh) E-polarization and Rayleigh (thermal) intensity signal, may be detectable with future CMB missions even in the presence of foregrounds, and how this new information might help to better constrain the cosmological parameters.

J1649+2635: a grand-design spiral with a large double-lobed radio source

We report the discovery of a grand-design spiral galaxy associated with a double-lobed radio source. J1649+2635 (z = 0.0545) is a red spiral galaxy with a prominent bulge that it is associated with a L$_{1.4{\rm GHz}}\sim$10$^{24}$WHz$^{-1}$ double-lobed radio source that spans almost 100kpc. J1649+2635 has a black hole mass of M$_{\rm BH} \sim$ 3--7 $\times$ 10$^8$M$_{\odot}$ and SFR$\sim$ 0.26 -- 2.6M$_{\odot}$year$^{-1}$. The galaxy hosts a $\sim$96kpc diffuse optical halo, which is unprecedented for spiral galaxies. We find that J1649+2635 resides in an overdense environment with a mass of M$_{dyn} = 7.7^{+7.9}_{-4.3} \times 10^{13}$M$_{\odot}$, likely a galaxy group below the detection threshold of the ROSAT All-Sky Survey. We suggest one possible scenario for the association of double-lobed radio emission from J1649+2635 is that the source may be similar to a Seyfert galaxy, located in a denser-than-normal environment. The study of spiral galaxies that host large-scale radio emission is important because although rare in the local Universe, these sources may be more common at high-redshifts.

Dual-Band Volterra Series Digital Pre-Distortion for Envelope Tracking Power Amplifiers

This letter presents a new dual band Volterra-based model suitable for the linearization of envelope tracking (ET) power amplifiers (PAs) driven concurrently with two widely spaced modulated signals. The model has two modules: a dual-band baseband equivalent Volterra series to compensate for the dynamic nonlinear distortions associated with the PA (assuming a constant drain supply voltage) and a polynomial term added to mitigate the distortions introduced by a dynamic drain supply modulation. The proposed model was successfully applied to linearize a $10~{\rm W}$ and a $45~{\rm W}$ dual band ET PA concurrently driven with different arrangements of two signals modulated according to wideband code division multiple access and long-term evolution standards around $2.0$ and $2.2~{\rm GHz}$ , and $2.1$ and $2.9~{\rm GHz}$ . A measured error vector magnitude of 1.5% and an adjacent channel power ratio better than $-47~{\rm dBc}$ , demonstrated the excellent linearization capacity of the proposed dual-band ET Volterra digital pre-distortion scheme.

Dual-Band Substrate Integrated Waveguide Balun Bandpass Filter With High Selectivity

A new method of designing a dual-band balun bandpass filter (BPF) with high selectivity is proposed and implemented by taking advantage of the existence of multiple substrate integrated waveguide (SIW) cavity modes. The major design concept applied in this letter is based on two mechanisms: one is by properly placing the output ports to achieve the balanced output for both passbands, and the other is by taking cross coupling of higher/lower order modes to achieve transmission zeros (TZs) at each side of the passband. Two internal coupling slots are involved to separately control the coupling level between cascaded cavities for each passband. A prototype operating at $9.0~{\rm GHz}$ and $9.8~{\rm GHz}$ has been realized and shows the desired filtering performance. The differences between the two outputs are within $180^{\circ}\pm 2^{\circ}$ in phase and $0.6~{\rm dB}$ in magnitude across the two passbands. Measured frequency responses agree well with the simulated ones in this work.

Demonstration of a High Power, Wideband 220-GHz Traveling Wave Amplifier Fabricated by UV-LIGA

We present the first vacuum electronic traveling wave amplifier to incorporate an interaction circuit fabricated by ultraviolet (UV) photolithography and electroforming, demonstrating over 60 W of output power at 214.5 GHz from a 12.1 kV, 118 mA electron beam. The tube also achieved an instantaneous bandwidth of ${\sim}{\rm 15}~{\rm GHz}$ in $G$ -band in the small signal regime. The all-copper circuit was fabricated in two layers using a UV-transparent polymer monofilament embedded in the photoresist to form the beam tunnel prior to electroforming. Effects arising from fabrication errors and target tolerances are discussed. This microfabrication technique and demonstration paves the way for a new era of vacuum electron devices that could extend into the 1–2 THz range with advances in high-current-density electron guns.

SIMILAR RADIATION MECHANISM IN GAMMA-RAY BURSTS AND BLAZARS: EVIDENCE FROM TWO LUMINOSITY CORRELATIONS

Active galactic nuclei (AGNs) and gamma-ray bursts (GRBs) are powerful astrophysical events with relativistic jets. In this Letter the broadband spectral properties are compared between GRBs and the well-observed blazars. The distribution of GRBs are consistent with the well-known blazar sequence including the $\nu L_\nu(5\rm GHz)-\alpha_{\rm RX}$ and $\nu L_\nu(5\rm GHz)-\nu_{\rm peak}$ correlations, where $\alpha_{\rm RX}$ is defined as the broadband spectral slope in radio-to-X-ray bands, and $\nu_{\rm peak}$ is defined as the spectral peak frequency. Moreover, GRBs occupy the low radio luminosity end of these sequences. These two correlations suggest that GRBs could have a similar radiation process with blazars both in the prompt emission and afterglow phases, i.e., synchrotron radiation.

A Switchable Erbium Doped Fiber Ring Laser System for Temperature Sensors Multiplexing

In this paper, a proof of concept of a switchable erbium-doped fiber ring laser (EDFRL) system that demonstrates temperature sensors multiplexing is carried out showing a high linearity and a sensitivity of 1.55 ${\rm GHz}/^{\circ}{\rm C}$ . The system is based on the detection in the electrical domain of the resulting beat signal of two different laser lines generated by an EDFRL that operates in single longitudinal mode regime (SLM). The SLM operation is achieved by the use of phase shift fiber Bragg gratings with ultranarrow bandwidths of 6 pm. Two independent cavities for the reference signal and sensor signal generation are used to avoid the wavelength competition and to improve the stability. This configuration allows the control of the temperature operation point of the system by adjusting the temperature in the reference side.

Decadal variations of land surface temperature anomalies observed over the Tibetan Plateau by the Special Sensor Microwave Imager (SSM/I) from 1987 to 2008

In this paper, we analyze the standardized anomalies of land surface temperature (LST) retrieved from the Special Sensor Microwave Imager (SSM/I) vertically polarized 37 GHz (\(T^v_{B,37~{\rm GHz}}\)) brightness temperature over the Tibetan Plateau for the period 1987 to 2008. A radiative transfer model is used to derive LST from SSM/I \(T^v_{Bv,37~{\rm GHz}}\), which is calibrated and validated using time series of field measured soil surface temperatures. Additional Plateau-scale verification is performed with monthly LST products from the Moderate Resolution Imaging Spectroradiometer, the Noah land surface model and air temperature measured by Chinese Meteorological Administration. Trend analysis shows that the annual and monthly standardized anomalies are increasing at an averaged rate of 0.5 decade − 1. The highest positive trends are noted over the central part of the Plateau, which is on average 0.80 decade − 1 with a maximum of 1.44 decade − 1. Conversely, a negative trend in the anomalies is found for the Taklamakan desert and the Himalayan foothills with a rate of −0.27 decade − 1 and reaching a maximum of −1.4 decade − 1. In addition, we find that LST anomaly trends on the Plateau are seasonally dependent and increase with the elevation. These observed trends are in agreement with previous studies conducted with in-situ measurements, which demonstrates the use of long-term earth observation programmes for climate studies as has also been articulated in the 2007 IPCC report.

An all-solid-state laser source at 671 nm for cold-atom experiments with lithium

We present an all solid-state narrow line-width laser source emitting $670\,\mathrm{mW}$ output power at $671\,\mathrm{nm}$ delivered in a diffraction-limited beam. The \linebreak source is based on a fre-quency-doubled diode-end-linebreak pumped ring laser operating on the ${^4F}_{3/2} \rightarrow {^4I}_{13/2}$ transition in Nd:YVO$_4$. By using periodically-poled po-tassium titanyl phosphate (ppKTP) in an external build-up cavity, doubling efficiencies of up to 86% are obtained. Tunability of the source over $100\,\rm GHz$ is accomplished. We demonstrate the suitability of this robust frequency-stabilized light source for laser cooling of lithium atoms. Finally a simplified design based on intra-cavity doubling is described and first results are presented.

Hydrogen 2p–2sTransition: Signals from the Epochs of Recombination and Reionization

We propose a method to study the epoch of reionization based on the possible observation of 2p--2s fine structure lines from the neutral hydrogen outside the cosmological H {\sc ii} regions enveloping QSOs and other ionizing sources in the reionization era. We show that for parameters typical of luminous sources observed at $z \simeq 6.3$ the strength of this signal, which is proportional to the H {\sc i} fraction, has a brightness temperature $\simeq 20 \mu K$ for a fully neutral medium. The fine structure line from this redshift is observable at $\nu \simeq 1 \rm GHz$ and we discuss prospects for the detection with several operational and future radio telescopes. We also compute the characteristics of this signal from the epoch of recombination: the peak brightness is expected to be $\simeq 100 \mu K$; this signal appears in the frequency range 5-10 MHz. The signal from the recombination era is nearly impossible to detect owing to the extreme brightness of the Galactic emission at these frequencies.

A supernova factory in Mrk 273?

We report on 1.6 and 5.0 GHz observations of the ultraluminous infrared galaxy (ULIRG) Mrk 273, using the European VLBI Network (EVN) and the Multi-Element Radio-Linked Interferometer Network (MERLIN). We also make use of published 1.4 GHz VLBA observations of Mrk 273 by Carilli & Taylor (2000). Our 5 GHz images have a maximum resolution of 5-10 mas, which corresponds to linear resolutions of 3.5-7 pc at the distance of Mrk 273, and are the most sensitive high-resolution radio observations yet made of this ULIRG. Component N1, often pinpointed as a possible AGN, displays a steep spectral index ($\alpha = 1.2 \pm 0.1; S_\nu \propto \nu^{-\alpha}$); hence it is very difficult to reconcile with N1 being an AGN, and rather suggests that the compact nonthermal radio emission is produced by an extremely high luminous individual radio supernova (RSN), or a combination of unresolved emission from nested supernova remnants (SNR), luminous RSNe, or both. Component N2 is partly resolved out into several compact radio sources --none of which clearly dominates-- and a region of extended emission about 30 pc in size. The integrated spectral index of this region is flat ($\alpha = 0.15 \pm 0.1$), which can be interpreted as due to a superposition of several unresolved components, e.g., RSNe or SNRs, whose radio emission peaks at different frequencies and is partially free-free absorbed. The overall extended radio emission from component N is typical of nonthermal, optically thin radio emission ($\alpha = 0.8 \pm 0.1$), and its 1.4 GHz luminosity ($L_{1.4 \rm GHz} = (2.2 \pm 0.1)\times 10^{23} $ WHz$^{-1}$) is consistent with being produced by relativistic electrons diffused away from supernova remnants in an outburst.

The 2dF Galaxy Redshift Survey: the population of nearby radio galaxies at the 1-mJy level

We use redshift determinations and spectral analysis of galaxies in the 2dF Galaxy Redshift Survey to study the properties of local radio sources with $S\ge 1$ mJy. 557 objects drawn from the FIRST survey, corresponding to 2.3 per cent of the total radio sample, are found in the 2dFGRS cataloge within the area $9^h 48^m \simlt {\rm RA}({\rm 2000}) \simlt 14^h 32^m$ and $-2.77^\circ \simlt {\rm dec}({\rm 2000}) \simlt 2.25^\circ$, down to a magnitude limit $b_J= 19.45$. The excellent quality of 2dF spectra allows us to divide these sources into classes, according to their optical spectra. Radio galaxies (i.e. absorption systems, mainly belonging to the class of FR I sources, whose spectra may or may not show emission lines due to AGN activity) make up 63 per cent of the spectroscopic sample; they are characterized by relatively high radio-to-optical ratios, red colours and luminosities $10^{21}\simlt P_{1.4{\rm GHz}} W Hz^${-1}$ sr$^{-1}$ \simlt 10^{24}$. Actively star-forming galaxies instead contribute with 30 per cent to the total sample. These objects -- principally found at low redshifts ($z \simlt 0.1$) -- in general show low radio-to-optical ratios, blue colours and low radio luminosities. We also found 18 Seyfert 2 galaxies and 4 Seyfert 1's. Analysis of the local radio luminosity function shows that radio galaxies are well described by models that assume pure luminosity evolution, at least down to radio powers $P_{1.4{\rm GHz}}\simlt 10^{20.5} W Hz$^{-1}$ sr$^{-1}$ Late-type galaxies, whose relative contribution to the RLF is found to be lower than was predicted by previous work, present a luminosity function which is compatible with the IRAS galaxy LF, and therefore plausibly constitute the radio counterpart of the dusty spirals and starbursts that dominate the counts at 60 $\mu$m.