Rm mW Research Articles

On the anisotropic distribution of clusters in the local Universe

ABSTRACT In his 2021 lecture to the Canadian Association of Physicists Congress, P.J.E. Peebles pointed out that the brightest extragalactic radio sources tend to be aligned with the plane of the de Vaucouleur Local Supercluster up to redshifts of z = 0.02 ($d_{\rm MW}\approx 85~\rm {Mpc}$). He then asked whether such an alignment of clusters is anomalous in the standard Lambda cold dark matter (ΛCDM) framework. In this letter, we employ an alternative, absolute orientation agnostic, measure of the anisotropy based on the inertia tensor axial ratio of these brightest sources and use a large cosmological simulation from the flamingo suite to measure how common such an alignment of structures is. We find that only 3.5 per cent of randomly selected regions display an anisotropy of their clusters more extreme than the one found in the local Universe’s radio data. This sets the region around the Milky Way as a 1.85σ outlier. Varying the selection parameters of the objects in the catalogue, we find that the clusters in the local Universe are never more than 2σ away from the simulations’ prediction for the same selection. We thus conclude that the reported anisotropy, whilst noteworthy, is not in tension with the ΛCDM paradigm.

Binary neutron star populations in the Milky Way

ABSTRACT Galactic binary neutron stars (BNSs) are a unique laboratory to probe the evolution of BNSs and their progenitors. Here, we use a new version of the population synthesis code sevn to evolve the population of Galactic BNSs, by modelling the spin up and down of pulsars self-consistently. We analyse the merger rate $\mathcal {R}_{\rm MW}$, orbital period Porb, eccentricity e, spin period P, and spin period derivative $\dot{P}$ of the BNS population. Values of the common envelope parameter α = 1−3 and an accurate model of the Milky Way star formation history best reproduce the BNS merger rate in our Galaxy ($\mathcal {R}_{\rm MW}\approx {}30$ Myr−1). We apply radio-selection effects to our simulated BNSs and compare them to the observed population. Using a Dirichlet process Gaussian mixture method, we evaluate the four-dimensional likelihood in the $(P_{\rm orb}, e, P, \dot{P})$ space, by comparing our radio-selected simulated pulsars against Galactic BNSs. Our analysis favours an uniform initial distribution for both the magnetic field (1010−13 G) and the spin period (10−100 ms). The implementation of radio selection effects is critical to match not only the spin period and period derivative, but also the orbital period and eccentricity of Galactic BNSs. According to our fiducial model, the Square Kilometre Array will detect ∼20 new BNSs in the Milky Way.

Graphene-based autonomous pyroelectric system for near-field energy conversion

In the close vicinity of a hot solid, at distances smaller than the thermal wavelength, a strong electromagnetic energy density exists because of the presence of evanescent field. Here we introduce a many-body conversion principle to harvest this energy using graphene-based pyroelectric conversion devices made with an active layer encapsulated between two graphene field-effect transistors which are deposited on the source and on the cold sink. By tuning the bias voltage applied to the gates of these transistors, the thermal state and the spontaneous polarization of the active layer can be controlled at kHz frequencies. We demonstrate that the power density generated by these conversion systems can reach 130,{rm mW,cm}^{-2} using pyroelectric Ericsson cycles, a value which surpasses the current production capacity of near-field thermophotovoltaic conversion devices by more than three orders of magnitude with low grade heat sources (T<500,{rm K}) and small temperature differences (Delta Tsim 100,K).

On the Approximability of the Minimum Weight $t$-partite Clique Problem

The ${\rm M{\small INIMUM}~W\small{EIGHT}}$ $t$-${\rm {\small PARTITE}~C{\small LIQUE}~P{\small ROBLEM}~MW} t {\rm CP}$ is the problem of finding a $t$-clique with minimum weight in a complete edge-weighted $t$-partite graph. The motivation for studying this problem is its potential in modelling the problem of identifying sets of commonly existing putative co-regulated, co-expressed genes, called gene clusters. In this paper, we show that ${\rm MW} t {\rm CP}$ is NP-hard, APX-hard in the general case. We also present a 2-approximation algorithm that runs in $O(n^2)$ for the metric case and has 1+$ \frac{1}{t}$-approximation performance guarantee for the ultrametric subclass of instances. We further show how relaxing or tightening the application of the metricity property affects the approximation ratio. Finally insights on the application ${\rm MW} t {\rm CP}$ to gene cluster discovery are presented.

Designing an electro-optical encoder based on photonic crystals using the graphene-Al2O3 stacks.

In this paper, an electro-optical 4-to-2 encoder based on a photonic crystal is presented. The structure is composed of four silicon waveguides, four photonic crystal structures including the graphene-${{\rm Al}_2}{{\rm O}_3}$Al2O3 stacks, and two optical combiners. Two one-dimensional arrays of air holes in the silicon background are designed parallel to the waveguides. Also, a graphene-${{\rm Al}_2}{{\rm O}_3}$Al2O3 stack is placed at the center of each array, which provides the desired interferences. This feature is used for controlling the optical wave transmission through the waveguides. Using two optical combiners at the end of two waveguides, the received signals from the waveguides will be guided toward the output ports. The amount of the transmitted signal from input ports to the output of the encoder can be controlled by applying the proper chemical potential to the graphene-based stacks. The simulation results show that the encoding operation can be achieved by using 0.2 eV and 0.8 eV for chemical potentials. In addition, the normalized output power margins for logic 0 and 1 are calculated to be 8.2% and 46.7%, respectively. The footprint for the proposed structure is approximately equal to ${127}\;\unicode{x00B5} {{\rm m}^2}$127µm2. Also, the required optical power intensity at input ports is ${100}\;{\rm mW/}\unicode{x00B5} {{\rm m}^2}$100mW/µm2.

An Updated Galactic Double Neutron Star Merger Rate Based on Radio Pulsar Populations

Following the procedure described in Pol et al., we update the Galactic double neutron star (DNS) merger rate by including the new, highly eccentric DNS system J0509+3801 (Lynch et al.). This leads to a new Galactic DNS merger rate of $\mathcal{R}_{\rm MW} = 37^{+24}_{-11}$ Myr$^{-1}$, where the errors represent 90% confidence intervals. The corresponding DNS merger detection rate for Advanced LIGO is $\mathcal{R} = 1.9^{+1.2}_{-0.6} \times \left( D_{\rm r} / 100 \ \rm Mpc \right)^3 \rm yr^{-1},$ where $D_{\rm r}$ is the range distance. Using the LIGO O3 range distance of 130 Mpc (Abbott et al.), we predict that LIGO will detect anywhere between three and seven DNS mergers per year of observing at O3 sensitivity.

Constraining the Milky Way halo potential with the GD-1 stellar stream

Abstract We use ESA/Gaia astrometry together with SEGUE and LAMOST measurements of the GD-1 stellar stream to explore the improvement on the Galactic gravitational potential that these new data provide. Assuming a realistic universal model for the dark matter halo together with reasonable models of the baryonic components, we find that the orbital solutions for GD-1 require the circular velocity at the Solar radius to be $V_{\rm circ}({\rm R}_\odot) =244\pm 4{\rm \, km\, s^{-1}}$, and also that the density flattening of the dark halo is $q_{\rho }=0.82^{+0.25}_{-0.13}$. The corresponding Galactic mass within $20{\rm \, kpc}$ was estimated to be $M_{\rm MW}(\lt 20{\rm \, kpc})=2.5\pm 0.2 \times 10^{11} {\rm \, M_\odot }$. Moreover, Gaia’s excellent proper motions also allowed us to constrain the velocity dispersion of the GD-1 stream in the direction tangential to the line of sight to be $\lt 2.30{\rm \, km\, s^{-1}}$ (95 per cent confidence limit), confirming the extremely cold dynamical nature of this system.

Probing Galactic Halos with Fast Radio Bursts

The precise localization (<1'') of multiple fast radio bursts (FRBs) to z>0.1 galaxies has confirmed that the dispersion measures (DMs) of these enigmatic sources afford a new opportunity to probe the diffuse ionized gas around and in between galaxies. In this manuscript, we examine the signatures of gas in dark matter halos (aka halo gas) on DM observations in current and forthcoming FRB surveys. Combining constraints from observations of the high velocity clouds, OVII absorption, and the DM to the Large Magellanic Cloud with hydrostatic models of halo gas, we estimate that our Galactic halo will contribute ${\rm DM}_{\rm MW,halo} \approx 50-80 \rm pc/cm^{-3}$ from the Sun to 200 kpc independent of any contribution from the Galactic ISM. Extending analysis to the Local Group, we demonstrate that M31's halo will be easily detected by high-sample FRB surveys (e.g. CHIME) although signatures from a putative Local Group medium may compete. We then review current empirical constraints on halo gas in distant galaxies and discuss the implications for their DM contributions. We further examine the DM probability distribution function of a population of FRBs at z >> 0 using an updated halo mass function and new models for the halo density profile. Lastly, we illustrate the potential of FRB experiments for resolving the baryonic fraction of halos by analyzing simulated sightlines through the CASBaH survey. All of the code and data products of our analysis are available at https://github.com/FRBs.

Double neutron stars: merger rates revisited

We revisit double neutron star (DNS) formation in the classical binary evolution scenario in light of the recent LIGO/Virgo DNS detection (GW170817). The observationally estimated Galactic DNS merger rate of $R_{\rm MW}=21^{+28}_{-14}$ Myr$^{-1}$, based on 3 Galactic DNS systems, fully supports our standard input physics model with $R_{\rm MW} =24$ Myr$^{-1}$. This estimate for the Galaxy translates in a non-trivial way (due to cosmological evolution of progenitor stars in chemically evolving Universe) into a local ($z\approx0$) DNS merger rate density of $R_{\rm local}=48$ Gpc$^{-3}$yr$^{-1}$, which {\em is not} consistent with the current LIGO/Virgo DNS merger rate estimate ($1540^{+3200}_{-1220}$ Gpc$^{-3}$yr$^{-1}$). Within our study of the parameter space we find solutions that allow for DNS merger rates as high as $R_{\rm local} \approx 600^{+600}_{-300}$ Gpc$^{-3}$yr$^{-1}$ which are thus consistent with the LIGO/Virgo estimate. However, our corresponding BH-BH merger rates for the models with high DNS merger rates exceed the current LIGO/Virgo estimate of local BH-BH merger rate ($12$-$213$ Gpc$^{-3}$yr$^{-1}$). Apart from being particularly sensitive to the common envelope treatment, DNS merger rates are rather robust against variations of several of the key factors probed in our study (e.g. mass transfer, angular momentum loss, natal kicks). This might suggest that either common envelope development/survival works differently for DNS ($\sim$ 10-20 Msun stars) than for BH-BH ($\sim$ 40-100 Msun stars) progenitors, or high BH natal kicks are needed to meet observational constraints for both types of binaries. Note that our conclusion is based on a limited number of (21) evolutionary models and is valid only within this particular DNS and BH-BH isolated binary formation scenario.

THE YOUNG SOLAR ANALOGS PROJECT. I. SPECTROSCOPIC AND PHOTOMETRIC METHODS AND MULTI-YEAR TIMESCALE SPECTROSCOPIC RESULTS

This is the first in a series of papers presenting methods and results from the Young Solar Analogs Project, which began in 2007. This project monitors both spectroscopically and photometrically a set of 31 young (300 - 1500 Myr) solar-type stars with the goal of gaining insight into the space environment of the Earth during the period when life first appeared. From our spectroscopic observations we derive the Mount Wilson $S$ chromospheric activity index ($S_{\rm MW}$), and describe the method we use to transform our instrumental indices to $S_{\rm MW}$ without the need for a color term. We introduce three photospheric indices based on strong absorption features in the blue-violet spectrum -- the G-band, the Ca I resonance line, and the Hydrogen-$\gamma$ line -- with the expectation that these indices might prove to be useful in detecting variations in the surface temperatures of active solar-type stars. We also describe our photometric program, and in particular our "Superstar technique" for differential photometry which, instead of relying on a handful of comparison stars, uses the photon flux in the entire star field in the CCD image to derive the program star magnitude. We present time series plots of our spectroscopic data for all four indices, and carry out extensive statistical tests on those time series demonstrating the reality of variations on timescales of years in all four indices. We also statistically test for and discover correlations and anti-correlations between the four indices. We discuss the physical basis of those correlations. As it turns out, the "photospheric" indices appear to be most strongly affected by continuum emission. We thus anticipate that these indices may prove to be useful proxies for monitoring continuum emission in the near ultraviolet.

A timing constraint on the (total) mass of the Large Magellanic Cloud

Abstract This paper explores the effect of the Large Magellanic Cloud (LMC) on the mass estimates obtained from the timing argument. We show that accounting for the presence of the LMC systematically lowers the Local Group mass (MLG) derived from the relative motion of the Milky Way–Andromeda pair. Motivated by this result, we apply a Bayesian technique devised by Peñarrubia et al. to simultaneously fit (i) distances and velocities of galaxies within 3 Mpc and (ii) the relative motion between the Milky Way and Andromeda derived from HST observations, with the LMC mass (MLMC) as a free parameter. Our analysis returns a Local Group mass $M_{\rm LG}=2.64^{+0.42}_{-0.38}\times 10^{12}\,\mathrm{M}_{\odot }$ at a 68 per cent confidence level. The masses of the Milky Way, $M_{\rm MW}=1.04_{-0.23}^{+0.26}\times 10^{12}\,\mathrm{M}_{\odot }$, and Andromeda, $M_{{\rm M}31}=1.33_{-0.33}^{+0.39}\times 10^{12}\,\mathrm{M}_{\odot }$, are consistent with previous estimates that neglect the impact of the LMC on the observed Hubble flow. We find a (total) LMC mass $M_{\rm LMC}=0.25_{-0.08}^{+0.09}\times 10^{12}\,\mathrm{M}_{\odot }$, which is indicative of an extended dark matter halo and supports the scenario where this galaxy is just past its first pericentric approach. Consequently, these results suggest that the LMC may induce significant perturbations on the Galactic potential.

A 76.2–89.1 GHz Phase-Locked Loop With 15.6% Tuning Range in 90 nm CMOS for W-Band Applications

In this letter, a wide tuning range W-band phase-locked loop (PLL) in 90 nm CMOS is presented. A novel frequency tripling topology with a single cross-coupled pair and a dual tank is proposed for the voltage-controlled oscillator (VCO) to achieve wide tuning characteristics under low power consumption. The locking range of the PLL at the fundamental tone is 25.4–29.7 GHz, and an excellent tuning range at the third harmonic frequency up to 12.9 GHz (from 76.2 to 89.1 GHz, 15.6%) is obtained. Under a 1.2 V supply voltage $({\rm P}_{\rm diss}=62.4 {\rm mW})$ , the measured closed-loop phase noise of the PLL is $-$ 83.5 dBc/Hz at 78.34 GHz. To the best of our knowledge, the achieved turning range is the highest currently reported for the PLLs operating in a similar frequency range in CMOS technology.

MMW Ultra-Compact ${\rm N}$-Way Transformer PAs Using Bowtie-Radial Architecture in 65-nm CMOS

In this letter, the bowtie-radial and balanced dual-radial PA architectures are proposed to combine 4-way and 8-way power units. Moreover, they also make breakthrough on the power area density (PAD) performances of ${\rm N}$ -way combined PAs. These two CMOS PAs can both achieve the highest output power of 26.1 dBm at 23.5 GHz with PAD of 635 ${\rm mW}/{\rm mm}^{2}$ and 23 dBm at 60 GHz with PAD of 277 ${\rm mW}/{\rm mm}^{2}$ , respectively.

SSR Damping Controller Design and Optimal Placement in Rotor-Side and Grid-Side Converters of Series-Compensated DFIG-Based Wind Farm

This paper deals with subsynchronous resonance (SSR) phenomena in a capacitive series-compensated DFIG-based wind farm. Using both modal analysis and time-domain simulation, it is shown that the DFIG wind farm is potentially unstable due to the SSR mode. In order to damp the SSR, the rotor-side converter (RSC) and grid-side converter (GSC) controllers of the DFIG are utilized. The objective is to design a simple proportional SSR damping controller (SSRDC) by properly choosing an optimum input control signal (ICS) to the SSRDC block, so that the SSR mode becomes stable without decreasing or destabilizing the other system modes. Moreover, an optimum point within the RSC and GSC controllers to insert the SSRDC is identified. Three different signals are tested as potential ICSs including rotor speed, line real power, and voltage across the series capacitor, and an optimum ICS is identified using residue-based analysis and root-locus method. Moreover, two methods are discussed in order to estimate the optimum ICS, without measuring it directly. The studied power system is a $\mathbf{100\;{\rm MW}}$ DFIG-based wind farm connected to a series-compensated line whose parameters are taken from the IEEE first benchmark model (FBM) for computer simulation of the SSR. MATLAB/Simulink is used as a tool for modeling and designing the SSRDC, and power system computer aided design/electromagnetic transients including dc (PSCAD/EMTDC) is used to perform time-domain simulation for design process validation.

ON THE MASS OF THE LOCAL GROUP

We use recent proper motion measurements of the tangential velocity of M31, along with its radial velocity and distance, to derive the likelihood of the sum of halo masses of the Milky Way and M31. This is done using a sample halo pairs in the Bolshoi cosmological simulation of $\Lambda$CDM cosmology selected to match properties and environment of the Local Group. The resulting likelihood gives estimate of the sum of masses of $M_{\rm MW,200}+M_{\rm M31,200}=$ $2.40_{-1.05}^{+1.95}\times10^{12}\,M_{\odot}$ ($90\%$ confidence interval). This estimate is consistent with individual mass estimates for the Milky Way and M31 and is consistent, albeit somewhat on the low side, with the mass estimated using the timing argument. We show that although the timing argument is unbiased on average for all pairs, for pairs constrained to have radial and tangential velocities similar to that of the Local Group the argument overestimates the sum of masses by a factor of $1.6$. Using similar technique we estimate the total dark matter mass enclosed within $1$ Mpc from the Local Group barycenter to be $M_{\rm LG}(r<1\, {\rm Mpc})=4.2_{-2.0}^{+3.4}\times10^{12}\,M_{\odot}$ ($90\%$ confidence interval).

Correction to “A Miniaturization Strategy for Harvesting Vibration Energy Utilizing Helmholtz Resonance and Vortex Shedding Effect” [Feb 14 271-273

In the above-named paper there are two typos in the abstract and last page. The 95.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">${\rm mW}/{\rm cm}^{3}$ </tex-math></inline-formula> should be 95.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\mu{\rm W}/{\rm cm}^{3}$ </tex-math></inline-formula> . The calculation based on the power output and the volume of the device. The dimension of the device is shown in the following figure:

First Operation of a Step-Frequency Tunable 1-MW Gyrotron With a Diamond Brewster Angle Output Window

Experimental results using a step-frequency tunable D-band gyrotron are reported. The short pulse $({\sim}{\rm 3}~{\rm ms})$ gyrotron is equipped with an elliptically brazed chemical vapor deposition (CVD) diamond Brewster angle output window. It is designed for the operation in the frequency range from 111.6 up to 165.7 GHz. Operating parameters for ten different frequencies corresponding to an equal number of different cavity operating modes has been measured. A minimum output power of 830 kW and a peak output power of 1.3 MW have been realized. For all frequencies, the parameters of the RF beam generated by the internal quasi-optical converter, such as fundamental Gaussian contents and beam waist, are sufficiently good to allow an efficient coupling of the RF power out of the window. This is the first time a diamond Brewster angle window has been used in a high power gyrotron $({\sim}{\rm 1}~{\rm MW})$ . Such a system offers the path to a simple and compact window solution for high power broadband applications using gyrotrons.

The Accomplishments and Next-Step Plan of EAST in Support of Fusion

The experimental advanced superconducting tokamak (EAST) is a superconducting tokamak, which successfully achieved the first plasma discharge in 2006. The major radius of EAST plasma is 1.9 m, and its central magnet field is 3.5 T. In the past few years, EAST has made many achievements, such as 60-s double-null divertor configuration plasma and 1-MA plasma. In 2012, 411-s long-pulse discharge with 0.28-MA plasma current and 32-s H-mode operation was achieved at the seventh campaign. In addition, various means for mitigating ELMs have also been demonstrated to facilitate long-pulse operation. The experimental results and engineering experience obtained from EAST can be used as a reference for fusion next step. To make further progress, much optimization work should be done in next step. Based on the present EAST heating system, two sets of 4-MW neutral beam injection, one set of electron cyclotron resonance heating, and lower hybrid current drive will be installed to achieve more than 30-MW total heating power. The upper divertor will be updated to W–Cu divertor, which consists of monoblock structure and tungsten armor that can withstand 10- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MW}\cdot{\rm m}^{-2}$</tex></formula> heat load. To increase the upper divertor's ash removal efficiency, one new cryopump will be added on the behind of it. Aiming to improve plasma configuration and enhance its stabilization, the EAST resonant magnetic perturbation (RMP) coils will be designed, fabricated, and installed. The RMP coils will integrate the functions of error field correction, edge localized mode, and resistive wall mode. About 45 kinds of diagnostics will be used in the next campaign and all of them will be integrated on six ports as port plug. In addition, some fusion technologies are also considered in EAST to validate for ITER and future reactor.

Epitaxial-Side Mounting of Terahertz Quantum- Cascade Lasers for Improved Heat Management

First results on epitaxial-side (epi-down) mounting of terahertz quantum-cascade lasers (QCLs) on sapphire submounts using indium solder are presented. The single-plasmon ridge waveguide lasers emit in the range 3.1–3.3 THz. An epi-down mounting scheme for stressless assembly is realized, which provides enhanced heat dissipation at the corresponding operating temperature and high stability against thermal cycling. The thermal conductance of the devices is improved by 30%, and the maximum continuous-wave operating temperature is increased by 10 K for epi-down mounted lasers achieving output power levels ${>}{\rm 3}~{\rm mW}$ at 55 K.

High Voltage Pulse Generator Using Transformer Parasitic Components for Pulsed Corona Discharge Generation

This paper proposes a new topology of a nanosecond, high voltage pulse generator devoted to pulsed corona discharge (PCD) reactor supply. The proposed topology is based on solid state, semiconductor switches and uses parasitic components of transformers. A prototype construction of the proposed generator loaded with a PCD reactor with 6.4-pF capacitance is able to generate high voltage pulses with maximum amplitude of 14 kV (using 5.4-kV supply and up to six modules of proposed topology, each equipped with a MOSFET transistor with 1-kV blocking capability) with voltage steepness of 730 V/ns. Obtained pulses are 65-ns long. The peak power delivered to the PCD reactor is ${>}{\rm 0.3}~{\rm MW}$ while the energy consumed reaches 7 mJ/pulse. This paper also compares two different mechanical constructions of such generators and gives an overview of analytical and numerical voltage waveform analyzes.