arXiv subjects

M. Zhang

Publications and source records attributed to M. Zhang.

At least 55 records · Page 3Linked to original sources

arXiv2021

Nanoparticle acts as a light source to make atom interferometers

Atomic Kapitza-Dirac (KD) scattering in the classical standing wave of lights is widely used to make the laser-pulsed atom interferometers. In this theoretical work, we show that the dielectric nanoparticle can be used as a weak light source to generate atomic KD scattering and make atom interferometer. We consider a cavity system consisting of atoms and a single nanoparticle, where the nanoparticle is illuminated by the external laser pulses. Atoms and the cavity mirrors are not illuminated by the laser beam, so nanoparticle acts as a pulsed source to excite the cavity mode which non-resonantly excites atomic internal state and generates a weak KD scattering of atomic external motion. We use twice such scattering to split atomic path and consequently use two classical laser pulses to recombine the separated paths for generating the Ramsey-Bordé atom interferometer. This atom interferometer is entangled with the centre-of-mass motion of nanoparticle and could be developed to search the small nonclassicality of motional nanoparticle, because the cavity mode excitation is associated with nanoparticle's position relative to the node or antinode of that optical mode.

quant-ph↗

arXiv2021

Interaction and transformation of metastable defects in intercalation materials

Non-equilibrium defects often dictate macroscopic functional properties of materials. In intercalation hosts, widely used in rechargeable batteries, high-dimensional defects largely define reversibility and kinetics1,2,3,4. However, transient defects briefly appearing during ionic transport have been challenging to capture, limiting the understanding of their life cycle and impact. Here, we overcome this challenge and track operando the interaction and impact of metastable defects within NaxNi1-xMnyO2 intercalation hosts in a charging sodium-ion battery. Three-dimensional coherent X-ray imaging3,4,5 reveals transformation and self-healing of a metastable domain boundary, glissile dislocation loop, and stacking fault. A local strain gradient suggests a quantifiable difference in ion diffusion, coincident with the macroscopic change in diffusion coefficient. Analysis of the unexpected4,6 defect anisotropy highlights the importance of mesostructure, suggesting a possible control approach and disputing the rigidity of the framework layers. The shared nature of oxygen framework layers makes our results applicable to a wide range of intercalation materials.

cond-mat.mtrl-sci↗

arXiv2021

The orbital effect on the anomalous magnetism and evolution in La$_x$Y$_{1-x}$VO$_3$($0\le x \le 0.2$) single crystals

The orbital effect on the anomalous magnetism and evolution of low La-doping single crystals, La$_x$Y$_{1-x}$VO$_{3}$ (x = 0, 0.1, and 0.2), has been investigated by applying the X-ray diffraction, specific heat, magnetization and Raman scattering techniques. The larger nearest-neighbor (NN) exchange interaction along c-axis stabilizes the fluctuant G-type orbital ordering (G-OO) which favors the exotic C-type antiferromagnetic order (C-AF). It is found that the NN exchange interaction in ab plane is anisotropy relating to the in plane magnetic anisotropy, which becomes smaller in high La-doped sample. Most interestingly, with increasing the La$^{3+}$ content the orbital fluctuation and hybridization are decreased which stabilizes the C-OO phase and destabilizes the G-OO phase. Meanwhile, the diamagnetism in the exotic C-AF phase becomes weak and the possible mechanism relates to the change of the competition between the single-ion magnetic anisotropy and the Dzyaloshinsky-Moriya (DM) interaction with increasing x. Finally, the strong spin-orbital coupling has been observed at temperature just above T$_N$ in La$_{0.2}$Y$_{0.8}$VO$_{3}$ and a short range spin-orbital correlation is suggested.

cond-mat.str-el↗

arXiv2021

Study of quasi-particle dynamics using the optical pulse response of asuperconducting resonator

We study the optical pulse response of a superconducting half-wavelength coplanar waveguide (CPW) resonator. We apply a short optical pulse to the center strip of the CPW resonator, where the current distribution shows antinodes or nodes for different resonance modes, and measure the frequency response. We develop a time-dependent variable inductance circuit model with which we can simulate the optical pulse response of the resonator. By fitting this model to experimental data, we extract the temporal kinetic inductance variations, which directly reflect the quasi-particle recombination with time and diffusion in space. We also retrieve the spatial size of the quasi-particle distribution and the quasi-particle diffusion constant. Our study is very useful for the design of photon-counting kinetic inductance detectors, and the method developed in this work provides a useful way to study the quasi-particle dynamics in the superconductor.

cond-mat.supr-con↗

arXiv2021

Evolutionary games on simplicial complexes

Elucidating the mechanisms that lead to cooperation is still one of the main scientific challenges of current times, as many common cooperative scenarios remain elusive and at odds with Darwin's natural selection theory. Here, we study evolutionary games on populations that are structured beyond pairwise interactions. Specifically, we introduce a general evolutionary approach that allows studying situations in which indirect interactions via a neighbor other than the direct pairwise connection (or via a group of neighbors), impact the strategy of the focal player. To this end, we consider simplicial graphs that encode two- and three-body interactions, which enables to study competition between all possible pairs of social dilemmas and to scrutinize the role of three-body interactions in all the observed phenomenology. We simultaneously investigate how social dilemma with different Nash equilibria compete in simplicial structures and how such a competition is modulated by the unbalance of 2- and 1-simplices, which in its turn reflects the relative prevalence of pairwise or group interactions among the players. We report a number of results that: (i) support that higher-order games allow for non-dominant strategists to emerge and coexist with dominant ones, a scenario that can't be explained by any pairwise schemes, no matter the network of contacts; (ii) characterize a novel transition from dominant defection to dominant cooperation as a function of the simplicial structure of the population; and (iii) demonstrate that 2-simplex interactions are a source of strategy diversity, i.e. increasing the relative prevalence of group interactions always promotes diverse strategic identities of individuals. Our study constitutes a step forward in the quest for understanding the roots of cooperation and the mechanisms that sustain it in real-world and social environments.

physics.soc-ph↗

arXiv2020

Particle identification and revolution time corrections for the isochronous mass spectrometry in storage rings

In the isochronous mass spectrometry (IMS) performed at storage rings, masses of short-lived nuclides are determined through precision measurements of their mean revolution times. However, the distribution of revolution times could be seriously deteriorated by instabilities of the ring's magnetic fields. This becomes a significant obstacle for the particle identifications and mass determinations. A data analysis method is described in this paper which is able to largely remove the uncertainties caused by the magnetic field instabilities in the particle identifications and the mean revolution times. We show that this method is very effective for the IMS experiments even when the magnetic fields of a storage ring vary slowly up to a level of $ΔB/B\sim 10^{-4}$.

nucl-ex↗

arXiv2020

A catalogue of H$α$ emission-line point sources in the vicinity fields of M31 and M33 from the LAMOST survey

We present a catalogue of 3,305 H$α$ emission-line point sources observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in the vicinity fields of M31 and M33 during September 2011 and January 2016. The catalogue contains 1,487 emission-line stars, 532 emission-line nebulae including 377 likely planetary nebulae (PNe), 83 H~{\textsc{ii}} regions candidates and 20 possible supernovae remnants (SNRs) and 1,286 unknown objects. Among them, 24 PN candidates, 19 H~{\sc ii} region candidates, 10 SNR candidates and 1 symbiotic star candidate are new discoveries. Radial velocities and fluxes estimated from the H$α$ line and those quantities of seven other major emission lines including H$β$, [O~{\textsc{iii}}]~$λ$4959, [O~{\textsc{iii}}]~$λ$5007, [N~{\textsc{ii}}]~$λ$6548, [N~{\textsc{ii}}]~$λ$6583, [S~{\textsc{ii}}]~$λ$6717 and [S~{\textsc{ii}}]~$λ$6731 lines of all the catalogued sources yielded from the LAMOST spectra are also presented in our catalogue. Our catalogue is an ideal starting point to study the chemistry properties and kinematics of M31 and M33.

astro-ph.GA↗

arXiv2020

Nonclassical effects in geodesic motion

Gravity gradient is known as a serious systematic effect in atomic tests of the universality of free fall, where the initial central position and velocity of atoms need to be exactly controlled. In this paper, we study quantum free fall with high-order gravity gradients. It is shown that the cubic terms in the Newtonian potential shall generate a new phase shift in atom interferometers, which depends on the position and velocity uncertainties of the incident atoms. We further investigate the nonclassicality of free fall and show that, due to the cubic potential, the gravitational Wigner equation in phase space of position and velocity is different from the classical Liouville equation. There exists a mass-dependent correction in the dynamical equation regardless of initial state. Nevertheless, this is just a quantum mechanical effect of microparticles, which does not violate equivalence principle that inertia mass is equal to the gravitational mass.

quant-ph↗

arXiv2019

Exotic Spin-Dependent Interaction Searches at Indiana University

The axion is a hypothesized particle appearing in various theories beyond the Standard Model. It is a light spin-0 boson initially postulated to solve the strong CP problem and is also a strong candidate for dark matter. If the axion or an axion-like particle exists, it would mediate a P-odd and T-odd spin-dependent interaction. We describe two experiments under development at Indiana University-Bloomington to search for such an interaction.

hep-ph↗

arXiv2019

The Galactic disc phase spirals at different Galactic positions revealed by Gaia and LAMOST data

We have investigated the distributions of stellar azimuthal and radial velocity components $V_Φ$ and $V_{R}$ in the vertical position-velocity plane $Z$-$V_{Z}$ across the Galactic disc of $6.34 \lesssim R \lesssim 12.34$\,kpc and $|Φ| \lesssim 7.5^{\circ}$ using a Gaia and Gaia-LAMOST sample of stars. As found in previous works, the distributions exhibit significant spiral patterns. The $V_{R}$ distributions also show clear quadrupole patterns, which are the consequence of the well-known tilt of the velocity ellipsoid. The observed spiral and quadrupole patterns in the phase space plane vary strongly with radial and azimuthal positions. The phase spirals of $V_Φ$ become more and more relaxed as $R$ increases. The spiral patterns of $V_Φ$ and $V_{R}$ and the quadrupole patterns of $V_{R}$ are strongest at $-2^{\circ} < Φ< 2^{\circ}$ but negligible at $4^{\circ} < Φ< 6^{\circ}$ and $-6^{\circ} < Φ< -4^{\circ}$. Our results suggest an external origin of the phase spirals. In this scenario, the intruder, most likely the previously well-known Sagittarius dwarf galaxy, passed through the Galactic plane in the direction towards either Galactic center or anti-center. The azimuthal variations of the phase spirals also help us constrain the passage duration of the intruder. A detailed model is required to reproduce the observed radial and azimuthal variations of the phase spirals of $V_Φ$ and $V_{R}$.

astro-ph.GA↗

arXiv2019

Compact radio emission indicates a structured jet was produced by a binary neutron star merger

The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow. High spatial resolution measurements of the source size and displacement can discriminate between these scenarios. We present Very Long Baseline Interferometry observations, performed 207.4 days after the merger, using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milliarcseconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.

astro-ph.HE↗

arXiv2019

Near-infrared spectroscopy of the massive stellar population of W51: evidence for multi-seeded star formation

The interplay between the formation of stars, stellar feedback and cloud properties strongly influences the star formation history of giant molecular clouds. The formation of massive stars leads to a variety of stellar clusters, ranging from low stellar density OB associations to dense, gravitationally bound starburst clusters. We aimed at identifying the massive stellar content and reconstructing the star formation history of the W51 giant molecular cloud. We performed near-infrared imaging and K-band spectroscopy of the massive stars in W51. We analyzed the stellar populations using colour-magnitude and colour-colour diagrams and compared the properties of the spectroscopically identified stars with stellar evolution models. We derived the ages of the different sub-clusters in W51 and, based on our spectroscopy derived an age for W51 of 3 Myrs or less. The age of the P Cygni star LS1 and the presence of two still forming proto-clusters suggests that the star formation history of W51 is more complex than a single burst. We did not find evidence for triggered star formation and we concluded that the star formation in W51 is multi seeded. We finally concluded that W51 is a OB association where different sub-clusters form over a time span of at least 3-5 Myrs.

astro-ph.SR↗

arXiv2018

Test beam measurement of ams H35 HV-CMOS capacitively coupled pixel sensor prototypes with high-resistivity substrate

In the context of the studies of the ATLAS High Luminosity LHC programme, radiation tolerant pixel detectors in CMOS technologies are investigated. To evaluate the effects of substrate resistivity on CMOS sensor performance, the H35DEMO demonstrator, containing different diode and amplifier designs, was produced in ams H35 HV-CMOS technology using four different substrate resistivities spanning from $\mathrm{80}$ to $\mathrm{1000~Ω\cdot cm}$. A glueing process using a high-precision flip-chip machine was developed in order to capacitively couple the sensors to FE-I4 Readout ASIC using a thin layer of epoxy glue with good uniformity over a large surface. The resulting assemblies were measured in beam test at the Fermilab Test Beam Facilities with 120 GeV protons and CERN SPS H8 beamline using 80 GeV pions. The in-time efficiency and tracking properties measured for the different sensor types are shown to be compatible with the ATLAS ITk requirements for its pixel sensors.

physics.ins-det↗

arXiv2018

Measurement of optical constants of TiN and TiN/Ti/TiN multilayer films for microwave kinetic inductance photon-number-resolving detectors

We deposit thin titanium-nitride (TiN) and TiN/Ti/TiN multilayer films on sapphire substrates and measure the reflectance and transmittance in the wavelength range from 400 nm to 2000 nm using a spectrophotometer. The optical constants (complex refractive indices), including the refractive index n and the extinction coefficient k, have been derived. With the extracted refractive indices, we propose an optical stack structure using low-loss amorphous Si (a-Si) anti-reflective coating and a backside aluminum (Al) reflecting mirror, which can in theory achieve 100% photon absorption at 1550 nm. The proposed optical design shows great promise in enhancing the optical efficiency of TiN-based microwave kinetic inductance photon-number-resolving detectors.

physics.optics↗

arXiv2018

A search for faint high-redshift radio galaxy candidates at 150 MHz

Ultra-steep spectrum (USS) radio sources are good tracers of powerful radio galaxies at $z > 2$. Identification of even a single bright radio galaxy at $z > 6$ can be used to detect redshifted 21cm absorption due to neutral hydrogen in the intervening IGM. Here we describe a new sample of high-redshift radio galaxy (HzRG) candidates constructed from the TGSS ADR1 survey at 150 MHz. We employ USS selection ($α\le -1.3$) in $\sim10000$ square degrees, in combination with strict size selection and non-detections in all-sky optical and infrared surveys. We apply flux density cuts that probe a unique parameter space in flux density ($50 < S_{\textrm{150}} < 200$ mJy) to build a sample of 32 HzRG candidates. Follow-up Karl G. Jansky Very Large Array (VLA) observations at 1.4 GHz with an average beam size of $1.3$ arcseconds ($"$) revealed $\sim 48\%$ of sources to have a single radio component. P-band (370 MHz) imaging of 17 of these sources revealed a flattening radio SED for ten sources at low frequencies, which is expected from compact HzRGs. Two of our sources lie in fields where deeper multi-wavelength photometry and ancillary radio data are available and for one of these we find a best-fit photo-z of $4.8 \pm 2.0$. The other source has $z_{\textrm{phot}}=1.4 \pm 0.1$ and a small angular size ($3.7"$), which could be associated with an obscured star forming galaxy or with a "dead" elliptical. One USS radio source not part of the HzRG sample but observed with the VLA nonetheless is revealed to be a candidate giant radio galaxy with a host galaxy photo-z of $1.8\pm0.5$, indicating a size of 875 kpc.

astro-ph.GA↗

arXiv2018

Observations of white-light flares in NOAA active region 11515: high occurrence rate and relationship with magnetic transients

There are two goals in this study. One is to investigate how frequently white-light flares (WLFs) occur in a flare-productive active region (NOAA active region 11515). The other is to investigate the relationship between WLFs and magnetic transients (MTs). We use the full-disk continuum filtergrams and line-of-sight magnetograms taken by SDO/HMI to identify WLFs and MTs, respectively. Images taken by SDO/AIA are also used to show the morphology of the flares in the upper atmosphere. We found at least 20 WLFs out of a total of 70 flares above C class (28.6%) in NOAA active region 11515 during its passage across the solar disk. Each of these WLFs occurred in a small region, with a short duration of about 5 minutes. The enhancement of white-light continuum intensity is usually small, with an average enhancement of 8.1%. The 20 WLFs observed were found along an unusual configuration of the magnetic field characterized by a narrow ribbon of negative field. Furthermore, the WLFs were found to be accompanied by MTs, with radical changes in magnetic field strength (or even a sign reversal) observed during the flare. In contrast, there is no obvious signature of MTs in those 50 flares without white-light enhancements. Our results suggest that WLFs occur much more frequently than what was previously thought, with most WLFs being fairly weak enhancements. This may explain why WLFs are not frequently reported. Our observations also suggest that MTs and WLFs are closely related and appear co-spatial and co-temporal, when considering HMI data. A larger enhancement of WL emission is often accompanied by a larger change of the line-of-sight component of the unsigned magnetic field. Considering the close relationship between MTs and WLFs, many previously reported flares with MTs may be WLFs.

astro-ph.SR↗

arXiv2018

Observations of a white-light flare associated with a filament eruption

We present observations of an M5.7 white-light flare (WLF) associated with a small filament eruption in NOAA active region 11476 on 2012 May 10. During this flare, a circular flare ribbon appeared in the east and a remote brightening occurred in the northwest of the active region. Multi-wavelength data are employed to analyze the WLF, including white light (WL), ultraviolet, extreme ultraviolet, hard X-ray (HXR) and microwave. A close spatial and temporal relationship between the WL, HXR and microwave emissions is found in this WLF. However, the peak time of the WL emission lagged that of the HXR and microwave emissions by about 1-2 minutes. Such a result tends to support the back-warming mechanism for the WL emission. Interestingly, the enhanced WL emission occurred at the two footpoints of the filament. Through forced and potential field extrapolations, we find that the three-dimensional magnetic field in the flare region has a fan-spine feature and that a flux rope lies under the dome-like field structure. We describe the entire process of flare evolution into several steps, each producing the sequent brightening below the filament, the circular flare ribbons and the WL enhancement respectively. We suggest that reconnection between the magnetic field of the filament and the overlying magnetic field or reconnection within the flux rope leads to the WL enhancement.

astro-ph.SR↗

arXiv2017

Efficient implementation of the adaptive scale pixel decomposition algorithm

Context. Most popular algorithms in use to remove the effects of a telescope's point spread function (PSF) in radio astronomy are variants of the CLEAN algorithm. Most of these algorithms model the sky brightness using the delta-function basis, which results in undesired artefacts when used on image extended emission. The adaptive scale pixel decomposition (Asp-Clean) algorithm models the sky brightness on a scale-sensitive basis and thus gives a significantly better imaging performance when imaging fields that contain both resolved and unresolved emission. Aims. However, the runtime cost of Asp-Clean is higher than that of scale-insensitive algorithms. In this paper, we identify the most expensive step in the original Asp-Clean algorithm and present an efficient implementation of it, which significantly reduces the computational cost while keeping the imaging performance comparable to the original algorithm. The PSF sidelobe levels of modern wide-band telescopes are significantly reduced, allowing us to make approximations to reduce the computing cost, which in turn allows for the deconvolution of larger images on reasonable timescales. Methods. As in the original algorithm, scales in the image are estimated through function fitting. Here we introduce an analytical method to model extended emission, and a modified method for estimating the initial values used for the fitting procedure, which ultimately leads to a lower computational cost. Results.The new implementation was tested with simulated EVLA data and the imaging performance compared well with the original Asp-Clean algorithm. Tests show that the current algorithm can recover features at different scales with lower computational cost.

astro-ph.IM↗