arXiv subjects

Shaobo Zhang

Publications and source records attributed to Shaobo Zhang.

At least 37 records · Page 2Linked to original sources

arXiv2025

Gas Transfer Between the Inner 3-kpc Disk and the Galactic Central Molecular Zone

We uncovered a more tilted molecular gas structure with highly negative velocities located near the dust lane. Our observations also show that the approaching gas flows from the overshoot process are captured by the bar gravitational and then flows towards the Galactic central molecular zone (CMZ) through the bar channel. The recycling gas from the overshoot effect, in conjunction with freshly accreted gas from the inner 3-kpc disk, accumulates significantly near R_GC~1/2R_bar and R_GC~2/3R_bar regions by adopting a bar length of ~3.2--3.4kpc. Importantly, within these regions, there are frequent collisions and substantial angular momentum exchanges between gas flows with different trajectories. In this scenario, the DISSIPATION processes arising from interactions between colliding flows, together with the varying torques induced by the nonaxisymmetric bar, effectively transfer the angular momentum of viscous gas outward, thereby driving the molecular gas to settle into the CMZ within ~3 orbital periods. A long-term gas inflow with an average rate of >1.1Msun/yr, coupled with intense transient accretion events that exceed the average rate by several times due to the overshoot effect, significantly regulates the gas distribution, physical properties, and dynamical evolution of the CMZ. These findings provide robust observational evidence for elucidating the intricate dynamics of molecular gas flows towards the CMZ. Our results show that gas dynamics has a significant impact on the secular evolution of both the Milky Way and the extragalactic gas-rich galaxies.

astro-ph.GA↗

arXiv2025

Fast and Noise-aware Machine Learning Variational Quantum Eigensolver Optimiser

The Variational Quantum Eigensolver (VQE) is a hybrid quantum-classical algorithm for preparing ground states in the current era of noisy devices. The classical component of the algorithm requires a large number of measurements on intermediate parameter values that are typically discarded. However, intermediate steps across many calculations can contain valuable information about the relationship between the quantum circuit parameters, resultant measurements, and noise specific to the device. In this work, we use supervised machine learning on the intermediate parameter and measurement data to predict optimal final parameters. Our technique optimises parameters leading to chemically accurate ground state energies much faster than conventional techniques. It requires significantly fewer iterations and simultaneously shows resilience to coherent errors if trained on noisy devices. We demonstrate this technique on IBM quantum devices by predicting ground state energies of H$_2$ for one and two qubits; H$_3$ for three qubits; and HeH$^+$ for four qubits where it finds optimal angles using only modeled data for training.

quant-ph↗

arXiv2025

Examining Turbulence in Galactic Molecular Clouds -- I: A Statistical Analysis of Velocity Structures

We present a systematic analysis of the velocity structure functions (VSFs) of 167 molecular clouds with angular sizes greater than $\sim$176 arcmin$^2$ in three sectors of the Galactic mid-plane. We calculated the 1st- to 3rd-order VSFs and found that 60\% of the VSFs exhibit power-law distributions. The relative power-law exponents are consistent with predictions from intermittent turbulence models. Column density weighting reduces the proportion of power-law VSFs and steepens the VSF slopes, implying a reduction of turbulent energy in high-density regions. All clouds show small-scale intermittency, with slightly stronger intermittency in those molecular clouds showing none power-law VSFs. Negative VSF exponents that may indicate gravitational collapse are not observed in our sample. The scaling exponents of the observed VSFs do not correlate with the virial parameters of the molecular clouds. These two observations suggest that gravity-dominated scales in molecular clouds still need further investigation. Consistent VSF scaling exponents for the molecular clouds with significant power-law VSFs suggest large-scale external driving of turbulence in these molecular clouds. However, the driving mechanisms are likely not universal, as the power-law scaling coefficients in our results show relatively large scatter. The fact that nearly 40\% of the VSFs deviate to some extent from power-law distributions suggests that the influence of local environments on the internal turbulence of molecular clouds may not be negligible.

astro-ph.GA↗

arXiv2024

A new view of the Spiral Structure of the Northern Outer Milky Way in Carbon Monoxide

Based on 32162 molecular clouds from the Milky Way Imaging Scroll Painting project, we obtain new face-on molecular gas maps of the northern outer Galaxy. The total molecular gas surface density map reveals three segments of spirals, extending 16-43 kiloparsecs in length. The Perseus and Outer arms stand out prominently, appearing as quasi-continuous structures along most of their length. At the Galactic outskirts, about 1306 clouds connect the two segments of the new spiral arm discovered by Dame & Thaddeus (2011) in the first quadrant and Sun et al. (2015) in the second quadrant, possibly extending the arm into the outer third quadrant. Logarithmic spirals can be fitted to the CO arm segments with pitch angles ranging from 4 to 12 degree. These CO arms extend beyond previous CO studies and the optical radius, reaching a galactic radius of about 22 kiloparsecs, comparable to the HI radial range.

astro-ph.GA↗

arXiv2024

Low Depth Virtual Distillation of Quantum Circuits by Deterministic Circuit Decomposition

Virtual distillation (VD) using measurements of multiple copies of a quantum circuit have recently been proposed as a method of noise mitigation of expectation values. Circuit decompositions known as B gates were found only for single qubit expectation values however practical calculations require multi-qubit expectation values which cannot be corrected with B gates. We discover low depth circuit decompositions for multi-qubit expectation values by combining multiple projections to recover the correct measurement statistics or expectation values. Our method adds linear entangling gates with number of qubits, but requires extra measurements. Furthermore, in applications to find ground states such as the variational quantum eigensolver (VQE) algorithm, the variational principle is required which states the energy cannot go below the ground state energy. We discover that the variational principle is violated if noise is higher on single expectation values than multi-qubit which renders VQE useless. We show this occurs when using B gates and is preserved if using our low depth decomposition on all expectation values. We perform demonstration on real devices and demonstrate our decomposition can mitigate real experimental noise in VQE for the H$_2$ molecule with a two qubit tapered mapping, H$_3$ with three qubits, and H$_2$ with four qubits. Our decomposition provides a way to perform duplicate circuit virtual distillation on real devices at significantly lower depth and for arbitrary observables.

quant-ph↗

arXiv2024

Revealing Gas Inflows towards the Galactic Central Molecular Zone

We study the gas inflows towards the Galactic Central Molecular Zone (CMZ) based on the gas morphological and kinematic features from the MWISP in the region of l=1.2 deg--19.0 deg and |b|<3.0 deg. We find that the near dust lane extends to l~15 deg, in which the end of the large-scale gas structure intersects with the 3 kpc-ring at a distance of ~5 kpc. Intriguingly, many filamentary MCs, together with the bow-like/ballistic-like clouds and continuous CO features with notable velocity gradient, are finely outlined along the long structure. These MCs also have relatively large velocity dispersions, indicating the shocked gas generated by local continuous accretion and thus the enhanced turbulence along the entire gas structure. We suggest that the ~3.1--3.6 kpc long CO structure originates from the accretion molecular gas driven by the Galactic bar. The gas near the bar end at the 3 kpc-ring becomes an important reservoir for the large-scale accreting flows inwards to the CMZ through the bar channel. The inclination angle of the bar is estimated to be 20--26 deg, while the pattern speed of the bar is 30--35 km/s. The total mass of the whole gas lane is about (0.9-1.7)x10^7 Msun according to the calculated X_CO=(0.6-1.4)x10^20 cm^-2 (Kkm/s)^-1 from the large-scale CO data and the complementary HI data. The mean gas inflow rate is about 0.8-1.4 Msun/yr, which seems to be comparable to the outflow's rate of the Galactic nuclear winds after applying the updated lower X-factor value above.

astro-ph.GA↗

arXiv2024

Vapor cell Rydberg atom electrometry with time-separated fields

Rydberg atoms have large transition electric dipole moments and high sensitivity to electric fields. We describe a new method for microwave field sensing in a vapor cell consisting of separate excitation, quantum evolution between two Rydberg levels in the dark and state-dependent detection with probe laser transmission. Using microwave pulse techniques we study homogeneous and inhomogeneous relaxation of the coherence between Rydberg levels and demonstrate detection of a 10 GHz signal with electric field sensitivity of 10 nV/cm/Hz$^{1/2}$.

physics.atom-ph↗

arXiv2024

Full Band Structure Calculation of Semiconducting Materials on a Noisy Quantum Processor

Quantum chemistry is a promising application in the era of quantum computing since the unique effects of quantum mechanics that take exponential growing resources to simulate classically are controllable on quantum computers. Fermionic degrees of freedom can be encoded efficiently onto qubits and allow for algorithms such as the Quantum Equation-of-Motion method to find the entire energy spectrum of a quantum system. In this paper, we propose the Reduced Quantum Equation-of-Motion method by reducing the dimensionality of its generalized eigenvalue equation, which results in half the measurements required compared to the Quantum Equation-of-Motion method, leading to speed up the algorithm and less noise accumulation on real devices. In particular, we analyse the performance of our method on two noise models and calculate the excitation energies of a bulk Silicon and Gallium Arsenide using our method on an IBM quantum processor. Our method is fully robust to the uniform depolarizing error and we demonstrate that the selection of suitable atomic orbital complexity could increase the robustness of our algorithm under real noise. We also find that taking the average of multiple experiments tends towards the correct energies due to the fluctuations around the exact values. Such noise resilience of our approach could be used on current quantum devices to solve quantum chemistry problems.

quant-ph↗

arXiv2024

On the Flux-Intensity Relation of Molecular Clouds

In this work, we report a study on the relationship between flux and intensity for molecular clouds. Our analysis is established on high-quality CO images from the Milky Way Imaging Scroll Painting (MWISP) project. The new flux-intensity relation characterizes the flux variation of molecular clouds above specific intensity levels. We found that the flux-intensity relation exhibits two prominent features. First, the flux-intensity relation generally follows exponential shapes; secondly, hierarchical structures of molecular clouds are imprinted on flux-intensity relations. Specifically, 12CO flux-intensity relations are composed of one or more exponential segments, and for molecular clouds with segmented flux-intensity relations, the edge and the flux of the high-temperature component are strikingly consistent with 13CO emission. Further analysis shows that a similar relationship also exists between 13CO flux-intensity relations and C18O emission. The mean brightness temperature of molecular clouds is tightly associated with the decay rate of flux, the break temperature of exponential segments, and, to a certain extent, the flux fraction of the high-temperature component. Broadly, the flux-intensity relation of a molecular tracer, either in optically thick or in optically thin cases, has the capability to outline the silhouette of internal structures of molecular clouds, proving to be a potent tool for probing structures of molecular clouds.

astro-ph.GA↗

arXiv2024

The Multilayer Nature of Molecular Gas toward the Cygnus Region

We study the physical properties and 3D distribution of molecular clouds (MCs) toward the Cygnus region using the MWISP CO survey and Gaia DR3 data. Based on Gaussian decomposition and clustering for $\rm ^{13}CO$ lines, over 70% of the fluxes are recovered. With the identification result of $\rm ^{13}CO$ structures, two models are designed to measure the distances of the molecular gas in velocity crowding regions. The distances of more than 200 large $\rm ^{13}CO$ structures are obtained toward the 150 square degree region. Additionally, tens of the identified MC structures coincide well with masers and/or intense mid-IR emission. We find multiple gas layers toward the region: (1) the extensive gas structures composing the Cygnus Rift from 700 pc to 1 kpc across the whole region; (2) the $\sim$ 1.3 kpc gas layer mainly in the Cygnus X South region; and (3) the 1.5 kpc dense filament at the Cygnus X North region and many cometary clouds shaped by Cygnus OB2. We also note that the spatial distribution of YSO candidates is generally consistent with the molecular gas structures. The total molecular mass of the Cygnus region is estimated to be $\sim 2.7\times10^{6}~M_{\odot}$ assuming an X-factor ratio $X_{\rm CO} = 2 \times 10^{20} \rm cm^{-2} (K\cdot km\cdot s^{-1})^{-1}$. The foreground Cygnus Rift contributes $\sim$25% of the molecular mass in the whole region. Our work presents a new 3D view of the MCs' distribution toward the Cygnus X region, as well as the exact molecular gas mass distribution in the foreground Cygnus Rift.

astro-ph.GA↗

arXiv2024

Relative velocities between $^{13}$CO structures within $^{12}$CO Molecular clouds

Velocity fields of molecular clouds (MCs) can provide crucial information on the merger and split between clouds, as well as their internal kinematics and maintenance, energy injection and redistribution, even star formation within clouds. Using the CO spectral lines data from the Milky Way Imaging Scroll Painting (MWISP) survey, we measure the relative velocities along the line of sight ($Δ$V$_{\rm LOS}$) between $^{13}$CO structures within $^{12}$CO MCs. Emphasizing MCs with double and triple $^{13}$CO structures, we find that approximately 70$\%$ of $Δ$V$_{\rm LOS}$ values are less than $\sim$ 1 km s$^{-1}$, and roughly 10$\%$ of values exceed 2 km s$^{-1}$, with a maximum of $\sim$ 5 km s$^{-1}$. Additionally, we compare $Δ$V$_{\rm LOS}$ with the internal velocity dispersion of $^{13}$CO structures ($σ_{\rm ^{13}CO,in}$) and find that about 40$\%$ of samples in either double or triple regime display distinct velocity discontinuities, i.e. the relative velocities between $^{13}$CO structures are larger than the internal linewidths of $^{13}$CO structures. Among these 40$\%$ samples in the triple regime, 33$\%$ exhibit signatures of combinations through the two-body motion, whereas the remaining 7$\%$ show features of configurations through the multiple-body motion. The $Δ$V$_{\rm LOS}$ distributions for MCs with double and triple $^{13}$CO structures are similar, as well as their $Δ$V$_{\rm LOS}$/$σ_{\rm ^{13}CO,in}$ distributions. This suggests that relative motions of $^{13}$CO structures within MCs are random and independent of cloud complexities and scales.

astro-ph.GA↗

arXiv2024

Magnetically Aligned Striations in the L914 Filamentary Cloud

We present CO ($J = 1-0$) multi-line observations toward the L914 dark cloud in the vicinity of the Cygnus X region, using the 13.7 m millimeter telescope of the Purple Mountain Observatory (PMO). The CO observations reveal in the L914 cloud a long filament with an angular length of $\sim 3.\!\!^\circ 6$, corresponding to approximately $\rm 50~pc$ at the measured distance of $\sim\rm 760~pc$. Furthermore, a group of hair-like striations are discovered in the two subregions of the L914 cloud, which are connected with the dense ridge of the filament. These striations display quasi-periodic characteristics in both the CO intensity images and position-velocity diagrams. Two of the striations also show increasing velocity gradients and dispersions toward the dense ridge, which could be fitted by accretion flows under gravity. Based on the $Planck$ 353 GHz dust polarization data, we find that the striations are well aligned with the magnetic fields. Moreover, both the striations and magnetic fields are perpendicular to the dense ridge, which constructs a bimodal configuration. Using the classic method, we estimate the strength of magnetic field, and further evaluate the relative importance of gravity, turbulence and magnetic field, and find that the L914 cloud is strongly magnetized. Our results suggest that magnetic fields play an important role in the formation of filamentary structures by channelling the material along the striations toward the dense ridge. The comparison between the observations and simulations suggests that striations could be a product of the magnetohydrodynamic (MHD) process.

astro-ph.GA↗

arXiv2024

Learning to Retrieve for Job Matching

Web-scale search systems typically tackle the scalability challenge with a two-step paradigm: retrieval and ranking. The retrieval step, also known as candidate selection, often involves extracting standardized entities, creating an inverted index, and performing term matching for retrieval. Such traditional methods require manual and time-consuming development of query models. In this paper, we discuss applying learning-to-retrieve technology to enhance LinkedIns job search and recommendation systems. In the realm of promoted jobs, the key objective is to improve the quality of applicants, thereby delivering value to recruiter customers. To achieve this, we leverage confirmed hire data to construct a graph that evaluates a seeker's qualification for a job, and utilize learned links for retrieval. Our learned model is easy to explain, debug, and adjust. On the other hand, the focus for organic jobs is to optimize seeker engagement. We accomplished this by training embeddings for personalized retrieval, fortified by a set of rules derived from the categorization of member feedback. In addition to a solution based on a conventional inverted index, we developed an on-GPU solution capable of supporting both KNN and term matching efficiently.

cs.IR↗

arXiv2023

Understanding the Kinetic Energy deposition within Molecular Clouds

According to the structures traced by $^{13}$CO spectral lines within the $^{12}$CO molecular clouds (MCs), we investigate the contributions of their internal gas motions and relative motions to the total velocity dispersions of $^{12}$CO MCs. Our samples of 2851 $^{12}$CO MCs harbor a total of 9556 individual $^{13}$CO structures, among which 1848 MCs ($\sim$ 65$\%$) have one individual $^{13}$CO structure and the other 1003 MCs ($\sim$ 35$\%$) have multiple $^{13}$CO structures. We find that the contribution of the relative motion between $^{13}$CO structures ($σ_{\rm ^{13}CO, re}$) is larger than that from their internal gas motion ($σ_{\rm ^{13}CO, in}$) in $\sim$ 62$\%$ of 1003 MCs in the `multiple' regime. In addition, we find the $σ_{\rm ^{13}CO, re}$ tends to increase with the total velocity dispersion($σ_{\rm ^{12}CO, tot}$) in our samples, especially for the MCs having multiple $^{13}$CO structures. This result provides a manifestation of the macro-turbulent within MCs, which gradually becomes the dominant way to store the kinetic energy along with the development of MC scales.

astro-ph.GA↗

arXiv2023

A Systematic Study of Associations between Supernova Remnants and Molecular Clouds

We universally search for evidence of kinematic and spatial correlation of supernova remnant (SNR) and molecular cloud (MC) associations for nearly all SNRs in the coverage of the MWISP CO survey, i.e. 149 SNRs, 170 SNR candidates, and 18 pure pulsar wind nebulae (PWNe) in 1 deg < l < 230 deg and -5.5 deg < b < 5.5 deg. Based on high-quality and unbiased 12CO/13CO/C18O (J = 1--0) survey data, we apply automatic algorithms to identify broad lines and spatial correlations for molecular gas in each SNR region. The 91% of SNR-MC associations detected previously are identified in this paper by CO line emission. Overall, there could be as high as 80% of SNRs associated with MCs. The proportion of SNRs associated with MCs is high within the Galactic longitude less than ~50 deg. Kinematic distances of all SNRs that are associated with MCs are estimated based on systemic velocities of associated MCs. The radius of SNRs associated with MCs follows a lognormal distribution, which peaks at ~8.1 pc. The progenitor initial mass of these SNRs follows a power-law distribution with an index of ~-2.3 that is consistent with the Salpeter index of -2.35. We find that SNR-MC associations are mainly distributed in a thin disk along the Galactic plane, while a small amount distributed in a thick disk. With the height of these SNRs from the Galactic plane below ~45 pc, the distribution of the average radius relative to the height of them is roughly flat, and the average radius increases with the height when above ~45 pc.

astro-ph.GA↗

arXiv2023

Distributions and Physical Properties of Molecular Clouds in the Third Galactic Quadrant: $l$ = [219.75, 229.75]$^\circ$ and $b$ = [-5.25, 5.25]$^\circ$

We present the results of an unbiased $^{12}$CO/$^{13}$CO/C$^{18}$O ($J$ = 1-0) survey in a portion of the third Galactic quadrant (TGQ): $l$ = [219.75, 229.75]$^\circ$ and $b$ = [-5.25, 5.25]$^\circ$. The high-resolution and high-sensitivity data sets help to unravel the distributions and physical properties of the molecular clouds (MCs) in the mapped area. In the LSR velocity range from -1 to 85 km/s, the molecular material successfully traces the Local, Perseus, and Outer arms. In the TGQ, the Outer arm appears to be more prominent than that in the second Galactic quadrant (SGQ), but the Perseus arm is not as conspicuous as that in the SGQ. A total of 1,502 $^{12}$CO, 570 $^{13}$CO, and 53 C$^{18}$O molecular structures are identified, spanning over $\sim2$ and $\sim6$ orders of magnitude in size and mass, respectively. Tight mass-radius correlations and virial parameter-mass anticorrelations are observable. Yet, it seems that no clear correlations between velocity dispersion and effective radius can be found over the full dynamic range. The vertical distribution of the MCs renders evident pictures of the Galactic warp and flare.

astro-ph.GA↗

arXiv2023

The Role of Magnetic Fields in the Formation of the Filamentary Infrared Dark Cloud G11.11-0.12

We report on the near-infrared polarimetric observations of G11.11-0.12 (hereafter G11) obtained with SIRPOL on the 1.4 m IRSF telescope. The starlight polarisation of the background stars reveals the on-sky component of magnetic fields in G11, and these are consistent with the field orientation observed from polarised dust emission at $850\,μ$m. The magnetic fields in G11 are perpendicular to the filament, and are independent of the filament's orientation relative to the Galactic plane. The field strength in the envelope of G11 is in the range $50-100\,μ$G, derived from two methods. The analyses of the magnetic fields and gas velocity dispersion indicate that the envelope of G11 is supersonic but sub-Alfv{é}nic. The critical mass-to-flux ratio in the envelope of G11 is close to 1 and increases to $\gtrsim 1$ on the spine of G11. The relative weights on the importance of magnetic fields, turbulence and gravity indicate that gravity dominates the dynamical state of G11, but with significant contribution from magnetic fields. The field strength, $|\mathbf{B}|$, increases slower than the gas density, $n$, from the envelope to the spine of G11, characterized by $|\mathbf{B}|\propto n^{0.3}$. The observed strength and orientation of magnetic fields in G11 imply that supersonic and sub-Alfv{é}nic gas flow is channelled by the strong magnetic fields and is assembled into filaments perpendicular to the magnetic fields. The formation of low-mass stars is enhanced in the filaments with high column density, in agreement with the excess of low-mass protostars detected in the densest regions of G11.

astro-ph.GA↗

arXiv2023

A Semi-supervised Sensing Rate Learning based CMAB Scheme to Combat COVID-19 by Trustful Data Collection in the Crowd

The recruitment of trustworthy and high-quality workers is an important research issue for MCS. Previous studies either assume that the qualities of workers are known in advance, or assume that the platform knows the qualities of workers once it receives their collected data. In reality, to reduce costs and thus maximize revenue, many strategic workers do not perform their sensing tasks honestly and report fake data to the platform, which is called False data attacks. And it is very hard for the platform to evaluate the authenticity of the received data. In this paper, an incentive mechanism named Semi-supervision based Combinatorial Multi-Armed Bandit reverse Auction (SCMABA) is proposed to solve the recruitment problem of multiple unknown and strategic workers in MCS. First, we model the worker recruitment as a multi-armed bandit reverse auction problem and design an UCB-based algorithm to separate the exploration and exploitation, regarding the Sensing Rates (SRs) of recruited workers as the gain of the bandit. Next, a Semi-supervised Sensing Rate Learning (SSRL) approach is proposed to quickly and accurately obtain the workers' SRs, which consists of two phases, supervision and self-supervision. Last, SCMABA is designed organically combining the SRs acquisition mechanism with multi-armed bandit reverse auction, where supervised SR learning is used in the exploration, and the self-supervised one is used in the exploitation. We theoretically prove that our SCMABA achieves truthfulness and individual rationality and exhibits outstanding performances of the SCMABA mechanism through in-depth simulations of real-world data traces.

cs.HC↗