arXiv subjects

Lu Feng

Publications and source records attributed to Lu Feng.

89 records · Page 5Linked to original sources

arXiv2020

Site testing campaign for the Large Optical/infrared Telescope of China: Overview

The Large Optical/infrared Telescope (LOT) is a ground-based 12m diameter optical/infrared telescope which is proposed to be built in the western part of China in the next decade. Based on satellite remote sensing data, along with geographical, logistical and political considerations, three candidate sites were chosen for ground-based astronomical performance monitoring. These sites include: Ali in Tibet, Daocheng in Sichuan, and Muztagh Ata in Xinjiang. Up until now, all three sites have continuously collected data for two years. In this paper, we will introduce this site testing campaign, and present its monitoring results obtained during the period between March 2017 and March 2019.

astro-ph.IM↗

arXiv2019

A Case Study of Trust on Autonomous Driving

As autonomous vehicles have benefited the society, understanding the dynamic change of humans' trust during human-autonomous vehicle interaction can help to improve the safety and performance of autonomous driving. We designed and conducted a human subjects study involving 19 participants. Each participant was asked to enter their trust level in a Likert scale in real-time during experiments on a driving simulator. We also collected physiological data (e.g., heart rate, pupil size) of participants as complementary indicators of trust. We used analysis of variance (ANOVA) and Signal Temporal Logic (STL) to analyze the experimental data. Our results show the influence of different factors (e.g., automation alarms, weather conditions) on trust, and the individual variability in human reaction time and trust change.

cs.HC↗

arXiv2019

Models of vacuum energy interacting with cold dark matter: Constraints and comparison

In this paper, we investigate the observational constraints on the scenario of vacuum energy interacting with cold dark matter. We consider eight typical interaction forms in such an interacting vacuum energy scenario. The observational data used in this work to constrain these models include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors data of cosmic microwave background anisotropies observation, the baryon acoustic oscillations data, and the Hubble constant direct measurement. We find that the current observational data almost equally favor these interacting vacuum energy models. We also find that for all these models of vacuum energy interacting with cold dark matter the case of no interaction is actually well consistent with the current observational data within 1$σ$ range.

astro-ph.CO↗

arXiv2019

A Logic-Based Learning Approach to Explore Diabetes Patient Behaviors

Type I Diabetes (T1D) is a chronic disease in which the body's ability to synthesize insulin is destroyed. It can be difficult for patients to manage their T1D, as they must control a variety of behavioral factors that affect glycemic control outcomes. In this paper, we explore T1D patient behaviors using a Signal Temporal Logic (STL) based learning approach. STL formulas learned from real patient data characterize behavior patterns that may result in varying glycemic control. Such logical characterizations can provide feedback to clinicians and their patients about behavioral changes that patients may implement to improve T1D control. We present both individual- and population-level behavior patterns learned from a clinical dataset of 21 T1D patients.

cs.LO↗

arXiv2019

Exploring neutrino mass and mass hierarchy in interacting dark energy models

We investigate how the dark energy properties impact the constraints on the total neutrino mass in interacting dark energy (IDE) models. In this study, we focus on two typical interacting dynamical dark energy models, i.e., the interacting $w$ cold dark matter (I$w$CDM) model and the interacting holographic dark energy (IHDE) model. To avoid the large-scale instability problem in IDE models, we apply the parameterized post-Friedmann approach to calculate the perturbation of dark energy. We employ the Planck 2015 cosmic microwave background temperature and polarization data, combined with low-redshift measurements on baryon acoustic oscillation distance scales, type Ia supernovae, and the Hubble constant, to constrain the cosmological parameters. We find that the dark energy properties could influence the constraint limits on the total neutrino mass. Once dynamical dark energy is considered in the IDE models, the upper bounds of $\sum m_ν$ will be changed. By considering the values of $χ^2_{\rm min}$, we find that in these IDE models the normal hierarchy case is slightly preferred over the inverted hierarchy case; for example, $Δχ^2=2.720$ is given in the IHDE+$\sum m_ν$ model. In addition, we also find that in the I$w$CDM+$\sum m_ν$ model $β=0$ is consistent with current observational data inside the 1$σ$ range, and in the IHDE+$\sum m_ν$ model $β>0$ is favored at more than 2$σ$ level.

astro-ph.CO↗

arXiv2018

Search for sterile neutrinos in a universe of vacuum energy interacting with cold dark matter

We investigate the cosmological constraints on sterile neutrinos in a universe in which vacuum energy interacts with cold dark matter by using latest observational data. We focus on two specific interaction models, $Q=βHρ_{\rm v}$ and $Q=βHρ_{\rm c}$. To overcome the problem of large-scale instability in the interacting dark energy scenario, we employ the parametrized post-Friedmann (PPF) approach for interacting dark energy to do the calculation of perturbation evolution. The observational data sets used in this work include the Planck 2015 temperature and polarization data, the baryon acoustic oscillation measurements, the type-Ia supernova data, the Hubble constant direct measurement, the galaxy weak lensing data, the redshift space distortion data, and the Planck lensing data. Using the all-data combination, we obtain $N_{\rm eff}<3.522$ and $m_{ν,{\rm sterile}}^{\rm eff}<0.576$ eV for the $Q=βHρ_{\rm v}$ model, and $N_{\rm eff}=3.204^{+0.049}_{-0.135}$ and $m_{ν,{\rm sterile}}^{\rm eff}=0.410^{+0.150}_{-0.330}$ eV for the $Q=βHρ_{\rm c}$ model. The latter indicates $ΔN_{\rm eff}>0$ at the 1.17$σ$ level and a nonzero mass of sterile neutrino at the 1.24$σ$ level. In addition, for the $Q=βHρ_{\rm v}$ model, we find that $β=0$ is consistent with the current data, and for the $Q=βHρ_{\rm c}$ model, we find that $β>0$ is obtained at more than 1$σ$ level.

astro-ph.CO↗

arXiv2018

Exploring interacting holographic dark energy in a perturbed universe with parameterized post-Friedmann approach

The model of holographic dark energy in which dark energy interacts with dark matter is investigated in this paper. In particular, we consider the interacting holographic dark energy model in the context of a perturbed universe, which was never investigated in the literature. To avoid the large-scale instability problem in the interacting dark energy cosmology, we employ the generalized version of the parameterized post-Friedmann approach to treat the dark energy perturbations in the model. We use the current observational data to constrain the model. Since the cosmological perturbations are considered in the model, we can then employ the redshift-space distortions (RSD) measurements to constrain the model, in addition to the use of the measurements of expansion history, which was either never done in the literature. We find that, for both the cases with $Q=βHρ_{\rm c}$ and $Q=βH_0ρ_{\rm c}$, the interacting holographic dark energy model is more favored by the current data, compared to the holographic dark energy model without interaction. It is also found that, with the help of the RSD data, a positive coupling $β$ can be detected at the $2.95σ$ statistical significance for the case of $Q=βH_0ρ_{\rm c}$.

astro-ph.CO↗

arXiv2018

The Effect of Whole-Body Haptic Feedback on Driver's Perception in Negotiating a Curve

It remains uncertain regarding the safety of driving in autonomous vehicles that, after a long, passive control and inattention to the driving situation, how the drivers will be effectively informed to take-over the control in emergency. In particular, the active role of vehicle force feedback on the driver's risk perception on curves has not been fully explored. To investigate it, the current paper examined the driver's cognitive and visual responses to the whole-body haptic feedback during curve negotiations. The effects of force feedback on drivers' responses on curves were investigated in a high-fidelity driving simulator while measuring EEG and visual gaze over ten participants. The preliminary analyses of the first two participants revealed that pupil diameter and fixation time on the curves were significantly longer when the driver received whole-body feedback, compared to none. The findings suggest that whole-body feedback can be used as an effective "advance notification" of hazards.

cs.HC↗

arXiv2018

Counterexamples for Robotic Planning Explained in Structured Language

Automated techniques such as model checking have been used to verify models of robotic mission plans based on Markov decision processes (MDPs) and generate counterexamples that may help diagnose requirement violations. However, such artifacts may be too complex for humans to understand, because existing representations of counterexamples typically include a large number of paths or a complex automaton. To help improve the interpretability of counterexamples, we define a notion of explainable counterexample, which includes a set of structured natural language sentences to describe the robotic behavior that lead to a requirement violation in an MDP model of robotic mission plan. We propose an approach based on mixed-integer linear programming for generating explainable counterexamples that are minimal, sound and complete. We demonstrate the usefulness of the proposed approach via a case study of warehouse robots planning.

cs.RO↗

arXiv2018

Searching for sterile neutrinos in dynamical dark energy cosmologies

We investigate how the dark energy properties change the cosmological limits on sterile neutrino parameters by using recent cosmological observations. We consider the simplest dynamical dark energy models, the $w$CDM model and the holographic dark energy (HDE) model, to make an analysis. The cosmological observations used in this work include the Planck 2015 CMB temperature and polarization data, the baryon acoustic oscillation data, the type Ia supernova data, the Hubble constant direct measurement data, and the Planck CMB lensing data. We find that, $m_{ν,{\rm{sterile}}}^{\rm{eff}}<0.2675$ eV and $N_{\rm eff}<3.5718$ for $Λ$CDM cosmology, $m_{ν,{\rm{sterile}}}^{\rm{eff}}<0.5313$ eV and $N_{\rm eff}<3.5008$ for $w$CDM cosmology, and $m_{ν,{\rm{sterile}}}^{\rm{eff}}<0.1989$ eV and $N_{\rm eff}<3.6701$ for HDE cosmology, from the constraints of the combination of these data. Thus, without the addition of measurements of growth of structure, only upper limits on both $m_{ν,{\rm{sterile}}}^{\rm{eff}}$ and $N_{\rm eff}$ can be derived, indicating that no evidence of the existence of a sterile neutrino species with eV-scale mass is found in this analysis. Moreover, compared to the $Λ$CDM model, in the $w$CDM model the limit on $m_{ν,{\rm{sterile}}}^{\rm{eff}}$ becomes much looser, but in the HDE model the limit becomes much tighter. Therefore, the dark energy properties could significantly influence the constraint limits of sterile neutrino parameters.

astro-ph.CO↗

arXiv2017

Reexploration of interacting holographic dark energy model: Cases of interaction term excluding the Hubble parameter

In this paper, we make a deep analysis for the five typical interacting holographic dark energy models with the interaction terms $Q=3βH_{0}ρ_{\rm{de}}$, $Q=3βH_{0}ρ_{\rm{c}}$, $Q=3βH_{0}(ρ_{\rm{de}}+ρ_{\rm c})$, $Q=3βH_{0}\sqrt{ρ_{\rm{de}}ρ_{\rm c}}$, and $Q=3βH_{0}\frac{ρ_{\rm{de}}ρ_{c}}{ρ_{\rm{de}}+ρ_{\rm c}}$, respectively. We obtain observational constraints on these models by using the type Ia supernova data (the Joint Light-curve Analysis sample), the cosmic microwave background data (Planck 2015 distance priors), the baryon acoustic oscillations data, and the direct measurement of the Hubble constant. We find that the values of $χ_{\rm min}^2$ for all the five models are almost equal (around~699), indicating that the current observational data equally favor these IHDE models. In addition, a comparison with the cases of interaction term involving the Hubble parameter $H$ is also made.

astro-ph.CO↗

arXiv2017

A search for sterile neutrinos with the latest cosmological observations

We report the result of a search for sterile neutrinos with the latest cosmological observations. Both cases of massless and massive sterile neutrinos are considered in the $Λ$CDM cosmology. The cosmological observations used in this work include the Planck 2015 temperature and polarization data, the baryon acoustic oscillation data, the Hubble constant direct measurement data, the Planck Sunyaev-Zeldovich cluster counts data, the Planck lensing data, and the cosmic shear data. We find that the current observational data give a hint of the existence of massless sterile neutrino (as dark radiation) at the 1.44$σ$ level, and the consideration of an extra massless sterile neutrino can indeed relieve the tension between observations and improve the cosmological fit. For the case of massive sterile neutrino, the observations give a rather tight upper limit on the mass, which implies that actually a massless sterile neutrino is more favored. Our result is consistent with the recent result of neutrino oscillation experiment done by the Daya Bay and MINOS collaborations, as well as the recent result of cosmic ray experiment done by the IceCube collaboration.

astro-ph.CO↗

arXiv2016

Revisit of the interacting holographic dark energy model after Planck 2015

We investigate the observational constraints on the interacting holographic dark energy model. We consider five typical interacting models with the interaction terms $Q=3βHρ_{\rm{de}}$, $Q=3βHρ_{\rm{c}}$, $Q=3βH(ρ_{\rm{de}}+ρ_{\rm c})$, $Q=3βH\sqrt{ρ_{\rm{de}}ρ_{\rm c}}$, and $Q=3βH\frac{ρ_{\rm{de}}ρ_{c}}{ρ_{\rm{de}}+ρ_{\rm c}}$, respectively, where $β$ is a dimensionless coupling constant. The observational data we use in this paper include the JLA compilation of type Ia supernovae data, the Planck 2015 distance priors data of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the Hubble constant direct measurement. We make a comparison for these five interacting holographic dark energy models by employing the information criteria, and we find that, within the framework of holographic dark energy, the $Q=3βH\frac{ρ_{\rm{de}}ρ_{\rm c}}{ρ_{\rm{ de}}+ρ_{\rm c}}$ model is most favored by current data, and the $Q=3βHρ_{\rm c}$ model is relatively not favored by current data. For the $Q=3βHρ_{\rm{de}}$ and $Q=3βH\frac{ρ_{\rm{de}}ρ_{\rm c}}{ρ_{\rm{ de}}+ρ_{\rm c}}$ models, a positive coupling $β$ can be detected at more than 2$σ$ significance.

astro-ph.CO↗

arXiv2016

A new angle for probing field-aligned irregularities with the Murchison Widefield Array

Electron density irregularities in the ionosphere are known to be magnetically anisotropic, preferentially elongated along the lines of force. While many studies of their morphology have been undertaken by topside sounding and whistler measurements, it is only recently that detailed regional-scale reconstructions have become possible, enabled by the advent of widefield radio telescopes. Here we present a new approach for visualising and studying field-aligned irregularities (FAIs), which involves transforming interferometric measurements of TEC gradients onto a magnetic shell tangent plane. This removes the perspective distortion associated with the oblique viewing angle of the irregularities from the ground, facilitating the decomposition of dynamics along and across magnetic field lines. We apply this transformation to the dataset of Loi et al. [2015a], obtained on 15 October 2013 by the Murchison Widefield Array (MWA) radio telescope and displaying prominent FAIs. We study these FAIs in the new reference frame, quantifying field-aligned and field-transverse behaviour, examining time and altitude dependencies, and extending the analysis to FAIs on sub-array scales. We show that the inclination of the plane can be derived solely from the data, and verify that the best-fit value is consistent with the known magnetic inclination. The ability of the model to concentrate the fluctuations along a single spatial direction may find practical application to future calibration strategies for widefield interferometry, by providing a compact representation of FAI-induced distortions.

physics.space-ph↗

arXiv2015

Real-time imaging of density ducts between the plasmasphere and ionosphere

Ionization of the Earth's atmosphere by sunlight forms a complex, multi-layered plasma environment within the Earth's magnetosphere, the innermost layers being the ionosphere and plasmasphere. The plasmasphere is believed to be embedded with cylindrical density structures (ducts) aligned along the Earth's magnetic field, but direct evidence for these remains scarce. Here we report the first direct wide-angle observation of an extensive array of field-aligned ducts bridging the upper ionosphere and inner plasmasphere, using a novel ground-based imaging technique. We establish their heights and motions by feature-tracking and parallax analysis. The structures are strikingly organized, appearing as regularly-spaced, alternating tubes of overdensities and underdensities strongly aligned with the Earth's magnetic field. These findings represent the first direct visual evidence for the existence of such structures.

physics.space-ph↗

arXiv2014

The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14,110 Compact Radio Sources over 6,100 Square Degrees

We present the results of an approximately 6,100 square degree 104--196MHz radio sky survey performed with the Murchison Widefield Array during instrument commissioning between 2012 September and 2012 December: the Murchison Widefield Array Commissioning Survey (MWACS). The data were taken as meridian drift scans with two different 32-antenna sub-arrays that were available during the commissioning period. The survey covers approximately 20.5 h < Right Ascension (RA) < 8.5 h, -58 deg < Declination (Dec) < -14 deg over three frequency bands centred on 119, 150 and 180 MHz, with image resolutions of 6--3 arcmin. The catalogue has 3-arcmin angular resolution and a typical noise level of 40 mJy/beam, with reduced sensitivity near the field boundaries and bright sources. We describe the data reduction strategy, based upon mosaiced snapshots, flux density calibration and source-finding method. We present a catalogue of flux density and spectral index measurements for 14,110 sources, extracted from the mosaic, 1,247 of which are sub-components of complexes of sources.

astro-ph.IM↗

arXiv2010

Could the GRB-Supernovae GRB 031203 and XRF 060218 be Cosmic Twins?

The gamma-ray burst (GRB) / X-ray flash (XRF) events GRB 031203, discovered by INTEGRAL, and XRF 060218, discovered by Swift, represent two of only five GRB-SNe with optical spectroscopic confirmation of their SN components. Yet their observed high-energy properties offer a sharp contrast: While GRB 031203 was detected as a short 40-s burst with a spectrum peaking at E_peak > 190 keV, XRF 060218 was a T_90 ~ 2100-s long, smoothly-evolving burst with peak energy E_peak = 4.9 keV. At the same time, the properties of the two expanding dust-scattered X-ray halos observed in a fast-response XMM-Newton observation of GRB 031203 reveal that this event was accompanied by an "X-ray blast" with fluence comparable to or greater than that of the prompt gamma-ray event. Taking this observation as our starting point, we investigate the likely properties of the X-ray blast from GRB 031203 via detailed modeling of the XMM data, discovering a third halo due to scattering off a more distant dust sheet at d_3 = 9.94 +/- 0.39 kpc, and constraining the timing of the X-ray blast relative to the GRB trigger time to be t_0 = 11 +/- 417 s. Using our constraints, we compare the properties of GRB 031203 to those of other GRB-SNe in order to understand the likely nature of its X-ray blast, concluding that a bright X-ray flare, as in GRB 050502B, or shock breakout event, as in XRF 060218, provide the most likely explanations. In the latter case, we consider the added possibility that XRF 060218 may have manifested an episode of bright gamma-ray emission prior to the burst observed by Swift, in which case GRB 031203 and XRF 060218 would be "cosmic twin" explosions with nearly identical high-energy properties.

astro-ph.HE↗