Driving comfort significantly affects travel experiences. However, the most prevailing automated vehicle (AV) control strategies mainly focus on the safety and efficiency concerns, neglecting the ...comfort perspective. Moreover, pavement conditions, such as roughness and distress, cannot be directly detected by standard AV onboard sensors, although they are essential factors impacting driving comfort. This study aimed to present a vehicle-to-infrastructure system to adjust AV trajectories for alleviating the negative impacts of bumpy roads on comfort. The precollected lane-based roadway roughness information was used to optimally adjust the longitudinal and lateral AV trajectories. The method was validated by an eight-degree-of-freedom full-car simulation model. Specifically, the relationships among comfort, jerk, speed, and pavement parameters were revealed and applied to the adjustment process. The results showed that the trajectory adjustment approach improved the overall comfort level by 30 % in the numerical case. Furthermore, a framework was designed to facilitate data exchanges between vehicles and infrastructures in empirical scenarios. The proposed method had the potential to assist AVs in better-perceived driving quality.
A representative volume element method and a novel mesomechanical-based polyline model are proposed to describe the misalignment of in-plane fibers induced by the insertion of stitch thread. A ...multi-scale mathematical model of in-plane elastic parameters for stitched composite laminate is established with ply-angle and stitch parameters as well as material parameters taken into account. Based on the fabrication of specimens and the verification of experimental platform, the superposition influences of stitch on structural anisotropy are revealed by the developed theoretical model. Results indicate that the stitch orientation can increase the structural anisotropy. The decreases of stitch pitch and spacing as well as the increase of thread diameter obviously reduce the elastic and shear moduli of laminates. Furthermore, the elastic and shear moduli as well as Poisson’s ratios show sinusoidal changes with a period of 90° as the ply-angle increases. The theoretical model not only analyzes the in-plane mechanical properties of stitched laminate with ply-angle, but also lays a foundation for the dynamic studies of stitched sandwich structures with ribs in the future.
Seating capacity of a limited area significantly affects passenger crowding on a 12 m city bus, which is the main type of buses for public transport in China. This study aimed to provide an optimal ...solution for the seating capacity to adapt the passenger flow during operational periods. The study claimed that the seating capacity was defined by an overall crowding effect considering both the standees and seated passengers, whose demands for seat supply are different. It investigated the projected area of the seated passengers on board, defined the criteria regarding whether the current trip was a peak shift, and proposed a passenger crowding index for optimizing the seating capacity during two operational periods. It not only provided a recommended table between actual seating capacity and intensity coefficient varying along the two periods, but also discussed the number of 12 m buses with different seating capacities allocated to the bus line. It demonstrated the feasibility of the passenger crowding index through a case study and compared the effects of three main seat configurations existing on the 12 m city bus. It displayed that a seat capacity preferably ranged from 21 to 43 while only one seat configuration was allowed by the public transport enterprises.
In this paper, a fixed-time sliding mode control scheme is developed to fulfill the trajectory tracking task of a marine surface vehicle with unknown dynamics. To restrain the adverse effects of the ...unknown dynamics including the parameter inaccuracy and exogenous disturbances, a fixed-time disturbance observer is designed to estimate the lumped uncertainties using the bi-limit homogeneous theory without requiring any knowledge of the model uncertainties. Then, a nominal tracking controller is proposed to stabilize the error dynamic model in the sense of fixed-time Lyapunov stability, based on which a novel integral-type sliding mode manifold with bi-limit homogeneity is constructed to drive tracking error convergence in fixed time. To enhance the robustness of the vessel control system, a disturbance observer–based fixed-time integral sliding mode tracking controller is finally proposed, and the chattering phenomenon is effectively alleviated by direct estimation compensations. The analysis of Lyapunov stability indicates that the closed-loop system is fixed-time stable. Numerical simulations on a model vessel are carried out to validate theoretical results of the proposed control scheme.
We study a sample of 16 Type Ia supernovae (SNe Ia) having both spectroscopic and photometric observations within 2-3 days after the first light. The early B − V colors of such a sample tend to show ...a continuous distribution. For objects with normal ejecta velocity (NV), the C ii λ6580 feature is always visible in the early spectra, while it is absent or very weak in the high-velocity (HV) counterpart. Moreover, the velocities of the detached high-velocity features (HVFs) of the Ca II near-IR triplet (CaIR3) above the photosphere are found to be much higher in HV objects than in NV objects, with typical values exceeding 30,000 km s−1 at 2-3 days. We further analyze the relation between the velocity shift of late-time Fe II lines (vFe II) and host galaxy mass. We find that all HV objects have redshifted vFe II, while NV objects have both blue- and redshifted vFe II. It is interesting to point out that the objects with redshifted vFe II are all located in massive galaxies, implying that HV and a portion of NV objects may have similar progenitor metallicities and explosion mechanisms. We propose that, with a geometric/projected effect, the He-detonation model may account for the similarity in birthplace environment and the differences seen in some SNe Ia, including B − V colors, C II features, CaIR3 HVFs at early times, and vFe II in the nebular phase. Nevertheless, some features predicted by He-detonation simulation, such as the rapidly decreasing light curve, deviate from the observations, and some NV objects with blueshifted nebular vFe II may involve other explosion mechanisms.
Abstract
In this paper, we present photometric and spectroscopic observations of the subluminous Type Ia supernova (SN Ia) 2012ij, which has an absolute
B
-band peak magnitude
M
B
,
max
=
−
17.95
±
...0.15
mag. The
B
-band light curve exhibits a fast postpeak decline with Δ
m
15
(
B
) = 1.86 ± 0.05 mag. All the
R
- and
I
/
i
-band light curves show a weak secondary peak/shoulder feature at about 3 weeks after the peak, like some transitional subclass of SNe Ia, which could result from an incomplete merger of near-infrared (NIR) double peaks. The spectra are characterized by Ti
ii
and strong Si
ii
λ
5972 absorption features that are usually seen in low-luminosity objects like SN 1999by. The NIR spectrum before maximum light reveals weak carbon absorption features, implying the existence of unburned materials. We compare the observed properties of SN 2012ij with those predicted by the sub-Chandrasekhar-mass and the Chandrasekhar-mass delayed-detonation models and find that both optical and NIR spectral properties can be explained to some extent by these two models. By comparing the secondary maximum features in the
I
and
i
bands, we suggest that SN 2012ij is a transitional object linking normal SNe Ia to typical 91bg-like ones. From the published sample of SNe Ia from the Carnegie Supernova Project II, we estimate that the fraction of SN 2012ij–like SNe Ia is not lower than ∼2%.
This paper proposes a novel decoupled approach of a regenerative braking system for an electric city bus, aiming at improving the utilization of the kinetic energy for rear axle during a braking ...process. Three contributions are added to distinguish from the previous research. Firstly, an energy-flow model of the electric bus is established to identify the characteristic parameters which affect the energy-saving efficiency of the vehicle, while the key parameters (e.g., driving cycles and the recovery rate of braking energy) are also analyzed. Secondly, a decoupled braking energy recovery scheme together with the control strategy is developed based on the characteristics of the power assistance for electric city bus which equips an air braking system, as well as the regulatory requirements of ECE R13. At last, the energy consumption of the electric city bus is analyzed by both the simulation and vehicle tests, when the superimposed and the decoupled regenerative braking system are, respectively, employed for the vehicle. The simulation and actual road test results show that compared with the superposition braking system of the basic vehicle, the decoupled braking energy recovery system after the reform can improve the braking energy recovery rate and vehicle energy-saving degree. The decoupled energy recovery system scheme and control strategy proposed in this paper can be adopted by bus factories to reduce the energy consumption of pure-electric buses.
Passenger crowding in a city bus is uneven and the most crowded area always appears in the wheelbase of the carriage. The present study aimed to provide a sensitive indicator of the most crowded area ...to schedule bus headways online using a binocular camera sensor. The algorithm of standee density in the wheelbase area (SDWA) was given by a nonlinear regression model considering standees’ preferences for the standing area, and its goodness of fit and continuity were tested. Considering the characteristics of city bus operation, the proportion of the number of interstops determined from the SDWA was used as a judgment index for passenger crowding. Based on the SDWA algorithm and the judgment index, an online headway model of city buses was proposed, and the feasibility of such a model was verified through a case study in Xi’an city. The proposed model might be beneficial to bus scheduling, seating provision, and bus design.
Abstract
ASASSN-14ms may represent the most luminous Type Ibn supernova (SN Ibn) ever detected, with an absolute
U
-band magnitude brighter than −22.0 mag and a total bolometric luminosity >1.0 × 10
...44
erg s
−1
near maximum light. The early-time spectra of this SN are characterized by a blue continuum on which are superimposed narrow P Cygni profile lines of He
i
, suggesting the presence of slowly moving (∼1000 km s
−1
), He-rich circumstellar material (CSM). At 1–2 months after maximum brightness, the He
i
line profiles become only slightly broader, with blueshifted velocities of 2000–3000 km s
−1
, consistent with the CSM shell being continuously accelerated by the SN light and ejecta. Like most SNe Ibn, the light curves of ASASSN-14ms show rapid post-peak evolution, dropping by ∼7 mag in the
V
band over three months. Such a rapid post-peak decline and high luminosity can be explained by interaction between SN ejecta and helium-rich CSM of 0.9
M
⊙
at a distance of ∼10
15
cm. The CSM around ASASSN-14ms is estimated to originate from a pre-explosion event with a mass-loss rate of 6.7
M
⊙
yr
−1
(assuming a velocity of ∼1000 km s
−1
), which is consistent with abundant He-rich material violently ejected during the late Wolf–Rayet (WN9-11 or Opfe) stage. After examining the light curves for a sample of SNe Ibn, we find that the more luminous ones tend to have slower post-peak decline rates, reflecting that the observed differences may arise primarily from discrepancies in the CSM distribution around the massive progenitors.
Abstract We present optical observations and analysis of the bright type Iax supernova SN 2020udy hosted by NGC 0812. The evolution of the light curve of SN 2020udy is similar to that of other bright ...type Iax SNe. Analytical modeling of the quasi-bolometric light curves of SN 2020udy suggests that 0.08 ± 0.01 M ⊙ of 56 Ni would have been synthesized during the explosion. The spectral features of SN 2020udy are similar to those of the bright members of type Iax class, showing a weak Si ii line. The late-time spectral sequence is mostly dominated by iron group elements with broad emission lines. Abundance tomography modeling of the spectral time series of SN 2020udy using TARDIS indicates stratification in the outer ejecta; however, to confirm this, spectral modeling at a very early phase is required. After maximum light, uniform mixing of chemical elements is sufficient to explain the spectral evolution. Unlike in the case of normal type Ia SNe, the photospheric approximation remains robust until +100 days, requiring an additional continuum source. Overall, the observational features of SN 2020udy are consistent with the deflagration of a carbon–oxygen white dwarf.
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