Rise Phase Research Articles

Investigation into the transient flow characteristics of noble gas propellants using the pulsed inductive discharge in electric propulsion

The Pulsed Inductive Thruster (PIT) has the advantages of repeatable startup, no corruption and in-situ propellant feed. To study the flow expansion and circuit characteristics of PITs, the circuit-fluid model is developed, and the high temperature thermodynamic and transport models are combined with the circuit-fluid model to predict the critical plasma parameters. The flow fields of initial mass of 2–8 mg and charge voltages of 10–14 kV are simulated. Comparison of the flow fields of argon and helium propellants suggests that, the flow field structures are similar. Slight differences exist on the magnitude of the density and magnetic field, caused by larger velocity in lighter atom case and difference on the ionization gap between adjacent ionization levels. Analysis of the circuit characteristics by the two-dimensional results indicates that the ratio of coil inductance to circuit inductance affects both the rise rate and phase of the plasma current, the larger the ratio, the greater the rise rate and the better the following characteristic. The calculations show that the magnetic energy obtained within the decoupling distance determines the overall performance the thruster can be obtained; self-induced field maintained by the thermal motion after the main pulse leads to the long attenuation process and difference on the total impulse when the angle of conical pylon is varied under constant coil dimension.

Forecast of Major Solar X-Ray Flare Flux Profiles Using Novel Deep Learning Models

Abstract In this Letter, we present the application of a couple of novel deep learning models to the forecast of major solar X-ray flare flux profiles. These models are based on a sequence-to-sequence framework using long short-term memory cell and an attention mechanism. For this, we use Geostationary Operational Environmental Satellite 10 X-ray flux data from 1998 August to 2006 April. Seven hundred sixty events are used for training and 85 for testing. The models forecast 30 minutes of X-ray flux profiles during the rise phase of the solar flare with a minute time cadence. We evaluate the models using the 10-fold cross-validation and rms error (RMSE) based on flux profiles and RMSE based on its peak flux. For comparison we consider two simple deep learning models and four conventional regression models. Major results of this study are as follows. First, we successfully apply our deep learning models to the forecast of solar flare X-ray flux profiles, without any preprocessing to extract features from data. Second, our proposed models outperform the other models. Third, our models achieve better performance for forecasting X-ray flux profiles with low-peak fluxes than those with high-peak fluxes. Fourth, our models successfully predict flare duration with high correlations for both all cases and cases at peak times. Our study indicates that our deep learning models can be useful for forecasting time-series data in astronomy and space weather, even for impulsive events such as major flares.

Numerical simulation of the inhibition process of methane-air explosion under cold aerosol

In order to study the methane-air explosion suppression problem, a certain size experimental tube was used as the physical model, and Gambit was used for modelling. The ANSYS 15.0 software was used to simulate the methane-air explosion suppression process under the action of cold aerosol, and the simulation results were compared with the results of the experimental studies in the open literature. It can be seen from the numerical simulation results that the concentration of cold aerosol had a significant effect on the methane-air explosion process. When the concentration of cold aerosol was low, the methane-air would explode. The pressure-time curve in the experimental tube showed four stages: the explosion induction period, the pressure rise phase, the explosion pressure peak value phase and the explosion pressure decay phase. With the increase of the aerosol concentration, the explosion induction period was significantly prolonged, and the maximum explosion pressure was slightly decreased, and the time to reach the maximum explosion pressure was also significantly prolonged. When the cold aerosol concentration reached a certain threshold, the methane-air no longer exploded. Compared with the experimental results, the simulated values of the explosion induction period, the maximum explosion pressure value, the maximum explosion pressure time and the final pressure value under different cold aerosol concentrations matched well with the experimental measurements. Therefore, numerical simulation can provide a reference for the study of methane-air explosion suppression performance under cold aerosol.

Overexpression of Na+-HCO3– cotransporter contributes to the exacerbation of cardiac remodeling in mice with myocardial infarction by increasing intracellular calcium overload

The role of the cardiac isoform of the electrogenic sodium-bicarbonate ion cotransporter (NBCe1) in cardiac remodeling is not fully understood. The aim of this study was to assess the effects of NBCe1 overexpression on cardiac remodeling induced by myocardial infarction (MI) in mice. We generated NBCe1 transgenic (Tg) mice and NBCe1 overexpressing adult mouse ventricular myocytes (AMVMs) to investigate the role of NBCe1 on post-MI remodeling and calcium kinetics. Tg mice showed a markedly higher mortality rate and larger infarct size after MI. At 6 weeks after MI, the maximum rising rates of left ventricular pressure (dp/dt), contractility index, and the exponential time constant of relaxation (τ) were markedly lower, and there was higher cardiomyocyte apoptosis, in Tg mice compared with WT mice. In cultured AMVMs, overexpression of NBCe1 decreased sarcomere shortening and calcium amplitude. In WT AMVMs, the rates of the rise and decay phase of calcium transients, indicated by the rising time (Tpeak, time to peak) and decay time constant (τd), and the number of apoptotic cells, were increased following hypoxia, while overexpression of NBCe1 further increased Tpeak and cellular apoptosis, but not τd. Intracellular resting calcium and sodium concentrations were significantly increased following both hypoxia and NBCe1 overexpression. Co-treatment with S0859, an NBCe1 antagonist, blocked the hypoxia-induced increase in Tpeak, τd, intracellular resting calcium and sodium concentrations, and apoptosis in cardiomyocytes. These findings indicate that NBCe1 overexpression promotes cardiac remodeling by increasing intracellular calcium overload. Therefore, NBCe1 should be a potential target for treatment of cardiac remodeling.

Statistical analysis of interplanetary coronal mass ejections and their geoeffectiveness during the solar cycles 23 and 24

Interplanetary coronal mass ejections (ICMEs) are believed to be the most common and important drivers of the strongest geomagnetic storms. In this work, the geoeffective characteristics of the ICMEs occurred during the last solar cycles 23 and 24 (years 1996–2017) have been studied in detail. The maximum velocity $V$max, either of the ICME’s Sheath region or of the ICME itself, the mean velocity of the ICME, the minimum value of the southward component of the Interplanetary magnetic field Bs and the $y$-component of the solar wind convective electric field $E= -V \times B$ observed at L1 point during the pass of the ICME, were used. It was found that, in accordance to past similar studies, the most dominant characteristic of ICMEs in the generation of geomagnetic storms is the Bs component along with the Ey parameter, while the maximum velocity seems to be of less importance. Nevertheless the maximum speed is an good forecasting factor due to the fact that it is much easier to estimate the velocity of an ICME-structure many hours before it arrives at Earth compared with the observations of Bs and Ey that can only be done, for the time being, at the L1 point. That means we can use the velocity of ICME-structure to forecast the possible generation and magnitude of the geomagnetic storms. From a comparison of the ICME-generated geomagnetic storms with the total number of geomagnetic storms generated during the last two solar cycles, it seems that approximately half of the ICMEs (49% for Dst index and 53% for Kp index) produced geomagnetic storms during the solar cycles 23 and 24. Moreover the velocities of ICMEs are more in accordance with the rising and maximum phases of solar cycles 23 and 24 than the geomagnetic activity (storms) are, as well as during the first stages of the declining phases of these cycles, especially during solar cycle 23.

A Comparison of the X-Ray Properties of FU Ori-type Stars to Generic Young Stellar Objects

Abstract Like other young stellar objects (YSOs), FU Ori-type stars have been detected as strong X-ray emitters. However, little is known about how the outbursts of these stars affect their X-ray properties. We assemble available X-ray data from XMM-Newton and Chandra observations of 16 FU Ori stars, including a new XMM-Newton observation of Gaia 17bpi during its optical rise phase. Of these stars, six were detected at least once, while 10 were non-detections, for which we calculate upper limits on intrinsic X-ray luminosity (L X) as a function of plasma temperature (kT) and column density (N H). The detected FU Ori stars tend to be more X-ray luminous than is typical for non-outbursting YSOs, based on comparison to a sample of low-mass stars in the Orion Nebula Cluster. FU Ori stars with high L X have been observed both at the onset of their outbursts and decades later. We use the Kaplan–Meier estimator to investigate whether the higher X-ray luminosities for FU Ori stars are characteristic or a result of selection effects, and we find the difference to be statistically significant (p < 0.01) even when non-detections are taken into account. The additional X-ray luminosity of FU Ori stars relative to non-outbursting YSOs cannot be explained by accretion shocks, given the high observed plasma temperatures. This suggests that, for many FU Ori stars, either (1) the outburst leads to a restructuring of the magnetosphere in a way that enhances X-ray emission, or (2) FU Ori outbursts are more likely to occur among YSOs with the highest quiescent X-ray luminosity.

Time-varying Polarized Gamma-Rays from GRB 160821A: Evidence for Ordered Magnetic Fields

Abstract GRB 160821A is the third most energetic gamma-ray burst observed by the Fermi gamma-ray space telescope. Based on the observations made by the Cadmium Zinc Telluride Imager on board AstroSat, here we report the most conclusive evidence to date of (i) high linear polarization ( detection), and (ii) variation of polarization angle with time, occurring twice during the rise and decay phase of the burst at 3.5σ and 3.1σ detections, respectively. All confidence levels are reported for two parameters of interest. These observations strongly suggest synchrotron radiation produced in magnetic field lines that are highly ordered on angular scales of 1/Γ, where Γ is the Lorentz factor of the outflow.

A physical model of the high‐frequency seismic signal generated by debris flows

AbstractWe propose a physical model for the high‐frequency (>1 Hz) spectral distribution of seismic power generated by debris flows. The modeled debris flow is assumed to have four regions where the impact rate and impulses are controlled by different mechanisms: the flow body, a coarser‐grained snout, a snout lip where particles fall from the snout on the bed, and a dilute front composed of saltating particles. We calculate the seismic power produced by this impact model in two end‐member scenarios, a thin‐flow and thick‐flow limit, which assume that the ratio of grain sizes to flow thicknesses are either near unity or much less than unity. The thin‐flow limit is more appropriate for boulder‐rich flows that are most likely to generate large seismic signals. As a flow passes a seismic station, the rise phase of the seismic amplitude is generated primarily by the snout while the decay phase is generated first by the snout and then the main flow body. The lip and saltating front generate a negligible seismic signal. When ground properties are known, seismic power depends most strongly on both particle diameter and average flow speed cubed, and also depends on length and width of the flow. The effective particle diameter for producing seismic power is substantially higher than the median grain size and close to the 73rd percentile for a realistic grain size distribution. We discuss how the model can be used to estimate effective particle diameter and average flow speed from an integrated measure of seismic power. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.

Evolution of the hard X-ray photon index in black-hole X-ray binaries: hints for accretion physics

ABSTRACT Negative and positive correlations between the X-ray photon index and the Eddington-scaled X-ray luminosity were found in the decay phase of X-ray binary outbursts and a sample of active galactic nuclei in former works. We systematically investigate the evolution of the X-ray spectral index, along with the X-ray flux and Eddington ratio, in eight outbursts of four black-hole X-ray binaries, where all selected outbursts have observational data from the Rossi X-ray Timing Explorer in both rise and decay phases. In the initial rise phase, the X-ray spectral index is anticorrelated with the flux and the X-ray spectrum quickly softens when the X-ray flux is approaching the peak value. In the decay phase, the X-ray photon index and the flux follow two different positive correlations and they become anticorrelated again when the X-ray flux is below a critical value, where the anticorrelation part follows the same trend as found in the initial rise phase. Compared with other X-ray binaries, GRO J1655−40 has an evident lower critical Eddington ratio for the anticorrelation and positive transition, which suggests that its black-hole mass and distance are not well constrained, or its intrinsic physics is different.

Different Signatures of Chromospheric Evaporation in Two Solar Flares Observed with IRIS

Abstract We present different signatures of chromospheric evaporation in two solar flares observed by the Interface Region Imaging Spectrograph (IRIS). In the B1.6 flare on 2016 December 6 (SOL2016-12-06T10:40), the transition region Si iv line and the chromospheric C ii and Mg ii lines show blueshifts with low velocities up to 20 km s−1 at the flare loop footpoints in the rise phase, indicative of a gentle chromospheric evaporation. While in the C1.6 flare on 2015 December 19 (SOL2015-12-19T10:51), the Si iv, C ii, and Mg ii lines exhibit redshifts with velocities from several to tens of km s−1 at the footpoints, which might suggest an explosive chromospheric evaporation. Explosive evaporation has been observed in many flares that were captured by IRIS; however, gentle evaporation, especially manifested as blueshifts in the cool Si iv, C ii, and Mg ii lines, has scarcely been reported. Our results bring some new insights into chromospheric evaporation in the IRIS era.

Remote examination of the seasonal succession of phytoplankton assemblages from time-varying trends

The seasonal succession of phytoplankton assemblages is important to ascertain the dynamics of an aquatic ecosystem structure, whereas its occurrence in response to hydrodynamic alterations is not clearly understood. In view of the characteristics of annual water level variation formed by the Three Gorges Dam Project (TGDP), our understanding about how these changes affect phytoplankton structure and dynamics is still very limited due to the shortage of long-term observation data. In this study, we used Huan Jing 1 charge-coupled device images over the past decade to examine the phytoplankton succession dates between cyanobacterial and green algal blooms in the backwater area of the Three Gorges Reservoir (TGR). The results indicated continuous wavelet transform-based peak analysis is an efficiency tool that can illustrate the temporal pattern of phytoplankton succession using satellite-derived chlorophyll ɑ and Cyano-Chlorophyta index thresholds. Water level, air temperature, pH and total nitrogen/total phosphorus ratio were four important factors affecting the decline and rise phase of cyanobacterial blooms in the TGR from 2008 to 2018. Given that the upstream dam operation is likely to alter ecological and environmental conditions in the backwater area, this mechanism, so-called “water-level linkage”, could alleviate the persistent period of cyanobacterial and green algal blooms. Remote sensing together with time series analysis provided a useful method to examine the seasonal succession of phytoplankton assemblages in the TGR, and these findings provided strategic insight for the water-quality management in the post-TGDP period.

Open-Loop Gate Control for Optimizing the Turn-ON Transition of SiC MOSFETs

This paper presents a novel open-loop gate control of the turn-ON transient for SiC MOSFETs in hard switching conditions. The gate control could reduce the SiC MOSFETs turn-ON gate voltage overshoot and control turn-ON $di/dt$ and $dv/dt$ independently. Because of the high turn-ON speed, SiC MOSFETs bring serious electromagnetic interference (EMI) in the half-bridge topology. A conventional gate driver decreases EMI by increasing the gate resistor, but clearly increasing the turn-ON loss. To address this tradeoff and optimize SiC MOSFETs turn-ON transition, the drain current slope and the drain–source voltage slope are controlled independently by controlling the gate–source voltage profile during the current rise phase and the gate current during the voltage falling phase. In addition, gate voltage overshoot is considered and discussed. By adding a considerably higher gate resistance during the ON-state operation stage, gate voltage overshoot is almost nonexistent while maintaining low turn-ON loss. The experimental verifications of the proposed approach are finally conducted, and the advantages of proposed driver are analyzed and discussed.

An Empirical Oil, Steam, and Produced-Water Forecasting Model for Steam-Assisted Gravity Drainage With Linear Steam-Chamber Geometry

Summary Presented here is a steam–assisted–gravity–drainage (SAGD) forecasting technique for oil and water production and steam injection based on linear steam–chamber geometry and an empirical form for the progression of the steam/oil interface with time. The oil forecast model generates full–cycle SAGD production profiles using three empirical inputs (the initial plateau oil rate qo,si, an exponent n, and the rising–phase–chamber angle θ) and volumetric parameters (well length, pay thickness, porosity, half–well spacing, and initial and residual oil saturation). Steam and produced–water forecasts are derived analytically using the resulting steam–chamber geometry and the heat required for the fluids, rock, and overburden. Peak rate is a direct input in this methodology, and as a result only volumetric and some thermodynamic parameters are required, but not fluid or transmissibility inputs, such as viscosity and permeability. This allows for direct use of commercial SAGD production data in the forecasting process. The model predictions are validated at a high level with field data from Devon Canada Corporation's Jackfish SAGD project and numerical simulation.

Mechanical Properties, Failure Mode, and Microstructure of Soil-Cement Modified with Fly Ash and Polypropylene Fiber

In order to investigate the effects of fly ash and polypropylene fiber on mechanical properties, failure mode, and microstructure of soil-cement, the unconfined compression test, splitting tension test, and scanning electron microscopy (SEM) test of soil-cement with different polypropylene fiber contents (0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight of dry soil) and fly ash contents (0%, 4%, 8%, and 12% by weight of dry soil) were carried out. The compressive and tensile strengths, deformation characteristics, failure mode, and microstructure of soil-cement modified with fly ash and polypropylene fiber were analyzed. The results show that the unconfined compressive strength and splitting tensile strength of soil-cement show a trend of increasing first and then decreasing with the increase of polypropylene fiber and fly ash content. Under the condition of 0.4% polypropylene fiber and 8% fly ash, the unconfined compressive strength and the splitting tensile strength are 4.90 MPa and 0.91 MPa, respectively, which increased by 32.79% and 51.67% as compared with the plain soil-cement, respectively. When 8% fly ash was used in the experiment, the unconfined compressive peak strain and the splitting tensile peak strain of the inclusion of 0.4% polypropylene fiber were 0.0410 and 0.0196, respectively. The corresponding peak strains were increased by 20.94% and 68.97% as compared with non-fiber-stabilized soil-cement, respectively. The stress-strain curve of fly ash soil-cement modified with polypropylene fiber can be divided into compaction phase, linear rise phase, nonlinear rise phase, and failure phase. Polypropylene fiber constrains the lateral deformation of fly ash soil-cement, which improves the peak strain and the failure mode of soil-cement.

The Energy Distribution of Nanoflares at the Minimum and Rising Phase of Solar Cycle 24

The energy distribution of weak emission events (nanoflares) in the solar corona measured for two stages of solar cycle 24, at the minimum and at the beginning of the rise in solar activity, is presented. Our study is based on data from two instruments, TESIS/CORONAS-PHOTON (for the cycle minimum; 2009) and AIA/SDO (the rising phase, 2010–2011), for which we have applied a unified event detection algorithm. The database collected by us comprises more than 105 flares. For all events we have measured the flux in the EUV spectral range and determined the thermal energy located in the range from 1023 to 1026 erg and distributed according to a power law: N(E)dE ∼ N−αdE. The index of the power-law distribution α in all of the cases studied has turned out to be more than two (α = 2.2–2.9). This means that the integrated energy of nanoflares increases when passing to weaker events. This scenario argues for the model of coronal heating by nanoflares. The index α reaches its maximum at the cycle minimum and then drops, implying a decrease in the fraction of weak events. This may be because part of the energy is redistributed in favor of large flares. The total energy of nanoflares in the range 1023–1026 erg has turned out to be lower than the energy losses of the solar corona through radiation by a factor of 30. For the coronal heating to be explained by nanoflares, their distribution with the same power-law index must extend at least to 1021 erg.

Kinematics of a balanced vane pump with circular tip vanes

This paper analyzes the kinematics of the vane-cam ring mechanism in balanced vane pumps, by considering both vanes with centered and not-centered circular tip. The motion of the vane, the position of the contact point and the evolution of the pressure angle are analytically determined in reference to a generic cam ring profile. The results of the kinematic analysis are used to obtain the constraints defining the admissibility of the vane geometry, which is described in terms of tip radius, vane thickness and tip center eccentricity. A parametric study is performed to show the capabilities of the proposed formulation and the influence of the vane design parameters on its kinematics. The analysis demonstrates that the vane kinematic motion in balanced vane pumps is mainly controlled by the tip radius and the tip center eccentricity, as long as the cam ring profile is defined. The tip radius is mainly responsible for the shape of the vane motion, while the tip center eccentricity has a major influence on its timing. Furthermore the effect of the cam ring profile is evaluated by demonstrating that shape and extension of the rise and fall phases influence on the vane geometry admissibility.

Flooding effects on abundance of an exploited, long-lived fish population in river-floodplains of the Amazon

Flooding regulates the amount and quality of habitat available for fish populations in river-floodplains. Although previous studies assessed fish population responses to river hydrology, the processes by which flooding affects fish abundance and catch remain unclear. Here, we investigated whether degree of flooding affects abundance and catch of Colossoma macropomum, a long-lived, overexploited fish population of the central Amazon Basin. We computed the degree of flooding corresponding to the feeding area of young-of-the-year C. macropomum as the annual magnitude of the moving littoral zone (ML). We estimated abundance of age classes one, two, and three of C. macropomum using a modeling program based on catch, fishing effort, and fish length frequency data from the principal commercial fishery. We found that flooding positively and non-linearly affected abundance of the age-one cohort but not of older age classes. ML data corresponding to a late rising water phase in which zooplankton, seeds, and fruits dominated the diet provided the strongest effect on age-one abundance. However, flooding effects on total catch were not found, likely due to catches comprising several age classes. These results provide support to existing evidence that the magnitude of the moving littoral zone regulates abundance of juvenile fish. Because the ML quantifies food and habitat availability for various other fish species, it may constitute an important control of fish abundance in these systems. Management of these fisheries may be improved by adjusting fishing effort based on hydrology. More generally, the information also serves to assess the impacts of hydrological alterations (e.g., dams) on fish recruitment.

Plume dispersion behaviour and hazard identification for large quantities of liquid hydrogen leakage

AbstractHydrogen is a promising energy carrier. The primary issue of hydrogen utilisation is safety in various scenarios for the coming hydrogen economy. This study focuses on liquid hydrogen leakage, which is typically induced by structural failure in refuelling stations and transit vehicles. In the present study, the authors reveal the plume dispersion behaviour and the underlying mechanism from a macro perspective and identify the associated hazards in the whole dispersion history. These problems have drawn little attention in previous studies. A numerical investigation was conducted, and the flow‐field data were deeply investigated, which were insufficient in the previous experiment. The local turbulence and mixing induced by the temperature difference was revealed to be the major cause of hydrogen dispersion. The lift force induced by the density difference enhanced the dispersion. The dispersion behaviour was classified into three phases: the dense‐gas phase, rise phase, and passive phase. The rise phase is the major one for cryogenic hydrogen dispersion. The frostbite hazard can be ignored, owing to insufficient exposure duration. For wind velocities of 2.2, 5.0, and 10.0 m/s, the durations of the hazardous cloud are 56, 51, and 47 s, respectively. The maximum heights of the hazardous cloud are 23.6, 12.1, and 6.2 m, respectively. There is a high fire/explosion probability in the dense‐gas phase and a low probability in the latter two phases.

On the Possible Mechanism of GLE Initiation

Abstract With the goal of understanding the initiations of solar energetic particle (SEP) (MeV) and ground-level enhancement (GLE) (GeV) particles, we have studied relative timings at approximately the Sun between temporal evolutions of the particles and some electromagnetic radiation components representing flares and shocks. Results show that GLE onsets appear after flare prompt onsets and m-type II onsets, while the GLE-associated SEP onsets appear before the flare prompt onsets and m-type II onsets, thus specifying that the GLE-associated SEPs originate over the flare initial phases and get accelerated intensively over the flare prompt phases associated with coronal shocks. The flare initial phase is found always earlier than the coronal mass ejection (CME) initial phase, further justifying that the MeV particles are initiated particularly by the flare initial phases and are accelerated to GeV energetic by flare prompt phases associated with the coronal shocks. On the contrary, most of the non-GLE-SEP onsets appear well after the flare prompt onsets and m-type II onsets, demonstrating that the non-GLE-SEPs mostly generate over the most intense part of the flare rise phases associated with the coronal shocks. In another development, the relative timings of flare prompt onset and peak times to the m- and DH-type II onsets show that usually the m-type II bursts commence before the flare peaks and DH-type II bursts commence after the flare peaks, signifying that the coronal shocks manifested in m-type II bursts operate over the flare main acceleration phases, while the coronal shocks manifested in DH-type II bursts operate over the flare decay and/or CME propagation phases, thereby suggesting that the evolution of the particles accelerated at the flare main acceleration phases can be prolonged by the shocks associated with the CME propagation phases.

Geometry, Kinematics, and Heliospheric Impact of a Large CME-driven Shock in 2017 September

Abstract A powerful coronal mass ejection (CME) occurred on 2017 September 10 near the end of the declining phase of the historically weak solar cycle 24. We obtain new insights concerning the geometry and kinematics of CME-driven shocks in relation to their heliospheric impacts from the optimal, multispacecraft observations of the eruption. The shock, which together with the CME driver can be tracked from the early stage to the outer corona, shows a large oblate structure produced by the vast expansion of the ejecta. The expansion speeds of the shock along the radial and lateral directions are much larger than the translational speed of the shock center, all of which increase during the flare rise phase, peak slightly after the flare maximum and then decrease. The near simultaneous arrival of the CME-driven shock at the Earth and Mars, which are separated by 156.°6 in longitude, is consistent with the dominance of expansion over translation observed near the Sun. The shock decayed and failed to reach STEREO A around the backward direction. Comparison between ENLIL MHD simulations and the multipoint in situ measurements indicates that the shock expansion near the Sun is crucial for determining the arrival or nonarrival and space weather impact at certain heliospheric locations. The large shock geometry and kinematics have to be taken into account and properly treated for accurate predictions of the arrival time and space weather impact of CMEs.