The operating mode of a single shaft hybrid electric vehicle （SSHEV） in which the electric motor exerts negative torque on the shaft to imitate engine braking is analyzed. The method of determining the quantity of r...The operating mode of a single shaft hybrid electric vehicle （SSHEV） in which the electric motor exerts negative torque on the shaft to imitate engine braking is analyzed. The method of determining the quantity of regenerative braking torque is proposed with the premise that the braking intensity required by the driver is satisfied. On this basis, factors that affect torque generated by the motor are listed, and how the battery＇ s temperature and state of charge （ SOC ） restrict and correct the braking torque is expounded. Finally, road test results show that the motor＇ s constant power or constant torque control is an effective way to recover the mechanical energy during decelerating.展开更多
Decelerating open-channel flow is a type of flow that gradually moves forward with decreasing velocity and increasing water depth.Although all flow parameters change along the streamwise direction,previous studies hav...Decelerating open-channel flow is a type of flow that gradually moves forward with decreasing velocity and increasing water depth.Although all flow parameters change along the streamwise direction,previous studies have revealed that these parameters’vertical distributions at different sections can be universally described with a single profile when being nondimensionalised by appropriate scales.This study focuses on the population trends of spanwise rotational motions at various sections along the main flow direction by particle imaging velocimetry(PIV)measurement.The wall-normal population distributions of density,radius,swirling strength,and convection velocity of the prograde and retrograde motions show similar trends in uniform open-channel flows.The dimensionless representation is invariant along the main flow direction.This study’s results indicate the self-similar characteristic of population trends of spanwise rotational motions prevails in decelerating open-channel flow.展开更多
This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first ...This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first determined from the engagement geometry in conjunction with the nonlinear engagement kinematics in the proposed approach.The heading error defined in the collision course is then adopted as a variable to be nullified for accomplishing the intercept condition.The proposed guidance law is derived based on the heading error dynamics and the optimal error dynamics to ensure optimality and finite-time convergence.As illustrative examples,the proposed guidance command for a constant target acceleration and a target deceleration in the form of a quadratic function of speed are provided.Additionally,the time-to-go prediction method is suggested for implementing the proposed method.The characteristics of the proposed guidance command are analytically investigated to provide insight into the proposed method.The key benefits of the proposed method lie in not producing unnecessary guidance commands near a target compared to other methods and ensuring optimality in guidance command even in the nonlinear engagement kinematics.Finally,numerical simulations are performed to validate the proposed method and to show our findings.展开更多
In 1998, two groups of astronomers, one led by Saul Perlmutter and the other by Brian Schmidt, set out to determine the deceleration—and hence the total mass/energy—of the universe by measuring the recession speeds ...In 1998, two groups of astronomers, one led by Saul Perlmutter and the other by Brian Schmidt, set out to determine the deceleration—and hence the total mass/energy—of the universe by measuring the recession speeds of type la supernovae (SN1a), came to an unexpected conclusion: ever since the universe was about 7 billion years old, its expansion rate has not been decelerating. Instead, the expansion rate has been speeding up. To justify this acceleration, they suggested that the universe does have a mysterious dark energy and they have emerged from oblivion the cosmological constant, positive this time, which is consistent with the image of an inflationary universe. To explain the observed dimming of high-redshift SN1a they have bet essentially on their distance revised upwards. We consider that an accelerated expansion leads right to a “dark energy catastrophe” (i.e., the chasm between the current cosmological vacuum density value of 10 GeV/m<sup>3</sup> and the vacuum energy density proposed by quantum field theory of ~10<sup>122</sup> GeV/m<sup>3</sup>). We suppose rather that the universe knows a slowdown expansion under the positive pressure of a dark energy, otherwise called a variable cosmological constant. The dark luminosity of the latter would be that of a “tired light” which has lost energy with distance. As for the low brilliance of SN1a, it is explained by two physical processes: The first relates to their intrinsic brightness—supposedly do not vary over time—which would depend on the chemical conditions which change with the temporal evolution;the second would concern their apparent luminosity. Besides the serious arguments already known, we strongly propose that their luminosity continually fades by interactions with cosmic magnetic fields, like the earthly PVLAS experiment which loses much more laser photons than expected by crossing a magnetic field. It goes in the sense of a “tired light” which has lost energy with distance, and therefore, a decelerated expansion of the universe. Moreover, we propose the “centrist” principle to complete the hypothesis of the cosmological principle of homogeneity and isotropy considered verified. Without denying the Copernican principle, he is opposed to a “spatial” theoretical construction which accelerates the world towards infinity. The centrist principle gives a “temporal” and privileged vision which tends to demonstrate the deceleration of expansion.展开更多
In order to examine the fundamental characteristics of corner separation in a decelerating cascade flow,the experimental apparatus was made and separations around a NACA65 blade in a decelerating channel flow were exa...In order to examine the fundamental characteristics of corner separation in a decelerating cascade flow,the experimental apparatus was made and separations around a NACA65 blade in a decelerating channel flow were examined.Two-dimensional calculations show that the NACA65 cascade flow that has 45 deg.of turning,1.24 of solidity and 17 deg.of stagger angle is equivalent to the channel flow that has 14 deg.of stagger angle in terms of pitchwise blade force.Experimental investigation by five-hole probe shows that the accumulations of low energy fluid can be seen around the corner part and the overturning flow due to the secondary flow exists.And,as the periodicity of the blade wake in a pitchwise direction is comparably good,the wake of this channel flow is similar to the wake of the cascade flow for two pitch portion.PIV measurement results shows that a vortex pattern can be seen in the momentary streamline on the suction surface of the blade and in the averaged streamline on the perpendicular to both the suction surface and the endwall.展开更多
An experimental investigation was made into three-dimensional separated flow and the vortices within the flow separation in a decelerating channel flow generated by the suction from a porous side wall. The flows along...An experimental investigation was made into three-dimensional separated flow and the vortices within the flow separation in a decelerating channel flow generated by the suction from a porous side wall. The flows along the side and bottom walls were visualized by the surface tuft method. The turbulent internal flow was measured by the split-film probe to investigate the turbulent flow including the reverse flow. In the flow visualization for the strong decelerating flow （the suction flow ratio：0.8）, two typical flow patterns appear alternatively. One is that the flow near the bottom wall separates more upstream than the flow near the top wall and a clockwise vortex can be seen in the separation region. Another is the reversal flow pattern with a counterclockwise vortex. By the turbulent flow measurement using the split-film probe, two peaks of turbulence level are observed for the strong decelerating flow case. These peaks can be related with two flow patterns mentioned above.展开更多
An experimental apparatus was developed to study the three dimensional separated flow with spiral-foci. The internal decelerating flow was generated by the air suction from a side wall to produce the separation on an ...An experimental apparatus was developed to study the three dimensional separated flow with spiral-foci. The internal decelerating flow was generated by the air suction from a side wall to produce the separation on an opposite-side wall. The relation between the upstream boundary layer and the generation of spiral-foci in the separation region was observed by a tuft method. As a result, it was clarified that the spiral-focus type separation could be produced on the side wall and its behavior was closely related to the vortices supplied into the separation region from the boundary layer developing along top wall or bottom one.展开更多
Terahertz(THz) radiation, spanning the frequency range 100 GHz to 10 THz, offers diverse applications in spectroscopy, materials characterization, medical diagnostics and environmental monitoring. Despite its potentia...Terahertz(THz) radiation, spanning the frequency range 100 GHz to 10 THz, offers diverse applications in spectroscopy, materials characterization, medical diagnostics and environmental monitoring. Despite its potential, the generation of high-intensity, tunable THz radiation remains a significant challenge. In this work, we explore a novel approach to the efficient generation of THz radiation based on laser–plasma interactions, utilizing the principles of photon deceleration.When a relativistic CO_(2) laser passes through a pre-ionized plasma, the laser induces a nonlinear wakefield, creating a strong refractive index gradient. This gradient, combined with the lower-density region of the wakefield, slows down the laser, facilitating the accumulation of THz radiation. The resulting THz pulse exhibits extreme collimation, high energy efficiency and tunability. Our work shows that this method can achieve up to 10% conversion efficiency with optimal plasma density near the critical density. This technique presents a promising solution for overcoming current limitations in THz source development and offers potential for diverse applications.展开更多
Variable Cycle Engine(VCE)serves as the core system in achieving future advanced fighters with cross-generational performance and mission versatility.However,the resultant complex configuration and strong coupling of ...Variable Cycle Engine(VCE)serves as the core system in achieving future advanced fighters with cross-generational performance and mission versatility.However,the resultant complex configuration and strong coupling of control parameters present significant challenges in designing acceleration and deceleration control schedules.To thoroughly explore the performance potential of engine,a global integration design method for acceleration and deceleration control schedule based on inner and outer loop optimization is proposed.The outer loop optimization module employs Integrated Surrogate-Assisted Co-Differential Evolutionary(ISACDE)algorithm to optimize the variable geometry adjustment laws based on B-spline curve,and the inner loop optimization module adopts the fixed-state method to design the open-loop fuel–air ratio control schedules,which are aimed at minimizing the acceleration and deceleration time under multiple constraints.Simulation results demonstrate that the proposed global integration design method not only furthest shortens the acceleration and deceleration time,but also effectively safeguards the engine from overlimit.展开更多
Obtaining a reasonable mold flow field for casting slabs with different sections is challenging by solely modifying the nozzle structure and continuous casting process. Research was conducted on small-sectioned (1000 ...Obtaining a reasonable mold flow field for casting slabs with different sections is challenging by solely modifying the nozzle structure and continuous casting process. Research was conducted on small-sectioned (1000 mm × 220 mm) and large-sectioned (3250 mm × 220 mm) slab continuous casting molds with a fixed nozzle form (concave bottom nozzle, side port inclination angle of 0°). A three-dimensional electromagnetic model is established to analyze the current frequency, installation position, and rotation angle under the active deceleration mode and acceleration mode. The results indicate that, regardless of the deceleration mode for small-sectioned slabs or the acceleration mode for large-sectioned slabs, the magnetic flux density in the mold decreases with increasing current frequency. However, the maximum electromagnetic force initially increases and then decreases, suggesting that both electromagnetic modes have the same optimal current frequency (3 Hz). The optimal mechanical design parameters for the deceleration mode of electromagnetic variable flow device (EM-VFD) with the small-sectioned slab are as follows: installation position Z = 115 mm and rotation angle of 15°, ensuring that the maximum electromagnetic force is applied to the nozzle jet area. For the acceleration mode of the large-sectioned slab EM-VFD, the optimal mechanical design parameters are as follows: Z = 115 mm and rotation angle of 10°, ensuring that the maximum electromagnetic force is applied to 1/4 and 3/4 areas of the wide face. These findings indicate that the new electromagnetic variable flow device, which can actively adjust the flow rate and angle of the steel even under given working conditions, provides the possibility for reasonable control of the mold’s flow field.展开更多
As a common transportation facility, speed humps can control the speed of vehicles on special road sections to reduce traffic risks. At the same time, they also cause instantaneous traffic emissions. Based on the clas...As a common transportation facility, speed humps can control the speed of vehicles on special road sections to reduce traffic risks. At the same time, they also cause instantaneous traffic emissions. Based on the classic instantaneous traffic emission model and the limited deceleration capacity microscopic traffic flow model with slow-to-start rules, this paper has investigated the impact of speed humps on traffic flow and the instantaneous emissions of vehicle pollutants in a single lane situation. The numerical simulation results have shown that speed humps have significant effects on traffic flow and traffic emissions. In a free-flow region, the increase of speed humps leads to the continuous rise of CO_(2), NO_(X) and PM emissions. Within some density ranges, one finds that these pollutant emissions can evolve into some higher values under some random seeds. Under other random seeds, they can evolve into some lower values. In a wide moving jam region, the emission values of these pollutants sometimes appear as continuous or intermittent phenomenon. Compared to the refined Na Sch model, the present model has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher volatile organic components(VOC) emissions. Compared to the limited deceleration capacity model without slow-to-start rules, the present model also has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher VOC emissions in a wide moving jam region. These results can also be confirmed or explained by the statistical values of vehicle velocity and acceleration.展开更多
The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo-...The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo- lation preprocessing, the sensitive zones of feedrate variations are processed with acceleration-deceleration control. By using the proposed algorithm, the machining accuracy is guaranteed and the feedrate is adaptively adjusted to he smoothed. The mechanical shock imposed in the servo system is avoided by the first and the second time derivatives of feedrates. A simulation of NURBS interpolation is given to demonstrate the validity and the effectiveness of the algorithm. The proposed interpolator can also be applied to the trajectory planning of the other parametric curves.展开更多
This paper makes an attempt to answer why the observed critical Shields stress for incipient sediment motion deviates from the Shields curve. The measured dataset collected from literature show that the critical Shiel...This paper makes an attempt to answer why the observed critical Shields stress for incipient sediment motion deviates from the Shields curve. The measured dataset collected from literature show that the critical Shields stress widely deviates from the Shields diagram’s prediction. This paper has re-examined the possible mechanisms responsible for the validity of Shields’ diagram and found that, among many factors, the vertical velocity in the sediment layer plays a leading role for the invalidity of Shield’s prediction. A closer look of the positive/negative deviation reveals that they correspond to the up/downward vertical velocity, and the Shields diagram is valid only when flow is uniform. Therefore, this diagram needs to be modified to account for hydraulic environments when near bed vertical velocities are significant. A new theory for critical shear stress has been developed and a unified critical Shields stress for sediment transport has been established, which is valid to predict the critical shear stress of sediment in both uniform and nonuniform flows.展开更多
This study was to investigate the decoloration effects of activated clay, activated carbon, diatomite, Ca group bentonite, kaolin, activated aluminum oxide, magnesium oxide and attapulgite. Ultraviolet-visible spectro...This study was to investigate the decoloration effects of activated clay, activated carbon, diatomite, Ca group bentonite, kaolin, activated aluminum oxide, magnesium oxide and attapulgite. Ultraviolet-visible spectroscopywas adopted to de- tect the absorbanees of the extracts of Schisandra chinensis fruit and rattan stems, the contents of total triterpenoids in S. chinensis fruit and rattan stems were deter- mined, and the decoloration rate and the retention rate of total triterpenoids of S. chi- nensis fruit and rattan stems were calculated. The results indicated that, attapulgite exhibited the best decoloration effect on the extract of S. chinensis fruit, with a de- coloration rate up to 60.47%, activated carbon exhibited a better decoloration effect on the extract of S. chinensis rattan stems, with a decoloration rate up to 69.24%, and they had relatively higher retention rates of total triterpenoids. In the eight de- colorants, attapulgite showed the best decoloration effect on the extract of S. chi- nensis fruit, and activated carbon exhibited the best decoloration effect on the ex- tract of S. chinensisrattan stems.展开更多
In this paper, we describe three different phenomena occurring on scales of 1 mm, 100 km, and almost a light year. The smallest scale is a laboratory experiment. The intermediate scale is a rocket-borne space experime...In this paper, we describe three different phenomena occurring on scales of 1 mm, 100 km, and almost a light year. The smallest scale is a laboratory experiment. The intermediate scale is a rocket-borne space experiment and the largest is an exploding star. In each case, deceleration creates a situation that is unstable to the Rayleigh-Taylor instability. The similarity exists in the spatial and in the Fourier domains;that is, not only are there obvious spatial similarities but the power spectra of the two phenomena are also nearly identical. The data compare favorably to published simulations.展开更多
The current disagreement about the Hubble constant H0 was described as a “Crisis in Cosmology”, at the April (2018) Meeting of the American Physical Society, and hence its resolution is of utmost importance. This wo...The current disagreement about the Hubble constant H0 was described as a “Crisis in Cosmology”, at the April (2018) Meeting of the American Physical Society, and hence its resolution is of utmost importance. This work proposes that the solution to the disagreement between the Planck Collaboration cosmic microwave background (CMB) value of H0, together with the very close BOSS Collaboration baryon acoustic oscillation (BAO) value, and the significantly higher value of H0 found by the SHOES Collaboration cosmic distance ladder (CDL) work, is due to the fact that the CMB and BAO values of H0 are not for an accelerating universe, as generally believed, but are actually the values for a decelerating universe. In contrast, the CDL value of H0 is indeed that for an accelerating universe. It is shown that by replacing the negative deceleration parameter in the expression for logH0 in the CDL work by a positive deceleration parameter, the value of H0 can be brought down to agree with the CMB and BAO lower values. There is a brief review of the author’s decelerating model based on the Einstein de Sitter universe, augmented by a model of dark energy that does not have a negative pressure, but instead has a non-dispersive index of refraction n, causing the speed of light through the dark energy of intergalactic space to be reduced to c/n. As reported earlier, this assumption is sufficient to accommodate the increase in apparent magnitude of the Type Ia supernovae (SNe Ia). Additional support for the model is presented, together with a proposal for astronomical falsification.展开更多
A new adaptive cruise control (ACC) method based on the desired safety headway distance is investigated for improving the vehicle traffic safety at high speed by regulating the additional throttle opening and braking ...A new adaptive cruise control (ACC) method based on the desired safety headway distance is investigated for improving the vehicle traffic safety at high speed by regulating the additional throttle opening and braking torque of driving wheels only. The selection of headway distance sensors, the determination of desired safety headway distance and desired deceleration are elaborated. The ACC flowchart and simulation, as well as signal misinformation and its resolutions are described. The simulation proves that the new ACC method is simpler and feasible. The new method is easily integrated ACC with ABS/ASR to form an organic ABS/ASR/ACC system.展开更多
This work continues the previous study (2018) Journal of Modern Physics. 9, 1827-1837, that proposes that the disagreement arises because the cosmic microwave background (CMB) value for the Hubble constant <em>H...This work continues the previous study (2018) Journal of Modern Physics. 9, 1827-1837, that proposes that the disagreement arises because the cosmic microwave background (CMB) value for the Hubble constant <em>H</em><sub><em>0</em></sub> is actually for a universe which is decelerating rather than accelerating. It is shown that when <em>H</em><sub><em>0</em></sub> of Freedman et al. (2019) Astrophysical Journal, 882: 34 (24 pp.) is re-determined for redshift <em>z </em>= 0.07, by replacing <em>q</em><sub><em>0 </em></sub>= <span style="white-space:nowrap;">−</span>0.53 with <em style="white-space:normal;">q</em><sub style="white-space:normal;"><em>0 </em></sub><span style="white-space:normal;">= <span style="white-space:nowrap;">−</span>0.5</span>, the new lower value is in excellent agreement (0.1%) with the CMB <em>H</em><sub><em>0</em></sub>. The model is modified to include the clustering of galaxies, and the recognition that there are clusters that do not experience the Hubble expansion, such as the Local Group, and hence, in accordance with the model, within the Local Group the speed of light is <em>c</em>. The bearing of this result on the neutrino and light time delay from SN1987a is discussed. It is suggested that the possible emission of a neutrino from the blazar TXS-0506+56, that was flaring at the time, as well as possible neutrino emission earlier, may arise instead from a more distant source that happens to be, angle-wise, near the blazar, and hence the correlation is accidental. The model is further modified to allow for a variable index of refraction, and a comparison with the ΛCDM model is given. The age of the universe for different values of<em> H</em><sub><em>0</em></sub> is studied, and comparison with the ages of the oldest stars in the Milky Way is discussed. Also, gravitational wave determination of <em>H</em><sub><em>0</em></sub> is briefly discussed.展开更多
The enumerating algorithm has been introduced into the fitting procedure of the ASR model. Based on the detailed study of 21 large earthquakes with M≥6. 8 in the Chinese Mainland,the statistical features of seismic s...The enumerating algorithm has been introduced into the fitting procedure of the ASR model. Based on the detailed study of 21 large earthquakes with M≥6. 8 in the Chinese Mainland,the statistical features of seismic strain release before large earthquakes have been summarized. In the mass,the strain release models can be divided into five types. The first is the DA model,in which the strain release accelerates in broader areas and decelerates in small areas around the epicenter. Approximately 38% of earthquake samples are of this type. The second is the AD model,in which the strain release decelerates in broader areas and accelerates in smaller areas around the epicenter with an occupying ratioof approximately 19%. The third is ASR,in which only accelerating strain release can be observed. Cases of this model amount to about 14%. The fourth is DSR,in which only decelerating strain release can be checked,amounting to about 24%. There is only one earthquake sample of the fifth type (LSR),which shows a linear strain release. There is a 3～6 years difference in the duration of pre-shock sequences between the accelerating and decelerating models. This means that seismic quiescence against a background of increased seismicity of small earthquakes before large earthquakes are a typical feature in general. For the DA model,the average size of critical regions for steady accelerating and decelerating strain release is about 260km to 400km and 100km to 200km,respectively,3 to 5 times and 1 to 2 times the rupture size of an earthquake of magnitude 7. 0. The AD model is the opposite of the DA model. The model parameter,m value,has good stability. The ratio of ASR is about the same for accelerating seismic strain release phenomena,no matter what the strain release models are,or how large the strain release quantity is. With regard to decelerating seismic strain release phenomena, the DA model has the most distinctive decelerating strain release characteristic and is the typical feature of seismic strain release,i. e. "decelerating in-accelerating out seismic strain model".展开更多
Transient control law ensures that the aeroengine transits to the command operating state rapidly and reliably. Most of the existing approaches for transient control law design have complicated principle and arithmeti...Transient control law ensures that the aeroengine transits to the command operating state rapidly and reliably. Most of the existing approaches for transient control law design have complicated principle and arithmetic. As a result, those approaches are not convenient for application. This paper proposes an extrapolation approach based on the set-point parameters to construct the transient control law, which has a good practicability. In this approach, the transient main fuel control law for acceleration and deceleration process is designed based on the main fuel flow on steady operating state. In order to analyze the designing feature of the extrapolation approach, the simulation results of several different transient control laws designed by the same approach are compared together. The analysis indicates that the aeroengine has a good performance in the transient process and the designing feature of the extrapolation approach conforms to the elements of the turbofan aeroengine.展开更多
基金Supported by the National High Technology Research and Development Program of China(2011AA11A252)
文摘The operating mode of a single shaft hybrid electric vehicle （SSHEV） in which the electric motor exerts negative torque on the shaft to imitate engine braking is analyzed. The method of determining the quantity of regenerative braking torque is proposed with the premise that the braking intensity required by the driver is satisfied. On this basis, factors that affect torque generated by the motor are listed, and how the battery＇ s temperature and state of charge （ SOC ） restrict and correct the braking torque is expounded. Finally, road test results show that the motor＇ s constant power or constant torque control is an effective way to recover the mechanical energy during decelerating.
基金the National Natural Science Foundation of China(Grant No.51679020)the Science and Technology Research Program of Chongqing Municipal Education Commission(Grant No.KJQN202100731).
文摘Decelerating open-channel flow is a type of flow that gradually moves forward with decreasing velocity and increasing water depth.Although all flow parameters change along the streamwise direction,previous studies have revealed that these parameters’vertical distributions at different sections can be universally described with a single profile when being nondimensionalised by appropriate scales.This study focuses on the population trends of spanwise rotational motions at various sections along the main flow direction by particle imaging velocimetry(PIV)measurement.The wall-normal population distributions of density,radius,swirling strength,and convection velocity of the prograde and retrograde motions show similar trends in uniform open-channel flows.The dimensionless representation is invariant along the main flow direction.This study’s results indicate the self-similar characteristic of population trends of spanwise rotational motions prevails in decelerating open-channel flow.
文摘This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first determined from the engagement geometry in conjunction with the nonlinear engagement kinematics in the proposed approach.The heading error defined in the collision course is then adopted as a variable to be nullified for accomplishing the intercept condition.The proposed guidance law is derived based on the heading error dynamics and the optimal error dynamics to ensure optimality and finite-time convergence.As illustrative examples,the proposed guidance command for a constant target acceleration and a target deceleration in the form of a quadratic function of speed are provided.Additionally,the time-to-go prediction method is suggested for implementing the proposed method.The characteristics of the proposed guidance command are analytically investigated to provide insight into the proposed method.The key benefits of the proposed method lie in not producing unnecessary guidance commands near a target compared to other methods and ensuring optimality in guidance command even in the nonlinear engagement kinematics.Finally,numerical simulations are performed to validate the proposed method and to show our findings.
文摘In 1998, two groups of astronomers, one led by Saul Perlmutter and the other by Brian Schmidt, set out to determine the deceleration—and hence the total mass/energy—of the universe by measuring the recession speeds of type la supernovae (SN1a), came to an unexpected conclusion: ever since the universe was about 7 billion years old, its expansion rate has not been decelerating. Instead, the expansion rate has been speeding up. To justify this acceleration, they suggested that the universe does have a mysterious dark energy and they have emerged from oblivion the cosmological constant, positive this time, which is consistent with the image of an inflationary universe. To explain the observed dimming of high-redshift SN1a they have bet essentially on their distance revised upwards. We consider that an accelerated expansion leads right to a “dark energy catastrophe” (i.e., the chasm between the current cosmological vacuum density value of 10 GeV/m<sup>3</sup> and the vacuum energy density proposed by quantum field theory of ~10<sup>122</sup> GeV/m<sup>3</sup>). We suppose rather that the universe knows a slowdown expansion under the positive pressure of a dark energy, otherwise called a variable cosmological constant. The dark luminosity of the latter would be that of a “tired light” which has lost energy with distance. As for the low brilliance of SN1a, it is explained by two physical processes: The first relates to their intrinsic brightness—supposedly do not vary over time—which would depend on the chemical conditions which change with the temporal evolution;the second would concern their apparent luminosity. Besides the serious arguments already known, we strongly propose that their luminosity continually fades by interactions with cosmic magnetic fields, like the earthly PVLAS experiment which loses much more laser photons than expected by crossing a magnetic field. It goes in the sense of a “tired light” which has lost energy with distance, and therefore, a decelerated expansion of the universe. Moreover, we propose the “centrist” principle to complete the hypothesis of the cosmological principle of homogeneity and isotropy considered verified. Without denying the Copernican principle, he is opposed to a “spatial” theoretical construction which accelerates the world towards infinity. The centrist principle gives a “temporal” and privileged vision which tends to demonstrate the deceleration of expansion.
文摘In order to examine the fundamental characteristics of corner separation in a decelerating cascade flow,the experimental apparatus was made and separations around a NACA65 blade in a decelerating channel flow were examined.Two-dimensional calculations show that the NACA65 cascade flow that has 45 deg.of turning,1.24 of solidity and 17 deg.of stagger angle is equivalent to the channel flow that has 14 deg.of stagger angle in terms of pitchwise blade force.Experimental investigation by five-hole probe shows that the accumulations of low energy fluid can be seen around the corner part and the overturning flow due to the secondary flow exists.And,as the periodicity of the blade wake in a pitchwise direction is comparably good,the wake of this channel flow is similar to the wake of the cascade flow for two pitch portion.PIV measurement results shows that a vortex pattern can be seen in the momentary streamline on the suction surface of the blade and in the averaged streamline on the perpendicular to both the suction surface and the endwall.
文摘An experimental investigation was made into three-dimensional separated flow and the vortices within the flow separation in a decelerating channel flow generated by the suction from a porous side wall. The flows along the side and bottom walls were visualized by the surface tuft method. The turbulent internal flow was measured by the split-film probe to investigate the turbulent flow including the reverse flow. In the flow visualization for the strong decelerating flow （the suction flow ratio：0.8）, two typical flow patterns appear alternatively. One is that the flow near the bottom wall separates more upstream than the flow near the top wall and a clockwise vortex can be seen in the separation region. Another is the reversal flow pattern with a counterclockwise vortex. By the turbulent flow measurement using the split-film probe, two peaks of turbulence level are observed for the strong decelerating flow case. These peaks can be related with two flow patterns mentioned above.
文摘An experimental apparatus was developed to study the three dimensional separated flow with spiral-foci. The internal decelerating flow was generated by the air suction from a side wall to produce the separation on an opposite-side wall. The relation between the upstream boundary layer and the generation of spiral-foci in the separation region was observed by a tuft method. As a result, it was clarified that the spiral-focus type separation could be produced on the side wall and its behavior was closely related to the vortices supplied into the separation region from the boundary layer developing along top wall or bottom one.
基金Project supported by the China Postdoctoral Science Foundation (Grant No. 2024T170021)the Beijing Municipal Science & Technology Commission, Administrative Commission of Zhongguancun Science Park (Grant No. Z231100006023003)+2 种基金the National Natural Science Foundation of China (Grant Nos. 12175058, 12205007, and 11921006)the National Science Fund of Hunan Province for Distinguished Young Scholars (Grant No. 2024JJ2009)The computing was supported by the High-performance Computing Platform of Peking University。
文摘Terahertz(THz) radiation, spanning the frequency range 100 GHz to 10 THz, offers diverse applications in spectroscopy, materials characterization, medical diagnostics and environmental monitoring. Despite its potential, the generation of high-intensity, tunable THz radiation remains a significant challenge. In this work, we explore a novel approach to the efficient generation of THz radiation based on laser–plasma interactions, utilizing the principles of photon deceleration.When a relativistic CO_(2) laser passes through a pre-ionized plasma, the laser induces a nonlinear wakefield, creating a strong refractive index gradient. This gradient, combined with the lower-density region of the wakefield, slows down the laser, facilitating the accumulation of THz radiation. The resulting THz pulse exhibits extreme collimation, high energy efficiency and tunability. Our work shows that this method can achieve up to 10% conversion efficiency with optimal plasma density near the critical density. This technique presents a promising solution for overcoming current limitations in THz source development and offers potential for diverse applications.
基金supported by the Basic Research on Dynamic Real-time Modeling and Onboard Adaptive Modeling of Aero Engine,China(No.QZPY202308)。
文摘Variable Cycle Engine(VCE)serves as the core system in achieving future advanced fighters with cross-generational performance and mission versatility.However,the resultant complex configuration and strong coupling of control parameters present significant challenges in designing acceleration and deceleration control schedules.To thoroughly explore the performance potential of engine,a global integration design method for acceleration and deceleration control schedule based on inner and outer loop optimization is proposed.The outer loop optimization module employs Integrated Surrogate-Assisted Co-Differential Evolutionary(ISACDE)algorithm to optimize the variable geometry adjustment laws based on B-spline curve,and the inner loop optimization module adopts the fixed-state method to design the open-loop fuel–air ratio control schedules,which are aimed at minimizing the acceleration and deceleration time under multiple constraints.Simulation results demonstrate that the proposed global integration design method not only furthest shortens the acceleration and deceleration time,but also effectively safeguards the engine from overlimit.
基金supported by the Science and Technology Talent Support Project of Hunan province in China(Grant No.2023TJ-Z14).
文摘Obtaining a reasonable mold flow field for casting slabs with different sections is challenging by solely modifying the nozzle structure and continuous casting process. Research was conducted on small-sectioned (1000 mm × 220 mm) and large-sectioned (3250 mm × 220 mm) slab continuous casting molds with a fixed nozzle form (concave bottom nozzle, side port inclination angle of 0°). A three-dimensional electromagnetic model is established to analyze the current frequency, installation position, and rotation angle under the active deceleration mode and acceleration mode. The results indicate that, regardless of the deceleration mode for small-sectioned slabs or the acceleration mode for large-sectioned slabs, the magnetic flux density in the mold decreases with increasing current frequency. However, the maximum electromagnetic force initially increases and then decreases, suggesting that both electromagnetic modes have the same optimal current frequency (3 Hz). The optimal mechanical design parameters for the deceleration mode of electromagnetic variable flow device (EM-VFD) with the small-sectioned slab are as follows: installation position Z = 115 mm and rotation angle of 15°, ensuring that the maximum electromagnetic force is applied to the nozzle jet area. For the acceleration mode of the large-sectioned slab EM-VFD, the optimal mechanical design parameters are as follows: Z = 115 mm and rotation angle of 10°, ensuring that the maximum electromagnetic force is applied to 1/4 and 3/4 areas of the wide face. These findings indicate that the new electromagnetic variable flow device, which can actively adjust the flow rate and angle of the steel even under given working conditions, provides the possibility for reasonable control of the mold’s flow field.
基金funded by the National Natural Science Foundation of China (Grant No. 11875031)the key research projects of Natural Science of Anhui Provincial Colleges and Universities (Grant No. 2022AH050252)。
文摘As a common transportation facility, speed humps can control the speed of vehicles on special road sections to reduce traffic risks. At the same time, they also cause instantaneous traffic emissions. Based on the classic instantaneous traffic emission model and the limited deceleration capacity microscopic traffic flow model with slow-to-start rules, this paper has investigated the impact of speed humps on traffic flow and the instantaneous emissions of vehicle pollutants in a single lane situation. The numerical simulation results have shown that speed humps have significant effects on traffic flow and traffic emissions. In a free-flow region, the increase of speed humps leads to the continuous rise of CO_(2), NO_(X) and PM emissions. Within some density ranges, one finds that these pollutant emissions can evolve into some higher values under some random seeds. Under other random seeds, they can evolve into some lower values. In a wide moving jam region, the emission values of these pollutants sometimes appear as continuous or intermittent phenomenon. Compared to the refined Na Sch model, the present model has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher volatile organic components(VOC) emissions. Compared to the limited deceleration capacity model without slow-to-start rules, the present model also has lower instantaneous emissions such as CO_(2), NO_(X) and PM and higher VOC emissions in a wide moving jam region. These results can also be confirmed or explained by the statistical values of vehicle velocity and acceleration.
基金Supported by the Natural Science Foundation of Jiangsu Province(BK2003005)~~
文摘The feedrate profile of non-uniform rational B-spline （NURBS） interpolation due to the contour errors is analyzed. A NURBS curve interpolator with adaptive acceleration-deceleration control is presented. In interpo- lation preprocessing, the sensitive zones of feedrate variations are processed with acceleration-deceleration control. By using the proposed algorithm, the machining accuracy is guaranteed and the feedrate is adaptively adjusted to he smoothed. The mechanical shock imposed in the servo system is avoided by the first and the second time derivatives of feedrates. A simulation of NURBS interpolation is given to demonstrate the validity and the effectiveness of the algorithm. The proposed interpolator can also be applied to the trajectory planning of the other parametric curves.
文摘This paper makes an attempt to answer why the observed critical Shields stress for incipient sediment motion deviates from the Shields curve. The measured dataset collected from literature show that the critical Shields stress widely deviates from the Shields diagram’s prediction. This paper has re-examined the possible mechanisms responsible for the validity of Shields’ diagram and found that, among many factors, the vertical velocity in the sediment layer plays a leading role for the invalidity of Shield’s prediction. A closer look of the positive/negative deviation reveals that they correspond to the up/downward vertical velocity, and the Shields diagram is valid only when flow is uniform. Therefore, this diagram needs to be modified to account for hydraulic environments when near bed vertical velocities are significant. A new theory for critical shear stress has been developed and a unified critical Shields stress for sediment transport has been established, which is valid to predict the critical shear stress of sediment in both uniform and nonuniform flows.
基金Supported by Key Science and Technology Research and Development Program of Jilin Province(20140204068YY,20140204062YY)Special Fund for Pharmaceutical Industry Development of Jilin Province(YYZW201246)~~
文摘This study was to investigate the decoloration effects of activated clay, activated carbon, diatomite, Ca group bentonite, kaolin, activated aluminum oxide, magnesium oxide and attapulgite. Ultraviolet-visible spectroscopywas adopted to de- tect the absorbanees of the extracts of Schisandra chinensis fruit and rattan stems, the contents of total triterpenoids in S. chinensis fruit and rattan stems were deter- mined, and the decoloration rate and the retention rate of total triterpenoids of S. chi- nensis fruit and rattan stems were calculated. The results indicated that, attapulgite exhibited the best decoloration effect on the extract of S. chinensis fruit, with a de- coloration rate up to 60.47%, activated carbon exhibited a better decoloration effect on the extract of S. chinensis rattan stems, with a decoloration rate up to 69.24%, and they had relatively higher retention rates of total triterpenoids. In the eight de- colorants, attapulgite showed the best decoloration effect on the extract of S. chi- nensis fruit, and activated carbon exhibited the best decoloration effect on the ex- tract of S. chinensisrattan stems.
文摘In this paper, we describe three different phenomena occurring on scales of 1 mm, 100 km, and almost a light year. The smallest scale is a laboratory experiment. The intermediate scale is a rocket-borne space experiment and the largest is an exploding star. In each case, deceleration creates a situation that is unstable to the Rayleigh-Taylor instability. The similarity exists in the spatial and in the Fourier domains;that is, not only are there obvious spatial similarities but the power spectra of the two phenomena are also nearly identical. The data compare favorably to published simulations.
文摘The current disagreement about the Hubble constant H0 was described as a “Crisis in Cosmology”, at the April (2018) Meeting of the American Physical Society, and hence its resolution is of utmost importance. This work proposes that the solution to the disagreement between the Planck Collaboration cosmic microwave background (CMB) value of H0, together with the very close BOSS Collaboration baryon acoustic oscillation (BAO) value, and the significantly higher value of H0 found by the SHOES Collaboration cosmic distance ladder (CDL) work, is due to the fact that the CMB and BAO values of H0 are not for an accelerating universe, as generally believed, but are actually the values for a decelerating universe. In contrast, the CDL value of H0 is indeed that for an accelerating universe. It is shown that by replacing the negative deceleration parameter in the expression for logH0 in the CDL work by a positive deceleration parameter, the value of H0 can be brought down to agree with the CMB and BAO lower values. There is a brief review of the author’s decelerating model based on the Einstein de Sitter universe, augmented by a model of dark energy that does not have a negative pressure, but instead has a non-dispersive index of refraction n, causing the speed of light through the dark energy of intergalactic space to be reduced to c/n. As reported earlier, this assumption is sufficient to accommodate the increase in apparent magnitude of the Type Ia supernovae (SNe Ia). Additional support for the model is presented, together with a proposal for astronomical falsification.
文摘A new adaptive cruise control (ACC) method based on the desired safety headway distance is investigated for improving the vehicle traffic safety at high speed by regulating the additional throttle opening and braking torque of driving wheels only. The selection of headway distance sensors, the determination of desired safety headway distance and desired deceleration are elaborated. The ACC flowchart and simulation, as well as signal misinformation and its resolutions are described. The simulation proves that the new ACC method is simpler and feasible. The new method is easily integrated ACC with ABS/ASR to form an organic ABS/ASR/ACC system.
文摘This work continues the previous study (2018) Journal of Modern Physics. 9, 1827-1837, that proposes that the disagreement arises because the cosmic microwave background (CMB) value for the Hubble constant <em>H</em><sub><em>0</em></sub> is actually for a universe which is decelerating rather than accelerating. It is shown that when <em>H</em><sub><em>0</em></sub> of Freedman et al. (2019) Astrophysical Journal, 882: 34 (24 pp.) is re-determined for redshift <em>z </em>= 0.07, by replacing <em>q</em><sub><em>0 </em></sub>= <span style="white-space:nowrap;">−</span>0.53 with <em style="white-space:normal;">q</em><sub style="white-space:normal;"><em>0 </em></sub><span style="white-space:normal;">= <span style="white-space:nowrap;">−</span>0.5</span>, the new lower value is in excellent agreement (0.1%) with the CMB <em>H</em><sub><em>0</em></sub>. The model is modified to include the clustering of galaxies, and the recognition that there are clusters that do not experience the Hubble expansion, such as the Local Group, and hence, in accordance with the model, within the Local Group the speed of light is <em>c</em>. The bearing of this result on the neutrino and light time delay from SN1987a is discussed. It is suggested that the possible emission of a neutrino from the blazar TXS-0506+56, that was flaring at the time, as well as possible neutrino emission earlier, may arise instead from a more distant source that happens to be, angle-wise, near the blazar, and hence the correlation is accidental. The model is further modified to allow for a variable index of refraction, and a comparison with the ΛCDM model is given. The age of the universe for different values of<em> H</em><sub><em>0</em></sub> is studied, and comparison with the ages of the oldest stars in the Milky Way is discussed. Also, gravitational wave determination of <em>H</em><sub><em>0</em></sub> is briefly discussed.
基金supported by a grant from the National Key Technology R&D Program in the Eleventh"Five-year Plan"Period ( 20070403-2006BAC01B03-02-02)fund for earthquake research (200708020),China
文摘The enumerating algorithm has been introduced into the fitting procedure of the ASR model. Based on the detailed study of 21 large earthquakes with M≥6. 8 in the Chinese Mainland,the statistical features of seismic strain release before large earthquakes have been summarized. In the mass,the strain release models can be divided into five types. The first is the DA model,in which the strain release accelerates in broader areas and decelerates in small areas around the epicenter. Approximately 38% of earthquake samples are of this type. The second is the AD model,in which the strain release decelerates in broader areas and accelerates in smaller areas around the epicenter with an occupying ratioof approximately 19%. The third is ASR,in which only accelerating strain release can be observed. Cases of this model amount to about 14%. The fourth is DSR,in which only decelerating strain release can be checked,amounting to about 24%. There is only one earthquake sample of the fifth type (LSR),which shows a linear strain release. There is a 3～6 years difference in the duration of pre-shock sequences between the accelerating and decelerating models. This means that seismic quiescence against a background of increased seismicity of small earthquakes before large earthquakes are a typical feature in general. For the DA model,the average size of critical regions for steady accelerating and decelerating strain release is about 260km to 400km and 100km to 200km,respectively,3 to 5 times and 1 to 2 times the rupture size of an earthquake of magnitude 7. 0. The AD model is the opposite of the DA model. The model parameter,m value,has good stability. The ratio of ASR is about the same for accelerating seismic strain release phenomena,no matter what the strain release models are,or how large the strain release quantity is. With regard to decelerating seismic strain release phenomena, the DA model has the most distinctive decelerating strain release characteristic and is the typical feature of seismic strain release,i. e. "decelerating in-accelerating out seismic strain model".
基金support of Aeronautical Science Foundation of China (2011ZB51019)
文摘Transient control law ensures that the aeroengine transits to the command operating state rapidly and reliably. Most of the existing approaches for transient control law design have complicated principle and arithmetic. As a result, those approaches are not convenient for application. This paper proposes an extrapolation approach based on the set-point parameters to construct the transient control law, which has a good practicability. In this approach, the transient main fuel control law for acceleration and deceleration process is designed based on the main fuel flow on steady operating state. In order to analyze the designing feature of the extrapolation approach, the simulation results of several different transient control laws designed by the same approach are compared together. The analysis indicates that the aeroengine has a good performance in the transient process and the designing feature of the extrapolation approach conforms to the elements of the turbofan aeroengine.
