A novel scanning technique using a rotating-head sonar profiler attached to a slider mechanism is presented as a means to directly measure the complex erosion and deposition features of local scour holes developing in...A novel scanning technique using a rotating-head sonar profiler attached to a slider mechanism is presented as a means to directly measure the complex erosion and deposition features of local scour holes developing in clear-water conditions around vertical cylinders mimicking bridge piers.Extensive validation shows that the method produces high-density elevation surfaces to within y1.5±2 mm accuracy in a quasi-non-invasive manner.This equates to 0.5±0.7%relative to the flow depth which sonar resolution is well known to scale with.Experimental data from three trials using different cylinder diameters indicate that monitoring of the entire scour hole over time(instead of only the maximum depth as is commonly done in laboratory experiments)can reveal important information about local scour evolution.In particular,results show that the scour-hole volume scales with the maximum scour depth cubed(VOLy3s)through three linear regimes.The transition to the third linear regime was found to represent a step change in the scour evolution process.Following the recent theoretical framework proposed by Manes and Brocchini(2015),this change,termed the crossover point,was interpreted as the point where the production of turbulent kinetic energy plateaus which corresponds to a stabilization in the erosive power of the horseshoe vortex.Scour development beyond the crossover point is characterised by a significant reduction in the rate of volumetric scour,relative to the steadily-increasing maximum scour depth.This overall reduction in volume-development is attributed to a balance between erosion from in-front of the pier and deposition around the sides using topography analysis.It is speculated that the existence of the crossover point may help to identify the characteristic length and time scales describing the evolution of local scour,which may be used for modeling purposes.展开更多
The algebraic methods represented by Wu's method have made significant breakthroughs in the field of geometric theorem proving.Algebraic proofs usually involve large amounts of calcula- tions,thus making it diffic...The algebraic methods represented by Wu's method have made significant breakthroughs in the field of geometric theorem proving.Algebraic proofs usually involve large amounts of calcula- tions,thus making it difficult to understand intuitively.However,if the authors look at Wu's method from the perspective of identity,Wu's method can be understood easily and can be used to generate new geometric propositions.To make geometric reasoning simpler,more expressive,and richer in geometric meaning,the authors establish a geometric algebraic system (point geometry built on nearly 20 basic properties/formulas about operations on points)while maintaining the advantages of the coordinate method,vector method,and particle geometry method and avoiding their disadvantages.Geometric relations in the propositions and conclusions of a geometric problem are expressed as identical equations of vector polynomials according to point geometry.Thereafter,a proof method that maintains the essence of Wu's method is introduced to find the relationships between these equations.A test on more than 400 geometry statements shows that the proposed proof method,which is based on identical equations of vector polynomials,is simple and effective.Furthermore,when solving the original problem,this proof method can also help the authors recognize the relationship between the propositions of the problem and help the authors generate new geometric propositions.展开更多
Lateral migration of the Bhagirathi River temporally creates unavoidable geomorphic hazards in West Bengal,India.The Bhagirathi River flows SW for-67.30 km betwee n the confluenee point of Ajay and Jalangi rivers in E...Lateral migration of the Bhagirathi River temporally creates unavoidable geomorphic hazards in West Bengal,India.The Bhagirathi River flows SW for-67.30 km betwee n the confluenee point of Ajay and Jalangi rivers in East Burdwan and Nadia districts of West Bengal.The course of Bhagirathi is notably migration prone and cultivates problematic changes along its course over time.In the study,we have looked into its migration tendency and unpredictability for past 238 years and then predicted the lateral shifting of river centerline using temporal satellite imageries-Landsat-5(TM)of 1987(8,December),1995(28,January),2005(7,January)and LISS-IV satellite imagery(2017,5 January);SOI Toposheet-1968-1969(79A/2,79A/3,79A/6 and 79A/7)and RennelPs map of 1779.Other highlights are the quest of fluvial features,oxbow lakes,mid-channel bars,channel migration rate,meander geometry,channel sinuosity in different parts of river course and the parts that experience intensive bank erosion.The entire river course has been subdivided into three segments;viz.reaches A,B and C.Investigation displays that degree of sinuosity decreases from its anterior course(1968)to the existing course(2017).Reach-specific outputs display that reach B is highly sinuous(SI value 1.94 in 2017)and SI increases temporarily,whereas for reaches A and C it decreases with time.The rate of migration is higher in reach B than that in reaches C and A.The study displays a notably decreasing trend of migration in comparison with its previous lateral migration and shows that the migration nature over time is intensively inconsistent and unpredictable except very few portions of the river course.The nature of deposition within the river channel shows an unstable behavior during the entire period of the study.Meander geometry depicts a rapid change of river course innate to meander bends and shows a higher rate of migration by meander loop cut-off rather than lateral migration that reflects the inconsistency,erosion vulnerability and unpredictable nature of migration.Th展开更多
With the increasing demands for remote spectroscopy in many fields ranging from homeland security to environmental monitoring, terahertz (THz) spectroscopy has drawn a significant amount of attention because of its ca...With the increasing demands for remote spectroscopy in many fields ranging from homeland security to environmental monitoring, terahertz (THz) spectroscopy has drawn a significant amount of attention because of its capability to acquire chemical spectral signatures non-invasively. However, advanced THz remote sensing techniques are obstructed by quite a few factors, such as THz waves being strongly absorbed by water vapor in the ambient air, difficulty to generate intense broadband coherent THz source remotely, and hard to transmit THz waveform information remotely without losing the signal to noise ratio, etc. In this review, after introducing different THz air-photonics techniques to overcome the difficulties of THz remote sensing, we focus mainly on theoretical and experimental methods to improve THz generation and detection performance for the purpose of remote sensing through tailoring the generation and detection media, air-plasma. For the THz generation part, auto-focusing ring-Airy beam was introduced to enhance the THz wave generation yield from two-color laser induced air plasma. By artificially modulated exotic wave packets, it is exhibited that abruptly auto-focusing beam induced air-plasma can give an up to 5.3-time-enhanced THz wave pulse energy compared to normal Gaussian beam induced plasma under the same conditions. At the same time, a red shift on the THz emission spectrum is also observed. A simulation using an interference model to qualitatively describe these behaviors has be developed. For the THz detection part, the results of THz remote sensing at 30 m using THz-radiation-enhanced-emission- of-fluorescence (THz-REEF) technique are demonstrated, which greatly improved from the 10 m demonstration last reported. The THz-REEF technique in the counter-propagation geometry was explored, which is proved to be more practical for stand-off detections than co-propagation geometry. We found that in the counter- propagating geometry the maximum amplitude of the REEF signal is comparable to that in the展开更多
The feasibility of a volumetric modulated arc therapy (VMAT) based coronal arc (cARC) technique for treating a single brain metastasis or lesion proximal to the brainstem or optic chiasm was evaluated. Coplanar (CP) a...The feasibility of a volumetric modulated arc therapy (VMAT) based coronal arc (cARC) technique for treating a single brain metastasis or lesion proximal to the brainstem or optic chiasm was evaluated. Coplanar (CP) and non-coplanar (NCP) treatment plans to an anthropomorphic head/neck phantom scanned head-first supine were compared to a cARC plan with the phantom rotated vertically. A set of planning target volumes (PTVs) were contoured centrally between the brainstem and optic chiasm (“Ant PTVs”) and posterior to brainstem (“Post PTVs”). Dosimetric indices such as conformity index (C.I.), gradient measure (G.M.), and dose volume histograms (DVHs) were compared for CP, NCP and cARC techniques. The TG101 guidelines for organs-at-risk (OARs), and 95% of PTV receiving at least 100% of the prescription dose (D95 = 100%) were used as plan objectives. Reductions in D50 and D30 to the brainstem of 85.1% ± 3.9% and 87.6% ± 3.2%, respectively were seen for “Post PTVs”, and 51.1% ± 17.8% and 85.6% ± 6.0% respectively for “Ant PTVs” using cARC versus CP (p ≤ 0.01). For chiasm, reductions of D50 and D30 were 61.7% ± 3.2% and 44.2% ± 8.9% for “Ant PTVs”, by 69.3% ± 8.0% and 74.3% ± 8.2% for “Post PTVs” (p ≤ 0.01). Comparing cARC to NCP led to similar dosimetric improvements. The conformity index (C.I.) was measured to be 1.101 ± 0.038, 1.088 ± 0.054, and 1.060 ± 0.040 for cARC, CP and NCP respectively (p ≤ 0.01). The overall GM in cm was 0.581 ± 0.097, 0.708 ± 0.064, and 0.476 ± 0.050 for cARC, CP and NCP respectively (p ≤ 0.01). The mean distance gradient fall-off (in cm) was 0.249 ± 0.038 (cARC), 0.749 ± 0.107 (CP), and 0.621 ± 0.068 (NCP) at the center slice in anterior-posterior direction of the target volume (p ≤ 0.01). The objective of this study is to compare the dosimetric indices of cARC with CP and NCP techniques. In conclusion, cARC can provide improved dosimetry as compared to CP and NCP for lesion proximal to the brainstem or optic chiasm.展开更多
The idea of envelope of a family of plane curves is an elementary notion in differential geometry.As such,its implementation in dynamic geometry environments is quite universal (Cabri, The Geometer's Sketchpad,Cin...The idea of envelope of a family of plane curves is an elementary notion in differential geometry.As such,its implementation in dynamic geometry environments is quite universal (Cabri, The Geometer's Sketchpad,Cinderella,GeoGebra,...).Nevertheless,most of these programs return, when computing certain envelopes,both some spurious solutions and the curves that truly fit in the intuitive definition of envelope.The precise distinction between spurious and genuine parts has not been made before:This paper proposes such distinction in an algorithmic way,ready for its implementation in interactive geometry systems,allowing a finer classification of the different parts resulting from the current,advanced approach to envelope computation and,thus,yielding a more precise output,free from extraneous components.展开更多
The droplet formation dynamics of a Newtonian liquid in a drop-on-demand (DOD) inkjet process is numerically investigated by using a volume-of-fluid (VOF) method. We focus on the nozzle geometry, wettability of the in...The droplet formation dynamics of a Newtonian liquid in a drop-on-demand (DOD) inkjet process is numerically investigated by using a volume-of-fluid (VOF) method. We focus on the nozzle geometry, wettability of the interior surface, and the fluid properties to achieve the stable droplet formation with higher velocity. It is found that a nozzle with contracting angle of 45° generates the most stable and fastest single droplet, which is beneficial for the enhanced printing quality and high-throughput printing rate. For this nozzle with the optimal geometry, we systematically change the wettability of the interior surface, i.e., different contact angles. As the contact angle increases, pinch-off time increases and the droplet speed reduces. Finally, fluids with different properties are investigated to identify the printability range.展开更多
Physics success is largely determined by using mathematics.Physics often themselves create the necessary mathematical apparatus.This article shows how you can construct a fractal calculus-mathematics of fractal geomet...Physics success is largely determined by using mathematics.Physics often themselves create the necessary mathematical apparatus.This article shows how you can construct a fractal calculus-mathematics of fractal geometry.In modem scientific literature often write from a firm that"there is no strict definition of fractals",to the more moderate that"objects in a certain sense,fractal and similar."We show that fractal geometry is a strict mathematical theory,defined by their axioms.This methodology allows the geometry of axiomatised naturally define fractal integrals and differentials.Consistent application on your input below the axiom gives the opportunity to develop effective methods of measurement of fractal dimension,geometri-cal interpretation of fractal derivative gain and open dual symmetry.展开更多
The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satell...The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.展开更多
The scaled boundary finite element method (SBFEM)is applied to the static analysis of two dimensional elasticity problem,boundary value problems domain with the domain completely described by a circular defining curve...The scaled boundary finite element method (SBFEM)is applied to the static analysis of two dimensional elasticity problem,boundary value problems domain with the domain completely described by a circular defining curve. The scaled boundary finite element equations is formulated within a general framework integrating the influence of the distributed body force,general boundary conditions,and bounded and unbounded domain.This paper investigates the possibility of using exact geometry to form the exact description of the circular defining curve and the standard finite element shape function to approximate the defining curve.Three linear elasticity problems are presented to verify the proposed method with the analytical solution.Numerical examples show the accuracy and efficiency of the proposed method,and the performance is found to be better than using standard linear element for the approximation defining curve on the scaled boundary method.展开更多
Recently, positioning services have received considerable attention. The primary source of the positioning error is non-line-of-sight(NLOS) propagation. To address this problem, we propose a novel NLOS mitigation sche...Recently, positioning services have received considerable attention. The primary source of the positioning error is non-line-of-sight(NLOS) propagation. To address this problem, we propose a novel NLOS mitigation scheme, in which the geometric relationship between a base station and a mobile station is used.This makes it possible to identify range measurements corrupted by NLOS errors, and the mobile station can then estimate its position through line-of-sight(LOS) measurements. Moreover, the threshold of the NLOS detector is derived via a hybrid method using both the analytical derivation and computer simulation, which significantly reduces the difficulty of identifying thresholds. After identifying the NLOS measurements, a two-step weighted-least-squares algorithm is used to obtain the localization, in which both range and angle measurements are considered. The simulation results reveal that the proposed algorithm yields a high identification probability of NLOS measurements, which results in improved localization performance.展开更多
To reveal the geometry of the seismogenic structure of the Aug.8,2017 MS 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct.31,2017 were used to...To reveal the geometry of the seismogenic structure of the Aug.8,2017 MS 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct.31,2017 were used to relocate the earthquake sequence by the tomoDD program,and the focal mechanism solutions and centroid depths of the ML≥3.5 events in the sequence were determined using the CAP waveform inversion method.Further,the segmental tectonic deformation characteristics of the seismogenic faults were analyzed preliminarily by using strain rosettes and areal strains(As).The results indicate:(1)The relocated MS 7.0 Jiuzhaigou earthquake sequence displays a narrow~38 km long NNW-SSE-trending zone between the NW-striking Tazang Fault and the nearly NSstriking Minjiang Fault,two branches of the East Kunlun Fault Zone.The spatial distribution of the sequence is narrow and deep for the southern segment,and relatively wide and shallow for the northern segment.The initial rupture depth of the mainshock is 12.5 km,the dominant depth range of the aftershock sequence is between 0 and 10 km with an average depth of 6.7 km.The mainshock epicenter is located in the middle of the aftershock region,showing a bilateral rupture behavior.The centroid depths of 32 ML≥3.5 events range from 3 to 12 km with a mean of about 7.3 km,consistent with the predominant focal depth of the whole sequence.(2)The geometric structure of the seismogenic fault on the southern section of the aftershock area(south of the mainshock)is relatively simple,with overall strike of~150°and dip angle~75°,but the dip angle and dip-orientation exhibit some variation along the segment.The seismogenic structure on the northern segment is more complicated;several faults,including the Minjiang Fault,may be responsible for the aftershock activities.The overall strike of this section is~159°and dip angle is~59°,illustrating a certain clockwise rotation and a smaller dip angle than the southern segment.The differences between the two segments demonstrate vari展开更多
This paper presents an efficient and accurate numerical technique based upon the scaled boundary finite element method for the analysis of two-dimensional,linear,second-order,boundary value problems with a domain comp...This paper presents an efficient and accurate numerical technique based upon the scaled boundary finite element method for the analysis of two-dimensional,linear,second-order,boundary value problems with a domain completely described by a circular defining curve.The scaled boundary finite element formulation is established in a general framework allowing single-field and multi-field problems,bounded and unbounded bodies,distributed body source,and.general boundary conditions to be treated in a unified fashion.The conventional polar coordinates together with a properly selected scaling center are utilized to achieve the exact description of the circular defining curve,exact geometry of the domain,and exact spatial differential operators.Standard finite element shape functions are employed in the discretization of both trial and test functions in the circumferential direction and the resulting eigenproblem is solved by a selected efficient algorithm.The computational performance of the implemented procedure is then fully investigated for various scenarios to demonstrate the accuracy in comparison with standard linear elements.展开更多
The geometry relation and the contact point-pairs detection between two three dimensional(3D) objects with arbitrary shapes are essential problems involved in discontinuous computation and computational geometry. This...The geometry relation and the contact point-pairs detection between two three dimensional(3D) objects with arbitrary shapes are essential problems involved in discontinuous computation and computational geometry. This paper reported a geometry relation judgment and contact searching algorithm based on Contact Theory. A contact cover search algorithm is proposed to find all the possible contact cover between two blocks. Two blocks can come to contact only on these covers. Each contact cover can define a possible contact point-pair between two blocks. Data structure and flow chart are provided, as well as some examples in details.Contact problems involving concave blocks or parallel planes are considered to be very difficult in past and are solved by this algorithm. The proposed algorithm is compacted and applicable to the discontinuous computation, such as robotic control, rock mass stability, dam stability etc. A 3D cutting and block searching algorithm is also proposed in this study and used to search the outer boundary of the 3D entrance block when 3D concave blocks are encountered. The 3D cutting and block searching algorithm can be also used to form the block system for jointed rock.展开更多
Definition of hydraulic geometry of navigable canals and its expression are studied in this paper.The hydrodynamic and morphologic characteristics of navigable canals are analyzed on the basis of the data collected fr...Definition of hydraulic geometry of navigable canals and its expression are studied in this paper.The hydrodynamic and morphologic characteristics of navigable canals are analyzed on the basis of the data collected from field surveys conducted at two segments of the Grand Canal in Jiangsu Province,China.The channel morphologic factor and the ship hydrodynamic factor are adopted to describe the hydraulic geometry relation of navigable canals.The correlation analysis shows that the ship hydrodynamics can be a dominant factor influencing the channel evolution with larger determination coefficient.Furthermore,the undetermined index in the proposed hydraulic geometry relation is also discussed,which indicates that the index related to the intensity of water flow(qualitatively reflected by the integrated ship flow intensity)is within a range of 0.5 to 1.0.展开更多
文摘A novel scanning technique using a rotating-head sonar profiler attached to a slider mechanism is presented as a means to directly measure the complex erosion and deposition features of local scour holes developing in clear-water conditions around vertical cylinders mimicking bridge piers.Extensive validation shows that the method produces high-density elevation surfaces to within y1.5±2 mm accuracy in a quasi-non-invasive manner.This equates to 0.5±0.7%relative to the flow depth which sonar resolution is well known to scale with.Experimental data from three trials using different cylinder diameters indicate that monitoring of the entire scour hole over time(instead of only the maximum depth as is commonly done in laboratory experiments)can reveal important information about local scour evolution.In particular,results show that the scour-hole volume scales with the maximum scour depth cubed(VOLy3s)through three linear regimes.The transition to the third linear regime was found to represent a step change in the scour evolution process.Following the recent theoretical framework proposed by Manes and Brocchini(2015),this change,termed the crossover point,was interpreted as the point where the production of turbulent kinetic energy plateaus which corresponds to a stabilization in the erosive power of the horseshoe vortex.Scour development beyond the crossover point is characterised by a significant reduction in the rate of volumetric scour,relative to the steadily-increasing maximum scour depth.This overall reduction in volume-development is attributed to a balance between erosion from in-front of the pier and deposition around the sides using topography analysis.It is speculated that the existence of the crossover point may help to identify the characteristic length and time scales describing the evolution of local scour,which may be used for modeling purposes.
基金the National Key Research and Development Program of China under Grant No.2017YFB1401302the National Natural Science Foundation of China under Grant No.41671377.
文摘The algebraic methods represented by Wu's method have made significant breakthroughs in the field of geometric theorem proving.Algebraic proofs usually involve large amounts of calcula- tions,thus making it difficult to understand intuitively.However,if the authors look at Wu's method from the perspective of identity,Wu's method can be understood easily and can be used to generate new geometric propositions.To make geometric reasoning simpler,more expressive,and richer in geometric meaning,the authors establish a geometric algebraic system (point geometry built on nearly 20 basic properties/formulas about operations on points)while maintaining the advantages of the coordinate method,vector method,and particle geometry method and avoiding their disadvantages.Geometric relations in the propositions and conclusions of a geometric problem are expressed as identical equations of vector polynomials according to point geometry.Thereafter,a proof method that maintains the essence of Wu's method is introduced to find the relationships between these equations.A test on more than 400 geometry statements shows that the proposed proof method,which is based on identical equations of vector polynomials,is simple and effective.Furthermore,when solving the original problem,this proof method can also help the authors recognize the relationship between the propositions of the problem and help the authors generate new geometric propositions.
文摘Lateral migration of the Bhagirathi River temporally creates unavoidable geomorphic hazards in West Bengal,India.The Bhagirathi River flows SW for-67.30 km betwee n the confluenee point of Ajay and Jalangi rivers in East Burdwan and Nadia districts of West Bengal.The course of Bhagirathi is notably migration prone and cultivates problematic changes along its course over time.In the study,we have looked into its migration tendency and unpredictability for past 238 years and then predicted the lateral shifting of river centerline using temporal satellite imageries-Landsat-5(TM)of 1987(8,December),1995(28,January),2005(7,January)and LISS-IV satellite imagery(2017,5 January);SOI Toposheet-1968-1969(79A/2,79A/3,79A/6 and 79A/7)and RennelPs map of 1779.Other highlights are the quest of fluvial features,oxbow lakes,mid-channel bars,channel migration rate,meander geometry,channel sinuosity in different parts of river course and the parts that experience intensive bank erosion.The entire river course has been subdivided into three segments;viz.reaches A,B and C.Investigation displays that degree of sinuosity decreases from its anterior course(1968)to the existing course(2017).Reach-specific outputs display that reach B is highly sinuous(SI value 1.94 in 2017)and SI increases temporarily,whereas for reaches A and C it decreases with time.The rate of migration is higher in reach B than that in reaches C and A.The study displays a notably decreasing trend of migration in comparison with its previous lateral migration and shows that the migration nature over time is intensively inconsistent and unpredictable except very few portions of the river course.The nature of deposition within the river channel shows an unstable behavior during the entire period of the study.Meander geometry depicts a rapid change of river course innate to meander bends and shows a higher rate of migration by meander loop cut-off rather than lateral migration that reflects the inconsistency,erosion vulnerability and unpredictable nature of migration.Th
基金the Army Research Office and was accomplished under Grant Nos. US ARMY W911NF-14-1- 0343, W911NF-16-1-0436, and W911NF-17-1-0428. And we would like to appreciate the National Natural Science Foundation of China (NSFC) for supporting Pingjie Huang (Grant Nos. 61473255 and 61873234).
文摘With the increasing demands for remote spectroscopy in many fields ranging from homeland security to environmental monitoring, terahertz (THz) spectroscopy has drawn a significant amount of attention because of its capability to acquire chemical spectral signatures non-invasively. However, advanced THz remote sensing techniques are obstructed by quite a few factors, such as THz waves being strongly absorbed by water vapor in the ambient air, difficulty to generate intense broadband coherent THz source remotely, and hard to transmit THz waveform information remotely without losing the signal to noise ratio, etc. In this review, after introducing different THz air-photonics techniques to overcome the difficulties of THz remote sensing, we focus mainly on theoretical and experimental methods to improve THz generation and detection performance for the purpose of remote sensing through tailoring the generation and detection media, air-plasma. For the THz generation part, auto-focusing ring-Airy beam was introduced to enhance the THz wave generation yield from two-color laser induced air plasma. By artificially modulated exotic wave packets, it is exhibited that abruptly auto-focusing beam induced air-plasma can give an up to 5.3-time-enhanced THz wave pulse energy compared to normal Gaussian beam induced plasma under the same conditions. At the same time, a red shift on the THz emission spectrum is also observed. A simulation using an interference model to qualitatively describe these behaviors has be developed. For the THz detection part, the results of THz remote sensing at 30 m using THz-radiation-enhanced-emission- of-fluorescence (THz-REEF) technique are demonstrated, which greatly improved from the 10 m demonstration last reported. The THz-REEF technique in the counter-propagation geometry was explored, which is proved to be more practical for stand-off detections than co-propagation geometry. We found that in the counter- propagating geometry the maximum amplitude of the REEF signal is comparable to that in the
文摘The feasibility of a volumetric modulated arc therapy (VMAT) based coronal arc (cARC) technique for treating a single brain metastasis or lesion proximal to the brainstem or optic chiasm was evaluated. Coplanar (CP) and non-coplanar (NCP) treatment plans to an anthropomorphic head/neck phantom scanned head-first supine were compared to a cARC plan with the phantom rotated vertically. A set of planning target volumes (PTVs) were contoured centrally between the brainstem and optic chiasm (“Ant PTVs”) and posterior to brainstem (“Post PTVs”). Dosimetric indices such as conformity index (C.I.), gradient measure (G.M.), and dose volume histograms (DVHs) were compared for CP, NCP and cARC techniques. The TG101 guidelines for organs-at-risk (OARs), and 95% of PTV receiving at least 100% of the prescription dose (D95 = 100%) were used as plan objectives. Reductions in D50 and D30 to the brainstem of 85.1% ± 3.9% and 87.6% ± 3.2%, respectively were seen for “Post PTVs”, and 51.1% ± 17.8% and 85.6% ± 6.0% respectively for “Ant PTVs” using cARC versus CP (p ≤ 0.01). For chiasm, reductions of D50 and D30 were 61.7% ± 3.2% and 44.2% ± 8.9% for “Ant PTVs”, by 69.3% ± 8.0% and 74.3% ± 8.2% for “Post PTVs” (p ≤ 0.01). Comparing cARC to NCP led to similar dosimetric improvements. The conformity index (C.I.) was measured to be 1.101 ± 0.038, 1.088 ± 0.054, and 1.060 ± 0.040 for cARC, CP and NCP respectively (p ≤ 0.01). The overall GM in cm was 0.581 ± 0.097, 0.708 ± 0.064, and 0.476 ± 0.050 for cARC, CP and NCP respectively (p ≤ 0.01). The mean distance gradient fall-off (in cm) was 0.249 ± 0.038 (cARC), 0.749 ± 0.107 (CP), and 0.621 ± 0.068 (NCP) at the center slice in anterior-posterior direction of the target volume (p ≤ 0.01). The objective of this study is to compare the dosimetric indices of cARC with CP and NCP techniques. In conclusion, cARC can provide improved dosimetry as compared to CP and NCP for lesion proximal to the brainstem or optic chiasm.
基金the Spanish Ministerio de Economia y Competitividadthe European Regional Development Fund (ERDF)under Grant No.MTM2017-88796-P.
文摘The idea of envelope of a family of plane curves is an elementary notion in differential geometry.As such,its implementation in dynamic geometry environments is quite universal (Cabri, The Geometer's Sketchpad,Cinderella,GeoGebra,...).Nevertheless,most of these programs return, when computing certain envelopes,both some spurious solutions and the curves that truly fit in the intuitive definition of envelope.The precise distinction between spurious and genuine parts has not been made before:This paper proposes such distinction in an algorithmic way,ready for its implementation in interactive geometry systems,allowing a finer classification of the different parts resulting from the current,advanced approach to envelope computation and,thus,yielding a more precise output,free from extraneous components.
基金the National Natural Science Foundation of China (No. 11802004)the Chinese Scholarship Council (CSC) for providing Chinese Government Scholarship (CGS).
文摘The droplet formation dynamics of a Newtonian liquid in a drop-on-demand (DOD) inkjet process is numerically investigated by using a volume-of-fluid (VOF) method. We focus on the nozzle geometry, wettability of the interior surface, and the fluid properties to achieve the stable droplet formation with higher velocity. It is found that a nozzle with contracting angle of 45° generates the most stable and fastest single droplet, which is beneficial for the enhanced printing quality and high-throughput printing rate. For this nozzle with the optimal geometry, we systematically change the wettability of the interior surface, i.e., different contact angles. As the contact angle increases, pinch-off time increases and the droplet speed reduces. Finally, fluids with different properties are investigated to identify the printability range.
文摘Physics success is largely determined by using mathematics.Physics often themselves create the necessary mathematical apparatus.This article shows how you can construct a fractal calculus-mathematics of fractal geometry.In modem scientific literature often write from a firm that"there is no strict definition of fractals",to the more moderate that"objects in a certain sense,fractal and similar."We show that fractal geometry is a strict mathematical theory,defined by their axioms.This methodology allows the geometry of axiomatised naturally define fractal integrals and differentials.Consistent application on your input below the axiom gives the opportunity to develop effective methods of measurement of fractal dimension,geometri-cal interpretation of fractal derivative gain and open dual symmetry.
基金Under the auspices the Fundamental Research Funds for the Central Universities,China(No.2017TD-26)the Plan for Changbai Mountain Scholars of Jilin Province,China(No.JJLZ[2015]54).
文摘The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.
文摘The scaled boundary finite element method (SBFEM)is applied to the static analysis of two dimensional elasticity problem,boundary value problems domain with the domain completely described by a circular defining curve. The scaled boundary finite element equations is formulated within a general framework integrating the influence of the distributed body force,general boundary conditions,and bounded and unbounded domain.This paper investigates the possibility of using exact geometry to form the exact description of the circular defining curve and the standard finite element shape function to approximate the defining curve.Three linear elasticity problems are presented to verify the proposed method with the analytical solution.Numerical examples show the accuracy and efficiency of the proposed method,and the performance is found to be better than using standard linear element for the approximation defining curve on the scaled boundary method.
基金supported by National Natural Science Foundation of China(Grant No.61471322)Open Project of Zhejiang Provincial Key Laboratory of Information Processing,Communication and Networking,Zhejiang,China.
文摘Recently, positioning services have received considerable attention. The primary source of the positioning error is non-line-of-sight(NLOS) propagation. To address this problem, we propose a novel NLOS mitigation scheme, in which the geometric relationship between a base station and a mobile station is used.This makes it possible to identify range measurements corrupted by NLOS errors, and the mobile station can then estimate its position through line-of-sight(LOS) measurements. Moreover, the threshold of the NLOS detector is derived via a hybrid method using both the analytical derivation and computer simulation, which significantly reduces the difficulty of identifying thresholds. After identifying the NLOS measurements, a two-step weighted-least-squares algorithm is used to obtain the localization, in which both range and angle measurements are considered. The simulation results reveal that the proposed algorithm yields a high identification probability of NLOS measurements, which results in improved localization performance.
基金National Science Foundation of China(41574047)National Key R&D Program of China(2018YFC150330501).
文摘To reveal the geometry of the seismogenic structure of the Aug.8,2017 MS 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct.31,2017 were used to relocate the earthquake sequence by the tomoDD program,and the focal mechanism solutions and centroid depths of the ML≥3.5 events in the sequence were determined using the CAP waveform inversion method.Further,the segmental tectonic deformation characteristics of the seismogenic faults were analyzed preliminarily by using strain rosettes and areal strains(As).The results indicate:(1)The relocated MS 7.0 Jiuzhaigou earthquake sequence displays a narrow~38 km long NNW-SSE-trending zone between the NW-striking Tazang Fault and the nearly NSstriking Minjiang Fault,two branches of the East Kunlun Fault Zone.The spatial distribution of the sequence is narrow and deep for the southern segment,and relatively wide and shallow for the northern segment.The initial rupture depth of the mainshock is 12.5 km,the dominant depth range of the aftershock sequence is between 0 and 10 km with an average depth of 6.7 km.The mainshock epicenter is located in the middle of the aftershock region,showing a bilateral rupture behavior.The centroid depths of 32 ML≥3.5 events range from 3 to 12 km with a mean of about 7.3 km,consistent with the predominant focal depth of the whole sequence.(2)The geometric structure of the seismogenic fault on the southern section of the aftershock area(south of the mainshock)is relatively simple,with overall strike of~150°and dip angle~75°,but the dip angle and dip-orientation exhibit some variation along the segment.The seismogenic structure on the northern segment is more complicated;several faults,including the Minjiang Fault,may be responsible for the aftershock activities.The overall strike of this section is~159°and dip angle is~59°,illustrating a certain clockwise rotation and a smaller dip angle than the southern segment.The differences between the two segments demonstrate vari
基金CU Scholarship for ASEAN Countries 2013 and Thailand Research Fund (Grant No.RSA5980032).
文摘This paper presents an efficient and accurate numerical technique based upon the scaled boundary finite element method for the analysis of two-dimensional,linear,second-order,boundary value problems with a domain completely described by a circular defining curve.The scaled boundary finite element formulation is established in a general framework allowing single-field and multi-field problems,bounded and unbounded bodies,distributed body source,and.general boundary conditions to be treated in a unified fashion.The conventional polar coordinates together with a properly selected scaling center are utilized to achieve the exact description of the circular defining curve,exact geometry of the domain,and exact spatial differential operators.Standard finite element shape functions are employed in the discretization of both trial and test functions in the circumferential direction and the resulting eigenproblem is solved by a selected efficient algorithm.The computational performance of the implemented procedure is then fully investigated for various scenarios to demonstrate the accuracy in comparison with standard linear elements.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51479001, 41471052)the China Institute of Water Resources and Hydropower Research Research & Development Support Program(Grant Nos. GE0145B462017, GE0145B692017)
文摘The geometry relation and the contact point-pairs detection between two three dimensional(3D) objects with arbitrary shapes are essential problems involved in discontinuous computation and computational geometry. This paper reported a geometry relation judgment and contact searching algorithm based on Contact Theory. A contact cover search algorithm is proposed to find all the possible contact cover between two blocks. Two blocks can come to contact only on these covers. Each contact cover can define a possible contact point-pair between two blocks. Data structure and flow chart are provided, as well as some examples in details.Contact problems involving concave blocks or parallel planes are considered to be very difficult in past and are solved by this algorithm. The proposed algorithm is compacted and applicable to the discontinuous computation, such as robotic control, rock mass stability, dam stability etc. A 3D cutting and block searching algorithm is also proposed in this study and used to search the outer boundary of the 3D entrance block when 3D concave blocks are encountered. The 3D cutting and block searching algorithm can be also used to form the block system for jointed rock.
基金the National Natural Science Foundation of China(No.51479035)the Scientific Research Foundation of Graduate School of Southeast University(No.YBPY1883).
文摘Definition of hydraulic geometry of navigable canals and its expression are studied in this paper.The hydrodynamic and morphologic characteristics of navigable canals are analyzed on the basis of the data collected from field surveys conducted at two segments of the Grand Canal in Jiangsu Province,China.The channel morphologic factor and the ship hydrodynamic factor are adopted to describe the hydraulic geometry relation of navigable canals.The correlation analysis shows that the ship hydrodynamics can be a dominant factor influencing the channel evolution with larger determination coefficient.Furthermore,the undetermined index in the proposed hydraulic geometry relation is also discussed,which indicates that the index related to the intensity of water flow(qualitatively reflected by the integrated ship flow intensity)is within a range of 0.5 to 1.0.