Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity,i.e.,the impact velocity at which interface defeat ceases and ceramic penetration occurs,decreased as the lengt...Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity,i.e.,the impact velocity at which interface defeat ceases and ceramic penetration occurs,decreased as the length scale increased.A possible explanation of how this scale effect is related to the formation of a cone crack in the ceramic has been presented by the authors in an earlier paper.Here,the influence of confinement and prestress on cone cracking and transition velocity is investigated.The hypothesis is that prestress will suppress the formation and growth of the cone crack by lowering the driving stress.A set of impact experiments has been performed in which the transition velocity for four different levels of prestress has been determined.The transition velocities as a function of the level of confining prestress is compared to an analytical model for the influence of prestress on the formation and extension of the cone crack in the ceramic material.Both experiments and model indicate that prestress has a strong influence on the transition from interface defeat to penetration,although the model underestimates the influence of prestress.展开更多
A model for the tendency of fragmentation of a long rod projectile subjected to armour components in add-on armours such as reactive armour and active protection systems is presented. The model is based on studies of ...A model for the tendency of fragmentation of a long rod projectile subjected to armour components in add-on armours such as reactive armour and active protection systems is presented. The model is based on studies of the interaction between a cylindrical streamlined projectile and moving thin plates(backwards moving like the front plate in a reactive armour panel and forwards moving like the rear plate in a reactive armour panel).The assumption behind the model is that the sliding force, with velocity vslidebetween the projectile and the plate, gives rise to a transverse velocity vtransof the projectile segment it passes, which will deflect the projectile segment. This deflection is assumed to be a major reason for the fractures that can emerge along the projectile. The velocity, geometry and material of the projectile and the plate are of importance for the fragmentation of the projectile and the dimensionless parameterδ? = v trans vslideexpresses how these parameters influence the break-up tendency. Experiments and simulations have verified that the identifiedδ?-parameter predicts an increased amount of fragmentation of the projectile with increasing value of this parameter.展开更多
Two different finite element software,LS-DYNA and Impetus,have been evaluated to test their ability to predict the deformation,fragmentation and acceleration of a controlled fragmentation charge casing.The general-pur...Two different finite element software,LS-DYNA and Impetus,have been evaluated to test their ability to predict the deformation,fragmentation and acceleration of a controlled fragmentation charge casing.The general-purpose program LS-DYNA was used with a multi-material ALE formulation and a masspreserving erosion criterion coupled to a Johnson-Cook fracture criterion.In the Impetus simulations,a third order Lagrangian element formulation was used for the casing and a node-splitting element erosion treatment coupled to a Cockcroft-Latham failure criterion was used to describe casing fracture.The high-explosive gases were described by a discrete particle formalism.In order to acquire data to validate our computational tools and constitutive models,a series of experiments have been performed using a laboratory charge with an internal grooved casing.In the test series,the charge geometry was fixed except that the groove depth were varied from very shallow to very deep resulting in different deformation patterns,fracture modes and terminal velocities.Various diagnostic tools captured the different stages of the expansion and fragmentation of the casing.A high-speed framing camera depicted the deformation pattern before fragmentation and was used to determine the moment when the casing failed.Three different complementary techniques were used to follow the acceleration of the fragments;a Photon Doppler velocimetry to determine the initial acceleration of the casing,double exposed radiographs to estimate the fragment velocity after break-up and a high-speed video to determine the terminal velocity of the fragment after leaving the fireball.In addition,the fragments were soft recovered in a set of sawdust pit tests and their final shape and weight were measured.A SEM was used to characterise the fracture surfaces and to determine the modus of fracture(tensile or shear failure).Comparisons to experiments show that both software can predict the change in deformation behaviour when the groove depth increases,from tangential necking for shallow grooves to radial punching for deep groves.Both software could also reasonable well predict the acceleration of the fragments,though both overestimates the terminal velocity for the charge with the deepest grooves.展开更多
Reactive armour is a very efficient add-on armour against shaped charge threats.Explosive reactive armour consists of one or several plates that are accelerated by an explosive.Similar but less violent acceleration of...Reactive armour is a very efficient add-on armour against shaped charge threats.Explosive reactive armour consists of one or several plates that are accelerated by an explosive.Similar but less violent acceleration of plates can also be achieved in a completely inert reactive armour.To be efficient against elongated jets,the motion of the plates needs to be inclined against the jet such that a sliding contact between the jet and the plates is established.This sliding contact causes a deflection and thinning of the jet.Under certain circumstances,the contact will become unstable,leading to severe disturbances on the jet.These disturbances will drastically reduce the jet penetration performance and it is therefore of interest to study the conditions that leads to an unstable contact.Previous studies on the interaction between shaped charge jets and flyer plates have shown that it is mainly the forward moving plate in an explosive reactive armour that is effective in disturbing the jet.This is usually attributed to the higher plate-to-jet mass flux ratio involved in the collision of the forward moving plate compared to the backward moving plate.For slow moving plates,as occurs in inert reactive armour,the difference in mass flux for the forward and backward moving plate is much lesser,and it is therefore of interest to study if other factors than the mass flux influences on the protection capability.In this work,experiments have been performed where a plate is accelerated along its length,interacting with a shaped charge jet that is fired at an oblique angle to the plate’s normal,either against or along the plate’s velocity.The arrangement corresponds to a jet interacting with a flyer plate from a reactive armour,with the exception that the collision velocity is the same for both types of obliquities in these experiments.The experiments show that disturbances on the jet are different in the two cases even though the collision velocities are the same.Numerical simulations of the interaction support the observation.The difference is attributed to the character of the contact pressure in the interaction region.For a backward moving plate,the maximum contact pressure is obtained at the beginning of the interaction zone and the contact pressure is therefore higher upstream than downstream of the jet while the opposite is true for a forward moving plate.A negative interface pressure gradient with respect to the jet motion results in a more stable flow than a positive,which means that the jet-plate contact is more stable for a backward moving plate than for a forward moving plate.A forward moving plate is thus more effective in disturbing the jet than a backward moving plate,not only because of the higher jet to plate mass flux ratio but also because of the character of the contact with the jet.展开更多
The development of a pseudo-one pot synthesis of 3（5）,4-dinitropyrazole enabled us to use it as a starting material for energetic plasticisers. Its acidic proton allowed simple derivatisation on one of the ring nitr...The development of a pseudo-one pot synthesis of 3（5）,4-dinitropyrazole enabled us to use it as a starting material for energetic plasticisers. Its acidic proton allowed simple derivatisation on one of the ring nitrogens. The thermal characteristics of two derivatives were evaluated. For instance, the N-allyl compound was a liquid with very low glass transition temperature, whereas the N-propargyl compound was a sticky solid at ambient temperature. The two compounds were both thermally stable according to STANAG 4582.展开更多
Maximum entropy likelihood (MEEL) methods also known as exponential tilted empirical likelihood methods using constraints from model Laplace transforms (LT) are introduced in this paper. An estimate of overall loss of...Maximum entropy likelihood (MEEL) methods also known as exponential tilted empirical likelihood methods using constraints from model Laplace transforms (LT) are introduced in this paper. An estimate of overall loss of efficiency based on Fourier cosine series expansion of the density function is proposed to quantify the loss of efficiency when using MEEL methods. Penalty function methods are suggested for numerical implementation of the MEEL methods. The methods can easily be adapted to estimate continuous distribution with support on the real line encountered in finance by using constraints based on the model generating function instead of LT.展开更多
Three surface integral approaches of the acoustic analogies are studied to predict the noise from three concep- tual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff...Three surface integral approaches of the acoustic analogies are studied to predict the noise from three concep- tual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings （FW-H） method of the permeable integral surface and the Curle method that is known as a special case of the FW-H method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specially from the pressure perturbation on the wall. A new way to con- struct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex object-the actual wing with high-lift devices-the integral surface based on the vorticity is constructed to follow the flow structures. The surface location is discussed for the Kirchhoff method and the FW-H method because a common surface is used for them. The noise from the core flow region is studied on the basis of the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FW-H formulation. The role of each wall component on noise contribution is analyzed using the Curle formulation. Effects of the volume integral terms of Lighthill＇s stress tensors on the noise pre-diction are then evaluated by comparing the results of the Curle method with the other two methods.展开更多
GMM inference procedures based on the square of the modulus of the model characteristic function are developed using sample moments selected using estimating function theory and bypassing the use of empirical characte...GMM inference procedures based on the square of the modulus of the model characteristic function are developed using sample moments selected using estimating function theory and bypassing the use of empirical characteristic function of other GMM procedures in the literature. The procedures are relatively simple to implement and are less simulation-oriented than simulated methods of inferences yet have the potential of good efficiencies for models with densities without closed form. The procedures also yield better estimators than method of moment estimators for models with more than three parameters as higher order sample moments tend to be unstable.展开更多
Generalized method of moments based on probability generating function is considered. Estimation and model testing are unified using this approach which also leads to distribution free chi-square tests. The estimation...Generalized method of moments based on probability generating function is considered. Estimation and model testing are unified using this approach which also leads to distribution free chi-square tests. The estimation methods developed are also related to estimation methods based on generalized estimating equations but with the advantage of having statistics for model testing. The methods proposed overcome numerical problems often encountered when the probability mass functions have no closed forms which prevent the use of maximum likelihood (ML) procedures and in general, ML procedures do not lead to distribution free model testing statistics.展开更多
Using the fact that a multivariate random sample of n observations also generates n nearest neighbour distance (NND) univariate observations and from these NND observations, a set of n auxiliary observations can be ob...Using the fact that a multivariate random sample of n observations also generates n nearest neighbour distance (NND) univariate observations and from these NND observations, a set of n auxiliary observations can be obtained and with these auxiliary observations when combined with the original multivariate observations of the random sample, a class of pseudodistance?Dh?is allowed to be used and inference methods can be developed using this class of pseudodistances. The Dh?estimators obtained from this class can achieve high efficiencies and have robustness properties. Model testing also can be handled in a unified way by means of goodness-of-fit tests statistics derived from this class which have an asymptotic normal distribution. These properties make the developed inference methods relatively simple to implement and appear to be suitable for analyzing multivariate data which are often encountered in applications.展开更多
Dizziness, chest discomfort, chest depression and dyspnea are a group of symptoms that are common complaints in clinical practice. Patients with these symptoms are usually informed that while neurosis consequent to co...Dizziness, chest discomfort, chest depression and dyspnea are a group of symptoms that are common complaints in clinical practice. Patients with these symptoms are usually informed that while neurosis consequent to coronary heart disease is excluded nonetheless they remain unhealthy with no rational explanation or treatment. 165 cases of these symptoms and 85 control subjects were reviewed and underwent further medical history inquiry, routine EKG test and cardiac ultrasound examination. Thirty-five patients received coronary artery angiography to exclude coronary heart disease. Serum myocardial autoantibodies against beta1-adrenoceptor, alpha-myosin heavy chain, M2-muscarinic receptor and adenine-nucleotide translocator were tested, and inflammatory cytokines and high sensitivity C-reaction protein were measured and lymphocyte subclass was assayed by flow cytometry. All patients had a complex of four symptoms or tetralogy： （1） persistent throat or upper respiratory tract infection, （2） neck pain, （3） chest pain and （4） chest depression or dyspnea, some of them with anxiety. Anti-myocardial autoantibodies （AMCAs） were present in all patients vs. 8% in controls. TNF-α, IL-1 and IL-6 were significantly higher in patients than in controls （P〈0.01）. CD3^＋ and CD4-CD8^＋ lymphocytes were significantly higher and CD56＋ lymphocytes lower in patients than those in controls （P〈0.01）. The ratio of serum pathogen antibodies positive against Coxsackie virus-B, cytomegalovirus, Mycoplasma pneumoniae and Chlamydia pneumoniae were all markedly higher in patients. These data led to identification of a persistent respiratory infection-related clinical syndrome, including persistent throat infection, neck spinal lesion, rib cartilage inflammation, symptoms of cardiac depression and dyspnea with or without anxiety.展开更多
Quadratic distance estimation making use of the sample quantile function over a continuous range is introduced. It extends previous methods which are based only on a few sample quantiles and it parallels the continuou...Quadratic distance estimation making use of the sample quantile function over a continuous range is introduced. It extends previous methods which are based only on a few sample quantiles and it parallels the continuous GMM method. Asymptotic properties are established for the continuous quadratic distance estimators (CQDE) and the implementation of the methods are discussed. The methods appear to be useful for balancing robustness and efficiency and useful for fitting distribution with model quantile function being simpler than its density function or distribution function.展开更多
A class of pseudo distances is used to derive test statistics using transformed data or spacings for testing goodness-of-fit for parametric models. These statistics can be considered as density based statistics and ex...A class of pseudo distances is used to derive test statistics using transformed data or spacings for testing goodness-of-fit for parametric models. These statistics can be considered as density based statistics and expressible as simple functions of spacings. It is known that when the null hypothesis is simple, the statistics follow asymptotic normal distributions without unknown parameters. In this paper we emphasize results for the null composite hypothesis: the parameters can be estimated by a generalized spacing method (GSP) first which is equivalent to minimize a pseudo distance from the class which is considered;subsequently the estimated parameters are used to replace the parameters in the pseudo distance used for estimation;goodness-of-fit statistics for the composite hypothesis can be constructed and shown to have again an asymptotic normal distribution without unknown parameters. Since these statistics are related to a discrepancy measure, these tests can be shown to be consistent in general. Furthermore, due to the simplicity of these statistics and they come a no extra cost after fitting the model, they can be considered as alternative statistics to chi-square statistics which require a choice of intervals and statistics based on empirical distribution (EDF) using the original data with a complicated null distribution which might depend on the parametric family being considered and also might depend on the vector of true parameters but EDF tests might be more powerful against some specific models which are specified by the alternative hypothesis.展开更多
The Burgers＇ equation with uncertain initial and boundary conditions is approximated using a Polynomial Chaos Expansion （PCE） approach where the solution is represented as a series of stochastic, orthogonal polynom...The Burgers＇ equation with uncertain initial and boundary conditions is approximated using a Polynomial Chaos Expansion （PCE） approach where the solution is represented as a series of stochastic, orthogonal polynomials. The resulting truncated PCE system is solved using a novel numerical discretization method based on spatial derivative operators satisfying the summation by parts property and weak boundary conditions to ensure stability. The resulting PCE solution yields an accurate quantitative description of the stochastic evolution of the system, provided that appropriate boundary conditions are available. The specification of the boundary data is shown to influence the solution; we will discuss the problematic implications of the lack of precisely characterized boundary data and possible ways of imposing stable and accurate boundary conditions.展开更多
Every year,numerous environmental disasters and emergencies occur across the globe with far-reaching impacts on human health and the environment.The ability to rapidly assess an environmental emergency to mitigate pot...Every year,numerous environmental disasters and emergencies occur across the globe with far-reaching impacts on human health and the environment.The ability to rapidly assess an environmental emergency to mitigate potential risks and impacts is paramount.However,collating the necessary evidence in the early stages of an emergency to conduct a robust risk assessment is a major challenge.This article presents a methodology developed to help assess the risks and impacts during the early stages of such incidents,primarily to support the European Union Civil Protection Mechanism but also the wider global community in the response to environmental emergencies.An online rapid risk and impact assessment tool has also been developed to promote enhanced collaboration between experts who are working remotely,considering the impact of a disaster on the environment and public health in the short,medium,and long terms.The methodology developed can support the appropriate selection of experts and assets to be deployed to affected regions to ensure that potential public health and environmental risks and impacts are mitigated whenever possible.This methodology will aid defensible decision making,communication,planning,and risk management,and presents a harmonized understanding of the associated impacts of an environmental emergency.展开更多
基金funded by the Swedish Armed Forces and by the Army Research Laboratory through US Naval Regional Contracting Centre,Contract No.W911NF0810271
文摘Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity,i.e.,the impact velocity at which interface defeat ceases and ceramic penetration occurs,decreased as the length scale increased.A possible explanation of how this scale effect is related to the formation of a cone crack in the ceramic has been presented by the authors in an earlier paper.Here,the influence of confinement and prestress on cone cracking and transition velocity is investigated.The hypothesis is that prestress will suppress the formation and growth of the cone crack by lowering the driving stress.A set of impact experiments has been performed in which the transition velocity for four different levels of prestress has been determined.The transition velocities as a function of the level of confining prestress is compared to an analytical model for the influence of prestress on the formation and extension of the cone crack in the ceramic material.Both experiments and model indicate that prestress has a strong influence on the transition from interface defeat to penetration,although the model underestimates the influence of prestress.
基金the Swedish Armed Forces for the research fund that has financed this work
文摘A model for the tendency of fragmentation of a long rod projectile subjected to armour components in add-on armours such as reactive armour and active protection systems is presented. The model is based on studies of the interaction between a cylindrical streamlined projectile and moving thin plates(backwards moving like the front plate in a reactive armour panel and forwards moving like the rear plate in a reactive armour panel).The assumption behind the model is that the sliding force, with velocity vslidebetween the projectile and the plate, gives rise to a transverse velocity vtransof the projectile segment it passes, which will deflect the projectile segment. This deflection is assumed to be a major reason for the fractures that can emerge along the projectile. The velocity, geometry and material of the projectile and the plate are of importance for the fragmentation of the projectile and the dimensionless parameterδ? = v trans vslideexpresses how these parameters influence the break-up tendency. Experiments and simulations have verified that the identifiedδ?-parameter predicts an increased amount of fragmentation of the projectile with increasing value of this parameter.
基金funded by the Swedish Armed Forces under Grant No AF.9220616
文摘Two different finite element software,LS-DYNA and Impetus,have been evaluated to test their ability to predict the deformation,fragmentation and acceleration of a controlled fragmentation charge casing.The general-purpose program LS-DYNA was used with a multi-material ALE formulation and a masspreserving erosion criterion coupled to a Johnson-Cook fracture criterion.In the Impetus simulations,a third order Lagrangian element formulation was used for the casing and a node-splitting element erosion treatment coupled to a Cockcroft-Latham failure criterion was used to describe casing fracture.The high-explosive gases were described by a discrete particle formalism.In order to acquire data to validate our computational tools and constitutive models,a series of experiments have been performed using a laboratory charge with an internal grooved casing.In the test series,the charge geometry was fixed except that the groove depth were varied from very shallow to very deep resulting in different deformation patterns,fracture modes and terminal velocities.Various diagnostic tools captured the different stages of the expansion and fragmentation of the casing.A high-speed framing camera depicted the deformation pattern before fragmentation and was used to determine the moment when the casing failed.Three different complementary techniques were used to follow the acceleration of the fragments;a Photon Doppler velocimetry to determine the initial acceleration of the casing,double exposed radiographs to estimate the fragment velocity after break-up and a high-speed video to determine the terminal velocity of the fragment after leaving the fireball.In addition,the fragments were soft recovered in a set of sawdust pit tests and their final shape and weight were measured.A SEM was used to characterise the fracture surfaces and to determine the modus of fracture(tensile or shear failure).Comparisons to experiments show that both software can predict the change in deformation behaviour when the groove depth increases,from tangential necking for shallow grooves to radial punching for deep groves.Both software could also reasonable well predict the acceleration of the fragments,though both overestimates the terminal velocity for the charge with the deepest grooves.
基金funded by the Swedish Armed Forces under Contract No AT.9220620。
文摘Reactive armour is a very efficient add-on armour against shaped charge threats.Explosive reactive armour consists of one or several plates that are accelerated by an explosive.Similar but less violent acceleration of plates can also be achieved in a completely inert reactive armour.To be efficient against elongated jets,the motion of the plates needs to be inclined against the jet such that a sliding contact between the jet and the plates is established.This sliding contact causes a deflection and thinning of the jet.Under certain circumstances,the contact will become unstable,leading to severe disturbances on the jet.These disturbances will drastically reduce the jet penetration performance and it is therefore of interest to study the conditions that leads to an unstable contact.Previous studies on the interaction between shaped charge jets and flyer plates have shown that it is mainly the forward moving plate in an explosive reactive armour that is effective in disturbing the jet.This is usually attributed to the higher plate-to-jet mass flux ratio involved in the collision of the forward moving plate compared to the backward moving plate.For slow moving plates,as occurs in inert reactive armour,the difference in mass flux for the forward and backward moving plate is much lesser,and it is therefore of interest to study if other factors than the mass flux influences on the protection capability.In this work,experiments have been performed where a plate is accelerated along its length,interacting with a shaped charge jet that is fired at an oblique angle to the plate’s normal,either against or along the plate’s velocity.The arrangement corresponds to a jet interacting with a flyer plate from a reactive armour,with the exception that the collision velocity is the same for both types of obliquities in these experiments.The experiments show that disturbances on the jet are different in the two cases even though the collision velocities are the same.Numerical simulations of the interaction support the observation.The difference is attributed to the character of the contact pressure in the interaction region.For a backward moving plate,the maximum contact pressure is obtained at the beginning of the interaction zone and the contact pressure is therefore higher upstream than downstream of the jet while the opposite is true for a forward moving plate.A negative interface pressure gradient with respect to the jet motion results in a more stable flow than a positive,which means that the jet-plate contact is more stable for a backward moving plate than for a forward moving plate.A forward moving plate is thus more effective in disturbing the jet than a backward moving plate,not only because of the higher jet to plate mass flux ratio but also because of the character of the contact with the jet.
文摘The development of a pseudo-one pot synthesis of 3（5）,4-dinitropyrazole enabled us to use it as a starting material for energetic plasticisers. Its acidic proton allowed simple derivatisation on one of the ring nitrogens. The thermal characteristics of two derivatives were evaluated. For instance, the N-allyl compound was a liquid with very low glass transition temperature, whereas the N-propargyl compound was a sticky solid at ambient temperature. The two compounds were both thermally stable according to STANAG 4582.
文摘Maximum entropy likelihood (MEEL) methods also known as exponential tilted empirical likelihood methods using constraints from model Laplace transforms (LT) are introduced in this paper. An estimate of overall loss of efficiency based on Fourier cosine series expansion of the density function is proposed to quantify the loss of efficiency when using MEEL methods. Penalty function methods are suggested for numerical implementation of the MEEL methods. The methods can easily be adapted to estimate continuous distribution with support on the real line encountered in finance by using constraints based on the model generating function instead of LT.
基金supported by the Clean Sky Joint Undertaking(CSJU)(CS-GA-2009-255714)
文摘Three surface integral approaches of the acoustic analogies are studied to predict the noise from three concep- tual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings （FW-H） method of the permeable integral surface and the Curle method that is known as a special case of the FW-H method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specially from the pressure perturbation on the wall. A new way to con- struct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex object-the actual wing with high-lift devices-the integral surface based on the vorticity is constructed to follow the flow structures. The surface location is discussed for the Kirchhoff method and the FW-H method because a common surface is used for them. The noise from the core flow region is studied on the basis of the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FW-H formulation. The role of each wall component on noise contribution is analyzed using the Curle formulation. Effects of the volume integral terms of Lighthill＇s stress tensors on the noise pre-diction are then evaluated by comparing the results of the Curle method with the other two methods.
文摘GMM inference procedures based on the square of the modulus of the model characteristic function are developed using sample moments selected using estimating function theory and bypassing the use of empirical characteristic function of other GMM procedures in the literature. The procedures are relatively simple to implement and are less simulation-oriented than simulated methods of inferences yet have the potential of good efficiencies for models with densities without closed form. The procedures also yield better estimators than method of moment estimators for models with more than three parameters as higher order sample moments tend to be unstable.
文摘Generalized method of moments based on probability generating function is considered. Estimation and model testing are unified using this approach which also leads to distribution free chi-square tests. The estimation methods developed are also related to estimation methods based on generalized estimating equations but with the advantage of having statistics for model testing. The methods proposed overcome numerical problems often encountered when the probability mass functions have no closed forms which prevent the use of maximum likelihood (ML) procedures and in general, ML procedures do not lead to distribution free model testing statistics.
文摘Using the fact that a multivariate random sample of n observations also generates n nearest neighbour distance (NND) univariate observations and from these NND observations, a set of n auxiliary observations can be obtained and with these auxiliary observations when combined with the original multivariate observations of the random sample, a class of pseudodistance?Dh?is allowed to be used and inference methods can be developed using this class of pseudodistances. The Dh?estimators obtained from this class can achieve high efficiencies and have robustness properties. Model testing also can be handled in a unified way by means of goodness-of-fit tests statistics derived from this class which have an asymptotic normal distribution. These properties make the developed inference methods relatively simple to implement and appear to be suitable for analyzing multivariate data which are often encountered in applications.
基金supported by a grant from National Basic Research Program (973) of China (2007CB512004)NSFC (30430320 & 30571841).
文摘Dizziness, chest discomfort, chest depression and dyspnea are a group of symptoms that are common complaints in clinical practice. Patients with these symptoms are usually informed that while neurosis consequent to coronary heart disease is excluded nonetheless they remain unhealthy with no rational explanation or treatment. 165 cases of these symptoms and 85 control subjects were reviewed and underwent further medical history inquiry, routine EKG test and cardiac ultrasound examination. Thirty-five patients received coronary artery angiography to exclude coronary heart disease. Serum myocardial autoantibodies against beta1-adrenoceptor, alpha-myosin heavy chain, M2-muscarinic receptor and adenine-nucleotide translocator were tested, and inflammatory cytokines and high sensitivity C-reaction protein were measured and lymphocyte subclass was assayed by flow cytometry. All patients had a complex of four symptoms or tetralogy： （1） persistent throat or upper respiratory tract infection, （2） neck pain, （3） chest pain and （4） chest depression or dyspnea, some of them with anxiety. Anti-myocardial autoantibodies （AMCAs） were present in all patients vs. 8% in controls. TNF-α, IL-1 and IL-6 were significantly higher in patients than in controls （P〈0.01）. CD3^＋ and CD4-CD8^＋ lymphocytes were significantly higher and CD56＋ lymphocytes lower in patients than those in controls （P〈0.01）. The ratio of serum pathogen antibodies positive against Coxsackie virus-B, cytomegalovirus, Mycoplasma pneumoniae and Chlamydia pneumoniae were all markedly higher in patients. These data led to identification of a persistent respiratory infection-related clinical syndrome, including persistent throat infection, neck spinal lesion, rib cartilage inflammation, symptoms of cardiac depression and dyspnea with or without anxiety.
文摘Quadratic distance estimation making use of the sample quantile function over a continuous range is introduced. It extends previous methods which are based only on a few sample quantiles and it parallels the continuous GMM method. Asymptotic properties are established for the continuous quadratic distance estimators (CQDE) and the implementation of the methods are discussed. The methods appear to be useful for balancing robustness and efficiency and useful for fitting distribution with model quantile function being simpler than its density function or distribution function.
文摘A class of pseudo distances is used to derive test statistics using transformed data or spacings for testing goodness-of-fit for parametric models. These statistics can be considered as density based statistics and expressible as simple functions of spacings. It is known that when the null hypothesis is simple, the statistics follow asymptotic normal distributions without unknown parameters. In this paper we emphasize results for the null composite hypothesis: the parameters can be estimated by a generalized spacing method (GSP) first which is equivalent to minimize a pseudo distance from the class which is considered;subsequently the estimated parameters are used to replace the parameters in the pseudo distance used for estimation;goodness-of-fit statistics for the composite hypothesis can be constructed and shown to have again an asymptotic normal distribution without unknown parameters. Since these statistics are related to a discrepancy measure, these tests can be shown to be consistent in general. Furthermore, due to the simplicity of these statistics and they come a no extra cost after fitting the model, they can be considered as alternative statistics to chi-square statistics which require a choice of intervals and statistics based on empirical distribution (EDF) using the original data with a complicated null distribution which might depend on the parametric family being considered and also might depend on the vector of true parameters but EDF tests might be more powerful against some specific models which are specified by the alternative hypothesis.
基金Supported by the US Department of Energy under the PSAAP Program
文摘The Burgers＇ equation with uncertain initial and boundary conditions is approximated using a Polynomial Chaos Expansion （PCE） approach where the solution is represented as a series of stochastic, orthogonal polynomials. The resulting truncated PCE system is solved using a novel numerical discretization method based on spatial derivative operators satisfying the summation by parts property and weak boundary conditions to ensure stability. The resulting PCE solution yields an accurate quantitative description of the stochastic evolution of the system, provided that appropriate boundary conditions are available. The specification of the boundary data is shown to influence the solution; we will discuss the problematic implications of the lack of precisely characterized boundary data and possible ways of imposing stable and accurate boundary conditions.
基金The European Multiple Environmental Threats emergency NETwork(EMETNET)project was co-funded by the European Union.
文摘Every year,numerous environmental disasters and emergencies occur across the globe with far-reaching impacts on human health and the environment.The ability to rapidly assess an environmental emergency to mitigate potential risks and impacts is paramount.However,collating the necessary evidence in the early stages of an emergency to conduct a robust risk assessment is a major challenge.This article presents a methodology developed to help assess the risks and impacts during the early stages of such incidents,primarily to support the European Union Civil Protection Mechanism but also the wider global community in the response to environmental emergencies.An online rapid risk and impact assessment tool has also been developed to promote enhanced collaboration between experts who are working remotely,considering the impact of a disaster on the environment and public health in the short,medium,and long terms.The methodology developed can support the appropriate selection of experts and assets to be deployed to affected regions to ensure that potential public health and environmental risks and impacts are mitigated whenever possible.This methodology will aid defensible decision making,communication,planning,and risk management,and presents a harmonized understanding of the associated impacts of an environmental emergency.
