the application of segment axial density profiles to a human body inertia model the intention of this study was to construct segment density profiles and compare segment inertias calculated when uniform densities and profile densities are used in a mathematical model axial densities from computerized tomography ct slices for the body segments of a sample of chinese females zheng et al proceedings of the beijing asian games scientific congress 1990 were used to form profiles which could be employed in body segment models polynomials based on proportion of segment length were fitted to the reported mean slice densities these profiles were then used with five widely divergent samples n 10 young adult females young adult males infants male children and elderly adults the mathematical model used is based on an assumption that all segments can be represented by stacked elliptic cylinders the results show that when the profile densities were substituted for average cadaver densities the increase in the estimated total body mass was less than 0 85 for the individual segments use of the profile rather than average density increased the average segment mass estimate by up to 2 7 the centres of mass and the principal moments were affected by the variations in density along the axis as well as the magnitudes by up to 0 54 and 3 8 respectively although the effects of using the profiles appear to be small the differences for individual samples segments and parameters ranged up to 22 5 it is not possible to decide if average or profile densities produce more accurate estimates of inertia but the profile allows for axial variation in density and is therefore recommended

adjustments to zatsiorsky seluyanov s segment inertia parameters zatsiorsky et al in contemporary problems in biomechanics pp 272 291 crc press massachusetts 1990a obtained by means of a gamma ray scanning technique the relative body segment masses center of mass cm positions and radii of gyration for samples of college aged caucasian males and females although these data are the only available and comprehensive set of inertial parameters regarding young adult caucasians they have been rarely utilized for biomechanical analyses of subjects belonging to the same or a similar population the main reason is probably that zatsiorsky et al used bony landmarks as reference points for locating segment cms and defining segment lengths some of these landmarks were markedly distant from the joint centers currently used by most researchers as reference points the purpose of this study was to adjust the mean relative cm positions and radii of gyration reported by zatsiorsky et al in order to reference them to the joint centers or other commonly used landmarks rather than the original landmarks the adjustments were based on a number of carefully selected sources of anthropometric data

a new geometric based model to accurately estimate arm and leg inertial estimates segment estimates of mass center of mass and moment of inertia are required input parameters to analyze the forces and moments acting across the joints the objectives of this study were to propose a new geometric model for limb segments to evaluate it against criterion values obtained from dxa and to compare its performance to five other popular models twenty five female and 24 male college students participated in the study for the criterion measures the participants underwent a whole body dxa scan and estimates for segment mass center of mass location and moment of inertia frontal plane were directly computed from the dxa mass units for the new model the volume was determined from two standing frontal and sagittal photographs each segment was modeled as a stack of slices the sections of which were ellipses if they are not adjoining another segment and sectioned ellipses if they were adjoining another segment e g upper arm and trunk length of axes of the ellipses was obtained from the photographs in addition a sex specific non uniform density function was developed for each segment a series of anthropometric measurements were also taken by directly following the definitions provided of the different body segment models tested and the same parameters determined for each model comparison of models showed that estimates from the new model were consistently closer to the dxa criterion than those from the other models with an error of less than 5 for mass and moment of inertia and less than about 6 for center of mass location

trunk density profile estimates from dual x ray absorptiometry accurate body segment parameters are necessary to estimate joint loads when using biomechanical models geometric methods can provide individualized data for these models but the accuracy of the geometric methods depends on accurate segment density estimates the trunk which is important in many biomechanical models has the largest variability in density along its length therefore the objectives of this study were to 1 develop a new method for modeling trunk density profiles based on dual x ray absorptiometry dxa and 2 develop a trunk density function for college aged females and males that can be used in geometric methods to this end the density profiles of 25 females and 24 males were determined by combining the measurements from a photogrammetric method and dxa readings a discrete fourier transformation was then used to develop the density functions for each sex the individual density and average density profiles compare well with the literature there were distinct differences between the profiles of two of participants one female and one male and the average for their sex it is believed that the variations in these two participants density profiles were a result of the amount and distribution of fat they possessed further studies are needed to support this possibility the new density functions eliminate the uniform density assumption associated with some geometric models thus providing more accurate trunk segment parameter estimates in turn more accurate moments and forces can be estimated for the kinetic analyses of certain human movements

tests for parameter instability and structural change with unknown change point this paper considers tests for parameter instability and structural change with unknown change point the results apply to a wide class of parametric models that are suitable for estimation by generalized method of moments procedures the asymptotic distributions of the test statistics considered here are nonstandard because the change point parameter only appears under the alternative hypothesis and not under the null the tests considered here are shown to have nontrivial asymptotic local power against all alternatives for which the parameters are nonconstant the tests are found to perform quite well in a monte carlo experiment reported elsewhere copyright 1993 by the econometric society

on the finite containment problem for petri nets abstract we prove that the finite containment problem fcp for petri nets is dtime ackermann complete for the reducibility p t thus sharpening previous results due to mcaloon 1984 and to mayr and meyer 1981 our principal technique is to replace an application of the infinite ramsey theorem by a certain finite ramsey theorem previously studied by paris 1980 and by ketonen and solovay 1981 such techniques may have further applications in obtaining upper bounds for combinatorial problems

petri nets and large finite sets an upper bound is given for the complexity of the karp miller decision procedure for the finite containment problem for pairs of petri nets the procedure is shown to be primitive recursive in the ackermann function bounds for the lengths of the searches involved are obtained in terms of large finite sets in the sense of paris harrington and of ketonen solovay

geometric and inertial data of the trunk in adult males in this study investigations on geometric and inertial quantities of 15 male patients trunks are described layers of 8 mm were scanned using computerized tomography thorax abdomen pelvis and two shoulders and their unchangeable and changeable muscle fat and skin tissues were investigated the trunk was also divided into portions and subportions according to anthropological landmarks by comparing subportions to right non circular frusta the volume of the trunk is obtained volume mass and density of trunk s segments and their tissues are given the location of the centers of mass of the segments is also provided regression equations are presented for the calculation of volume of tissues and of subportions application of the data for locating the center of mass of the body for building anthropometric dummies and for calculating the load acting on any level of a spine are presented

nonparametric inference on structural breaks this paper proposes estimators of location and size of structural breaks in a possibly dynamic nonparametric regression model the structural breaks can be located at given periods of time and or they can be explained by the values taken by some regressor as in threshold models no previous knowledge of the underlying regression function is required the paper also studies the case in which several regressors explain the breaks we derive the rate of convergence and provide central limit theorems for the estimators of the location s and size s a monte carlo experiment illustrates the performance of our estimators in small samples

the complexity of the finite containment problem for petri nets if the reachability set of a petri net or equivalently vector addition system is finite it can be effectively constructed furthermore the finiteness is decidable thus the containment and equality problem for finite reachability sets become solvable we investigate the complexity of decision procedures for these two problems and show by reducing a bounded version of hilbert s tenth problem to the finite containment problem that these two problems are extremely hard that in fact the complexity of each decision procedure exceeds any primitive recursive function infinitely often the finite containment and quality problem are thus the first uncontrived decidable problems with provably non primitive recursive complexity

nonprimitive recursive complexity and undecidability for petri net equivalence the aim of this note is twofold firstly it shows that the undecidability result for bisimilarity in theor comput sci 148 1995 281 301 can be immediately extended for the whole range of equivalences and preorders on labelled petri nets secondly it shows that restricting our attention to nets with finite reachable space the respective decidable problems are nonprimitive recursive this approach also applies to mayr and meyer s result j acm 28 1981 561 576 for the reachability set equality yielding a more direct proof

linearizing well quasi orders and bounding the length of bad sequences we study the length functions of controlled bad sequences over some well quasi orders wqo s and classify them in the fast growing hierarchy we develop a new and self contained study of the length of bad sequences over the disjoint product in n n dickson s lemma which leads to recently discovered upper bounds but through a simpler argument we also give a tight upper bound for the length of controlled decreasing sequences of multisets of n n with the underlying lexicographic ordering and use it to give an upper bound for the length of controlled bad sequences in the majoring ordering with the underlying disjoint product ordering we apply this last result to attain complexity upper bounds for the emptiness problem of itca and atra automata for the case of the product and majoring wqo s the idea is to linearize bad sequences i e to transform a bad sequence over a wqo into a decreasing one over a well order for which upper bounds can be more easily handled

a comparison between a new model and current models for estimating trunk segment inertial parameters modeling of the body segments to estimate segment inertial parameters is required in the kinetic analysis of human motion a new geometric model for the trunk has been developed that uses various cross sectional shapes to estimate segment volume and adopts a non uniform density function that is gender specific the goal of this study was to test the accuracy of the new model for estimating the trunk s inertial parameters by comparing it to the more current models used in biomechanical research trunk inertial parameters estimated from dual x ray absorptiometry dxa were used as the standard twenty five female and 24 male college aged participants were recruited for the study comparisons of the new model to the accepted models were accomplished by determining the error between the models trunk inertial estimates and that from dxa results showed that the new model was more accurate across all inertial estimates than the other models the new model had errors within 6 0 for both genders whereas the other models had higher average errors ranging from 10 to over 50 and were much more inconsistent between the genders in addition there was little consistency in the level of accuracy for the other models when estimating the different inertial parameters these results suggest that the new model provides more accurate and consistent trunk inertial estimates than the other models for both female and male college aged individuals however similar studies need to be performed using other populations such as elderly or individuals from a distinct morphology e g obese in addition the effect of using different models on the outcome of kinetic parameters such as joint moments and forces needs to be assessed

estimating and testing linear models with multiple structural changes this paper develops the statistical theory for testing and estimating multiple change points in regression models the rate of convergence and limiting distribution for the estimated parameters are obtained several test statistics are proposed to determine the existence as well as the number of change points a partial structural change model is considered the authors study both fixed and shrinking magnitudes of shifts in addition the models allow for serially correlated disturbances mixingales an estimation strategy for which the location of the breaks need not be simultaneously determined is discussed instead the authors method successively estimates each break point

decidability of bisimilarity for one counter processes it is shown that bisimulation equivalence is decidable for the processes generated by nondeterministic pushdown automata where the pushdown behaves like a counter also finiteness up to bisimilarity is shown to be decidable for the mentioned processes

some complexity bounds for problems concerning finite and 2 dimensional vector addition systems with states abstract in this paper we analyse the complexity of the reachability containment and equivalence problems for two classes of vector addition systems with states vasss finite vasss and 2 dimensional vasss both of these classes are known to have effectively computable semilinear reachibility sets slss by giving upper bounds on the sizes of the sls representations we achieve upper bounds on each of the aforementioned problems in the case of the finite vasss the sls representation is simply a listing of the reachability set therefore we derive a bound on the norm of any reachable vector based on the dimension number of states and amount of increment caused by any move in the vass the bound we derive shows an improvement of two levels in the primitive recursive hierarchy over results previously obtained by mcaloon 1984 thus answering a question posed by clote 1986 we then show this bound to be optimal we feel that the techniques we use in deriving our upper bounds represent an original approach to the problem and since they yield improvements over previous results we feel these techniques may have applications to other problems in the case of 2 dimensional vasss we analyse an algorithm given by hopcroft and pansiot 1979 that generates an sls representation of the reachability set specifically we show that the algorithm operates in 2 2 cln nondeterministic time where l is the length of the binary representation of the largest integer in the vass n is the number of transitions and c is some fixed constant we also give examples for which this algorithm will take 2 2 dln nondeterministic time for some positive constant d finally we give a method of determinizing the algorithm in such a way that it requires no more than 2 2 cln deterministic time from this upper bound and special properties of the generated slss we derive upper bounds of dtime 2 2 cln for the three problems mentioned above

τ estimators of regression models with structural change of unknown location abstract this paper concerns with robust estimation of linear regression models with structural change of unknown location under possibly contaminated distributions both for the regressors and for the perturbance term existing estimators will be inefficient in this context furthermore they may protect against outlying yt but cannot cope with leverage points namely outliers in the factor space which could have large influence on the fit as a result these estimators could not discriminate between outlier observations and structural break points misplacing the shift location this fact can be of special importance in practice therefore it may be advisable to consider robust estimators under possible leverage points in a structural change context thus we propose the estimator introduced by yohai and zamar j am stat assoc 83 1988 406 in the standard context of no change this type of estimator is qualitatively robust with the best possible breakdown point and highly efficient under normal errors the asymptotic distribution of the break location estimator is obtained both for fixed magnitude of shift and for shift with magnitude converging to zero as the sample size increases the analysis is carried out in the framework of general ned dependence conditions for the data monte carlo experiments illustrates the performance of our estimators in finite samples

methods for investigating the sensitivity of joint resultants to body segment parameter variations two methods are presented for determining the sensitivity of joint resultants to variations in body segment parameters bsps when solving inverse dynamics problems the exact sampling method esm and the approximate variational method avm these methods are illustrated by applying them to a single segment in fixed axis rotation the results indicate that a the avm provides first order linear approximations to the total variations in joint resultants obtained when using the esm b the esm should be used when bsp variations become large and higher order terms in these variations can no longer be ignored as negligible in the bsp dependent expansions for the joint resultants c small percent variations in bsps can propagate into considerably larger percent variations in the joint resultants obtained when solving inverse dynamics problems and d if bsp variations are sufficiently small to allow nonlinear terms in these variations to be ignored as negligible the avm is much simpler and easier to use than the esm

completeness results for single path petri nets we define a new subclass of persistent petri nets called single path petri nets our intention is to provide a class of petri nets whose study might yield some insight into the mathematical properties of persistent petri nets or even general petri nets we conjecture that the karp miller coverability tree for a persistent net is small enough to be searched in polynomial space although we are unable to prove this conjecture we do show that single path petri nets have this property we then use this fact to show that the canonical analysis problems i e boundedness reachability containment and equivalence for single path petri nets are pspace complete in the strong sense furthermore we show that the problem of recognizing a single path petri net is also pspace complete

optimal algorithms for the coverability the subword the containment and the equivalence problems for commutative semigroups abstract in this paper we present decision procedures for the coverability the subword the containment and the equivalence problems for commutative semigroups these procedures require at most space 2c n where n is the size of the problem instance and c is some problem independent constant furthermore we show that the exponential space hardness of the above problems follows from the work of mayr and meyer thus the presented algorithms are space optimal our results close the gap between the 2c n log n space upper bound shown by rackoff for the coverability problem and shown by huynh for the containment and the equivalence problems and the exponential space lower bound resulting from the corresponding bound for the uniform word problem established by mayr and meyer

high breakdown point estimates of regression by means of the minimization of an efficient scale abstract a new class of robust estimates estimates is introduced the estimates have simultaneously the following properties a they are qualitatively robust b their breakdown point is 5 and c they are highly efficient for regression models with normal errors they are defined by minimizing a new scale estimate applied to the residuals asymptotically a estimate is equivalent to an m estimate with a function given by a weighted average of two functions one corresponding to a very robust estimate and the other to a highly efficient estimate the weights are adaptive and depend on the underlying error distribution we prove consistency and asymptotic normality and give a convergent iterative computing algorithm finally we compare the biases produced by gross error contamination in the estimates and optimal bounded influence estimates

the complexity of the word problems for commutative semigroups and polynomial ideals abstract any decision procedure for the word problems for commutative semigroups and polynomial deals inherently requires computational storage space growing exponentially with the size of the problem instance to which the procedure is applied this bound is achieved by a simple procedure for the semigroup problem