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A de Lange

Publications and source records attributed to A de Lange.

13 recordsLinked to original sources
PubMed2001

Double-well states of ungerade symmetry in H2: first observation and comparison with Ab initio calculations.

The observation of a new class of long-lived outer well states of ungerade symmetry (B"B1Sigma+u) in molecular hydrogen, lying above the ionization threshold, is reported. Rovibrational levels within a potential extended over internuclear separations of R = 7-25 a.u. are experimentally investigated in a triple resonance scheme. Good agreement ( <0.5 cm(-1)) with updated ab initio calculations is found for vibrational levels up to v = 26, demonstrating that such calculations can now be extended to this energetic range above ionization, as long as interaction with the Rydberg manifolds is shielded by a barrier. The dynamical behavior (predissociation and autoionization) of this class of " u" symmetry states is remarkably different from similar outer well states of " g" symmetry; this phenomenon can be understood from the structure of doubly excited electronic states.

Journal Article↗
PubMed1996

Microcirculation in the footsole as a function of mechanical pressure.

OBJECTIVE: In this study an experimental set-up for measuring skin microvascular responses of the footsole to changes in externally applied pressure was analysed. DESIGN: A clinical study. Skin microvascular blood flow was measured in healthy volunteers, during and after external mechanical pressure of different magnitudes. BACKGROUND: During standing and walking the footsole is commonly exposed to high static and dynamic mechanical pressure, resulting in changes in the microcirculation of the footsole. In diabetic patients a disturbed interaction between externally applied pressure and skin microvascular response seems to be involved in the development of a foot ulcer. METHODS: Eleven volunteers participated in the study. Static loads were applied to the heel part of the footsole with the person in a supine position. Contact pressure and skin blood flux, based on the laser Doppler technique, were simultaneously monitored. The pressure used was varied in five discrete steps between 10 and 160 kPa and applied during a period of 5 min each. The microcirculation was measured during as well as after pressure loading. RESULTS: Pressures of 40 kPa and higher do stop the blood flow in the skin microcirculation. Releasing the applied pressure resulted in a hyperaemic response. This response appears to increase in amplitude at increasing pressures up to 800% of the baseline laser Doppler fluxmetry level. Beyond a pressure level of 80 kPa the hyperaemic response seems not to be influenced by the pressure level. The time needed to achieve the maximal laser Doppler fluxmetry level decreased when the pressure was raised from 10 to 80 kPa, but increased again when higher pressures were applied (P = 0.051). An intraindividual variation of 11-50% was observed for the parameters describing the blood flux before, during, and after pressure application. CONCLUSION: Simultaneously measuring changes in contact pressure and laser Doppler flux of the footsole is a useful method to study the interaction of external mechanical pressure and skin microvascular reactions. Pressures above 40 kPa stop skin microvascular blood flow. Releasing the applied pressure results in a hyperaemic response, which increases when the applied pressure increases from 40 to 80 kPa. Higher pressures do not influence the amplitude in skin microvascular response, but result in a longer delay to maximal hyperaemia.

Journal Article↗
PubMed1991

Recruitment of knee joint ligaments.

On the basis of earlier reported data on the in vitro kinematics of passive knee-joint motions of four knee specimens, the length changes of ligament fiber bundles were determined by using the points of insertion on the tibia and femur. The kinematic data and the insertions of the ligaments were obtained by using Roentgenstereophotogrammetry. Different fiber bundles of the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments were identified. On the basis of an assumption for the maximal strain of each ligament fiber bundle during the experiments, the minimal recruitment length and the probability of recruitment were defined and determined. The motions covered the range from extension to 95 degrees flexion and the loading conditions included internal or external moments of 3 Nm and anterior or posterior forces of 30 N. The ligament length and recruitment patterns were found to be consistent for some ligament bundles and less consistent for other ligament bundles. The most posterior bundle of each ligament was recruited in extension and the lower flexion angles, whereas the anterior bundle was recruited for the higher flexion angles. External rotation generally recruited the collateral ligaments, while internal rotation recruited the cruciate ligaments. However, the anterior bundle of the posterior cruciate ligament was recruited with external rotation at the higher flexion angles. At the lower flexion angles, the anterior cruciate and the lateral collateral ligaments were recruited with an anterior force. The recruitment of the posterior cruciate ligament with a posterior force showed that neither its most anterior nor its most posterior bundle was recruited at the lower flexion angles. Hence, the posterior restraint must have been provided by the intermediate fiber bundles, which were not considered in the experiment. At the higher flexion angles, the anterior bundles of the anterior cruciate ligament and the posterior cruciate ligament were found to be recruited with anterior and posterior forces, respectively. The minimal recruitment length and the recruitment probability of ligament fiber bundles are useful parameters for the evaluation of ligament length changes in those experiments where no other method can be used to determine the zero strain lengths, ligament strains and tensions.

Adult↗
PubMed1990

Wrist-joint ligament length changes in flexion and deviation of the hand: an experimental study.

A method to study ligament-length patterns in situ with roentgen-stereophotogrammetry, using strings of glued tantalum markers, was developed. The method was tested against a bone-to-bone marking method in five carpal ligaments in three specimens, whereby the hand was moved through dorsopalmar flexion and radioulnar deviation. The "glued-string" marking method was found to be superior to the bone-to-bone marking method. The length patterns obtained were found to be reproducible in the specimens and different from earlier expectations presented in the literature. The radiocapitate ligament seems to limit the displacements of the capitate in both radial and ulnar deviation, and dorsal flexion. The radiolunate ligament has the same effect for the lunate. Both the dorsal radiotriquetrum and the palmar triquetrocapitate ligaments seem to play a stabilizing role in the neutral position of the hand, whereas the radiotriquetrum ligament also has a function in palmar flexion and the triquetrocapitate ligament functions in dorsal flexion, ultimately resisting these excursions. These findings require confirmation in more extensive experiments, whereby the relationship between ligament length patterns and carpal motion axes is investigated.

Adult↗
PubMed1990

Measurement errors in roentgen-stereophotogrammetric joint-motion analysis.

In many biomechanical motion studies, kinematic parameters are estimated from position measurements on a number of landmarks. In the present investigation, dummy motion experiments are performed in order to study the error dependence of kinematic parameters on geometric factors (number of markers, isotropic vs anisotropic landmark distributions, landmark distribution size), on kinematic factors (rotation step magnitude, the presence of translational displacements, the distance of the landmarks' mean position to the rotation axis), and on anisotropically distributed measurement errors. The experimental results are compared with theoretical predictions of a previous error analysis assuming isotropic conditions for the measurement errors and for the spatial landmark distribution. In general, the experimental findings agree with the predictions of the error model. The kinematic parameters such as translations and rotations are well-determined by the model. In the helical motion description, the same applies for the finite rotation angle about and the finite shift along the helical axis. However, the direction and position of the helical axis are ill-determined. An anisotropic landmark distribution with relatively few markers located in the direction of the rotation axis will even aggravate the ill-posed nature of the finite helical axis estimation.

Biomechanical Phenomena↗
PubMed1990

Helical axes of passive knee joint motions.

The purpose of this study was to determine finite helical axes for passive knee joint motions in vitro and to evaluate the descriptive value of the finite helical axes for step-by-step flexion motions, with respect to consistency and reproducibility. An accurate Roentgenstereophotogrammetric system was used for motion measurements. Four knees were tested in a motion and loading rig with one and the same experimental protocol. A fifth specimen was used to study the effects of some of the experimental conditions on the axis parameters. On the basis of earlier reported motion characteristics in terms of Euler rotations and translations, two motion pathways were chosen to be reported here: a flexion motion with an internal torque of 3 Nm and one with an external torque of 3 Nm on the tibia. The positions and orientations of the axes were described relative to the insertions of the four major ligaments and the geometry of the articular surfaces of the femur, and also as intersections with a medial and a lateral sagittal plane. The three-dimensional patterns of the helical axes of the four knee specimens were found to be highly reproducible and consistent for each of the two motion pathways. The axis patterns were not unique, but reflected the particular combination of flexion and axial rotation for each particular motion pathway. Although small, the helical translations indicated medial motions of the tibia relative to the femur. This medial helical translation was more pronounced for the internal pathway compared with the external pathway. Above 70 degrees flexion, the axes move posteriorly relative to the femur.

Biomechanical Phenomena↗
PubMed1990

Effects of data smoothing on the reconstruction of helical axis parameters in human joint kinematics.

In biomechanical joint-motion analyses, the continuous motion to be studied is often approximated by a sequence of finite displacements, and the Finite Helical Axis (FHA) or "screw axis" for each displacement is estimated from position measurements on a number of anatomical or artificial landmarks. When FHA parameters are directly determined from raw (noisy) displacement data, both the position and the direction of the FHA are ill-determined, in particular when the sequential displacement steps are small. This implies, that under certain conditions, the continuous pathways of joint motions cannot be adequately described. The purpose of the present experimental study is to investigate the applicability of smoothing (or filtering) techniques, in those cases where FHA parameters are ill-determined. Two different quintic-spline smoothing methods were used to analyze the motion data obtained with Roentgenstereophotogrammetry in two experiments. One concerning carpal motions in a wrist-joint specimen, and one relative to a kinematic laboratory model, in which the axis positions are a priori known. The smoothed and non-smoothed FHA parameter errors were compared. The influences of the number of samples and the size of the sampling interval (displacement step) were investigated, as were the effects of equidistant and nonequidistant sampling conditions and noise invariance.

Adult↗
PubMed1988

The envelope of passive knee joint motion.

The purpose of this study is to create an accurate experimental database for the passive (in vitro) freedom-of-motion characteristics of the human knee joint on a subject to subject basis, suitable for the verification and enhancement of mathematical knee-joint models. Knee-joint specimens in a six degree-of-freedom motion rig are moved through flexion under several combinations of external loads, including tibial torques, axial forces and AP-forces. Euler rotation angles and translation vectors, describing the relative, spatial motions of the joint are measured using an accurate Roentgen Stereo Photogrammetric system. Conceptually the joint is considered as a two degrees-of-freedom of motion mechanism (flexion-tibial rotation), whereby the limits of internal and external tibial rotation are defined at torques of +/- 3 Nm. The motion pathways along these limits are defined as the envelopes of passive knee joint motion. It is found that these envelope pathways are consistent and hardly influenced by additional axial forces up to 300 N and AP-forces of 30 N. Within the envelope of motion, however, the motion patterns are highly susceptible to small changes in the external load configuration. It is shown that the external tibial rotation during extension ('screw-home mechanism') is not an obligatory effect of the passive joint characteristics, but a direct result of the external loads. Anatomical differences notwithstanding, the inter-individual discrepancies in the motion patterns of the four specimens tested, showed to be relatively small in a qualitative sense. Quantitative differences can be explained by small differences in the alignment of the coordinate systems relative to the joint anatomy and by differences in rotatory laxity.

Adult↗
PubMed1987

The carpal joint. Anatomy and function.

The carpal joint can be approached as a mechanism consisting of kinematic chains. In these chains, the proximal carpals function as intercalated segments. Intercarpal displacements are linked to one another and are based upon the mutual attuning of carpal bone geometry, joint contacts, and ligamentous interconnections.

Biomechanical Phenomena↗
PubMed1985

Kinematic behavior of the human wrist joint: a roentgen-stereophotogrammetric analysis.

Using a roentgen-stereophotogrammetric measurement system, the three-dimensional kinematic characteristics of each carpal bone in two human wrist joints were obtained as the hands were moved in vitro through dorsopalmar flexion and through radioulnar deviation, both in the supinated and pronated positions of the hand. The results were described in terms of Euler rotation angles and showed that in flexion, the distal carpal bones may be considered as one fixed group while the proximal carpals may not. For the deviation motion, quite different rotational excursions for the carpal bones were observed, therefore, none of the two rows may be assumed acting as rigid groups. In both of the hand motions performed, all carpal bones moved synchronously and uniformly. These results demonstrate that accurate measurements of three-dimensional carpal-bone motions are feasible by using an adequately refined roentgen-stereophotogrammetric system. The detailed and precise kinematic information obtained can serve as a database for future developments of functional wrist-joint models, and will provide more insight into carpal-bone behavior, useful in clinical diagnosis and surgical reconstruction procedures.

Adult↗
PubMed1985

Analytical stereophotogrammetric determination of three-dimensional knee-joint geometry.

An analytical stereophotogrammetric method is introduced to measure the three-dimensional geometry of articular surfaces in vitro. Information of this kind is particularly useful for mathematical joint models and anthropological studies. The method requires no specific equipment, such as a stereocomparator, contrarily to other techniques reported (e.g. Ghosh, 1983) and is relatively simple and inexpensive. The background of the method is outlined in the present paper, and results of accuracy and precision tests are presented. It is shown that an accuracy on the order of 0.2 mm (95% confidence interval) is well feasible in actual knee-joint evaluations, if the measuring procedure is conducted carefully. The method is illustrated by measuring and comparing the articular surface geometries of a bilateral pair of knee joints.

Biomechanical Phenomena↗
PubMed1985

Finite centroid and helical axis estimation from noisy landmark measurements in the study of human joint kinematics.

Recent work on joint kinematics indicates that the finite centroid (centre of rotation) and the finite helical axis (axis of rotation, screw axis, twist axis) are highly susceptible to measurement errors when they are experimentally determined from landmark position data. This paper presents an analytical model to describe these effects, under isotropic conditions for the measurement errors and for the spatial landmark distribution. It appears that the position and direction errors are inversely proportional to the rotation magnitude, and that they are much more error-prone than the relatively well-determined rotation and translation magnitudes. Furthermore, the direction and rotation magnitude errors are inversely proportional to the landmark distribution radius, and the position and translation magnitude errors are minimal if the mean position of the landmarks coincides with the centroid or helical axis. For the planar centroid, the use of rigid-body constraints results in considerable precision improvement relative to the classical, finite Reuleaux method for centroid reconstruction. These analytical results can be used to define suitable measurement configurations, and they are used in this paper to explain experimental results on Röntgenphotogrammetrically acquired in vitro wrist joint movement.

Biomechanical Phenomena↗