Transverse resonance island buckets for synchrotron-radiation based electron time-of-flight spectroscopy.

At the Metrology Light Source (MLS), the compact electron storage ring of the Physikalisch-Technische Bundesanstalt (PTB) with a circumference of 48 m, a specific operation mode with two stable closed orbits for stored electrons was realized by transverse resonance island buckets. One of these orbits is closing only after three turns. In combination with single-bunch operation, the new mode was applied for electron time-of-flight spectroscopy with an interval of the synchrotron radiation pulses which is three times the revolution period at the MLS of 160 ns. The achievement is of significant importance for PTB's future programs of angular-resolved electron spectroscopy with synchrotron radiation and similar projects at other compact electron storage rings. The scheme applied here for selecting the photons originating from a particular orbit by optical imaging has been used before in fs slicing applications and may be relevant for the BESSY VSR project of the Helmholtz-Zentrum Berlin.

A model describing stable coherent synchrotron radiation in storage rings.

We present a model describing high power stable broadband coherent synchrotron radiation (CSR) in the terahertz frequency region in an electron storage ring. The model includes distortion of bunch shape from the synchrotron radiation (SR), which enhances higher frequency coherent emission, and limits to stable emission due to an instability excited by the SR wakefield. It gives a quantitative explanation of several features of the recent observations of CSR at the BESSY II storage ring. We also use this model to optimize the performance of a source for stable CSR emission.

Brilliant, coherent far-infrared (THz) synchrotron radiation.

A new technology for generating steady state, brilliant, broadband, coherent, far-infrared (FIR) radiation in electron storage rings is presented, suitable for FIR spectroscopy. An FIR power increase of up to 100 000 compared to the normal, incoherent synchrotron radiation in the range of approximately 5 to approximately 40 cm(-1) could be achieved. The source is up to 1000 times more brillant compared to a standard Hg arc lamp. The coherent synchrotron radiation is produced in a "low alpha" optics mode of the synchrotron light source BESSY, by bunch shortening and non-Gaussian bunch deformation.

A constraint-based approach to modelling the mobility of the human knee joint.

A model of knee mobility able to predict the range and pattern of movement in the unloaded joint was proposed by Wilson et al. (J. Biomech. 31 (1998) 1127-1136). The articular surfaces in the lateral and medial compartments and isometric fascicles in three of the knee ligaments were represented as five constraints on motion between the femur and tibia in a single degree-of-freedom parallel spatial mechanism. The path of movement of the bones during passive flexion was found by solving the forward kinematics of the mechanism using an iterative method. The present paper shows that such a mechanism-based solution approach can lead to an underestimation of the flexion range. This is due to the mechanism reaching a 'stationary configuration' and 'locking'. A new, constraint-based approach to the solution of the model joint displacement is proposed. It avoids the representation of ligaments and articular surfaces by kinematically equivalent chains of one degree-of-freedom pairs which are prone to singularities. It relies instead on a numerical solution of five non-linear constraint equations to find the relative positions of the bones at a series of flexion angles. The method is successful both in its ability to predict motion through a physiological range and in its efficiency with a solution rate forty times faster than the original algorithm. The new approach may be extended to include more complex joint surface geometry, allowing a study of the effects of articular surface shape and ligament arrangement on joint kinematics.

Steady-state far-infrared coherent synchrotron radiation detected at BESSY II.

At BESSY II it is demonstrated that far-infrared coherent synchrotron radiation (CSR) can be generated by a controlled, steady-state process at storage rings. As an indication for coherent emission, the radiated power grows with the square of the beam current. The spectrum was analyzed by an interferometer in the 1-mm to 0.3-mm wavelength range. The CSR was enhanced more than 3000 times above background; the incoherent radiation remained below the background level. Steady-state and bursting CSR were discriminated by time resolved analysis from micro seconds to seconds.

In vitro evaluation of the resistance to dislocation of a meniscal-bearing total knee prosthesis between 30 degrees and 90 degrees of knee flexion.

An increased incidence of dislocation is the most important potential disadvantage introduced by the use of meniscal-bearing prostheses. The aim of this in vitro study was to measure the resistance to dislocation of a meniscal-bearing total knee arthroplasty in various circumstances and to establish which anatomic structures contribute to bearing stability. The prosthesis was implanted into cadaver knee specimens mounted in a 6 df rig. Dislocation was provoked by applying anteriorly or posteriorly directed forces (20-100N) to the tibia in the plane of the tibial plateau. Dislocation was defined as any stable displacement of the bearing (relative to the tibia or the femur) that persisted after release of the load applied to provoke it. The specimens were tested in an arc of knee flexion between 30 degrees and 90 degrees, with and without simulated quadriceps loads, with and without abducting and adducting loads, and before and after division of the posterior cruciate ligament and the lateral retinaculum. In the presence of quadriceps load, dislocation could not be provoked. In the absence of quadriceps load, dislocation was not provoked by posteriorly directed force but sometimes was caused by anteriorly directed force. All but 1 of the dislocations were unicompartmental, the lateral compartment proving much less stable than the medial. The tendency toward dislocation increased from 30 degrees to 60 degrees and from 60 degrees to 90 degrees of knee flexion. Adducting moments applied to the knee caused lift-off of the lateral femoral condyle from the bearing and increased the tendency toward dislocation. Abducting moments had the opposite effect. Division of the posterior cruciate ligament had no significant effect. Division of the lateral retinaculum increased the tendency toward dislocation. A femoral component that can be implanted without lateral release is desirable.

The components of passive knee movement are coupled to flexion angle.

Movement of the unloaded knee has been described in several studies by an "envelope of passive flexion", a description that does not describe or explain the widely reported coupling of internal tibial rotation to flexion. The objective of the current study was to show that the envelope of passive knee flexion can be reduced to a coupled path. Two hypotheses were tested: (1) in normal knees flexed passively, internal/external rotation, abduction/adduction and all three components of translation are coupled to flexion angle, and (2) the tibia rotates internally as the knee is flexed passively. Fifteen cadaver knees were flexed in a rig designed to apply minimal resistance to knee movement while three-dimensional kinematics of the femur relative to the tibia were measured with an electromagnetic tracking system. Each specimen displayed internal tibial rotation and posterior, proximal and medial displacement of a reference point with flexion, while a range of ab/adduction behaviour was observed. Mean absolute differences between the flexing and extending paths in normal specimens were under 2 and 0.2 degrees for internal/external tibial rotation and ab/adduction, respectively. Deviation from the movement path was resisted: when released after being displaced, the femur of each normal joint sprang back to its original position on the motion path. It was concluded that passive knee flexion can be described by a coupled path. Although the exact shape of the path is very sensitive to load and varies between knees, knee rotations and translations were always coupled to flexion, and internal tibial rotation with flexion was always observed.

Ligaments and articular contact guide passive knee flexion.

The aim of this study was to test the hypothesis that the coupled features of passive knee flexion are guided by articular contact and by the isometric fascicles of the ACL, PCL and MCL. A three-dimensional mathematical model of the knee was developed, in which the articular surfaces in the lateral and medial compartments and the isometric fascicles in the ACL, PCL and MCL were represented as five constraints in a one degree-of-freedom parallel spatial mechanism. Mechanism analysis techniques were used to predict the path of motion of the tibia relative to the femur. Using a set of anatomical parameters obtained from a cadaver specimen, the model predicts coupled internal rotation and ab/adduction with flexion. These predictions correspond well to measurements of the cadaver specimen's motion. The model also predicts posterior translation of contact on the tibia with flexion. Although this is a well-known feature of passive knee flexion, the model predicts more translation than has been reported from experiments in the literature. Modelling of uncertainty in the anatomical parameters demonstrated that the discrepancy between theoretical predictions and experimental measurement can be attributed to parameter sensitivity of the model. This study shows that the ligaments and articular surfaces work together to guide passive knee motion. A principal implication of the work is that both articular surface geometry and ligament geometry must be preserved or replicated by surgical reconstruction and replacement procedures to ensure normal knee kinematics and by extension, mechanics.

Pericardioperitoneal shunt: an alternative treatment for malignant pericardial effusion.

The treatment of 37 consecutive cases of symptomatic malignant pericardial effusion over a period of 13 years was retrospectively analyzed. The most common diagnoses were lung cancer (59%) and breast cancer (11%). In the most recent 4 patients, the Denver pleuroperitoneal shunt was used to drain the pericardial effusion into the peritoneal cavity. In each case, the procedure was performed under local anesthesia, and the patient was discharged 2 to 4 days later without complications. Three of the patients subsequently died of the disease process without evidence of cardiac failure or tamponade during 6-month follow-up. The more traditional means of pericardial drainage, the subxiphoid approach (14 patients) and the anterior thoracotomy approach (19 patients), were associated with higher postoperative morbidity (21% and 53%, respectively) and mortality (7% and 42%, respectively). Because of the small number of patients treated by pericardioperitoneal shunting, a significant difference was demonstrated only in the length of hospital stay (shunt, 2.8 +/- 0.5 days; subxiphoid, 11.2 +/- 4.6 days; thoracotomy, 14.9 +/- 6.1 days). Median survivals were essentially the same (shunt, 3.5 months; subxiphoid, 2.7 months; thoracotomy, 1.2 months). It is apparent that the pericardioperitoneal shunt, although a much simpler procedure, can accomplish similar palliation effectively in the treatment of malignant pericardial effusion.