Variational collision integrator for polymer chains

The numerical simulation of many-particle systems (e.g., in molecular dynamics) often involves constraints of various forms. We present a symplectic integrator for mechanical systems with holonomic (bilateral) and unilateral contact constraints, the latter being in the form of a nonpenetration condition. The scheme is based on a discrete variant of Hamilton’s principle in which both the discrete trajectory and the unknown collision time are varied (cf. [Fetecau et al., 2003, SIAM J. Applied Dynamical Systems, 2, pp. 381–416]). As a consequence, the collision event enters the discrete equations of motion as an unknown that has to be computed on-the-fly whenever a collision is imminent. The additional bilateral constraints are e ciently dealt with employing a discrete null space reduction (including a projection and a local reparametrisation step) which considerably reduces the number of unknowns and improves the condition number during each time-step as compared to a standard treatment with Lagrange multipliers. We illustrate the numerical scheme with a simple example from polymer dynamics, a linear chain of beads, and test it against other standard numerical schemes for collision problems

Retention of gait stability improvements over 1.5 years in older adults:effects of perturbation exposure and triceps surae neuromuscular exercise

The plantarflexors play a crucial role in recovery from sudden disturbances to gait. The objective of this study was to investigate whether medium (months)- or long(years)-term exercise-induced enhancement of triceps surae (TS) neuromuscular capacities affects older adults' ability to retain improvements in reactive gait stability during perturbed walking acquired from perturbation training sessions. Thirty-four adult women (65 +/- 7 yr) were recruited to a perturbation training group (n = 13) or a group that additionally completed 14 wk of TS neuromuscular exercise (n = 21), 12 of whom continued with the exercise for 1.5 yr. The margin of stability (MoS) was analyzed at touchdown of the perturbed step and the first recovery step following eight separate unexpected trip perturbations during treadmill walking. TS muscle-tendon unit mechanical properties and motor skill performance were assessed with ultrasonography and dynamometry. Two perturbation training sessions (baseline and after 14 wk) caused an improvement in the reactive gait stability to the perturbations (increased MoS) in both groups. The perturbation training group retained the reactive gait stability improvements acquired over 14 wk and over 1.5 yr. with a minor decay over time. Despite the improvements in TS capacities in the additional exercise group. no benefits for the reactive gait stability following perturbations were identified. Therefore, older adults' neuromotor system shows rapid plasticity to repeated unexpected perturbations and an ability to retain these adaptations in reactive gait stability over a long time period, but an additional exercise-related enhancement of TS capacities seems not to further improve these effects. NEW & NOTEWORTHY Older adults' neuromotor system shows rapid plasticity to repeated exposure to unexpected perturbations to gait and an ability to retain the majority of these adaptations in reactive recovery responses over a prolonged time period of 1.5 yr. However, an additional exercise-related enhancement of TS neuromuscular capacities is not necessarily transferred to the recovery behavior during unexpected perturbations to gait in older adults

Differential Geometry applied to Acoustics : Non Linear Propagation in Reissner Beams

Although acoustics is one of the disciplines of mechanics, its "geometrization" is still limited to a few areas. As shown in the work on nonlinear propagation in Reissner beams, it seems that an interpretation of the theories of acoustics through the concepts of differential geometry can help to address the non-linear phenomena in their intrinsic qualities. This results in a field of research aimed at establishing and solving dynamic models purged of any artificial nonlinearity by taking advantage of symmetry properties underlying the use of Lie groups. The geometric constructions needed for reduction are presented in the context of the "covariant" approach.Comment: Submitted to GSI2013 - Geometric Science of Informatio

Effect Of Triceps Surae Muscle-Tendon Unit Mechanical Properties On Gait Stability And Adaptability In Older Female Adults

INTRODUCTION Ageing induces a gradual degradation in the human neuro-motor system resulting in decreased mobility and locomotor performance (Beijersbergen et al., 2013). Moreover, inadequate recovery responses following tripping have been associated with age-related deteriorations in ankle plantar flexion moment output (magnitude and rate) in the push-off phase (Pijnappels et al., 2004). Therefore, the objective of this study was (1) to examine if gait stability and adaptability during perturbed walking is associated with TS muscle strength and Achilles tendon (AT) stiffness in older female adults, and (2) to determine whether elderly with different TS muscle strength capacities show an altered dynamic stability control during perturbed walking, and (3) whether gait plasticity is preserved in old age. METHODS Thirty-four older female adults (65±7yrs) experienced unexpected trip perturbations to the swing phase of the right leg while walking on a treadmill (Süptitz et al., 2013). Using a motion capture system (VICON; Oxford, UK) the margin of stability (MoS) and base of support (BoS) were assessed at touchdown (TD) of the perturbed leg and at each following six recovery steps. In order to examine the reactive adaptation potential, the MoS at TD of the perturbed leg was examined in eight unexpected perturbation trials. In an additional session, TS muscle strength and AT stiffness were determined using simultaneous ultrasonography and dynamometry. Pearson correlations were used to inspect the relationship between TS MTU mechanical properties and dynamic stability parameters (both MoS and BoS) of the recovery steps in first perturbation trial. A median split was implemented to classify the subjects into two groups based on their TS muscle strength (strong: n = 16; weak: n = 18). RESULTS The strong group had about 42% higher voluntary isometric plantarflexion moments and 33% higher AT stiffness than the weak group (138±22Nm vs. 97±10Nm; 588±156Nmm-1 vs. 441±129Nmm-1; p<0.01). The gait perturbation reduced the MoS at TD of the perturbed leg (-0.10±0.08m) compared to baseline unperturbed walking, indicating instability. The strong group needed three recovery steps to return to MoS baseline and the weak group was unable to return to baseline level within the analysed six recovery steps. Significant correlations between both TS muscle strength and AT stiffness, and MoS and BoS at TD of the first recovery step were found (0.41<r<0.68; p<0.05). After eight gait perturbations, both groups were able to adapt their reactive response to the perturbation (increasing MoS at TD), with no between-group differences. DISCUSSION The current data suggest that TS muscle strength and AT stiffness partly limit dynamic gait stability control after an unexpected perturbation during walking in older female adults. Recovery stepping behaviour seems to be less effective in weaker older adults, which is explained mainly by the reduced ability to effectively increase the BoS after perturbations. However, independent of TS MTU mechanical properties, older adults seem to be able to improve their reactive response. CONCLUSION TS MTU mechanical properties partly limit dynamic stability during perturbed walking in older adults, but they preserve their gait plasticity independent of their TS muscle strength. Thus, in order to reduce falls risk, older adults may benefit from interventions increasing TS muscle strength and tendon stiffness, and by improving reactive recovery responses via repeated gait perturbations. REFERENCES Beijersbergen et al., (2013). Ageing Res Rev. 12, 618-27. doi:10.1016/j.arr.2013.03.001 Pijnappels et al., (2004). J Biomech. 37, 1811-18. doi:10.1016/j.jbiomech.2004.02.038 Süptitz et al., (2013). Hum Mov Sci 32, 1404-14. doi:10.1016/j.humov.2013.07.00

Small primary adenocarcinoma in adenomyosis with nodal metastasis: a case report

<p>Abstract</p> <p>Background</p> <p>Malignant transformation of adenomyosis is a very rare event. Only about 30 cases of this occurrence have been documented till now.</p> <p>Case presentation</p> <p>The patient was a 57-year-old woman with a slightly enlarged uterus, who underwent total hysterectomy and unilateral adnexectomy. On gross inspection, the uterine wall displayed a single nodule measuring 5 cm and several small gelatinous lesions. Microscopic examination revealed a common leiomyoma and multiple adenomyotic foci. A few of these glands were transformed into a moderately differentiated adenocarcinoma. The endometrium was completely examined and tumor free. The carcinoma was, therefore, considered to be an endometrioid adenocarcinoma arising from adenomyosis. Four months later, an ultrasound scan revealed enlarged pelvic lymph nodes: a cytological diagnosis of metastatic adenocarcinoma was made.</p> <p>Immunohistochemical studies showed an enhanced positivity of the tumor site together with the neighbouring adenomyotic foci for estrogen receptors, aromatase, p53 and COX-2 expression when compared to the distant adenomyotic glands and the endometrium. We therefore postulate that the neoplastic transformation of adenomyosis implies an early carcinogenic event involving p53 and COX-2; further tumor growth is sustained by an autocrine-paracrine loop, based on a modulation of hormone receptors as well as aromatase and COX-2 local expression.</p> <p>Conclusion</p> <p>Adenocarcinoma in adenomyosis may be affected by local hormonal influence and, despite its small size, may metastasize.</p

MRI characterization of 124 CT-indeterminate focal hepatic lesions: evaluation of clinical utility

Objective. To evaluate the diagnostic yield of MRI performed for characterization of focal hepatic lesions that are interpreted as indeterminate on CT. Patients and methods. In a retrospective investigation, 124 indeterminate focal hepatic lesions in 96 patients were identified on CT examinations over 5 years from 1997 to 2001. All patients had MRI performed for the liver within 6 weeks of their CT examination. CT and MR images were reviewed independently by two separate groups of two radiologists. The value of MRI in characterizing these lesions was assessed. Diagnoses were confirmed based on histology, characteristic imaging features, and clinical follow-up . Results. MRI definitely characterized 73 lesions (58%) that were indeterminate on CT. MRI was accurate in 72/73 of these lesions. MRI could not definitely characterize 51 lesions (42%). Ten lesions were not visualized on MRI, and follow-up imaging confirmed that no lesion was present in eight of these cases (pseudolesions). Conclusion. MRI is valuable for the characterization of indeterminate focal hepatic lesions detected on CT.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75168/1/13651820701216950.pd

Is adenomyosis the neglected phenotype of an endomyometrial dysfunction syndrome?

Since the dissociation between adenomyoma and endometriosis in the 1920s and the laparoscopic progress in the diagnosis and surgery of endometriosis, the literature has been greatly focused on the disease endometriosis. The study of adenomyosis, on the other hand, has been neglected as the diagnosis remained based on hysterectomy specimens. However, since the introduction of magnetic resonance and sonographic imaging techniques in the 1980s, the myometrial junctional zone has been identified as a third uterine zone and interest in adenomyosis was renewed. This has also been the start for the interest in the role of the myometrial junctional zone dysfunction and adenomyosis in reproductive and obstetrical disorders

Physical fitness, fatigue, and quality of life after liver transplantation

Fatigue is often experienced after liver transplantation. The aims of this cross-sectional study were to assess physical fitness (cardiorespiratory fitness, neuromuscular fitness, body composition) in liver transplant recipients and to explore whether physical fitness is related to severity of fatigue. In addition, we explored the relationship between physical fitness and health-related quality of life. Included were 18 patients 1–5 years after transplantation (aged 48.0 ± 11.8 years) with varying severity of fatigue. Peak oxygen uptake during cycle ergometry, 6-min walk distance, isokinetic muscle strength of the knee extensors, body mass index, waist circumference, skinfold thickness, severity of fatigue, and health-related quality of life were measured. Cardiorespiratory fitness in the liver transplant recipients was on average 16–34% lower than normative values (P ≤ 0.05). Furthermore, the prevalence of obesity seemed to be higher than in the general population (17 vs. 10%). We found no deficit in neuromuscular fitness. Cardiorespiratory fitness was the only fitness component that was related with severity of fatigue (rs = −0.61 to rs = -0.50, P ≤ 0.05). Particularly cardiorespiratory fitness was related with several aspects of health-related quality of life (rs = 0.48 to rs = 0.70, P ≤ 0.05). Results of our study imply that cardiorespiratory fitness and body composition are impaired in liver transplant recipients and that fitness is related with severity of fatigue (only cardiorespiratory fitness) and quality of life (particularly cardiorespiratory fitness) in this group. These findings have implications for the development of rehabilitation programs for liver transplant recipients