Silvio Lorenzetti

Formation of Metal and Silicate Globules in Gujba: A New Bencubbin-like Meteorite Fall

Gujba is a coarse-grained meteorite fall composed of 41 vol% large kamacite globules, 20 vol% large light-colored silicate globules with cryptocrystalline, barred pyroxene and barred olivine textures, 39 vol% dark-colored, silicate-rich matrix, and rare refractory inclusions. Gujba resembles Bencubbin and Weatherford in texture, oxygen-isotopic composition and in having high bulk δ15N values (∼+685‰). The 3He cosmic-ray exposure age of Gujba (26 ± 7 Ma) is essentially identical to that of Bencubbin, suggesting that they were both reduced to meter-size fragments in the same parent-body collision. The Gujba metal globules exhibit metal-troilite quench textures and vary in their abundances of troilite and volatile siderophile elements. We suggest that the metal globules formed as liquid droplets either via condensation in an impact-generated vapor plume or by evaporation of preexisting metal particles in a plume. The lower the abundance of volatile elements in the metal globules, the higher the globule quench temperature. We infer that the large silicate globules also formed from completely molten droplets; their low volatile-element abundances indicate that they also formed at high temperatures, probably by processes analogous to those that formed the metal globules. The coarse-grained Bencubbin-Weatherford-Gujba meteorites may represent a depositional component from the vapor cloud enriched in coarse and dense particles. A second class of Bencubbin-like meteorites (represented by Hammadah al Hamra 237 and QUE 94411) may be a finer fraction derived from the same vapor cloud.

Kinematics of the Trunk and the Lower Extremities During Restricted and Unrestricted Squats

Abstract List, R, Gülay, T, Stoop, M, and Lorenzetti, S. Kinematics of the trunk and the lower extremities during restricted and unrestricted squats. J Strength Cond Res 27(6): 1529–1538, 2013—Squatting is a common strength training exercise used for rehabilitation, fitness training, and in preparation for competition. Knowledge about the loading and the motion of the back during the squat exercise is crucial to avoid overuse or injury. The aim of this study was the measurement and comparison of the kinematics of the lower leg, trunk, and spine during unrestricted and restricted (knees are not allowed beyond toes) squats. A total of 30 subjects performed unrestricted and restricted barbell squats with an extra load of 0, 25, and 50% bodyweight. Motion was tracked using a 12-camera Vicon system. A newly developed marker set with 24 trunk and 7 pelvic markers allowed us to measure 3D segmental kinematics between the pelvic and the lumbar regions, between the lumbar and the thoracic segments, and the sagittal curvatures of the lumbar and the thoracic spine. In an unrestricted squat, the angle of the knee is larger and the range of motion (ROM) between the lumbar and the thoracic segments is significantly smaller compared with a restricted squat (p < 0.05). The studied subjects showed significantly increased ROM for thoracic curvature during restricted squats. The unrestricted execution of a squat leads to a larger ROM in the knee and smaller changes in the curvature of the thoracic spine and the range of smaller segmental motions within the trunk. This execution in turn leads to lower stresses in the back. To strengthen the muscles of the leg, the unrestricted squat may be the best option for most people. Thus, practitioners should not be overly strict in coaching against anterior knee displacement during performance of the squat.

The effect of a cognitive-motor intervention on voluntary step execution under single and dual task conditions in older adults: a randomized controlled pilot study

Background This randomized controlled pilot study aimed to explore whether a cognitive-motor exercise program that combines traditional physical exercise with dance video gaming can improve the voluntary stepping responses of older adults under attention demanding dual task conditions. Methods Elderly subjects received twice weekly cognitive-motor exercise that included progressive strength and balance training supplemented by dance video gaming for 12 weeks (intervention group). The control group received no specific intervention. Voluntary step execution under single and dual task conditions was recorded at baseline and post intervention (Week 12). Results After intervention between-group comparison revealed significant differences for initiation time of forward steps under dual task conditions (U = 9, P = 0.034, r = 0.55) and backward steps under dual task conditions (U = 10, P = 0.045, r = 0.52) in favor of the intervention group, showing altered stepping levels in the intervention group compared to the control group. Conclusion A cognitive-motor intervention based on strength and balance exercises with additional dance video gaming is able to improve voluntary step execution under both single and dual task conditions in older adults.

History and origin of aubrites

The cosmic ray exposure (CRE) ages of aubrites are among the longest of stone meteorites. New aubrites have been recovered in Antarctica, and these meteorites permit a substantial extension of the database on CRE ages, compositional characteristics, and regolith histories. We report He, Ne, and Ar isotopic abundances of nine aubrites and discuss the compositional data, the CRE ages, and regolith histories of this class of achondrites. A Ne three-isotope correlation reveals a solar-type ratio of 20Ne/22Ne = 12.1, which is distinct from the present solar wind composition and lower than most ratios observed on the lunar surface. For some aubrites, the cosmic ray-produced noble gas abundances include components produced on the surface of the parent object. The Kr isotopic systematics reveal significant neutron-capture-produced excesses in four aubrites, which is consistent with Sm and Gd isotopic anomalies previously documented in some aubrites. The nominal CRE ages confirm a non-uniform distribution of exposure times, but the evidence for a CRE age cluster appears doubtful. Six meteorites are regolith breccias with solar-type noble gases, and the observed neutron effects indicate a regolith history. ALH aubrites, which were recovered from the same location and are considered to represent a multiple fall, yield differing nominal CRE ages and, if paired, document distinct precompaction histories.

Soft Tissue Artefacts of the Human Back: Comparison of the Sagittal Curvature of the Spine Measured Using Skin Markers and an Open Upright MRI

Soft tissue artefact affects the determination of skeletal kinematics. Thus, it is important to know the accuracy and limitations of kinematic parameters determined and modelled based on skin marker data. Here, the curvature angles, as well as the rotations of the lumbar and thoracic segments, of seven healthy subjects were determined in the sagittal plane using a skin marker set and compared to measurements taken in an open upright MRI scanner in order to understand the influence of soft tissue artefact at the back. The mean STA in the flexed compared to the extended positions were 10.2±6.1 mm (lumbar)/9.3±4.2 mm (thoracic) and 10.7±4.8 mm (lumbar)/9.2±4.9 mm (thoracic) respectively. A linear regression of the lumbar and thoracic curvatures between the marker-based measurements and MRI-based measurements resulted in coefficients of determination, R2, of 0.552 and 0.385 respectively. Skin marker measurements therefore allow for the assessment of changes in the lumbar and thoracic curvature angles, but the absolute values suffer from uncertainty. Nevertheless, this marker set appears to be suitable for quantifying lumbar and thoracic spinal changes between quasi-static whole body postural changes.

Comparison of the angles and corresponding moments in the knee and hip during restricted and unrestricted squats.

Abstract Lorenzetti, S, Gülay, T, Stoop, M, List, R, Gerber, H, Schellenberg, F, and Stüssi, E. Comparison of the angles and corresponding moments in the knee and hip during restricted and unrestricted squats. J Strength Cond Res 26(10): 2829–2836, 2012—The aim of this study was to compare the angles and corresponding moments in the knee and hip during squats. Twenty subjects performed restricted and unrestricted squats with barbell loads that were 0, ¼, and ½ their body weight. The experimental setup consisted of a motion capture system and 2 force plates. The moments were calculated using inverse dynamics. During the unrestricted squats, the maximum moments in the knee were significantly higher, and those in the hip were significantly lower than during restricted squats. At the lowest position, the maximum knee flexion angles were approximately 86° for the restricted and approximately 106° for the unrestricted techniques, whereas the maximum hip flexion angle was between 95° and 100°. The higher moments in the hip during restricted squats suggest a higher load of the lower back. Athletes who aim to strengthen their quadriceps should consider unrestricted squats because of the larger knee load and smaller back load.

Towards patient‐specific material modeling of trabecular bone post‐yield behavior

Bone diseases such as osteoporosis are one of the main causes of bone fracture and often result in hospitalization and long recovery periods. Researchers are aiming to develop new tools that consider the multiple determinants acting at the different scales of bone, and which can be used to clinically estimate patient-specific fracture risk and also assess the efficacy of new therapies. The main step towards this goal is a deep understanding of the bone organ, and is achieved by modeling the complexity of the structure and the high variability of the mechanical outcome. This review uses a hierarchical approach to evaluate bone mechanics at the macroscale, microscale, and nanoscale levels and the interactions between scales. The first section analyzes the experimental evidence of bone mechanics in the elastic and inelastic regions, microdamage generation, and post-yield toughening mechanisms from the organ level to the ultrastructural level. On the basis of these observations, the second section provides an overview of the constitutive models available to describe bone mechanics and predict patient-specific outcomes. Overall, the role of the hierarchical structure of bone and the interplay between each level is highlighted, and their effect is evaluated in terms of modeling biological variability and patient specificity.

Using Skin Markers for Spinal Curvature Quantification in Main Thoracic Adolescent Idiopathic Scoliosis: An Explorative Radiographic Study.

Background and Purpose Although the relevance of understanding spinal kinematics during functional activities in patients with complex spinal deformities is undisputed among researchers and clinicians, evidence using skin marker-based motion capture systems is still limited to a handful of studies, mostly conducted on healthy subjects and using non-validated marker configurations. The current study therefore aimed to explore the validity of a previously developed enhanced trunk marker set for the static measurement of spinal curvature angles in patients with main thoracic adolescent idiopathic scoliosis. In addition, the impact of inaccurate marker placement on curvature angle calculation was investigated. Methods Ten patients (Cobb angle: 44.4±17.7 degrees) were equipped with radio-opaque markers on selected spinous processes and underwent a standard biplanar radiographic examination. Subsequently, radio-opaque markers were replaced with retro-reflective markers and the patients were measured statically using a Vicon motion capture system. Thoracolumbar / lumbar and thoracic curvature angles in the sagittal and frontal planes were calculated based on the centers of area of the vertebral bodies and radio-opaque markers as well as the three-dimensional position of the retro-reflective markers. To investigate curvature angle estimation accuracy, linear regression analyses among the respective parameters were used. The impact of inaccurate marker placement was explored using linear regression analyses among the radio-opaque marker- and spinous process-derived curvature angles. Results and Discussion The results demonstrate that curvatures angles in the sagittal plane can be measured with reasonable accuracy, whereas in the frontal plane, angles were systematically underestimated, mainly due to the positional and structural deformities of the scoliotic vertebrae. Inaccuracy of marker placement had a greater impact on thoracolumbar / lumbar than thoracic curvature angles. It is suggested that spinal curvature measurements are included in marker-based clinical gait analysis protocols in order to enable a deeper understanding of the biomechanical behavior of the healthy and pathological spine in dynamic situations as well as to comprehensively evaluate treatment effects.

Are pressure measurements effective in the assessment of office chair comfort/discomfort? A review

Nowadays, the majority of jobs in the western world involves sitting in an office chair. As a result, a comfortable and supported sitting position is essential for employees. In the literature, various objective methods (e.g. pressure measurements, measurements of posture, EMG etc.) have been used to assess sitting comfort/discomfort, but their validity remains unknown. This review therefore examines the relationship between subjective comfort/discomfort and pressure measurements while sitting in office chairs. The literature search resulted in eight papers that met all our requirements. Four studies identified a relationship between subjective comfort/discomfort and pressure distribution parameters (including correlations of up to r = 0.7 ± 0.13). However, the technique for evaluating subjective comfort/discomfort seems to play an important role on the results achieved, therefore placing their validity into question. The peak pressure on the seat pan, the pressure distribution on the backrest and the pressure pattern changes (seat pan and backrest) all appear to be reliable measures for quantifying comfort or discomfort.

Novel method to analyze post-yield mechanical properties at trabecular bone tissue level

Tissue level mechanics is a key factor to be investigated to improve the knowledge of how the overall trabecular structure reacts to loading and overloading. The aim of this study was to develop a new device for measuring the mechanical competence of single trabeculae in the post-yield region for both tensile and bending tests, characterized by high accuracy and precision, and to assess the effect of testing mode, donor age and material composition. A novel approach for measuring the displacement and deformation was developed (accuracy error of 0.3% and a precision of 2.7%). A total of 30 samples from two bovine femora of different ages (from <3-year-old and 14-year-old cows) were tested in tension or bending, while average material properties have been acquired by means of Raman spectroscopy. A group of trabeculae was tested in bending after treatment for collagen degradation. As a result, a complete set of post-yield properties has been reported. The results highlight significant differences between tensile and bending groups, with higher values for the bending test mode for yield strain, ultimate strain and post-yield work and lower for the elastic modulus. Significant higher values were found for the old donor (differences in the range of 30-60%) for elastic modulus, yield stress and ultimate stress as well as for material properties measured by Raman spectroscopy. We quantified that changes in materials properties induced by collagen degradation corresponded to a substantial decrease (up to 120% for post-yield work) of mechanical competence, both in the elastic and inelastic region.