102,241 research outputs found
Risoluzione protesica dei disparallelismi tra impianti e monconi naturali collegati insieme
No full textDuctility assessment of a 17-4PH steel through simple multiaxial tests
No full textThe present work summarizes the results of an experimental campaign aimed at assessing the ductility of a wrought 17-4PH steel alloy. A simple specimen reproducing multiaxial stress states through a universal testing machine is selected. A Finite Element Model (FEM) for each test is setup to extract the local values of stress and strain in the most critical point on the onset of failure. A Digital Image Correlation (DIC) technique is employed to assess the strain field estimated via FEM. The collected data are used to analyse the material ductility, calculating the triaxiality and deviatoric parameter at the fracture strain. The proposed tests fall in the range of low triaxialities, which are less investigated in the literature. The results obtained are compared with the prediction of a damage model, previously calibrated on the material through more conventional tests. The prediction accuracy of the damage model was fully confirmed by the outcome of the new tests. Eventually, the possibility of replacing some of the conventional tests used for calibration with the proposed specimen is explored
Simple multiaxial tests to assess dynamic ductility of 17-4PH
No full textTo investigate material ductility, the use of simple multiaxial specimens which can be
tested through a common tensile machine or by a Split Hopkinson bar facility would allow
avoiding the use of more complex equipment to induce different stress states in the investigated
material. In this work, experimental dynamic tests have been performed on four different specimen
geometries on a 17-4PH steel by a direct Split Hopkinson Bar (SHB). Finite element models of
the experiments are set up and used jointly with experimental data to calibrate and validate a strain
rate dependent plasticity model, and to extract the local values of stress and ultimate strain in the
most critical point of the samples, at fracture. These latter results allowed the calibration of a
ductile damage model, whose predictions, compared with a previous calibration using tests carried
out in quasi-static conditions, confirmed the effectiveness of the proposed specimens and test
methodology to assess material ductility under dynamic conditions
Development of a wayside measurement system for the evaluation of wheel-rail lateral contact force
No full textConsidering the safety against derailment, it is essentially that a vehicle respects the force limits imposed by standards. This paper presents an experimental wayside measurement system for the measurement of the wheel-rail lateral contact force. While there are several well-known solutions for the monitoring of the vertical force, the measurement of the lateral one by means wayside systems is rather uncommon because of overlapping effects that are always present with vertical loads. The system, thanks to its particular sensors configuration, is instead able to isolate the strain effects of the vertical force from those of the lateral one. The research is based on laboratory tests, finite element simulations and on field test directly on a railway line in service. Besides, combining the system with another one for monitoring of the vertical force, it has shown the possibility to evaluate the derailment ratio for each train passing over the measurement site
Impact of the plant competition for water use on the Soil Water Balance of a Water-limited Mediterranean Ecosystem
No full textRail strain under different loads and conditions as a source of information for operation
No full textThe structural analysis and knowledge of the forces acting between the wheel and the rail, can give important information about the safety of the operation and the track maintenance of railways. The complexity of the analysis comes from the variability of the wheel-rail contact point modelled by the use of multi-body simulations. The theoretical calculations, used to study this problem, are based on the finite element method. The purpose of the work, described in this paper, is to find specific areas on the rail surfaces with stress and strain features, which allow evaluation of the influence of different loading factors. The ratio between the forces and strains could be a good index to study the rail stress. Using this ratio, it is possible to identify the effects of the different kinds of load and how the corresponding strains are affected by the boundary condition
Power training in young athletes: Is it all in the genes?
No full textIntroduction. The aim of the study was to evaluate the effects of plyometric and isometric training protocol on power in 46 team sports (basketball: n = 23; volleyball: n = 23) players, also in relation to genetic background (i.e., ACE and PPARA genes polymorphisms). Methods. The following tests were administered: squat jump (SJ), countermovement jump (CMJ), drop jump (dJ), sprint, handgrip, and agility test. Genetic analysis was based on saliva samples. Results. The training protocol proved to be effective in improving jump performance in basketball players and volleyball players, respectively: 25-meter sprint test (p = 0.006; p = 0.008); agility test (p = 0.000; p = 0.000); SJ test (p = 0.001; p = 0.000); CMJ test (p = 0.005; p = 0.000); and dJ test (p = 0.03 only for basketball players; dJ test improvement in volleyball players was not significant), regardless of sports practice. Furthermore, data confirm that the 'd' allele of ACE and the 'C' allele of PPARA are positive alleles associated to power and strength performances. Conclusions. The importance to train strength skills should be emphasized, above all through isometric and plyometric exercises, not neglecting the key role played by the genetic background
LOAD DISTRIBUTION DURING SUSPENSION TRAINING EXERCISE
No full textINTRODUCTION: Suspension training (ST) uses body weight in multi-directional movements as a form of exercise and due to its feasibility
promotes a large variety of workouts within a low space occupancy. However, only few studies (1,2) investigated the load distribution
during ST, especially during pulling exercises. Therefore, the aims of this study were to evaluate body inclination and ground reaction
force and to predict equations to estimate the training load distribution during ST static back-row at different length of the straps.
METHODS: Thirty volunteers (men=16, women=14; age=23.3±1.7years; body weight=63.9±13.3kg; height=167.9±9.2cm; Body Mass Index
[BMI]=22.5±3.4kg·m-2) performed 14 static ST back-row (holding for 5s) at seven different lengths of ST device (148cm, 158cm, 168cm,
178cm, 188cm, 198cm, 208cm) ranging from the simplest to the most challenging, in 2 different elbow (flexed, extended) positions. A ST
device (AINS ST FIPE, Italy) was anchored at 2.65m above a force platform. Subjects stood barefoot on the force plate, with their feet
shoulder width apart positioned under the anchored point and visual reflective markers applied to subjects’ left lateral malleolus and at
the acromion process. The force platform was used to evaluate the ground reaction force, whereas a video camera was used to record
all the trials. The recorded videos were then analyzed to calculate the body inclination angle with respect to the horizontal plane. Ground
reaction force and body inclination were used to predict training load equations trough multi-level regression models (P<0.05).
RESULTS: Two multi-level regression models were created. In the first one, ground reaction force was used as dependent variable,
whereas body inclination angle, body weight, height, BMI and elbow position were used as independent variables. Significant effects
were found for all variables included in the model, with an Intraclass Correlation Coefficient (ICC) of 0.31. Analyzing the model, the follow-ing equation to estimate the ground reaction force was extrapolated: Load=-132.9134+0.3724671·Angle-1.299028·Body
weight+0.9844512·Height+3.675008·BMI-2.073684·Elbow.
In the second model (ICC of 0.37), the body inclination angle was replaced by the ST device’s length. By analyzing this model, the following equation to estimate the ground reaction force knowing the length of the straps was extrapolated: Load=-69.80267-
0.2199257·Length-1.281452·Body weight+0.8883487·Height+3.624841·BMI+5.188559·Elbow.
CONCLUSION: The proposed models could provide different methods to quantify the training load distribution, even if the use of the
straps’ length could result easier and faster than body inclination angle, helping practitioners and instructors to personalize the workout
to reach specific purposes and provide load progression.
References
1) Giancotti et. al., J Strength Cond Res, 2018.
2) Gulmez, J Strength Cond Res, 2017.
Key-words: body weight; instability; back-row; resistance training; functional training; biomechanic
Relationship between Anthropometrics and Dynamic Balance Performances
No full textDynamic balance performances are highly affected by the base of support, the
center of gravity and its projection within the base of support. Although anthropometric
characteristics could be expected to affect dynamic balance performances1,
there is a need to substantiate this relationship. Therefore, the aim of this study was
to evaluate the relationship between anthropometric measurements and dynamic balance
performances. After signing an informed consent, 26 (female, n=14; male, n=12)
college students (25.7±3.4years) were involved in the study. Body mass, height, sitting
height, and foot size were measured, whereas lower limbs length was calculated
as the difference between standing and sitting height. Dynamic balance performance
was assessed on a wobble board (Balance Board WSP, GSJ Service, Rome, Italy;
diameter=40cm) as the time spent in the target zone (diameter=6.3cm) displayed on
a screen. Participants were asked to stand barefoot on the wobble board with a comfortable
double leg stance, keeping their hands on the hip and looking at the screen
(displaying performance in real time). After a 3-minute familiarization, three 30-second
trials were performed with one minute sitting recovery in between. A correlation
analysis (p<0.05) was applied to anthropometrics and balance performances (the best
score out of three trials). Time in the target zone (12.7±5.9s) was significantly related
to weight (63.8±12.6kg; r=-0.46, p=0.02) and foot size (25.3±1.5cm; r=-0.42, p=0.03),
whereas no significant correlation emerged with respect to height (167.0±10.3cm) and
lower limbs length (79.6±6.7cm). Therefore, individual anthropometric characteristics
should be considered when evaluating dynamic balance performances. Further studies
are needed to investigate the relationship between anthropometric characteristics
and the length and area of sways, and lateral movements of the center of mass
Validation of Correlates of Risk of TB Disease in High Risk Populations (CORTIS-HR) Study: Public, subject-level RISK11 signature scores and metadata
No full textThe Validation of Correlates of Risk of TB Disease in High Risk Populations (CORTIS-HR) Study, a companion study of the CORTIS-01 Trial (ClinicalTrials.gov: NCT02735590), was conducted to test the diagnostic and prognostic performance of the RISK11 biomarker for tuberculosis (TB) disease in people living with HIV (PLHIV) in an ambulant community setting. The “CORTIS-HR pubdata.csv” is a public, subject-level dataset for the CORTIS-HR study containing key variables necessary to reconstruct the study findings. A data dictionary is provided below. The “CORTIS-HR PCR data.csv” provides subject-level TaqMan qPCR probe raw CT (cycle threshold) gene expression data from the Fluidigm microfluidic 96.96 Gene Expression Integrated Fluidic Circuits (chips) with sample quality control (“SAMPLE_QC”) results. Analyses of the qPCR probe data are ongoing; the embargo on this data ends 1 July 2021 when the data will be available on ZivaHub. “CORTIS-HR Protocol Version 1.0.pdf” and “CORTIS-HR SAP Version 1.0.pdf” are the protocol and the statistical analysis plan for the study respectively and have been included for reference
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