782 research outputs found
Rotational excitation of methylidynium (CH+) by a helium atom at high temperature
We aim to obtain accurate rate coefficients for the collisional excitation of
CH+ by He for high gas temperatures. The ab initio coupled-cluster [CCSD(T)]
approximation was used to compute the interaction potential energy. Cross
sections are then derived in the close coupling (CC) approach and rate
coefficients inferred by averaging these cross sections over a
Maxwell-Boltzmann distribution of kinetic energies. Cross sections are
calculated up to 10'000 cm^-1 for J ranging from 0 to 10. Rate coefficients are
obtained at high temperatures up to 2000 K.Comment: 4 pages, 3 figures, table with rate coefficients, accepted for
publication by A&
The Effects of Eccentric and Plyometric Training Programs and Their Combination on Stability and the Functional Performance in the Post-ACL-Surgical Rehabilitation Period of Elite Female Athletes
BackgroundThe standard method to treat physically active patients with anterior cruciate ligament (ACL) rupture is ligament reconstruction surgery. The rehabilitation training program is very important to improve functional performance in recreational athletes following ACL reconstruction.ObjectivesThe aims of this study were to compare the effects of three different training programs, eccentric training (ECC), plyometric training (PLYO), or combined eccentric and plyometric training (COMB), on dynamic balance (Y-BAL), the Lysholm Knee Scale (LKS), the return to sport index (RSI), and the leg symmetry index (LSI) for the single leg hop test for distance in elite female athletes after ACL surgery.Materials and MethodsFourteen weeks after rehabilitation from surgery, 40 elite female athletes (20.3 ± 3.2 years), who had undergone an ACL reconstruction, participated in a short-term (6 weeks; two times a week) training study. All participants received the same rehabilitation protocol prior to the training study. Athletes were randomly assigned to three experimental groups, ECC (n = 10), PLYO (n = 10), and COMB (n = 10), and to a control group (CON: n = 10). Testing was conducted before and after the 6-week training programs and included the Y-BAL, LKS, and RSI. LSI was assessed after the 6-week training programs only.ResultsAdherence rate was 100% across all groups and no training or test-related injuries were reported. No significant between-group baseline differences (pre-6-week training) were observed for any of the parameters. Significant group-by-time interactions were found for Y-BAL (p < 0.001, ES = 1.73), LKS (p < 0.001, ES = 0.76), and RSI (p < 0.001, ES = 1.39). Contrast analysis demonstrated that COMB yielded significantly greater improvements in Y-BAL, LKS, and RSI (all p < 0.001), in addition to significantly better performances in LSI (all p < 0.001), than CON, PLYO, and ECC, respectively.ConclusionIn conclusion, combined (eccentric/plyometric) training seems to represent the most effective training method as it exerts positive effects on both stability and functional performance in the post-ACL-surgical rehabilitation period of elite female athletes
Efficiency prediction on a 2.5 MW wind turbine gearbox
This paper is a case study of the efficiency of a 2.5 MW wind turbine gearbox including
the influence of each gearbox element: gear tooth geometry, rolling bearings and oil
formulation. The power loss model used to predict the gearbox efficiency was
previously validated with experimental results. The calculations showed that the
efficiency of a wind turbine gearbox can be improved by selecting different wind turbine
gear oil formulations, modifying gear tooth geometry. The energy savings can be even
more significant if both gear tooth geometry and oil formulation are adequately
selected.The authors gratefully acknowledge the funding supported by:
National Funds through Fundação para a Ciência e a Tecnologia (FCT), under
the project EXCL/SEM-PRO/0103/2012;
COMPETE and National Funds through Fundação para a Ciência e a
Tecnologia (FCT), under the project Incentivo/EME/LA0022/2014;
Quadro de Referência Estratégico Nacional (QREN), through Fundo Europeu
de Desenvolvimento Regional (FEDER), under the project NORTE-07-0124-
FEDER-000009 - Applied Mechanics and Product Development;
without whom this work would not be possible
A capacitor voltage balancing approach based on mapping strategy for MMC applications
This paper proposes a new strategy to achieve balanced capacitor voltages in modular multilevel converters. Among the possible solutions, centralized arm control approaches are often adopted. These methods require a balancing technique based on a sorted list of the sub-modules according to their capacitor voltages. In order to achieve the aforementioned sorted list, different algorithms have been proposed in literature, such as: Sorting algorithms, max/min approaches, etc. However, the sorting algorithms require a long execution time, while the max/min approaches affect the converter dynamic response during faults. To overcome these issues, a new mapping strategy providing a quasi-sorted list is proposed in this paper. The suggested method is compared in simulation with both the classical bubble sorting algorithm, and the max/min method during both normal and faulty conditions. Moreover, the three methods have been implemented in a Xilinx Zynq-7000 System-on-Chip (SoC) device, in order to analyze the corresponding execution time and the required computational effort. Hardware-in-the-loop results are presented for demonstrating the superior performance of the proposed balancing strategy
Isokinetic muscle strengthening after acquired cerebral damage: A literature review
AbstractObjectiveIsokinetic strengthening is a rehabilitation technique rarely used in stroke patients. However, the potential benefits of force and endurance training in this population are strongly suspected.MethodThis literature review synthesizes the results of clinical trials on this topic. The research was conducted on PubMed, using “Stroke”, “rehabilitation”, “isokinetic”, “upper limb” and “training” as keywords.ResultsSeventeen studies focusing on the use of isokinetics in assessment or rehabilitation (six studies) following stroke were reviewed. For the lower limb, muscle strength and walking ability improved after isokinetic rehabilitation programs. For the upper limb, the only two studies found in the literature suggest improvement in the strength of the trained muscles, of grip force, of the Fugl-Meyer motor score and of global functional capacities. This review does not reveal any consensus on the protocols to be implemented: type of muscle contraction, velocities….ConclusionWhile isokinetic strengthening has not proven its efficiency in rehabilitation of the upper limb following stroke, its interest with regard to rehabilitation of the lower limbs has been recognized. Randomized controlled trials in this field are necessary to confirm its efficiency, especially concerning upper arm rehabilitation
A deformation based blank design method for formed parts
peer reviewedBlank design is an important task in sheet metal forming process optimization. The initial blank shape has direct effect on the part quality. This paper presents a deformation based blank design approach to determine the initial blank shape for a formed part. The blank design approach is integrated separately into ABAQUS, and DD3IMP, a research purpose in-house FEA code, to demonstrate its compatibility with any FEA code. The algorithm uses FE results to optimize the blank shape for a part. Deep drawing simulation of a rectangular cup geometry was carried out with an initial blank shape determined empirically. The blank shape was iteratively modified, based on the deformation history, until an optimal blank shape for the part is achieved. The optimal blank shapes predicted by the algorithm using both FEA softwares were similar. Marginal differences in the shape error indicate that the deformation history based push/pull technique can effectively determine an optimal blank shape for a part with any FEA software. For the shape error selected, both procedures estimate the optimal blank shape for the part within five iterations
Effects of nitrogen rates on grain yield and nitrogen agronomic efficiency of durum wheat genotypes under different environments
Durum wheat is an important staple food crop in Tunisia and other Mediterranean
countries and is grown in various climatic conditions. Production and
yield are however severely limited not only by drought events but also by
reduced levels of nitrogen fertilisation. A study was carried out at two locations
in the sub-humid area of Tunisia: Mateur in 2009–10 and 2010–11 and Beja in
2011–12 and 2012–13 under rainfed conditions. Four durum wheat genotypes
(landraces: Bidi, Azizi; improved: Om Rabia, Khiar) were evaluated for nitrogen
agronomic efficiency and related agronomic traits under various nitrogen
rates: 0, 50, 100, 150, 200 and 250 kgNha−1, with three replications. There was
a significant interaction effect (P ≤ 0.001) environments × genotypes ×N treatments
for grain yield (GY), biomass yield (BY), harvest index (HI), partial factor
productivity of applied nitrogen (PFPN) and nitrogen agronomic use efficiencies
(NAE). GY was the most affected trait by nitrogen applied showing an increase
of 94% under high N treatment (250 kgNha−1) compared to control plots without
N treatments. A significant linear regression exists between GY (0 N) and
GY for the different N rates (r =0.70; P < 0.001). This effect was more pronounced
for improved genotypes than landraces for all parameters excepting
BY and NAEBY. BY showed +11% increase in landraces than improved genotypes.
PFPN showed an average decrease of 65% under high-N fertilisation with
10% prevalence for improved genotypes. Landraces tend to promote vegetative
growth while grain filling efficiency was higher for improved genotype
Association Between Mental Imagery and Change of Direction Performance in Young Elite Soccer Players of Different Maturity Status
Previous studies have not considered the potential influence of maturity status on the relationship between mental imagery and change of direction (CoD) speed in youth soccer. Accordingly, this cross-sectional study examined the association between mental imagery and CoD performance in young elite soccer players of different maturity status. Forty young male soccer players, aged 10-17 years, were assigned into two groups according to their predicted age at peak height velocity (PHV) (Pre-PHV; n = 20 and Post-PHV; n = 20). Participants were evaluated on soccer-specific tests of CoD with (CoDBall-15m) and without (CoD-15m) the ball. Participants completed the movement imagery questionnaire (MIQ) with the three- dimensional structure, internal visual imagery (IVI), external visual imagery (EVI), as well as kinesthetic imagery (KI). The Post-PHV players achieved significantly better results than Pre-PHV in EVI (ES = 1.58, large; p < 0.001), CoD-15m (ES = 2.09, very large; p < 0.001) and CoDBall-15m (ES = 1.60, large; p < 0.001). Correlations were significantly different between maturity groups, where, for the pre-PHV group, a negative very large correlation was observed between CoDBall-15m and KI (r = –0.73, p = 0.001). For the post-PHV group, large negative correlations were observed between CoD-15m and IVI (r = –0.55, p = 0.011), EVI (r = –062, p = 0.003), and KI (r = –0.52, p = 0.020). A large negative correlation of CoDBall-15m with EVI (r = –0.55, p = 0.012) and very large correlation with KI (r = –0.79, p = 0.001) were also observed. This study provides evidence of the theoretical and practical use for the CoD tasks stimulus with imagery. We recommend that sport psychology specialists, coaches, and athletes integrated imagery for CoD tasks in pre-pubertal soccer players to further improve CoD related performance
Effects of game weekly frequency on subjective training load, wellness, and injury rate in male elite soccer players
Producción CientíficaTo compare the effects of playing one or two games per week on subjective perceived exertion (RPE) and (RPE-based) training load, monotony index, sleep, stress, fatigue, and muscle soreness (Hooper index), total mood disturbance, and injury rate in elite soccer players. Fourteen males from a first-division soccer club (age: 24.42 ± 4.80 years) competed in two games per week for six weeks and one game per week for twelve weeks (a total of 24 games). Paired t-tests and non-parametric Wilcoxon signed ranks evaluated the significance of the differences (p < 0.05). The main findings were that RPE was significantly larger when playing two games per week compared with one game. However, subject total and mean training load, mood disturbance, monotony, and subjective perception of sleep, stress, fatigue, muscle soreness monitoring (Hooper index), and the number of injuries were not different. The findings suggested that competing in two matches per week does not negatively influence injury rate and players’ perceptions of training load or wellness, even though players perceive two games per week as more physically demanding compared with one game per week
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