Charged anisotropic compact star core-envelope model with polytropic core and linear envelope

This manuscript is related to the construction of relativistic core-envelope model for spherically symmetric charged anisotropic compact objects. The polytropic equation of state is considered for core, while it is linear in the case of envelope. We present that core, envelope and the Reissner Nordstr$$\ddot{o}$$ o ¨ m exterior regions of stars match smoothly. It has been verified that all physical parameters are well behaved in the core and envelope region for the compact stars SAX J1808.4-3658 and 4U1608-52. Various physical parameters inside star are discussed herein, non-singularity and continuity at the junction has been catered as well. Impact of charged compact object together with core-envelope model on the mass, radius and compactification factor is described by graphical representation in both core and envelop regions. The stability of the model is worked out with the help of Tolman–Oppenheimer–Volkoff equations and radial sound speed.

The Effect of Fatigue on Leg Muscle Activation and Tibial Acceleration During a Jumping Task

Context: Lower-extremity stress fractures (SFx) are a common occurrence during load-bearing activities of jumping and landing. To detect biomechanical changes during jumping postinjury, a fatigue model could be used. Objective: To evaluate muscle activation in the lower leg and tibial accelerations (TAs) prefatigue to postfatigue following a jumping task in those with and without a history of SFx. Design: Repeated-measures. Setting: Athletic Training Research Lab. Participants: A total of 30 active college-aged students with and without a history of lower-extremity (leg or foot) SFx (15 males and 15 females; 21.5 [5.04] y, height = 173.5 [12.7] cm, weight = 72.65 [16.4] kg). Intervention: A maximal vertical jump on one leg 3 times with arms folded across the chest prefatigue to postfatigue was performed. Fatigue protocol was standing heel raises on a custom-built platform at a pace controlled by a metronome until task failure was reached. Legs were tested using a randomized testing order. Electromyographic (EMG) surface electrodes were placed on the medial gastrocnemius, soleus, and tibialis anterior following a standardized placement protocol. A triaxial accelerometer was attached to the proximal anteromedial surface of the tibia. Main Outcome Measures: Linear envelopes of the medial gastrocnemius, soleus, and tibialis anterior and peak accelerations (resultant acceleration takeoff and landing). Results: Significant interaction for leg × test for tibialis anterior with a posttest difference between SFx and control (P = .05). There were decreases in EMG linear envelope following fatigue for medial gastrocnemius (P < .01) and tibialis anterior (P = .12) pretest to posttest. At takeoff, TA was greater in the SFx contralateral leg in comparison with the control leg (P = .04). At landing, TA was greater in posttest (P < .01) and in the SFx leg compared with SFx contralateral (P = .14). Conclusion: A decrease in muscle activity and an increase in TA following fatigue were noted for all subjects but especially for those with a history of SFx.

Osteoarthrosis: Analyze of the Molar Bite Force, Thickness and Masticatory Efficiency

Osteoarthrosis is a disorder of synovial joints, resulting from destruction of the cartilage and subchondral bone. The present study is aimed to investigate the molar bite force, thickness and efficiency of the masseter and temporalis muscles of subjects with osteoarthrosis. A total of forty-eight subjects participated in the study. They were distributed into two groups: with osteoarthrosis (n=24) and asymptomatic controls (n=24). Subjects were analyzed on the basis of maximal molar bite force (right and left side), thickness (mandibular rest and dental clenching in maximal voluntary contraction) and electromyographic activity of masticatory cycles through the linear envelope integral in habitual (raisins and peanuts) and non-habitual (Parafilm M) chewing of the masseter and temporalis muscles. All the data were analyzed statistically using t-test with a significance level of p≤0.05. There was no difference between groups in maximal molar bite force, muscle thickness and non-habitual chewing. Differences were found on the raisins (p=0.02) and peanuts (p=0.05) chewing for right temporal muscle, with reduced masticatory muscle efficiency in osteoarthrosis subjects. This study showed that osteoarthrosis induces negative changes in habitual chewing, highlighting the efficiency of the right temporalis muscles. The greater temporal muscle activity in subjects with osteoarthrosis may compromise chewing and consequently the nutritional status of adult subjects.

Acceleration Profiles and the Isoinertial Squatting Exercise: Is There a Direct Effect on Concentric–Eccentric Force, Power, and Neuromuscular Efficiency?

Objective: To examine the selective influences of distinct acceleration profiles on the neuromuscular efficiency, force, and power during concentric and eccentric phases of isoinertial squatting exercise. Design: Cross-sectional study. Setting: Biomechanics laboratory of the university. Participants: A total of 38 active adults were divided according to their acceleration profiles: higher (n = 17; >2.5 m/s2) and lower acceleration group (n = 21; <2.5 m/s2). Intervention: All subjects performed squats until failure attached to an isoinertial conic pulley device monitored by surface electromyography of rectus femoris, vastus medialis, vastus lateralis, biceps femoris, and semitendinosus. Main Outcome Measures: An incremental optical encoder was used to assess maximal and mean power and force during concentric and eccentric phases. The neuromuscular efficiency was calculated using the mean force and the electromyographic linear envelope. Results: Between-group differences were observed for the maximal and mean force (Prange = .001–.005), power (P = .001), and neuromuscular efficiency (Prange = .001–.03) with higher significant values for the higher acceleration group in both concentric and eccentric phases. Conclusion: Distinct acceleration profiles affect the neuromuscular efficiency, force, and power during concentric and eccentric phases of isoinertial squatting exercise. To ensure immediate higher levels of power and force output without depriving the neuromuscular system, acceleration profiles higher than 2.5 m/s2 are preferable. The acceleration profiles could be an alternative to evolve the isoinertial exercise.

Muscle recruitment and co-contraction when walking in young women with chronic lumbar pain

Introduction: The lumbar pain is the main musculoskeletal complaint reported by the active population, and it prevents daily activities such as walking. Objective: To assess muscle recruitment and the co-contraction of the trunk muscles during different walking speed in individuals with and without chronic lumbar pain. Method: Thirty-four sedentary young women attended the study, in which 18 belonged to the lumbar pain team (LPT) and 16 to the team without lumbar pain (WLP). We assessed the electromyography activity of the internal oblique (IO) local muscle and lumbar multifidus (MUL), and global external oblique (EO), abdominal rectus (AR) and lumbar iliocostalis (LIC), during walking. The electromyography analysis was performed from the average of the linear envelope value, normalized by the peak of muscle activation. The muscle co-contraction (IO/MUL, EO/LIC, AR/LIC, IO/EO, and the abdominal/paravertebral muscle groups) was calculated with the Falconer and Winter formula. The Shapiro-Wilk test, Multivariate Analysis, mixed Variance Analyses with Bonferroni post-hoc, and Pearson (p < 0.05) correlation coefficient were made by the statistical analysis. Results: In the WLP we could notice that the higher the speed, the higher the MUL activation. The co-contraction data demonstrated that IO/MUL muscles activate 20% more in the LPT, during the preferred speed; however, in the WLP, the results showed that the higher the walking speed, the higher the EO/LIC (21.8%) and IO/MUL (17.8%) muscles activation. Conclusion: The recruitment of local muscles doesn’t differ among the evaluated groups and conditions; however, in WLP, the higher the MUL muscle action, the higher the walking speed.

Wellbore stability evaluation method based on the continuous tangent envelope of a Mohr circle

It is of great practical significance to accurately obtain formation collapse pressure and determine an effective three-pressure profile with a correct strength criterion in the drilling process to identify the best drilling fluid density. Taking the tight sandstone of the XuJiahe formation as an example, we conducted a series of rock mechanics tests, focusing on large-scale, high-density confining pressure triaxial experiments; determined a mathematical expression for the continuous tangent envelope of a nonlinear Mohr circle envelope based on a series of triaxial tests; and clarified the variation rules of cohesion force and internal friction angle with confining pressure. The impact of rock mechanics parameters determined by using the traditional method and the continuous tangent envelope method on wellbore stability is compared and analyzed by using the MathCAD program, and then the collapse pressure is obtained. The results show that the parabolic curve derived from the uniaxial rock mechanics test data of the XuJiahe formation is not suitable for the triaxial test results under high confining pressure. By means of the continuous tangent envelope method, the relationship between rock cohesion and internal friction angle and confining pressure is obtained; this replaces the traditional collapse pressure calculation results using geophysical logging data or uniaxial tests, and the relationship between cohesion and friction angle is more consistent with confining pressure. The MathCAD simulation analysis shows that the rock mechanics parameters determined by the continuous tangent envelope can reflect the stratum situation more truly than the linear envelope method. Compared with the linear envelope method and parabolic envelope method under the same conditions, the continuous tangent envelope method has certain advantages in determining the critical density, which provides a theoretical basis for the accuracy of sandstone formation collapse pressure calculation and can give significant guidance for the study of wellbore stability of deep sandstone formations.

Application of Phase Decomposition to the Analysis of Random Time Series From Wave Basin Tests

Many ocean engineering problems involve bound harmonics which are slaved to some underlying assumed close to linear time series. When analyzing signals we often want to remove the bound harmonics so as to “linearise” the data or to extract individual bound harmonic components so that they may be studied. For even moderately broadbanded systems filtering in the frequency domain is not sufficient to separate components as they overlap in frequency. One way to overcome this difficulty is to use input signals with the same linear envelope but with different phases and then use simple addition and subtraction of the resulting signals to extract different harmonics. This approach has been established for the analysis of wave groups. In this paper we examine whether this approach can be used on random time series as well. We analyse random wave time series of wave elevation from the towing tank in Shanghai Jiao Tong University and force measurements on a cylinder taken in the Kelvin tank at the University of Strathclyde.