Forcing Frequency Research Articles

Parametric optimization of frequency oscillation minimum surface shell on a rectangular contour under thermal load

Providing all parameters according to two groups of limit states at the design stage is a multi–criteria task. Optimal design helps to perform such tasks. When the phenomenon of resonance occurs, it is necessary to change the frequency of forced oscillations of the load–bearing structures of various tanks and coatings in order to ensure sufficient strength and stability of the structure and the building in general. For this purpose, there is a separate type of problem in optimal design that allows us to change the forced frequencies of oscillations using the example of the shell of the minimum surface on a rectangular contour.
 In mathematical point of view, optimal design tasks are optimization tasks, finding the extremum of the target function (maximum or minimum). Methods of solving optimal design problems can be conditionally divided into two groups. One of them will include methods that are based on using necessary conditions for the extremum of the objective function. The second group includes methods: linear, convex and dynamic programming, random search methods. The application of modern methods of mathematical optimization requires powerful PCs with a large RAM, therefore, when choosing optimization, it is necessary to take into account the capabilities of computer equipment.
 The optimization algorithm for single–criteria parametric optimization is performed as follows: the objective function is the weight of the shell of the minimum surface on a rectangular contour, the design variables are the shell thickness from 1 to 50 mm, the constraints are presented with first forced oscillation frequency is 0,15 Hz.
 Using software complex Femap with Nastran and our own software, a single–criterion parametric optimization was made. The results of changing the objective function are reducing the weight of the shell by 2300 kg of C240 steel, which is equivalent to 10,3% without losing the strength and stability of the minimum surface shell on a rectangular contour. Using author's methodology and own software, it is possible to perform an effective optimization calculation for the minimum surface shell on a rectangular contour.

The Use of the Forced Frequency of a Bridge Due to a Truck Fleet for Estimating Stiffness Losses at Low Speed

The influence of traffic loads on the dynamic features of a bridge is an external factor that can hinder the true condition of the structure. This paper aims to effectuate a shift in the way this factor is viewed. If the interaction between vehicle and bridge is modeled using the finite element method, the response is based on mass, stiffness, and damping matrices of a coupled vehicle-bridge system that vary with the location of the load at each point in time. The time-varying forced frequencies of a beam bridge model due to a fleet of 3-axle trucks based on eigenvalue analysis (i.e., derived from the matrices of the coupled system) are compared to those obtained using dynamic transient analysis (i.e., derived from the frequency content of the acceleration response of the beam due to a truck crossing). Truck properties are randomly varied within a realistic range to obtain a pattern for the forced vibration due to a truck fleet traveling at an ideal speed of 1 m/s on a 15 m bridge with a smooth surface, and at 10 m/s on a 30 m bridge. These patterns reveal a trend that allows for locating and quantifying the stiffness loss associated with a crack using only the forced frequency. The implementation of this methodology requires the installation of accelerometers on the bridge, and a nearby weigh-in-motion system to identify the traffic fleet of interest. High requirements for frequency resolution limit the application to bridges located on low speed routes.

Nonlinear dynamics and snap-through regimes of a bistable buckled beam excited by an electromagnetic Laplace force

We study the nonlinear forced dynamics of a bistable buckled beam. Depending on the forcing frequency and amplitude, we observe three different regimes: (i) small intra-well oscillations in the neighborhood of one of the equilibria, (ii) transient snap-through ending into intra-well oscillations, (iii) persistent dynamic snap-through. We build experimentally and numerically phase-diagrams determining the forcing amplitude and frequency leading to each of the three regimes. The experiments leverage an original setup based on the use of the electromagnetic Laplace forces. The controlled flow of an electric current through a metallic beam immersed in an electromagnetic field is at the origin of the electromechanical coupling. This non-invasive excitation system allows us to easily tune the forcing frequency and amplitude. The results of our numerical model, based on a weakly nonlinear geometrical approximation and a three-mode Galërkin expansion for the space discretization, are in excellent agreement with the experimental findings. We show that higher-order modes, often neglected in the modal models of the literature, have a major influence on the nonlinear dynamics.

Modal analysis of the liquid sheet breakup with and without acoustic forcing

• The coupling between the acoustic field and the liquid sheet atomization process is studied. • Modal decomposition techniques like Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are employed. • Frequency response of the liquid sheet is found to be dependent on the laminar or turbulent nature of the impacting jets. • Liquid sheet breakup gets coupled with the external forcing when the acoustic energy goes into low frequency modes. • Decoupling occurs when the acoustic energy goes into the dominant modes which are higher ones having a higher frequency. The objective of the present study is to understand the coupling between the acoustics and the sheet atomization process. The phenomenon is studied through modal decompositions of time-resolved images of acoustically perturbed liquid sheets by employing the proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) techniques. The injector operating conditions are selected in order to allow the transition of a smooth liquid sheet to a highly turbulent sheet or fully developed spray. The sheet is destabilized by the traveling acoustic waves of known frequency and sound pressure level. POD modes of the smooth sheets and DMD modes of the turbulent sheets clearly highlight distinct effects of the acoustic perturbations on the liquid sheets. The frequency response of the liquid sheet is found to be dependent on the laminar or turbulent nature of the impacting jets. When the impinging jets are laminar, interestingly the dominant POD mode frequencies are either equal to or harmonics of the external acoustic excitation frequency which confirms the coupling of the atomization process with the acoustic perturbations. Below the lower cutoff frequency, the POD mode having frequency equal to the forcing frequency always dominates other modes. Also, for laminar jets, the DMD growth rate is maximum for the mode having frequency equal to the external forcing. However, for the turbulent impinging jets, the first DMD mode frequency is not always equal to the external forcing frequency but one of the mode in the DMD frequency spectrum show the frequency which is either close to the forcing frequency or close to its integer multiple.

Unsteady disturbances in a swept wing boundary layer due to plasma forcing

This work investigates the response of a transitional boundary layer to spanwise-invariant dielectric barrier discharge plasma actuator (PA) forcing on a 45° swept wing at a chord Reynolds number of 2.17×106. Two important parameters of the PA operation are scrutinized, namely, the forcing frequency and the streamwise location of forcing. An array of passive discrete roughness elements is installed near the leading edge to promote and condition a set of critical stationary crossflow (CF) instability modes. Numerical solutions of the boundary layer equations and linear stability theory are used in combination with the experimental pressure distribution to provide predictions of critical stationary and traveling CF instabilities. The laminar–turbulent transition front is visualized and quantified by means of infrared thermography. Measurements of velocity fields are performed using hotwire anemometry scans at specific chordwise locations. The results demonstrate the inherent introduction of unsteady velocity disturbances by the plasma forcing. It is shown that, depending on actuator frequency and location, these disturbances can evolve into typical CF instabilities. Positive traveling low-frequency type III modes are generally amplified by PA in all tested cases, while the occurrence of negative traveling high-frequency type I secondary modes is favored when PA is operating at high frequency and at relatively downstream locations, with respect to the leading edge.

Influence of runner eccentricity on the hydraulic performance of tubular turbine: A comparative case study

The self-excited vibration of runner is an important factor affecting the stable operation of hydro-turbines. Due to the particularity of structure, there is always a gap between the runner and the shell of the tubular turbine, and the eccentricity of the runner often occurs due to manufacturing or installation. The uneven clearance caused by runner eccentricity will lead to Alford effect and may induce the self-excited vibration. Based on a model tubular turbine, the Alford effect and Alford force of different runner eccentricity is deeply explored through the combination of experiment and numerical simulation. Based on the investigation under a common high-efficiency condition, it is found that the difference of runner eccentricity will cause obvious changes in performance. With the increase of runner eccentricity, the average value of runner radial force increases gradually. The overall frequency of radial force shows several frequency bands and the frequency may shift with the increase of eccentricity level. The runner eccentricity causes obvious changes of internal flow and tip leakage vortex in the blade tip clearances. In the narrowest clearance due to eccentricity, the turbulence kinetic energy and vortex intensity obviously rise up. The pressure in the clearances with different widths are also different. The influence of flow field inside clearance will be the main reason of Alford effect. This study is meaningful for tubular turbines for the operation stability and security.

Genetic algorithm shape optimization to manipulate the nonlinear response of a clamped-clamped beam

Dynamical systems, which are described by differential equations, can have an enhanced response because of their nonlinearity. As one example, the Duffing oscillator can exhibit multiple stable vibratory states for some external forcing frequencies. Although discrete systems that are described by ordinary differential equations have helped to build fundamental groundwork, further efforts are needed in order to tailor nonlinearity into distributed parameter, continuous systems, which are described by partial differential equations. To modify the nonlinear response of continuous systems, topology optimization can be used to change the shape of the mechanical system. While topology optimization is well-developed for linear systems, less work has been pursued to optimize the nonlinear vibratory response of continuous systems. In this paper, a genetic algorithm implementation of shape optimization for continuous systems is described. The method is very general, with flexible objective functions and very few assumptions; it is applicable to any continuous system. As a case study, a clamped-clamped beam is optimized to have a more nonlinear or less nonlinear vibratory response. This genetic algorithm implementation of shape optimization could provide a tool to improve the performance of many continuous structures, including MEMS sensors, actuators, and macroscale civil structures.

Large Eddy Simulations of excited flames issuing from rectangular nozzles

In the current study we assess an impact of passive and active flow control methods applied to the flames emanating from rectangular nozzles. The passive control is realised by varying a jet aspect ratio using differently shaped nozzles, while the active control relies on applying a forcing to the axial component of velocity. The analysis is performed through a series of high fidelity Large Eddy Simulations (LES) using a high order in-house solver. Combustion process is modelled using the detailed chemistry model of a hydrogen oxidation with a corresponding set of species transport equations. It is shown that the passive flow control affects the jet flames significantly only up to a moderate forcing frequency. For a high frequency excitation the effect of the aspect ratio is weak. A combination of both control methods is found as very efficient in altering important practical flame features like a lift-off height and flame shape.

Hypersonic Boundary-Layer Receptivity over Circular Cones with Ellipsoidal/Spherical Noses

The hypersonic boundary-layer receptivity to planar and axisymmetric freestream slow acoustic waves is investigated for a Mach 6 flow over a 5 deg half-angle circular cone with three different ellipsoidal/spherical noses. To fully characterize the boundary-layer response, a wide frequency range of the first and second instability modes is considered. The results show that the receptivity mechanisms for both instability modes are similar to those for a previously investigated sphere-nosed cone. Furthermore, the variation of the receptivity coefficient with the frequency is obtained. For the second mode, the nose effect on the receptivity coefficient is dependent on the forcing frequency; whereas for the first mode, the receptivity coefficient monotonously decreases with increasing bluntness. An empirical similarity parameter is identified to collapse the receptivity coefficient of the first mode for the cones investigated. Considering that the receptivity coefficient of the first mode is nearly two orders of magnitude higher than that of the second mode, the traditional method, which ignores receptivity, may underestimate the role of the first mode in causing transition.

Nonlinear Bloch dynamics and spin-wave generation in a Bose-Hubbard ladder subject to effective magnetic field.

The two-leg magnetic ladder is the simplest and ideal model to reflect the coupling effects of lattice and magnetic field. It is of great significance to study some novel phases, topological characteristics, and chiral characteristics in condensed matter physics. In particular, the left-right leg degree of freedom can be regarded as a pseudospin, and the two-leg magnetic ladder also provides an ideal platform for the study of spin dynamics. Here the ground state, Bloch oscillations (BOs), and spin dynamics of the interacting two-leg magnetic ladder subject to an external linear force are studied by using variational approach and numerical simulation. In the absence of the external linear force, the critical condition of transition between the zero-momentum state and plane-wave state is obtained analytically, and the physical mechanism of the ground-state transition is revealed. When the external linear force presents, the occurrence of BOs excites the spin dynamics, and we reveal the chiral BOs and the accompanied spin dynamics of the system in different ground states. In particular, we further study the influence of periodically modulated linear force on BOs and spin dynamics. The frequencies of the linear force corresponding to the resonances and pseudoresonances are obtained analytically, which result in rich nonlinear dynamics. In resonances, stable and strong BOs (with larger amplitude) are observed. In pseudoresonances, because the pseudoresonance frequencies are related to the initial momentum and phase of the wave packet, a dispersion effect takes place and strong diffusion of wave packet occurs. When the frequency is nonresonant, drift and weak dispersion of wave packet occur simultaneously with the wave-packet oscillation. In all cases, the wave-packet dynamics is accompanied with periodic but anharmonic pseudospin oscillation. The BOs and spin dynamics are effectively controlled by periodically modulating the linear force.

An iterated map model with CaMKII feedback in modeling the force frequency relationship of a cardiac cell

Experiment data on isolated rat hearts shows that the transient behaviors after switching pacing intervals are very complicated with increasing, decreasing, and rebound of the contraction force. The strength of contraction in the heart muscle is strongly related to intracellular free Ca2+ mediated by an action potential. This behavior can be explained by calcium cycling inside the excitable cardiac myocytes coupled with their action potential. The previous and recently proposed models can only explain a short period of time after changing the pacing frequency. Our aim is to develop a simple feedback model based on the role of the enzyme CaMKII to describe the whole dynamic picture captured from experiments.

Tension identification method of structural cable based on calibration principle in engineering

This paper proposes a practical cable tension identification method based on the calibration principle for in-service building cables in engineering. Based on the beam model theory of vibration method and Zui. H theory formula, a general cable force-frequency model is proposed. Then, the tension and frequency of the cable during the construction is calibrated to fit the model parameters. The cable force identification is realized by testing the cable frequency during service. In this paper, the cable force frequency calibration test is carried out on the semi-parallel wire cable and typical pre-stressed structures, and the cable force frequency database is obtained. The tension prediction model is fitted by some data and verified by the rest data. The root mean square error and the goodness of fit are calculated, and the applicability of the method is verified by comparing with the existing method. The cable tension identification method provides a new idea for the cable force identification of in-service cables in engineering.

The Role of Ca2+ Sparks in Force Frequency Relationships in Guinea Pig Ventricular Myocytes.

Calcium sparks are the elementary Ca2+ release events in excitation-contraction coupling that underlie the Ca2+ transient. The frequency-dependent contractile force generated by cardiac myocytes depends upon the characteristics of the Ca2+ transients. A stochastic computational local control model of a guinea pig ventricular cardiomyocyte was developed, to gain insight into mechanisms of force-frequency relationship (FFR). This required the creation of a new three-state RyR2 model that reproduced the adaptive behavior of RyR2, in which the RyR2 channels transition into a different state when exposed to prolonged elevated subspace [Ca2+]. The model simulations agree with previous experimental and modeling studies on interval-force relations. Unlike previous common pool models, this local control model displayed stable action potential trains at 7 Hz. The duration and the amplitude of the [Ca2+]myo transients increase in pacing rates consistent with the experiments. The [Ca2+]myo transient reaches its peak value at 4 Hz and decreases afterward, consistent with experimental force-frequency curves. The model predicts, in agreement with previous modeling studies of Jafri and co-workers, diastolic sarcoplasmic reticulum, [Ca2+]sr, and RyR2 adaptation increase with the increased stimulation frequency, producing rising, rather than falling, amplitude of the myoplasmic [Ca2+] transients. However, the local control model also suggests that the reduction of the L-type Ca2+ current, with an increase in pacing frequency due to Ca2+-dependent inactivation, also plays a role in the negative slope of the FFR. In the simulations, the peak Ca2+ transient in the FFR correlated with the highest numbers of SR Ca2+ sparks: the larger average amplitudes of those sparks, and the longer duration of the Ca2+ sparks.

Experimental investigation of three-dimensional modes in the wake of a rotationally oscillating cylinder

Three-dimensionalities in the wake of flow past a circular cylinder executing sinusoidal rotary oscillations about its axis is studied experimentally. The results of water tunnel experiments on a rotationally oscillating cylinder for Reynolds number of 250 with varying amplitude and forcing frequency are discussed. Qualitative studies using hydrogen bubble and laser-induced fluorescence flow visualisation techniques are performed. Observation made for oscillating amplitude, $\theta _{0} = {\rm \pi}/4$ and $\theta _{0}=3{\rm \pi} /4$ , and a low normalised forcing frequency, $FR$ , of 0.75 and 0.5, respectively, confirmed a mode having a spanwise non-dimensional wavelength of $\sim$ 1.8 which is also observed for a rotating cylinder. On increasing forcing frequency this mode disappears and a new mode with a bean-shaped structure and a much smaller spanwise normalised wavelength of $\sim$ 0.8 appears at an $FR$ of 1 and an oscillation amplitude of ${\rm \pi} /2$ . This mode remains almost stable until a forcing frequency of $FR=1.4$ . At higher forcing frequency, $FR=2.75$ , and oscillation amplitude of $3{\rm \pi} /4$ , a mode with cellular structure and a normalised spanwise wavelength of $\sim$ 1.6 is identified. The cells in this mode flatten up with increasing downstream distance and are shed alternately with respect to the adjacent cell. Certain combinations of forcing parameters resulted in a forced two-dimensionality of the wake. Quantitative studies using hot-wire measurements and particle image velocimetry confirm the presence of these modes and wake characteristics. Wake mode map in the forcing frequency and amplitude plane is presented showing regions of newly discovered modes and wake lock-on boundaries.

Entropy transfer function measurement with tunable diode laser absorption spectroscopy

Tunable diode laser absorption spectroscopy (TDLAS) with wavelength modulation spectroscopy (WMS) has been widely applied to measure the gas temperature and species concentration in combustion environments. In this work, we show the capability of TDLAS in measuring the coherent temperature fluctuations of a turbulent swirled flame. Two distributed feedback grating (DFB) lasers are used to probe the H2O absorption transitions near 7185.59 cm−1 and 6806.03 cm−1. Using WMS, the 2f/1f absorption spectra are converted into temperature at a rate of 5 kHz. The quantity of interest that we measure is the Entropy Transfer Function (ETF) which, for low Mach numbers, relates the upstream acoustic perturbation to the temperature fluctuation downstream of the flame. The ETF is obtained by taking the ratio between the measured temperature fluctuation downstream of the flame, measured with TDLAS and the upstream acoustic perturbation input, induced by loudspeakers with forcing frequency ranging from 40 to 250 Hz, reconstructed with the multi-microphone method. We show that the TDLAS-WMS technique can measure relatively low coherent temperature fluctuations as low as 5 K. It is found that the gain of ETFs of the swirling flame does not decrease monotonically with respect to the forcing frequency and exhibits a minimum response at particular frequencies depending on the operating conditions. Moreover, the ETFs for different operating conditions collapse on each other when plotted against the Strouhal number. The similarity between the measured ETFs and Flame Transfer Functions (FTFs) indicates a strong link between flame heat release rate response and the temperature fluctuation downstream of the flame. Furthermore, the measurement series demonstrate the strong capability and suitability of the TDLAS-WMS technique for entropy waves measurements, leading to the discovery of peculiar entropy responses at high frequencies.

Active control of thermoacoustic fluctuations by nanosecond repetitively pulsed glow discharges

In this study, the use of nanosecond repetitively pulsed (NRP) glow discharges to mitigate thermoacoustic fluctuations was investigated. Two strategies in applying the discharges were compared: continuous forcing and closed-loop gated forcing. It was found that NRP glow discharges could mitigate thermoacoustic fluctuations in a wall-stabilized methane-air flame either by applying the discharges continuously or using a closed-loop control scheme. A parametric study was done to investigate the role of the forcing phase, the applied voltage (6.3–6.8 kV), the pulse repetition frequency (15–30 kHz), the duty cycle (24–50%), and the forcing frequency on the performance of the plasma actuator. The most effective control of the thermoacoustic fluctuations was obtained when using the closed-loop control scheme with an applied voltage of 6.8 kV, a forcing frequency matching the instability frequency, close to phase opposition with the instability, and a power input of 0.8% of the flame thermal power. It was also found that the duty cycle in the tested range did not have a significant effect on the performance of the scheme when the number of discharges per cycle was constant. Phase-locked imaging of the flame was employed and showed that the flame’s base location, surface area, and surface area gradient oscillated over the thermoacoustic period. For the best discharge forcing, the oscillations in the flame’s base location and surface area were suppressed making the flame temporally and spatially stable.

Using Competing Theories to Explain Variations in U.S. Police Departments’ Reported use of Force Counts

Using data from the 2013 Law Enforcement Management and Administrative Statistics (LEMAS) survey, the current study provides a cross-sectional analysis of U.S. police departments’ reported use of force. The goal of this study was to examine the extent to which departments’ reported force counts were explained by rational bureaucratic and/or institutional theory. Given the stark variations in reported force counts, a hurdle model was used to examine the potential effects of the theories on departments’ likelihoods of reporting force and the frequency in which they reported it. The results highlighted the significance of both theories. In terms of rational bureaucratic theory, the results illustrate that the absence of a collective bargaining agreement and greater professionalism requirements reduced departments’ likelihoods of reporting force, while less restrictive administrative policies increased departments’ likelihoods of reporting force and the frequencies in which they reported it. In terms of institutional theory, the results revealed that black officer representation reduced both the likelihood of reporting force and the frequency of force reported. However, increases in jurisdictions’ population and crime rates, for the most part, increased force reports. Combined the theories explained over one-fifth of the variations in departments’ reported use of force for the observed year. The findings suggest that successful efforts to reduce force-related injuries and deaths should consider the contextual environments in which rules and regulations regarding force are made.

Study on Contact Force and Vibration Characteristics of Composite Cylindrical Roller Bearing

The composite cylindrical roller is composed of a hollow cylindrical roller and a filler body and is a new type of structure roller bearing. In order to explore the influence of different parameters on the contact characteristics and vibration characteristics of bearings, finite element models of static contact, modal analysis, and harmonic response analysis of composite cylindrical roller bearings were established based on ABAQUS software. The effects of filling rate, radial force, and the number of rollers on parameters such as contact force, contact stress, and natural frequency were studied. The results show that when the filling rate of the cylindrical roller increases from 0% to 70%, the natural frequency of bearing and the peak frequency of its harmonic response decrease, the force distribution in the contact area is also more uniform, and the maximum contact stress of the roller is reduced by 29.1%; the radial force has no effect on the peak frequency of the harmonic response of the bearing, but the increase of the radial force will increase the peak value of the response displacement, and the contact force and stress of the rollers will also increase. When the number of rollers increases from 11 to 15, the natural frequency and the peak frequency of harmonic response increase, the peak displacement decreases, the contact force distribution of the rollers in the bearing area is more uniform, and the maximum contact stress of the roller is reduced by 21.1%. The research result can provide a theoretical reference for the structural optimization and engineering application of elastic composite cylindrical roller bearings.

Fetal muscle extract improves muscle function and performance in aged mice.

Background: Loss of skeletal muscle mass and function is one of the major musculoskeletal health problems in the aging population. Recent studies have demonstrated differential proteomic profiles at different fetal stages, which might be associated with muscle growth and development. We hypothesized that extract derived from fetal muscle tissues at the stage of hypertrophy could ameliorate the loss of muscle mass and strength in aged mice. Methods: To allow sufficient raw materials for investigation, skeletal muscle extract from fetal sheep at week 16 of gestation and maternal tissue were used in the present study. iTRAQ (isobaric tags for relative and absolute quantitation) and KEGG pathway analyses identified differentially expressed proteins in fetal sheep muscle extract vs. adult sheep muscle extract. Effects of FSME and ASME on human myoblast proliferation were studied. To examine the effect of FSME in vivo, C57BL/6 male mice at 20 months of age were subjected to intramuscular administration of FSME or vehicle control for 8 weeks. A grip strength test and ex vivo muscle force frequency test were conducted. Finally, serum samples were collected for multiplex analysis to determine potential changes in immunological cytokines upon FSME injection. Results: Compared with ASME, 697 and 412 peptides were upregulated and downregulated, respectively, in FSME, as indicated by iTRAQ analysis. These peptides were highly related to muscle development, function, and differentiation from GO enrichment analysis. FSME promoted cell proliferation of myoblast cells (+300%, p < 0.01) without causing significant cytotoxicity at the tested concentration range compared with ASME. After 8 weeks of FSME treatment, the percentage of lean mass (+10%, p < 0.05), grip strength (+50%, p < 0.01), and ability in fatigue resistance were significantly higher than those of the control group. Isometric forces stimulated by different frequencies were higher in the control group. Histologically, the control group showed a larger cross-sectional area (+20%, p < 0.01) than the FSME group. The multiplex assay indicated that FSME treatment did not lead to an elevated circulatory level of inflammatory cytokines. Of note, after FSME treatment, we observed a significant drop in the circulating level of IL-12 (p40) from 90.8 ± 48.3 pg/ml to 82.65 ± 4.4 pg/ml, G-CSF from 23476 ± 8341.9 pg/ml to 28.35 ± 24.2 pg/ml, KC from 97.09 ± 21.2 pg/ml to 29.2 ± 7.2 pg/ml, and RANTES from 325.4 ± 17.3 pg/ml to 49.96 ± 32.1 pg/ml. Conclusion: This is the first study demonstrating the beneficial effect of fetal muscle extract on muscle health in aged mice. Further analysis of the active ingredients of the extract will shed light on the development of a novel treatment for sarcopenia.

Modeling Gas Flow Velocities in Soils Induced by Variations in Surface Pressure, Heat, and Moisture Dynamics

AbstractChanges in atmospheric pressure continuously ventilate soils and snowpacks. This physical process, known as pressure pumping, is a major factor in the exchange fluxes of H2O, CO2, and other trace gases between the soil and atmosphere. Thus models of pressure pumping are relevant to many areas of critical importance. This study compares the three principal models used to describe pressure pumping. Beginning with the fundamental physical principles and whether the flow field is compressible or incompressible, these models are categorized as linear parabolic (one model—compressible) or nonlinear hyperbolic (two models—incompressible). Using observed soil surface pressure data, measured vertical profiles of soil permeability and standard linear analysis and numerical methods, this study shows that nonlinear models produce advective velocities that are one to two orders of magnitude greater than those associated with the linear model. Incorporating soil temperature and moisture dynamics made very little difference to the linear model, but a significant difference in the nonlinear models suggesting that advective velocities induced by pressure changes associated with soil heating and moisture dynamics may not always be small enough to ignore. All numerical results are sensitive to the frequency of the pressure forcing, which was band‐pass filtered into low, mid and high frequencies with the greatest model differences at low frequencies. Partitioning the pressure forcing and model responses helped to establish that mid‐frequency weather‐related phenomena (empirically identified as inertia gravity waves and solitons) are important drivers of gas exchange between the soil and the atmosphere.