Ex Situ Conservation Of Holstein-Friesian Cattle - Comparing The Dutch, French And USA Germplasm Collections

The establishment of gene banks using cryopreservation to secure the genetic diversity of farm breeds have been widely assessed. France, the Netherlands and the USA were among the first countries to organize national cryobanks and these banks are now 10 to 20 years old. All three countries have started Holstein-Friesian (HF) collections to conserve as much genetic diversity as possible for this globally important breed. In order better understand the diversity captured in these collections, the genetic variability of HF collections within and between countries was assessed, and genetic variability of germplasm collections were compared with active bulls in each country. The overall aim of the project was to determine the breed’s security and to guide future collection activities

Convective instability and transient growth in flow over a backward-facing step

Transient energy growths of two- and three-dimensional optimal linear perturbations to two-dimensional flow in a rectangular backward-facing-step geometry with expansion ratio two are presented. Reynolds numbers based on the step height and peak inflow speed are considered in the range 0–500, which is below the value for the onset of three-dimensional asymptotic instability. As is well known, the flow has a strong local convective instability, and the maximum linear transient energy growth values computed here are of order 80×103 at Re = 500. The critical Reynolds number below which there is no growth over any time interval is determined to be Re = 57.7 in the two-dimensional case. The centroidal location of the energy distribution for maximum transient growth is typically downstream of all the stagnation/reattachment points of the steady base flow. Sub-optimal transient modes are also computed and discussed. A direct study of weakly nonlinear effects demonstrates that nonlinearity is stablizing at Re = 500. The optimal three-dimensional disturbances have spanwise wavelength of order ten step heights. Though they have slightly larger growths than two-dimensional cases, they are broadly similar in character. When the inflow of the full nonlinear system is perturbed with white noise, narrowband random velocity perturbations are observed in the downstream channel at locations corresponding to maximum linear transient growth. The centre frequency of this response matches that computed from the streamwise wavelength and mean advection speed of the predicted optimal disturbance. Linkage between the response of the driven flow and the optimal disturbance is further demonstrated by a partition of response energy into velocity components

Convective instability and transient growth in steady and pulsatile stenotic flows

We show that suitable initial disturbances to steady or long-period pulsatile flows in a straight tube with an axisymmetric 75%-occlusion stenosis can produce very large transient energy growths. The global optimal disturbances to an initially axisymmetric state found by linear analyses are three-dimensional wave packets that produce localized sinuous convective instability in extended shear layers. In pulsatile flow, initial conditions that trigger the largest disturbances are either initiated at, or advect to, the separating shear layer at the stenosis in phase with peak systolic flow. Movies are available with the online version of the paper

Estimation of unsteady aerodynamic forces using pointwise velocity data

A novel method to estimate unsteady aerodynamic force coefficients from pointwise velocity measurements is presented. The methodology is based on a resolvent-based reduced-order model which requires the mean flow to obtain physical flow structures and pointwise measurement to calibrate their amplitudes. A computationally-affordable time-stepping methodology to obtain resolvent modes in non-trivial flow domains is introduced and compared to previous existing matrix-free and matrix-forming strategies. The technique is applied to the unsteady flow around an inclined square cylinder at low Reynolds number. The potential of the methodology is demonstrated through good agreement between the fluctuating pressure distribution on the cylinder and the temporal evolution of the unsteady lift and drag coefficients predicted by the model and those computed by direct numerical simulation.Comment: In revie

A Prospective Design Identifying Etiological Risk Factors Associated with MTSS and Stress Fractures in Female Intercollegiate Athletes.

The identification of risk factors associated with overuse injuries, specifically Medial Tibial Stress Syndrome (MTSS) and Tibial Stress Fractures (TSF), may help professionals with management and prevention of these injuries. The purpose of this study was to identify risk factors associated with MTSS and TSF in female intercollegiate athletes. This study used a mulitifactorial, prospective design for 13-26 weeks. Thirty-nine Division I intercollegiate female student-athletes in volleyball, soccer, and track were examined. Anatomical, physiological (eating disorder and menstrual history), and training (duration and recovery time) characteristics were examined as possible risk factors. Only two injuries were reported during the study; therefore, analysis for risk factors was not possible. Descriptive statistics for the dependent variables were calculated, and comparisons across sport were performed. Differences in leg length values and dorsiflexion ROM were observed across sports. No conclusions could be drawn regarding possible risk factors for MTSS and TSF in this population