Acoustic receptivity and transition modeling of Tollmien-Schlichting disturbances induced by distributed surface roughness

Acoustic receptivity to Tollmien-Schlichting waves in the presence of surface roughness is investigated for a flat plate boundary layer using the time-harmonic incompressible linearized Navier-Stokes equations. It is shown to be an accurate and efficient means of predicting receptivity amplitudes, and therefore to be more suitable for parametric investigations than other approaches with DNS-like accuracy. Comparison with literature provides strong evidence of the correctness of the approach, including the ability to quantify non-parallel flow effects. These effects are found to be small for the efficiency function over a wide range of frequencies and local Reynolds numbers. In the presence of a two-dimensional wavy-wall, non-parallel flow effects are quite significant, producing both wavenumber detuning and an increase in maximum amplitude. However, a smaller influence is observed when considering an oblique Tollmien-Schlichting wave. This is explained by considering the non-parallel effects on receptivity and on linear growth which may, under certain conditions, cancel each other out. Ultimately, we undertake a Monte-Carlo type uncertainty quantification analysis with two-dimensional distributed random roughness. Its power spectral density (PSD) is assumed to follow a power law with an associated uncertainty following a probabilistic Gaussian distribution. The effects of the acoustic frequency over the mean amplitude of the generated two-dimensional Tollmien-Schlichting waves are studied. A strong dependence on the mean PSD shape is observed and discussed according to the basic resonance mechanisms leading to receptivity. The growth of Tollmien-Schlichting waves is predicted with non-linear parabolized stability equations computations to assess the effects of stochasticity in transition location

Phyllotactic description of hard sphere packing in cylindrical channels

We develop a simple analytical theory that relates dense sphere packings in a cylinder to corresponding disk packings on its surface. It applies for ratios R=D/d (where d and D are the diameters of the hard spheres and the bounding cylinder, respectively) up to R=1+1/sin(pi/5). Within this range the densest packings are such that all spheres are in contact with the cylindrical boundary. The detailed results elucidate extensive numerical simulations by ourselves and others by identifying the nature of all competing phases

Triumph of hope over experience: learning from interventions to reduce avoidable hospital admissions identified through an Academic Health and Social Care Network.

BACKGROUND: Internationally health services are facing increasing demands due to new and more expensive health technologies and treatments, coupled with the needs of an ageing population. Reducing avoidable use of expensive secondary care services, especially high cost admissions where no procedure is carried out, has become a focus for the commissioners of healthcare. METHOD: We set out to identify, evaluate and share learning about interventions to reduce avoidable hospital admission across a regional Academic Health and Social Care Network (AHSN). We conducted a service evaluation identifying initiatives that had taken place across the AHSN. This comprised a literature review, case studies, and two workshops. RESULTS: We identified three types of intervention: pre-hospital; within the emergency department (ED); and post-admission evaluation of appropriateness. Pre-hospital interventions included the use of predictive modelling tools (PARR - Patients at risk of readmission and ACG - Adjusted Clinical Groups) sometimes supported by community matrons or virtual wards. GP-advisers and outreach nurses were employed within the ED. The principal post-hoc interventions were the audit of records in primary care or the application of the Appropriateness Evaluation Protocol (AEP) within the admission ward. Overall there was a shortage of independent evaluation and limited evidence that each intervention had an impact on rates of admission. CONCLUSIONS: Despite the frequency and cost of emergency admission there has been little independent evaluation of interventions to reduce avoidable admission. Commissioners of healthcare should consider interventions at all stages of the admission pathway, including regular audit, to ensure admission thresholds don't change

Acoustic-roughness receptivity in subsonic boundary-layer flows over aerofoils

The generation of a viscous–inviscid instability through scattering of an acoustic wave by localised and distributed roughness on the upper surface of a NACA 0012 aerofoil is studied with a time-harmonic compressible adjoint linearised Navier–Stokes approach. This extends previous work by the authors dedicated to flat plate geometries. The key advancement lies in the modelling of the inviscid acoustic field external to the aerofoil boundary layer, requiring a numerical solution of the convected Helmholtz equation in a non-uniform inviscid field to determine the unsteady pressure field on the curved aerofoil surface. This externally imposed acoustic pressure field subsequently drives the acoustic boundary layer, which fundamentally determines the amplitudes of acoustic-roughness receptivity. A study of receptivity in the presence of Gaussian-shaped roughness and sinusoidally distributed roughness at Mach number M∞ = 0.4 and Strouhal numbers S ≈ {46, 69, 115} shows the effects of various parameters, most notably angle of attack, angle of incidence of the externally imposed plane acoustic wave and geometry of surface roughness; the latter is varied from viewpoint of its placement on the aerofoil surface and its wavelength. The parametric study suggests that non-parallel effects are quite substantial and that considerable differences arise when using parallel flow theory to estimate the optimal width of Gaussian-shaped roughness elements to provoke the greatest response. Furthermore, receptivity amplitudes for distributed roughness are observed to be generally higher for lower angles of attack, i.e. for less adverse pressure gradients. It is also shown that the boundary layer is more receptive to upstream-travelling acoustic waves

The factors influencing cesarean-section rates-A narrative review from Pakistan

The significant increase in the rate of cesarean section is a major public health issue. The World Health Organization recommends C-section rates not to be greater than 10% and not lower than 5% as both the indicated limits can adversely affect maternal and newborn health. The rate of C-section deliveries is 22% according to recent Pakistan demographics and Health Survey of 2017-2018. This study contributes to the existing literature by examining the factors influencing high C-section rates in Pakistan. A narrative review of published literature between 2000 to 2020, on “factors influencing C-section rates in Pakistan” was done. The findings highlighted five factors that primarily influence utilization of C-section which include: 1. Accessibility to utilize C-section, 2. Association of C-section rates with socioeconomic profile, 3. Elective C-section, 4. Medical conditions as a cause of C-section, 5. C-section as a source of business. Pakistan like other Low middle income countries (LMICs) is facing the increased disease burden on its week and fragile health system. The over utilization of C-section rates has imposed additional burden on the health care system of Pakistan as well as increased economic and health resource liability on maternal care

Dense packings of spheres in cylinders: Simulations

We study the optimal packing of hard spheres in an infinitely long cylinder, using simulated annealing, and compare our results with the analogous problem of packing disks on the unrolled surface of a cylinder. The densest structures are described and tabulated in detail up to D/d=2.873 (ratio of cylinder and sphere diameters). This extends previous computations into the range of structures which include internal spheres that are not in contact with the cylinder.Comment: 18 pages, 14 figures, 1 table, to be submitted to PR

From traditional to modern: easing students transition to problem-based learning.

Letter to the Edito

SDN next generation integrated architecture for HEP and global science

I describe a software-defined global system under development by Caltech and partner network teams in support of the LHC and other major science programs that coordinates workflows among hundreds of multi-petabyte data stores and petascale computing facilities interlinked by 100 Gbps networks, and the Exascale systems needed by the next decade

Cone and seed maturity indices in Pinus wallichiana under temperate conditions of Kashmir Himalayas, India

Pinus wallichiana (Blue pine) does not have a good seed every year and hence it becomes necessary to collect abundant quantity of seed during good seed year. It becomes necessary to know the exact time of seed ma-turity. To overcome this problem, the present investigation was conducted in Kashmir valley at four different altitudes and locations i.e. (1,600-2,000 masl–KFD), (2,000-2,400 masl -LFD), (2,400-2,800-PFD) and (2,800-3200 masl– SFD). The results revealed that seed collection clearly showed wide variation in the maturity of cones. Cone colour served as an indicator of maturity and it changed from light green to green and green with brown patches at maturity-ty. Seed colour changed from whitish to light brown and dark brown at maturity. The mean cone weight (118.67- 88.17gm) and specific gravity (1.13-0.90) decreased as the cones proceeded towards maturity. The mean seed weight of 21.79 to 57.13gm increased at all altitudes as the cones advanced towards maturity. Cone length, cone diameter and germination percent differed (P?0.05) significantly between altitudes and increased when the cones advanced towards maturity. The germination per cent was recorded more at altitudinal range of 1,600-2,400 masl (67.25-70.26%) at maturity, while as it was recorded lower at higher altitudes (42.12-47.25%). It is concluded that the altitudinal range of 1,600-2,400 masl is best sites for collection of phenotypically superior seeds in terms of maxi-mum cone length (18.18cm), diameter (5.23mm) and weight (108.94gm), number of seeds per cone (117.72), seed weight (79.99) and germinability (68.75)