The impact of two-dimensional (2-D) periodic forcing on transition dynamics in laminar separation bubbles (LSBs) generated on a flat plate is investigated experimentally. Laminar separation is caused by the favourable-to-adverse pressure gradient under an inverted modified NACA $64_3\text{-}618$ and periodic disturbances are generated by an alternating current dielectric barrier discharge plasma actuator located near the onset of the adverse pressure gradient. Surface pressure and time-resolved particle image velocimetry measurements along the centreline and several wall-parallel planes show significant reductions in bubble size with active flow control. Periodic excitation leads to amplification of the Kelvin–Helmholtz (K–H) instability resulting in strong 2-D coherent roller structures. Spanwise modulation of these structures is observed and varies with the forcing amplitude. Intermediate forcing amplitudes result in periodic spanwise deformation of the mean flow at large wavelength ($\lambda _z/L_{b,5kVpp} \approx 0.76$). For high-amplitude forcing, the spanwise modulation of the mean flow agrees with the much smaller wavelength of the difference interaction of two oblique subharmonic modes ($\lambda _z/L_{b,5kVpp} \approx 0.24$). Modal decomposition shows nonlinear interaction of the forced 2-D mode leading to growth of subharmonic and harmonic content, and the observation of several half-harmonics ($[n+1/2]f_{\textit{AFC}}$) at intermediate forcing amplitudes. Strongest amplitudes of the 2-D mode and delay of transition downstream of the time-averaged reattachment are observed for the intermediate forcing amplitudes, previously only observed in numerical simulations. Consistent with numerical results, further increase of the forcing amplitude leads to rapid breakdown to turbulence in the LSB. This suggests that the most effective exploitation of the K–H instability for transition delay is connected to an optimal (moderate) forcing amplitude.

In 1959 the Libraries Committee of the African Studies Association undertook a survey of holdings of Africana in American Theological libraries. The official approval of both the American Theological Library Association and the Catholic Library Association was received and inquiries were sent to a selected group of libraries in each Association. The main purpose was to ascertain the location of significant collections of printed material and to uncover, if possible, unknown or unrecorded manuscripts.

In discussing these three papers as they relate to history, it is an essential starting point to realize that the discipline of history is changing and has changed considerably in the last quarter century. History began as an account of the great deeds of our own ancestors, a record of the past that was essentially a backward extension of our own group personality. It long ago outgrew its concern with our tribal past and came to be concerned with the past of other peoples who share our Western culture. More recently, historians have become increasingly concerned with the past of other cultures as well. Some remnants of the older historical tradition are still around, but broadly speaking history now can be defined as the study of change in human society.

With this shifting focus inside the discipline itself, some of the barriers that used to surround history have also begun to disappear. One of these barriers was a distinction between history and pre-history, made according to the kind of evidence that each used. Historians worked with documentary evidence, leaving the pre-historians to worry with the kind of problem that could be solved only through the combined use of archaeology, oral tradition, linguistic evidence, and the like. In African history no such distinction is possible, and it is now generally abandoned. Documentary evidence about the history of Africa south of the Sahara begins about the ninth century, but it has to be used alongside non-documentary evidence. Documentary evidence, used by itself, only begins to tell the whole story when we come to the twentieth century, and even here it overlaps with the oral evidence of people still alive. African history is thus dominantly a history based on mixed data. The old line between history and pre-history is no longer useful, and theJournal of African History recognized this fact when, for convenience, it set a new division between history and pre-history at the beginning of the Iron Age — a date which will, of course, be somewhat different for different parts of Africa.

Benjamin Britten’s Noye’s Fludde (1958) was arguably the first community opera with an environmental message. It explored the potential extinction of animal and human life, and since then environmentalism as a social issue has begun to emerge in community operas as a distinctive trope. This article examines some more recent examples produced in the UK, from The Split Goose Feather (1979) by Christopher Brown, to Timber! (1990) by Timothy Kraemer, to Russell Hepplewhite’s Till the Summer Comes Again (2012) inspired by Glyndebourne’s wind turbine. It concludes with some reflections on the questions that arise in relation to contemporary opera, the environment and sustainability – notably how the professional operatic world can respond to concerns about the environment, and what steps are necessary to ensure the sustainability of opera for the future.

To synthesize evidence on the relations among multiple constructs, measures, or concepts, meta-analyzing correlation matrices across primary studies has become a crucial analytic approach. Common meta-analytic approaches employ univariate or multivariate models to estimate a pooled correlation matrix, which is subjected to further analyses, such as structural equation modeling. In practice, meta-analysts often extract multiple correlation matrices per study from various samples, study sites, labs, or countries, thus introducing hierarchical effect size multiplicity into the meta-analytic data. However, this feature has largely been ignored when pooling correlation matrices for meta-analysis. To contribute to the methodological development in this area, we describe a multilevel, multivariate, and random-effects modeling approach, which pools correlation matrices meta-analytically and, at the same time, addresses hierarchical effect size multiplicity. Specifically, it allows meta-analysts to test various assumptions on the dependencies among random effects, aiding the selection of a meta-analytic baseline model. We describe this approach, present four working models within it, and illustrate them with an example and the corresponding R code.

This paper explores the impact of handle silicon substrate resistivity on substrate noise coupling and its influence on the spectral purity of voltage-controlled oscillators (VCOs). Three VCOs were designed using the 28 nm fully depleted silicon-on-insulator (FD-SOI) technology and fabricated on process-of-reference wafer featuring a handle Si substrate resistivity value of 10 Ω.cm and also on high-resistivity (HR) Si handle wafer of 1 kΩ.cm. The output spectrum of the VCOs was measured under two conditions: with and without a 0 dBm noise signal injected into the substrate. The results demonstrate that passivated HR substrates achieve more than 26 dB reduction in parasitic spurs induced by substrate noise. To the best of the authors’ knowledge, this work presents the first fabrication and measurement of VCOs on HR substrates in FD-SOI technology, highlighting their effectiveness in mitigating substrate noise coupling.