Thin-film flow in helically wound rectangular channels with small torsion

Laminar gravity-driven thin-film flow down a helically-wound channel of rectangular cross-section with small torsion in which the fluid depth is small is considered. Neglecting the entrance and exit regions we obtain the steady-state solution that is independent of position along the axis of the channel, so that the flow, which comprises a primary flow in the direction of the axis of the channel and a secondary flow in the cross-sectional plane, depends only on position in the two-dimensional cross-section of the channel. A thin-film approximation yields explicit expressions for the fluid velocity and pressure in terms of the free-surface shape, the latter satisfying a non-linear ordinary differential equation that has a simple exact solution in the special case of a channel of rectangular cross-section. The predictions of the thin-film model are shown to be in good agreement with much more computationally intensive solutions of the small-helix-torsion Navier–Stokes equations. The present work has particular relevance to spiral particle separators used in the mineral-processing industry. The validity of an assumption commonly used in modelling flow in spiral separators, namely that the flow in the outer region of the separator cross-section is described by a free vortex, is shown to depend on the problem parameters

Thin-film flow in helically wound shallow channels of arbitrary cross-sectional shape

We consider the steady, gravity-driven flow of a thin film of viscous fluid down a helically wound shallow channel of arbitrary cross-sectional shape with arbitrary torsion and curvature. This extends our previous work [D. J. Arnold et al., “Thin-film flow in helically-wound rectangular channels of arbitrary torsion and curvature,” J. Fluid Mech. 764, 76–94 (2015)] on channels of rectangular cross section. The Navier-Stokes equations are expressed in a novel, non-orthogonal coordinate system fitted to the channel bottom. By assuming that the channel depth is small compared to its width and that the fluid depth in the vertical direction is also small compared to its typical horizontal extent, we are able to solve for the velocity components and pressure analytically. Using these results, a differential equation for the free surface shape is obtained, which must in general be solved numerically. Motivated by the aim of understanding flows in static spiral particle separators used in mineral processing, we investigate the effect of cross-sectional shape on the secondary flow in the channel cross section. We show that the competition between gravity and inertia in non-rectangular channels is qualitatively similar to that in rectangular channels, but that the cross-sectional shape has a strong influence on the breakup of the secondary flow into multiple clockwise-rotating cells. This may be triggered by small changes to the channel geometry, such as one or more bumps in the channel bottom that are small relative to the fluid depth. In contrast to the secondary flow which is quite sensitive to small bumps in the channel bottom, the free-surface profile is relatively insensitive to these. The sensitivity of the flow to the channel geometry may have important implications for the design of efficient spiral particle separators.D. J. Arnold, Y. M. Stokes, and J. E. F. Gree

Follicle Structure Influences the Availability of Oxygen to the Oocyte in Antral Follicles

The ability of an oocyte to successfully mature is highly dependent on intrafollicular conditions, including the size and structure of the follicle. Here we present a mathematical model of oxygen transport in the antral follicle. We relate mean oxygen concentration in follicular fluid of bovine follicles to the concentration in the immediate vicinity of the cumulus-oocyte complex (COC). The model predicts that the oxygen levels within the antral follicle are dependent on the size and structure of the follicle and that the mean level of dissolved oxygen in follicular fluid does not necessarily correspond to that reaching the COC

Isospin splittings of meson and baryon masses from three-flavor lattice QCD + QED

Lattice QCD simulations are now reaching a precision where isospin breaking effects become important. Previously, we have developed a program to systematically investigate the pattern of flavor symmetry beaking within QCD and successfully applied it to meson and baryon masses involving up, down and strange quarks. In this Letter we extend the calculations to QCD + QED and present our first results on isospin splittings in the pseudoscalar meson and baryon octets. In particular, we obtain the nucleon mass difference of M_n-M_p=1.35(18)(8)\,\mbox{MeV} and the electromagnetic contribution to the pion splitting M_{\pi^+}-M_{\pi^0}=4.60(20)\,\mbox{MeV}. Further we report first determination of the separation between strong and electromagnetic contributions in the $\bar{MS}$ scheme.Comment: 14 pages, 10 figures, text and figures added, Journal versio

An Empirical Charge Transfer Potential with Correct Dissociation Limits

The empirical valence bond (EVB) method [J. Chem. Phys. 52, 1262 (1970)] has always embodied charge transfer processes. The mechanism of that behavior is examined here and recast for use as a new empirical potential energy surface for large-scale simulations. A two-state model is explored. The main features of the model are: (1) Explicit decomposition of the total system electron density is invoked; (2) The charge is defined through the density decomposition into constituent contributions; (3) The charge transfer behavior is controlled through the resonance energy matrix elements which cannot be ignored; and (4) A reference-state approach, similar in spirit to the EVB method, is used to define the resonance state energy contributions in terms of "knowable" quantities. With equal validity, the new potential energy can be expressed as a nonthermal ensemble average with a nonlinear but analytical charge dependence in the occupation number. Dissociation to neutral species for a gas-phase process is preserved. A variant of constrained search density functional theory is advocated as the preferred way to define an energy for a given charge.Comment: Submitted to J. Chem. Phys. 11/12/03. 14 pages, 8 figure

Rockfall Hazard Analysis at Small Scale: A Numerical Study for the Estimation of Representative Slope Parameters

The identification of rockfall-affected areas depends on a large number of stochastic variables influencing both triggering and propagation phases. Therefore, rockfall hazard assessment presents huge uncertainties linked to the various scales of analysis. At the small scale (e.g. valley scale), a quick evaluation of rockfall hazard zones is generally required in order to highlight the most critical situations where more detailed analyses should be carried out. The Cone Method (Jaboyedoff and Labiouse 2011), recently implemented in the QPROTO plugin for QGIS, allows to reach this goal with simplified geometrical considerations. In a 3D analysis, the energy line angle and the lateral spreading angle α define a cone of propagation whose apex is located in the rockfall source point. The most significant issue in using the plugin is the evaluation of these angles, which must be defined by the users to consider all the rockfall dissipative processes included in the energy line method (Evans and Hungr 1993). In this paper a study concerning the influence of slope properties (forest coverage and slope inclination) and block characteristics (shape and volume) is proposed, in order to provide to the users of the plugin a preliminary dataset of calibrated angles

Universal phase transitions of B1 structured stoichiometric transition-metal carbides

The high-pressure phase transitions of B1-structured stoichiometric transition metal carbides (TMCs, TM=Ti, Zr, Hf, V, Nb, and Ta) were systematically investigated using ab initio calculations. These carbides underwent universal phase transitions along two novel phase-transition routes, namely, B1\rightarrowdistorted TlI (TlI')\rightarrowTlI and/or B1\rightarrowdistorted TiB (TiB')\rightarrowTiB, when subjected to pressures. The two routes can coexist possibly because of the tiny enthalpy differences between the new phases under corresponding pressures. Four new phases result from atomic slips of the B1-structured parent phases under pressure. After completely releasing the pressure, taking TiC as a representative of TMCs, only its new TlI'-type phase is mechanically and dynamically stable, and may be recovered.Comment: [email protected]

The Performative University: ‘Targets and Terror’ in Academia (Stream18),

The performative university: ‘targets and terror’ in academia Stream proposal, 10th International Critical Management Studies Conference, Liverpool, 3-5 July 2017 The year 1917 saw the advent of the Russian Revolution, which gradually gave way to the Soviet economic system that has been characterized as governed by ‘targets and terror’ and which was notorious for its almost epidemic ‘gaming’ (Bevan & Hood, 2006; Nove, 1958). The same decades that saw the gradual demise of the Soviet system also witnessed the advent of the neo-liberal policy doctrines of ‘Reinventing government’ and ‘New Public Management,’ according to which public sector organizations (including universities) should become more ‘business-like,’ intent on managing performance and building accountability on the basis of quantitative, mostly financial targets (Clegg, 2015; Diefenbach, 2009). It was a historical coincidence in relation to which Bevin & Hood (2006, p. 519) observed: ‘ironically perhaps, just as the targets system was collapsing in the USSR, the same basic approach came to be much advocated for public services in the West by those who believed in ‘results-driven government’ from the 1980s.... It resonated with the ideas put forward by economists about the power of well-chosen numéraires linked with well-crafted incentive systems.’ Exactly a century after the Russsian Revolution, due to these developments it appears that within universities not only the ‘targets and terror’ have persisted from these old and troubled times, but other totalitarian characteristics as well (Geppert & Hollinshead, 2017; Lave et al., 2010). The ‘terror’ has become manifest in the demise of older, more collegial forms of university administration and their large-scale replacement by authoritarian, top-down management by ‘professional’ managers who have no connection or affinity with academic teaching and research (Chandler et al., 2002; Parker, 2014). It has led to a division among university staff between ‘regime sweethearts,’ ‘silent collaborators,’ ‘pragmatist survivors’ and a small ‘active resistance,’ and also to a concomitant closed, anxious and defensive working climate, typical of most totalitarian systems (Alvesson & Spicer, 2016, Butler & Spoelstra, 2014; Teelken, 2012). The ‘targets’ have become manifest in the demise of older, more qualitative forms of collegial feedback and intervision and their large-scale replacement by quantitative performance measurement and management systems that reduce academic teaching and research to ‘scores’ in student surveys and abstract publication ‘points’ in journal ranking systems, respectively (Burrows, 2012; Craig et al., 2014; Mingers & Willmott, 2013). It has led to forms of performance evaluation and accountability that have become more judgmental and punitive and less developmental and supportive, thus further increasing employee anxiety and defensiveness (Kallio et al., 2016; Ter Bogt & Scapens, 2012; Visser, 2016). And, even old forms of propaganda have returned, flooding university campuses and websites with posters, banners and proclamations extolling the virtues and accomplishments of the ‘corporate university’ (Geppert & Hollinshead, 2017; Parker, 2014). In addition, government cutbacks and a neo-liberal penchant for competition and semi-markets have increasingly forced universities to compete with each other for external funds (Wigger & Buch-Hansen, 2013). This has not only led to an increasing commercialization of university teaching and research, catering to business’ interest in ‘commodified’ students and research (Wilmott, 1995), but also a increasing precariousness of university work, in which low-paid, high-stress temporary staff appointments gradually replace existing tenured staff positions and in which academic identities become insecure and fragile (Knights & Clarke, 2014; Lynch & Ivancheva, 2015). Admittedly, not all universities in all parts of the world are equally affected by these developments. The situations appears most alarming in many UK business schools, followed by business schools and faculties in the rest of the Anglo-Saxon world, while many schools and faculties on the Continent appear less affected (Craig et al., 2014; Geppert & Hollinshead, 2017; Parker, 2014; Teelken, 2012)