bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical assessment of biomethane production from algal residues after biodiesel production
Authors: Zhu Liandong , Li Zhaohua , Hiltunen Erkki
Published: October 2017

Energy shortage, global warming, and climate changes call for the creation and breakthroughs of renewable and sustainable energy technologies, and thus biofuels from microalgae have been the object of ever‐increasing interest. Microalgal biodiesel production presents as one of the promising options for biofuel production, since most microalgal species contain rich lipids. However, large amounts of residues are left behind after microalgal biodiesel production. In an effort to improve the potential economics of microalgal biofuels, it is essential to make full use of microalgal post‐extracts. This Focus Article determines the theoretical yields of microalgal biodiesel and biomethane together with the relevant calorific values during the continuous production. Based on the investigated species, the microalgal biodiesel and biomethane yields widely range from 6 to 134 g/kg‐VS and from 0.24 to 0.63 L/g‐VS, respectively, while the total calorific values experience the range of between 6.88 and 18.80 MJ/kg‐VS. Microalgal biodiesel production is not always required before anaerobic digestion, especially for those microalgal species with low lipid contents. Net energy ratio and cost‐effectiveness analysis are highlighted in order to evaluate the viability of the biorefinery process. Well‐funded research and development programs can help develop technologies and policies, thus driving the industry toward prosperity. WIREs Energy Environ 2018, 7:e273. doi: 10.1002/wene273.

This article is categorized under:

Bioenergy > Science and Materials

Bioenergy > Systems and Infrastructure
Long Head of Biceps Tendon Management: A Survey of the American Shoulder and Elbow Surgeons
Authors: Corpus Keith T. , Garcia Grant H. , Liu Joseph N. , Dines David M. , O'Brien Stephen J. , Dines Joshua S. , Taylor Samuel A.
Published: October 2017

Background:

Management of symptomatic long head of biceps tendon (LHBT) pathology remains a source of debate.

Questions/Purposes:

The purpose of this study was to identify consensus trends for the treatment of LHBT pathology among specialists.

Methods:

A survey was distributed to members of the American Shoulder and Elbow Society (ASES), consisting of three sections—demographics, case scenarios, and general LHBT pathology management. Cases presented common clinical scenarios, and surgeons reported their management preferences. Consensus responses were defined as > 50% of participants giving a single response.

Results:

One hundred and forty-two of 417 (34%) surgeons completed surveys. Forty-seven percent of questions reached a consensus answer. Biceps tenodesis was the overwhelmingly preferred technique in cases demonstrating LHBT pathology, as compared to tenotomy. No consensus, however, was reached regarding a specific surgical technique for biceps tenodesis. The two most popular techniques were arthroscopic tenodesis to bone and open subpectoral biceps tenodesis. Fellowship-trained arthroscopic surgeons and surgeons with a largely arthroscopic practice were more likely to perform tenodesis arthroscopically.

Conclusion:

ASES members favored biceps tenodesis over tenotomy for surgical management of LHBT pathology, without consensus regarding a specific surgical technique.
No Difference in Conventional Polyethylene Wear Between Yttria-stabilized Zirconia and Cobalt-chromium-molybdenum Femoral Heads at 10 Years
Authors: Morrison Todd A. , Moore Rebecca D. , Meng Jia , Rimnac Clare M. , Kraay Matthew J.
Published: October 2017

Background

Concerns have arisen regarding deterioration of wear properties of yttria-stabilized zirconia (YSZ) femoral head on conventional polyethylene (PE) bearings due to YSZ phase transformation.

Questions/Purposes

The purpose of this study was to determine if there is a difference in long-term PE wear properties between YSZ and cobalt-chromium-molybdenum (Co-Cr-Mo) femoral heads.

Methods

Ten-year radiographic wear assessment was performed on a cohort of patients enrolled in a prospective randomized clinical trial comparing total hip arthroplasty with YSZ or Co-Cr-Mo femoral heads on conventional, non-cross-linked PE.

Results

PE linear wear, annualized wear, and steady-state wear rates remained low and similar between groups. No cases of osteolysis were observed.

Conclusions

Measured conventional PE wear was similar between YSZ and Co-Cr-Mo femoral heads with the steady-state wear rates for both remaining below the generally accepted threshold at which osteolysis typically occurs. Whether clinically relevant phase transformation with YSZ femoral heads occurs is uncertain; however, the use of YSZ femoral heads in this study was not associated with increased PE wear, osteolysis, or deterioration of wear properties.
Discrimination of Olive Oil by Cultivar, Geographical Origin and Quality Using Potentiometric Electronic Tongue Fingerprints
Authors: Souayah Fatma , Rodrigues Nuno , Veloso Ana C. A. , Dias Luís G. , Pereira José A. , Oueslati Souheib , Peres António M.
Published: October 2017

Legal regulations are set for protecting claims regarding olive oil geographical denomination. When meteorological or agroecological factors similarly affect different regions, the origin identification is a challenging task. This study demonstrated the use of a potentiometric electronic tongue coupled with linear discriminant analysis to discriminate the geographical origin of monovarietal Tunisian olive oil produced from local cv Chemlali (Kairouan, Sidi Bouzid or Sfax regions) and cv Sahli (Kairouan, Mahdia or Sousse regions). The potentiometric fingerprints of 12 or eight lipid sensors (for Chemlali and Sahli, respectively), selected using a simulated annealing meta‐heuristic algorithm, allowed the correct prediction (repeated K‐fold cross‐validation) of the geographic production region with sensitivities of 92 ± 7% (Chemlali) and 97 ± 8% (Sahli). It was also confirmed the electronic tongue capability to classify Tunisian olive oil according to olive cultivar or quality grade. The results indicated the possible use of potentiometric fingerprints as a promising innovative strategy for olive oil analysis allowing assessing geographical origin, olive cultivar and quality grade, which are key factors determining olive oil price and consumers’ preference.
Involvement of N-methyl-D-aspartate receptors and nitric oxide in the anticonvulsant effects of dantrolene against pentylenetetrazole-induced seizures in mice
Authors: Samad Akbarzadeh , Fatemeh Heidary , Mojtaba Keshavarz
Published: October 2017

Objective N-methyl-d-aspartate (NMDA) receptors and nitric oxide (NO) have important roles in the pathology and treatment of pentylenetetrazole (PTZ)-induced seizures. We aimed to show the involvement of these two systems in the anticonvulsant effects of dantrolene against PTZ-induced seizures.

Methods The male albino Swiss strain of mice (N = 56) randomly allocated to the seven separate groups and treated with dantrolene (40 mg/kg), dantrolene (40 mg/kg) + L-arginine (100 mg/kg, a NO donor), dantrolene (40 mg/kg) + N-Nitroarginine methyl ester (L-NAME) (100 mg/kg, a NO synthase inhibitor), dantrolene (40 mg/kg) + NMDA (50 mg/kg), dantrolene (40 mg/kg) + MK801 (1 mg/kg, a selective NMDA antagonist), Diazepam (5 mg/kg, the positive control) and saline (the negative control). Seizures were induced by intraperitonial injection of PTZ (90 mg/kg). The onsets of clonic and tonic-clonic seizures, as well as the death of animals, were recorded.

Results Dantrolene significantly increased the onset of clonic, tonic-clonic seizures and death of animals challenged with PTZ. The onset of tonic-clonic seizure in animals treated with dantrolene alone and dantrolene + L-NAME was higher than the control group. In contrast, the onset of tonic-clonic seizure in the animals treated with dantrolene + L-arginine was significantly lower than the dantrolene-treated group. The onset of clonic and tonic-clonic seizures in animals treated with dantrolene + MK801 were significantly higher than the control and dantrolene + NMDA groups.

Conclusion Dantrolene protected animals against PTZ-induced seizures and mortality. The inhibition of NO synthase and NMDA receptors may contribute to the dantrolene anticonvulsant effects on the PTZ-induced seizure.
Neuropsychiatric symptoms as risk factors of dementia in a Mexican population: A 10/66 Dementia Research Group study
Authors: Acosta Isaac , Borges Guilherme , Aguirre‐Hernandez Rebeca , Sosa Ana Luisa , Prince Martin ,   10/66 Dementia Research Group
Published: October 2017

Introduction

Cognitive and/or memory impairment are the main clinical markers currently used to identify subjects at risk of developing dementia. This study aimed to explore the relationship between the presence of neuropsychiatric symptoms and dementia incidence.

Methods

We analyzed the association between neuropsychiatric symptoms and incident dementia in a cohort of 1355 Mexican older adults from the general population over 3 years of follow‐up, modeling cumulative incidence ratios using Poisson models.

Results

Five neuropsychiatric symptoms were associated with incident dementia: delusions, hallucinations, anxiety, aberrant motor behavior, and depression. The simultaneous presence of two symptoms had a relative risk, adjusted for mild cognitive impairment, diabetes, indicators of cognitive function, and sociodemographic factors, of 1.9 (95% confidence interval, 1.2–2.9), whereas the presence of three to five, similarly adjusted, had a relative risk of 3.0 (95% confidence interval, 1.9–4.8).

Discussion

Neuropsychiatric symptoms are common in predementia states and may independently contribute as risk factors for developing dementia.
Transition to turbulence in pulsating pipe flow
Authors: Xu Duo , Warnecke Sascha , Song Baofang , Ma Xingyu , Hof Björn
Published: October 2017

Fluid flows in nature and applications are frequently subject to periodic velocity modulations. Surprisingly, even for the generic case of flow through a straight pipe, there is little consensus regarding the influence of pulsation on the transition threshold to turbulence: while most studies predict a monotonically increasing threshold with pulsation frequency (i.e. Womersley number, $\unicode[STIX]{x1D6FC}$), others observe a decreasing threshold for identical parameters and only observe an increasing threshold at low $\unicode[STIX]{x1D6FC}$. In the present study we apply recent advances in the understanding of transition in steady shear flows to pulsating pipe flow. For moderate pulsation amplitudes we find that the first instability encountered is subcritical (i.e. requiring finite amplitude disturbances) and gives rise to localized patches of turbulence (‘puffs’) analogous to steady pipe flow. By monitoring the impact of pulsation on the lifetime of turbulence we map the onset of turbulence in parameter space. Transition in pulsatile flow can be separated into three regimes. At small Womersley numbers the dynamics is dominated by the decay turbulence suffers during the slower part of the cycle and hence transition is delayed significantly. As shown in this regime thresholds closely agree with estimates based on a quasi-steady flow assumption only taking puff decay rates into account. The transition point predicted in the zero $\unicode[STIX]{x1D6FC}$ limit equals to the critical point for steady pipe flow offset by the oscillation Reynolds number (i.e. the dimensionless oscillation amplitude). In the high frequency limit on the other hand, puff lifetimes are identical to those in steady pipe flow and hence the transition threshold appears to be unaffected by flow pulsation. In the intermediate frequency regime the transition threshold sharply drops (with increasing $\unicode[STIX]{x1D6FC}$) from the decay dominated (quasi-steady) threshold to the steady pipe flow level.
Gas depletion through single gas bubble diffusive growth and its effect on subsequent bubbles
Authors: Moreno Soto Álvaro , Prosperetti Andrea , Lohse Detlef , van der Meer Devaraj
Published: October 2017

When a gas bubble grows by diffusion in a gas–liquid solution, it affects the distribution of gas in its surroundings. If the density of the solution is sensitive to the local amount of dissolved gas, there is the potential for the onset of natural convection, which will affect the bubble growth rate. The experimental study of the successive quasi-static growth of many bubbles from the same nucleation site described in this paper illustrates some consequences of this effect. The enhanced growth due to convection causes a local depletion of dissolved gas in the neighbourhood of each bubble beyond that due to pure diffusion. The quantitative data of sequential bubble growth provided in the paper show that the radius-versus-time curves of subsequent bubbles differ from each other due to this phenomenon. A simplified model accounting for the local depletion is able to collapse the experimental curves and to predict the progressively increasing bubble detachment times.
Consistent equations for open-channel flows in the smooth turbulent regime with shearing effects
Authors: Richard G. L. , Rambaud A. , Vila J. P.
Published: October 2017

Consistent equations for turbulent open-channel flows on a smooth bottom are derived using a turbulence model of mixing length and an asymptotic expansion in two layers. A shallow-water scaling is used in an upper – or external – layer and a viscous scaling is used in a thin viscous – or internal – layer close to the bottom wall. A matching procedure is used to connect both expansions in an overlap domain. Depth-averaged equations are then obtained in the approximation of weakly sheared flows which is rigorously justified. We show that the Saint-Venant equations with a negligible deviation from a flat velocity profile and with a friction law are a consistent set of equations at a certain level of approximation. The obtained friction law is of the Kármán–Prandtl type and successfully compared to relevant experiments of the literature. At a higher precision level, a consistent three-equation model is obtained with the mathematical structure of the Euler equations of compressible fluids with relaxation source terms. This new set of equations includes shearing effects and adds corrective terms to the Saint-Venant model. At this level of approximation, energy and momentum resistances are clearly distinguished. Several applications of this new model that pertains to the hydraulics of open-channel flows are presented including the computation of backwater curves and the numerical resolution of the growing and breaking of roll waves.
Instability wave–streak interactions in a supersonic boundary layer
Authors: Paredes Pedro , Choudhari Meelan M. , Li Fei
Published: October 2017

The interaction of stationary streaks undergoing non-modal growth with modally unstable instability waves in a supersonic flat-plate boundary-layer flow is studied using numerical computations. For incompressible flows, previous studies have shown that boundary-layer modulation due to streaks below a threshold amplitude level can stabilize the Tollmien–Schlichting instability waves, resulting in a delay in the onset of laminar–turbulent transition. In the supersonic regime, the most-amplified linear waves become three-dimensional, corresponding to oblique, first-mode waves. This change in the character of dominant instabilities leads to an important change in the transition process, which is now dominated by oblique breakdown via nonlinear interactions between pairs of first-mode waves that propagate at equal but opposite angles with respect to the free stream. Because the oblique breakdown process is characterized by a strong amplification of stationary streamwise streaks, artificial excitation of such streaks may be expected to promote transition in a supersonic boundary layer. Indeed, suppression of those streaks has been shown to delay the onset of transition in prior literature. This paper investigates the nonlinear evolution of initially linear optimal disturbances that evolve into finite-amplitude streaks in a two-dimensional, Mach 3 adiabatic flat-plate boundary-layer flow, followed by the modal instability characteristics of the perturbed, streaky boundary-layer flow. Both parts of the investigation are performed with the plane-marching parabolized stability equations. Consistent with previous findings, the present study shows that optimally growing stationary streaks can destabilize the first-mode waves, but only when the spanwise wavelength of the instability waves is equal to or smaller than twice the streak spacing. Transition in a benign disturbance environment typically involves first-mode waves with significantly longer spanwise wavelengths, and hence, these waves are stabilized by the optimal growth streaks. Thus, as long as the amplification factors for the destabilized, short wavelength instability waves remain below the threshold level for transition, a significant net stabilization is achieved, yielding a potential transition delay that may be comparable to the length of the laminar region in the uncontrolled case.
Prograde, retrograde, and oscillatory modes in rotating Rayleigh–Bénard convection
Authors: Horn Susanne , Schmid Peter J.
Published: October 2017

Rotating Rayleigh–Bénard convection is typified by a variety of regimes with very distinct flow morphologies that originate from several instability mechanisms. Here we present results from direct numerical simulations of three representative set-ups: first, a fluid with Prandtl number $Pr=6.4$, corresponding to water, in a cylinder with a diameter-to-height aspect ratio of $\unicode[STIX]{x1D6E4}=2$; second, a fluid with $Pr=0.8$, corresponding to $\text{SF}_{6}$ or air, confined in a slender cylinder with $\unicode[STIX]{x1D6E4}=0.5$; and third, the main focus of this paper, a fluid with $Pr=0.025$, corresponding to a liquid metal, in a cylinder with $\unicode[STIX]{x1D6E4}=1.87$. The obtained flow fields are analysed using the sparsity-promoting variant of the dynamic mode decomposition (DMD). By means of this technique, we extract the coherent structures that govern the dynamics of the flow, as well as their associated frequencies. In addition, we follow the temporal evolution of single modes and present a criterion to identify their direction of travel, i.e. whether they are precessing prograde or retrograde. We show that for moderate $Pr$ a few dynamic modes suffice to accurately describe the flow. For large aspect ratios, these are wall-localised waves that travel retrograde along the periphery of the cylinder. Their DMD frequencies agree with the predictions of linear stability theory. With increasing Rayleigh number $Ra$, the interior gradually fills with columnar vortices, and eventually a regular pattern of convective Taylor columns prevails. For small aspect ratios and close enough to onset, the dominant flow structures are body modes that can precess either prograde or retrograde. For $Pr=0.8$, DMD additionally unveiled the existence of so far unobserved low-amplitude oscillatory modes. Furthermore, we elucidate the multi-modal character of oscillatory convection in low-$Pr$ fluids. Generally, more dynamic modes must be retained to accurately approximate the flow. Close to onset, the flow is purely oscillatory and the DMD reveals that these high-frequency modes are a superposition of oscillatory columns and cylinder-scale inertial waves. We find that there are coexisting prograde and retrograde modes, as well as quasi-axisymmetric torsional modes. For higher $Ra$, the flow also becomes unstable to wall modes. These low-frequency modes can both coexist with the oscillatory modes, and also couple to them. However, the typical flow feature of rotating convection at moderate $Pr$, the quasi-steady Taylor vortices, is entirely absent in low-$Pr$ flows.
The instability of a moving interface in a narrow tapering channel of finite length
Authors: Grenfell-Shaw John C. , Woods Andrew W.
Published: October 2017

We analyse the displacement of one fluid by a second immiscible fluid through a narrow channel of finite length which connects two reservoirs. We assume that the channel width slowly decreases in the direction of flow, and that the fluids have different viscosity and density. We examine the stability of the interface and find that there are Saffman–Taylor and Rayleigh–Taylor type modes, which may dominate in the narrow and wide regions of the channel, respectively. The gradient of the pressure jump across the interface associated with the surface tension acts to stabilise the interface, and for intermediate channel widths, this effect may dominate the destabilisation associated with both the Rayleigh–Taylor and Saffman–Taylor instabilities, provided the rate of change of the channel width with distance along the channel is sufficient. We also note that the effect of the converging channel leads to instability of long-wavelength modes owing to the quasi-static acceleration of the flow through the cell: we consider cases in which this effect only occurs at much lower wavenumbers than the most unstable Saffman–Taylor and Rayleigh–Taylor modes. We show that there is a maximum wavenumber for instability, which varies with position in the channel. By integrating the growth rate of each wavenumber in time as the interface moves across the channel, we predict the mode which grows to the greatest amplitude as the interface traverses the channel.
Velocity profiles, flow structures and scalings in a wide-gap turbulent Taylor–Couette flow
Authors: Froitzheim A. , Merbold S. , Egbers C.
Published: October 2017

Fully turbulent Taylor–Couette flow between independently rotating cylinders is investigated experimentally in a wide-gap configuration ($\unicode[STIX]{x1D702}=0.5$) around the maximum transport of angular momentum. In that regime turbulent Taylor vortices are present inside the gap, leading to a pronounced axial dependence of the flow. To account for this dependence, we measure the radial and azimuthal velocity components in horizontal planes at different cylinder heights using particle image velocimetry. The ratio of angular velocities of the cylinder walls $\unicode[STIX]{x1D707}$, where the torque maximum appears, is located in the low counter-rotating regime ($\unicode[STIX]{x1D707}_{max}(\unicode[STIX]{x1D702}=0.5)=-0.2$). This point coincides with the smallest radial gradient of angular velocity in the bulk and the detachment of the neutral surface from the outer cylinder wall, where the azimuthal velocity component vanishes. The structure of the flow is further revealed by decomposing the flow field into its large-scale and turbulent contributions. Applying this decomposition to the kinetic energy, we can analyse the formation process of the turbulent Taylor vortices in more detail. Starting at pure inner cylinder rotation, the vortices are formed and strengthened until $\unicode[STIX]{x1D707}=-0.2$ quite continuously, while they break down rapidly for higher counter-rotation. The same picture is shown by the decomposed Nusselt number, and the range of rotation ratios, where turbulent Taylor vortices can exist, shrinks strongly in comparison to investigations at much lower shear Reynolds numbers. Moreover, we analyse the scaling of the Nusselt number and the wind Reynolds number with the shear Reynolds number, finding a communal transition at approximately $Re_{S}\approx 10^{5}$ from classical to ultimate turbulence with a transitional regime lasting at least up to $Re_{S}\geqslant 2\times 10^{5}$. Including the axial dispersion of the flow into the calculation of the wind amplitude, we can also investigate the wind Reynolds number as a function of the rotation ratio $\unicode[STIX]{x1D707}$, finding a maximum in the low counter-rotating regime slightly larger than $\unicode[STIX]{x1D707}_{max}$. Based on our study it becomes clear that the investigation of counter-rotating Taylor–Couette flows strongly requires an axial exploration of the flow.
Spectral energy cascade in thermoacoustic shock waves
Authors: Gupta Prateek , Lodato Guido , Scalo Carlo
Published: October 2017

We have investigated thermoacoustically amplified quasi-planar nonlinear waves driven to the limit of shock-wave formation in a variable-area looped resonator geometrically optimized to maximize the growth rate of the quasi-travelling-wave second harmonic. Optimal conditions result in velocity leading pressure by approximately $40^{\circ }$ in the thermoacoustic core and not in pure travelling-wave phasing. High-order unstructured fully compressible Navier–Stokes simulations reveal three regimes: (i) modal growth, governed by linear thermoacoustics; (ii) hierarchical spectral broadening, resulting in a nonlinear inertial energy cascade, (iii) shock-wave-dominated limit cycle, where energy production is balanced by dissipation occurring at the captured shock-thickness scale. The acoustic energy budgets in regime (i) have been analytically derived, yielding an expression of the Rayleigh index in closed form and elucidating the effect of geometry and hot-to-cold temperature ratio on growth rates. A time-domain nonlinear dynamical model is formulated for regime (ii), highlighting the role of second-order interactions between pressure and heat-release fluctuations, causing asymmetry in the thermoacoustic energy production cycle and growth rate saturation. Moreover, energy cascade is inviscid due to steepening in regime (ii), with the $k$th harmonic growing at $k/2$-times the modal growth rate of the thermoacoustically sustained second harmonic. The frequency energy spectrum in regime (iii) is shown to scale with a $-5/2$ power law in the inertial range, rolling off at the captured shock-thickness scale in the dissipation range. We have thus shown the existence of equilibrium thermoacoustic energy cascade analogous to hydrodynamic turbulence.
Boundary element methods for particles and microswimmers in a linear viscoelastic fluid
Authors: Ishimoto Kenta , Gaffney Eamonn A.
Published: October 2017

The consideration of viscoelasticity within fluid dynamical boundary element methods has traditionally required meshing over the whole flow domain. In turn, a major advantage of the boundary element method is lost, namely the need to consider only surface boundary integrals. Here, using a generalised reciprocal relation and viscoelastic force singularities, a boundary element method is developed for linear viscoelastic flows. We proceed to explore finite-deformation microswimming in a linear Maxwell fluid. We firstly deduce a finite-amplitude generalisation of a previously reported result that the flow field is unchanged between a Newtonian and linear Maxwell fluid for prescribed small-amplitude deformations. Hence Purcell’s theorem holds for a linear Maxwell fluid. We proceed to consider deformation swimming in a linear Maxwell fluid given an external forcing. Boundary scattering trajectories for an exemplar squirmer approaching a surface are observed to exhibit a weak dependence on the Deborah number, while the trajectories of a sperm and monotrichous bacterium near a surface are predicted to be essentially unaffected at moderate Deborah number. In turn, the latter supports the common simplification of using Newtonian Stokes flows for studying flagellate swimming in linear Maxwell media. In addition, the motion of a magnetic helix under the influence of an external magnetic field is considered, and highlights that linear viscoelasticity can significantly impact the propagation of the helix, in turn demonstrating that even linear rheology is important to consider for forced swimmers. Finally, the presented framework requires minimalistic adjustments to Newtonian boundary element codes, enabling rapid implementation, and is more generally applicable, for instance to studies of particle interactions in active linear rheology on the microscale.
Turbulent horizontal convection under spatially periodic forcing: a regime governed by interior inertia
Authors: Rosevear Madelaine G. , Gayen Bishakhdatta , Griffiths Ross W.
Published: October 2017

Differential heating applied at a single horizontal boundary forces ‘horizontal convection’, even when there is no net heat flux through the boundary. However, almost all studies of horizontal convection have been limited to a special class of problem in which temperature or heat flux differences were applied in only one direction and over the horizontal length of a box (the Rossby problem; Rossby, Deep-Sea Res., vol. 12, 1965, pp. 9–16). These conditions strongly constrain the flow. Here we report laboratory experiments and direct numerical simulations (DNS) extending the results of Griffiths & Gayen (Phys. Rev. Lett., vol. 115, 2015, 204301) for horizontal convection forced by boundary conditions imposed in a two-dimensional periodic array at a horizontal boundary. The experiments use saline and freshwater fluxes at a permeable base with the imposed boundary salinity having a horizontal length scale one quarter of the width of the box. The flow reaches a state in which the net boundary buoyancy flux vanishes and the bulk of the fluid shows an inertial range of turbulence length scales. A regime transition is seen for increasing water depth, from an array of individual coherent plumes on the forcing scale to convection dominated by emergent larger scales of overturning. The DNS explore the analogous thermally forced case with sinusoidal boundary temperature of wavenumber $n=4$, and are used to examine the Rayleigh number ($Ra$) dependence for shallow- and deep-water cases. For shallow water the flow transitions with increasing $Ra$ from laminar to turbulent boundary layer regimes that are familiar from the Rossby problem and which have normalised heat transport scaling as $Nu\sim Ra^{1/5}$ and $Nu\sim (Ra\,Pr)^{1/5}$, with $Nu$ the Nusselt number and $Pr$ the Prandtl number, in this case maintaining a stable array of coherent turbulent plumes. For deep-water and large $Ra$ the laminar scaling transitions to $Nu\sim (Ra\,Pr)^{1/4}$, with the scales of turbulence extending to the dimensions of the box. The $1/4$ power law regime is explained in terms of the momentum of symmetric, inviscid large scales of motion in the interior coupled to diffusive loss of heat through stabilised parts of the boundary layer. The turbulence production is predominantly by shear instability rather than convection, with viscous dissipation distributed throughout the bulk of the fluid. These conditions are not seen in the highly asymmetric flow in the Rossby problem even at Rayleigh numbers up to six orders of magnitude greater than the transition found here. The new inertial interior regime has the rate of supply of available potential energy, and its removal by mixing of density, increasing as $Ra^{5/4}$, which is faster than $Ra^{6/5}$ in the Rossby problem. Irreversible mixing is confined close to the forcing boundary and is very much larger than the viscous dissipation, which is proportional to $Ra$.
Isolating strain and curvature effects in premixed flame/vortex interactions
Authors: Thiesset F. , Halter F. , Bariki C. , Lapeyre C. , Chauveau C. , Gökalp I. , Selle L. , Poinsot T.
Published: October 2017

This study focuses on the response of premixed flames to a transient hydrodynamic perturbation in an intermediate situation between laminar stretched flames and turbulent flames: an axisymmetric vortex interacting with a flame. The reasons motivating this choice are discussed in the framework of turbulent combustion models and flame response to the stretch rate. We experimentally quantify the dependence of the flame kinematic properties (displacement and consumption speeds) to geometrical scalars (stretch rate and curvature) in flames characterized by different effective Lewis numbers. Whilst the displacement speed can be readily measured using particle image velocimetry and tomographic diagnostics, providing a reliable estimate of the consumption speed from experiments remains particularly challenging. In the present work, a method based on a budget of fuel on a well chosen domain is proposed and validated both experimentally and numerically using two-dimensional direct numerical simulations of flame/vortex interactions. It is demonstrated that the Lewis number impact neither the geometrical nor the kinematic features of the flames, these quantities being much more influenced by the vortex intensity. While interacting with the vortex, the flame displacement (at an isotherm close to the leading edge) and consumption speeds are found to increase almost independently of the type of fuel. We show that the total stretch rate is not the only scalar quantity impacting the flame displacement and consumption speeds and that curvature has a significant influence. Experimental data are interpreted in the light of asymptotic theories revealing the existence of two distinct Markstein numbers, one characterizing the dependence of flame speed to curvature, the other to the total stretch rate. This theory appears to be well suited for representing the evolution of the displacement speed with respect to either the total stretch rate, curvature or strain rate. It also explains the limited dependence of the flame displacement speed to Lewis number and the strong correlation with curvature observed in the experiments. An explicit relationship between displacement and consumption speeds is also given, indicating that the fuel consumption rate is likely to be altered by both the total stretch rate and curvature.
Sloshing in a Hele-Shaw cell: experiments and theory
Authors: Viola Francesco , Gallaire François , Dollet Benjamin
Published: October 2017

The response of the free liquid surface in a Hele-Shaw cell subjected to a horizontal oscillation is investigated. We study the low-oscillation-amplitude regime and we show, by varying the fluid viscosity, $\unicode[STIX]{x1D708}$, and the forcing frequency, $\unicode[STIX]{x1D714}$, that the ratio between the Stokes viscous length, $\sqrt{2\unicode[STIX]{x1D708}/\unicode[STIX]{x1D714}}$, and the cell thickness greatly affects the amplitude and phase lag of the gravity waves. In particular, the sloshing system undergoes an underdamped/overdamped transition for sufficiently large viscosities. A consistent theoretical model, based on a modification of Darcy’s law to include unsteadiness, is then introduced to rationalize the experimental observations. Contrary to traditional sloshing wave theory, the viscous flow dissipation comes at leading order in the analysis, rather than as a higher-order asymptotic correction to the inviscid sloshing dynamics. The analytical expression for the resonance curves agrees well with experimental results without tunable parameters.
The UTMOST: A Hybrid Digital Signal Processor Transforms the Molonglo Observatory Synthesis Telescope
Authors: Bailes M. , Jameson A. , Flynn C. , Bateman T. , Barr E. D. , Bhandari S. , Bunton J. D. , Caleb M. , Campbell-Wilson D. , Farah W. , Gaensler B. , Green A. J. , Hunstead R. W. , Jankowski F. , Keane E. F. , Krishnan V. Venkatraman , Murphy Tara , O’Neill M. , Osłowski S. , Parthasarathy A. , Ravi V. , Rosado P. , Temby D.
Published: October 2017

The Molonglo Observatory Synthesis Telescope (MOST) is an 18000 m2 radio telescope located 40 km from Canberra, Australia. Its operating band (820–851 MHz) is partly allocated to telecommunications, making radio astronomy challenging. We describe how the deployment of new digital receivers, Field Programmable Gate Array-based filterbanks, and server-class computers equipped with 43 Graphics Processing Units, has transformed the telescope into a versatile new instrument (UTMOST) for studying the radio sky on millisecond timescales. UTMOST has 10 times the bandwidth and double the field of view compared to the MOST, and voltage record and playback capability has facilitated rapid implementaton of many new observing modes, most of which operate commensally. UTMOST can simultaneously excise interference, make maps, coherently dedisperse pulsars, and perform real-time searches of coherent fan-beams for dispersed single pulses. UTMOST operates as a robotic facility, deciding how to efficiently target pulsars and how long to stay on source via real-time pulsar folding, while searching for single pulse events. Regular timing of over 300 pulsars has yielded seven pulsar glitches and three Fast Radio Bursts during commissioning. UTMOST demonstrates that if sufficient signal processing is applied to voltage streams, innovative science remains possible even in hostile radio frequency environments.
A Network Anatomy of Chinese State-Owned Enterprises
Authors: LIN LI-WEN
Published: October 2017

This Article provides an anatomy of Chinese state-owned enterprises (SOEs) by unpacking their various relations with different types of state organs. It shows that Chinese SOEs are embedded in a network composed of dense and complex links with the state. Shareholding ties, albeit important, are only one of the many relations with the state. This network perspective provides a rather comprehensive overview of the basic architecture of China's state-owned sector. It illustrates important governance institutions that are unobservable from the laws on the book and distinctive from international standards. It clarifies some SOE behaviors that appear puzzling when taking the individual firm as the unit of analysis. It also raises challenging questions on various areas of law in the context of globalization.
China's Export Restrictions and the Limits of WTO Law
Authors: WU MARK
Published: October 2017

In recent years, China has enacted export restrictions on a range of minerals and other raw materials. They include export quotas, export duties, export licenses, and other administrative actions. Although such export restrictions have already been found to be inconsistent with China's WTO obligations, the practice persists. This article advances an explanation for why this is the case. It argues that the problem lies with the lack of retrospective remedies in WTO dispute settlement. Consequently, China is able to breach its WTO obligations temporarily with minimal consequence. Although such restrictions may have negative consequences for upstream extraction firms, China is able to implement the restrictions because several upstream firms are state-owned enterprises. As a result, China is able to utilize export restrictions on minerals and other raw materials effectively to foster the development of strategic emerging industries downstream. Given existing negotiating standoffs and domestic political constraints, this article suggests that it is unlikely that any potential WTO legal reforms will be enacted any time soon to address this problem.
Sunshine over Shanghai: Can the WTO Illuminate the Murky World of Chinese SOEs?
Authors: WOLFE ROBERT
Published: October 2017

State-owned enterprises (SOEs) are a major force in the Chinese economy and a growing presence in international trade and investment. The challenge to the WTO legal regime is commercial, given the size of SOEs and their share of Chinese output, and political, given worries that trade and investment by SOEs may be driven by public policy goals. And both challenges may be exacerbated by the murky world of Chinese SOEs. In this article, I first review whether Chinese SOEs are a problem for the WTO, and whether more sunshine on their operations might be a useful discipline. I then ask what we know about SOEs inside the WTO, including in the Trade Policy Review Mechanism. Since the answer is, not much, I consider whether mega-regional trade negotiations offer a better approach. My answer being negative, I finally consider whether an attempt to negotiate a WTO Reference Paper on SOEs might help. I conclude that transparency is likely to be a better discipline on the spillovers associated with SOEs than a search for binding rules, while also helping everyone better understand the efficiency effects.
From Reconstruction to Reform: Modernization and the Interest Group State, 1875–1900
Authors: Chamberlain Adam , Yanus Alixandra B. , Pyeatt Nicholas
Published: October 2017

The rise of voluntary associations in the late nineteenth century has received significant scholarly attention over the last few decades. Some studies argue that modernization facilitates group formation, but other analyses (e.g., Crowley and Skocpol 2001; Gamm and Putnam 1999) find little support for the argument that modernization caused group formation. Here, we extend this debate to the study of the strength of state-level, voluntary associations with clear political objectives. Using state-level dues paid to national organizations as a measure of group strength, we find evidence that more modernized states typically had the strongest state-level organizations in the 1880s and 1890s. These empirical findings lend support to the modernization thesis but also suggest that group formation and strength may be explained by different processes.
History for Justice: Michael Katz and the History of Education
Authors: Gordon Leah N.
Published: October 2017

I recently told one of my graduate students that I was contributing to the panel on which these papers are based, and he replied that reading Michael Katz'sThe Irony of Early School Reform: Educational Innovation in Mid-Nineteenth Century Massachusetts(2001a) led him to apply to graduate school. My story is the same. When I was deciding whether to pursue a graduate degree, Katz'sClass, Bureaucracy, and Schools(1975) convinced me to study the history of education. What Katz's scholarship, and later his mentorship, taught me was that one could be a historian with an eye toward justice, that one need not compartmentalize scholarly, political, and ethical commitments.
Michael Katz and the Academic-Activist Tension
Authors: Chowkwanyun Merlin
Published: October 2017

All Dr. Katz's students admired how quickly he expressed a point, often through tidy lists. In honor of that style, I want to focus these remarks about Michael Katz and activism on four dimensions: (1) his understanding of the activist/academic tension; (2) how he advised his graduate students to wrestle with it; (3) how he engaged nonhistorians; and (4) how his work's prognosis of the prospects for social change transformed markedly in the last five years of his career.
How Do Clouds React to Regional Warming?
Authors: Witman Sarah
Published: October 2017

Researchers illuminate how and why cloud feedbacks depend on spatial patterns of global warming.
AGU Welcomes Congressional Science Fellow in Program’s 40th Year
Authors:   AGU
Published: October 2017

Isaac “Ike” Irby brings to his upcoming year as a science expert in a congressional office advanced training in marine science and public policy plus experience as an executive branch intern.
Geobiological feedbacks and the evolution of thermoacidophiles
Authors: Colman Daniel R , Poudel Saroj , Hamilton Trinity L , Havig Jeff R , Selensky Matthew J , Shock Everett L , Boyd Eric S
Published: October 2017

Oxygen-dependent microbial oxidation of sulfur compounds leads to the acidification of natural waters. How acidophiles and their acidic habitats evolved, however, is largely unknown. Using 16S rRNA gene abundance and composition data from 72 hot springs in Yellowstone National Park, Wyoming, we show that hyperacidic (pH<3.0) hydrothermal ecosystems are dominated by a limited number of archaeal lineages with an inferred ability to respire O2. Phylogenomic analyses of 584 existing archaeal genomes revealed that hyperacidophiles evolved independently multiple times within the Archaea, each coincident with the emergence of the ability to respire O2, and that these events likely occurred in the recent evolutionary past. Comparative genomic analyses indicated that archaeal thermoacidophiles from independent lineages are enriched in similar protein-coding genes, consistent with convergent evolution aided by horizontal gene transfer. Because the generation of acidic environments and their successful habitation characteristically require O2, these results suggest that thermoacidophilic Archaea and the acidity of their habitats co-evolved after the evolution of oxygenic photosynthesis. Moreover, it is likely that dissolved O2 concentrations in thermal waters likely did not reach levels capable of sustaining aerobic thermoacidophiles and their acidifying activity until ~0.8 Ga, when present day atmospheric levels were reached, a time period that is supported by our estimation of divergence times for archaeal thermoacidophilic clades.
Aquatic urban ecology at the scale of a capital: community structure and interactions in street gutters
Authors: Hervé Vincent , Leroy Boris , Da Silva Pires Albert , Lopez Pascal Jean
Published: October 2017

In most cities, streets are designed for collecting and transporting dirt, litter, debris, storm water and other wastes as a municipal sanitation system. Microbial mats can develop on street surfaces and form microbial communities that have never been described. Here, we performed the first molecular inventory of the street gutter-associated eukaryotes across the entire French capital of Paris and the non-potable waters sources. We found that the 5782 OTUs (operational taxonomic units) present in the street gutters which are dominated by diatoms (photoautotrophs), fungi (heterotrophs), Alveolata and Rhizaria, includes parasites, consumers of phototrophs and epibionts that may regulate the dynamics of gutter mat microbial communities. Network analyses demonstrated that street microbiome present many species restricted to gutters, and an overlapping composition between the water sources used for street cleaning (for example, intra-urban aquatic networks and the associated rivers) and the gutters. We propose that street gutters, which can cover a significant surface area of cities worldwide, potentially have important ecological roles in the remediation of pollutants or downstream wastewater treatments, might also be a niche for growth and dissemination of putative parasite and pathogens.
Polymorphism of antibiotic-inactivating enzyme driven by ecology expands the environmental resistome
Authors: Kim Dae-Wi , Thawng Cung Nawl , Choi Jung-Hye , Lee Kihyun , Cha Chang-Jun
Published: October 2017

The environmental resistome has been recognized as the origin and reservoir of antibiotic resistance genes and considered to be dynamic and ever expanding. In this study, a targeted gene sequencing approach revealed that the polymorphic diversity of the aminoglycoside-inactivating enzyme AAC(6′)-Ib was ecological niche-specific. AAC(6′)-Ib-cr, previously known as a clinical variant, was prevalent in various soils and the intestines of chickens and humans, suggesting that this variant might not have arisen from adaptive mutations in the clinic but instead originated from the environment. Furthermore, ecologically dominant polymorphic variants of AAC(6′)-Ib were characterized and found to display different substrate specificities for quinolones and aminoglycosides, conferring the altered resistance spectra. Interestingly, a novel variant with the D179Y substitution showed an extended resistance spectrum to the recently developed fluoroquinolone gemifloxacin. Our results suggest that soil and animal microbiomes could be major reservoirs of antibiotic resistance; polymorphic diversity expands the antibiotic resistome in the environment, resulting in the potential emergence of novel resistance.