Cascade time-scales for energy and helicity in homogeneous isotropic turbulence

We extend the Kolmogorov phenomenology for the scaling of energy spectra in high-Reynolds number turbulence, to explicitly include the effect of helicity. There exists a time-scale $\tau_H$ for helicity transfer in homogeneous, isotropic turbulence with helicity. We arrive at this timescale using the phenomenological arguments used by Kraichnan to derive the timescale $\tau_E$ for energy transfer (J. Fluid Mech. {\bf 47}, 525--535 (1971)). We show that in general $\tau_H$ may not be neglected compared to $\tau_E$, even for rather low relative helicity. We then deduce an inertial range joint cascade of energy and helicity in which the dynamics are dominated by $\tau_E$ in the low wavenumbers with both energy and helicity spectra scaling as $k^{-5/3}$; and by $\tau_H$ at larger wavenumbers with spectra scaling as $k^{-4/3}$. We demonstrate how, within this phenomenology, the commonly observed ``bottleneck'' in the energy spectrum might be explained. We derive a wavenumber $k_h$ which is less than the Kolmogorov dissipation wavenumber, at which both energy and helicity cascades terminate due to dissipation effects. Data from direct numerical simulations are used to check our predictions.Comment: 14 pages, 5 figures, accepted to Physical Review

Sick and tired: how molecular regulators of human sleep schedules and duration impact immune function.

Why do we need to sleep? What regulates when we sleep? And what dictates the number of hours we require? These are often viewed as three separate biological questions. Here, we propose they share molecular etiologies, whereby regulators of sleep schedules and sleep duration also govern the physiological purposes of sleep. To support our hypothesis, we review Mendelian human genetic variants sufficient to advance sleep-wake onset (PER2) and shorten sleep length (DEC2), and evaluate their emerging roles in immune responses that may rely on a sound night of slumber

Estimating intermittency in three-dimensional Navier-Stokes turbulence

The issue of why computational resolution in Navier-Stokes turbulence is so hard to achieve is addressed. It is shown that Navier-Stokes solutions can potentially behave differently in two distinct regions of space-time $\mathbb{R}^{\pm}$ where $\mathbb{R}^{-}$ is comprised of a union of disjoint space-time `anomalies'. Large values of |\nabla\bom| dominate $\mathbb{R}^{-}$, which is consistent with the formation of vortex sheets or tightly-coiled filaments. The local number of degrees of freedom $\mathcal{N}^{\pm}$ needed to resolve the regions in $\mathbb{R}^{\pm}$ satisfies \mathcal{N}^{\pm}(\bx, t)\lessgtr c_{\pm}\mathcal{R}_{u}^{3} where $\mathcal{R}_{u} = uL/\nu$ is a Reynolds number dependent on the local velocity field u(\bx, t)

Cambodia's aquarian reforms : the emerging challenges for policy and research

The main objective of the document is to make a modest attempt to highlight the challenges which are emerging with the current phase of Cambodia's aquarian reforms -- the most important component of which is the current transition from fishing lots to community fisheries. The challenges include the realms of institutional and policy reform, local action, innovation and research. We contextualize our effort by commencing with an assessment of the importance of the aquatic resources and by providing a brief historical background to the reforms. This is followed by an examination of the changes in the access and property rights and the system changes which have been brought about as a result of the reform. How some of the transitional changes can be assessed and the manner in which the efforts at community fisheries can be made more economically and socially viable are also addressed. We deal with the complex issue of social identity and the aspirations for creating a new sense of community. The new role of women, the importance of creating networks and closer collaboration with Cambodia's local governance structures and vibrant civil society organisations are also highlighted. The reforms have created new legal realms of local 'micro' ecosystem space and resource governance. But this should not detract from the need for an understanding of the larger 'global' context -- be it in relation to the ecosystem dynamics or governance priorities. We suggest that research and development priorities must be re-oriented to consider ways of dealing with the vast number of new and evolving 'local realities' and yet, link them up contemporaneously to the big 'global picture'. We end with a few recommendations addressed to different actors involved in the process of aquarian reforms. There is a call for a new mission and greater collaboration by research institutions; new methodologies for data collection; greater participation with local governance structures; an exit strategy for aid agencies and the need for setting up a national institute for co-management applications and training.Policies, Research, Cambodia,

Dynamical equations for high-order structure functions, and a comparison of a mean field theory with experiments in three-dimensional turbulence

Two recent publications [V. Yakhot, Phys. Rev. E {\bf 63}, 026307, (2001) and R.J. Hill, J. Fluid Mech. {\bf 434}, 379, (2001)] derive, through two different approaches that have the Navier-Stokes equations as the common starting point, a set of steady-state dynamic equations for structure functions of arbitrary order in hydrodynamic turbulence. These equations are not closed. Yakhot proposed a "mean field theory" to close the equations for locally isotropic turbulence, and obtained scaling exponents of structure functions and an expression for the tails of the probability density function of transverse velocity increments. At high Reynolds numbers, we present some relevant experimental data on pressure and dissipation terms that are needed to provide closure, as well as on aspects predicted by the theory. Comparison between the theory and the data shows varying levels of agreement, and reveals gaps inherent to the implementation of the theory.Comment: 16 pages, 23 figure

Closure of two dimensional turbulence: the role of pressure gradients

Inverse energy cascade regime of two dimensional turbulence is investigated by means of high resolution numerical simulations. Numerical computations of conditional averages of transverse pressure gradient increments are found to be compatible with a recently proposed self-consistent Gaussian model. An analogous low order closure model for the longitudinal pressure gradient is proposed and its validity is numerically examined. In this case numerical evidence for the presence of higher order terms in the closure is found. The fundamental role of conditional statistics between longitudinal and transverse components is highlighted.Comment: 4 pages, 2 figures, in press on PR

OASIS: clinical audit in a tertiary care centre

Background: Obstetric anal sphincter injury involves injury to the anal sphincter and rectal mucosa sustained at time of vaginal delivery and can result in significant long-term morbidity. These injuries have been defined as 3rd and 4th degree lacerations that involve disruption of the anal sphincter and rectal mucosa respectively. Objectives of this study were to find out the incidence of obstetrical anal sphincter injuries, to identify the risk factors for of OASIS and the outcome of primary repair in terms of anal incontinence and its associated complications.Methods: We did a descriptive study of OASIS by retrospective analysis of the labour case records. The study period was 1 year between August 2016 to July 2017. Inclusion criteria were singleton pregnancy, vertex presentation, instrumental and normal vaginal delivery. Exclusion criteria were multiple pregnancy, non-vertex presentation and caesarean section. Proforma was developed to capture the age, parity, gestational age in weeks, induction of labour, epidural analgesia, delivery duration, type of episiotomy, instrumentation, shoulder dystocia, occipito posterior position,manual support, weight of the baby, suturing method. Postnatal evaluation after 6 weeks and 6 months for perineal discomfort, pain, incontinence, wound infection, breakdown, fistula were noted. Results: The incidence of OASIS was 1.4%. 81.8% women had 3rd degree perineal and 18.1% had 4th degree perineal tear. The mean age of the patients were 27.9 years, gestational age of 39.45 weeks, 72.7% were primiparous. Induction of labour with prostaglandins was done in 36.36% and Pitocin augmentation for 81.81%. The duration of second 36.36% had 60-89 min and 27.27% had duration more than 90 min. 54.54% had epidural analgesia, 36.36% had shoulder dystocia, 36.36% had instrumental delivery. 72.72% babies had birth weight between 3-3.5 kg, 9% between 3.5-4 kg. Ano vaginal fistula developed in 9%.Conclusions: Appropriate training, anticipating and identifying major degrees of perineal tear helps in reducing the complications. Anovaginal fistula is distressing and disabling the patient and to her near ones

Anomalous scaling of a passive scalar advected by the turbulent velocity field with finite correlation time and uniaxial small-scale anisotropy

The influence of uniaxial small-scale anisotropy on the stability of the scaling regimes and on the anomalous scaling of the structure functions of a passive scalar advected by a Gaussian solenoidal velocity field with finite correlation time is investigated by the field theoretic renormalization group and operator product expansion within one-loop approximation. Possible scaling regimes are found and classified in the plane of exponents $\epsilon-\eta$, where $\epsilon$ characterizes the energy spectrum of the velocity field in the inertial range $E\propto k^{1-2\epsilon}$, and $\eta$ is related to the correlation time of the velocity field at the wave number $k$ which is scaled as $k^{-2+\eta}$. It is shown that the presence of anisotropy does not disturb the stability of the infrared fixed points of the renormalization group equations which are directly related to the corresponding scaling regimes. The influence of anisotropy on the anomalous scaling of the structure functions of the passive scalar field is studied as a function of the fixed point value of the parameter $u$ which represents the ratio of turnover time of scalar field and velocity correlation time. It is shown that the corresponding one-loop anomalous dimensions, which are the same (universal) for all particular models with concrete value of $u$ in the isotropic case, are different (nonuniversal) in the case with the presence of small-scale anisotropy and they are continuous functions of the anisotropy parameters, as well as the parameter $u$. The dependence of the anomalous dimensions on the anisotropy parameters of two special limits of the general model, namely, the rapid-change model and the frozen velocity field model, are found when $u\to \infty$ and $u\to 0$, respectively.Comment: revtex, 25 pages, 37 figure