Sign-symmetry of temperature structure functions

New scalar structure functions with different sign-symmetry properties are defined. These structure functions possess different scaling exponents even when their order is the same. Their scaling properties are investigated for second and third orders, using data from high-Reynolds-number atmospheric boundary layer. It is only when structure functions with disparate sign-symmetry properties are compared can the extended self-similarity detect two different scaling ranges that may exist, as in the example of convective turbulence.Comment: 18 pages, 5 figures, accepted for publication in Physical Review

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

Scaling Exponents in Anisotropic Hydrodynamic Turbulence

In anisotropic turbulence the correlation functions are decomposed in the irreducible representations of the SO(3) symmetry group (with different "angular momenta" $\ell$). For different values of $\ell$ the second order correlation function is characterized by different scaling exponents $\zeta_2(\ell)$. In this paper we compute these scaling exponents in a Direct Interaction Approximation (DIA). By linearizing the DIA equations in small anisotropy we set up a linear operator and find its zero-modes in the inertial interval of scales. Thus the scaling exponents in each $\ell$-sector follow from solvability condition, and are not determined by dimensional analysis. The main result of our calculation is that the scaling exponents $\zeta_2(\ell)$ form a strictly increasing spectrum at least until $\ell=6$, guaranteeing that the effects of anisotropy decay as power laws when the scale of observation diminishes. The results of our calculations are compared to available experiments and simulations.Comment: 10 pages, 4 figures, PRE submitted. Fixed problems with figure

Spectral scaling of the Leray-α\alpha model for two-dimensional turbulence

We present data from high-resolution numerical simulations of the Navier-Stokes-$\alpha$ and the Leray-$\alpha$ models for two-dimensional turbulence. It was shown previously (Lunasin et al., J. Turbulence, 8, (2007), 751-778), that for wavenumbers $k$ such that $k\alpha\gg 1$, the energy spectrum of the smoothed velocity field for the two-dimensional Navier-Stokes-$\alpha$ (NS-$\alpha$) model scales as $k^{-7}$. This result is in agreement with the scaling deduced by dimensional analysis of the flux of the conserved enstrophy using its characteristic time scale. We therefore hypothesize that the spectral scaling of any $\alpha$-model in the sub-$\alpha$ spatial scales must depend only on the characteristic time scale and dynamics of the dominant cascading quantity in that regime of scales. The data presented here, from simulations of the two-dimensional Leray-$\alpha$ model, confirm our hypothesis. We show that for $k\alpha\gg 1$, the energy spectrum for the two-dimensional Leray-$\alpha$ scales as $k^{-5}$, as expected by the characteristic time scale for the flux of the conserved enstrophy of the Leray-$\alpha$ model. These results lead to our conclusion that the dominant directly cascading quantity of the model equations must determine the scaling of the energy spectrum.Comment: 11 pages, 4 figure

PTU-112 Incidence and predictors of buried bumper syndrome following gastrostomy insertion: a systematic review

Introduction Gastrostomies are widely used to provide enteral nutrition support. Buried Bumper Syndrome (BBS) is a recognised complication seen following gastrostomy insertion, describing the migration of the internal bumper along the stoma tract towards the skin. The consequences of BBS can be fatal. Currently, there is a paucity of knowledge about the incidence and predictors of BBS, which is addressed in this study by systematically reviewing the medical literature. Method A systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Guidelines (PRISMA). Four databases (EMBASE, MEDLINE, CINHAL, Web of Science) were utilised, and studies identified by searching for key terms relating to gastrostomy and BBS (Jan 1980 -Dec 2016). Unpublished studies were identified from conference abstract booklets. Two independent reviewers screened studies to identify those that included description of adult patients with BBS. Data was extracted relating to patient demographics, incidence, time to presentation and factors associated with BBS. Results 434 studies were initially identified (database search and grey literature). Of these, 299 (68.9%) were excluded following screening review of title and abstract (Kappa coefficient of reviewers=0.753). Of the remaining 135 studies, 85 met inclusion criteria (35 case studies, 11 case series and 39 cohort studies). No controlled trials were retrieved. In total, 16 627 patients were described post gastrostomy placement. 473 cases of BBS were reported in the literature, giving a pooled estimate incidence of 2.8% (0.46%–8.80%). The median age of presentation was 66 years, with 59.1% being in males. BBS was most frequently associated with gastrostomy tubes with thinner internal bumpers (40.7% of all reported cases), however reporting bias may have heavily influenced this outcome. The time to BBS presentation ranged from 3 days to 7 years. Common predictors of BBS reported in the literature include tight external bumpers and increased external traction made directly by the patient or during gastrostomy care. Conclusion This is the first study to systematically review the incidence of Buried Bumper syndrome and assess factors predicting its development. The paucity of high quality studies identified in this systematic review, provides the impetus to develop a national gastrostomy registry accurately assessing gastrostomy outcomes. Healthcare professionals, patients and their caregivers need to be appropriately educated about BBS, considering factors such as tightness of external bumpers and minimising external traction

EVALUATION OF THE ANTIBACTERIAL ACTIVITY OF CALCIUM ALGINATE BEADS MODIFIED WITH ETHANOLIC EXTRACT OF ADHATODA VASICA LEAF EXTRACT ON STAPHYLOCOCCUS AUREUS AND ESCHERICHIA COLI

 Objective: The objective of the present study was to investigate the antibacterial activity of calcium alginate (Ca-ALG) loaded with ethanolic extract of Adhatoda vasica (A. vasica) leaves against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli).Methods: Ca-ALG beads containing ethanolic extract of A. vasica leaves were developed by ionic gelation technique. The prepared Ca-ALG beads were characterized by Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The antibacterial effect of A. vasica leaf extract loaded Ca-ALG beads was examined against S. aureus and E. coli. Results: FT-IR studies revealed the cross-linking of ALG and calcium ions. The spherical morphology of the beads was designated by SEM. The prepared beads were found to display distinctive growth inhibition against S. aureus and E. coli.Conclusion: The antibacterial activity analysis indicated that the prepared beads have good activity against S. aureus and E. coli. The present study proposes a strategy to enhance antibacterial properties of ALG which are widely used in biomedical applications