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In this paper we investigate the effect of an inhomogeneous and unsteady velocity field incident on an array of rigid circular cylinders arranged within a circular perimeter (diameter
) of varying solid fraction
, where the unsteady flow is generated by placing a cylinder (diameter
) upwind of the array. Unsteady two-dimensional viscous simulations at a moderate Reynolds number (
) and also, as a means of extrapolating to a flow with a very high Reynolds number, inviscid rapid distortion theory (RDT) calculations were carried out. These novel RDT calculations required the circulation around each cylinder to be zero which was enforced using an iterative method. The two main differences which were highlighted was that the RDT calculations indicated that the tangential velocity component is amplified, both, at the front and sides of the array. For the unsteady viscous simulations this result did not occur as the two-dimensional vortices (of similar size to the array) are deflected away from the boundary and do not penetrate into the boundary layer. Secondly, the amplification is greater for the RDT calculations as for the unsteady finite Reynolds number calculations. For the two highest solid fraction arrays, the mean flow field has two recirculation regions in the near wake of the array, with closed streamlines that penetrate into the array which will have important implications for scalar transport. The increased bleed through the array at the lower solid fraction results in this recirculation region being displaced further downstream. The effect of inviscid blocking and viscous drag on the upstream streamwise velocity and strain field is investigated as it directly influences the ability of the large coherent structures to penetrate into the array and the subsequent forces exerted on the cylinders in the array. The average total force on the array was found to increase monotonically with increasing solid fraction. For high solid fraction
, although the fluctuating forces on the individual cylinders is lower than for low
, these forces are more correlated due to the proximity of the cylinders. The result is that for mid to high solid fraction arrays the fluctuating force on the array is insensitive to
. For low
, where the interaction of the cylinders is weak, the force statistics on the individual cylinders can be accurately estimated from the local slip velocity that occurs if the cylinders were removed.
OBJECTIVES/SPECIFIC AIMS: The Indiana CTSI is investigating innovative approaches to integrate resources that will enrich scientific investigators. Our goals are to enhance the availability and communication among CTSI resources, for example internal funding, and to expand existing mentorship. METHODS/STUDY POPULATION: Developed a reviewer database that serves to streamline reviewer identification, decrease reviewer fatigue, and promote collaboration among disciplines. We started with a pool of NIH-funded investigators from across the Indiana CTSI core institutions and merged this list with previous CTSI reviewers and internal funding awardees. To expand this list, names and expertise from new faculty hires were added. RESULTS/ANTICIPATED RESULTS: Though this tool is relatively new, we have already observed an increase in junior faculty awareness and engagement with the CTSI. This database allows for increased opportunities of junior faculty to serve as reviewers and to refine grant writing skills and provides a platform for networking and collaborating across disciplines. It also allows for increased integration of programs with a shared reviewer database and promotes grant review standardization. DISCUSSION/SIGNIFICANCE OF IMPACT: Our database utilization seeks to decrease the time for junior faculty to obtain their first extramural grant, to enhance promotion and tenure packages, strengthen integration among CTSI programs, increase interactions between clinical and basic science investigators, and promote team science.
The scaling of turbulent motions is investigated by considering the flow in the eigenframe of the local strain-rate tensor. The flow patterns in this frame of reference are evaluated using existing direct numerical simulations of homogeneous isotropic turbulence over a Reynolds number range from
up to 1131, and also with reference to data for inhomogeneous, anisotropic wall turbulence. The average flow in the eigenframe reveals a shear layer structure containing tube-like vortices and a dissipation sheet, whose dimensions scale with the Kolmogorov length scale,
. The vorticity stretching motions scale with the Taylor length scale,
, while the flow outside the shear layer scales with the integral length scale,
. Furthermore, the spatial organization of the vortices and the dissipation sheet defines a characteristic small-scale structure. The overall size of this characteristic small-scale structure is
in all directions based on the coherence length of the vorticity. This is considerably larger than the typical size of individual vortices, and reflects the importance of spatial organization at the small scales. Comparing the overall size of the characteristic small-scale structure with the largest flow scales and the vorticity stretching motions on the scale of
shows that transitions in flow structure occur where
and 250. Below these respective transitional Reynolds numbers, the small-scale motions and the vorticity stretching motions are progressively less well developed. Scale interactions are examined by decomposing the average shear layer into a local flow, which is induced by the shear layer vorticity, and a non-local flow, which represents the environment of the characteristic small-scale structure. The non-local strain is
in width and height, which is consistent with observations in high Reynolds number flow of a
wide instantaneous shear layer with many
-scale vortical structures inside (Ishihara et al., Flow Turbul. Combust., vol. 91, 2013, pp. 895–929). In the average shear layer, vorticity aligns with the intermediate principal strain at small scales, while it aligns with the most stretching principal strain at larger scales, consistent with instantaneous turbulence. The length scale at which the alignment changes depends on the Reynolds number. When conditioning the flow in the eigenframe on extreme dissipation, the velocity is strongly affected over large distances. Moreover, the associated peak velocity remains Reynolds number dependent when normalized by the Kolmogorov velocity scale. It signifies that extreme dissipation is not simply a small-scale property, but is associated with large scales at the same time.
During 1990 we surveyed the southern sky using a multi-beam receiver at frequencies of 4850 and 843 MHz. The half-power beamwidths were 4 and 25 arcmin respectively. The finished surveys cover the declination range between +10 and −90 degrees declination, essentially complete in right ascension, an area of 7.30 steradians. Preliminary analysis of the 4850 MHz data indicates that we will achieve a five sigma flux density limit of about 30 mJy. We estimate that we will find between 80 000 and 90 000 new sources above this limit. This is a revised version of the paper presented at the Regional Meeting by the first four authors; the surveys now have been completed.
The objective of this study was to determine the genetic parameters of methane (CH4) emissions and their genetic correlations with key production traits. The trial measured the CH4 emissions, at 5-min intervals, from 1225 sheep placed in respiration chambers for 2 days, with repeat measurements 2 weeks later for another 2 days. They were fed in the chambers, based on live weight, a pelleted lucerne ration at 2.0 times estimated maintenance requirements. Methane outputs were calculated for g CH4/day and g CH4/kg dry matter intake (DMI) for each of the 4 days. Single trait models were used to obtain estimates of heritability and repeatability. Heritability of g CH4/day was 0.29 ± 0.05, and for g CH4/kg DMI 0.13 ± 0.03. Repeatability between measurements 14 days apart were 0.55 ± 0.02 and 0.26 ± 0.02, for the two traits. The genetic and phenotypic correlations of CH4 outputs with various production traits (weaning weight, live weight at 8 months of age, dag score, muscle depth and fleece weight at 12 months of age) measured in the first year of life, were estimated using bivariate models. With the exception of fleece weight, correlations were weak and not significantly different from zero for the g CH4/kg DMI trait. For fleece weight the phenotypic and genetic correlation estimates were −0.08 ± 0.03 and −0.32 ± 0.11 suggesting a low economically favourable relationship. These results indicate that there is genetic variation between animals for CH4 emission traits even after adjustment for feed intake and that these traits are repeatable. Current work includes the establishment of selection lines from these animals to investigate the physiological, microbial and anatomical changes, coupled with investigations into shorter and alternative CH4 emission measurement and breeding value estimation techniques; including genomic selection.
Psychiatric in-patients are at high risk of suicide. Recent reductions in bed numbers in many countries may have affected this risk but few studies have specifically investigated temporal trends. We aimed to explore trends in psychiatric in-patient suicide over time.
A prospective study of all patients admitted to National Health Service (NHS) in-patient psychiatric care in England (1997–2008). Suicide rates were determined using National Confidential Inquiry and Hospital Episode Statistics (HES) data.
Over the study period there were 1942 psychiatric in-patient suicides. Between the first 2 years of the study (1997, 1998) and the last 2 years (2007, 2008) the rate of in-patient suicide fell by nearly one-third from 2.45 to 1.68 per 100 000 bed days. This fall in rate was observed for males and females, across ethnicities and diagnoses. It was most marked for patients aged 15–44 years. Rates also fell for the most common suicide methods, particularly suicide by hanging on the ward (a 59% reduction). Although the number of post-discharge suicides fell, the rate of post-discharge suicide may have increased by 19%. The number of suicide deaths in those under the care of crisis resolution/home treatment teams has increased in recent years to approximately 160 annually.
The rate of suicide among psychiatric in-patients in England has fallen considerably. Possible explanations include falling general population rates, changes in the at-risk population or improved in-patient safety. However, a transfer of risk to the period after discharge or other clinical settings such as crisis resolution teams cannot be ruled out.
During a series of submersible surveys of the Shiribeshi Seamount, northern Sea of Japan, by the remotely-operated vehicle (ROV) ‘Dolphin 3K’ and the human-occupied vehicle (HOV) ‘Shinkai 2000’ in July 2001, dense patches of golden skate eggs were observed. Given the lack of information for this species, an analysis was performed to estimate the abundance of the eggs and to ascertain if any patterns could be determined from the distribution of eggs on the sea-floor as recorded by the ROV and HOV video cameras. Eggs, including some with viable embryos, were found on only one of four ROV benthic transect surveys and one crewed submersible dive in the same location. The site where eggs were laid was relatively small and appeared to have been revisited through time. This work is part of an ongoing collaborative effort between East Stroudsburg University and the Marine Biodiversity Research Programme at the Japan Agency for Marine–Earth Science and Technology to characterize the midwater and benthic deep-sea faunas around Japan.
The interactions between shear-free turbulence in two regions (denoted as + and − on either side of a nearly flat horizontal interface are shown here to be controlled by several mechanisms, which depend on the magnitudes of the ratios of the densities, ρ+/ρ−, and kinematic viscosities of the fluids, μ+/μ−, and the root mean square (r.m.s.) velocities of the turbulence, u0+/u0−, above and below the interface. This study focuses on gas–liquid interfaces so that ρ+/ρ− ≪ 1 and also on where turbulence is generated either above or below the interface so that u0+/u0− is either very large or very small. It is assumed that vertical buoyancy forces across the interface are much larger than internal forces so that the interface is nearly flat, and coupling between turbulence on either side of the interface is determined by viscous stresses. A formal linearized rapid-distortion analysis with viscous effects is developed by extending the previous study by Hunt & Graham (J. Fluid Mech., vol. 84, 1978, pp. 209–235) of shear-free turbulence near rigid plane boundaries. The physical processes accounted for in our model include both the blocking effect of the interface on normal components of the turbulence and the viscous coupling of the horizontal field across thin interfacial viscous boundary layers. The horizontal divergence in the perturbation velocity field in the viscous layer drives weak inviscid irrotational velocity fluctuations outside the viscous boundary layers in a mechanism analogous to Ekman pumping. The analysis shows the following. (i) The blocking effects are similar to those near rigid boundaries on each side of the interface, but through the action of the thin viscous layers above and below the interface, the horizontal and vertical velocity components differ from those near a rigid surface and are correlated or anti-correlated respectively. (ii) Because of the growth of the viscous layers on either side of the interface, the ratio uI/u0, where uI is the r.m.s. of the interfacial velocity fluctuations and u0 the r.m.s. of the homogeneous turbulence far from the interface, does not vary with time. If the turbulence is driven in the lower layer with ρ+/ρ− ≪ 1 and u0+/u0− ≪ 1, then uI/u0− ~ 1 when Re (=u0−L−/ν−) ≫ 1 and R = (ρ−/ρ+)(v−/v+)1/2 ≫ 1. If the turbulence is driven in the upper layer with ρ+/ρ− ≪ 1 and u0+/u0− ≫ 1, then uI/u0+ ~ 1/(1 + R). (iii) Nonlinear effects become significant over periods greater than Lagrangian time scales. When turbulence is generated in the lower layer, and the Reynolds number is high enough, motions in the upper viscous layer are turbulent. The horizontal vorticity tends to decrease, and the vertical vorticity of the eddies dominates their asymptotic structure. When turbulence is generated in the upper layer, and the Reynolds number is less than about 106–107, the fluctuations in the viscous layer do not become turbulent. Nonlinear processes at the interface increase the ratio uI/u0+ for sheared or shear-free turbulence in the gas above its linear value of uI/u0+ ~ 1/(1 + R) to (ρ+/ρ−)1/2 ~ 1/30 for air–water interfaces. This estimate agrees with the direct numerical simulation results from Lombardi, De Angelis & Bannerjee (Phys. Fluids, vol. 8, no. 6, 1996, pp. 1643–1665). Because the linear viscous–inertial coupling mechanism is still significant, the eddy motions on either side of the interface have a similar horizontal structure, although their vertical structure differs.
In many turbulent flows near obstacles or in ducts, the turbulence is inhomogeneous in two directions perpendicular to the main flow direction. In convective flows, there may initially be no mean motion. In both types of flow the gradients of Reynolds stresses drive mean motions in directions of inhomogeneity. Using the method of rapid distortion theory developed by Hunt & Graham (J. Fluid Mech., vol. 84, 1978, p. 209), we analyse these gradients where homogeneous isotropic turbulence is impinging onto two semi-infinite flat rigid surfaces intersecting at right angles. The mean velocity is assumed to be uniform (i.e. the surfaces move at free-stream velocity, or the boundary layers are very thin). The inhomogeneous spectra, variances and Reynolds-stress gradients are evaluated. For isotropic free-stream turbulence with mean square velocity u2∞1, the mean square velocity fluctuation at a high Reynolds number in the corner is u21(X, 0, 0) = 2.121u2∞1, independent of the form of the spectrum. This is explained by estimating how the free-stream eddies are blocked by the two walls. The gradients of Reynolds stresses force a mean secondary flow to develop; its direction is into the corner, and its magnitude at time t is of order tu2∞1/L∞, where L∞ is the integral scale. These results are tested in a wind tunnel experiment. A turbulence-generating grid installed at the entrance to the test section generates nearly isotropic, grid-generated turbulence. A corner plate with faces parallel to the mean flow and sharp edges is placed downstream of the grid so that shear-free turbulence impinges onto the corner plate. The turbulent Reynolds number based on , is 1400 at the leading edge of the plate. A hot-wire anemometry is used to measure instantaneous velocities. The experimental results are consistent with the rapid distortion theory estimates for the variances and the secondary mean motion, which is in the same direction and has the same order of magnitude as Prandtl's analysis of shear-driven secondary flow (of the second kind). We conclude that the blocking mechanism adds to the shear effects and has a significant and sometimes dominant contribution to the crossflows wherever it acts in two non-parallel directions, such as convection in a corner. Consequently, mean transport into corners occurs for most kinds of distorted flow with weak viscous stresses, which has many engineering and environmental implications. There are also implications for the chaotic nature of many confined flows near corners.
A theoretical description of the turbulent mixing within and the draining of a dense fluid layer from a box connected to a uniform density, quiescent environment through openings in the top and the base of the box is presented in this paper. This is an extension of the draining model developed by Linden et al. (Annu. Rev. Fluid Mech. vol. 31, 1990, pp. 201–238) and includes terms that describe localized mixing within the emptying box at the density interface. Mixing is induced by a turbulent flow of replacement fluid into the box and as a consequence we predict, and observe in complementary experiments, the development of a three-layer stratification. Based on the data collated from previous researchers, three distinct formulations for entrainment fluxes across density interfaces are used to account for this localized mixing. The model was then solved numerically for the three mixing formulations. Analytical solutions were developed for one formulation directly and for a second on assuming that localized mixing is relatively weak though still significant in redistributing buoyancy on the timescale of the draining process. Comparisons between our theoretical predictions and the experimental data, which we have collected on the developing layer depths and their densities show good agreement. The differences in predictions between the three mixing formulations suggest that the normalized flux turbulently entrained across a density interface tends to a constant value for large values of a Froude number FrT, based on conditions of the inflow through the top of the box, and scales as the cube of FrT for small values of FrT. The upper limit on the rate of entrainment into the mixed layer results in a minimum time (tD) to remove the original dense layer. Using our analytical solutions, we bound this time and show that 0.2tE ≲ tD ≲ tE, i.e. the original dense layer may be depleted up to five times more rapidly than when there is no internal mixing and the box empties in a time tE.
The buoyancy-driven flushing of fluid from a rectangular box via connections in the base and top into quiescent surroundings of uniform density is examined. Our focus is on the transient flows that develop when the interior is either initially stably stratified in two homogeneous layers – a dense layer below a layer at ambient density, or is filled entirely with dense fluid. Experiments with saline stratifications show that four distinct patterns of flow are possible. We classify these patterns in terms of the direction of flow through the base opening and the propensity of replacement fluid through the top opening to induce interfacial mixing. Unidirectional or bidirectional flow through the base opening may occur and within these two flow types either weak or vigorous interfacial mixing. We identify the three controlling geometrical parameters that determine which flow pattern is established, namely the fractional initial layer depths, the relative areas of the top and base openings and the horizontal length scale of the top opening relative to the initial dense layer depth. We show that these parameters may be reduced to two Froude numbers – one based on the fluxes through the base opening and whose value sets the direction of flow, and a second based on conditions at the top opening whose value determines the vigour of interfacial mixing. Theoretical models are developed for predicting the conditions for transition between each flow pattern and expressed as critical values of the Froude numbers identified.