Viscous coupling of shear-free turbulence across nearly flat fluid interfaces

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

The Creation and Propagation of Radiation: Fields Inside and Outside of Sources

We present a new algorithm for computing the electromagnetic fields of currents inside and outside of finite current sources, for arbitrary time variations in the currents. Unexpectedly, we find that our solutions for these fields are free of the concepts of differential calculus, in that our solutions only involve the currents and their time integrals, and do not involve the time derivatives of the currents. As examples, we give the solutions for two configurations of current: a planar solenoid and a rotating spherical shell carrying a uniform charge density. For slow time variations in the currents, we show that our general solutions reduce to the standard expressions for the fields in classic magnetic dipole radiation. In the limit of extremely fast turn-on of the currents, we show that for our general solutions the amount of energy radiated is exactly equal to the magnetic energy stored in the static fields a long time after current creation. We give three associated problem statements which can be used in courses at the undergraduate level, and one problem statement suitable for courses at the graduate level. These problems are of physical interest because: (1) they show that current systems of finite extent can radiate even during time intervals when the currents are constant; (2) they explicitly display transit time delays across a source associated with its finite dimensions; and (3) they allow students to see directly the origin of the reaction forces for time-varying systemsComment: 25 pages, 5 figure

Cornell University remote sensing program

The major activities of the program staff from December 1, 1973 to May 31, 1974 are reported and include: (1) communication and instruction; (2) data and facilities; (3) research completed; (4) research in progress; (5) selected correspondence; (6) grant sponsored travel; and (7) seminars and newsletters. Detailed information and maps are given for the following selected projects: (1) ERTS mapping of waterways in the Tug Hill region of New York State; (2) photo-archeological investigation of Great Gully, New York; and (3) evaluation of selected highway impacts using aerial photography

A Descriptive Analysis of the Perceived Importance and Use of Scientific Research-Based Instructional Strategies Among West Virginia Teachers

This study was designed to examine the perceived importance and extent of use of scientific research-based instructional strategies among West Virginia teachers. Specifically, the study investigated the extent to which perceived importance and frequency of use of scientific research-based instructional strategies differ between highly qualified teachers and non-highly qualified teachers. The core of the research was focused on ten scientific research-based instructional strategies identified by the MidContinental Regional Educational Laboratory. Participants were asked to complete a researcher-designed survey, the Instructional Strategies Inventory, to rate perceived importance and frequency of use for each of the ten strategies. The population for this study consisted of teachers employed in West Virginia public schools pre-kindergarten through twelfth grades during the 2005-06 school year according to the West Virginia Education Information System (N=21,625). The sample was stratified based on the highly qualified status of the teacher. Of the 440 teachers randomly selected, an overall return of 229 responses or 52% was obtained with two mailings. Results of the study revealed that West Virginia teachers perceive scientific research-based instructional strategies as important to instruction. Moreover, results confirmed that West Virginia teachers have incorporated the use of scientific research-based instructional strategies into weekly classroom practices. Closer inspection of the results, however, revealed no significant difference between highly qualified teachers and non-highly qualified teachers with regard to perceived importance or frequency of use of the strategies. These findings address the problem that NCLB defines highly qualified teacher by credential only, failing to address teacher quality in the definition. This disconnect ignores a significant body of research that provides evidence that the teacher is the most decisive factor in student learning. The results of this study add to the body of knowledge on scientific research-based instructional strategies as well as inform lawmakers in the task of developing powerful legislation that brings about substantive change

The Impact of a Rural School-Based Health Center on Students and Their Families in Sneedville, Tennessee: A Case Study.

The purpose of this study was to describe the impact that the school-based health center in Sneedville, Tennessee had on students who attended Hancock County High School. The study documented how the school-based health center affected students, families, and the community of Sneedville. Case study methodology was used to determine if the school-based health center impacted school attendance, mental and emotional health, sexual practices, and overall quality of life for students and their families. Data were collected through 25 interviews with health center stakeholders. The methodology included working with the staff at the school-based health center to identify the key players and key center users over the seven years of the center\u27s existence. An interview protocol was designed for each of the seven groups that were interviewed. Data were collected from current and former students, parents of current and former students, school counselors, teachers, and the school nurse. Students who attended Hancock County High School as well as their parents were impacted by their direct access to primary comprehensive health care services. Benefits to parents included a reduction of time in missed work and lower medical care costs for students without health insurance. The center promoted and improved school attendance while distributing valuable health education information to students and parents. Because the city of Sneedville has only one medical center and no hospital, the school-based health center served the rural residents well. Beginning as one of only three such centers in the United States, the school-based health center endured and evolved into a full-service, comprehensive health care provider. The center is located in an isolated region of Northeast Tennessee; the location added to the center\u27s impact on the residents. This study could provide a model for rural communities seeking ways to serve the health care needs of youth. In this time of economic instability and educational accountability, this school-based health center appeared to impact student care, thus allowing students to be more capable and ready to learn

A new approach to scoring systems to improve identification of acute medical admissions that will require critical care

Removal of the intensive care unit (ICU) at the Vale of Leven Hospital mandated the identification and transfer out of those acute medical admissions with a high risk of requiring ICU. The aim of the study was to develop triaging tools that identified such patients and compare them with other scoring systems. The methodology included a retrospective analysis of physiological and arterial gas measurements from 1976 acute medical admissions produced PREEMPT-1 (PRE-critical Emergency Medical Patient Triage). A simpler one for ambulance use (PREAMBLE-1 [PRE-Admission Medical Blue-Light Emergency]) was produced by the addition of peripheral oxygen saturation to a modification of MEWS (Modified Early Warning Score). Prospective application of these tools produced a larger database of 4447 acute admissions from which logistic regression models produced PREEMPT-2 and PREAMBLE-2, which were then compared with the original systems and seven other early warning scoring systems. Results showed that in patients with arterial gases, the area under the receiver operator characteristic curve was significantly higher in PREEMPT-2 (89·1%) and PREAMBLE-2 (84.4%) than all other scoring systems. Similarly, in all patients, it was higher in PREAMBLE-2 (92·4%) than PREAMBLE-1 (88·1%) and the other scoring systems. In conclusion, risk of requiring ICU can be more accurately predicted using PREEMPT-2 and PREAMBLE-2, as described here, than by other early warning scoring systems developed over recent years

Sunward-propagating Alfv\'enic fluctuations observed in the heliosphere

The mixture/interaction of anti-sunward-propagating Alfv\'enic fluctuations (AFs) and sunward-propagating Alfv\'enic fluctuations (SAFs) is believed to result in the decrease of the Alfv\'enicity of solar wind fluctuations with increasing heliocentric distance. However, SAFs are rarely observed at 1 au and solar wind AFs are found to be generally outward. Using the measurements from Voyager 2 and Wind, we perform a statistical survey of SAFs in the heliosphere inside 6 au. We first report two SAF events observed by Voyager 2. One is in the anti-sunward magnetic sector with a strong positive correlation between the fluctuations of magnetic field and solar wind velocity. The other one is in the sunward magnetic sector with a strong negative magnetic field-velocity correlation. Statistically, the percentage of SAFs increases gradually with heliocentric distance, from about 2.7% at 1.0 au to about 8.7% at 5.5 au. These results provide new clues for understanding the generation mechanism of SAFs