Flight-measured laminar boundary-layer transition phenomena including stability theory analysis

Flight experiments were conducted on a single-engine turboprop aircraft fitted with a 92-in-chord, 3-ft-span natural laminar flow glove at glove section lift coefficients from 0.15 to 1.10. The boundary-layer transition measurement methods used included sublimating chemicals and surface hot-film sensors. Transition occurred downstream of the minimum pressure point. Hot-film sensors provided a well-defined indication of laminar, laminar-separation, transitional, and turbulent boundary layers. Theoretical calculations of the boundary-layer parameters provided close agreement between the predicted laminar-separation point and the measured transition location. Tollmien-Schlichting (T-S) wave growth n-factors between 15 and 17 were calculated at the predicted point of laminar separation. These results suggest that for many practical airplane cruise conditions, laminar separation (as opposed to T-S instability) is the major cause of transition in predominantly two-dimensional flows

Natural laminar flow experiments on modern airplane surfaces

Flight and wind-tunnel natural laminar flow experiments have been conducted on various lifting and nonlifting surfaces of several airplanes at unit Reynolds numbers between 0.63 x 10 to the 6th power/ft and 3.08 x 10 to the 6th power/ft, at Mach numbers from 0.1 to 0.7, and at lifting surface leading-edge sweep angles from 0 deg to 63 deg. The airplanes tested were selected to provide relatively stiff skin conditions, free from significant roughness and waviness, on smooth modern production-type airframes. The observed transition locations typically occurred downstream of the measured or calculated pressure peak locations for the test conditions involved. No discernible effects on transition due to surface waviness were observed on any of the surfaces tested. None of the measured heights of surface waviness exceeded the empirically predicted allowable surface waviness. Experimental results consistent with spanwise contamination criteria were observed. Large changes in flight-measured performance and stability and control resulted from loss of laminar flow by forced transition. Rain effects on the laminar boundary layer caused stick-fixed nose-down pitch-trim changes in two of the airplanes tested. No effect on transition was observed for flight through low-altitude liquid-phase clouds. These observations indicate the importance of fixed-transition tests as a standard flight testing procedure for modern smooth airframes

Influence of Selected Alternative Extension Approaches on the Acquisition of Knowledge, Skills for Agricultural Productivity in the Lake Victoria Region, Kenya

The role of agricultural extension is vital to the diffusion of new technologies, but extension is currently not very effective in many African nations, with traditional extension approaches having minimal impact. In Kenya, there have been gaps on the availability of studies and documentation of the specific extension approaches and their influence on the acquisition of knowledge, skills and productivity for household food security despite the various extension efforts and resources put in place in many parts of the country. This study therefore investigated the influence of three selected alternative extension approaches on the acquisition of knowledge, skills and productivity for household food security in the Lake Victoria region, Kenya. The main objective of the study was to compare the individual and collective influence of Farmer Field Schools, On-Farm Research and Focal Area approaches on the acquisition of knowledge, skills and farm productivity for enhanced household security in the Lake Victoria region of Kenya. A cross sectional survey design was adopted in order to develop a detailed account of the effect of the three approaches. The total population of the study area was 188,661 households from which a random sample of 396 was selected comprising of small-scale farmers from three sub counties: Bondo, Rachuonyo and Nyamira. Data was analyzed using both descriptive and inferential statistics with the aid of Statistical Package for Social Sciences (SPSS 18.0) at 5 percent level of significance. Findings revealed that Farmer Field School contributed to the acquisition of knowledge and skills in various agricultural production activities and an increase in farm productivity. Results on On-Farm Research revealed that it contributed to knowledge and skills as well as improvement of farm productivity. However, a hypothesis test showed no significant influence on knowledge, skills and productivity for household food security. Findings about Focal Area approach revealed that it contributed to the acquisition of knowledge, skills and productivity for household food security. Focal Area approach proved to be the most effective of the three approache

Influence of Farmer FFS Approach on the Acquisition of Knowledge, Skills for Agricultural Productivity in the Lake Victoria Region, Kenya

The role of agricultural extension is vital to the diffusion of new technologies, but extension is currently not very effective in many African nations, with traditional extension approaches having minimal impact. In Kenya, there have been gaps on the availability of studies and documentation of the specific extension approaches and their influence on the acquisition of knowledge, skills and productivity for household food security despite the various extension efforts and resources put in place in many parts of the country. This study therefore investigated the influence of Farmer Field Schools extension approaches on the acquisition of knowledge, skills and productivity for household food security in the Lake Victoria region, Kenya. The main objective of the study was to compare the influence of Farmer Field Schools and Conventional extension on the acquisition of knowledge, skills and farm productivity for enhanced household security in the Lake Victoria region of Kenya. A cross sectional survey design was adopted in order to develop a detailed account of the effect of the three approaches. The total population of the study area was 188,661 households from which a random sample of 236 was selected comprising of small-scale farmers from three sub counties: Bondo, Rachuonyo and Nyamira. Data was analyzed using both descriptive and inferential statistics with the aid of Statistical Package for Social Sciences (SPSS 18.0) at 5 percent level of significance. Findings revealed that Farmer Field School contributed to the acquisition of knowledge and skills in various agricultural production activities and an increase in farm productivity. Results on On-Farm Research revealed that it contributed more in the acquisition of knowledge and skills as well as improvement of farm productivity as compared to Conventional Extension. Furthermore a hypothesis test showed a significant difference between the two approaches. It is hoped that the findings of this study will contribute to greater understanding of agricultural extension approaches especially in policy formulation and design of the provision of extension services to communities in Kenya

Status report on a natural laminar-flow nacelle flight experiment

The natural laminar flow (NLF) nacelle experiment is part of a drag reduction production program, and has the dual objectives of studying the extent of NLF on full scale nacelles in a flight environment and the effect of acoustic disturbance on the location of transition on the nacelle surface. The experiment is being conducted in two phases: (1) an NLF fairing was flown on a full scale Citation nacelle to develop the experiment technique and establish feasibility; (2) full scale, flow through, NLF nacelles located below the right wing of an experimental NASA OV-1 aircraft are evaluated. The measurements of most interest are the static pressure distribution and transition location on the nacelle surface, and the fluctuating pressure levels associated with the noise sources. Data are collected in combinations of acoustic frequencies and sound pressure levels. The results of phase 2 tests to date indicate that on shape GE2, natural laminar flow was maintained as far aft as the afterbody joint at 50 percent of the nacelle length. An aft facing step at this joint caused premature transition at this station. No change was observed in the transition pattern when the noise sources were operated

Publisher Correction: Deep learning enables fast and dense single-molecule localization with high accuracy

In the version of this Article initially published, Jacob H. Macke and Jonas Ries were not listed as corresponding authors. Their contact information and designation as corresponding authors are now included. The error has been corrected in the online version of the Article

Flow diagnostics and visualization in wind tunnels and flight

The Langley Research Center has a concentrated and directed effort under way to develop both conventional and non-intrusive diagnostic instrumentation. These instruments are being developed to operate over large Mach number, total temperature, and total pressure ranges. Efforts are being made to evaluate the measurements made by the various instruments to determine the most accurate and reliable instrument to be used under a given flow environment. Although only one flow visualization technique was described, there are many different types presently being used at Langley Research Center

Field-driven topological glass transition in a model flux line lattice

We show that the flux line lattice in a model layered HTSC becomes unstable above a critical magnetic field with respect to a plastic deformation via penetration of pairs of point-like disclination defects. The instability is characterized by the competition between the elastic and the pinning energies and is essentially assisted by softening of the lattice induced by a dimensional crossover of the fluctuations as field increases. We confirm through a computer simulation that this indeed may lead to a phase transition from crystalline order at low fields to a topologically disordered phase at higher fields. We propose that this mechanism provides a model of the low temperature field--driven disordering transition observed in neutron diffraction experiments on ${\rm Bi_2Sr_2CaCu_2O_8\, }$ single crystals.Comment: 11 pages, 4 figures available upon request via snail mail from [email protected]

Increased spatiotemporal resolution reveals highly dynamic dense tubular matrices in the peripheral ER

The endoplasmic reticulum (ER) is an expansive, membrane-enclosed organelle that plays crucial roles in numerous cellular functions. We used emerging superresolution imaging technologies to clarify the morphology and dynamics of the peripheral ER, which contacts and modulates most other intracellular organelles. Peripheral components of the ER have classically been described as comprising both tubules and flat sheets. We show that this system consists almost exclusively of tubules at varying densities, including structures that we term ER matrices. Conventional optical imaging technologies had led to misidentification of these structures as sheets because of the dense clustering of tubular junctions and a previously uncharacterized rapid form of ER motion. The existence of ER matrices explains previous confounding evidence that had indicated the occurrence of ER "sheet" proliferation after overexpression of tubular junction-forming proteins