Experiments of Propeller-Induced Flow Effects on a Low-Reynolds-Number Wing

Novel findings are discussed in this paper that will be especially beneficial to designers and modelers of small-scale unmanned air vehicles and high-altitude long-endurance vehicles that both operate at low Reynolds numbers (Re = 50,000-300,000). Propeller-induced Oow effects in both tractor and pusher configurations on a recta ngular wing using the Wortmann FX 63-137 airfoil (a common low-Reynolds-number high-lift airfoil) are presented in this paper . Significant performance benefits can be found for a wing in the tractor configuration. Experiments, including trip tests and upper-surface oil Dow visualization, show and verify that the propeller slipstream induces early transition to turbulent Oow in the regions within the slipstrean1 and the premature fomiation of a separation bubble in the regions outside the slipstream. The result is a reduction of pressure drag and an increase in lift of the wing where lift-to-drag ratios arc as high as 10-12 (a maximum of\u27 70% increase in lift-to-drag ratio from a clean wing configuration) and are measured at both low and high angles of attack up to s tall (0-16 deg). Similar performance benefits are n ot observed in pusher configuration results where only increased local Oow velocity and varying inOow angle effects are apparent. Thus, contrary to the design rules for optimal performance of wings at high Reynolds number s, at low Reynolds numbers, a propeller in the tractor configuration exhibits significant performance improvements, especially in cruise configurations Oow angles of attack), as compared with a propeller in the pusher configuration or even a clean wing

Large Steel Tank Fails and Rockets to Height of 30 meters - Rupture Disc Installed Incorrectly

AbstractAt a brewery, the base plate-to-shell weld seam of a 90-m3 vertical cylindrical steel tank failed catastrophically. The 4 ton tank “took off” like a rocket leaving its contents behind, and landed on a van, crushing it. The top of the tank reached a height of 30 m. The internal overpressure responsible for the failure was an estimated 60 kPa. A rupture disc rated at < 50 kPa provided overpressure protection and thus prevented the tank from being covered by the European Pressure Equipment Directive. This safeguard failed and it was later discovered that the rupture disc had been installed upside down. The organizational root cause of this incident may be a fundamental lack of appreciation of the hazards of large volumes of low-pressure compressed air or gas. A contributing factor may be that the standard piping and instrumentation diagram (P&ID) symbol for a rupture disc may confuse and lead to incorrect installation. Compressed air systems are ubiquitous. The medium is not toxic or flammable. Such systems however, when operated at “slight overpressure” can store a great deal of energy and thus constitute a hazard that ought to be addressed by safety managers

Slipstream Measurements of Small-Scale Propellers at Low Reynolds Numbers

The continuing growth in the use of small UAVs has required the need to more fully understand the propellers that power them. Part of this understanding is the behavior of the propeller slipstream. Using a 7-hole probe, the slipstreams of several small-scale propellers (diameters of 4.2, 5, and 9 in) were measured in both static (V∞ = 0) and advancing-flow (V∞ \u3e 0) conditions at several locations downstream. For static conditions, as the slipstream expanded downstream, the maximum values of the axial and swirl velocities decreased. The general shape of the static slipstream was also found to be nearly the same for the propellers even though their planforms were different. During advancing-flow conditions, a contraction in the slipstream occurred by 0.5 diameters behind the propeller. Beyond that location, the size of the slipstream was relatively constant up to 3 diameters downstream (furthest distance measured). For advancing-flow slipstreams, the shape of the axial velocity distribution was observed to be dependent on the planform shape of the propeller. The static slipstream of a propeller-wing configuration showed that the slipstream portions above and below the wing moved away from each other towards opposite wing tips. However, the maximum axial and swirl velocities in the propeller-wing slipstream did not diminish compared with the isolated propeller slipstream

Differential neuroproteomic and systems biology analysis of spinal cord injury

Acute spinal cord injury (SCI) is a devastating condition with many consequences and no known effective treatment. Although it is quite easy to diagnose traumatic SCI, the assessment of injury severity and projection of disease progression or recovery are often challenging, as no consensus biomarkers have been clearly identified. Here rats were subjected to experimental moderate or severe thoracic SCI. At 24h and 7d postinjury, spinal cord segment caudal to injury center versus sham samples was harvested and subjected to differential proteomic analysis. Cationic/anionic-exchange chromatography, followed by 1D polyacrylamide gel electrophoresis, was used to reduce protein complexity. A reverse phase liquid chromatography-tandem mass spectrometry proteomic platform was then utilized to identify proteome changes associated with SCI. Twenty-two and 22 proteins were up-regulated at 24 h and 7 day after SCI, respectively; whereas 19 and 16 proteins are down-regulated at 24 h and 7 day after SCI, respectively, when compared with sham control. A subset of 12 proteins were identified as candidate SCI biomarkers - TF (Transferrin), FASN (Fatty acid synthase), NME1 (Nucleoside diphosphate kinase 1), STMN1 (Stathmin 1), EEF2 (Eukaryotic translation elongation factor 2), CTSD (Cathepsin D), ANXA1 (Annexin A1), ANXA2 (Annexin A2), PGM1 (Phosphoglucomutase 1), PEA15 (Phosphoprotein enriched in astrocytes 15), GOT2 (Glutamic-oxaloacetic transaminase 2), and TPI-1 (Triosephosphate isomerase 1), data are available via ProteomeXchange with identifier PXD003473. In addition, Transferrin, Cathepsin D, and TPI-1 and PEA15 were further verified in rat spinal cord tissue and/or CSF samples after SCI and in human CSF samples from moderate/severe SCI patients. Lastly, a systems biology approach was utilized to determine the critical biochemical pathways and interactome in the pathogenesis of SCI. Thus, SCI candidate biomarkers identified can be used to correlate with disease progression or to identify potential SCI therapeutic targets

Examination of the role of cGMP in long-term potentiation in the CA1 region of the hippocampus

The mechanisms underlying the generation of NMDA receptor-dependent LTP in the CA1 region of the hippocampus continue to receive a great deal of attention because of the postulated importance of LTP as a synaptic mechanism for learning and memory. It is well accepted that the initial induction of LTP occurs in the postsynaptic cell, but the site of expression remains controversial. One prominent hypothesis is that LTP involves the release of one or more retrograde messengers that act on the presynaptic terminal to enhance transmitter release. Recently, evidence has been presented that retrograde messengers function to activate presynaptic guanylyl cyclase and that the resulting rise in presynaptic cGMP levels, when accompanied by presynaptic activity, is responsible for generating an early component of LTP. We have tested this hypothesis by examining whether synaptic strength is increased by coupling tetanic stimulation with application of a membrane-permeable analog of cGMP. The experiments were done in the presence of an NMDA receptor antagonist to block postsynaptic induction mechanisms. Under a variety of experimental conditions, this manipulation failed to generate LTP, suggesting that an increase in cGMP levels accompanied by presynaptic activity is not sufficient to generate LTP in the CA1 region of the hippocampus

Spatial and temporal changes in cumulative human impacts on the world's ocean

Human pressures on the ocean are thought to be increasing globally, yet we know little about their patterns of cumulative change, which pressures are most responsible for change, and which places are experiencing the greatest increases. Managers and policymakers require such information to make strategic decisions and monitor progress towards management objectives. Here we calculate and map recent change over 5 years in cumulative impacts to marine ecosystems globally from fishing, climate change, and ocean- and land-based stressors. Nearly 66% of the ocean and 77% of national jurisdictions show increased human impact, driven mostly by climate change pressures. Five percent of the ocean is heavily impacted with increasing pressures, requiring management attention. Ten percent has very low impact with decreasing pressures. Our results provide large-scale guidance about where to prioritize management efforts and affirm the importance of addressing climate change to maintain and improve the condition of marine ecosystems

Collective Epithelial Migration Drives Kidney Repair after Acute Injury

Acute kidney injury (AKI) is a common and significant medical problem. Despite the kidney’s remarkable regenerative capacity, the mortality rate for the AKI patients is high. Thus, there remains a need to better understand the cellular mechanisms of nephron repair in order to develop new strategies that would enhance the intrinsic ability of kidney tissue to regenerate. Here, using a novel, laser ablation-based, zebrafish model of AKI, we show that collective migration of kidney epithelial cells is a primary early response to acute injury. We also show that cell proliferation is a late response of regenerating kidney epithelia that follows cell migration during kidney repair. We propose a computational model that predicts this temporal relationship and suggests that cell stretch is a mechanical link between migration and proliferation, and present experimental evidence in support of this hypothesis. Overall, this study advances our understanding of kidney repair mechanisms by highlighting a primary role for collective cell migration, laying a foundation for new approaches to treatment of AKI

Empirical Models of Transitions between Coral Reef States: Effects of Region, Protection, and Environmental Change

There has been substantial recent change in coral reef communities. To date, most analyses have focussed on static patterns or changes in single variables such as coral cover. However, little is known about how community-level changes occur at large spatial scales. Here, we develop Markov models of annual changes in coral and macroalgal cover in the Caribbean and Great Barrier Reef (GBR) regions

Mode-selective vibrational control of charge transport in ππ-conjugated molecular materials

The soft character of organic materials leads to strong coupling between molecular nuclear and electronic dynamics. This coupling opens the way to control charge transport in organic electronic devices by inducing molecular vibrational motions. However, despite encouraging theoretical predictions, experimental realization of such control has remained elusive. Here we demonstrate experimentally that photoconductivity in a model organic optoelectronic device can be controlled by the selective excitation of molecular vibrations. Using an ultrafast infrared laser source to create a coherent superposition of vibrational motions in a pentacene/C60 photoresistor, we observe that excitation of certain modes in the 1500-1700 cm$^{-1}$ region leads to photocurrent enhancement. Excited vibrations affect predominantly trapped carriers. The effect depends on the nature of the vibration and its mode-specific character can be well described by the vibrational modulation of intermolecular electronic couplings. Vibrational control thus presents a new tool for studying electron-phonon coupling and charge dynamics in (bio)molecular materials.This work was supported by the Netherlands Organization for Scientific Research (NWO) through the ‘Stichting voor Fundamenteel Onderzoek der Materie’ (FOM) research programme. A.A.B. also acknowledges a VENI grant from the NWO. A.A.B. is currently a Royal Society University Research Fellow. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 639750). R.L. acknowledges a Marie Curie IE Fellowship from the EU, held at the Weizmann Institute (FP7-PEOPLE-2011-IEF no. 29866). X.Y. thanks the Council for Higher Education (Israel) for a PBC programme postdoctoral research fellowship. V.C. thanks support from the Office of Naval Research and MURI Center on Advanced Molecular Photovoltaics, award No. N00014-14-1-0580. J.L.B. acknowledges support by competitive research funding from King Abdullah University of Science and Technology (KAUST) and by ONR Global, Grant N62909-15-1-2003. D.C. thanks the Israel Science Foundation Centre of Excellence program, the Grand Centre for Sensors and Security and the Schmidt Minerva Centre for Supramolecular Architecture for partial support. D.C. holds the Sylvia and Rowland Schaefer Chair in Energy Research.This is the final published version. It first appeared at http://dx.doi.org/10.1038/ncomms888

A geometrical introduction to screw theory

This work introduces screw theory, a venerable but yet little known theory aimed at describing rigid body dynamics. This formulation of mechanics unifies in the concept of screw the translational and rotational degrees of freedom of the body. It captures a remarkable mathematical analogy between mechanical momenta and linear velocities, and between forces and angular velocities. For instance, it clarifies that angular velocities should be treated as applied vectors and that, under the composition of motions, they sum with the same rules of applied forces. This work provides a short and rigorous introduction to screw theory intended to an undergraduate and general readership.Comment: Latex2e, 24 pages. v2: expanded introduction, added 2 figure