A numerical study of viscous vortex rings using a spectral method

Viscous, axisymmetric vortex rings are investigated numerically by solving the incompressible Navier-Stokes equations using a spectral method designed for this type of flow. The results presented are axisymmetric, but the method is developed to be naturally extended to three dimensions. The spectral method relies on divergence-free basis functions. The basis functions are formed in spherical coordinates using Vector Spherical Harmonics in the angular directions, and Jacobi polynomials together with a mapping in the radial direction. Simulations are performed of a single ring over a wide range of Reynolds numbers (Re approximately equal gamma/nu), 0.001 less than or equal to 1000, and of two interacting rings. At large times, regardless of the early history of the vortex ring, it is observed that the flow approaches a Stokes solution that depends only on the total hydrodynamic impulse, which is conserved for all time. At small times, from an infinitely thin ring, the propagation speeds of vortex rings of varying Re are computed and comparisons are made with the asymptotic theory by Saffman. The results are in agreement with the theory; furthermore, the error is found to be smaller than Saffman's own estimate by a factor square root ((nu x t)/R squared) (at least for Re=0). The error also decreases with increasing Re at fixed core-to-ring radius ratio, and appears to be independent of Re as Re approaches infinity). Following a single ring, with Re=500, the vorticity contours indicate shedding of vorticity into the wake and a settling of an initially circular core to a more elliptical shape, similar to Norbury's steady inviscid vortices. Finally, we consider the case of leapfrogging vortex rings with Re=1000. The results show severe straining of the inner vortex core in the first pass and merging of the two cores during the second pass

Investigating postharvest chilling injury in tomato (Solanum lycopersicum L.) fruit using magnetic resonance imaging and 5-azacytidine, a hypomethylation agent

Tomato, like most species from tropical and subtropical regions, exhibits postharvest chilling injury (PCI) when stored at low temperatures. Because of its economic importance and the functional genomics tools available, we used tomato to investigate aspects of fruit PCI development. We asked two questions: First, are there spatial-temporal differences in the development of PCI that can be detected by magnetic resonance imaging (MRI)? Here, the aim was to use a non-invasive method to study PCI progression in vivo. At mature green and breaker, the pericarp, locular tissue and columella produced distinct D-values while in contrast, there was no such differentiation in riper fruit. Although the pericarp is where most PCI symptoms are visible, this tissue showed less dynamism upon cold exposure, compared to the inner tissues as detected by MRI. This suggests the occurrence of distinct, independently modulated mechanisms contributing to the development of PCI-symptomatology. Collectively our data showed that the MRI could detect fruit ripening, its attenuation by cold, and fruit tissue-specific responses to chilling stress. The second question we asked was if epigenetic modification of the tomato genome or transcriptome influences PCI response. We examined PCI severity in fruit injected with a demethylating agent, 5- azacytidine (AZA). Two tomato genotypes exposed to varying severities of cold-stress were studied. Results suggested that AZA was able to moderate PCI in 'Micro-Tom' after 3 weeks at 2.5°C, while different patterns were observed in 'Sun Cherry' across various cold treatments. The effects of AZA on PCI were complex, multilayered and highly context-dependent

Black Carbon Concentrations and Sources in the Marine Boundary Layer of the Tropical Atlantic Ocean using Four Methodologies

Combustion-derived aerosols in the marine boundary layer have been poorly studied, especially in remote environments such as the open Atlantic Ocean. The tropical Atlantic has the potential to contain a high concentration of aerosols, such as black carbon, due to the African emission plume of biomass and agricultural burning products. Atmospheric particulate matter samples across the tropical Atlantic boundary layer were collected in the summer of 2010 during the southern hemispheric dry season when open fire events were frequent in Africa and South America. The highest black carbon concentrations were detected in the Caribbean Sea and within the African plume, with a regional average of 0.6 μg m−3 for both. The lowest average concentrations were measured off the coast of South America at 0.2 to 0.3 μg m−3. Samples were quantified for black carbon using multiple methods to provide insights into the form and stability of the carbonaceous aerosols (i.e., thermally unstable organic carbon, soot like, and charcoal like). Soot-like aerosols composed up to 45% of the carbonaceous aerosols in the Caribbean Sea to as little as 4% within the African plume. Charcoal-like aerosols composed up to 29% of the carbonaceous aerosols over the oligotrophic Sargasso Sea, suggesting that non-soot-like particles could be present in significant concentrations in remote environments. To better apportion concentrations and forms of black carbon, multiple detection methods should be used, particularly in regions impacted by biomass burning emissions

Deep-Sea Debris in the Central and Western Pacific Ocean

Marine debris is a growing problem in the world’s deep ocean. The naturally slow biological and chemical processes operating at depth, coupled with the types of materials that are used commercially, suggest that debris is likely to persist in the deep ocean for long periods of time, ranging from hundreds to thousands of years. However, the realized scale of marine debris accumulation in the deep ocean is unknown due to the logistical, technological, and financial constraints related to deep-ocean exploration. Coordinated deep-water exploration from 2015 to 2017 enabled new insights into the status of deep-sea marine debris throughout the central and western Pacific Basin via ROV expeditions conducted onboard NOAA Ship Okeanos Explorer and RV Falkor. These expeditions included sites in United States protected areas and monuments, other Exclusive Economic Zones, international protected areas, and areas beyond national jurisdiction. Metal, glass, plastic, rubber, cloth, fishing gear, and other marine debris were encountered during 17.5% of the 188 dives from 150 to 6,000 m depth. Correlations were observed between deep-sea debris densities and depth, geological features, and distance from human-settled land. The highest densities occurred off American Samoa and the main Hawaiian Islands. Debris, mostly consisting of fishing gear and plastic, were also observed in most of the large-scale marine protected areas, adding to the growing body of evidence that even deep, remote areas of the ocean are not immune from human impacts. Interactions with and impacts on biological communities were noted, though further study is required to understand the full extent of these impacts. We also discuss potential sources and long-term implications of this debris.This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms

Stanford Synchrotron Radiation Laboratory 1991 activity report. Facility developments January 1991--March 1992

SSRL is a national facility supported primarily by the Department of Energy for the utilization of synchrotron radiation for basic and applied research in the natural sciences and engineering. It is a user-oriented facility which welcomes proposals for experiments from all researchers. The synchrotron radiation is produced by the 3.5 GeV storage ring, SPEAR, located at the Stanford Linear Accelerator Center (SLAC). SPEAR is a fully dedicated synchrotron radiation facility which operates for user experiments 7 to 9 months per year. SSRL currently has 24 experimental stations on the SPEAR storage ring. There are 145 active proposals for experimental work from 81 institutions involving approximately 500 scientists. There is normally no charge for use of beam time by experimenters. This report summarizes the activity at SSRL for the period January 1, 1991 to December 31, 1991 for research. Facility development through March 1992 is included

Fluxes of soot black carbon to South Atlantic sediments

Deep sea sediment samples from the South Atlantic Ocean were analyzed for soot black carbon (BC), total organic carbon (TOC), stable carbon isotope ratios (delta C-13), and polycyclic aromatic hydrocarbons (PAHs). Soot BC was present at low concentrations (0.04-0.17% dry weight), but accounted for 3-35% of TOC. Fluxes of soot BC were calculated on the basis of known sedimentation rates and ranged from 0.5 to 7.8 mu g cm(-2) a(-1), with higher fluxes near Africa compared to South America. Values of delta C-13 indicated a marine origin for the organic carbon but terrestrial sources for the soot BC. PAH ratios implied a pyrogenic origin for most samples and possibly a predominance of traffic emissions over wood burning off the African coast. A coupled ocean-atmosphere-aerosol-climate model was used to determine fluxes of BC from 1860 to 2000 to the South Atlantic. Model simulation and measurements both yielded higher soot BC fluxes off the African coast and lower fluxes off the South American coast; however, measured sedimentary soot BC fluxes exceeded simulated values by similar to 1 mu g cm(-2) a(-1) on average (within a factor of 2-4). For the sediments off the African coast, soot BC delivery from the Congo River could possibly explain the higher flux rates, but no elevated soot BC fluxes were detected in the Amazon River basin. In total, fluxes of soot BC to the South Atlantic were similar to 480-700 Gg a(-1) in deep sea sediments. Our results suggest that attempts to construct a global mass balance of BC should include estimates of the atmospheric deposition of BC

Full Causal Bulk Viscous Cosmologies with time-varying Constants

We study the evolution of a flat Friedmann-Robertson-Walker Universe, filled with a bulk viscous cosmological fluid, in the presence of time varying ``constants''. The dimensional analysis of the model suggests a proportionality between the bulk viscous pressure of the dissipative fluid and the energy density. On using this assumption and with the choice of the standard equations of state for the bulk viscosity coefficient, temperature and relaxation time, the general solution of the field equations can be obtained, with all physical parameters having a power-law time dependence. The symmetry analysis of this model, performed by using Lie group techniques, confirms the unicity of the solution for this functional form of the bulk viscous pressure. In order to find another possible solution we relax the hypotheses assuming a concrete functional dependence for the ``constants''.Comment: 28 pages, RevTeX

Braking and Propulsion Phase Characteristics of Traditional and Accentuated Eccentric Loaded Back Squats

The purpose of this study was to examine the differences in braking and propulsion force-time characteristics and barbell velocity between traditional (TRAD) and accentuated eccentric loaded (AEL) back squats using various load combinations. Sixteen resistance-trained men participated in four separate testing sessions which included a one repetition maximum (1RM) back squat during the first session and three squat testing sessions. During the squat testing sessions, participants either performed sets of three repetitions of TRAD back squats each with 50, 60, 70, and 80% 1RM or performed the same loads with the addition of weight releasers that increased the total eccentric weight of the first repetition of each set to either 100 (AEL-MAX) or 110% 1RM (AEL-SUPRA). Braking and propulsion mean force, duration, and impulse as well as mean and peak barbell velocity were compared between each condition and load. Significantly greater braking impulses were produced during the AEL-MAX and AEL-SUPRA conditions compared to TRAD (p \u3c 0.03) with small-moderate effect sizes favoring AEL-SUPRA. No other significant differences existed among conditions for other braking, propulsion, or barbell velocity variables. AEL-MAX and AEL-SUPRA back squats may provide a greater braking stimulus compared to TRAD squats; however, the propulsion phase of the movement does not appear to be impacted. From a loading standpoint, larger and smaller load spreads may favor rapid and maximal force production characteristics, respectively. Further research on this topic is needed as a large portion of the braking stimulus experienced during AEL back squats may be influenced by relative strength

From Acting What’s next to Speeding Trap: Co-Evolutionary Dynamics of an Emerging Technology-Leader

JEL Classifications: O33, O53, L63[[abstract]]How does technological innovation emerge and evolve? We approach such an inquiry by synthesizing the perspectives of dynamic capabilities and co-evolutionary dynamics to portray organizational routines and multi-phase strategic renewals of an emerging technology-leader. To untangle the emergence of technological innovation, we conducted a longitudinal case study on the first and the largest dedicated semiconductor foundry, TSMC, located in the emerging economy of Taiwan. The firm-case of TSMC illustrates two unique co-evolutionary paths, that is, transforming from industry-latecomer to technology-leader and from process innovation to product innovation. We found multi-motor co-evolutionary dynamics between TSMC and the semiconductor industry, where its co-evolutionary mechanism of managed selection in its creating phase of mature process-innovation (1987-1998) has migrated to hierarchical renewal in its extending phase of advanced process-innovation (1999-2001), and then to holistic renewal in its modifying phase of product-innovation (2002-2007). During such paths, our research discovered a unique type of organizational routines, acting what’s next because TSMC has proactively searched for potential problems sooner than its competitors. However, such routines, although driving technological innovation, also lead to a unique type of success-trap, that is, speeding trap. When an emerging technology-leader fundamentally changes the industrial structures to over-specs, the growth driven by technology speeding may trap such a leader in a loop of over-exploration.[[sponsorship]]The authors are grateful to the research grant from the National Science Council (NSC) in Taiwan. The earlier manuscript of this paper was presented at the 2009 Annual Meeting of Academy of International Business (AIB) in San Diego, USA.[[notice]]補正完畢[[journaltype]]國外[[ispeerreviewed]]Y[[booktype]]紙本[[booktype]]電子版[[countrycodes]]CA

Fabrication and Assessment of 3D Printed Anatomical Models of the Lower Limb for Anatomical Teaching and Femoral Vessel Access Training in Medicine

For centuries, cadaveric dissection has been the touchstone of anatomy education. It offers a medical student intimate access to his or her first patient. In contrast to idealized artisan anatomical models, it presents the natural variation of anatomy in fine detail. However, a new teaching construct has appeared recently in which artificial cadavers are manufactured through three-dimensional (3D) printing of patient specific radiological data sets. In this article, a simple powder based printer is made more versatile to manufacture hard bones, silicone muscles and perfusable blood vessels. The approach involves blending modern approaches (3D printing) with more ancient ones (casting and lost-wax techniques). These anatomically accurate models can augment the approach to anatomy teaching from dissection to synthesis of 3D-printed parts held together with embedded rare earth magnets. Vascular simulation is possible through application of pumps and artificial blood. The resulting arteries and veins can be cannulated and imaged with Doppler ultrasound. In some respects, 3D-printed anatomy is superior to older teaching methods because the parts are cheap, scalable, they can cover the entire age span, they can be both dissected and reassembled and the data files can be printed anywhere in the world and mass produced. Anatomical diversity can be collated as a digital repository and reprinted rather than waiting for the rare variant to appear in the dissection room. It is predicted that 3D printing will revolutionize anatomy when poly-material printing is perfected in the early 21st century. (C) 2015 American Association of Anatomists