200 research outputs found
Role of the tip vortex in the force generation of low-aspect-ratio normal flat plates
We investigate experimentally the force generated by the unsteady vortex formation of low-aspect-ratio normal flat plates with one end free. The objective of this study is to determine the role of the free end, or tip, vortex. Understanding this simple case provides insight into flapping-wing propulsion, which involves the unsteady motion of low-aspect-ratio appendages. As a simple model of a propulsive half-stroke, we consider a rectangular normal flat plate undergoing a translating start-up motion in a towing tank. Digital particle image velocimetry is used to measure multiple perpendicular sections of the flow velocity and vorticity, in order to correlate vortex circulation with the measured plate force. The three-dimensional wake structure is captured using flow visualization. We show that the tip vortex produces a significant maximum in the plate force. Suppressing its formation results in a force minimum. Comparing plates of aspect ratio six and two, the flow is similar in terms of absolute distance from the tip, but evolves faster for aspect ratio two. The plate drag coefficient increases with decreasing aspect ratio
The Unsteady Lift Produced by a Flat-Plate Wing Translating Past Finite Obstacles
The unsteady lift of a high-angle-of-attack, flat-plate wing encountering
finite-length obstacles is studied using towing-tank force measurements. The
wing translates from rest and interacts with a rectangular channel, ceiling, or
ground obstacle. Variations with angle of attack, obstacle length, mid-chord
height to the obstacle, and starting distance between the wing leading edge
(LE) and obstacle (typically 1 chord) are examined. For channels, as the gap
height decreases, circulatory-lift peaks attributed to leading-edge vortices
(LEVs) are the largest, and from the second peak onward occur earliest. This is
likely from wing blockage enhancing the flow speed. The lift reduces while
exiting a channel, and is lowest afterward if exiting during a lift peak. For
ceilings, the first circulatory-lift maximum increases for smaller
LE-to-ceiling gaps, but for gaps of 0.5 chords or less, subsequent peaks are
below the no-obstacle case yet still earlier. For grounds, with lower wing
height the first circulatory-lift peak is larger but the second peak's behavior
varies with angle of attack, and the lift decreases near the ground end.
Grounds affect peak timing the least, indicating a reduced influence on the
LEV. Changing the starting distance to a channel alters the lift, likely from
different LEV timing
Cultural Preservation of Ethnomedicine in Peru
In conjunction with the Minority Health & Health Disparities International Research Training program at San Diego State University, three Linfield students contributed to the ongoing Peru Ethnomedical Project in Trujillo, Peru by: Conducting surveys in two neighborhoods on the edge of the city; Creating a medicinal plant garden in the Chan Chan archaeological site museum.
Surveys conducted in Moche, Trujillo were part of a larger study supervised by anthropologists Douglas Sharon and Thomas Love. The research aims to evaluate the usage of medicinal plants in rural and urban Peruvian communities. Linfieldâs contribution focused on the creation of the medicinal garden to serve as a community model and educational program. The overall purpose of the 2015 summer faculty collaborative project was to: Preserve the knowledge of these practices; Analyze the plant properties; Publish the information; Provide the community with a garden that reflects the commonly used plants; Educate new generations; Bring back and apply this knowledge in the Linfield community
Sortilin regulates sorting and secretion of Sonic hedgehog
Sonic Hedgehog (Shh) is a secreted morphogen that is an essential regulator of patterning and growth. The Shh full-length protein undergoes autocleavage in the ER to generate the biologically active amino-terminal ShhN fragment, which is destined for secretion. Few receptors have been identified that control the trafficking of this morphogen through the secretory pathway. We identified Sortilin (Sort1), a member of the VPS10P domain receptor family, as a novel Shh trafficking receptor. We demonstrate that Sort/Shh interact using co-IP and proximity ligation in transfected cells and that they co-localize to the Golgi. Sort1 overexpression causes re-distribution of ShhN, and to a lesser extent ShhFL, to the Golgi and reduces Shh secretion. We show loss of Sort1 can partially rescue Hedgehog-associated patterning defects in a mouse model of deficient Shh processing and that Sort1 levels negatively regulate anterograde Shh transport in axons in vitro and Hh-dependent axon-glial interactions in vivo Taken together, we conclude that Shh and Sort1 can interact at the level of the Golgi and that Sort1 directs Shh away from the pathways that promote its secretion
Summit of the N=40 Island of Inversion: precision mass measurements and ab initio calculations of neutron-rich chromium isotopes
Mass measurements continue to provide invaluable information for elucidating
nuclear structure and scenarios of astrophysical interest. The transition
region between the and proton shell closures is particularly
interesting due to the onset and evolution of nuclear deformation as nuclei
become more neutron rich. This provides a critical testing ground for emerging
ab-initio nuclear structure models. Here, we present high-precision mass
measurements of neutron-rich chromium isotopes using the sensitive
electrostatic Multiple-Reflection Time-Of-Flight Mass Spectrometer (MR-TOF-MS)
at TRIUMF's Ion Trap for Atomic and Nuclear Science (TITAN) facility. Our
high-precision mass measurements of Cr confirm previous results,
and the improved precision in measurements of Cr refine the mass
surface beyond N=40. With the ab initio in-medium similarity renormalization
group, we examine the trends in collectivity in chromium isotopes and give a
complete picture of the N=40 island of inversion from calcium to nickel.Comment: 12 pages, 7 figure
Hydrogen Epoch of Reionization Array (HERA)
The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to
measure 21 cm emission from the primordial intergalactic medium (IGM)
throughout cosmic reionization (), and to explore earlier epochs of our
Cosmic Dawn (). During these epochs, early stars and black holes
heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is
designed to characterize the evolution of the 21 cm power spectrum to constrain
the timing and morphology of reionization, the properties of the first
galaxies, the evolution of large-scale structure, and the early sources of
heating. The full HERA instrument will be a 350-element interferometer in South
Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz.
Currently, 19 dishes have been deployed on site and the next 18 are under
construction. HERA has been designated as an SKA Precursor instrument.
In this paper, we summarize HERA's scientific context and provide forecasts
for its key science results. After reviewing the current state of the art in
foreground mitigation, we use the delay-spectrum technique to motivate
high-level performance requirements for the HERA instrument. Next, we present
the HERA instrument design, along with the subsystem specifications that ensure
that HERA meets its performance requirements. Finally, we summarize the
schedule and status of the project. We conclude by suggesting that, given the
realities of foreground contamination, current-generation 21 cm instruments are
approaching their sensitivity limits. HERA is designed to bring both the
sensitivity and the precision to deliver its primary science on the basis of
proven foreground filtering techniques, while developing new subtraction
techniques to unlock new capabilities. The result will be a major step toward
realizing the widely recognized scientific potential of 21 cm cosmology.Comment: 26 pages, 24 figures, 2 table
Mapping the N=40 island of inversion: Precision mass measurements of neutron-rich Fe isotopes
International audienceNuclear properties across the chart of nuclides are key to improving and validating our understanding of the strong interaction in nuclear physics. We present high-precision mass measurements of neutron-rich Fe isotopes performed at the TITAN facility. The multiple-reflection time-of-flight mass spectrometer (MR-ToF-MS), achieving a resolving power greater than 600000 for the first time, enabled the measurement of Fe63â70, including first-time high-precision direct measurements (ÎŽm/mâ10â7) of Fe68â70, as well as the discovery of a long-lived isomeric state in Fe69. These measurements are accompanied by both mean-field and ab initio calculations using the most recent realizations which enable theoretical assignment of the spin-parities of the Fe69 ground and isomeric states. Together with mean-field calculations of quadrupole deformation parameters for the Fe isotope chain, these results benchmark a maximum of deformation in the N=40 island of inversion in Fe and shed light on trends in level densities indicated in the newly refined mass surface
Mass measurements of 60â63Ga reduce x-ray burst model uncertainties and extend the evaluated T=1 isobaric multiplet mass equation
We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of Ga60â63 performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of Ga61 and mark the first direct mass measurement of Ga60. The improved precision of the Ga61 mass has important implications for the astrophysical rp process, as it constrains essential reaction Q values near the Zn60 waiting point. Based on calculations with a one-zone model, we demonstrate the impact of the improved mass data on prediction uncertainties of x-ray burst models. The first-time measurement of the Ga60 ground-state mass establishes the proton-bound nature of this nuclide, thus constraining the location of the proton drip line along this isotopic chain. Including the measured mass of Ga60 further enables us to extend the evaluated T=1 isobaric multiplet mass equation up to A=60
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