473 research outputs found
Tropical Cyclone Movement Forecasts Based on Observations from Satellites
The article of record as published may be found at http://dx.doi.org/10.1175/1520-0450(1975)0142.0.CO;2A method to predict 24 h movement of tropical cyclones using consecutive daily satellite views is
described. The method is based on the observation that changes in the location of major structural
features of the storm are correlated with changes in the direction of movement of the storm centers.
Major structural features appear to retain the same relative location with respect to the direction of
movement of the storm center. The rotation of features noted in comparing satellite views over a 24 h
period is frequently found to approximate in sense and value the further deflection the storm will.take
in its track during the following 24 h. A test evaluation of the method was conducted by seven individuals
using 31 separate data sets of satellite data. For the purposes of the test only direction of movement
forecasts were made and storm center displacement was neglected. The results on a post-analysis, nonreal-
time, basis compared favorably with official 24 h forecasts
Whole-plant mineral partitioning during the reproductive development of rice (Oryza sativa L.)
Minimal information exists on whole-plant dynamics of mineral flow. Understanding these phenomena in a model plant such as rice could help in the development of nutritionally enhanced cultivars. A whole-plant mineral accumulation study was performed in rice (cv. Kitaake), using sequential harvests during reproductive development panicle exertion, grain filling, and full maturity stages in order to characterize mineral accumulation in roots, non-flag leaves, flag leaves, stems/sheaths, and panicles. Partition quotient analysis showed that Fe, Zn, Cu and Ni are preferentially accumulated in roots; Mn and Mg are accumulated in leaves; Mo, Ca, and S in roots and leaves; and K in roots, leaves and stems/sheaths. Correlation analysis indicated that changes in the concentrations of mineral pairs Fe-Mn, K-S, Fe-Ni, Cu-Mg, Mn-Ni, S-Mo, Mn-Ca, and Mn-Mg throughout the reproductive development of rice were positively correlated in all four of the above ground organs evaluated, with Fe-Mn and K-S being positively correlated also in roots, which suggest that root-to-shoot transfer is not driven simply by concentrations in roots. These analyses will serve as a starting point for a more detailed examination of mineral transport and accumulation in rice plants
Maser threshold characterization by resonator Q-factor tuning
Whereas the laser is nowadays an ubiquitous technology, applications for its microwave
analog, the maser, remain highly specialized, despite the excellent low-noise microwave
amplification properties. The widespread application of masers is typically limited by the need
of cryogenic temperatures. The recent realization of a continuous-wave room-temperature
maser, using NV− centers in diamond, is a first step towards establishing the maser as a
potential platform for microwave research and development, yet its design is far from optimal. Here, we design and construct an optimized setup able to characterize the operating
space of a maser using NV− centers. We focus on the interplay of two key parameters for
emission of microwave photons: the quality factor of the microwave resonator and the degree
of spin level-inversion. We characterize the performance of the maser as a function of these
two parameters, identifying the parameter space of operation and highlighting the requirements for maximal continuous microwave emission
Maser Threshold Characterization by Resonator Q-Factor Tuning
Whereas the laser is nowadays an ubiquitous technology, applications for its
microwave analogue, the maser, remain highly specialized, despite the excellent
low-noise microwave amplification properties. The widespread application of
masers is typically limited by the need of cryogenic temperatures. The recent
realization of a continuous-wave room-temperature maser, using NV centers
in diamond, is a first step towards establishing the maser as a potential
platform for microwave research and development, yet its design is far from
optimal. Here, we design and construct an optimized setup able to characterize
the operating space of a maser using NV centers. We focus on the interplay
of two key parameters for emission of microwave photons: the quality factor of
the microwave resonator and the degree of spin level-inversion. We characterize
the performance of the maser as a function of these two parameters, identifying
the parameter space of operation and highlighting the requirements for maximal
continuous microwave emission
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Fatigue threshold R-curves predict small crack fatigue behavior of bridging toughened materials
Small crack fatigue is a widely recognized problem in the fatigue of materials; however, there has been limited progress in developing methods for predicting small crack fatigue behavior. In this paper, small crack effects due to crack bridging are addressed. A fatigue threshold R-curve was measured for a 99.5% pure polycrystalline alumina using standard compact tension specimens and it was used to 1) determine the bridging stress profile for the material and 2) make fatigue endurance strength predictions for realistic semi-elliptical surface cracks. Furthermore, is has been shown that the fatigue threshold R-curve can equivalently be determined by measuring the bridging stress distribution, in this case using fluorescence spectroscopy, using only a long crack compact tension specimen without the need for difficult small crack experiments. It is expected that this method will be applicable to a wide range of bridging toughened materials, including composites, toughened ceramics, intermetallics, and multi-phase materials.Keywords: fracture, toughness, fatigue, crack bridgingKeywords: fracture, toughness, fatigue, crack bridgin
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A direct comparison of non-destructive techniques for determining bridging stress distributions
Crack bridging is an important source of crack propagation resistance in many materials and the bridging stress distribution as a function of crack opening displacement is widely believed to represent a true material property uninfluenced by sample geometry, loading conditions, and other extrinsic factors. Accordingly, accurate measurement of the bridging stress distribution is needed and many non-destructive methods have been developed. However, there are many challenges to accurately determining bridging stresses. A comparison of bridging stresses measured using R-curve, crack opening displacement (COD), and spectroscopy methods has been made using two bridging ceramics, Y₂O₃ and MgO doped Si₃N₄ and 99.5% pure Al₂O₃. The COD method is surface sensitive and gives a lower peak bridging stress compared to the R-curve technique which samples through the entire material thickness. This is attributed to a more compliant near surface bridging zone. Conversely, when R-curves rise steeply over the first few micrometers of growth from a notch, an effect of negative T-stress is expected to raise the R-curve determined peak bridging stress. Spectroscopy methods were only found to yield reliable bridging stress results if a reasonable through thickness volume of material is sampled. It was found that 2.5% of the specimen thickness achieved using fluorescence spectroscopy appears adequate for Al₂O₃ while 0.1–0.2% of the sample thickness achieved using Raman spectroscopy for Si₃N₄ appears inadequate. Overall, it is concluded that in the absence of T-stresses a bridging distribution can be determined that is a true material property. Also, a new method is proposed for determining the bridging stresses of fatigue cracks from (1) the bridging stress distribution for monotonically loaded cracks and (2) experimental fatigue data.Keywords: R-curves, Fracture mechanisms, Bridging stress distribution, T-stress, Ceramic materialKeywords: R-curves, Fracture mechanisms, Bridging stress distribution, T-stress, Ceramic materia
Inhibition of Progenitor Dendritic Cell Maturation by Plasma from Patients with Peripartum Cardiomyopathy: Role in Pregnancy-associated Heart Disease
Dendritic cells (DCs) play dual roles in innate and adaptive immunity based
on their functional maturity, and both innate and adaptive immune responses have
been implicated in myocardial tissue remodeling associated with
cardiomyopathies. Peripartum cardiomyopathy (PPCM) is a rare disorder which
affects women within one month antepartum to five months postpartum. A high
occurrence of PPCM in central Haiti (1 in 300 live births) provided the unique
opportunity to study the relationship of immune activation and DC maturation
to the etiology of this disorder. Plasma samples from two groups (n = 12) of
age- and parity-matched Haitian women with or without evidence of PPCM were
tested for levels of biomarkers of cardiac tissue remodeling and immune
activation. Significantly elevated levels of GM-CSF, endothelin-1, proBNP and
CRP and decreased levels of TGF- were measured in PPCM subjects relative
to controls. Yet despite these findings, in vitro maturation of normal human
cord blood derived progenitor dendritic cells (CBDCs) was significantly
reduced (p < 0.001) in the presence of plasma from PPCM patients relative
to plasma from post-partum control subjects as determined by expression of
CD80, CD86, CD83, CCR7, MHC class II and the ability of these matured CBDCs
to induce allo-responses in PBMCs. These results represent the first findings
linking inhibition of DC maturation to the dysregulation of normal physiologic
cardiac
tissue remodeling during pregnancy and the pathogenesis of PPCM
Tensile Creep and Creep-Recovery Behavior of a SiC-Fiber Si 3 N 4 -Matrix Composite
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65802/1/j.1151-2916.1993.tb03753.x.pd
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