5,050 research outputs found
Longitude distribution of solar flares
Longitude distribution of solar flare
A simplified particulate model for coarse-grained hemodynamics simulations
Human blood flow is a multi-scale problem: in first approximation, blood is a
dense suspension of plasma and deformable red cells. Physiological vessel
diameters range from about one to thousands of cell radii. Current
computational models either involve a homogeneous fluid and cannot track
particulate effects or describe a relatively small number of cells with high
resolution, but are incapable to reach relevant time and length scales. Our
approach is to simplify much further than existing particulate models. We
combine well established methods from other areas of physics in order to find
the essential ingredients for a minimalist description that still recovers
hemorheology. These ingredients are a lattice Boltzmann method describing rigid
particle suspensions to account for hydrodynamic long range interactions
and---in order to describe the more complex short-range behavior of
cells---anisotropic model potentials known from molecular dynamics simulations.
Paying detailedness, we achieve an efficient and scalable implementation which
is crucial for our ultimate goal: establishing a link between the collective
behavior of millions of cells and the macroscopic properties of blood in
realistic flow situations. In this paper we present our model and demonstrate
its applicability to conditions typical for the microvasculature.Comment: 12 pages, 11 figure
Richardson's pair diffusion and the stagnation point structure of turbulence
DNS and laboratory experiments show that the spatial distribution of
straining stagnation points in homogeneous isotropic 3D turbulence has a
fractal structure with dimension D_s = 2. In Kinematic Simulations the time
exponent gamma in Richardson's law and the fractal dimension D_s are related by
gamma = 6/D_s. The Richardson constant is found to be an increasing function of
the number of straining stagnation points in agreement with pair duffusion
occuring in bursts when pairs meet such points in the flow.Comment: 4 pages; Submitted to Phys. Rev. Let
Geometrical dependence of low frequency noise in superconducting flux qubits
A general method for directly measuring the low-frequency flux noise (below
10 Hz) in compound Josephson junction superconducting flux qubits has been used
to study a series of 85 devices of varying design. The variation in flux noise
across sets of qubits with identical designs was observed to be small. However,
the levels of flux noise systematically varied between qubit designs with
strong dependence upon qubit wiring length and wiring width. Furthermore,
qubits fabricated above a superconducting ground plane yielded lower noise than
qubits without such a layer. These results support the hypothesis that
localized magnetic impurities in the vicinity of the qubit wiring are a key
source of low frequency flux noise in superconducting devices.Comment: 5 pages, 5 figure
The measurement of the winds near the ocean surface with a radiometer-scatterometer on Skylab
The author has identified the following significant results. There were a total of twenty-six passes in the ZLV mode that yielded useful data. Six were in the in-track noncontiguous mode; all others were in the cross-track noncontiguous mode. The wind speed and direction, as effectively determined in a neutral atmosphere at 19.5 m above the sea surface, were found for each cell scanned by S193. It is shown how the passive microwave measurements were used both to compute the attenuation of the radar beam and to determine those cells where the backscatter measurement was suspect. Given the direction of the wind from some independent source, with the typical accuracy of measurement by available meteorological methods, a backscatter measurement at a nadir angle of 50, 43, or 32 deg can be used to compute the speed of the wind averaged over the illuminated area
The equation of state of solid nickel aluminide
The pressure-volume-temperature equation of state of the intermetallic
compound NiAl was calculated theoretically, and compared with experimental
measurements. Electron ground states were calculated for NiAl in the CsCl
structure, using density functional theory, and were used to predict the cold
compression curve and the density of phonon states. The Rose form of
compression curve was found to reproduce the ab initio calculations well in
compression but exhibited significant deviations in expansion. A
thermodynamically-complete equation of state was constructed for NiAl. Shock
waves were induced in crystals of NiAl by the impact of laser-launched Cu
flyers and by launching NiAl flyers into transparent windows of known
properties. The TRIDENT laser was used to accelerate the flyers to speeds
between 100 and 600m/s. Point and line-imaging laser Doppler velocimetry was
used to measure the acceleration of the flyer and the surface velocity history
of the target. The velocity histories were used to deduce the stress state, and
hence states on the principal Hugoniot and the flow stress. Flyers and targets
were recovered from most experiments. The effect of elasticity and plastic flow
in the sample and window was assessed. The ambient isotherm reproduced static
compression data very well, and the predicted Hugoniot was consistent with
shock compression data
Skylab S-193 Radscat microwave measurements of sea surface winds
The S-193 Radscat made extensive measurements of many sea conditions. Measurements were taken in a tropical hurricane (Ava), a tropical storm (Christine), and in portions of extratropical cyclones. Approximately 200 scans of ocean data at 105 kilometer spacings were taken during the first two Skylab missions and another 200 during the final mission when the characteristics of the measurements changed due to damage of the antenna. Backscatter with four transmit/receive polarization combinations and emissions with horizontal and vertical receive polarizations were measured. Other surface parameters investigated for correlation with the measurements included sea temperature, air/sea temperature difference, and gravity-wave spectrum. Methods were developed to correct the microwave measurements for atmospheric effects. The radiometric data were corrected accurately for clear sky and light cloud conditions only. The radiometer measurements were used to recover the surface scattering characteristics for all atmospheric conditions excluding rain. The radiometer measurements also detected the presence of rain which signaled when the scattering measurement should not be used for surface wind estimation. Regression analysis was used to determine empirically the relation between surface parameters and the microwave measurements, after correction for atmospheric effects. Results indicate a relationship approaching square-law at 50 deg between differential scattering coefficient and wind speed with horizontally polarized scattering data showing slightly more sensitivity to wind speed than vertically polarized data
The future of social is personal: the potential of the personal data store
This chapter argues that technical architectures that facilitate the longitudinal, decentralised and individual-centric personal collection and curation of data will be an important, but partial, response to the pressing problem of the autonomy of the data subject, and the asymmetry of power between the subject and large scale service providers/data consumers. Towards framing the scope and role of such Personal Data Stores (PDSes), the legalistic notion of personal data is examined, and it is argued that a more inclusive, intuitive notion expresses more accurately what individuals require in order to preserve their autonomy in a data-driven world of large aggregators. Six challenges towards realising the PDS vision are set out: the requirement to store data for long periods; the difficulties of managing data for individuals; the need to reconsider the regulatory basis for third-party access to data; the need to comply with international data handling standards; the need to integrate privacy-enhancing technologies; and the need to future-proof data gathering against the evolution of social norms. The open experimental PDS platform INDX is introduced and described, as a means of beginning to address at least some of these six challenges
Impacts of wet market modernization levels and hygiene practices on the microbiome and microbial safety of wooden cutting boards in Hong Kong
Accessing food through wet markets is a common global daily occurrence, where fresh meat can be purchased to support an urbanizing world population. Similar to the wet markets in many other metropolitan cities in Asia, Hong Kong wet markets vary and are characterized by differing hygiene routines and access to essential modern technologies. The lack of risk assessments of food contact surfaces in these markets has led to substantial gaps in food safety knowledge and information that could help improve and maintain public health. Microbial profiling analyses were conducted on cutting boards that had been used to process pork, poultry, and seafood at 11 different wet markets. The markets differed in hygiene protocols and access to modern facilities. Irrespective of whether wet markets have access of modern infrastructure, the hygiene practices were largely found to be inefficient based on the prevalence of bacterial species typically associated with foodborne pathogens such as Campylobacter fetus, Clostridium perfringens, Staphylococcus aureus, and Vibrio parahaemolyticus; indicator organisms such as Escherichia coli; as well as nonfoodborne pathogenic bacterial species potentially associated with nosocomial infections, such as Klebsiella pneumoniae and Enterobacter cloacae. Other Vibrio species, V. parahaemolyticus and V. vulnificus, typically associated with contaminated raw or undercooked seafood with the potential to cause illness in humans, were also found on wooden cutting boards. This study indicated that the hygienic practices used in Hong Kong wet markets are not sufficient for preventing the establishment of spoilage or pathogenic organisms. This study serves as a basis to review current hygiene practices in wet markets and provides a framework to reassess existing safety protocols
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