8,181 research outputs found
Propagating Waves in a Monolayer of Gas-Fluidized Rods
We report on an observation of propagating compression waves in a
quasi-two-dimensional monolayer of apolar granular rods fluidized by an upflow
of air. The collective wave speed is an order of magnitude faster than the
speed of the particles. This gives rise to anomalously large number
fluctuations dN ~ , which are greater than ordinary number
fluctuations of N^{1/2}. We characterize the waves by calculating the
spatiotemporal power spectrum of the density. The position of observed peaks,
as a function of frequency w and wavevector k, yields a linear dispersion
relationship in the long-time, long-wavelength limit and a wavespeed c = w/k.
Repeating this analysis for systems at different densities and air speeds, we
observe a linear increase in the wavespeed with increasing packing fraction
with no dependence on the airflow. Although air-fluidized rods self-propel
individually or in dilute collections, the parallel and perpendicular
root-mean-square speeds of the rods indicate that they no longer self-propel
when propagating waves are present. Based on this mutual exclusivity, we map
out the phase behavior for the existence of waves vs self-propulsion as a
function of density and fluidizing airflow
Diamonds and related minerals from the Dokolwayo Kimberlite, Kingdom of Swaziland
Includes bibliography.Several physical characteristics, the carbon isotopic compositions, inclusion mineralogy, and distribution of the Dokolwayo diamonds were investigated. A representative suite of concentrate garnet megacrysts and macrocrysts were analyzed for their compositions. Concentrate macrocryst spinels and silicate inclusions recovered from these spinels were analyzed. The physical characteristics of the diamonds investigated were mass, size, morphology and colour. The relationship between mass and size in a population of diamonds recovered from a single hypabyssal intrusion and the general production as a whole, was found to be statistically the same. The most recognizable morphology is the dodecahedron. Octahedra decrease in significance with a decrease in size. Colourless stones predominate. Brown stones are more common than yellow stones, which is uncommon in primary southern Africa diamond populations. Diamonds characterized by "Tanganyika naats" have hitherto not been described from southern Africa. The relationship between the various physical characteristics investigated indicate that the general Dokolwayo diamond population consists of at least four sub-populations
Limitations in Predicting Radiation-Induced Pharmaceutical Instability during Long-Duration Spaceflight
As human spaceflight seeks to expand beyond low-Earth orbit, NASA and its
international partners face numerous challenges related to ensuring the safety
of their astronauts, including the need to provide a safe and effective
pharmacy for long-duration spaceflight. Historical missions have relied upon
frequent resupply of onboard pharmaceuticals; as a result, there has been
little study into the effects of long-term exposure of pharmaceuticals to the
space environment. Of particular concern are the long-term effects of space
radiation on drug stability, especially as missions venture away from the
protective proximity of the Earth. Here we highlight the risk of space
radiation to pharmaceuticals during exploration spaceflight, identifying the
limitations of current understanding. We further seek to identify ways in which
these limitations could be addressed through dedicated research efforts aimed
towards the rapid development of an effective pharmacy for future spaceflight
endeavors.Comment: in press, Nature Microgravit
Defect turbulence in inclined layer convection
We report experimental results on the defect turbulent state of undulation
chaos in inclined layer convection of a fluid withPrandtl number .
By measuring defect density and undulation wavenumber, we find that the onset
of undulation chaos coincides with the theoretically predicted onset for
stable, stationary undulations. At stronger driving, we observe a competition
between ordered undulations and undulation chaos, suggesting bistability
between a fixed-point attractor and spatiotemporal chaos. In the defect
turbulent regime, we measured the defect creation, annihilation, entering,
leaving, and rates. We show that entering and leaving rates through boundaries
must be considered in order to describe the observed statistics. We derive a
universal probability distribution function which agrees with the experimental
findings.Comment: 4 pages, 5 figure
Hysterectomy, endometrial destruction, and levonorgestrel releasing intrauterine system (Mirena) for heavy menstrual bleeding : systematic review and meta-analysis of data from individual patients
Peer reviewedPublisher PD
Hysterectomy, endometrial ablation, and levonorgestrel releasing intrauterine system (Mirena) for treatment of heavy menstrual bleeding : cost effectiveness analysis
Peer reviewedPublisher PD
Power-law carrier dynamics in semiconductor nanocrystals at nanosecond time scales
We report the observation of power law dynamics on nanosecond to microsecond
time scales in the fluorescence decay from semiconductor nanocrystals, and draw
a comparison between this behavior and power-law fluorescence blinking from
single nanocrystals. The link is supported by comparison of blinking and
lifetime data measured simultaneously from the same nanocrystal. Our results
reveal that the power law coefficient changes little over the nine decades in
time from 10 ns to 10 s, in contrast with the predictions of some diffusion
based models of power law behavior.Comment: 3 pages, 2 figures, compressed for submission to Applied Physics
Letter
Cloaked Facebook pages: Exploring fake Islamist propaganda in social media
This research analyses cloaked Facebook pages that are created to spread political propaganda by cloaking a user profile and imitating the identity of a political opponent in order to spark hateful and aggressive reactions. This inquiry is pursued through a multi-sited online ethnographic case study of Danish Facebook pages disguised as radical Islamist pages, which provoked racist and anti-Muslim reactions as well as negative sentiments towards refugees and immigrants in Denmark in general. Drawing on Jessie Daniels’ critical insights into cloaked websites, this research furthermore analyses the epistemological, methodological and conceptual challenges of online propaganda. It enhances our understanding of disinformation and propaganda in an increasingly interactive social media environment and contributes to a critical inquiry into social media and subversive politics
Radiation Impact on Pharmaceutical Stability: Retrospective Data Review
Historical studies performed by the JSC Pharmacotherapeutics Discipline suggest that exposure to spaceflight conditions may compromise the safety and efficacy of some medications. Follow-on studies have revealed that affected medications demonstrate reductions in active pharmaceutical ingredient (API) concentrations and altered release characteristics. It was hypothesized that the changes in API potency and release were from the medication's exposure to the harsh environmental conditions of spaceflight. Subsequent review of the spaceflight environmental control records from the time of these studies indicated that temperature and humidity levels aboard all spacecraft remained within United States Pharmacopeia (USP) recommended ranges to maintain optimal pharmaceutical stability. Therefore, space radiation was presumed to be the source of observed drug degradation. The Pharmacotherapeutics Discipline conducted a ground analog radiation experiment in 2006 at the NASA Space Radiation Laboratory (NSRL) at Brookhaven to validate this theory and to characterize the effects of high-energy radioactive particles on pharmaceutical stability. These data were never published. Recently, the Exploration Medical Capability (ExMC) Element finalized a research plan (RP) aimed at providing a safe and effective medication formulary for exploration spaceflight. As ExMC begins to design new flight and ground analog radiation studies, further analysis of the 2006 NSRL study data is essential for the characterization of the impact of radiation on medication potency and efficacy in the exploration spaceflight environment
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