161 research outputs found
Aerosol Emission Monitoring and Assessment of Potential Exposure to Multi-walled Carbon Nanotubes in the Manufacture of Polymer Nanocomposites
Recent animal studies have shown that carbon nanotubes (CNTs) may pose a significant health risk to those exposed in the workplace. To further understand this potential risk, effort must be taken to measure the occupational exposure to CNTs. Results from an assessment of potential exposure to multi-walled carbon nanotubes (MWCNTs) conducted at an industrial facility where polymer nanocomposites were manufactured by an extrusion process are presented. Exposure to MWCNTs was quantified by the thermal-optical analysis for elemental carbon (EC) of respirable dust collected by personal sampling. All personal respirable samples collected (n = 8) had estimated 8-h time weighted average (TWA) EC concentrations below the limit of detection for the analysis which was about one-half of the recommended exposure limit for CNTs, 1 µg EC/m3 as an 8-h TWA respirable mass concentration. Potential exposure sources were identified and characterized by direct-reading instruments and area sampling. Area samples analyzed for EC yielded quantifiable mass concentrations inside an enclosure where unbound MWCNTs were handled and near a pelletizer where nanocomposite was cut, while those analyzed by electron microscopy detected the presence of MWCNTs at six locations throughout the facility. Through size selective area sampling it was identified that the airborne MWCNTs present in the workplace were in the form of large agglomerates. This was confirmed by electron microscopy where most of the MWCNT structures observed were in the form of micrometer-sized ropey agglomerates. However, a small fraction of single, free MWCNTs was also observed. It was found that the high number concentrations of nanoparticles, ~200000 particles/cm3, present in the manufacturing facility were likely attributable to polymer fumes produced in the extrusion proces
Non-Markovian dynamics for an open two-level system without rotating wave approximation: Indivisibility versus backflow of information
By use of the two measures presented recently, the indivisibility and the
backflow of information, we study the non-Markovianity of the dynamics for a
two-level system interacting with a zero-temperature structured environment
without using rotating wave approximation (RWA). In the limit of weak coupling
between the system and the reservoir, and by expanding the time-convolutionless
(TCL) generator to the forth order with respect to the coupling strength, the
time-local non-Markovian master equation for the reduced state of the system is
derived. Under the secular approximation, the exact analytic solution is
obtained and the sufficient and necessary conditions for the indivisibility and
the backflow of information for the system dynamics are presented. In the more
general case, we investigate numerically the properties of the two measures for
the case of Lorentzian reservoir. Our results show the importance of the
counter-rotating terms to the short-time-scale non-Markovian behavior of the
system dynamics, further expose the relations between the two measures and
their rationality as non-Markovian measures. Finally, the complete positivity
of the dynamics of the considered system is discussed
Physics of Solar Prominences: II - Magnetic Structure and Dynamics
Observations and models of solar prominences are reviewed. We focus on
non-eruptive prominences, and describe recent progress in four areas of
prominence research: (1) magnetic structure deduced from observations and
models, (2) the dynamics of prominence plasmas (formation and flows), (3)
Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and
large-scale patterns of the filament channels in which prominences are located.
Finally, several outstanding issues in prominence research are discussed, along
with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape
Measurement of the Atmospheric Muon Spectrum from 20 to 3000 GeV
The absolute muon flux between 20 GeV and 3000 GeV is measured with the L3
magnetic muon spectrometer for zenith angles ranging from 0 degree to 58
degree. Due to the large exposure of about 150 m2 sr d, and the excellent
momentum resolution of the L3 muon chambers, a precision of 2.3 % at 150 GeV in
the vertical direction is achieved.
The ratio of positive to negative muons is studied between 20 GeV and 500
GeV, and the average vertical muon charge ratio is found to be 1.285 +- 0.003
(stat.) +- 0.019 (syst.).Comment: Total 32 pages, 9Figure
Holographic \Lambda(t)CDM model in a non-flat universe
The holographic CDM model in a non-flat universe is studied in
this paper. In this model, to keep the form of the stress-energy of the vacuum
required by general covariance, the holographic vacuum is enforced to exchange
energy with dark matter. It is demonstrated that for the holographic model the
best choice for the IR cutoff of the effective quantum field theory is the
event horizon size of the universe. We derive the evolution equations of the
holographic CDM model in a non-flat universe. We constrain the
model by using the current observational data, including the 557 Union2 type Ia
supernovae data, the cosmic microwave background anisotropy data from the 7-yr
WMAP, and the baryon acoustic oscillation data from the SDSS. Our fit results
show that the holographic CDM model tends to favor a spatially
closed universe (the best-fit value of is -0.042), and the 95%
confidence level range for the spatial curvature is .
We show that the interaction between the holographic vacuum and dark matter
induces an energy flow of which the direction is first from vacuum to dark
matter and then from dark matter to vacuum. Thus, the holographic
CDM model is just a time-varying vacuum energy scenario in which
the interaction between vacuum and dark matter changes sign during the
expansion of the universe.Comment: 8 pages, 4 figures. version for publication in EPJC. arXiv admin
note: text overlap with arXiv:1112.235
Evaluation of water resources conserved by forests in the Hani rice terraces system of Honghe County, Yunnan, China: an application of the fuzzy comprehensive evaluation model
Measurement of multi-wall carbon nanotube penetration through a screen filter and single-fiber analysis
ISSN:1388-0764ISSN:1572-896
Two 2-D layered coordination polymers based on 5-aminoisophthalate and 1,10-phenanthroline
Evaluation of a practical expert defined approach to patient population segmentation: A case study in Singapore
10.1186/s12913-017-2736-8BMC Health Services Research17177
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