38,637 research outputs found
The density, construction and drag coefficient of electrostatic volcanic ash aggregates.
No full textRecent laboratory experiments have demonstrated that electrostatic charges generated during the fragmentation of volcanic pumice cause rapid aggregation of the silicate particles produced. Here, we present measurements of the mass and component particle size distribution of individual, electrostatically bound aggregates produced during these experiments. Particles produced by fracturing pumice aggregated as they fell ∼1.5 m within an enclosed fall chamber. Aggregate mass measurements indicate aggregate densities of ∼200 kg m−3 or less. The component particle size analysis demonstrates exponential-type cumulative distributions which are dominated (on a volume basis) by particles ∼10–40 μm in diameter and contain few particles >70 μm. By representing these particles as disks of 5 μm thickness the calculated aggregate densities are in agreement with those derived from the aggregate mass measurements and indicate a relatively constant aggregate density with size (in contrast with previous results from fall velocities). Combining the density measurements with fall velocity data allows the drag coefficient of aggregates to be determined. Empirical equations developed to describe the particle size distribution within aggregates are used to derive relative aggregation coefficients for the electrostatic aggregation process. Our results can be used within numerical models of volcanic plumes in order to improve their representation of electrostatic aggregation processes
The origin and early development of wheat glutenin particles
No full textBreadmaking quality is strongly related to the glutenin macropolymer (GMP) fraction. Don and co-workers [Don, C., Lichtendonk, W.J., Plijter, J.J., Hamer, R.J., 2003a. Glutenin macropolymer: a gel formed by particles. Journal of Cereal Science 37, 1¿7] showed that GMP consists of spherical glutenin particles and suggested that these originate from the protein bodies (PBs) observed in developing grain. We have tested this hypothesis by systematically comparing SDS-soluble and SDS-insoluble protein fractions from both PBs and flour. These preparations were analysed at the molecular, oligomer, particle and microscopic levels. Comparison of PBs isolated from immature seeds with glutenin particles isolated from mature seeds revealed strong similarities in protein composition and the presence of large glutenin oligomers. However, the glutenin particles from mature wheat were significantly larger than PBs. We suggest that PBs are the building blocks for the formation of much larger glutenin particles which are formed during the desiccation phase of kernel development
African origin of the malaria parasite Plasmodium vivax.
No full textPlasmodium vivax is the leading cause of human malaria in Asia and Latin America but is absent from most of central Africa due to the near fixation of a mutation that inhibits the expression of its receptor, the Duffy antigen, on human erythrocytes. The emergence of this protective allele is not understood because P. vivax is believed to have originated in Asia. Here we show, using a non-invasive approach, that wild chimpanzees and gorillas throughout central Africa are endemically infected with parasites that are closely related to human P. vivax. Sequence analyses reveal that ape parasites lack host specificity and are much more diverse than human parasites, which form a monophyletic lineage within the ape parasite radiation. These findings indicate that human P. vivax is of African origin and likely selected for the Duffy-negative mutation. All extant human P. vivax parasites are derived from a single ancestor that escaped out of Africa
The M, E, and N structural proteins of the severe acute respiratory syndrome coronavirus are required for efficient assembly, trafficking, and release of virus-like particles
No full textCopyright @ 2008 American Society for Microbiology.The production of virus-like particles (VLPs) constitutes a relevant and safe model to study molecular determinants of virion egress. The minimal requirement for the assembly of VLPs for the coronavirus responsible for severe acute respiratory syndrome in humans (SARS-CoV) is still controversial. Recent studies have shown that SARS-CoV VLP formation depends on either M and E proteins or M and N proteins. Here we show that both E and N proteins must be coexpressed with M protein for the efficient production and release of VLPs by transfected Vero E6 cells. This suggests that the mechanism of SARS-CoV assembly differs from that of other studied coronaviruses, which only require M and E proteins for VLP formation. When coexpressed, the native envelope trimeric S glycoprotein is incorporated onto VLPs. Interestingly, when a fluorescent protein tag is added to the C-terminal end of N or S protein, but not M protein, the chimeric viral proteins can be assembled within VLPs and allow visualization of VLP production and trafficking in living cells by state-of-the-art imaging technologies. Fluorescent VLPs will be used further to investigate the role of cellular machineries during SARS-CoV egress.The University of Hong Kong and the French Ministry of Health
How Classical Particles Emerge from the Quantum World.
No full textThe symmetrization postulates of quantum mechanics (symmetry for bosons, antisymmetry for fermions) are usually taken to entail that quantum particles of the same kind (e.g., electrons) are all in exactly the same state and therefore indistinguishable in the strongest possible sense. These symmetrization postulates possess a general validity that survives the classical limit, and the conclusion seems therefore unavoidable that even classical particles of the same kind must all be in the same state--in clear conflict with what we know about classical particles. In this article we analyze the origin of this paradox. We shall argue that in the classical limit classical particles emerge, as new entities that do not correspond to the "particle indices" defined in quantum mechanics. Put differently, we show that the quantum mechanical symmetrization postulates do not pertain to particles, as we know them from classical physics, but rather to indices that have a merely formal significance. This conclusion raises the question of whether the discussions about the status of identical quantum particles have not been misguided from the very start
Observations of meteoric material and implications for aerosol nucleation in the winter Arctic lower stratosphere derived from in situ particle measurements
No full textNumber concentrations of total and non-volatile aerosol particles with size diameters >0.01 μm as well as particle size distributions (0.4–23 μm diameter) were measured in situ in the Arctic lower stratosphere (10–20.5 km altitude). The measurements were obtained during the campaigns European Polar Stratospheric Cloud and Lee Wave Experiment (EUPLEX) and Envisat-Arctic-Validation (EAV). The campaigns were based in Kiruna, Sweden, and took place from January to March 2003. Measurements were conducted onboard the Russian high-altitude research aircraft Geophysica using the low-pressure Condensation Nucleus Counter COPAS (COndensation PArticle Counter System) and a modified FSSP 300 (Forward Scattering Spectrometer Probe). Around 18–20 km altitude typical total particle number concentrations nt range at 10–20 cm−3 (ambient conditions). Correlations with the trace gases nitrous oxide (N2O) and trichlorofluoromethane (CFC-11) are discussed. Inside the polar vortex the total number of particles >0.01 μm increases with potential temperature while N2O is decreasing which indicates a source of particles in the above polar stratosphere or mesosphere. A separate channel of the COPAS instrument measures the fraction of aerosol particles non-volatile at 250°C. Inside the polar vortex a much higher fraction of particles contained non-volatile residues than outside the vortex (~67% inside vortex, ~24% outside vortex). This is most likely due to a strongly increased fraction of meteoric material in the particles which is transported downward from the mesosphere inside the polar vortex. The high fraction of non-volatile residual particles gives therefore experimental evidence for downward transport of mesospheric air inside the polar vortex. It is also shown that the fraction of non-volatile residual particles serves directly as a suitable experimental vortex tracer. Nanometer-sized meteoric smoke particles may also serve as nuclei for the condensation of gaseous sulfuric acid and water in the polar vortex and these additional particles may be responsible for the increase in the observed particle concentration at low N2O. The number concentrations of particles >0.4 μm measured with the FSSP decrease markedly inside the polar vortex with increasing potential temperature, also a consequence of subsidence of air from higher altitudes inside the vortex. Another focus of the analysis was put on the particle measurements in the lowermost stratosphere. For the total particle density relatively high number concentrations of several hundred particles per cm3 at altitudes below ~14 km were observed in several flights. To investigate the origin of these high number concentrations we conducted air mass trajectory calculations and compared the particle measurements with other trace gas observations. The high number concentrations of total particles in the lowermost stratosphere are probably caused by transport of originally tropospheric air from lower latitudes and are potentially influenced by recent particle nucleation
ASEAN Rules of Origin: Lessons and Recommendations for Best Practice
No full textRules of Origin (ROO) set the criteria in determining the nationality of a product and where a product was made. The importance of ROO has increased in the past years as more countries engage in Free Trade Agreements (FTAs) and begun treating goods differently according to where the product was made, along with trade-specific preferences or restrictions to the imported good once its origin is determined. This study is done to cull the lessons from ASEAN's experience in determining and implementing the Rules of Origin. It draws the important lessons and makes recommendations for best practice that would contribute to the cooperation and integration efforts in the region. The paper examines the various design and implementation practice in ROO regimes, focusing on RTAs where the ASEAN is involved. The paper presents findings from recent studies on the cost of ROO compliance and the FTA utilization rates. It concludes with recommendations on simplification of ROO and some reforms on administrative procedures, bringing in the development country dimension, and some general guidelines to follow to improve ROOs.Rules of Origin, Free Trade Agreements, ASEAN.
Replication Data for: Recycling Diesel Soot Particles for Use as Activated Carbon in Li Ion Batteries [Dataset landing page Title]
No full textUSDOT Grant 69A3551747114National Transportation Library (NTL) Curation Note: As this dataset is preserved in a repository outside U.S. DOT control, as allowed by the U.S. DOT's Public Access Plan (https://doi.org/10.21949/1503647) Section 7.4.2 Data, the NTL staff has performed NO additional curation actions on this dataset. The current level of dataset documentation is the responsibility of the dataset creator. NTL staff last accessed this dataset at its repository URL on 2022-11-11. If, in the future, you have trouble accessing this dataset at the host repository, please email [email protected] describing your problem. NTL staff will do its best to assist you at that time.This report documents the successful capture and reuse of diesel exhaust soot particles as a conductive additive in lithium manganese oxide (LMO) and lithium iron phosphate (LFP) cathodes in Li-ion batteries. This approach enables an abundant toxic pollutant to be converted into a valuable material for energy storage devices. This study consists of an initial characterization of the diesel soot particles, a high-temperature annealing step to remove residual organics and unburned hydrocarbons, and characterization of the electrical performance in a Li-ion battery configuration. Here, composite electrodes are fabricated by mixing active materials (LFP or LMO) with conductive carbon and binders. The performance of the diesel soot particles as conductive additives is compared with that of commercially available activated carbon (i.e., Super P\uae). The current evolution of the composite electrode made with diesel soot particles demonstrates comparable performance to the electrodes containing the Super P\uae carbon. Based on high-resolution transmission electron microscope (HRTEM) images and scanning mobility particle sizer (SMPS) spectra, it is found that these diesel soot nanoparticles follow a narrow log-normal distribution centered around 100 nm in diameter and consist of highly porous amorphous carbon, which provide a large surface-to-volume ratio, making them ideal candidates for electrode materials in Li ion batteries. The total size of the described zip file is 22.4 MB. TIF files are high quality images files that can be viewed using the system's photo viewer. PNG files can be opened using the system's photo viewer. Docx files are document files created in Microsoft Word. These files can be opened using Microsoft Word or with an open source text viewer such as Apache OpenOffice. An .OPJ file is a project file created by the graphing software Origin. To open this file, open it using Origin or an open source alternative such as LabPlot
Propulsion of polymer particles on caesium ion-exchanged channel waveguides for stem cell sorting applications
No full textOptical trapping of particles has become a powerful non-mechanical and nondestructive technique for precise particle positioning. The manipulation of particles in the evanescent field of a channel waveguide potentially allows for sorting and trapping of several particles and cells simultaneously. In the evanescent field above an optical channel waveguide, particles experience three optical forces; i) a transverse gradient force, which acts in the direction of the intensity gradient, ii) a scattering force, which acts in the direction of the wave propagation and is proportional to the surface intensity and, iii) an absorption force, which is dependent upon the complex refractive index of the particle. A particle in the evanescent field will be propelled and trapped with a dependence on the intensity gradient (a property dependent upon the physical characteristic of the waveguide). A channel waveguide producing such an evanescent field can be photolithographically defined on a glass substrate and thus has the potential to be integrated into a single chip device.This thesis describes the studies carried out, both theoretically and experimentally, to establish optimum waveguide fabrication conditions and the experimental requirements to ultimately allow for the separation of polymer particles and mammalian cells according to their size and refractive index. Theoretical aspects of the interaction of particles and cells on surfaces were evaluated and their Brownian motion was investigated. Optical channel waveguides of different characteristics have been fabricated using caesium ion-exchange process on soda-lime substrates. The propulsion of polymer particles has been achieved and characterised against different optical parameters, waveguide conditions and particle’s characteristics on different surfaces. The propulsion of lymphoblastoma cells was demonstrated and the trapping of teratocarcinoma cells was evaluated. These results provide evidence for the potential application of the system for trapping and sorting stem cells
The role of organic aerosols in homogeneous ice formation
No full textKärcher B, Koop T. The role of organic aerosols in homogeneous ice formation. ATMOSPHERIC CHEMISTRY AND PHYSICS. 2005;5(3):703-714.Recent field observations suggest that the fraction of organic-containing aerosol particles in ice cloud particles is diminished when compared to the background aerosol prior to freezing. In this work, we use model calculations to investigate possible causes for the observed behavior. In particular, homogeneous freezing processes in cooling air parcels containing aqueous inorganic particles and organic particles are studied with a detailed microphysical model. A disparate water uptake and resulting size differences that occur between organic and inorganic particles prior to freezing are identified as the most likely reason for the poor partitioning of organic aerosols into the ice phase. The differences in water uptake can be caused by changes in the relationship between solute mass fraction and water activity of the supercooled liquid phase, by modifications of the accommodation coefficient for water molecules, or by a combination thereof. The behavior of peak ice saturation ratios and total ice crystal number concentrations is examined, and the dependence of the results on cooling rate is investigated. Finally, processes are discussed that could possibly modify the homogeneous freezing behavior of organic particles
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