High-density Particles Research Articles

Morphological Characterization and Fusion Properties of Triglyceride-rich Lipoproteins Obtained from Cells Transduced with Hepatitis C Virus Glycoproteins

The density of hepatitis C virus (HCV) particles circulating in the blood of chronically infected patients and of cell-culture produced HCV is heterogeneous. Specific infectivity and fusion of low density particles are higher than those of high density particles. We recently characterized hybrid particles produced by Caco-2 colon or Huh-7.5 liver cells transduced with HCV E1 and E2 envelope glycoproteins. Caco-2-derived particles, called empty lipo-viral particles (eLVP), are composed of triglyceride-rich lipoproteins positive for apolipoproteins B (i.e. apoB100 and apoB48) and contain HCV E1 and E2. Here we aimed at characterizing the morphology and in vitro fusion properties of eLVP using electron microscopy and fluorescence spectroscopy. They displayed the aspect of beta-lipoproteins, and immunogold labeling confirmed the presence of apoB and HCV E1 and E2 at their surface. These particles are able to fuse with lipid bilayers (liposomes) in a fusion process leading to the coalescence of internal contents of triglyceride-rich lipoproteins particles and liposomes. Fusion was pH-dependent and could be inhibited by either Z-fFG, a peptide known to inhibit viral fusion, or by monoclonal antibodies directed against HCV E2 or the apolipoprotein moiety of the hybrid particle. Interestingly, particles derived from Huh-7.5 cells failed to display equivalent efficient fusion. Optimal fusion activity is, thus, observed when HCV envelope proteins are associated to apoB-positive hybrid particles. Our results, therefore, point to a crucial role of the E1 and E2 proteins in HCV fusion with a subtle interplay with the apolipoprotein part of eLVP.

Supersonic Beams at High Particle Densities: Model Description beyond the Ideal Gas Approximation

Supersonic molecular beams constitute a very powerful technique in modern chemical physics. They offer several unique features such as a directed, collision-free flow of particles, very high luminosity, and an unsurpassed strong adiabatic cooling during the jet expansion. While it is generally recognized that their maximum flow velocity depends on the molecular weight and the temperature of the working fluid in the stagnation reservoir, not a lot is known on the effects of elevated particle densities. Frequently, the characteristics of supersonic beams are treated in diverse approximations of an ideal gas expansion. In these simplified model descriptions, the real gas character of fluid systems is ignored, although particle associations are responsible for fundamental processes such as the formation of clusters, both in the reservoir at increased densities and during the jet expansion. In this contribution, the various assumptions of ideal gas treatments of supersonic beams and their shortcomings are reviewed. It is shown in detail that a straightforward thermodynamic approach considering the initial and final enthalpy is capable of characterizing the terminal mean beam velocity, even at the liquid-vapor phase boundary and the critical point. Fluid properties are obtained using the most accurate equations of state available at present. This procedure provides the opportunity to naturally include the dramatic effects of nonideal gas behavior for a large variety of fluid systems. Besides the prediction of the terminal flow velocity, thermodynamic models of isentropic jet expansions permit an estimate of the upper limit of the beam temperature and the amount of condensation in the beam. These descriptions can even be extended to include spinodal decomposition processes, thus providing a generally applicable tool for investigating the two-phase region of high supersaturations not easily accessible otherwise.

NAD + hydrogenation on Au electrode deposited on modified glassy carbon

Gold nanoparticles(AuNP) were electrodeposited on a glassy carbon(GC) which was electrochemically modified by potentiodynamic cyclic polarization in acidic medium. The AuNP deposits were characterized by scanning electron microscopy, cyclic voltammetry, chronoamperometry and linear sweep voltammetry. Results of these studies showed that very small sized AuNP are deposited with significantly high particle density which is attributed to the surface modification of GC. The resulted AuNP/GC electrode showed high catalytic activity for electrochemical reduction of NAD + to NADH, indicating its potential for electrocatalytic applications.

Hydrodynamic predictions of dense gas–particle flows using a second-order-moment frictional stress model

Based on the Eulerian–Eulerian two-fluid continuum approach, an improved unified second-order-moment two-phase turbulence model combining with the kinetic theory of particle collision frictional stress model is developed to simulate the dense gas–particle flows in downer, where the effective coefficient of restitution is incorporated into the particle–particle collision. The interaction term between gas and particle turbulence is fully taken into account by the transport equation of two-phase stress correlation. Hydrodynamics of high density particle flow, measured by Wang et al. [27] are predicted and the simulated results are in good agreement with experimental data. On the conditions of considering the realistic energy dissipation due to frictional stress, particle concentration and particle axial averaged velocity are closely the measured and they are better than without frictional stress model. Furthermore, the particle Reynolds stress is redistributed and the particle temperature is reduced. Effect of frictional stress leads to increase obviously the collision frequency at the outlet and inlet regions and the magnitude of frequency of particle collisions is 102.

Commissioning and performance of the LHCb outer tracker

The LHCb experiment is a single arm spectrometer, designed to study CP violation in B-decays at the Large Hadron Collider (LHC). It is crucial to accurately and efficiently detect the charged decay particles, in the high-density particle environment of the LHC. For this, the Outer Tracker was constructed, consisting of ∼ 55 , 000 straw tubes, covering in total an area of 360 m 2 of double layers. The detector is foreseen to operate under large particle rates, up to 100 kHz/cm in the region closest to the beam. The front-end electronics is expected to provide the precise (0.5 ns) drift-time measurement, at an average occupancy of 5% and at 1 MHz trigger rate. At the time of the conference, the detector has been commissioned with cosmic-ray events and with the first LHC beam collision data. After dedicated studies to establish timing and spatial alignment, the first results on the detector performance (efficiency, resolutions, etc.) have been obtained.

Regulation of cholesterol efflux by amyloid β secretion

Amyloid beta (Abeta) is a key molecule in the pathogenesis of Alzheimer's disease, but its physiological function remains unclear. Abeta is produced from amyloid precursor protein (APP) by beta- and gamma-secretases, which is enhanced by high levels of cellular cholesterol, so cholesterol is a risk factor for Alzheimer's disease. This linkage led us to hypothesize that Abeta is produced to regulate cellular cholesterol levels in response to high-cholesterol stimulation. Here we show that Abeta production caused a reduction of cellular cholesterol levels in transfected HEK293 cells and neuronal IMR-32 and Neuro2a cells, which was accompanied by an increase in efflux of cholesterol from cells. Fractionation of the culture media by ultracentrifugation and subsequent immunoelectron microscopic observation revealed that Abeta assembled high-density lipoprotein-like particles with cellular cholesterol during its secretion. This assembly was mediated by the ATP-binding cassette transporter A1. APP transgenic and knockout mice exhibited lower and higher levels of cellular cholesterol in their brains, suggesting that Abeta-mediated regulation of cellular cholesterol is physiological. Furthermore, we found that, when injected into mouse cerebral ventricle, reconstituted lipoproteins with Abeta were excreted into the peripheral tissues more efficiently than those without Abeta. This result suggests that Abeta mediates cholesterol transport from the brain to the circulation. We propose, based on these findings, a novel, apolipoprotein-like function for Abeta that is involved in maintenance of cellular and cerebral cholesterol homeostasis.

Effects of different additives on bimetallic Au–Pt nanoparticles electrodeposited onto indium tin oxide electrodes

Bimetallic Au–Pt nanoparticles (Au–Pt NPs) have been synthesized using an electrochemical reduction approach. The effects of the addition of different additives in the electrodeposition bath namely KI, 1-nonanesulfonic acid sodium salt and Triton X-100 have been investigated. The structural characterization of the bimetallic nanoparticles has been carried out using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV–vis spectroscopy, X-ray diffraction (XRD) and cyclic voltammetry (CV). The Au–Pt NPs prepared in the presence of KI and Triton X-100 characterized by a relatively narrow size distribution as well as a higher particle density and surface coverage whereas no changes in the morphology were observed. These results suggest a dependence of the size and distribution of the bimetallic nanoparticles from the type and concentration of the additives employed.

Fatigue Crack Growth Behavior in a Rolled Plate of Aluminum Alloy

Aluminum alloys generally contain constituent particles. The population density and size these particles are important while considering fatigue performance. In present study, the crack growth process in stage II in the rolled plate of a high strength aluminum alloy AA 2219 was studied on samples prepared along the rolling direction. A three fold approach was adopted to understand the fatigue crack growth process: i) microstructural analysis ii) fatigue testing iii) post-fracture analysis. Microstructural analysis revealed a high density of constituent particles in the material. EDS analysis showed that the particles were mainly of CuAl2 type. However, particles with high concentration of Fe and Mn were also present in the material. Fatigue crack propagation tests were performed by using middle tension (MT) specimens prepared in rolling direction under constant amplitude loads. The da/dN vs ΔK plot on log-log scale showed a sigmoidal shape with a sharp increase of crack growth rate in the steady state regime. Topographical features were studied to understand the interaction of fatigue crack with the microstructural features. Post fracture analysis revealed that the macro fracture appearance changed with the change of stress level. However, the general mechanism of crack growth, in all the stress levels studied, was by formation of striations. At lower stress levels almost flat region with striations is present upto the final fracture. The crack growth surface showed crystallographic features with crack propagation almost perpendicular to the loading direction. However, a comparatively tortuous fatigue region was evident in the sample tested at high level of stress. The observation of crack path surface at high magnification did not reveal any influence of particles on the crack growth process. However, in sections taken from the fractured samples cracking and debonding of the constituent particles was observed near the fatigue crack path.

Optimization of sub-Doppler absorption contour in gas-dynamic beams

The formation of the Doppler contour PD(?) of absorption lines upon the excitation of particles in the volume of a gas-dynamic beam by light propagating in a direction orthogonal (reduced) to the beam axis is analyzed. Integral representations of PD(?) are obtained for arbitrary relations between the nozzle outlet diameter D and the collimating aperture diameter B in the excitation region are obtained. An optimal configuration at which the reduced Doppler contour is the narrowest at a high density of beam particles is revealed to be B/D = 2.

Influence of precipitation on dislocation substructure and creep properties of P91 steel weld joints

Two trial weld joints were prepared using the GTAW and SMAW methods and they underwent creep testing at temperatures between 525 and 625°C. The longest time to rupture was 45,811 h. Two main processes occurred during creep exposures: recovery and precipitation of secondary phases. Slight coarsenings of the M23C6 carbide, precipitation of Laves phase and Z-phase were observed after long tests at high temperatures. Some differences in microstructure and creep failure were found in the individual zones of weldments. After long exposure at temperatures up to 600°C, fractures occurred in the fine-grain heat-affected zone as a result of a low density of fine vanadium nitride and a high density of coarse particles at grain and subgrain boundaries. At 625°C, growth of Laves phase caused a softening of the ferritic matrix and crack propagation in the weld metal.

Particle Densities and Distributions in Cloud Lightning Channels

AbstractAccording to the plasma theories, the temperature and electron density are calculated based on the wavelengths, relative intensities and transition parameters of lines in cloud lightning spectra which have been obtained on the Tibetan plateau. By using Saha equations, electric charge conservation equations and particle conservation equations, the particle densities in every ionized‐state, the mass density, pressure and the average ionizability of discharge channel are obtained. Moreover, the characteristics of particle distributions in each discharge channel are analyzed. The results show that cloud lightning channels are almost completely ionized, and the most particles are singly ionized while NII has the highest particle density. In general, the particle densities and relative concentrations of different channel positions also have positive correlations with temperatures except for NII, OII and ArII, of which relative concentrations show tiny tendencies of becoming low along with the temperature increasing. Differing from cloud‐to‐ground lightning, the particle densities of different positions along the same cloud discharge channel change in a bigger range but show no regularities. The pressures of channels change from a few tenths of one MPa to several MPa.

The enhanced aerosol performance of salbutamol from dry powders containing engineered mannitol as excipient

The aim of the present study was to investigate the effect of crystallising mannitol from different binary mixtures of acetone/water on the resultant physical properties and to determine the effects of any changes on in vitro aerosolisation performance, when the different mannitol crystals were used as a carrier in dry powder inhaler formulations containing salbutamol sulphate. Mannitol particles were crystallised under controlled conditions by dissolving the sugar in water and precipitating the sugar using binary mixtures of acetone/water in different percentages as anti-solvent media. For comparison purposes the physical properties and deposition behaviour of commercially available mannitol were also studied. SEM showed that all crystallised mannitol particles were more elongated than the commercial mannitol. Solid state studies revealed that commercial mannitol and mannitol crystallised using acetone in the presence of 10–25% v/v water as anti-solvent was β-polymorphic form whereas mannitol crystallised in the presence of a small amount of water (0–7.5%) was the α-form. All the crystallised mannitol samples showed poor flowability. Nevertheless, the powdered crystallised mannitol and commercial samples were blended with salbutamol in the ratio 67.5:1. The aerosolisation performance of the formulations containing the engineered mannitol (evaluated using Multi Stage Liquid Impinger) was considerably better than that of the commercial mannitol formulation (the fine particle fraction was increased from 15.42% to 33.07–43.99%, for the formulations containing crystallised mannitol). Generally, carriers having a high tapped density and high fraction of fine carrier particles produced a high FPF. The improvement in the DPI performance could be attributed to the presence of elongated carrier particles with smooth surfaces since these are believed to have less adhesive forces between carrier and the drug resulting in easier detachment of the drug during the inhalation.

Palladium nanostructures from galvanic displacement as hydrogen peroxide sensor

Electroless plating of palladium on silicon has been developed, resulting in the formation of palladium films and nanoparticles. The deposition process has been monitored by atomic and Kelvin probe force microscopies (AFM/KPFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) in order to understand the deposition mechanism. A fabrication process is developed to yield a high density of Pd particles, while ensuring the formation of a palladium thin film underneath. The formed substrates have been used as amperometric sensors without further modification for the determination of hydrogen peroxide concentrations. The substrates are found to exhibit excellent linear electrocatalytic response down to the micromolar range and under an applied potential of 0.0 V, with the lowest quantifiable concentration of 1 μM. The simplicity in substrate fabrication coupled with the potential for integration in microfabrication processes, as well as the low applied potential needed in the measurements, offers the possibility of using the device in enzymatic biosensors with low interference signals.

Physical Properties of Ground Parboiled Fresh Rice Hulls Used as a Horticultural Root Substrate

Fresh parboiled rice hulls ground in a hammer mill and screened through a 1.18-mm screen and collected on a 0.18-mm screen (RH3) and particles with a specific diameter of 0.5 to 1.0 mm had total pore space (TPS), air-filled pore space (AFP), and water-holding capacity (WHC) similar to that of Canadian sphagnum peat (peat). However, RH3 had more available water, a higher bulk density (BD), and a higher particle density (PD) than peat. When blended with 20% to 40% perlite or 1 cm aged pine bark, RH3-based substrates had lower TPS, similar AFP, and lower WHC than equivalent peat-based substrates. The RH3-containing substrates had higher BD and average PD than equivalent peat-based substrates. When blended with parboiled rice hulls (PBH), RH3-based substrates had lower TPS than equivalent peat-based substrates. When blended with 20% to 40% PBH, RH3-based substrates had lower AFP than equivalent peat-based substrates. RH3-based substrates containing up to 20% PBH had lower WHC than equivalent peat-based substrates. RH3-based substrates containing 40% PBH had a higher WHC than equivalent peat-based substrates. When blended with PBH, all RH3-based substrates had higher BD and average PD than equivalent peat-based substrates. The addition of 40% RH3 to a peat-based substrate containing 20% perlite decreased substrate TPS, whereas the addition of 10% to 40% decreased AFP. The addition of 10% to 30% RH3 increased WHC. The addition of 30% RH3 to a peat-based substrate containing 20% 1 cm aged pine bark decreased substrate TPS and the addition of 20% to 40% RH3 decreased AFP. The addition of 10% RH3 increased WHC, but the addition of 20% or more RH3 did not affect WHC. The addition of 30% RH3 increased the BD, but the addition of RH3 had no effect on average PD. The addition of 20% or more and 30% or more RH3 to a peat-based substrate containing 20% PBH decreased substrate TPS and AFP, respectively. The addition 20% RH3 decreased WHC. The addition of 10% to 40% RH3 increased BD. Overall, RH3 was the ground rice hull product that had physical properties most similar to peat. Peat-based substrates in which up to 40% of the peat was replaced with RH3 had physical properties that, although different from peat controls, were within commonly recommended ranges for substrates used to grow greenhouse crops.

The Rab11 Pathway Is Required for Influenza A Virus Budding and Filament Formation

Influenza A virus buds through the apical plasma membrane, forming enveloped virus particles that can take the shape of pleomorphic spheres or vastly elongated filaments. For either type of virion, the factors responsible for separation of viral and cell membranes are not known. We find that cellular Rab11 (a small GTP-binding protein involved in endocytic recycling) and Rab11-family interacting protein 3 ([FIP3] which plays a role in membrane trafficking and regulation of actin dynamics) are both required to support the formation of filamentous virions, while Rab11 is additionally involved in the final budding step of spherical particles. Cells transfected with Rab11 GTP-cycling mutants or depleted of Rab11 or FIP3 content by small interfering RNA treatment lost the ability to form virus filaments. Depletion of Rab11 resulted in up to a 100-fold decrease in titer of spherical virus released from cells. Scanning electron microscopy of Rab11-depleted cells showed high densities of virus particles apparently stalled in the process of budding. Transmission electron microscopy of thin sections confirmed that Rab11 depletion resulted in significant numbers of abnormally formed virus particles that had failed to pinch off from the plasma membrane. Based on these findings, we see a clear role for a Rab11-mediated pathway in influenza virus morphogenesis and budding.

Effect of Electron Density of Pt Catalysts Supported on Alkali Titanate Nanotubes in Cinnamaldehyde Hydrogenation

Pt nanoparticles of diameter 0.5−1.5 nm were dispersed homogeneously on the inner and outer surfaces of alkali metal titanate nanotubes (M2Ti3O7, M = Li+, Na+, and K+) by ion exchange with Pt(NH3)2Cl2 followed by calcination in ambient air at 673 K and reduction in H2 at 448 K. Both XPS and DRIFTS revealed that these titanate nanotubes donated their electrons to the Pt particles, yielding a negative Pt oxidation state, and that the degree of electron donation increased with the size of the alkali metal cation. The high electron density of the Pt particles promoted the activation of both C═C and C═O functional groups in cinnamaldehyde. Therefore, the order of the catalytic activity in the hydrogenation of cinnamaldehyde was Pt/KTNTs > Pt/NaTNTs > Pt/LiTNTs. Since the Pt particles were very small, Pt/MTNTs selectively hydrogenated the C═C bond, yielding a hydrocinnamaldehyde with selectivities of 80−87% (at cinnamaldehyde conversions of 27−50%). The alkali metal ions of the titanate nanotubes were able to modify the mode of adsorption of cinnamaldehyde. Therefore, when a KOH promoter was added to the reaction mixture, cinnamyl alcohol became the main product and the cinnamyl alcohol selectivities were 77−83% (at cinnamaldehyde conversions of 49−74%).

The Front-End Electronics of the straw tube tracker for the LHCb experiment

The LHCb experiment is a single-arm spectrometer, designed to study CP violation in B-decays at the Large Hadron Collider (LHC). It is crucial to accurately and efficiently track the charged decay products, in the high-density particle environment of the LHC. For this, the Outer Tracker has been constructed, consisting of ∼55,000 straw tubes, distributed over a sensitive area of 12 double layers of 6×5m2 each. The detector is foreseen to operate up to 100kHz/cm per straw in the region closest to the beam. The task of the Front-End Electronics is to provide the precise (0.5ns) drift-time measurement, at an average occupancy of 5% and at a 1MHz trigger rate. The tracking procedure requires high-efficiency (low thresholds), while at the same time putting stringent limits on the noise level. The modular detector structure reflects on the FE electronics: 128 channels are read out by one FE “Box”. The mass production and installation of 450 FE-Boxes is completed. Quality checks have been performed in several stages, at the level of individual boards and at the global level with dedicated test systems mimicking the real detector and capable of simulating all the readout functionalities. At the time of the conference, all FE electronics has been commissioned in situ with test-pulses, cosmic rays and the with first beam events from LHC. No dead channels and very few noisy channels have been found. An upgrade is currently under study, aiming at digitizing and reading out events at each beam-crossing.

Characterization of Beach Sedimentary Environments in the Batinah Region, Oman

In this study, 252 surface sediment samples were collected for sand properties from three sites on the North Batinah coast: Harmul, North of Sohar industrial area, Majees South of Sohar industrial area and Zafaran 9 km South of Majees. Sampling was conducted in four occasions: November 2005, February 2006, June 2006 and November 2006. Almost, 52% of all samples were unimodal, 32% were bimodal and 16% were polymodal. June 2006 samples had a higher particle density than November 2006 samples. This is most probably due to rework and suspension, which lead to removal of light particles from the upper layer of the beach and high density particles to be concentrated in the bottom layer in June 2006 and deposition of light fraction of lower density in November 2006. Only Harmul samples had a significant difference between June 2006 samples and November 2006 samples in bulk density. The difference between the two sets in percentage water by volume was significant in Harmul and Zafaran but not in Majees. All sites showed significant difference between the two sets in percentage of air filled porosity and percentage of saturation. However, the sand pattern was the same in the three sites.

Installation and commissioning of a high-efficiency and high-resolution straw tube tracker for the LHCb experiment

The LHCb experiment is a single arm spectrometer, designed to study CP violation in B-decays at the Large Hadron Collider (LHC). It is crucial to accurately and efficiently detect the charged decay particles, in the high-density particle environment of the LHC. For this, the Outer Tracker (OT) was constructed, consisting of ∼55,000 straw tubes, covering in total an area of 360m2 of double layers. The detector is foreseen to operate under large particle rates, up to 100kHz/cm per straw in the region closest to the beam. The front-end electronics is expected to provide the precise (0.5ns) drift-time measurement, at an average occupancy of 5% and at 1MHz trigger rate. The tracking procedure requires high-efficiency (low thresholds), while at the same time putting stringent limits on the noise level. The modular detector structure reflects on the FE electronics: 128 channels are read out by one FE Box. During installation, the dark current, the response to radioactive sources, and the gas-tightness of all detector units was checked and only a handful of bad channels were found. Special hardware and dedicated procedures, integrated within the experimental control system, have been designed for the detector calibration during data taking. At the time of the conference, the detector has been installed and commissioned with the help of cosmic rays events producing tracks through OT. During the first days of the LHC commissioning, the detector was operated on nominal voltage and large-multiplicity events originating at the circulating beam were recorded and studied.

The use of peat granules in a fluidized bed bioreactor

AbstractThis study describes the particle characteristics and fluidized hydrodynamics of peat granules. Peat granules, moistened with water, are a potential packing material in a gas–solid fluidized bed bioreactor used for treating air pollution. Information on the fluidization of wet peat granules is lacking. In order to advance this new type of bioreactor and to scale up its design for industrial use, fluidization studies of suitable packing material are required. Using abiotic experiments, three sizes of peat granules have been fluidized with air and fluidization characteristics were observed at different superficial gas velocities. Relative to other biomass particles, peat granules have a high particle density and sphericity, which contributes to favourable fluidization behaviour, without gas channelling. Fluidization experiments demonstrate that as the mean size of peat particles increased, minimum fluidization velocity increased. Increasing the moisture content of the peat granules resulted in a transition from bubbling bed fluidization to poor fluidization behaviour. Other types of moist biomass particles such as sawdust are difficult to fluidize and typically exhibit Geldart group C behaviour. In contrast, it was observed that wet peat granules could be fluidized in a bubbling bed regime, typical of group B particles.