Seasonal Influence on Vapor-and Particle-Phase Polycyclic Aromatic Hydrocarbon Concentrations in School Communities Located in Southern California

Ambient concentrations of 15 vapor-and particle-phase (PM _2.5 ) polycyclic aromatic hydrocarbons (PAHs), listed by the US EPA as priority pollutants, were measured between July 2002 and November 2003 in six Southern California communities participating in a multi-year chronic respiratory health study of schoolchildren. The communities were geographically distributed over two hundred kilometers, extending from Long Beach in coastal Los Angeles, to high mountain areas to the north and west of the Los Angeles basin, and south into Eastern San Diego County. Seasonal and spatial variation in the atmospheric concentrations of PAHs is of interest because this class of compounds includes potent mutagens, carcinogens, and species capable of generating reactive oxygen species (ROS) that may lead to oxidative stress. Naphthalene accounted for 95% of the total PAH mass; annual averages ranged from 89 to 142 ng m ^{? 3} . Benzo[ghi]perylene (BGP) and the pro-carcinogen benzo[a]pyrene (BAP), present almost exclusively in the particle-phase, ranged respectively from 38 to 231 pg m ^?3 and 75 and 111 pg m ^{? 3} , with the highest values observed in Long Beach, a community with a high volume of seaport-related activities, and Lancaster, a commuter dormitory community. A considerable increase in the particle-phase PAH concentration, relative to the vapor-phase, was observed as ambient temperature decreased. Cold/hot season ratios for PAHs in PM _2.5 averaged 5.7, reaching 54 at Long Beach. The presented data underscore the importance of seasonal variations on atmospheric PAH concentrations. These observations are relevant to future interpretation and analysis of community-scale human health effects research.     

Analysis of Scanning DMA Transfer Functions

A new approach to determine transfer functions of scanning differential mobility analyzers (DMAs) is introduced. An expression for non-diffusive particle trajectories in a cylindrical DMA operating in a scanning voltage mode is obtained analytically. Particle trajectory simulations are then used to determine the scanning DMA transfer functions. The results suggest that the shape of the scanning DMA transfer functions may vary with mobility for scan times smaller than a certain value, which depends on the DMA flowrates, and this provides one criteria limiting the fastest scan possible with the conventional DMAs. A simple approach to determine upscan scanning DMA transfer functions in near real-time with minimal number of simulations is described. For upscan operation, the choice of the scantime is seen to impose upper and lower limits on the particle mobility range classified by a scanning DMA. The predicted effect of voltage scanning on altering DMA transfer functions is validated with fast scan experiments.     

Theoretical Modeling of Filtration by Nonuniform Fibrous Filters

Modeling commercial filter media using classical theories results in incorrect filter pressure drop and efficiencies and this is attributed to media inhomogeneity. The use of an arbitrary inhomogeneity factor is seen to be inadequate in accounting for the effect of operating conditions on the performance of inhomogeneous filter media. A simplistic theoretical modeling approach is described here to account for the variations in filter packing densities and to estimate their effect on the media particle capture characteristics. The theoretical modeling results are used in obtaining an equivalent filter packing density distribution from media local efficiency measurements. Considering this variation in the theoretical models is seen to result in better prediction of media performance over a wide range of operating conditions. The observed deviation of experimental efficiencies from the theory at smaller Peclet numbers can be explained from the results of the theoretical analysis.     

Novel Aerosol/Gas Inlet for Aircraft-Based Measurements

A novel inlet has been designed for selective sampling of gas and aerosol phases of volatile species from high-speed aircraft. A multistage flow system brings the flow nearly isokinetically towards the sampling port. Two small airfoil-shaped "blades" are placed close to the sample port to provide the flow conditions required for aerosol and gas sampling. Aerosols are sampled when these blades are positioned to operate the inlet as a counterflow virtual impactor (CVI). The design enables sampling of particles as small as 0.1 w m from a high-speed aircraft under stratospheric conditions, a substantial improvement over that possible with previous CVI designs. For gas sampling, one of the blades is moved by a stepper motor to occlude the inlet opening and gas is sampled perpendicular to the bulk flow. Boundary layer suction is used to prevent the sampled gas from coming in contact with the impactor walls. This is one of the first designs of an inlet that enables gas sampling free of wall contact. The inlet was flown on the NASA ER-2 aircraft during the SOLVE 2000 campaign to study aerosol/gas partitioning of nitric acid in the lower stratosphere. Data from the flight tests show that the inlet flow characteristics are broadly in agreement with computational fluid dynamics (CFD) simulations.     

Effect of dual reinforced ceramic particles on high temperature tribological properties of aluminum composites

The nature and distribution of hard ceramic particles in composite materials influences the properties to greater extent. In the present work, the role of hard ceramic reinforced particles on the tribological behaviour of aluminum metal matrix composites consisting of single (SRP) and dual reinforced particles (DRP) is studied at different temperatures. Zircon sand and silicon carbide particles of size 20–32 μm were used as reinforcement in commercial grade LM13 piston alloy. Composites of dual reinforced particles in aluminum matrix (DRP-AMCs) were developed by mixing 15 wt% reinforced particles by two step stir casting technique. The wear behaviour of DRP-AMCs and SRP-AMCs (single reinforced particles aluminum matrix composite) was investigated using a pin-on-disc method at high temperatures under dry sliding condition. The microstructural examination of developed composites shows globular and finely distributed eutectic silicon in the vicinity of the reinforced particles. Metallographic investigation revealed that the wear zone of the SRP composite consisted of a hardened layer, which is responsible for high wear loss observed in the SRP composite. The results further indicate a transition in the wear mode that occurs after 150 °C for all composites. Study reveals that the dual reinforcement of particles enhances the wear resistance as compared to single reinforced particles if mixed in a definite ratio. A combination of 3% zircon sand and 12% silicon carbide particle reinforced composite exhibits better wear resistance as compared to other combinations at all the temperatures for low and high loads both.     

Development of HDPE/EPDM‐g‐TMEVS nanocomposites with enhanced electrical and flame properties

Nanoclay reinforced HDPE/silane grafted EPDM composites have been developed using an epoxy functionalized HDPE as compatibilizer.The nanoclay has been varied from 0% to 10% in the composites along with the incorporation of compatibilizer and without compatibilizer in a brabender plasticorder.The dielectric and fire retardant properties of these nanocomposites have been examined. Addition of nanoclay enhanced char formation with increased values of limiting oxygen index. Electrical properties such as volume and surface Resistivity improved with addition of nanoclay and compatibilizer. The values of tan δ increased with increase in grafted EPDM and silanated nanoclay loading. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Cytogenetic analysis of quinoa chromosomes using nanoscale imaging and spectroscopy techniques

Here we present a high-resolution chromosomal spectral map derived from synchrotron-based soft X-ray spectromicroscopy applied to quinoa species. The label-free characterization of quinoa metaphase chromosomes shows that it consists of organized substructures of DNA-protein complex. The analysis of spectra of chromosomes using the scanning transmission X-ray microscope (STXM) and its superposition of the pattern with the atomic force microscopy (AFM) and scanning electron microscopy (SEM) images proves that it is possible to precisely locate the gene loci and the DNA packaging inside the chromosomes. STXM has been successfully used to distinguish and quantify the DNA and protein components inside the quinoa chromosomes by visualizing the interphase at up to 30-nm spatial resolution. Our study represents the successful attempt of non-intrusive interrogation and integrating imaging techniques of chromosomes using synchrotron STXM and AFM techniques. The methodology developed for 3-D imaging of chromosomes with chemical specificity and temporal resolution will allow the nanoscale imaging tools to emerge from scientific research and development into broad practical applications such as gene loci tools and biomarker libraries.     

On‐line mixing during injection and simultaneous curing in liquid composite molding processes

Liquid composite molding (LCM) processes such as resin transfer molding (RTM) and vacuum assisted RTM (VARTM) are used to manufacture high quality and net‐shape fiber reinforced composite parts. All LCM processes impregnate fiber preforms packed in a mold cavity with a thermoset resin. After the preform is fully saturated, the injection is discontinued but the resin continues to cure. Once the curing step is complete, the part is de‐molded. The resin has to be mixed with a curing agent to cure. Typically, the resin and the curing agent are mixed together in a pressure pot before the injection. This has several disadvantages, such as storage of large amounts of hazardous polymerizing resin, wastage, and cleaning of cured resin from the injection line. This paper proposes the implementation and calibration of an alternative to this technique. The approach is to mix the curing agent with the resin as the resin enters the mold through a separate system featuring two feed‐lines. Such a system will enable one to maintain a uniform gel time throughout the part by varying the mixing ratio of resin and the catalyst during the injection. An experimental study of such on‐line mixing to obtain simultaneous curing and to reduce the overall curing time is conducted and presented in this paper. Implementation of a control scheme that varies the curing agent during injection and its effect on cure time is benchmarked with the process in which the percentage of curing agent is held constant. The gel time for the fabricated parts was reduced by 20–25% by continuously varying the percentage of curing agent during injection. POLYM. COMPOS., 26:74–83, 2005. © 2004 Society of Plastics Engineers     

Design and Compressive Analysis of Junctionless Multigate FinFET Towards Low Power and High Frequency Applications

Silicon - Advances in microelectronics have enabled smaller technical nodes, lower threshold voltages, and greater working frequencies. Even though VLSI circuit performance and power consumption...     

Niobium oxide-activated yttrium barium titanate nanorod structured ceramics for energy storage applications

Structure, morphology, and electrical properties of 10 mol% of Nb₂O₅-activated yttrium barium titanate (BT) Ba_(60-z)Ti_(40-x)Nb_zY_xO₃ (BTY₁₀Nb₁₀), barium titanate (BT), and 10 mol% of Y₂O₃-activated BT were explored with calcination and sintering temperatures of 1000°C at 8 h and 1200°C at 6 h, respectively. The thermogravimetric and differential scanning calorimetry (TG–DSC) analysis reported that the total weight loss and residual mass of BT at 1300°C were 16.8 and 83.2%, respectively. The X-ray diffraction (XRD) pattern confirmed that BTY₁₀Nb₁₀ ceramics containing the BaNbO₃ phase were developed. A Raman band of BT at 307 cm^–1 unveiled a blue shift slightly for BTY₁₀ to 298 cm^–1 and for BTY₁₀Nb₁₀ to 306 cm^–1. Average pore area of the ferroelectric BTY₁₀Nb₁₀ was found to be 6.96 nm for the total scanning electron microscopy (SEM) image area of 20.31 nm. Formation of BT nanorods analyzed from transmission electron microscopy (TEM) has been reported in three samples that regulate surface roughness. Moreover, Nyquist diagram of BTY₁₀Nb₁₀ shows two overlapping semicircles as a function of frequency. Nanorod structures led to change the morphology and surface roughness. Recoverable energy storage density and energy storage efficiency were estimated as 2.63 µJ/cm³ and 57%, and BTY₁₀Nb₁₀ ferroelectric showed potential for energy storage applications due to changes in surface morphology and porosity.