Search

The phase states of primarily emitted and secondarily formed aerosols from gasoline vehicle exhausts were investigated by quantifying the particle rebound fraction (f). The rebound behaviors of gasoline vehicle emission-related aerosols varied with engines, fuel types, and photochemical aging time, showing distinguished differences from biogenic secondary organic aerosols. The nonliquid-to-liquid phase transition of primary aerosols emitted from port fuel injection (PFI) and gasoline direct injection (GDI) vehicles started at a relative humidity (RH) = 50 and 60%, and liquefaction was accomplished at 60 and 70%, respectively. The RH at which f declined to 0.5 decreased from 70 to 65% for the PFI case with 92# fuel, corresponding to the photochemical aging time from 0.37 to 4.62 days. For the GDI case, such RH enhanced from 60 to 65%. Our results can be used to imply the phase state of traffic-related aerosols and further understand their roles in urban atmospheric chemistry. Taking Beijing, China, as an example, traffic-related aerosols were mainly nonliquid during winter with the majority ambient RH below 50%, whereas they were mostly liquid during the morning rush hour of summer, and traffic-related secondary aerosols fluctuated between nonliquid and liquid during the daytime and tended to be liquid at night with increased ambient RH.

In the present work, we conducted experiments of secondary organic aerosol (SOA) formation from urban cooking and vehicular sources to characterize the mass spectral features of primary organic aerosol (POA) and SOA using an high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Our results showed that the cooking styles have a greater impact on aged COA (cooking organic aerosol) mass spectra than oxidation conditions. However, the oxidation conditions affect the aged HOA (hydrocarbon-like OA) spectra more significantly than vehicle operating conditions. In our study, we use mass spectra similarity analysis and positive matrix factorization (PMF) analysis to establish the POA and SOA mass spectra of these two sources. These mass spectra are used as source constraints in a multilinear engine (ME-2) model to apportion the OA (organic aerosol) sources in the atmosphere. Compared with the traditional ambient PMF results, the improved ME-2 model can better quantify the contribution of POA and SOA from cooking and vehicular sources. Our work, for the first time, establishes the vehicle and cooking SOA source profiles, and can be further used in the OA source apportionment in the ambient atmosphere.

In the present work, we conducted experiments of secondary organic aerosol (SOA) formation from urban lifestyle sources (cooking and vehicle) to characterize the mass spectral features of primary organic aerosol (POA) and SOA using an high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Our results showed that the cooking styles have greater impact on aged COA mass spectra than oxidation condition. However, the oxidation conditions affect the aged HOA spectra more significantly than vehicle operation conditions. In our study, we use mass spectra similarity analysis and positive matrix factorization (PMF) analysis to establish the POA and SOA mass spectra of these two typical lifestyle sources. These mass spectra are used as source constraints in a multilinear engine (ME-2) model to apportion the OA sources in the atmosphere. Comparing with the traditional ambient PMF results, the improved ME-2 model can better quantify the contribution of POA and SOA from life-style sources. Our work, for the first time, establishes the vehicle and cooking SOA source profiles, and can be further used in the OA source apportionment in the ambient atmosphere.

A project of 14C trace on deep water in South China Sea requires an accuracy of AMS radiocarbon measurement better than 2.5‰, which is higher than the accuracy for routine measurements of the NEC compact AMS system at Peking University. A series of modifications have enhanced the stability of the AMS system, minimizing fractionation effects and improving the accuracy and quality control of measurements. The ripple of terminal voltage has been reduced from 100 V to less than 50 V. The variation of beam currents from different samples is within 20% and a special tool is designed for proper installation of sample wheels. Measurements on standards and secondary samples demonstrate an improvement in accuracy to

Intermediate volatility organic compounds (IVOCs) have been proposed to be great contributors to SOA formation. In this study, we performed comprehensive measurement of ambient IVOCs and calculated their SOA production at an urban site Peking University Urban Atmospheric Environment Monitoring Stations (PKUERS). Results showed that the campaign-average concentration IVOCs was 62.5 ± 45.2 μg·m-3 (average ± standard deviation), which is comparable to the emission of VOCs. Only ~10% of the IVOCs could be speciated, with most of the IVOCs existing as unresolved complex mixture (UCM). Back trajectory analysis showed that clusters from near south has the highest IVOC concentration, suggesting the importance to control the IVOC emissions from the polluted regions of China. Using the OH exposure estimated by o-xylene to benzene and m/p-xylene to benzene, the estimated daily average SOA concentration was 5.8 ±3.4 μg·m-3, in which IVOCs contributed 15 times that of single-ring aromatics. The estimated vehicular-SOA could be 1.04 ± 0.7 μg·m-3. Considering its high SOA formation potential, this study highlights the importance to study the IVOC emissions in China.

Chassis dynamometer experiments were conducted to investigate the effect of vehicle speed and usage of ethanol-blended gasoline (E10) on formation and evolution of gasoline vehicular secondary organic aerosol (SOA) using a Gothenburg Potential Aerosol Mass (Go: PAM) reactor. The SOA forms rapidly, and its concentration exceeds that of primary organic aerosol (POA) at an equivalent photochemical age (EPA) of ~1 day. The particle effective densities grow from 0.62 ± 0.02 g cm−3 to 1.43 ± 0.07 g cm−3 with increased hydroxyl radical (OH) exposure. The maximum SOA production under idling conditions (4259–7394 mg kg-fuel−1) is ~20 times greater than under cruising conditions. There was no statistical difference between SOA formation from pure gasoline and its formation from E10. The slopes in Van Krevelen diagram indicate that the formation pathways of bulk SOA includes the addition of both alcohol/peroxide functional groups and carboxylic acid formation from fragmentation. A closure estimation of SOA based on bottom-up and top-down methods shows that only 16%–38% of the measured SOA can be explained by the oxidation of measured volatile organic compounds (VOCs), suggesting the existence of missing precursors, e.g. unmeasured VOCs and probably semivolatile or intermediate volatile organic compounds (S/IVOCs). Our results suggest that applying parameters obtained from unified driving cycles to model SOA concentrations may lead to large discrepancies between modeled and ambient vehicular SOA. No reduction in vehicular `SOA production is realized by replacing normal gasoline with E10.

The 14C level in annual plants is a sensitive tracer for monitoring fossil fuel derived CO2 in the atmosphere. Corn leave samples were selected from different regions of China, including high mountains in the Tibetan Plateau, grassland in Inner Mongolia, and inland and coastal cities during the summer of 2010. The 14C/12C ratio of the samples was measured with the NEC compact AMS system at the Institute of Heavy Ion Physics, Peking University. The fossil fuel derived CO2 was estimated by comparing the measured Δ14C values of corn leave samples to background atmospheric Δ14C level. The influences of topography, meteorological conditions and carbon cycling processes on the fossil fuel derived CO2 concentration are considered when interpreting the data. Our results show a clear association of the low Δ14C values with regions where human activities are intensive.

In order to investigate the origin and age of a bowl-shaped crater with 1.8 km diameter in northeastern China, a core drilling about 110 m in total was carried out in 2009 at the center of the crater. A 106-m-thick unit of lacustrine sediment is revealed under a surface layer of about 1 m of yellow soil. The impact origin has been confirmed based on geological analysis. In this paper, we report the AMS 14 C dating results of lacustrine sediment. The data suggest that the meteorite impact in Xiuyan happened more than 50,000 years ago and a two-section linear relationship of 14 C ages with the depth shows a stable sediment environment through the two time stages.

Milu (Elaphurus davidianus, Pere David’s deer) is one of the few species of large mammals that became extinct in the wild, but survived domestically. A good understanding of expansion and habitat is required if the reintroduction of Milu into the wild is to be implemented. Among the widely reported findings of Milu sub-fossils, only a small fraction have been dated. Here we report new AMS radiocarbon dates on Milu sub-fossil samples unearthed from two sites at Qingdun, Jiangsu and Fujiashan, Zhejiang in southeast China. These AMS 14C ages of Milu sub-fossils provide new evidence for the presence of Milu expansion in the lower reaches of the Yangtze River during the Holocene Optimum interval from 5000 yr BC to 3000 yr BC. These new ages also have important implications for the reconstruction of the paleoclimate and paleogeography during the Neolithic Period in southeast China.

An experimental technique for initially applied hydrostatic pressure in specimens subjected to axial impact has been developed to study the dynamic mechanical properties of materials. The technique was employed for the purpose of examining the dynamic mechanical properties of lead zirconate titanate (PZT) at zero to 15 MPa hydrostatic pressures. Experimental results unambiguously exhibit the ductile behavior of PZT when hydrostatic pressure is involved. The compressive strength is demonstrated sensitive to the initial hydrostatic pressure and the strain-rate. The fracture modes are analyzed by means of scanning electron microscopy (SEM). Moreover, a failure criterion based on Mohr–Coulomb failure theory is suggested to explain the brittle and ductile failure of PZT.

Cosmogenic 10Be is produced in the atmosphere, and deposits onto the surface of the earth mainly through wet precipitation and dust. Based on the analysis of 10Be in Chinese loess, we believe that 10Be in loess is composed of two components: locally precipitated atmospheric 10Be, and windblown 10Be adsorbed on the surface of silt grains. On the Loess Plateau, 10Be concentrations in loess and paleosol range from (1.4 to 2.8) × 108 atoms/g and (2.7 to 4.5) × 108 atoms/g, respectively. To investigate the sources of 10Be in loess, we measured 10Be in sand grains from deserts in western China and falling dust from the deposition regions. The results show that the 10Be concentrations in sand and dust are (1.1–5.1) × 107 atoms/g and (1.3–2.8) × 108 atoms/g, respectively. Loess and paleosol on the Loess Plateau both contain inherited 10Be adsorbed on silt grains from dust; most of the windblown deposited loess materials do not directly come from the Gobi and other sand deserts, but mainly from the loess–desert transitional zones, which are characterized by silt and dust holding areas.

The NaB–DNA adduction and its decay in mouse liver and kidney at environmental exposure doses were studied by accelerator mass spectrometry. The number of DNA adducts increased nonlinearly with increasing dose. At dose >500 μg/kg b.w., the DNA adducts level of kidney was higher than that of liver. After a single dose exposure, the DNA adducts level declined quickly to one-fourth within 1 d in liver and within 3 d in kidney, and then kept steady. Presumably, the initial fast decay process results from the metabolism via hippurate and the subsequent slow process from the easily persistent benzoyl glucuronide. Based on the low level of adducts formed and quick decrease of adducts, our experimental results are basically consistent with the previous safety assessment of NaB. However, it should be prudent on using NaB chronically, particularly in a large amount, because the stable harmful adducts remained quite long even after a single low dose exposure.

The pneumatic elastic model establishing and analysis of the high-aspect-ratio composite wing is an important task for the long-endurance aircraft's design. The pneumatic elastic analysis theory and fluid- structure interaction(FSI) analysis method are applied in this paper to establish the structured finite element model for the high-aspect-ratio composite wing. Based on the analysis of initialized static model, the software MpCCI is used to analyze the model with the bidirectional FSI theory, and discuss the pneumatic elasticity characteristics of the wing model in the coupling state. And the relative structure and flow field parameters are supported. KEYWORD: high aspect ratio; composite; fluid structure interaction; pneumatic elasticity

Bones are very important samples to determine the hosts of the cemetery of Jin Marquises which were excavated at Tianma-Qucun site in Shanxi Province in China. In order to obtain accurate AMS radiocarbon dates, bones were pretreated by two kinds of methods, the gelatin-extraction method and the amino-acid method. Charcoals collected from the same sites were also used. The measured dates agree with historical record.

The decay kinetics of nicotine–DNA adducts and NNK–DNA adducts in mice liver after single dosing was studied by accelerator mass spectrometry (AMS). The decay is characterized by a two-stage process. The half-lives of nicotine–DNA adducts are 1.3 d (4–24 h) and 7.0 d (1–21 d), while for NNK–DNA adducts are 0.7 d (4–24 h) and 18.0 d (1–21 d). The relatively faster decay of nicotine–DNA adducts suggests that the genotoxicity of nicotine is weaker than that of NNK. The in vitro study shows that the metabolization of nicotine is necessary for the final formation of nicotine–DNA adducts, and nicotine Δ1′(5′) iminium ion is a probable metabolite species that binds to DNA molecule covalently.

A third-harmonic gyro-TWT amplifier operating in the TE/sub 41/ mode is described that is predicted to generate 2 MW at 35 GHz. The device is based on the proven concept that the electron beam current can be significantly higher in a stable harmonic gyro-TWT amplifier than at the fundamental due to the comparatively weaker harmonic interaction. For stability, the circuit is sliced to suppress electromagnetic modes without the desired symmetry and the 100 kV, 100 A electron beam from a magnetron injection gun is placed at the null of the strongest remaining gyro-BWO mode. The single-stage gyro-TWT is predicted to produce 2 MW with 20% efficiency, 30 dB saturated gain and 3.5% constant-drive bandwidth.

Spectral characteristics of stimulated Raman scattering (SRS) in optical fibers are examined in a regime (nanosecond pulses or longer) for which effects such a self-phase modulation, cross-phase modulation, and group velocity dispersion are negligible. An XeF excimer laser was used to pump a multimode fused silica UV optical fiber to observe SRS multiple-order Stokes generation. A theoretical model in which SRS is the only nonlinear effect induced was developed to simulate the SRS spectra of excimer laser pumped silica fibers. Good agreement has been achieved on spectral characteristics of SRS between the computer simulation and experimental results, which clarifies several puzzling features observed in experiment. The most important parameters to the evolution of SRS spectra in fibers were found to be the Raman gain curve, and the linewidth and temporal profile of the input pump. >

This paper presents some preliminary findings in the performance of bamboo reinforced brick wall against blast load. The high specific strength and high ultimate strain of bamboo make it ideal as an energy absorptive material for protective structures. High fidelity physics based Finite Element Method program LS-DYNA was used as a tool to simulate the mechanical response of bamboo reinforced structures under blast loading. This paper is part of a preliminary study to investigate the feasibility of using bamboo in protective structures.

An analysis is presented of optical coupling loss associated with mechanical tolerance for two fibers butt-coupled in a glass capillary. The analysis includes tolerance statistics and the statistics of fiber alignment in the capillary.

This paper demonstrated sub-microsecond photoresponse on gated Si field emitter array (FEA) using lightly p-doped Si, which is two orders of magnitude better than the authors' previous results. The authors anticipated that a device structure optimized to reduce series resistance and an improved RF circuit would result in pulse response approaching the sub-nanosecond regime.

Successful integration of gated field emitter arrays (FEAs) on p-Si substrates with an improved fabrication procedure that results in dramatically reduced leakage current to the gate is presented. Improved fabrication procedure enables a maximum anode-to-gate current ratio of 3300 and high photocurrent to dark current contrast. The dark current at 150 V is 6 /spl mu/A, about 40 times less than an earlier device. I-V curve shows an abrupt transition from field emission to the supply-limited emission at around 50 V. A linear response of the photocurrent to optical power up to sub-milliamp range is achieved. Analyses show that sub-nanosecond response time is possible. These results show promising applications of gated FEA photocathodes in microwave tubes and electron accelerators.

Methyl tert-butyl ether (MTBE) is a gasoline oxygenate and antiknock additive substituting for lead alkyls currently in use worldwide. Previous studies have shown that MTBE at very high doses induces tumors in rodents. The aim of the present study was to examine directly the binding ability of MTBE onto DNA, demonstrating its potential genotoxicity. MTBE–DNA adducts and their decay kinetics in mice have been measured by using doubly 14C-labeled MTBE with an advanced, ultrasensitive technique: accelerator mass spectrometry (AMS). It was found that MTBE definitely formed adducts with DNA in mouse lung, liver, and kidney in a log/log linear dose–response relationship. The distribution sequence of DNA adducts in these tissues is: lung > liver > kidney. The level of MTBE–DNA adducts peaked at 12 h postadministration in the lung and peaked at 6 h postadministration in the liver. Then the adducts declined rapidly until 5 days postadministration and thereafter declined much more slowly. To our knowledge, this is the first report on DNA adduction with MTBE in vivo. The mechanism of the formation of MTBE–DNA adducts also is discussed. © 2005 Wiley Periodicals, Inc. Environ Toxicol 20: 397–401, 2005.

Photofield emission from gated silicon field emitter array showed improvements on efficiency and dynamic range at the expense of higher dark current as the gate voltage increased. For 830 nm, efficiency approached 19% and dynamic range approached 7.2 at 100 V. Measured saturation behavior was attributed to screening of the applied field. Ratio of field emission current over leakage current peaked at 75 before the onset of current interception by the gate. Nanosecond time scale response was detected with short pulse excitation at 82 MHz repetition.

Summary form only given.We report on the measurements of efficient CW photo-induced emission from silicon tip arrays as well as its saturation behaviour and nanosecond scale temporal response. We fabricated field emission arrays on 500 /spl mu/m thick p-type silicon substrates. The silicon emitters were formed by using a dry etching process followed by oxidation sharpening.

Summary form only given, as follows. Harmonic gyro-TWT amplifiers can stably generate much higher power than at the fundamental because the start-oscillation current for the absolute instability is significantly increased due to the relatively weaker harmonic interaction. The concept has recently been successfully demonstrated by a 207 kW second-harmonic TE/sub 21/ gyro-TWT amplifier. Here, the concept is extended to a higher power third-harmonic gyro-TWT. The TE/sub 41/ cylindrical circuit is sliced to suppress modes without an m=4 azimuthal symmetry by interrupting their wall currents, a technique employed in the second-harmonic gyro-TWT, where the round-trip loss was measured to be 40 dB for the odd-order azimuthal modes and negligible for the operating mode. The guiding center of the 100 kV MIG electron beam is placed on the null of the strongest remaining gyro-BWO modes. The peak power predicted by the self-consistent large-signal code is 2 MW with an efficiency of 20%, 30 dB saturated gain, and 6% saturated bandwidth.

Monoclonal antibody (MAb) 3B5 generated against canine mesothelioma cells was applied to canine tumors and normal tissues via immunohistochemical and immunoblotting techniques to evaluate antigen binding. By use of an avidin-biotin immunoperoxidase complex (ABC) method, immunoreactivity was noted in reactive mesothelial cells and in normal tissues was observed primarily in mesothelial cell linings, endothelial cells, and smooth muscle of blood vessels and soft tissues; the reactivity was nearly equivalent in frozen or formalin-fixed, paraffin-embedded tissue sections. Use of the ABC method on formalin-fixed, paraffin-embedded tumors yielded moderate to strong cytoplasmic immunostaining of neoplastic cells in 10/11 (91%) mesotheliomas, 18/23 (78%) hemangiosarcomas, 4/10 (40%) intestinal and lung carcinomas, and ≤20% of hemangiomas, leiomyosarcomas, leiomyomas, mammary carcinomas, and squamous cell carcinomas. No immunostaining of tumor cells was observed in fibrosarcomas, hemangiopericytomas, perianal gland carcinomas, and melanomas. Immunoblotting was performed on samples that demonstrated strong immunoreactivity with MAb 3B5 by the ABC method: mesothelioma, hemangiosarcoma, urinary bladder (smooth muscle), and lung (alveolar capillaries). These analyses showed that MAb 3B5 bound a major antigen of 78 kilodaltons (kd) and minor antigens at 56 and 54 kd in normal and neoplastic tissues. The preliminary immunohistochemical results suggest that MAb 3B5 may possess utility in diagnosis of mesotheliomas and hemangiosarcomas, discrimination of cell types in proliferative serosal lesions, and demonstration of vascularity or angiogenesis in neoplastic and inflammatory lesions.