Particle Signatures Research Articles

Interactions between boreal wildfire and urban emissions

A suite of particulate, gaseous and meteorological measurements during the Pittsburgh Supersite experiment were used to characterize the impact of the 2002 Quebec wildfires on pollutant concentrations and physical and chemical processes dominant in the region. Temporal trends in the number distribution of wildfire particles (isolated using Rapid Single‐ultrafine‐particle Mass Spectrometry data) combined with CO, NOx and O3 mixing ratios identified two separate periods (Periods I and II) when the measurement site was directly impacted by plumes of relatively unprocessed wildfire emissions; i.e., increases in primary ultrafine wildfire particles, CO and NOx concomitant with a decrease in O3 from intraplume NOx titration. Carbonaceous particle number distributions predominantly associated with vehicular emissions, PM2.5 sulfate mass concentration and SO2 mixing ratio resolved individual components of local and regional sources. Single particle signatures indicated a period of intense atmospheric processing following Period II that caused rapid growth of the ultrafine mode due to simultaneous sulfate and secondary organic mass accumulation, resulting in significant changes to particle physical and chemical properties. Particle growth was concurrent with large increases in O3 and maxima in incoming solar radiation and ambient temperature and is posited to have occurred in situ as the air mass, containing a mixture of urban and wildfire emissions, was advected past the site. In total, the current work demonstrates significant added severity for pollution episodes in an area already burdened by large anthropogenic emission rates due to the impact of the 2002 Quebec wildfires. High levels of atmospheric processing increased sulfate accumulation and SOA formation and brought PM2.5 mass concentrations close to, and O3 mixing ratios in excess of, the National Ambient Air Quality Standards. Projections of increasing wildfire activity under a warming climate may increase the frequency and severity of such events.

Evidence for reconnection at Saturn's magnetopause

Observations of Saturn's magnetopause by the Cassini Plasma Spectrometer (CAPS) and magnetometer have revealed clear instances of magnetic reconnection signatures, two of which are described here. Both encounters occurred at the equator in the prenoon sector as Cassini was exiting the magnetosphere. Evidence of heating in the electrons and ions is highly suggestive of energization comparable to that associated with the reconnection process at Earth. In one case, the fields are strongly antiparallel and the magnetic data indicate the presence of a locally open magnetic field. In the other example, magnetic data indicate a locally closed magnetic field compatible with the field lines being locally parallel, but the particle signatures lead to the conclusion of a distant reconnection site poleward of the cusps being active. The reconnection voltage for the first case is calculated to be 48 kV, which is of the same order as previous estimates at Saturn. This is lower than the corotational voltage but is not insignificant.

Analysis of dilute aerosol flow and noise generation in an acoustic transducer

This combined experimental and computational study is an extension of prior efforts by the present authors to provide a physical explanation of the ability of a particle detection technique based on the acoustic signature of airborne particles. As a particle-laden flow accelerates through a converging–diverging tube consisting of a capillary (called the acoustic transducer), the suspended particles cannot follow the rapidly changing flow velocity. Consequently, vortices are generated in the wake of the particle, which excite the air column inside the transducer tube producing noise. Experimental results show how the frequency content of the acoustic signatures relates to the fundamental frequency of the transducer's air column. The acoustic transducer is able to detect micron-sized particles and the sound intensity is a function of flow rate but not of particle size. The ability of the transducer to determine particle concentration (as low as a few ppl) is also experimentally shown and compared to data obtained from a commercially available aerodynamic particle sizer. A computational model is developed which incorporates detailed treatment of air compressibility as well as the variability in Reynolds number and particle drag coefficient. Computational results help determine the location of the acoustic disturbance, which is at the entrance of the capillary section of the transducer where the flow speed is nearly sonic and the acceleration is the greatest throughout the flow.

Pair production of charged Higgs bosons in the left–right twin Higgs model at the ILC and LHC

The left–right twin Higgs (LRTH) model predicts the existence of a pair of charged Higgs bosons φ±. In this paper, we study the production of the charged Higgs boson pair φ± at the international linear collider (ILC) and the CERN large hadron collider (LHC). The numerical results show that the production rates are at the level of several tens fb at the ILC, and the process e+e-→φ+φ- can produce adequately distinct multi-jet final states. We also discuss the charged Higgs boson pair production via the process qq̄→φ+φ- at the LHC and estimate in this case the production rates. We find that, as long as the charged Higgs bosons are not too heavy, they can be abundantly produced at the LHC. The possible signatures of these new particles might be detected at the ILC and LHC experiments.

Digital holographic particle validation via complex wave

The inability to distinguish between particle images and noise in holographic reconstruction of dense particle fields hampers the advancement of holographic particle diagnostic techniques including holographic particle image velocimetry. We developed a method to separate particles from the noise by unlocking a unique particle signature in the complex reconstructed field. This complex-wave signature is present in digital particle holograms recorded at any scattering angle. Simulations of single and multiple particle holograms, as well as preliminary laboratory particle-field experiments, not only demonstrated the existence of the particle signature but also evaluated its ability to remove noise. Regardless of particle seeding density, scattering angle of hologram recording and particle size range, the particle identification/validation routine consistently provides >50% removal of "bad" particles and <8% of good particles.

Signatures of axionlike particles in the spectra of TeV gamma-ray sources

One interpretation of the unexplained signature observed in the PVLAS experiment invokes a new axionlike particle (ALP) with a two-photon vertex, allowing for photon-ALP oscillations in the presence of magnetic fields. In the range of masses and couplings suggested by PVLAS, the same effect would lead to a peculiar dimming of high-energy photon sources. For typical parameters of the turbulent magnetic field in the galaxy, the effect sets in at ${E}_{\ensuremath{\gamma}}\ensuremath{\gtrsim}10\text{ }\text{ }\mathrm{TeV}$, providing an ALP signature in the spectra of TeV gamma sources that can be probed with Cherenkov telescopes. A dedicated search will be strongly motivated if the ongoing photon regeneration experiments confirm the PVLAS particle interpretation.

Single particle Raman spectroscopy for investigating atmospheric heterogeneous reactions of organic aerosols

Heterogeneous reactions of organic aerosols with atmospheric oxidants are important processes that affect the hygroscopicity and cloud condensation nuclei (CCN) activities of atmospheric aerosols. An electrodynamic balance (EDB) coupled with Raman spectroscopy is a particularly attractive platform for studying atmospheric reactions since it allows long-duration (days) particle levitation and reactions at atmospherically relevant low-oxidant concentrations can be investigated. In this study, we demonstrated the use of an EDB/Raman system to investigate the heterogeneous reactions of oleic acid particles with ozone (240–280 ppb) under ambient temperatures (22–24 °C) and dry conditions (relative humidity <5%) over a period of 20 h. The Raman signatures of the ozone-processed oleic acid particles indicate the formation of oxidation products predominately consisting of peroxidic compounds (O O groups of peroxides and/or ozonides), carbonyl (C O) and hydroxyl (O H) functional characteristics, which are consistent with the predictions of the Criegee mechanism as well as the results reported in the literature. We also confirmed that the Raman signatures of the reacted particles at atmospheric and much higher (>10 ppm) ozone concentrations are practically the same, which provides assurance to the use of elevated ozone concentrations in reaction studies of the oleic acid–ozone system in the literature. The ratio of the percentage of mass loss (due to evaporation of volatile organic products) to the percentage of oleic acid conversion was estimated to be 0.05. Furthermore, the oxidation products that remained in the particle phase were more hygroscopic than were their hydrophobic parent molecules.

Nitric acid particles in cold thick ice clouds observed at global scale: Link with lightning, temperature, and upper tropospheric water vapor

Signatures of nitric acid particles (NAP) in cold thick ice clouds have been derived from satellite observations. Most NAP are detected in the tropics (9 to 20% of clouds with T &lt; 202.5 K). Higher occurrences were found in the rare midlatitudes very cold clouds. NAP occurrence increases as cloud temperature decreases, and NAP are more numerous in January than July. Comparisons of NAP and lightning distributions show that lightning seems to be the main source of the NOx, which forms NAP in cold clouds over continents. Qualitative comparisons of NAP with upper tropospheric humidity distributions suggest that NAP may play a role in the dehydration of the upper troposphere when the tropopause is colder than 195 K.

Observation of Exclusive Electron-Positron Production in Hadron-Hadron Collisions

We present the first observation of exclusive e(+)e(-) production in hadron-hadron collisions, using pp[over] collision data at (square root) s = 1.96 TeV taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb(-1). We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E(T) > 5 GeV and pseudorapidity |eta| < 2. With these criteria, 16 events are observed compared to a background expectation of 1.9+/-0.3 events. These events are consistent in cross section and properties with the QED process pp[over] --> p + e(+)e(-) + p[over] through two-photon exchange. The measured cross section is 1.6(-0.3)(+0.5)(stat) +/- 0.3(syst) pb. This agrees with the theoretical prediction of 1.71+/-0.01 pb.

Large geomagnetic storms of extreme solar event periods in solar cycle 23

During extreme solar events such as big flares or/and energetic coronal mass ejections (CMEs) high energy particles are accelerated by the shocks formed in front of fast interplanetary coronal mass ejections (ICMEs). The ICMEs (and their sheaths) also give rise to large geomagnetic storms which have significant effects on the Earth’s environment and human life. Around 14 solar cosmic ray ground level enhancement (GLE) events in solar cycle 23 we examined the cosmic ray variation, solar wind speed, ions density, interplanetary magnetic field, and geomagnetic disturbance storm time index ( D st). We found that all but one of GLEs are always followed by a geomagnetic storm with D st ⩽ −50 nT within 1–5 days later. Most(10/14) geomagnetic storms have D st index ⩽ −100 nT therefore generally belong to strong geomagnetic storms. This suggests that GLE event prediction of geomagnetic storms is 93% for moderate storms and 71% for large storms when geomagnetic storms preceded by GLEs. All D st depressions are associated with cosmic ray decreases which occur nearly simultaneously with geomagnetic storms. We also investigated the interplanetary plasma features. Most geomagnetic storm correspond significant periods of southward B z and in close to 80% of the cases that the B z was first northward then turning southward after storm sudden commencement (SSC). Plasma flow speed, ion number density and interplanetary plasma temperature near 1 AU also have a peak at interplanetary shock arrival. Solar cause and energetic particle signatures of large geomagnetic storms and a possible prediction scheme are discussed.

In-Situ Solar Wind and Magnetic Field Signatures of Interplanetary Coronal Mass Ejections

The heliospheric counterparts of coronal mass ejections (CMEs) at the Sun, interplanetary coronal mass ejections (ICMEs), can be identified in situ based on a number of magnetic field, plasma, compositional and energetic particle signatures as well as combinations thereof. We summarize these signatures and their implications for understanding the nature of these structures and the physical properties of coronal mass ejections. We conclude that our understanding of ICMEs is far from complete and formulate several challenges that, if addressed, would substantially improve our knowledge of the relationship between CMEs at the Sun and in the heliosphere.

Production of the top-pions from the higgsless–top-Higgs model at the LHC

The top-pions ( π t 0 , ± ) predicted by extra-dimensional descriptions of the topcolor scenario have similar feature with those in four-dimensional topcolor scenario, which have large Yukawa couplings to the third generation quarks. In the context of the higgsless–top-Higgs (HTH) model, we discuss the production of these new particles at the CERN Large Hadron Collider (LHC) via various suitable mechanisms (gluon–gluon fusion, bottom–bottom fusion, gluon–bottom fusion, and the usual Drell–Yan processes) and estimate their production rates. We find that, as long as the top-pions are not too heavy, they can be abundantly produced at the LHC. The possible signatures of these new particles might be detected at the LHC experiments.

Adaptive AR and Neurofuzzy Approaches: Access to Cerebral Particle Signatures

In recent years, a relationship has been suggested between the occurrence of cerebral embolism and stroke. Ultrasound has therefore become essential in the detection of emboli when monitoring cerebral vascular disorders and forms part of ultrasound brain-imaging techniques. Such detection is based on investigating the middle cerebral artery using a TransCranial Doppler (TCD) system, and analyzing the Doppler signal of the embolism. Most of the emboli detected in practical experiments are large emboli because their signatures are easy to recognize in the TCD signal. However, detection of small emboli remains a challenge. Various approaches have been proposed to solve the problem, ranging from the exclusive use of expert human knowledge to automated collection of signal parameters. Many studies have recently been performed using time-frequency distributions and classical parameter modeling for automatic detection of emboli. It has been shown that autoregressive (AR) modeling associated with an abrupt change detection technique is one of the best methods for detection of microemboli. One alternative to this is a technique based on taking expert knowledge into account. This paper aims to unite these two approaches using AR modeling and expert knowledge through a neurofuzzy approach. The originality of this approach lies in combining these two techniques and then proposing a parameter referred to as score ranging from 0 to 1. Unlike classical techniques, this score is not only a measure of confidence of detection but also a tool enabling the final detection of the presence or absence of microemboli to be performed by the practitioner. Finally, this paper provides performance evaluation and comparison with an automated technique, i.e., AR modeling used in vitro.

Comparison of oil and fuel particle chemical signatures with particle emissions from heavy and light duty vehicles

In order to establish effective vehicle emission control strategies, efforts are underway to perform studies which provide insight into the origin of the source of vehicle particle emissions. In this study, the mass spectral signatures of individual particles produced from atomized auto and diesel oil and fuel samples were obtained using aerosol time-of-flight mass spectrometry (ATOFMS). The major particle types produced by these samples show distinct chemistry, falling into several major categories for each sample. Lubricating oils contain calcium and phosphate based additives and although the additives are present in low abundance (∼1–2% by mass), calcium and phosphate ions dominate the mass spectra for all new and used oil samples. Mass spectra from used oil contain more elemental carbon (EC) and organic carbon (OC) marker ions when compared to new oils and exhibit a very high degree of similarity to heavy duty diesel vehicle (HDDV) exhaust particles sampled by an ATOFMS. Fewer similarities exist between the used oil particles and light duty vehicle (LDV) emissions. Diesel and unleaded fuel mass spectra contain polycyclic aromatic hydrocarbon (PAH) molecular ions, as well as intense PAH fragment ions 25(C 2H) −, 49(C 4H) −, and inorganic ions 23Na +, 39K +, 95(PO 4) −. Unleaded fuel produced spectra which contained Na + and K +; likewise, LDV particle emission spectra also contained Na + and K +. Comparing oil and fuel particle signatures with HDDV and LDV emissions enhances our ability to differentiate between these sources and understand the origin of specific marker ions from these major ambient particle sources.

Single magnetic particle detection: Experimental verification of simulated behavior

In the past, magnetoresistive sensor based biosensors, using superparamagnetic particles, have shown to be promising candidates for highly sensitive biosensors. These sensors can detect a single micron-sized magnetic particle. For single particle detection, research groups have developed models to predict the signal per particle. In these models, the separation distance plays an important role for the quantitative determination of the signal. However, mostly only the passivation layer thickness is included as the separation distance. In this paper, we describe a detection system based on a magnetic spin-valve sensor that is capable of giving position-time information of the magnetic behavior of one single bead. The results obtained with this system for the detection of a single particle signature are then compared with simulations. For this comparison, we developed a model where an additional particle-substrate separation distance is included. This distance is determined by a force balance of the perpendicular forces acting on the magnetic particle, including the magnetic and electrostatic force. These simulations agree well with the single particle detection experiment.

Dust Production from the Hypervelocity Impact Disruption of Hydrated Targets

More than half of the C-type asteroids, which are the dominant type of asteroid in the outer half of the main belt, show evidence of hydration in their reflectance spectra. In order to understand the collisional evolution of asteroids, the production of interplanetary dust, and to model the infrared signature of small particles in the Solar System it is important to characterize the dust production from primary impact disruption events, and compare the disruption of hydrous and anhydrous targets. We performed impact disruption experiments of three “greenstone” targets, a hydrothermally metamorphosed basalt, and compared the results of these disruptions to our previous disruption experiments on porous, anhydrous basalt targets and to literature data on the disruption of non-porous, anhydrous basalt targets. The greenstone targets were selected because their major hydrous alteration phase is serpentine, the same hydrous alteration phase found in hydrous CM meteorites, like Murchison. The porous, anhydrous basalt targets were selected because their structure, consisting of millimeter-size olivine phenocrysts in a more porous, anhydrous matrix is similar to the structure of anhydrous chondritic meteorites, which consist of millimeter-size olivine chondrules embedded in a more porous, anhydrous matrix. The disruption measurements indicate the threshold collisional specific energy, QD*, is 570 J/kg for the greenstone, which is lower than the literature values for non-porous basalt targets, and significantly lower than the value of 2500 J/kg that we have measured for porous anhydrous basalt targets. We determined the mass-frequency distribution of the debris from the disruption of the greenstone targets, which ranged in mass from 80 to 280 g, over a nine order-of-magnitude mass range, from ~10−9 g to the mass of the largest fragment. The cumulative mass-frequency distribution from the greenstone targets is fit by two power–law segments, one for masses >10−2 g, which is significantly steeper than the corresponding segment from the disruption of similar-sized anhydrous basalt, and one in the range from 10−9 to 10−2 g, which is significantly flatter than the corresponding segment from the disruption of similar size anhydrous basalt. These hydrous greenstone targets overproduce small fragments (10−4 to 100 g) compared to anhydrous basalt targets, but underproduce dust-size grains (10−9 to 10−4 g) compared to anhydrous basalt targets.

On-road and laboratory evaluation of combustion aerosols—Part 2:: Summary of spark ignition engine results

The primary objective was to characterize exhaust aerosols from a small group of in-use, light-duty, spark ignition (SI) vehicles operated on-road, and on a chassis dynamometer. A significant particle signature above background was not measured at highway cruise condition. Number emissions were much higher during acceleration, at high-speed cruise, and during cold–cold starts. Group average fuel-specific number emissions range from 3.9 × 10 14 to 1.0 × 10 17 particles/kg of fuel. Cold–cold start temperatures, driving cycles and vehicular condition influence SI emissions. Elemental carbon was a major contributor to mass emissions measured in chassis dynamometer Unified Driving Cycle (UDC) tests averaging 64% and 34% of the mass emissions for cold–cold and hot start cycles, respectively. Average ratios of cold–cold to hot start emissions were 3.3, 7.6, and 22 for CPC number, filter mass and SMPS volume, respectively. Apportionment results showed that on a weekly weighted basis and on weekdays, the majority of observed particle number was attributed to heavy-duty diesel traffic. Weekend production of particles was attributable to light-duty automobiles. On a per vehicle basis, heavy-duty vehicles produced substantially greater number concentrations. On a fuel-specific basis, heavy-duty vehicles produce slightly higher concentrations of particles than light-duty vehicles. The relative contribution of light-duty vehicles to particle number emissions increased as particle size decreased, for the smallest particles apportioned number emissions were 1.3 × 10 16 and 7.1 × 10 15 particles/kg of fuel for heavy-duty and light-duty vehicles, respectively. Comparison of on-road chase and apportionment results with chassis dynamometer tests in a certification type facility suggests that the latter may underestimate real-world number emissions.

Automatic tracking of individual fluorescence particles: application to the study of chromosome dynamics

We present a new, robust, computational procedure for tracking fluorescent markers in time-lapse microscopy. The algorithm is optimized for finding the time-trajectory of single particles in very noisy dynamic (two- or three-dimensional) image sequences. It proceeds in three steps. First, the images are aligned to compensate for the movement of the biological structure under investigation. Second, the particle's signature is enhanced by applying a Mexican hat filter, which we show to be the optimal detector of a Gaussian-like spot in 1/omega2 noise. Finally, the optimal trajectory of the particle is extracted by applying a dynamic programming optimization procedure. We have used this software, which is implemented as a Java plug-in for the public-domain ImageJ software, to track the movement of chromosomal loci within nuclei of budding yeast cells. Besides reducing trajectory analysis time by several 100-fold, we achieve high reproducibility and accuracy of tracking. The application of the method to yeast chromatin dynamics reveals different classes of constraints on mobility of telomeres, reflecting differences in nuclear envelope association. The generic nature of the software allows application to a variety of similar biological imaging tasks that require the extraction and quantitation of a moving particle's trajectory.

Characterisation of Soot Emitted by Domestic Heating, Aircraft and Cars Using Diesel or Biodiesel

The characterisation of aggregates, like soot, firstly requires the determination of the size distribution of the primary particles. The primary particle size of combustion generated aggregates depends upon the combustion environment and the formation conditions, such as temperature, pressure and fuel-to-air ratio, among others. Since the combustion characteristics are different in the different types of burners, the characterisation of primary particles may offer the possibility to distinguish soot from different sources. In this paper, we present the signature of the primary particles and the aggregates of soot emitted by cars using diesel or biodiesel, by domestic heating, and by aircraft exhausts, which can be considered as the major sources as derived from measurements on transmission electron micrographs. The size distributions of all aggregates types with different aerodynamic diameter were log-normal and quasi-monodisperse. The size distribution of the primary particles for soot emitted by different sources showed minor differences. However, a comparison between the diameter of the primary particles and those obtained using a standard method for carbon black revealed discrepancies. The median diameter of the primary particles was combined with the median number of primary particles in an aggregate to calculate the relative particle surface area available for adsorption. In a similar way, the relative specific surface area was determined. The surface area was measured using the Brunauer-Emmett-Teller (B.E.T.) nitrogen adsorption method and the relative surface area available for adsorption was calculated.

Relation between the solar wind dynamic pressure at Voyager 2 and the energetic particle events at Voyager 1

Starting in 2001, Voyager 1 observed three events characterized by enhanced fluxes of energetic particles. These events suggest that Voyager 1 made a close approach to, or a crossing of, the termination shock. Although the plasma experiment on Voyager 1 is not providing useful data, plasma data from Voyager 2 may shed light on the plasma conditions at Voyager 1. Before the first particle event, Voyagers 1 and 2 see similar particle signatures. Voyager 2 pressure and energetic particle flux profiles have similar structure. The merged interaction regions (MIRs) observed at Voyager 2 have counterparts in the Voyager 1 data. We propagate solar wind data from Voyager 2 to Voyager 1 and show that at the predicted MIR arrival times, there is always a response in the Voyager 1 particle data. These effects vary, from an increase in particle flux to a rapid turnoff of the particle event. We discuss the observed energetic particle effects and how the MIRs produce them.