The light scattered from dust grains in debris disks is typically modeled as compact spheres using the Lorenz-Mie theory or as porous spheres by incorporating an effective medium theory. In this work ...we examine the effect of incorporating a more realistic particle morphology on estimated radiation-pressure blowout sizes. To calculate the scattering and absorption cross-sections of irregularly shaped dust grains, we use the discrete dipole approximation. These cross-sections are necessary to calculate the β-ratio, which determines whether dust grains can remain gravitationally bound to their star. We calculate blowout sizes for a range of stellar spectral types corresponding with stars known to host debris disks. As with compact spheres, more luminous stars blow out larger irregularly shaped dust grains. We also find that dust grain composition influences blowout size such that absorptive grains are more readily removed from the disk. Moreover, the difference between blowout sizes calculated assuming spherical particles versus particle morphologies more representative of real dust particles is compositionally dependent as well, with blowout size estimates diverging further for transparent grains. We find that the blowout sizes calculated have a strong dependence on the particle model used, with differences in the blowout size calculated being as large as an order of magnitude for particles of similar porosities.
Abstract
The lack of quantitative characterization of aerosol particles and their loading in the atmosphere is one of the greatest uncertainties in climate-change science. Improved instrumentation ...capable of determining the size and shape of aerosol particles is needed in efforts to reduce this uncertainty. We describe a new instrument carried by an unmanned aerial vehicle (UAV) that images free-floating aerosol particles in the atmosphere. Using digital holography, the instrument obtains the images in a non-contact manner, resolving particles larger than ten micrometers in size in a sensing volume of approximately three cubic centimeters. The instrument, called the holographic aerosol particle imager (HAPI), has the unique ability to image multiple particles freely entering its sensing volume from any direction via a single measurement. The construction of HAPI consists of 3D printed polymer structures that enable a sufficiently low size and weight that it may be flown on a commercial-grade UAV. Examples from field trials of HAPI show images of freshly emitted tree pollen and mineral dust.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We present numerical methods for modeling the dynamics of arbitrarily shaped particles trapped within optical tweezers, which improve the predictive power of numerical simulations for practical use. ...We study the dependence of trapping on the shape and size of particles in a single continuous wave beam setup. We also consider the implications of different particle compositions, beam types and media. The major result of the study is that for different irregular particle shapes, a range of beam powers generally leads to trapping. The trapping power range depends on whether the particle can be characterized as elongated or flattened, and the range is also limited by Brownian forces.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
The detection and identification of bioaerosol particles, especially a potential threat from aerosolized biowarfare agents (BWAs), has become increasingly important. Here, we report on ...single-particle optical-trapping Raman spectroscopy (OT-RS) for the detection and identification of airborne biological particles. OT enables the capture of single particles in air for several minutes or longer, more than sufficient to capture the Raman spectra and minimize the interference from background aerosol particles. Simultaneously, the embedded imaging system can provide real-time information on the shape and size of the trapped particles. Several kinds of bioaerosol particles were analyzed using OT-RS including four BWA surrogates:
Bacillus globigii, Yersinia rhodei
, MS2, and
Bacillus subtilis
, along with some interfering bioaerosol particles commonly presented in the atmosphere. Similarities and differences of the Raman spectra of these biological particles are discussed. In addition, the BWA surrogates are well classified by using the principal component analysis. The results demonstrate that single-particle OT-RS can be used not only for the potential detection of BWAs but also for the identification of BWAs.
Characterization, identification, and detection of aerosol particles in their native atmospheric states remain a challenge. Recently, optical trapping-Raman spectroscopy (OT-RS) has been developed ...and demonstrated for characterization of single, airborne particles. Such particles in different chemical groups have been characterized by OT-RS in recent years and many more are being studied. In this work, we collected single-particle Raman spectra measured using the OT-RS technique and began construction of a library of OT-RS fingerprints that may be used as a reference for potential detection and identification of aerosol particles in the atmosphere. We collected OT-RS fingerprints of aerosol particles from eight different categories including carbons, bioaerosols (pollens, fungi, vitamins, spores), dusts, biological warfare agent surrogates, etc. Among the eight categories, spectral fingerprints of six groups of aerosol particles have been published previously and two other groups are new. We also discussed challenges, limitations, and advantages of using single-particle optical trapping-Raman spectroscopy for aerosol-particle characterization, identification, and detection.
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8.
Light-scattering evolution from particles to regolith Videen, Gorden; Muinonen, Karri
Journal of Quantitative Spectroscopy & Radiative Transfer/Journal of quantitative spectroscopy & radiative transfer,
01/2015, Volume:
150
Journal Article
Peer reviewed
Open access
The radiative-transfer coherent-backscattering (RT–CB) model is unique among light-scattering methodologies as it can be used to calculate accurate light-scattering properties of sparsely populated ...particle volumes with sizes ranging from subwavelength to infinity. We use the RT–CB model to examine the evolution of light-scattering properties as a volume of particles increases from wavelength-sized to several hundreds of wavelengths. We examine the evolution of light-scattering intensity phase function and polarization, as well as linear and circular polarization ratios. We confirm the expected trends for backscattering features to shift to smaller phase angles as the volume increases. In addition, we also see the amplitude of these features increases to some maximum for volumes having size parameters kR~100, before decaying to less than half this amplitude as their volumes approach infinity.
•We use the RT–CB method to examine how gross light-scattering properties evolve as particle size increases.•The transition from a wavelength-sized particle to a large particle is not monotonic.•Backscattering properties associated with the CB mechanism appear to have a peak value before decaying asymptotically.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We examine the dispersion of the degree of linear polarization P in comets at phase angle ~90° where the maximum amplitude of positive polarization Pmax occurs. The range of polarization observed in ...comets is from 7% up to more than 30%, and this cannot be explained through depolarization by gaseous emissions. Instead, we suggest that the observed dispersion of P results from different properties in cometary dust. We simulate the spectral polarimetric observations of comets using model agglomerated debris particles. The vast majority of observations can be reproduced with a mixture of weakly absorbing and highly absorbing agglomerated debris particles, which obey the same power-law size distribution. Within this extremely simple approach, polarization at side-scattering angles in a given comet is governed by the relative abundance of weakly and strongly absorbing particles. We find that in comets with the highest polarization, the weakly absorbing particles appear in proportions of only 14–23% by volume; whereas, in comets with the lowest polarization Pmax, their abundance is much greater, 82–95%. We conclude that the polarization at side-scattering angles unambiguously measures the relative abundance of Mg-rich silicates and refractory organics or amorphous carbon in comets. We put forth a hypothesis that low Pmax could be an indicator for presence of a well-developed refractory surface layer covering cometary nucleus.
•We study the dispersion of the linear polarization P in comets at phase angle ~90°.•Depolarization by gaseous emissions cannot explain the low P in some comets.•The entire range of P can be explained from different properties of their dust.•P is governed by the relative abundance of weakly and strongly absorbing particles.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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