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Papers by Steven Spielman

Aerosol Science and Technology, 2018

Aerosol Science and Technology, 2016

. Aerosol hygroscopic growth plays an important role in atmospheric particle chemistry and the ef... more . Aerosol hygroscopic growth plays an important role in atmospheric particle chemistry and the effects of aerosol on radiation and hence climate. The hygroscopic growth is often characterized by a growth factor probability density function (GF-PDF), where the growth factor is defined as the ratio of the particle size at a specified relative humidity to its dry size. Parametric, least-square methods are the most widely used algorithms for inverting the GF-PDF from measurements of humidified tandem differential mobility analyzers (HTDMA) and have been recently applied to the GF-PDF inversion from measurements of the humidity-controlled fast integrated mobility spectrometer (HFIMS). However, these least square methods suffer from noise amplification due to the lack of regularization in solving the ill-posed problem, resulting in significant fluctuations in the retrieved GF-PDF and even occasional failures of convergence. In this study, we introduce nonparametric, regularized methods to invert aerosol GF-PDF and apply them to HFIMS measurements. Based on the HFIMS kernel function, the forward convolution is transformed into a matrix-based form, which facilitates the application of the nonparametric inversion methods with regularizations, including Tikhonov regularization and Twomey’s iterative regularization. Inversions of the GF-PDF using the nonparameteric methods with regularization are demonstrated using HFIMS measurements simulated from representative GF-PDFs of ambient aerosols. The characteristics of reconstructed GF-PDFs resulting from different inversion methods, including previously developed least-square methods, are quantitively compared. The result shows that Twomey’s method generally outperforms other inversion methods. The capabilities of the Twomey’s method in reconstructing the pre-defined GF-PDFs and recovering the mode parameters are validated.

Time-domain spectroscopy is a powerful probe of the electrical response of high-Tc thin films in ... more Time-domain spectroscopy is a powerful probe of the electrical response of high-Tc thin films in the millimeter and submillimeter regime. The ability to measure both the real and imaginary parts of the response without Kramers-Kronig analysis is particularly useful in understanding the dynamics of the superconducting state. We have recently designed a time- domain spectrometer which operates in conjunction with a superconducting magnet-cryostat in order to measure the change in the resistivity with field. Using this system we have measured the resistivity tensor of YBCO as a function of frequency from 100 to 800 GHz in a field of 0 to 6 Tesla. We interpret these results in terms of the combined vortex and quasiparticle response in the mixed state, and we believe we have made the first observation of the Hall response of quasiparticles at temperatures well below T.

This technology relates to the enlargement of air particles with diameters on the order of a few ... more This technology relates to the enlargement of air particles with diameters on the order of a few nanometers to hundreds of nanometers by water condensation in a laminar flow to form droplets with diameters of the order of several micrometers. The technology introduces more sophisticated designs, including the use of two-stage capacitors. It finds application in the measurement of the number concentration of particles suspended in air or other gas, in the collection of these particles or in the focusing of these particles.

La presente invention concerne un systeme et un procede de collecte d'aerosol. Le systeme com... more La presente invention concerne un systeme et un procede de collecte d'aerosol. Le systeme comprend un dispositif de distribution de bioaerosol concu pour envoyer des bioparticules dans un flux gazeux, un dispositif d'echange d'humidite comprenant un element de separation couple au flux gazeux et concu pour humidifier ou deshumidifier les bioparticules dans le flux gazeux, et un milieu de collecte d'aerosol en aval du dispositif d'echange d'humidite et concu pour collecter les bioparticules. Le procede consiste a distribuer des bioparticules dans un flux gazeux, a humidifier ou deshumidifier les bioparticules dans le flux gazeux par le transport de l'eau a travers un element de separation et dans une phase vapeur du flux gazeux, et a collecter les bioparticules au moyen d'un milieu de collecte.

Optical measurements have been made on rm YBa_2Cu_3O_7 and rm Bi_2Sr_2CaCu_2O_8 to search for bot... more Optical measurements have been made on rm YBa_2Cu_3O_7 and rm Bi_2Sr_2CaCu_2O_8 to search for both spontaneous Faraday rotation (in transmission) and spontaneous Kerr rotation (reflection). The observation of these magneto-optical effects near T _{c} would be a clear indication that the superconductivity in the cuprate superconductors can be explained by a theory which predicts broken time -reversal (T) symmetry. In particular, the "anyon" model of these materials predicts that T symmetry will be broken spontaneously as the material is cooled. The magneto-optical effects are expected to be quite small compared to the birefringence of the material. A method has been developed that uses a fiber-optic Sagnac interferometer to search for the magneto-optic signal. Incident upon the sample are two counter-propagating circularly polarized beams, whose electric fields have opposite time dependence. The interferometer detects Faraday or Kerr rotation by measuring the difference in phase between these beams after they have interacted with the sample. Because it is immune to birefringence in the sample, this method is superior to simply analyzing the polarization state of a single beam. Transmission experiments at 1060 nm wavelength were done with a modified fiber-optic gyroscope (a type of Sagnac interferometer). The nonreciprocal phase shift observed in the cuprates was less than the sensitivity (2 murad). A 670 nm interferometer was constructed to look for these effects in the visible portion of the spectrum, where other researchers have witnessed unusual polarization effects. Both reflection and transmission measurements at this wavelength indicate there are no magneto -optic effects to a sensitivity of 5 murad. This technique has been applied successfully to study ferromagnetic phase transitions in films of EuO and Gd.

Es wird eine Technologie fur die hocheffiziente Konzentration von feinen und ultrafeinen Schwebst... more Es wird eine Technologie fur die hocheffiziente Konzentration von feinen und ultrafeinen Schwebstoffteilchen zu einer kleinen Fraktion des beprobten Luftstroms durch Kondensationsvergroserung, aerodynamisches Fokussieren und Stromtrennung prasentiert. Eine Dusenkonzentratorstruktur, die eine Beschleunigungsduse mit einer Stromextraktionsstruktur enthalt, konnte an einen Aufnahmebehalter gekoppelt sein. Der Aufnahmebehalter konnte ein Wasserkondensationswachstumsrohr enthalten, um die Konzentration ultrafeiner Teilchen zu erleichtern. Der Aufnahmebehalter konnte ferner einen separaten Tragerstrom enthalten, der in der Mitte des beprobten Stroms eingeleitet wird, stromaufwarts der Beschleunigungsduse des Dusenkonzentrators, um die Trennung von Teilchen- und Dampfbestandteilen zu erleichtern.

. Capturing the vertical profiles and horizontal variations of atmospheric aerosols often require... more . Capturing the vertical profiles and horizontal variations of atmospheric aerosols often requires accurate airborne measurements. With the advantage of avoiding health and safety concerns related to the use of butanol or other chemicals, a water-based condensation particle counter (wCPC) has emerged to provide measurements under various environments. However, the airborne deployment of wCPC is relatively rare due to the lack of characterization of wCPC performance. This study investigates the performance of a commercial "versatile" water CPC (vWCPC Model 3789, TSI) under low-pressure conditions. The effect of conditioner temperature on wCPC performance at low pressure is examined through numerical simulation and laboratory experiments. We show that the default instrument temperature setting of 30 °C for the conditioner is not suitable for airborne measurement and that the optimal conditioner temperature for low-pressure operation is 27 °C. Additionally, we show that insufficient droplet growth becomes more significant under the low-pressure operation. The variation in the chemical composition can contribute up to 20 % uncertainty in the counting efficiency of the wCPC, but this variation is independent of pressure.

Aerosol Science and Technology

Aerosol Science and Technology

Abstract Hygroscopicity describes the tendency of aerosol particle to uptake water and is among t... more Abstract Hygroscopicity describes the tendency of aerosol particle to uptake water and is among the key parameters in determining the impact of atmospheric aerosols on global radiation and climate. A hygroscopicity tandem differential mobility analyzer (HTDMA) system is the most widely used instrument for determining the aerosol hygroscopic growth. Because of the time needed to scan the classifying voltage of the DMA, HTDMA measurement often requires a minimum of 30 min to characterize the particle hygroscopic growth at a single relative humidity for five to six different sizes. This slow speed is often inadequate for measurements onboard mobile platforms or when aerosols evolve rapidly. Recently, a humidity-controlled fast integrated mobility spectrometer (HFIMS) was developed for measuring the hygroscopic growth of particles. The measurement speed of the HFIMS is about one order of magnitude faster than that of the conventional HTDMA. In this work, a data inversion routine is developed to retrieve the growth factor probability density function (GF-PDF) of particles measured by the HFIMS. The inversion routine considers the transfer functions of the upstream DMA and the downstream water-based fast integrated mobility spectrometer (FIMS), and derives the GF-PDF that reproduces the measured responses of the HFIMS. The performance of the inversion routine is examined using ambient measurements with different assumptions for the spectral shape of the particle GF-PDF (multimodal lognormal or piecewise linear). The influences of the data inversion parameters and counting statistics on the inverted GF-PDFs were further investigated, and an approach to determine the optimized inversion parameters is presented. Copyright © 2019 American Association for Aerosol Research

Aerosol Science and Technology

Abstract The Spider differential mobility analyzer (DMA) is a novel, miniaturized radial DMA deve... more Abstract The Spider differential mobility analyzer (DMA) is a novel, miniaturized radial DMA developed to provide size classification in the 10–500 nm range for applications requiring high portability and time resolution. Its external dimensions are ∼12 cm in diameter by 6 cm in height (excluding tubing); it weighs ∼350 g, and is designed to operate at 0.6–1.5 L/min sheath and 0.3 L/min sample flowrates. It features a new sample inlet geometry that is designed to produce a uniform azimuthal particle distribution at the entrance of the classifier, optimized sample/sheath flow streams introduction in the classifier to minimize particle delays, and extension of the electric field interaction volume for ∼30% enhanced dynamic range. Based on three-dimensional finite element simulations of flows, electric fields, and particle trajectories, we demonstrate that the Spider DMA transfer functions can be predicted with high fidelity using a parameterized fit based on the Stolzenburg semi-analytical model. Experimental characterization of the instrument response with size-selected particles confirmed close agreement with model prediction; mobility size response is linear over three orders of magnitude in mobility span. Electrical ground shielding of the external surfaces of the DMA has been found to be necessary to avoid particle losses associated with field effects as the high voltage operating limit is approached. The mean deviation between the reference size of polystyrene latex spheres and the Spider DMA measurement is less than 2%, corroborating its high sizing precision and potential for high quality size distribution measurements. Copyright © 2019 American Association for Aerosol Research

Atmospheric Measurement Techniques Discussions

Aerosol Science and Technology, 2018

Aerosol Science and Technology, 2016

. Aerosol hygroscopic growth plays an important role in atmospheric particle chemistry and the ef... more . Aerosol hygroscopic growth plays an important role in atmospheric particle chemistry and the effects of aerosol on radiation and hence climate. The hygroscopic growth is often characterized by a growth factor probability density function (GF-PDF), where the growth factor is defined as the ratio of the particle size at a specified relative humidity to its dry size. Parametric, least-square methods are the most widely used algorithms for inverting the GF-PDF from measurements of humidified tandem differential mobility analyzers (HTDMA) and have been recently applied to the GF-PDF inversion from measurements of the humidity-controlled fast integrated mobility spectrometer (HFIMS). However, these least square methods suffer from noise amplification due to the lack of regularization in solving the ill-posed problem, resulting in significant fluctuations in the retrieved GF-PDF and even occasional failures of convergence. In this study, we introduce nonparametric, regularized methods to invert aerosol GF-PDF and apply them to HFIMS measurements. Based on the HFIMS kernel function, the forward convolution is transformed into a matrix-based form, which facilitates the application of the nonparametric inversion methods with regularizations, including Tikhonov regularization and Twomey’s iterative regularization. Inversions of the GF-PDF using the nonparameteric methods with regularization are demonstrated using HFIMS measurements simulated from representative GF-PDFs of ambient aerosols. The characteristics of reconstructed GF-PDFs resulting from different inversion methods, including previously developed least-square methods, are quantitively compared. The result shows that Twomey’s method generally outperforms other inversion methods. The capabilities of the Twomey’s method in reconstructing the pre-defined GF-PDFs and recovering the mode parameters are validated.

Time-domain spectroscopy is a powerful probe of the electrical response of high-Tc thin films in ... more Time-domain spectroscopy is a powerful probe of the electrical response of high-Tc thin films in the millimeter and submillimeter regime. The ability to measure both the real and imaginary parts of the response without Kramers-Kronig analysis is particularly useful in understanding the dynamics of the superconducting state. We have recently designed a time- domain spectrometer which operates in conjunction with a superconducting magnet-cryostat in order to measure the change in the resistivity with field. Using this system we have measured the resistivity tensor of YBCO as a function of frequency from 100 to 800 GHz in a field of 0 to 6 Tesla. We interpret these results in terms of the combined vortex and quasiparticle response in the mixed state, and we believe we have made the first observation of the Hall response of quasiparticles at temperatures well below T.

This technology relates to the enlargement of air particles with diameters on the order of a few ... more This technology relates to the enlargement of air particles with diameters on the order of a few nanometers to hundreds of nanometers by water condensation in a laminar flow to form droplets with diameters of the order of several micrometers. The technology introduces more sophisticated designs, including the use of two-stage capacitors. It finds application in the measurement of the number concentration of particles suspended in air or other gas, in the collection of these particles or in the focusing of these particles.

La presente invention concerne un systeme et un procede de collecte d'aerosol. Le systeme com... more La presente invention concerne un systeme et un procede de collecte d'aerosol. Le systeme comprend un dispositif de distribution de bioaerosol concu pour envoyer des bioparticules dans un flux gazeux, un dispositif d'echange d'humidite comprenant un element de separation couple au flux gazeux et concu pour humidifier ou deshumidifier les bioparticules dans le flux gazeux, et un milieu de collecte d'aerosol en aval du dispositif d'echange d'humidite et concu pour collecter les bioparticules. Le procede consiste a distribuer des bioparticules dans un flux gazeux, a humidifier ou deshumidifier les bioparticules dans le flux gazeux par le transport de l'eau a travers un element de separation et dans une phase vapeur du flux gazeux, et a collecter les bioparticules au moyen d'un milieu de collecte.

Optical measurements have been made on rm YBa_2Cu_3O_7 and rm Bi_2Sr_2CaCu_2O_8 to search for bot... more Optical measurements have been made on rm YBa_2Cu_3O_7 and rm Bi_2Sr_2CaCu_2O_8 to search for both spontaneous Faraday rotation (in transmission) and spontaneous Kerr rotation (reflection). The observation of these magneto-optical effects near T _{c} would be a clear indication that the superconductivity in the cuprate superconductors can be explained by a theory which predicts broken time -reversal (T) symmetry. In particular, the "anyon" model of these materials predicts that T symmetry will be broken spontaneously as the material is cooled. The magneto-optical effects are expected to be quite small compared to the birefringence of the material. A method has been developed that uses a fiber-optic Sagnac interferometer to search for the magneto-optic signal. Incident upon the sample are two counter-propagating circularly polarized beams, whose electric fields have opposite time dependence. The interferometer detects Faraday or Kerr rotation by measuring the difference in phase between these beams after they have interacted with the sample. Because it is immune to birefringence in the sample, this method is superior to simply analyzing the polarization state of a single beam. Transmission experiments at 1060 nm wavelength were done with a modified fiber-optic gyroscope (a type of Sagnac interferometer). The nonreciprocal phase shift observed in the cuprates was less than the sensitivity (2 murad). A 670 nm interferometer was constructed to look for these effects in the visible portion of the spectrum, where other researchers have witnessed unusual polarization effects. Both reflection and transmission measurements at this wavelength indicate there are no magneto -optic effects to a sensitivity of 5 murad. This technique has been applied successfully to study ferromagnetic phase transitions in films of EuO and Gd.

Es wird eine Technologie fur die hocheffiziente Konzentration von feinen und ultrafeinen Schwebst... more Es wird eine Technologie fur die hocheffiziente Konzentration von feinen und ultrafeinen Schwebstoffteilchen zu einer kleinen Fraktion des beprobten Luftstroms durch Kondensationsvergroserung, aerodynamisches Fokussieren und Stromtrennung prasentiert. Eine Dusenkonzentratorstruktur, die eine Beschleunigungsduse mit einer Stromextraktionsstruktur enthalt, konnte an einen Aufnahmebehalter gekoppelt sein. Der Aufnahmebehalter konnte ein Wasserkondensationswachstumsrohr enthalten, um die Konzentration ultrafeiner Teilchen zu erleichtern. Der Aufnahmebehalter konnte ferner einen separaten Tragerstrom enthalten, der in der Mitte des beprobten Stroms eingeleitet wird, stromaufwarts der Beschleunigungsduse des Dusenkonzentrators, um die Trennung von Teilchen- und Dampfbestandteilen zu erleichtern.

. Capturing the vertical profiles and horizontal variations of atmospheric aerosols often require... more . Capturing the vertical profiles and horizontal variations of atmospheric aerosols often requires accurate airborne measurements. With the advantage of avoiding health and safety concerns related to the use of butanol or other chemicals, a water-based condensation particle counter (wCPC) has emerged to provide measurements under various environments. However, the airborne deployment of wCPC is relatively rare due to the lack of characterization of wCPC performance. This study investigates the performance of a commercial "versatile" water CPC (vWCPC Model 3789, TSI) under low-pressure conditions. The effect of conditioner temperature on wCPC performance at low pressure is examined through numerical simulation and laboratory experiments. We show that the default instrument temperature setting of 30 °C for the conditioner is not suitable for airborne measurement and that the optimal conditioner temperature for low-pressure operation is 27 °C. Additionally, we show that insufficient droplet growth becomes more significant under the low-pressure operation. The variation in the chemical composition can contribute up to 20 % uncertainty in the counting efficiency of the wCPC, but this variation is independent of pressure.

Aerosol Science and Technology

Aerosol Science and Technology

Abstract Hygroscopicity describes the tendency of aerosol particle to uptake water and is among t... more Abstract Hygroscopicity describes the tendency of aerosol particle to uptake water and is among the key parameters in determining the impact of atmospheric aerosols on global radiation and climate. A hygroscopicity tandem differential mobility analyzer (HTDMA) system is the most widely used instrument for determining the aerosol hygroscopic growth. Because of the time needed to scan the classifying voltage of the DMA, HTDMA measurement often requires a minimum of 30 min to characterize the particle hygroscopic growth at a single relative humidity for five to six different sizes. This slow speed is often inadequate for measurements onboard mobile platforms or when aerosols evolve rapidly. Recently, a humidity-controlled fast integrated mobility spectrometer (HFIMS) was developed for measuring the hygroscopic growth of particles. The measurement speed of the HFIMS is about one order of magnitude faster than that of the conventional HTDMA. In this work, a data inversion routine is developed to retrieve the growth factor probability density function (GF-PDF) of particles measured by the HFIMS. The inversion routine considers the transfer functions of the upstream DMA and the downstream water-based fast integrated mobility spectrometer (FIMS), and derives the GF-PDF that reproduces the measured responses of the HFIMS. The performance of the inversion routine is examined using ambient measurements with different assumptions for the spectral shape of the particle GF-PDF (multimodal lognormal or piecewise linear). The influences of the data inversion parameters and counting statistics on the inverted GF-PDFs were further investigated, and an approach to determine the optimized inversion parameters is presented. Copyright © 2019 American Association for Aerosol Research

Aerosol Science and Technology

Abstract The Spider differential mobility analyzer (DMA) is a novel, miniaturized radial DMA deve... more Abstract The Spider differential mobility analyzer (DMA) is a novel, miniaturized radial DMA developed to provide size classification in the 10–500 nm range for applications requiring high portability and time resolution. Its external dimensions are ∼12 cm in diameter by 6 cm in height (excluding tubing); it weighs ∼350 g, and is designed to operate at 0.6–1.5 L/min sheath and 0.3 L/min sample flowrates. It features a new sample inlet geometry that is designed to produce a uniform azimuthal particle distribution at the entrance of the classifier, optimized sample/sheath flow streams introduction in the classifier to minimize particle delays, and extension of the electric field interaction volume for ∼30% enhanced dynamic range. Based on three-dimensional finite element simulations of flows, electric fields, and particle trajectories, we demonstrate that the Spider DMA transfer functions can be predicted with high fidelity using a parameterized fit based on the Stolzenburg semi-analytical model. Experimental characterization of the instrument response with size-selected particles confirmed close agreement with model prediction; mobility size response is linear over three orders of magnitude in mobility span. Electrical ground shielding of the external surfaces of the DMA has been found to be necessary to avoid particle losses associated with field effects as the high voltage operating limit is approached. The mean deviation between the reference size of polystyrene latex spheres and the Spider DMA measurement is less than 2%, corroborating its high sizing precision and potential for high quality size distribution measurements. Copyright © 2019 American Association for Aerosol Research

Atmospheric Measurement Techniques Discussions