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1

Characterisation of coated aerosols using optical tweezers and neutron reflectometry  

NASA Astrophysics Data System (ADS)

Thin organic films are believed to form naturally on the surface of aerosols [1,2] and influence aerosol properties. Cloud condensation nuclei formation and chemical reactions such as aerosol oxidation are effected by the presence of thin films [3]. There is a requirement to characterise the physical properties of both the core aerosol and its organic film in order to fully understand the contribution of coated aerosols to the indirect effect. Two complementary techniques have been used to study the oxidation of thin organic films on the surface of aerosols; laser optical tweezers and neutron reflectometry. Micron sized polystyrene beads coated in oleic acid have been trapped in air using two counter propagating laser beams. Polystyrene beads are used as a proxy for solid aerosol. The trapped aerosol is illuminated with a white LED over a broadband wavelength range and the scattered light collected to produce a Mie spectrum [4]. Analysis of the Mie spectrum results in determination of the core polystyrene bead radius, the oleic acid film thickness and refractive index dispersion of the core and shell [5]. A flow of ozone gas can then be introduced into the aerosol environment to oxidise the thin film of oleic acid and the reaction followed by monitoring the changes in the Mie spectrum. The results demonstrate complete removal of the oleic acid film. We conclude that the use of a counter propagating optical trap combined with white light Mie spectroscopy can be used to study a range of organic films on different types of aerosols and their oxidation reactions. Neutron reflectometry has been used as a complementary technique to study the oxidation of monolayer films at the air-water interface in order to gain information on reaction kinetics. The oxidation of an oleic acid film at the air-water interface by the common tropospheric oxidant ozone has been studied using a Langmuir trough. Results indicate complete removal of the oleic acid film with ozone in agreement with the optical tweezers study, which confounds a previous study [6]. Findings also show complicated reaction kinetics that depend on the surface coverage of the film. Combining single particle studies using optical tweezing with macromolecular studies of thin films using neutron reflectometry provides a detailed atmospheric understanding of thin films on aerosols and their oxidation reactions. 1. Tervahattu H., Hartonen K., Kerminen V-H., Kupianen K., Aarnio P., Koskentalo T., Tuck A. and Vaida V., 2002, J. Geophys. Res. 107, 4053-4060. 2. Ellison G., Tuck A. and Vaida V., 1999, J. Geophys. Res. 104, 11633-11641. 3. King M.D., Thompson K.C., Ward A.D., 2004, JACS, 51, 16710-16711. 4. Ward A.D., Zhang M. and Hunt O., 2008, Opt. Express, 16, 16390-16403. 5. C.F. Bohren and D.R. Huffman, Absorption and Scattering of Light by Small Particles, (Wiley Scientific 1998). 6. King M.D., Rennie A.R., Thompson K.C., Fisher F.N., Dong C.C., Thomas R.K., Pfrang C., Hughes A.V., 2009, PCCP, 11, 7699-7707.

Jones, S. H.; Ward, A.; King, M. D.

2013-12-01

2

Micro-rheology and interparticle interactions in aerosols probed with optical tweezers  

NASA Astrophysics Data System (ADS)

Using optical tweezers for micro-rheological investigations of a surrounding fluid has been routinely demonstrated. In this work, we will demonstrate that rheological measurements of the bulk and surface properties of aerosol particles can be made directly using optical tweezers, providing important insights into the phase behavior of materials in confined environments and the rate of molecular diffusion in viscous phases. The use of holographic optical tweezers to manipulate aerosol particles has become standard practice in recent years, providing an invaluable tool to investigate particle dynamics, including evaporation/ condensation kinetics, chemical aging and phase transformation. When combined with non-linear Raman spectroscopy, the size and refractive index of a particle can be determined with unprecedented accuracy <+/- 0.05%). Active control of the relative positions of pairs of particles can allow studies of the coalescence of particles, providing a unique opportunity to investigate the bulk and surface properties that govern the hydrodynamic relaxation in particle shape. In particular, we will show how the viscosity and surface tension of particles can be measured directly in the under-damped regime at low viscosity. In the over-damped regime, we will show that viscosity measurements can extend close to the glass transition, allowing measurements over an impressive dynamic range of 12 orders of magnitude in relaxation timescale and viscosity. Indeed, prior to the coalescence event, we will show how the Brownian trajectories of trapped particles can yield important and unique insights into the interactions of aerosol particles.

Reid, Jonathan P.; Power, Rory M.; Cai, Chen; Simpson, Stephen H.

2014-09-01

3

Probing the micro-rheological properties of aerosol particles using optical tweezers  

NASA Astrophysics Data System (ADS)

The use of optical trapping techniques to manipulate probe particles for performing micro-rheological measurements on a surrounding fluid is well-established. Here, we review recent advances made in the use of optical trapping to probe the rheological properties of trapped particles themselves. In particular, we review observations of the continuous transition from liquid to solid-like viscosity of sub-picolitre supersaturated solution aerosol droplets using optical trapping techniques. Direct measurements of the viscosity of the particle bulk are derived from the damped oscillations in shape following coalescence of two particles, a consequence of the interplay between viscous and surface forces and the capillary driven relaxation of the approximately spheroidal composite particle. Holographic optical tweezers provide a facile method for the manipulation of arrays of particles allowing coalescence to be controllably induced between two micron-sized aerosol particles. The optical forces, while sufficiently strong to confine the composite particle, are several orders of magnitude weaker than the capillary forces driving relaxation. Light, elastically back-scattered by the particle, is recorded with sub-100 ns resolution allowing measurements of fast relaxation (low viscosity) dynamics, while the brightfield image can be used to monitor the shape relaxation extending to times in excess of 1000 s. For the slowest relaxation dynamics studied (particles with the highest viscosity) the presence and line shape of whispering gallery modes in the cavity enhanced Raman spectrum can be used to infer the relaxation time while serving the dual purpose of allowing the droplet size and refractive index to be measured with accuracies of ±0.025% and ±0.1%, respectively. The time constant for the damped relaxation can be used to infer the bulk viscosity, spanning from the dilute solution limit to a value approaching that of a glass, typically considered to be >1012 Pa s, whilst the frequencies of the normal modes of the oscillations of the particle can be used to infer surface properties. We will review the use of optical tweezers for studying the viscosity of aerosol particles and discuss the potential use of this micro-rheological tool for probing the fundamental concepts of phase, thermodynamic equilibrium and metastability.

Power, Rory M.; Reid, Jonathan P.

2014-07-01

4

Probing the micro-rheological properties of aerosol particles using optical tweezers.  

PubMed

The use of optical trapping techniques to manipulate probe particles for performing micro-rheological measurements on a surrounding fluid is well-established. Here, we review recent advances made in the use of optical trapping to probe the rheological properties of trapped particles themselves. In particular, we review observations of the continuous transition from liquid to solid-like viscosity of sub-picolitre supersaturated solution aerosol droplets using optical trapping techniques. Direct measurements of the viscosity of the particle bulk are derived from the damped oscillations in shape following coalescence of two particles, a consequence of the interplay between viscous and surface forces and the capillary driven relaxation of the approximately spheroidal composite particle. Holographic optical tweezers provide a facile method for the manipulation of arrays of particles allowing coalescence to be controllably induced between two micron-sized aerosol particles. The optical forces, while sufficiently strong to confine the composite particle, are several orders of magnitude weaker than the capillary forces driving relaxation. Light, elastically back-scattered by the particle, is recorded with sub-100 ns resolution allowing measurements of fast relaxation (low viscosity) dynamics, while the brightfield image can be used to monitor the shape relaxation extending to times in excess of 1000 s. For the slowest relaxation dynamics studied (particles with the highest viscosity) the presence and line shape of whispering gallery modes in the cavity enhanced Raman spectrum can be used to infer the relaxation time while serving the dual purpose of allowing the droplet size and refractive index to be measured with accuracies of ±0.025% and ±0.1%, respectively. The time constant for the damped relaxation can be used to infer the bulk viscosity, spanning from the dilute solution limit to a value approaching that of a glass, typically considered to be >10(12) Pa s, whilst the frequencies of the normal modes of the oscillations of the particle can be used to infer surface properties. We will review the use of optical tweezers for studying the viscosity of aerosol particles and discuss the potential use of this micro-rheological tool for probing the fundamental concepts of phase, thermodynamic equilibrium and metastability. PMID:24994710

Power, Rory M; Reid, Jonathan P

2014-07-01

5

Organic component vapor pressures and hygroscopicities of aqueous aerosol measured by optical tweezers.  

PubMed

Measurements of the hygroscopic response of aerosol and the particle-to-gas partitioning of semivolatile organic compounds are crucial for providing more accurate descriptions of the compositional and size distributions of atmospheric aerosol. Concurrent measurements of particle size and composition (inferred from refractive index) are reported here using optical tweezers to isolate and probe individual aerosol droplets over extended timeframes. The measurements are shown to allow accurate retrievals of component vapor pressures and hygroscopic response through examining correlated variations in size and composition for binary droplets containing water and a single organic component. Measurements are reported for a homologous series of dicarboxylic acids, maleic acid, citric acid, glycerol, or 1,2,6-hexanetriol. An assessment of the inherent uncertainties in such measurements when measuring only particle size is provided to confirm the value of such a correlational approach. We also show that the method of molar refraction provides an accurate characterization of the compositional dependence of the refractive index of the solutions. In this method, the density of the pure liquid solute is the largest uncertainty and must be either known or inferred from subsaturated measurements with an error of <±2.5% to discriminate between different thermodynamic treatments. PMID:25522920

Cai, Chen; Stewart, David J; Reid, Jonathan P; Zhang, Yun-Hong; Ohm, Peter; Dutcher, Cari S; Clegg, Simon L

2015-01-29

6

On chip shapeable optical tweezers  

PubMed Central

Particles manipulation with optical forces is known as optical tweezing. While tweezing in free space with laser beams was established in the 1980s, integrating the optical tweezers on a chip is a challenging task. Recent experiments with plasmonic nanoantennas, microring resonators, and photonic crystal nanocavities have demonstrated optical trapping. However, the optical field of a tweezer made of a single microscopic resonator cannot be shaped. So far, this prevents from optically driven micromanipulations. Here we propose an alternative approach where the shape of the optical trap can be tuned by the wavelength in coupled nanobeam cavities. Using these shapeable tweezers, we present micromanipulation of polystyrene microspheres trapped on a silicon chip. These results show that coupled nanobeam cavities are versatile building blocks for optical near-field engineering. They open the way to much complex integrated tweezers using networks of coupled nanobeam cavities for particles or bio-objects manipulation at a larger scale. PMID:23887310

Renaut, C.; Cluzel, B.; Dellinger, J.; Lalouat, L.; Picard, E.; Peyrade, D.; Hadji, E.; de Fornel, F.

2013-01-01

7

Interferometer Control of Optical Tweezers  

NASA Technical Reports Server (NTRS)

This paper discusses progress in using spatial light modulators and interferometry to control the beam profile of an optical tweezers. The approach being developed is to use a spatial light modulator (SLM) to control the phase profile of the tweezers beam and to use a combination of the SLM and interferometry to control the intensity profile. The objective is to perform fine and calculable control of the moments and forces on a tip or tool to be used to manipulate and interrogate nanostructures. The performance of the SLM in generating multiple and independently controllable tweezers beams is also reported. Concurrent supporting research projects are mentioned and include tweezers beam scattering and neural-net processing of the interference patterns for control of the tweezers beams.

Decker, Arthur J.

2002-01-01

8

Undergraduate Construction of Optical Tweezers  

NASA Astrophysics Data System (ADS)

I will present a poster on the construction of optical tweezers. This will demonstrate the full process one must go through when working on a research project. First I sifted through the internet for papers and information pertaining to the tweezers. Afterwards I discussed the budget with the lab manager. Next I made purchases, however some items, such as the sample mount, needed to be custom made. These I built in the machine shop. Once the tweezers were operational I spent some time ensuring that the mirrors and lenses were adjusted just right, so that the trap performed at full strength. Finally, I used video data of the Brownian motion of trapped silica microspheres to get a reasonable estimate of the trapping stiffness with such particles. As a general note, all of this was done with the intent of leaving the tweezers for future use by other undergraduates. Because of this extra effort was taken to ensure the tweezers were as safe to use as possible. For this reason a visible LASER was chosen over an infrared LASER, in addition, the LASER was oriented parallel to the surface of the table in order to avoid stray upwards beams.

Hubbell, Lawrence

2012-10-01

9

Advantages of holographic optical tweezers  

NASA Astrophysics Data System (ADS)

In the last decade optical tweezers became an important tool in microbiology. However, the setup becomes very complex if more than one trap needs to be moved. Holographic tweezers offer a very simple and cost efficient way of manipulating several traps independently in all three dimensions with an accuracy of less 100 nm. No mechanically moving parts are used therefore making them less vulnerable to vibration. They use computer-generated holograms (CGHs) written into a spatial light modulator (SLM) to control the position of each trap in space and to manipulate their shape. The ability to change the shape of the optical trap makes it possible to adapt the light field to a specific particle shape or in the case of force measurements to adjust the trapping potential. Furthermore the SLM can be used to correct for aberrations within the optical setup.

Reicherter, Marcus; Liesener, Jan; Haist, Tobias; Tiziani, Hans J.

2003-10-01

10

Optical tweezers technique and its applications  

NASA Astrophysics Data System (ADS)

Since their advent in the 1980s, optical tweezers have attracted more and more attention due to their unique non-contact and non-invasion characteristics and their wide applications in physics, biology, chemistry, medical science and nanoscience. In this paper, we introduce the basic principle, the history and typical applications of optical tweezers and review our recent experimental works on the development and application of optical tweezers technique. We will discuss in detail several technological issues, including high precision displacement and force measurement in single-trap and dual-trap optical tweezers, multi-trap optical tweezers with each trap independently and freely controlled by means of space light modulator, and incorporation of cylindrical vector optical beams to build diversified optical tweezers beyond the conventional Gaussian-beam optical tweezers. We will address the application of these optical tweezers techniques to study biophysical problems such as mechanical deformation of cell membrane and binding energy between plant microtubule and microtubule associated proteins. Finally we present application of the optical tweezers technique for trapping, transporting, and patterning of metallic nanoparticles, which can be harnessed to manipulate surface plasmon resonance properties of these nanoparticles.

Guo, HongLian; Li, ZhiYuan

2013-12-01

11

Fluorescence support in optical tweezers  

NASA Astrophysics Data System (ADS)

This paper presents the development of an installation for proves for characterization by fluorescence of micrometer and nanometer particles supported on the trapping and manipulation by optical trapping technique (optical tweezers). The system features an laser operating at 480 nm, CCD camera for image acquisition, Thor Labs micrometric table X, Y, Z for the movement of the sample and the trap in the visual field. The design includes the use of intensity modulated optical trap, with the option of being used in pulsed, opening up possibilities for the use of resonant phenomena optomechanical type for particle capture.

Animas, J. G.; Arronte, M.; Flores, T.; Ponce, L.

2013-11-01

12

Absolute calibration of optical tweezers  

SciTech Connect

As a step toward absolute calibration of optical tweezers, a first-principles theory of trapping forces with no adjustable parameters, corrected for spherical aberration, is experimentally tested. Employing two very different setups, we find generally very good agreement for the transverse trap stiffness as a function of microsphere radius for a broad range of radii, including the values employed in practice, and at different sample chamber depths. The domain of validity of the WKB ('geometrical optics') approximation to the theory is verified. Theoretical predictions for the trapping threshold, peak position, depth variation, multiple equilibria, and 'jump' effects are also confirmed.

Viana, N.B.; Mazolli, A.; Maia Neto, P.A.; Nussenzveig, H.M.; Rocha, M.S.; Mesquita, O.N. [LPO-COPEA and Instituto de Fisica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-590 (Brazil); Departamento de Fisica, Instituto de Ciencias ExatasUniversidade Federal de Minas Gerais, Belo Horizonte, MG, 30123-970 (Brazil)

2006-03-27

13

optical tweezers tractor beams  

E-print Network

; force/extension) cell membrane mech props molecular motors (kinesin stepping on microtubules) In vitro fertilization; sperm cell motility optical scissors (chromosomes dissection + manipulation) In vivo..? K

14

Quantum limited particle sensing in optical tweezers  

SciTech Connect

Particle sensing in optical tweezers systems provides information on the position, velocity, and force of the specimen particles. The conventional quadrant detection scheme is applied ubiquitously in optical tweezers experiments to quantify these parameters. In this paper, we show that quadrant detection is nonoptimal for particle sensing in optical tweezers and propose an alternative optimal particle sensing scheme based on spatial homodyne detection. A formalism for particle sensing in terms of transverse spatial modes is developed and numerical simulations of the efficacies of both quadrant and spatial homodyne detection are shown. We demonstrate that 1 order of magnitude improvement in particle sensing sensitivity can be achieved using spatial homodyne over quadrant detection.

Tay, J.W. [Jack Dodd Centre for Photonics and Ultracold Atoms, Department of Physics, University of Otago, Dunedin (New Zealand); Hsu, Magnus T. L. [School of Mathematics and Physics, University of Queensland, St. Lucia, Queensland 4072 (Australia); Bowen, Warwick P. [Jack Dodd Centre for Photonics and Ultracold Atoms, Department of Physics, University of Otago, Dunedin (New Zealand); School of Mathematics and Physics, University of Queensland, St. Lucia, Queensland 4072 (Australia)

2009-12-15

15

Optical tweezers: light for manipulating microscopic world  

NASA Astrophysics Data System (ADS)

Optical tweezers make use of a tightly focused laser beam to trap, move, guide, rotate and even sort microscopic objects solely with light. Although the basic laser tweezers, making use of a TEM00 laser beam to create a single trap point, have proved to be useful for any applications in areas ranging from physics to biology, a major breakthrough in this field came as the use of computer generated holograms enabled researchers to create multiple trap sites from single laser source (holographic optical tweezers). Coupled with microfluidic techniques, holographic optical tweezers have promised development of optical techniques for high throughput sorting of different cell types under a single micro-chip platform. The holographic methods have also helped the use of specialized laser beams like Laguerre-Gaussian beams instead of the conventional laser beam for interesting applications like orienting/rotating the trapped objects or trapping cells with minimum photodamage. Further, combining optical tweezers with Raman spectroscopy is becoming increasingly popular for studying single cell biochemistry as use of optical forces to immobilize the cells under investigations not only avoids the negative effects of fixing the cells onto substrate but also improve the quality of the recorded spectra. These advanced optical trapping techniques as outlined above along with some illustrative biophotonics applications have been explored.

Dasgupta, Raktim

2012-05-01

16

Quantum computation architecture using optical tweezers  

SciTech Connect

We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits require the transport of atoms to neighboring sites. We numerically optimize the nonadiabatic transport of the atoms through the lattice and the intensity ramps of the optical tweezer in order to maximize the gate fidelities. We find overall gate times of a few 100 {mu}s, while keeping the error probability due to vibrational excitations and spontaneous scattering below 10{sup -3}. The requirements on the positioning error and intensity noise of the optical tweezer and the magnetic field stability are analyzed and we show that atoms in optical lattices could meet the requirements for fault-tolerant scalable quantum computing.

Weitenberg, Christof [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); Kuhr, Stefan [Max-Planck-Institut fuer Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching (Germany); University of Strathclyde, Department of Physics, SUPA, Glasgow G4 0NG (United Kingdom); Moelmer, Klaus; Sherson, Jacob F. [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2011-09-15

17

Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy  

PubMed Central

Single-molecule force spectroscopy has emerged as a powerful tool to investigate the forces and motions associated with biological molecules and enzymatic activity. The most common force spectroscopy techniques are optical tweezers, magnetic tweezers and atomic force microscopy. These techniques are described and illustrated with examples highlighting current capabilities and limitations. PMID:18511917

Neuman, Keir C.; Nagy, Attila

2012-01-01

18

Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic  

E-print Network

Single-molecule force spectroscopy: optical tweezers, magnetic tweezers and atomic force microscopy Keir C Neuman1 & Attila Nagy2 Single-molecule force spectroscopy has emerged as a powerful tool and displacement generated by single molecules ranging from cells to proteins. Although there is an ever

Ritort, Felix

19

"Red Tweezers": Fast, customisable hologram generation for optical tweezers  

NASA Astrophysics Data System (ADS)

Holographic Optical Tweezers (HOT) are a versatile way of manipulating microscopic particles in 3D. However, their ease of use has been hampered by the computational load of calculating the holograms, resulting in an unresponsive system. We present a program for generating these holograms on a consumer Graphics Processing Unit (GPU), coupled to an easy-to-use interface in LabVIEW (National Instruments). This enables a HOT system to be set up without writing any additional code, as well as providing a platform enabling the fast generation of other holograms. The GPU engine calculates holograms over 300 times faster than the same algorithm running on a quad core CPU. The hologram algorithm can be altered on-the-fly without recompiling the program, allowing it to be used to control Spatial Light Modulators in any situation where the hologram can be calculated in a single pass. The interface has also been rewritten to take advantage of new features in LabVIEW 2010. It is designed to be easily modified and extended to integrate with hardware other than our own.

Bowman, Richard W.; Gibson, Graham M.; Linnenberger, Anna; Phillips, David B.; Grieve, James A.; Carberry, David M.; Serati, Steven; Miles, Mervyn J.; Padgett, Miles J.

2014-01-01

20

Investigating hydrodynamic synchronisation using holographic optical tweezers  

NASA Astrophysics Data System (ADS)

Coordinated motion at low Reynolds number is widely observed in biological micro-systems, but the underlying mechanisms are often unclear. A holographic optical tweezers system is used to experimentally study this phenomenon, by employing optical forces to drive a pair of coplanar microspheres in circular orbits with a constant tangential force. In this system synchronisation is caused by hydrodynamic forces arising from the motion of the two spheres. The timescales of their synchronisation from large initial phase differences are explored and found to be dependent on how stiffly the microspheres are confined to their circular orbits. These measured timescales show good agreement with numerical simulations.

Box, Stuart; Debono, Luke; Bruot, Nicolas; Kotar, Jurij; Cicuta, Pietro; Miles, Mervyn; Hanna, Simon; Phillips, David; Simpson, Stephen

2014-09-01

21

Measuring storage and loss moduli using optical tweezers: broadband microrheology  

E-print Network

We present an experimental procedure to perform broadband microrheological measurements with optical tweezers. A generalised Langevin equation is adopted to relate the time-dependent trajectory of a particle in an imposed flow to the frequency-dependent moduli of the complex fluid. This procedure allows us to measure the material linear viscoelastic properties across the widest frequency range achievable with optical tweezers.

Manlio Tassieri; Graham M. Gibson; R. M. L. Evans; Alison M. Yao; Rebecca Warren; Miles J. Padgett; Jonathan M. Cooper

2009-10-07

22

Absolute calibration of forces in optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers are highly versatile laser traps for neutral microparticles, with fundamental applications in physics and in single molecule cell biology. Force measurements are performed by converting the stiffness response to displacement of trapped transparent microspheres, employed as force transducers. Usually, calibration is indirect, by comparison with fluid drag forces. This can lead to discrepancies by sizable factors. Progress achieved in a program aiming at absolute calibration, conducted over the past 15 years, is briefly reviewed. Here we overcome its last major obstacle, a theoretical overestimation of the peak stiffness, within the most employed range for applications, and we perform experimental validation. The discrepancy is traced to the effect of primary aberrations of the optical system, which are now included in the theory. All required experimental parameters are readily accessible. Astigmatism, the dominant effect, is measured by analyzing reflected images of the focused laser spot, adapting frequently employed video microscopy techniques. Combined with interface spherical aberration, it reveals a previously unknown window of instability for trapping. Comparison with experimental data leads to an overall agreement within error bars, with no fitting, for a broad range of microsphere radii, from the Rayleigh regime to the ray optics one, for different polarizations and trapping heights, including all commonly employed parameter domains. Besides signaling full first-principles theoretical understanding of optical tweezers operation, the results may lead to improved instrument design and control over experiments, as well as to an extended domain of applicability, allowing reliable force measurements, in principle, from femtonewtons to nanonewtons.

Dutra, R. S.; Viana, N. B.; Maia Neto, P. A.; Nussenzveig, H. M.

2014-07-01

23

Micromechanics of Dipolar Chains Using Optical Tweezers  

NASA Technical Reports Server (NTRS)

Here we present our initial study of the micromechanical properties of dipolar chains and columns in a magnetorheological (MR) suspension. Using dual-trap optical tweezers, we are able to directly measure the deformation of the dipolar chains parallel and perpendicular to the applied magnetic field. We observe the field dependence of the mechanical properties such as resistance to deformation, chain reorganization, and rupturing of the chains. These forms of energy dissipation are important for understanding and tuning the yield stress and rheological behavior of an MR suspension.

Furst, Eric M.; Gast, Alice P.

1999-01-01

24

Multiplexed spectroscopy with holographic optical tweezers  

NASA Astrophysics Data System (ADS)

We have developed a multiplexed holographic optical tweezers system with an imaging spectrometer to manipulate multiple optically trapped nanosensors and detect multiple fluorescence spectra. The system uses a spatial light modulator (SLM) to control the positions of infrared optical traps in the sample so that multiple nanosensors can be positioned into regions of interest. Spectra of multiple nanosensors are detected simultaneously with the application of an imaging spectrometer. Nanosensors are capable of detecting changes in their environment such as pH, ion concentration, temperature, and voltage by monitoring changes in the nanosensors' emitted fluorescence spectra. We use streptavidin labeled quantum dots bound to the surface of biotin labeled polystyrene microspheres to measure temperature changes by observing a corresponding shift in the wavelength of the spectral peak. The fluorescence is excited at 532 nm with a wide field source.

Cibula, Matthew A.; McIntyre, David H.

2014-09-01

25

Stretching DNA with optical tweezers.  

PubMed Central

Force-extension (F-x) relationships were measured for single molecules of DNA under a variety of buffer conditions, using an optical trapping interferometer modified to incorporate feedback control. One end of a single DNA molecule was fixed to a coverglass surface by means of a stalled RNA polymerase complex. The other end was linked to a microscopic bead, which was captured and held in an optical trap. The DNA was subsequently stretched by moving the coverglass with respect to the trap using a piezo-driven stage, while the position of the bead was recorded at nanometer-scale resolution. An electronic feedback circuit was activated to prevent bead movement beyond a preset clamping point by modulating the light intensity, altering the trap stiffness dynamically. This arrangement permits rapid determination of the F-x relationship for individual DNA molecules as short as -1 micron with unprecedented accuracy, subjected to both low (approximately 0.1 pN) and high (approximately 50 pN) loads: complete data sets are acquired in under a minute. Experimental F-x relationships were fit over much of their range by entropic elasticity theories based on worm-like chain models. Fits yielded a persistence length, Lp, of approximately 47 nm in a buffer containing 10 mM Na1. Multivalent cations, such as Mg2+ or spermidine 3+, reduced Lp to approximately 40 nm. Although multivalent ions shield most of the negative charges on the DNA backbone, they did not further reduce Lp significantly, suggesting that the intrinsic persistence length remains close to 40 nm. An elasticity theory incorporating both enthalpic and entropic contributions to stiffness fit the experimental results extremely well throughout the full range of extensions and returned an elastic modulus of approximately 1100 pN. Images FIGURE 1 FIGURE 2 PMID:9138579

Wang, M D; Yin, H; Landick, R; Gelles, J; Block, S M

1997-01-01

26

Optical tweezers calibration with Bayesian inference  

NASA Astrophysics Data System (ADS)

We present a new method for calibrating an optical-tweezer setup that is based on Bayesian inference1. This method employs an algorithm previously used to analyze the confined trajectories of receptors within lipid rafts2,3. The main advantages of this method are that it does not require input parameters and is insensitive to systematic errors like the drift of the setup. Additionally, it exploits a much larger amount of the information stored in the recorded bead trajectory than standard calibration approaches. The additional information can be used to detect deviations from the perfect harmonic potential or detect environmental influences on the bead. The algorithm infers the diffusion coefficient and the potential felt by a trapped bead, and only requires the bead trajectory as input. We demonstrate that this method outperforms the equipartition method and the power-spectrum method in input information required (bead radius and trajectory length) and in output accuracy. Furthermore, by inferring a higher order potential our method can reveal deviations from the assumed second-order potential. More generally, this method can also be used for magnetic-tweezer calibration.

Türkcan, Silvan; Richly, Maximilian U.; Le Gall, Antoine; Fiszman, Nicolas; Masson, Jean-Baptiste; Westbrook, Nathalie; Perronet, Karen; Alexandrou, Antigoni

2014-09-01

27

Universal axial fluctuations in optical tweezers.  

PubMed

Optical tweezers (OTs) allow the measurement of fluctuations at the nanoscale, in particular fluctuations in the end-to-end distance in single molecules. Fluctuation spectra can yield valuable information, but they can easily be contaminated by instrumental effects. We identify axial fluctuations, i.e., fluctuations of the trapped beads in the direction of light propagation, as one of these instrumental effects. Remarkably, axial fluctuations occur on a characteristic timescale similar to that of conformational (folding) transitions, which may lead to misinterpretation of the experimental results. We show that a precise measurement of the effect of force on both axial and conformational fluctuations is crucial to disentangle them. Our results on axial fluctuations are captured by a simple and general formula valid for all OT setups and provide experimentalists with a general strategy to distinguish axial fluctuations from conformational transitions. PMID:25723436

Ribezzi-Crivellari, Marco; Alemany, Anna; Ritort, Felix

2015-03-01

28

Exploring the mechanome with optical tweezers and single molecule fluorescence  

E-print Network

The combination of optical tweezers and single molecule fluorescence into an instrument capable of making combined, coincident measurements adds an observable dimension that allows for the examination of the localized ...

Brau, Ricardo R. (Ricardo Rafael), 1979-

2008-01-01

29

Optical capsule and tweezer array for molecular motor use.  

PubMed

A generation of optical capsules and tweezers within a modified optical add-drop filter known as PANDA ring resonator with a new concept is proposed. By using dark and bright solitons, the orthogonal tweezers can be formed within the system and observed simultaneously at the output ports. Under the resonant condition, the optical capsules and tweezers generated by dark and bright soliton pair corresponding to the left-hand and right-hand rotating solitons (tweezers) can be generated. When a soliton is interacted by an object, an angular momentum of either bright or dark tweezers is imparted to the object, in which two possible spin states known as tweezer spins are exhibited. Furthermore, an array of molecular capsules and spins, i.e., trapped molecules can be generated and detected by using the proposed system, which can be used to form large scale tweezer or capsule spins. In application, the trapped molecules can be moved and rotated securely to the required destinations, which can be useful for many applications, especially, in medical diagnosis, therapy and surgery. PMID:23955778

Yupapin, Preecha P; Kulsirirat, Kathawut; Techithdeera, Wicharn

2013-09-01

30

Measuring storage and loss moduli using optical tweezers: broadband microrheology.  

PubMed

We present an experimental procedure to perform broadband microrheological measurements with optical tweezers. A generalized Langevin equation is adopted to relate the time-dependent trajectory of a particle in an imposed flow to the frequency-dependent moduli of the complex fluid. This procedure allows us to measure the material linear viscoelastic properties across the widest frequency range achievable with optical tweezers. PMID:20365652

Tassieri, Manlio; Gibson, Graham M; Evans, R M L; Yao, Alison M; Warren, Rebecca; Padgett, Miles J; Cooper, Jonathan M

2010-02-01

31

Sorting out bacterial viability with optical tweezers.  

PubMed

We have developed a method, using laser, optical tweezers and direct microscopic analysis of reproductive potential and membrane integrity, to assess single-cell viability in a stationary-phase Escherichia coli population. It is demonstrated here that a reduction in cell integrity, determined by using the fluorescent nucleic acid stain propidium iodide, correlated well with a reduction in cell proliferating potential during the stationary-phase period studied. Moreover, the same cells that exhibited reduced integrity were found to be the ones that failed to divide upon nutrient addition. A small but significant number of the intact cells (496 of 7,466 [6.6%]) failed to replicate. In other words, we did not find evidence for the existence of a large population of intact but nonculturable cells during the stationary-phase period studied but it is clear that reproductive ability can be lost prior to the loss of membrane integrity. In addition, about 1% of the stationary-phase cells were able to divide only once upon nutrient addition, and in a few cases, only one of the two cells produced by division was able to divide a second time, indicating that localized cell deterioration, inherited by only one of the daughters, may occur. The usefulness of the optical trapping methodology in elucidating the mechanisms involved in stationary-phase-induced bacterial death and population heterogeneity is discussed. PMID:10986260

Ericsson, M; Hanstorp, D; Hagberg, P; Enger, J; Nyström, T

2000-10-01

32

Tunable optical tweezers for wavelength-dependent measurements  

PubMed Central

Optical trapping forces depend on the difference between the trap wavelength and the extinction resonances of trapped particles. This leads to a wavelength-dependent trapping force, which should allow for the optimization of optical tweezers systems, simply by choosing the best trapping wavelength for a given application. Here we present an optical tweezer system with wavelength tunability, for the study of resonance effects. With this system, the optical trap stiffness is measured for single trapped particles that exhibit either single or multiple extinction resonances. We include discussions of wavelength-dependent effects, such as changes in temperature, and how to measure them. PMID:22559522

Hester, Brooke; Campbell, Gretchen K.; López-Mariscal, Carlos; Filgueira, Carly Levin; Huschka, Ryan; Halas, Naomi J.; Helmerson, Kristian

2012-01-01

33

Optical Tweezers Array and Nimble Tweezers Probe Generated by Spatial- Light Modulator  

NASA Technical Reports Server (NTRS)

An optical tweezers is being developed at the NASA Glenn Research Center as a visiblelight interface between ubiquitous laser technologies and the interrogation, visualization, manufacture, control, and energization of nanostructures such as silicon carbide (SiC) nanotubes. The tweezers uses one or more focused laser beams to hold micrometer-sized particles called tools (sometimes called tips in atomic-force-microscope terminology). A strongly focused laser beam has an associated light-pressure gradient that is strong enough to pull small particles to the focus, in spite of the oppositely directed scattering force; "optical tweezers" is the common term for this effect. The objective is to use the tools to create carefully shaped secondary traps to hold and assemble nanostructures that may contain from tens to hundreds of atoms. The interaction between a tool and the nanostructures is to be monitored optically as is done with scanning probe microscopes. One of the initial efforts has been to create, shape, and control multiple tweezers beams. To this end, a programmable spatial-light modulator (SLM) has been used to modify the phase of a laser beam at up to 480 by 480 points. One program creates multiple, independently controllable tweezer beams whose shapes can be tailored by making the SLM an adaptive mirror in an interferometer (ref. 1). The beams leave the SLM at different angles, and an optical Fourier transform maps these beams to different positions in the focal plane of a microscope objective. The following figure shows two arrays of multiple beams created in this manner. The patterns displayed above the beam array control the intensity-to-phase transformation required in programming the SLM. Three of the seven beams displayed can be used as independently controllable beams.

Decker, Arthur J.; Jassemnejad, Baha; Seibel, Robin E.; Weiland, Kenneth E.

2003-01-01

34

Optical tweezers reveal how proteins alter replication  

NASA Astrophysics Data System (ADS)

Single molecule force spectroscopy is a powerful method that explores the DNA interaction properties of proteins involved in a wide range of fundamental biological processes such as DNA replication, transcription, and repair. We use optical tweezers to capture and stretch a single DNA molecule in the presence of proteins that bind DNA and alter its mechanical properties. We quantitatively characterize the DNA binding mechanisms of proteins in order to provide a detailed understanding of their function. In this work, we focus on proteins involved in replication of Escherichia coli (E. coli ), endogenous eukaryotic retrotransposons Ty3 and LINE-1, and human immunodeficiency virus (HIV). DNA polymerases replicate the entire genome of the cell, and bind both double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) during DNA replication. The replicative DNA polymerase in the widely-studied model system E. coli is the DNA polymerase III subunit alpha (DNA pol III alpha). We use optical tweezers to determine that UmuD, a protein that regulates bacterial mutagenesis through its interactions with DNA polymerases, specifically disrupts alpha binding to ssDNA. This suggests that UmuD removes alpha from its ssDNA template to allow DNA repair proteins access to the damaged DNA, and to facilitate exchange of the replicative polymerase for an error-prone translesion synthesis (TLS) polymerase that inserts nucleotides opposite the lesions, so that bacterial DNA replication may proceed. This work demonstrates a biophysical mechanism by which E. coli cells tolerate DNA damage. Retroviruses and retrotransposons reproduce by copying their RNA genome into the nuclear DNA of their eukaryotic hosts. Retroelements encode proteins called nucleic acid chaperones, which rearrange nucleic acid secondary structure and are therefore required for successful replication. The chaperone activity of these proteins requires strong binding affinity for both single- and double-stranded nucleic acids. We use single molecule DNA stretching to show that the nucleocapsid protein (NC) of the yeast retrotransposon Ty3, which is likely to be an ancestor of HIV NC, has optimal nucleic acid chaperone activity with only a single zinc finger. We also show that the chaperone activity of the ORF1 protein is responsible for successful replication of the mouse LINE-1 retrotransposon. LINE-1 is also 17% of the human genome, where it generates insertion mutations and alters gene expression. Retrotransposons such as LINE-1 and Ty3 are likely to be ancestors of retroviruses such as HIV. Human APOBEC3G (A3G) inhibits HIV-1 replication via cytidine deamination of the viral ssDNA genome, as well as via a distinct deamination-independent mechanism. Efficient deamination requires rapid on-off binding kinetics, but a slow dissociation rate is required for the proposed deaminase-independent mechanism. We resolve this apparent contradiction with a new quantitative single molecule method, which shows that A3G initially binds ssDNA with fast on-off rates and subsequently converts to a slow binding mode. This suggests that oligomerization transforms A3G from a fast enzyme to a slow binding protein, which is the biophysical mechanism that allows A3G to inhibit HIV replication. A complete understanding of the mechanism of A3G-mediated antiviral activity is required to design drugs that disrupt the viral response to A3G, enhance A3G packaging inside the viral core, and other potential strategies for long-term treatment of HIV infection. We use single molecule biophysics to explore the function of proteins involved in bacterial DNA replication, endogenous retrotransposition of retroelements in eukaryotic hosts such yeast and mice, and HIV replication in human cells. Our quantitative results provide insight into protein function in a range of complex biological systems and have wide-ranging implications for human health.

Chaurasiya, Kathy

35

Magneto-optical tweezers built around an inverted microscope  

SciTech Connect

We present a simple experimental setup of magneto-optical tweezers built around an inverted microscope. Two pairs of coils placed around the focal point of the objective generate a planar-rotating magnetic field that is perpendicular to the stretching direction. This configuration allows us to control the rotary movement of a paramagnetic bead trapped in the optical tweezers. The mechanical design is universal and can be simply adapted to any inverted microscope and objective. The mechanical configuration permits the use of a rather large experimental cell and the simple assembly and disassembly of the magnetic attachment.

Claudet, Cyril; Bednar, Jan

2005-06-10

36

Magneto-optical tweezers built around an inverted microscope.  

PubMed

We present a simple experimental setup of magneto-optical tweezers built around an inverted microscope. Two pairs of coils placed around the focal point of the objective generate a planar-rotating magnetic field that is perpendicular to the stretching direction. This configuration allows us to control the rotary movement of a paramagnetic bead trapped in the optical tweezers. The mechanical design is universal and can be simply adapted to any inverted microscope and objective. The mechanical configuration permits the use of a rather large experimental cell and the simple assembly and disassembly of the magnetic attachment. PMID:16007842

Claudet, Cyril; Bednar, Jan

2005-06-10

37

Marker-free cell discrimination by holographic optical tweezers  

NASA Astrophysics Data System (ADS)

We introduce a method for marker-free cell discrimination based on optical tweezers. Cancerous, non-cancerous, and drug-treated cells could be distinguished by measuring the trapping forces using holographic optical tweezers. We present trapping force measurements on different cell lines: normal pre-B lymphocyte cells (BaF3; "normal cells"), their Bcr-Abl transformed counterparts (BaF3-p185; "cancer cells") as a model for chronic myeloid leukaemia (CML) and Imatinib treated BaF3-p185 cells. The results are compared with reference measurements obtained by a commercial flow cytometry system.

Schaal, F.; Warber, M.; Zwick, S.; van der Kuip, H.; Haist, T.; Osten, W.

2009-06-01

38

Dynamic optical tweezers based assay for monitoring early drug resistance  

NASA Astrophysics Data System (ADS)

In this letter, a dynamic optical tweezers based assay is proposed and investigated for monitoring early drug resistance with Pemetrexed-resistant non-small cell lung cancer (NSCLC) cell lines. The validity and stability of the method are verified experimentally in terms of the physical parameters of the optical tweezers system. The results demonstrate that the proposed technique is more convenient and faster than traditional techniques when the capability of detecting small variations of the response of cells to a drug is maintained.

Wu, Xiaojing; Zhang, Yuquan; Min, Changjun; Zhu, Siwei; Feng, Jie; Yuan, X.-C.

2013-06-01

39

Cluster formation in ferrofluids induced by holographic optical tweezers.  

PubMed

Holographic optical tweezers were used to show the interaction between a strongly focused laser beam and magnetic nanoparticles in ferrofluid. When the light intensity was high enough, magnetic nanoparticles were removed from the beam center and formed a dark ring. The same behavior was observed when focusing vortex or Bessel beams. The interactions between two or more separated rings of magnetic nanoparticles created by independent optical traps were also observed. PMID:24081086

Masajada, Jan; Bacia, Marcin; Drobczy?ski, S?awomir

2013-10-01

40

Multiplying optical tweezers force using a micro-lever  

E-print Network

Multiplying optical tweezers force using a micro-lever Chih-Lang Lin1* , Yi-Hsiung Lee2 , Yi-Jui Liu2,3 , Jiann-Lih Hwang2 , Chin-Te Lin,4 Tien-Tung Chung4 , and Patrice L. Baldeck 1,5 1 Inst-driven micro-lever fabricated to multiply optical forces using the two-photon polymerization 3D

Boyer, Edmond

41

A microscopic steam engine implemented in an optical tweezer.  

PubMed

The introduction of improved steam engines at the end of the 18th century marked the start of the industrial revolution and the birth of classical thermodynamics. Currently, there is great interest in miniaturizing heat engines, but so far traditional heat engines operating with the expansion and compression of gas have not reached length scales shorter than one millimeter. Here, a micrometer-sized piston steam engine is implemented in an optical tweezer. The piston is a single colloidal microparticle that is driven by explosive vapourization of the surrounding liquid (cavitation bubbles) and by optical forces at a rate between a few tens of Hertz and one kilo-Hertz. The operation of the engine allows to exert impulsive forces with optical tweezers and induce streaming in the liquid, similar to the effect of transducers when driven at acoustic and ultrasound frequencies. PMID:25523395

Quinto-Su, Pedro A

2014-01-01

42

A microscopic steam engine implemented in an optical tweezer  

NASA Astrophysics Data System (ADS)

The introduction of improved steam engines at the end of the 18th century marked the start of the industrial revolution and the birth of classical thermodynamics. Currently, there is great interest in miniaturizing heat engines, but so far traditional heat engines operating with the expansion and compression of gas have not reached length scales shorter than one millimeter. Here, a micrometer-sized piston steam engine is implemented in an optical tweezer. The piston is a single colloidal microparticle that is driven by explosive vapourization of the surrounding liquid (cavitation bubbles) and by optical forces at a rate between a few tens of Hertz and one kilo-Hertz. The operation of the engine allows to exert impulsive forces with optical tweezers and induce streaming in the liquid, similar to the effect of transducers when driven at acoustic and ultrasound frequencies.

Quinto-Su, Pedro A.

2014-12-01

43

Probing DNA with micro- and nanocapillaries and optical tweezers  

NASA Astrophysics Data System (ADS)

We combine for the first time optical tweezer experiments with the resistive pulse technique based on capillaries. Quartz glass capillaries are pulled into a conical shape with tip diameters as small as 27 nm. Here, we discuss the translocation of ?-phage DNA which is driven by an electrophoretic force through the nanocapillary. The resulting change in ionic current indicates the folding state of single ?-phage DNA molecules. Our flow cell design allows for the straightforward incorporation of optical tweezers. We show that a DNA molecule attached to an optically trapped colloid is pulled into a capillary by electrophoretic forces. The detected electrophoretic force is in good agreement with measurements in solid-state nanopores.

Steinbock, L. J.; Otto, O.; Skarstam, D. R.; Jahn, S.; Chimerel, C.; Gornall, J. L.; Keyser, U. F.

2010-11-01

44

Optical tweezers experiments for fibroblast cell growth stimulation  

NASA Astrophysics Data System (ADS)

Optical tweezers constitute an increasingly used tool for the study of biomechanical properties of cells. Here we report experiments for the projection induction of NIH3T3 fibroblast cells, using a single-trap optical tweezers. The system is based on a 1064-nm, 50mW infrared gaussian laser beam, a 100x microscope objective with 1.25 numerical aperture and a temperature-controlled warming plate to maintain cell viability. Eighteen cells were exposed to the focussed laser beam in different cell zones and another 18 cells were observed without laser stimulation as a control population. The results show that the probability of lamelipodia growth increases on exposed cells by a factor 1.5.

Avila, Remy; Medina-Villalobos, Norma; Tamariz, Elisa; Chiu, Roger; Lopez-Marín, Luz María.; Acosta, Angélica; Castaño, Victor

2014-05-01

45

Construction of an optical tweezer for nanometer scale rheology  

NASA Astrophysics Data System (ADS)

The optical tweezer is a versatile set-up that can be employed in a wide variety of studies investigating the microscopic properties of materials. In particular, this set-up has in recent times been gainfully employed in probing rheological properties of materials that exhibit viscoelasticity. These measurements can provide data at the micro and nanometer scales, not normally accessible by rheometers that are used for measurements on bulk samples. In this work we describe a single laser beam optical tweezer set-up, which is built around an inverted open microscope. The trapped polystyrene particle bead's deviation from the trap potential minimum is monitored by laser back-scattering technique and the bead position measured by a quadrant photodiode detector. Additionally, a provision is made for video microscopic studies on dispersed beads using a CCD camera. A single particle microrheological experiment that can be performed using the set-up is described with relevant calculations.

Raghu, A.; Ananthamurthy, Sharath

2005-10-01

46

Optical tweezers for mechanical control over DNA in a nanopore.  

PubMed

The translocation of long-chain molecules, such as DNA or peptides, through membranes is an integral process for the function of living cells. During the translocation process, a number of interactions of electrostatic or hydrophobic nature govern the translocation velocity. Most of these interactions remain largely unexplored on the single-molecule level due to a lack of suitable instrumentation. We have shown that a combination of optical tweezers, single solid-state nanopores, and electrophysiological ionic current detection can provide further insight into the behavior of polymers in confinement. Here, we describe the experimental procedures necessary for manipulation of single biopolymers in a single nanopore not only by electrical fields, but also through mechanical forces using optical tweezers. PMID:22528261

Keyser, Ulrich F

2012-01-01

47

Optical manipulation of aerosol particle arrays  

NASA Astrophysics Data System (ADS)

Aerosols play a crucial role in many areas of science, ranging from atmospheric chemistry and physics, to drug delivery to the lungs, combustion science and spray drying. The development of new methods to characterise the properties and dynamics of aerosol particles is of crucial importance if the complex role that particles play is to be more fully understood. Optical tweezers provide a valuable new tool to address fundamental questions in aerosol science. Single or multiple particles 1-15 ?m in diameter can be manipulated over indefinite timescales using optical tweezing. Linear and non-linear Raman and fluorescence spectroscopies can be used to probe a particle's composition and size. In this paper we will report on the latest developments in the use of holographic optical trapping (HOT) to study aerosols. Although widely used to trap and manipulate arrays of particles in the condensed phase, the application of HOT to aerosols is still in its infancy. We will explore the opportunities provided by the formation of complex optical landscapes for controlling aerosol flow, for comparing the properties of multiple particles, for performing the first ever digital microfluidic operations in the aerosol phase and for examining interparticle interactions that can lead to coalescence/coagulation. Although aerosol coagulation is the primary process driving the evolution of particle size distributions, it remains very poorly understood. Using HOT, we can resolve the time-dependent motion of trapped particles and the light scattering from particles during the coalescence process.

Reid, J. P.; Haddrell, A. E.; Walker, J. S.; Power, R.; Bones, D. L.; Davies, J. F.

2011-10-01

48

An easier way to improve the trapping performance of optical tweezers by donut-shaped beam  

Microsoft Academic Search

In optical tweezers, it can be comprehended that the larger the inclination angle between the condensed laser beam and the optical axis contributes more to axial trapping force, while the central part of laser beam with smaller inclination angle contributes more transverse trapping force. Therefore donut-shaped beam is used to improve the problem of lessaxial trapping for common optical tweezers.

Che-Liang Tsai; Hang-Ping Huang; Long Hsu; Ken-Yuh Hsu

2010-01-01

49

Single and dual fiber nano-tip optical tweezers: trapping and analysis  

E-print Network

Single and dual fiber nano-tip optical tweezers: trapping and analysis Jean-Baptiste Decombe tweezers using one or two chemically etched fiber nano-tips is developed. We demonstrate optical trapping-position adjustment," Opt. Lett. 38, 2617­2620 (2013). 15. S. K. Mondal, S. S. Pal, and P. Kapur, "Optical fiber nano

Paris-Sud XI, Université de

50

Experiments with a rubidium condensate in an optical tweezer  

NASA Astrophysics Data System (ADS)

We report on experiments with a rubidium Bose-Einstein condensate in an optical tweezer. The condensate is loaded into the focus of a red-detuned laser beam from a cloverleaf Ioffe-Pritchard magnetic trap to allow for translation into a glass at 73 cm distance from the production chamber. The tweezer is oriented perpendicular to the long axis of the condensate. Loading into this geometry is complicated by the large three-body loss and high mass of rubidium as compared to similar experiments in sodium, which have been performed recently in our group. We have explored methods to optimize the transfer efficiency and will report progress towards the transport and manipulation of the condensate

Campbell, Gretchen; Boyd, Micah; Streed, Erik; Mun, Jongchul; Schneble, Dominik; Steinhauer, Jeff; Pritchard, David E.; Ketterle, Wolfgang

2003-05-01

51

The optical manipulation and characterisation of aerosol particles  

NASA Astrophysics Data System (ADS)

Aerosols play a crucial role in many areas of science, ranging from atmospheric chemistry and physics, to pharmaceutical aerosols and drug delivery to the lungs, to combustion science and spray drying. The development of new methods for characterising the properties and dynamics of aerosol particles is of crucial importance if the complex role that particles play is to be more fully understood. Optical tweezers provide a valuable new tool to address fundamental questions in aerosol science. Single or multiple particles 1-15 ?m in diameter can be manipulated for indefinite timescales. Linear and non-linear Raman and fluorescence spectroscopies can be used to probe particle composition, phase, component mixing state, and size. In particular, size can be determined with nanometre accuracy, allowing accurate measurements of the thermodynamic properties of aerosols, the kinetics of particle transformation and of light absorption. Further, the simultaneous manipulation of multiple particles in parallel optical traps provides a method for performing comparative measurements on particles of different composition. We will present some latest work in which optical tweezers are used to characterise aerosol dynamics, demonstrating that optical tweezers can find application in studies of hygroscopicity, the mixing state of different chemical components, including the phase separation of immiscible phases, and the kinetics of chemical transformation.

Reid, Jonathan P.

2008-08-01

52

A simple optical tweezers for trapping polystyrene particles  

NASA Astrophysics Data System (ADS)

Optical tweezers is an optical trap. For decades, it has become an optical tool that can trap and manipulate any particle from the very small size like DNA to the big one like bacteria. The trapping force comes from the radiation pressure of laser light which is focused to a group of particles. Optical tweezers has been used in many research areas such as atomic physics, medical physics, biophysics, and chemistry. Here, a simple optical tweezers has been constructed using a modified Leybold laboratory optical microscope. The ocular lens of the microscope has been removed for laser light and digital camera accesses. A laser light from a Coherent diode laser with wavelength ? = 830 nm and power 50 mW is sent through an immersion oil objective lens with magnification 100 × and NA 1.25 to a cell made from microscope slides containing polystyrene particles. Polystyrene particles with size 3 ?m and 10 ?m are used. A CMOS Thorlabs camera type DCC1545M with USB Interface and Thorlabs camera lens 35 mm are connected to a desktop and used to monitor the trapping and measure the stiffness of the trap. The camera is accompanied by camera software which makes able for the user to capture and save images. The images are analyzed using ImageJ and Scion macro. The polystyrene particles have been trapped successfully. The stiffness of the trap depends on the size of the particles and the power of the laser. The stiffness increases linearly with power and decreases as the particle size larger.

Shiddiq, Minarni; Nasir, Zulfa; Yogasari, Dwiyana

2013-09-01

53

Multi-functional optical tweezers using computer-generated holograms  

NASA Astrophysics Data System (ADS)

Optical tweezers are capable of trapping microscopic particles by photon momentum transfer. The use of dynamic computer-generated holograms for beam shaping allows a high flexibility in terms of trap characteristics and features. We use a liquid crystal display (LCD) to display the holograms. Efficiency losses caused by the periodic electrode structure of the LCD have been clearly reduced by use of an optically addressed spatial light modulator. We realized multiple traps, which can hold and move at least seven silica spheres independently in real time. We also demonstrate the controllability of trapped particles in three dimensions without the need for mechanical elements in the setup.

Liesener, J.; Reicherter, M.; Haist, T.; Tiziani, H. J.

2000-11-01

54

Hybrid optical tweezers for dynamic micro-bead arrays  

NASA Astrophysics Data System (ADS)

Dynamic micro-bead arrays offer great flexibility and potential as sensing tools in various scientific fields. Two optical trapping techniques, the GPC method using a spatial light modulator and a mechanical scanning method using galvano mirrors, are combined in a hybrid optical tweezers system to handle dynamic micro-bead arrays. This system provides greater versatility while the GPC method creates massive micro-bead arrays in a 2D space, where the trapped beads can be manipulated smoothly and very quickly in a 3D space using the mechanical scanning method. Four typical examples are demonstrated in real time.

Tanaka, Yoshio; Tsutsui, Shogo; Ishikawa, Mitsuru; Kitajima, Hiroyuki

2011-08-01

55

Stiffer optical tweezers through real-time feedback control  

NASA Astrophysics Data System (ADS)

Using real-time re-programmable signal processing we connect acousto-optic steering and back-focal-plane interferometric position detection in optical tweezers to create a fast feedback controlled instrument. When trapping 3?m latex beads in water we find that proportional-gain position-clamping increases the effective lateral trap stiffness ˜13-fold. A theoretical power spectrum for bead fluctuations during position-clamped trapping is derived and agrees with the experimental data. The loop delay, ˜19?s in our experiment, limits the maximum achievable effective trap stiffness.

Wallin, Anders E.; Ojala, Heikki; Hæggström, Edward; Tuma, Roman

2008-06-01

56

Forming Three-Dimensional Colloidal Structures Using Holographic Optical Tweezers  

E-print Network

A method for forming permanent three dimensional structures from colloidal particles using holographic optical trapping is described. Holographic optical tweezers (HOT) are used to selectively position charge stabilized colloidal particles within a flow cell. Once the particles are in the desired location an electrolyte solution is pumped into the cell which reduces the Debye length and induces aggregation caused by the van der Waals attraction. This technique allows for the formation of three dimensional structures both on and away from the substrate that can be removed from solution without the aid of critical point drying. This technique is inexpensive, fast, and versatile as it relies on forces acting on almost all colloidal suspensions.

C. R. Knutson; J. Plewa

2005-08-05

57

A general method for manipulating DNA sequences from any organism with optical tweezers  

E-print Network

A general method for manipulating DNA sequences from any organism with optical tweezers Derek N sequences from any organism with optical tweezers. Molecules are produced from either genomic or cloned DNA method for manipulating DNA sequences from any organism. Here we describe and char- acterize

Ritort, Felix

58

MatLab program for precision calibration of optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers are used as force transducers in many types of experiments. The force they exert in a given experiment is known only after a calibration. Computer codes that calibrate optical tweezers with high precision and reliability in the ( x, y)-plane orthogonal to the laser beam axis were written in MatLab (MathWorks Inc.) and are presented here. The calibration is based on the power spectrum of the Brownian motion of a dielectric bead trapped in the tweezers. Precision is achieved by accounting for a number of factors that affect this power spectrum. First, cross-talk between channels in 2D position measurements is tested for, and eliminated if detected. Then, the Lorentzian power spectrum that results from the Einstein-Ornstein-Uhlenbeck theory, is fitted to the low-frequency part of the experimental spectrum in order to obtain an initial guess for parameters to be fitted. Finally, a more complete theory is fitted, a theory that optionally accounts for the frequency dependence of the hydrodynamic drag force and hydrodynamic interaction with a nearby cover slip, for effects of finite sampling frequency (aliasing), for effects of anti-aliasing filters in the data acquisition electronics, and for unintended "virtual" filtering caused by the position detection system. Each of these effects can be left out or included as the user prefers, with user-defined parameters. Several tests are applied to the experimental data during calibration to ensure that the data comply with the theory used for their interpretation: Independence of x- and y-coordinates, Hooke's law, exponential distribution of power spectral values, uncorrelated Gaussian scatter of residual values. Results are given with statistical errors and covariance matrix. Program summaryTitle of program: tweezercalib Catalogue identifier: ADTV Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland. Program Summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTV Computer for which the program is designed and others on which it has been tested: General computer running MatLab (MathWorks Inc.). Programming language used: MatLab (MathWorks Inc.). Uses "Optimization Toolbox" and "Statistics Toolbox". Memory required to execute with typical data: Of order 4 times the size of the data file. High speed storage required: None No. of lines in distributed program, including test data, etc.: 133 183 No. of bytes in distributed program, including test data, etc.: 1 043 674 Distribution format: tar gzip file Nature of physical problem: Calibrate optical tweezers with precision by fitting theory to experimental power spectrum of position of bead doing Brownian motion in incompressible fluid, possibly near microscope cover slip, while trapped in optical tweezers. Thereby determine spring constant of optical trap and conversion factor for arbitrary-units-to-nanometers for detection system. Method of solution: Elimination of cross-talk between quadrant photo-diode's output channels for positions (optional). Check that distribution of recorded positions agrees with Boltzmann distribution of bead in harmonic trap. Data compression and noise reduction by blocking method applied to power spectrum. Full accounting for hydrodynamic effects: Frequency-dependent drag force and interaction with nearby cover slip (optional). Full accounting for electronic filters (optional), for "virtual filtering" caused by detection system (optional). Full accounting for aliasing caused by finite sampling rate (optional). Standard non-linear least-squares fitting. Statistical support for fit is given, with several plots suitable for inspection of consistency and quality of data and fit. Restrictions on the complexity of the problem: Data should be positions of bead doing Brownian motion while held by optical tweezers. For high precision in final results, data should be time series measured over a long time, with sufficiently high experimental sampling rate: The sampling rate should be well above the characteristic frequency of the trap,

Toli?-Nørrelykke, Iva Marija; Berg-Sørensen, Kirstine; Flyvbjerg, Henrik

2004-06-01

59

All-Optical Constant-Force Laser Tweezers  

PubMed Central

Optical tweezers are a powerful tool for the study of single biomolecules. Many applications require that a molecule be held under constant tension while its extension is measured. We present two schemes based on scanning-line optical tweezers to accomplish this, providing all-optical alternatives to force-clamp traps that rely on electronic feedback to maintain constant-force conditions for the molecule. In these schemes, a laser beam is rapidly scanned along a line in the focal plane of the microscope objective, effectively creating an extended one-dimensional optical potential over distances of up to 8 ?m. A position-independent lateral force acting on a trapped particle is created by either modulating the laser beam intensity during the scan or by using an asymmetric beam profile in the back focal plane of the microscope objective. With these techniques, forces of up to 2.69 pN have been applied over distances of up to 3.4 ?m with residual spring constants of <26.6 fN/?m. We used these techniques in conjunction with a fast position measurement scheme to study the relaxation of ?-DNA molecules against a constant external force with submillisecond time resolution. We compare the results to predictions from the wormlike chain model. PMID:15345573

Nambiar, Rajalakshmi; Gajraj, Arivalagan; Meiners, Jens-Christian

2004-01-01

60

Stabilization of distribution of radiation energy in optical tweezers wand  

NASA Astrophysics Data System (ADS)

Considered is a correlation method of forming of specified distribution of radiation energy over the target, particularly in the optical tweezers wand. The method exploits an interaction of beforehand spatially modulated in phase wand beam with synthesized hologram specific to the modulation. The specified energy distribution is obtained as the convolution of the required field distribution and of cross-correlation function of the ideal wand beam and the real one. Because of beams wave fronts modulation the result of such a convolution is weakly dependent on the difference of the ideal and the real beams. Examined is the possibility of dynamic operation mode involving the spatial light modulation (SLM) device.

Derzhypolskyi, A.; Melenevskyi, D.; Gnatovskyi, O.; Negriyko, A.

2008-05-01

61

Moving average process underlying the holographic-optical-tweezers experiments  

NASA Astrophysics Data System (ADS)

We study statistical properties of the recordings which contain time-dependent positions of a bead trapped in optical tweezers. Analysis of such a time series indicates that the commonly accepted model, i.e., the autoregressive process of first order, is not sufficient to fit the data. We show a presence of the first-order moving average part in the dynamical model of the system. We explain origin of this part as an influence of the high frequency CCD camera on the measurements. The proposed autoregressive moving average model appears to reflect perfectly all statistical features of the high-frequency recording data.

?lezak, Jakub; Drobczy?ski, S?awomir; Weron, Karina; Masajada, Jan

2013-12-01

62

Translation and manipulation of silicon nanomembranes using holographic optical tweezers  

PubMed Central

We demonstrate the use of holographic optical tweezers for trapping and manipulating silicon nanomembranes. These macroscopic free-standing sheets of single-crystalline silicon are attractive for use in next-generation flexible electronics. We achieve three-dimensional control by attaching a functionalized silica bead to the silicon surface, enabling non-contact trapping and manipulation of planar structures with high aspect ratios (high lateral size to thickness). Using as few as one trap and trapping powers as low as several hundred milliwatts, silicon nanomembranes can be rotated and translated in a solution over large distances. PMID:21867504

2011-01-01

63

Imaging microscopic viscosity with confocal scanning optical tweezers  

NASA Astrophysics Data System (ADS)

The techniques of confocal microscopy and optical tweezers have shown themselves to be powerful tools in biological and medical research. We combine these methods to develop a minimally invasive instrument that is capable of making hydrodynamic measurements more rapidly than is possible with other devices. This result leads to the possibility of making scanning images of the viscosity distribution of materials around biopolymer-producing cells, 100 × 100 images can be taken with 0.5-?m spatial resolution in 3 min. An image of the viscosity distribution around a pullulan-producing cell of Aureobasidium pullulans is shown as an example.

Nemet, Boaz A.; Shabtai, Yossef; Cronin-Golomb, Mark

2002-02-01

64

Mechanical properties of a giant liposome studied using optical tweezers  

NASA Astrophysics Data System (ADS)

The mechanical properties of a micrometer-sized giant liposome are studied by deforming it from the inside using dual-beam optical tweezers. As the liposome is extended, its shape changes from a sphere to a lemon shape, and finally, a tubular part is generated. The surface tension ? and the bending rigidity ? of the lipid membrane are obtained from the measured force-extension curve. In a one-phase liposome, it was found that ? increases as the charged component increases but ? remains approximately constant. In a two-phase liposome, the characteristic deformation and the force-extension curve differ from those observed for the one-phase liposome.

Shitamichi, Yoko; Ichikawa, Masatoshi; Kimura, Yasuyuki

2009-09-01

65

TweezPal - Optical tweezers analysis and calibration software  

NASA Astrophysics Data System (ADS)

Optical tweezers, a powerful tool for optical trapping, micromanipulation and force transduction, have in recent years become a standard technique commonly used in many research laboratories and university courses. Knowledge about the optical force acting on a trapped object can be gained only after a calibration procedure which has to be performed (by an expert) for each type of trapped objects. In this paper we present TweezPal, a user-friendly, standalone Windows software tool for optical tweezers analysis and calibration. Using TweezPal, the procedure can be performed in a matter of minutes even by non-expert users. The calibration is based on the Brownian motion of a particle trapped in a stationary optical trap, which is being monitored using video or photodiode detection. The particle trajectory is imported into the software which instantly calculates position histogram, trapping potential, stiffness and anisotropy. Program summaryProgram title: TweezPal Catalogue identifier: AEGR_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEGR_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 44 891 No. of bytes in distributed program, including test data, etc.: 792 653 Distribution format: tar.gz Programming language: Borland Delphi Computer: Any PC running Microsoft Windows Operating system: Windows 95, 98, 2000, XP, Vista, 7 RAM: 12 Mbytes Classification: 3, 4.14, 18, 23 Nature of problem: Quick, robust and user-friendly calibration and analysis of optical tweezers. The optical trap is calibrated from the trajectory of a trapped particle undergoing Brownian motion in a stationary optical trap (input data) using two methods. Solution method: Elimination of the experimental drift in position data. Direct calculation of the trap stiffness from the positional variance. Calculation of 1D optical trapping potential from the positional distribution of data points. Trap stiffness calculation by fitting a parabola to the trapping potential. Presentation of X-Y positional density for close inspection of the 2D trapping potential. Calculation of the trap anisotropy. Running time: Seconds

Osterman, Natan

2010-11-01

66

Direct measurement of colloidal interactions with holographic optical tweezers  

NASA Astrophysics Data System (ADS)

This thesis describes experimental studies of colloidal interactions. After a brief introduction to some essential aspects of colloidal physics in Chapter 1, and to optical tweezers and digital video microscopy in Chapter 2, we present in Chapter 3 an analysis of the hydrodynamic interactions among colloidal particles. We propose a simple model for the hydrodynamic interactions among sufficiently separated colloidal particles, and prove its validity analyzing the vibrations of a one dimensional lattice of colloidal particles held by holographic optical tweezers. This model predicts a crossover from highly overdamped lattice vibrations, to propagating modes for systems having a sufficient number of particles. In Chapter 4 we study the equilibrium structure of highly deionized colloidal dispersions sedimented on a bounding surface. The particles in these systems develop an identical charge, and interact with an effective electrostatic interaction predicted to be purely repulsive. Several previous experiments, however, report a long ranged attractive component in the effective potential, but only for sufficiently low ionic concentrations. We present evidence for a qualitative dependence of the effective interparticle forces on the bounding surface's chemistry, with the attraction disappearing altogether when the bounding surface is coated with a thin layer of gold. We interpret this as evidence of the influence that ionizable groups on the glass surface have on the interactions among sedimented colloidal particles. We conclude by introducing in Chapter 5 a new method to measure directly the effective interaction among two colloidal particles. This method, based on the analysis of the diffusion of pairs of colloids along a line tweezer, is both local and fast, and it does not require a separate calibration for the line potential. It is strictly valid even in presence of light induced colloidal interactions, which have been a concern in previous experiments. We test the validity of our analysis using both simulations and experiments.

Polin, Marco

67

Processing carbon nanotubes with holographic optical tweezers  

E-print Network

, and perhaps even individual nanotubes, can be transported at high speeds, deposited onto substrates, untangled processing with light. © 2012 Optical Society of America OCIS codes: (140.7010) Trapping; (090.1760) Computer of aligned carbon nanotubes via laser trimming,'' Nanotechnology 14, 433--437 (2003). 16. L. A. Nagahara, I

Grier, David

68

Processing carbon nanotubes with holographic optical tweezers  

E-print Network

nanotubes, can be transported at high speeds, deposited onto substrates, untangled, and selectively ablated. © 2012 Optical Society of America OCIS codes: (140.7010) Trapping; (090.1760) Computer holography; (120, "Large area patterned arrays of aligned carbon nanotubes via laser trimming," Nanotechnology 14, 433

Grier, David

69

Peculiarities of RBC aggregation studied by double trap optical tweezers  

NASA Astrophysics Data System (ADS)

Aggregation peculiarities of red blood cells (RBCs) in autologous plasma are studied using double trap optical tweezers technique. The positions of RBCs are controlled with submicrometer accuracy by two optical traps formed by strongly focused laser beams (?=1064 nm). Quantitative measurements of interaction forces between RBCs in pair aggregates are performed. Depending on the RBCs aggregation force, four different end-points of disaggregation induced by optical trap movement are revealed. Analysis of experimental force dependence on the distance between two RBCs during disaggregation is in a good agreement with the model of ring-shaped interaction surfaces of RBCs in pair aggregate. Aggregation velocities measured are shown to be strongly different for healthy and pathologic (System Lupus Erythematosis - SLE) blood samples.

Khokhlova, Maria D.; Lyubin, Evgeny V.; Zhdanov, Alexander G.; Rykova, Sofia Yu.; Krasnova, Tatyana N.; Sokolova, Irina A.; Fedyanin, Andrey A.

2010-04-01

70

Precision Assembly of Complex Cellular Microenvironments using Holographic Optical Tweezers  

PubMed Central

The accurate study of cellular microenvironments is limited by the lack of technologies that can manipulate cells in 3D at a sufficiently small length scale. The ability to build and manipulate multicellular microscopic structures will facilitate a more detailed understanding of cellular function in fields such as developmental and stem cell biology. We present a holographic optical tweezers based technology to accurately generate bespoke cellular micro-architectures. Using embryonic stem cells, 3D structures of varying geometries were created and stabilized using hydrogels and cell-cell adhesion methods. Control of chemical microenvironments was achieved by the temporal release of specific factors from polymer microparticles positioned within these constructs. Complex co-culture micro-environmental analogues were also generated to reproduce structures found within adult stem cell niches. The application of holographic optical tweezers-based micromanipulation will enable novel insights into biological microenvironments by allowing researchers to form complex architectures with sub-micron precision of cells, matrices and molecules. PMID:25716032

Kirkham, Glen R.; Britchford, Emily; Upton, Thomas; Ware, James; Gibson, Graham M.; Devaud, Yannick; Ehrbar, Martin; Padgett, Miles; Allen, Stephanie; Buttery, Lee D.; Shakesheff, Kevin

2015-01-01

71

Calibration of optical tweezers based on an autoregressive model.  

PubMed

The power spectrum density (PSD) has long been explored for calibrating optical tweezers stiffness. Fast Fourier Transform (FFT) based spectral estimator is typically used. This approach requires a relatively longer data acquisition time to achieve adequate spectral resolution. In this paper, an autoregressive (AR) model is proposed to obtain the Spectrum Density using a limited number of samples. According to our method, the arithmetic model has been established with burg arithmetic, and the final prediction error criterion has been used to select the most appropriate order of the AR model, the power spectrum density has been estimated based the AR model. Then, the optical tweezers stiffness has been determined with the simple calculation from the power spectrum. Since only a small number of samples are used, the data acquisition time is significantly reduced and real-time stiffness calibration becomes feasible. To test this calibration method, we study the variation of the trap stiffness as a function of the parameters of the data length and the trapping depth. Both of the simulation and experiment results have showed that the presented method returns precise results and outperforms the conventional FFT method when using a limited number of samples. PMID:25090511

Wang, Zi-Qiang; Zhou, Jin-Hua; Zhong, Min-Cheng; Li, Di; Li, Yin-Mei

2014-07-14

72

Robotic manipulation of human red blood cells with optical tweezers for cell property characterization  

Microsoft Academic Search

Cell manipulation has received considerable attentions in recent years. Most of cell manipulations are performed manually without guarantee of high precision and high throughput. This paper reports our latest research on integrating robotics technologies into optical tweezers system for manipulation and biomechanical characterization of human red blood cells (RBCs). We first demonstrate the effectiveness of the robot-tweezers system in manipulation

Youhua Tan; Dong Sun; Wenhao Huang; Jinping Cheng; Shuk Han Cheng

2010-01-01

73

Optimization of holographic optical tweezers for multiplexed fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

We are developing a multiplexed spectroscopy technique that employs holographic optical tweezers to trap and excite multiple sensor particles. Our goal is to develop a lab-on-a-chip measurement platform for monitoring pH and other ion concentrations with high spatial resolution in a microfluidic device or within biological cells. To ensure efficient use of the available laser power required to trap multiple particles, we address three aspects of the spatial light modulator (SLM) used in the holographic technique. We measure and optimize the input and output polarizations used before and after the birefringent SLM. We reduce optical aberrations by adding appropriate Zernike polynomials to the computed hologram. We optimize the diffraction efficiency of the SLM by adjusting the gray scale input-to-output table to account for the nonlinear phase response of the SLM.

Cibula, Matthew; McIntyre, David

2012-10-01

74

An automated and user-friendly optical tweezers for biomolecular investigations  

NASA Astrophysics Data System (ADS)

Optical tweezers are not new to biological applications but building a tweezers which is versatile, automated, precise, stable and user-friendly is quite challenging. Such a tweezers usually require not only a hefty budget but vast understanding of engineering of optomechanical systems. I describe in this dissertation a versatile, automated, precise, stable and user-friendly optical tweezers that we developed for biomolecular investigations under limited budget. I describe automation and control improvements along with newly-developed surface detection software. I also describe cost-effective optomechanical devices used in tweezers with potential for broader application. Finally, I present new results of single-molecule force spectroscopy of DNA overstretching as a function of water isotope type. Single DNA unzipping is also presented as a proof of concept.

Rathi, Pranav

75

Use of optical tweezers to probe epithelial mechanosensation  

NASA Astrophysics Data System (ADS)

Cellular mechanosensation mechanisms have been implicated in a variety of disease states. Specifically in renal tubules, the primary cilium and associated mechanosensitive ion channels are hypothesized to play a role in water and salt homeostasis, with relevant disease states including polycystic kidney disease and hypertension. Previous experiments investigating ciliary-mediated cellular mechanosensation have used either fluid flow chambers or micropipetting to elicit a biological response. The interpretation of these experiments in terms of the ``ciliary hypothesis'' has been difficult due the spatially distributed nature of the mechanical disturbance-several competing hypotheses regarding possible roles of primary cilium, glycocalyx, microvilli, cell junctions, and actin cytoskeleton exist. I report initial data using optical tweezers to manipulate individual primary cilia in an attempt to elicit a mechanotransduction response-specifically, the release of intracellular calcium. The advantage of using laser tweezers over previous work is that the applied disturbance is highly localized. I find that stimulation of a primary cilium elicits a response, while stimulation of the apical surface membrane does not. These results lend support to the hypothesis that the primary cilium mediates transduction of mechanical strain into a biochemical response in renal epithelia.

Resnick, Andrew

2010-01-01

76

Optical manipulation and rotation of liquid crystal drops using high-index fiber-optic tweezers  

NASA Astrophysics Data System (ADS)

We report an optical fiber tweezer based on high-index material for trapping and optical manipulation of microscale particles in water. The use of a high-index material increases the trapping force with respect to the more common silica, through tighter focusing of light. We demonstrate the potential of this simple and versatile device by trapping and rotating nematic liquid crystal drops. We monitor the rotation of the drop by detecting light modulation observed with the same fiber using backscattered light, which exhibits modulation in intensity due to the rotation of the drop; this further extends the capabilities of the fiber tweezers.

Abedin, Kazi Sarwar; Kerbage, Charles; Fernandez-Nieves, Alberto; Weitz, David A.

2007-08-01

77

Combined holographic-mechanical optical tweezers: Construction, optimisation and calibration  

E-print Network

A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers set-up. This provides great flexibility as the SLM creates an array of traps which can be moved smoothly and quickly with the GMM. To optimise performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45 degrees, smaller angles give a full 2pi phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.

Richard D. L. Hanes; Matthew C. Jenkins; Stefan U. Egelhaaf

2009-07-21

78

Simultaneous measurements of electrophoretic and dielectrophoretic forces using optical tweezers  

E-print Network

Herein, charged microbeads handled with optical tweezers are used as a sensitive probe for simultaneous measurements of electrophoretic and dielectrophoretic forces. We first determine the electric charge carried by a single bead by keeping it in a predictable uniform electric field produced by two parallel planar electrodes, then, we examine same bead's response in proximity to a tip electrode. In this case, besides electric forces, the bead simultaneously experiences non-negligible dielectrophoretic forces produced by the strong electric field gradient. The stochastic and deterministic motions of the trapped bead are theoretically and experimentally analysed in terms of the autocorrelation function. By fitting the experimental data, we are able to extract simultaneously the spatial distribution of electrophoretic and dielectrophoretic forces around the tip. Our approach can be used for determining actual, total force components in the presence of high-curvature electrodes or metal scanning probe tips.

Giuseppe Pesce; Giulia Rusciano; Gianluigi Zito; Antonio Sasso

2015-03-16

79

Using Optical Tweezers to Study Cell Mechanics during Airway Reopening  

NASA Astrophysics Data System (ADS)

Patients suffering from the acute respiratory distress syndrome (ARDS) must be mechanically ventilated in order to survive. However, these ventilation protocols may generate injurious hydrodynamic stresses especially during low tidal volume (VT) ventilation when the flow of micron-sized air bubbles displace the surrounding liquid. In-vitro studies in our lab revealed that microbubble flows can severally damage lung epithelial cells (EC). The degree of injury was elevated for sub-confluent monolayers in small channel heights. Under these conditions, the micromechanics of individual EC may influence the degree of cellular injury. To investigate the role of cell mechanics, we used an oscillating Optical Tweezers (OT) technique to measure the intrinsic mechanical properties of EC before and after the flow of microbubbles. Knowledge of how the EC's micromechanical properties influence cell viability may lead to the development of novel treatment therapies that enhance the EC's ability to withstand injurious hydrodynamic stresses during ventilation treatment.

Yalcin, Huseyin; Wang, Jing; Ghadiali, Samir; Ou-Yang, H. Daniel

2006-03-01

80

Combined holographic-mechanical optical tweezers: Construction, optimization, and calibration  

SciTech Connect

A spatial light modulator (SLM) and a pair of galvanometer-mounted mirrors (GMM) were combined into an optical tweezers setup. This provides great flexibility as the SLM creates an array of traps, which can be moved smoothly and quickly with the GMM. To optimize performance, the effect of the incidence angle on the SLM with respect to phase and intensity response was investigated. Although it is common to use the SLM at an incidence angle of 45 deg., smaller angles give a full 2{pi} phase shift and an output intensity which is less dependent on the magnitude of the phase shift. The traps were calibrated using an active oscillatory technique and a passive probability distribution method.

Hanes, Richard D. L.; Jenkins, Matthew C.; Egelhaaf, Stefan U. [Condensed Matter Physics Laboratory, Heinrich-Heine University, 40225 Duesseldorf (Germany)

2009-08-15

81

Design and construction of a space-borne optical tweezer apparatus  

NASA Astrophysics Data System (ADS)

A compact optical tweezer package has been developed for use on a microscope to be flown on the International Space Station as part of a series of experiments in colloid crystallization. A brief introduction to the principles of single-beam optical tweezer operation will be presented, after which a detailed system layout will be shown. Special design requirements due to the spaceflight nature of the hardware will also be discussed. The tweezer apparatus is capable of trapping many particles through use of a two-axis acousto-optical deflector. The trap strength is sufficient to perform the required science (50 pN at ?n=0.2). The trap beam behaves approximately as a diffraction limited single mode Gaussian beam of numerical aperture, NA=1.4, as shown through spot size measurements and confocal-type images of the focal region. This is the first time optical tweezers will be deployed in a microgravity environment.

Resnick, Andrew

2001-11-01

82

Interrogating Biology with Force: Single Molecule High-Resolution Measurements with Optical Tweezers  

PubMed Central

Single molecule force spectroscopy methods, such as optical and magnetic tweezers and atomic force microscopy, have opened up the possibility to study biological processes regulated by force, dynamics of structural conformations of proteins and nucleic acids, and load-dependent kinetics of molecular interactions. Among the various tools available today, optical tweezers have recently seen great progress in terms of spatial resolution, which now allows the measurement of atomic-scale conformational changes, and temporal resolution, which has reached the limit of the microsecond-scale relaxation times of biological molecules bound to a force probe. Here, we review different strategies and experimental configurations recently developed to apply and measure force using optical tweezers. We present the latest progress that has pushed optical tweezers’ spatial and temporal resolution down to today’s values, discussing the experimental variables and constraints that are influencing measurement resolution and how these can be optimized depending on the biological molecule under study. PMID:24047980

Capitanio, Marco; Pavone, Francesco S.

2013-01-01

83

Coherence and Raman Sideband Cooling of a Single Atom in an Optical Tweezer  

E-print Network

We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect ...

Thompson, J. D.

84

Microrheology with Optical Tweezers of gel-like materials 'is not an option'!  

E-print Network

Optical tweezers have been successfully adopted as exceptionally sensitive transducers for microrheology studies of complex 'fluids'. Despite the general trend, a similar approach cannot be adopted for microrheology studies of 'gel-like' materials, e.g. living cells.

Tassieri, Manlio

2015-01-01

85

Optical tweezers as manufacturing and characterization tool in microfluidics  

NASA Astrophysics Data System (ADS)

Pumping and mixing of small volumes of liquid samples are basic processes in microfluidic applications. Among the number of different principles for active transportation of the fluids microrotors have been investigated from the beginning. The main challenge in microrotors, however, has been the driving principle. In this work a new approach for a very simple magnetic driving principle has been realized. More precisely, we take advantage of optical grippers to fabricate various microrotors and introduce an optical force method to characterize the fluid flow generated by rotating the structures through magnetic actuation. The microrotors are built of silica and magnetic microspheres which are initially coated with Streptavidin or Biotin molecules. Holographic optical tweezers (HOT) are used to trap, to position, and to assemble the microspheres with the chemical interaction of the biomolecules leading to a stable binding. Using this technique, complex designs of microrotors can be realized. The magnetic response of the magnetic microspheres enables the rotation and control of the structures through an external magnetic field. The generated fluid flow around the microrotor is measured optically by inserting a probe particle next to the rotor. While the probe particle is trapped by optical forces the flow force leads to a displacement of the particle from the trapping position. This displacement is directly related to the flow velocity and can be measured and calibrated. Variations of the microrotor design and rotating speed lead to characteristic flow fields.

Köhler, J.; Ghadiri, R.; Ksouri, S. I.; Gurevich, E. L.; Ostendorf, A.

2014-09-01

86

Measurement of interaction forces between red blood cells in aggregates by optical tweezers  

SciTech Connect

We have fabricated double-beam optical tweezers and demonstrated the possibility of their use for measuring the interaction forces between red blood cells (erythrocytes). It has been established experimentally that prolonged trapping of red blood cells in a tightly focused laser beam does not cause any visible changes in their shape or size. We have measured the interaction between red blood cells in the aggregate, deformed by optical tweezers.

Maklygin, A Yu; Priezzhev, A V; Karmenian, A; Nikitin, Sergei Yu; Obolenskii, I S; Lugovtsov, Andrei E; Kisun Li

2012-06-30

87

Dynamic holographic optical tweezers using a twisted-nematic liquid crystal display  

Microsoft Academic Search

In this paper, we realize dynamic holographic optical tweezers (HOT) using a commercial twisted-nematic liquid crystal display (TN-LCD) removed from a video projector, and manipulate multiple particles simultaneously. After measuring the parameters of the TN-LCD, we find that it is not suited to work as a phase-only modulator for infrared optical tweezers because of the small range of its phase

Guangfu Wang; Cheng Wen; Anpei Ye

2006-01-01

88

Cooling a Single Atom in an Optical Tweezer to Its Quantum Ground State  

NASA Astrophysics Data System (ADS)

We report cooling of a single neutral atom to its three-dimensional vibrational ground state in an optical tweezer. After employing Raman sideband cooling for tens of milliseconds, we measure via sideband spectroscopy a three-dimensional ground-state occupation of about 90%. We further observe coherent control of the spin and motional state of the trapped atom. Our demonstration shows that an optical tweezer, formed simply by a tightly focused beam of light, creates sufficient confinement for efficient sideband cooling. This source of ground-state neutral atoms will be instrumental in numerous quantum simulation and logic applications that require a versatile platform for storing and manipulating ultracold single neutral atoms. For example, these results will improve current optical-tweezer experiments studying atom-photon coupling and Rydberg quantum logic gates, and could provide new opportunities such as rapid production of single dipolar molecules or quantum simulation in tweezer arrays.

Kaufman, A. M.; Lester, B. J.; Regal, C. A.

2012-10-01

89

Optical nanofiber integrated into an optical tweezers for particle manipulation and in-situ fiber probing  

NASA Astrophysics Data System (ADS)

Precise control of particle positioning is desirable in many optical propulsion and sorting applications. Here, we develop an integrated platform for particle manipulation consisting of a combined optical nanofiber and optical tweezers system. Individual silica microspheres were introduced to the nanofiber at arbitrary points using the optical tweezers, thereby producing pronounced dips in the fiber transmission. We show that such consistent and reversible transmission modulations depend on both particle and fiber diameter, and may be used as a reference point for in-situ nanofiber or particle size measurement. Therefore we combine SEM size measurements with nanofiber transmission data to provide calibration for particle-based fiber assessment. We also demonstrate how the optical tweezers can be used to create a `particle jet' to feed a supply of microspheres to the nanofiber surface, forming a particle conveyor belt. This integrated optical platform provides a method for selective evanescent field manipulation of micron-sized particles and facilitates studies of optical binding and light-particle interaction dynamics.

Gusachenko, Ivan; Frawley, Mary C.; Truong, Viet. G.; Nic Chormaic, Síle

2014-09-01

90

Advanced optical tweezers for the study of cellular and molecular biomechanics.  

PubMed

Optical tweezers are an important tool for studying cellular and molecular biomechanics. We present a robust optical tweezers device with advanced features including: multiple optical traps, acousto-optic trap steering, and back focal plane interferometry position detection. We integrate these features into an upright microscope, with no compromise to its capabilities (differential interference contrast microscopy, fluorescence microscopy, etc.). Acousto-optic deflectors (AODs) steer each beam and can create multiple time-shared traps. Position detection, force calibrations and AOD performance are presented. The system can detect subnanometer displacements and forces below 0.1 pN. PMID:12617534

Brouhard, Gary J; Schek, Henry T; Hunt, Alan J

2003-01-01

91

Compact microscope-based optical tweezers system for molecular manipulation  

NASA Astrophysics Data System (ADS)

A compact single beam optical tweezers system for force measurements and manipulation of individual double-stranded deoxyribonucleic acid (DNA) molecules was integrated into a commercial inverted optical microscope. A maximal force of 150 pN combined with a force sensitivity of less than 0.5 pN allows measurements of elastic properties of single molecules which complements and overlaps the force regime accessible with atomic force microscopy (AFM). The manipulation and measurement performance of this system was tested with individual ?-DNA molecules and renders new aspects of dynamic forces phenomena with higher precision in contrast to AFM studies. An integrated liquid handling system with a fluid cell allows investigation of the force response of individual DNA molecules in the presence of DNA binding agents. Comparison of YOYO-1-, ethidium bromide intercalated DNA, and distamycin-A complexed DNA revealed accurate and reproducible differences in the force response to an external load. This opens the possibility to use it as a single molecule biosensor to investigate DNA binding agents and even to identify molecular binding mechanisms.

Sischka, Andy; Eckel, Rainer; Toensing, Katja; Ros, Robert; Anselmetti, Dario

2003-11-01

92

Manipulation of Suspended Single Cells by Microfluidics and Optical Tweezers  

PubMed Central

Chondrocytes and osteoblasts experience multiple stresses in vivo. The optimum mechanical conditions for cell health are not fully understood. This paper describes the optical and microfluidic mechanical manipulation of single suspended cells enabled by the ?PIVOT, an integrated micron resolution particle image velocimeter (?PIV) and dual optical tweezers instrument (OT). In this study, we examine the viability and trap stiffness of cartilage cells, identify the maximum fluid-induced stresses possible in uniform and extensional flows, and compare the deformation characteristics of bone and muscle cells. These results indicate cell photodamage of chondrocytes is negligible for at least 20 min for laser powers below 30 mW, a dead cell presents less resistance to internal organelle rearrangement and deforms globally more than a viable cell, the maximum fluid-induced shear stresses are limited to ~15 mPa for uniform flows but may exceed 1 Pa for extensional flows, and osteoblasts show no deformation for shear stresses up to 250 mPa while myoblasts are more easily deformed and exhibit a modulated response to increasing stress. This suggests that global and/or local stresses can be applied to single cells without physical contact. Coupled with microfluidic sensors, these manipulations may provide unique methods to explore single cell biomechanics. PMID:20824110

Nève, Nathalie; Kohles, Sean S.; Winn, Shelley R.; Tretheway, Derek C.

2010-01-01

93

Optical tweezers for free-solution label-free single bio-molecule studies  

NASA Astrophysics Data System (ADS)

Nanoaperture based trapping has developed as a significant tool among the various optical tweezer systems for trapping of very small particles down to the single nanometer range. The double nanohole aperture based trap provides a method for efficient, highly-sensitive, label-free, low-cost, free-solution single molecule trapping and detection. We use the double nanohole tweezer to understand biomolecular phenomena like protein unfolding, binding, structural conformation of DNA, protein-DNA interactions, and protein small molecule interactions.

Kotnala, Abhay; Al-Balushi, Ahmed A.; Gordon, Reuven

2014-09-01

94

Computer-automated program for calibration of optical tweezers  

NASA Astrophysics Data System (ADS)

An optical tweezers (OT) system uses focused laser light to contain and manipulate nano-scale to micro-scale particles. Trap stiffness is the quantitative measurement of the ability to trap a particle. For some techniques, this measurement depends on an accurate knowledge of the particle's position in time. A position sensing detector (PSD) is used to track particle motion by detecting laser light from the trapping region. The PSD outputs voltages corresponding to the x- and y-coordinates of particle motion, providing a means of knowing the location of the particle in time. An OT system requires a calibration to convert the measured voltages into accurate distances. This process is time-consuming and frequently needs to be repeated, however, with the growing availability of computer-aided data acquisition and control, the complete process can now be automated, reducing time spent by researchers and increasing level of accuracy of future measurements. We have developed a program written in LabVIEW that will, after initialization, 1) via image processing, calibrate the pixel size of the camera, 2) calibrate the optical tweezer position detector by controlling a motorized mirror to move a trapped bead through a detection laser with simultaneous position detector signal measurements, 3) re-align the trap beam and the detection beam by motorized mirror control, 4) measure position data for the same trapped particle being illuminated by the detection beam, and 5) analyze the position signal via the power spectrum method and equipartition method to give two trap stiffness values for comparison. Previous automated calibration methods require additional and sometimes costly equipment as well as some precalibration of stage motion or pixel size. Here, the user only needs to input the known size of the bead (provided by the manufacturer) into the program, insert their prepared slide into their microscope, input some parameters and make selections, and click "start" in order to achieve experimental values of the camera and position detector calibrations, as well as trap stiffness. We intend to implement many other calibration techniques that require additional equipment, but have designed this initial system for use in a standard position-detection-capable OT setup as long as it has a digital camera and motorized mirror that can be controlled with LabVIEW.

Taylor, C. D.; Foley, T. W.; Chang, A. N.; Mowa, S.; Burris, J. L.; Hester, B. C.

2012-10-01

95

Membrane tether formation from outer hair cells with optical tweezers.  

PubMed Central

Optical tweezers were used to characterize the mechanical properties of the outer hair cell (OHC) plasma membrane by pulling tethers with 4.5-microm polystyrene beads. Tether formation force and tether force were measured in static and dynamic conditions. A greater force was required for tether formations from OHC lateral wall (499 +/- 152 pN) than from OHC basal end (142 +/- 49 pN). The difference in the force required to pull tethers is consistent with an extensive cytoskeletal framework associated with the lateral wall known as the cortical lattice. The apparent plasma membrane stiffness, estimated under the static conditions by measuring tether force at different tether length, was 3.71 pN/microm for OHC lateral wall and 4.57 pN/microm for OHC basal end. The effective membrane viscosity was measured by pulling tethers at different rates while continuously recording the tether force, and estimated in the range of 2.39 to 5.25 pN x s/microm. The viscous force most likely results from the viscous interactions between plasma membrane lipids and the OHC cortical lattice and/or integral membrane proteins. The information these studies provide on the mechanical properties of the OHC lateral wall is important for understanding the mechanism of OHC electromotility. PMID:11867454

Li, Zhiwei; Anvari, Bahman; Takashima, Masayoshi; Brecht, Peter; Torres, Jorge H; Brownell, William E

2002-01-01

96

Mapping force of interaction between PLGA nanoparticle with cell membrane using optical tweezers  

NASA Astrophysics Data System (ADS)

Drug delivery using magnetic (Fe3O4) Poly Lactic-co-Glycolic Acid (PLGA) nanoparticles is finding increasing usage in therapeutic applications due to its biodegradability, biocompatibility and targeted localization. Since optical tweezers allow non-contact, highly sensitive force measurement, we utilized optical tweezers for studying interaction forces between the Fe3O4-PLGA nanoparticles with prostate cancer PC3 cells. Presence of Fe3O4 within the PLGA shell allowed efficient trapping of these nanoparticles in near-IR optical tweezers. The conglomerated PLGA nanoparticles could be dispersed by use of the optical tweezers. Calibration of trapping stiffness as a function of laser beam power was carried out using equipartition theorem method, where the mean square displacement was measured with high precision using time-lapse fluorescence imaging of the nanoparticles. After the trapped PLGA nanoparticle was brought in close vicinity of the PC3 cell membrane, displacement of the nanoparticle from trap center was measured as a function of time. In short time scale (< 30sec), while the force of interaction was within 0.2 pN, the force increased beyond 1pN at longer time scales (˜ 10 min). We will present the results of the time-varying force of interactions between PLGA nanoparticles with PC3 cells using optical tweezers.

Chhajed, Suyash; Gu, Ling; Homayoni, Homa; Nguyen, Kytai; Mohanty, Samarendra

2011-03-01

97

Silicon photonics for functional on-chip optical tweezers devices and circuits  

NASA Astrophysics Data System (ADS)

Silicon photonics using waveguide- and microresonator-based devices are finding technologically important applications in the field of optofluidics. By integrating microfluidic channels on top of silicon-based planar devices, silicon photonic devices can function as on-chip optical tweezers to manipulate micro/nanoparticles. In this paper, we will highlight our recent progress in the field of optofluidics using silicon nitride devices for on-chip optical manipulation including the experimental demonstrations of: (i) planar optical tweezers using waveguide junctions with and without tapers, (ii) microparticle buffering and dropping on microring resonator devices upon linearly polarized light and (iii) microparticle trapping and assembling on circular microdisk resonators. Such devices can function as basic building blocks for "optical tweezers circuits" in lab-on-chip applications.

Cai, Hong; Wang, Jiawei; Poon, Andrew W.

2013-02-01

98

Characterisation of Au nanorod dynamics in optical tweezers via localised surface plasmon resonance spectroscopy  

NASA Astrophysics Data System (ADS)

We present a study of the trapping properties of Au nanorods of different aspect ratios in an optical tweezers and comparison with other characterization techniques like transmission electron microscope (TEM) imaging and dynamic light scattering (DLS). This study provides information on the dynamics and orientation of Au nanorods inside an optical trap based on a time study of their localised surface plasmon resonance (LSPR) features. The results indicate that the orientation of the Au nanorods trapped in our optical tweezers varies with time and LSPR spectra can provide information on the angle of the nanorod with respect to the direction of propagation of the trapping laser.

Andres-Arroyo, Ana; Kemp, Scott; Toe, Wen Jun; Wang, Fan; Coleman, Victoria; Reece, Peter J.

2014-09-01

99

Near-field enhanced optical tweezers utilizing femtosecond-laser nanostructured substrates  

E-print Network

We present experimental evidence of plasmonic-enhanced optical tweezers, of polystyrene beads in deionized water in the vicinity of metal-coated nanostructures. The optical tweezers operate with a continuous wave (CW) near-infrared laser. We employ a Cu/Au bilayer that significantly improves dissipation of heat generated by the trapping laser beam and avoid de-trapping from heat convection currents. We investigate the improvement of the optical trapping force, the effective trapping quality factor, and observe an exponential distance dependence of the trapping force from the nanostructures, expected from the evanescent plasmon field.

Kotsifaki, Domna G; Lagoudakis, Pavlos G

2015-01-01

100

Single and dual fiber nano-tip optical tweezers: trapping and analysis  

E-print Network

An original optical tweezers using one or two chemically etched fiber nano-tips is developed. We demonstrate optical trapping of 1 micrometer polystyrene spheres at optical powers down to 2 mW. Harmonic trap potentials were found in the case of dual fiber tweezers by analyzing the trapped particle position fluctuations. The trap stiffness was deduced using three different models. Consistent values of up to 1 fN/nm were found. The stiffness linearly decreases with decreasing light intensity and increasing fiber tip-to-tip distance.

Decombe, Jean-Baptiste; Fick, Jochen

2013-01-01

101

Wavefront analysis and optimization from conventional liquid crystal displays for low-cost holographic optical tweezers and digital holographic microscopy  

Microsoft Academic Search

In different study fields the manipulation and imaging of micro-sized particles is essential. The use of holographic optical tweezers (HOT) and digital holographic microscopy (DHM) facilitates this task in a non-mechanical way by providing the proper computer generated hologram and the required amount of light. Electrically addressed spatial light modulators (EASLM) found in holographic optical tweezers are typically of the

Andreas Weber; Valentin Ortega Clavero; Werner Schröder

2011-01-01

102

Cleaved fiber optic double nanohole optical tweezers for trapping nanoparticles.  

PubMed

We demonstrate the trapping of single 20 and 40 nm polystyrene spheres at the cleaved end of a fiber optic with a double nanohole aperture in gold and without any microscope optics. An optical transmission increase of 15% indicates a trapping event for the 40 nm particle, and the jump is 2% for the 20 nm particle. This modular technique can be used to replace those used with current optical trapping setups that require complicated free space optics and frequent calibration, with one that is modular and requires no free space optics. This simple arrangement with the potential for fiber translation is of interest for future biosensor and optical nano-pipette devices. PMID:25490482

Gelfand, Ryan M; Wheaton, Skylar; Gordon, Reuven

2014-11-15

103

Nonlinear Stabilization of a Spherical Particle Trapped in an Optical Tweezer Aruna Ranaweera  

E-print Network

Nonlinear Stabilization of a Spherical Particle Trapped in an Optical Tweezer Aruna Ranaweera-5070 Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106-9560 Abstract-- We describe the nonlinear equations of mo- tion of a spherical particle trapped in an optical

Sontag, Eduardo

104

Mechanical properties of stored red blood cells using optical tweezers  

NASA Astrophysics Data System (ADS)

We have developed a method for measuring the red blood cell (RBC) membrane overall elasticity ? by measuring the deformation of the cells when dragged at a constant velocity through a plasma fluid by an optical tweezers. The deformability of erythrocytes is a critical determinant of blood flow in the microcirculation. We tested our method and hydrodynamic models, which included the presence of two walls, by measuring the RBC deformation as a function of drag velocity and of the distance to the walls. The capability and sensitivity of this method can be evaluated by its application to a variety of studies, such as, the measurement of RBC elasticity of sickle cell anemia patients comparing homozygous (HbSS), including patients taking hydroxyrea (HU) and heterozygous (HbAS) with normal donors and the RBC elasticity measurement of gamma irradiated stored blood for transfusion to immunosupressed patients as a function of time and dose. These studies show that the technique has the sensitivity to discriminate heterozygous and homozygous sickle cell anemia patients from normal donors and even follow the course of HU treatment of Homozygous patients. The gamma irradiation studies show that there is no significant change in RBC elasticity over time for up to 14 days of storage, regardless of whether the unit was irradiated or not, but there was a huge change in the measured elasticity for the RBC units stored for more than 21 days after irradiation. These finds are important for the assessment of stored irradiated RBC viability for transfusion purposes because the present protocol consider 28 storage days after irradiation as the limit for the RBC usage.

Fontes, Adriana; Alexandre de Thomaz, Andre; de Ysasa Pozzo, Liliana; de Lourdes Barjas-Castro, Maria; Brandao, Marcelo M.; Saad, Sara T. O.; Barbosa, Luiz Carlos; Cesar, Carlos Lenz

2005-08-01

105

Dynamic properties of bacterial pili measured by optical tweezers  

NASA Astrophysics Data System (ADS)

The ability of uropathogenic Escherichia coli (UPEC) to cause urinary tract infections is dependent on their ability to colonize the uroepithelium. Infecting bacteria ascend the urethra to the bladder and then kidneys by attaching to the uroepithelial cells via the differential expression of adhesins. P pili are associated with pyelonephritis, the more severe infection of the kidneys. In order to find means to treat pyelonephritis, it is therefore of interest to investigate the properties P pili. The mechanical behavior of individual P pili of uropathogenic Escherichia coli has recently been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of ~1000 PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. We have earlier studied P pili regarding its stretching/elongation properties where we have found and characterized three different elongation regions, of which one constitute an unfolding of the quaternary (helical) structure of the PapA rod. It was shown that this unfolding takes place at an elongation independent force of 27 +/- 2 pN. We have also recently performed studies on its folding properties and shown that the unfolding/folding of the PapA rod is completely reversible. Here we present a study of the dynamical properties of the PapA rod. We show, among other things, that the unfolding force increases and that the folding force decreases with the speed of unfolding and folding respectively. Moreover, the PapA rod can be folded-unfolded a significant number of times without loosing its characteristics, a phenomenon that is believed to be important for the bacterium to keep close contact to the host tissue and consequently helps the bacterium to colonize the host tissue.

Fallman, Erik G.; Andersson, Magnus J.; Schedin, Staffan S.; Jass, Jana; Uhlin, Bernt Eric; Axner, Ove

2004-10-01

106

Analysis of optical trap mediated aerosol coalescence  

NASA Astrophysics Data System (ADS)

The use of optical tweezers for the analysis of aerosols is valuable for understanding the dynamics of atmospherically relevant particles. However to be able to make accurate measurements that can be directly tied to real-world phenomena it is important that we understand the influence of the optical trap on those processes. One process that is seemingly straightforward to study with these techniques is binary droplet coalescence, either using dual beam traps, or by particle collision with a single trapped droplet. This binary coalescence is also of interest in many other processes that make use of dense aerosol sprays such as spray drying and the use of inhalers for drug delivery in conditions such as asthma or hay fever. In this presentation we discuss the use of high speed (~5000 frames per second) video microscopy to track the dynamics of particles as they approach and interact with a trapped aqueous droplet and develop this analysis further by considering elastic light scattering from droplets as they undergo coalescence. We find that we are able to characterize the re-equilibration time of droplets of the same phase after they interact and that the trajectories taken by airborne particles influenced by an optical trap are often quite complex. We also examine the role of parameters such as the salt concentration of the aqueous solutions used and the influence of laser wavelength.

Mistry, N. S.; Power, R.; Anand, S.; McGloin, D.; Almohamedi, A.; Downie, M.; Reid, J. P.; Hudson, A. J.

2012-10-01

107

Mechanical and electrical properties of red blood cells using optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers are a very sensitive tool, based on photon momentum transfer, for individual, cell by cell, manipulation and measurements, which can be applied to obtain important properties of erythrocytes for clinical and research purposes. Mechanical and electrical properties of erythrocytes are critical parameters for stored cells in transfusion centers, immunohematological tests performed in transfusional routines and in blood diseases. In this work, we showed methods, based on optical tweezers, to study red blood cells and applied them to measure apparent overall elasticity, apparent membrane viscosity, zeta potential, thickness of the double layer of electrical charges and adhesion in red blood cells.

Fontes, A.; Barjas Castro, M. L.; Brandão, M. M.; Fernandes, H. P.; Thomaz, A. A.; Huruta, R. R.; Pozzo, L. Y.; Barbosa, L. C.; Costa, F. F.; Saad, S. T. O.; Cesar, C. L.

2011-04-01

108

Geometrical Optics of Dense Aerosols  

SciTech Connect

Assembling a free-standing, sharp-edged slab of homogeneous material that is much denser than gas, but much more rare ed than a solid, is an outstanding technological challenge. The solution may lie in focusing a dense aerosol to assume this geometry. However, whereas the geometrical optics of dilute aerosols is a well-developed fi eld, the dense aerosol limit is mostly unexplored. Yet controlling the geometrical optics of dense aerosols is necessary in preparing such a material slab. Focusing dense aerosols is shown here to be possible, but the nite particle density reduces the eff ective Stokes number of the flow, a critical result for controlled focusing. __________________________________________________

Hay, Michael J.; Valeo, Ernest J.; Fisch, Nathaniel J.

2013-04-24

109

Optical tweezers in concentrated colloidal dispersions : Manipulating and imaging individual particles  

NASA Astrophysics Data System (ADS)

Using a laser beam that is focused down to a diffraction-limited spot, particles with a size ranging from several nanometers up to tens of micrometers can be trapped and manipulated. This technique, known as optical tweezers or optical trapping, has been used in a wide variety of (interdisciplinary) fields and its use is expanding fast. Recent improvements allow for new exciting and promising applications. First an introduction to the technique of optical tweezers is given and the setup that combines optical tweezers with confocal microscopy is described. By time-sharing a single laser beam, hundreds of optical traps can be created and changed dynamically. Independent three-dimensional trapping and imaging of individual particles is possible because two microscope objectives are used, one below and one above the sample. We demonstrate that large two-dimensional patterns of colloidal particles can be created using optical tweezers by positioning particles on a coated surface. These structures of colloidal particles can subsequently be used as masks for colloidal lithography. These masks can be modified further using ion beam deformation or, alternatively, chemical methods. Large arrays of metal nanoparticles with sizes in the range of tens of nanometers have been created using these techniques. Using our setup we have also studied crystallization and melting in colloidal dispersions. A single optical trap was used on collections of particles to crystallize two- and three-dimensional colloidal dispersions. With specially synthesized mixtures of core-shell colloidal particles it is now possible to manipulate individual articles selectively inside concentrated dispersions. Arrays of optical tweezers were used to trap core-shell particles that act as nuclei for homogeneous and heterogeneous nucleation in concentrated colloidal dispersions. We show a single particle driven through a three-dimensional colloidal crystal.

Vossen, Dirk Leo Joep

2004-11-01

110

TweezPal Optical tweezers analysis and calibration software Natan Osterman1  

E-print Network

TweezPal ­ Optical tweezers analysis and calibration software Natan Osterman1 J. Stefan Institute and calibration software Authors: Natan Osterman Program title: TweezPal Licensing provisions: CPC non-profit use two 1 E-mail address: natan.osterman@ijs.si 1 #12;methods. Solution method: Elimination

Osterman, Natan

111

Quantitation of Malaria Parasite-Erythrocyte Cell-Cell Interactions Using Optical Tweezers  

E-print Network

Article Quantitation of Malaria Parasite-Erythrocyte Cell-Cell Interactions Using Optical Tweezers falciparum merozoites is an essential step for parasite survival and hence the pathogenesis of malaria in unraveling the blood-stage biology of malaria. BACKGROUND Most cases of severe and fatal malaria in humans

Cicuta, Pietro

112

Force Spectroscopy with Dual-Trap Optical Tweezers: Molecular Stiffness Measurements and Coupled Fluctuations Analysis  

PubMed Central

Dual-trap optical tweezers are often used in high-resolution measurements in single-molecule biophysics. Such measurements can be hindered by the presence of extraneous noise sources, the most prominent of which is the coupling of fluctuations along different spatial directions, which may affect any optical tweezers setup. In this article, we analyze, both from the theoretical and the experimental points of view, the most common source for these couplings in dual-trap optical-tweezers setups: the misalignment of traps and tether. We give criteria to distinguish different kinds of misalignment, to estimate their quantitative relevance and to include them in the data analysis. The experimental data is obtained in a, to our knowledge, novel dual-trap optical-tweezers setup that directly measures forces. In the case in which misalignment is negligible, we provide a method to measure the stiffness of traps and tether based on variance analysis. This method can be seen as a calibration technique valid beyond the linear trap region. Our analysis is then employed to measure the persistence length of dsDNA tethers of three different lengths spanning two orders of magnitude. The effective persistence length of such tethers is shown to decrease with the contour length, in accordance with previous studies. PMID:23199920

Ribezzi-Crivellari, M.; Ritort, F.

2012-01-01

113

Mechanical characterization of human red blood cells by robotic manipulation with optical tweezers  

Microsoft Academic Search

Human red blood cells (RBCs) are responsible to transport oxygen and carbon dioxide for human bodies. The physiological functions of RBCs are greatly influenced by their mechanical properties. Any alteration of the cell mechanics may cause human diseases. In this paper, to understand the correlation between the cell properties and their osmotic environments, robotic manipulation technology with optical tweezers is

Youhua Tan; Dong Sun; Wenhao Huang; Hanxiong Li

2009-01-01

114

Measurement of adhesive forces between bacteria and protein-coated surfaces using optical tweezers  

Microsoft Academic Search

Bacterial adhesion is a primary cause of failure in implanted medical devices. Bacteria commonly found in device-related infections, such as S. aureus, have multiple cell surface adhesins which mediate specific adhesion to molecules found in extracellular matrix and blood plasma. Adhesins recognizing fibrinogen, fibronectin, collagen, and elastin molecules have been isolated in S. aureus. We have used optical tweezers to

Kathryn H. Simpson; Gabriela Bowden; Magnus Hook; Bahman Anvari

2002-01-01

115

Femtosecond optical tweezers for in-situ control of two-photon fluorescence.  

PubMed

We perform a comparison of optical tweezing using continuous wave (cw) and femtosecond lasers. Measurement of the relative Q-values in the femtosecond and cw regimes shows that femtosecond optical tweezers are just as effective as cw optical tweezers. We also demonstrate simultaneous optical tweezing and in-situ control of two-photon fluorescence (at 400nm) from dye-doped polymer microspheres. By switching the 800 nm tweezing laser source between femtosecond and cw regimes, we turned the fluorescent signal from the tweezed particle on and off while maintaining an equivalent tweezing action. Femtosecond lasers can thus be used for optical tweezing and simultaneously utilized to induce nonlinear multi-photon processes such as two-photon excitation or even photoporation. PMID:19483818

Agate, B; Brown, C; Sibbett, W; Dholakia, K

2004-06-28

116

Parallel optical tweezers with combining a diffractive optical element and a spatial light modulator for photonic DNA memory  

Microsoft Academic Search

To overcome the restriction of the density of optical memory systems due to diffraction limit, we have been studying photonic DNA memory, which utilizes photonic technologies and the DNA computing methodology. Our scheme is on the basis of local DNA reaction using laser irradiation and transportation of DNA using parallel optical tweezers with fabricating DNA clusters by attaching DNA onto

MingJie Zheng; Naoya Tate; Yusuke Ogura; Jun Tanida

2007-01-01

117

3D Raman sideband cooling of single atoms in an optical tweezer trap  

NASA Astrophysics Data System (ADS)

We have cooled a single atom in an optical tweezer trap very close to its three-dimensional ground state. An atom loaded with an initial temperature of around 110 uK has radial and axial occupation numbers of nr= 23 and na= 170; after cooling, we achieve final occupation numbers of nr< 0.1 and na=7.5. The principal technical challenge we encountered was effective magnetic field gradients arising from distortions of the dipole trap polarization in the optical tweezer focus, which we will discuss in some detail. Additionally, we will present ongoing work on two fronts: using the tightly localized atom to sense optical fields on the nanometer-scale, and bringing the atom close to nanoscale optical waveguides and can ities with the goal of achieving strong atom-photon interactions.

Thompson, Jeff; Tiecke, Tobias; Vuletic, Vladan; Lukin, Mikhail

2012-06-01

118

Optical properties of red blood cells: an optical tweezer based analysis  

NASA Astrophysics Data System (ADS)

A microscopic object finds an equilibrium orientation under a laser tweezer such that a maximum of its volume lies in the region of highest electric field. Furthermore, birefringent microscopic objects show no rotational diffusion after reorienting under a linearly polarized optical trap and also are seen to follow the plane of polarization when the latter is changed using a half wave plate. We observe that a healthy human Red Blood Cell (RBC) reproduces these observations in an optical tweezer, which confirms it to be birefringent. Polarization microscopy based measurements reveal that the birefringence is confined to the cell's dimple region and the mean value of retardation for polarized green light (? = 546nm) is 9 +/- 1.5nm. We provide a simple geometrical model that attributes the birefringence to the nature of arrangement of the phospholipid molecules of the bilayer. This predicts the observed variation in the measured birefringence, from the dimple to the rim of the cell which we further show, can serve to demarcate the extent of the dimple region. This points to the value of birefringence measurements in revealing cell membrane contours. . We extend this technique to understand the birefringence of a chicken RBC, an oblate shaped cell, wherein the slow axis is identified to be coincident with the long axis of the cell. Further, we observe the birefringence to be confined to the edges of the cell. Experiments to probe the optomechanical response of the chicken RBC are in progress.

Nagesh, B. V.; Lakkegowda, Yogesha; Pratibha, R.; Praveen, P.; Bhattacharya, Sarbari; Ananthamurthy, Sharath

2014-03-01

119

Using optical tweezers, single molecule fluorescence and the ZIF268 protein-DNA system to probe mechanotransduction mechanisms  

E-print Network

Optical tweezers instruments use laser radiation pressure to trap microscopic dielectric beads. With the appropriate chemistry, such a bead can be attached to a single molecule as a handle, permitting the application of ...

Lee, Peter, S.M. Massachusetts Institute of Technology

2006-01-01

120

An Improved Optical Tweezers Assay for Measuring the Force Generation of Single Kinesin Molecules  

PubMed Central

Numerous microtubule-associated molecular motors, including several kinesins and cytoplasmic dynein, produce opposing forces that regulate spindle and chromosome positioning during mitosis. The motility and force generation of these motors are therefore critical to normal cell division, and dysfunction of these processes may contribute to human disease. Optical tweezers provide a powerful method for studying the nanometer motility and piconewton force generation of single motor proteins in vitro. Using kinesin-1 as a prototype, we present a set of step-by-step, optimized protocols for expressing a kinesin construct (K560-GFP) in Escherichia coli, purifying it, and studying its force generation in an optical tweezers microscope. We also provide detailed instructions on proper alignment and calibration of an optical trapping microscope. These methods provide a foundation for a variety of similar experiments. PMID:24633799

Nicholas, Matthew P.; Rao, Lu; Gennerich, Arne

2014-01-01

121

Microrheology of non mulberry silk varieties by optical tweezer and video microscopy based techniques  

E-print Network

We have carried out a comparative study of the microrheological properties of silk fibroin solutions formed from a variety of silks indigenous to the Indian subcontinent. We present the measured viscoelastic moduli of Tasar silk fibroin solution using both a single and dual optical tweezer at 0.16% and 0.25% (w/v). The bandwidth of the measurements carried out using optical tweezers is extended down to the lower frequency regime by a video microscopy measurement. Further, we have measured the viscoelastic moduli of Eri and Muga varieties of silk fibroin solutions at a higher concentration (1.00% w/v) limiting the tool of measurement to video microscopy, as the reduced optical transparencies of these solutions at higher concentration preclude an optical tweezer based investigation. The choice of a higher concentration of fibroin solution of the latter silk varieties is so as to enable a comparison of the shear moduli obtained from optical methods with their corresponding fibre stiffness obtained from wide angle X-ray scattering data. We report a correlation between the microstructure and microrheological parameters of these silk varieties for the concentration of fibroin solutions studied.

Yogesha; Raghu A; Siddaraju G N; G Subramanya; Somashekar R; Sharath Ananthamurthy

2011-02-15

122

Differential detection of dual traps improves the spatial resolution of optical tweezers  

PubMed Central

The drive toward more sensitive single-molecule manipulation techniques has led to the recent development of optical tweezers capable of resolving the motions of biological systems at the subnanometer level, approaching the fundamental limit set by Brownian fluctuations. One successful approach has been the dual-trap optical tweezers, in which the system of study is held at both ends by microspheres in two separate optical traps. We present here a theoretical description of the Brownian limit on the spatial resolution of such systems and verify these predictions by direct measurement in a Brownian noise-limited dual-trap optical tweezers. We find that by detecting the positions of both trapped microspheres, correlations in their motions can be exploited to maximize the resolving power of the instrument. Remarkably, we show that the spatial resolution of dual optical traps with dual-trap detection is always superior to that of more traditional, single-trap designs, despite the added Brownian noise of the second trapped microsphere. PMID:16751267

Moffitt, Jeffrey R.; Chemla, Yann R.; Izhaky, David; Bustamante, Carlos

2006-01-01

123

Low cost optical tweezers systems using double coil driving stepping motor to controlling sample stage  

NASA Astrophysics Data System (ADS)

In this research, the low cost optical tweezers systems using X-Y stage has been developed by using 5-phase stepping motor. By using sequential double coil driving, we can obtain the driving torque larger than using the single coil driving. The moving scale is fine resolution at 0.2 micrometer. The overall systems based on microcontroller PIC18F458 and joystick controller with LabView® graphical user interface (GUI). The mechanical damping has been included in the system for decreasing the vibrational noise. By using this method, our optical tweezers system is cheaper than the other commercial system that has been used the piezoelectric driving, and still has the same efficiency.

Laowattanatham, N.; Cheamanunkul, N.; Plaipichit, S.; Buranasiri, P.; Nuansri, R.

2013-06-01

124

Practical lab tool for living cells based on microstereolithography and multiple dynamic holographic optical tweezers  

NASA Astrophysics Data System (ADS)

Recent studies have shown that the cell is mechanically differentiated both spatially and temporally, leading to a regional approach in cell behaviour essays. Most experiments are based on spatially-controlled contacts between microbeads and cells. We here propose an apparatus based on holographic optical tweezers to put on a target cell a two- or three-dimensional custom-built pattern of beads, with respect to the target cell shape, with both temporal and spatial dynamic control of each contact. In order to avoid disturbance or contact from the excess beads with the target cell, we keep the beads under isolated condition, by placing them in a confinement chamber made by microstereolithography. Our system exploits a digital display to project binary images on a photocurable resin surface, and induce space-resolved photopolymerisation reactions, constructing three-dimensional micro structures with complex shapes, including reservoirs for the filling, outlets, and confinement chambers. Combination of microfluidics, holographic optical tweezers and one supplementary single manually steerable optical tweezers leads to several experimental procedures allowing the sequential or parallel deposition of beads onto a target, with both a spatial and temporal control.

Monneret, Serge; Belloni, Federico; Marguet, Didier

2006-02-01

125

Chromosomal analysis and identification based on optical tweezers and Raman spectroscopy  

NASA Astrophysics Data System (ADS)

The ability to identify specific chromosomes with certainty has been established by the development of several cytogenetic techniques based on staining. Here, we report the use of a new optical technique, laser tweezers and Raman spectroscopy (LTRS), to capture and manipulate chromosomes in order to obtain their spectral patterns for molecular analysis without the need for staining. The purpose of this study was to obtain Raman spectroscopy patterns for chromosomes number 1, 2, and 3 and to test if the Raman spectroscopy pattern could be used to distinguish these three chromosomes. In our experiment, optical tweezers were used to capture the individual chromosomes and the Raman spectral patterns were collected for the trapped chromosomes. Then, the captured chromosome was manipulated with the optical tweezers and moved to another chamber through a micro - channel, in which the chromosomes were G banded for positive identification as chromosome number 1, 2, or 3. Generalized discriminate analysis (GDA) was used to compare the Raman signatures. This analysis revealed that chromosomes 1, 2, and 3 could be distinguished and identified based on their Raman spectra. Development of this approach will lead to more rapid automatic methods for chromosome analysis and identification without the use of prior staining. Moreover, the Raman spectral patterns may lend themselves to more detailed analysis of chromosomal structure than is currently available with standard staining protocols. Such analysis may some day be useful for rapid, automated screening and diagnosis for certain cancers.

Ojeda, Jenifer F.; Xie, Changan; Li, Yong-Qing; Bertrand, Fred E.; Wiley, John; McConnell, Thomas J.

2006-06-01

126

Single-cell optoporation and transfection using femtosecond laser and optical tweezers  

PubMed Central

In this paper, we demonstrate a new single-cell optoporation and transfection technique using a femtosecond Gaussian laser beam and optical tweezers. Tightly focused near-infrared (NIR) femtosecond laser pulse was employed to transiently perforate the cellular membrane at a single point in MCF-7 cancer cells. A distinct technique was developed by trapping the microparticle using optical tweezers to focus the femtosecond laser precisely on the cell membrane to puncture it. Subsequently, an external gene was introduced in the cell by trapping and inserting the same plasmid-coated microparticle into the optoporated cell using optical tweezers. Various experimental parameters such as femtosecond laser exposure power, exposure time, puncture hole size, exact focusing of the femtosecond laser on the cell membrane, and cell healing time were closely analyzed to create the optimal conditions for cell viability. Following the insertion of plasmid-coated microparticles in the cell, the targeted cells exhibited green fluorescent protein (GFP) under the fluorescent microscope, hence confirming successful transfection into the cell. This new optoporation and transfection technique maximizes the level of selectivity and control over the targeted cell, and this may be a breakthrough method through which to induce controllable genetic changes in the cell. PMID:24049675

Waleed, Muhammad; Hwang, Sun-Uk; Kim, Jung-Dae; Shabbir, Irfan; Shin, Sang-Mo; Lee, Yong-Gu

2013-01-01

127

Atmospheric aerosols: Their Optical Properties and Effects  

NASA Technical Reports Server (NTRS)

Measured properties of atmospheric aerosol particles are presented. These include aerosol size frequency distribution and complex retractive index. The optical properties of aerosols are computed based on the presuppositions of thermodynamic equilibrium and of Mie-theory.

1976-01-01

128

Template stripped double nanohole in a gold film for nano-optical tweezers.  

PubMed

Double nanohole (DNH) laser tweezers can optically trap and manipulate objects such as proteins, nanospheres, and other nanoparticles; however, precise fabrication of those DNHs has been expensive with low throughput. In this work, template stripping was used to pattern DNHs with gaps as small as 7 nm, in optically thick Au films. These DNHs were used to trap streptavidin as proof of operation. The structures were processed multiple times from the same template to demonstrate reusability. Template stripping is a promising method for high-throughput, reproducible, and cost efficient fabrication of DNH apertures for optical trapping. PMID:25407447

Zehtabi-Oskuie, Ana; Zinck, Aurora A; Gelfand, Ryan M; Gordon, Reuven

2014-12-12

129

Template stripped double nanohole in a gold film for nano-optical tweezers  

NASA Astrophysics Data System (ADS)

Double nanohole (DNH) laser tweezers can optically trap and manipulate objects such as proteins, nanospheres, and other nanoparticles; however, precise fabrication of those DNHs has been expensive with low throughput. In this work, template stripping was used to pattern DNHs with gaps as small as 7 nm, in optically thick Au films. These DNHs were used to trap streptavidin as proof of operation. The structures were processed multiple times from the same template to demonstrate reusability. Template stripping is a promising method for high-throughput, reproducible, and cost efficient fabrication of DNH apertures for optical trapping.

Zehtabi-Oskuie, Ana; Zinck, Aurora A.; Gelfand, Ryan M.; Gordon, Reuven

2014-12-01

130

Stretching of red blood cells by optical tweezers quantified by digital holographic microscopy  

NASA Astrophysics Data System (ADS)

Red blood cells (RBC) possess unique viscoelastic characteristics which allow them to pass through capillaries narrower than their size. Measurement of viscoelastic property of cells (e.g. RBC) in low-force regime is of high significance as it represents conditions of membrane fluctuation in response to physiological conditions. Estimation of visco-elastic properties of RBC requires measurement of extent of deformation in RBC subjected to known force. Optical tweezers, being gentle and absolutely sterile, are emerging as the tool of choice for application of localized force on cells. However, stretching of RBC in very low force regime has not been quantified. Further, though deformations in transverse directions have been measured, vertical deformations due to stretching of cells cannot be quantified by classical microscopic images. Here, we report realization of offaxis digital holographic microscopy (DHM) for highly sensitive axial changes in RBC shape due to stretching by optical tweezers without attaching microscopic beads. The RBC was stretched in axial direction with nanometer precision by change of divergence of the trapping beam. The obtained deformation patterns were compared with the axial position of the tweezers focus. Since the pathophysiology of progression of diseases like malaria and cancer is reflected in the biophysical (both mechanical and material) properties of the cells, it is possible to identify the changes by simultaneous measurement of refractive index and elasticity using this approach.

Cardenas, Nelson; Yu, Lingfeng; Mohanty, Samarendra K.

2011-03-01

131

Neural Network for Image-to-Image Control of Optical Tweezers  

NASA Technical Reports Server (NTRS)

A method is discussed for using neural networks to control optical tweezers. Neural-net outputs are combined with scaling and tiling to generate 480 by 480-pixel control patterns for a spatial light modulator (SLM). The SLM can be combined in various ways with a microscope to create movable tweezers traps with controllable profiles. The neural nets are intended to respond to scattered light from carbon and silicon carbide nanotube sensors. The nanotube sensors are to be held by the traps for manipulation and calibration. Scaling and tiling allow the 100 by 100-pixel maximum resolution of the neural-net software to be applied in stages to exploit the full 480 by 480-pixel resolution of the SLM. One of these stages is intended to create sensitive null detectors for detecting variations in the scattered light from the nanotube sensors.

Decker, Arthur J.; Anderson, Robert C.; Weiland, Kenneth E.; Wrbanek, Susan Y.

2004-01-01

132

Analysis of the influence of manufacturing and alignment related errors on an optical tweezer system  

NASA Astrophysics Data System (ADS)

In this work we present the design process as well as experimental results of an optical system for trapping particles in air. For positioning applications of micro-sized objects onto a glass wafer we developed a highly efficient optical tweezer. The focus of this paper is the iterative design process where we combine classical optics design software with a ray optics based force simulation tool. Thus we can find the best compromise which matches the optical systems restrictions with stable trapping conditions. Furthermore we analyze the influence of manufacturing related tolerances and errors in the alignment process of the optical elements on the optical forces. We present the design procedure for the necessary optical elements as well as experimental results for the aligned system.

Kampmann, R.; Sinzinger, S.

2014-12-01

133

Crosstalk elimination in the detection of dual-beam optical tweezers by spatial filtering  

SciTech Connect

In dual-beam optical tweezers, the accuracy of position and force measurements is often compromised by crosstalk between the two detected signals, this crosstalk leading to systematic and significant errors on the measured forces and distances. This is true both for dual-beam optical traps where the splitting of the two traps is done by polarization optics and for dual optical traps constructed by other methods, e.g., holographic tweezers. If the two traps are orthogonally polarized, most often crosstalk is minimized by inserting polarization optics in front of the detector; however, this method is not perfect because of the de-polarization of the trapping beam introduced by the required high numerical aperture optics. Here we present a simple and easy-to-implement method to efficiently eliminate crosstalk. The method is based on spatial filtering by simply inserting a pinhole at the correct position and is highly compatible with standard back focal plane photodiode based detection of position and force. Our spatial filtering method reduces crosstalk up to five times better than polarization filtering alone. The effectiveness is dependent on pinhole size and distance between the traps and is here quantified experimentally and reproduced by theoretical modeling. The method here proposed will improve the accuracy of force-distance measurements, e.g., of single molecules, performed by dual-beam optical traps and hence give much more scientific value for the experimental efforts.

Ott, Dino; Oddershede, Lene B., E-mail: oddershede@nbi.dk [Niels Bohr Institute (NBI), University of Copenhagen, Blegdamsvej 17, DK-2100 Copenhagen (Denmark); Reihani, S. Nader S. [Department of Physics, Sharif University of Technology, 11369-9161 Tehran (Iran, Islamic Republic of)

2014-05-15

134

Holographic optical tweezers: microassembling of shape-complementary 2PP building blocks  

NASA Astrophysics Data System (ADS)

Based on an ongoing trend in miniaturization and due to the increased complexity in MEMS-technology new methods of assembly need to be developed. Recent developments show that particularly optical forces are suitable to meet the requirements. The unique advantages of optical tweezers (OT) are attractive due to their contactless and precise manipulation forces. Spherical as well as non-spherical shaped pre-forms can already be assembled arbitrarily by using appropriate beam profiles generated by a spatial light modulator (SLM), resulting in a so called holographic optical tweezer (HOT) setup. For the fabrication of shape-complementary pre-forms, a two-photon-polymerization (2PP) process is implemented. The purpose of the process combination of 2PP and HOT is the development of an optical microprocessing platform for assembling arbitrary building blocks. Here, the optimization of the 2PP and HOT processes is described in order to allow the fabrication and 3D assembling of interlocking components. Results include the analysis of the dependence of low and high qualities of 2PP microstructures and their manufacturing accuracy for further HOT assembling processes. Besides, the applied detachable interlocking connections of the 2PP building blocks are visualized by an application example. In the long-term a full optical assembly method without applying any mechanical forces can thus be realized.

Ksouri, Sarah Isabelle; Mattern, Manuel; Köhler, Jannis; Aumann, Andreas; Zyla, Gordon; Ostendorf, Andreas

2014-09-01

135

Optical-tweezer-induced microbubbles as scavengers of carbon nanotubes This article has been downloaded from IOPscience. Please scroll down to see the full text article.  

E-print Network

Optical-tweezer-induced microbubbles as scavengers of carbon nanotubes This article has been.1088/0957-4484/21/24/245102 Optical-tweezer-induced microbubbles as scavengers of carbon nanotubes Hema Ramachandran1 , A K fragmentation of the bundles. Thus, microbubbles may be used for scavenging, transporting and dispersal

Sharma, Shobhona

136

Counter-propagating dual-trap optical tweezers based on linear momentum conservation.  

PubMed

We present a dual-trap optical tweezers setup which directly measures forces using linear momentum conservation. The setup uses a counter-propagating geometry, which allows momentum measurement on each beam separately. The experimental advantages of this setup include low drift due to all-optical manipulation, and a robust calibration (independent of the features of the trapped object or buffer medium) due to the force measurement method. Although this design does not attain the high-resolution of some co-propagating setups, we show that it can be used to perform different single molecule measurements: fluctuation-based molecular stiffness characterization at different forces and hopping experiments on molecular hairpins. Remarkably, in our setup it is possible to manipulate very short tethers (such as molecular hairpins with short handles) down to the limit where beads are almost in contact. The setup is used to illustrate a novel method for measuring the stiffness of optical traps and tethers on the basis of equilibrium force fluctuations, i.e., without the need of measuring the force vs molecular extension curve. This method is of general interest for dual trap optical tweezers setups and can be extended to setups which do not directly measure forces. PMID:23635178

Ribezzi-Crivellari, M; Huguet, J M; Ritort, F

2013-04-01

137

Counter-propagating dual-trap optical tweezers based on linear momentum conservation  

SciTech Connect

We present a dual-trap optical tweezers setup which directly measures forces using linear momentum conservation. The setup uses a counter-propagating geometry, which allows momentum measurement on each beam separately. The experimental advantages of this setup include low drift due to all-optical manipulation, and a robust calibration (independent of the features of the trapped object or buffer medium) due to the force measurement method. Although this design does not attain the high-resolution of some co-propagating setups, we show that it can be used to perform different single molecule measurements: fluctuation-based molecular stiffness characterization at different forces and hopping experiments on molecular hairpins. Remarkably, in our setup it is possible to manipulate very short tethers (such as molecular hairpins with short handles) down to the limit where beads are almost in contact. The setup is used to illustrate a novel method for measuring the stiffness of optical traps and tethers on the basis of equilibrium force fluctuations, i.e., without the need of measuring the force vs molecular extension curve. This method is of general interest for dual trap optical tweezers setups and can be extended to setups which do not directly measure forces.

Ribezzi-Crivellari, M.; Huguet, J. M. [Small Biosystems Lab, Dept. de Fisica Fonamental, Universitat de Barcelona, Avda. Diagonal 647, 08028 Barcelona (Spain); Ritort, F. [Small Biosystems Lab, Dept. de Fisica Fonamental, Universitat de Barcelona, Avda. Diagonal 647, 08028 Barcelona (Spain); Ciber-BBN de Bioingenieria, Biomateriales y Nanomedicina, Instituto de Salud Carlos III, Madrid (Spain)

2013-04-15

138

A focal spot with variable intensity distribution for optical tweezers  

NASA Astrophysics Data System (ADS)

An optical setup that can generate a focused light spot, with its shape tunable from a very sharp peak-centered beam to a donut-shaped dark-centered beam, is always desired in optical tweezing. This setup is now realized by incorporating an image inverting interferometer (III) and a helical phase element into a radially polarized beam generator, which enables the trapping and control of a large variety of particles with a single optical tweezing system. The performance of this system is investigated theoretically.

Hao, X.; Kuang, C. F.; Li, Y. H.; Liu, X.

2013-04-01

139

High-resolution, long-term characterization of bacterial motility using optical tweezers  

PubMed Central

We present a single-cell motility assay, which allows the quantification of bacterial swimming in a well-controlled environment, for durations of up to an hour and with a temporal resolution higher than the flagellar rotation rates of ~100 Hz. The assay is based on an instrument combining optical tweezers, light and fluorescence microscopy, and a microfluidic chamber. Using this device we characterized the long-term statistics of the run-tumble time series in individual Escherichia coli cells. We also quantified higher-order features of bacterial swimming, such as changes in velocity and reversals of swimming direction. PMID:19801991

Min, Taejin L.; Mears, Patrick J.; Chubiz, Lon M.; Rao, Christopher V.; Golding, Ido; Chemla, Yann R.

2009-01-01

140

Laser-induced fusion of human embryonic stem cells with optical tweezers  

NASA Astrophysics Data System (ADS)

We report a study on the laser-induced fusion of human embryonic stem cells (hESCs) at the single-cell level. Cells were manipulated by optical tweezers and fused under irradiation with pulsed UV laser at 355 nm. Successful fusion was indicated by green fluorescence protein transfer. The influence of laser pulse energy on the fusion efficiency was investigated. The fused products were viable as gauged by live cell staining. Successful fusion of hESCs with somatic cells was also demonstrated. The reported fusion outcome may facilitate studies of cell differentiation, maturation, and reprogramming.

Chen, Shuxun; Cheng, Jinping; Kong, Chi-Wing; Wang, Xiaolin; Han Cheng, Shuk; Li, Ronald A.; Sun, Dong

2013-07-01

141

The self-orientation of mammalian cells in optical tweezers—the importance of the nucleus  

NASA Astrophysics Data System (ADS)

Here we present the first evidence showing that eukaryotic cells can be stably trapped in a single focused Gaussian beam with an orientation that is defined by the nucleus. A mammalian eukaryotic cell (in suspension) is trapped and is re-oriented in the focus of a linearly polarized Gaussian beam with a waist of dimension smaller than the radius of the nucleus. The cell reaches a position relative to the focus that is dictated by the nucleus and nuclear components. Our studies illustrate that the force exerted by the optical tweezers at locations within the cell can be predicted theoretically; the data obtained in this way is consistent with the experimental observations.

Perney, Nicolas M. B.; Horak, Peter; Hanley, Neil A.; Melvin, Tracy

2012-04-01

142

Laser-induced fusion of human embryonic stem cells with optical tweezers  

SciTech Connect

We report a study on the laser-induced fusion of human embryonic stem cells (hESCs) at the single-cell level. Cells were manipulated by optical tweezers and fused under irradiation with pulsed UV laser at 355 nm. Successful fusion was indicated by green fluorescence protein transfer. The influence of laser pulse energy on the fusion efficiency was investigated. The fused products were viable as gauged by live cell staining. Successful fusion of hESCs with somatic cells was also demonstrated. The reported fusion outcome may facilitate studies of cell differentiation, maturation, and reprogramming.

Chen Shuxun; Wang Xiaolin; Sun Dong [Department of Mechanical and Biomedical Engineering, City University of Hong Kong (Hong Kong); Cheng Jinping; Han Cheng, Shuk [Department of Biology and Chemistry, City University of Hong Kong (Hong Kong); Kong, Chi-Wing [Stem Cell and Regenerative Medicine Consortium, and Departments of Medicine and Physiology, LKS Faculty of Medicine, University of Hong Kong (Hong Kong); Li, Ronald A. [Stem Cell and Regenerative Medicine Consortium, and Departments of Medicine and Physiology, LKS Faculty of Medicine, University of Hong Kong (Hong Kong); Center of Cardiovascular Research, Mount Sinai School of Medicine, New York, New York 10029 (United States)

2013-07-15

143

Single beam optical vortex tweezers with tunable orbital angular momentum  

SciTech Connect

We propose a single beam method for generating optical vortices with tunable optical angular momentum without altering the intensity distribution. With the initial polarization state varying from linear to circular, we gradually control the torque transferred to the trapped non-absorbing and non-birefringent silica beads. The continuous transition from the maximum rotation speed to zero without changing the trapping potential gives a way to study the complex tribological interactions.

Gecevi?ius, Mindaugas; Drevinskas, Rokas, E-mail: rd1c12@orc.soton.ac.uk; Beresna, Martynas; Kazansky, Peter G. [Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ (United Kingdom)

2014-06-09

144

Combined versatile high-resolution optical tweezers and single-molecule fluorescence microscopy  

PubMed Central

Optical trapping and single-molecule fluorescence are two major single-molecule approaches. Their combination has begun to show greater capability to study more complex systems than either method alone, but met many fundamental and technical challenges. We built an instrument that combines base-pair resolution dual-trap optical tweezers with single-molecule fluorescence microscopy. The instrument has complementary design and functionalities compared with similar microscopes previously described. The optical tweezers can be operated in constant force mode for easy data interpretation or in variable force mode for maximum spatiotemporal resolution. The single-molecule fluorescence detection can be implemented in either wide-field or confocal imaging configuration. To demonstrate the capabilities of the new instrument, we imaged a single stretched ? DNA molecule and investigated the dynamics of a DNA hairpin molecule in the presence of fluorophore-labeled complementary oligonucleotide. We simultaneously observed changes in the fluorescence signal and pauses in fast extension hopping of the hairpin due to association and dissociation of individual oligonucleotides. The combined versatile microscopy allows for greater flexibility to study molecular machines or assemblies at a single-molecule level. PMID:23020384

Sirinakis, George; Ren, Yuxuan; Gao, Ying; Xi, Zhiqun; Zhang, Yongli

2012-01-01

145

Trapping volume control in optical tweezers using cylindrical vector beams.  

PubMed

We present the result of an investigation into the optical trapping of spherical microparticles using laser beams with a spatially inhomogeneous polarization direction [cylindrical vector beams (CVBs)]. We perform three-dimensional tracking of the Brownian fluctuations in the position of a trapped particle and extract the trap spring constants. We characterize the trap geometry by the aspect ratio of spring constants in the directions transverse and parallel to the beam propagation direction and evaluate this figure of merit as a function of polarization angle. We show that the additional degree of freedom present in CVBs allows us to control the optical trap strength and geometry by adjusting only the polarization of the trapping beam. Experimental results are compared with a theoretical model of optical trapping using CVBs derived from electromagnetic scattering theory in the T-matrix framework. PMID:23282827

Skelton, S E; Sergides, M; Saija, R; Iatì, M A; Maragó, O M; Jones, P H

2013-01-01

146

Single and dual fiber nanotip optical tweezers: trapping and analysis  

E-print Network

. Picard, F. d. Fornel, and E. Hadji, ``Assembly of microparticles by optical trapping with a photonic crystal nanocavity,'' Appl. Phys. Lett. 100, 101103 (2012). 4. K. Wang, E. Schonbrun, P. Steinvurzel nanoparticles using plasmonic dipole antennas,'' Nano Lett. 10, 1006--1011 (2010). 6. Y. Tanaka and K. Sasaki

Paris-Sud XI, Université de

147

Chemotaxis study using optical tweezers to observe the strength and directionality of forces of Leishmania amazonensis  

NASA Astrophysics Data System (ADS)

The displacements of a dielectric microspheres trapped by an optical tweezers (OT) can be used as a force transducer for mechanical measurements in life sciences. This system can measure forces on the 50 femto Newtons to 200 pico Newtons range, of the same order of magnitude of a typical forces induced by flagellar motion. The process in which living microorganisms search for food and run away from poison chemicals is known is chemotaxy. Optical tweezers can be used to obtain a better understanding of chemotaxy by observing the force response of the microorganism when placed in a gradient of attractors and or repelling chemicals. This report shows such observations for the protozoa Leishmania amazomenzis, responsible for the leishmaniasis, a serious tropical disease. We used a quadrant detector to monitor the movement of the protozoa for different chemicals gradient. This way we have been able to observe both the force strength and its directionality. The characterization of the chemotaxis of these parasites can help to understand the infection mechanics and improve the diagnosis and the treatments employed for this disease.

Pozzo, Liliana d. Y.; Fontes, Adriana; de Thomaz, André A.; Barbosa, Luiz C.; Ayres, Diana C.; Giorgio, Selma; Cesar, Carlos L.

2006-08-01

148

Investigation of the mechanical property of individual cell using axial optical tweezers  

NASA Astrophysics Data System (ADS)

Optical tweezers is a technique that can trap and manipulate small objects using a highly focused laser beam. Because optical tweezers can also be used to measure small forces, it has been extensively used for the measurement of the mechanical forces of cells. Previous research works typically study particle manipulation and cell force measurement in the lateral direction, hence excluding valuable insights about the axial mechanical properties of cells. Other works that investigate axial cell force measurements utilize spatial light modulators and other devices that are expensive and complicate the setup. Thus, in our study, we designed a simple scheme that can axially manipulate particles by adjusting the position of one lens, called L1-lens, in our setup. Image processing techniques were utilized to determine the changes in the axial particle translation, providing nanometer sensitivity. We investigated the capability of our system using two different-sized particles and results show that for a given L1-lens default position and movement, a 2-micron particle and a 4.26-micron particle were moved axially for 7.68 µm and 4.83 µm, respectively. Axial trapping stiffness was also measured for the stated bead sizes in different magnification. Using the computed trapping sti_ness, we will investigate the axial reactive forces of cells.

Dy, Mary-Clare; Sugiura, Tadao; Minato, Kotaro

2013-02-01

149

Absolute position total internal reflection microscopy with an optical tweezer.  

PubMed

A noninvasive, in situ calibration method for total internal reflection microscopy (TIRM) based on optical tweezing is presented, which greatly expands the capabilities of this technique. We show that by making only simple modifications to the basic TIRM sensing setup and procedure, a probe particle's absolute position relative to a dielectric interface may be known with better than 10 nm precision out to a distance greater than 1 ?m from the surface. This represents an approximate 10× improvement in error and 3× improvement in measurement range over conventional TIRM methods. The technique's advantage is in the direct measurement of the probe particle's scattering intensity vs. height profile in situ, rather than relying on assumptions, inexact system analogs, or detailed knowledge of system parameters for calibration. To demonstrate the improved versatility of the TIRM method in terms of tunability, precision, and range, we show our results for the hindered near-wall diffusion coefficient for a spherical dielectric particle. PMID:25512542

Liu, Lulu; Woolf, Alexander; Rodriguez, Alejandro W; Capasso, Federico

2014-12-30

150

Global modeling of multicomponent aerosol species: Aerosol optical parameters  

NASA Astrophysics Data System (ADS)

Canadian Aerosol Module (CAM) has been developed to simulate the atmospheric cycling of principal aerosol species, with the Third Generation Canadian Climate Center General Circulation Model (CCC GCM III) as its climatological driver. Adding an aerosol optical module to this modeling framework, the optical parameters of aerosols are simulated and compared to Sun photometer (AERONET) and satellite (MODIS) observations, as well as lidar observations of aerosol vertical profiles. The model captures well the global distribution and seasonal variation of aerosol optical parameters, showing seasonal maxima of optical depth and absorption over desert and biomass-burning regions. For most sites and months, the modeled optical depths are within MODIS and AERONET means and standard deviations, and modeled single-scattering albedo (SSA) and asymmetry factor are within 10% of AERONET retrievals. Fairly good agreement is found between modeled and observed optical depths over tropical oceans, where most models show significant underestimation. The model's overestimation of observed optical depths over parts of Europe by about 0.1 is most likely due to overestimates by older emission inventories. Modeled optical depths and SSA above observed means and standard deviations over areas and at sites within Central Africa and Central and South America suggest overprediction of organic carbon contribution by the model. Common to other models, however, our simulations underestimate the strength of the tropical biomass burning season. Modeled aerosol vertical profiles show better agreement with lidar observations at European sites than at an East Asian site, and more so at upper than at lower altitudes.

Ayash, T.; Gong, S. L.; Jia, C. Q.; Huang, P.; Zhao, T. L.; Lavoue, D.

2008-06-01

151

Development of a two-photon polymerization and optical tweezers microscope for fabrication and manipulation of microstructures  

NASA Astrophysics Data System (ADS)

We report development of a two-photon polymerization (TPP) microscope, for micro-fabrication of microstructures, which is capable of optical manipulation by use of optical tweezers. The system is based on an inverted Nikon microscope with a tunable Ti: Sapphire femto-second (fs) laser coupled to the upper back port. While in modelocked condition, nanoparticles and wires were fabricated in photo-polymerizable synthetic materials using TPP. By axial positioning of the focused TPP laser beam, 1D-structures (for use as wave guide) were fabricated at desired height above the surface of the substrate. In the mode lock-OFF condition the same tunable laser microbeam was employed as optical tweezers to the hold the nanostructures and manipulate them even in highly viscous medium before immobilizing. Size of the TPP induced structure was found to depend on the fs laser intensity and exposure. Further, by shaping the fs laser beam to line pattern, linear 1D structures could be fabricated without scanning the beam or stage, which remain aligned along the line intensity profile due to anisotropic trapping force of the line tweezers in X and Y-directions. Use of optical tweezers with two-photon polymerization not only allowed in-situ corrective positioning of the polymerized structures, but also the integration of fluorescent microspheres (resonator/detector) with polymerized waveguide.

Ingle, Ninad; Mohanty, Samarendra K.

2011-03-01

152

Forces due to pulsed beams in optical tweezers: linear effects.  

PubMed

We present a method for the precise calculation of optical forces due to a tightly-focused pulsed laser beam using generalized Lorenz-Mie theory or the T-matrix method. This method can be used to obtain the fields as a function of position and time, allowing the approximate calculation of weak non-linear effects, and provides a reference calculation for validation of calculations including non-linear effects. We calculate forces for femtosecond pulses of various widths, and compare with forces due to a continuous wave (CW) beam. The forces are similar enough so that the continuous beam case provides a useful approximation for the pulsed case, with trap parameters such as the radial spring constant usually differing by less than 1% for pulses of 100 fs or longer. For large high-index (e.g., polystyrene, with n = 1.59) particles, the difference can be as large as 3% for 100 fs pulses, and up to 8% for 25 fs pulses. A weighted average of CW forces for individual spectral components of the pulsed beam provides a simple improved approximation, which we use to illustrate the physical principles responsible for the differences between pulsed and CW beams. PMID:25837064

Preez-Wilkinson, Nathaniel du; Stilgoe, Alexander B; Alzaidi, Thuraya; Rubinsztein-Dunlop, Halina; Nieminen, Timo A

2015-03-23

153

Comparison of T-matrix calculation methods for scattering by cylinders in optical tweezers.  

PubMed

The T-matrix method, or the T-matrix formulation of scattering, is a framework for mathematically describing the scattering properties of an object as a linear relationship between expansion coefficients of the incident and scattering fields in a basis of vector spherical wave functions (VSWFs). A variety of methods can be used to calculate the T-matrix. We explore the applicability of the extended boundary condition method (EBCM) and point matching (PM) method to calculate the T-matrix for scattering by cylinders in optical tweezers and hence the optical force acting on them. We compare both methods with the discrete-dipole approximation (DDA) to measure their accuracy for different sizes and aspect ratios (ARs) for Rayleigh and wavelength-size cylinders. We determine range of sizes and ARs giving errors below 1% and 10%. These results can help researchers choose the most efficient method to calculate the T-matrix for nonspherical particles with acceptable accuracy. PMID:25121885

Qi, Xiaoqiong; Nieminen, Timo A; Stilgoe, Alexander B; Loke, Vincent L Y; Rubinsztein-Dunlop, Halina

2014-08-15

154

Optical tweezers assisted imaging of the Z-ring in Escherichia coli: measuring its radial width  

NASA Astrophysics Data System (ADS)

Using single-beam, oscillating optical tweezers we can trap and rotate rod-shaped bacterial cells with respect to the optical axis. This technique allows imaging fluorescently labeled three-dimensional sub-cellular structures from different, optimized viewpoints. To illustrate our method we measure D, the radial width of the Z-ring in unconstricted Escherichia coli. We use cells that express FtsZ-GFP and have their cytoplasmic membrane stained with FM4-64. In a vertically oriented cell, both the Z-ring and the cytoplasmic membrane images appear as symmetric circular structures that lend themselves to quantitative analysis. We found that D ? 100 nm, much larger than expected.

Carmon, G.; Kumar, P.; Feingold, M.

2014-01-01

155

Tuning the size and configuration of nanocarbon microcapsules: aqueous method using optical tweezers  

NASA Astrophysics Data System (ADS)

To date, optical manipulation techniques for aqueous dispersions have been developed that deposit and/or transport nanoparticles not only for fundamental studies of colloidal dynamics, but also for either creating photonic devices or allowing accurate control of liquids on micron scales. Here, we report that optical tweezers (OT) system is able to direct three-dimensional assembly of graphene, graphite, and carbon nanotubes (CNT) into microcapsules of hollow spheres. The OT technique facilitates both to visualize the elasticity of a CNT microcapsule and to arrange a triplet of identical graphene microcapsules in aqueous media. Furthermore, the similarity of swelling courses has been found over a range of experimental parameters such as nanocarbon species, the power of the incident light, and the suspension density. Thanks to the universality in evolutions of rescaled capsule size, we can precisely control the size of various nanocarbon microcapsules by adjusting the duration time of laser emission.

Frusawa, Hiroshi; Matsumoto, Youei

2014-02-01

156

Tuning the size and configuration of nanocarbon microcapsules: aqueous method using optical tweezers  

PubMed Central

To date, optical manipulation techniques for aqueous dispersions have been developed that deposit and/or transport nanoparticles not only for fundamental studies of colloidal dynamics, but also for either creating photonic devices or allowing accurate control of liquids on micron scales. Here, we report that optical tweezers (OT) system is able to direct three-dimensional assembly of graphene, graphite, and carbon nanotubes (CNT) into microcapsules of hollow spheres. The OT technique facilitates both to visualize the elasticity of a CNT microcapsule and to arrange a triplet of identical graphene microcapsules in aqueous media. Furthermore, the similarity of swelling courses has been found over a range of experimental parameters such as nanocarbon species, the power of the incident light, and the suspension density. Thanks to the universality in evolutions of rescaled capsule size, we can precisely control the size of various nanocarbon microcapsules by adjusting the duration time of laser emission. PMID:24509866

Frusawa, Hiroshi; Matsumoto, Youei

2014-01-01

157

Micro- and nano-particle trapping using fibered optical nano-tweezers  

NASA Astrophysics Data System (ADS)

We present the stable trapping of luminescent 300-nm cerium-doped YAG particles in aqueous suspension using a dual fiber tip optical tweezers. The particles were elaborated using a specific glycothermal synthesis route together with an original protected annealing step. We obtained harmonic trap potentials in the direction transverse to the optical fiber axes. In the longitudinal direction, the potential shows some sub-structure revealed by two peaks in the distribution statistics with a distance of about half the wavelength of the trapping laser. We calculated intensity normalized trapping stiffness of 36 pN•?m-1W-1. These results are compared to previous work of microparticle trapping and discussed thanks to numerical simulations based on finite element method.

Decombe, Jean-Baptiste; Dantelle, Géraldine; Gacoin, Thierry; Valdivia-Valero, Francisco J.; Colas des Francs, Gérard; Huant, Serge; Fick, Jochen

2014-09-01

158

Application of vertical-cavity laser-based optical tweezers for particle manipulation in microfluidic channels  

NASA Astrophysics Data System (ADS)

The combination of microfluidics and optical manipulation offers new possibilities for particle handling and sorting on a single-cell level in the field of biophotonics. We present particle manipulation in microfluidics based on vertical-cavity surface-emitting lasers (VCSELs) which constitute a new low-cost, high beam quality nanostructured laser source for optical trapping, additionally allowing easy formation of small-sized, two-dimensional laser arrays. Single devices as well as densely packed linear VCSEL arrays with a pitch of only 24 ?m are fabricated. Microfluidic channels with widths of 50 to 150 ?m forming T- and Y-junctions are made of PDMS using common soft-lithography. With a single laser, selected polystyrene particles are trapped in the inlet channel and transferred to the desired outlet branch by moving the chip relatively to the optical trap. In a second approach, a tilted, linear laser array is introduced into the setup, effectively forming an optical lattice. While passing the continuously operating tweezers array, particles are not fully trapped, but deflected by each single laser beam. Therefore, non-mechanical particle separation in microfluidics is achieved. We also show the route to ultra-miniaturization of the system avoiding any external optics. Simulations of an integrated particle deflection and sorting scheme as well as first fabrication steps for the integrated optical trap are presented.

Kroner, Andrea; Schneck, Carolin; Rinaldi, Fernando; Rösch, Rudolf; Michalzik, Rainer

2008-04-01

159

Optical Tweezers as a Micromechanical Tool for Studying Defects in 2D Colloidal Crystals  

E-print Network

This paper reports on some new results from the analyses of the video microscopy data obtained in a prior experiment on two-dimensional (2D) colloidal crystals. It was reported previously that optical tweezers can be used to create mono- and di-vacancies in a 2D colloidal crystal. Here we report the results on the creation of a vacancy-interstitial pair, as well as tri-vacancies. It is found that the vacancy-interstitial pair can be long-lived, but they do annihilate each other. The behavior of tri-vacancies is most intriguing, as it fluctuates between a configuration of bound pairs of dislocations and that of a locally amorphous state. The relevance of this observation to the issue of the nature of 2D melting is discussed.

Sungcheol Kim; Lichao Yu; Stephanie Huang; Alexandros Pertsinidis; Xinsheng Sean Ling

2011-08-09

160

Mechanism of termination of bacteriophage DNA packaging investigated with optical tweezers  

NASA Astrophysics Data System (ADS)

The genomes of many dsDNA viruses are replicated by a mechanism that produces a long concatemer of multiple genomes. These viruses utilize multifunctional molecular motor complexes referred to as "terminases" that can excise a unit genome length of DNA and package it into preformed viral shells. Remarkably, the terminase motor can initiate packaging at the appropriate start point, translocate DNA, sense when a sufficient length has been packaged, and then switch into a mode where it arrests and cleaves the DNA to release a filled virus particle. We have recently developed an improved method to measure single phage lambda DNA packaging using dual-trap optical tweezers and pre-stalled motor-DNA-procapsid complexes. We are applying this method to test proposed mechanisms for the sensor that triggers termination; specifically a velocity-monitor model vs. energy-monitor model vs. capsid-filling monitor model.

delToro, Damian J.; Smith, Douglas E.

2012-10-01

161

Measurement of PLGA-NP interaction with single smooth muscle cells using optical tweezers  

NASA Astrophysics Data System (ADS)

For intervention of cardiovascular diseases, biodegradable and biocompatible, poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NP) are emerging as agents of choice for controlled and targeted drug delivery. Therefore development of PLGA-NP with optimal physico-chemical properties will allow efficient binding and thus delivery of drug to targeted cells under various patho-physiological conditions. The force kinetics and its dependence on size of the NPs will be crucial for designing the NPs. Since optical tweezers allow non-contact, highly sensitive force measurement with high spatial and temporal resolution, we utilized it for studying interaction forces between magnetic PLGA nanoparticles with smooth muscle cells (SMC). In order to investigate effect of size, interaction force for 200 to 1100nm PLGA NP was measured. For similar interaction duration, the force was found to be higher with increase in size. The rupture force was found to depend on time of interaction of SMC with NPs.

Gu, Ling; Mondal, Argha; Homayoni, Homa; Nguyen, Kytai; Mohanty, Samarendra

2012-10-01

162

Accurate measurement of force and displacement with optical tweezers using DNA molecules as metrology standards  

NASA Astrophysics Data System (ADS)

Optical tweezers facilitate measurement of piconewton-level forces and nanometer-level displacements and have broad applications in biophysics and soft matter physics research. We have shown previously that DNA molecules can be used as metrology standards to define such measurements. Force-extension measurements on two DNA molecules of different lengths can be used to determine four necessary measurement parameters. Here, we show that the accuracy of determining these parameters can be improved by more than 7-fold by incorporating measurements of the DNA overstretching transition and using a multi-step data analysis procedure. This method results in very robust and precise fitting of DNA force-extension measurements to the worm-like chain model. We verify the accuracy through independent measurements of DNA stretching, DNA unzipping, and microsphere contact forces.

delToro, Damian; Smith, Douglas E.

2014-04-01

163

Rapid feedback control and stabilization of an optical tweezers with a budget microcontroller  

NASA Astrophysics Data System (ADS)

Laboratories ranging the scientific disciplines employ feedback control to regulate variables within their experiments, from the flow of liquids within a microfluidic device to the temperature within a cell incubator. We have built an inexpensive, yet fast and rapidly deployed, feedback control system that is straightforward and flexible to implement from a commercially available Arduino Due microcontroller. This is in comparison with the complex, time-consuming and often expensive electronics that are commonly implemented. As an example of its utility, we apply our feedback controller to the task of stabilizing the main trapping laser of an optical tweezers. The feedback controller, which is inexpensive yet fast and rapidly deployed, was implemented from hacking an open source Arduino Due microcontroller. Our microcontroller based feedback system can stabilize the laser intensity to a few tenths of a per cent at 200 kHz, which is an order of magnitude better than the laser's base specifications, illustrating the utility of these devices.

Nino, Daniel; Wang, Haowei; Milstein, Joshua N.

2014-09-01

164

Evaluating the toxic effect of an antimicrobial agent on single bacterial cells with optical tweezers  

PubMed Central

We implement an optical tweezers technique to assess the effects of chemical agents on single bacterial cells. As a proof of principle, the viability of a trapped Escherichia coli bacterium is determined by monitoring its flagellar motility in the presence of varying concentrations of ethyl alcohol. We show that the “killing time” of the bacterium can be effectively identified from the correlation statistics of the positional time series recorded from the trap, while direct quantification from the time series or associated power spectra is intractable. Our results, which minimize the lethal effects of bacterial photodamage, are consistent with previous reports of ethanol toxicity that used conventional culture-based methods. This approach can be adapted to study other pairwise combinations of drugs and motile bacteria, especially to measure the response times of single cells with better precision. PMID:25657879

Samadi, Akbar; Zhang, Chensong; Chen, Joseph; Reihani, S. N. S.; Chen, Zhigang

2014-01-01

165

Imaging microscopic fluid viscosity and velocity fields using confocal scanning optical tweezers  

NASA Astrophysics Data System (ADS)

Confocal microscopy and optical tweezers were combined to develop a minimally invasive instrument capable of making hydrodynamic measurements more rapidly than is possible with other devices. This result leads to the possibility of making scanning images of the viscosity distribution of materials around bipolymer producing cells. An image of the viscosity distribution around a pullulan producing cell of Aureobasidium pullulans is shown as an example. We present results from experiments supporting a linearized model for the motion of a trapped bead in an oscillating harmonic potential. Fluid velocity measurements are tested by comparing to an independent video based measurement. We apply the technique to obtain a 2-D map of the flow past a microscopic wedge and compare to a theoretical solution for the stream lines assuming potential flow. Since the velocity is measured simultaneously with the trap relaxation time, it requires practically no calibration and is independent of the trap stiffness and the particle size.

Nemet, Boaz A.; Harnik, Nili; Cronin-Golomb, Mark

2002-05-01

166

Double nanohole optical tweezers visualize protein p53 suppressing unzipping of single DNA-hairpins  

PubMed Central

Here we report on the use of double-nanohole (DNH) optical tweezers as a label-free and free-solution single-molecule probe for protein–DNA interactions. Using this approach, we demonstrate the unzipping of individual 10 base pair DNA-hairpins, and quantify how tumor suppressor p53 protein delays the unzipping. From the Arrhenius behavior, we find the energy barrier to unzipping introduced by p53 to be 2 × 10?20 J, whereas cys135ser mutant p53 does not show suppression of unzipping, which gives clues to its functional inability to suppress tumor growth. This transformative approach to single molecule analysis allows for ultra-sensitive detection and quantification of protein–DNA interactions to revolutionize the fight against genetic diseases. PMID:24940547

Kotnala, Abhay; Gordon, Reuven

2014-01-01

167

Coherence and Raman Sideband Cooling of a Single Atom in an Optical Tweezer  

NASA Astrophysics Data System (ADS)

We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers n¯x=n¯y=0.01, n¯z=8) even for a trap beam waist as small as w=900nm. The small atomic wave packet with ?x=?y=24nm and ?z=270nm represents a promising starting point for future hybrid quantum systems where atoms are placed in close proximity to surfaces.

Thompson, J. D.; Tiecke, T. G.; Zibrov, A. S.; Vuleti?, V.; Lukin, M. D.

2013-03-01

168

Coherence and Raman sideband cooling of a single atom in an optical tweezer.  

PubMed

We investigate quantum control of a single atom in a tightly focused optical tweezer trap. We show that inevitable spatially varying polarization gives rise to significant internal-state decoherence but that this effect can be mitigated by an appropriately chosen magnetic bias field. This enables Raman sideband cooling of a single atom close to its three-dimensional ground state (vibrational quantum numbers n(x)=n(y)=0.01, n(z)=8) even for a trap beam waist as small as w=900??nm. The small atomic wave packet with ?x=?y=24??nm and ?z=270??nm represents a promising starting point for future hybrid quantum systems where atoms are placed in close proximity to surfaces. PMID:23581312

Thompson, J D; Tiecke, T G; Zibrov, A S; Vuleti?, V; Lukin, M D

2013-03-29

169

Development of optical-based array devices using imaging fiber bundles: Optical tweezer arrays, nanoscale arrays, and microelectrode arrays  

NASA Astrophysics Data System (ADS)

The work in this dissertation describes the development of imaging fiber-based array devices, specifically the fabrication and application of an optical tweezer array, a fiber-based nanoarray, and a nanotip array. With regards for the fabrication of an optical tweezer array, this thesis describes how fiber bundles have been used as a method to create multiple beams, which are used as optical traps. By coupling a single beam into an imaging fiber bundle, the light energy is distributed across the face of the fiber bundle. Each illuminated individual fiber in the array propagates light to the distal face of the bundle, where light focusing elements at the end of each fiber focus the laser light and form optical traps. These optical traps are capable of capturing and arraying microspheres in parallel. The number of optical traps is determined by the number of fibers in the optical fiber bundle and is capable of creating a dense array (˜104 traps/mm2) of optical tweezers. This dissertation also describes the fabrication of fiber bundle-based nanoarrays with two different size formats---one with 700 nm array elements and one with 300 nm array elements. These arrays have an ultra-high packing density in that they contain 1 x 106 or 4.5 x 10 6 array elements/mm2. Current fiber bundle-based arrays have micron feature sizes and a high packing density, up to 5 x 10 4 fibers/mm2. These nanoarrays have feature sizes at least 4 times smaller than the micron-sized arrays used and contain up to 4.5 x 106 fibers/mm2. Nanofiber bundles were chemically etched to create nanowells into which sensors were deposited. The number of sensor elements in these arrays provides enough sensing positions such that they could be used to screen an entire genome while also moving towards the concept of a universal array. In addition, this high density of sensors allows for a large number of replicates, leading to an improvement in the signal to noise ratio. An improvement on creating nanoapertures that was originally developed by Paul Pantano, a former postdoctoral fellow in the Walt lab, is also discussed in this thesis. The original technique employed a mechanical puller that heated and pulled a fiber bundle, which was then polished and etched to create nanowells. Although effective, the technique was difficult to reproduce. (Abstract shortened by UMI.)

Tam, Jenny M.

170

Measurements of the force fields within an acoustic standing wave using holographic optical tweezers  

SciTech Connect

Direct measurement of the forces experienced by micro-spheres in an acoustic standing wave device have been obtained using calibrated optical traps generated with holographic optical tweezers. A micro-sphere, which is optically trapped in three dimensions, can be moved through the acoustic device to measure forces acting upon it. When the micro-sphere is subjected to acoustic forces, it's equilibrium position is displaced to a position where the acoustic forces and optical forces are balanced. Once the optical trapping stiffness has been calibrated, observation of this displacement enables a direct measurement of the forces acting upon the micro-sphere. The measured forces are separated into a spatially oscillating component, attributed to the acoustic radiation force, and a constant force, attributed to fluid streaming. As the drive conditions of the acoustic device were varied, oscillating forces (>2.5 pN{sub pp}) and streaming forces (<0.2 pN) were measured. A 5??m silica micro-sphere was used to characterise a 6.8?MHz standing wave, ??=?220??m, to a spatial resolution limited by the uncertainty in the positioning of the micro-sphere (here to within 2?nm) and with a force resolution on the order of 10 fN. The results have application in the design and testing of acoustic manipulation devices.

Bassindale, P. G.; Drinkwater, B. W. [Faculty of Engineering, Queens building, University of Bristol, Bristol BS8 1TR (United Kingdom); Phillips, D. B. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Barnes, A. C. [Department of Physics, H.H.Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom)

2014-04-21

171

Measurements of the force fields within an acoustic standing wave using holographic optical tweezers  

NASA Astrophysics Data System (ADS)

Direct measurement of the forces experienced by micro-spheres in an acoustic standing wave device have been obtained using calibrated optical traps generated with holographic optical tweezers. A micro-sphere, which is optically trapped in three dimensions, can be moved through the acoustic device to measure forces acting upon it. When the micro-sphere is subjected to acoustic forces, it's equilibrium position is displaced to a position where the acoustic forces and optical forces are balanced. Once the optical trapping stiffness has been calibrated, observation of this displacement enables a direct measurement of the forces acting upon the micro-sphere. The measured forces are separated into a spatially oscillating component, attributed to the acoustic radiation force, and a constant force, attributed to fluid streaming. As the drive conditions of the acoustic device were varied, oscillating forces (>2.5 pNpp) and streaming forces (<0.2 pN) were measured. A 5 ?m silica micro-sphere was used to characterise a 6.8 MHz standing wave, ? = 220 ?m, to a spatial resolution limited by the uncertainty in the positioning of the micro-sphere (here to within 2 nm) and with a force resolution on the order of 10 fN. The results have application in the design and testing of acoustic manipulation devices.

Bassindale, P. G.; Phillips, D. B.; Barnes, A. C.; Drinkwater, B. W.

2014-04-01

172

Single-molecule manipulation of double-stranded DNA using optical tweezers: Interaction studies of DNA with RecA and YOYO-1  

Microsoft Academic Search

By using optical tweezers and a specially designed flow cell with an integrated glass micropipette, we constructed a setup similar to that of Smith et al. (Science 271:795-799, 1996) in which an individual double-stranded DNA (dsDNA) molecule can be captured between two polystyrene beads. The first bead is immobilized by the optical tweezers and the second by the micropipette. Movement

Martin L. Bennink; Orlando D. Scharer; Ronald Kanaar; Kumiko Sakata-Sogawa; Juleon M. Schins; Johannes S. Kanger; Grooth de Bart G; Jan Greve

1999-01-01

173

Cone and rod cells have different target preferences in vitro as revealed by optical tweezers  

PubMed Central

Purpose When neural circuits are damaged in adulthood, regenerating and sprouting processes must distinguish appropriate targets to recreate the normal circuitry. We tested the ability of adult nerve cells to target specific cells in culture using the retina as a model system. Methods Under sterile culture conditions, retinal cells, isolated from tiger salamander retina, were micromanipulated with optical tweezers to create pairs of first-order photoreceptor cells with second- or third-order retinal neurons. The development of cell contact and presynaptic varicosities, the direction and amount of neuritic growth, and nerve cell polarity were assessed after seven days in vitro. Cultures were labeled for rod opsin to distinguish rod from cone cells and for the alpha subunit of the trimeric G protein Go (Go?) to identify cone-dominated and mixed rod-cone ON bipolar cells. Results Quantitative analysis of growth demonstrated that target preferences were cell-specific: Cone cells preferred second-order bipolar cells, whereas rod cells grew toward third-order neurons, which include amacrine and ganglion cells. In addition, when rod cells grew toward bipolar cells, they chose an abnormally high number of Go?-positive bipolar cells. These growth patterns were not affected by tweezers manipulation or the amount of growth. Cell orientation of the photoreceptor also did not affect preferences: Cells oriented away from dendritic processes could reorient their axonal pole toward the target cell. Conclusions Cone cells preferred normal partners, and rod cells preferred novel partners. These intrinsic preferences indicate that adult nerve cells can have differing capacities for targeting even if they come from the same cell class. Further, these differences may help explain the patterns of photoreceptor sprouting seen in retinal degeneration in which rod, but not cone, cells invade the inner retinal layers where third-order neurons are located. PMID:18432315

Clarke, Robert J.; Högnason, Kormákur; Brimacombe, Michael

2008-01-01

174

The ?PIVOT: an integrated particle image velocimeter and optical tweezers instrument for microenvironment investigations  

PubMed Central

A novel instrument to manipulate and characterize the mechanical environment in and around microscale objects in a fluidic environment has been developed by integrating two laser-based techniques: micron-resolution particle image velocimetry (?PIV) and optical tweezers (OT). This instrument, the ?PIVOT, enables a new realm of microscale studies, yet still maintains the individual capabilities of each optical technique. This was demonstrated with individual measurements of optical trap stiffness (?70 pN ?m?1 for a 20 ?m polystyrene sphere and a linear relationship between trap stiffness and laser power) and fluid velocities within 436 nm of a microchannel wall. The integrated device was validated by comparing computational flow predictions to the measured velocity profile around a trapped particle in either a uniform flow or an imposed, gravity-driven microchannel flow (R2 = 0.988, RMS error = 13.04 ?m s?1). Interaction between both techniques is shown to be negligible for 15 ?m to 35 ?m diameter trapped particles subjected to fluid velocities from 50 ?m s?1 to 500 ?m s?1 even at the highest laser power (1.45 W). The integrated techniques will provide a unique perspective toward understanding microscale phenomena including single-cell biomechanics, non-Newtonian fluid mechanics and single particle or particle–particle hydrodynamics. PMID:18953424

Nève, N; Lingwood, J K; Zimmerman, J; Kohles, S S; Tretheway, D C

2008-01-01

175

Cell manipulation tool with combined microwell array and optical tweezers for cell isolation and deposition  

NASA Astrophysics Data System (ADS)

Isolation from rare cells and deposition of sorted cells with high accuracy for further study are critical to a wide range of biomedical applications. In the current paper, we report an automated cell manipulation tool with combined optical tweezers and a uniquely designed microwell array, which functions for recognition, isolation, assembly, transportation and deposition of the interesting cells. The microwell array allows the passive hydrodynamic docking of cells, while offering the opportunity to inspect the interesting cell phenotypes with high spatio-temporal resolution based on the flexible image processing technique. In addition, dynamic and parallel cell manipulation in three dimensions can realize the target cell levitation from microwell and pattern assembly with multiple optical traps. Integrated with the programmed motorized stage, the optically levitated and assembled cells can be transported and deposited to the predefined microenvironment, so the tool can facilitate the integration of other on-chip functionalities for further study without removing these isolated cells from the chip. Experiments on human embryonic stem cells and yeast cells are performed to demonstrate the effectiveness of the proposed cell manipulation tool. Besides the application to cell isolation and deposition, three other biological applications with this tool are also presented.

Wang, Xiaolin; Gou, Xue; Chen, Shuxun; Yan, Xiao; Sun, Dong

2013-07-01

176

Parallel optical tweezers with combining a diffractive optical element and a spatial light modulator for photonic DNA memory  

NASA Astrophysics Data System (ADS)

To overcome the restriction of the density of optical memory systems due to diffraction limit, we have been studying photonic DNA memory, which utilizes photonic technologies and the DNA computing methodology. Our scheme is on the basis of local DNA reaction using laser irradiation and transportation of DNA using parallel optical tweezers with fabricating DNA clusters by attaching DNA onto beads. This paper reports on a new dynamic optical tweezers system, which combines a spatial light modulator (SLM) and a diffractive optical element (DOE) for manipulating DNA clusters. With this combination, real-time programmable manipulation of DNA clusters is achievable in a large spatial range. We also can choose simple patterns for the SLM, and decrease computation cost. In this experiment, a laser beam (633nm wavelength) illuminates a SLM (Hamamatsu Photonics K. K.; PPM8267), which is imaged on an 80-lp/mm transmission-type grating, then the beam is focused with a water immersible objective lens (x 100, NA 1). Simple blazed-phase patterns have different grating constants that are perpendicular to that of the grating are displayed on the SLM. We succeeded in lifting up three 6-micron-diameter polystyrene beads on a glass slide with light spots duplicated by the grating, then transporting the beads in three dimensions simultaneously with changing the grating constants on the SLM. We demonstrated that a same manipulation was implemented at different positions by duplicating a pattern that was generated when only using the SLM. This is usable in implementing a same operation for different data at multiple positions with a single instruction. The promising applications of the method include a nano-scale image memory with encryption.

Zheng, MingJie; Tate, Naoya; Ogura, Yusuke; Tanida, Jun

2007-09-01

177

3D manipulation and visualization of in-vitro cells by optical tweezers and digital holographic microscopy  

NASA Astrophysics Data System (ADS)

We present the possibility to trap cells (mouse fibroblasts, bovine spermatozoa and diatoms), to manage their position and to induce rotation, by using optical tweezers. The aim is to place them in desired positions, in order to record holographic images in a microscope configuration. Then we are able to recover the 3D shape and to calculate the biovolume of the cells starting from the reconstructed quantitative phase maps (QPMs).

Merola, F.; Miccio, L.; Memmolo, P.; Di Caprio, G.; Coppola, G.; Netti, P.; Ferraro, P.

2014-03-01

178

Normal and system lupus erythematosus red blood cell interactions studied by double trap optical tweezers: direct measurements of aggregation forces  

NASA Astrophysics Data System (ADS)

Direct measurements of aggregation forces in piconewton range between two red blood cells in pair rouleau are performed under physiological conditions using double trap optical tweezers. Aggregation and disaggregation properties of healthy and pathologic (system lupus erythematosis) blood samples are analyzed. Strong difference in aggregation speed and behavior is revealed using the offered method which is proposed to be a promising tool for SLE monitoring at single cell level.

Khokhlova, Maria D.; Lyubin, Eugeny V.; Zhdanov, Alexander G.; Rykova, Sophia Yu.; Sokolova, Irina A.; Fedyanin, Andrey A.

2012-02-01

179

Combining Optical Tweezers, Single-Molecule Fluorescence Microscopy, and Microfluidics for Studies of DNA–Protein Interactions  

Microsoft Academic Search

The technically challenging field of single-molecule biophysics has established itself in the last decade by granting access to detailed information about the fate of individual biomolecules, unattainable in traditional biochemical assays. The appeal of single-molecule methods lies in the directness of the information obtained from individual biomolecules. Technological improvements in single-molecule methods have made it possible to combine optical tweezers,

Peter Gross; Géraldine Farge; Erwin J. G. Peterman; Gijs J. L. Wuite

2010-01-01

180

Determination of fluid viscosity and femto Newton forces of Leishmania amazonensis using optical tweezers  

NASA Astrophysics Data System (ADS)

The displacements of a polystyrene microsphere trapped by an optical tweezers (OT) can be used as a force transducer for mechanical measurements in life sciences such as the measurement of forces of living microorganisms or the viscosity of local fluids. The technique we used allowed us to measure forces on the 200 femto Newtons to 4 pico Newtons range of the protozoa Leishmania amazonensis, responsible for a serious tropical disease. These observations can be used to understand the infection mechanism and chemotaxis of these parasites. The same technique was used to measure viscosities of few microliters sample with agreement with known samples better than 5%. To calibrate the force as a function of the microsphere displacement we first dragged the microsphere in a fluid at known velocity for a broad range of different optical and hydrodynamical parameters. The hydrodynamical model took into account the presence of two walls and the force depends on drag velocity, fluid viscosity and walls proximities, while the optical model in the geometric optics regime depends on the particle and fluid refractive indexes and laser power. To measure the high numerical (NA) aperture laser beam power after the objective we used an integration sphere to avoid the systematic errors of usual power meters for high NA beams. After this careful laser power measurement we obtained an almost 45 degrees straight line for the plot of the optical force (calculated by the particle horizontal displacement) versus hydrodynamic force (calculated by the drag velocity) under variation of all the parameters described below. This means that hydrodynamic models can be used to calibrate optical forces, as we have done for the parasite force measurement, or vice-versa, as we did for the viscosity measurements.

Fontes, Adriana; Giorgio, Selma; de Castro, Archimedes, Jr.; Neto, Vivaldo M.; de Y. Pozzo, Liliana; de Thomaz, Andre A.; Barbosa, Luiz C.; Cesar, Carlos L.

2005-08-01

181

Haptic Manipulation of Microspheres Using Optical Tweezers Under the Guidance of Artificial Force Fields  

E-print Network

Using optical tweezers and a haptic device, microspheres having diameters ranging from 3 to 4 um (floating in a fluid solution) are manipulated in order to form patterns of coupled optical microresonators by assembling the spheres via chemical binding. For this purpose, biotin-coated microspheres trapped by a laser beam are steered and chemically attached to an immobilized streptavidin-coated sphere (i.e. anchor sphere) one by one using an XYZ piezo scanner controlled by a haptic device. The positions of all spheres in the scene are detected using a CCD camera and a collision-free path for each manipulated sphere is generated using the potential field approach. The forces acting on the manipulated particle due to the viscosity of the fluid and the artificial potential field are scaled and displayed to the user through the haptic device for better guidance and control during steering. In addition, a virtual fixture is implemented such that the desired angle of approach and strength are achieved during the bind...

Bukusoglu, Ibrahim; Kiraz, Alper; Kurt, Adnan

2007-01-01

182

Calibration of optical tweezers with positional detection in the back focal plane  

SciTech Connect

We explain and demonstrate a new method of force and position calibrations for optical tweezers with back-focal-plane photodetection. The method combines power spectral measurements of thermal motion and the response to a sinusoidal motion of a translation stage. It consequently does not use the drag coefficient of the trapped object as an input. Thus, neither the viscosity, nor the size of the trapped object, nor its distance to nearby surfaces needs to be known. The method requires only a low level of instrumentation and can be applied in situ in all spatial dimensions. It is both accurate and precise: true values are returned, with small error bars. We tested this experimentally, near and far from surfaces in the lateral directions. Both position and force calibrations were accurate to within 3%. To calibrate, we moved the sample with a piezoelectric translation stage, but the laser beam could be moved instead, e.g., by acousto-optic deflectors. Near surfaces, this precision requires an improved formula for the hydrodynamical interaction between an infinite plane and a microsphere in nonconstant motion parallel to it. We give such a formula.

Tolic-Noerrelykke, Simon F.; Schaeffer, Erik; Howard, Jonathon; Pavone, Francesco S.; Juelicher, Frank; Flyvbjerg, Henrik [Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, 01187 Dresden (Germany) and European Laboratory for Non-linear Spectroscopy, via Nello Carrara 1, 50019 Sesto Fiorentino, Florence (Italy) and Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden (Germany); European Laboratory for Non-linear Spectroscopy, via Nello Carrara 1, 50019 Sesto Fiorentino, Florence (Italy); Max Planck Institute for the Physics of Complex Systems, Noethnitzer Strasse 38, 01187 Dresden (Germany); Isaac Newton Institute for Mathematical Sciences, Cambridge CB3 0EH (United Kingdom); Biosystems Department, Risoe National Laboratory, DK-4000 Roskilde (Denmark) and Danish Polymer Centre, Risoe National Laboratory, DK-4000 Roskilde (Denmark)

2006-10-15

183

Dynamic translocation of ligand-complexed DNA through solid-state nanopores with optical tweezers  

NASA Astrophysics Data System (ADS)

We investigated the threading and controlled translocation of individual lambda-DNA (?-DNA) molecules through solid-state nanopores with piconewton force sensitivity, millisecond time resolution and picoampere ionic current sensitivity with a set-up combining quantitative 3D optical tweezers (OT) with electrophysiology. With our virtually interference-free OT set-up the binding of RecA and single peroxiredoxin protein molecules to ?-DNA was quantitatively investigated during dynamic translocation experiments where effective forces and respective ionic currents of the threaded DNA molecule through the nanopore were measured during inward and outward sliding. Membrane voltage-dependent experiments of reversible single protein/DNA translocation scans yield hysteresis-free, asymmetric single-molecule fingerprints in the measured force and conductance signals that can be attributed to the interplay of optical trap and electrostatic nanopore potentials. These experiments allow an exact localization of the bound protein along the DNA strand and open fascinating applications for label-free detection of DNA-binding ligands, where structural and positional binding phenomena can be investigated at a single-molecule level.

Sischka, Andy; Spiering, Andre; Khaksar, Maryam; Laxa, Miriam; König, Janine; Dietz, Karl-Josef; Anselmetti, Dario

2010-11-01

184

Angular and position stability of a nanorod trapped in an optical tweezers.  

PubMed

We analyze the trap stiffness and trapping force potential for a nano-cylinder trapped in the optical tweezers against its axial and lateral shift and tilt associated to the natural Brownian motion. We explain the physical properties of the optical trapping by computing and integrating the radiation stress distribution on the nano-cylinder surfaces using the T-matrix approach. Our computation shows that the force stiffness to the lateral shift is several times higher than that to the axial shift of the nano-cylinder, and lateral torque due to the stress on the side-face is 1-2 orders of magnitude higher than that on the end-faces of a nano-cylinder with the aspect ratio of 2 - 20. The torque due to the stress on the nano-cylinder surface is 2-3 orders of magnitude higher than the spin torque. We explain why a nano-cylinder of low aspect ratio is trapped and aligned normal to the trapping beam axis. PMID:21164989

Bareil, Paul B; Sheng, Yunlong

2010-12-01

185

Combined optical tweezers and laser dissector for controlled ablation of functional connections in neural networks  

NASA Astrophysics Data System (ADS)

Regeneration of functional connectivity within a neural network after different degrees of lesion is of utmost clinical importance. To test pharmacological approaches aimed at recovering from a total or partial damage of neuronal connections within a circuit, it is necessary to develop a precise method for controlled ablation of neuronal processes. We combined a UV laser microdissector to ablate neural processes in vitro at single neuron and neural network level with infrared holographic optical tweezers to carry out force spectroscopy measurements. Simultaneous force spectroscopy, down to the sub-pico-Newton range, was performed during laser dissection to quantify the tension release in a partially ablated neurite. Therefore, we could control and measure the damage inflicted to an individual neuronal process. To characterize the effect of the inflicted injury on network level, changes in activity of neural subpopulations were monitored with subcellular resolution and overall network activity with high temporal resolution by concurrent calcium imaging and microelectrode array recording. Neuronal connections have been sequentially ablated and the correlated changes in network activity traced and mapped. With this unique combination of electrophysiological and optical tools, neural activity can be studied and quantified in response to controlled injury at the subcellular, cellular, and network level.

Difato, Francesco; Dal Maschio, Marco; Marconi, Emanuele; Ronzitti, Giuseppe; Maccione, Alessandro; Fellin, Tommasso; Berdondini, Luca; Chieregatti, Evelina; Benfenati, Fabio; Blau, Axel

2011-05-01

186

An Interactive Virtual Reality Simulation for Nanoparticle Manipulation for Nanoassembly using Optical Tweezers  

NSDL National Science Digital Library

Nanotechnology and nano devices is believed to be one of the most promising steps that science is taking to the future. This paper proposes virtual reality (VR) as a tool to simulate nano particle manipulation using optical tweezers towards achieving nano- assembly for effectively handling issues such as difficulty in viewing, perceiving and controlling the nano-scale objects. The nano simulation is modeled, using virtual reality, displaying all the forces acting on nano particle during the manipulation. The simulation is developed for particles that belong to Rayleigh region and, represents interactions of OT (a laser beam) with the nano particle. The laser beam aimed on to the nano particle traps the particle by applying optical forces. The trapped particle is then moved by moving the laser beam. The proposed VR based simulation tool with its capabilities can be easily extended and used for creating an open system framework by connecting it to a real OT setup to control nano particles manipulation. In addition, a feedback system can be build to increase of precision of movement.

Bhavaraju, Krishna

187

Drug-DNA interactions at single molecule level: A view with optical tweezers  

NASA Astrophysics Data System (ADS)

Studies of small molecule--DNA interactions are essential for developing new drugs for challenging diseases like cancer and HIV. The main idea behind developing these molecules is to target and inhibit the reproduction of the tumor cells and infected cells. We mechanically manipulate single DNA molecule using optical tweezers to investigate two molecules that have complex and multiple binding modes. Mononuclear ruthenium complexes have been extensively studied as a test for rational drug design. Potential drug candidates should have high affinity to DNA and slow dissociation kinetics. To achieve this, motifs of the ruthenium complexes are altered. Our collaborators designed a dumb-bell shaped binuclear ruthenium complex that can only intercalate DNA by threading through its bases. Studying the binding properties of this complex in bulk studies took hours. By mechanically manipulating a single DNA molecule held with optical tweezers, we lower the barrier to thread and make it fast compared to the bulk experiments. Stretching single DNA molecules with different concentration of drug molecules and holding it at a constant force allows the binding to reach equilibrium. By this we can obtain the equilibrium fractional ligand binding and length of DNA at saturated binding. Fitting these results yields quantitative measurements of the binding thermodynamics and kinetics of this complex process. The second complex discussed in this study is Actinomycin D (ActD), a well studied anti-cancer agent that is used as a prototype for developing new generations of drugs. However, the biophysical basis of its activity is still unclear. Because ActD is known to intercalate double stranded DNA (dsDNA), it was assumed to block replication by stabilizing dsDNA in front of the replication fork. However, recent studies have shown that ActD binds with even higher affinity to imperfect duplexes and some sequences of single stranded DNA (ssDNA). We directly measure the on and off rates by stretching the DNA molecule to a certain force and holding it at constant force while adding the drug and then while washing off the drug. Our finding resolves the long lasting controversy of ActD binding modes, clearly showing that both the dsDNA binding and ssDNA binding converge to the same single mode. The result supports the hypothesis that the primary characteristic of ActD that contributes to its biological activity is its ability to inhibit cellular replication by binding to transcription bubbles and causing cell death.

Paramanathan, Thayaparan

188

Stretching Short Sequences of DNA with Constant Force Axial Optical Tweezers  

PubMed Central

Single-molecule techniques for stretching DNA of contour lengths less than a kilobase are fraught with experimental difficulties. However, many interesting biological events such as histone binding and protein-mediated looping of DNA1,2, occur on this length scale. In recent years, the mechanical properties of DNA have been shown to play a significant role in fundamental cellular processes like the packaging of DNA into compact nucleosomes and chromatin fibers3,4. Clearly, it is then important to understand the mechanical properties of short stretches of DNA. In this paper, we provide a practical guide to a single-molecule optical tweezing technique that we have developed to study the mechanical behavior of DNA with contour lengths as short as a few hundred basepairs. The major hurdle in stretching short segments of DNA is that conventional optical tweezers are generally designed to apply force in a direction lateral to the stage5,6, (see Fig. 1). In this geometry, the angle between the bead and the coverslip, to which the DNA is tethered, becomes very steep for submicron length DNA. The axial position must now be accounted for, which can be a challenge, and, since the extension drags the microsphere closer to the coverslip, steric effects are enhanced. Furthermore, as a result of the asymmetry of the microspheres, lateral extensions will generate varying levels of torque due to rotation of the microsphere within the optical trap since the direction of the reactive force changes during the extension. Alternate methods for stretching submicron DNA run up against their own unique hurdles. For instance, a dual-beam optical trap is limited to stretching DNA of around a wavelength, at which point interference effects between the two traps and from light scattering between the microspheres begin to pose a significant problem. Replacing one of the traps with a micropipette would most likely suffer from similar challenges. While one could directly use the axial potential to stretch the DNA, an active feedback scheme would be needed to apply a constant force and the bandwidth of this will be quite limited, especially at low forces. We circumvent these fundamental problems by directly pulling the DNA away from the coverslip by using a constant force axial optical tweezers7,8. This is achieved by trapping the bead in a linear region of the optical potential, where the optical force is constant-the strength of which can be tuned by adjusting the laser power. Trapping within the linear region also serves as an all optical force-clamp on the DNA that extends for nearly 350 nm in the axial direction. We simultaneously compensate for thermal and mechanical drift by finely adjusting the position of the stage so that a reference microsphere stuck to the coverslip remains at the same position and focus, allowing for a virtually limitless observation period. PMID:22025209

Raghunathan, Krishnan; Milstein, Joshua N.; Meiners, Jens -Christian

2011-01-01

189

Tracking of single quantum dot labeled EcoRV sliding along DNA manipulated by double optical tweezers.  

PubMed

Fluorescence microscopy provides a powerful method to directly observe single enzymes moving along a DNA held in an extended conformation. In this work, we present results from single EcoRV enzymes labeled with quantum dots which interact with DNA manipulated by double optical tweezers. The application of quantum dots facilitated accurate enzyme tracking without photobleaching whereas the tweezers allowed us to precisely control the DNA extension. The labeling did not affect the biochemical activity of EcoRV checked by directly observing DNA digestion on the single molecule level. We used this system to demonstrate that during sliding, the enzyme stays in close contact with the DNA. Additionally, slight overstretching of the DNA resulted in a significant decrease of the 1D diffusion constant, which suggests that the deformation changes the energy landscape of the sliding interaction. Together with the simplicity of the setup, these results demonstrate that the combination of optical tweezers with fluorescence tracking is a powerful tool for the study of enzyme translocation along DNA. PMID:19383444

Biebricher, Andreas; Wende, Wolfgang; Escudé, Christophe; Pingoud, Alfred; Desbiolles, Pierre

2009-04-22

190

Optical tweezers reveal relationship between microstructure and nanoparticle penetration of pulmonary mucus.  

PubMed

In this study, the mobility of nanoparticles in mucus and similar hydrogels as model systems was assessed to elucidate the link between microscopic diffusion behavior and macroscopic penetration of such gels. Differences in particle adhesion to mucus components were strongly dependent on particle coating. Particles coated with 2 kDa PEG exhibited a decreased adhesion to mucus components, whereas chitosan strongly increased the adhesion. Despite such mucoinert properties of PEG, magnetic nanoparticles of both coatings did not penetrate through native respiratory mucus, resisting high magnetic forces (even for several hours). However, model hydrogels were, indeed, penetrated by both particles in dependency of particle coating, obeying the theory of particle mobility in an external force field. Comparison of penetration data with cryogenic scanning EM images of mucus and the applied model systems suggested particularly high rigidity of the mucin scaffold and a broad pore size distribution in mucus as reasons for the observed particle immobilization. Active probing of the rigidity of mucus and model gels with optical tweezers was used in this context to confirm such properties of mucus on the microscale, thus presenting the missing link between micro- and macroscopical observations. Because of high heterogeneity in the size of the voids and pores in mucus, on small scales, particle mobility will depend on adhesive or inert properties. However, particle translocation over distances larger than a few micrometers is restricted by highly rigid structures within the mucus mesh. PMID:23091027

Kirch, Julian; Schneider, Andreas; Abou, Bérengère; Hopf, Alexander; Schaefer, Ulrich F; Schneider, Marc; Schall, Christian; Wagner, Christian; Lehr, Claus-Michael

2012-11-01

191

Optical tweezers based measurement of PLGA-NP interaction with prostate cancer cells  

NASA Astrophysics Data System (ADS)

In order to quantify the binding capacities of polymeric, biodegradable and biocompatible poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs), conjugated with either R11 peptides or Folic Acid, the strength by detach from prostate cancer cells (PCCs) was measured via optical tweezers based measurements. Specific nanoparticle drug delivery eliminates the previously used diffuse, full-body application of potent cancer drugs by localizing drug delivery to malignant cells. Precise monitoring of NP position in the trap near the PCC membrane using a fluorescence imaging based method enabled calibration of the trap stiffness and subsequent force measurements. By defining the force with which the many diverse conjugates and coatings of different types of NPs bind the vast array of cancer cell types, chemotherapeutic drugs can be delivered in a specific manner with the optimal particle and corresponding conjugates. Further, and most significantly, the rupture force measurements will reveal whether or not targeted nanoparticles can overcome the force of blood attempting to pull the particle from designated cells. Our preliminary study revealed that the binding between PLGA-NPs and prostate cancer cells is enhanced by coating with folic acid or R11 peptides. These conjugates increase the force required to detach the particle thus allowing particles to overcome drag force of the blood in prostate capillary systems.

Blesener, Thea; Mondal, Argha; Menon, Jyothi U.; Nguyen, Kytai T.; Mohanty, Samarendra

2013-02-01

192

Optical tweezers reveal a dynamic mechanical response of cationic peptide-DNA complexes  

NASA Astrophysics Data System (ADS)

Nonviral carriers have been developed to deliver nucleic acids by forming nanoscale complexes; however, there has been limited success in achieving high transfection efficiency. Our hypothesis is that a factor affecting gene delivery efficiency is the mechanical response of the condensed complex. To begin to test this hypothesis, we directly measured the mechanical properties of DNA-carrier complexes using optical tweezers. Histidine-lysine (HK) polymer, Asparagine-lysine (NK) polymer and poly-L-lysine were used to form complexes with a single DNA molecule. As carriers were introduced, a sudden decrease in DNA extension occurrs at a force level which is defined as critical force (Fc). Fc is carrier and concentration dependent. Pulling revealed reduction in DNA extension length for HK-DNA complexes. The characteristics of force profiles vary by agent and can be dynamically manipulated by changes in environmental conditions such as ionic strength of the buffer as well as pH. Heparin can remove cationic reagents which are otherwise irreversibly bound to DNA. The implications for optimizing molecular interactions to enhance transfection efficiency will be discussed.

Lee, Amy; Zheng, Tai; Sucayan, Sarah; Chou, Szu-Ting; Tricoli, Lucas; Hustedt, Jason; Kahn, Jason; Mixson, A. James; Seog, Joonil

2013-03-01

193

Force measuring optical tweezers system for long time measurements of P pili stability  

NASA Astrophysics Data System (ADS)

A force-measuring optical tweezers instrumentation and long time measurements of the elongation and retraction of bacterial fimbriae from Uropathogenic E. coli (UPEC) under strain are presented. The instrumentation is presented in some detail. Special emphasis is given to measures taken to reduce the influence of noise and drifts in the system and from the surrounding, which makes long term force measurements possible. Individual P pili from UPEC bacteria were used as a biological model system for repetitive unfolding and refolding cycles of bacterial fimbriae under equilibrium conditions. P pili have evolved into a three-dimensional helix-like structure, the PapA rod, that can be successively and significantly elongated and/or unfolded when exposed to external forces. The instrumentation is used for characterization of the force-vs.-elongation response of the PapA rod of individual P pili, with emphasis on the long time stability of the forced unfolding and refolding of the helical structure of the PapA rod. The results show that the PapA rod is capable of withstanding extensive strain, leading to a complete unfolding of the helical structure, repetitive times during the life cycle of a bacterium without any noticeable alteration of the mechanical properties of the P pili. This function is believed to be importance for UPEC bacteria in vivo since it provides a close contact to a host cell (which is an initial step of invasion) despite urine cleaning attempts.

Andersson, Magnus; Fällman, Erik; Uhlin, Bernt Eric; Axner, Ove

2006-02-01

194

Dynamic deformation of a soft particle in dual-trap optical tweezers  

NASA Astrophysics Data System (ADS)

A dual-trap optical tweezers is used for deforming the red blood cell (RBC) in suspension and studying its elasticity. The radiation force is applied directly to the cell without physical contact. The 3D radiation stress distribution was computed by ray tracing, the generalized Lorentz-Mie theory with the T-matrix and the FDTD via the Maxwell stress tensor. The 3D deformation of the cells was computed with the elastic membrane theory. The calculated deformation can fit to experimental data resulting in cell's elasticity coefficient. The static approach is valid only for small deformation (5- 10%). For a large deformation such as that of the RBC, we consider re-distribution of the radiation stress on the morphologically deformed cell. This stress re-distribution in turn induces subsequent deformation of the deformed cell and new stress re-distribution. The recursive process continues until a final equilibrium state is achieved. This iterative computation was implemented with the finite element method using the COMSOLTM multi-physics models. The deformation results can fit to the experimental data for cell's deformation up to 20%.

Rancourt-Grenier, Sebastien; Wei, Ming-Tzo; Bai, Jar-Jin; Chiou, Arthur; Bareil, Paul; Duval, Pierre-Luc; Sheng, Yunlong

2010-08-01

195

Removal forces and adhesion properties of Saccharomyces cerevisiae on glass substrates probed by optical tweezer.  

PubMed

In agroindustry, the hygiene of solid surfaces is of primary importance in order to ensure that products are safe for consumers. To improve safety, one of the major ways consists in identifying and understanding the mechanisms of microbial cell adhesion to nonporous solid surfaces or filtration membranes. In this paper we investigate the adhesion of the yeast cell Saccharomyces cerevisiae (about 5 mum in diameter) to a model solid surface, using well-defined hydrophilic glass substrates. An optical tweezer device developed by Piau [J. Non-Newtonian Fluid Mech. 144, 1 (2007)] was applied to yeast cells in contact with well-characterized glass surfaces. Two planes of observation were used to obtain quantitative measurements of removal forces and to characterize the corresponding mechanisms at a micrometer length scale. The results highlight various adhesion mechanisms, depending on the ionic strength, contact time, and type of yeast. The study has allowed to show a considerable increase of adhering cells with the ionic strength and has provided a quantitative measurement of the detachment forces of cultured yeast cells. Force levels are found to grow with ionic strength and differences in mobility are highlighted. The results clearly underline that a microrheological approach is essential for analyzing the adhesion mechanisms of biological systems at the relevant local scales. PMID:17919057

Castelain, Mickaël; Pignon, Frédéric; Piau, Jean-Michel; Magnin, Albert; Mercier-Bonin, Muriel; Schmitz, Philippe

2007-10-01

196

Studying red blood cell agglutination by measuring membrane viscosity with optical tweezers  

NASA Astrophysics Data System (ADS)

The red blood cell (RBC) viscoelastic membrane contains proteins and glycoproteins embedded in a fluid lipid bilayer that are responsible for cell agglutination. Manipulating RBCs rouleaux with a double optical tweezers, we observed that the cells slide easily one over the others but are strongly connected by their edges. An explanation for this behavior could be the fact that when the cells slide one over the others, proteins are dragged through the membrane. It confers to the movement a viscous characteristic that is dependent of the velocity between the RBCs and justifies why is so easy to slide them apart. Therefore, in a first step of this work, by measuring the force as a function of the relative velocity between two cells, we confirmed this assumption and used this viscous characteristic of the RBC rouleaux to determine the apparent membrane viscosity of the cell. As this behavior is related to the proteins interactions, we can use the apparent membrane viscosity to obtain a better understanding about cell agglutination. Methods related to cell agglutination induced by antigen-antibody interactions are the basis of most of tests used in transfusion centers. Then, in a second step of this work, we measured the apparent membrane viscosity using antibodies. We observed that this methodology is sensitive to different kinds of bindings between RBCs. Better comprehension of the forces and bindings between RBCs could improve the sensibility and specificity of the hemagglutination reactions and also guides the development of new potentiator substances.

Fernandes, Heloise P.; Fontes, Adriana; de Thomaz, André A.; Barbosa, Luiz C.; Barjas-Castro, Maria L.; Cesar, Carlos L.

2007-09-01

197

Removal forces and adhesion properties of Saccharomyces cerevisiae on glass substrates probed by optical tweezer  

NASA Astrophysics Data System (ADS)

In agroindustry, the hygiene of solid surfaces is of primary importance in order to ensure that products are safe for consumers. To improve safety, one of the major ways consists in identifying and understanding the mechanisms of microbial cell adhesion to nonporous solid surfaces or filtration membranes. In this paper we investigate the adhesion of the yeast cell Saccharomyces cerevisiae (about 5?m in diameter) to a model solid surface, using well-defined hydrophilic glass substrates. An optical tweezer device developed by Piau [J. Non-Newtonian Fluid Mech. 144, 1 (2007)] was applied to yeast cells in contact with well-characterized glass surfaces. Two planes of observation were used to obtain quantitative measurements of removal forces and to characterize the corresponding mechanisms at a micrometer length scale. The results highlight various adhesion mechanisms, depending on the ionic strength, contact time, and type of yeast. The study has allowed to show a considerable increase of adhering cells with the ionic strength and has provided a quantitative measurement of the detachment forces of cultured yeast cells. Force levels are found to grow with ionic strength and differences in mobility are highlighted. The results clearly underline that a microrheological approach is essential for analyzing the adhesion mechanisms of biological systems at the relevant local scales.

Castelain, Mickaël; Pignon, Frédéric; Piau, Jean-Michel; Magnin, Albert; Mercier-Bonin, Muriel; Schmitz, Philippe

2007-10-01

198

Optical tweezers reveal force plateau and internal friction in PEG-induced DNA condensation.  

PubMed

The simplified artificial environments in which highly complex biological systems are studied do not represent the crowded, dense, salty, and dynamic environment inside the living cell. Consequently, it is important to investigate the effect of crowding agents on DNA. We used a dual-trap optical tweezers instrument to perform force spectroscopy experiments at pull speeds ranging from 0.3 to 270 ?m/s on single dsDNA molecules in the presence of poly(ethylene glycol) (PEG) and monovalent salt. PEG of sizes 1,500 and 4,000 Da condensed DNA, and force-extension data contained a force plateau at approximately 1 pN. The level of the force plateau increased with increasing pull speed. During slow pulling the dissipated work increased linearly with pull speed. The calculated friction coefficient did not depend on amount of DNA incorporated in the condensate, indicating internal friction is independent of the condensate size. PEG300 had no effect on the dsDNA force-extension curve. The force plateau implies that condensation induced by crowding agents resembles condensation induced by multivalent cations. PMID:24477280

Ojala, Heikki; Ziedaite, Gabija; Wallin, Anders E; Bamford, Dennis H; Hæggström, Edward

2014-03-01

199

Effect of salicylate on outer hair cell plasma membrane viscoelasticity: studies using optical tweezers  

NASA Astrophysics Data System (ADS)

The plasma membrane (PM) of mammalian outer hair cells (OHCs) generates mechanical forces in response to changes in the transmembrane electrical potential. The resulting change in the cell length is known as electromotility. Salicylate (Sal), the anionic, amphipathic derivative of aspirin induces reversible hearing loss and decreases electromotile response of the OHCs. Sal may change the local curvature and mechanical properties of the PM, eventually resulting in reduced electromotility or it may compete with intracellular monovalent anions, particularly Cl-, which are essential for electromotility. In this work we have used optical tweezers to study the effects of Sal on viscoelastic properties of the OHC PM when separated from the underlying composite structures of the cell wall. In this procedure, an optically trapped microsphere is brought in contact with PM and subsequently pulled away to form a tether. We measured the force exerted on the tether as a function of time during the process of tether growth at different pulling rates. Effective tether viscosity, steady-state tethering force extrapolated to zero pulling rate, and the time constant for tether growth were estimated from the measurements of the instantaneous tethering force. The time constant for the tether growth measured for the OHC basal end decreased 1.65 times after addition of 10 mM Sal, which may result from an interaction between Sal and cholesterol, which is more prevalent in the PM of OHC basal end. The time constants for the tether growth calculated for the OHC lateral wall and control human embryonic kidney cells as well as the other calculated viscoelastic parameters remained the same after Sal perfusion, favoring the hypothesis of competitive inhibition of electromotility by salicylate.

Ermilov, Sergey A.; Brownell, William E.; Anvari, Bahman

2004-06-01

200

Wavefront analysis and optimization from conventional liquid crystal displays for low-cost holographic optical tweezers and digital holographic microscopy  

NASA Astrophysics Data System (ADS)

In different study fields the manipulation and imaging of micro-sized particles is essential. The use of holographic optical tweezers (HOT) and digital holographic microscopy (DHM) facilitates this task in a non-mechanical way by providing the proper computer generated hologram and the required amount of light. Electrically addressed spatial light modulators (EASLM) found in holographic optical tweezers are typically of the reflective liquid crystal on silicon (LCoS) type which can achieve a phase shift of more than 2? but they are expensive. Similar components like transmissive twisted nematic liquid crystal displays (TN-LCD) are produced in large quantities, their optical characteristics improve rapidly and they are inexpensive. Under certain circumstances these devices can be used instead of expensive spatial light modulators. Consumer grade objectives are not always well corrected for spherical aberration. In that case conventional liquid crystal displays can also compensate these undesired optical effects. For this purpose software-corrected computer generated holograms are calculated. Procedures to analyze and compensate different parameters of a conventional low-cost liquid crystal display, e.g. phase shift evaluation and aberration correction of objectives by Zernike polynomials approximation are explained. The applied software compensation of the computer generated hologram has shown significant improvement of the focus quality. An important price reduction of holographic devices could be achieved by replacing special optical elements if correction algorithms for conventional liquid crystal displays are provided.

Weber, Andreas; Ortega Clavero, Valentin; Schröder, Werner

2011-05-01

201

The Reno Aerosol Optics Study: An Evaluation of Aerosol Absorption Measurement Methods  

Microsoft Academic Search

The Reno Aerosol Optics Study (RAOS) was designed and conducted to compare the performance of many existing and new instruments for the in situ measurement of aerosol optical properties with a focus on the determination of aerosol light absorption. For this study, simple test aerosols of black and white particles were generated and combined in external mixtures under low relative

Patrick J. Sheridan; W. Patrick Arnott; John A. Ogren; Elisabeth Andrews; Dean B. Atkinson; Hans Moosmüller; Andreas Petzold; Beat Schmid; Anthony W. Strawa; Ravi Varma; Aki Virkkula

2005-01-01

202

Physiological monitoring of optically trapped cells: assessing the effects of confinement by 1064-nm laser tweezers using microfluorometry.  

PubMed Central

We report the results of microfluorometric measurements of physiological changes in optically trapped immotile Chinese hamster ovary cells (CHOs) and motile human sperm cells under continuous-wave (CW) and pulsed-mode trapping conditions at 1064 nm. The fluorescence spectra derived from the exogenous fluorescent probes laurdan, acridine orange, propidium iodide, and Snarf are used to assess the effects of optical confinement with respect to temperature, DNA structure, cell viability, and intracellular pH, respectively. In the latter three cases, fluorescence is excited via a two-photon process, using a CW laser trap as the fluorescence excitation source. An average temperature increase of < 0.1 +/- 0.30 degrees C/100 mW is measured for cells when held stationary with CW optical tweezers at powers of up to 400 mW. The same trapping conditions do not appear to alter DNA structure or cellular pH. In contrast, a pulsed 1064-nm laser trap (100-ns pulses at 40 microJ/pulse and average power of 40 mW) produced significant fluorescence spectral alterations in acridine orange, perhaps because of thermally induced DNA structural changes or laser-induced multiphoton processes. The techniques and results presented herein demonstrate the ability to perform in situ monitoring of cellular physiology during CW and pulsed laser trapping, and should prove useful in studying mechanisms by which optical tweezers and microbeams perturb metabolic function and cellular viability. PMID:8889192

Liu, Y; Sonek, G J; Berns, M W; Tromberg, B J

1996-01-01

203

PHYSICAL REVIEW A 82, 023623 (2010) Measurement of the atom number distribution in an optical tweezer using single-photon counting  

E-print Network

tweezers [2] or of magnetic traps [3], double- well potential geometries [4], and optical lattices (e], or in arrays of magnetic microtraps [14]. For all these applications, the knowledge of the distribution atomic cloud can be measured by usual optical techniques, such as laser-induced fluorescence

Boyer, Edmond

204

Mechanical properties of neuronal growth cone membranes studied by tether formation with laser optical tweezers.  

PubMed Central

Many cell phenomena involve major morphological changes, particularly in mitosis and the process of cell migration. For cells or neuronal growth cones to migrate, they must extend the leading edge of the plasma membrane as a lamellipodium or filopodium. During extension of filopodia, membrane must move across the surface creating shear and flow. Intracellular biochemical processes driving extension must work against the membrane mechanical properties, but the forces required to extend growth cones have not been measured. In this paper, laser optical tweezers and a nanometer-level analysis system were used to measure the neuronal growth cone membrane mechanical properties through the extension of filopodia-like tethers with IgG-coated beads. Although the probability of a bead attaching to the membrane was constant irrespective of treatment; the probability of forming a tether with a constant force increased dramatically with cytochalasin B or D and dimethylsulfoxide (DMSO). These are treatments that alter the organization of the actin cytoskeleton. The force required to hold a tether at zero velocity (F0) was greater than forces generated by single molecular motors, kinesin and myosin; and F0 decreased with cytochalasin B or D and DMSO in correlation with the changes in the probability of tether formation. The force of the tether on the bead increased linearly with the velocity of tether elongation. From the dependency of tether force on velocity of tether formation, we calculated a parameter related to membrane viscosity, which decreased with cytochalasin B or D, ATP depletion, nocodazole, and DMSO. These results indicate that the actin cytoskeleton affects the membrane mechanical properties, including the force required for membrane extension and the viscoelastic behavior. Images FIGURE 4 PMID:7756561

Dai, J.; Sheetz, M. P.

1995-01-01

205

Optical tweezers for single molecule force spectroscopy on bacterial adhesion organelles  

NASA Astrophysics Data System (ADS)

Instrumentation and methodologies for single molecule force spectroscopy on bacterial adhesion organelles by the use of force measuring optical tweezers have been developed. A thorough study of the biomechanical properties of fimbrial adhesion organelles expressed by uropathogenic E. coli, so-called pili, is presented. Steady-state as well as dynamic force measurements on P pili, expressed by E. coli causing pyelonephritis, have revealed, among other things, various unfolding and refolding properties of the helical structure of P pili, the PapA rod. Based on these properties an energy landscape model has been constructed by which specific biophysical properties of the PapA rod have been extracted, e.g. the number of subunits, the length of a single pilus, bond lengths and activation energies for bond opening and closure. Moreover, long time repetitive measurements have shown that the rod can be unfolded and refolded repetitive times without losing its intrinsic properties. These properties are believed to be of importance for the bacteria's ability to maintain close contact with host cells during initial infections. The results presented are considered to be of importance for the field of biopolymers in general and the development of new pharmaceuticals towards urinary tract infections in particular. The results show furthermore that the methodology can be used to gain knowledge of the intrinsic biomechanical function of adhesion organelles. The instrumentation is currently used for characterization of type 1 pili, expressed by E. coli causing cystitis, i.e. infections in the bladder. The first force spectrometry investigations of these pili will be presented.

Andersson, Magnus; Axner, Ove; Uhlin, Bernt Eric; Fällman, Erik

2006-08-01

206

Force Mapping during the Formation and Maturation of Cell Adhesion Sites with Multiple Optical Tweezers  

PubMed Central

Focal contacts act as mechanosensors allowing cells to respond to their biomechanical environment. Force transmission through newly formed contact sites is a highly dynamic process requiring a stable link between the intracellular cytoskeleton and the extracellular environment. To simultaneously investigate cellular traction forces in several individual maturing adhesion sites within the same cell, we established a custom-built multiple trap optical tweezers setup. Beads functionalized with fibronectin or RGD-peptides were placed onto the apical surface of a cell and trapped with a maximum force of 160 pN. Cells form adhesion contacts around the beads as demonstrated by vinculin accumulation and start to apply traction forces after 30 seconds. Force transmission was found to strongly depend on bead size, surface density of integrin ligands and bead location on the cell surface. Highest traction forces were measured for beads positioned on the leading edge. For mouse embryonic fibroblasts, traction forces acting on single beads are in the range of 80 pN after 5 minutes. If two beads were positioned parallel to the leading edge and with a center-to-center distance less than 10 µm, traction forces acting on single beads were reduced by 40%. This indicates a spatial and temporal coordination of force development in closely related adhesion sites. We also used our setup to compare traction forces, retrograde transport velocities, and migration velocities between two cell lines (mouse melanoma and fibroblasts) and primary chick fibroblasts. We find that maximal force development differs considerably between the three cell types with the primary cells being the strongest. In addition, we observe a linear relation between force and retrograde transport velocity: a high retrograde transport velocity is associated with strong cellular traction forces. In contrast, migration velocity is inversely related to traction forces and retrograde transport velocity. PMID:23372781

Schwingel, Melanie; Bastmeyer, Martin

2013-01-01

207

Modeling highly focused laser beam in optical tweezers with the vector Gaussian beam in the T-matrix method.  

PubMed

The vector Gaussian beam with high-order corrections is used to describe accurately the laser beam up to numerical aperture NA=1.20 in the optical tweezers for trapping nanoparticles. The beam is then expanded in the T-matrix method into the vector spherical wave function (VSWF) series using the point matching method with a new selection of the matching points. The errors in the beam description and in the VSWF expansion are much lower than those that occur in the paraxial Gaussian beam model. PMID:23455996

Bareil, Paul B; Sheng, Yunlong

2013-01-01

208

Annual distributions and sources of Arctic aerosol components, aerosol optical depth, and aerosol absorption  

NASA Astrophysics Data System (ADS)

Radiative forcing by aerosols and tropospheric ozone could play a significant role in recent Arctic warming. These species are in general poorly accounted for in climate models. We use the GEOS-Chem global chemical transport model to construct a 3-D representation of Arctic aerosols and ozone that is consistent with observations and can be used in climate simulations. We focus on 2008, when extensive observations were made from different platforms as part of the International Polar Year. Comparison to aircraft, surface, and ship cruise observations suggests that GEOS-Chem provides in general a successful year-round simulation of Arctic black carbon (BC), organic carbon (OC), sulfate, and dust aerosol. BC has major fuel combustion and boreal fire sources, OC is mainly from fires, sulfate has a mix of anthropogenic and natural sources, and dust is mostly from the Sahara. The model is successful in simulating aerosol optical depth (AOD) observations from Aerosol Robotics Network stations in the Arctic; the sharp drop from spring to summer appears driven in part by the smaller size of sulfate aerosol in summer. The anthropogenic contribution to Arctic AOD is a factor of 4 larger in spring than in summer and is mainly sulfate. Simulation of absorbing aerosol optical depth (AAOD) indicates that non-BC aerosol (OC and dust) contributed 24% of Arctic AAOD at 550 nm and 37% of absorbing mass deposited to the snow pack in 2008. Open fires contributed half of AAOD at 550 nm and half of deposition to the snowpack.

Breider, Thomas J.; Mickley, Loretta J.; Jacob, Daniel J.; Wang, Qiaoqiao; Fisher, Jenny A.; Chang, Rachel. Y.-W.; Alexander, Becky

2014-04-01

209

Two-dimensional transport and transfer of a single atomic qubit in optical tweezers  

E-print Network

that these manipulations of the external degrees of freedom preserve the coherence of the qubit, and do not induce any. An attractive architecture is a large set of physically independent qubits arranged in three spatial regions­6 . Furthermore, we transfer a qubit between two tweezers, and show that this manipulation also preserves

Loss, Daniel

210

Single-cell adhesion probed in-situ using optical tweezers: A case study with Saccharomyces cerevisiae  

NASA Astrophysics Data System (ADS)

A facile method of using optical trapping to measure cell adhesion forces is presented and applied to the adhesion of Saccharomyces cerevisiae on glass, in contact with solutions of different compositions. Trapping yeast cells with optical tweezers (OT) is not perturbed by cell wall deformation or cell deviation from a spherical shape. The trapping force calibration requires correction not only for the hydrodynamic effect of the neighboring wall but also for spherical aberrations affecting the focal volume and the trap stiffness. Yeast cells trapped for up to 5 h were still able to undergo budding but showed an increase of doubling time. The proportion of adhering cells showed the expected variation according to the solution composition. The detachment force varied in the same way. This observation and the fact that the detachment stress was exerted parallel to the substrate surface point to the role of interactions involving solvated macromolecules. Both the proportion of adhering cells and the removal force showed a distribution which, in our experimental conditions, must be attributed to a heterogeneity of surface properties at the cell level or at the subcellular scale. As compared with magnetic tweezers, atomic force microscopy, and more conventional ways of studying cell adhesion (shear-flow cells), OT present several advantages that are emphasized in this paper.

Castelain, Mickaël; Rouxhet, Paul G.; Pignon, Frédéric; Magnin, Albert; Piau, Jean-Michel

2012-06-01

211

Cell-scaffold adhesion dynamics measured in first seconds predicts cell growth on days scale - optical tweezers study.  

PubMed

Understanding the cell-biomaterial interface from the very first contact is of crucial importance for their successful implementation and function in damaged tissues. However, the lack of bio- and mechano-analytical methods to investigate and probe the initial processes on the interface, especially in 3D, raises the need for applying new experimental techniques. In our study, optical tweezers combined with confocal fluorescence microscopy were optimized to investigate the initial cell-scaffold contact and to investigate its correlation with the material-dependent cell growth. By the optical tweezers-induced cell manipulation accompanied by force detection up to 100 pN and position detection by fluorescence microscopy, accurate adhesion dynamics and strength analysis was implemented, where several attachment sites were formed on the interface in the first few seconds. More importantly, we have shown that dynamics of cell adhesion on scaffold surfaces correlates with cell growth on the days scale, which indicates that the first seconds of the contact could markedly direct further cell response. Such a contact dynamics analysis on 3D scaffold surfaces, applied for the first time, can thus serve to predict scaffold biocompatibility. PMID:25764169

Podlipec, Rok; Štrancar, Janez

2015-04-01

212

Measuring nanoscale interactions and dynamics of DNA-grafted colloids with line optical tweezers  

NASA Astrophysics Data System (ADS)

Much of the excitement regarding nanotechnology stems from the idea of "bottom-up" self-assembly: the possibility of spontaneously growing complex structures or devices out of molecular scale components rather than using conventional microfabrication. Realizing such goals requires a reliable method for inducing specific interactions between multiple particle species. The preferred method for inducing such interactions is to use hybridization, the sequence-specific assembly of single stranded DNA grafted onto the particles into double strands. Linking bridges of DNA can either glue two objects together strongly or cause them to weakly and reversibly adhere. While the strong adhesion limit has been studied, the weak reversible interactions required for equilibrium self-assembly and annealing remain poorly characterized, hindering experimental and theoretical progress. All previous attempts to assemble non-DNA objects using DNA interactions have created highly disordered aggregates rather than the hoped for crystal-like structures. Here we report the first direct measurements of such DNA-induced colloidal interactions, as well as the first colloidal crystals assembled using them. The pair interactions measured with our optical tweezer method can be modeled in detail by well-known statistical physics and chemistry, boding well for their application to directed self-assembly. The microspheres' binding dynamics, however, have a surprising power-law scaling that can significantly slow annealing and crystallization. We separated effects due to multiple bridge kinetics from those due to individual DNA hybridization by adjusting the microspheres' DNA surface density. The process of DNA hybridization requires the traversing of a multitude of intermediate steps to get from two random coil oligonucleotides to a tidy duplex DNA. We probed the nature of these intermediate states by measuring the lifetime distribution of single 16-bp duplexes subject to thermal dissociation under effectively zero tension. Unlike comparable single molecule experiments performed at finite tension, we find an unusual stretched exponential lifetime distribution, suggesting that thermal dissociation proceeds via a number of competing intermediate pathways. Similar measurements with higher DNA density indicate that multiple-bridged states are highly unstable, indicating that the duplexes are extremely force sensitive. Our power-law kinetics are a likely consequence of the exquisite force sensitivity and nonexponential dissociation kinetics of the DNA bridges.

Biancaniello, Paul Louis

213

Using a new aerosol relative optical thickness concept to identify aerosol particle species  

NASA Astrophysics Data System (ADS)

We developed an aerosol relative optical thickness concept and then established an effective aerosol particle recognition model by analyzing variations in aerosol optical thicknesses in Beijing between 2001 and 2006. The accuracy of the model was verified using inverse calculations. The aerosol particle types and size distributions were assessed for several typical atmospheric phenomena, and the characteristic relative optical thicknesses for several typical aerosols were identified. Finally, we analyzed annual variations in the aerosol particle species in several eastern Asian cities using the model.

Yuan, Yuan; Shuai, Yong; Li, Xiao-Wei; Liu, Bin; Tan, He-Ping

2014-12-01

214

Three-Dimensional Optical Trapping of a Plasmonic Nanoparticle using Low Numerical Aperture Optical Tweezers  

PubMed Central

It was previously believed that larger metal nanoparticles behave as tiny mirrors that are pushed by the light beam radiative force along the direction of beam propagation, without a chance to be confined. However, several groups have recently reported successful optical trapping of gold and silver particles as large as 250?nm. We offer a possible explanation based on the fact that metal nanoparticles naturally occur in various non-spherical shapes and their optical properties differ significantly due to changes in localized plasmon excitation. We demonstrate experimentally and support theoretically three-dimensional confinement of large gold nanoparticles in an optical trap based on very low numerical aperture optics. We showed theoretically that the unique properties of gold nanoprisms allow an increase of trapping force by an order of magnitude at certain aspect ratios. These results pave the way to spatial manipulation of plasmonic nanoparticles using an optical fibre, with interesting applications in biology and medicine. PMID:25630432

Brzobohatý, Oto; Šiler, Martin; Trojek, Jan; Chvátal, Lukáš; Karásek, Vít?zslav; Paták, Aleš; Pokorná, Zuzana; Mika, Filip; Zemánek, Pavel

2015-01-01

215

Optical Properties of Atmospheric Aerosol in Maritime Environments  

Microsoft Academic Search

Systematic characterization of aerosol over the oceans is needed to understand the aerosol effect on climate and on transport of pollutants between continents. Reported are the results of a comprehensive optical and physical characterization of ambient aerosol in five key island locations of the Aerosol Robotic Network (AERONET) of sun and sky radiometers, spanning over 2-5 yr. The results are

Alexander Smirnov; Brent N. Holben; Yoram J. Kaufman; Oleg Dubovik; Thomas F. Eck; Ilya Slutsker; Christophe Pietras; Rangasayi N. Halthore

2002-01-01

216

An emerging ground-based aerosol climatology: Aerosol optical depth from AERONET  

Microsoft Academic Search

Long-term measurements by the AERONET program of spectral aerosol optical depth, precipitable water, and derived Angstrom exponent were analyzed and compiled into an aerosol optical properties climatology. Quality assured monthly means are presented and described for 9 primary sites and 21 additional multiyear sites with distinct aerosol regimes representing tropical biomass burning, boreal forests, midlatitude humid climates, midlatitude dry climates,

B. N. Holben; D. Tanré; A. Smirnov; T. F. Eck; I. Slutsker; N. Abuhassan; W. W. Newcomb; J. S. Schafer; B. Chatenet; F. Lavenu; Y. J. Kaufman; J. Vande Castle; A. Setzer; B. Markham; D. Clark; R. Frouin; R. Halthore; A. Karneli; N. T. O'Neill; C. Pietras; R. T. Pinker; K. Voss; G. Zibordi

2001-01-01

217

Using optical tweezers for measuring the interaction forces between human bone cells and implant surfaces: System design and force calibration  

SciTech Connect

Optical tweezers were used to study the interaction and attachment of human bone cells to various types of medical implant materials. Ideally, the implant should facilitate cell attachment and promote migration of the progenitor cells in order to decrease the healing time. It is therefore of interest, in a controlled manner, to be able to monitor the cell adhesion process. Results from such studies would help foresee the clinical outcome of integrating medical implants. The interactions between two primary cell culture models, human gingival fibroblasts and bone forming human osteoblast cells, and three different implant materials, glass, titanium, and hydroxyapatite, were studied. A novel type of optical tweezers, which has a newly designed quadrant detector and a powerful 3 W laser was constructed and force calibrated using two different methods: one method in which the stiffness of the optical trap was obtained by monitoring the phase lag between the trap and the moved object when imposing a forced oscillation on the trapped object and another method in which the maximum trapping force was derived from the critical velocity at which the object escapes the trap. Polystyrene beads as well as cells were utilized for the calibrations. This is the first time that cells have been used directly for these types of force calibrations and, hence, direct measurements of forces exerted on cells can be performed, thus avoiding the difficulties often encountered when translating the results obtained from cell measurements to the calibrations obtained with reference materials. This more straightforward approach represents an advantage in comparison to established methods.

Andersson, Martin; Madgavkar, Ashwin; Stjerndahl, Maria; Wu, Yanrong; Tan, Weihong; Duran, Randy; Niehren, Stefan; Mustafa, Kamal; Arvidson, Kristina; Wennerberg, Ann [Department of Chemistry, University of Florida, Gainesville, Florida 32611 (United States); Molecular Machines and Industries GmbH, Breslauerstrasse 2, 85386 Eching (Germany); Center for Clinical Dental Research, University of Bergen, N-5009 Bergen (Norway); Department of Prosthodontics/Dental Material Science, University of Goeteborg, S-40530 Goeteborg, Sweden and Department of Biomaterials, University of Goeteborg, S-40530 Goeteborg (Sweden)

2007-07-15

218

Using optical tweezers for measuring the interaction forces between human bone cells and implant surfaces: System design and force calibration  

NASA Astrophysics Data System (ADS)

Optical tweezers were used to study the interaction and attachment of human bone cells to various types of medical implant materials. Ideally, the implant should facilitate cell attachment and promote migration of the progenitor cells in order to decrease the healing time. It is therefore of interest, in a controlled manner, to be able to monitor the cell adhesion process. Results from such studies would help foresee the clinical outcome of integrating medical implants. The interactions between two primary cell culture models, human gingival fibroblasts and bone forming human osteoblast cells, and three different implant materials, glass, titanium, and hydroxyapatite, were studied. A novel type of optical tweezers, which has a newly designed quadrant detector and a powerful 3W laser was constructed and force calibrated using two different methods: one method in which the stiffness of the optical trap was obtained by monitoring the phase lag between the trap and the moved object when imposing a forced oscillation on the trapped object and another method in which the maximum trapping force was derived from the critical velocity at which the object escapes the trap. Polystyrene beads as well as cells were utilized for the calibrations. This is the first time that cells have been used directly for these types of force calibrations and, hence, direct measurements of forces exerted on cells can be performed, thus avoiding the difficulties often encountered when translating the results obtained from cell measurements to the calibrations obtained with reference materials. This more straightforward approach represents an advantage in comparison to established methods.

Andersson, Martin; Madgavkar, Ashwin; Stjerndahl, Maria; Wu, Yanrong; Tan, Weihong; Duran, Randy; Niehren, Stefan; Mustafa, Kamal; Arvidson, Kristina; Wennerberg, Ann

2007-07-01

219

Optical Properties of Aerosols and Clouds: The Software Package OPAC  

Microsoft Academic Search

The software package OPAC (Optical Properties of Aerosols and Clouds) is described. It easily provides optical properties in the solar and terrestrial spectral range of atmospheric particulate matter. Microphysical and optical properties of six water clouds, three ice clouds, and 10 aerosol components, which are considered as typical cases, are stored as ASCII files. The optical properties are the extinction,

M. Hess; P. Koepke; I. Schult

1998-01-01

220

Trapping and transporting aerosols with a single optical bottle  

E-print Network

Trapping and transporting aerosols with a single optical bottle beam generated by moiré techniques and manipulation of aerosols with an optical bottle beam generated by the moiré techniques. We observe stable Optical Society of America OCIS codes: 350.4855, 260.6042, 050.0050, 160.4236. Optical bottle beams

Chen, Zhigang

221

Contribution of different aerosol species to the global aerosol extinction optical thickness: Estimates from model results  

Microsoft Academic Search

We combine global distributions of aerosol loading resulting from transport models for soil dust, sulfate, sea salt, and carbonaceous aerosol. From the aerosol distributions we estimate optical thickness and compare them with Sun photometer measurements and satellite retrievals, thereby revealing problems with both model results and comparisons with such measurements. Globally, sulfate, dust, and carbonaceous particles appear to contribute equally

Ina Tegen; Peter Hollrig; Mian Chin; Inez Fung; Daniel Jacob; Joyce Penner

1997-01-01

222

GOES 8 aerosol optical thickness assimilation in a mesoscale model: Online integration of aerosol radiative effects  

Microsoft Academic Search

To investigate the importance of aerosol radiative effects in the troposphere, numerical simulation of a dust event during the Puerto Rico Dust Experiment is presented by using the Colorado State University Regional Atmospheric Modeling System (RAMS). Through assimilation of geostationary satellite-derived aerosol optical thickness (AOT) into the RAMS, spatial and temporal aerosol distribution is optimally characterized, facilitating direct comparison with

Jun Wang; Sundar A. Christopher

2004-01-01

223

GOES 8 aerosol optical thickness assimilation in a mesoscale model: Online integration of aerosol radiative effects  

Microsoft Academic Search

To investigate the importance of aerosol radiative effects in the troposphere, numerical simulation of a dust event during the Puerto Rico Dust Experiment (PRIDE) is presented by using the Colorado State University (CSU) Regional Atmospheric Modeling System (RAMS). Through assimilation of geostationary satellite-derived aerosol optical thickness (AOT) into the RAMS, spatial and temporal aerosol distribution is optimally characterized, facilitating direct

Jun Wang; U. S. Nair; Sundar A. Christopher

2004-01-01

224

Optical Properties of Atmospheric Aerosol in Maritime Environments  

Microsoft Academic Search

Atmospheric aerosol optical properties over the oceans based on the AERONET data are presented. The results are compared with the historical shipborne data acquired over the last 30 years. A model of the maritime aerosol component derived using AERONET data from island locations in the Pacific, Atlantic and Indian Ocean is presented. Maritime aerosol properties in the Central Pacific are

Alexander Smirnov; B. N. Holben; O. Dubovik; T. F. Eck; I. Slutsker

2004-01-01

225

A review of aerosol optical properties and radiative effects  

NASA Astrophysics Data System (ADS)

Atmospheric aerosols influence the earth's radiative balance directly through scattering and absorbing solar radiation, and indirectly through affecting cloud properties. An understanding of aerosol optical properties is fundamental to studies of aerosol effects on climate. Although many such studies have been undertaken, large uncertainties in describing aerosol optical characteristics remain, especially regarding the absorption properties of different aerosols. Aerosol radiative effects are considered as either positive or negative perturbations to the radiation balance, and they include direct, indirect (albedo effect and cloud lifetime effect), and semi-direct effects. The total direct effect of anthropogenic aerosols is negative (cooling), although some components may contribute a positive effect (warming). Both the albedo effect and cloud lifetime effect cool the atmosphere by increasing cloud optical depth and cloud cover, respectively. Absorbing aerosols, such as carbonaceous aerosols and dust, exert a positive forcing at the top of atmosphere and a negative forcing at the surface, and they can directly warm the atmosphere. Internally mixed black carbon aerosols produce a stronger warming effect than externally mixed black carbon particles do. The semidirect effect of absorbing aerosols could amplify this warming effect. Based on observational (ground- and satellite-based) and simulation studies, this paper reviews current progress in research regarding the optical properties and radiative effects of aerosols and also discusses several important issues to be addressed in future studies.

Liu, Yuzhi; Jia, Rui; Dai, Tie; Xie, Yongkun; Shi, Guangyu

2014-12-01

226

Aerosol Optical Depth Determinations for BOREAS  

NASA Technical Reports Server (NTRS)

Automated tracking sun photometers were deployed by NASA/Ames Research Center aboard the NASA C-130 aircraft and at a ground site for all three Intensive Field Campaigns (IFCs) of the Boreal Ecosystem-Atmosphere Study (BOREAS) in central Saskatchewan, Canada during the summer of 1994. The sun photometer data were used to derive aerosol optical depths for the total atmospheric column above each instrument. The airborne tracking sun photometer obtained data in both the southern and northern study areas at the surface prior to takeoff, along low altitude runs near the ground tracking sun photometer, during ascents to 6-8 km msl, along remote sensing flightlines at altitude, during descents to the surface, and at the surface after landing. The ground sun photometer obtained data from the shore of Candle Lake in the southern area for all cloud-free times. During the first IFC in May-June ascents and descents of the airborne tracking sun photometer indicated the aerosol optical depths decreased steadily from the surface to 3.5 kni where they leveled out at approximately 0.05 (at 525 nm), well below levels caused by the eruption of Mt. Pinatubo. On a very clear day, May 31st, surface optical depths measured by either the airborne or ground sun photometers approached those levels (0.06-0.08 at 525 nm), but surface optical depths were often several times higher. On June 4th they increased from 0.12 in the morning to 0.20 in the afternoon with some evidence of brief episodes of pollen bursts. During the second IFC surface aerosol optical depths were variable in the extreme due to smoke from western forest fires. On July 20th the aerosol optical depth at 525 nm decreased from 0.5 in the morning to 0.2 in the afternoon; they decreased still further the next day to 0.05 and remained consistently low throughout the day to provide excellent conditions for several remote sensing missions flown that day. Smoke was heavy for the early morning of July 24th but cleared partially by 10:30 local time and cleared fully by 11:30. Heavy smoke characterized the rest of the IFC in both study areas.

Wrigley, R. C.; Livingston, J. M.; Russell, P. B.; Guzman, R. P.; Ried, D.; Lobitz, B.; Peterson, David L. (Technical Monitor)

1994-01-01

227

Optical Properties of Titan's Aerosol Analogues  

NASA Astrophysics Data System (ADS)

In the upper Titan's atmosphere its main constituents, CH4 and N2, are photolyzed and radiolyzed by solar photons and magnetospheric electrons. The primary products of these chemical interactions evolve to heavier organic compounds which are likely to associate to form the haze layers observed on Titan's upper atmosphere. Different theories and models have been used to explain the physical, chemical and optical properties of the haze material, but only with limited success. Among the parameters involved in these models, the complex refractive index is one of the most critical due to the influence that chemical composition and structural organization of the solid have on the n and k values. As part of a continued systematical study for the synthesis and characterization of Titan's aerosol analogues initiated in our group, we have subjected mixtures of CH4 in N2 to laser irradiation to produce layer of aerosol analogues. A set of optical properties values directly calculated from the transmission and reflectance curves, as well as a chemical characterization, by tandem mass spectroscopy, of the laboratory analogues will be presented. Our experimental protocol avoids some of the difficulties usually faced on laboratory simulations (over-irradiation, contamination with atmospheric oxygen, accurate ratio of initial gas mixture), porosity influences will also be discussed. The optical values can be used to determine how the chemical and optical properties of these aerosols influence the matching with the observed geometric albedo spectrum and how they participate in the radiative equilibrium processes in Titan's atmosphere. They will certainly help in the interpretation of the observations made by the Huygens descend through Titan's atmosphere last January and in all the new information about Titan generated since then. Financial support from CONACyT (40449) and PROMEP (103.5/03/1134) is acknowledged. SIRJ acknowledges a travel grant from PIFI 3.2.

Ramirez, Sandra I.; Contreras, G.; Agarwal, V.

2006-09-01

228

Using optical tweezers to examine the chemotactic force to a single inflammatory cell--eosinophil stimulated by chemoattractants prepared from Toxocara Canis larvae  

NASA Astrophysics Data System (ADS)

Granulocytes are a group of white blood cells belonging to the innate immune system in human and in murine in which eosinophils play an important role in worm infection-induced inflammation. The migration of these cells is well characterized and has been separated into four steps: rolling, adhesion, transendothelial migration, and chemotaxis, however, the physical characteristics of the chemotactic force to eosinophils from worm component remain largely unknown. Note that optical tweezers are featured in the manipulation of a single cell and the measurement of biological forces. Therefore, we propose to use optical tweezers to examine the chemotactic force to a eosinophil from a T. canis lavae preparation in terms of distance during the migration of eosinophil.

Shih, Po-Chen; Su, Yi-Jr; Chen, Ke-Min; Jen, Lin-Ni; Liu, Cheng-tzu; Hsu, Long

2005-08-01

229

Trapping and two-photon fluorescence excitation of microscopic objects using ultrafast single-fiber optical tweezers  

NASA Astrophysics Data System (ADS)

Analysis of trapped microscopic objects using fluorescence and Raman spectroscopy is gaining considerable interest. We report on the development of single fiber ultrafast optical tweezers and its use in simultaneous two-photon fluorescence (TPF) excitation of trapped fluorescent microscopic objects. Using this method, trapping depth of a few centimeters was achieved inside a colloidal sample with TPF from the trapped particle being visible to the naked eye. Owing to the propagation distance of the Bessel-like beam emerging from the axicon-fiber tip, a relatively longer streak of fluorescence was observed along the microsphere length. The cone angle of the axicon was engineered so as to provide better trapping stability and high axial confinement of TPF. Trapping of the floating objects led to stable fluorescence emission intensity over a long period of time, suitable for spectroscopic measurements. Furthermore, the stability of the fiber optic trapping was confirmed by holding and maneuvering the fiber by hand so as to move the trapped fluorescent particle in three dimensions. Apart from miniaturization capability into lab-on-a-chip microfluidic devices, the proposed noninvasive microaxicon tipped optical fiber can be used in multifunctional mode for in-depth trapping, rotation, sorting, and ablation, as well as for two-photon fluorescence excitation of a motile sample.

Mishra, Yogeshwar N.; Ingle, Ninad; Mohanty, Samarendra K.

2011-10-01

230

Aerosol Optical Depth Measurements in the Southern Ocean Within the Framework of Maritime Aerosol Network  

NASA Astrophysics Data System (ADS)

Aerosol production sources over the World Ocean and various factors determining aerosol spatial and temporal distribution are important for understanding the Earth's radiation budget and aerosol-cloud interactions. The Maritime Aerosol Network (MAN) as a component of AERONET has been collecting aerosol optical depth data over the oceans since 2006. A significant progress has been made in data acquisition over areas that previously had very little or no coverage. Data collection included intensive study areas in the Southern Ocean and off the coast of Antarctica including a number of circumnavigation cruises in high southern latitudes. It made an important contribution to MAN and provided a valuable reference point in atmospheric aerosol optical studies. The paper presents results of this international and multi-agency effort in studying aerosol optical properties over Southern Ocean and adjacent areas. The ship-borne aerosol optical depth measurements offer an excellent opportunity for comparison with global aerosol transport models, satellite retrievals and provide useful information on aerosol distribution over the World Ocean. A public domain web-based database dedicated to the MAN activity can be found at http://aeronet.gsfc.nasa.gov/new_web/maritime_aerosol_network.html.

Smirnov, A.; Holben, B. N.; Sayer, A. M.; Sakerin, S. M.; Radionov, V. F.; Courcoux, Y.; Broccardo, S. P.; Evangelista, H.; Croot, P. L.; Disterhoft, P.; Piketh, S.; Milinevsky, G. P.; O'Neill, N. T.; Slutsker, I.; Giles, D. M.

2013-12-01

231

Quantifying the response of the ORAC aerosol optical depth retrieval for MSG SEVIRI to aerosol model assumptions  

E-print Network

Quantifying the response of the ORAC aerosol optical depth retrieval for MSG SEVIRI to aerosolRed Imager (MSG SEVIRI) to changes in the aerosol properties used in the dust aerosol model, using data from retrieval for MSG SEVIRI to aerosol model assumptions, J. Geophys. Res., 116, D05208, doi:10.1029/2010JD

Oxford, University of

232

Relative humidity and its effect on aerosol optical depth in the vicinity of convective clouds  

E-print Network

The hygroscopic growth of aerosols is controlled by the relative humidity (RH) and changes the aerosols' physical and hence optical properties. Observational studies of aerosol–cloud interactions evaluate the aerosol ...

Altaratz, O

233

Hyperspectral Aerosol Optical Depths from TCAP Flights  

SciTech Connect

4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research), the world’s first hyperspectral airborne tracking sunphotometer, acquired aerosol optical depths (AOD) at 1 Hz during all July 2012 flights of the Two Column Aerosol Project (TCAP). Root-mean square differences from AERONET ground-based observations were 0.01 at wavelengths between 500-1020 nm, 0.02 at 380 and 1640 nm and 0.03 at 440 nm in four clear-sky fly-over events, and similar in ground side-by-side comparisons. Changes in the above-aircraft AOD across 3-km-deep spirals were typically consistent with integrals of coincident in situ (on DOE Gulfstream 1 with 4STAR) and lidar (on NASA B200) extinction measurements within 0.01, 0.03, 0.01, 0.02, 0.02, 0.02 at 355, 450, 532, 550, 700, 1064 nm, respectively, despite atmospheric variations and combined measurement uncertainties. Finer vertical differentials of the 4STAR measurements matched the in situ ambient extinction profile within 14% for one homogeneous column. For the AOD observed between 350-1660 nm, excluding strong water vapor and oxygen absorption bands, estimated uncertainties were ~0.01 and dominated by (then) unpredictable throughput changes, up to +/-0.8%, of the fiber optic rotary joint. The favorable intercomparisons herald 4STAR’s spatially-resolved high-frequency hyperspectral products as a reliable tool for climate studies and satellite validation.

Shinozuka, Yohei; Johnson, Roy R.; Flynn, Connor J.; Russell, P. B.; Schmid, Beat; Redemann, Jens; Dunagan, Stephen; Kluzek, Celine D.; Hubbe, John M.; Segal-Rosenheimer, Michal; Livingston, J. M.; Eck, T.; Wagener, Richard; Gregory, L.; Chand, Duli; Berg, Larry K.; Rogers, Ray; Ferrare, R. A.; Hair, John; Hostetler, Chris A.; Burton, S. P.

2013-11-13

234

Multiwavelength multistatic optical scattering for aerosol characterization  

NASA Astrophysics Data System (ADS)

The main focus of this research is the development of a technique to remotely characterize aerosol properties, such as particle size distribution, concentration, and refractive index as a function of wavelength, through the analysis of optical scattering measurements. The proposed technique is an extension of the multistatic polarization ratio technique that has been developed by prior students at the Penn State Lidar Lab to include multiple wavelengths. This approach uses the ratio of polarized components of the scattering phase functions at multiple wavelengths across the visible region of the electromagnetic spectrum to extract the microphysical and optical properties of aerosols. The scattering intensities at each wavelength are vertically separated across the face of the imager using a transmission diffraction grating, so that scattering intensities for multiple wavelengths at many angles are available for analysis in a single image. The ratio of the scattering phase function intensities collected using parallel and perpendicular polarized light are formed for each wavelength and analysis of the ratio is used to determine the microphysical properties of the aerosols. One contribution of the present work is the development of an inversion technique based on a genetic algorithm that retrieves lognormal size distributions from scattering measurements by minimizing the squared error between measured polarization ratios and polarization ratios calculated using the Mie solution to Maxwell's equations. The opportunities and limitations of using the polarization ratio are explored, and a genetic algorithm is developed to retrieve single mode and trimodal lognormal size distributions from multiwavelength, angular scattering data. The algorithm is designed to evaluate particles in the diameter size range of 2 nm to 60 im, and uses 1,000 linear spaced diameters within this range to compute the modeled polarization ratio. The algorithm returns geometric mean radii and geometric standard deviations within 2% of the correct value when inverting a single lognormal probability size distribution from simulated polarization ratios that include random Gaussian noise added to limit the signal-to-noise ratio to 25. The genetic algorithm performed reasonably well when retrieving results using a single complex refractive index for all three wavelengths while finding the lognormal particle size parameters. Three inversion runs of the algorithm on simulated noisy data showed that the algorithm could retrieved a trimodal size distribution and a single complex refractive index that produced a very good fit between the simulated noisy polarization ratios and the forward-calculated polarization ratios. A significant contribution of the present work is a set of tests conducted at the Environmental Protection Agency's (EPA) Aerosol Test Facility (ATF), which is a controlled environment, where direct measurements of the size distribution and concentration of the scattering volume are available. The aerosol size distribution results obtained from inversion of the measured scattering phase functions, a lognormal size distribution with a geometric mean diameter of ˜450 nm and a geometric standard deviation of ˜1.3, compare favorably with measurements from an aerodynamic particle sizer and a condensation particle counter. This is one of the first large scale experiments where a comparison between multistatic inversion results and known properties of the interrogated volume of aerosols are made under controlled conditions. The eventual goal is to develop a prototype sensor and an analysis approach to provide an important and useful tool to better define the atmospheric aerosol properties.

Brown, Andrea M.

235

Climatology of Aerosol Optical Properties in Southern Africa  

NASA Technical Reports Server (NTRS)

A thorough regionally dependent understanding of optical properties of aerosols and their spatial and temporal distribution is required before we can accurately evaluate aerosol effects in the climate system. Long term measurements of aerosol optical depth, Angstrom exponent and retrieved single scattering albedo and size distribution, were analyzed and compiled into an aerosol optical properties climatology for southern Africa. Monitoring of aerosol parameters have been made by the AERONET program since the middle of the last decade in southern Africa. This valuable information provided an opportunity for understanding how aerosols of different types influence the regional radiation budget. Two long term sites, Mongu in Zambia and Skukuza in South Africa formed the core sources of data in this study. Results show that seasonal variation of aerosol optical thicknesses at 500 nm in southern Africa are characterized by low seasonal multi-month mean values (0.11 to 0.17) from December to May, medium values (0.20 to 0.27) between June and August, and high to very high values (0.30 to 0.46) during September to November. The spatial distribution of aerosol loadings shows that the north has high magnitudes than the south in the biomass burning season and the opposite in none biomass burning season. From the present aerosol data, no long term discernable trends are observable in aerosol concentrations in this region. This study also reveals that biomass burning aerosols contribute the bulk of the aerosol loading in August-October. Therefore if biomass burning could be controlled, southern Africa will experience a significant reduction in total atmospheric aerosol loading. In addition to that, aerosol volume size distribution is characterized by low concentrations in the non biomass burning period and well balanced particle size contributions of both coarse and fine modes. In contrast high concentrations are characteristic of biomass burning period, combined with significant dominance of fine mode particles.

Queface, Antonio J.; Piketh, Stuart J.; Eck, Thomas F.; Tsay, Si-Chee

2011-01-01

236

Path radiance technique for retrieving aerosol optical thickness over land  

NASA Astrophysics Data System (ADS)

The key issue in retrieving aerosol optical thickness over land from shortwave satellite radiances is to identify and separate the signal due to scattering by a largely transparent aerosol layer from the noise due to reflection by the background surface, where the signal is relatively uniform compared to the highly inhomogeneous surface contribution. Sensitivity studies in aerosol optical thickness retrievals reveal that the apparent reflectance at the top of the atmosphere is very susceptible to the surface reflectance, especially when aerosol optical thickness is small. Uncertainties associated with surface reflectance estimation can greatly amplify the error of the aerosol optical thickness retrieval. To reduce these uncertainties, we have developed a "path radiance" method to retrieve aerosol optical thickness over land by extending the traditional technique that uses the "dark object" approach to extract the aerosol signal. This method uses the signature of the correlation of visible and middle-IR reflectance at the surface and couples the correlation with the atmospheric effect. We have applied this method to a Landsat TM (Thematic Mapper) image acquired over the Oklahoma southern Great Plains site of the Department of Energy Atmospheric Radiation Measurement (ARM) program on September 27, 1997, a very clear day (aerosol optical thickness of 0.07 at 0.5 ?m) during the first Landsat Intensive Observation Period. The retrieved mean aerosol optical thickness for TM band 1 at 0.49 ?m and band 3 at 0.66 ?m agree very well with the ground-based Sun photometer measurements at the ARM site. The ability to retrieve small aerosol optical thickness makes this path radiance technique promising. More importantly, the path radiance is relatively insensitive to surface inhomogeneity. The retrieved mean path radiances in reflectance units have very small standard deviations for both TM blue and red bands. This small variability of path radiance further supports the current aerosol retrieval method.

Wen, Guoyong; Tsay, Si-Chee; Cahalan, Robert F.; Oreopoulos, Lazaros

1999-01-01

237

Global Aerosol Optical Models and Lookup Tables for the New MODIS Aerosol Retrieval over Land  

NASA Technical Reports Server (NTRS)

Since 2000, MODIS has been deriving aerosol properties over land from MODIS observed spectral reflectance, by matching the observed reflectance with that simulated for selected aerosol optical models, aerosol loadings, wavelengths and geometrical conditions (that are contained in a lookup table or 'LUT'). Validation exercises have showed that MODIS tends to under-predict aerosol optical depth (tau) in cases of large tau (tau greater than 1.0), signaling errors in the assumed aerosol optical properties. Using the climatology of almucantur retrievals from the hundreds of global AERONET sunphotometer sites, we found that three spherical-derived models (describing fine-sized dominated aerosol), and one spheroid-derived model (describing coarse-sized dominated aerosol, presumably dust) generally described the range of observed global aerosol properties. The fine dominated models were separated mainly by their single scattering albedo (omega(sub 0)), ranging from non-absorbing aerosol (omega(sub 0) approx. 0.95) in developed urban/industrial regions, to neutrally absorbing aerosol (omega(sub 0) approx.90) in forest fire burning and developing industrial regions, to absorbing aerosol (omega(sub 0) approx. 0.85) in regions of savanna/grassland burning. We determined the dominant model type in each region and season, to create a 1 deg. x 1 deg. grid of assumed aerosol type. We used vector radiative transfer code to create a new LUT, simulating the four aerosol models, in four MODIS channels. Independent AERONET observations of spectral tau agree with the new models, indicating that the new models are suitable for use by the MODIS aerosol retrieval.

Levy, Robert C.; Remer, Loraine A.; Dubovik, Oleg

2007-01-01

238

In vivo X-ray elemental imaging of single cell model organisms manipulated by laser-based optical tweezers.  

PubMed

We report on a radically new elemental imaging approach for the analysis of biological model organisms and single cells in their natural, in vivo state. The methodology combines optical tweezers (OT) technology for non-contact, laser-based sample manipulation with synchrotron radiation confocal X-ray fluorescence (XRF) microimaging for the first time. The main objective of this work is to establish a new method for in vivo elemental imaging in a two-dimensional (2D) projection mode in free-standing biological microorganisms or single cells, present in their aqueous environment. Using the model organism Scrippsiella trochoidea, a first proof of principle experiment at beamline ID13 of the European Synchrotron Radiation Facility (ESRF) demonstrates the feasibility of the OT XRF methodology, which is applied to study mixture toxicity of Cu-Ni and Cu-Zn as a result of elevated exposure. We expect that the new OT XRF methodology will significantly contribute to the new trend of investigating microorganisms at the cellular level with added in vivo capability. PMID:25762511

Vergucht, Eva; Brans, Toon; Beunis, Filip; Garrevoet, Jan; De Rijcke, Maarten; Bauters, Stephen; Deruytter, David; Vandegehuchte, Michiel; Van Nieuwenhove, Ine; Janssen, Colin; Burghammer, Manfred; Vincze, Laszlo

2015-01-01

239

In vivo X-ray elemental imaging of single cell model organisms manipulated by laser-based optical tweezers  

NASA Astrophysics Data System (ADS)

We report on a radically new elemental imaging approach for the analysis of biological model organisms and single cells in their natural, in vivo state. The methodology combines optical tweezers (OT) technology for non-contact, laser-based sample manipulation with synchrotron radiation confocal X-ray fluorescence (XRF) microimaging for the first time. The main objective of this work is to establish a new method for in vivo elemental imaging in a two-dimensional (2D) projection mode in free-standing biological microorganisms or single cells, present in their aqueous environment. Using the model organism Scrippsiella trochoidea, a first proof of principle experiment at beamline ID13 of the European Synchrotron Radiation Facility (ESRF) demonstrates the feasibility of the OT XRF methodology, which is applied to study mixture toxicity of Cu-Ni and Cu-Zn as a result of elevated exposure. We expect that the new OT XRF methodology will significantly contribute to the new trend of investigating microorganisms at the cellular level with added in vivo capability.

Vergucht, Eva; Brans, Toon; Beunis, Filip; Garrevoet, Jan; de Rijcke, Maarten; Bauters, Stephen; Deruytter, David; Vandegehuchte, Michiel; van Nieuwenhove, Ine; Janssen, Colin; Burghammer, Manfred; Vincze, Laszlo

2015-03-01

240

Optical tweezers studies of viral DNA packaging: Motor function and DNA confinement in Bacteriophages phi29, lambda, and T4  

NASA Astrophysics Data System (ADS)

In the assembly of many viruses a powerful molecular motor translocates the genome into a pre-assembled capsid. We use optical tweezers to directly measure translocation of a single DNA molecule into the viral capsid. Improved techniques allow us to measure initiation and early stages of packaging. With phi29 the DNA terminal protein was found to cause large variations in the starting point of packaging. Removal of this protein results in terminal initiation, permitting more accurate assessment of motor function and DNA confinement forces. We investigated the role of electrostatic repulsion by varying ionic screening of the DNA. The observed trends are in accord with those theoretically expected considering counter-ion competition; however the forces are larger than expected in comparison with recent theories and DNA ejection measurements. We have recently succeeded in extending our methods to study two other phages: lambda and T4. These systems have unique structural and functional features, presenting an opportunity for comparative studies in this family of molecular motors. Initial measurements show that lambda and T4 translocate DNA several times faster than the phi29 motor, but are more sensitive to applied load.

Smith, Douglas

2007-03-01

241

In vivo X-ray elemental imaging of single cell model organisms manipulated by laser-based optical tweezers  

PubMed Central

We report on a radically new elemental imaging approach for the analysis of biological model organisms and single cells in their natural, in vivo state. The methodology combines optical tweezers (OT) technology for non-contact, laser-based sample manipulation with synchrotron radiation confocal X-ray fluorescence (XRF) microimaging for the first time. The main objective of this work is to establish a new method for in vivo elemental imaging in a two-dimensional (2D) projection mode in free-standing biological microorganisms or single cells, present in their aqueous environment. Using the model organism Scrippsiella trochoidea, a first proof of principle experiment at beamline ID13 of the European Synchrotron Radiation Facility (ESRF) demonstrates the feasibility of the OT XRF methodology, which is applied to study mixture toxicity of Cu-Ni and Cu-Zn as a result of elevated exposure. We expect that the new OT XRF methodology will significantly contribute to the new trend of investigating microorganisms at the cellular level with added in vivo capability. PMID:25762511

Vergucht, Eva; Brans, Toon; Beunis, Filip; Garrevoet, Jan; De Rijcke, Maarten; Bauters, Stephen; Deruytter, David; Vandegehuchte, Michiel; Van Nieuwenhove, Ine; Janssen, Colin; Burghammer, Manfred; Vincze, Laszlo

2015-01-01

242

Laser microbeams for DNA damage induction, optical tweezers for the search on blood pressure relaxing drugs: contributions to ageing research  

NASA Astrophysics Data System (ADS)

One essential cause of human ageing is the accumulation of DNA damages during lifetime. Experimental studies require quantitative induction of damages and techniques to visualize the subsequent DNA repair. A new technique, the "immuno fluorescent comet assay", is used to directly visualize DNA damages in the microscope. Using DNA repair proteins fluorescently labeled with green fluorescent protein, it could be shown that the repair of the most dangerous DNA double strand breaks starts with the inaccurate "non homologous end joining" pathway and only after 1 - 1 ½ minutes may switch to the more accurate "homologous recombination repair". One might suggest investigating whether centenarians use "homologous recombination repair" differently from those ageing at earlier years and speculate whether it is possible, for example by nutrition, to shift DNA repair to a better use of the error free pathway and thus promote healthy ageing. As a complementary technique optical tweezers, and particularly its variant "erythrocyte mediated force application", is used to simulate the effects of blood pressure on HUVEC cells representing the inner lining of human blood vessels. Stimulating one cell induces in the whole neighbourhood waves of calcium and nitric oxide, known to relax blood vessels. NIFEDIPINE and AMLODIPINE, both used as drugs in the therapy of high blood pressure, primarily a disease of the elderly, prolong the availability of nitric oxide. This partially explains their mode of action. In contrast, VERAPAMILE, also a blood pressure reducing drug, does not show this effect, indicating that obviously an alternative mechanism must be responsible for vessel relaxation.

Grigaravicius, P.; Monajembashi, S.; Hoffmann, M.; Altenberg, B.; Greulich, K. O.

2009-08-01

243

Dependence of bacteriophage ?29 DNA packaging on ionic conditions studied by optical tweezers manipulation of single DNA molecules  

NASA Astrophysics Data System (ADS)

The bacteriophage ?29 portal motor is capable of packaging the ?29, 19.3 Kbp, genome to high density into its preformed capsid. The packaging process must overcome the forces due to confining the highly negative charge of the DNA to a small volume, as well as the forces due to bending the DNA on length scales smaller than one persistence length. Both of these energetic considerations can be modulated by the ionic nature of the buffer DNA packaging occurs in. To measure the effects of DNA charge shielding on the packaging process, we studied the dynamics of DNA packaging by optical tweezers in a variety of different ionic conditions. We looked at the effects monovalent, divalent, and trivalent cations have on the motor function and its dependence on external force and, we observed the rate of DNA packaging at nominal force as a function of capsid filling. Specifically, we varied the concentrations of Na +, Mg +2, and cobalt hexamine in the solution bathing the bacteriophage during packaging to see what effects, if any, these cations have. From these measurements, we present an inferred internal force as a function of percent filling of the bacteriophage capsid in a variety of ionic environments. Preliminary analysis suggests the ionic environment can modulate internal pressure, with the presence of higher valence cations better shielding the packaged DNA resulting in lower internal pressures.

Fuller, Derek N.; Rickgauer, John P.; Grimes, Shelley; Jardine, Paul J.; Anderson, Dwight L.; Smith, Douglas E.

2006-08-01

244

A new technique for high sensitive detection of rotational motion in optical tweezers by a differential measurement of backscattered intensity  

NASA Astrophysics Data System (ADS)

Asymmetric particles, such as biological cells, often experience torque under optical tweezers due to birefringence or unbalanced scattering forces, which makes precise determination of the torque crucial for calibration and control of the particles. The estimate of torque relies on the accurate measurement of rotational motion, which has been achieved by various techniques such as measuring the intensity fluctuations of the forward scattered light, or the polarization component orthogonal to the trapping light polarization in plasmonic nanoparticles and vaterite crystals. Here we present a simple yet high sensitive technique to measure rotation of such an asymmetric trapped particle by detecting the light backscattered onto a quadrant photodiode, and subtracting the signals along the two diagonals of the quadrants. This automatically suppresses the common mode translational signal obtained by taking the difference signal of the adjacent quadrants, while amplifying the rotational signal. Using this technique, we obtain a S/N of 200 for angular displacement of a trapped micro-rod by 5 degrees, which implies a sensitivity of 50 mdeg with S/N of 2. The technique is thus independent of birefringence and polarization properties of the asymmetric particle and depends only on the scattering cross-section.

Roy, Basudev; Bera, Sudipta K.; Mondal, Argha; Banerjee, Ayan

2014-09-01

245

Physiological Monitoring of Optically Trapped Cells: Studying the Effects of Confinement by 1064 NM Lazer Tweezers Using Microfluorometry  

NASA Astrophysics Data System (ADS)

A novel technique that combines microfluorometric detection and optical laser trapping has been developed for in-situ assessing the physiological state of an optically trapped biological sample. This optical diagnostic technique achieves high sensitivity (>30 dB signal -to-noise ratio) and high spatial resolution (~ 1 ?m) over a broad spectral range (>400 nm). The fluorescence spectra derived from exogenous fluorescent probes, including laurdan, acridine orange, propidium iodide and Snarf, are used to assess the effects of optical confinement with respect to temperature, DNA structure, cell viability, and intracellular pH, respectively. In the latter three cases, fluorescence is excited via a two-photon absorption process, using the cw laser trap itself as the fluorescence excitation source. This enables the cw near infrared laser trapping beam to be used simultaneously as an optical diagnostic probe as well as an optical micromanipulator. Using microfluorometry, a temperature increase of less than several degrees centigrade was measured for test samples, including liposomes, Chinese hamster ovary (CHO) cells and human sperm cells that were held stationary by 1064 nm optical tweezers having a power density of ~10^7 W/cm^2. Additional physiological monitoring experiments indicated that there is no observable denaturation of DNA, or change of intracellular pH under typical continuous wave laser trapping conditions (P <= 400 mW). Under some circumstances, however, it was possible to achieve a decrease in cell viability with cw trapping, as monitored by a live/dead vital stain. In comparison, significant DNA denaturation and cellular physiological changes (e.g. cell death) were observed when a Q-switched pulsed laser at a threshold of ~30mu J/pulse was used as trapping source. These results generally support the conclusion that cw laser trapping at 1064 nm wavelength is a safe, non-invasive process and should prove to be of great value for understanding the mechanisms of laser microirradiation effects on living cells held stationary in a near-infrared trapping beam.

Liu, Yagang

246

Airborne Lidar Measurements of Aerosol Optical Properties During SAFARI-2000  

NASA Technical Reports Server (NTRS)

The Cloud Physics Lidar (CPL) operated onboard the NASA ER-2 high altitude aircraft during the SAFARI-2000 field campaign. The CPL provided high spatial resolution measurements of aerosol optical properties at both 1064 nm and 532 nm. We present here results of planetary boundary layer (PBL) aerosol optical depth analysis and profiles of aerosol extinction. Variation of optical depth and extinction are examined as a function of regional location. The wide-scale aerosol mapping obtained by the CPL is a unique data set that will aid in future studies of aerosol transport. Comparisons between the airborne CPL and ground-based MicroPulse Lidar Network (MPL-Net) sites are shown to have good agreement.

McGill, M. J.; Hlavka, D. L.; Hart, W. D.; Welton, E. J.; Campbell, J. R.; Starr, David OC. (Technical Monitor)

2002-01-01

247

Aerosol Optical Properties in Southeast Asia From AERONET Observations  

NASA Astrophysics Data System (ADS)

There is little published data available on measured optical properties of aerosols in the Southeast Asian region. The AERONET project and collaborators commenced monitoring of aerosol optical properties in February 2003 at four sites in Thailand and two sites in Viet Nam to measure the primarily anthropogenic aerosols generated by biomass burning and fossil fuel combustion/ industrial emissions. Automatic sun/sky radiometers at each site measured spectral aerosol optical depth in 7 wavelengths from 340 to 1020 nm and combined with directional radiances in the almucantar, retrievals were made of spectral single scattering albedo and aerosol size distributions. Angstrom exponents, size distributions and spectral single scattering albedo of primarily biomass burning aerosols at rural sites are compared to measurements made at AERONET sites in other major biomass burning regions in tropical southern Africa, South America, and in boreal forest regions. Additionally, the aerosol single scattering albedo and size distributions measured in Bangkok, Thailand are compared with those measured at other urban sites globally. The influences of aerosols originating from other regions outside of Southeast Asia are analyzed using trajectory analyses. Specifically, cases of aerosol transport and mixing from Southern China and from India are presented.

Eck, T. F.; Holben, B. N.; Boonjawat, J.; Le, H. V.; Schafer, J. S.; Reid, J. S.; Dubovik, O.; Smirnov, A.

2003-12-01

248

Photochemical formation rates and optical properties of organic aerosols  

E-print Network

´amkovics 1/18 #12;Relevance of Aerosols Ubiquitous in planetary atmospheres Terrestrial planets: Earth, Venus of Aerosols Ubiquitous in planetary atmospheres Terrestrial planets: Earth, Venus All gas giants Satellites-invasive measurements Measure concentration of all gas-phase species (mass-spec) Measure optical scattering Determine

Adamkovics, Mate

249

Aerosol Optical Depth Value-Added Product Report  

SciTech Connect

This document describes the process applied to retrieve aerosol optical depth (AOD) from multifilter rotating shadowband radiometers (MFRSR) and normal incidence multifilter radiometers (NIMFR) operated at the ARM Climate Research Facility’s ground-based facilities.

Koontz, A; Hodges, G; Barnard, J; Flynn, C; Michalsky, J

2013-03-17

250

Determining the binding mode and binding affinity constant of tyrosine kinase inhibitor PD153035 to DNA using optical tweezers  

SciTech Connect

Research highlights: {yields} PD153035 is a DNA intercalator and intercalation occurs only under very low salt concentration. {yields} The minimum distance between adjacent bound PD153035 {approx} 11 bp. {yields} Binding affinity constant for PD153035 is 1.18({+-}0.09) x 10{sup 4} (1/M). {yields} The change of binding free energy of PD153035-DNA interaction is -5.49 kcal mol{sup -1} at 23 {+-} 0.5 {sup o}C. -- Abstract: Accurately predicting binding affinity constant (K{sub A}) is highly required to determine the binding energetics of the driving forces in drug-DNA interactions. Recently, PD153035, brominated anilinoquinazoline, has been reported to be not only a highly selective inhibitor of epidermal growth factor receptor but also a DNA intercalator. Here, we use a dual-trap optical tweezers to determining K{sub A} for PD153035, where K{sub A} is determined from the changes in B-form contour length (L) of PD153035-DNA complex. Here, L is fitted using a modified wormlike chain model. We found that a noticeable increment in L in 1 mM sodium cacodylate was exhibited. Furthermore, our results showed that K{sub A} = 1.18({+-}0.09) x 10{sup 4} (1/M) at 23 {+-} 0.5 {sup o}C and the minimum distance between adjacent bound PD153035 {approx} 11 bp. We anticipate that by using this approach we can determine the complete thermodynamic profiles due to the presence of DNA intercalators.

Cheng, Chih-Ming [School of Dental Technology, Taipei Medical University, Taipei 110, Taiwan (China) [School of Dental Technology, Taipei Medical University, Taipei 110, Taiwan (China); Research Center for Biomedical Implants and Microsurgery Devices, Taipei Medical University, Taipei 110, Taiwan (China); Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu 30043, Taiwan (China); Lee, Yuarn-Jang [Section of Infectious Diseases, Department of Internal Medicine, Taipei Medical University Hospital, Taipei 110, Taiwan (China)] [Section of Infectious Diseases, Department of Internal Medicine, Taipei Medical University Hospital, Taipei 110, Taiwan (China); Wang, Wei-Ting [School of Dental Technology, Taipei Medical University, Taipei 110, Taiwan (China) [School of Dental Technology, Taipei Medical University, Taipei 110, Taiwan (China); Institute of Biomedical Materials and Engineering, Taipei Medical University, Taipei 110, Taiwan (China); Research Center for Biomedical Implants and Microsurgery Devices, Taipei Medical University, Taipei 110, Taiwan (China); Hsu, Chien-Ting [Institute of Biomedical Materials and Engineering, Taipei Medical University, Taipei 110, Taiwan (China) [Institute of Biomedical Materials and Engineering, Taipei Medical University, Taipei 110, Taiwan (China); Research Center for Biomedical Implants and Microsurgery Devices, Taipei Medical University, Taipei 110, Taiwan (China); Tsai, Jing-Shin [School of Dental Technology, Taipei Medical University, Taipei 110, Taiwan (China) [School of Dental Technology, Taipei Medical University, Taipei 110, Taiwan (China); Institute of Biomedical Materials and Engineering, Taipei Medical University, Taipei 110, Taiwan (China); Research Center for Biomedical Implants and Microsurgery Devices, Taipei Medical University, Taipei 110, Taiwan (China); Wu, Chien-Ming [Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu 30043, Taiwan (China)] [Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu 30043, Taiwan (China); Ou, Keng-Liang [Institute of Biomedical Materials and Engineering, Taipei Medical University, Taipei 110, Taiwan (China) [Institute of Biomedical Materials and Engineering, Taipei Medical University, Taipei 110, Taiwan (China); Research Center for Biomedical Implants and Microsurgery Devices, Taipei Medical University, Taipei 110, Taiwan (China); and others

2011-01-07

251

Leishmania amazonensis chemotaxis under glucose gradient studied by the strength and directionality of forces measured with optical tweezers  

NASA Astrophysics Data System (ADS)

Chemotaxis is the mechanism microorganisms use to sense the environment surrounding them and to direct their movement towards attractive, or away from the repellent, chemicals. The biochemical sensing is almost the only way for communication between unicellular organisms. Prokaryote and Eukaryote chemotaxis has been mechanically studied mainly by observing the directionality and timing of the microorganisms movements subjected to a chemical gradient, but not through the directionality and strength of the forces it generates. To observe the vector force of microorganisms under a chemical gradient we developed a system composed of two large chambers connected by a tiny duct capable to keep the chemical gradient constant for more than ten hours. We also used the displacements of a microsphere trapped in an Optical Tweezers as the force transducer to measure the direction and the strength of the propulsion forces of flagellum of the microorganism under several gradient conditions. A 9?m diameter microsphere particle was trapped with a Nd:YAG laser and its movement was measured through the light scattered focused on a quadrant detector. We observed the behavior of the protozoa Leishmania amazonensis (eukaryote) under several glucose gradients. This protozoa senses the gradient around it by swimming in circles for three to five times following by tumbling, and not by the typical straight swimming/tumbling of bacteria. Our results also suggest that force direction and strength are also used to control its movement, not only the timing of swimming/tumbling, because we observed a higher force strength clearly directed towards the glucose gradient.

de Ysasa Pozzo, Liliana; Fontes, Adriana; de Thomaz, André A.; Barbosa, Luiz Carlos; Ayres, Diana Copi; Giorgio, Selma; Cesar, Carlos Lenz

2007-02-01

252

Vertical Profiles of Cloud Condensation Nuclei, Condensation Nuclei, Optical Aerosol, Aerosol Optical Properties, and Aerosol Volatility Measured from Balloons  

NASA Technical Reports Server (NTRS)

Under the support of this grant a balloon-borne gondola containing a variety of aerosol instruments was developed and flown from Laramie, Wyoming, (41 deg N, 105 deg W) and from Lauder, New Zealand (45 deg S, 170 deg E). The gondola includes instruments to measure the concentrations of condensation nuclei (CN), cloud condensation nuclei (CCN), optically detectable aerosol (OA.) (r greater than or equal to 0.15 - 2.0 microns), and optical scattering properties using a nephelometer (lambda = 530 microns). All instruments sampled from a common inlet which was heated to 40 C on ascent and to 160 C on descent. Flights with the CN counter, OA counter, and nephelometer began in July 1994. The CCN counter was added in November 1994, and the engineering problems were solved by June 1995. Since then the flights have included all four instruments, and were completed in January 1998. Altogether there were 20 flights from Laramie, approximately 5 per year, and 2 from Lauder. Of these there were one or more engineering problems on 6 of the flights from Laramie, hence the data are somewhat limited on those 6 flights, while a complete data set was obtained from the other 14 flights. Good CCN data are available from 12 of the Laramie flights. The two flights from Lauder in January 1998 were successful for all measurements. The results from these flights, and the development of the balloon-bome CCN counter have formed the basis for five conference presentations. The heated and unheated CN and OA measurements have been used to estimate the mass fraction of the aerosol volatile, while comparisons of the nephelometer measurements were used to estimate the light scattering, associated with the volatile aerosol. These estimates were calculated for 0.5 km averages of the ascent and descent data between 2.5 km and the tropopause, near 11.5 km.

Deshler, T.; Snider, J. R.; Vali, G.

1998-01-01

253

A method for an approximate determination of a polymer-rich-domain concentration in phase-separated poly(N-isopropylacrylamide) aqueous solution by means of confocal Raman microspectroscopy combined with optical tweezers.  

PubMed

The paper demonstrates that a confocal Raman microspectroscope combined with optical tweezers is a promising technique to estimate polymer concentration in polymer-rich domain in phase-separated-aqueous polymer solution. The sample polymer is poly-(N-isopropylacrylamide) (PNIPAM) that is well-known as a representative thermo-responsive polymer. Optical tweezers can selectively trap the polymer-rich domain at the focal point in non-contact and non-intrusive modes. Such situation allows us to determine polymer concentration in the domain, which has been unclear due to a lack of appropriate analytical technique. It is applicable for a variety of other thermo-responsive polymers. PMID:25479874

Shoji, Tatsuya; Nohara, Riku; Kitamura, Noboru; Tsuboi, Yasuyuki

2015-01-01

254

Using Optical Tweezers for the Characterization of Polyelectrolyte Solutions with Very Low Viscoelasticity  

PubMed Central

Recently, optical tweezing has been used to provide a method for microrheology addressed to measure the rheological properties of small volumes of samples. In this work, we corroborate this emerging field of microrheology by using these optical methods for the characterization of polyelectrolyte solutions with very low viscoelasticity. The influence of polyelectrolyte (i.e., polyacrylamide, PAM) concentration, specifically its aging, of the salt concentration is shown. The close agreement of the technique with classical bulk rheological measurements is demonstrated, illustrating the advantages of the technique. PMID:23786307

2013-01-01

255

Towards Raman Cooling of a Single Atom in a Tightly Focused Optical Tweezer  

NASA Astrophysics Data System (ADS)

When loading a single Rb atom from a magneto-optical trap into a tightly focused optical dipole trap we infer an average kinetic energy corresponding to a temperature of tens of microkelvin from release/recapture experiments. In order to bring the atom close to the vibrational ground state of the trap with characteristic frequencies of 20-60 kHz, we implement a Raman cooling technique similar to the one commonly used in ion traps. We expect to resolve the vibrational sidebands. This will lead to a better localization of the atom in free-space atom-photon interaction experiments. We present current experimental progress towards this goal.

Lee, Jianwei; Abdullah Aljunid, Syed; Paesold, Martin; Chng, Brenda; Maslennikov, Gleb; Kurtsiefer, Christian

2010-03-01

256

Dynamic Excitations in Membranes Induced by Optical Tweezers Roy Bar-Ziv,* Elisha Moses,* and Philip Nelson#  

E-print Network

and water, with laser tweezers as the energy source. Artificial membrane vesicles made of lipids ("lipo ABSTRACT We present the phenomenology of transformations in lipid bilayers that are excited by laser picture of the laser-membrane interaction is based on the generation of tension in the bilayer and loss

Moses, Elisha

257

Sources of optically active aerosol particles over the Amazon forest  

NASA Astrophysics Data System (ADS)

Size-fractionated ambient aerosol samples were collected at a pasture site and a primary rainforest site in the Brazilian Amazon Basin during two field campaigns (April-May and September-October 1999), as part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The samples were analyzed for up to 19 trace elements by particle-induced X-ray emission analysis (PIXE), for equivalent black carbon (BC e) by a light reflectance technique and for mass concentration by gravimetric analysis. Additionally, we made continuous measurements of absorption and light scattering by aerosol particles. The vertical chemical composition gradients at the forest site have been discussed in a companion article (Journal of Geophysical Research-Atmospheres 108 (D18), 4591 (doi:4510.1029/2003JD003465)). In this article, we present the results of a source identification and quantitative apportionment study of the wet and dry season aerosols, including an apportionment of the measured scattering and absorption properties of the total aerosol in terms of the identified aerosol sources. Source apportionments (obtained from absolute principal component analysis) revealed that the wet and dry season aerosols contained the same three main components, but in different (absolute and relative) amounts: the wet season aerosol consisted mainly of a natural biogenic component, whereas pyrogenic aerosols dominated the dry season aerosol mass. The third component identified was soil dust, which was often internally mixed with the biomass-burning aerosol. All three components contributed significantly to light extinction during both seasons. At the pasture site, up to 47% of the light absorption was attributed to biogenic particles during the wet season, and up to 35% at the tower site during the wet-to-dry transition period. The results from the present study suggest that, in addition to pyrogenic particles, biogenic and soil dust aerosols must be taken into account when modeling the physical and optical properties of aerosols in forested regions such the Amazon Basin.

Guyon, Pascal; Graham, Bim; Roberts, Gregory C.; Mayol-Bracero, Olga L.; Maenhaut, Willy; Artaxo, Paulo; Andreae, Meinrat O.

258

To Study the Effect of Paclitaxel on the Cytoplasmic Viscosity of Murine Macrophage Immune Cell RAW 264.7 Using Self-Developed Optical Tweezers System  

NASA Astrophysics Data System (ADS)

In recent years, optical tweezers have become one of the tools to measure the mechanical properties of living cells. In this study, we first constructed an optical tweezers to investigate the cytoplasmic viscosity of immune cells. In addition to measuring viscosity of cells in a normal condition, we also treated cells with anti-cancer drug, Paclitaxel, and in order to study its effect on the cytoplasmic viscosity. The results showed that the viscosity decreased dramatically during the first 3 h. After 3 h, the change started to slow down and it remained nearly flat by the end of the experiment. In addition, we used the confocal laser scanning microscope to observe the cytoskeleton of the cell after drug treatment for 3 and 5 h, respectively, and found that actin filaments were disrupted and that the nucleus had disintegrated in some drug-treated cells, similar to the process of apoptosis. This study presents a new way for measuring the changes in cytoplasmic viscosity, and to determine if a cell is going into apoptosis as a result of a drug treatment.

Chen, Ying-chun; Wu, Chien-ming

2012-12-01

259

Microrheology with Optical Tweezers: Measuring the relative viscosity of solutions 'at a glance'.  

PubMed

We present a straightforward method for measuring the relative viscosity of fluids via a simple graphical analysis of the normalised position autocorrelation function of an optically trapped bead, without the need of embarking on laborious calculations. The advantages of the proposed microrheology method are evident when it is adopted for measurements of materials whose availability is limited, such as those involved in biological studies. The method has been validated by direct comparison with conventional bulk rheology methods, and has been applied both to characterise synthetic linear polyelectrolytes solutions and to study biomedical samples. PMID:25743468

Tassieri, Manlio; Giudice, Francesco Del; Robertson, Emma J; Jain, Neena; Fries, Bettina; Wilson, Rab; Glidle, Andrew; Greco, Francesco; Netti, Paolo Antonio; Maffettone, Pier Luca; Bicanic, Tihana; Cooper, Jonathan M

2015-01-01

260

Microrheology with Optical Tweezers: Measuring the relative viscosity of solutions `at a glance'  

NASA Astrophysics Data System (ADS)

We present a straightforward method for measuring the relative viscosity of fluids via a simple graphical analysis of the normalised position autocorrelation function of an optically trapped bead, without the need of embarking on laborious calculations. The advantages of the proposed microrheology method are evident when it is adopted for measurements of materials whose availability is limited, such as those involved in biological studies. The method has been validated by direct comparison with conventional bulk rheology methods, and has been applied both to characterise synthetic linear polyelectrolytes solutions and to study biomedical samples.

Tassieri, Manlio; Giudice, Francesco Del; Robertson, Emma J.; Jain, Neena; Fries, Bettina; Wilson, Rab; Glidle, Andrew; Greco, Francesco; Netti, Paolo Antonio; Maffettone, Pier Luca; Bicanic, Tihana; Cooper, Jonathan M.

2015-03-01

261

Unzipping DNA with optical tweezers: high sequence sensitivity and force flips.  

PubMed Central

Force measurements are performed on single DNA molecules with an optical trapping interferometer that combines subpiconewton force resolution and millisecond time resolution. A molecular construction is prepared for mechanically unzipping several thousand-basepair DNA sequences in an in vitro configuration. The force signals corresponding to opening and closing the double helix at low velocity are studied experimentally and are compared to calculations assuming thermal equilibrium. We address the effect of the stiffness on the basepair sensitivity and consider fluctuations in the force signal. With respect to earlier work performed with soft microneedles, we obtain a very significant increase in basepair sensitivity: presently, sequence features appearing at a scale of 10 basepairs are observed. When measured with the optical trap the unzipping force exhibits characteristic flips between different values at specific positions that are determined by the base sequence. This behavior is attributed to bistabilities in the position of the opening fork; the force flips directly reflect transitions between different states involved in the time-averaging of the molecular system. PMID:11867467

Bockelmann, U; Thomen, Ph; Essevaz-Roulet, B; Viasnoff, V; Heslot, F

2002-01-01

262

Atmospheric Aerosol Optical Properties in the Persian Gulf.  

NASA Astrophysics Data System (ADS)

Aerosol optical depth measurements over Bahrain acquired through the ground-based Aerosol Robotic Network (AERONET) are analyzed. Optical depths obtained from ground-based sun/sky radiometers showed a pronounced temporal trend, with a maximum dust aerosol loading observed during the March-July period. The aerosol optical depth probability distribution is rather narrow with a modal value of about 0.25. The Ångström parameter frequency distribution has two peaks. One peak around 0.7 characterizes a situation when dust aerosol is more dominant, the second peak around 1.2 corresponds to relatively dust-free cases. The correlation between aerosol optical depth and water vapor content in the total atmospheric column is strong (correlation coefficient of 0.82) when dust aerosol is almost absent (Ångström parameter is greater than 0.7), suggesting possible hygroscopic growth of fine mode particles or source region correlation, and much weaker (correlation coefficient of 0.45) in the presence of dust (Ångström parameter is less than 0.7). Diurnal variations of the aerosol optical depth and precipitable water were insignificant. Ångström parameter diurnal variability (20%-25%) is evident during the April-May period, when dust dominated the atmospheric optical conditions. Variations in the aerosol volume size distributions retrieved from spectral sun and sky radiance data are mainly associated with the changes in the concentration of the coarse aerosol fraction (variation coefficient of 61%). Geometric mean radii for the fine and coarse aerosol fractions are 0.14 m (std dev = 0.02) and 2.57 m (std dev = 0.27), respectively. The geometric standard deviation of each fraction is 0.41 and 0.73, respectively. In dust-free conditions the single scattering albedo (SSA) decreases with wavelength, while in the presence of dust the SSA either stays neutral or increases slightly with wavelength. The changes in the Ångström parameter derived from a ground-based nephelometer and a collocated sun photometer during the initial checkout period were quite similar.

Smirnov, Alexander; Holben, Brent N.; Dubovik, Oleg; O'Neill, Norm T.; Eck, Thomas F.; Westphal, Douglas L.; Goroch, Andreas K.; Pietras, Christophe; Slutsker, Ilya

2002-02-01

263

Surface charge and hydrodynamic coefficient measurements of {\\it Bacillus subtilis} spore by Optical Tweezers  

E-print Network

In this work we report on the simultaneous measurement of the hydrodynamic coefficient and the electric charge of single {\\it Bacillus subtilis} spores. The latter has great importance in protein binding to spores and in the adhesion of spores onto surfaces. The charge and the hydrodynamic coefficient were measured by an accurate procedure based on the analysis of the motion of single spores confined by an optical trap. The technique has been validated using charged spherical polystyrene beads. The excellent agreement of our results with the expected values demonstrates the quality of our procedure. We measured the charge of spores of {\\it B. subtilis} purified from a wild type strain and from two isogenic mutants characterized by an altered spore surface. Our technique is able to discriminate the three spore types used, by their charge and by their hydrodynamic coefficient which is related to the hydrophobic properties of the spore surface.

Giuseppe Pesce; Giulia Rusciano; Antonio Sasso; Rachele Isticato; Teja Sirec; Ezio Ricca

2014-03-18

264

Strategies for Improved CALIPSO Aerosol Optical Depth Estimates  

NASA Technical Reports Server (NTRS)

In the spring of 2010, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) project will be releasing version 3 of its level 2 data products. In this paper we describe several changes to the algorithms and code that yield substantial improvements in CALIPSO's retrieval of aerosol optical depths (AOD). Among these are a retooled cloud-clearing procedure and a new approach to determining the base altitudes of aerosol layers in the planetary boundary layer (PBL). The results derived from these modifications are illustrated using case studies prepared using a late beta version of the level 2 version 3 processing code.

Vaughan, Mark A.; Kuehn, Ralph E.; Tackett, Jason L.; Rogers, Raymond R.; Liu, Zhaoyan; Omar, A.; Getzewich, Brian J.; Powell, Kathleen A.; Hu, Yongxiang; Young, Stuart A.; Avery, Melody A.; Winker, David M.; Trepte, Charles R.

2010-01-01

265

Independent trapping and manipulation of microparticles using dexterous acoustic tweezers  

SciTech Connect

An electronically controlled acoustic tweezer was used to demonstrate two acoustic manipulation phenomena: superposition of Bessel functions to allow independent manipulation of multiple particles and the use of higher-order Bessel functions to trap particles in larger regions than is possible with first-order traps. The acoustic tweezers consist of a circular 64-element ultrasonic array operating at 2.35?MHz which generates ultrasonic pressure fields in a millimeter-scale fluid-filled chamber. The manipulation capabilities were demonstrated experimentally with 45 and 90-?m-diameter polystyrene spheres. These capabilities bring the dexterity of acoustic tweezers substantially closer to that of optical tweezers.

Courtney, Charles R. P., E-mail: c.r.p.courtney@bath.ac.uk [Department of Mechanical Engineering, University of Bath, Bath (United Kingdom); Demore, Christine E. M.; Wu, Hongxiao; Cochran, Sandy [Institute of Medical Science and Technology, University of Dundee, Dundee (United Kingdom); Grinenko, Alon; Wilcox, Paul D.; Drinkwater, Bruce W. [Department of Mechanical Engineering, University of Bristol, Bristol (United Kingdom)

2014-04-14

266

Optical Properties of Ammonium Nitrate Aerosols  

NASA Astrophysics Data System (ADS)

Warming of the Earth by greenhouse gases is offset, to some degree, by airborne particulate matter; i.e., by atmospheric aerosols. The degree of this offset is currently the greatest source of uncertainty in atmospheric radiation models used to predict climate change. In order to reduce this uncertainty, it is necessary to develop a better understanding of the abundance and physical nature of different particle species present in the aerosol, and of their radiative properties. We will present newly available data on the complex refractive index of NH_4NO_3, an important constituent of the atmospheric aerosol. We will then discuss how these data bear on lidar retrievals of aerosol loading and chemical speciation, particularly with respect to the use of a tunable, coherent, CW CO2 lidar developed at the Marshall Space Flight Center. Solid and concentrated aqueous solution aerosol will be discussed and comparisons of back scatter cross sections will be made with those of the more pervasive (NH_4)_2SO4 aerosol constituent. The utility of the Lorentz oscillator model in work of this nature will also be addressed.

Fuller, Kirk; Downing, Harry; Coffman, Rebecca; Jarzembski, Maurice; Srivastava, Vandana

2002-03-01

267

Optical extinction of highly porous aerosol following atmospheric freeze drying  

NASA Astrophysics Data System (ADS)

Porous glassy particles are a potentially significant but unexplored component of atmospheric aerosol that can form by aerosol processing through the ice phase of high convective clouds. The optical properties of porous glassy aerosols formed from a freeze-dry cycle simulating freezing and sublimation of ice particles were measured using a cavity ring down aerosol spectrometer (CRD-AS) at 532 nm and 355 nm wavelength. The measured extinction efficiency was significantly reduced for porous organic and mixed organic-ammonium sulfate particles as compared to the extinction efficiency of the homogeneous aerosol of the same composition prior to the freeze-drying process. A number of theoretical approaches for modeling the optical extinction of porous aerosols were explored. These include effective medium approximations, extended effective medium approximations, multilayer concentric sphere models, Rayleigh-Debye-Gans theory, and the discrete dipole approximation. Though such approaches are commonly used to describe porous particles in astrophysical and atmospheric contexts, in the current study, these approaches predicted an even lower extinction than the measured one. Rather, the best representation of the measured extinction was obtained with an effective refractive index retrieved from a fit to Mie scattering theory assuming spherical particles with a fixed void content. The single-scattering albedo of the porous glassy aerosols was derived using this effective refractive index and was found to be lower than that of the corresponding homogeneous aerosol, indicating stronger relative absorption at the wavelengths measured. The reduced extinction and increased absorption may be of significance in assessing direct, indirect, and semidirect forcing in regions where porous aerosols are expected to be prevalent.

Adler, Gabriela; Haspel, Carynelisa; Moise, Tamar; Rudich, Yinon

2014-06-01

268

Measuring Aerosol Optical Properties with the Ozone Monitoring Instrument (OMI)  

NASA Technical Reports Server (NTRS)

The Ozone Monitoring Instrument (OMI) is the Dutch-Finnish contribution to the NASA EOS-Aura mission scheduled for launch in January 2004. OM1 is an imaging spectrometer that will measure the back-scattered Solar radiance between 270 an 500 nm. With its relatively high spatial resolution (13x24 sq km at nadir) and daily global coverage. OM1 will make a major contribution to our understanding of atmospheric chemistry and to climate research. OM1 will provide data continuity with the TOMS instruments. One of the pleasant surprises of the TOMS data record was its information on aerosol properties. First, only the absorbing aerosol index, which is sensitive to elevated lay- ers of aerosols such as desert dust and smoke aerosols, was derived. Recently these methods were further improved to yield aerosol optical thickness and single scattering albedo over land and ocean for 19 years of TOMS data (1979-1992,1997-2002), making it one of the longest and most valuable time series for aerosols presently available. Such long time series are essential to quantify the effect of aerosols on the Earth& climate. The OM1 instrument is better suited to measure aerosols than the TOMS instruments because of the smaller footprint, and better spectral coverage. The better capabilities of OMI will enable us to provide an improved aerosol product, but the knowledge will also be used for further analysis of the aerosol record from TOMS. The OM1 aerosol product that is currently being developed for OM1 combines the TOMS experience and the multi-spectral techniques that are used in the visible and near infrared. The challenge for this new product is to provide aerosol optical thickness and single scattering albedo from the near ultraviolet to the visible (330-500 nm) over land and ocean. In this presentation the methods for deriving the OM1 aerosol product will be presented. Part of these methods developed for OM1 can already be applied to TOMS data and results of such analysis will be shown.

Veefkind, J. P.; Torres, O.; Syniuk, A.; Decae, R.; deLeeuw, G.

2003-01-01

269

Aerosol optical properties in the ABL over arctic sea ice from airborne aerosol lidar measurements  

NASA Astrophysics Data System (ADS)

Between 2009 and 2013 aerosols, sea ice properties and meteorological variables were measured during several airborne campaigns covering a wide range of the western Arctic Ocean. The campaigns were carried out with the aircraft Polar 5 of the German Alfred-Wegener-Institute (AWI) during spring and summer periods. Optical properties of accumulation mode aerosol and clouds were measured with the nadir looking AMALi aerosol lidar covering the atmospheric boundary layer and the free troposphere up to 3000m, while dropsondes provided coincident vertical profiles of meteorological quantities. Based on these data we discuss the vertical distribution of aerosol backscatter in and above the atmospheric boundary layer and its dependence on relative humidity, dynamics and underlying sea ice properties. We analyze vertical profiles of lidar and coincident dropsonde measurements from various locations in the European and Canadian Arctic from spring and summer campaigns. Sea ice cover is derived from modis satellite and aircraft onboard camera images. The aerosol load in the arctic atmospheric boundary layer shows a high variability. Various meteorological parameters and in particular boundary layer properties are discussed with their respective influence on aerosol features. To investigate the effect of the frequency and size of open water patches on aerosol properties, we relate the profiles to the sea ice properties influencing the atmosphere in the upwind region.

Schmidt, Lukas; Neuber, Roland; Ritter, Christoph; Maturilli, Marion; Dethloff, Klaus; Herber, Andreas

2014-05-01

270

Variations in organic aerosol optical and hygroscopic properties upon heterogeneous OH oxidation  

Microsoft Academic Search

Organic aerosol optical properties are not staticOrganic aerosol optical properties are directly related to the mean compositionOA hygroscopicity depends on both atomic composition and molecular volume

Christopher D. Cappa; Daphne L. Che; Sean H. Kessler; Jesse H. Kroll; Kevin R. Wilson

2011-01-01

271

Aerosol Radiative Forcing Derived From SeaWIFS - Retrieved Aerosol Optical Properties  

NASA Technical Reports Server (NTRS)

To understand climatic implications of aerosols over global oceans, the aerosol optical properties retrieved from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) are analyzed, and the effects of the aerosols on the Earth's radiation budgets (aerosol radiative forcing, ARF) are computed using a radiative transfer model. It is found that the distribution of the SeaWiFS-retrieved aerosol optical thickness is distinctively zonal. The maximum in the equatorial region coincides with the Intertropical Convergence Zone, and the maximum in the Southern Hemispheric high latitudes coincides with the region of prevailing westerlies. The minimum aerosol optical thickness is found in the subtropical high pressure regions, especially in the Southern Hemisphere. These zonal patterns clearly demonstrate the influence of atmospheric circulation on the oceanic aerosol distribution. Over global oceans, aerosols reduce the annual mean net downward solar flux by 5.4 W m-2 at the top of the atmosphere and by 6.1 W m-2 at the surface. The largest ARF is found in the tropical Atlantic, Arabian Sea, Bay of Bengal, the coastal regions of Southeast and East Asia, and the Southern Hemispheric high latitudes. During the period of the Indonesian big fires (September-December 1997), the cooling due to aerosols is greater than 15 W m-2 at the top of the atmosphere and greater than 30 W m(exp -1) at the surface in the vicinity of the maritime continents. The atmosphere receives extra solar radiation by greater than 15 W m(exp -1) over a large area. These large changes in radiative fluxes are expected to have enhanced the atmospheric stability, weakened the atmospheric circulation, and augmented the drought condition during that period. It would be very instructive to simulate the regional climatic. The model-calculated clear sky solar flux at the top of the atmosphere is compared with that derived from the Clouds and the Earth's Radiant Energy System (CERES). The net downward solar flux of CERES is systematically larger than the model calculations by -3 W M-2. In the equatorial region, the CERES-derived net downward solar flux is even larger than the model calculations without including aerosols. It is possible that the CERES incorrectly identified regions of high humidity and high aerosol concentration as being cloud contaminated and, hence, overestimated the clear sky net downward solar flux.

Chou, Mong-Dah; Chan, Pui-King; Wang, Menghua; Einaudi, Franco (Technical Monitor)

2000-01-01

272

Toward Investigating Optically Trapped Organic Aerosols with CARS Microspectroscopy  

NASA Astrophysics Data System (ADS)

The Intergovernmental Panel on Climate Change notes the huge uncertainty in the effect that atmospheric aerosols play in determining overall global temperature, specifically in their ability to nucleate clouds. To better understand aerosol chemistry, the novel coupling of gradient force optical trapping with broad bandwidth coherent anti-Stokes Raman scattering (CARS) spectroscopy is being developed to study single particles suspended in air. Building on successful designs employed separately for the techniques, this hybrid technology will be used to explain how the oxidation of organic compounds changes the chemical and physical properties of aerosols. By trapping the particles, an individual aerosol can be studied for up to several days. Using a broad bandwidth pulse for one of the incident beams will result in a Raman vibrational spectrum from every laser pulse. Combined with signal enhancement due to resonance and coherence of nonlinear CARS spectroscopy, this technique will allow for acquisition of data on the millisecond time scale, facilitating the study of dynamic processes. This will provide insights on how aerosols react with and absorb species from the gas phase. These experiments will increase understanding of aerosol oxidation and growth mechanisms and the effects that aerosols have on our atmosphere and climate. Progress in efforts developing this novel technique to study model systems is presented.

Voss, L. F.

2009-12-01

273

Background Maritime Aerosol: Their Optical Thickness and Scattering Properties  

NASA Technical Reports Server (NTRS)

The effect of human induced change in the aerosol concentration and properties, or the aerosol response to climate change (e.g. droughts producing fires or dust) should be measured relative to a "background aerosol". How to define this background aerosol, so that it is both measurable and useful? Here we use 10 stations located in the Pacific, Atlantic and Indian Oceans to answer this question. Using a data set of the spectral optical thickness measured by the Aerosol Robotic network (AERONET), extending 1-3 years, we find the background conditions for these stations. The oceanic background aerosol is the result of ocean emission and spray, and some residual long lived continental aerosol. Its source is very broadly spread and is expected to vary little in time. Pollution or dust sources are from specific locations, emitted and transported to the measuring site in specific combination of meteorological conditions. Therefore they are expected to vary with time. It follows that the background aerosol can be identified as the median for conditions with small variations. To define the background we compute the median of N consequent measurements. We use N=50 that in average cloudy conditions corresponds to 2-3 days of measurements and N=100 (4-5 days). Most high polluted or dusty conditions correspond to data sequences with high standard deviation (greater than 0.02 in optical thickness) and are excluded. From the remaining N point running medians with low standard deviations we derive again the median. This excludes those rare cases of pollution or dust that is stable during the N measurements. The results show that the background aerosol over the Pacific Ocean is characterize by optical thickness of 0.055 at 500 nm and Angstrom exponent of 0.74. Over the Atlantic Ocean the values are 0.070 and 1.1 respectively, with little influence of the assumed value of N (50 or 100). The derivation of the background uses 20,000 and 5000 medians respectively that passed the criteria. The contribution of coarse and fine aerosol to the background aerosol is also calculated.

Kaufman, Yoram J.; Smirnov, Alexander; Holben, Brent N.; Dubovik, Oleg; Einaudi, Franco (Technical Monitor)

2001-01-01

274

Black carbon aerosol mixing state, organic aerosols and aerosol optical properties over the United Kingdom  

Microsoft Academic Search

Black carbon (BC) aerosols absorb sunlight thereby leading to a positive radiative forcing and a warming of climate and can also impact human health through their impact on the respiratory system. The state of mixing of BC with other aerosol species, particularly the degree of internal\\/external mixing, has been highlighted as a major uncertainty in assessing its radiative forcing and

G. R. McMeeking; W. T. Morgan; M. Flynn; E. J. Highwood; K. Turnbull; J. Haywood; H. Coe

2011-01-01

275

Black carbon aerosol mixing state, organic aerosols and aerosol optical properties over the UK  

Microsoft Academic Search

Black carbon (BC) aerosols absorb sunlight thereby leading to a positive radiative forcing and a warming of climate and can also impact human health through their impact on the respiratory system. The state of mixing of BC with other aerosol species, particularly the degree of internal\\/external mixing, has been highlighted as a major uncertainty in assessing its radiative forcing and

G. R. McMeeking; W. T. Morgan; M. Flynn; E. J. Highwood; K. Turnbull; J. Haywood; H. Coe

2011-01-01

276

Retrieval of aerosol optical properties for cloudy scenes from METOP  

NASA Astrophysics Data System (ADS)

The retrieval of aerosol optical properties is an important task for industry and climate forecasting. An ideal instrument should include observations with moderate spectral and high spatial resolutions for a wide range of wavelengths (from the UV to the TIR), measurements of the polarization state at different wavelengths and measurements of the same scene for different observation geometries. As such an ideal instrument is currently unavailable the usage of different instruments on one satellite platform is an alternative choice. We present the Polar Multi sensor Aerosol Product (PMAp) which is delivered as operational GOME-2 product starting in February 2014. The algorithms retrieve aerosol optical depth, further aerosol classifications like volcanic ash and cloud properties (geometric cloud fraction, cloud optical depth) combining different METOP instruments like GOME-2, AVHRR and IASI. These instruments provide high spatial resolution (AVHRR), moderate and high spectral resolution in the UV/VIS range (GOME-2), measurements in the infrared (AVHRR, IASI) and the determination of the polarization state (GOME-2). The multi-sensor approach allows a simultaneous retrieval of aerosol and cloud properties for GOME pixels with cloud coverage smaller than 30%. We demonstrate the benefit of our approach by verifications and comparisons to other data products (e.g. AERONET, MODIS/Terra).

Grzegorski, Michael; Poli, Gabriele; Holdak, Andriy; Lang, Ruediger; Munro, Rosemary

2014-05-01

277

Optical properties of aerosols over the eastern Mediterranean  

NASA Astrophysics Data System (ADS)

Measurements of aerosol optical properties, size distribution and chemical composition were conducted at Finokalia, a remote coastal site on the Greek island of Crete (35°19'N, 25°40'E) during July 2000 and January 2001. During the summer campaign the total scattering coefficient, ?, (at a wavelength of 550 nm) ranged from 13 to 120 Mm -1 (mean=44.2 Mm -1, standard deviation=17.5) whilst during the winter it ranged from 7.22 to 37.8 Mm -1 (mean=18.42 Mm -1, standard deviation=6.61). A distinct diurnal variation in scattering coefficients was observed, with minima occurring during the early morning and maxima in the late afternoon during the summer and late evening during the winter. The mean value of the Ångström exponent was 1.47 during the summer and 1.28 during the winter, suggesting a larger fraction of smaller particles at the site during the summer. This was confirmed by continuous measurements of the aerosol size distribution. An analysis of the single scattering albedo suggests that there is a more absorbing fraction in the particle composition in the summer than during the winter. An investigation of air mass origins on aerosol optical properties indicated that those from Turkey and Central/Eastern Europe were highly polluted with a corresponding impact on aerosol optical properties. A linear relationship was obtained between the total scattering coefficient and both the non-sea-salt sulphate concentrations and the fine aerosol fraction.

Bryant, C.; Eleftheriadis, K.; Smolik, J.; Zdimal, V.; Mihalopoulos, N.; Colbeck, I.

278

Holographic optical tweezers  

Microsoft Academic Search

The craze for miniaturization has swept o'er most every nation, but should a hand e'er so slightly tremble no micro-machine can it assemble: and so all those really small bits leave the technicians in ts

Gabriel C. Spalding; Johannes Courtial; Roberto Di Leonardo

279

Seasonal variations in aerosol optical properties over China  

NASA Astrophysics Data System (ADS)

Seasonal variations in background aerosol optical depth (AOD) and aerosol type are investigated over various ecosystems in China based upon three years' worth of meteorological data and data collected by the Chinese Sun Hazemeter Network. In most parts of China, AODs are at a maximum in spring or summer and at a minimum in autumn or winter. Minimum values (0.10˜0.20) of annual mean AOD at 500 nm are found in the Qinghai-Tibetan Plateau, the remote northeast corner of China, the northern forest ecosystems and Hainan Island. Annual mean AOD ranges from 0.25 to 0.30 over desert and oasis areas, as well as the desertification grasslands in northern China; the annual mean AOD over the Loess Plateau is moderately high at 0.36. Regions where the highest density of agricultural and industrial activities are located and where anthropogenic sulphate aerosol and soil aerosol emissions are consistently high throughout the whole year (e.g., the central-eastern, southern and eastern coastal regions of China) experience annual mean AODs ranging from 0.50˜0.80. Remarkable seasonal changes in the main types of aerosol over northern China (characterized by the Angstrom exponent, ?) are seen. Due to biomass and fossil fuel burning from extensive agricultural practices in northern rural areas, concentrations of smoke and soot aerosols rise dramatically during autumn and winter (high ?), while the main types of aerosol during spring and summer are dust and soil aerosols (low ?). Over southeastern Asia, biomass burning during the spring leads to increases in smoke and soot emissions. Over the Tibetan Plateau and Hainan Island where the atmosphere is pristine, the main types of aerosol are dust and sea salt, respectively.

Wang, Yuesi; Xin, Jinyuan; Li, Zhanqing; Wang, Shigong; Wang, Pucai; Hao, Wei Min; Nordgren, Bryce L.; Chen, Hongbin; Wang, Lili; Sun, Yang

2011-09-01

280

The complex folding behavior of HIV-1-protease monomer revealed by optical-tweezer single-molecule experiments and molecular dynamics simulations.  

PubMed

We have used optical tweezers and molecular dynamics simulations to investigate the unfolding and refolding process of a stable monomeric form of HIV-1-protease (PR). We have characterized the behavior under tension of the native state (N), and that of the ensemble of partially folded (PF) conformations the protein visits en route to N, which collectively act as a long-lived state controlling the slow kinetic phase of the folding process. Our results reveal a rich network of unfolding events, where the native state unfolds either in a two-state manner or by populating an intermediate state I, while the PF state unravels through a multitude of pathways, underscoring its structural heterogeneity. Refolding of mechanically denatured HIV-1-PR monomers is also a multiple-pathway process. Molecular dynamics simulations allowed us to gain insight into possible conformations the protein adopts along the unfolding pathways, and provide information regarding possible structural features of the PF state. PMID:25194276

Caldarini, M; Sonar, P; Valpapuram, I; Tavella, D; Volonté, C; Pandini, V; Vanoni, M A; Aliverti, A; Broglia, R A; Tiana, G; Cecconi, C

2014-12-01

281

Hydrodynamic slip on DNA observed by optical tweezers-controlled translocation experiments with solid-state and lipid-coated nanopores.  

PubMed

We use optical tweezers to investigate the threading force on a single dsDNA molecule inside silicon-nitride nanopores between 6 and 70 nm in diameter, as well as lipid-coated solid-state nanopores. We observe a strong increase of the threading force for decreasing nanopore size that can be attributed to a significant reduction in the electroosmotic flow (EOF), which opposes the electrophoresis. Additionally, we show that the EOF can also be reduced by coating the nanopore wall with an electrically neutral lipid bilayer, resulting in an 85% increase in threading force. All experimental findings can be described by a quantitative theoretical model that incorporates a hydrodynamic slip effect on the DNA surface with a slip length of 0.5 nm. PMID:24935198

Galla, Lukas; Meyer, Andreas J; Spiering, Andre; Sischka, Andy; Mayer, Michael; Hall, Adam R; Reimann, Peter; Anselmetti, Dario

2014-07-01

282

Retrieval of Aerosol Optical Properties under Thin Cirrus from MODIS  

NASA Technical Reports Server (NTRS)

Retrieval of aerosol optical properties using shortwave bands from passive satellite sensors, such as MODIS, is typically limited to cloud-free areas. However, if the clouds are thin enough (i.e. thin cirrus) such that the satellite-observed reflectance contains signals under the cirrus layer, and if the optical properties of this cirrus layer are known, the TOA reflectance can be corrected for the cirrus layer to be used for retrieving aerosol optical properties. To this end, we first correct the TOA reflectances in the aerosol bands (0.47, 0.55, 0.65, 0.86, 1.24, 1.63, and 2.12 micron for ocean algorithm and 0.412, 0.47, and 0.65 micron for deep blue algorithm) for the effects of thin cirrus using 1.38 micron reflectance and conversion factors that convert cirrus reflectance in 1.38 micron band to those in aerosol bands. It was found that the conversion factors can be calculated by using relationships between reflectances in 1.38 micron band and minimum reflectances in the aerosol bands (Gao et al., 2002). Refer to the example in the figure. Then, the cirrus-corrected reflectance can be calculated by subtracting the cirrus reflectance from the TOA reflectance in the optically thin case. A sensitivity study suggested that cloudy-sky TOA reflectances can be calculated with small errors in the form of simple linear addition of cirrus-only reflectances and clear-sky reflectances. In this study, we correct the cirrus signals up to TOA reflectance at 1.38 micron of 0.05 where the simple linear addition is valid without extensive radiative transfer simulations. When each scene passes the set of tests shown in the flowchart, the scene is corrected for cirrus contamination and passed into aerosol retrieval algorithms.

Lee, Jaehwa; Hsu, Nai-Yung Christina; Bettenhausen, Corey; Sayer, Andrew Mark.

2014-01-01

283

Identification of stepped changes of binding affinity during interactions between the disintegrin rhodostomin and integrin ?IIb?3 in living cells using optical tweezers  

NASA Astrophysics Data System (ADS)

Integrin receptors serve as both mechanical links and signal transduction mediators between the cell and its environment. Experimental evidence demonstrates that conformational changes and lateral clustering of the integrin proteins may affect their binding to ligands and regulate downstream cellular responses; however, experimental links between the structural and functional correlations of the ligand-receptor interactions are not yet elucidated. In the present report, we utilized optical tweezers to measure the dynamic binding between the snake venom rhodostomin, coated on a microparticle and functioned as a ligand, and the membrane receptor integrin alpha(IIb)beta(3) expressed on a Chinese Hamster Ovary (CHO) cell. A progressive increase of total binding affinity was found between the bead and CHO cell in the first 300 sec following optical tweezers-guided contact. Further analysis of the cumulative data revealed the presence of "unit binding force" presumably exerted by a single rhodostomin-integrin pair. Interestingly, two such units were found. Among the measurements of less total binding forces, presumably taken at the early stage of ligand-receptor interactions, a unit of 4.15 pN per molecule pair was derived. This unit force dropped to 2.54 pN per molecule pair toward the later stage of interactions when the total binding forces were relatively large. This stepped change of single molecule pair binding affinity was not found when mutant rhodostomin proteins were used as ligands (a single unit of 1.81 pN per pair was found). These results were interpreted along with the current knowledge about the conformational changes of integrins during the "molecule activation" process.

Hsieh, Chia-Fen; Chang, Bo-Jui; Pai, Chyi-Huey; Chen, Hsuan-Yi; Chi, Sien; Hsu, Long; Tsai, Jin-Wu; Lin, Chi-Hung

2004-10-01

284

Aerosol Optical Depth over Africa retrieved from AATSR  

NASA Astrophysics Data System (ADS)

Aerosols produced over the African continent have important consequences for climate. In particular, large amounts of desert dust are produced over the Sahara and transported across the North Atlantic where desert dust deposition influences the eco system by iron fertilization, and further North over Europe with outbreaks as far as Scandinavia. Biomass burning occurs in most of the African continent south of the Sahara and causes a net positive radiating forcing resulting in local warming of the atmosphere layers. These effects have been studied during large field campaigns. Satellites can systematically provide information on aerosols over a large area such as Africa and beyond. To this end, we retrieved the Aerosol Optical Depth (AOD) at three wavelengths (555nm, 670nm, and 1600nm) over Africa from the reflectance measured at the top of the atmosphere by the AATSR (Advances Along Track Scanning Radiometer) flying on ENVISAT, for one year (1 May 2008 to 30 April 2009) to obtain information on the seasonal and spatial behaviour of the AOD, episodes of high AOD events and connect the retrieved AOD with the ground-based aerosol measurements. The AOD retrieval algorithm, which is applied to cloud-free pixels over land, is based on the comparison of the measured and modeled reflectance at the top of the atmosphere (TOA). The algorithm uses look-up-tables (LUTs) to compute the modeled TOA reflectance. For AOD retrieval, an aerosol in the atmosphere is assumed to be an external mixture of fine and coarse mode particles. The two aerosol types are mixed such that the spectral behavior of the reflectance due to aerosol best fits the measurements. Comparison with AERONET (Aerosol Roboric NETwork), which is a network of ground-based sun photometers which measure atmospheric aerosol properties, shows good agreement but with some overestimation of the AATSR retrieved AOD. Different aerosol models have been used to improve the comparison. The lack of AERONET stations in Africa, its location in similar-type environments, while Africa is a continent with desert-to-rainforest lands with steppe, savanna, woodlands in between, makes it difficult to select the most appropriate aerosol types in the retrieval. We aim to find the connection of the aerosol types used in retrieval with the seasonality (rainy season, dry season, biomass burning season) and air mass transport (e.g., transport of Sahara dust).

Sogacheva, Larisa; de Leeuw, Gerrit; Kolmonen, Pekka; Sundström, Anu-Maija; Rodriques, Edith

2010-05-01

285

Correction to “Hyperspectral Aerosol Optical Depths from TCAP Flights”  

SciTech Connect

In the paper “Hyperspectral aerosol optical depths from TCAP flights” by Y. Shinozuka et al. (Journal of Geophysical Research: Atmospheres, 118, doi:10.1002/2013JD020596, 2013), Tables 1 and 2 were published with the column heads out of order. Tables 1 and 2 are published correctly here. The publisher regrets the error.

Shinozuka, Yohei; Johnson, Roy R.; Flynn, Connor J.; Russell, P. B.; Schmid, Beat; Redemann, Jens; Dunagan, Stephen; Kluzek, Celine D.; Hubbe, John M.; Segal-Rosenheimer, Michal; Livingston, J. M.; Eck, T.; Wagener, Richard; Gregory, L.; Chand, Duli; Berg, Larry K.; Rogers, Ray; Ferrare, R. A.; Hair, John; Hostetler, Chris A.; Burton, S. P.

2014-02-16

286

Aerosol optical properties over the midcontinental United States  

Microsoft Academic Search

This work is part of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE), an international land-surface-atmosphere experiment aimed at improving the way climate models represent energy, water, heat, and carbon exchanges, and improving the utilization of satellite based remote sensing to monitor such parameters. Here the authors report on measurements of aerosol optical depth over the

R. N. Halthore; B. L. Markham; R. A. Ferrare; T. O. Aro

1992-01-01

287

Optical and radiative-transfer properties of mixed atmospheric aerosols  

NASA Astrophysics Data System (ADS)

The optical and radiative-transfer properties of mixed atmospheric aerosols have been investigated. The aerosol medium is considered as a plane-parallel anisotropic scattering medium with diffusive reflecting boundaries and containing an internal radiation source. The basic components are defined by their complex refractive index, a lognormal size distribution and humidity dependence in hygroscopic particles. The aerosol particles are assumed to be spherical, so the scattering parameters in the form of single scattering albedo, asymmetry factor, scattering, absorption, extinction efficiencies and linear anisotropic coefficient are calculated using the Mie theory. The calculations have been performed for individual aerosol particles, internal and external mixing media. Radiation transfer problem through the considered aerosol medium has been solved in terms of the solution of the corresponding source-free problem with simple boundary conditions. For the solution of the source-free problem, the Variational Pomraning-Eddington technique has been employed. The variation of the radiative-transfer properties (partial radiative fluxes at the medium boundaries) have been calculated and represented graphically for the different aerosols with their different mixing states. A comparison of the obtained results versus available published data has been performed and a very good agreement was observed.

Degheidy, A. R.; Sallah, M.; Elgarayhi, A.; Shaaban, S. M.

2015-04-01

288

Effect of Dust and Anthropogenic Aerosols on Columnar Aerosol Optical Properties over Darjeeling (2200 m asl), Eastern Himalayas, India  

PubMed Central

Background The loading of atmospheric particulate matter (aerosol) in the eastern Himalaya is mainly regulated by the locally generated anthropogenic aerosols from the biomass burning and by the aerosols transported from the distance sources. These different types of aerosol loading not only affect the aerosol chemistry but also produce consequent signature on the radiative properties of aerosol. Methodology/Principal Findings An extensive study has been made to study the seasonal variations in aerosol components of fine and coarse mode aerosols and black carbon along with the simultaneous measurements of aerosol optical depth on clear sky days over Darjeeling, a high altitude station (2200 masl) at eastern Himalayas during the year 2008. We observed a heavy loading of fine mode dust component (Ca2+) during pre-monsoon (Apr – May) which was higher by 162% than its annual mean whereas during winter (Dec – Feb), the loading of anthropogenic aerosol components mainly from biomass burning (fine mode SO42? and black carbon) were higher (76% for black carbon and 96% for fine mode SO42?) from their annual means. These high increases in dust aerosols during pre-monsoon and anthropogenic aerosols during winter enhanced the aerosol optical depth by 25 and 40%, respectively. We observed that for every 1% increase in anthropogenic aerosols, AOD increased by 0.55% during winter whereas for every 1% increase in dust aerosols, AOD increased by 0.46% during pre-monsoon. Conclusion/Significance The natural dust transport process (during pre-monsoon) plays as important a role in the radiation effects as the anthropogenic biomass burning (during winter) and their differential effects (rate of increase of the AOD with that of the aerosol concentration) are also very similar. This should be taken into account in proper modeling of the atmospheric environment over eastern Himalayas. PMID:22792264

Chatterjee, Abhijit; Ghosh, Sanjay K.; Adak, Anandamay; Singh, Ajay K.; Devara, Panuganti C. S.; Raha, Sibaji

2012-01-01

289

Aerosol particle vertical distributions and optical properties over Singapore  

NASA Astrophysics Data System (ADS)

As part of the Seven Southeast Asian Studies (7SEAS) program, an Aerosol Robotic Network (AERONET) sun photometer and a Micro-Pulse Lidar Network (MPLNET) instrument have been deployed at Singapore to study the regional aerosol environment of the Maritime Continent (MC). Using coincident AERONET Level 2.0 and MPLNET Level 2.0a data from 24 September 2009 to 31 March 2011, the seasonal variability of aerosol particle vertical distributions and optical properties is examined. On average, the bulk (˜65%) of aerosol extinction is found below 1.5 km with substantial aerosol loading (˜35%) above. Possibly due to the transition from El Niño to La Niña conditions and subsequent reduction in fire events, the MPLNET mean integrated aerosol extinction is observed to be the lowest for July-September 2010, which coincides with the typical MC biomass burning season. On the other hand, the highest mean integrated extinctions are derived for January-March 2010 and 2011, which can be attributed to off-season MC biomass burning smoke and anthropogenic pollution. The seasonal lidar ratios also show higher occurrences ?60 sr, which are indicative of biomass burning smoke, for October 2009-June 2010, but such occurrences decrease from July 2010 to March 2011 when La Niña conditions prevail. In addition, principal component analysis (PCA) identifies five primary aerosol vertical profile types over Singapore, i.e. strongly-capped/deep near-surface layer (SCD; 0-1.35 km), enhanced mid-level layer (EML; 1.35-2.4 km), enhanced upper-level layer (EUL; 2.4-3.525 km), deep contiguous layer (DCL; 3.525-4.95 km) and deep multi-layer (DML; >4.95 km). PCA also identifies an off-season MC biomass burning smoke event from 22 February to 8 March 2010, which is subsequently examined in detail.

Chew, Boon Ning; Campbell, James R.; Salinas, Santo V.; Chang, Chew Wai; Reid, Jeffrey S.; Welton, Ellsworth J.; Holben, Brent N.; Liew, Soo Chin

2013-11-01

290

Seasonal variability of aerosol optical depth over Indian subcontinent  

USGS Publications Warehouse

Ganga basin extends 2000 km E-W and about 400 km N-S and is bounded by Himalayas in the north. This basin is unequivocally found to be affected by high aerosols optical depth (AOD) (>0.6) throughout the year. Himalayas restricts movement of aerosols toward north and as a result dynamic nature of aerosol is seen over the Ganga basin. High AOD in this region has detrimental effects on health of more than 460 million people living in this part of India besides adversely affecting clouds formation, monsoonal rainfall pattern and Normalized Difference Vegetation Index (NDVI). Severe drought events (year 2002) in Ganga basin and unexpected failure of monsoon several times, occurred in different parts of Indian subcontinent. Significant rise in AOD (18.7%) over the central part of basin (Kanpur region) have been found to cause substantial decrease in NDVI (8.1%) since 2000. A negative relationship is observed between AOD and NDVI, magnitude of which differs from region to region. Efforts have been made to determine general distribution of AOD and its dominant departure in recent years spatially using Moderate Resolution Imaging Spectroradiometer (MODIS) data. The seasonal changes in aerosol optical depth over the Indo-Gangetic basin is found to very significant as a result of the increasing dust storm events in recent years. ?? 2005 IEEE.

Prasad, A.K.; Singh, R.P.; Singh, A.; Kafatos, M.

2005-01-01

291

Cloud-Driven Changes in Aerosol Optical Properties - Final Technical Report  

SciTech Connect

The optical properties of aerosol particles are the controlling factors in determining direct aerosol radiative forcing. These optical properties depend on the chemical composition and size distribution of the aerosol particles, which can change due to various processes during the particles’ lifetime in the atmosphere. Over the course of this project we have studied how cloud processing of atmospheric aerosol changes the aerosol optical properties. A counterflow virtual impactor was used to separate cloud drops from interstitial aerosol and parallel aerosol systems were used to measure the optical properties of the interstitial and cloud-scavenged aerosol. Specifically, aerosol light scattering, back-scattering and absorption were measured and used to derive radiatively significant parameters such as aerosol single scattering albedo and backscatter fraction for cloud-scavenged and interstitial aerosol. This data allows us to demonstrate that the radiative properties of cloud-processed aerosol can be quite different than pre-cloud aerosol. These differences can be used to improve the parameterization of aerosol forcing in climate models.

Ogren, John A.; Sheridan, Patrick S.; Andrews, Elisabeth

2007-09-30

292

Quantifying Aerosol Direct Effects from Broadband Irradiance and Spectral Aerosol Optical Depth Observations  

SciTech Connect

We outline a methodology using broadband and spectral irradiances to quantify aerosol direct effects on the surface diffuse shortwave (SW) irradiance. Best Estimate Flux data span a 13 year timeframe at the Department of Energy Atmospheric Radiation Measurement Program’s Southern Great Plains (SGP) site. Screened clear-sky irradiances and aerosol optical depth (AOD), for solar zenith angles ? 65°, are used to estimate clear-sky diffuse irradiances. We validate against detected clear-sky observations from SGP’s Basic Radiation System (BRS). BRS diffuse irradiances were in accordance with estimates, producing a root-mean-square error and mean bias errors of 4.0 W/m2 and -1.4 W/m2, respectively. Absolute differences show 99% of estimates within ±10 W/m2 (10%) of the mean BRS observations. Clear-sky diffuse estimates are used to derive quantitative estimates of aerosol radiative effects, represented as the aerosol diffuse irradiance (ADI). ADI is the contribution of diffuse SW to global SW, attributable to scattering of atmospheric transmission by natural plus anthropogenic aerosols. Estimated slope for the ADI as a function of AOD indicates an increase of ~22 W/m2 in diffuse SW for every 0.1 increase in AOD. Such significant increases in the diffuse fraction could possibly increase photosynthesis. Annual mean ADI is 28.2 W/m2, and heavy aerosol loading at SGP provides up to a maximum increase of 120 W/m2 in diffuse SW over background conditions. With regard to seasonal variation, the mean diffuse forcings are 17.2, 33.3, 39.0, and 23.6 W/m2 for winter, spring, summer, and fall, respectively.

Creekmore, Torreon N.; Joseph, Everette; Long, Charles N.; Li, Siwei

2014-05-16

293

Evaluating UVA aerosol optical depth using a smartphone camera.  

PubMed

This research evaluates a smartphone complementary metal oxide semiconductor (CMOS) image sensor's ability to detect and quantify incident solar UVA radiation and subsequently, aerosol optical depth at 340 and 380 nm. Earlier studies revealed that the consumer grade CMOS sensor has inherent UVA sensitivities, despite attenuating effects of the lens. Narrow bandpass and neutral density filters were used to protect the image sensor and to not allow saturation of the solar images produced. Observations were made on clear days, free from clouds. The results of this research demonstrate that there is a definable response to changing solar irradiance and aerosol optical depth can be measured within 5% and 10% error margins at 380 and 340 nm respectively. The greater relative error occurs at lower wavelengths (340 nm) due to increased atmospheric scattering effects, particularly at higher air masses and due to lower signal to noise ratio in the image sensor. The relative error for solar irradiance was under 1% for observations made at 380 nm. The results indicate that the smartphone image sensor, with additional external narrow bandpass and neutral density filters can be used as a field sensor to evaluate solar UVA irradiance and aerosol optical depth. PMID:23581749

Igoe, Damien P; Parisi, Alfio V; Carter, Brad

2013-01-01

294

Investigating Molecular Level Stress-Strain Relationships in Entangled F-Actin Networks by Combined Force-Measuring Optical Tweezers and Fluorescence Microscopy  

NASA Astrophysics Data System (ADS)

Actin is an important cytoskeletal protein involved in cell structure and motility, cancer invasion and metastasis, and muscle contraction. The intricate viscoelastic properties of filamentous actin (F-actin) networks allow for the many dynamic roles of actin, thus warranting investigation. Exploration of this unique stress-strain/strain-rate relationship in complex F-actin networks can also improve biomimetic materials engineering. Here, we use optical tweezers with fluorescence microscopy to study the viscoelastic properties of F-actin networks on the microscopic level. Optically trapped microspheres embedded in various F-actin networks are moved through the network using a nanoprecision piezoelectric stage. The force exerted on the microspheres by the F-actin network and subsequent force relaxation are measured, while a fraction of the filaments in the network are fluorescent-labeled to observe filament deformation in real-time. The dependence of the viscoelastic properties of the network on strain rates and amplitudes as well as F-actin concentration is quantified. This approach provides the much-needed link between induced force and deformation over localized regimes (tens of microns) and down to the single molecule level.

Lee, Kent; Henze, Dean; Robertson-Anderson, Rae M.

2013-03-01

295

Optical Properties of Mixed Black Carbon, Inorganic and Secondary Organic Aerosols  

SciTech Connect

Summarizes the achievements of the project, which are divided into four areas: 1) Optical properties of secondary organic aerosols; 2) Development and of a polar nephelometer to measure aerosol optical properties and theoretical approaches to several optical analysis problems, 3) Studies on the accuracy of measurements of absorbing carbon by several methods, and 4) Environmental impacts of biodiesel.

Paulson, S E

2012-05-30

296

Can satellite-derived aerosol optical depth quantify the surface aerosol radiative forcing?  

NASA Astrophysics Data System (ADS)

Aerosols play an important role in the climate of the Earth through aerosol radiative forcing (ARF). Nowadays, aerosol particles are detected, quantified and monitored by remote sensing techniques using low Earth orbit (LEO) and geostationary (GEO) satellites. In the present article, the use of satellite-derived AOD (aerosol optical depth) products is investigated in order to quantify on a daily basis the ARF at the surface level (SARF). By daily basis we mean that an average SARF value is computed every day based upon the available AOD satellite measurements for each station. In the first part of the study, the performance of four state-of-art different AOD products (MODIS-DT, MODIS-DB, MISR, and SEVIRI) is assessed through comparison against ground-based AOD measurements from 24 AERONET stations located in Europe and Africa during a 6-month period. While all AOD products are found to be comparable in terms of measured value (RMSE of 0.1 for low and average AOD values), a higher number of AOD estimates is made available by GEO satellites due to their enhanced frequency of scan. Experiments show a general lower agreement of AOD estimates over the African sites (RMSE of 0.2), which show the highest aerosol concentrations along with the occurrence of dust aerosols, coarse particles, and bright surfaces. In the second part of this study, the lessons learned about the confidence in aerosol burden derived from satellites are used to estimate SARF under clear sky conditions. While the use of AOD products issued from GEO observations like SEVIRI brings improvement in the SARF estimates with regard to LEO-based AOD products, the resulting absolute bias (13 W/m2 in average when AERONET AOD is used as reference) is judged to be still high in comparison with the average values of SARF found in this study (from - 25 W/m2 to - 43 W/m2) and also in the literature (from - 10 W/m2 to - 47 W/m2).

Xu, Hui; Ceamanos, Xavier; Roujean, Jean-Louis; Carrer, Dominique; Xue, Yong

2014-12-01

297

The contribution of different aerosol sources to the Aerosol Optical Depth in Hong Kong  

NASA Astrophysics Data System (ADS)

The contribution of major aerosol components emitted from local and remote regions to Hong Kong's Aerosol Optical Depth (AOD) in 2007 is quantitatively determined using the chemical transport model GOCART (Global Ozone Chemistry Aerosol Radiation and Transport). Of the major aerosol components, sulphur has the largest influence (68%) on Hong Kong, followed by organic carbon (OC, 13%) and dust (11%), and the influences of black carbon (BC, 5%) and sea salt (3%) are the lowest. The highest AOD is seen in September 2007 and is composed mainly of sulphur aerosols (85%). The high AOD values in March and April 2007 are caused by sulphur and OC. OC has a relative contribution of 39% in March and 30% in April. The anthropogenic sulphur, BC, and OC emitted from every continent, as well as from China and South China, are considered respectively. In summer, South China's contribution of sulphur aerosols from anthropogenic SO2 emissions to the total sulphur AOD in Hong Kong is more than 20%. In other seasons, sulphur aerosols from anthropogenic SO2 emissions in Rest China (all of China except South China) accounts for more than 25%. Anthropogenic BC from South China accounts for more than 20% of total BC AOD in Hong Kong in summer. The contribution of anthropogenic BC from Rest China exceeds 40% in autumn and winter. Anthropogenic BC from Rest Asia (all of Asia except China) accounts for more than 30% in summer and autumn. The contribution of anthropogenic OC from Rest China is more than 35% in autumn and winter. The contribution of anthropogenic OC from Rest Asia exceeds 20% in summer. Gobi dust accounts for more than 40% of the total dust AOD in winter, and its impact appears mainly in the Atmospheric Boundary Layer (ABL), where it is responsible for 50% of the dust concentration. The contribution of Sahara dust to the dust AOD in spring exceeds 35%, and its contribution to the dust concentration in the free atmosphere (40%) is larger than that in the ABL (10%). More than 35% of the dust AOD in summer and autumn comes from Taklamakan dust, which exists mainly in the free atmosphere, where it accounts for 40% of the dust concentration.

Zhang, Zhenxi; Wenig, Mark; Zhou, Wen; Diehl, Thomas; Chan, Ka-Lok; Wang, Lingna

2014-02-01

298

Simulations of the Aerosol Index and the Absorption Aerosol Optical Depth and Comparisons with OMI Retrievals During ARCTAS-2008 Campaign  

NASA Technical Reports Server (NTRS)

We have computed the Aerosol Index (AI) at 354 nm, useful for observing the presence of absorbing aerosols in the atmosphere, from aerosol simulations conducted with the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) module running online the GEOS-5 Atmospheric GCM. The model simulates five aerosol types: dust, sea salt, black carbon, organic carbon and sulfate aerosol and can be run in replay or data assimilation modes. In the assimilation mode, information's provided by the space-based MODIS and MISR sensors constrains the model aerosol state. Aerosol optical properties are then derived from the simulated mass concentration and the Al is determined at the OMI footprint using the radiative transfer code VLIDORT. In parallel, model derived Absorption Aerosol Optical Depth (AAOD) is compared with OMI retrievals. We have focused our study during ARCTAS (June - July 2008), a period with a good sampling of dust and biomass burning events. Our ultimate goal is to use OMI measurements as independent validation for our MODIS/MISR assimilation. Towards this goal we document the limitation of OMI aerosol absorption measurements on a global scale, in particular sensitivity to aerosol vertical profile and cloud contamination effects, deriving the appropriate averaging kernels. More specifically, model simulated (full) column integrated AAOD is compared with model derived Al, this way identifying those regions and conditions under which OMI cannot detect absorbing aerosols. Making use of ATrain cloud measurements from MODIS, C1oudSat and CALIPSO we also investigate the global impact on clouds on OMI derived Al, and the extent to which GEOS-5 clouds can offer a first order representation of these effects.

2010-01-01

299

Optical Absorptivity versus Molecular Composition of Model Organic Aerosol Matter  

NASA Astrophysics Data System (ADS)

Aerosol particles affect the Earth's energy balance by absorbing and scattering radiation according to their chemical composition, size, and shape. It is generally believed that their optical properties could be deduced from the molecular composition of the complex organic matter contained in these particles, a goal pursued by many groups via high-resolution mass spectrometry, although: (1) absorptivity is associated with structural chromophores rather than with molecular formulas, (2) compositional space is a small projection of structural space, and (3) mixtures of polar polyfunctional species usually exhibit supramolecular interactions. Here we report a suite of experiments showing that the photolysis of aqueous pyruvic acid (a proxy for aerosol ?-dicarbonyls absorbing at ? > 300 nm) generates mixtures of identifiable aliphatic polyfunctional oligomers that develop absorptions in the visible upon standing in the dark. These absorptions and their induced fluorescence emissions can be repeatedly bleached and retrieved without carbon loss or ostensible changes in the electrospray mass spectra of the corresponding mixtures and display unambiguous signatures of supramolecular effects. The nonlinear additivity of the properties of the components of these mixtures supports the notion that full structural speciation is insufficient and possibly unnecessary for understanding the optical properties of aerosol particles and their responses to changing ambient conditions.

Rincón, Angela G.; Guzmán, Marcelo I.; Hoffmann, M. R.; Colussi, A. J.

2009-08-01

300

Optical and microphysical properties of atmospheric aerosols in Moldova  

NASA Astrophysics Data System (ADS)

Measurements of aerosol properties in Kishinev, Moldova are being carried out within the framework of the international AERONET program managed by NASA/GSFC since 1999. Direct solar and sky diffuse radiances are measured by using of sunphotometer Cimel-318. Aerosol optical properties are retrieved from measured radiances by using of smart computational procedures developed by the AERONET's team. The instrument is situated at the ground-based solar radiation monitoring station giving the opportunity to make simultaneous spectral (win sunphotometer) and broadband (with the set of sensors from radiometric complex) solar radiation. Detailed description of the station and investigations in progress can be found at the http://arg.phys.asm.md. Ground station is placed in an urban environment of Kishinev city (47.00N; 28.56E; 205 m a.s.l). Summary of aerosol optical and microphysical properties retrieved from direct solar and diffuse sky radiance observations at Moldova site from September 1999 to June 2009 are presented below. Number of measurements (total): 1695 Number of measurements (for ?o, n, k): 223 Range of aerosol optical depth (AOD) @440 nm: 0.03 < ?(440) < 2.30, < ?(440)>=0.25 Range of Ångström parameter < ?440_870 >: 0.14 < ? < 2.28 Asymmetry factor (440/670/870/1020): 0.70/0.63/0.59/0.58 ±0.04 Refraction (n) and absorption (k) indices@440 nm: 1.41 ± 0.06; 0.009 ± 0.005 Single scattering albedo < ?o >(440/670/870/1020): 0.93/0.92/0.90/0.89 ±0.04 Parameters of volume particle size distribution function: (fine mode) volume median radius r v,f , ?m: 0.17 ± 0.06 particle volume concentration Cv,f, ?m3/?m2: 0.04 ± 0.03 (coarse mode) volume median radius rv,c , ?m: 3.08 ± 0.64 particle volume concentration Cv,c, ?m3/?m2: 0.03 ± 0.03 Climatic norms of AOD@500 nm and Ångström parameter < ?440_870 > at the site of observation are equal to 0.21 ± 0.06 and 1.45 ± 0.14, respectively. The aerosol type in Moldova may be considered as 'urban-industrial and mixed' in accordance with the classification of aerosol type models systematized and developed by AERONET team (O.Dubovik et al., 2002, J. Atmosph. Sci., 59, 590-608) on the basis of datasets acquired from worldwide observations at the network of sunphotometers. It should be noted the presence of increased value of absorption index and reduced values of albedo. This may be due to influence of absorptive aerosols (soot). These aerosols are originated from local dust sources and exhausts from intensive urban traffic, from sources of biomass and household garbage burning both in and around the city, and from long-range transport over regions with high loading of aerosols (dust, smoke).

Aculinin, Alexandr; Smicov, Vladimir

2010-05-01

301

Variability of Absorption and Optical Properties of Key Aerosol Types Observed in Worldwide Locations  

Microsoft Academic Search

Aerosol radiative forcing is a critical, though variable and uncertain, component of the global climate. Yet climate models rely on sparse information of the aerosol optical properties. In situ measurements, though important in many respects, seldom provide measurements of the undisturbed aerosol in the entire atmospheric column. Here, 8 yr of worldwide distributed data from the AERONET network of ground-based

Oleg Dubovik; Brent Holben; Thomas F. Eck; Alexander Smirnov; Yoram J. Kaufman; Michael D. King; Didier Tanré; Ilya Slutsker

2002-01-01

302

AEROSOL OPTICAL DEPTH RETRIEVAL OVER LAND FROM NOAA AVHRR: SENSITIVITY STUDIES  

Microsoft Academic Search

The large archive of NOAA AVHRR data, covering more than 25 years, bears the potential to detect aerosol trends. However, remote sensing of aerosol optical depth over land is a difficult task, because the aerosol signal gets weaker over bright surface targets and the quality of the retrieval mainly depends on the quality of the surface reflectance estimate. In this

Michael Riffler; Christoph Popp; Adrian Hauser; Stefan Wunderle

303

Compiled aerosol optical depth and extinction-to-backscatter climatology for Tucson, AZ  

Microsoft Academic Search

The Aeronet network has had a wide-ranging impact on the study of atmospheric aerosols, both temporally and geographically. This paper examines the results of measurements from the Aeronet network from a radiometer deployed in Tucson, Arizona during 1999 and 2000. Monthly averages of aerosol optical depth and Angstrom parameter values are presented. These show that a maximum in aerosol loading

Matthew E. Mavko; Kurtis J. Thome; John A. Reagan

2003-01-01

304

Tropospheric Aerosol Optical Thickness from the GOCART Model and Comparisons with Satellite and Sun Photometer Measurements  

Microsoft Academic Search

The Georgia Institute of Technology-Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model is used to simulate the aerosol optical thickness for major types of tropospheric aerosols including sulfate, dust, organic carbon (OC), black carbon (BC), and sea salt. The GOCART model uses a dust emission algorithm that quantifies the dust source as a function of the degree of

Mian Chin; Paul Ginoux; Stefan Kinne; Omar Torres; Brent N. Holben; Bryan N. Duncan; Randall V. Martin; Jennifer A. Logan; Akiko Higurashi; Teruyuki Nakajima

2002-01-01

305

Regional quantitative retrieval of aerosol optical depth by exploiting the synergy of VISSR and MODIS data  

Microsoft Academic Search

Atmospheric aerosol particles influence the Earth's radiation balance directly by scattering of infrared energy and indirectly by modifying the properties of clouds through microphysical processes. For the sake of effectively monitoring it, many atmospheric aerosol observation networks are set up and provide associated informational services in the wide world. However, the aerosol optical depth show large spatial and temporal variations

Linyan Bai; Jianzhong Feng

2010-01-01

306

Nephelometer derived and directly measured aerosol optical depth of the atmospheric boundary layer  

Microsoft Academic Search

The aerosol optical depth of the atmospheric boundary layer was determined both from direct solar irradiance measurements and from vertical extrapolation of ground-based nephelometry, during a period with cloudless skies and high aerosol mass loadings in the Netherlands. The vertical profile of the aerosol was obtained from lidar measurements. From humidity controlled nephelometry at the ground and humidity profiles from

J. P. Veefkind; J. C. H. van der Hage; H. M. ten Brink

1996-01-01

307

The active digestion of uniparental chloroplast DNA in a single zygote of Chlamydomonas reinhardtii is revealed by using the optical tweezer  

PubMed Central

The non-Mendelian inheritance of organelle genes is a phenomenon common to almost all eukaryotes, and in the isogamous alga Chlamydomonas reinhardtii, chloroplast (cp) genes are transmitted from the mating type positive (mt+) parent. In this study, the preferential disappearance of the fluorescent cp nucleoids of the mating type negative (mt?) parent was observed in living young zygotes. To study the change in cpDNA molecules during the preferential disappearance, the cpDNA of mt+ or mt? origin was labeled separately with bacterial aadA gene sequences. Then, a single zygote with or without cp nucleoids was isolated under direct observation by using optical tweezers and investigated by nested PCR analysis of the aadA sequences. This demonstrated that cpDNA molecules are digested completely during the preferential disappearance of mt? cp nucleoids within 10 min, whereas mt+ cpDNA and mitochondrial DNA are protected from the digestion. These results indicate that the non-Mendelian transmission pattern of organelle genes is determined immediately after zygote formation. PMID:10535964

Nishimura, Yoshiki; Misumi, Osami; Matsunaga, Sachihiro; Higashiyama, Tetsuya; Yokota, Akiho; Kuroiwa, Tsuneyoshi

1999-01-01

308

Aerosol direct radiative effect on solar radiation on planetary scale based on 7-year spectral aerosol optical properties from MODIS  

NASA Astrophysics Data System (ADS)

Atmospheric aerosols, both natural and anthropogenic, can cause climate change through their direct, indirect and semi-direct effects on the radiative energy budget of the Earth-atmosphere system. However, the quantification of the aerosol effects is difficult because aerosol physical, chemical and optical properties are highly variable in space and time. Another difficulty is the lack of continuous and long-term measurements of aerosol properties. In the present study the mean monthly direct radiative effect (DRE) of aerosols on solar radiation is estimated on global scale for a 7-year period (March 2000 - February 2007), by using a deterministic spectral radiation transfer model and long-term satellite spectral aerosol data. The model uses climatological input data for various surface and atmospheric parameters, taken from the International Satellite Cloud Climatology Project (ISCCP-D2), the National Centers for Environmental Prediction - National Center for Atmospheric Research (NCEP-NCAR) Global Reanalysis project, and other global data bases. The aerosol DRE computations are performed in the ultraviolet, visible and near-infrared, spanning the total shortwave (SW) spectral range 0.2-10 m. The model computes the aerosol effect on the SW radiation budget of the Earth-atmosphere system, namely at the top of atmosphere (TOA reflected solar radiation), within the atmosphere (absorbed solar radiation), and at the surface (incoming and absorbed solar radiation). The multiyear global distributions of spectral aerosol optical properties (aerosol optical depth, AOD, asymmetry parameter, gaer, and single scattering albedo, ?aer), which are of primary importance for aerosol DREs, are taken from the MODerate resolution Imaging Spectroradiometer (MODIS) of NASA (National Aeronautics and Space Administration) and they are supplemented by the Global Aerosol Data Set (GADS). More specifically, we use MODIS AOD and gaer data at 7 wavelengths extending from 470 to 2130 nm, over land and ocean. The computations of aerosol DREs are performed at a spatial resolution of 2.5°x2.5° latitude-longitude. According to the model results, the 7-year global mean aerosol direct radiative effect on the outgoing (reflected) SW radiation at TOA (DRETOA) is equal -2.88 W/m2, indicating thus a significant planetary cooling. At the regional scale, however, the cooling effect is much stronger, while a planetary warming is found over highly reflecting surfaces like deserts. The global effect of aerosols on the atmospheric absorption of SW radiation (DREatmab) is equal to 3.94 W/m2, indicating an atmospheric warming due to aerosols. In addition, aerosols are found to decrease the downward SW radiation at the Earth's surface (FSurfDown) by -7.97 W/m2, producing thus a very important surface radiative cooling. Based on the model computations, the inter-annual change of aerosol DRE from 2000 to 2007 is -3.7% for DRETOA (less aerosol planetary cooling), -13.4% for DREatmab (less aerosol atmospheric warming) and -10.4% for DREsurf (less aerosol surface cooling). Our results indicate that a significant reduction in the magnitude of aerosol radiative effects has taken place from 2000 to 2007, which is primarily due to a corresponding decrease in aerosol loads over many world regions, Asian, European and American countries included.

Papadimas, C. D.; Hatzianastassiou, N.; Matsoukas, C.; Vardavas, I.

2009-04-01

309

The Optical Constants of Several Atmospheric Aerosol Species: Ammonium Sulfate, Aluminum Oxide, and Sodium Chloride  

Microsoft Academic Search

The optical constants of substances composing atmospheric aerosols are required to evaluate properly the effects of aerosols on the earth's radiation balance. We briefly review techniques for determining optical constants and also discuss pitfalls in using measured optical constants to simulate the optical constants of the real particles found in the atmosphere. We then compile the optical constants of (NH4hSO4,

Owen B. Toon; James B. Pollack; Bishun N. Khare

1976-01-01

310

Optoelectronic tweezers for microparticle and cell manipulation  

NASA Technical Reports Server (NTRS)

An optical image-driven light induced dielectrophoresis (DEP) apparatus and method are described which provide for the manipulation of particles or cells with a diameter on the order of 100 .mu.m or less. The apparatus is referred to as optoelectric tweezers (OET) and provides a number of advantages over conventional optical tweezers, in particular the ability to perform operations in parallel and over a large area without damage to living cells. The OET device generally comprises a planar liquid-filled structure having one or more portions which are photoconductive to convert incoming light to a change in the electric field pattern. The light patterns are dynamically generated to provide a number of manipulation structures that can manipulate single particles and cells or groups of particles/cells. The OET preferably includes a microscopic imaging means to provide feedback for the optical manipulation, such as detecting position and characteristics wherein the light patterns are modulated accordingly.

Wu, Ming Chiang (Inventor); Chiou, Pei Yu (Inventor); Ohta, Aaron T. (Inventor)

2009-01-01

311

Optoelectronic Tweezers for Microparticle and Cell Manipulation  

NASA Technical Reports Server (NTRS)

An optical image-driven light induced dielectrophoresis (DEP) apparatus and method are described which provide for the manipulation of particles or cells with a diameter on the order of 100 micromillimeters or less. The apparatus is referred to as optoelectric tweezers (OET) and provides a number of advantages over conventional optical tweezers, in particular the ability to perform operations in parallel and over a large area without damage to living cells. The OET device generally comprises a planar liquid-filled structure having one or more portions which are photoconductive to convert incoming light to a change in the electric field pattern. The light patterns are dynamically generated to provide a number of manipulation structures that can manipulate single particles and cells or group of particles/cells. The OET preferably includes a microscopic imaging means to provide feedback for the optical manipulation, such as detecting position and characteristics wherein the light patterns are modulated accordingly.

Wu, Ming Chiang (Inventor); Chiou, Pei-Yu (Inventor); Ohta, Aaron T. (Inventor)

2014-01-01

312

Single-sided lateral-field and phototransistor-based optoelectronic tweezers  

NASA Technical Reports Server (NTRS)

Described herein are single-sided lateral-field optoelectronic tweezers (LOET) devices which use photosensitive electrode arrays to create optically-induced dielectrophoretic forces in an electric field that is parallel to the plane of the device. In addition, phototransistor-based optoelectronic tweezers (PhOET) devices are described that allow for optoelectronic tweezers (OET) operation in high-conductivity physiological buffer and cell culture media.

Ohta, Aaron (Inventor); Chiou, Pei-Yu (Inventor); Hsu, Hsan-Yin (Inventor); Jamshidi, Arash (Inventor); Wu, Ming-Chiang (Inventor); Neale, Steven L. (Inventor)

2011-01-01

313

Global measurements of aerosols in remote continental and marine regions: concentrations, size distributions, and optical properties  

SciTech Connect

The phase I GAMETAG (global atmospheric measurements experiment of tropospheric aerosols and gases) aerosol measurements were to provide an initial assessment of the levels, types, and optical effects of tropospheric aerosols in remote marine and continental regions and examine the possible causal relationships between the observed distributions and the dominant factors controlling aerosol population. The aerosol population consists primarily of crustal aerosols with r less than or equal to 0.5 micrometer and sulfate and combustion aerosols with r < 0.5 micrometer, with only a minor sea salt component. Owing to vertical mixing, there are no qualitative differences between the boundary layer and the free troposphere. Our data indicate that crustal aerosols represent a significant component of a background tropospheric aerosol in western North America. Pacific marine measurements show a qualitative difference between the boundary layer and the free troposphere. The boundary-layer aerosol population is dominated by a bimodal sea spray aerosol; optical effects and mass concentration are dominated by a mode with a volume mean radius of approx 1 micrometer. Our measurements show only a small crustal component of the marine boundary-layer aerosol. We have inferred a background concentration of 0.2 ppBM for our measured particles that does not appear to be directly related to the sea spray aerosol. We have identified some of these particles as locally produced secondary aerosols; simultaneous measurements of gaseous species support this interpretation. Our Pacific free tropospheric aerosol measurements show a highly variable aerosol component, with local variations in concentration by 1 order of magnitude within a few kilometers. Our measured total aerosol and crustal component concentrations show a general decrease from north to south.

Patterson, E.M.; Kiang, C.S.; Delany, A.C.; Wartburg, A.F.; Leslie, A.C.D.; Hubert, B.J.

1980-01-01

314

Retrieval of Aerosol Optical Depth (AOD) using NOAA AVHRR data in an Alpine Environment  

E-print Network

) generates operational maps of the aerosol optical depth (AOD) over oceans.1 Many remote sensing applicationsRetrieval of Aerosol Optical Depth (AOD) using NOAA AVHRR data in an Alpine Environment Adrian of Bern, Hallerstrasse 12, 3012 Bern, Switzerland ABSTRACT The aim of this study is the retrieval

Wunderle, Stefan

315

Aerosol optical thicknesses over North Africa: 1. Development of a product for model validation using Ozone  

E-print Network

and results. While previous studies have examined the Total Ozone Mapping Spectrometer AI with limited groundAerosol optical thicknesses over North Africa: 1. Development of a product for model validation 11 March 2008; accepted 28 March 2008; published 29 July 2008. [1] Daily aerosol optical thickness

Christopher, Sundar A.

316

Comparison of CALIOP and MODIS aerosol optical depths for aerosol types over the ocean  

NASA Astrophysics Data System (ADS)

The aerosol optical depth (AOD) obtained by vertical integration of the CALIOP (The Cloud-Aerosol Lidar with Orthogonal Polarization) level 2 aerosol extinction coefficient at 532 nm is compared with AOD from MODIS (The Moderate Resolution Imaging Spectroradiometer)-Aqua level 2 product at 550 nm for five aerosol subtypes (clean marine, dust, polluted dust, polluted continental, and biomass burning) identified by CALIOP algorithm over the ocean from June 2006 to December 2010. The mean AOD of MODIS (0.108±0.081) for all collocated dataset is 61% higher than that of CALIOP (0.067±0.074). The difference of AOD between CALIOP and MODIS for five aerosol types and potential reasons for the difference are discussed. (i) Clean marine: For the clean marine, which accounts for 84% of total collocated dataset, the mean AOD of MODIS (0.107±0.066) is almost twice higher than CALIOP (0.056±0.041) having strong latitude dependency related with surface wind speed over the ocean. The difference of AOD increases up to ~0.074 (MODIS AOD minus CALIOP AOD) at 52°S where the surface wind speed is maximum, while the difference is ~0.030 at 32°S where the surface wind speed is minimum. (ii) Dust: The difference of AOD between two sensors for dust (~12.4%) is smallest among five aerosols types but shows regional variation. CALIOP AOD is similar or even slightly higher than MODIS AOD for the dust from Saharan and Arabian deserts, whereas CALIOP AOD for the Asian dust is much less than MODIS AOD. This result suggests that the Asian dust is often mixed with polluted aerosols, thus the lidar ratio for the Asian dust would be higher than current value used in CALIOP algorithm. The difference of AOD for dust also shows distinguishable dependency on the layer mean of particulate depolarization ratio (?). The lidar ratio for dust should increase as ? increases to reduce the AOD difference between two sensors. (iii) Polluted dust and polluted continental: The differences of AOD for polluted dust and polluted continental show similar results; the number of collocated datasets is still high over the remote ocean far from their source region, and CALIOP AOD is overestimated compared to MODIS for most part of the ocean. One of possible reasons for the difference is misclassification of clean marine as polluted dust and polluted continental in CALIOP algorithm. (iv) Biomass burning: The uncertainty on the determination of base altitude for the biomass burning layer is thought to be one of the main reasons for the underestimation of CALIOP AOD because all the biomass burning layers are elevated layers in the CALIOP algorithm. Moreover, for more than 70% of biomass burning cases, the marine boundary layer is excluded for the aerosol extinction retrieval.

Kim, M.; Yoon, S.; Kim, S.; Omar, A. H.

2012-12-01

317

Retrieval of aerosol optical thickness over snow using AATSR observations  

NASA Astrophysics Data System (ADS)

Remote sensing of aerosols experiences lack of products over very bright surfaces, such as deserts and snow, due to difficulties with the subtraction of the surface reflection contribution, when a small error in accounting for surface reflectance can cause a large error in retrieved aerosol optical thickness (AOT). Cloud screening over bright surface is also not easy because of low contrast between clouds and surface in visible range of spectrum, and additional infrared chan-nels are not always available. Luckily, AATSR instrument onboard ENVISAT has necessary features to solve both of these problems. In current work we present an improved version of discussed earlier [1,2] dual-view algorithm to retrieve AOT over snow. The retrieval algorithm still consists of cloud screening, based on spectral shape analysis of AATSR pixel in order to extract clear snow pixels, and of AOT retrieval over snow and water. Current version of AOT retrieval over open ocean now contains improved accounting for ocean reflectance (in previous version the ocean was assumed to be absolutely black). The AOT retrieval over snow has been improved to account more accurately for the bidirectional features of the surface reflection function. For this we now use the approach described in [4] instead of [3], which has been used in the previous version of the retrieval. The accuracy of both approaches [3] and [4] has been evaluated via comparison to forward radiative-transfer model for the case of a very bright surface. The new algorithm has been applied to various scenes in European Arctic and Alaska in different scales, up to global AOT maps. The correspondence of AOT over snow to AOT over water is quite good, which proves the reliability of the retrieval. The algorithm has been validated against AERONET and other Arctic ground based AOT data and shows reasonably good correlation. The presented cloud screening method has been validated via comparison to MODIS cloud mask and Micro Pulse Lidar data. 1. L.G. Istomina, W. Von Hoyningen-Huene, A.A.Kokhanovsky, V.V. Rozanov, M. Schreier, K. Dethloff, M.Stock, R. Treffeisen, A. Herber, J.P.Burrows (2008). Sensitivity study of the dual-view algorithm for aerosol optical thickness retrieval over snow and ice, Proceedings of the 2nd MERIS/(A)ATSR User Workshop, 22-26 September 2008, ESRIN, Frascati, Italy. 2. L.G. Istomina, W. Von Hoyningen-Huene, A.A. Kokhanovsky, J.P. Burrows (2009) Retrieval of aerosol optical thickness in Arctic region using dual-view AATSR observations, Proceedings of ESA Atmospheric Science Conference, 9-11 September 2009, Barcelona, Spain. 3. Y.R. Kaufman, D. Tanre, H.R. Gordon, T. Nakajima, J. Lenoble, R. Frouin, H. Grassl, B.M. Herman, M.D. King, P.M. Teillet (1997) Passive remote sensing of tropospheric aerosol and atmorpheric correction for the aerosol effect. J. Geophys. Res. 102, 16.815-16.830 4. D.Tanre, M. Herman, P.Y.Deschamps, A. De Leffe (1979) Atmosperic modeling for space measurements of ground reflectances, including bidirectional properties. Appl. Optics, 18, 21. 3587-3594

Istomina, Larysa; von Hoyningen-Huene, Wolfgang; Rozanov, Vladimir; Kokhanovsky, Alexander; Burrows, John P.

318

Preliminary results of the aerosol optical depth retrieval in Johor, Malaysia  

NASA Astrophysics Data System (ADS)

Monitoring of atmospheric aerosols over the urban area is important as tremendous amounts of pollutants are released by industrial activities and heavy traffic flow. Air quality monitoring by satellite observation provides better spatial coverage, however, detailed aerosol properties retrieval remains a challenge. This is due to the limitation of aerosol retrieval algorithm on high reflectance (bright surface) areas. The aim of this study is to retrieve aerosol optical depth over urban areas of Iskandar Malaysia; the main southern development zone in Johor state, using Moderate Resolution Imaging Spectroradiometer (MODIS) 500 m resolution data. One of the important steps is the aerosol optical depth retrieval is to characterise different types of aerosols in the study area. This information will be used to construct a Look Up Table containing the simulated aerosol reflectance and corresponding aerosol optical depth. Thus, in this study we have characterised different aerosol types in the study area using Aerosol Robotic Network (AERONET) data. These data were processed using cluster analysis and the preliminary results show that the area is consisting of coastal urban (65%), polluted urban (27.5%), dust particles (6%) and heavy pollution (1.5%) aerosols.

Lim, H. Q.; Kanniah, K. D.; Lau, A. M. S.

2014-02-01

319

Influence of observed diurnal cycles of aerosol optical depth on aerosol direct radiative effect  

NASA Astrophysics Data System (ADS)

The diurnal variability of aerosol optical depth (AOD) can be significant, depending on location and dominant aerosol type. However, these diurnal cycles have rarely been taken into account in measurement-based estimates of aerosol direct radiative forcing (ADRF) or aerosol direct radiative effect (ADRE). The objective of our study was to estimate the influence of diurnal aerosol variability at the top of the atmosphere ADRE estimates. By including all the possible AERONET sites, we wanted to assess the influence on global ADRE estimates. While focusing also in more detail on some selected sites of strongest impact, our goal was to also see the possible impact regionally. We calculated ADRE with different assumptions about the daily AOD variability: taking the observed daily AOD cycle into account and assuming diurnally constant AOD. Moreover, we estimated the corresponding differences in ADREs, if the single AOD value for the daily mean was taken from the the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra or Aqua overpass times, instead of accounting for the true observed daily variability. The mean impact of diurnal AOD variability on 24 h ADRE estimates, averaged over all AERONET sites, was rather small and it was relatively small even for the cases when AOD was chosen to correspond to the Terra or Aqua overpass time. This was true on average over all AERONET sites, while clearly there can be much stronger impact in individual sites. Examples of some selected sites demonstrated that the strongest observed AOD variability (the strongest morning afternoon contrast) does not typically result in a significant impact on 24 h ADRE. In those cases, the morning and afternoon AOD patterns are opposite and thus the impact on 24 h ADRE, when integrated over all solar zenith angles, is reduced. The most significant effect on daily ADRE was induced by AOD cycles with either maximum or minimum AOD close to local noon. In these cases, the impact on 24 h ADRE was typically around 0.1-0.2 W m-2 (both positive and negative) in absolute values, 5-10% in relative ones.

Eck, T. F.; Huttunen, J.; Lehtinen, K. E. J.; Lindfors, A. V.; Myhre, G.; Smirnov, A.; Tripathi, S. N.; Yu, H.

2013-08-01

320

Model analysis of influences of aerosol mixing state upon its optical properties in East Asia  

NASA Astrophysics Data System (ADS)

The air quality model system RAMS (Regional Atmospheric Modeling System)-CMAQ (Models-3 Community Multi-scale Air Quality) coupled with an aerosol optical/radiative module was applied to investigate the impact of different aerosol mixing states (i.e., externally mixed, half externally and half internally mixed, and internally mixed) on radiative forcing in East Asia. The simulation results show that the aerosol optical depth (AOD) generally increased when the aerosol mixing state changed from externally mixed to internally mixed, while the single scattering albedo (SSA) decreased. Therefore, the scattering and absorption properties of aerosols can be significantly affected by the change of aerosol mixing states. Comparison of simulated and observed SSAs at five AERONET (Aerosol Robotic Network) sites suggests that SSA could be better estimated by considering aerosol particles to be internally mixed. Model analysis indicates that the impact of aerosol mixing state upon aerosol direct radiative forcing (DRF) is complex. Generally, the cooling effect of aerosols over East Asia are enhanced in the northern part of East Asia (Northern China, Korean peninsula, and the surrounding area of Japan) and are reduced in the southern part of East Asia (Sichuan Basin and Southeast China) by internal mixing process, and the variation range can reach ±5 W m-2. The analysis shows that the internal mixing between inorganic salt and dust is likely the main reason that the cooling effect strengthens. Conversely, the internal mixture of anthropogenic aerosols, including sulfate, nitrate, ammonium, black carbon, and organic carbon, could obviously weaken the cooling effect.

Han, Xiao; Zhang, Meigen; Zhu, Lingyun; Xu, Liren

2013-07-01

321

Field Studies of Broadband Aerosol Optical Extinction in the Ultraviolet Spectral Region  

NASA Astrophysics Data System (ADS)

Aerosols influence the Earth's radiative budget by scattering and absorbing incoming solar radiation. The optical properties of aerosols vary as a function of wavelength, but few measurements have reported the wavelength dependence of aerosol extinction cross sections and complex refractive indices. In the case of brown carbon, its wavelength-dependent absorption in the ultraviolet spectral region has been suggested as an important component of aerosol radiative forcing. We describe a new field instrument to measure aerosol optical extinction as a function of wavelength, using cavity enhanced spectroscopy with a broadband light source. The instrument consists of two broadband channels which span the 360-390 and 385-420 nm spectral regions using two light emitting diodes (LED) and a grating spectrometer with charge-coupled device (CCD) detector. We deployed this instrument during the Fire Lab at Missoula Experiment during Fall 2012 to measure biomass burning aerosol, and again during the Southern Oxidant and Aerosol Study in summer 2013 to measure organic aerosol in the Southeastern U.S. In both field experiments, we determined aerosol optical extinction as a function of wavelength and can interpret this together with size distribution and composition measurements to characterize the aerosol optical properties and radiative forcing.

Washenfelder, R. A.; Attwood, A.; Brock, C. A.; Brown, S. S.

2013-12-01

322

Retrieval of Aerosol Optical Depth Above Clouds from OMI Observations: Sensitivity Analysis, Case Studies  

NASA Technical Reports Server (NTRS)

A large fraction of the atmospheric aerosol load reaching the free troposphere is frequently located above low clouds. Most commonly observed aerosols above clouds are carbonaceous particles generally associated with biomass burning and boreal forest fires, and mineral aerosols originated in arid and semi-arid regions and transported across large distances, often above clouds. Because these aerosols absorb solar radiation, their role in the radiative transfer balance of the earth atmosphere system is especially important. The generally negative (cooling) top of the atmosphere direct effect of absorbing aerosols, may turn into warming when the light-absorbing particles are located above clouds. The actual effect depends on the aerosol load and the single scattering albedo, and on the geometric cloud fraction. In spite of its potential significance, the role of aerosols above clouds is not adequately accounted for in the assessment of aerosol radiative forcing effects due to the lack of measurements. In this paper we discuss the basis of a simple technique that uses near-UV observations to simultaneously derive the optical depth of both the aerosol layer and the underlying cloud for overcast conditions. The two-parameter retrieval method described here makes use of the UV aerosol index and reflectance measurements at 388 nm. A detailed sensitivity analysis indicates that the measured radiances depend mainly on the aerosol absorption exponent and aerosol-cloud separation. The technique was applied to above-cloud aerosol events over the Southern Atlantic Ocean yielding realistic results as indicated by indirect evaluation methods. An error analysis indicates that for typical overcast cloudy conditions and aerosol loads, the aerosol optical depth can be retrieved with an accuracy of approximately 54% whereas the cloud optical depth can be derived within 17% of the true value.

Torres, O.; Jethva, H.; Bhartia, P. K.

2012-01-01

323

ModelE2-TOMAS development and evaluation using aerosol optical depths, mass and number concentrations  

NASA Astrophysics Data System (ADS)

The TwO-Moment Aerosol Sectional microphysics model (TOMAS) has been integrated into the state-of-the-art general circulation model, GISS ModelE2. TOMAS has the flexibility to select a size resolution as well as the lower size cutoff. A computationally efficient version of TOMAS is used here, which has 15 size bins covering 3 nm to 10 ?m aerosol dry diameter. For each bin, it simulates the total aerosol number concentration and mass concentrations of sulphate, pure elementary carbon (hydrophobic), mixed elemental carbon (hydrophilic), hydrophobic organic matter, hydrophilic organic matter, sea salt, mineral dust, ammonium, and aerosol-associated water. This paper provides a detailed description of the ModelE2-TOMAS model and evaluates the model against various observations including aerosol precursor gas concentrations, aerosol mass and number concentrations, and aerosol optical depths. Additionally, global budgets in ModelE2-TOMAS are compared with those of other global aerosol models, and the TOMAS model is compared to the default aerosol model in ModelE2, which is a bulk aerosol model. Overall, the ModelE2-TOMAS predictions are within the range of other global aerosol model predictions, and the model has a reasonable agreement with observations of sulphur species and other aerosol components as well as aerosol optical depth. However, ModelE2-TOMAS (as well as the bulk aerosol model) cannot capture the observed vertical distribution of sulphur dioxide over the Pacific Ocean possibly due to overly strong convective transport. The TOMAS model successfully captures observed aerosol number concentrations and cloud condensation nuclei concentrations. Anthropogenic aerosol burdens in the bulk aerosol model running in the same host model as TOMAS (ModelE2) differ by a few percent to a factor of 2 regionally, mainly due to differences in aerosol processes including deposition, cloud processing, and emission parameterizations. Larger differences are found for naturally emitted aerosols such as sea salt and mineral dust. With TOMAS, ModelE2 has three different aerosol models (the bulk aerosol model and modal-based aerosol microphysics model, MATRIX) and allows exploration of the uncertainties associated with aerosol modelling within the same host model, NASA GISS ModelE2.

Lee, Y. H.; Adams, P. J.; Shindell, D. T.

2014-09-01

324

Validation of MODIS aerosol optical depth over the Mediterranean Coast  

NASA Astrophysics Data System (ADS)

Atmospheric aerosols, due to their high spatial and temporal variability, are considered one of the largest sources of uncertainty in different processes affecting visibility, air quality, human health, and climate. Among their effects on climate, they play an important role in the energy balance of the Earth. On one hand they have a direct effect by scattering and absorbing solar radiation; on the other, they also have an impact in precipitation, modifying clouds, or affecting air quality. The application of remote sensing techniques to investigate aerosol effects on climate has advanced significatively over last years. In this work, the products employed have been obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS). MODIS is a sensor located onboard both Earth Observing Systems (EOS) Terra and Aqua satellites, which provide almost complete global coverage every day. These satellites have been acquiring data since early 2000 (Terra) and mid 2002 (Aqua) and offer different products for land, ocean and atmosphere. Atmospheric aerosol products are presented as level 2 products with a pixel size of 10 x 10 km2 in nadir. MODIS aerosol optical depth (AOD) is retrieved by different algorithms depending on the pixel surface, distinguishing between land and ocean. For its validation, ground based sunphotometer data from AERONET (Aerosol Robotic Network) has been employed. AERONET is an international operative network of Cimel CE318 sky-sunphotometers that provides the most extensive aerosol data base globally available of ground-based measurements. The ground sunphotometric technique is considered the most accurate for the retrieval of radiative properties of aerosols in the atmospheric column. In this study we present a validation of MODIS C051 AOD employing AERONET measurements over different Mediterranean coastal sites centered over an area of 50 x 50 km2, which includes both pixels over land and ocean. The validation is done comparing spatial statistics from MODIS with corresponding temporal statistics from AERONET, as proposed by Ichoku et al. (2002). Eight Mediterranean coastal sites (in Spain, France, Italy, Crete, Turkey and Israel) with available AERONET and MODIS data have been used. These stations have been selected following QA criteria (minimum 1000 days of level 2.0 data) and a maximum distance of 8 km from the coast line. Results of the validation over each site show analogous behaviour, giving similar results regarding to the accuracy of the algorithms. Greatest differences are found for the AOD obtained over land, especially for drier regions, where the surface tends to be brighter. In general, the MODIS AOD has better a agreement with AERONET retrievals for the ocean algorithm than the land algorithm when validated over coastal sites, and the agreement is within the expected uncertainty estimated for MODIS data. References: - C. Ichoku et al., "A spatio-temporal approach for global validation and analysis of MODIS aerosol products", Geophysical Research Letters, 219, 12, 10.1029/2001GL013206, 2002.

Díaz-Martínez, J. Vicente; Segura, Sara; Estellés, Víctor; Utrillas, M. Pilar; Martínez-Lozano, J. Antonio

2013-04-01

325

Three dimensional optical manipulation and structural imaging of soft materials by use of laser tweezers and multimodal nonlinear microscopy  

E-print Network

We develop an integrated system of holographic optical trapping and multimodal nonlinear microscopy and perform simultaneous three-dimensional optical manipulation and non-invasive structural imaging of composite soft-matter systems. We combine different nonlinear microscopy techniques such as coherent anti-Stokes Raman scattering, multi-photon excitation fluorescence and multi-harmonic generation, and use them for visualization of long-range molecular order in soft materials by means of their polarized excitation and detection. The combined system enables us to accomplish both, manipulation in composite soft materials such as colloidal inclusions in liquid crystals as well as imaging of each separate constituents of the composite material in different nonlinear optical modalities. We also demonstrate optical generation and control of topological defects and simultaneous reconstruction of their three-dimensional long-range molecular orientational patterns from the nonlinear optical images.

Rahul P. Trivedi; Taewoo Lee; Kris A. Bertness; Ivan I. Smalyukh

2010-11-17

326

Baseline Maritime Aerosol: Methodology to Derive the Optical Thickness and Scattering Properties  

NASA Technical Reports Server (NTRS)

Satellite Measurements of the global distribution of aerosol and their effect on climate should be viewed in respect to a baseline aerosol. In this concept, concentration of fine mode aerosol particles is elevated above the baseline by man-made activities (smoke or urban pollution), while coarse mode by natural processes (e.g. dust or sea-spray). Using 1-3 years of measurements in 10 stations of the Aerosol Robotic network (ACRONET we develop a methodology and derive the optical thickness and properties of this baseline aerosol for the Pacific and Atlantic Oceans. Defined as the median for periods of stable optical thickness (standard deviation < 0.02) during 2-6 days, the median baseline aerosol optical thickness over the Pacific Ocean is 0.052 at 500 am with Angstrom exponent of 0.77, and 0.071 and 1.1 respectively, over the Atlantic Ocean.

Kaufman, Yoram J.; Smirnov, Alexander; Holben, Brent N.; Dubovik, Oleg; Einaudi, Franco (Technical Monitor)

2001-01-01

327

Spatial variation of aerosol optical properties in North China Plain  

NASA Astrophysics Data System (ADS)

The column-integrated optical properties of aerosol in Beijing and Xianghe situated at North China Plain were investigated based on Sun/sky radiometer measurements made at Aerosol Robotic Network (AERONET) sites. Only version 2 and level 2 quality-assured data were presented and analyzed in this paper. Time intervals differ for the two sites, with Beijing having 9 years of data (Mar.-May, 2001; Apr., 2002-Dec., 2011),while Xianghe having 6 years of data (Mar.-Apr., 2001;Sep., 2004-Dec.,2011). Monthly mean 500 nm AOT values reach a maximum in June (0.95) and exceed 0.55 from March through September, and the minimum values occur during the late fall and winter months of November through February at Beijing. The monthly mean AOT values at Xianghe are very close to those measured at Beijing. The absolute differences of AOT between the two sites are less than 0.1 except in June and July. The reason of large difference in June and July is the frequently cloud contamination in summer result in the monthly means over the two sites computed from a large number of measurements of different date. The monthly averaged AOT with the same date in June and July are re-computed and the absolute difference of AOT between Beijing and Xianghe reduced to 0.01 and 0.03 in June and July respectively. The monthly mean Angstrom Exponent (AE) in Beijing and Xianghe sites are very close, with the absolute difference less than 0.075. The monthly mean AE in the two sites varied between ~1.0 and ~1.3 except in spring (March-May), therefore clearly dominated by fine mode aerosol for most of the year. All monthly averaged SSA at Beijing showed much lower value as compared to Xianghe though the seasonal variations are similar for the two sites, which indicates that aerosol absorption is greater in Beijing. All monthly averaged imaginary part of refractive index at Beijing has much higher value than Xianghe. The absolute differences of SSA between the two sites range from 0.016 to 0.037 except that the difference in September is only 0.0005. All the significant differences but September exceed the 95% confidence level based on t-test technique. This very large difference in SSA over a relatively small distance (~70 km) suggests the significant variability in aerosol absorption between Beijing and Xianghe and the reasons for this difference should be investigated.

Fan, Xuehua

2013-04-01

328

High aerosol optical depth biomass burning events: A comparison of optical properties for different source regions  

NASA Astrophysics Data System (ADS)

The optical properties of aerosols such as smoke from biomass burning vary due to aging processes and these particles reach larger sizes at high concentrations. We compare the spectra of aerosol optical depth (?a), column-integrated volume size distributions, refractive indices, and single scattering albedo retrieved from AERONET observations for four selected events of very high smoke optical depth (?a ~ 2 at 500 nm). Two case studies are from tropical biomass burning regions (Brazil and Zambia) and two are cases of boreal forest and peat fire smoke transported long distances to sites in the US and Moldova. Smoke properties for these extreme events can be significantly different from those reported in more typical plumes. In particular, large differences in smoke fine mode particle radius (~0.17 to 0.25 ?m) and single scattering albedo (~0.88 to 0.99 at 440 nm) were observed as a result of differences in fuels burned, combustion phase, and aging.

Eck, T. F.; Holben, B. N.; Reid, J. S.; O'Neill, N. T.; Schafer, J. S.; Dubovik, O.; Smirnov, A.; Yamasoe, M. A.; Artaxo, P.

2003-10-01

329

Two steps forward, one step back: determining XPD helicase mechanism by single-molecule fluorescence and high-resolution optical tweezers.  

PubMed

XPD-like helicases constitute a prominent DNA helicase family critical for many aspects of genome maintenance. These enzymes share a unique structural feature, an auxiliary domain stabilized by an iron-sulphur (FeS) cluster, and a 5'-3' polarity of DNA translocation and duplex unwinding. Biochemical analyses alongside two single-molecule approaches, total internal reflection fluorescence microscopy and high-resolution optical tweezers, have shown how the unique structural features of XPD helicase and its specific patterns of substrate interactions tune the helicase for its specific cellular function and shape its molecular mechanism. The FeS domain forms a duplex separation wedge and contributes to an extended DNA binding site. Interactions within this site position the helicase in an orientation to unwind the duplex, control the helicase rate, and verify the integrity of the translocating strand. Consistent with its cellular role, processivity of XPD is limited and is defined by an idiosyncratic stepping kinetics. DNA duplex separation occurs in single base pair steps punctuated by frequent backward steps and conformational rearrangements of the protein-DNA complex. As such, the helicase in isolation mainly stabilizes spontaneous base pair opening and exhibits a limited ability to unwind stable DNA duplexes. The presence of a cognate ssDNA binding protein converts XPD into a vigorous helicase by destabilizing the upstream dsDNA as well as by trapping the unwound strands. Remarkably, the two proteins can co-exist on the same DNA strand without competing for binding. The current model of the XPD unwinding mechanism will be discussed along with possible modifications to this mechanism by the helicase interacting partners and unique features of such bio-medically important XPD-like helicases as FANCJ (BACH1), RTEL1 and CHLR1 (DDX11). PMID:24560558

Spies, Maria

2014-08-01

330

Two steps forward, one step back: determining XPD helicase mechanism by single-molecule fluorescence and high-resolution optical tweezers  

PubMed Central

XPD-like helicases constitute a prominent DNA helicase family critical for many aspects of genome maintenance. These enzymes share a unique structural feature, an auxiliary domain stabilized by an iron-sulphur (FeS) cluster, and a 5?-3? polarity of DNA translocation and duplex unwinding. Biochemical analyses alongside two single-molecule approaches, total internal reflection fluorescence microscopy and high-resolution optical tweezers, have shown how the unique structural features of XPD helicase and its specific patterns of substrate interactions tune the helicase for its specific cellular function and shape its molecular mechanism. The FeS domain forms a duplex separation wedge and contributes to an extended DNA binding site. Interaction within this site position the helicase in an orientation to unwind the duplex, control the helicase rate, and verify the integrity of the translocating strand. Consistent with its cellular role, processivity of XPD is limited and is defined by an idiosyncratic stepping kinetics. DNA duplex separation occurs in single base pair steps punctuated by frequent backward steps and conformational rearrangements of the protein-DNA complex. As such, the helicase in isolation mainly stabilizes spontaneous base pair opening and exhibits a limited ability to unwind stable DNA duplexes. The presence of a cognate ssDNA binding protein converts XPD into a vigorous helicase by destabilizing the upstream dsDNA as well as by trapping the unwound strands. Remarkably, the two proteins can co-exist on the same DNA strand without competing for binding. The current model of the XPD unwinding mechanism will be discussed along with possible modifications to this mechanism by the helicase interacting partners and unique features of such bio-medically important XPD-like helicases as FANCJ (BACH1), RTEL1 and CHLR1 (DDX11). PMID:24560558

Spies, Maria

2014-01-01

331

The Smallest Tweezers in the World  

ERIC Educational Resources Information Center

A pair of fine tweezers and a steady hand may well be enough to pick up a grain of sand, but what would you use to hold something hundreds of times smaller still, the size of only one micron? The answer is to use a device that is not mechanical in nature but that relies instead on the tiny forces that light exerts on small particles: "optical

Lewalle, Alexandre

2008-01-01

332

Relationship between column aerosol optical properties and surface aerosol gravimetric concentrations during the Distributed Regional Aerosol Gridded Observation Network - Northeast ASIA 2012 campaign  

NASA Astrophysics Data System (ADS)

One of the main objectives of Distributed Regional Aerosol Gridded Observation Network (DRAGON) campaign in Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) mission is to understand the relationship between the column optical properties of the atmosphere and the surface level air quality in terms of aerosols and gases. This study aims to identify the important parameters that affecting the relationship between those variables during the DRAGON - northeast Asia 2012 campaign. Column aerosol optical properties from ten Cimel sun photometers at DRAGON sites in Seoul, MODIS (Moderate Resolution Imaging Spectroradiometer), and GOCI (Geostationary Ocean Color Imager) and particulate matter (PM10) sampling from 40 NIER (National Institute of Environmental Research of South Korea) measurement sites in Seoul during the period of 1st March - 31th May 2012 were employed in this study. The key parameters in relationship between aerosol optical depth (AOD) and PM are reported to be aerosol vertical profile and hygroscopicity of the aerosols. The meteorological conditions including relative humidity, surface temperature, and wind speed that could affect those parameters were investigated.

Jeong, U.; Kim, J.; Seo, S.; Choi, M.; Kim, W. V.; Holben, B. N.; Lee, S.; Kim, J.

2012-12-01

333

DNA tethering characterization, enzyme-mediated DNA looping under tension, and nucleosome stability in the force measuring optical tweezers  

E-print Network

revealed by single-molecule video-microscopy and scanningof a single DNA molecule observed by optical microscopy.single molecule techniques such as fluorescent resonant energy transfer and atomic force microscopy

Gemmen, Gregory John

2006-01-01

334

Observations and projections of visibility and aerosol optical thickness (1956–2100) in the Netherlands: impacts of time-varying aerosol composition and hygroscopicity  

NASA Astrophysics Data System (ADS)

Time series of visibility and aerosol optical thickness for the Netherlands have been constructed for 1956–2100 based on observations and aerosol mass scenarios. Aerosol optical thickness from 1956 to 2013 has been reconstructed by converting time series of visibility to visible extinction which in turn are converted to aerosol optical thickness using an appropriate scaling depth. The reconstruction compares closely with remote sensing observations of aerosol optical thickness between 1960 and 2013. It appears that aerosol optical thickness was relatively constant over the Netherlands in the years 1955–1985. After 1985, visibility has improved, while at the same time aerosol optical thickness has decreased. Based on aerosol emission scenarios for the Netherlands three aerosol types have been identified: (1) a constant background consisting of sea salt and mineral dust, (2) a hydrophilic anthropogenic inorganic mixture, and (3) a partly hydrophobic mixture of black carbon (BC) and organic aerosols (OAs). A reduction in overall aerosol concentration turns out to be the most influential factor in the reduction in aerosol optical thickness. But during 1956–1985, an upward trend in hydrophilic aerosols and associated upward trend in optical extinction has partly compensated the overall reduction in optical extinction due to the reduction in less hydrophilic BC and OAs. A constant optical thickness ensues. This feature highlights the influence of aerosol hygroscopicity on time-varying signatures of atmospheric optical properties. Within the hydrophilic inorganic aerosol mixture there is a gradual shift from sulfur-based (1956–1985) to a nitrogen-based water aerosol chemistry (1990 onwards) but always modulated by the continual input of sodium from sea salt. From 2013 to 2100, visibility is expected to continue its increase, while at the same time optical thickness is foreseen to continue to decrease. The contribution of the hydrophilic mixture to the aerosol optical thickness will increase from 30% to 35% in 1956 to more than 70% in 2100. At the same time the contribution of black and organic aerosols will decrease by more than 80%.

Boers, R.; van Weele, M.; van Meijgaard, E.; Savenije, M.; Siebesma, A. P.; Bosveld, F.; Stammes, P.

2015-01-01

335

A new real non-invasive single fiber tweezers  

NASA Astrophysics Data System (ADS)

A new real non-invasive two-core single fiber optical tweezers is proposed and fabricated by fiber grinding and polishing technology. The yeast cells trapping performance of this special designed truncated cone tip fiber probe is demonstrated and investigated. The distributions of the optical field emerging from the truncated cone fiber tip are simulated by Beam Prop Method. Both axial and transverse trapping forces are calculated by FDTD method. This new optical tweezers can realize truly non-invasive remote trapping and manipulating bio-cells.

Zhang, Yu; Liu, Zhihai; Yang, Jun; Yuan, Libo

2012-02-01

336

Aeronet-based Microphysical and Optical Properties of Smoke-dominated Aerosol near Source Regions and Transported over Oceans, and Implications for Satellite Retrievals of Aerosol Optical Depth  

NASA Technical Reports Server (NTRS)

Smoke aerosols from biomass burning are an important component of the global aerosol cycle. Analysis of Aerosol Robotic Network (AERONET) retrievals of size distribution and refractive index reveals variety between biomass burning aerosols in different global source regions, in terms of aerosol particle size and single scatter albedo (SSA). Case studies of smoke transported to coastal/island AERONET sites also mostly lie within the range of variability at near-source sites. Two broad families of aerosol properties are found, corresponding to sites dominated by boreal forest burning (larger, broader fine mode, with midvisible SSA 0.95), and those influenced by grass, shrub, or crop burning with additional forest contributions (smaller, narrower particles with SSA 0.88-0.9 in the midvisible). The strongest absorption is seen in southern African savanna at Mongu (Zambia), with average SSA 0.85 in the midvisible. These can serve as candidate sets of aerosol microphysicaloptical properties for use in satellite aerosol optical depth (AOD) retrieval algorithms. The models presently adopted by these algorithms over ocean are often insufficiently absorbing to represent these biomass burning aerosols. A corollary of this is an underestimate of AOD in smoke outflow regions, which has important consequences for applications of these satellite datasets.

Sayer, A. M.; Hsu, N. C.; Eck, T. F.; Smirnov, A.; Holben, B. N.

2013-01-01

337

Deriving atmospheric visibility from satellite retrieved aerosol optical depth  

NASA Astrophysics Data System (ADS)

Atmospheric visibility is a measure that reflects different physical and chemical properties of the atmosphere. In general, poor visibility conditions come along with risks for transportation (e.g. road traffic, aviation) and can negatively impact human health since visibility impairment often implies the presence of atmospheric pollution. Ambient pollutants, particulate matter, and few gaseous species decrease the perceptibility of distant objects. Common estimations of this parameter are usually based on human observations or devices that measure the transmittance of light from an artificial light source over a short distance. Such measurements are mainly performed at airports and some meteorological stations. A major disadvantage of these observations is the gap between the measurements, leaving large areas without any information. As aerosols are one of the most important factors influencing atmospheric visibility in the visible range, the knowledge of their spatial distribution can be used to infer visibility with the so called Koschmieder equation, which relates visibility and atmospheric extinction. In this study, we evaluate the applicability of satellite aerosol optical depth (AOD) products from the Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) to infer atmospheric visibility on large spatial scale. First results applying AOD values scaled with the planetary boundary layer height are promising. For the comparison we use a full automated and objective procedure for the estimation of atmospheric visibility with the help of a digital panorama camera serving as ground truth. To further investigate the relation between the vertical measure of AOD and the horizontal visibility data from the Aerosol Robotic Network (AERONET) site Laegeren (Switzerland), where the digital camera is mounted, are included as well. Finally, the derived visibility maps are compared with synoptical observations in central Europe.

Riffler, M.; Schneider, Ch.; Popp, Ch.; Wunderle, S.

2009-04-01

338

Modeling the spectral optical properties of ammonium sulfate and biomass burning aerosols: parameterization of relative humidity effects and model results  

Microsoft Academic Search

The importance of including the global and regional radiative effects of aerosols in climate models has increasingly been realized. Accurate modeling of solar radiative forcing due to aerosols from anthropogenic sulfate and biomass burning emissions requires adequate spectral resolution and treatment of spatial and temporal variability. The variation of aerosol spectral optical properties with local relative humidity and dry aerosol

Keith Eric Grant; Catherine C. Chuang; Allen S. Grossman; Joyce E. Penner

1999-01-01

339

Nanoscale Molecular Tweezers  

NSDL National Science Digital Library

The featured molecules for this month are drawn from the "Research Advances" column by Angela G. King, and represent some of the structures from the research on molecular tweezers (published in J. Am. Chem. Soc. 2004, 126, 8124). The structures below are based on the figure on page 1690 showing two types of receptors that switch between U and W shapes upon coordination of soft metal cations, acting in the manner of mechanical tweezers. When viewing these molecules in Chime you must render in ball and stick or space filling modes in order to see the incorporated metal ions. In several cases the torsion angles connecting the anthracene substituents to the rest of the molecule are not well defined and have been drawn as either coplanar or orthogonal to the central ring system. At a moderate level of theory, the torsion angle in those instances where it has been set to 90° displays a broad minimum ranging for 50?130°.

340

Journal of the Korean Physical Society, Vol. 48, February 2006, pp. S222S225 Rotation of Irregularly Shaped Liposome Using Optical Tweezers  

E-print Network

with a laser beam in 1970 [1], op- tical tweezers have been widely used in trapping and ma- nipulating microscopic materials, such as colloidal par- ticles, red blood cells, and artificially synthesized lipo], a 1064 nm Nd:YVO4 laser (TEM00, Golden Light Co., HSR70) is used as a laser source. The laser light

Pak, Hyuk Kyu

341

Scientists at the Ris National Laboratory in Roskilde, Denmark, have developed an optical tweezers system that moves tiny particles in  

E-print Network

optical imaging methods of the skin detected singly backscattered photons to achieve spatial resolution mm with rat skin, but the team believes that they can obtain much higher penetrations--up to 5 cm, and depth information was obtained by measuring the time of return of the ultrasound pulse. A 15- m depth

Wang, Lihong

342

Improved understanding of aerosol processes using satellite observations of aerosol optical properties   

E-print Network

Atmospheric aerosols are the largest remaining uncertainty in the Earth’s radiative budget and it is important that we improve our knowledge of aerosol processes if we are to understand current radiative forcing and ...

Bulgin, Claire Elizabeth

2010-01-01

343

Atmospheric aerosols: Their Optical Properties and Effects (supplement)  

NASA Technical Reports Server (NTRS)

A digest of technical papers is presented. Topics include aerosol size distribution from spectral attenuation with scattering measurements; comparison of extinction and backscattering coefficients for measured and analytic stratospheric aerosol size distributions; using hybrid methods to solve problems in radiative transfer and in multiple scattering; blue moon phenomena; absorption refractive index of aerosols in the Denver pollution cloud; a two dimensional stratospheric model of the dispersion of aerosols from the Fuego volcanic eruption; the variation of the aerosol volume to light scattering coefficient; spectrophone in situ measurements of the absorption of visible light by aerosols; a reassessment of the Krakatoa volcanic turbidity, and multiple scattering in the sky radiance.

1976-01-01

344

Algorithm for retrieval of aerosol optical properties over the ocean from the Geostationary Ocean Color Imager  

Microsoft Academic Search

An aerosol retrieval algorithm for the first Geostationary Ocean Color Imager (GOCI) to be launched in March 2010 onboard the Communication, Ocean, and Meteorological Satellite (COMS) is presented. The algorithm retrieves aerosol optical depth (AOD), fine-mode fraction (FMF), and aerosol type in 500m×500m resolution. All the products are retrieved over clear water which is defined by surface reflectance ratio between

Jaehwa Lee; Jhoon Kim; Chul H. Song; Joo-Hyung Ryu; Yu-Hwan Ahn; C. K. Song

2010-01-01

345

Aerosol optical properties over the midcontinental United States  

NASA Technical Reports Server (NTRS)

Solar and sky radiation measurements were analyzed to obtain aerosol properties such as the optical thickness and the size distribution. The measurements were conducted as part of the First International Satellite Land Surface Climatology Project Field Experiment during the second intensive field campaign (IFC) from June 25 to July 14, 1987, and the fifth IFC from July 25 to August 12, 1989, on the Konza Prairie near Manhattan, Kansas. Correlations with climatological and meteorological parameters show that during the period of observations in 1987, two types of air masses dominated the area: an air mass with low optical thickness and low temperature air associated with a northerly breeze, commonly referred to as the continental air, and an air mass with a higher optical thickness and higher temperature air associated with a southerly wind which we call 'Gulf air'. The size distributions show a predominance of the larger size particles in 'Gulf air'. Because of the presence of two contrasting air masses, correlations with parameters such as relative humidity, specific humidity, pressure, temperature, and North Star sky radiance reveal some interesting aspects. In 1989, clear distinctions between continental and Gulf air cannot be made; the reason for this will be discussed.

Halthore, Rangasayi N.; Markham, Brian L.; Ferrare, Richard A.; Aro, Theo. O.

1992-01-01

346

Hardware manual of dexterous tweezers(1/25) Hardware manual of dexterous tweezers  

E-print Network

Hardware manual of dexterous tweezers(1/25) Hardware manual of dexterous tweezers Version 0 ..................................................................... 23 #12;Hardware manual of dexterous tweezers(2/25) 1 Overview The prototype tweezers for micro stage X stage Y stageX finger Y finger #12;Hardware manual of dexterous tweezers(3/25) 2 Setup outline 2

Fearing, Ron

347

Optical properties and radiative forcing of urban aerosols in Nanjing, China  

NASA Astrophysics Data System (ADS)

Continuous measurements of atmospheric aerosols were made in Nanjing, a megacity in China, from 18 January to 18 April, 2011 (Phase 1) and from 22 April 2011 to 21 April 2012 (Phase 2). Aerosol characteristics, optical properties, and direct radiative forcing (DRF) were studied through interpretations of these measurements. We found that during Phase 1, mean PM2.5, black carbon (BC), and aerosol scattering coefficient (Bsp) in Nanjing were 76.1 ± 59.3 ?g m-3, 4.1 ± 2.2 ?g m-3, and 170.9 ± 105.8 M m-1, respectively. High pollution episodes occurred during Spring and Lantern Festivals when hourly PM2.5 concentrations reached 440 ?g m-3, possibly due to significant discharge of fireworks. Temporal variations of PM2.5, BC, and Bsp were similar to each other. It is estimated that inorganic scattering aerosols account for about 49 ± 8.6% of total aerosols while BC only accounted for 6.6 ± 2.9%, and nitrate was larger than sulfate. In Phase 2, optical properties of aerosols show great seasonality. High relative humidity (RH) in summer (June, July, August) likely attributed to large optical depth (AOD) and small Angstrom exponent (AE) of aerosols. Due to dust storms, AE of total aerosols was the smallest in spring (March, April, May). Annual mean 550-nm AOD and 675/440-nm AE were 0.6 ± 0.3 and 1.25 ± 0.29 for total aerosols, 0.04 ± 0.02 and 1.44 ± 0.50 for absorbing aerosols, 0.48 ± 0.29 and 1.64 ± 0.29 for fine aerosols, respectively. Annual single scattering albedo of aerosols ranged from 0.90 to 0.92. Real time wavelength-dependent surface albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS) was used to assess aerosol DRFs. Both total and absorbing aerosol DRFs had significant seasonal variations in Nanjing and they were the strongest in summer. Annual mean clear sky TOA DRF (including daytime and nighttime) of total and absorbing aerosols was about -6.9 and +4.5 W m-2, respectively. Aerosol DRFs were found to be sensitive to surface albedo. Over brighter surfaces, solar radiation was more absorbed by absorbing aerosols and less scattered by scattering aerosols.

Zhuang, B. L.; Wang, T. J.; Li, S.; Liu, J.; Talbot, R.; Mao, H. T.; Yang, X. Q.; Fu, C. B.; Yin, C. Q.; Zhu, J. L.; Che, H. Z.; Zhang, X. Y.

2014-02-01

348

Optical Tweezers-Assisted Cross-Correlation Analysis for a Non-intrusive Fluid Temperature Measurement in Microdomains  

NASA Astrophysics Data System (ADS)

An image-based approach to predict the fluid temperature in microfluidic flow cell is presented. We apply Fourier-based cross-correlation processing to determine the lateral displacement of the optically trapped bead; therefore, both the mean square displacement (MSD) and the diffusion coefficient (D) can be obtained. On the other hand, applying the Stokes-Einstein equation, together with Faxen's law correction, the theoretical relation showed that D is proportional to (T/?), where T and ? are temperature and temperature-dependent fluid viscosity, respectively. Hence, the fluid temperature can be determined by MSD-based thermometry.

Cheng, Chih-Ming; Chang, Ming-Chih; Chang, Yu-Fen; Wang, Wei-Ting; Hsu, Chien-Ting; Tsai, Jing-Shin; Liu, Chia-Yeh; Wu, Chien-Ming; Ou, Keng-Liang; Yang, Tzu-Sen

2012-06-01

349

Validation of a modified AVHRR aerosol optical depth retrieval algorithm over Central Europe  

Microsoft Academic Search

The Advanced Very High Resolution Radiometer (AVHRR) carried on board the National Oceanic and Atmospheric Administration (NOAA) and the Meteorological Operational Satellite (MetOp) polar orbiting satellites is the only instrument offering more than 25 years of satellite data to analyse aerosols on a daily basis. The present study assessed a modified AVHRR aerosol optical depth taua retrieval over land. The

M. Riffler; C. Popp; A. Hauser; F. Fontana; S. Wunderle

2010-01-01

350

Validation of a modified AVHRR aerosol optical depth retrieval algorithm over Central Europe  

Microsoft Academic Search

The Advanced Very High Resolution Radiometer (AVHRR) carried on board the National Oceanic and Atmospheric Administration (NOAA) and the Meteorological Operational Satellite (MetOp) polar orbiting satellites is the only instrument offering more than 25 years of satellite data to analyse aerosols on a daily basis. The present study assessed a modified AVHRR aerosol optical depth taua retrieval over land for

M. Riffler; C. Popp; A. Hauser; F. Fontana; S. Wunderle

2010-01-01

351

Anthropogenic and natural contributions to regional trends in aerosol optical depth, 1980–2006  

Microsoft Academic Search

Understanding the roles of human and natural sources in contributing to aerosol concentrations around the world is an important step toward developing efficient and effective mitigation measures for local and regional air quality degradation and climate change. In this study we test the hypothesis that changes in aerosol optical depth (AOD) over time are caused by the changing patterns of

David G. Streets; Fang Yan; Mian Chin; Thomas Diehl; Natalie Mahowald; Martin Schultz; Martin Wild; Ye Wu; Carolyne Yu

2009-01-01

352

Anthropogenic and natural contributions to regional trends in aerosol optical depth, 1980-2006  

Microsoft Academic Search

Understanding the roles of human and natural sources in contributing to aerosol concentrations around the world is an important step toward developing efficient and effective mitigation measures for local and regional air quality degradation and climate change. In this study we test the hypothesis that changes in aerosol optical depth (AOD) over time are caused by the changing patterns of

David G. Streets; Fang Yan; Mian Chin; Thomas Diehl; Natalie Mahowald; Martin Schultz; Martin Wild; Ye Wu; Carolyne Yu; Forschungszentrum

2009-01-01

353

Using Artificial Sky Glow to Retrieve Night Time Aerosol Optical Depth  

Microsoft Academic Search

Measuring the Aerosol Optical Depth (AOD) is of particular importance in monitoring aerosol contributions to global radiative forcing. Most measuring methods are based on direct or indirect observation of sunlight and thus are only available for use during daylight hours. Attempts have been made to measure AOD behavior at night from star photometry, and more recently moon photometry. Star photometry

M. Aubé; N. T. O'Neill; J.-D. Giguère; A. Royer

2009-01-01

354

Optical characteristics of biomass burning aerosols over Southeastern Europe determined from UV-Raman lidar measurements  

Microsoft Academic Search

The influence of smoke on the aerosol loading in the free troposphere over Thessaloniki, Greece is examined in this paper. Ten cases during 2001-2005 were identified when very high aerosol optical depth values in the free troposphere were observed with a UV-Raman lidar. Particle dispersion modeling (FLEXPART) and satellite hot spot fire detection (ATSR) showed that these high free tropospheric

V. Amiridis; D. S. Balis; E. Giannakaki; A. Stohl; S. Kazadzis; M. E. Koukouli; P. Zanis

2009-01-01

355

A flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurements  

Microsoft Academic Search

The problem of deriving a complete set of aerosol optical properties from Sun and sky radiance measurements is discussed. Algorithm development is focused on improving aerosol retrievals by means of including a detailed statistical optimization of the influence of noise in the inversion procedure. The methodological aspects of such an optimization are discussed in detail and revised according to both

Oleg Dubovik; Michael D. King

2000-01-01

356

Latitudinal distribution of the aerosol optical depth over oceans in southern hemisphere  

NASA Astrophysics Data System (ADS)

Latitudinal distribution of the aerosol optical depth (AOD) of the atmosphere over ocean in southern hemisphere is considered on the basis of data of long-term measurements (AERONET MAN). It is shown that the aerosol turbidity of the atmosphere decreases with increasing latitude in Atlantic, Indian, and Pacific oceans. Simple linear relationships are proposed to describe the latitudinal distribution of AOD.

Kabanov, Dmitry M.; Gulev, Sergey K.; Holben, Brent N.; Radionov, Vladimir F.; Sakerin, Sergey M.; Smirnov, Alexander

2014-11-01

357

A Critical Look at Deriving Monthly Aerosol Optical Depth From Satellite Data  

Microsoft Academic Search

Satellite-derived aerosol data sets, such as those provided by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, are greatly improving our understanding of global aerosol optical depth (AOD). Yet, there are sampling issues. MODIS' specific orbital geometry, convolved with the need to avoid bright surfaces (glint, desert, clouds, etc.), means that AOD can be under- or over-sampled in places. When deriving

Robert C. Levy; Gregory G. Leptoukh; Ralph Kahn; Victor Zubko; Arun Gopalan; Lorraine A. Remer

2009-01-01

358

Aerosol optical depth spatio-temporal characterization over the Canadian BOREAS domain  

Microsoft Academic Search

A complete set of Advanced Very High Resolution Radiometer (AVHRR) data (75 images) is used to retrieve aerosol optical depth (AOD) over dense vegetation and over lake water in the visible AVHRR channel. The present approach for remote sensing of aerosols from the National Oceanic and Atmospheric Administration (NOAA)-11 AVHRR sensor is based on the detection of atmospherically dominated signals

C. Bertrand; A. Royer

2004-01-01

359

Variability of Aerosol Optical Properties from Long-term  

E-print Network

Aerosol Forcing Forest fires in Canada on June 10, 1997. #12;NOAA Aerosol Network South PoleSouth Pole SamoaSamoa Mauna LoaMauna Loa BarrowBarrow HungaryHungary Sable IslandSable Island So. Great Plains stations Bondville, Illinois Lamont, Oklahoma Barrow, Alaska #12;Aerosol Sampling System 1 and 10 µm Size

Delene, David J.

360

Effects of atmospheric water on the optical properties of soot aerosols with different mixing states  

NASA Astrophysics Data System (ADS)

Soot aerosols have become the second most important contributor to global warming after carbon dioxide in terms of direct forcing, which is the dominant absorber of visible solar radiation. The optical properties of soot aerosols depend strongly on the mixing mechanism of black carbon with other aerosol components and its hygroscopic properties. In this study, the effects of atmospheric water on the optical properties of soot aerosols have been investigated using a superposition T-matrix method that accounts for the mixing mechanism of soot aerosols with atmospheric water. The dramatic changes in the optical properties of soot aerosols were attributed to its different mixing states with atmospheric water (externally mixed, semi-embedded mixed, and internally mixed). Increased absorption is accompanied by a larger increase in scattering, which is reflected by the increased single scattering albedo. The asymmetry parameter also increased when increasing the atmospheric water content. Moreover, atmospheric water intensified the radiative absorption enhancement attributed to the mixing states of the soot aerosols, with values ranging from 1.5 to 2.5 on average at 0.870 ?m. The increased absorption and scattering ability of soot aerosols, which is attributed to atmospheric water, exerted an opposing effect on climate change. These findings should improve our understanding of the effects of atmospheric water on the optical properties of soot aerosols and their effects on climate. The mixing mechanism for soot aerosols and atmospheric water is important when evaluating the climate effects of soot aerosols, which should be explicitly considered in radiative forcing models.

Cheng, Tianhai; Gu, Xingfa; Wu, Yu; Chen, Hao

2014-11-01

361

Analysis of satellite-based aerosol optical thickness over China in 2013  

NASA Astrophysics Data System (ADS)

The spatial and temporal variations in regional aerosol optical thickness (AOT) over China during 2013 were investigated in this study using Visible Infrared Imaging Radiometer Suite (VIIRS) aerosol intermediate product (IP) data obtained from the NOAA CLASS. It is found that high level AOT in China mainly occurs in the spring and summer. The study compared the aerosols in the economically developed eastern China to those in the western region; urban areas versus rural areas; inland versus coastal cities. Further investigation was also performed to validate VIIRS derived AOT data and aerosol type with in situ ground measurements.

Meng, F.; Cao, C. Y.; Shao, X.

2014-11-01

362

Aerosol Optical Properties Measured Onboard the Ronald H. Brown During ACE Asia as a Function of Aerosol Chemical Composition and Source Region  

NASA Technical Reports Server (NTRS)

During the ACE Asia intensive field campaign conducted in the spring of 2001 aerosol properties were measured onboard the R/V Ronald H. Brown to study the effects of the Asian aerosol on atmospheric chemistry and climate in downwind regions. Aerosol properties measured in the marine boundary layer included chemical composition; number size distribution; and light scattering, hemispheric backscattering, and absorption coefficients. In addition, optical depth and vertical profiles of aerosol 180 deg backscatter were measured. Aerosol within the ACE Asia study region was found to be a complex mixture resulting from marine, pollution, volcanic, and dust sources. Presented here as a function of air mass source region are the mass fractions of the dominant aerosol chemical components, the fraction of the scattering measured at the surface due to each component, mass scattering efficiencies of the individual components, aerosol scattering and absorption coefficients, single scattering albedo, Angstrom exponents, optical depth, and vertical profiles of aerosol extinction. All results except aerosol optical depth and the vertical profiles of aerosol extinction are reported at a relative humidity of 55 +/- 5%. An over-determined data set was collected so that measured and calculated aerosol properties could be compared, internal consistency in the data set could be assessed, and sources of uncertainty could be identified. By taking into account non-sphericity of the dust aerosol, calculated and measured aerosol mass and scattering coefficients agreed within overall experimental uncertainties. Differences between measured and calculated aerosol absorption coefficients were not within reasonable uncertainty limits, however, and may indicate the inability of Mie theory and the assumption of internally mixed homogeneous spheres to predict absorption by the ACE Asia aerosol. Mass scattering efficiencies of non-sea salt sulfate aerosol, sea salt, submicron particulate organic matter, and dust found for the ACE Asia aerosol are comparable to values estimated for ACE 1, Aerosols99, and INDOEX. Unique to the ACE Asia aerosol was the large mass fractions of dust, the dominance of dust in controlling the aerosol optical properties, and the interaction of dust with soot aerosol.

Quinn, P. K.; Coffman, D. J.; Bates, T. S.; Welton, E. J.; Covert, D. S.; Miller, T. L.; Johnson, J. E.; Maria, S.; Russell, L.; Arimoto, R.

2004-01-01

363

Photometric measurements of spring aerosol optical properties in dust and non-dust periods in China  

E-print Network

Photometric measurements of spring aerosol optical properties in dust and non-dust periods in China) increased by 33% in dust weather than in non- dust weather over the three years under study. Further

Li, Zhanqing

364

A COMPARISON OF AEROSOL OPTICAL DEPTH SIMULATED USING CMAQ WITH SATELLITE ESTIMATES  

EPA Science Inventory

Satellite data provide new opportunities to study the regional distribution of particulate matter. The aerosol optical depth (AOD) - a derived estimate from the satellite measured irradiance, can be compared against model derived estimate to provide an evaluation of the columnar ...

365

The impact of aerosol optical depth assimilation on aerosol forecasts and radiative effects during a wild fire event over the United States  

NASA Astrophysics Data System (ADS)

The Gridpoint Statistical Interpolation three-dimensional variational data assimilation (DA) system coupled with the Weather Research and Forecasting/Chemistry (WRF/Chem) model was utilized to improve aerosol forecasts and study aerosol direct and semi-direct radiative feedbacks during a US wild fire event. Assimilation of MODIS total 550 nm aerosol optical depth (AOD) retrievals clearly improved WRF/Chem forecasts of surface PM2.5 and organic carbon (OC) compared to the corresponding forecasts without aerosol data assimilation. The scattering aerosols in the fire downwind region typically cooled layers both above and below the aerosol layer and suppressed convection and clouds, which led to an average of 2% precipitation decrease during the fire week. This study demonstrated that, even with no input of fire emissions, AOD DA improved the aerosol forecasts and allowed a more realistic model simulation of aerosol radiative effects.

Chen, D.; Liu, Z.; Schwartz, C. S.; Lin, H.-C.; Cetola, J. D.; Gu, Y.; Xue, L.

2014-11-01

366

Sources of discrepancy between aerosol optical depth obtained from AERONET and in-situ aircraft profiles  

NASA Astrophysics Data System (ADS)

Aerosol optical properties were measured by NOAA's Airborne Aerosol Observatory over Bondville, Illinois, during more than two years using a light aircraft. Measured properties included total light scattering, backscattering, and absorption, while calculated parameters included aerosol optical depth (AOD), Ångström exponent, single-scattering albedo, hemispheric backscatter fraction, asymmetry parameter, and submicrometer mode fraction of scattering. The in-situ aircraft measurements are compared here with AERONET measurements and retrievals of the aerosol optical properties at the same location, although it is difficult to verify the AERONET retrieval algorithm at a site that is not highly polluted. The comparison reveals discrepancies between the aerosol properties retrieved from AERONET and from in-situ aircraft measurements. These discrepancies are smaller for the AOD, while the biggest discrepancies are for the other derived aerosol properties. Possible sources of discrepancy between the AOD measured by AERONET and the one calculated from the in-situ aircraft measurements are investigated. The largest portion of the AOD discrepancy is likely due to an incorrect adjustment to ambient RH of the scattering coefficient. Another significant part (along with uncertain nephelometer truncation corrections) may come from the possibility that there might be less aerosol below the lowest flight altitude or that the aircraft inlet excludes aerosol particles larger than 5-7 ?m diameter.

Esteve, A. R.; Ogren, J. A.; Sheridan, P. J.; Andrews, E.; Holben, B. N.; Utrillas, M. P.

2012-03-01

367

Climatological Aspects of the Optical Properties of Fine/Coarse Mode Aerosol Mixtures  

NASA Technical Reports Server (NTRS)

Aerosol mixtures composed of coarse mode desert dust combined with fine mode combustion generated aerosols (from fossil fuel and biomass burning sources) were investigated at three locations that are in and/or downwind of major global aerosol emission source regions. Multiyear monitoring data at Aerosol Robotic Network sites in Beijing (central eastern China), Kanpur (Indo-Gangetic Plain, northern India), and Ilorin (Nigeria, Sudanian zone of West Africa) were utilized to study the climatological characteristics of aerosol optical properties. Multiyear climatological averages of spectral single scattering albedo (SSA) versus fine mode fraction (FMF) of aerosol optical depth at 675 nm at all three sites exhibited relatively linear trends up to 50% FMF. This suggests the possibility that external linear mixing of both fine and coarse mode components (weighted by FMF) dominates the SSA variation, where the SSA of each component remains relatively constant for this range of FMF only. However, it is likely that a combination of other factors is also involved in determining the dynamics of SSA as a function of FMF, such as fine mode particles adhering to coarse mode dust. The spectral variation of the climatological averaged aerosol absorption optical depth (AAOD) was nearly linear in logarithmic coordinates over the wavelength range of 440-870 nm for both the Kanpur and Ilorin sites. However, at two sites in China (Beijing and Xianghe), a distinct nonlinearity in spectral AAOD in logarithmic space was observed, suggesting the possibility of anomalously strong absorption in coarse mode aerosols increasing the 870 nm AAOD.

Eck, T. F.; Holben, B. N.; Sinyuk, A.; Pinker, R. T.; Goloub, P.; Chen, H.; Chatenet, B.; Li, Z.; Singh, R. P.; Tripathi, S.N.; Reid, J. S.; Giles, D. M.; Dubovik O.; O'Neill, N. T.; Smirnov, A.; Wang, P.; Xia, X.

2010-01-01

368

Characteristic aerosol optical depths during the Harmattan season on sub-Sahara Africa  

NASA Technical Reports Server (NTRS)

Aerosol optical depths were derived from sun photometer measurements in three narrow bands centered at 500, 675 and 875 nm, taken at Ilorin, Nigeria, located in sub-Saharan Africa. Selected results will be presented on the diurnal, seasonal, and interannual variability of spectral aerosol optical depth for two Harmattan seasons, during 1987-1989. At 500 nm values between 0.9-1.6 were quite common while the averages were between 1-1.2.

Pinker, Rachel T.; Idemudia, G.; Aro, T. O.

1994-01-01

369

Characterisation of solution-based pressurised metered-dose inhaler aerosols with an optical particle counter.  

PubMed

The White Light Aerosol Spectrometer (welas(R)) is an alternative method to multistage cascade impaction in the analysis of particle-size distribution (PSD) that allows measurements in high concentrations by single particle measurement. Correspondence of the PSD measured by the welas(R) system in combination with a new aerosol sampling system has been discussed before for aqueous aerosols from nebulisers [M. Kuhli, M. Weiss, H. Steckel, A sampling and dilution system for droplet aerosols from medical nebulisers developed for use with an optical particle counter, Journal of Aerosol Science 40 (2009) 523-533]. For aerosols from solution-based pressurised metered-dose inhalers (pMDI), both the apparent density and the dynamic shape factor of the dry solid particles come into account for correlation of aerodynamic to scattered light equivalent diameter. The aim of this study was to enable welas(R) measurements for pMDI aerosols. Equal particle drying properties in cascade impaction (Next Generation Impactor, NGI) and the aerosol sampling system for the welas(R) should be assured. Therefore, an additional, optionally preheated, extension device was included to modify the aerosol sampling system. The PSD measured with the aerosol sampling system that allowed most complete particle drying was compared to the PSD measured by NGI. The introduction of an empiric calibration allows correlation of NGI and welas(R) measurements for the investigated solution-based pMDIs. PMID:20347974

Kuhli, M; Weiss, M; Steckel, H

2010-08-01

370

Analysis of aerosol optical and microphysical properties observed during the DC3 field study  

NASA Astrophysics Data System (ADS)

The Deep Convective Clouds and Chemistry Experiment (DC3) consisted of 18 research flights from Salina, KS. During cloud inflow and outflow surveys, various aged aerosol layers and plumes, including biomass burning, were sampled by the NASA DC-8 aircraft which was equipped with a broad suite of instruments for aerosol optical, microphysical, and chemical properties. As a result, the DC3 dataset includes detailed aerosol number size distribution, bulk aerosol mass concentration, black carbon mass concentration, and mass size distribution for sulfate, nitrate, ammonium and organics, together with scattering and absorption coefficients. We use this comprehensive dataset to perform a detailed closure analysis to examine the consistency between the observed aerosol properties and the literature reported aerosol refractive index values. In this context, we report aerosol observations, and comparisons between the aerosol mass and number size distribution for various aerosol layers. Closure tests will also be presented in terms of the impact of the aerosol composition and size distribution on the scattering and absorption.

Chen, G.; Schuster, G. L.; Anderson, B. E.; Jimenez, J. L.; Campuzano Jost, P.; Dibb, J. E.; Scheuer, E. M.; Ziemba, L. D.; Beyersdorf, A. J.; Thornhill, K. L.; Moore, R.; Winstead, E.; Markovic, M. Z.

2013-12-01

371

Aerosol optical properties at Lampedusa (Central Mediterranean). 1. Influence of transport and identification of different aerosol types  

NASA Astrophysics Data System (ADS)

Aerosol optical depth and Ångström exponent were obtained from multi filter rotating shadowband radiometer (MFRSR) observations carried out at the island of Lampedusa, in the Central Mediterranean, in the period July 2001-September 2003. The average aerosol optical depth at 495.7 nm, ?, is 0.24±0.14; the average Ångström exponent, ?, is 0.86±0.63. The observed values of ? range from 0.03 to 1.13, and the values of ? vary from -0.32 to 2.05, indicating a large variability in aerosol content and size. In cloud-free conditions, 36% of the airmasses come from Africa, 25% from Central-Eastern Europe, and 19% from Western France, Spain and the North Atlantic. In summer, 42% of the airmasses is of African origin. In almost all cases African aerosols display high values of ? and low values of ?, typical of Saharan dust (average values of ? and ? are 0.36 and 0.42, respectively). Particles originating from Central-Eastern Europe show relatively large average values of ? and ? (0.23 and 1.5, respectively), while particles from Western France, Spain and the North Atlantic show the lowest average values of ? (0.15), and relatively small values of ? (0.92). Intermediate values of ? are often connected with relatively fast changes of the airmass originating sector, suggesting the contemporary presence of different types of particles in the air column. Clean marine conditions are rare at Lampedusa, and are generally associated with subsidence of the airmasses reaching the island. Average values of ? and ? for clean marine conditions are 0.11 and 0.86, respectively. The largest values of ? (about 2) were observed in August 2003, when large scale forest fires in Southern Europe produced consistent amounts of fine combustion particles, that were transported to the Central Mediterranean by a persistent high pressure system over Central Europe. Smoke particles in some cases mix with desert dust, producing intermediate values of ?. The seasonal distribution of the meteorological patterns over the Mediterranean, the efficiency of the aerosol production mechanisms, and the variability of the particles' residence time produce a distinct seasonal cycle of aerosol optical depths and Ångström exponent values. Particles originating from all sectors show a summer maximum in aerosol optical depth. The summer increase in optical depth for European aerosols is linked with an increment in the values of ?, that indicates an enhancement in the number of fine particles. The summer maximum of ? for African particles is associated with a weak reduction in the Ångström exponent, suggesting an increase in the total number of particles and a relatively more intense transport of large particles. The observations were classified according to the aerosol optical properties, and two main classes have been identified: desert dust and biomass burning/urban-industrial aerosols. Values of ? and ? averaged over the whole observing period are 0.37 and 0.15 for desert dust, and 0.27 and 1.77 for urban-industrial/biomass burning aerosols.

Pace, G.; di Sarra, A.; Meloni, D.; Piacentino, S.; Chamard, P.

2006-03-01

372

Aerosol optical properties at Lampedusa (Central Mediterranean) 1. Influence of transport and identification of different aerosol types  

NASA Astrophysics Data System (ADS)

Aerosol optical depth andÅngström exponent were obtained from multi filter rotating shadowband radiometer (MFRSR) observations carried out at the island of Lampedusa, in the Central Mediterranean, in the period July 2001-September 2003. The average aerosol optical depth at 495.7 nm, ?, is 0.24±0.14; the averageÅngström exponent, ?, is 0.86±0.63. The observed values of ? range from 0.03 to 1.13, and the values of ? vary from -0.32 to 2.05, indicating a large variability in aerosol content and size. In cloud-free conditions, 36% of the airmasses come from Africa, 25% from Central-Eastern Europe, and 19% from Western France, Spain and the North Atlantic. In summer, 42% of the airmasses are of African origin. In almost all cases African aerosols display high values of ? and low values of ?, typical of Saharan dust (average values of ? and ? are 0.36 and 0.42, respectively). Particles originating from Central-Eastern Europe show relatively large average values of ? and ? (0.23 and 1.5, respectively), while particles from Western France, Spain and the North Atlantic show the lowest average values of ? (0.15), and relatively small values of ? (0.92). Intermediate values of ? are often connected with relatively fast changes of the airmass originating sector, suggesting the contemporary presence of different types of particles in the air column. The largest values of ? (about 2) were observed in August 2003, when large scale forest fires in Southern Europe produced consistent amounts of fine combustion particles that were transported to the Central Mediterranean by a persistent high pressure system over Central Europe. Smoke particles in some cases mix with desert dust, producing intermediate values of ?. The seasonal distribution of the meteorological patterns over the Mediterranean, the efficiency of the aerosol production mechanisms, and the variability of the particles' residence time produce a distinct seasonal cycle of aerosol optical depths andÅngström exponent values. Particles originating from all sectors show a summer maximum in aerosol optical depth. The summer increase in optical depth for European aerosols is linked with an increment in the values of ? that indicates an enhancement in the number of fine particles. The summer maximum of ? for African particles is associated with a weak reduction in theÅngström exponent, suggesting an increase in the total number of particles and a relatively more intense transport of large particles. The observations were classified according to the aerosol optical properties, and two main classes have been identified: desert dust and biomass burning/urban-industrial aerosols. Values of ? and ? averaged over the whole observing period are 0.37 and 0.15 for desert dust, and 0.27 and 1.77 for urban-industrial/biomass burning aerosols. Lampedusa reveals a stronger influence of desert dust compared to other Mediterranean sites (mostly located on the coasts of Europe).

Pace, G.; di Sarra, A.; Meloni, D.; Piacentino, S.; Chamard, P.

2005-07-01

373

Measurements of Aerosol Vertical Profiles and Optical Properties during INDOEX 1999 Using Micro-Pulse Lidars  

NASA Technical Reports Server (NTRS)

Micro-pulse lidar systems (MPL) were used to measure aerosol properties during the Indian Ocean Experiment (INDOEX) 1999 field phase. Measurements were made from two platforms: the NOAA ship RN Ronald H. Brown, and the Kaashidhoo Climate Observatory (KCO) in the Maldives. Sunphotometers were used to provide aerosol optical depths (AOD) needed to calibrate the MPL. This study focuses on the height distribution and optical properties (at 523 nm) of aerosols observed during the campaign. The height of the highest aerosols (top height) was calculated and found to be below 4 km for most of the cruise. The marine boundary layer (MBL) top was calculated and found to be less than 1 km. MPL results were combined with air mass trajectories, radiosonde profiles of temperature and humidity, and aerosol concentration and optical measurements. Humidity varied from approximately 80% near the surface to 50% near the top height during the entire cruise. The average value and standard deviation of aerosol optical parameters were determined for characteristic air mass regimes. Marine aerosols in the absence of any continental influence were found to have an AOD of 0.05 +/- 0.03, an extinction-to-backscatter ratio (S-ratio) of 33 +/- 6 sr, and peak extinction values around 0.05/km (near the MBL top). The marine results are shown to be in agreement with previously measured and expected values. Polluted marine areas over the Indian Ocean, influenced by continental aerosols, had AOD values in excess of 0.2, S-ratios well above 40 sr, and peak extinction values approximately 0.20/km (near the MBL top). The polluted marine results are shown to be similar to previously published values for continental aerosols. Comparisons between MPL derived extinction near the ship (75 m) and extinction calculated at ship-level using scattering measured by a nephelometer and absorption using a PSAP were conducted. The comparisons indicated that the MPL algorithm (using a constant S-ratio throughout the lower troposphere) calculates extinction near the surface in agreement with the ship-level measurements only when the MBL aerosols are well mixed with aerosols above. Finally, a review of the MPL extinction profiles showed that the model of aerosol vertical extinction developed during an earlier INDOEX field campaign (at the Maldives) did not correctly describe the true vertical distribution over the greater Indian Ocean region. Using the average extinction profile and AOD obtained during marine conditions, a new model of aerosol vertical extinction was determined for marine atmospheres over the Indian Ocean. A new model of aerosol vertical extinction for polluted marine atmospheres was also developed using the average extinction profile and AOD obtained during marine conditions influenced by continental aerosols.

Welton, Ellsworth J.; Voss, Kenneth J.; Quinn, Patricia K.; Flatau, Piotr J.; Markowicz, Krzysztof; Campbell, James R.; Spinhirne, James D.; Gordon, Howard R.; Johnson, James E.; Starr, David OC. (Technical Monitor)

2001-01-01

374

Estimation of cloud condensation nuclei concentration from aerosol optical quantities: influential factors and uncertainties  

NASA Astrophysics Data System (ADS)

Large-scale measurements of cloud condensation nuclei (CCN) are difficult to obtain on a routine basis, whereas aerosol optical quantities are more readily available. This study investigates the relationship between CCN and aerosol optical quantities for some distinct aerosol types using extensive observational data collected at multiple Atmospheric Radiation Measurement (ARM) Climate Research Facility (CRF) sites around the world. The influences of relative humidity (RH), aerosol hygroscopicity (fRH) and single scattering albedo (SSA) on the relationship are analyzed. Better relationships are found between aerosol optical depth (AOD) and CCN at the Southern Great Plains (US), Ganges Valley (India) and Black Forest sites (Germany) than those at the Graciosa Island (the Azores) and Niamey (Niger) sites, where sea salt and dust aerosols dominate, respectively. In general, the correlation between AOD and CCN decreases as the wavelength of the AOD measurement increases, suggesting that AOD at a shorter wavelength is a better proxy for CCN. The correlation is significantly improved if aerosol index (AI) is used together with AOD. The highest correlation exists between CCN and aerosol scattering coefficients (?sp) and scattering AI measured in situ. The CCN-AOD (AI) relationship deteriorates with increasing RH. If RH exceeds 75%, the relationship where AOD is used as a proxy for CCN becomes invalid, whereas a tight ?sp-CCN relationship exists for dry particles. Aerosol hygroscopicity has a weak impact on the ?sp-CCN relationship. Particles with low SSA are generally associated with higher CCN concentrations, suggesting that SSA affects the relationship between CCN concentration and aerosol optical quantities. It may thus be used as a constraint to reduce uncertainties in the relationship. A significant increase in ?sp and decrease in CCN with increasing SSA is observed, leading to a significant decrease in their ratio (CCN / ?sp) with increasing SSA. Parameterized relationships are developed for estimating CCN, which account for RH, particle size, and SSA.

Liu, Jianjun; Li, Zhanqing

2014-01-01

375

Aerosol optical depth measurements and their impact on surface levels of ultraviolet-B radiation  

NASA Astrophysics Data System (ADS)

Surface measurements of total and diffuse UV irradiance at the seven narrowband wavelength channels of the ultraviolet multifilter rotating shadow-band radiometer (UVMFR) were used to determine total column ozone and aerosol optical depth for two 6-month periods in 1997 and 1999 at a site in the Blue Ridge Mountains of North Carolina. The retrieved column ozone displayed a seasonal dependence and consistent agreement with the Total Ozone Mapping Spectrometer (TOMS). The mean ratio of retrieved ozone to TOMS ozone was 0.98 with standard deviations of 0.02 and 0.01 for 1997 and 1999, respectively. Aerosol optical depth at 317, 325, 332, and 368 nm was derived for a 6-month period of 1999. The seasonal trend exhibited is influenced by the persistent summertime haze that occurs in the region. The retrieved aerosol optical depths are used as input in a radiative transfer model to investigate the effect of their realistic values on the calculation of the UV index (UVI) forecasted by the National Weather Service. The percentage change in calculated surface erythemally weighted UV (versus calculations using the standard UVI aerosol inputs) ranges from a 4% increase to a nearly 50% decrease, dependent upon the aerosol optical depth and amount of absorption by aerosols. Based on our measurements, it was found that during the summertime the UV index can deviate by up to -5 index units from the forecast using the standard aerosol inputs.

Wenny, B. N.; Saxena, V. K.; Frederick, J. E.

2001-01-01

376

Aerosol optical hygroscopicity measurements during the 2010 CARES Campaign  

NASA Astrophysics Data System (ADS)

Measurements of the effect of water uptake on particulate light extinction or scattering made at two locations during the 2010 CARES study around Sacramento, CA are reported. The observed influence of water uptake, characterized through the dimensionless optical hygroscopicity parameter ?, is compared with calculations constrained by observed particle size distributions and size-dependent particle composition. A closure assessment has been carried out that allowed for determination of the average hygroscopic growth factors (GF) at 85% relative humidity and the dimensionless hygroscopicity parameter ? for oxygenated organic aerosol (OA) and for supermicron particles, yielding ? = 0.1-0.15 and 0.9-1.0, respectively. The derived range of oxygenated OA ? values are in line with previous observations. The relatively large values for supermicron particles is consistent with substantial contributions of sea salt-containing particles in this size range. Analysis of time-dependent variations in the supermicron particle hygroscopicity suggest that atmospheric processing, specifically chloride displacement by nitrate and the accumulation of secondary organics on supermicron particles, can lead to substantial depression of the observed GF.

Atkinson, D. B.; Radney, J. G.; Lum, J.; Kolesar, K. R.; Cziczo, D. J.; Pekour, M. S.; Zhang, Q.; Setyan, A.; Zelenyuk, A.; Cappa, C. D.

2014-12-01

377

Spatiotemporal modeling of irregularly spaced Aerosol Optical Depth data  

PubMed Central

Many advancements have been introduced to tackle spatial and temporal structures in data. When the spatial and/or temporal domains are relatively large, assumptions must be made to account for the sheer size of the data. The large data size, coupled with realities that come with observational data, make it difficult for all of these assumptions to be met. In particular, air quality data are very sparse across geographic space and time, due to a limited air pollution monitoring network. These “missing” values make it diffcult to incorporate most dimension reduction techniques developed for high-dimensional spatiotemporal data. This article examines aerosol optical depth (AOD), an indirect measure of radiative forcing, and air quality. The spatiotemporal distribution of AOD can be influenced by both natural (e.g., meteorological conditions) and anthropogenic factors (e.g., emission from industries and transport). After accounting for natural factors influencing AOD, we examine the spatiotemporal relationship in the remaining human influenced portion of AOD. The presented data cover a portion of India surrounding New Delhi from 2000 – 2006. The proposed method is demonstrated showing how it can handle the large spatiotemporal structure containing so much missing data for both meteorologic conditions and AOD over time and space. PMID:24470786

Oleson, Jacob J.; Kumar, Naresh; Smith, Brian J.

2012-01-01

378

Aerosol optical properties and radiative effects over Manora Peak in the Himalayan foothills: seasonal variability and role of transported aerosols.  

PubMed

The higher altitude regions of Himalayas and Tibetan Plateau are influenced by the dust and black carbon (BC) aerosols from the emissions and long-range transport from the adjoining areas. In this study, we present impacts of advection of polluted air masses of natural and anthropogenic emissions, on aerosol optical and radiative properties at Manora Peak (~2000 m amsl) in central Himalaya over a period of more than two years (February 2006-May 2008). We used the most updated and comprehensive data of chemical and optical properties available in one of the most climatically sensitive region, the Himalaya, to estimate atmospheric radiative forcing and heating rate. Aerosol optical depth (AOD) was found to vary from 0.04 to 0.45 with significantly higher values in summer mainly due to an increase in mineral dust and biomass burning aerosols due to transport. In contrast, single scattering albedo (SSA) varied from 0.74 to 0.88 with relatively lower values during summer, suggesting an increase in absorbing BC and mineral dust aerosols. As a result, a large positive atmospheric radiative forcing (about 28 ± 5 Wm(-2)) and high values of corresponding heating rate (0.80 ± 0.14 Kday(-1)) has been found during summer. During the entire observation period, radiative forcing at the top of the atmosphere varied from -2 to +14 Wm(-2) and from -3 to -50 Wm(-2) at the surface whereas atmospheric forcing was in the range of 3 to 65 Wm(-2) resulting in a heating rate of 0.1-1.8 Kday(-1). PMID:25261819

Srivastava, A K; Ram, K; Singh, Sachchidanand; Kumar, Sanjeev; Tiwari, S

2015-01-01

379

Effect of Wind Speed on Aerosol Optical Depth over Remote Oceans, Based on Data from the Maritime Aerosol Network  

NASA Technical Reports Server (NTRS)

The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. The MAN archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we investigate correlations between ship-borne aerosol optical depth (AOD) and near-surface wind speed, either measured (onboard or from satellite) or modeled (NCEP). According to our analysis, wind speed influences columnar aerosol optical depth, although the slope of the linear regression between AOD and wind speed is not steep (approx. 0.004 - 0.005), even for strong winds over 10m/s. The relationships show significant scatter (correlation coefficients typically in the range 0.3 - 0.5); the majority of this scatter can be explained by the uncertainty on the input data. The various wind speed sources considered yield similar patterns. Results are in good agreement with the majority of previously published relationships between surface wind speed and ship-based or satellite-based AOD measurements. The basic relationships are similar for all the wind speed sources considered; however, the gradient of the relationship varies by around a factor of two depending on the wind data used

Smirnov, A.; Sayer, A. M.; Holben, B. N.; Hsu, N. C.; Sakerin, S. M.; Macke, A.; Nelson, N. B.; Courcoux, Y.; Smyth, T. J.; Croot, P.; Quinn, P. K.; Sciare, J.; Gulev, S. K.; Piketh, S.; Losno, R.; Kinne, S.; Radionov, V. F.

2012-01-01

380

Improved method to retrieve aerosol optical properties from combined elastic backscatter and Raman lidar data  

NASA Astrophysics Data System (ADS)

An improved method that has the potential to improve the retrieval of aerosol optics properties (backscatter/extinction coefficients) from elastic-Raman lidar data is presented. Aerosol backscatter coefficients can be retrieved by choosing the reference height at near-range rather than conventional far-range when the signal-to-noise ratios are low at the far-range or aloft aerosol layers and clouds appear there. Significant retrieval errors in aerosol backscatter coefficients caused by large uncertainties of the aerosol reference value at far-range can be reduced. To avoid the ill-posed retrievals of aerosol extinction from the conventional Raman method, the new method derives the aerosol extinction and lidar ratio with the constrained Fernald inversions by independent aerosol backscatter coefficients from above proposed method. The numerical simulations demonstrated that the proposed method provides good accuracy and resolution of aerosol profile retrievals. And the method is also applied to elastic-Raman lidar measurements at the Hampton University, Hampton, Virginia.

Su, Jia; Wu, Yonghua; McCormick, M. Patrick; Lei, Liqiao; Lee, Robert B.

2014-07-01

381

How safe is gamete micromanipulation by laser tweezers?  

NASA Astrophysics Data System (ADS)

Laser tweezers, used as novel sterile micromanipulation tools of living cells, are employed in laser-assisted in vitro fertilization (IVF). For example, controlled spermatozoa transport with 1064 nm tweezers to human egg cells has been performed in European clinics in cases of male infertility. The interaction of approximately 100 mW near infrared (NIR) trapping beams at MW/cm2 intensity with human gametes results in low mean less than 2 K temperature increases and less than 100 pN trapping forces. Therefore, photothermal or photomechanical induced destructive effects appear unlikely. However, the high photon flux densities may induce simultaneous absorption of two NIR photons resulting in nonlinear interactions. These nonlinear interactions imply non-resonant two-photon excitation of endogenous cellular chromophores. In the case of less than 800 nm tweezers, UV- like damage effects may occur. The destructive effect is amplified when multimode cw lasers are used as tweezer sources due to longitudinal mode-beating effects and partial mode- locking. Spermatozoa damage within seconds using 760 nm traps due to formation of unstable ps pulses in a cw Ti:Sa ring laser is demonstrated. We recommend the use of greater than or equal to 800 nm traps for optical gamete micromanipulation. To our opinion, further basic studies on the influence of nonlinear effects of laser tweezers on human gamete are necessary.

Koenig, Karsten; Tromberg, Bruce J.; Tadir, Yona; Berns, Michael W.

1998-04-01

382

Aerosol optical properties in the Marine Environment during the TCAP-I campaign  

NASA Astrophysics Data System (ADS)

The role of direct radiative forcing by atmospheric aerosol is one of the largest sources of uncertainty in predicting climate change. Much of this uncertainty comes from the limited knowledge of observed aerosol optical properties. In this presentation we discuss derived aerosol optical properties based on measurements made during the summer 2012 Two-Column Aerosol Project-I (TCAP) campaign and relate these properties to the corresponding chemical and physical properties of the aerosol. TCAP was designed to provide simultaneous, in-situ observations of the size distribution, chemical properties, and optical properties of aerosol within and between two atmospheric columns over the Atlantic Ocean near the eastern seaboard of the United States. These columns are separated by 200-300 km and were sampled in July 2012 during a summer intensive operation period (IOP) using the U.S. Department of Energy's Gulfstream-1 (G-1) and NASA's B200 aircraft, winter IOP using G-1 aircraft in February 2013, and the surface-based DOE Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) located on Cape Cod. In this presentation we examine the spectral dependence of the aerosol optical properties measured from the aircraft over the TCAP-I domain, with an emphasis on in-situ derived intensive properties measured by a 3-? Nephelometer, a Particle Soot Absorption Photometer (PSAP), a humidograph (f(RH)), and a Single Particle Soot Photometer (SP2). Preliminary results indicate that the aerosol are more light-absorbing as well as more hygroscopic at higher altitudes (2-4 km) compared to the corresponding values made within residual layers near the surface (0-2 km altitude). The average column (0-4 km) single scattering albedo (?) and hygroscopic scattering factor (F) are found to be ~0.96 and 1.25, respectively. Additional results on key aerosol intensive properties such as the angstrom exponent (å), asymmetry parameter (g), backscattering fraction (b), and gamma parameter (?) will be presented and discussed.

Chand, D.; Berg, L. K.; Barnard, J.; Berkowitz, C. M.; Burton, S. P.; Chapman, E. G.; Comstock, J. M.; Fast, J. D.; Ferrare, R. A.; Connor, F. J.; Hair, J. W.; Hostetler, C. A.; Hubbe, J.; Kluzek, C.; Mei, F.; Pekour, M. S.; Sedlacek, A. J.; Schmid, B.; Shilling, J. E.; Shinozuka, Y.; Tomlinson, J. M.; Wilson, J. M.; Zelenyuk-Imre, A.

2013-12-01

383

Microphysical and optical properties of aerosol particles in urban zone during ESCOMPTE  

NASA Astrophysics Data System (ADS)

Microphysical and optical properties of the main aerosol species on a peri-urban site have been investigated during the ESCOMPTE experiment. Ammonium sulfate (AS), nitrate (N), black carbon (BC), particulate organic matter (POM), sea salt (SS) and mineral aerosol (D) size distributions have been used, associated with their refractive index, to compute, from the Mie theory, the key radiative aerosol properties as the extinction coefficient Kext, the mass extinction efficiencies ?ext, the single scattering albedo ?0 and the asymmetry parameter g at the wavelength of 550 nm. Optical computations show that 90% of the light extinction is due to anthropogenic aerosol and only 10% is due to natural aerosol (SS and D). 44±6% of the extinction is due to (AS) and 40±6% to carbonaceous particles (20±4% to BC and 21±4% to POM). Nitrate aerosol has a weak contribution of 5±2%. Computations of the mass extinction efficiencies ?ext, single scattering albedo ?0 and asymmetry parameter g indicate that the optical properties of the anthropogenic aerosol are often quite different from those yet published and generally used in global models. For example, the (AS) mean specific mass extinction presents a large difference with the value classically adopted at low relative humidity ( h<60%) (2.6±0.5 instead of 6 m 2 g -1 at 550 nm). The optical properties of the total aerosol layer, including all the aerosol species, indicate a mean observed single-scattering albedo ?0=0.85±0.05, leading to an important absorption of the solar radiation and an asymmetry parameter g=0.59±0.05 which are in a reasonably good agreements with the AERONET retrieval of ?0 (=0.86±0.05) and g (=0.64±0.05) at this wavelength.

Mallet, M.; Roger, J. C.; Despiau, S.; Dubovik, O.; Putaud, J. P.

2003-10-01

384

Parallel trapping of multiwalled carbon nanotubes with optoelectronic tweezers  

PubMed Central

Here we report the use of optoelectronic tweezers and dynamic virtual electrodes to address multiwalled carbon nanotubes (MWCNTs) with trap stiffness values of approximately 50 fN??m. Both high-speed translation (>200 ?m?s) of individual-MWCNTs and two-dimensional trapping of MWCNT ensembles are achieved using 100,000 times less optical power density than single beam laser tweezers. Modulating the virtual electrode’s intensity enables tuning of the MWCNT ensemble’s number density by an order of magnitude on the time scale of seconds promising a broad range of applications in MWCNT science and technology. PMID:19884988

Pauzauskie, Peter J.; Jamshidi, Arash; Valley, Justin K.; Satcher, Joe H.; Wu, Ming C.

2009-01-01

385

Optical properties of aerosols at Grand Canyon National Park  

Microsoft Academic Search

Visibility in the United States is expected to improve over the next few decades because of reduced emissions, especially sulfur dioxide. In the eastern United States, sulfates make up about 60–70% of aerosol extinction, while in the inner mountain west that fraction is only about 30%. In the inner mountain west, carbon aerosols make up about 35% of extinction, while

William C. Malm; Derek E. Day

2000-01-01

386

Fast hologram computation and aberration control for holographic tweezers  

NASA Astrophysics Data System (ADS)

Holographic tweezers offer a very versatile tool in many trapping applications. Compared to tweezers working with acousto optical modulators or using the generalized phase contrast, holographic tweezers so far were relatively slow. The computation time for a hologram was much longer than the modulation frequency of the modulator. To overcome this drawback we present a method using modified algorithms which run on state of the art graphics boards and not on the CPU. This gives the potential for a fast manipulation of many traps, for cell sorting for example, as well as for a real-time aberration control. The control of aberrations which can vary spatially or temporally is relevant to many real world applications. This can be accomplished by applying an iterative approach based on image processing.

Reicherter, M.; Haist, T.; Zwick, S.; Burla, A.; Seifert, L.; Osten, W.

2005-08-01

387

A new approach to characterise pharmaceutical aerosols: Measurement of aerosol from a single dose aqueous inhaler with an optical particle counter  

Microsoft Academic Search

An in-line sampling system with dilution units for aqueous droplet aerosols from single dose inhalers (Berodual Respimat®, Boehringer Ingelheim Pharma GmbH & Co. KG, Germany) for an optical particle counter is described. The device has been designed to interface with a white light aerosol spectrometer (welas® digital 2100, Palas® GmbH, Germany) that allows the time-resolved measurement of highly concentrated aerosols.

Maren Kuhli; Maximilian Weiss; Hartwig Steckel

2010-01-01

388

Comparative Optical Measurements of Airspeed and Aerosols on a DC-8 Aircraft  

NASA Technical Reports Server (NTRS)

NASA Dryden supported a cooperative flight test program on the NASA DC-8 aircraft in November 1993. This program evaluated optical airspeed and aerosol measurement techniques. Three brassboard optical systems were tested. Two were laser Doppler systems designed to measure free-stream-referenced airspeed. The third system was designed to characterize the natural aerosol statistics and airspeed. These systems relied on optical backscatter from natural aerosols for operation. The DC-8 aircraft carried instrumentation that provided real-time flight situation information and reference data on the aerosol environment. This test is believed to be the first to include multiple optical airspeed systems on the same carrier aircraft, so performance could be directly compared. During 23 hr of flight, a broad range of atmospheric conditions was encountered, including aerosol-rich layers, visible clouds, and unusually clean (aerosol-poor) regions. Substantial amounts of data were obtained. Important insights regarding the use of laser-based systems of this type in an aircraft environment were gained. This paper describes the sensors used and flight operations conducted to support the experiments. The paper also briefly describes the general results of the experiments.

Bogue, Rodney; McGann, Rick; Wagener, Thomas; Abbiss, John; Smart, Anthony

1997-01-01

389

Comparison of aerosol optical depth from four solar radiometers during the fall 1997 ARM Intensive Observation Period  

Microsoft Academic Search

In the Fall of 1997 the Atmospheric Radiation Measurement (ARM) program conducted an Intensive Observation Period (IOP) to study aerosols. Five sun-tracking radiometers were present to measure the total column aerosol optical depth. This comparison performed on the Southern Great Plains (SGP) demonstrates the capabilities and limitations of modern tracking sunphotometers at a location typical of where aerosol measurements are

B. Schmid; J. Michalsky; R. Halthore; M. Beauharnois; L. Harrison; J. Livingston; P. Russell; B. Holben; T. Eck; A. Smirnov

1999-01-01

390

MONITORING AEROSOL OPTICAL DEPTH AT BARROW, ALASKA AND SOUTH POLE; HISTORICAL OVERVIEW, RECENT RESULTS, AND FUTURE GOALS  

Microsoft Academic Search

Atmospheric aerosols affect the Earth's radiation budget through interactions with solar and terrestrial radiation. Various committees involved with assessing global climate change recognize that aerosols can significantly impact the earth's radiation balance. In particular, the Scientific Committee on Antarctic Research has recommended the establishment of an international network of solar spectrophotometers to monitor aerosol optical depth (AOD) at high latitudes.

Robert S. Stone

391

Preliminary Study on Remote Sensing of Aerosol Optical Properties over Ocean around the Korean Peninsula from Geostationary Ocean Color Imager  

Microsoft Academic Search

An aerosol retrieval algorithm for the first Geostationary Ocean Color Imager (GOCI) to be launched in September 2009 onboard the Communication, Ocean, and Meteorological Satellite (COMS) is presented by applying the algorithm to the MODIS data. Over clear water, the algorithm retrieves aerosol optical depth (AOD) and fine-mode fraction (FMF) together with aerosol type in 1 km × 1 km

J. Lee; J. Kim; J. Ryu; Y. Ahn

2009-01-01

392

Aerosol optical properties variations over the southern and northern slopes of the Himalayas  

NASA Astrophysics Data System (ADS)

The Himalayas is the highest mountain on the earth. It blocks off the aerosols obviously, especially during the monsoon seasons. The aerosol optical properties derived from Aerosol Robotic Network (AERONET) dataset over the southern (Pokhara station in Nepal and EVK2-CNR station in Nepal) and northern (Qomolangma(Mt. Everest) station (QOMS_CAS) in Tibet, China) slopes of the Himalayas are analyzed in this study. The low aerosol optical depth (AOD) at QOMS_CAS and EVK2-CNR indicates they are background sites in Himalaya regions. AOD at Pokhara is much higher than the former two sites with a seasonal variation pattern. This is maybe because Pokhara is more influenced by human activities and India summer monsoon. There are both fine and coarse particle mode aerosol in all three sites. Diurnal variation of AOD and Ångström exponent (AE) has a wide range at all three stations. QOMS_CAS mostly influenced by distant sources reveals AOD has no diurnal cycle in all seasons. Simultaneously, there are smaller particles in the morning and late afternoon, however, particles are larger at noon. The diurnal variation at Pokhara shows a higher AOD value in the morning and late afternoon, and reaches its minimum at noon except JJA (June to August). In all seasons, AOD at EVK2-CNR increases continuously during a day, and reaches maximum at late afternoon due to evolution of mountain-valley flows. AE indicating the particle size has no fixed mode at Pokhara and EVK2-CNR. The aerosols in the northern slope are mostly from distinct regions, and transport from the upper troposphere to atmospheric boundary layer (ABL) probably. The changes of ABL make no apparent effect on aerosol daytime variation. Conversely, the aerosols in the southern slope are mostly from local regions, and maybe spread upwards from the ground gradually. Atmospheric mixing layer height changes with the evolution of the ABL, which diffuses aerosols in the troposphere. Therefore, this process leads aerosol daytime variation.

Xu, Chao; Ma, Yaoming; Yang, Kun; Qin, Jun; Zhu, Zhikun

2013-04-01

393

First measurements of aerosol optical depth and Angstrom exponent number from AERONET's Kuching site  

NASA Astrophysics Data System (ADS)

We report our first measurements, over the 2011 dry season period, of aerosol optical depth, Angstrom exponent number and its fine mode counterpart obtained from photometric measurements at AERONET's newest site located at the city of Kuching, Sarawak, East Malaysia. This site was set up as part of the collaborative efforts of the Seven South East Asian Studies (7SEAS) regional aerosol measurements initiative. Located at the converging zone between peninsular Malaysia and the land masses of Sumatra, Borneo, Java and Sulawesi, this site is expected to provide first hand evidence about the physical and optical characteristics of the regional aerosol environment, specially during the biomass burning months. Moreover, given its relative proximity to our Singapore radiation measurement super-site, Kuching is expected to provide further insight on aerosol transport pathways caused by seasonal winds transporting smoke to other parts of the maritime continent and the South Asia region.

Salinas, Santo V.; Chew, Boon N.; Mohamad, M.; Mahmud, M.; Liew, Soo C.

2013-10-01

394

Retrieval of aerosol optical thickness for desert conditions using MERIS observations during the SAMUM campaign  

NASA Astrophysics Data System (ADS)

ABSTRACT Approximately 30% of the land surface is arid, having desert or semi-desert conditions. Aerosol originating from these regions plays a significant role in climate and atmospheric chemistry of the atmosphere. Retrieving aerosol properties from space-borne platforms above desert conditions, where the surface reflectance is usually very bright, is a challenging task. The proportion of the surface to top of atmosphere (TOA) reflectance can reach values over 90%, especially for wavelength above 500nm. For these reasons detailed knowledge of aerosol and surface optical properties from these regions is required to separate atmosphere from intrinsically bright surfaces. An approach to retrieve aerosol properties over arid and semi-arid regions based on the Bremen Aerosol Retrieval (BAER) has been developed and validated within the Dust Aerosol Retrievals from Space-Born Instruments (DREAMS) Project, which is part of the Saharan Mineral Dust Experiment (SAMUM, 2006). Combining measurements of the backscattered radiation from the Medium Resolution Imaging Spectrometer (MERIS) instrument aboard Environmental Satellite (ENVISAT) and ground-based measurements in Morocco in radiation closure experiments yields the aerosol optical properties of mineral dust at selected locations.

Dinter, Tilman; von Hoyningen-Huene, Wolfgang; Burrows, John P.; Kokhanovsky, Alexander; Bierwirth, Eike; Wendisch, Manfred; Müller, Detlef; Kahn, Ralph; Diouri, Mohammed

2009-02-01

395

Aerosol optical properties and types over the tropical urban region of Hyderabad, India  

NASA Astrophysics Data System (ADS)

India is densely populated, industrialized and in the recent years has witnessed an impressive economic development. Aerosols over and around India not only affect the Indian monsoon but also the global climate. The growing population coupled with revolution in industry has resulted in higher demands for energy and transport. With more and more urbanization the usage pattern of fossil and bio-fuels are leading to changes in aerosol properties, which may cause changes in precipitation and can decelerate the hydrological cycle. Over urban areas of India aerosol emissions from fossil fuels such as coal, petrol and diesel oil dominate. Further-more, the Indian subcontinent exhibits different land characteristics ranging from vegetated areas and forests to semiarid and arid environments and tall mountains. India experiences large seasonal climatic variations, which result in extreme temperatures, rainfall and relative humidity. These meteorological and climatic features introduce large variabilities in aerosol op-tical and physico-chemical characteristics at spatial and temporal scales. In the present study, seasonal variations in aerosol properties and types were analysed over tropical urban region of Hyderabad, India during October 2007-September 2008 using MICROTOPS II sun photometer measurements. Higher aerosol optical depth (AOD) values are observed in premonsoon, while the variability of the ?ngstrüm exponent (?) seems to be more pronounced with higher values A in winter and premonsoon and lower in the monsoon periods. The AOD at 500 nm (AOD500 ) is very large over Hyderabad, varying from 0.46±0.17 in postmonsoon to 0.65±0.22 in premon-soon periods. A discrimination of the different aerosol types over Hyderabad is also attempted using values of AOD500 and ?380-870. Such discrimination is rather difficult to interpret since a single aerosol type can partly be identified only under specific conditions (e.g. anthropogenic emissions, biomass burning or dust outbreaks), while the presence of mixed aerosols, without dominance of the coarse or accumulation mode is the usual situation. According to the analysis the three individual components of differing origin, composition and optical characteristics are, a) an urban/industrial aerosol type composed of aerosols produced locally and all year round by combustion activities in the city or long-range transported (mainly in spring) biomass burning, b) an aerosol type of mineral origin raised by the wind in the deserts (mainly in premonsoon) or constitutes coarse-mode aerosols under high relative humidity conditions mainly in the monsoon period, and c) an aerosol type with a marine influence under background conditions occurred in monsoon and postmonsoon periods. Nevertheless, the mixed or undetermined aerosol type dominates with percentages varying from 44.3% (premonsoon) to 72.9% (postmonsoon). Spec-tral AOD and ? data are analyzed to obtain information about the adequacy of the simple use of the ?ngstrüm exponent for characterizing the aerosols. This is achieved by taking advantage A of the spectral variation of lnAOD vs ln?, the so-called curvature. The results show that the spectral curvature can be effectively used as a tool for aerosol types discrimination, since the fine-mode aerosols exhibit negative curvature, while the coarse-mode particles positive. The present study is among the first over Hyderabad focusing on the seasonal pattern of aerosol properties and types and aiming at associating them with local emissions, regional climatology and long-range transport. Keywords: AOD, aerosol types; sun photometer; back trajectories; Hyderabad; India

Kharol, Shailesh Kumar; Kaskaoutis, D. G.; Rani Sharma, Anu; Kvs, Badarinath; Kambezidis, H. D.

396

A Hybrid Regularization for Remote Determination of Atmospheric Aerosol Distribution from Multi-Frequency Optical Measurements  

Microsoft Academic Search

The notion of ill-posed and possibly rank-deficient linear inverse problems of determining the unknown input parameters from sensor measurements forms the underlying mathematical equations in many science and engineering situations. One example is the retrieval of atmospheric-aerosol (microphysical) parameters from the optical measurements. Light scattering by atmospheric aerosols, based on the Mie scattering theory, provides a physical framework for remote

S. Lim; J. Shin

2009-01-01

397

Beyond the Alphabet Soup: Molecular Properties of Aerosol Components Influence Optics. (Invited)  

NASA Astrophysics Data System (ADS)

Components within atmospheric aerosols exhibit almost every imaginable model of chemical bonding and physical diversity. The materials run the spectrum from crystalline to amorphous, covalent to ionic, and have varying viscosities, phase, and hygroscopicity. This seminar will focus on the molecular properties of materials that influence the optical behavior of aerosols. Special focus will be placed on the polarizability of materials, hygroscopic growth, and particle phase.

Thompson, J. E.

2013-12-01

398

Development of a polarization optical particle counter capable of aerosol type classification  

NASA Astrophysics Data System (ADS)

We developed a polarization optical particle counter (POPC) for measuring the concentrations of aerosol types, which were classified using polarization information from particle-scattered light. Polarization sensors that detect P and S polarization components of scattered light were placed at a scattering angle of 120°. The polarization ratio is calculated as the ratio of the S component to the sum of the S and P components, and it is used to help distinguish proposed aerosol types. The POPC field observation was conducted in Fukuoka, located in the western part of Japan, in 2012. The classification rule for three aerosol types (mineral dust, air pollution, and sea-salt particles) was determined empirically on the basis of measurements during typical conditions dominated by each aerosol type. The mass concentration of each aerosol type was estimated from the POPC measurement with some assumptions. The results indicate independent seasonal variation in each aerosol mass concentration. Using black carbon as an indicator of anthropogenic aerosols, we show a correlation of 0.770 with our estimated pollution aerosol type.

Kobayashi, Hiroshi; Hayashi, Masahiko; Shiraishi, Koichi; Nakura, Yoshinobu; Enomoto, Takayuki; Miura, Kazuhiko; Takahashi, Hiroshi; Igarashi, Yasuhito; Naoe, Hiroaki; Kaneyasu, Naoki; Nishizawa, Tomoaki; Sugimoto, Nobuo

2014-11-01

399

Near-field-magnetic-tweezer manipulation of single DNA molecules Jie Yan, Dunja Skoko, and John F. Marko  

E-print Network

with 3- m-diameter paramagnetic particles. A small, permanent magnet that can be moved as close as 10 m in other recent "magnetic-tweezer" studies. Our instrument generates these forces in the focal plane include optical trapping (OT), glass microfibers (GM), magnetic tweezers (MT), and atomic-force microscopy

Croquette, Vincent

400

Aerosols  

Atmospheric Science Data Center

... is needed for monitoring air quality and for understanding climate change. During the last weeks of March 2003, widespread aerosol ... MISR Team. Text acknowledgment: Clare Averill (Acro Service Corporation/Jet Propulsion Laboratory). Other formats available ...

2013-04-17