A magnetic gradient induced force in NMR restricted diffusion experiments

International Nuclear Information System (INIS)

Ghadirian, Bahman; Stait-Gardner, Tim; Castillo, Reynaldo; Price, William S.

2014-01-01

We predict that the phase cancellation of a precessing magnetisation field carried by a diffusing species in a bounded geometry under certain nuclear magnetic resonance pulsed magnetic field gradient sequences results in a small force over typically micrometre length scales. Our calculations reveal that the total magnetisation energy in a pore under the influence of a pulsed gradient will be distance-dependent thus resulting in a force acting on the boundary. It is shown that this effect of the magnetisation of diffusing particles will appear as either an attractive or repulsive force depending on the geometry of the pore and magnetic properties of the material. A detailed analysis is performed for the case of a pulsed gradient spin-echo experiment on parallel planes. It is shown that the force decays exponentially in terms of the spin-spin relaxation. The proof is based on classical electrodynamics. An application of this effect to soft matter is suggested

Polarization-dependent ponderomotive gradient force in a standing wave

NARCIS (Netherlands)

Smorenburg, P.W.; Kanters, J.H.M.; Lassise, A.; Brussaard, G.J.H.; Kamp, L.P.J.; Luiten, O.J.

2011-01-01

The ponderomotive force is derived for a relativistic charged particle entering an electromagnetic standing wave with a general three-dimensional field distribution and a nonrelativistic intensity, using a perturbation expansion method. It is shown that the well-known ponderomotive gradient force

An inverse method for determining the interaction force between the probe and sample using scanning near-field optical microscopy

International Nuclear Information System (INIS)

Chang, Win-Jin; Fang, Te-Hua

2006-01-01

This study proposes a means for calculating the interaction force during the scanning process using a scanning near-field optical microscope (SNOM) probe. The determination of the interaction force in the scanning system is regarded as an inverse vibration problem. The conjugate gradient method is applied to treat the inverse problem using available displacement measurements. The results show that the conjugate gradient method is less sensitive to measurement errors and prior information on the functional form of quality was not required. Furthermore, the initial guesses for the interaction force can be arbitrarily chosen for the iteration process

Orbital forcing and role of the latitudinal insolation/temperature gradient

Energy Technology Data Exchange (ETDEWEB)

Davis, Basil A.S. [University of Newcastle, School of Geography, Politics and Sociology, Newcastle upon Tyne (United Kingdom); ARVE Group, ISTE, EPFL, Lausanne (Switzerland); Brewer, Simon [CEREGE, Europole de l' Arbois, Aix-en-Provence (France)

2009-02-15

Orbital forcing of the climate system is clearly shown in the Earths record of glacial-interglacial cycles, but the mechanism underlying this forcing is poorly understood. Traditional Milankovitch theory suggests that these cycles are driven by changes in high latitude summer insolation, yet this forcing is dominated by precession, and cannot account for the importance of obliquity in the Ice Age record. Here, we investigate an alternative forcing based on the latitudinal insolation gradient (LIG), which is dominated by both obliquity (in summer) and precession (in winter). The insolation gradient acts on the climate system through differential solar heating, which creates the Earths latitudinal temperature gradient (LTG) that drives the atmospheric and ocean circulation. A new pollen-based reconstruction of the LTG during the Holocene is used to demonstrate that the LTG may be much more sensitive to changes in the LIG than previously thought. From this, it is shown how LIG forcing of the LTG may help explain the propagation of orbital signatures throughout the climate system, including the Monsoon, Arctic Oscillation and ocean circulation. These relationships are validated over the last (Eemian) Interglacial, which occurred under a different orbital configuration to the Holocene. We conclude that LIG forcing of the LTG explains many criticisms of classic Milankovitch theory, while being poorly represented in climate models. (orig.)

Light gradients and optical microniches in coral tissues

Directory of Open Access Journals (Sweden)

Daniel eWangpraseurt

2012-08-01

Full Text Available Light quantity and quality are among the most important factors determining the physiology and stress response of zooxanthellate corals. Yet, almost nothing is known about the light field that Symbiodinium experiences within their coral host, and the basic optical properties of coral tissue are unknown. We used scalar irradiance microprobes to characterise vertical and lateral light gradients within and across tissues of several coral species. Our results revealed the presence of steep light gradients with PAR (photosynthetically available radiation decreasing by about one order of magnitude from the tissue surface to the coral skeleton. Surface scalar irradiance was consistently higher over polyp tissue than over coenosarc tissue in faviid corals. Coral bleaching increased surface scalar irradiance by ~150% (between 500-700 nm relative to a healthy coral. Photosynthesis peaked around 300 µm within the tissue, which corresponded to a zone exhibiting strongest depletion of scalar irradiance. Deeper coral tissue layers, e.g. ~1000 µm into aboral polyp tissues, harbor optical microniches, where only ~10% of the incident irradiance remains. We conclude that the optical microenvironment of corals exhibits strong lateral and vertical gradients of scalar irradiance, which are affected by both tissue and skeleton optical properties. Our results imply that zooxanthellae populations inhabit a strongly heterogeneous light environment and highlight the presence of different optical microniches in corals; an important finding for understanding the photobiology, stress response, as well as the phenotypic and genotypic plasticity of coral symbionts.

Higher-order force gradient symplectic algorithms

Science.gov (United States)

Chin, Siu A.; Kidwell, Donald W.

2000-12-01

We show that a recently discovered fourth order symplectic algorithm, which requires one evaluation of force gradient in addition to three evaluations of the force, when iterated to higher order, yielded algorithms that are far superior to similarly iterated higher order algorithms based on the standard Forest-Ruth algorithm. We gauge the accuracy of each algorithm by comparing the step-size independent error functions associated with energy conservation and the rotation of the Laplace-Runge-Lenz vector when solving a highly eccentric Kepler problem. For orders 6, 8, 10, and 12, the new algorithms are approximately a factor of 103, 104, 104, and 105 better.

Universal spin-momentum locked optical forces

Energy Technology Data Exchange (ETDEWEB)

Kalhor, Farid [Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta T6G 1H9 (Canada); Thundat, Thomas [Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 1H9 (Canada); Jacob, Zubin, E-mail: zjacob@purdue.edu [Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta T6G 1H9 (Canada); Birck Nanotechnology Center, Department of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47906 (United States)

2016-02-08

Evanescent electromagnetic waves possess spin-momentum locking, where the direction of propagation (momentum) is locked to the inherent polarization of the wave (transverse spin). We study the optical forces arising from this universal phenomenon and show that the fundamental origin of recently reported non-trivial optical chiral forces is spin-momentum locking. For evanescent waves, we show that the direction of energy flow, the direction of decay, and the direction of spin follow a right hand rule for three different cases of total internal reflection, surface plasmon polaritons, and HE{sub 11} mode of an optical fiber. Furthermore, we explain how the recently reported phenomena of lateral optical force on chiral and achiral particles are caused by the transverse spin of the evanescent field and the spin-momentum locking phenomenon. Finally, we propose an experiment to identify the unique lateral forces arising from the transverse spin in the optical fiber and point to fundamental differences of the spin density from the well-known orbital angular momentum of light. Our work presents a unified view on spin-momentum locking and how it affects optical forces on chiral and achiral particles.

Interrelation between striction forces in dielectrics and optically induced forces in transparent media

International Nuclear Information System (INIS)

Torchigin, V P; Torchigin, A V

2012-01-01

Optically induced forces applied to a transparent optical medium, which is inserted in a closed plane optical resonator, are calculated by means of an analysis of the changes in the eigenfrequency and energy stored in the resonator at various positions of the medium. These forces are compared with striction forces applied to the medium considered as a dielectric placed in an alternate electrical field within the resonator. It is shown that the optically induced forces are equal to the striction forces. The results of using the classical formula for striction forces in electrostatics are considered. (paper)

Optical force and torque on a dielectric Rayleigh particle by a circular Airy vortex beam

Science.gov (United States)

Chen, Musheng; Huang, Sujuan; Shao, Wei; Liu, Xianpeng

2018-03-01

Optical force and torque exerted on the Rayleigh particles by tightly focused circularly polarized circular Airy vortex beams (CAVB) in the far field are studied in this paper. The relation between parameters of circularly polarized CAVB and the trapping properties is numerically analyzed based on Rayleigh models and the Debye diffraction theory. The results show that both the high refractive index and low refractive index particles can be fully stably trapped in three dimensions by circularly polarized CAVB. The parameters of circularly polarized CAVB greatly affect the optical force. The longitudinal and transverse gradient force increase with the increase of decay factor and scaling factor, and decrease with the increase of the radius of the first primary ring and topological charges. The positions of the longitudinal stable equilibrium move toward the high numerical aperture lens when the scaling factor and the radius of the primary ring increase. The trapping range is broadened with the decrease of scaling factor. The optical orbital torque (OOT) of circularly polarized CAVB has circular symmetry and remains positive or negative. With the increase of topological charges, the peak value of OOT first increases and then decreases after reaches a maximum. These results are useful for optical trapping, optical levitation and particle acceleration.

Testing thermal gradient driving force for grain boundary migration using molecular dynamics simulations

International Nuclear Information System (INIS)

Bai, Xian-Ming; Zhang, Yongfeng; Tonks, Michael R.

2015-01-01

Strong thermal gradients in low-thermal-conductivity ceramics may drive extended defects, such as grain boundaries and voids, to migrate in preferential directions. In this work, molecular dynamics simulations are conducted to study thermal gradient driven grain boundary migration and to verify a previously proposed thermal gradient driving force equation, using uranium dioxide as a model system. It is found that a thermal gradient drives grain boundaries to migrate up the gradient and the migration velocity increases under a constant gradient owing to the increase in mobility with temperature. Different grain boundaries migrate at very different rates due to their different intrinsic mobilities. The extracted mobilities from the thermal gradient driven simulations are compared with those calculated from two other well-established methods and good agreement between the three different methods is found, demonstrating that the theoretical equation of the thermal gradient driving force is valid, although a correction of one input parameter should be made. The discrepancy in the grain boundary mobilities between modeling and experiments is also discussed.

The Origins of UV-optical Color Gradients in Star-forming Galaxies at z ˜ 2: Predominant Dust Gradients but Negligible sSFR Gradients

Science.gov (United States)

Liu, F. S.; Jiang, Dongfei; Faber, S. M.; Koo, David C.; Yesuf, Hassen M.; Tacchella, Sandro; Mao, Shude; Wang, Weichen; Guo, Yicheng; Fang, Jerome J.; Barro, Guillermo; Zheng, Xianzhong; Jia, Meng; Tong, Wei; Liu, Lu; Meng, Xianmin

2017-07-01

The rest-frame UV-optical (I.e., NUV - B) color is sensitive to both low-level recent star formation (specific star formation rate—sSFR) and dust. In this Letter, we extend our previous work on the origins of NUV - B color gradients in star-forming galaxies (SFGs) at z˜ 1 to those at z˜ 2. We use a sample of 1335 large (semimajor axis radius {R}{SMA}> 0\\buildrel{\\prime\\prime}\\over{.} 18) SFGs with extended UV emission out to 2{R}{SMA} in the mass range {M}* ={10}9{--}{10}11 {M}⊙ at 1.5negative NUV - B color gradients (redder centers), and their color gradients strongly increase with galaxy mass. We also show that the global rest-frame FUV - NUV color is approximately linear with {A}{{V}}, which is derived by modeling the observed integrated FUV to NIR spectral energy distributions of the galaxies. Applying this integrated calibration to our spatially resolved data, we find a negative dust gradient (more dust extinguished in the centers), which steadily becomes steeper with galaxy mass. We further find that the NUV - B color gradients become nearly zero after correcting for dust gradients regardless of galaxy mass. This indicates that the sSFR gradients are negligible and dust reddening is likely the principal cause of negative UV-optical color gradients in these SFGs. Our findings support that the buildup of the stellar mass in SFGs at Cosmic Noon is self-similar inside 2{R}{SMA}.

NIF optical specifications - the importance of the RMS gradient specification

International Nuclear Information System (INIS)

Auerbach, J. M.; Cotton, C. T.; English, R. E.; Henesian, M. A.; Hunt, J. T.; Kelly, J. H.; Lawson, J. K.; Sacks, J. B.; Shoup, M. J.; Trenholme, W. H.

1998-01-01

The performance of the National Ignition Facility (NIF), especially in terms of laser focusability, will be determined by several key factors. One of these key factors is the optical specification for the thousands of large aperture optics that will comprise the 192 beamlines. We have previously reported on the importance of the specification of the power spectral density (PSD) on NIF performance. Recently, we have been studying the importance of long spatial wavelength (>33 mm) phase errors on focusability. We have concluded that the preferred metric for determining the impact of these long spatial wavelength phase errors is the rms phase gradient. In this paper, we outline the overall approach to NIF optical specifications, detail the impact of the rms phase gradient on NIF focusability, discuss its trade-off with the PSD in determining the spot size and review measurements of optics similar to those to be manufactured for NIF

On configurational forces for gradient-enhanced inelasticity

Science.gov (United States)

Floros, Dimosthenis; Larsson, Fredrik; Runesson, Kenneth

2018-04-01

In this paper we discuss how configurational forces can be computed in an efficient and robust manner when a constitutive continuum model of gradient-enhanced viscoplasticity is adopted, whereby a suitably tailored mixed variational formulation in terms of displacements and micro-stresses is used. It is demonstrated that such a formulation produces sufficient regularity to overcome numerical difficulties that are notorious for a local constitutive model. In particular, no nodal smoothing of the internal variable fields is required. Moreover, the pathological mesh sensitivity that has been reported in the literature for a standard local model is no longer present. Numerical results in terms of configurational forces are shown for (1) a smooth interface and (2) a discrete edge crack. The corresponding configurational forces are computed for different values of the intrinsic length parameter. It is concluded that the convergence of the computed configurational forces with mesh refinement depends strongly on this parameter value. Moreover, the convergence behavior for the limit situation of rate-independent plasticity is unaffected by the relaxation time parameter.

Magnus force effect in optical manipulation

International Nuclear Information System (INIS)

Cipparrone, Gabriella; Pagliusi, Pasquale; Hernandez, Raul Josue; Provenzano, Clementina

2011-01-01

The effect of the Magnus force in optical micromanipulation has been observed. An ad hoc experiment has been designed based on a one-dimensional optical trap that carries angular momentum. The observed particle dynamics reveals the occurrence of this hydrodynamic force, which is neglected in the common approach. Its measured value is larger than the one predicted by the existing theoretical models for micrometric particles and low Reynolds number, showing that the Magnus force can contribute to unconventional optohydrodynamic trapping and manipulation.

Cantilever-based optical interfacial force microscope in liquid using an optical-fiber tip

Directory of Open Access Journals (Sweden)

Byung I. Kim

2013-03-01

Full Text Available We developed a novel cantilever-based optical interfacial force microscope (COIFM to study molecular interaction in liquid environments. The force sensor was created by attaching a chemically etched optical-fiber tip to the force sensor with UV epoxy, and characterized by imaging on a calibration grid. The performance of the COIFM was then demonstrated by measuring the force between two oxidized silicon surfaces in 1 mM KCl as a function of distance. The result was consistent with previously reported electrical double layer forces, suggesting that a COIFM using an optical-fiber tip is capable of measuring force in a liquid environment.

Realization of preconditioned Lanczos and conjugate gradient algorithms on optical linear algebra processors.

Science.gov (United States)

Ghosh, A

1988-08-01

Lanczos and conjugate gradient algorithms are important in computational linear algebra. In this paper, a parallel pipelined realization of these algorithms on a ring of optical linear algebra processors is described. The flow of data is designed to minimize the idle times of the optical multiprocessor and the redundancy of computations. The effects of optical round-off errors on the solutions obtained by the optical Lanczos and conjugate gradient algorithms are analyzed, and it is shown that optical preconditioning can improve the accuracy of these algorithms substantially. Algorithms for optical preconditioning and results of numerical experiments on solving linear systems of equations arising from partial differential equations are discussed. Since the Lanczos algorithm is used mostly with sparse matrices, a folded storage scheme to represent sparse matrices on spatial light modulators is also described.

OPTICAL-NEAR-INFRARED COLOR GRADIENTS AND MERGING HISTORY OF ELLIPTICAL GALAXIES

International Nuclear Information System (INIS)

Kim, Duho; Im, Myungshin

2013-01-01

It has been suggested that merging plays an important role in the formation and the evolution of elliptical galaxies. While gas dissipation by star formation is believed to steepen metallicity and color gradients of the merger products, mixing of stars through dissipation-less merging (dry merging) is believed to flatten them. In order to understand the past merging history of elliptical galaxies, we studied the optical-near-infrared (NIR) color gradients of 204 elliptical galaxies. These galaxies are selected from the overlap region of the Sloan Digital Sky Survey (SDSS) Stripe 82 and the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). The use of optical and NIR data (g, r, and K) provides large wavelength baselines, and breaks the age-metallicity degeneracy, allowing us to derive age and metallicity gradients. The use of the deep SDSS Stripe 82 images makes it possible for us to examine how the color/age/metallicity gradients are related to merging features. We find that the optical-NIR color and the age/metallicity gradients of elliptical galaxies with tidal features are consistent with those of relaxed ellipticals, suggesting that the two populations underwent a similar merging history on average and that mixing of stars was more or less completed before the tidal features disappeared. Elliptical galaxies with dust features have steeper color gradients than the other two types, even after masking out dust features during the analysis, which can be due to a process involving wet merging. More importantly, we find that the scatter in the color/age/metallicity gradients of the relaxed and merging feature types decreases as their luminosities (or masses) increase at M > 10 11.4 M ☉ but stays large at lower luminosities. Mean metallicity gradients appear nearly constant over the explored mass range, but a possible flattening is observed at the massive end. According to our toy model that predicts how the distribution of metallicity gradients

The Optical Bichromatic Force in Molecular Systems

Science.gov (United States)

Aldridge, Leland; Galica, Scott; Eyler, E. E.

2015-05-01

The optical bichromatic force has been demonstrated to be useful for slowing atomic beams much more rapidly than radiative forces. Through numerical simulations, we examine several aspects of applying the bichromatic force to molecular beams. One is the unavoidable existence of out-of-system radiative decay, requiring one or more repumping beams. We find that the average deceleration varies strongly with the repumping intensity, but when using optimal parameters, the force approaches the limiting value allowed by population statistics. Another consideration is the effect of fine and hyperfine structure. We examine a simplified multlevel model based on the B X transition in calcium monofluoride. To circumvent optical pumping into coherent dark states, we include two possible schemes: (1) a skewed dc magnetic field, and (2) rapid optical polarization switching. Our results indicate that the bichromatic force remains a viable option for creating large forces in molecular beams, with a reduction in the peak force by approximately an order of magnitude compared to a two-level atom, but little effect on the velocity range over which the force is effective. We also describe our progress towards experimental tests of the bichromatic force on a molecular beam of CaF. Supported by the National Science Foundation.

Moving force identification based on modified preconditioned conjugate gradient method

Science.gov (United States)

Chen, Zhen; Chan, Tommy H. T.; Nguyen, Andy

2018-06-01

This paper develops a modified preconditioned conjugate gradient (M-PCG) method for moving force identification (MFI) by improving the conjugate gradient (CG) and preconditioned conjugate gradient (PCG) methods with a modified Gram-Schmidt algorithm. The method aims to obtain more accurate and more efficient identification results from the responses of bridge deck caused by vehicles passing by, which are known to be sensitive to ill-posed problems that exist in the inverse problem. A simply supported beam model with biaxial time-varying forces is used to generate numerical simulations with various analysis scenarios to assess the effectiveness of the method. Evaluation results show that regularization matrix L and number of iterations j are very important influence factors to identification accuracy and noise immunity of M-PCG. Compared with the conventional counterpart SVD embedded in the time domain method (TDM) and the standard form of CG, the M-PCG with proper regularization matrix has many advantages such as better adaptability and more robust to ill-posed problems. More importantly, it is shown that the average optimal numbers of iterations of M-PCG can be reduced by more than 70% compared with PCG and this apparently makes M-PCG a preferred choice for field MFI applications.

Complex Light and Optical Forces X

DEFF Research Database (Denmark)

This year marked the 10th Anniversary Edition of the conference on Complex Light and Optical Forces that is part of Photonics West. We again had a record number of submissions, indicative of the rising visibility and stature of this conference. Indeed, Complex Light and Optical Forces is still...... the only yearly venue worldwide for presenting research on complex light. This year we did not find a need to organize joint sessions with other conferences at Photonics West....

Optical force rectifiers based on PT-symmetric metasurfaces

Science.gov (United States)

Alaee, Rasoul; Gurlek, Burak; Christensen, Johan; Kadic, Muamer

2018-05-01

We introduce here the concept of optical force rectifier based on parity-time symmetric metasurfaces. Directly linked to the properties of non-Hermitian systems engineered by balanced loss and gain constituents, we show that light can exert asymmetric pulling or pushing forces on metasurfaces depending on the direction of the impinging light. This generates a complete force rectification in the vicinity of the exceptional point. Our findings have the potential to spark the design of applications in optical manipulation where the forces, strictly speaking, act unidirectionally.

Cellular and colloidal separation using optical forces

Czech Academy of Sciences Publication Activity Database

Dholakia, K.; MacDonald, M. P.; Zemánek, Pavel; Čižmár, Tomáš

2007-01-01

Roč. 82, - (2007), s. 467-495 ISSN 0091-679X R&D Projects: GA MŠk(CZ) LC06007 EU Projects: European Commission(XE) 508952 - ATOM3D Institutional research plan: CEZ:AV0Z20650511 Keywords : optical sorting * FACS * MACS * optical forces * dielectrophoresis * optical chromatography * optical manipulation Subject RIV: BH - Optics, Masers, Lasers Impact factor: 1.582, year: 2006

Optical force on diseased blood cells: Towards the optical sorting of biological matter

KAUST Repository

Gongora, J. S. Totero

2015-05-01

By employing a series of massively parallel ab-initio simulations, we study how optical forces act on biological matter subject to morphological disease. As a representative case study, we here consider the case of Plasmodium falciparum on red blood cells (RBC) illuminated by a monochromatic plane wave. Realistic parameters for the geometry and the refractive index are then taken from published experiments. In our theoretical campaign, we study the dependence of the optical force on the disease stage for different incident wavelengths. We show that optical forces change significantly with the disease, with amplitude variation in the hundreds of pN range. Our results open up new avenues for the design of new optical systems for the treatment of human disease. © 2015 Elsevier Ltd.

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

Science.gov (United States)

Neuman, Keir C.; Nagy, Attila

2012-01-01

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

Optical forces through guided light deflections

DEFF Research Database (Denmark)

Palima, Darwin; Bañas, Andrew Rafael; Vizsnyiczai, Gaszton

2013-01-01

. In this work we look into the object shaping aspect and its potential for controlled optical manipulation. Using a simple bent waveguide as example, our numerical simulations show that the guided deflection of light efficiently converts incident light momentum into optical force with one order...

Dynamic steering beams for efficient force measurement in optical manipulation

Institute of Scientific and Technical Information of China (English)

Xiaocong Yuan; Yuquan Zhang; Rui Cao; Xing Zhao; Jing Bu; Siwei Zhu

2011-01-01

@@ An efficient and inexpensive method that uses a glass plate mounted onto a motorized rotating stage as a beam-steering device for the generation of dynamic optical traps is reported.Force analysis reveals that there are drag and trapping forces imposed on the bead in the opposite directions, respectively, in a viscous medium.The trapped bead will be rotated following the beam's motion before it reaches the critical escape velocity when the drag force is equal to the optical trapping force.The equilibrium condition facilitates the experimental measurement of the drag force with potential extensions to the determination of the viscosity of the medium or the refractive index of the bead.The proposed technique can easily be integrated into conventional optical microscopic systems with minimum modifications.%An efficient and inexpensive method that uses a glass plate mounted onto a motorized rotating stage as a beam-steering device for the generation of dynamic optical traps is reported. Force analysis reveals that there are drag and trapping forces imposed on the bead in the opposite directions, respectively, in a viscous medium. The trapped bead will be rotated following the beam's motion before it reaches the critical escape velocity when the drag force is equal to the optical trapping force. The equilibrium condition facilitates the experimental measurement of the drag force with potential extensions to the determination of the viscosity of the medium or the refractive index of the bead. The proposed technique can easily be integrated into conventional optical microscopic systems with minimum modifications.

On radiation forces acting on a transparent nanoparticle in the field of a focused laser beam

Energy Technology Data Exchange (ETDEWEB)

Afanas' ev, A A; Rubinov, A N [B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk (Belarus); Gaida, L S; Guzatov, D V; Svistun, A Ch [Yanka Kupala State University of Grodno, Grodno (Belarus)

2015-10-31

Radiation forces acting on a transparent spherical nanoparticle in the field of a focused Gaussian laser beam are studied theoretically in the Rayleigh scattering regime. Expressions are derived for the scattering force and Cartesian components of the gradient force. The resultant force acting on a nanoparticle located in the centre of a laser beam is found. The parameters of the focused beam and optical properties of the nanoparticle for which the longitudinal component of the gradient force exceeds the scattering force are determined. Characteristics of the transverse gradient force are discussed. (nanophotonics)

Precision force sensing with optically-levitated nanospheres

Science.gov (United States)

Geraci, Andrew

2017-04-01

In high vacuum, optically-trapped dielectric nanospheres achieve excellent decoupling from their environment and experience minimal friction, making them ideal for precision force sensing. We have shown that 300 nm silica spheres can be used for calibrated zeptonewton force measurements in a standing-wave optical trap. In this optical potential, the known spacing of the standing wave anti-nodes can serve as an independent calibration tool for the displacement spectrum of the trapped particle. I will describe our progress towards using these sensors for tests of the Newtonian gravitational inverse square law at micron length scales. Optically levitated dielectric objects also show promise for a variety of other precision sensing applications, including searches for gravitational waves and other experiments in quantum optomechanics. National Science Foundation PHY-1205994, PHY-1506431, PHY-1509176.

Optimized phase gradient measurements and phase-amplitude interplay in optical coherence elastography

Science.gov (United States)

Zaitsev, Vladimir Y.; Matveyev, Alexander L.; Matveev, Lev A.; Gelikonov, Grigory V.; Sovetsky, Aleksandr A.; Vitkin, Alex

2016-11-01

In compressional optical coherence elastography, phase-variation gradients are used for estimating quasistatic strains created in tissue. Using reference and deformed optical coherence tomography (OCT) scans, one typically compares phases from pixels with the same coordinates in both scans. Usually, this limits the allowable strains to fairly small values advantages of the proposed optimized phase-variation methodology.

Resonance-enhanced optical forces between coupled photonic crystal slabs.

Science.gov (United States)

Liu, Victor; Povinelli, Michelle; Fan, Shanhui

2009-11-23

The behaviors of lateral and normal optical forces between coupled photonic crystal slabs are analyzed. We show that the optical force is periodic with displacement, resulting in stable and unstable equilibrium positions. Moreover, the forces are strongly enhanced by guided resonances of the coupled slabs. Such enhancement is particularly prominent near dark states of the system, and the enhancement effect is strongly dependent on the types of guided resonances involved. These structures lead to enhancement of light-induced pressure over larger areas, in a configuration that is directly accessible to externally incident, free-space optical beams.

Optical forces, torques, and force densities calculated at a microscopic level using a self-consistent hydrodynamics method

Science.gov (United States)

Ding, Kun; Chan, C. T.

2018-04-01

The calculation of optical force density distribution inside a material is challenging at the nanoscale, where quantum and nonlocal effects emerge and macroscopic parameters such as permittivity become ill-defined. We demonstrate that the microscopic optical force density of nanoplasmonic systems can be defined and calculated using the microscopic fields generated using a self-consistent hydrodynamics model that includes quantum, nonlocal, and retardation effects. We demonstrate this technique by calculating the microscopic optical force density distributions and the optical binding force induced by external light on nanoplasmonic dimers. This approach works even in the limit when the nanoparticles are close enough to each other so that electron tunneling occurs, a regime in which classical electromagnetic approach fails completely. We discover that an uneven distribution of optical force density can lead to a light-induced spinning torque acting on individual particles. The hydrodynamics method offers us an accurate and efficient approach to study optomechanical behavior for plasmonic systems at the nanoscale.

Graded-index fiber tip optical tweezers: numerical simulation and trapping experiment.

Science.gov (United States)

Gong, Yuan; Ye, Ai-Yan; Wu, Yu; Rao, Yun-Jiang; Yao, Yao; Xiao, Song

2013-07-01

Optical fiber tweezers based on a graded-index multimode fiber (GIMMF) tip is proposed. Light propagation characteristics and gradient force distribution near the GIMMF tip are numerically investigated, which are further compared with that of optical fiber tips based on conventional single mode fibers. The simulated results indicated that by selecting optimal GIMMF length, the gradient force of the GIMMF tip tweezers is about 4 times higher than that of the SMF tip tweezers with a same shape. To prove the feasibility of such a new concept, optical trapping of yeast cells with a diameter of ~5 μm using the chemically-etched GIMMF tip is experimentally demonstrated and the trapping force is also calculated.

[Gradient-index (GRIN) endoscopic examinations from the inner structures of the optic nerve meninges].

Science.gov (United States)

Sens, Frank Michael; Killer, Hanspeter Esriel; Meyer, Peter

2003-03-01

Due to the excellent image quality and the small outer diameter of the GRIN-(gradient index) endoscope tips we were able to examine the subdural and the subarachnoidal space of the optic nerve meninges by endoscopy. This examination was performed to obtain more information about the inner structure of the optic nerve meninges. In this post-mortem study 7 optic nerves were examined from the chiasm to the globe by GRIN endoscopy (Volpi, Schlieren, Switzerland), with an outer diameter of 0.89 mm, integrated optic of 0.5 mm diameter and an integrated fluid channel of 0.2 mm diameter. In all cases the endoscopic examination of the optic nerve meninges was technically easy to perform. It was possible to study the inner surface of the nerve sheaths and the nerve sheath spaces in close-up. We found horizontal and vertical cords on the inner surface of the dura mater, which could tighten by movements of the optic nerve. With a gradient-index (GRIN) endoscope we obtained new information about the inner structure of the optic nerve meninges. New theories about the changes of the optic nerve meninges during movements of the optic nerve may evolve from this study. Further studies with this new method should be encouraged.

Adjustment of gripping force by optical systems

Science.gov (United States)

Jalba, C. K.; Barz, C.

2018-01-01

With increasing automation, robotics also requires ever more intelligent solutions in the handling of various tasks. In this context, many grippers must also be re-designed. For this, they must always be adapted for different requirements. The equipment of the gripper systems with sensors should help to make the gripping process more intelligent. In order to achieve such objectives, optical systems can also be used. This work analyzes how the gripping force can be adjusted by means of an optical recognition. The result of this work is the creation of a connection between optical recognition, tolerances, gripping force and real-time control. In this way, algorithms can be created, with the aid of which robot grippers as well as other gripping systems become more intelligent.

Optical properties of gold films and the Casimir force

International Nuclear Information System (INIS)

Svetovoy, V. B.; Zwol, P. J. van; Palasantzas, G.; De Hosson, J. Th. M.

2008-01-01

Precise optical properties of metals are very important for accurate prediction of the Casimir force acting between two metallic plates. Therefore we measured ellipsometrically the optical responses of Au films in a wide range of wavelengths from 0.14 to 33 μm. The films at various thicknesses were deposited at different conditions on silicon or mica substrates. Considerable variation of the frequency dependent dielectric function from sample to sample was found. Detailed analysis of the dielectric functions was performed to check the Kramers-Kronig consistency, and extract the Drude parameters of the films. It was found that the plasma frequency varies in the range from 6.8 to 8.4 eV. It is suggested that this variation is related with the film density. X-ray reflectivity measurements support qualitatively this conclusion. The Casimir force is evaluated for the dielectric functions corresponding to our samples, and for that typically used in the precise prediction of the force. The force for our films was found to be 5%-14% smaller at a distance of 100 nm between the plates. Noise in the optical data is responsible for the force variation within 1%. It is concluded that prediction of the Casimir force between metals with a precision better than 10% must be based on the material optical response measured from visible to mid-infrared range

Vandenberg Air Force Base Pressure Gradient Wind Study

Science.gov (United States)

Shafer, Jaclyn A.

2013-01-01

Warning category winds can adversely impact day-to-day space lift operations at Vandenberg Air Force Base (VAFB) in California. NASA's Launch Services Program and other programs at VAFB use wind forecasts issued by the 30 Operational Support Squadron Weather Flight (30 OSSWF) to determine if they need to limit activities or protect property such as a launch vehicle. The 30 OSSWF tasked the AMU to develop an automated Excel graphical user interface that includes pressure gradient thresholds between specific observing stations under different synoptic regimes to aid forecasters when issuing wind warnings. This required the AMU to determine if relationships between the variables existed.

Robust approach to maximize the range and accuracy of force application in atomic force microscopes with nonlinear position-sensitive detectors

International Nuclear Information System (INIS)

Silva, E C C M; Vliet, K J van

2006-01-01

The atomic force microscope is used increasingly to investigate the mechanical properties of materials via sample displacement under an applied force. However, both the extent of forces attainable and the accuracy of those forces measurements are significantly limited by the optical lever configuration that is commonly used to infer nanoscale deflection of the cantilever. We present a robust and general approach to characterize and compensate for the nonlinearity of the position-sensitive optical device via data processing, requiring no modification of existing instrumentation. We demonstrate that application of this approach reduced the maximum systematic error on the gradient of a force-displacement response from 50% to 5%, and doubled the calibrated force application range. Finally, we outline an experimental protocol that optimizes the use of the quasi-linear range of the most commonly available optical feedback configurations and also accounts for the residual systematic error, allowing the user to benefit from the full detection range of these indirect force sensors

Electro-optic deflectors deliver advantages over acousto-optical deflectors in a high resolution, ultra-fast force-clamp optical trap.

Science.gov (United States)

Woody, Michael S; Capitanio, Marco; Ostap, E Michael; Goldman, Yale E

2018-04-30

We characterized experimental artifacts arising from the non-linear response of acousto-optical deflectors (AODs) in an ultra-fast force-clamp optical trap and have shown that using electro-optical deflectors (EODs) instead eliminates these artifacts. We give an example of the effects of these artifacts in our ultra-fast force clamp studies of the interaction of myosin with actin filaments. The experimental setup, based on the concept of Capitanio et al. [Nat. Methods 9, 1013-1019 (2012)] utilizes a bead-actin-bead dumbbell held in two force-clamped optical traps which apply a load to the dumbbell to move it at a constant velocity. When myosin binds to actin, the filament motion stops quickly as the total force from the optical traps is transferred to the actomyosin attachment. We found that in our setup, AODs were unsuitable for beam steering due to non-linear variations in beam intensity and deflection angle as a function of driving frequency, likely caused by low-amplitude standing acoustic waves in the deflectors. These aberrations caused instability in the force feedback loops leading to artifactual jumps in the trap position. We demonstrate that beam steering with EODs improves the performance of our instrument. Combining the superior beam-steering capability of the EODs, force acquisition via back-focal-plane interferometry, and dual high-speed FPGA-based feedback loops, we apply precise and constant loads to study the dynamics of interactions between actin and myosin. The same concept applies to studies of other biomolecular interactions.

Combined short scale roughness and surface dielectric function gradient effects on the determination of tip-sample force in atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Gusso, André, E-mail: gusso@metal.eeimvr.uff.br [Departamento de Ciências Exatas-EEIMVR, Universidade Federal Fluminense, Volta Redonda, RJ 27255-125 (Brazil)

2013-11-11

The contribution of tip roughness to the van der Waals force between an atomic force microscopy probe tip and the sample is calculated using the multilayer effective medium model, which allows us to consider the relevant case of roughness characterized by correlation length and amplitude in the nanometer scale. The effect of the surface dielectric function gradient is incorporated in the tip-sample force model. It is concluded that for rms roughness in the few nanometers range the effect of short scale tip roughness is quite significant.

Geometrical-optics approximation of forward scattering by gradient-index spheres.

Science.gov (United States)

Li, Xiangzhen; Han, Xiang'e; Li, Renxian; Jiang, Huifen

2007-08-01

By means of geometrical optics we present an approximation method for acceleration of the computation of the scattering intensity distribution within a forward angular range (0-60 degrees ) for gradient-index spheres illuminated by a plane wave. The incident angle of reflected light is determined by the scattering angle, thus improving the approximation accuracy. The scattering angle and the optical path length are numerically integrated by a general-purpose integrator. With some special index models, the scattering angle and the optical path length can be expressed by a unique function and the calculation is faster. This method is proved effective for transparent particles with size parameters greater than 50. It fails to give good approximation results at scattering angles whose refractive rays are in the backward direction. For different index models, the geometrical-optics approximation is effective only for forward angles, typically those less than 60 degrees or when the refractive-index difference of a particle is less than a certain value.

Using Spherical-Harmonics Expansions for Optics Surface Reconstruction from Gradients.

Science.gov (United States)

Solano-Altamirano, Juan Manuel; Vázquez-Otero, Alejandro; Khikhlukha, Danila; Dormido, Raquel; Duro, Natividad

2017-11-30

In this paper, we propose a new algorithm to reconstruct optics surfaces (aka wavefronts) from gradients, defined on a circular domain, by means of the Spherical Harmonics. The experimental results indicate that this algorithm renders the same accuracy, compared to the reconstruction based on classical Zernike polynomials, using a smaller number of polynomial terms, which potentially speeds up the wavefront reconstruction. Additionally, we provide an open-source C++ library, released under the terms of the GNU General Public License version 2 (GPLv2), wherein several polynomial sets are coded. Therefore, this library constitutes a robust software alternative for wavefront reconstruction in a high energy laser field, optical surface reconstruction, and, more generally, in surface reconstruction from gradients. The library is a candidate for being integrated in control systems for optical devices, or similarly to be used in ad hoc simulations. Moreover, it has been developed with flexibility in mind, and, as such, the implementation includes the following features: (i) a mock-up generator of various incident wavefronts, intended to simulate the wavefronts commonly encountered in the field of high-energy lasers production; (ii) runtime selection of the library in charge of performing the algebraic computations; (iii) a profiling mechanism to measure and compare the performance of different steps of the algorithms and/or third-party linear algebra libraries. Finally, the library can be easily extended to include additional dependencies, such as porting the algebraic operations to specific architectures, in order to exploit hardware acceleration features.

Experimental and theoretical determination of optical binding forces

Czech Academy of Sciences Publication Activity Database

Brzobohatý, Oto; Čižmár, T.; Karásek, Vítězslav; Šiler, Martin; Dholakia, K.; Zemánek, Pavel

2010-01-01

Roč. 18, č. 24 (2010), s. 25389-25402 ISSN 1094-4087 R&D Projects: GA ČR GA202/09/0348; GA MŠk OC08034; GA MŠk(CZ) LC06007; GA MŠk ED0017/01/01 Institutional research plan: CEZ:AV0Z20650511 Keywords : optical binding forces * micro-particles * inter-particle effects * optical manipulation * optical tweezers Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.749, year: 2010

Optical force exerted on a Rayleigh particle by a vector arbitrary-order Bessel beam

International Nuclear Information System (INIS)

Yang, Ruiping; Li, Renxian

2016-01-01

An analytical description of optical force on a Rayleigh particle by a vector Bessel beam is investigated. Linearly, radially, azimuthally, and circularly polarized Bessel beams are considered. The radial, azimuthal, and axial forces by a vector Bessel beam are numerically simulated. The effect of polarization, order of beams, and half-cone angle to the optical force are mainly discussed. For Bessel beams of larger half-cone angle, the non-paraxiality of beams plays an important role in optical forces. Numerical calculations show that optical forces, especially azimuthal forces, are very sensitive to the polarization of beams. - Highlights: • Optical force exerted on a Rayleigh particle by a vector Bessel beam is analytically derived. • Radial, azimuthal, and axial forces are numerically analyzed. • The effect of polarization, order of beam, and non-paraxiality is analyzed.

Optical and force nanoscopy in microbiology.

Science.gov (United States)

Xiao, Jie; Dufrêne, Yves F

2016-10-26

Microbial cells have developed sophisticated multicomponent structures and machineries to govern basic cellular processes, such as chromosome segregation, gene expression, cell division, mechanosensing, cell adhesion and biofilm formation. Because of the small cell sizes, subcellular structures have long been difficult to visualize using diffraction-limited light microscopy. During the last three decades, optical and force nanoscopy techniques have been developed to probe intracellular and extracellular structures with unprecedented resolutions, enabling researchers to study their organization, dynamics and interactions in individual cells, at the single-molecule level, from the inside out, and all the way up to cell-cell interactions in microbial communities. In this Review, we discuss the principles, advantages and limitations of the main optical and force nanoscopy techniques available in microbiology, and we highlight some outstanding questions that these new tools may help to answer.

Optical pulling force and conveyor belt effect in resonator-waveguide system.

Science.gov (United States)

Intaraprasonk, Varat; Fan, Shanhui

2013-09-01

We present the theoretical condition and actual numerical design that achieves an optical pulling force in resonator-waveguide systems, where the direction of the force on the resonator is in the opposite direction to the input light in the waveguide. We also show that this pulling force can occur in conjunction with the lateral optical equilibrium effect, such that the resonator is maintained at the fixed distance from the waveguide while experiencing the pulling force.

OPTICAL PULLING FORCES IN “NANOPARTICLES DIMER IN THE STRUCTURED FIELD” SYSTEM

Directory of Open Access Journals (Sweden)

S. V. Sukhov

2015-01-01

Full Text Available The subject area of this research is optical pulling forces as one of the manifestations of light mechanical action on material objects. In particular, we investigated optical forces acting on a dimer composed of nanoparticles with a small radius as compared to wavelength. The calculation of Lorentz optical forces was carried out by solving self-consistent system of equations, which made it possible to calculate electromagnetic fields in every point of the structure. We worked out analytic formula, representing the dependence of optical force on the parameters of dimer system and structured radiation made up of two crossing plane waves. For the first time we showed that dimer consisting of two equal dipolar particles can experience an optical pulling force (“negative radiation pressure” in the field of two crossing plane waves. It is shown that the increase of photons momentum (the projection of photons momentum on the direction of structured light propagation after scattering is responsible for this negative radiation pressure. The corresponding scattering diagram showed the increase of forward scattering, that is the conformation of the considered mechanism of pulling forces origination. Our findings would be very useful for increasing capabilities of optical manipulation of nano- and micro-particles.

Influence of energy and duration of laser pulses on stability of dielectric nanoparticles in optical trap

International Nuclear Information System (INIS)

Ho Quang Quy; Mai Van Luu; Hoang Dinh Hai

2010-01-01

In this article the gradient force of optical trap using two counter- propagating pulsed Gaussian beam and the Brownian motion in optical force field are investigated. The influence of the energy and duration time of optical pulsed Gaussian beams on stability of nano-particle in trap is simulated and discussed. (author)

Control of colloids with gravity, temperature gradients, and electric fields

CERN Document Server

Sullivan, M; Harrison, C; Austin, R H; Megens, M; Hollingsworth, A; Russel, W B; Cheng Zhen; Mason, T; Chaikin, P M

2003-01-01

We have used a variety of different applied fields to control the density, growth, and structure of colloidal crystals. Gravity exerts a body force proportional to the buoyant mass and in equilibrium produces a height-dependent concentration profile. A similar body force can be obtained with electric fields on charged particles (electrophoresis), a temperature gradient on all particles, or an electric field gradient on uncharged particles (dielectrophoresis). The last is particularly interesting since its magnitude and sign can be changed by tuning the applied frequency. We study these effects in bulk (making 'dielectrophoretic bottles' or traps), to control concentration profiles during nucleation and growth and near surfaces. We also study control of non-spherical and optically anisotropic particles with the light field from laser tweezers.

Control of colloids with gravity, temperature gradients, and electric fields

Energy Technology Data Exchange (ETDEWEB)

Sullivan, Matt [Department of Physics, Princeton University, Princeton, NJ (United States); Zhao Kun [Department of Physics, Princeton University, Princeton, NJ (United States); Harrison, Christopher [Department of Physics, Princeton University, Princeton, NJ (United States); Austin, Robert H [Department of Physics, Princeton University, Princeton, NJ (United States); Megens, Mischa [Department of Physics, Princeton University, Princeton, NJ (United States); Hollingsworth, Andrew [Department of Chemical Engineering, Princeton University, Princeton, NJ (United States); Russel, William B [Department of Chemical Engineering, Princeton University, Princeton, NJ (United States); Cheng Zhengdong [ExxonMobil Research, Annandale, NJ (United States); Mason, Thomas [ExxonMobil Research, Annandale, NJ (United States); Chaikin, P M [Department of Physics, Princeton University, Princeton, NJ (United States)

2003-01-15

We have used a variety of different applied fields to control the density, growth, and structure of colloidal crystals. Gravity exerts a body force proportional to the buoyant mass and in equilibrium produces a height-dependent concentration profile. A similar body force can be obtained with electric fields on charged particles (electrophoresis), a temperature gradient on all particles, or an electric field gradient on uncharged particles (dielectrophoresis). The last is particularly interesting since its magnitude and sign can be changed by tuning the applied frequency. We study these effects in bulk (making 'dielectrophoretic bottles' or traps), to control concentration profiles during nucleation and growth and near surfaces. We also study control of non-spherical and optically anisotropic particles with the light field from laser tweezers.

Noninvasive determination of optical lever sensitivity in atomic force microscopy

International Nuclear Information System (INIS)

Higgins, M.J.; Proksch, R.; Sader, J.E.; Polcik, M.; Mc Endoo, S.; Cleveland, J.P.; Jarvis, S.P.

2006-01-01

Atomic force microscopes typically require knowledge of the cantilever spring constant and optical lever sensitivity in order to accurately determine the force from the cantilever deflection. In this study, we investigate a technique to calibrate the optical lever sensitivity of rectangular cantilevers that does not require contact to be made with a surface. This noncontact approach utilizes the method of Sader et al. [Rev. Sci. Instrum. 70, 3967 (1999)] to calibrate the spring constant of the cantilever in combination with the equipartition theorem [J. L. Hutter and J. Bechhoefer, Rev. Sci. Instrum. 64, 1868 (1993)] to determine the optical lever sensitivity. A comparison is presented between sensitivity values obtained from conventional static mode force curves and those derived using this noncontact approach for a range of different cantilevers in air and liquid. These measurements indicate that the method offers a quick, alternative approach for the calibration of the optical lever sensitivity

Noninvasive determination of optical lever sensitivity in atomic force microscopy

Science.gov (United States)

Higgins, M. J.; Proksch, R.; Sader, J. E.; Polcik, M.; Mc Endoo, S.; Cleveland, J. P.; Jarvis, S. P.

2006-01-01

Atomic force microscopes typically require knowledge of the cantilever spring constant and optical lever sensitivity in order to accurately determine the force from the cantilever deflection. In this study, we investigate a technique to calibrate the optical lever sensitivity of rectangular cantilevers that does not require contact to be made with a surface. This noncontact approach utilizes the method of Sader et al. [Rev. Sci. Instrum. 70, 3967 (1999)] to calibrate the spring constant of the cantilever in combination with the equipartition theorem [J. L. Hutter and J. Bechhoefer, Rev. Sci. Instrum. 64, 1868 (1993)] to determine the optical lever sensitivity. A comparison is presented between sensitivity values obtained from conventional static mode force curves and those derived using this noncontact approach for a range of different cantilevers in air and liquid. These measurements indicate that the method offers a quick, alternative approach for the calibration of the optical lever sensitivity.

Using Spherical-Harmonics Expansions for Optics Surface Reconstruction from Gradients

Directory of Open Access Journals (Sweden)

Juan Manuel Solano-Altamirano

2017-11-01

Full Text Available In this paper, we propose a new algorithm to reconstruct optics surfaces (aka wavefronts from gradients, defined on a circular domain, by means of the Spherical Harmonics. The experimental results indicate that this algorithm renders the same accuracy, compared to the reconstruction based on classical Zernike polynomials, using a smaller number of polynomial terms, which potentially speeds up the wavefront reconstruction. Additionally, we provide an open-source C++ library, released under the terms of the GNU General Public License version 2 (GPLv2, wherein several polynomial sets are coded. Therefore, this library constitutes a robust software alternative for wavefront reconstruction in a high energy laser field, optical surface reconstruction, and, more generally, in surface reconstruction from gradients. The library is a candidate for being integrated in control systems for optical devices, or similarly to be used in ad hoc simulations. Moreover, it has been developed with flexibility in mind, and, as such, the implementation includes the following features: (i a mock-up generator of various incident wavefronts, intended to simulate the wavefronts commonly encountered in the field of high-energy lasers production; (ii runtime selection of the library in charge of performing the algebraic computations; (iii a profiling mechanism to measure and compare the performance of different steps of the algorithms and/or third-party linear algebra libraries. Finally, the library can be easily extended to include additional dependencies, such as porting the algebraic operations to specific architectures, in order to exploit hardware acceleration features.

Comparison between iterative wavefront control algorithm and direct gradient wavefront control algorithm for adaptive optics system

International Nuclear Information System (INIS)

Cheng Sheng-Yi; Liu Wen-Jin; Chen Shan-Qiu; Dong Li-Zhi; Yang Ping; Xu Bing

2015-01-01

Among all kinds of wavefront control algorithms in adaptive optics systems, the direct gradient wavefront control algorithm is the most widespread and common method. This control algorithm obtains the actuator voltages directly from wavefront slopes through pre-measuring the relational matrix between deformable mirror actuators and Hartmann wavefront sensor with perfect real-time characteristic and stability. However, with increasing the number of sub-apertures in wavefront sensor and deformable mirror actuators of adaptive optics systems, the matrix operation in direct gradient algorithm takes too much time, which becomes a major factor influencing control effect of adaptive optics systems. In this paper we apply an iterative wavefront control algorithm to high-resolution adaptive optics systems, in which the voltages of each actuator are obtained through iteration arithmetic, which gains great advantage in calculation and storage. For AO system with thousands of actuators, the computational complexity estimate is about O(n 2 ) ∼ O(n 3 ) in direct gradient wavefront control algorithm, while the computational complexity estimate in iterative wavefront control algorithm is about O(n) ∼ (O(n) 3/2 ), in which n is the number of actuators of AO system. And the more the numbers of sub-apertures and deformable mirror actuators, the more significant advantage the iterative wavefront control algorithm exhibits. (paper)

Measurement of asymmetric optical pumping of ions accelerating in a magnetic-field gradient

International Nuclear Information System (INIS)

Sun Xuan; Scime, Earl; Miah, Mahmood; Cohen, Samuel; Skiff, Frederick

2004-01-01

We report observations of asymmetric optical pumping of argon ions accelerating in a magnetic-field gradient. The signature is a difference in the laser-induced-fluorescence emission amplitude from a pair of Zeeman-split states. A model that reproduces the dependence of the asymmetry on magnetic-field and ion-velocity gradients is described. With the model, the fluorescence intensity ratio provides a new method of measuring ion collisionality. This phenomenon has implications for interpreting stellar plasma spectroscopy data which often exhibit unequal Zeeman state intensities

Measurement of Asymmetric Optical Pumping of Ions Accelerating in a Magnetic-field Gradient

Energy Technology Data Exchange (ETDEWEB)

Xuan Sun; Earl Scime; Mahmood Miah; Samuel Cohen; Frederick Skiff

2004-10-28

We report observations of asymmetric optical pumping of argon ions accelerating in a magnetic field gradient. The signature is a difference in the laser-induced-fluorescence (LIF) emission amplitude from a pair of Zeeman-split states. A model that reproduces the dependence of the asymmetry on magnetic-field and ion-velocity gradients is described. With the model, the fluorescence intensity ratio provides a new method of measuring ion collisionality. This phenomenon has implications for interpreting stellar plasma spectroscopy data which often exhibit unequal Zeeman state intensities.

Measurement of Asymmetric Optical Pumping of Ions Accelerating in a Magnetic-field Gradient

International Nuclear Information System (INIS)

Xuan Sun; Earl Scime; Mahmood Miah; Samuel Cohen; Frederick Skiff

2004-01-01

We report observations of asymmetric optical pumping of argon ions accelerating in a magnetic field gradient. The signature is a difference in the laser-induced-fluorescence (LIF) emission amplitude from a pair of Zeeman-split states. A model that reproduces the dependence of the asymmetry on magnetic-field and ion-velocity gradients is described. With the model, the fluorescence intensity ratio provides a new method of measuring ion collisionality. This phenomenon has implications for interpreting stellar plasma spectroscopy data which often exhibit unequal Zeeman state intensities

Lateral migration of a microdroplet under optical forces in a uniform flow

International Nuclear Information System (INIS)

Cho, Hyunjun; Chang, Cheong Bong; Jung, Jin Ho; Sung, Hyung Jin

2014-01-01

The behavior of a microdroplet in a uniform flow and subjected to a vertical optical force applied by a loosely focused Gaussian laser beam was studied numerically. The lattice Boltzmann method was applied to obtain the two-phase flow field, and the dynamic ray tracing method was adopted to calculate the optical force. The optical forces acting on the spherical droplets agreed well with the analytical values. The numerically predicted droplet migration distances agreed well with the experimentally obtained values. Simulations of the various flow and optical parameters showed that the droplet migration distance nondimensionalized by the droplet radius is proportional to the S number (z d /r p = 0.377S), which is the ratio of the optical force to the viscous drag. The effect of the surface tension was also examined. These results indicated that the surface tension influenced the droplet migration distance to a lesser degree than the flow and optical parameters. The results of the present work hold for the refractive indices of the mean fluid and the droplet being 1.33 and 1.59, respectively

Electromagnetic Wave Chaos in Gradient Refractive Index Optical Cavities

International Nuclear Information System (INIS)

Wilkinson, P. B.; Fromhold, T. M.; Taylor, R. P.; Micolich, A. P.

2001-01-01

Electromagnetic wave chaos is investigated using two-dimensional optical cavities formed in a cylindrical gradient refractive index lens with reflective surfaces. When the planar ends of the lens are cut at an angle to its axis, the geometrical ray paths are chaotic. In this regime, the electromagnetic mode spectrum of the cavity is modulated by both real and ghost periodic ray paths, which also 'scar' the electric field intensity distributions of many modes. When the cavity is coupled to waveguides, the eigenmodes generate complex series of resonant peaks in the electromagnetic transmission spectrum

Characteristics of single-atom trapping in a magneto-optical trap with a high magnetic-field gradient

International Nuclear Information System (INIS)

Yoon, Seokchan; Choi, Youngwoon; Park, Sangbum; Ji, Wangxi; Lee, Jai-Hyung; An, Kyungwon

2007-01-01

A quantitative study on characteristics of a magneto-optical trap with a single or a few atoms is presented. A very small number of 85 Rb atoms were trapped in a micron-size magneto-optical trap with a high magnetic-field gradient. In order to find the optimum condition for a single-atom trap, we have investigated how the number of atoms and the size of atomic cloud change as various experimental parameters, such as a magnetic-field gradient and the trapping laser intensity and detuning. The averaged number of atoms was measured very accurately with a calibration procedure based on the single-atom saturation curve of resonance fluorescence. In addition, the number of atoms in a trap could be controlled by suppressing stochastic loading events by means of a real-time active feedback on the magnetic-field gradient

Gradient Alloy for Optical Packaging

Data.gov (United States)

National Aeronautics and Space Administration — Advances in additive manufacturing, such as Laser Engineered Net Shaping (LENS), enables the fabrication of compositionally gradient microstructures, i.e. gradient...

Optical performance of the SO/PHI full disk telescope due to temperature gradients effect on the heat rejection entrance window

Science.gov (United States)

Garranzo, D.; Núñez, A.; Zuluaga-Ramírez, P.; Barandiarán, J.; Fernández-Medina, A.; Belenguer, T.; Álvarez-Herrero, A.

2017-11-01

The Polarimetric Helioseismic Imager for Solar Orbiter (SO/PHI) is an instrument on board in the Solar Orbiter mission. The Full Disk Telescope (FDT) will have the capability of providing images of the solar disk in all orbital faces with an image quality diffraction-limited. The Heat Rejection Entrance Window (HREW) is the first optical element of the instrument. Its function is to protect the instrument by filtering most of the Solar Spectrum radiation. The HREW consists of two parallel-plane plates made from Suprasil and each surface has a coating with a different function: an UV shield coating, a low pass band filter coating, a high pass band filter coating and an IR shield coating, respectively. The temperature gradient on the HREW during the mission produces a distortion of the transmitted wave-front due to the dependence of the refractive index with the temperature (thermo-optic effect) mainly. The purpose of this work is to determine the capability of the PHI/FDT refocusing system to compensate this distortion. A thermal gradient profile has been considered for each surface of the plates and a thermal-elastic analysis has been done by Finite Element Analysis to determine the deformation of the optical elements. The Optical Path Difference (OPD) between the incident and transmitted wavefronts has been calculated as a function of the ray tracing and the thermo-optic effect on the optical properties of Suprasil (at the work wavelength of PHI) by means of mathematical algorithms based on the 3D Snell Law. The resultant wavefronts have been introduced in the optical design of the FDT to evaluate the performance degradation of the image at the scientific focal plane and to estimate the capability of the PHI refocusing system for maintaining the image quality diffraction-limited. The analysis has been carried out considering two different situations: thermal gradients due to on axis attitude of the instrument and thermal gradients due to 1° off pointing attitude

Theory of optical-tweezers forces near a plane interface

DEFF Research Database (Denmark)

Dutra, Rafael de Sousa; Neto, P. A. Maia; Nussenzveig, H. M.

2016-01-01

Optical-tweezers experiments in molecular and cell biology often take place near the surface of the microscope slide that defines the bottom of the sample chamber. There, as elsewhere, force measurements require forcecalibrated tweezers. In bulk, one can calculate the tweezers force from first pr...

Plasmon-mediated binding forces on gold or silver homodimer and heterodimer

International Nuclear Information System (INIS)

Liaw, Jiunn-Woei; Kuo, Ting-Yu; Kuo, Mao-Kuen

2016-01-01

This study theoretically investigates plasmon-mediated optical binding forces, which are exerted on metal homo or heterodimers, induced by the normal illumination of a linearly polarized plane wave or Gaussian beam. Using the multiple multipole method, we analyzed the optical force in terms of Maxwell's stress tensor for various interparticle distance at some specific wavelengths. Numerical results show that for a given wavelength there are several stable equilibrium distances between two nanoparticles (NPs) of a homodimer, which are slightly shorter than some integer multiples of the wavelength in medium, such that metal dimer acts as bonded together. At these specific interparticle distances, the optical force between dimer is null and serves a restoring force, which is repulsive and attractive, respectively, as the two NPs are moving closer to and away from each other. The spring constant of the restoring force at the first stable equilibrium is always the largest, indicating that the first stable equilibrium distance is the most stable one. Moreover, the central line (orientation) of a dimer tends to be perpendicular to the polarization of light. For the cases of heterodimers, the phenomenon of stable equilibrium interparticle distance still exists, except there is an extra net photophoretic force drifting the heterodimer as one. Moreover, gradient force provided by a Gaussian beam may reduce the stability of these equilibriums, so larger NPs are preferred to stabilize a dimer under illumination of Gaussian beam. The finding may pave the way for using optical manipulation on the gold or silver colloidal self-assembly. - Highlights: • Optical binding force on Au/Ag dimer by linearly polarized light is studied. • For a wavelength several stable equilibriums for homodimer bound together exist. • The central line of a dimer tends to be perpendicular to the polarization of light. • For a heterodimer, stable equilibriums still exist with a net photophoretic

Gradient waveform synthesis for magnetic propulsion using MRI gradient coils

International Nuclear Information System (INIS)

Han, B H; Lee, S Y; Park, S

2008-01-01

Navigating an untethered micro device in a living subject is of great interest for both diagnostic and therapeutic applications. Magnetic propulsion of an untethered device carrying a magnetic core in it is one of the promising methods to navigate the device. MRI gradients coils are thought to be suitable for navigating the device since they are capable of magnetic propulsion in any direction while providing magnetic resonance images. For precise navigation of the device, especially in the peripheral region of the gradient coils, the concomitant gradient fields, as well as the linear gradient fields in the main magnetic field direction, should be considered in driving the gradient coils. For simple gradient coil configurations, the Maxwell coil in the z-direction and the Golay coil in the x- and y-directions, we have calculated the magnetic force fields, which are not necessarily the same as the conventional linear gradient fields of MRI. Using the calculated magnetic force fields, we have synthesized gradient waveforms to navigate the device along a desired path

Detection of thermal gradients through fiber-optic Chirped Fiber Bragg Grating (CFBG): Medical thermal ablation scenario

Science.gov (United States)

Korganbayev, Sanzhar; Orazayev, Yerzhan; Sovetov, Sultan; Bazyl, Ali; Schena, Emiliano; Massaroni, Carlo; Gassino, Riccardo; Vallan, Alberto; Perrone, Guido; Saccomandi, Paola; Arturo Caponero, Michele; Palumbo, Giovanna; Campopiano, Stefania; Iadicicco, Agostino; Tosi, Daniele

2018-03-01

In this paper, we describe a novel method for spatially distributed temperature measurement with Chirped Fiber Bragg Grating (CFBG) fiber-optic sensors. The proposed method determines the thermal profile in the CFBG region from demodulation of the CFBG optical spectrum. The method is based on an iterative optimization that aims at minimizing the mismatch between the measured CFBG spectrum and a CFBG model based on coupled-mode theory (CMT), perturbed by a temperature gradient. In the demodulation part, we simulate different temperature distribution patterns with Monte-Carlo approach on simulated CFBG spectra. Afterwards, we obtain cost function that minimizes difference between measured and simulated spectra, and results in final temperature profile. Experiments and simulations have been carried out first with a linear gradient, demonstrating a correct operation (error 2.9 °C); then, a setup has been arranged to measure the temperature pattern on a 5-cm long section exposed to medical laser thermal ablation. Overall, the proposed method can operate as a real-time detection technique for thermal gradients over 1.5-5 cm regions, and turns as a key asset for the estimation of thermal gradients at the micro-scale in biomedical applications.

Communication: atomic force detection of single-molecule nonlinear optical vibrational spectroscopy.

Science.gov (United States)

Saurabh, Prasoon; Mukamel, Shaul

2014-04-28

Atomic Force Microscopy (AFM) allows for a highly sensitive detection of spectroscopic signals. This has been first demonstrated for NMR of a single molecule and recently extended to stimulated Raman in the optical regime. We theoretically investigate the use of optical forces to detect time and frequency domain nonlinear optical signals. We show that, with proper phase matching, the AFM-detected signals closely resemble coherent heterodyne-detected signals. Applications are made to AFM-detected and heterodyne-detected vibrational resonances in Coherent Anti-Stokes Raman Spectroscopy (χ((3))) and sum or difference frequency generation (χ((2))).

Manipulating Light and Matter with Photonic Structures: Numerical Investigations on Photonic Crystals and Optical Forces

Science.gov (United States)

Zhang, Peng

The highly developed nano-fabrication techniques allow light to be modulated with photonic structures in a more intensive way. These photonic structures involve photonic crystals, metals supporting surface plasmon polaritons, metamaterials, etc. In this thesis work, three different ways for light manipulation are numerically investigated. First, the light propagation is modulated using a photonic crystal with Dirac cones. It is demonstrated that the zero-index behavior of this photonic crystal which happens for normal incident waves, is lost at oblique incidence. A new method combining complex-k band calculations and absorbing boundary conditions for Bloch modes is developed to analyze the Bloch mode interaction in details. Second, the mechanic states of graphene are modulated through the optical gradient force. This force is induced by the coupled surface plasmons on the double graphene sheets and is greatly enhanced in comparison to the regular waveguides. By applying different strengths of forces in accordance to the input power, the mechanic state transition is made possible, accompanied by an abrupt change in the transmission and reflection spectra. Third, the helicity/chirality of light is studied to modulate the lateral force on a small particle. A left-hand material slab which supports coherent TE ad TM plasmons simultaneously is introduced. By mixing the TE and TM surface plasmons with different relative phases, the lateral force on a chiral particle can be changed, which will be beneficial for chiral particle sorting.

Calculation of forces acting on an impurity in a metal subjected to a temperature gradient

International Nuclear Information System (INIS)

Gerl, M.

1966-01-01

In a metal subject to a temperature gradient, an impurity is submitted to both an electrostatic force due to the thermoelectric field and a force due to the scattering of electrons and phonons by this point defect. The scattering of the electrons is treated using a semi-classical approach and a quantum mechanical method. The numerical computation for several impurities in Cu, Ag, and Au requires the knowledge of the resistivity cross-section. and of the thermoelectric power of the impurity in the metal. A tentative estimation of the force due to the phonon-scattering is given for the self-diffusion in Cu. However, the approximations of this calculation do not allow a good comparison with the force due to the electrons. (author) [fr

Abnormal optical anisotropy in correlated disorder KTa1-xNbxO3:Cu with refractive index gradient.

Science.gov (United States)

Zhang, Xin; He, Shan; Zhao, Zhuan; Wu, Pengfei; Wang, Xuping; Liu, Hongliang

2018-02-13

In this report, an abnormal optical anisotropy in KTa 1-x Nb x O 3 :Cu (Cu:KTN) crystals with refractive index gradient is presented. Contrary to general regulation in a cross-polarization setup, the transmitted intensity of both TE (horizontally polarized) and TM (vertically polarized) lasers aligned with the basic crystallographic directions can be modulated quasiperiodically. The mechanism is supposed to be based on the polarization induced by the temperature gradient and the refractive index gradient. Meanwhile, the correlated disorder property of the crystals in the range of the freezing temperature (T f ) and the intermediate temperature (T  * ) also plays an important role. With the results verified both theoretically and experimentally, we believe this work is not only beneficial for the development of the theory associated with the correlated disorder structures in relaxor ferroelectrics, but also significant for the exploitation of numerous optical functional devices.

Enhancing Optical Forces in InP-Based Waveguides.

Science.gov (United States)

Aryaee Panah, Mohammad Esmail; Semenova, Elizaveta S; Lavrinenko, Andrei V

2017-06-08

Cantilever sensors are among the most important microelectromechanical systems (MEMS), which are usually actuated by electrostatic forces or piezoelectric elements. Although well-developed microfabrication technology has made silicon the prevailing material for MEMS, unique properties of other materials are overlooked in this context. Here we investigate optically induced forces exerted upon a semi-insulating InP waveguide suspended above a highly doped InP:Si substrate, in three different regimes: the epsilon-near-zero (ENZ), with excitation of surface plasmon polaritons (SPPs) and phonons excitation. An order of magnitude amplification of the force is observed when light is coupled to SPPs, and three orders of magnitude amplification is achieved in the phonon excitation regime. In the ENZ regime, the force is found to be repulsive and higher than that in a waveguide suspended above a dielectric substrate. Low losses in InP:Si result in a big propagation length. The induced deflection can be detected by measuring the phase change of the light when passing through the waveguide, which enables all-optical functioning, and paves the way towards integration and miniaturization of micro-cantilevers. In addition, tunability of the ENZ and the SPP excitation wavelength ranges, via adjusting the carrier concentration, provides an extra degree of freedom for designing MEMS devices.

An optical flow algorithm based on gradient constancy assumption for PIV image processing

International Nuclear Information System (INIS)

Zhong, Qianglong; Yang, Hua; Yin, Zhouping

2017-01-01

Particle image velocimetry (PIV) has matured as a flow measurement technique. It enables the description of the instantaneous velocity field of the flow by analyzing the particle motion obtained from digitally recorded images. Correlation based PIV evaluation technique is widely used because of its good accuracy and robustness. Although very successful, correlation PIV technique has some weakness which can be avoided by optical flow based PIV algorithms. At present, most of the optical flow methods applied to PIV are based on brightness constancy assumption. However, some factors of flow imaging technology and the nature property of the fluids make the brightness constancy assumption less appropriate in real PIV cases. In this paper, an implementation of a 2D optical flow algorithm (GCOF) based on gradient constancy assumption is introduced. The proposed GCOF assumes the edges of the illuminated PIV particles are constant during motion. It comprises two terms: a combined local-global gradient data term and a first-order divergence and vorticity smooth term. The approach can provide accurate dense motion fields. The approach are tested on synthetic images and on two experimental flows. The comparison of GCOF with other optical flow algorithms indicates the proposed method is more accurate especially in conditions of illumination variation. The comparison of GCOF with correlation PIV technique shows that the proposed GCOF has advantages on preserving small divergence and vorticity structures of the motion field and getting less outliers. As a consequence, the GCOF acquire a more accurate and better topological description of the turbulent flow. (paper)

Comparison between iterative wavefront control algorithm and direct gradient wavefront control algorithm for adaptive optics system

Science.gov (United States)

Cheng, Sheng-Yi; Liu, Wen-Jin; Chen, Shan-Qiu; Dong, Li-Zhi; Yang, Ping; Xu, Bing

2015-08-01

Among all kinds of wavefront control algorithms in adaptive optics systems, the direct gradient wavefront control algorithm is the most widespread and common method. This control algorithm obtains the actuator voltages directly from wavefront slopes through pre-measuring the relational matrix between deformable mirror actuators and Hartmann wavefront sensor with perfect real-time characteristic and stability. However, with increasing the number of sub-apertures in wavefront sensor and deformable mirror actuators of adaptive optics systems, the matrix operation in direct gradient algorithm takes too much time, which becomes a major factor influencing control effect of adaptive optics systems. In this paper we apply an iterative wavefront control algorithm to high-resolution adaptive optics systems, in which the voltages of each actuator are obtained through iteration arithmetic, which gains great advantage in calculation and storage. For AO system with thousands of actuators, the computational complexity estimate is about O(n2) ˜ O(n3) in direct gradient wavefront control algorithm, while the computational complexity estimate in iterative wavefront control algorithm is about O(n) ˜ (O(n)3/2), in which n is the number of actuators of AO system. And the more the numbers of sub-apertures and deformable mirror actuators, the more significant advantage the iterative wavefront control algorithm exhibits. Project supported by the National Key Scientific and Research Equipment Development Project of China (Grant No. ZDYZ2013-2), the National Natural Science Foundation of China (Grant No. 11173008), and the Sichuan Provincial Outstanding Youth Academic Technology Leaders Program, China (Grant No. 2012JQ0012).

Pushing nanoparticles with light — A femtonewton resolved measurement of optical scattering forces

Directory of Open Access Journals (Sweden)

C. Zensen

2016-05-01

Full Text Available Optomechanical manipulation of plasmonic nanoparticles is an area of current interest, both fundamental and applied. However, no experimental method is available to determine the forward-directed scattering force that dominates for incident light of a wavelength close to the plasmon resonance. Here, we demonstrate how the scattering force acting on a single gold nanoparticle in solution can be measured. An optically trapped 80 nm particle was repetitively pushed from the side with laser light resonant to the particle plasmon frequency. A lock-in analysis of the particle movement provides a measured value for the scattering force. We obtain a resolution of less than 3 femtonewtons which is an order of magnitude smaller than any measurement of switchable forces performed on nanoparticles in solution with single beam optical tweezers to date. We compared the results of the force measurement with Mie simulations of the optical scattering force on a gold nanoparticle and found good agreement between experiment and theory within a few fN.

Magnet polepiece design for uniform magnetic force on superparamagnetic beads

OpenAIRE

Fallesen, Todd; Hill, David B.; Steen, Matthew; Macosko, Jed C.; Bonin, Keith; Holzwarth, George

2010-01-01

Here we report construction of a simple electromagnet with novel polepieces which apply a spatially uniform force to superparamagnetic beads in an optical microscope. The wedge-shaped gap was designed to keep ∂Bx∕∂y constant and B large enough to saturate the bead. We achieved fields of 300–600 mT and constant gradients of 67 T∕m over a sample space of 0.5×4 mm2 in the focal plane of the microscope and 0.05 mm along the microscope optic axis. Within this space the maximum force on a 2.8 μm di...

Fano resonance of the ultrasensitve optical force excited by Gaussian evanescent field

International Nuclear Information System (INIS)

Yang, Yang; Li, Jiafang; Li, Zhi-Yuan

2015-01-01

In this paper, we study the angle-dependent Fano-like optical force spectra of plasmonic Ag nanoparticles, which exhibit extraordinary transformation from Lorentzian resonance to Fano resonance when excited by a Gaussian evanescent wave. We systematically analyze the behavior of this asymmetric scattering induced optical force under different conditions and find that this Fano interference-induced force is ultrasensitive to the excitation wavelength, incident angle and particle size, as well as the core–shell configuration, which could be useful for wavelength- and angle-dependent size-selective optical manipulation. The origin of this Fano resonance is further identified as the interference between the two adjacent-order multipolar plasmonic modes excited in the Ag particle under the excitation of an inhomogeneously distributed evanescent field. (paper)

Mechanical Kerr nonlinearities due to bipolar optical forces between deformable silicon waveguides.

Science.gov (United States)

Ma, Jing; Povinelli, Michelle L

2011-05-23

We use an analytical method based on the perturbation of effective index at fixed frequency to calculate optical forces between silicon waveguides. We use the method to investigate the mechanical Kerr effect in a coupled-waveguide system with bipolar forces. We find that a positive mechanical Kerr coefficient results from either an attractive or repulsive force. An enhanced mechanical Kerr coefficient several orders of magnitude larger than the intrinsic Kerr coefficient is obtained in waveguides for which the optical mode approaches the air light line, given appropriate design of the waveguide dimensions.

Refractive index gradient diagnostics: analysis of different optical systems and application to COBRA ion diode

Energy Technology Data Exchange (ETDEWEB)

Knyazev, B A; Greenly, J B; Hammer, D A; Krastelev, E G [Cornell Univ., Ithaca, NY (United States). Laboratory of Plasma Studies; Cuneo, M E [Sandia National Laboratories, Albuquerque, NM (United States)

1997-12-31

Different optical system variations for refractive index gradient diagnostics with a laser beam probe have been analyzed. A `three-telescope` optical system which permits simultaneous measurement of both the laser beam centroid deflection by a bi-cell photodiode and the spatial Fourier spectrum of the deflected beam by a streak camera has been implemented on the COBRA ion diode. The dynamics of the anode plasma layer was studied with these techniques. (author). 3 figs., 8 refs.

Optical force on diseased blood cells: Towards the optical sorting of biological matter

KAUST Repository

Gongora, J. S. Totero; Fratalocchi, Andrea

2015-01-01

By employing a series of massively parallel ab-initio simulations, we study how optical forces act on biological matter subject to morphological disease. As a representative case study, we here consider the case of Plasmodium falciparum on red blood

Combined use of heat and saline tracer to estimate aquifer properties in a forced gradient test

Science.gov (United States)

Colombani, N.; Giambastiani, B. M. S.; Mastrocicco, M.

2015-06-01

Usually electrolytic tracers are employed for subsurface characterization, but the interpretation of tracer test data collected by low cost techniques, such as electrical conductivity logging, can be biased by cation exchange reactions. To characterize the aquifer transport properties a saline and heat forced gradient test was employed. The field site, located near Ferrara (Northern Italy), is a well characterized site, which covers an area of 200 m2 and is equipped with a grid of 13 monitoring wells. A two-well (injection and pumping) system was employed to perform the forced gradient test and a straddle packer was installed in the injection well to avoid in-well artificial mixing. The contemporary continuous monitor of hydraulic head, electrical conductivity and temperature within the wells permitted to obtain a robust dataset, which was then used to accurately simulate injection conditions, to calibrate a 3D transient flow and transport model and to obtain aquifer properties at small scale. The transient groundwater flow and solute-heat transport model was built using SEAWAT. The result significance was further investigated by comparing the results with already published column experiments and a natural gradient tracer test performed in the same field. The test procedure shown here can provide a fast and low cost technique to characterize coarse grain aquifer properties, although some limitations can be highlighted, such as the small value of the dispersion coefficient compared to values obtained by natural gradient tracer test, or the fast depletion of heat signal due to high thermal diffusivity.

THE UV–OPTICAL COLOR GRADIENTS IN STAR-FORMING GALAXIES AT 0.5 < z < 1.5: ORIGINS AND LINK TO GALAXY ASSEMBLY

International Nuclear Information System (INIS)

Liu, F. S.; Jiang, Dongfei; Li, Yao; Li, Dingpeng; Guo, Yicheng; Koo, David C.; Faber, S. M.; Yesuf, Hassen M.; Barro, Guillermo; Fang, Jerome J.; Zheng, Xianzhong; Wang, Weichen; Mao, Shude

2016-01-01

The rest-frame UV–optical (i.e., NUV − B ) color index is sensitive to the low-level recent star formation and dust extinction, but it is insensitive to the metallicity. In this Letter, we have measured the rest-frame NUV − B color gradients in ∼1400 large ( r _e > 0.″18), nearly face-on ( b / a > 0.5) main sequence star-forming galaxies (SFGs) between redshift 0.5 and 1.5 in the CANDELS/GOODS-S and UDS fields. With this sample, we study the origin of UV–optical color gradients in the SFGs at z ∼ 1 and discuss their link with the buildup of stellar mass. We find that the more massive, centrally compact, and more dust extinguished SFGs tend to have statistically more negative raw color gradients (redder centers) than the less massive, centrally diffuse, and less dusty SFGs. After correcting for dust reddening based on optical-spectral energy distribution fitting, the color gradients in the low-mass ( M _* 10"1"0"."5 M _⊙) SFGs still retain shallow negative color gradients. These findings imply that dust reddening is likely the principal cause of negative color gradients in the low-mass SFGs, while both increased central dust reddening and buildup of compact old bulges are likely the origins of negative color gradients in the high-mass SFGs. These findings also imply that at these redshifts the low-mass SFGs buildup their stellar masses in a self-similar way, while the high-mass SFGs grow inside out.

Optical pulling and pushing forces exerted on silicon nanospheres with strong coherent interaction between electric and magnetic resonances.

Science.gov (United States)

Liu, Hongfeng; Panmai, Mingcheng; Peng, Yuanyuan; Lan, Sheng

2017-05-29

We investigated theoretically and numerically the optical pulling and pushing forces acting on silicon (Si) nanospheres (NSs) with strong coherent interaction between electric and magnetic resonances. We examined the optical pulling and pushing forces exerted on Si NSs by two interfering waves and revealed the underlying physical mechanism from the viewpoint of electric- and magnetic-dipole manipulation. As compared with a polystyrene (PS) NS, it was found that the optical pulling force for a Si NS with the same size is enlarged by nearly two orders of magnitude. In addition to the optical pulling force appearing at the long-wavelength side of the magnetic dipole resonance, very large optical pushing force is observed at the magnetic quadrupole resonance. The correlation between the optical pulling/pushing force and the directional scattering characterized by the ratio of the forward to backward scattering was revealed. More interestingly, it was found that the high-order electric and magnetic resonances in large Si NSs play an important role in producing optical pulling force which can be generated by not only s-polarized wave but also p-polarized one. Our finding indicates that the strong coherent interaction between the electric and magnetic resonances existing in nanoparticles with large refractive indices can be exploited to manipulate the optical force acting on them and the correlation between the optical force and the directional scattering can be used as guidance. The engineering and manipulation of optical forces will find potential applications in the trapping, transport and sorting of nanoparticles.

Longitudinal Lorentz force on a subwavelength-diameter optical fiber

International Nuclear Information System (INIS)

Yu Huakang; Fang Wei; Gu Fuxing; Yang Zongyin; Tong Limin; Qiu Min

2011-01-01

We analyze the longitudinal Lorentz forces that a propagating continuous-wave light exerts on a subwavelength-diameter optical fiber. Our theoretical results show that, during the propagating process, the guided light exerts no net time-averaged force on the fiber. Via numerical simulation, we find a significant overall pull force of 0.4 pN/mW acting on a 450-nm-diam fiber tip at a wavelength of 980 nm due to the scattering of the end face and a calculated force distribution reveals the feature of a near-field accumulation. Our results may be helpful to the configuration of optomechanical components or devices based on these fibers.

Enhancing Optical Forces in InP-Based Waveguides

DEFF Research Database (Denmark)

Panah, Mohammad Esmail Aryaee; Semenova, Elizaveta; Lavrinenko, Andrei

2017-01-01

Cantilever sensors are among the most important microelectromechanical systems (MEMS), which are usually actuated by electrostatic forces or piezoelectric elements. Although well-developed microfabrication technology has made silicon the prevailing material for MEMS, unique properties of other...... materials are overlooked in this context. Here we investigate optically induced forces exerted upon a semi-insulating InP waveguide suspended above a highly doped InP: Si substrate, in three different regimes: the epsilon-near-zero (ENZ), with excitation of surface plasmon polaritons (SPPs) and phonons...... excitation. An order of magnitude amplification of the force is observed when light is coupled to SPPs, and three orders of magnitude amplification is achieved in the phonon excitation regime. In the ENZ regime, the force is found to be repulsive and higher than that in a waveguide suspended above...

Fiber optic micro sensor for the measurement of tendon forces

Directory of Open Access Journals (Sweden)

Behrmann Gregory P

2012-10-01

Full Text Available Abstract A fiber optic sensor developed for the measurement of tendon forces was designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporated fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings were designed to convert radial forces applied to the housing into axial forces that could be sensed by the fiber Bragg grating. The metal housings were fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurements as well as for simultaneous resolution of multi-axis forces. The sensor was experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester was used to provide uniform pressures on the sensor in order to establish the linearity, repeatability, and accuracy characteristics of the sensor. The in vitro experiments were performed in excised tendon and in a dynamic gait simulator to simulate biological conditions. In both experimental conditions, the sensor was found to be a sensitive and reliable method for acquiring minimally invasive measurements of soft tissue forces. Our results suggest that this sensor will prove useful in a variety of biomechanical measurements.

Fiber optic micro sensor for the measurement of tendon forces.

Science.gov (United States)

Behrmann, Gregory P; Hidler, Joseph; Mirotznik, Mark S

2012-10-03

A fiber optic sensor developed for the measurement of tendon forces was designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporated fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings were designed to convert radial forces applied to the housing into axial forces that could be sensed by the fiber Bragg grating. The metal housings were fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurements as well as for simultaneous resolution of multi-axis forces.The sensor was experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester was used to provide uniform pressures on the sensor in order to establish the linearity, repeatability, and accuracy characteristics of the sensor. The in vitro experiments were performed in excised tendon and in a dynamic gait simulator to simulate biological conditions. In both experimental conditions, the sensor was found to be a sensitive and reliable method for acquiring minimally invasive measurements of soft tissue forces. Our results suggest that this sensor will prove useful in a variety of biomechanical measurements.

Optical design for increased interaction length in a high gradient dielectric laser accelerator

OpenAIRE

Cesar, D.; Maxson, J.; Musumeci, P.; Shen, X.; England, R. J.; Wootton, K. P.

2018-01-01

We present a methodology for designing and measuring pulse front tilt in an ultrafast laser for use in dielectric laser acceleration. Previous research into dielectric laser accelerating modules has focused on measuring high accelerating gradients in novel structures, but has done so only for short electron-laser coupling lengths. Here we demonstrate an optical design to extend the laser-electron interaction to 1mm.

Force-detected nanoscale absorption spectroscopy in water at room temperature using an optical trap

Science.gov (United States)

Parobek, Alexander; Black, Jacob W.; Kamenetska, Maria; Ganim, Ziad

2018-04-01

Measuring absorption spectra of single molecules presents a fundamental challenge for standard transmission-based instruments because of the inherently low signal relative to the large background of the excitation source. Here we demonstrate a new approach for performing absorption spectroscopy in solution using a force measurement to read out optical excitation at the nanoscale. The photoinduced force between model chromophores and an optically trapped gold nanoshell has been measured in water at room temperature. This photoinduced force is characterized as a function of wavelength to yield the force spectrum, which is shown to be correlated to the absorption spectrum for four model systems. The instrument constructed for these measurements combines an optical tweezer with frequency domain absorption spectroscopy over the 400-800 nm range. These measurements provide proof-of-principle experiments for force-detected nanoscale spectroscopies that operate under ambient chemical conditions.

Manipulation of nanoparticles and biological samples through enhanced optical forces

Science.gov (United States)

Wilson, Benjamin

Non-invasive optical manipulation of particles has emerged as a powerful and versatile tool for biological study and nanotechnology. We propose and demonstrate large scale nanoparticle assembly using opto-thermal force produced by conventional optical tweezers. This method is shown to allow precise concentration and assembly of particles including carbon-nanotubes, VO2 nanorods, and CdTe quantum dots. Assembled devices were shown to have good contact with patterned electrodes. In addition, we propose and demonstrate a purely optical approach to rotate and align particles using the interaction of polarized light with photonic crystal nanostructures to generate enhanced trapping force. With a weakly focused laser beam we observed efficient trapping and transportation of polystyrene beads with sizes ranging from 10 microm down to 190 nm as well as cancer cell nuclei. In addition, we demonstrated alignment of non-spherical particles using a 1-D photonic crystal structure. Bacterial cells were trapped, rotated and aligned with optical intensity as low as 17 microW/microm 2. This approach can be extended to using 2-D photonic crystal nanostructures for full rotation control.

Atomic force microscope with integrated optical microscope for biological applications

OpenAIRE

Putman, Constant A.J.; Putman, C.A.J.; van der Werf, Kees; de Grooth, B.G.; van Hulst, N.F.; Segerink, Franciscus B.; Greve, Jan

1992-01-01

Since atomic force microscopy (AFM) is capable of imaging nonconducting surfaces, the technique holds great promises for high‐resolution imaging of biological specimens. A disadvantage of most AFMs is the fact that the relatively large sample surface has to be scanned multiple times to pinpoint a specific biological object of interest. Here an AFM is presented which has an incorporated inverted optical microscope. The optical image from the optical microscope is not obscured by the cantilever...

Dynamic analysis of trapping and escaping in dual beam optical trap

Science.gov (United States)

Li, Wenqiang; Hu, Huizhu; Su, Heming; Li, Zhenggang; Shen, Yu

2016-10-01

In this paper, we simulate the dynamic movement of a dielectric sphere in optical trap. This dynamic analysis can be used to calibrate optical forces, increase trapping efficiency and measure viscous coefficient of surrounding medium. Since an accurate dynamic analysis is based on a detailed force calculation, we calculate all forces a sphere receives. We get the forces of dual-beam gradient radiation pressure on a micron-sized dielectric sphere in the ray optics regime and utilize Einstein-Ornstein-Uhlenbeck to deal with its Brownian motion forces. Hydrodynamic viscous force also exists when the sphere moves in liquid. Forces from buoyance and gravity are also taken into consideration. Then we simulate trajectory of a sphere when it is subject to all these forces in a dual optical trap. From our dynamic analysis, the sphere can be trapped at an equilibrium point in static water, although it permanently fluctuates around the equilibrium point due to thermal effects. We go a step further to analyze the effects of misalignment of two optical traps. Trapping and escaping phenomena of the sphere in flowing water are also simulated. In flowing water, the sphere is dragged away from the equilibrium point. This dragging distance increases with the decrease of optical power, which results in escaping of the sphere with optical power below a threshold. In both trapping and escaping process we calculate the forces and position of the sphere. Finally, we analyze a trapping region in dual optical tweezers.

Importance of representing optical depth variability for estimates of global line-shaped contrail radiative forcing.

Science.gov (United States)

Kärcher, Bernd; Burkhardt, Ulrike; Ponater, Michael; Frömming, Christine

2010-11-09

Estimates of the global radiative forcing by line-shaped contrails differ mainly due to the large uncertainty in contrail optical depth. Most contrails are optically thin so that their radiative forcing is roughly proportional to their optical depth and increases with contrail coverage. In recent assessments, the best estimate of mean contrail radiative forcing was significantly reduced, because global climate model simulations pointed at lower optical depth values than earlier studies. We revise these estimates by comparing the probability distribution of contrail optical depth diagnosed with a climate model with the distribution derived from a microphysical, cloud-scale model constrained by satellite observations over the United States. By assuming that the optical depth distribution from the cloud model is more realistic than that from the climate model, and by taking the difference between the observed and simulated optical depth over the United States as globally representative, we quantify uncertainties in the climate model's diagnostic contrail parameterization. Revising the climate model results accordingly increases the global mean radiative forcing estimate for line-shaped contrails by a factor of 3.3, from 3.5 mW/m(2) to 11.6 mW/m(2) for the year 1992. Furthermore, the satellite observations and the cloud model point at higher global mean optical depth of detectable contrails than often assumed in radiative transfer (off-line) studies. Therefore, we correct estimates of contrail radiative forcing from off-line studies as well. We suggest that the global net radiative forcing of line-shaped persistent contrails is in the range 8-20 mW/m(2) for the air traffic in the year 2000.

Three-axis optical force plate for studies in small animal locomotor mechanics

International Nuclear Information System (INIS)

Hsieh, S. Tonia

2006-01-01

The use of force plates to measure whole-body locomotor mechanics is a well-established technique. However, commercially available force plates are not sensitive enough for use on small-bodied vertebrates or invertebrates. The standard design for single- and multiple-axis, high-sensitivity force plates built by individual research groups uses semiconductor foil strain gauges to measure deflections; yet foil strain gauges are highly temperature and position sensitive, resulting in a drifting base line and nonlinear responses. I present here a design for a three-axis optical force plate that was successfully calibrated to measure forces as small as 1.5 mN and is capable of determining the position of center of pressure with a mean error of 0.07 cm along the X axis and 0.13 cm along the Y axis. Using optical sensors instead of foil strain gauges to measure deflection, this force plate is not subject to temperature-related drift and is more robust against slight positioning inaccuracies. This force plate was used to measure forces produced by amphibious fishes weighing less than 2 g as they jumped off the force platform

Relative influences of the metocean forcings on the drifting ice pack and estimation of internal ice stress gradients in the Labrador Sea

Science.gov (United States)

Turnbull, I. D.; Torbati, R. Z.; Taylor, R. S.

2017-07-01

Understanding the relative influences of the metocean forcings on the drift of sea ice floes is a crucial component to the overall characterization of an ice environment and to developing an understanding of the factors controlling the ice dynamics. In addition, estimating the magnitude of the internal stress gradients on drifting sea ice floes generated by surrounding ice cover is important for modeling operations, informing the design of offshore structures and vessels in ice environments, and for the proper calibration of Discrete Element Models (DEM) of fields of drifting ice floes. In the spring of 2015 and 2016, four sea ice floes offshore Makkovik, Labrador were tagged with satellite-linked ice tracking buoys along with one satellite-linked weather station on each floe to transmit wind speed and direction. Twenty satellite-linked Lagrangian surface ocean current tracking buoys were also deployed in the open water adjacent to the targeted ice floes. In this paper, the dynamics of the four ice floes are explored in terms of the relative proportions which were forced by the wind, current, sea surface topography, Coriolis, and internal stress gradients. The internal ice stress gradients are calculated as residuals between the observed accelerations of the floes as measured by the tracking buoys and the sums of the other metocean forcings. Results show that internal ice stress gradients accounted for up to 50% of the observed forcing on the floes, and may have reached up to around 0.19 kPa.

Geometrical optics analysis of the structural imperfection of retroreflection corner cubes with a nonlinear conjugate gradient method.

Science.gov (United States)

Kim, Hwi; Min, Sung-Wook; Lee, Byoungho

2008-12-01

Geometrical optics analysis of the structural imperfection of retroreflection corner cubes is described. In the analysis, a geometrical optics model of six-beam reflection patterns generated by an imperfect retroreflection corner cube is developed, and its structural error extraction is formulated as a nonlinear optimization problem. The nonlinear conjugate gradient method is employed for solving the nonlinear optimization problem, and its detailed implementation is described. The proposed method of analysis is a mathematical basis for the nondestructive optical inspection of imperfectly fabricated retroreflection corner cubes.

Customizable Optical Force Sensor for Fast Prototyping and Cost-Effective Applications.

Science.gov (United States)

Díez, Jorge A; Catalán, José M; Blanco, Andrea; García-Perez, José V; Badesa, Francisco J; Gacía-Aracil, Nicolás

2018-02-07

This paper presents the development of an optical force sensor architecture directed to prototyping and cost-effective applications, where the actual force requirements are still not well defined or the most suitable commercial technologies would highly increase the cost of the device. The working principle of this sensor consists of determining the displacement of a lens by measuring the distortion of a refracted light beam. This lens is attached to an elastic interface whose elastic constant is known, allowing the estimation of the force that disturbs the optical system. In order to satisfy the requirements of the design process in an inexpensive way, this sensor can be built by fast prototyping technologies and using non-optical grade elements. To deal with the imperfections of this kind of manufacturing procedures and materials, four fitting models are proposed to calibrate the implemented sensor. In order to validate the system, two different sensor implementations with measurement ranges of ±45 N and ±10 N are tested with the proposed models, comparing the resulting force estimation with respect to an industrial-grade load cell. Results show that all models can estimate the loads with an error of about 6% of the measurement range.

Customizable Optical Force Sensor for Fast Prototyping and Cost-Effective Applications

Directory of Open Access Journals (Sweden)

Jorge A. Díez

2018-02-01

Full Text Available This paper presents the development of an optical force sensor architecture directed to prototyping and cost-effective applications, where the actual force requirements are still not well defined or the most suitable commercial technologies would highly increase the cost of the device. The working principle of this sensor consists of determining the displacement of a lens by measuring the distortion of a refracted light beam. This lens is attached to an elastic interface whose elastic constant is known, allowing the estimation of the force that disturbs the optical system. In order to satisfy the requirements of the design process in an inexpensive way, this sensor can be built by fast prototyping technologies and using non-optical grade elements. To deal with the imperfections of this kind of manufacturing procedures and materials, four fitting models are proposed to calibrate the implemented sensor. In order to validate the system, two different sensor implementations with measurement ranges of ±45 N and ±10 N are tested with the proposed models, comparing the resulting force estimation with respect to an industrial-grade load cell. Results show that all models can estimate the loads with an error of about 6% of the measurement range.

Parametric Amplification Protocol for Frequency-Modulated Magnetic Resonance Force Microscopy Signals

Science.gov (United States)

Harrell, Lee; Moore, Eric; Lee, Sanggap; Hickman, Steven; Marohn, John

2011-03-01

We present data and theoretical signal and noise calculations for a protocol using parametric amplification to evade the inherent tradeoff between signal and detector frequency noise in force-gradient magnetic resonance force microscopy signals, which are manifested as a modulated frequency shift of a high- Q microcantilever. Substrate-induced frequency noise has a 1 / f frequency dependence, while detector noise exhibits an f2 dependence on modulation frequency f . Modulation of sample spins at a frequency that minimizes these two contributions typically results in a surface frequency noise power an order of magnitude or more above the thermal limit and may prove incompatible with sample spin relaxation times as well. We show that the frequency modulated force-gradient signal can be used to excite the fundamental resonant mode of the cantilever, resulting in an audio frequency amplitude signal that is readily detected with a low-noise fiber optic interferometer. This technique allows us to modulate the force-gradient signal at a sufficiently high frequency so that substrate-induced frequency noise is evaded without subjecting the signal to the normal f2 detector noise of conventional demodulation.

Orbit and optics distortion in fixed field alternating gradient muon accelerators

Directory of Open Access Journals (Sweden)

Shinji Machida

2007-11-01

Full Text Available In a linear nonscaling fixed field alternating gradient (FFAG accelerator, betatron tunes vary over a wide range and a beam has to cross integer and half-integer tunes several times. Although it is plausible to say that integer and half-integer resonances are not harmful if the crossing speed is fast, no quantitative argument exists. With tracking simulation, we studied orbit and optics distortion due to alignment and magnet errors. It was found that the concept of integer and half-integer resonance crossing is irrelevant to explain beam behavior in a nonscaling FFAG when acceleration is fast and betatron tunes change quickly. In a muon FFAG accelerator, it takes 17 turns for acceleration and the betatron tunes change more than 10, for example. Instead, the orbit and optics distortion is excited by random dipole and quadrupole kicks. The latter causes beam size growth because the beam starts tumbling in phase space, but not necessarily with emittance growth.

Feature extraction for magnetic domain images of magneto-optical recording films using gradient feature segmentation

International Nuclear Information System (INIS)

Quanqing, Zhu.; Xinsai, Wang; Xuecheng, Zou; Haihua, Li; Xiaofei, Yang

2002-01-01

In this paper, we present a method to realize feature extraction on low contrast magnetic domain images of magneto-optical recording films. The method is based on the following three steps: first, Lee-filtering method is adopted to realize pre-filtering and noise reduction; this is followed by gradient feature segmentation, which separates the object area from the background area; finally the common linking method is adopted and the characteristic parameters of magnetic domain are calculated. We describe these steps with particular emphasis on the gradient feature segmentation. The results show that this method has advantages over other traditional ones for feature extraction of low contrast images

Projection and nested force-gradient methods for quantum field theories

Energy Technology Data Exchange (ETDEWEB)

Shcherbakov, Dmitry

2017-07-26

For the Hybrid Monte Carlo algorithm (HMC), often used to study the fundamental quantum field theory of quarks and gluons, quantum chromodynamics (QCD), on the lattice, one is interested in efficient numerical time integration schemes which preserve geometric properties of the flow and are optimal in terms of computational costs per trajectory for a given acceptance rate. High order numerical methods allow the use of larger step sizes, but demand a larger computational effort per step; low order schemes do not require such large computational costs per step, but need more steps per trajectory. So there is a need to balance these opposing effects. In this work we introduce novel geometric numerical time integrators, namely, projection and nested force-gradient methods in order to improve the efficiency of the HMC algorithm in application to the problems of quantum field theories.

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces

International Nuclear Information System (INIS)

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian; Cremer, Johannes; Chasovskikh, Egor; Signorell, Ruth

2015-01-01

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces

Energy Technology Data Exchange (ETDEWEB)

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian; Cremer, Johannes; Chasovskikh, Egor; Signorell, Ruth, E-mail: rsignorell@ethz.ch [Laboratory of Physical Chemistry, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich (Switzerland)

2015-04-21

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces.

Science.gov (United States)

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian; Cremer, Johannes; Chasovskikh, Egor; Signorell, Ruth

2015-04-21

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces

Science.gov (United States)

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian; Cremer, Johannes; Chasovskikh, Egor; Signorell, Ruth

2015-04-01

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.

Cooling optically levitated dielectric nanoparticles via parametric feedback

Science.gov (United States)

Neukirch, Levi; Rodenburg, Brandon; Bhattacharya, Mishkatul; Vamivakas, Nick

2015-05-01

The inability to leverage resonant scattering processes involving internal degrees of freedom differentiates optical cooling experiments performed with levitated dielectric nanoparticles, from similar atomic and molecular traps. Trapping in optical cavities or the application of active feedback techniques have proven to be effective ways to circumvent this limitation. We present our nanoparticle optical cooling apparatus, which is based on parametric feedback modulation of a single-beam gradient force optical trap. This scheme allows us to achieve effective center-of-mass temperatures well below 1 kelvin for our ~ 1 ×10-18 kg particles, at modest vacuum pressures. The method provides a versatile platform, with parameter tunability not found in conventional tethered nanomechanical systems. Potential applications include investigations of nonequilibrium nanoscale thermodynamics, ultra-sensitive force metrology, and mesoscale quantum mechanics and hybrid systems. Supported by the office of Naval Research award number N000141410442.

Temporal formation of optical anisotropy and surface relief during polarization holographic recording in polymethylmethacrylate with azobenzene side groups

Science.gov (United States)

Sasaki, Tomoyuki; Izawa, Masahiro; Noda, Kohei; Nishioka, Emi; Kawatsuki, Nobuhiro; Ono, Hiroshi

2014-03-01

The formation of polarization holographic gratings with both optical anisotropy and surface relief (SR) deformation was studied for polymethylmethacrylate with azobenzene side groups. Temporal contributions of isotropic and anisotropic phase gratings were simultaneously determined by observing transitional intensity and polarization states of the diffraction beams and characterizing by means of Jones calculus. To clarify the mechanism of SR deformation, cross sections of SR were characterized based on the optical gradient force model; experimental observations were in good agreement with the theoretical expectation. We clarified that the anisotropic phase change originating in the reorientation of the azobenzene side groups was induced immediately at the beginning of the holographic recording, while the response time of the isotropic phase change originating in the molecular migration due to the optical gradient force was relatively slow.

Frequency domain optical tomography using a conjugate gradient method without line search

International Nuclear Information System (INIS)

Kim, Hyun Keol; Charette, Andre

2007-01-01

A conjugate gradient method without line search (CGMWLS) is presented. This method is used to retrieve the local maps of absorption and scattering coefficients inside the tissue-like test medium, with the synthetic data. The forward problem is solved with a discrete-ordinates finite-difference method based on the frequency domain formulation of radiative transfer equation. The inversion results demonstrate that the CGMWLS can retrieve simultaneously the spatial distributions of optical properties inside the medium within a reasonable accuracy, by reducing cross-talk between absorption and scattering coefficients

Resonant acoustic radiation force optical coherence elastography

OpenAIRE

Qi, Wenjuan; Li, Rui; Ma, Teng; Li, Jiawen; Kirk Shung, K.; Zhou, Qifa; Chen, Zhongping

2013-01-01

We report on a resonant acoustic radiation force optical coherence elastography (ARF-OCE) technique that uses mechanical resonant frequency to characterize and identify tissues of different types. The linear dependency of the resonant frequency on the square root of Young's modulus was validated on silicone phantoms. Both the frequency response spectrum and the 3D imaging results from the agar phantoms with hard inclusions confirmed the feasibility of deploying the resonant frequency as a mec...

Electronic and Optical Properties of TiS_2 Determined from Generalized Gradient Approximation Study

International Nuclear Information System (INIS)

El-Kouch, Hamza; Farh, Larbi El; Sayah, Jamal; Challioui, Allal

2015-01-01

The electronic and optical properties of TiS_2 are studied by using an ab-initio calculation within the frame of density functional theory. A linearized and augmented plane wave basis set with the generalized gradient approximation as proposed by Perdew et al. is used for the energy exchange-correlation determination. The results show a metallic character of TiS_2, and the plots of total and partial densities of states of TiS_2 show the metallic character of the bonds and a strong hybridization between the states d of Ti and p of S below the Fermi energy. The optical properties of the material such as real and imaginary parts of dielectric constant (ϵ(ω) = ϵ_1(ω) + iϵ_2(ω)), refractive index n(ω), optical reflectivity R(ω), for E//x and E//z are performed for the energy range of 0–14 eV. (paper)

Development of optical FBG force measurement system for the medical application

Science.gov (United States)

Song, Hoseok; Kim, Kiyoung; Suh, Jungwook; Lee, Jungju

2010-03-01

Haptic feedback plays a very important role in medical surgery. In minimally invasive surgery (MIS), however, very long and stiff bar of instruments take haptic feeling away from the surgeon. In minimally invasive robotic surgery (MIRS), moreover, haptic feelings are totally eliminated. Previous researchers have reported that the absence of force feedback increased the average force magnitude applied to the tissue by at least 50%, and increased the peakforce magnitude by at least a factor of two. Therefore, it is very important to provide haptic information in MIRS. Recently, many sensors are being developed for MIS or MIRS, but they have some obstacles in their application to real situations of medical surgery. The most critical problems are size limit and sterilizability. Optical fiber sensors are one of the most suitable sensors for this environment. Especially, optical fiber Bragg grating (FBG) sensor has one additional advantage than the other optical fiber sensors. FBG sensor is not influenced by intensity of light source. In this paper, we would like to present the initial results of study on the application of the FBG sensor to measure reflected forces in MIRS environments and then suggest the possibility of successful application to the MIRS systems.

Spatial gradient tuning in metamaterials

Science.gov (United States)

Driscoll, Tom; Goldflam, Michael; Jokerst, Nan; Basov, Dimitri; Smith, David

2011-03-01

Gradient Index (GRIN) metamaterials have been used to create devices inspired by, but often surpassing the potential of, conventional GRIN optics. The unit-cell nature of metamaterials presents the opportunity to exert much greater control over spatial gradients than is possible in natural materials. This is true not only during the design phase but also offers the potential for real-time reconfiguration of the metamaterial gradient. This ability fits nicely into the picture of transformation-optics, in which spatial gradients can enable an impressive suite of innovative devices. We discuss methods to exert control over metamaterial response, focusing on our recent demonstrations using Vanadium Dioxide. We give special attention to role of memristance and mem-capacitance observed in Vanadium Dioxide, which simplify the demands of stimuli and addressing, as well as intersecting metamaterials with the field of memory-materials.

Optical forces induced behavior of a particle in a non-diffracting vortex beam

Czech Academy of Sciences Publication Activity Database

Šiler, Martin; Jákl, Petr; Brzobohatý, Oto; Zemánek, Pavel

2012-01-01

Roč. 20, č. 22 (2012), s. 24304-24319 ISSN 1094-4087 R&D Projects: GA ČR GPP205/11/P294; GA MŠk ED0017/01/01; GA MŠk LH12018 Institutional support: RVO:68081731 Keywords : optical vortex beam * tweezers * optical forces Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.546, year: 2012

Label-Free Detection of Bacillus anthracis Spore Uptake in Macrophage Cells Using Analytical Optical Force Measurements.

Science.gov (United States)

Hebert, Colin G; Hart, Sean; Leski, Tomasz A; Terray, Alex; Lu, Qin

2017-10-03

Understanding the interaction between macrophage cells and Bacillus anthracis spores is of significant importance with respect to both anthrax disease progression, spore detection for biodefense, as well as understanding cell clearance in general. While most detection systems rely on specific molecules, such as nucleic acids or proteins and fluorescent labels to identify the target(s) of interest, label-free methods probe changes in intrinsic properties, such as size, refractive index, and morphology, for correlation with a particular biological event. Optical chromatography is a label free technique that uses the balance between optical and fluidic drag forces within a microfluidic channel to determine the optical force on cells or particles. Here we show an increase in the optical force experienced by RAW264.7 macrophage cells upon the uptake of both microparticles and B. anthracis Sterne 34F2 spores. In the case of spores, the exposure was detected in as little as 1 h without the use of antibodies or fluorescent labels of any kind. An increase in the optical force was also seen in macrophage cells treated with cytochalasin D, both with and without a subsequent exposure to spores, indicating that a portion of the increase in the optical force arises independent of phagocytosis. These results demonstrate the capability of optical chromatography to detect subtle biological differences in a rapid and sensitive manner and suggest future potential in a range of applications, including the detection of biological threat agents for biodefense and pathogens for the prevention of sepsis and other diseases.

Gibbsian segregating alloys driven by thermal and concentration gradients: A potential grazing collector optics used in EUV lithography

Science.gov (United States)

Qiu, Huatan

A critical issue for EUV lithography is the minimization of collector degradation from intense plasma erosion and debris deposition. Reflectivity and lifetime of the collector optics will be heavily dependent on surface chemistry interactions between fuels and various mirror materials, in addition to high-energy ion and neutral particle erosion effects. An innovative Gibbsian segregation (GS) concept has been developed for being a self-healing, erosion-resistant collector optics. A Mo-Au GS alloy is developed on silicon using a DC dual-magnetron co-sputtering system in order for enhanced surface roughness properties, erosion resistance, and self-healing characteristics to maintain reflectivity over a longer period of mirror lifetime. A thin Au segregating layer will be maintained through segregation during exposure, even though overall erosion is taking place. The reflective material, Mo, underneath the segregating layer will be protected by this sacrificial layer which is lost due to preferential sputtering. The two dominant driving forces, thermal (temperature) and surface concentration gradient (surface removal flux), are the focus of this work. Both theoretical and experimental efforts have been performed to prove the effectiveness of the GS alloy used as EUV collection optics, and to elucidate the underlying physics behind it. The segregation diffusion, surface balance, erosion, and in-situ reflectivity will be investigated both qualitatively and quantitatively. Results show strong enhancement effect of temperature on GS performance, while only a weak effect of surface removal rate on GS performance. When equilibrium between GS and erosion is reached, the surface smoothness could be self-healed and reflectivity could be maintained at an equilibrium level, instead of continuously dropping down to an unacceptable level as conventional optic mirrors behave. GS process also shows good erosion resistance. The effectiveness of GS alloy as EUV mirror is dependent on

Fiber Optic Force Sensors for MRI-Guided Interventions and Rehabilitation: A Review

Science.gov (United States)

Iordachita, Iulian I.; Tokuda, Junichi; Hata, Nobuhiko; Liu, Xuan; Seifabadi, Reza; Xu, Sheng; Wood, Bradford; Fischer, Gregory S.

2017-01-01

Magnetic Resonance Imaging (MRI) provides both anatomical imaging with excellent soft tissue contrast and functional MRI imaging (fMRI) of physiological parameters. The last two decades have witnessed the manifestation of increased interest in MRI-guided minimally invasive intervention procedures and fMRI for rehabilitation and neuroscience research. Accompanying the aspiration to utilize MRI to provide imaging feedback during interventions and brain activity for neuroscience study, there is an accumulated effort to utilize force sensors compatible with the MRI environment to meet the growing demand of these procedures, with the goal of enhanced interventional safety and accuracy, improved efficacy and rehabilitation outcome. This paper summarizes the fundamental principles, the state of the art development and challenges of fiber optic force sensors for MRI-guided interventions and rehabilitation. It provides an overview of MRI-compatible fiber optic force sensors based on different sensing principles, including light intensity modulation, wavelength modulation, and phase modulation. Extensive design prototypes are reviewed to illustrate the detailed implementation of these principles. Advantages and disadvantages of the sensor designs are compared and analyzed. A perspective on the future development of fiber optic sensors is also presented which may have additional broad clinical applications. Future surgical interventions or rehabilitation will rely on intelligent force sensors to provide situational awareness to augment or complement human perception in these procedures. PMID:28652857

Fiber Optic Force Sensors for MRI-Guided Interventions and Rehabilitation: A Review.

Science.gov (United States)

Su, Hao; Iordachita, Iulian I; Tokuda, Junichi; Hata, Nobuhiko; Liu, Xuan; Seifabadi, Reza; Xu, Sheng; Wood, Bradford; Fischer, Gregory S

2017-04-01

Magnetic Resonance Imaging (MRI) provides both anatomical imaging with excellent soft tissue contrast and functional MRI imaging (fMRI) of physiological parameters. The last two decades have witnessed the manifestation of increased interest in MRI-guided minimally invasive intervention procedures and fMRI for rehabilitation and neuroscience research. Accompanying the aspiration to utilize MRI to provide imaging feedback during interventions and brain activity for neuroscience study, there is an accumulated effort to utilize force sensors compatible with the MRI environment to meet the growing demand of these procedures, with the goal of enhanced interventional safety and accuracy, improved efficacy and rehabilitation outcome. This paper summarizes the fundamental principles, the state of the art development and challenges of fiber optic force sensors for MRI-guided interventions and rehabilitation. It provides an overview of MRI-compatible fiber optic force sensors based on different sensing principles, including light intensity modulation, wavelength modulation, and phase modulation. Extensive design prototypes are reviewed to illustrate the detailed implementation of these principles. Advantages and disadvantages of the sensor designs are compared and analyzed. A perspective on the future development of fiber optic sensors is also presented which may have additional broad clinical applications. Future surgical interventions or rehabilitation will rely on intelligent force sensors to provide situational awareness to augment or complement human perception in these procedures.

A Multi-Gradient Generator in a Single Microfluidic Device for Optical Microscopy and Interferometry

Science.gov (United States)

Bedrossian, Manuel; Nadeau, Jay; Lindensmith, Chris

2016-11-01

The goal of this work was to create a single microfluidic device capable of establishing multiple types of gradients in a quantifiable manner. Many microbial species are known to exhibit directed motility in the presence of stimuli. This phenomenon, known as taxis, can be used as a bio-signature and a means of identifying microorganisms. Directed microbial motility has been seen as a response to the presence of certain chemicals, light, heat, magnetic fields, and other stimuli. Microbial movement along the gradient vector, that cannot be explained by passive hydrodynamics or Brownian motion, can shed light on whether the sample contains living microbes or not. The ability to create multiple types of gradients in a single microfluidic device allows for high throughput testing of heterogeneous samples to detect taxis. There has been increased interest in the search for life within our solar system where liquid water is known to exist. Induced directional motility can serve as a viable method for detecting living organisms that actively respond to their environment. The device developed here includes a chemical, photonic, thermal, and magnetic gradient generator, while maintaining high optical quality in order to be used for microscopy as well as quantitative phase imaging This work was funded by the Gordon and Betty Moore Foundation, who the authors wish to thank for their generosity.

Light at work: The use of optical forces for particle manipulation, sorting, and analysis

Czech Academy of Sciences Publication Activity Database

Jonáš, Alexandr; Zemánek, Pavel

2008-01-01

Roč. 29, č. 24 (2008), s. 4813-4851 ISSN 0173-0835 R&D Projects: GA MŠk(CZ) LC06007; GA MŠk OC08034 Institutional research plan: CEZ:AV0Z20650511 Keywords : microfluidics * optical chromatography and sorting * optical force and torque * optical tweezers and micro-manipulation / Optical tweezers and micro-manipulation / Raman microspectroscopy * Raman microspectroscopy Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.509, year: 2008

The truncated conjugate gradient (TCG), a non-iterative/fixed-cost strategy for computing polarization in molecular dynamics: Fast evaluation of analytical forces

Science.gov (United States)

Aviat, Félix; Lagardère, Louis; Piquemal, Jean-Philip

2017-10-01

In a recent paper [F. Aviat et al., J. Chem. Theory Comput. 13, 180-190 (2017)], we proposed the Truncated Conjugate Gradient (TCG) approach to compute the polarization energy and forces in polarizable molecular simulations. The method consists in truncating the conjugate gradient algorithm at a fixed predetermined order leading to a fixed computational cost and can thus be considered "non-iterative." This gives the possibility to derive analytical forces avoiding the usual energy conservation (i.e., drifts) issues occurring with iterative approaches. A key point concerns the evaluation of the analytical gradients, which is more complex than that with a usual solver. In this paper, after reviewing the present state of the art of polarization solvers, we detail a viable strategy for the efficient implementation of the TCG calculation. The complete cost of the approach is then measured as it is tested using a multi-time step scheme and compared to timings using usual iterative approaches. We show that the TCG methods are more efficient than traditional techniques, making it a method of choice for future long molecular dynamics simulations using polarizable force fields where energy conservation matters. We detail the various steps required for the implementation of the complete method by software developers.

Portable dual field gradient force multichannel flow cytometer device with a dual wavelength low noise detection scheme

Science.gov (United States)

James, Conrad D; Galambos, Paul C; Derzon, Mark S; Graf, Darin C; Pohl, Kenneth R; Bourdon, Chris J

2012-10-23

Systems and methods for combining dielectrophoresis, magnetic forces, and hydrodynamic forces to manipulate particles in channels formed on top of an electrode substrate are discussed. A magnet placed in contact under the electrode substrate while particles are flowing within the channel above the electrode substrate allows these three forces to be balanced when the system is in operation. An optical detection scheme using near-confocal microscopy for simultaneously detecting two wavelengths of light emitted from the flowing particles is also discussed.

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

International Nuclear Information System (INIS)

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

2007-01-01

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

Report and analysis of the BULLION forced-gradient experiment

Energy Technology Data Exchange (ETDEWEB)

NONE

1998-08-01

The BULLION Forced-Gradient Experiment (FGE) was conducted in the summer of 1997, starting June 2 and ending August 28. The site of the experiment was the ER-20-6 well field adjacent to the BULLION test. Figure 1-1 shows the location of this site on Pahute Mesa in Area 20 of the Nevada Test Site. Figure 1-2 shows the ER-20-6 site within the Pahute Mesa hydrogeologic framework, and Figure 1-3 shows the site layout with respect to the BULLION test. The purpose of the BULLION FGE was to provide information relevant to the transport of radionuclides in groundwater. Transport of radionuclides from Pahute Mesa is of special concern due to the potential for rapid movement of groundwater in the fractured volcanic rocks comprising the Mesa and formations along the anticipated downgradient path of groundwater. The objective was specifically to observe the transport process and characterize transport parameters (e.g., effective porosity, dispersivity and matrix diffusion) for use in predictive modeling of contaminant transport. Additional objectives were to characterize the hydrologic source term and the relative mobility of mobile radionuclides.

Thermal and optical properties of polycrystalline CdS thin films deposited by the gradient recrystallization and growth (GREG) technique using photoacoustic methods

International Nuclear Information System (INIS)

Albor-Aguilera, M.L.; Gonzalez-Trujillo, M.A.; Cruz-Orea, A.; Tufino-Velazquez, M.

2009-01-01

In this work we report the study of the thermal and optical properties of polycrystalline CdS thin films deposited by the gradient recrystallization and growth technique. CdS films were grown on pyrex glass substrates. These studies were carried out using an open photoacoustic cell made out of an electret microphone. From X-ray diffraction, atomic force microscope and photoluminescence measurements we observed polycrystalline CdS films with good morphology and crystalline quality. We obtained a thermal diffusivity coefficient of our samples with values ranging from 3.15 to 3.89 x 10 -2 cm 2 /s. For comparison, we measured a value of 1.0 x 10 -2 cm 2 /s for the thermal diffusivity coefficient of a CdS single crystal. We measured an energy gap value of 2.42 eV for our samples by using a photoacoustic spectroscopy system

TIGER: Development of Thermal Gradient Compensation Algorithms and Techniques

Science.gov (United States)

Hereford, James; Parker, Peter A.; Rhew, Ray D.

2004-01-01

In a wind tunnel facility, the direct measurement of forces and moments induced on the model are performed by a force measurement balance. The measurement balance is a precision-machined device that has strain gages at strategic locations to measure the strain (i.e., deformations) due to applied forces and moments. The strain gages convert the strain (and hence the applied force) to an electrical voltage that is measured by external instruments. To address the problem of thermal gradients on the force measurement balance NASA-LaRC has initiated a research program called TIGER - Thermally-Induced Gradients Effects Research. The ultimate goals of the TIGER program are to: (a) understand the physics of the thermally-induced strain and its subsequent impact on load measurements and (b) develop a robust thermal gradient compensation technique. This paper will discuss the impact of thermal gradients on force measurement balances, specific aspects of the TIGER program (the design of a special-purpose balance, data acquisition and data analysis challenges), and give an overall summary.

Enhanced settling of nonheavy inertial particles in homogeneous isotropic turbulence: The role of the pressure gradient and the Basset history force.

Science.gov (United States)

van Hinsberg, M A T; Clercx, H J H; Toschi, F

2017-02-01

The Stokes drag force and the gravity force are usually sufficient to describe the behavior of sub-Kolmogorov-size (or pointlike) heavy particles in turbulence, in particular when the particle-to-fluid density ratio ρ_{p}/ρ_{f}≳10^{3} (with ρ_{p} and ρ_{f} the particle and fluid density, respectively). This is, in general, not the case for smaller particle-to-fluid density ratios, in particular not for ρ_{p}/ρ_{f}≲10^{2}. In that case the pressure gradient force, added mass effects, and the Basset history force also play important roles. In this study we focus on the understanding of the role of these additional forces, all of hydrodynamic origin, in the settling of particles in turbulence. In order to qualitatively elucidate the complex dynamics of such particles in homogeneous isotropic turbulence, we first focus on the case of settling of such particles in the flow field of a single vortex. After having explored this simplified case we extend our analysis to homogeneous isotropic turbulence. In general, we found that the pressure gradient force leads to a decrease in the settling velocity. This can be qualitatively understood by the fact that this force prevents the particles from sweeping out of vortices, a mechanism known as preferential sweeping which causes enhanced settling. Additionally, we found that the Basset history force can both increase and decrease the enhanced settling, depending on the particle Stokes number. Finally, the role of the nonlinear Stokes drag has been explored, confirming that it affects settling of inertial particles in turbulence, but only in a limited way for the parameter settings used in this investigation.

Nanorotors using asymmetric inorganic nanorods in an optical trap

International Nuclear Information System (INIS)

Khan, Manas; Sood, A K; Deepak, F L; Rao, C N R

2006-01-01

We demonstrate how light force, irrespective of the polarization of the light, can be used to run a simple nanorotor. While the gradient force of a single beam optical trap is used to hold an asymmetric nanorod, we utilize the scattering force to generate a torque on the nanorod, making it rotate about the optic axis. The inherent textural irregularities or morphological asymmetries of the nanorods give rise to the torque under the radiation pressure. Even a small surface irregularity with non-zero chirality is sufficient to produce enough torque for moderate rotational speed. Different sized rotors can be used to set the speed of rotation over a wide range with fine tuning possible through the variation of the laser power. We present a simple dimensional analysis to qualitatively explain the observed trend of the rotational motion of the nanorods

Numerical model for the deformation of nucleated cells by optical stretchers

KAUST Repository

Sraj, Ihab

2015-07-01

In this paper, we seek to numerically study the deformation of nucleated cells by single diode-laser bar optical stretchers. We employ a recently developed computational model, the dynamic ray-tracing method, to determine the force distribution induced by optical stretchers on a cell encapsulating a nucleus of different optical properties. These optical forces are shape dependent and can deform real non-rigid objects; thus resulting in dynamically changing distributions with cell and nucleus deformation. A Chinese hamster ovary (CHO) cell is a common biological cell that is of interest to the biomedical community because of its use in recombinant protein therapeutics and is an example of a nucleated cell. To this end, we model CHO cells as two concentric three-dimensional elastic capsules immersed in a fluid where the hydrodynamic forces are calculated using the immersed boundary method. We vary the inner capsule size to simulate different nucleus sizes. Our results show that the presence of a nucleus has a major effect on the force distribution on the cell surface and consequently on its net deformation. Scattering and gradient forces are reported for different nucleus sizes and the effect of nucleus size on the cell deformation is discussed quantitatively. © 2015 IOP Publishing Ltd.

Identification of Random Dynamic Force Using an Improved Maximum Entropy Regularization Combined with a Novel Conjugate Gradient

Directory of Open Access Journals (Sweden)

ChunPing Ren

2017-01-01

Full Text Available We propose a novel mathematical algorithm to offer a solution for the inverse random dynamic force identification in practical engineering. Dealing with the random dynamic force identification problem using the proposed algorithm, an improved maximum entropy (IME regularization technique is transformed into an unconstrained optimization problem, and a novel conjugate gradient (NCG method was applied to solve the objective function, which was abbreviated as IME-NCG algorithm. The result of IME-NCG algorithm is compared with that of ME, ME-CG, ME-NCG, and IME-CG algorithm; it is found that IME-NCG algorithm is available for identifying the random dynamic force due to smaller root mean-square-error (RMSE, lower restoration time, and fewer iterative steps. Example of engineering application shows that L-curve method is introduced which is better than Generalized Cross Validation (GCV method and is applied to select regularization parameter; thus the proposed algorithm can be helpful to alleviate the ill-conditioned problem in identification of dynamic force and to acquire an optimal solution of inverse problem in practical engineering.

Gradient Correlation Method for the Stabilization of Inversion Results of Aerosol Microphysical Properties Retrieved from Profiles of Optical Data

Directory of Open Access Journals (Sweden)

Kolgotin Alexei

2016-01-01

Full Text Available Correlation relationships between aerosol microphysical parameters and optical data are investigated. The results show that surface-area concentrations and extinction coefficients are linearly correlated with a correlation coefficient above 0.99 for arbitrary particle size distribution. The correlation relationships that we obtained can be used as constraints in our inversion of optical lidar data. Simulation studies demonstrate a significant stabilization of aerosol microphysical data products if we apply the gradient correlation method in our traditional regularization technique.

Negative Knudsen force on heated microbeams

KAUST Repository

Zhu, Taishan; Ye, Wenjing; Zhang, Jun

2011-01-01

Knudsen force acting on a heated microbeam adjacent to a cold substrate in a rarefied gas is a mechanical force created by unbalanced thermal gradients. The measured force has its direction pointing towards the side with a lower thermal gradient

An Optically Controlled Microscale Elevator Using Plasmonic Janus Particles.

Science.gov (United States)

Nedev, Spas; Carretero-Palacios, Sol; Kühler, Paul; Lohmüller, Theobald; Urban, Alexander S; Anderson, Lindsey J E; Feldmann, Jochen

2015-04-15

In this article, we report how Janus particles, composed of a silica sphere with a gold half-shell, can be not only stably trapped by optical tweezers but also displaced controllably along the axis of the laser beam through a complex interplay between optical and thermal forces. Scattering forces orient the asymmetric particle, while strong absorption on the metal side induces a thermal gradient, resulting in particle motion. An increase in the laser power leads to an upward motion of the particle, while a decrease leads to a downward motion. We study this reversible axial displacement, including a hysteretic jump in the particle position that is a result of the complex pattern of a tightly focused laser beam structure above the focal plane. As a first application we simultaneously trap a spherical gold nanoparticle and show that we can control the distance between the two particles inside the trap. This photonic micron-scale "elevator" is a promising tool for thermal force studies, remote sensing, and optical and thermal micromanipulation experiments.

Analysis of adjusting effects of mounting force on frequency conversion of mounted nonlinear optics.

Science.gov (United States)

Su, Ruifeng; Liu, Haitao; Liang, Yingchun; Lu, Lihua

2014-01-10

Motivated by the need to increase the second harmonic generation (SHG) efficiency of nonlinear optics with large apertures, a novel mounting configuration with active adjusting function on the SHG efficiency is proposed and mechanically and optically studied. The adjusting effects of the mounting force on the distortion and stress are analyzed by the finite element methods (FEM), as well as the contribution of the distortion and stress to the change in phase mismatch, and the SHG efficiency are theoretically stated. Further on, the SHG efficiency is calculated as a function of the mounting force. The changing trends of the distortion, stress, and the SHG efficiency with the varying mounting force are obtained, and the optimal ones are figured out. Moreover, the mechanism of the occurrence of the optimal values is studied and the adjusting strategy is put forward. Numerical results show the robust adjustment of the mounting force, as well as the effectiveness of the mounting configuration, in increasing the SHG efficiency.

SPIDER. IV. OPTICAL AND NEAR-INFRARED COLOR GRADIENTS IN EARLY-TYPE GALAXIES: NEW INSIGHT INTO CORRELATIONS WITH GALAXY PROPERTIES

International Nuclear Information System (INIS)

La Barbera, F.; De Carvalho, R. R.; De La Rosa, I. G.; Gal, R. R.; Swindle, R.; Lopes, P. A. A.

2010-01-01

We present an analysis of stellar population gradients in 4546 early-type galaxies (ETGs) with photometry in grizYHJK along with optical spectroscopy. ETGs were selected as bulge-dominated systems, displaying passive spectra within the SDSS fibers. A new approach is described which utilizes color information to constrain age and metallicity gradients. Defining an effective color gradient, ∇ * , which incorporates all of the available color indices, we investigate how ∇ * varies with galaxy mass proxies, i.e., velocity dispersion, stellar (M * ) and dynamical (M dyn ) masses, as well as age, metallicity, and [α/Fe]. ETGs with M dyn larger than 8.5 x 10 10 M sun have increasing age gradients and decreasing metallicity gradients with respect to mass, metallicity, and enhancement. We find that velocity dispersion and [α/Fe] are the main drivers of these correlations. ETGs with 2.5 x 10 10 M sun ≤ M dyn ≤ 8.5 x 10 10 M sun show no correlation of age, metallicity, and color gradients with respect to mass, although color gradients still correlate with stellar population parameters, and these correlations are independent of each other. In both mass regimes, the striking anti-correlation between color gradient and α-enhancement is significant at ∼5σ and results from the fact that metallicity gradient decreases with [α/Fe]. This anti-correlation may reflect the fact that star formation and metallicity enrichment are regulated by the interplay between the energy input from supernovae, and the temperature and pressure of the hot X-ray gas in ETGs. For all mass ranges, positive age gradients are associated with old galaxies (>5-7 Gyr). For galaxies younger than ∼5 Gyr, mostly at low mass, the age gradient tends to be anti-correlated with the Age parameter, with more positive gradients at younger ages.

Optical trapping and Raman spectroscopy of single nanostructures using standing-wave Raman tweezers

Science.gov (United States)

Wu, Mu-ying; He, Lin; Chen, Gui-hua; Yang, Guang; Li, Yong-qing

2017-08-01

Optical tweezers integrated with Raman spectroscopy allows analyzing a single trapped micro-particle, but is generally less effective for individual nano-sized objects in the 10-100 nm range. The main challenge is the weak gradient force on nanoparticles that is insufficient to overcome the destabilizing effect of scattering force and Brownian motion. Here, we present standing-wave Raman tweezers for stable trapping and sensitive characterization of single isolated nanostructures with a low laser power by combining a standing-wave optical trap (SWOT) with confocal Raman spectroscopy. This scheme has stronger intensity gradients and balanced scattering forces, and thus is more stable and sensitive in measuring nanoparticles in liquid with 4-8 fold increase in the Raman signals. It can be used to analyze many nanoparticles that cannot be measured with single-beam Raman tweezers, including individual single-walled carbon nanotubes (SWCNT), graphene flakes, biological particles, polystyrene beads (100 nm), SERS-active metal nanoparticles, and high-refractive semiconductor nanoparticles with a low laser power of a few milliwatts. This would enable sorting and characterization of specific SWCNTs and other nanoparticles based on their increased Raman fingerprints.

Measuring microscopic forces and torques using optical tweezers

CSIR Research Space (South Africa)

Mc

2009-07-01

Full Text Available stream_source_info McLaren_2009.pdf.txt stream_content_type text/plain stream_size 2976 Content-Encoding UTF-8 stream_name McLaren_2009.pdf.txt Content-Type text/plain; charset=UTF-8 Measuring microscopic forces... and torques using optical tweezers M.G. McLaren1,2, A. Forbes2,3,4 and E. Sideras-Haddad2 1 CSIR National Laser Centre 2 School of Physics, University of Witwatersrand 3 School of Physics, University of KwaZulu-Natal 4 School of Physics, University...

Optical analog of the Iordanskii force in a Bose-Einstein condensate

International Nuclear Information System (INIS)

Leonhardt, U.; Oehberg, P.

2003-01-01

A vortex in a Bose-Einstein condensate generates the optical analog of the Aharonov-Bohm effect when illuminated with slow light. In contrast to the original Aharonov-Bohm effect the vortex will exchange forces with the light that leads to a measurable motion of the vortex

Optical Analog of the Iordanskii Force in a Bose-Einstein Condensate

OpenAIRE

Leonhardt, U.; Ohberg, P.

2001-01-01

A vortex in a Bose-Einstein condensate generates the optical analog of the Aharonov-Bohm effect when illuminated with slow light. In contrast to the original Aharonov-Bohm effect the vortex will exchange forces with the light that lead to a measurable motion of the vortex.

Plasma acceleration using. mu. -gradient(B) force

Energy Technology Data Exchange (ETDEWEB)

Nihei, H; Inoue, N; Ohara, Y; Nishino, O [Tokyo Univ. (Japan). Faculty of Engineering

1973-12-01

Several types of high flux beam sources have been developed for the purpose of heating and fuel feeding of the fusion reactor plasma. In our laboratory a duoPIGatron ion source and a ..mu..gradient B plasma accelerator are constructed. The former is used for the production of the beam with the energy of higher than several keV, and the latter is for the lower energy beam. The present paper describes the results of experiments on the ..mu..gradient B plasma accelerator. The absolute intensity of the beam is obtained by calorimetric measurement. The beam intensity increases as the microwave input power increases. Distribution of beam energy is measured with a multigrid electrostatic analyzer. The average energy of ions is about 60 eV and the total current is 0.5 A. In addition to the fusion reactor application, such a type of low energy and high intensity beam source is applicable to the investigation of atomic processes and the space craft propulsion.

High-speed atomic force microscopy combined with inverted optical microscopy for studying cellular events.

OpenAIRE

Suzuki, Yuki; Sakai, Nobuaki; Yoshida, Aiko; Uekusa, Yoshitsugu; Yagi, Akira; Imaoka, Yuka; Ito, Shuichi; Karaki, Koichi; Takeyasu, Kunio

2013-01-01

A hybrid atomic force microscopy (AFM)-optical fluorescence microscopy is a powerful tool for investigating cellular morphologies and events. However, the slow data acquisition rates of the conventional AFM unit of the hybrid system limit the visualization of structural changes during cellular events. Therefore, high-speed AFM units equipped with an optical/fluorescence detection device have been a long-standing wish. Here we describe the implementation of high-speed AFM coupled with an optic...

FDTD approach to optical forces of tightly focused vector beams on metal particles.

Science.gov (United States)

Qin, Jian-Qi; Wang, Xi-Lin; Jia, Ding; Chen, Jing; Fan, Ya-Xian; Ding, Jianping; Wang, Hui-Tian

2009-05-11

We propose an improved FDTD method to calculate the optical forces of tightly focused beams on microscopic metal particles. Comparison study on different kinds of tightly focused beams indicates that trapping efficiency can be altered by adjusting the polarization of the incident field. The results also show the size-dependence of trapping forces exerted on metal particles. Transverse tapping forces produced by different illumination wavelengths are also evaluated. The numeric simulation demonstrates the possibility of trapping moderate-sized metal particles whose radii are comparable to wavelength.

Characterizing conical refraction optical tweezers

Science.gov (United States)

McDonald, C.; McDougall, C.; Rafailov, E.; McGloin, D.

2014-12-01

Conical refraction occurs when a beam of light travels through an appropriately cut biaxial crystal. By focussing the conically refracted beam through a high numerical aperture microscope objective, conical refraction optical tweezers can be created, allowing for particle manipulation in both Raman spots and in the Lloyd/Poggendorff rings. We present a thorough quantification of the trapping properties of such a beam, focussing on the trap stiffness and how this varies with trap power and trapped particle location. We show that the lower Raman spot can be thought of as a single-beam optical gradient force trap, while radiation pressure dominates in the upper Raman spot, leading to optical levitation rather than trapping. Particles in the Lloyd/Poggendorff rings experience a lower trap stiffness than particles in the lower Raman spot but benefit from rotational control.

Stochastic parallel gradient descent based adaptive optics used for a high contrast imaging coronagraph

International Nuclear Information System (INIS)

Dong Bing; Ren Deqing; Zhang Xi

2011-01-01

An adaptive optics (AO) system based on a stochastic parallel gradient descent (SPGD) algorithm is proposed to reduce the speckle noises in the optical system of a stellar coronagraph in order to further improve the contrast. The principle of the SPGD algorithm is described briefly and a metric suitable for point source imaging optimization is given. The feasibility and good performance of the SPGD algorithm is demonstrated by an experimental system featured with a 140-actuator deformable mirror and a Hartmann-Shark wavefront sensor. Then the SPGD based AO is applied to a liquid crystal array (LCA) based coronagraph to improve the contrast. The LCA can modulate the incoming light to generate a pupil apodization mask of any pattern. A circular stepped pattern is used in our preliminary experiment and the image contrast shows improvement from 10 -3 to 10 -4.5 at an angular distance of 2λ/D after being corrected by SPGD based AO.

Observation and simulation of an optically driven micromotor

International Nuclear Information System (INIS)

Metzger, N K; Mazilu, M; Dholakia, K; Kelemen, L; Ormos, P

2011-01-01

In the realm of low Reynolds number flow there is a need to find methods to pump, move and mix minute amounts of analyte. Interestingly, micro-devices performing such actuation can be initiated by means of the light–matter interaction. Light induced forces and torques are exerted on such micro-objects, which are then driven by the optical gradient or scattering force. Here, different driving geometries can be realized to harness the light induced force. For example, the scattering force enables micro-gears to be operated in a tangential setup where the micromotor rotors are in line with an optical waveguide. The operational geometry we investigate has the advantage that it reduces the complexity of the driving of such a device in a microfluidic environment by delivering the actuating light by means of a waveguide or fiber optic. In this paper we explore the case of a micromotor being driven by a fiber optically delivered light beam. We experimentally investigate how the driving light interacts with and diffracts from the motor, utilizing two-photon imaging. The micromotor rotation rate dependence on the light field parameters is explored. Additionally, a theoretical model based on the paraxial approximation is used to simulate the torque and predict the rotation rate of such a device and compare it with experiment. The results presented show that our model can be used to optimize the micromotor performance and some example motor designs are evaluated

Observation and simulation of an optically driven micromotor

Science.gov (United States)

Metzger, N. K.; Mazilu, M.; Kelemen, L.; Ormos, P.; Dholakia, K.

2011-04-01

In the realm of low Reynolds number flow there is a need to find methods to pump, move and mix minute amounts of analyte. Interestingly, micro-devices performing such actuation can be initiated by means of the light-matter interaction. Light induced forces and torques are exerted on such micro-objects, which are then driven by the optical gradient or scattering force. Here, different driving geometries can be realized to harness the light induced force. For example, the scattering force enables micro-gears to be operated in a tangential setup where the micromotor rotors are in line with an optical waveguide. The operational geometry we investigate has the advantage that it reduces the complexity of the driving of such a device in a microfluidic environment by delivering the actuating light by means of a waveguide or fiber optic. In this paper we explore the case of a micromotor being driven by a fiber optically delivered light beam. We experimentally investigate how the driving light interacts with and diffracts from the motor, utilizing two-photon imaging. The micromotor rotation rate dependence on the light field parameters is explored. Additionally, a theoretical model based on the paraxial approximation is used to simulate the torque and predict the rotation rate of such a device and compare it with experiment. The results presented show that our model can be used to optimize the micromotor performance and some example motor designs are evaluated.

Optical studies of boiling heat transfer: insights and limitations

International Nuclear Information System (INIS)

Kenning, David B.R.

2004-01-01

Optical studies provide valuable insights into the complex mechanisms of boiling heat transfer but the large gradients of temperature (and therefore of refractive index) deflect light and multiple reflections at interfaces limit the distance over which observations can be made. Optical measurements are thought of as non-intrusive but this is rarely true. Because they are difficult and time consuming, they constrain the design of boiling experiments and are applied to limited ranges of conditions. There is a risk that deductions from the observations will be applied (not necessarily by the authors) more generally than is justified. These characteristics of optical studies are illustrated by examples from forced convective film boiling on spheres and pool nucleate boiling

Optical switching based on the manipulation of microparticles in a colloidal liquid using strong scattering force

International Nuclear Information System (INIS)

Liu Jin; Liu Zheng-Qi; Feng Tian-Hua; Dai Qiao-Feng; Wu Li-Jun; Lan Sheng

2010-01-01

This paper demonstrates the realization of an optical switch by optically manipulating a large number of polystyrene spheres contained in a capillary. The strong scattering force exerted on polystyrene spheres with a large diameter of 4.3 μm is employed to realize the switching operation. A transparent window is opened for the signal light when the polystyrene spheres originally located at the beam centre are driven out of the beam region by the strong scattering force induced by the control light. The switching dynamics under different incident powers is investigated and compared with that observed in the optical switch based on the formation of optical matter. It is found that a large extinction ratio of ∼ 30 dB and fast switching-on and switching-off times can be achieved in this type of switch. (classical areas of phenomenology)

Microscopic optical potential calculations of finite nuclei with extended skyrme forces

International Nuclear Information System (INIS)

Yuan Haiji; Ye Weilei; Gao Qin; Shen Qingbiao

1986-01-01

Microscopic optical potential calculations in the Hartree-Fock (HF) approximation with Extended Skyrme forces are investigated. The HF equation is derived from the variation principle and the potential formula of spherical nuclei is obtained by two different ways. Then the calculations for symmetrid nuclei 16 O, 40 Ca and asymmetric nucleus 90 Zr with eight sets of Skyrme force parameters are presented. Our results show that the potential form and variating tendency with incident energy are reasonable and there apparently appears a 'wine-bottle-bottom' shape in the intermediate energy region. Furthermore, our calculations reflect shell effects clearly

Fast optimal wavefront reconstruction for multi-conjugate adaptive optics using the Fourier domain preconditioned conjugate gradient algorithm.

Science.gov (United States)

Vogel, Curtis R; Yang, Qiang

2006-08-21

We present two different implementations of the Fourier domain preconditioned conjugate gradient algorithm (FD-PCG) to efficiently solve the large structured linear systems that arise in optimal volume turbulence estimation, or tomography, for multi-conjugate adaptive optics (MCAO). We describe how to deal with several critical technical issues, including the cone coordinate transformation problem and sensor subaperture grid spacing. We also extend the FD-PCG approach to handle the deformable mirror fitting problem for MCAO.

Fiber based optical tweezers for simultaneous in situ force exertion and measurements in a 3D polyacrylamide gel compartment.

Science.gov (United States)

Ti, Chaoyang; Thomas, Gawain M; Ren, Yundong; Zhang, Rui; Wen, Qi; Liu, Yuxiang

2015-07-01

Optical tweezers play an important role in biological applications. However, it is difficult for traditional optical tweezers based on objective lenses to work in a three-dimensional (3D) solid far away from the substrate. In this work, we develop a fiber based optical trapping system, namely inclined dual fiber optical tweezers, that can simultaneously apply and measure forces both in water and in a 3D polyacrylamide gel matrix. In addition, we demonstrate in situ, non-invasive characterization of local mechanical properties of polyacrylamide gel by measurements on an embedded bead. The fiber optical tweezers measurements agree well with those of atomic force microscopy (AFM). The inclined dual fiber optical tweezers provide a promising and versatile tool for cell mechanics study in 3D environments.

Forces in electromagnetic field and gravitational field

OpenAIRE

Weng, Zihua

2008-01-01

The force can be defined from the linear momentum in the gravitational field and electromagnetic field. But this definition can not cover the gradient of energy. In the paper, the force will be defined from the energy and torque in a new way, which involves the gravitational force, electromagnetic force, inertial force, gradient of energy, and some other new force terms etc. One of these new force terms can be used to explain why the solar wind varies velocity along the magnetic force line in...

Self-consistent Optomechanical Dynamics and Radiation Forces in Thermal Light Fields

International Nuclear Information System (INIS)

Sonnleitner, M.

2014-01-01

We discuss two different aspects of the mechanical interaction between neutral matter and electromagnetic radiation.The first part addresses the complex dynamics of an elastic dielectric deformed by optical forces. To do so we use a one-dimensional model describing the medium by an array of beam splitters such that the interaction with the incident waves can be described with a transfer-matrix approach. Since the force on each individual beam splitter is known we thus obtain the correct volumetric force density inside the medium. Sending a light field through an initially homogeneous dielectric then results in density modulations which in turn alter the optical properties of this medium.The second part is concerned with mechanical light-effects on atoms in thermal radiation fields. At hand of a generic setup of an atom interacting with a hot sphere emitting blackbody radiation we show that the emerging gradient force may surpass gravity by several orders of magnitude. The strength of the repulsive scattering force strongly depends on the spectrum of the involved atoms and can be neglected in some setups. A special emphasis lies on possible implications on astrophysical scenarios where the interactions between heated dust and atoms, molecules or nanoparticles are of crucial interest. (author) [de

Analysis of magnetic gradients to study gravitropism.

Science.gov (United States)

Hasenstein, Karl H; John, Susan; Scherp, Peter; Povinelli, Daniel; Mopper, Susan

2013-01-01

Gravitropism typically is generated by dense particles that respond to gravity. Experimental stimulation by high-gradient magnetic fields provides a new approach to selectively manipulate the gravisensing system. The movement of corn, wheat, and potato starch grains in suspension was examined with videomicroscopy during parabolic flights that generated 20 to 25 s of weightlessness. During weightlessness, a magnetic gradient was generated by inserting a wedge into a uniform, external magnetic field that caused repulsion of starch grains. The resultant velocity of movement was compared with the velocity of sedimentation under 1 g conditions. The high-gradient magnetic fields repelled the starch grains and generated a force of at least 0.6 g. Different wedge shapes significantly affected starch velocity and directionality of movement. Magnetic gradients are able to move diamagnetic compounds under weightless or microgravity conditions and serve as directional stimulus during seed germination in low-gravity environments. Further work can determine whether gravity sensing is based on force or contact between amyloplasts and statocyte membrane system.

Optical pulling force on a magneto-dielectric Rayleigh sphere in Bessel tractor polarized beams

International Nuclear Information System (INIS)

Mitri, F.G.; Li, R.X.; Yang, R.P.; Guo, L.X.; Ding, C.Y.

2016-01-01

The optical radiation force induced by Bessel (vortex) beams on a magneto-dielectric subwavelength sphere is investigated with particular emphasis on the beam polarization and order l (or topological charge). The analysis is focused on identifying the regions and some of the conditions to achieve retrograde motion of the sphere centered on the axis of wave propagation of the incident beam, or shifted off-axially. Exact non-paraxial analytical solutions are established, and computations for linear, circular, radial, azimuthal and mixed polarizations of the individual plane wave components forming the Bessel (vortex) beams by means of the angular spectrum decomposition method (ASDM) illustrate the theory with particular emphasis on the tractor (i.e. reversal) behavior of the force. This effect results in the pulling of the magneto-dielectric sphere against the forward linear momentum density flux associated with the incoming waves. Should some conditions related to the choice of the beam parameters as well as the permittivity and permeability of the sphere be met, the optical force vanishes and reverses sign. Moreover, the beam polarization is shown to affect differently the axial negative pulling force for either the zeroth- or the first-order Bessel beam. When the sphere is centered on the beam′s axis, the axial force component is always negative for the zeroth-order Bessel beam except for the radial and azimuthal polarization configurations. Nonetheless, for the first-order Bessel beam, the axial force is negative for the radial polarization case only. Additional tractor beam effects arise when the sphere departs from the center of the beam. It is also demonstrated that the tractor beam effect arises from the force component originating from the cross-interaction between the electric and magnetic dipoles. Potential applications are in particle manipulation, optical levitation, tractor beam tweezers, and other emergent technologies using polarized Bessel beams on

Theory of force detection using optically levitated nanoparticles

Science.gov (United States)

Rodenburg, Brandon; Neukirch, Levi; Pettit, Robert; Vamivakas, Nick; Bhattacharya, Mishkat

2016-05-01

Levitated nanoparticles offer the potential of being incredibly well isolated from the environment. This isolation makes such systems excellent candidates for tests of quantum mechanics at the macroscale and as versatile platforms for ultrasensitive metrology. Systems involving an optical cavity mode to provide the trapping field, as well as cooling mechanism of the particle's center of mass motion are well understood theoretically and provide a canonical system for the field of quantum optomechanics. However, techniques based on measurement based parametric cooling and feedback stabilization have made it possible to trap and manipulate a nanoparticle without the need for an optical cavity, even at extremely high vacuum where gas damping cannot stabilize the motion of the particle. For these cavityless systems, a fully quantum theory has recently been developed. In this talk we will present recent work that we have carried out to apply this theory to the use of such devices as force sensors, including a discussion of the ultimate limits placed on the sensitivity by the sources of fundamental quantum noise. Office of Naval Research.

Preconditioned conjugate gradient wave-front reconstructors for multiconjugate adaptive optics

Science.gov (United States)

Gilles, Luc; Ellerbroek, Brent L.; Vogel, Curtis R.

2003-09-01

Multiconjugate adaptive optics (MCAO) systems with 104-105 degrees of freedom have been proposed for future giant telescopes. Using standard matrix methods to compute, optimize, and implement wave-front control algorithms for these systems is impractical, since the number of calculations required to compute and apply the reconstruction matrix scales respectively with the cube and the square of the number of adaptive optics degrees of freedom. We develop scalable open-loop iterative sparse matrix implementations of minimum variance wave-front reconstruction for telescope diameters up to 32 m with more than 104 actuators. The basic approach is the preconditioned conjugate gradient method with an efficient preconditioner, whose block structure is defined by the atmospheric turbulent layers very much like the layer-oriented MCAO algorithms of current interest. Two cost-effective preconditioners are investigated: a multigrid solver and a simpler block symmetric Gauss-Seidel (BSGS) sweep. Both options require off-line sparse Cholesky factorizations of the diagonal blocks of the matrix system. The cost to precompute these factors scales approximately as the three-halves power of the number of estimated phase grid points per atmospheric layer, and their average update rate is typically of the order of 10-2 Hz, i.e., 4-5 orders of magnitude lower than the typical 103 Hz temporal sampling rate. All other computations scale almost linearly with the total number of estimated phase grid points. We present numerical simulation results to illustrate algorithm convergence. Convergence rates of both preconditioners are similar, regardless of measurement noise level, indicating that the layer-oriented BSGS sweep is as effective as the more elaborated multiresolution preconditioner.

Preconditioned conjugate gradient wave-front reconstructors for multiconjugate adaptive optics.

Science.gov (United States)

Gilles, Luc; Ellerbroek, Brent L; Vogel, Curtis R

2003-09-10

Multiconjugate adaptive optics (MCAO) systems with 10(4)-10(5) degrees of freedom have been proposed for future giant telescopes. Using standard matrix methods to compute, optimize, and implement wavefront control algorithms for these systems is impractical, since the number of calculations required to compute and apply the reconstruction matrix scales respectively with the cube and the square of the number of adaptive optics degrees of freedom. We develop scalable open-loop iterative sparse matrix implementations of minimum variance wave-front reconstruction for telescope diameters up to 32 m with more than 10(4) actuators. The basic approach is the preconditioned conjugate gradient method with an efficient preconditioner, whose block structure is defined by the atmospheric turbulent layers very much like the layer-oriented MCAO algorithms of current interest. Two cost-effective preconditioners are investigated: a multigrid solver and a simpler block symmetric Gauss-Seidel (BSGS) sweep. Both options require off-line sparse Cholesky factorizations of the diagonal blocks of the matrix system. The cost to precompute these factors scales approximately as the three-halves power of the number of estimated phase grid points per atmospheric layer, and their average update rate is typically of the order of 10(-2) Hz, i.e., 4-5 orders of magnitude lower than the typical 10(3) Hz temporal sampling rate. All other computations scale almost linearly with the total number of estimated phase grid points. We present numerical simulation results to illustrate algorithm convergence. Convergence rates of both preconditioners are similar, regardless of measurement noise level, indicating that the layer-oriented BSGS sweep is as effective as the more elaborated multiresolution preconditioner.

Direct Electrospray Printing of Gradient Refractive Index Chalcogenide Glass Films.

Science.gov (United States)

Novak, Spencer; Lin, Pao Tai; Li, Cheng; Lumdee, Chatdanai; Hu, Juejun; Agarwal, Anuradha; Kik, Pieter G; Deng, Weiwei; Richardson, Kathleen

2017-08-16

A spatially varying effective refractive index gradient using chalcogenide glass layers is printed on a silicon wafer using an optimized electrospray (ES) deposition process. Using solution-derived glass precursors, IR-transparent Ge 23 Sb 7 S 70 and As 40 S 60 glass films of programmed thickness are fabricated to yield a bilayer structure, resulting in an effective gradient refractive index (GRIN) film. Optical and compositional analysis tools confirm the optical and physical nature of the gradient in the resulting high-optical-quality films, demonstrating the power of direct printing of multimaterial structures compatible with planar photonic fabrication protocols. The potential application of such tailorable materials and structures as they relate to the enhancement of sensitivity in chalcogenide glass based planar chemical sensor device design is presented. This method, applicable to a broad cross section of glass compositions, shows promise in directly depositing GRIN films with tunable refractive index profiles for bulk and planar optical components and devices.

A compact CCD-monitored atomic force microscope with optical vision and improved performances.

Science.gov (United States)

Mingyue, Liu; Haijun, Zhang; Dongxian, Zhang

2013-09-01

A novel CCD-monitored atomic force microscope (AFM) with optical vision and improved performances has been developed. Compact optical paths are specifically devised for both tip-sample microscopic monitoring and cantilever's deflection detecting with minimized volume and optimal light-amplifying ratio. The ingeniously designed AFM probe with such optical paths enables quick and safe tip-sample approaching, convenient and effective tip-sample positioning, and high quality image scanning. An image stitching method is also developed to build a wider-range AFM image under monitoring. Experiments show that this AFM system can offer real-time optical vision for tip-sample monitoring with wide visual field and/or high lateral optical resolution by simply switching the objective; meanwhile, it has the elegant performances of nanometer resolution, high stability, and high scan speed. Furthermore, it is capable of conducting wider-range image measurement while keeping nanometer resolution. Copyright © 2013 Wiley Periodicals, Inc.

Simultaneous differential spinning disk fluorescence optical sectioning microscopy and nanomechanical mapping atomic force microscopy

International Nuclear Information System (INIS)

Miranda, Adelaide; De Beule, Pieter A. A.; Martins, Marco

2015-01-01

Combined microscopy techniques offer the life science research community a powerful tool to investigate complex biological systems and their interactions. Here, we present a new combined microscopy platform based on fluorescence optical sectioning microscopy through aperture correlation microscopy with a Differential Spinning Disk (DSD) and nanomechanical mapping with an Atomic Force Microscope (AFM). The illumination scheme of the DSD microscope unit, contrary to standard single or multi-point confocal microscopes, provides a time-independent illumination of the AFM cantilever. This enables a distortion-free simultaneous operation of fluorescence optical sectioning microscopy and atomic force microscopy with standard probes. In this context, we discuss sample heating due to AFM cantilever illumination with fluorescence excitation light. Integration of a DSD fluorescence optical sectioning unit with an AFM platform requires mitigation of mechanical noise transfer of the spinning disk. We identify and present two solutions to almost annul this noise in the AFM measurement process. The new combined microscopy platform is applied to the characterization of a DOPC/DOPS (4:1) lipid structures labelled with a lipophilic cationic indocarbocyanine dye deposited on a mica substrate

Simultaneous differential spinning disk fluorescence optical sectioning microscopy and nanomechanical mapping atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Miranda, Adelaide; De Beule, Pieter A. A., E-mail: pieter.de-beule@inl.int [Applied Nano-Optics Laboratory, International Iberian Nanotechnology Laboratory, Avenida Mestre José Veiga, s/n, 4715-330 Braga (Portugal); Martins, Marco [Nano-ICs Group, International Iberian Nanotechnology Laboratory, Avenida Mestre José Veiga, s/n, 4715-330 Braga (Portugal)

2015-09-15

Combined microscopy techniques offer the life science research community a powerful tool to investigate complex biological systems and their interactions. Here, we present a new combined microscopy platform based on fluorescence optical sectioning microscopy through aperture correlation microscopy with a Differential Spinning Disk (DSD) and nanomechanical mapping with an Atomic Force Microscope (AFM). The illumination scheme of the DSD microscope unit, contrary to standard single or multi-point confocal microscopes, provides a time-independent illumination of the AFM cantilever. This enables a distortion-free simultaneous operation of fluorescence optical sectioning microscopy and atomic force microscopy with standard probes. In this context, we discuss sample heating due to AFM cantilever illumination with fluorescence excitation light. Integration of a DSD fluorescence optical sectioning unit with an AFM platform requires mitigation of mechanical noise transfer of the spinning disk. We identify and present two solutions to almost annul this noise in the AFM measurement process. The new combined microscopy platform is applied to the characterization of a DOPC/DOPS (4:1) lipid structures labelled with a lipophilic cationic indocarbocyanine dye deposited on a mica substrate.

Optical Tweezers-Based Measurements of Forces and Dynamics at Microtubule Ends.

Science.gov (United States)

Baclayon, Marian; Kalisch, Svenja-Marei; Hendel, Ed; Laan, Liedewij; Husson, Julien; Munteanu, E Laura; Dogterom, Marileen

2017-01-01

Microtubules are dynamic cytoskeletal polymers that polymerize and depolymerize while interacting with different proteins and structures within the cell. The highly regulated dynamic properties as well as the pushing and pulling forces generated by dynamic microtubule ends play important roles in processes such as in cell division. For instance, microtubule end-binding proteins are known to affect dramatically the dynamic properties of microtubules, and cortical dyneins are known to mediate pulling forces on microtubule ends. We discuss in this chapter our efforts to reconstitute these systems in vitro and mimic their interactions with structures within the cell using micro-fabricated barriers. Using an optical tweezers setup, we investigate the dynamics and forces of microtubules growing against functionalized barriers in the absence and presence of end-binding proteins and barrier-attached motor proteins. This setup allows high-speed as well as nanometer and piconewton resolution measurements on dynamic microtubules.

A Subnano-g Electrostatic Force-Rebalanced Flexure Accelerometer for Gravity Gradient Instruments

Directory of Open Access Journals (Sweden)

Shitao Yan

2017-11-01

Full Text Available A subnano-g electrostatic force-rebalanced flexure accelerometer is designed for the rotating accelerometer gravity gradient instrument. This accelerometer has a large proof mass, which is supported inversely by two pairs of parallel leaf springs and is centered between two fixed capacitor plates. This novel design enables the proof mass to move exactly along the sensitive direction and exhibits a high rejection ratio at its cross-axis directions. Benefiting from large proof mass, high vacuum packaging, and air-tight sealing, the thermal Brownian noise of the accelerometer is lowered down to less than 0.2 ng / Hz with a quality factor of 15 and a natural resonant frequency of about 7.4 Hz . The accelerometer’s designed measurement range is about ±1 mg. Based on the correlation analysis between a commercial triaxial seismometer and our accelerometer, the demonstrated self-noise of our accelerometers is reduced to lower than 0.3 ng / Hz over the frequency ranging from 0.2 to 2 Hz, which meets the requirement of the rotating accelerometer gravity gradiometer.

Providing haptic feedback in robot-assisted minimally invasive surgery: a direct optical force-sensing solution for haptic rendering of deformable bodies.

Science.gov (United States)

Ehrampoosh, Shervin; Dave, Mohit; Kia, Michael A; Rablau, Corneliu; Zadeh, Mehrdad H

2013-01-01

This paper presents an enhanced haptic-enabled master-slave teleoperation system which can be used to provide force feedback to surgeons in minimally invasive surgery (MIS). One of the research goals was to develop a combined-control architecture framework that included both direct force reflection (DFR) and position-error-based (PEB) control strategies. To achieve this goal, it was essential to measure accurately the direct contact forces between deformable bodies and a robotic tool tip. To measure the forces at a surgical tool tip and enhance the performance of the teleoperation system, an optical force sensor was designed, prototyped, and added to a robot manipulator. The enhanced teleoperation architecture was formulated by developing mathematical models for the optical force sensor, the extended slave robot manipulator, and the combined-control strategy. Human factor studies were also conducted to (a) examine experimentally the performance of the enhanced teleoperation system with the optical force sensor, and (b) study human haptic perception during the identification of remote object deformability. The first experiment was carried out to discriminate deformability of objects when human subjects were in direct contact with deformable objects by means of a laparoscopic tool. The control parameters were then tuned based on the results of this experiment using a gain-scheduling method. The second experiment was conducted to study the effectiveness of the force feedback provided through the enhanced teleoperation system. The results show that the force feedback increased the ability of subjects to correctly identify materials of different deformable types. In addition, the virtual force feedback provided by the teleoperation system comes close to the real force feedback experienced in direct MIS. The experimental results provide design guidelines for choosing and validating the control architecture and the optical force sensor.

First-principles calculation of the polarization-dependent force driving the Eg mode in bismuth under optical excitation.

Science.gov (United States)

Murray, Eamonn; Fahy, Stephen

2014-03-01

Using first principles electronic structure methods, we calculate the induced force on the Eg (zone centre transverse optical) phonon mode in bismuth immediately after absorption of polarized light. When radiation with polarization perpendicular to the c-axis is absorbed in bismuth, the distribution of excited electrons and holes breaks the three-fold rotational symmetry and leads to a net force on the atoms in the direction perpendicular to the axis. We calculate the initial excited electronic distribution as a function of photon energy and polarization and find the resulting transverse and longitudinal forces experienced by the atoms. Using the measured, temperature-dependent rate of decay of the transverse force[2], we predict the approximate amplitude of induced atomic motion in the Eg mode as a function of temperature and optical fluence. This work is supported by Science Foundation Ireland and a Marie Curie International Incoming Fellowship.

Gradient index metamaterials realized by drilling hole arrays

International Nuclear Information System (INIS)

Mei Zhonglei; Cui Tiejun; Bai Jing

2010-01-01

Gradient index metamaterials have wide applications in the microwave and optical fields. Based on the quasi-static theory, such materials at the microwave band have been realized by drilling hole arrays on ordinary dielectric materials. As applications of the gradient index metamaterials, novel devices including a 45 0 dielectric wave-bending structure, a 16 0 wave-steering lens and a microwave focusing lens are designed and fabricated. Field mapping measurements validate the proposed gradient index metamaterials and the device designs. The method can be directly and easily extended to the design of cloaks, various lenses, beam shifters and beam-steering devices. It can also be applied in the optical band as long as quasi-static conditions are satisfied. The method and the devices may find applications in integrated circuit systems.

Upconverting Nanoparticles as Optical Sensors of Nano- to Micro-Newton Forces

Energy Technology Data Exchange (ETDEWEB)

Lay, Alice; Wang, Derek S.; Wisser, Michael D.; Mehlenbacher, Randy D.; Lin, Yu [Stanford; Goodman, Miriam B.; Mao, Wendy L.; Dionne, Jennifer A.

2017-06-08

Mechanical forces affect a myriad of processes, from bone growth to material fracture to touch-responsive robotics. While nano- to micro-Newton forces are prevalent at the microscopic scale, few methods have the nanoscopic size and signal stability to measure them in vivo or in situ. Here, we develop an optical force-sensing platform based on sub-25 nm NaYF4 nanoparticles (NPs) doped with Yb3+, Er3+, and Mn2+. The lanthanides Yb3+ and Er3+ enable both photoluminescence and upconversion, while the energetically coupled d-metal Mn2+ adds force tunability through its crystal field sensitivity. Using a diamond anvil cell to exert up to 3.5 GPa pressure or ~10 μN force per particle, we track stress-induced spectral responses. The red (660 nm) to green (520, 540 nm) emission ratio varies linearly with pressure, yielding an observed color change from orange to red for α-NaYF4 and from yellow–green to green for d-metal optimized β-NaYF4 when illuminated in the near infrared. Consistent readouts are recorded over multiple pressure cycles and hours of illumination. With the nanoscopic size, a dynamic range of 100 nN to 10 μN, and photostability, these nanoparticles lay the foundation for visualizing dynamic mechanical processes, such as stress propagation in materials and force signaling in organisms.

Upconverting Nanoparticles as Optical Sensors of Nano- to Micro-Newton Forces.

Science.gov (United States)

Lay, Alice; Wang, Derek S; Wisser, Michael D; Mehlenbacher, Randy D; Lin, Yu; Goodman, Miriam B; Mao, Wendy L; Dionne, Jennifer A

2017-07-12

Mechanical forces affect a myriad of processes, from bone growth to material fracture to touch-responsive robotics. While nano- to micro-Newton forces are prevalent at the microscopic scale, few methods have the nanoscopic size and signal stability to measure them in vivo or in situ. Here, we develop an optical force-sensing platform based on sub-25 nm NaYF 4 nanoparticles (NPs) doped with Yb 3+ , Er 3+ , and Mn 2+ . The lanthanides Yb 3+ and Er 3+ enable both photoluminescence and upconversion, while the energetically coupled d-metal Mn 2+ adds force tunability through its crystal field sensitivity. Using a diamond anvil cell to exert up to 3.5 GPa pressure or ∼10 μN force per particle, we track stress-induced spectral responses. The red (660 nm) to green (520, 540 nm) emission ratio varies linearly with pressure, yielding an observed color change from orange to red for α-NaYF 4 and from yellow-green to green for d-metal optimized β-NaYF 4 when illuminated in the near infrared. Consistent readouts are recorded over multiple pressure cycles and hours of illumination. With the nanoscopic size, a dynamic range of 100 nN to 10 μN, and photostability, these nanoparticles lay the foundation for visualizing dynamic mechanical processes, such as stress propagation in materials and force signaling in organisms.

Optical activity and ultraviolet absorbance detection of dansyl L-amino acids separated by gradient liquid chromatography

Energy Technology Data Exchange (ETDEWEB)

1987-04-01

Many scientific investigations (e.g., geochronology, pharmaceuticals) have the need to determine enantiometric ratios of amino acids and other compounds. It has been reported that OA/UV or OA/RI (refractive index) are ideal methods for the determination of enantiomeric ratios without the need for chiral columns, chiral eluents, or diasteromer preparation. Unfortunately, only three amino acids are naturally UV absorbing (254 nm), and RI sensitivity for amino acids is low. Derivatization by several methods (o-phthalaldehyde, dansyl, phenylisothiocyanate, fluorescamine, 2,4-dinitrofluorobenzene, and phenylthiohydantoin) renders all amino acids UV absorbing and makes UV or fluorescence viable techniques for amino acids determinations. A previously neglected aspect of derivatization is the effect on optical activity. These highly polar groups influence the chiral center of amino acids drastically (electronic and steric effects). The shifting of the absorption band to the proximity of the wavelength used for OA measurements further enhances the importance of the substituent. The authors report here the determination of 17 dansyl amino acids in a mixture by UV absorbance and optical activity. This involves gradient elution. Previously, the optical activity detector (OAD) has been used only with isocratic HPLC.

A wide-angle gradient index optical model of the crystalline lens and eye of the octopus.

Science.gov (United States)

Jagger, W S; Sands, P J

1999-08-01

Cephalopods and fish have had no common ancestor since the Cambrian, and their eyes are a classic example of convergent evolution. The octopus has no cornea, and immerson renders the trout cornea optically ineffective. As a result, the nearly spherical lens is responsible for all refraction in these eyes. In spite of the fact that the octopus lens consists of two joined parts, while the trout lens consists of one part, we show here that their optical properties are very similar. An index gradient bends rays within these lenses, adding power and correcting spherical aberration. High spherical symmetry in both lenses strongly reduces other monochromatic aberrations and yields a wide field of vision, advantageous in attack and evasion. The octopus Mattheissen's ratio, 2.83, an inverse measure of light-gathering power, lies above the trout value of 2.38 but within the range of values reported for fish. Strong uncorrected longitudinal chromatic aberration is nearly identical in both animals as a result of similar lens protein optical properties, and will limit resolution. We discuss how animal lifestyle requirements and lens material properties influence the design of these eyes.

Operation of a scanning near field optical microscope in reflection in combination with a scanning force microscope

NARCIS (Netherlands)

van Hulst, N.F.; Moers, M.H.P.; Moers, M.H.P.; Noordman, O.F.J.; Noordman, O.F.J.; Faulkner, T.; Segerink, Franciscus B.; van der Werf, Kees; de Grooth, B.G.; Bölger, B.; Bölger, B.

1992-01-01

Images obtained with a scanning near field optical microscope (SNOM) operating in reflection are presented. We have obtained the first results with a SiN tip as optical probe. The instrument is simultaneously operated as a scanning force microscope (SFM). Moreover, the instrument incorporates an

Solvent micro-evaporation and concentration gradient synergistically induced crystallization of poly(L-lactide) and ring banded supra-structures with radial periodic variation of thickness

DEFF Research Database (Denmark)

Huang, Shaoyong; Li, Hongfei; Wen, Huiying

2014-01-01

The crystalline morphology and structure of poly(L-lactide) (PLLA) in a PLLA film-chloroform system were investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and atomic force microscopy (AFM). Birefringent and nonbirefringent ring banded supra-structure......The crystalline morphology and structure of poly(L-lactide) (PLLA) in a PLLA film-chloroform system were investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and atomic force microscopy (AFM). Birefringent and nonbirefringent ring banded supra......-structures with radial periodic variation of thickness were obtained, which were induced by micro-evaporation of solvents and concentration gradient of PLLA. The ring banded morphologies consisted of multilayer lamellar crystals, which is a manifestation of alternating ridge and valley bands of periodic variation...

Factors affecting the transverse force measurements of an optical trap: I

Science.gov (United States)

Wood, Tiffany A.; Wright, Amanda; Gleeson, Helen F.; Dickenson, Mark; Mullin, Tom; Murray, Andrew

2002-03-01

The transverse force of an optical trap is usually measured by equating the trapping force to the viscous drag force applied to the trapped particle according to Stokes' Law. Under normal conditions, the viscous drag force on a trapped particle is proportional to the fluid velocity of the medium. In this paper we show that an increase of particle concentration within the medium affects force measurements. In order to trap the particle, 1064 nm light from a Nd:YVO4 laser was brought to a focus in a sample slide, of thickness around 380 microns, by using an inverted Zeiss microscope objective, with NA equals 1.3. The slide was filled with distilled water containing 6 micron diameter polystyrene spheres. Measurements were taken at a fluid velocity of 0.75 microns/sec, achieved by moving the sample stage with a piezo-electric transducer whilst a particle was held stationary in the trap. The laser power required to hold a sphere at different trap depths for various concentrations was measured. Significant weakening of the trap was found for concentrations >0.03% solids by weight, becoming weaker for higher trap depths. These results are explained in terms of aberrations, particle-particle interactions and distortion of the beam due to particle-light interactions.

Formation of optical gradient in chemical solution-derived PbZr.sub.0.52./sub.Ti.sub.0.48./sub.O.sub.3./sub. thin films: spectroscopic ellipsometry investigation

Czech Academy of Sciences Publication Activity Database

Aulika, I.; Corkovic, S.; Bencan, A.; D' Astorg, S.; Dejneka, Alexandr; Zhang, Q.; Kosec, M.; Zauls, V.

2009-01-01

Roč. 156, č. 12 (2009), G217-G225 ISSN 0013-4651 R&D Projects: GA ČR GC202/09/J017 Institutional research plan: CEZ:AV0Z10100522 Keywords : optical gradient * PZT Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.241, year: 2009

Compensating the electron beam energy spread by the natural transverse gradient of laser undulator in all-optical x-ray light sources.

Science.gov (United States)

Zhang, Tong; Feng, Chao; Deng, Haixiao; Wang, Dong; Dai, Zhimin; Zhao, Zhentang

2014-06-02

All-optical ideas provide a potential to dramatically cut off the size and cost of x-ray light sources to the university-laboratory scale, with the combination of the laser-plasma accelerator and the laser undulator. However, the large longitudinal energy spread of the electron beam from laser-plasma accelerator may hinder the way to high brightness of these all-optical light sources. In this paper, the beam energy spread effect is proposed to be significantly compensated by the natural transverse gradient of a laser undulator when properly transverse-dispersing the electron beam. Theoretical analysis and numerical simulations on conventional laser-Compton scattering sources and high-gain all-optical x-ray free-electron lasers with the electron beams from laser-plasma accelerators are presented.

A combined optical and atomic force microscope for live cell investigations

International Nuclear Information System (INIS)

Madl, Josef; Rhode, Sebastian; Stangl, Herbert; Stockinger, Hannes; Hinterdorfer, Peter; Schuetz, Gerhard J.; Kada, Gerald

2006-01-01

We present an easy-to-use combination of an atomic force microscope (AFM) and an epi-fluorescence microscope, which allows live cell imaging under physiological conditions. High-resolution AFM images were acquired while simultaneously monitoring either the fluorescence image of labeled membrane components, or a high-contrast optical image (DIC, differential interference contrast). By applying two complementary techniques at the same time, additional information and correlations between structure and function of living organisms were obtained. The synergy effects between fluorescence imaging and AFM were further demonstrated by probing fluorescence-labeled receptor clusters in the cell membrane via force spectroscopy using antibody-functionalized tips. The binding probability on receptor-containing areas identified with fluorescence microscopy ('receptor-positive sites') was significantly higher than that on sites lacking receptors

Optical tweezers for the measurement of binding forces: system description and application for the study of E. coli adhesion

Science.gov (United States)

Fallman, Erik G.; Schedin, Staffan; Andersson, Magnus J.; Jass, Jana; Axner, Ove

2003-06-01

Optical tweezers together with a position sensitive detection system allows measurements of forces in the pN range between micro-sized biological objects. A prototype force measurement system has been constructed around in inverted microscope with an argon-ion pumped Ti:sapphire laser as light source for optical trapping. A trapped particle in the focus of the high numerical aperture microscope-objective behaves like an omni-directional mechanical spring if an external force displaces it. The displacement from the equilibrium position is a measure of the exerted force. For position detection of the trapped particle (polystyrene beads), a He-Ne laser beam is focused a small distance below the trapping focus. An image of the bead appears as a distinct spot in the far field, monitored by a photosensitive detector. The position data is converted to a force measurement by a calibration procedure. The system has been used for measuring the binding forces between E-coli bacterial adhesin and their receptor sugars.

Inertial forces and the foundations of optical geometry

International Nuclear Information System (INIS)

Jonsson, Rickard

2006-01-01

Assuming a general timelike congruence of worldlines as a reference frame, we derive a covariant general formalism of inertial forces in general relativity. Inspired by the works of Abramowicz et al (see e.g. Abramowicz and Lasota 1997 Class. Quantum Grav. 14 A23-30), we also study conformal rescalings of spacetime and investigate how these affect the inertial force formalism. While many ways of describing spatial curvature of a trajectory have been discussed in papers prior to this, one particular prescription (which differs from the standard projected curvature when the reference congruence is shearing), appears novel. For the particular case of a hypersurface-forming congruence, using a suitable rescaling of spacetime, we show that a geodesic photon always follows a line that is spatially straight with respect to the new curvature measure. This fact is intimately connected to Fermat's principle, and allows for a certain generalization of the optical geometry as will be further pursued in a companion paper (Jonsson and Westman 2006 Class. Quantum Grav. 23 61). For the particular case when the shear tensor vanishes, we present the inertial force equation in a three-dimensional form (using the bold-face vector notation), and note how similar it is to its Newtonian counterpart. From the spatial curvature measures that we introduce, we derive corresponding covariant differentiations of a vector defined along a spacetime trajectory. This allows us to connect the formalism of this paper to that of Jantzen and co-workers (see e.g. Bini et al 1997 Int. J. Mod. Phys. D 6 143-98)

Spontaneous formation of small unilamellar vesicles by pH jump: A pH gradient across the bilayer membrane as the driving force

International Nuclear Information System (INIS)

Hauser, H.; Mantsch, H.H.; Casal, H.L.

1990-01-01

31 P NMR and infrared spectroscopic methods have been used to study the formation of small unilamellar vesicles by the pH-jump method. It is shown that increasing the pH of different lamellar phospholipid dispersions (phosphatidic acids and phosphatidylserines) induces a pH gradient. This pH gradient is estimated to be 4 ± 1 pH units, and its direction is such that the inner monolayer of the vesicles is at lower pH. There is spectroscopic evidence for tighter packing of the lipid hydrocarbon chains in the inner monolayer, probably due to the constraints imposed by the high curvature of the small vesicles formed. These results are discussed in terms of the driving force of the spontaneous vesiculation

Gradient metasurfaces: a review of fundamentals and applications

Science.gov (United States)

Ding, Fei; Pors, Anders; Bozhevolnyi, Sergey I.

2018-02-01

In the wake of intense research on metamaterials the two-dimensional analogue, known as metasurfaces, has attracted progressively increasing attention in recent years due to the ease of fabrication and smaller insertion losses, while enabling an unprecedented control over spatial distributions of transmitted and reflected optical fields. Metasurfaces represent optically thin planar arrays of resonant subwavelength elements that can be arranged in a strictly or quasi periodic fashion, or even in an aperiodic manner, depending on targeted optical wavefronts to be molded with their help. This paper reviews a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised to exhibit spatially varying optical responses resulting in spatially varying amplitudes, phases and polarizations of scattered fields. Starting with introducing the concept of gradient metasurfaces, we present classification of different metasurfaces from the viewpoint of their responses, differentiating electrical-dipole, geometric, reflective and Huygens’ metasurfaces. The fundamental building blocks essential for the realization of metasurfaces are then discussed in order to elucidate the underlying physics of various physical realizations of both plasmonic and purely dielectric metasurfaces. We then overview the main applications of gradient metasurfaces, including waveplates, flat lenses, spiral phase plates, broadband absorbers, color printing, holograms, polarimeters and surface wave couplers. The review is terminated with a short section on recently developed nonlinear metasurfaces, followed by the outlook presenting our view on possible future developments and perspectives for future applications.

Gradient metasurfaces: a review of fundamentals and applications.

Science.gov (United States)

Ding, Fei; Pors, Anders; Bozhevolnyi, Sergey I

2018-02-01

In the wake of intense research on metamaterials the two-dimensional analogue, known as metasurfaces, has attracted progressively increasing attention in recent years due to the ease of fabrication and smaller insertion losses, while enabling an unprecedented control over spatial distributions of transmitted and reflected optical fields. Metasurfaces represent optically thin planar arrays of resonant subwavelength elements that can be arranged in a strictly or quasi periodic fashion, or even in an aperiodic manner, depending on targeted optical wavefronts to be molded with their help. This paper reviews a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised to exhibit spatially varying optical responses resulting in spatially varying amplitudes, phases and polarizations of scattered fields. Starting with introducing the concept of gradient metasurfaces, we present classification of different metasurfaces from the viewpoint of their responses, differentiating electrical-dipole, geometric, reflective and Huygens' metasurfaces. The fundamental building blocks essential for the realization of metasurfaces are then discussed in order to elucidate the underlying physics of various physical realizations of both plasmonic and purely dielectric metasurfaces. We then overview the main applications of gradient metasurfaces, including waveplates, flat lenses, spiral phase plates, broadband absorbers, color printing, holograms, polarimeters and surface wave couplers. The review is terminated with a short section on recently developed nonlinear metasurfaces, followed by the outlook presenting our view on possible future developments and perspectives for future applications.

Designing optimal nanofocusing with a gradient hyperlens

Directory of Open Access Journals (Sweden)

Shen Lian

2017-11-01

Full Text Available We report the design of a high-throughput gradient hyperbolic lenslet built with real-life materials and capable of focusing a beam into a deep sub-wavelength spot of λ/23. This efficient design is achieved through high-order transformation optics and circular effective-medium theory (CEMT, which are used to engineer the radially varying anisotropic artificial material based on the thin alternating cylindrical metal and dielectric layers. The radial gradient of the effective anisotropic optical constants allows for matching the impedances at the input and output interfaces, drastically improving the throughput of the lenslet. However, it is the use of the zeroth-order CEMT that enables the practical realization of a gradient hyperlens with realistic materials. To illustrate the importance of using the CEMT versus the conventional planar effective-medium theory (PEMT for cylindrical anisotropic systems, such as our hyperlens, both the CEMT and PEMT are adopted to design gradient hyperlenses with the same materials and order of elemental layers. The CEMT- and PEMT-based designs show similar performance if the number of metal-dielectric binary layers is sufficiently large (9+ pairs and if the layers are sufficiently thin. However, for the manufacturable lenses with realistic numbers of layers (e.g. five pairs and thicknesses, the performance of the CEMT design continues to be practical, whereas the PEMT-based design stops working altogether. The accurate design of transformation optics-based layered cylindrical devices enabled by CEMT allow for a new class of robustly manufacturable nanophotonic systems, even with relatively thick layers of real-life materials.

Tissue-mimicking bladder wall phantoms for evaluating acoustic radiation force-optical coherence elastography systems.

Science.gov (United States)

Ejofodomi, O'tega A; Zderic, Vesna; Zara, Jason M

2010-04-01

Acoustic radiation force-optical coherence elastography (ARF-OCE) systems are novel imaging systems that have the potential to simultaneously quantify and characterize the optical and mechanical properties of in vivo tissues. This article presents the construction of bladder wall phantoms for use in ARF-OCE systems. Mechanical, acoustic, and optical properties are reported and compared to published values for the urinary bladder. The phantom consisted of 0.2000 +/- 0.0089 and 6.0000 +/- 0.2830 microm polystyrene microspheres (Polysciences Inc., Warrington, PA, Catalog Nos. 07304 and 07312), 7.5 +/- 1.5 microm copolymer microspheres composed of acrylonitrile and vinylidene chloride, (Expancel, Duluth, GA, Catalog No. 461 DU 20), and bovine serum albumin within a gelatin matrix. Young's modulus was measured by successive compression of the phantom and obtaining the slope of the resulting force-displacement data. Acoustic measurements were performed using the transmission method. The phantoms were submerged in a water bath and placed between transmitting and receiving 13 mm diameter unfocused transducers operating at a frequency of 3.5 MHz. A MATLAB algorithm to extract the optical scattering coefficient from optical coherence tomography (OCT) images of the phantom was used. The phantoms possess a Young's modulus of 17.12 +/- 2.72 kPa, a mass density of 1.05 +/- 0.02 g/cm3, an acoustic attenuation coefficient of 0.66 +/- 0.08 dB/cm/MHz, a speed of sound of 1591 +/- 8.76 m/s, and an optical scattering coefficient of 1.80 +/- 0.23 mm(-1). Ultrasound and OCT images of the bladder wall phantom are presented. A material that mimics the mechanical, optical, and acoustic properties of healthy bladder wall has been developed. This tissue-mimicking bladder wall phantom was developed as a control tool to investigate the feasibility of using ARF-OCE to detect the mechanical and optical changes that may be indicative of the onset or development of cancer in the urinary bladder

A combined optical and atomic force microscope for live cell investigations

Energy Technology Data Exchange (ETDEWEB)

Madl, Josef [Institute for Biophysics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz (Austria); Rhode, Sebastian [Institute for Biophysics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz (Austria); Stangl, Herbert [Institute for Medical Chemistry, Medical University Vienna, Waehringerstr. 10, 1090 Vienna (Austria); Stockinger, Hannes [Department of Molecular Immunology, Center for Biomolecular Medicine and Pharmacology, Medical University Vienna, Lazarettgasse 19, 1090 Vienna (Austria); Hinterdorfer, Peter [Institute for Biophysics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz (Austria); Schuetz, Gerhard J. [Institute for Biophysics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz (Austria); Kada, Gerald [Scientec, Mitterbauerweg 4, 4020 Linz (Austria)]. E-mail: gerald_kada@agilent.com

2006-06-15

We present an easy-to-use combination of an atomic force microscope (AFM) and an epi-fluorescence microscope, which allows live cell imaging under physiological conditions. High-resolution AFM images were acquired while simultaneously monitoring either the fluorescence image of labeled membrane components, or a high-contrast optical image (DIC, differential interference contrast). By applying two complementary techniques at the same time, additional information and correlations between structure and function of living organisms were obtained. The synergy effects between fluorescence imaging and AFM were further demonstrated by probing fluorescence-labeled receptor clusters in the cell membrane via force spectroscopy using antibody-functionalized tips. The binding probability on receptor-containing areas identified with fluorescence microscopy ('receptor-positive sites') was significantly higher than that on sites lacking receptors.

Progress in the Correlative Atomic Force Microscopy and Optical Microscopy

Directory of Open Access Journals (Sweden)

Lulu Zhou

2017-04-01

Full Text Available Atomic force microscopy (AFM has evolved from the originally morphological imaging technique to a powerful and multifunctional technique for manipulating and detecting the interactions between molecules at nanometer resolution. However, AFM cannot provide the precise information of synchronized molecular groups and has many shortcomings in the aspects of determining the mechanism of the interactions and the elaborate structure due to the limitations of the technology, itself, such as non-specificity and low imaging speed. To overcome the technical limitations, it is necessary to combine AFM with other complementary techniques, such as fluorescence microscopy. The combination of several complementary techniques in one instrument has increasingly become a vital approach to investigate the details of the interactions among molecules and molecular dynamics. In this review, we reported the principles of AFM and optical microscopy, such as confocal microscopy and single-molecule localization microscopy, and focused on the development and use of correlative AFM and optical microscopy.

Polarization-dependent force driving the Eg mode in bismuth under optical excitation: comparison of first-principles theory with ultra-fast x-ray experiments

Science.gov (United States)

Fahy, Stephen; Murray, Eamonn

2015-03-01

Using first principles electronic structure methods, we calculate the induced force on the Eg (zone centre transverse optical) phonon mode in bismuth immediately after absorption of a ultrafast pulse of polarized light. To compare the results with recent ultra-fast, time-resolved x-ray diffraction experiments, we include the decay of the force due to carrier scattering, as measured in optical Raman scattering experiments, and simulate the optical absorption process, depth-dependent atomic driving forces, and x-ray diffraction in the experimental geometry. We find excellent agreement between the theoretical predictions and the observed oscillations of the x-ray diffraction signal, indicating that first-principles theory of optical absorption is well suited to the calculation of initial atomic driving forces in photo-excited materials following ultrafast excitation. This work is supported by Science Foundation Ireland (Grant No. 12/IA/1601) and EU Commission under the Marie Curie Incoming International Fellowships (Grant No. PIIF-GA-2012-329695).

Very high geothermal gradient in near surface of the Whataroa Valley adjacent to the Alpine Fault: topographic driving forces and permeable mountains

Science.gov (United States)

Upton, P.; Sutherland, R.; Townend, J.; Coussens, J.; Capova, L.

2015-12-01

The first phase of the Deep Fault Drilling Project (DFDP-1B) yielded a geothermal gradient of 62.6 ± 2.1 °C/km from a depth of 126 m where it intersected the Alpine Fault principal slip surface beneath Gaunt Creek (Sutherland et al. 2012). Ambient fluid pressures in DFDP-2B at Whataroa River were 8-10% above hydrostatic and a geothermal gradient of >130°C/km was determined, the geothermal gradient being considerably higher than we had predicted previously. 3D coupled thermal/fluid flow models have been generated of the Whataroa Valley and the DFDP-2 drill site. Modelling confirms that the following features, present in the Whataroa Valley, are a requirement for a geothermal gradient of >130°C/km at a depth of 1km beneath the valley; high topography, permeability on the order of 10-15 m2 in both the mountains and beneath the valleys to depths of > 1km below the valley floor, and abundant fluid. The high permeability and large topographic driving force leads to abundant meteoric water flowing downward through the mountains, hitting the permeability barrier of the Alpine Fault and being pushed upward into the valleys. The high geothermal gradient of the DFDP-2B borehole implies that the valleys also have a very high permeability which is likely a result of rock damage along the Alpine Fault.

Degraded character recognition based on gradient pattern

Science.gov (United States)

Babu, D. R. Ramesh; Ravishankar, M.; Kumar, Manish; Wadera, Kevin; Raj, Aakash

2010-02-01

Degraded character recognition is a challenging problem in the field of Optical Character Recognition (OCR). The performance of an optical character recognition depends upon printed quality of the input documents. Many OCRs have been designed which correctly identifies the fine printed documents. But, very few reported work has been found on the recognition of the degraded documents. The efficiency of the OCRs system decreases if the input image is degraded. In this paper, a novel approach based on gradient pattern for recognizing degraded printed character is proposed. The approach makes use of gradient pattern of an individual character for recognition. Experiments were conducted on character image that is either digitally written or a degraded character extracted from historical documents and the results are found to be satisfactory.

Force and deflection sensor with shell membrane and optical gratings and method of manufacture

Science.gov (United States)

Park, Yong-Lae (Inventor); Moslehi, Behzad (Inventor); Black, Richard James (Inventor); Cutkosky, Mark R. (Inventor); Chau, Kelvin K (Inventor)

2011-01-01

A sensor for force is formed from an elastomeric cylinder having a region with apertures. The apertures have passageways formed between them, and an optical fiber is introduced into these passageways, where the optical fiber has a grating for measurement of tension positioned in the passageways between apertures. Optionally, a temperature measurement sensor is placed in or around the elastomer for temperature correction, and if required, a copper film may be deposited in the elastomer for reduced sensitivity to spot temperature variations in the elastomer near the sensors.

Size Dependent Orientation of Knudsen Force

KAUST Repository

Zhu, Taishan

2012-03-03

Knudsen force acting on a heated microbeam adjacent to a cold substrate in a rarefied gas is a mechanical force created by unbalanced thermal gradients. The measured force has its direction pointing towards the side with a lower thermal gradient and its magnitude vanishes in both continuum and free-molecule limits. In our previous study, negative Knudsen forces were discovered at the high Knudsen regime before diminishing in the free-molecule limit. Such a phenomenon was however not observed in the experiment. In this paper, the existence of such a negative Knudsen force is further confirmed using both numerical simulation and theoretical analysis. The asymptotic order of the Knudsen force near the collisionless limit is analyzed and the analytical expression of its leading term is provided, from which approaches for the enhancement of negative Knudsen forces are proposed. Copyright © 2012 by ASME.

Optical trapping of a spherically symmetric sphere in the ray-optics regime: a model for optical tweezers upon cells

International Nuclear Information System (INIS)

Chang Yiren; Hsu Long; Chi Sien

2006-01-01

Since their invention in 1986, optical tweezers have become a popular manipulation and force measurement tool in cellular and molecular biology. However, until recently there has not been a sophisticated model for optical tweezers on trapping cells in the ray-optics regime. We present a model for optical tweezers to calculate the optical force upon a spherically symmetric multilayer sphere representing a common biological cell. A numerical simulation of this model shows that not only is the magnitude of the optical force upon a Chinese hamster ovary cell significantly three times smaller than that upon a polystyrene bead of the same size, but the distribution of the optical force upon a cell is also much different from that upon a uniform particle, and there is a 30% difference in the optical trapping stiffness of these two cases. Furthermore, under a small variant condition for the refractive indices of any adjacent layers of the sphere, this model provides a simple approximation to calculate the optical force and the stiffness of an optical tweezers system

Pulsed laser manipulation of an optically trapped bead: Averaging thermal noise and measuring the pulsed force amplitude

DEFF Research Database (Denmark)

Lindballe, Thue Bjerring; Kristensen, Martin V. G.; Keiding, Søren Rud

2013-01-01

An experimental strategy for post-eliminating thermal noise on position measurements of optically trapped particles is presented. Using a nanosecond pulsed laser, synchronized to the detection system, to exert a periodic driving force on an optically trapped 10 polystyrene bead, the laser pulse-bead...... interaction is repeated hundreds of times. Traces with the bead position following the prompt displacement from equilibrium, induced by each laser pulse, are averaged and reveal the underlying deterministic motion of the bead, which is not visible in a single trace due to thermal noise. The motion of the bead...... is analyzed from the direct time-dependent position measurements and from the power spectrum. The results show that the bead is on average displaced 208 nm from the trap center and exposed to a force amplitude of 71 nanoNewton, more than five orders of magnitude larger than the trapping forces. Our...

Gradient Index Optics at DARPA

Science.gov (United States)

2013-11-01

for correcting vision. René Descartes proposed another idea to cor- rect vision in 1636: use a glass tube filled with liquid and place it in direct... Descartes published the present form of this law, a basis of modern geometric optics known as Snell’s Law (Fishman 2000, 405, 408) (see Figure 1-6). At

Atomic force and scanning near-field optical microscopy study of carbocyanine dye J-aggregates

Czech Academy of Sciences Publication Activity Database

Prokhorov, V.V.; Petrova, M.G.; Kovaleva, Natalia; Demikhov, E.I.

2014-01-01

Roč. 10, č. 5 (2014), s. 700-704 ISSN 1573-4137 Institutional support: RVO:68378271 Keywords : carbocyanine dye * elementary fibri * high-resolution atomic force microscopy * J-aggregate * probe microscopy * scanning near-field optical microscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.096, year: 2014

Two-step reconstruction method using global optimization and conjugate gradient for ultrasound-guided diffuse optical tomography.

Science.gov (United States)

Tavakoli, Behnoosh; Zhu, Quing

2013-01-01

Ultrasound-guided diffuse optical tomography (DOT) is a promising method for characterizing malignant and benign lesions in the female breast. We introduce a new two-step algorithm for DOT inversion in which the optical parameters are estimated with the global optimization method, genetic algorithm. The estimation result is applied as an initial guess to the conjugate gradient (CG) optimization method to obtain the absorption and scattering distributions simultaneously. Simulations and phantom experiments have shown that the maximum absorption and reduced scattering coefficients are reconstructed with less than 10% and 25% errors, respectively. This is in contrast with the CG method alone, which generates about 20% error for the absorption coefficient and does not accurately recover the scattering distribution. A new measure of scattering contrast has been introduced to characterize benign and malignant breast lesions. The results of 16 clinical cases reconstructed with the two-step method demonstrates that, on average, the absorption coefficient and scattering contrast of malignant lesions are about 1.8 and 3.32 times higher than the benign cases, respectively.

Control of dynamical self-assembly of strongly Brownian nanoparticles through convective forces induced by ultrafast laser

Science.gov (United States)

Ilday, Serim; Akguc, Gursoy B.; Tokel, Onur; Makey, Ghaith; Yavuz, Ozgun; Yavuz, Koray; Pavlov, Ihor; Ilday, F. Omer; Gulseren, Oguz

We report a new dynamical self-assembly mechanism, where judicious use of convective and strong Brownian forces enables effective patterning of colloidal nanoparticles that are almost two orders of magnitude smaller than the laser beam. Optical trapping or tweezing effects are not involved, but the laser is used to create steep thermal gradients through multi-photon absorption, and thereby guide the colloids through convective forces. Convective forces can be thought as a positive feedback mechanism that helps to form and reinforce pattern, while Brownian motion act as a competing negative feedback mechanism to limit the growth of the pattern, as well as to increase the possibilities of bifurcation into different patterns, analogous to the competition observed in reaction-diffusion systems. By steering stochastic processes through these forces, we are able to gain control over the emergent pattern such as to form-deform-reform of a pattern, to change its shape and transport it spatially within seconds. This enables us to dynamically initiate and control large patterns comprised of hundreds of colloids. Further, by not relying on any specific chemical, optical or magnetic interaction, this new method is, in principle, completely independent of the material type being assembled.

High-speed atomic force microscopy combined with inverted optical microscopy for studying cellular events.

Science.gov (United States)

Suzuki, Yuki; Sakai, Nobuaki; Yoshida, Aiko; Uekusa, Yoshitsugu; Yagi, Akira; Imaoka, Yuka; Ito, Shuichi; Karaki, Koichi; Takeyasu, Kunio

2013-01-01

A hybrid atomic force microscopy (AFM)-optical fluorescence microscopy is a powerful tool for investigating cellular morphologies and events. However, the slow data acquisition rates of the conventional AFM unit of the hybrid system limit the visualization of structural changes during cellular events. Therefore, high-speed AFM units equipped with an optical/fluorescence detection device have been a long-standing wish. Here we describe the implementation of high-speed AFM coupled with an optical fluorescence microscope. This was accomplished by developing a tip-scanning system, instead of a sample-scanning system, which operates on an inverted optical microscope. This novel device enabled the acquisition of high-speed AFM images of morphological changes in individual cells. Using this instrument, we conducted structural studies of living HeLa and 3T3 fibroblast cell surfaces. The improved time resolution allowed us to image dynamic cellular events.

Improving the performance of IPMCs with a gradient in thickness

International Nuclear Information System (INIS)

Zhao, Yang; Xu, Bing; Zheng, Gaofeng; Zheng, Jianyi; Qiu, Xiaochun; Zhuang, Mingfeng; Sun, Daoheng

2013-01-01

An ionic polymer metal composite (IPMC) is a kind of electro-active polymer. Due to the properties of low driving voltage, large deformation, flexibility and lightness, it is becoming one of the more popular from a diversity of smart materials. In this study, a novel structure of Nafion ® film is proposed to improve the performance of an IPMC. IPMC samples with a gradient structure in thickness are fabricated and their performance is investigated to confirm the validity of the gradient structure. The deformation displacement and the blocking force are compared under AC and DC voltage by experiments. The results indicate that the structure of gradient in thickness would improve the performance both in deformation displacement and blocking force. (paper)

Different elution modes and field programming in gravitational field-flow fractionation. III. Field programming by flow-rate gradient generated by a programmable pump.

Science.gov (United States)

Plocková, J; Chmelík, J

2001-05-25

Gravitational field-flow fractionation (GFFF) utilizes the Earth's gravitational field as an external force that causes the settlement of particles towards the channel accumulation wall. Hydrodynamic lift forces oppose this action by elevating particles away from the channel accumulation wall. These two counteracting forces enable modulation of the resulting force field acting on particles in GFFF. In this work, force-field programming based on modulating the magnitude of hydrodynamic lift forces was implemented via changes of flow-rate, which was accomplished by a programmable pump. Several flow-rate gradients (step gradients, linear gradients, parabolic, and combined gradients) were tested and evaluated as tools for optimization of the separation of a silica gel particle mixture. The influence of increasing amount of sample injected on the peak resolution under flow-rate gradient conditions was also investigated. This is the first time that flow-rate gradients have been implemented for programming of the resulting force field acting on particles in GFFF.

Optical Fiber Force Myography Sensor for Identification of Hand Postures

Directory of Open Access Journals (Sweden)

Eric Fujiwara

2018-01-01

Full Text Available A low-cost optical fiber force myography sensor for noninvasive hand posture identification is proposed. The transducers are comprised of 10 mm periodicity silica multimode fiber microbending devices mounted in PVC plates, providing 0.05 N−1 sensitivity over ~20 N range. Next, the transducers were attached to the user forearm by means of straps in order to monitor the posterior proximal radial, the anterior medial ulnar, and the posterior distal radial muscles, and the acquired FMG optical signals were correlated to the performed gestures using a 5 hidden layers, 20-neuron artificial neural network classifier with backpropagation architecture, followed by a competitive layer. The overall results for 9 postures and 6 subjects indicated a 98.4% sensitivity and 99.7% average accuracy, being comparable to the electromyographic approaches. Moreover, in contrast to the current setups, the proposed methodology allows the identification of poses characterized by different configurations of fingers and wrist joint displacements with the utilization of only 3 transducers and a simple interrogation scheme, being suitable to further applications in human-computer interfaces.

Pressure gradients fail to predict diffusio-osmosis

Science.gov (United States)

Liu, Yawei; Ganti, Raman; Frenkel, Daan

2018-05-01

We present numerical simulations of diffusio-osmotic flow, i.e. the fluid flow generated by a concentration gradient along a solid-fluid interface. In our study, we compare a number of distinct approaches that have been proposed for computing such flows and compare them with a reference calculation based on direct, non-equilibrium molecular dynamics simulations. As alternatives, we consider schemes that compute diffusio-osmotic flow from the gradient of the chemical potentials of the constituent species and from the gradient of the component of the pressure tensor parallel to the interface. We find that the approach based on treating chemical potential gradients as external forces acting on various species agrees with the direct simulations, thereby supporting the approach of Marbach et al (2017 J. Chem. Phys. 146 194701). In contrast, an approach based on computing the gradients of the microscopic pressure tensor does not reproduce the direct non-equilibrium results.

Escherichia coli Fiber Sensors Using Concentrated Dielectrophoretic Force with Optical Defocusing Method.

Science.gov (United States)

Tai, Yi-Hsin; Lee, Chia-Wei; Chang, Dao-Ming; Lai, Yu-Sheng; Huang, Ding-Wei; Wei, Pei-Kuen

2018-05-25

A sensitive tapered optical fiber tip combined with dielectrophoretic (DEP) trapping was used for rapid and label-free detection of bacteria in water. The angular spectrum of the optical field at the fiber tip was changed with the surrounding refractive index (RI). By measuring far-field intensity change at the defocus plane, the intensity sensitivity was up to 95 200%/RIU (RI unit), and the detection limit was 5.2 × 10 -6 RIU at 0.5% intensity stability. By applying an AC voltage to a Ti/Al coated fiber tip and an indium-tin-oxide glass, the DEP force effectively trapped the Escherichia coli ( E. coli) near the fiber tip. Those bacteria can be directly measured from optical intensity change due to the increase of surrounding RI. By immobilizing the antibody on the Ti/Al fiber tip, the tests for specific K12 bacteria and nonspecific BL21 bacteria verified the specificity. The antibody-immobilized Ti/Al coated fiber tip with DEP trapping can detect bacteria at a concentration about 100 CFU/mL.

Photometric correction for an optical CCD-based system based on the sparsity of an eight-neighborhood gray gradient.

Science.gov (United States)

Zhang, Yuzhong; Zhang, Yan

2016-07-01

In an optical measurement and analysis system based on a CCD, due to the existence of optical vignetting and natural vignetting, photometric distortion, in which the intensity falls off away from the image center, affects the subsequent processing and measuring precision severely. To deal with this problem, an easy and straightforward method used for photometric distortion correction is presented in this paper. This method introduces a simple polynomial fitting model of the photometric distortion function and employs a particle swarm optimization algorithm to get these model parameters by means of a minimizing eight-neighborhood gray gradient. Compared with conventional calibration methods, this method can obtain the profile information of photometric distortion from only a single common image captured by the optical CCD-based system, with no need for a uniform luminance area source used as a standard reference source and relevant optical and geometric parameters in advance. To illustrate the applicability of this method, numerical simulations and photometric distortions with different lens parameters are evaluated using this method in this paper. Moreover, the application example of temperature field correction for casting billets also demonstrates the effectiveness of this method. The experimental results show that the proposed method is able to achieve the maximum absolute error for vignetting estimation of 0.0765 and the relative error for vignetting estimation from different background images of 3.86%.

Optical properties and composition changes in chromophoric dissolved organic matter along trophic gradients: Implications for monitoring and assessing lake eutrophication.

Science.gov (United States)

Zhang, Yunlin; Zhou, Yongqiang; Shi, Kun; Qin, Boqiang; Yao, Xiaolong; Zhang, Yibo

2017-12-26

Chromophoric dissolved organic matter (CDOM) is an important optically active substance in aquatic environments and plays a key role in light attenuation and in the carbon, nitrogen and phosphorus biogeochemical cycles. Although the optical properties, abundance, sources, cycles, compositions and remote sensing estimations of CDOM have been widely reported in different aquatic environments, little is known about the optical properties and composition changes in CDOM along trophic gradients. Therefore, we collected 821 samples from 22 lakes along a trophic gradient (oligotrophic to eutrophic) in China from 2004 to 2015 and determined the CDOM spectral absorption and nutrient concentrations. The total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chla) concentrations and the Secchi disk depth (SDD) ranged from 0.02 to 24.75 mg/L, 0.002-3.471 mg/L, 0.03-882.66 μg/L, and 0.05-17.30 m, respectively. The trophic state index (TSI) ranged from 1.55 to 98.91 and covered different trophic states, from oligotrophic to hyper-eutrophic. The CDOM absorption coefficient at 254 nm (a(254)) ranged from 1.68 to 92.65 m -1 . Additionally, the CDOM sources and composition parameters, including the spectral slope and relative molecular size value, exhibited a substantial variability from the oligotrophic level to other trophic levels. The natural logarithm value of the CDOM absorption, lna(254), is highly linearly correlated with the TSI (r 2  = 0.92, p 10 m -1 , respectively. The results suggested that the CDOM absorption coefficient a(254) might be a more sensitive single indicator of the trophic state than TN, TP, Chla and SDD. Therefore, we proposed a CDOM absorption coefficient and determined the threshold for defining the trophic state of a lake. Several advantages of measuring and estimating CDOM, including rapid experimental measurements, potential in situ optical sensor measurements and large-spatial-scale remote sensing estimations, make it

Analysis of tracer responses in the BULLION Forced-Gradient Experiment at Pahute Mesa, Nevada

Energy Technology Data Exchange (ETDEWEB)

Paul W. Reimus; Marc J. Haga

1999-10-01

This report presents an analysis of the tracer data from the BULLION forced-gradient experiment (FGE) conducted on Pahute Mesa at the Nevada Test Site from June 2, 1997 through August 28, 1997, for the Underground Test Area (UGTA) Program. It also serves to document the polystyrene microsphere data from the FGE. The FGE involved the injection of solute and colloid tracers into wells ER-20-6 No. 1 and ER-20-6 No. 2 while ER-20-6 No. 3 was pumped at approximately 116 gallons per minute (gpm). The experimental configuration and test design are described briefly in this report; more details are provided elsewhere (IT, 1996, 1997, 1998). The tracer responses in the various wells yielded valuable information about transport processes such as longitudinal dispersion, matrix diffusion and colloid transport in the hydrogeologic system in the vicinity of the BULLION nuclear test cavity. Parameter values describing these processes are derived from the semi-analytical model interpretations presented in this report. A companion report (IT, 1998) presents more detailed numerical modeling interpretations of the solute tracer responses.

Analysis of tracer responses in the BULLION Forced-Gradient Experiment at Pahute Mesa, Nevada

International Nuclear Information System (INIS)

Reimus, Paul W.; Haga, Marc J.

1999-01-01

This report presents an analysis of the tracer data from the BULLION forced-gradient experiment (FGE) conducted on Pahute Mesa at the Nevada Test Site from June 2, 1997 through August 28, 1997, for the Underground Test Area (UGTA) Program. It also serves to document the polystyrene microsphere data from the FGE. The FGE involved the injection of solute and colloid tracers into wells ER-20-6 No. 1 and ER-20-6 No. 2 while ER-20-6 No. 3 was pumped at approximately 116 gallons per minute (gpm). The experimental configuration and test design are described briefly in this report; more details are provided elsewhere (IT, 1996, 1997, 1998). The tracer responses in the various wells yielded valuable information about transport processes such as longitudinal dispersion, matrix diffusion and colloid transport in the hydrogeologic system in the vicinity of the BULLION nuclear test cavity. Parameter values describing these processes are derived from the semi-analytical model interpretations presented in this report. A companion report (IT, 1998) presents more detailed numerical modeling interpretations of the solute tracer responses

The chirped-pulse inverse free-electron laser: A high-gradient vacuum laser accelerator

International Nuclear Information System (INIS)

Hartemann, F.V.; Landahl, E.C.; Troha, A.L.; Van Meter, J.R.; Baldis, H.A.; Freeman, R.R.; Luhmann, N.C. Jr.; Song, L.; Kerman, A.K.; Yu, D.U.

1999-01-01

The inverse free-electron laser (IFEL) interaction is studied theoretically and computationally in the case where the drive laser intensity approaches the relativistic regime, and the pulse duration is only a few optical cycles long. The IFEL concept has been demonstrated as a viable vacuum laser acceleration process; it is shown here that by using an ultrashort, ultrahigh-intensity drive laser pulse, the IFEL interaction bandwidth and accelerating gradient are increased considerably, thus yielding large energy gains. Using a chirped pulse and negative dispersion focusing optics allows one to take further advantage of the laser optical bandwidth and produce a chromatic line focus maximizing the gradient. The combination of these novel ideas results in a compact vacuum laser accelerator capable of accelerating picosecond electron bunches with a high gradient (GeV/m) and very low energy spread. copyright 1999 American Institute of Physics

The migration of fluid droplets and their interactions in a thermal gradient

International Nuclear Information System (INIS)

Subramanian, R.S.; Wilcox, W.R.

1979-01-01

When materials are processed in free fall, buoyant forces will be substantially reduced. Thus, the buoyant migration of droplets and bubbles which normally occurs on earth is expected to be overshadowed by migration due to other mechanisms in space processing. In particular, capillary forces on droplets due to the variation of interfacial tension around their periphery will play a significant role in governing their motion in space. While such interfacial tension gradients can be caused by thermal, compositional, and/or electrical gradients in the continuous phase, thermal gradients are convenient to use in controlled experimentation. On earth, due to interference from buoyant effects, it is difficult to study thermocapillary migration in sufficient detail. Also, the effects of a thermal gradient on the interactions among droplets are hard to study on Earth. Thus, an orbital facility for conducting experiments on the migration and interactions of fluid droplets in a continuous phase due to the action of a thermal gradient appears attractive

A Spectral Conjugate Gradient Method for Unconstrained Optimization

International Nuclear Information System (INIS)

Birgin, E. G.; Martinez, J. M.

2001-01-01

A family of scaled conjugate gradient algorithms for large-scale unconstrained minimization is defined. The Perry, the Polak-Ribiere and the Fletcher-Reeves formulae are compared using a spectral scaling derived from Raydan's spectral gradient optimization method. The best combination of formula, scaling and initial choice of step-length is compared against well known algorithms using a classical set of problems. An additional comparison involving an ill-conditioned estimation problem in Optics is presented

An integrated instrumental setup for the combination of atomic force microscopy with optical spectroscopy.

Science.gov (United States)

Owen, R J; Heyes, C D; Knebel, D; Röcker, C; Nienhaus, G U

2006-07-01

In recent years, the study of single biomolecules using fluorescence microscopy and atomic force microscopy (AFM) techniques has resulted in a plethora of new information regarding the physics underlying these complex biological systems. It is especially advantageous to be able to measure the optical, topographical, and mechanical properties of single molecules simultaneously. Here an AFM is used that is especially designed for integration with an inverted optical microscope and that has a near-infrared light source (850 nm) to eliminate interference between the optical experiment and the AFM operation. The Tip Assisted Optics (TAO) system consists of an additional 100 x 100-microm(2) X-Y scanner for the sample, which can be independently and simultaneously used with the AFM scanner. This allows the offset to be removed between the confocal optical image obtained with the sample scanner and the simultaneously acquired AFM topography image. The tip can be positioned exactly into the optical focus while the user can still navigate within the AFM image for imaging or manipulation of the sample. Thus the tip-enhancement effect can be maximized and it becomes possible to perform single molecule manipulation experiments within the focus of a confocal optical image. Here this is applied to simultaneous measurement of single quantum dot fluorescence and topography with high spatial resolution. (c) 2006 Wiley Periodicals, Inc.

Bioinspired adaptive gradient refractive index distribution lens

Science.gov (United States)

Yin, Kezhen; Lai, Chuan-Yar; Wang, Jia; Ji, Shanzuo; Aldridge, James; Feng, Jingxing; Olah, Andrew; Baer, Eric; Ponting, Michael

2018-02-01

Inspired by the soft, deformable human eye lens, a synthetic polymer gradient refractive index distribution (GRIN) lens with an adaptive geometry and focal power has been demonstrated via multilayer coextrusion and thermoforming of nanolayered elastomeric polymer films. A set of 30 polymer nanolayered films comprised of two thermoplastic polyurethanes having a refractive index difference of 0.05 were coextruded via forced-assembly technique. The set of 30 nanolayered polymer films exhibited transmission near 90% with each film varying in refractive index by 0.0017. An adaptive GRIN lens was fabricated from a laminated stack of the variable refractive index films with a 0.05 spherical GRIN. This lens was subsequently deformed by mechanical ring compression of the lens. Variation in the optical properties of the deformable GRIN lens was determined, including 20% variation in focal length and reduced spherical aberration. These properties were measured and compared to simulated results by placido-cone topography and ANSYS methods. The demonstration of a solid-state, dynamic focal length, GRIN lens with improved aberration correction was discussed relative to the potential future use in implantable devices.

Aerosol optical properties and direct radiative forcing at Taihu.

Science.gov (United States)

Lü, Rui; Yu, Xingna; Jia, Hailing; Xiao, Sihan

2017-09-01

Ground-based characteristics (optical, type, size, and radiative properties) of aerosols measured between 2005 and 2012 were investigated over the Taihu rim region, which encompasses the cities of Shanghai, Suzhou, Wuxi, and Changzhou. The aerosol optical depth (AOD) showed a distinct seasonal variation with the highest value in summer and the lowest AOD in winter. There was broadest frequency distribution with a multimodal structure in summer. The Ångström exponent (AE) showed high values during spring; the relative frequency of AE in the range of 0-0.8 was 5-10 times greater than that of other seasons. The samples with high AOD 440 and low AE 440-870 were mainly observed in spring, which is attributed to the relative abundance of coarse particles. The monthly aerosol volume size distributions presented a bimodal structure (fine and coarse modes). The coarse mode was dominant during spring, while the fine mode was predominant in other seasons. The main aerosol type over Taihu during all the seasons was the mixed small-particle category, followed by the urban/industrial category. The minimum single scattering albedo (SSA) occurred in winter, suggesting that atmosphere aerosol had a higher absorption. All monthly averaged asymmetry factors (ASY) had positive values and no distinct seasonal variation. Both high real (Re) and imaginary (Im) parts of the refractive index occurred in winter. The atmospheric warming effect of aerosol was more significant in winter compared with other seasons, with the averaged atmosphere aerosol radiative forcing (ARF) and the corresponding atmospheric heating rate up to +69.46  W·m -2 and 1.95  K·day -1 , respectively. There existed a significant positive correlation between AOD and ARF (absolute value), and the correlation coefficients (r) exceeded 0.86 in each season with maximum r in summer. Along with the increasing of the SSA, the aerosol radiative forcing efficiency (absolute value) showed a decreasing trend at the

Optical Characterization of Lorentz Force Based CMOS-MEMS Magnetic Field Sensor.

Science.gov (United States)

Dennis, John Ojur; Ahmad, Farooq; Khir, M Haris Bin Md; Bin Hamid, Nor Hisham

2015-07-27

Magnetic field sensors are becoming an essential part of everyday life due to the improvements in their sensitivities and resolutions, while at the same time they have become compact, smaller in size and economical. In the work presented herein a Lorentz force based CMOS-MEMS magnetic field sensor is designed, fabricated and optically characterized. The sensor is fabricated by using CMOS thin layers and dry post micromachining is used to release the device structure and finally the sensor chip is packaged in DIP. The sensor consists of a shuttle which is designed to resonate in the lateral direction (first mode of resonance). In the presence of an external magnetic field, the Lorentz force actuates the shuttle in the lateral direction and the amplitude of resonance is measured using an optical method. The differential change in the amplitude of the resonating shuttle shows the strength of the external magnetic field. The resonance frequency of the shuttle is determined to be 8164 Hz experimentally and from the resonance curve, the quality factor and damping ratio are obtained. In an open environment, the quality factor and damping ratio are found to be 51.34 and 0.00973 respectively. The sensitivity of the sensor is determined in static mode to be 0.034 µm/mT when a current of 10 mA passes through the shuttle, while it is found to be higher at resonance with a value of 1.35 µm/mT at 8 mA current. Finally, the resolution of the sensor is found to be 370.37 µT.

Substrate curvature gradient drives rapid droplet motion.

Science.gov (United States)

Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui

2014-07-11

Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42  m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100  m/s on tapered surfaces.

Negative Knudsen force on heated microbeams

KAUST Repository

Zhu, Taishan

2011-11-18

Knudsen force acting on a heated microbeam adjacent to a cold substrate in a rarefied gas is a mechanical force created by unbalanced thermal gradients. The measured force has its direction pointing towards the side with a lower thermal gradient and its magnitude vanishes in both continuum and free-molecule limits. In our previous study, negative Knudsen forces were discovered at the high Knudsen regime before diminishing in the free-molecule limit. Such a phenomenon was, however, neither observed in experiment [A. Passian et al., Phys. Rev. Lett. 90, 124503 (2003)], nor captured in the latest numerical study [J. Nabeth et al., Phys. Rev. E 83, 066306 (2011)]. In this paper, the existence of such a negative Knudsen force is further confirmed using both numerical simulation and theoretical analysis. The asymptotic order of the Knudsen force near the collisionless limit is analyzed and the analytical expression of its leading term is provided, from which approaches for the enhancement of negative Knudsen forces are proposed. The discovered phenomenon could find its applications in novel mechanisms for pressure sensing and actuation.

Conjugate gradient minimisation approach to generating holographic traps for ultracold atoms.

Science.gov (United States)

Harte, Tiffany; Bruce, Graham D; Keeling, Jonathan; Cassettari, Donatella

2014-11-03

Direct minimisation of a cost function can in principle provide a versatile and highly controllable route to computational hologram generation. Here we show that the careful design of cost functions, combined with numerically efficient conjugate gradient minimisation, establishes a practical method for the generation of holograms for a wide range of target light distributions. This results in a guided optimisation process, with a crucial advantage illustrated by the ability to circumvent optical vortex formation during hologram calculation. We demonstrate the implementation of the conjugate gradient method for both discrete and continuous intensity distributions and discuss its applicability to optical trapping of ultracold atoms.

Improvement of GaN epilayer by gradient layer method with molecular-beam epitaxy

International Nuclear Information System (INIS)

Chen, Yen-Liang; Lo, Ikai; Gau, Ming-Hong; Hsieh, Chia-Ho; Sham, Meng-Wei; Pang, Wen-Yuan; Hsu, Yu-Chi; Tsai, Jenn-Kai; Schuber, Ralf; Schaadt, Daniel

2012-01-01

We demonstrated a molecular beam epitaxy method to resolve the dilemma between structural and morphological quality in growth of the GaN epilayer. A gradient buffer layer was grown in such a way that the N/Ga ratio was gradually changed from nitrogen-rich to gallium-rich. The GaN epitaxial layer was then grown on the gradient buffer layer. In the X-ray diffraction analysis of GaN(002) rocking curves, we found that the full width at half-maximum was improved from 531.69″ to 59.43″ for the sample with a gradient buffer layer as compared to a purely gallium-rich grown sample. Atomic force microscopy analysis showed that the root-mean-square roughness of the surface was improved from 18.28 nm to 1.62 nm over an area of 5 × 5 μm 2 with respect to a purely nitrogen-rich grown sample. Raman scattering showed the presence of a slightly tilted plane in the gradient layer. Furthermore we showed that the gradient layer can also slash the strain force caused by either Ga-rich GaN epitaxial layer or AlN buffer layer. - Highlights: ► The samples were grown by plasma-assisted molecular beam epitaxy. ► The GaN epilayer was grown on sapphire substrate. ► The samples were characterized by X-ray diffraction and atomic force microscopy. ► The sample quality was improved by gradient buffer layer.

Effect of cantilever geometry on the optical lever sensitivities and thermal noise method of the atomic force microscope.

Science.gov (United States)

Sader, John E; Lu, Jianing; Mulvaney, Paul

2014-11-01

Calibration of the optical lever sensitivities of atomic force microscope (AFM) cantilevers is especially important for determining the force in AFM measurements. These sensitivities depend critically on the cantilever mode used and are known to differ for static and dynamic measurements. Here, we calculate the ratio of the dynamic and static sensitivities for several common AFM cantilevers, whose shapes vary considerably, and experimentally verify these results. The dynamic-to-static optical lever sensitivity ratio is found to range from 1.09 to 1.41 for the cantilevers studied - in stark contrast to the constant value of 1.09 used widely in current calibration studies. This analysis shows that accuracy of the thermal noise method for the static spring constant is strongly dependent on cantilever geometry - neglect of these dynamic-to-static factors can induce errors exceeding 100%. We also discuss a simple experimental approach to non-invasively and simultaneously determine the dynamic and static spring constants and optical lever sensitivities of cantilevers of arbitrary shape, which is applicable to all AFM platforms that have the thermal noise method for spring constant calibration.

A sensitivity function-based conjugate gradient method for optical tomography with the frequency-domain equation of radiative transfer

International Nuclear Information System (INIS)

Kim, Hyun Keol; Charette, Andre

2007-01-01

The Sensitivity Function-based Conjugate Gradient Method (SFCGM) is described. This method is used to solve the inverse problems of function estimation, such as the local maps of absorption and scattering coefficients, as applied to optical tomography for biomedical imaging. A highly scattering, absorbing, non-reflecting, non-emitting medium is considered here and simultaneous reconstructions of absorption and scattering coefficients inside the test medium are achieved with the proposed optimization technique, by using the exit intensity measured at boundary surfaces. The forward problem is solved with a discrete-ordinates finite-difference method on the framework of the frequency-domain full equation of radiative transfer. The modulation frequency is set to 600 MHz and the frequency data, obtained with the source modulation, is used as the input data. The inversion results demonstrate that the SFCGM can retrieve simultaneously the spatial distributions of optical properties inside the medium within a reasonable accuracy, by significantly reducing a cross-talk between inter-parameters. It is also observed that the closer-to-detector objects are better retrieved

Nonlinear nonresonant forces by radio-frequency waves in plasmas

International Nuclear Information System (INIS)

Gao Zhe; Fisch, Nathaniel J.; Qin, Hong; Myra, J. R.

2007-01-01

Nonresonant forces by applied rf waves in plasmas are analyzed. Along the background dc magnetic field, the force arises from the gradient of the ponderomotive potential. Only when the dc magnetic field is straight, however, is this parallel force completely consistent with that from the single particle picture, where the ponderomotive force depends on the gradients of rf fields only. Across the dc magnetic field, besides the ponderomotive force from the particle picture, additional Reynolds stress and polarization stress contribute to the total force. For waves with frequency much lower than the cyclotron frequency, the perpendicular forces from the particle and fluid pictures can have opposite signs. In plasmas with a symmetry angle (e.g., toroidal systems), nonresonant forces cannot drive net flow or current in the flux surface, but the radial force may influence macroscopic behavior of plasma. Moreover, nonresonant forces may drive flow or current in linear plasmas or in a localized region of toroidal plasmas

Characterizing the surface forces between two individual nanowires using optical microscopy based nanomanipulation

Science.gov (United States)

Xie, Hongtao; Mead, James L.; Wang, Shiliang; Fatikow, Sergej; Huang, Han

2018-06-01

The adhesion and friction between two Al2O3 nanowires (NWs) was characterized by the use of optical microscopy based nanomanipulation, with which peeling, shearing and sliding was performed. The elastically deformed shape of the NWs during peeling and shearing was used to calculate the adhesion and frictional forces; force sensing was not required. The obtained adhesion stress between two Al2O3 NWs varied from 0.14 to 0.25 MPa, lower than that observed for carbon nanotube junctions, and was attributed to van der Waals attraction. Stick-slip was observed during the shearing and sliding of two NWs, and was the consequence of discrete contact between surface asperities. The obtained static and kinetic frictional stresses varied from 0.7 to 1.3 MPa and 0.4 to 0.8 MPa, respectively; significantly greater than the obtained adhesion stress.

Observation of self-assembled fluorescent beads by scanning near-field optical microscopy and atomic force microscopy

International Nuclear Information System (INIS)

Oh, Y.J.; Jo, W.; Kim, Min-Gon; Kyu Park, Hyun; Hyun Chung, Bong

2006-01-01

Optical response and topography of fluorescent latex beads both on flat self-assembled monolayer and on a micron-patterned surface with poly(dimethylsiloxane) are studied. Scanning near-field optical microscopy and atomic force microscopy were utilized together for detecting fluorescence and imaging topography of the patterned latex beads, respectively. As a result, the micro-patterned latex beads where a specific chemical binding occurred show a strong signal, whereas no signals are observed in the case of nonspecific binding. With fluorescein isothiocyanate (FITC), it is convenient to measure fluorescence signal from the patterned beads allowing us to monitor the small balls of fluorescent latex

Matching bunched beams to alternating gradient focusing systems

International Nuclear Information System (INIS)

Lysenko, W.P.

1980-07-01

A numerical procedure for generating phase-space distributions matched to alternating gradient focusing systems has been tested. For a smooth-focusing system a matched distribution can be calculated. With a particle tracing simulation code such a distribution can be followed while adiabatically deforming the focusing forces until an alternating gradient configuration is reached. The distribution remains matched; that is, the final distribution is periodic with the structure period. This method is useful because it can produce distributions matched to nonlinear forces. This is a feature that elliptical distributions, with ellipse parameters obtained from the Courant-Snyder theory, do not have. External nonlinearities, including nonlinear couplings, were included in our examples but space charge was not. This procedure is expected to work with space charge but will require a three-dimensional space charge calculation in the simulation code

Fog-induced variations in aerosol optical and physical properties over the Indo-Gangetic Basin and impact to aerosol radiative forcing

Directory of Open Access Journals (Sweden)

S. K. Das

2008-06-01

Full Text Available A detailed study on the changes in aerosol physical and optical properties during fog events were made in December 2004 at Hissar (29.13° N, 75.70° E, a city located in the Indo-Gangetic basin. The visible aerosol optical depth was relatively low (0.3 during the initial days, which, however, increased (0.86 as the month progressed. The increasing aerosol amount, the decreasing surface temperature and a higher relative humidity condition were found favoring the formation of fog. The fog event is also found to alter the aerosol size distribution. An increase in the number concentration of the nucleation mode (radius<0.1 μm particles, along with a decrease in the mode radius showed the formation of freshly nucleated aerosols. In the case of accumulation mode (0.1 μmoptical depth spectra are model fitted to infer the aerosol components which are further used to compute the aerosol radiative forcing. The top of the atmosphere forcing is found to increase during foggy days due to large backscattering of radiation back to space. It is also shown that during foggy days, as the day progresses the RH value decreases, which reduces the forcing value while the increasing solar elevation increases the forcing value. Thus the fog event which prolongs longer into the daytime has a stronger effect on the diurnally averaged aerosol radiative forcing than those events which are confined only to the early morning hours.

Fog-induced variations in aerosol optical and physical properties over the Indo-Gangetic Basin and impact to aerosol radiative forcing

Energy Technology Data Exchange (ETDEWEB)

Das, S.K.; Misra, A. [Physical Research Lab., Ahmedabad (India); Jayaraman, A. [National Atmospheric Research Lab., Gadanki (India)

2008-07-01

A detailed study on the changes in aerosol physical and optical properties during fog events were made in December 2004 at Hissar (29.13 N, 75.70 E), a city located in the Indo-Gangetic basin. The visible aerosol optical depth was relatively low (0.3) during the initial days, which, however, increased (0.86) as the month progressed. The increasing aerosol amount, the decreasing surface temperature and a higher relative humidity condition were found favoring the formation of fog. The fog event is also found to alter the aerosol size distribution. An increase in the number concentration of the nucleation mode (radius<0.1 {mu}m) particles, along with a decrease in the mode radius showed the formation of freshly nucleated aerosols. In the case of accumulation mode (0.1 {mu}moptical depth spectra are model fitted to infer the aerosol components which are further used to compute the aerosol radiative forcing. The top of the atmosphere forcing is found to increase during foggy days due to large backscattering of radiation back to space. It is also shown that during foggy days, as the day progresses the RH value decreases, which reduces the forcing value while the increasing solar elevation increases the forcing value. Thus the fog event which prolongs longer into the daytime has a stronger effect on the diurnally averaged aerosol radiative forcing than those events which are confined only to the early morning hours. (orig.)

Improvement of GaN epilayer by gradient layer method with molecular-beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Chen, Yen-Liang [Department of Physics, Institute of Material Science and Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan, ROC (China); Lo, Ikai, E-mail: ikailo@mail.phys.nsysu.edu.tw [Department of Physics, Institute of Material Science and Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan, ROC (China); Gau, Ming-Hong; Hsieh, Chia-Ho; Sham, Meng-Wei; Pang, Wen-Yuan; Hsu, Yu-Chi [Department of Physics, Institute of Material Science and Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan, ROC (China); Tsai, Jenn-Kai [Department of Electronics Engineering, National Formosa University, Hu-Wei, Yun-Lin County 63208, Taiwan, ROC (China); Schuber, Ralf; Schaadt, Daniel [Institute of Applied Physics/DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology (KIT), Karlsruhe (Germany)

2012-07-31

We demonstrated a molecular beam epitaxy method to resolve the dilemma between structural and morphological quality in growth of the GaN epilayer. A gradient buffer layer was grown in such a way that the N/Ga ratio was gradually changed from nitrogen-rich to gallium-rich. The GaN epitaxial layer was then grown on the gradient buffer layer. In the X-ray diffraction analysis of GaN(002) rocking curves, we found that the full width at half-maximum was improved from 531.69 Double-Prime to 59.43 Double-Prime for the sample with a gradient buffer layer as compared to a purely gallium-rich grown sample. Atomic force microscopy analysis showed that the root-mean-square roughness of the surface was improved from 18.28 nm to 1.62 nm over an area of 5 Multiplication-Sign 5 {mu}m{sup 2} with respect to a purely nitrogen-rich grown sample. Raman scattering showed the presence of a slightly tilted plane in the gradient layer. Furthermore we showed that the gradient layer can also slash the strain force caused by either Ga-rich GaN epitaxial layer or AlN buffer layer. - Highlights: Black-Right-Pointing-Pointer The samples were grown by plasma-assisted molecular beam epitaxy. Black-Right-Pointing-Pointer The GaN epilayer was grown on sapphire substrate. Black-Right-Pointing-Pointer The samples were characterized by X-ray diffraction and atomic force microscopy. Black-Right-Pointing-Pointer The sample quality was improved by gradient buffer layer.

Motion of Drops on Surfaces with Wettability Gradients

Science.gov (United States)

Subramanian, R. Shankar; McLaughlin, John B.; Moumen, Nadjoua; Qian, Dongying

2002-11-01

A liquid drop present on a solid surface can move because of a gradient in wettability along the surface, as manifested by a gradient in the contact angle. The contact angle at a given point on the contact line between a solid and a liquid in a gaseous medium is the angle between the tangent planes to the liquid and the solid surfaces at that point and is measured within the liquid side, by convention. The motion of the drop occurs in the direction of increasing wettability. The cause of the motion is the net force exerted on the drop by the solid surface because of the variation of the contact angle around the periphery. This force causes acceleration of an initially stationary drop, and leads to its motion in the direction of decreasing contact angle. The nature of the motion is determined by the balance between the motivating force and the resisting hydrodynamic force from the solid surface and the surrounding gaseous medium. A wettability gradient can be chemically induced as shown by Chaudhury and Whitesides who provided unambiguous experimental evidence that drops can move in such gradients. The phenomenon can be important in heat transfer applications in low gravity, such as when condensation occurs on a surface. Daniel et al have demonstrated that the velocity of a drop on a surface due to a wettability gradient in the presence of condensation can be more than two orders of magnitude larger than that observed in the absence of condensation. In the present research program, we have begun to study the motion of a drop in a wettability gradient systematically using a model system. Our initial efforts will be restricted to a system in which no condensation occurs. The experiments are performed as follows. First, a rectangular strip of approximate dimensions 10 x 20 mm is cut out of a silicon wafer. The strip is cleaned thoroughly and its surface is exposed to the vapor from an alkylchlorosilane for a period lasting between one and two minutes inside a

Synthesis and characterization of erbium-doped SiO2-TiO2 thin films prepared by sol-gel and dip-coating techniques onto commercial glass substrates as a route for obtaining active GRadient-INdex materials

International Nuclear Information System (INIS)

Gómez-Varela, Ana I.; Castro, Yolanda; Durán, Alicia; De Beule, Pieter A.A.; Flores-Arias, María T.; Bao-Varela, Carmen

2015-01-01

In this work, SiO 2 -TiO 2 films doped with erbium were prepared by dip-coating sol-gel process onto commercial glass substrates. The surface morphology of the films was characterized using atomic force microscopy, while thickness, refractive index, extinction coefficient and porosity of the films were determined by ellipsometric measurements in a wavelength region of 400-1000 nm. Optical constants and porosity were found to vary with erbium concentration. The proof of principle presented in this paper is applicable to systems of different nature by tailoring the sol-gel precursors in such a way that active GRadient-INdex media described by a complex, parabolic-like refractive index distribution for beam shaping purposes is obtained. - Highlights: • Sol-gel route for preparation of active GRadient-INdex materials is proposed. • SiO 2 -TiO 2 films doped with erbium were prepared by dipping onto commercial glasses. • Morphological and optical characterization of the samples was performed. • Optical constants and porosity were found to vary with erbium concentration. • Refractive index diminishes with dopant content; the contrary occurs for porosity

Monthly and seasonal variations of aerosol optical properties and direct radiative forcing over Zanjan, Iran

Science.gov (United States)

Gharibzadeh, Maryam; Alam, Khan; Abedini, Yousefali; Bidokhti, Abbasali Aliakbari; Masoumi, Amir

2017-11-01

Aerosol optical properties and radiative forcing over Zanjan in northwest of Iran has been analyzed during 2010-2013. The aerosol optical and radiative properties are less studied over Zanjan, and therefore, require a careful and in depth analysis. The optical properties like Aerosol Optical Depth (AOD), Ångström Exponent (AE), ASYmmetry parameter (ASY), Single Scattering Albedo (SSA), and Aerosol Volume Size Distribution (AVSD) have been evaluated using the ground-based AErosol RObotic NETwork (AERONET) data. Higher AOD while relatively lower AE were observed in the spring and summer, which showed the presence of coarse mode particles in these seasons. An obvious increase of coarse mode particles in AVSD distribution, as well as a higher value of SSA represented considerable addition of coarse mode particles like dust into the atmosphere of Zanjan in these two seasons. Increase in AE, while a decrease in AOD was detected in the winter and fall. The presence of fine particles indicates the dominance of particles like urban-industrial aerosols from local sources especially in the winter. The Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model was utilized to calculate the Aerosol Radiative Forcing (ARF) at the Top of the Atmosphere (TOA), earth's surface and within the atmosphere. The annual averaged ARF values were -13.47 W m-2 and -36.1 W m-2 at the TOA and earth's surface, respectively, which indicate a significant cooling effect. Likewise, the ARF efficiencies at the TOA and earth's surface were -65.08 W m-2 and -158.43 W m-2, respectively. The annual mean atmospheric ARF and heating rate within the atmosphere were 22.63 W m-2 and 0.27 Kday-1 respectively, represented the warming effect within the atmosphere. Finally, a good agreement was found between AERONET retrieved ARF and SBDART simulated ARF.

Effects of acoustic radiation force and shear waves for absorption and stiffness sensing in ultrasound modulated optical tomography.

Science.gov (United States)

Li, Rui; Elson, Daniel S; Dunsby, Chris; Eckersley, Robert; Tang, Meng-Xing

2011-04-11

Ultrasound-modulated optical tomography (UOT) combines optical contrast with ultrasound spatial resolution and has great potential for soft tissue functional imaging. One current problem with this technique is the weak optical modulation signal, primarily due to strong optical scattering in diffuse media and minimal acoustically induced modulation. The acoustic radiation force (ARF) can create large particle displacements in tissue and has been shown to be able to improve optical modulation signals. However, shear wave propagation induced by the ARF can be a significant source of nonlocal optical modulation which may reduce UOT spatial resolution and contrast. In this paper, the time evolution of shear waves was examined on tissue mimicking-phantoms exposed to 5 MHz ultrasound and 532 nm optical radiation and measured with a CCD camera. It has been demonstrated that by generating an ARF with an acoustic burst and adjusting both the timing and the exposure time of the CCD measurement, optical contrast and spatial resolution can be improved by ~110% and ~40% respectively when using the ARF rather than 5 MHz ultrasound alone. Furthermore, it has been demonstrated that this technique simultaneously detects both optical and mechanical contrast in the medium and the optical and mechanical contrast can be distinguished by adjusting the CCD exposure time. © 2011 Optical Society of America

Near-field multiple traps of paraxial acoustic vortices with strengthened gradient force generated by sector transducer array

Science.gov (United States)

Wang, Qingdong; Li, Yuzhi; Ma, Qingyu; Guo, Gepu; Tu, Juan; Zhang, Dong

2018-01-01

In order to improve the capability of particle trapping close to the source plane, theoretical and experimental studies on near-field multiple traps of paraxial acoustic vortices (AVs) with a strengthened acoustic gradient force (AGF) generated by a sector transducer array were conducted. By applying the integration of point source radiation, numerical simulations for the acoustic fields generated by the sector transducer array were conducted and compared with those produced by the circular transducer array. It was proved that strengthened AGFs of near-field multiple AVs with higher peak pressures and smaller vortex radii could be produced by the sector transducer array with a small topological charge. The axial distributions of the equivalent potential gradient indicated that the AGFs of paraxial AVs in the near field were much higher than those in the far field, and the distances at the near-field vortex antinodes were also proved to be the ideal trapping positions with relatively higher AGFs. With the established 8-channel AV generation system, theoretical studies were also verified by the experimental measurements of pressure and phase for AVs with various topological charges. The formation of near-field multiple paraxial AVs was verified by the cross-sectional circular pressure distributions with perfect phase spirals around central pressure nulls, and was also proved by the vortex nodes and antinodes along the center axis. The favorable results demonstrated the feasibility of generating near-field multiple traps of paraxial AVs with strengthened AGF using the sector transducer array, and suggested the potential applications of close-range particle trapping in biomedical engineering.

Activation of lysosomal P2X4 by ATP transported into lysosomes via VNUT/SLC17A9 using V‐ATPase generated voltage gradient as the driving force

Science.gov (United States)

Zhong, Xi Zoë; Cao, Qi; Sun, Xue

2016-01-01

Key points SLC17A9 proteins function as a lysosomal ATP transporter responsible for lysosomal ATP accumulation.P2X4 receptors act as lysosomal ion channels activated by luminal ATP.SLC17A9‐mediated ATP transport across the lysosomal membrane is suppressed by Bafilomycin A1, the V‐ATPase inhibitor.SLC17A9 mainly uses voltage gradient but not pH gradient generated by the V‐ATPase as the driving force to transport ATP into the lysosome to activate P2X4. Abstract The lysosome contains abundant ATP which plays important roles in lysosome functions and in cell signalling. Recently, solute carrier family 17 member 9 (SLC17A9, also known as VNUT for vesicular nucleotide transporter) proteins were suggested to function as a lysosomal ATP transporter responsible for lysosomal ATP accumulation, and P2X4 receptors were suggested to be lysosomal ion channels that are activated by luminal ATP. However, the molecular mechanism of SLC17A9 transporting ATP and the regulatory mechanism of lysosomal P2X4 are largely unknown. In this study, we report that SLC17A9‐mediated ATP transport across lysosomal membranes is suppressed by Bafilomycin A1, the V‐ATPase inhibitor. By measuring P2X4 activity, which is indicative of ATP transport across lysosomal membranes, we further demonstrated that SLC17A9 mainly uses voltage gradient but not pH gradient as the driving force to transport ATP into lysosomes. This study provides a molecular mechanism for lysosomal ATP transport mediated by SLC17A9. It also suggests a regulatory mechanism of lysosomal P2X4 by SLC17A9. PMID:27477609

Force Measurement with a Piezoelectric Cantilever in a Scanning Force Microscope

OpenAIRE

Tansock, J.; Williams, C. C.

1992-01-01

Detection of surface forces between a tip and sample has been demonstrated with a piezoelectric cantilever in a scanning force microscope (SFM). The use of piezoelectric force sensing is particularly advantageous in semiconductor applications where stray light from conventional optical force-sensing methods can significantly modify the local carrier density. Additionally, the piezoelectric sensors are simple, provide good sensitivity to force, and can be batch fabricated. Our piezoelectric fo...

Simulation of co-phase error correction of optical multi-aperture imaging system based on stochastic parallel gradient decent algorithm

Science.gov (United States)

He, Xiaojun; Ma, Haotong; Luo, Chuanxin

2016-10-01

The optical multi-aperture imaging system is an effective way to magnify the aperture and increase the resolution of telescope optical system, the difficulty of which lies in detecting and correcting of co-phase error. This paper presents a method based on stochastic parallel gradient decent algorithm (SPGD) to correct the co-phase error. Compared with the current method, SPGD method can avoid detecting the co-phase error. This paper analyzed the influence of piston error and tilt error on image quality based on double-aperture imaging system, introduced the basic principle of SPGD algorithm, and discuss the influence of SPGD algorithm's key parameters (the gain coefficient and the disturbance amplitude) on error control performance. The results show that SPGD can efficiently correct the co-phase error. The convergence speed of the SPGD algorithm is improved with the increase of gain coefficient and disturbance amplitude, but the stability of the algorithm reduced. The adaptive gain coefficient can solve this problem appropriately. This paper's results can provide the theoretical reference for the co-phase error correction of the multi-aperture imaging system.

Dynamic properties of polydisperse colloidal particles in the presence of thermal gradient studied by a modified Brownian dynamic model

Science.gov (United States)

Song, Dongxing; Jin, Hui; Jing, Dengwei; Wang, Xin

2018-03-01

Aggregation and migration of colloidal particles under the thermal gradient widely exists in nature and many industrial processes. In this study, dynamic properties of polydisperse colloidal particles in the presence of thermal gradient were studied by a modified Brownian dynamic model. Other than the traditional forces on colloidal particles, including Brownian force, hydrodynamic force, and electrostatic force from other particles, the electrostatic force from the asymmetric ionic diffusion layer under a thermal gradient has been considered and introduced into the Brownian dynamic model. The aggregation ratio of particles (R A), the balance time (t B) indicating the time threshold when {{R}A} becomes constant, the porosity ({{P}BA} ), fractal dimension (D f) and distributions of concentration (DISC) and aggregation (DISA) for the aggregated particles were discussed based on this model. The aggregated structures formed by polydisperse particles are less dense and the particles therein are loosely bonded. Also it showed a quite large compressibility as the increases of concentration and interparticle potential can significantly increase the fractal dimension. The thermal gradient can induce two competitive factors leading to a two-stage migration of particles. When t{{t}B} , the thermophoresis becomes dominant thus the migrations of particles are against the thermal gradient. The effect of thermophoresis on the aggregate structures was found to be similar to the effect of increasing particle concentration. This study demonstrates how the thermal gradient affects the aggregation of monodisperse and polydisperse particles and can be a guide for the biomimetics and precise control of colloid system under the thermal gradient. Moreover, our model can be easily extended to other more complex colloidal systems considering shear, temperature fluctuation, surfactant, etc.

Acoustic force mapping in a hybrid acoustic-optical micromanipulation device supporting high resolution optical imaging† †Electronic supplementary information (ESI) available: Additional information about 1D model calculations for a piezoelectric transducer. See DOI: 10.1039/c6lc00182c Click here for additional data file.

Science.gov (United States)

McDougall, Craig; MacDonald, Michael Peter; Ritsch-Marte, Monika

2016-01-01

Many applications in the life-sciences demand non-contact manipulation tools for forceful but nevertheless delicate handling of various types of sample. Moreover, the system should support high-resolution optical imaging. Here we present a hybrid acoustic/optical manipulation system which utilizes a transparent transducer, making it compatible with high-NA imaging in a microfluidic environment. The powerful acoustic trapping within a layered resonator, which is suitable for highly parallel particle handling, is complemented by the flexibility and selectivity of holographic optical tweezers, with the specimens being under high quality optical monitoring at all times. The dual acoustic/optical nature of the system lends itself to optically measure the exact acoustic force map, by means of direct force measurements on an optically trapped particle. For applications with (ultra-)high demand on the precision of the force measurements, the position of the objective used for the high-NA imaging may have significant influence on the acoustic force map in the probe chamber. We have characterized this influence experimentally and the findings were confirmed by model simulations. We show that it is possible to design the chamber and to choose the operating point in such a way as to avoid perturbations due to the objective lens. Moreover, we found that measuring the electrical impedance of the transducer provides an easy indicator for the acoustic resonances. PMID:27025398

Optical Forces Near Microfabricated Devices

Science.gov (United States)

2013-08-01

gravitational, buoyant, brownian , electrostatic and those forces that develop from the interaction 4 15 between an external electromagnetic field and a...average Brownian force can be shown to be ∼ 1× 10−4 pN. For this system the Reynolds number is ∼ 1 × 10−7. At a low Reynolds number, the inertia plays no...modulator or any movement of the beam or sample, it can be easily adapted for a variety of integrated, lab-on-a-chip applications. Finally, by tuning

A substrate independent approach for generation of surface gradients

Energy Technology Data Exchange (ETDEWEB)

Goreham, Renee V. [Mawson Institute, University of South Australia, Mawson Lakes 5095 (Australia); Mierczynska, Agnieszka; Pierce, Madelene [Ian Wark Research Institute, University of South Australia, Mawson Lakes 5095 (Australia); Short, Robert D.; Taheri, Shima; Bachhuka, Akash; Cavallaro, Alex; Smith, Louise E. [Mawson Institute, University of South Australia, Mawson Lakes 5095 (Australia); Vasilev, Krasimir, E-mail: krasimir.vasilev@unisa.edu.au [Mawson Institute, University of South Australia, Mawson Lakes 5095 (Australia)

2013-01-01

Recently, surface gradients have attracted significant interest for various research and technological applications. In this paper, we report a facile and versatile method for generating surface gradients of immobilized nanoparticles, nanotopography and ligands that is independent from the substrate material. The method consists of first depositing a functional polymer layer on a substrate and subsequent time controlled immersion of this functionalized substrate in solution gold nanoparticles (AuNPs), silver nanoparticles (AgNPs) or poly (styrenesulfonate) (PSS). Chemical characterization by X-ray Photoelectron Spectroscopy (XPS) and morphological analysis by Atomic Force Microscopy (AFM) show that the density of nanoparticles and the concentration of PSS across the surface increases in a gradient manner. As expected, time of immersion determines the concentration of surface bound species. We also demonstrate the generation of surface gradients of pure nanotopography. This is achieved by depositing a 5 nm thick plasma polymer layer on top of the number density gradient of nanoparticles to achieve a homogeneous surface chemistry. The surface independent approach for generation of surface gradients presented in this paper may open opportunities for a wider use of surface gradient in research and in various technologies. - Highlights: ► We present a substrate independent approach for generation of surface gradients. ► We demonstrate well-defined density gradients of gold and silver nanoparticles. ► We provide an example of pure surface nanotopography gradients. ► We demonstrate concentration gradients of bound ligands.

A substrate independent approach for generation of surface gradients

International Nuclear Information System (INIS)

Goreham, Renee V.; Mierczynska, Agnieszka; Pierce, Madelene; Short, Robert D.; Taheri, Shima; Bachhuka, Akash; Cavallaro, Alex; Smith, Louise E.; Vasilev, Krasimir

2013-01-01

Recently, surface gradients have attracted significant interest for various research and technological applications. In this paper, we report a facile and versatile method for generating surface gradients of immobilized nanoparticles, nanotopography and ligands that is independent from the substrate material. The method consists of first depositing a functional polymer layer on a substrate and subsequent time controlled immersion of this functionalized substrate in solution gold nanoparticles (AuNPs), silver nanoparticles (AgNPs) or poly (styrenesulfonate) (PSS). Chemical characterization by X-ray Photoelectron Spectroscopy (XPS) and morphological analysis by Atomic Force Microscopy (AFM) show that the density of nanoparticles and the concentration of PSS across the surface increases in a gradient manner. As expected, time of immersion determines the concentration of surface bound species. We also demonstrate the generation of surface gradients of pure nanotopography. This is achieved by depositing a 5 nm thick plasma polymer layer on top of the number density gradient of nanoparticles to achieve a homogeneous surface chemistry. The surface independent approach for generation of surface gradients presented in this paper may open opportunities for a wider use of surface gradient in research and in various technologies. - Highlights: ► We present a substrate independent approach for generation of surface gradients. ► We demonstrate well-defined density gradients of gold and silver nanoparticles. ► We provide an example of pure surface nanotopography gradients. ► We demonstrate concentration gradients of bound ligands

Global direct radiative forcing by process-parameterized aerosol optical properties

Science.gov (United States)

KirkevâG, Alf; Iversen, Trond

2002-10-01

A parameterization of aerosol optical parameters is developed and implemented in an extended version of the community climate model version 3.2 (CCM3) of the U.S. National Center for Atmospheric Research. Direct radiative forcing (DRF) by monthly averaged calculated concentrations of non-sea-salt sulfate and black carbon (BC) is estimated. Inputs are production-specific BC and sulfate from [2002] and background aerosol size distribution and composition. The scheme interpolates between tabulated values to obtain the aerosol single scattering albedo, asymmetry factor, extinction coefficient, and specific extinction coefficient. The tables are constructed by full calculations of optical properties for an array of aerosol input values, for which size-distributed aerosol properties are estimated from theory for condensation and Brownian coagulation, assumed distribution of cloud-droplet residuals from aqueous phase oxidation, and prescribed properties of the background aerosols. Humidity swelling is estimated from the Köhler equation, and Mie calculations finally yield spectrally resolved aerosol optical parameters for 13 solar bands. The scheme is shown to give excellent agreement with nonparameterized DRF calculations for a wide range of situations. Using IPCC emission scenarios for the years 2000 and 2100, calculations with an atmospheric global cliamte model (AFCM) yield a global net anthropogenic DRF of -0.11 and 0.11 W m-2, respectively, when 90% of BC from biomass burning is assumed anthropogenic. In the 2000 scenario, the individual DRF due to sulfate and BC has separately been estimated to -0.29 and 0.19 W m-2, respectively. Our estimates of DRF by BC per BC mass burden are lower than earlier published estimates. Some sensitivity tests are included to investigate to what extent uncertain assumptions may influence these results.

An Optimization-Based Impedance Approach for Robot Force Regulation with Prescribed Force Limits

Directory of Open Access Journals (Sweden)

R. de J. Portillo-Vélez

2015-01-01

Full Text Available An optimization based approach for the regulation of excessive or insufficient forces at the end-effector level is introduced. The objective is to minimize the interaction force error at the robot end effector, while constraining undesired interaction forces. To that end, a dynamic optimization problem (DOP is formulated considering a dynamic robot impedance model. Penalty functions are considered in the DOP to handle the constraints on the interaction force. The optimization problem is online solved through the gradient flow approach. Convergence properties are presented and the stability is drawn when the force limits are considered in the analysis. The effectiveness of our proposal is validated via experimental results for a robotic grasping task.

Density gradients in ceramic pellets measured by computed tomography

International Nuclear Information System (INIS)

Sawicka, B.D.; Palmer, B.J.F.

1986-07-01

Density gradients are of fundamental importance in ceramic processing and computed tomography (CT) can provide accurate measurements of density profiles in sintered and unsintered ceramic parts. As a demonstration of this potential, the density gradients in an unsintered pellet pressed from an alumina powder were measured by CT scanning. To detect such small density gradients, the CT images must have good density resolution and be free from beam-hardening effects. This was achieved by measuring high-contrast (low-noise) images with the use of an Ir-192 isotopic source. A beam-hardening correction was applied. The resulting images are discussed relative to the transmission of forces through the powder mass during the pelletizing process

MEMS Bragg grating force sensor

DEFF Research Database (Denmark)

Reck, Kasper; Thomsen, Erik Vilain; Hansen, Ole

2011-01-01

We present modeling, design, fabrication and characterization of a new type of all-optical frequency modulated MEMS force sensor based on a mechanically amplified double clamped waveguide beam structure with integrated Bragg grating. The sensor is ideally suited for force measurements in harsh...... environments and for remote and distributed sensing and has a measured sensitivity of -14 nm/N, which is several times higher than what is obtained in conventional fiber Bragg grating force sensors. © 2011 Optical Society of America....

Fano resonances from gradient-index metamaterials.

Science.gov (United States)

Xu, Yadong; Li, Sucheng; Hou, Bo; Chen, Huanyang

2016-01-27

Fano resonances - resonant scattering features with a characteristic asymmetric profile - have generated much interest, due to their extensive and valuable applications in chemical or biological sensors, new types of optical switches, lasers and nonlinear optics. They have been observed in a wide variety of resonant optical systems, including photonic crystals, metamaterials, metallic gratings and nanostructures. In this work, a waveguide structure is designed by employing gradient-index metamaterials, supporting strong Fano resonances with extremely sharp spectra. As the changes in the transmission spectrum originate from the interaction of guided modes from different channels, instead of resonance structures or metamolecules, the Fano resonances can be observed for both transverse electric and transverse magnetic polarizations. These findings are verified by fine agreement with analytical calculations and experimental results at microwave, as well as simulated results at near infrared frequencies.

Research on a wavefront aberration calculation method for a laser energy gradient attenuator

International Nuclear Information System (INIS)

Dong, Tingting; Han, Xu; Chen, Chi; Fu, Yuegang; Li, Ming

2013-01-01

When a laser energy gradient attenuator is working, there is an inhomogeneous temperature distribution in the whole of the glass because of the non-uniform light energy absorption. This will lead to optical performance reduction. An integrated opto-thermal–mechanical method is proposed to calculate the wavefront aberration for analysis of the thermal effect of the system. Non-sequential optical analysis is used for computing the absorbed energy distribution. The finite element analysis program solves the temperature distribution and the deformations of nodes on the surfaces. An interface routine is created to fit the surface shape and the index field, and extended Zernike polynomials are introduced to get a higher fitting precision. Finally, the parameters are imported to the CodeV optical design program automatically, and the user defined gradient index material is ray traced to obtain the wavefront aberration. The method can also be used in other optical systems for thermal effect analysis. (letter)

Effect of diffraction and film-thickness gradients on wafer-curvature measurements of thin-film stress

International Nuclear Information System (INIS)

Breiland, W.G.; Lee, S.R.; Koleske, D.D.

2004-01-01

When optical measurements of wafer curvature are used to determine thin-film stress, the laser beams that probe the sample are usually assumed to reflect specularly from the curved surface of the film and substrate. Yet, real films are not uniformly thick, and unintended thickness gradients produce optical diffraction effects that steer the laser away from the ideal specular condition. As a result, the deflection of the laser in wafer-curvature measurements is actually sensitive to both the film stress and the film-thickness gradient. We present a Fresnel-Kirchhoff optical diffraction model of wafer-curvature measurements that provides a unified description of these combined effects. The model accurately simulates real-time wafer-curvature measurements of nonuniform GaN films grown on sapphire substrates by vapor-phase epitaxy. During thin-film growth, thickness gradients cause the reflected beam to oscillate asymmetrically about the ideal position defined by the stress-induced wafer curvature. This oscillating deflection has the same periodicity as the reflectance of the growing film, and the deflection amplitude is a function of the film-thickness gradient, the mean film thickness, the wavelength distribution of the light source, the illuminated spot size, and the refractive indices of the film and substrate. For typical GaN films grown on sapphire, misinterpretation of these gradient-induced oscillations can cause stress-measurement errors that approach 10% of the stress-thickness product; much greater errors occur in highly nonuniform films. Only transparent films can exhibit substantial gradient-induced deflections; strongly absorbing films are immune

Moderate Imaging Resolution Spectroradiometer (MODIS) Aerosol Optical Depth Retrieval for Aerosol Radiative Forcing

Science.gov (United States)

Asmat, A.; Jalal, K. A.; Ahmad, N.

2018-02-01

The present study uses the Aerosol Optical Depth (AOD) retrieved from Moderate Imaging Resolution Spectroradiometer (MODIS) data for the period from January 2011 until December 2015 over an urban area in Kuching, Sarawak. The results show the minimum AOD value retrieved from MODIS is -0.06 and the maximum value is 6.0. High aerosol loading with high AOD value observed during dry seasons and low AOD monitored during wet seasons. Multi plane regression technique used to retrieve AOD from MODIS (AODMODIS) and different statistics parameter is proposed by using relative absolute error for accuracy assessment in spatial and temporal averaging approach. The AODMODIS then compared with AOD derived from Aerosol Robotic Network (AERONET) Sunphotometer (AODAERONET) and the results shows high correlation coefficient (R2) for AODMODIS and AODAERONET with 0.93. AODMODIS used as an input parameters into Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model to estimate urban radiative forcing at Kuching. The observed hourly averaged for urban radiative forcing is -0.12 Wm-2 for top of atmosphere (TOA), -2.13 Wm-2 at the surface and 2.00 Wm-2 in the atmosphere. There is a moderate relationship observed between urban radiative forcing calculated using SBDART and AERONET which are 0.75 at the surface, 0.65 at TOA and 0.56 in atmosphere. Overall, variation in AOD tends to cause large bias in the estimated urban radiative forcing.

A hybrid scanning force and light microscope for surface imaging and three-dimensional optical sectioning in differential interference contrast.

Science.gov (United States)

Stemmer, A

1995-04-01

The design of a scanned-cantilever-type force microscope is presented which is fully integrated into an inverted high-resolution video-enhanced light microscope. This set-up allows us to acquire thin optical sections in differential interference contrast (DIC) or polarization while the force microscope is in place. Such a hybrid microscope provides a unique platform to study how cell surface properties determine, or are affected by, the three-dimensional dynamic organization inside the living cell. The hybrid microscope presented in this paper has proven reliable and versatile for biological applications. It is the only instrument that can image a specimen by force microscopy and high-power DIC without having either to translate the specimen or to remove the force microscope. Adaptation of the design features could greatly enhance the suitability of other force microscopes for biological work.

Modulation of monocytic leukemia cell function and survival by high gradient magnetic fields and mathematical modeling studies.

Science.gov (United States)

Zablotskii, Vitalii; Syrovets, Tatiana; Schmidt, Zoe W; Dejneka, Alexandr; Simmet, Thomas

2014-03-01

The influence of spatially modulated high gradient magnetic fields on cellular functions of human THP-1 leukemia cells is studied. We demonstrate that arrays of high-gradient micrometer-sized magnets induce i) cell swelling, ii) prolonged increased ROS production, and iii) inhibit cell proliferation, and iv) elicit apoptosis of THP-1 monocytic leukemia cells in the absence of chemical or biological agents. Mathematical modeling indicates that mechanical stress exerted on the cells by high magnetic gradient forces is responsible for triggering cell swelling and formation of reactive oxygen species followed by apoptosis. We discuss physical aspects of controlling cell functions by focused magnetic gradient forces, i.e. by a noninvasive and nondestructive physical approach. Copyright © 2014 Elsevier Ltd. All rights reserved.

Light Ray Displacements due to Air Temperature Gradient

CERN Document Server

Teymurazyan, A; CERN. Geneva

2000-01-01

Abstract In the optical monitoring systems suggested to control the geometry of tracking spectrometers, light beams serve as reference frames for the measurement of the tracking chamber displacements and deformations. It is shown that air temperature gradients can induce systematic errors which considerably exceed the intrinsic resolution of the monitoring system.

Fresnel formulas for the forced electromagnetic pulses and their application for optical-to-terahertz conversion in nonlinear crystals.

Science.gov (United States)

Bakunov, M I; Maslov, A V; Bodrov, S B

2007-11-16

We show that the usual Fresnel formulas for a free-propagating pulse are not applicable for a forced terahertz electromagnetic pulse supported by an optical pulse at the end of a nonlinear crystal. The correct linear reflection and transmission coefficients that we derive show that such pulses can experience a gain or loss at the boundary. This energy change depends on linear dielectric constants only. We also predict a regime where a complete disappearance of the forced pulse under oblique incidence occurs, an effect that has no counterpart for free-propagating pulses.

Assessment of aerosols optical properties and radiative forcing over an Urban site in North-Western India.

Science.gov (United States)

Mor, Vikram; Dhankhar, Rajesh; Attri, S D; Soni, V K; Sateesh, M; Taneja, Kanika

2017-05-01

The present work is aimed to analyze aerosols optical properties and to estimate aerosol radiative forcing (ARF) from January to December 2013, using sky radiometer data over Rohtak, an urban site in North-Western India. The results reveal strong wavelength dependency of aerosol optical depth (AOD), with high values of AOD at shorter wavelengths and lower values at longer wavelength during the study period. The highest AOD values of 1.07 ± 0.45 at 500 nm were observed during July. A significant decline in Ångström exponent was observed during April-May, which represents the dominance of coarse mode particles due to dust-raising convective activities. Aerosols' size distribution exhibits a bimodal structure with fine mode particles around 0.17 µm and coarse mode particles with a radius around 5.28 µm. Single scattering albedo values were lowest during November-December at all wavelengths, ranging from 0.87 to 0.76, which corresponds to the higher absorption during this period. Aerosols optical properties retrieved during observation period are used as input for SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) to estimate the direct ARF at the surface, in the atmosphere and at the top of the atmosphere (TOA). The ARF at the TOA, surface and in the atmosphere are found to be in the range of -4.98 to -19.35 W m -2 , -8.01 to -57.66 W m -2 and +3.02 to +41.64 W m -2 , respectively. The averaged forcing for the whole period of observations at the TOA is -11.26 W m -2 , while at the surface it is -38.64 W m -2 , leading to atmospheric forcing of 27.38 W m -2 . The highest (1.168 K day -1 ) values of heating rate was estimated during November, whereas the lowest value (0.084 K day -1 ) was estimated for the February.

Local smoothness for global optical flow

DEFF Research Database (Denmark)

Rakêt, Lars Lau

2012-01-01

by this technique and work on local-global optical flow we propose a simple method for fusing optical flow estimates of different smoothness by evaluating interpolation quality locally by means of L1 block match on the corresponding set of gradient images. We illustrate the method in a setting where optical flows...

Temporal variation of aerosol optical depth and associated shortwave radiative forcing over a coastal site along the west coast of India.

Science.gov (United States)

Menon, Harilal B; Shirodkar, Shilpa; Kedia, Sumita; S, Ramachandran; Babu, Suresh; Moorthy, K Krishna

2014-01-15

Optical characterization of aerosol was performed by assessing the columnar aerosol optical depth (AOD) and angstrom wavelength exponent (α) using data from the Microtops II Sunphotometer. The data were collected on cloud free days over Goa, a coastal site along the west coast of India, from January to December 2008. Along with the composite aerosol, the black carbon (BC) mass concentration from the Aethalometer was also analyzed. The AOD0.500 μm and angstrom wavelength exponent (α) were in the range of 0.26 to 0.7 and 0.52 to 1.33, respectively, indicative of a significant seasonal shift in aerosol characteristics during the study period. The monthly mean AOD0.500 μm exhibited a bi-modal distribution, with a primary peak in April (0.7) and a secondary peak in October (0.54), whereas the minimum of 0.26 was observed in May. The monthly mean BC mass concentration varied between 0.31 μg/m(3) and 4.5 μg/m(3), and the single scattering albedo (SSA), estimated using the OPAC model, ranged from 0.87 to 0.97. Modeled aerosol optical properties were used to estimate the direct aerosol shortwave radiative forcing (DASRF) in the wavelength range 0.25 μm4.0 μm. The monthly mean forcing at the surface, at the top of the atmosphere (TOA) and in the atmosphere varied between -14.1 Wm(-2) and -35.6 Wm(-2), -6.7 Wm(-2) and -13.4 Wm(-2) and 5.5 Wm(-2) to 22.5 Wm(-2), respectively. These results indicate that the annual SSA cycle in the atmosphere is regulated by BC (absorbing aerosol), resulting in a positive forcing; however, the surface forcing was governed by the natural aerosol scattering, which yielded a negative forcing. These two conditions neutralized, resulting in a negative forcing at the TOA that remains nearly constant throughout the year. © 2013.

Comparative Studies of High-Gradient Rf and Dc Breakdowns

CERN Document Server

Kovermann, Jan Wilhelm; Wuensch, Walter

2010-01-01

The CLIC project is based on normal-conducting high-gradient accelerating structures with an average accelerating gradient of 100 MV/m. The maximum achievable gradient in these structures is limited by the breakdown phenomenon. The physics of breakdowns is not yet fully understood quantitatively. A full knowledge could have strong impact on the design, material choice and construction of rf structures. Therefore, understanding breakdowns has great importance to reaching a gradient of 100MV/m with an acceptable breakdown probability. This thesis addresses the physics underlying the breakdown effect, focusing on a comparison of breakdowns in rf structures and in a dc spark setup. The dc system is simpler, easier to benchmark against simulations, with a faster turnaround time, but the relationship to rf breakdown must be established. To do so, an experimental approach based on optical diagnostics and electrical measurements methods was made. Following an introduction into the CLIC project, a general theoretical ...

Implementing the conjugate gradient algorithm on multi-core systems

NARCIS (Netherlands)

Wiggers, W.A.; Bakker, Vincent; Kokkeler, Andre B.J.; Smit, Gerardus Johannes Maria; Nurmi, J.; Takala, J.; Vainio, O.

2007-01-01

In linear solvers, like the conjugate gradient algorithm, sparse-matrix vector multiplication is an important kernel. Due to the sparseness of the matrices, the solver runs relatively slow. For digital optical tomography (DOT), a large set of linear equations have to be solved which currently takes

COLORS AND COLOR GRADIENTS IN BULGES OF GALAXIES

NARCIS (Netherlands)

BALCELLS, M; PELETIER, RF

We have obtained surface photometry in U, B, R, and I for a complete optically selected sample of 45 early-type spiral galaxies, to investigate the colors and color gradients of spiral bulges. Color profiles in U-R, B-R, U-B, and R-I have been determined in wedges opening on the semiminor axes.

System for optical sorting of microscopic objects

DEFF Research Database (Denmark)

2014-01-01

The present invention relates to a system for optical sorting of microscopic objects and corresponding method. An optical detection system (52) is capable of determining the positions of said first and/or said second objects. One or more force transfer units (200, 205, 210, 215) are placed...... in a first reservoir, the one or more force units being suitable for optical momentum transfer. An electromagnetic radiation source (42) yields a radiation beam (31, 32) capable of optically displacing the force transfer units from one position to another within the first reservoir (1R). The force transfer...... units are displaced from positions away from the first objects to positions close to the first objects, and then displacing the first objects via a contact force (300) between the first objects and the force transfer units facilitates an optical sorting of the first objects and the second objects....

Self-similar solutions for multi-species plasma mixing by gradient driven transport

Science.gov (United States)

Vold, E.; Kagan, G.; Simakov, A. N.; Molvig, K.; Yin, L.

2018-05-01

Multi-species transport of plasma ions across an initial interface between DT and CH is shown to exhibit self-similar species density profiles under 1D isobaric conditions. Results using transport theory from recent studies and using a Maxwell–Stephan multi-species approximation are found to be in good agreement for the self-similar mix profiles of the four ions under isothermal and isobaric conditions. The individual ion species mass flux and molar flux profile results through the mixing layer are examined using transport theory. The sum over species mass flux is confirmed to be zero as required, and the sum over species molar flux is related to a local velocity divergence needed to maintain pressure equilibrium during the transport process. The light ion species mass fluxes are dominated by the diagonal coefficients of the diffusion transport matrix, while for the heaviest ion species (C in this case), the ion flux with only the diagonal term is reduced by about a factor two from that using the full diffusion matrix, implying the heavy species moves more by frictional collisions with the lighter species than by its own gradient force. Temperature gradient forces were examined by comparing profile results with and without imposing constant temperature gradients chosen to be of realistic magnitude for ICF experimental conditions at a fuel-capsule interface (10 μm scale length or greater). The temperature gradients clearly modify the relative concentrations of the ions, for example near the fuel center, however the mixing across the fuel-capsule interface appears to be minimally influenced by the temperature gradient forces within the expected compression and burn time. Discussion considers the application of the self-similar profiles to specific conditions in ICF.

Optical pulling of airborne absorbing particles and smut spores over a meter-scale distance with negative photophoretic force

Energy Technology Data Exchange (ETDEWEB)

Lin, Jinda; Hart, Adam G.; Li, Yong-qing, E-mail: liy@ecu.edu [Department of Physics, East Carolina University, Greenville, North Carolina 27858-4353 (United States)

2015-04-27

We demonstrate optical pulling of single light-absorbing particles and smut spores in air over a meter-scale distance using a single collimated laser beam based on negative photophoretic force. The micron-sized particles are pulled towards the light source at a constant speed of 1–10 cm/s in the optical pulling pipeline while undergoing transverse rotation at 0.2–10 kHz. The pulled particles can be manipulated and precisely positioned on the entrance window with an accuracy of ∼20 μm, and their chemical compositions can be characterized with micro-Raman spectroscopy.

From conventional sensors to fibre optic sensors for strain and force measurements in biomechanics applications: a review.

Science.gov (United States)

Roriz, Paulo; Carvalho, Lídia; Frazão, Orlando; Santos, José Luís; Simões, José António

2014-04-11

In vivo measurement, not only in animals but also in humans, is a demanding task and is the ultimate goal in experimental biomechanics. For that purpose, measurements in vivo must be performed, under physiological conditions, to obtain a database and contribute for the development of analytical models, used to describe human biomechanics. The knowledge and control of the mechanisms involved in biomechanics will allow the optimization of the performance in different topics like in clinical procedures and rehabilitation, medical devices and sports, among others. Strain gages were first applied to bone in a live animal in 40's and in 80's for the first time were applied fibre optic sensors to perform in vivo measurements of Achilles tendon forces in man. Fibre optic sensors proven to have advantages compare to conventional sensors and a great potential for biomechanical and biomedical applications. Compared to them, they are smaller, easier to implement, minimally invasive, with lower risk of infection, highly accurate, well correlated, inexpensive and multiplexable. The aim of this review article is to give an overview about the evolution of the experimental techniques applied in biomechanics, from conventional to fibre optic sensors. In the next sections the most relevant contributions of these sensors, for strain and force in biomechanical applications, will be presented. Emphasis was given to report of in vivo experiments and clinical applications. Copyright © 2014 Elsevier Ltd. All rights reserved.

Photon storage in ¿-type optically dense atomic media. IV. Optimal control using gradient ascent

DEFF Research Database (Denmark)

Gorshkov, Alexey V.; Calarco, Tomasso; Lukin, Mikhail D.

2008-01-01

We use the numerical gradient ascent method from optimal control theory to extend efficient photon storage in -type media to previouslyinaccessible regimes and to provide simple intuitive explanations for our optimization techniques. In particular, by using gradient ascent to shape classical....... We also demonstrate that the often discussed connection between time reversal andoptimality in photon storage follows naturally from gradient ascent. Finally, we discuss the optimization of controlled reversible inhomogeneous broadening....

Atomic force microscopy deep trench and sidewall imaging with an optical fiber probe

Energy Technology Data Exchange (ETDEWEB)

Xie, Hui, E-mail: xiehui@hit.edu.cn; Hussain, Danish; Yang, Feng [The State Key Laboratory of Robotics and Systems, Harbin Institute of Technology, 2 Yikuang, 150080 Harbin (China); Sun, Lining [The State Key Laboratory of Robotics and Systems, Harbin Institute of Technology, 2 Yikuang, 150080 Harbin (China); Robotics and Microsystems Center, Soochow University, 215021 Suzhou (China)

2014-12-15

We report a method to measure critical dimensions of micro- and nanostructures using the atomic force microscope (AFM) with an optical fiber probe (OFP). This method is capable of scanning narrow and deep trenches due to the long and thin OFP tip, as well as imaging of steep sidewalls with unique profiling possibilities by laterally tilting the OFP without any modifications of the optical lever. A switch control scheme is developed to measure the sidewall angle by flexibly transferring feedback control between the Z- and Y-axis, for a serial scan of the horizontal surface (raster scan on XY-plane) and sidewall (raster scan on the YZ-plane), respectively. In experiments, a deep trench with tapered walls (243.5 μm deep) and a microhole (about 14.9 μm deep) have been imaged with the orthogonally aligned OFP, as well as a silicon sidewall (fabricated by deep reactive ion etching) has been characterized with the tilted OFP. Moreover, the sidewall angle of TGZ3 (AFM calibration grating) was accurately measured using the switchable scan method.

Atomic force and optical near-field microscopic investigations of polarization holographic gratings in a liquid crystalline azobenzene side-chain polyester

DEFF Research Database (Denmark)

Ramanujam, P.S.; Holme, N.C.R.; Hvilsted, S.

1996-01-01

Atomic force and scanning near-field optical microscopic investigations have been carried out on a polarization holographic grating recorded in an azobenzene side-chain Liquid crystalline polyester. It has been found that immediately following laser irradiation, a topographic surface grating...

Hypersonic force measurements using internal balance based on optical micromachined Fabry-Perot interferometry

Science.gov (United States)

Qiu, Huacheng; Min, Fu; Zhong, Shaolong; Song, Xin; Yang, Yanguang

2018-03-01

Force measurements using wind tunnel balance are necessary for determining a variety of aerodynamic performance parameters, while the harsh environment in hypersonic flows requires that the measurement instrument should be reliable and robust, in against strong electromagnetic interference, high vacuum, or metal (oxide) dusts. In this paper, we demonstrated a three-component internal balance for hypersonic aerodynamic force measurements, using novel optical micromachined Fabry-Perot interferometric (FPI) strain gauges as sensing elements. The FPI gauges were fabricated using Micro-Opto-Electro-Mechanical Systems (MOEMS) surface and bulk fabrication techniques. High-reflectivity coatings are used to form a high-finesse Fabry-Perot cavity, which benefits a high resolution. Antireflective and passivation coatings are used to reduce unwanted interferences. The FPI strain gauge based balance has been calibrated and evaluated in a Mach 5 hypersonic flow. The results are compared with the traditional technique using the foil resistive strain gauge balance, indicating that the proposed balance based on the MOEMS FPI strain gauge is reliable and robust and is potentially suitable for the hypersonic wind tunnel harsh environment.

Synthesis and characterization of erbium-doped SiO{sub 2}-TiO{sub 2} thin films prepared by sol-gel and dip-coating techniques onto commercial glass substrates as a route for obtaining active GRadient-INdex materials

Energy Technology Data Exchange (ETDEWEB)

Gómez-Varela, Ana I. [Microoptics and GRIN Optics Group, Department of Applied Physics, Faculty of Optics and Optometry and Faculty of Physics, Universidade de Santiago de Compostela, Campus Vida s/n, Santiago de Compostela E-15782 (Spain); Castro, Yolanda, E-mail: castro@icv.csic.es [Instituto de Cerámica y Vidrio (CSIC), Kelsen 5, Campus de Cantoblanco, Madrid 28049 (Spain); Durán, Alicia [Instituto de Cerámica y Vidrio (CSIC), Kelsen 5, Campus de Cantoblanco, Madrid 28049 (Spain); De Beule, Pieter A.A. [Applied Nano-Optics Laboratory, International Iberian Nanotechnology Laboratory, Braga 4715-330 (Portugal); Flores-Arias, María T. [Microoptics and GRIN Optics Group, Department of Applied Physics, Faculty of Optics and Optometry and Faculty of Physics, Universidade de Santiago de Compostela, Campus Vida s/n, Santiago de Compostela E-15782 (Spain); Bao-Varela, Carmen, E-mail: carmen.bao@usc.es [Microoptics and GRIN Optics Group, Department of Applied Physics, Faculty of Optics and Optometry and Faculty of Physics, Universidade de Santiago de Compostela, Campus Vida s/n, Santiago de Compostela E-15782 (Spain)

2015-05-29

In this work, SiO{sub 2}-TiO{sub 2} films doped with erbium were prepared by dip-coating sol-gel process onto commercial glass substrates. The surface morphology of the films was characterized using atomic force microscopy, while thickness, refractive index, extinction coefficient and porosity of the films were determined by ellipsometric measurements in a wavelength region of 400-1000 nm. Optical constants and porosity were found to vary with erbium concentration. The proof of principle presented in this paper is applicable to systems of different nature by tailoring the sol-gel precursors in such a way that active GRadient-INdex media described by a complex, parabolic-like refractive index distribution for beam shaping purposes is obtained. - Highlights: • Sol-gel route for preparation of active GRadient-INdex materials is proposed. • SiO{sub 2}-TiO{sub 2} films doped with erbium were prepared by dipping onto commercial glasses. • Morphological and optical characterization of the samples was performed. • Optical constants and porosity were found to vary with erbium concentration. • Refractive index diminishes with dopant content; the contrary occurs for porosity.

Magneto-motive detection of tissue-based macrophages by differential phase optical coherence tomography.

Science.gov (United States)

Oh, Junghwan; Feldman, Marc D; Kim, Jihoon; Kang, Hyun Wook; Sanghi, Pramod; Milner, Thomas E

2007-03-01

A novel method to detect tissue-based macrophages using a combination of superparamagnetic iron oxide (SPIO) nanoparticles and differential phase optical coherence tomography (DP-OCT) with an external oscillating magnetic field is reported. Magnetic force acting on iron-laden tissue-based macrophages was varied by applying a sinusoidal current to a solenoid containing a conical iron core that substantially focused and increased magnetic flux density. Nanoparticle motion was detected with DP-OCT, which can detect tissue movement with nanometer resolution. Frequency response of iron-laden tissue movement was twice the modulation frequency since the magnetic force is proportional to the product of magnetic flux density and gradient. Results of our experiments indicate that DP-OCT can be used to identify tissue-based macrophage when excited by an external focused oscillating magnetic field. (c) 2007 Wiley-Liss, Inc

Adjustable internal structure for reconstructing gradient index profile of crystalline lens.

Science.gov (United States)

Bahrami, Mehdi; Goncharov, Alexander V; Pierscionek, Barbara K

2014-03-01

Employing advanced technologies in studying the crystalline lens of the eye has improved our understanding of the refractive index gradient of the lens. Reconstructing and studying such a complex structure requires models with adaptable internal geometry that can be altered to simulate geometrical and optical changes of the lens with aging. In this Letter, we introduce an optically well-defined, geometrical structure for modeling the gradient refractive index profile of the crystalline lens with the advantage of an adjustable internal structure that is not available with existing models. The refractive index profile assigned to this rotationally symmetric geometry is calculated numerically, yet it is shown that this does not limit the model. The study provides a basis for developing lens models with sophisticated external and internal structures without the need for analytical solutions to calculate refractive index profiles.

Generation of metal composition gradients by means of bipolar electrodeposition

International Nuclear Information System (INIS)

Tisserant, Gwendoline; Fattah, Zahra; Ayela, Cédric; Roche, Jérome; Plano, Bernard; Zigah, Dodzi; Goudeau, Bertrand; Kuhn, Alexander; Bouffier, Laurent

2015-01-01

Highlights: • A bipolar electrochemistry approach for the preparation of surface gradients is reported. • Several metals are simultaneously deposited on a bipolar electrode. • The elemental composition and thickness of the deposit varies alongside the bipolar electrode. • The deposit affects the surface properties and exhibits a barcode feature. - Abstract: Bipolar electrochemistry is an unconventional technique that currently encounters a renewal of interest due to modern applications in the fields of analytical chemistry or materials science. The approach is particularly relevant for the preparation of asymmetric objects or surfaces such as Janus particles for example. Bipolar electrochemistry allows spatially controlled deposition of various layers from electroactive precursors, selectively at one side of a bipolar electrode. We report here the concomitant cathodic deposition of up to three different metals at the same time in a single experiment. The deposits were characterized by optical and electron microscopy imaging as well as profilometry and energy dispersive X-ray spectroscopy. As a result, the deposited layer is composed of several areas exhibiting both a composition and a thickness gradient. Such a variation directly modifies the optical and electronic properties alongside the surface and gives access to the design of composite surfaces exhibiting a visual gradient feature.

Micromanipulation and microfabrication for optical microrobotics

Science.gov (United States)

Palima, Darwin; Bañas, Andrew Rafael; Vizsnyiczai, Gaszton; Kelemen, Lóránd; Aabo, Thomas; Ormos, Pál.; Glückstad, Jesper

2012-10-01

Robotics can use optics feedback in vision-based control of intelligent robotic guidance systems. With light's miniscule momentum, shrinking robots down to the microscale regime creates opportunities for exploiting optical forces and torques in microrobotic actuation and control. Indeed, the literature on optical trapping and micromanipulation attests to the possibilities for optical microrobotics. This work presents an optical microrobotics perspective on the optical microfabrication and micromanipulation work that we performed. We designed different three-dimensional microstructures and fabricated them by two-photon polymerization. These microstructures were then handled using our biophotonics workstation (BWS) for proof-of-principle demonstrations of optical actuation, akin to 6DOF actuation of robotic micromanipulators. Furthermore, we also show an example of dynamic behavior of the trapped microstructure that can be achieved when using static traps in the BWS. This can be generalized, in the future, towards a structural shaping optimization strategy for optimally controlling microstructures to complement approaches based on lightshaping. We also show that light channeled to microfabricated, free-standing waveguides can be used not only to redirect light for targeted delivery of optical energy but can also for targeted delivery of optical force, which can serve to further extend the manipulation arms in optical robotics. Moreover, light deflection with waveguide also creates a recoil force on the waveguide, which can be exploited for controlling the optical force.

Restoration the domain structure from magnetic force microscopy image

Science.gov (United States)

Wu, Dongping; Lou, Yuanfu; Wei, Fulin; Wei, Dan

2012-04-01

This contribution gives an approximation method to calculate the stray field of the scanning plane from the magnetic force microscopy (MFM) force gradient image. Before calculation, a Butterworth low-pass filter has been used to remove a part of the noise of the image. The discrete Fourier transform (DFT) method has been used to calculate the magnetic potential of the film surface. It shows that the potential is not correct because the low-frequency noise has been enlarged. The approximation method gives a better result of the potential and proves that the MFM force gradient of the perpendicular component image also gives the perpendicular component of the stray field. Supposing that the distance between the tip and the sample is as small as near zero, the force gradient image also gives the magnetic charge distribution of the film surface. So if the orientation of the film from hysteresis loop is known, then the domain structure of the film can be determined. For perpendicular orientation, the absolution value of the perpendicular component of stray field gives the domain and domain wall position. For in-plane orientation, the absolution value of in-plane component of stray field gives the domain and domain wall position.

Truncated Conjugate Gradient: An Optimal Strategy for the Analytical Evaluation of the Many-Body Polarization Energy and Forces in Molecular Simulations.

Science.gov (United States)

Aviat, Félix; Levitt, Antoine; Stamm, Benjamin; Maday, Yvon; Ren, Pengyu; Ponder, Jay W; Lagardère, Louis; Piquemal, Jean-Philip

2017-01-10

We introduce a new class of methods, denoted as Truncated Conjugate Gradient(TCG), to solve the many-body polarization energy and its associated forces in molecular simulations (i.e. molecular dynamics (MD) and Monte Carlo). The method consists in a fixed number of Conjugate Gradient (CG) iterations. TCG approaches provide a scalable solution to the polarization problem at a user-chosen cost and a corresponding optimal accuracy. The optimality of the CG-method guarantees that the number of the required matrix-vector products are reduced to a minimum compared to other iterative methods. This family of methods is non-empirical, fully adaptive, and provides analytical gradients, avoiding therefore any energy drift in MD as compared to popular iterative solvers. Besides speed, one great advantage of this class of approximate methods is that their accuracy is systematically improvable. Indeed, as the CG-method is a Krylov subspace method, the associated error is monotonically reduced at each iteration. On top of that, two improvements can be proposed at virtually no cost: (i) the use of preconditioners can be employed, which leads to the Truncated Preconditioned Conjugate Gradient (TPCG); (ii) since the residual of the final step of the CG-method is available, one additional Picard fixed point iteration ("peek"), equivalent to one step of Jacobi Over Relaxation (JOR) with relaxation parameter ω, can be made at almost no cost. This method is denoted by TCG-n(ω). Black-box adaptive methods to find good choices of ω are provided and discussed. Results show that TPCG-3(ω) is converged to high accuracy (a few kcal/mol) for various types of systems including proteins and highly charged systems at the fixed cost of four matrix-vector products: three CG iterations plus the initial CG descent direction. Alternatively, T(P)CG-2(ω) provides robust results at a reduced cost (three matrix-vector products) and offers new perspectives for long polarizable MD as a production

Heterogeneous Cytoskeletal Force Distribution Delineates the Onset Ca2+ Influx Under Fluid Shear Stress in Astrocytes

Directory of Open Access Journals (Sweden)

Mohammad M. Maneshi

2018-03-01

Full Text Available Mechanical perturbations increase intracellular Ca2+ in cells, but the coupling of mechanical forces to the Ca2+ influx is not well understood. We used a microfluidic chamber driven with a high-speed pressure servo to generate defined fluid shear stress to cultured astrocytes, and simultaneously measured cytoskeletal forces using a force sensitive actinin optical sensor and intracellular Ca2+. Fluid shear generated non-uniform forces in actinin that critically depended on the stimulus rise time emphasizing the presence of viscoelasticity in the activating sequence. A short (ms shear pulse with fast rise time (2 ms produced an immediate increase in actinin tension at the upstream end of the cell with minimal changes at the downstream end. The onset of Ca2+ rise began at highly strained areas. In contrast to stimulus steps, slow ramp stimuli produced uniform forces throughout the cells and only a small Ca2+ response. The heterogeneity of force distribution is exaggerated in cells having fewer stress fibers and lower pre-tension in actinin. Disruption of cytoskeleton with cytochalasin-D (Cyt-D eliminated force gradients, and in those cells Ca2+ elevation started from the soma. Thus, Ca2+ influx with a mechanical stimulus depends on local stress within the cell and that is time dependent due to viscoelastic mechanics.

Study on the properties of infrared wavefront coding athermal system under several typical temperature gradient distributions

Science.gov (United States)

Cai, Huai-yu; Dong, Xiao-tong; Zhu, Meng; Huang, Zhan-hua

2018-01-01

Wavefront coding for athermal technique can effectively ensure the stability of the optical system imaging in large temperature range, as well as the advantages of compact structure and low cost. Using simulation method to analyze the properties such as PSF and MTF of wavefront coding athermal system under several typical temperature gradient distributions has directive function to characterize the working state of non-ideal temperature environment, and can effectively realize the system design indicators as well. In this paper, we utilize the interoperability of data between Solidworks and ZEMAX to simplify the traditional process of structure/thermal/optical integrated analysis. Besides, we design and build the optical model and corresponding mechanical model of the infrared imaging wavefront coding athermal system. The axial and radial temperature gradients of different degrees are applied to the whole system by using SolidWorks software, thus the changes of curvature, refractive index and the distance between the lenses are obtained. Then, we import the deformation model to ZEMAX for ray tracing, and obtain the changes of PSF and MTF in optical system. Finally, we discuss and evaluate the consistency of the PSF (MTF) of the wavefront coding athermal system and the image restorability, which provides the basis and reference for the optimal design of the wavefront coding athermal system. The results show that the adaptability of single material infrared wavefront coding athermal system to axial temperature gradient can reach the upper limit of temperature fluctuation of 60°C, which is much higher than that of radial temperature gradient.

Effect of temperature gradient on liquid-liquid phase separation in a polyolefin blend.

Science.gov (United States)

Jiang, Hua; Dou, Nannan; Fan, Guoqiang; Yang, Zhaohui; Zhang, Xiaohua

2013-09-28

We have investigated experimentally the structure formation processes during phase separation via spinodal decomposition above and below the spinodal line in a binary polymer blend system exposed to in-plane stationary thermal gradients using phase contrast optical microscopy and temperature gradient hot stage. Below the spinodal line there is a coupling of concentration fluctuations and thermal gradient imposed by the temperature gradient hot stage. Also under the thermal gradient annealing phase-separated domains grow faster compared with the system under homogeneous temperature annealing on a zero-gradient or a conventional hot stage. We suggest that the in-plane thermal gradient accelerates phase separation through the enhancement in concentration fluctuations in the early and intermediate stages of spinodal decomposition. In a thermal gradient field, the strength of concentration fluctuation close to the critical point (above the spinodal line) is strong enough to induce phase separation even in one-phase regime of the phase diagram. In the presence of a temperature gradient the equilibrium phase diagrams are no longer valid, and the systems with an upper critical solution temperature can be quenched into phase separation by applying the stationary temperature gradient. The in-plane temperature gradient drives enhanced concentration fluctuations in a binary polymer blend system above and below the spinodal line.

A picogram- and nanometre-scale photonic-crystal optomechanical cavity.

Science.gov (United States)

Eichenfield, Matt; Camacho, Ryan; Chan, Jasper; Vahala, Kerry J; Painter, Oskar

2009-05-28

The dynamic back-action caused by electromagnetic forces (radiation pressure) in optical and microwave cavities is of growing interest. Back-action cooling, for example, is being pursued as a means of achieving the quantum ground state of macroscopic mechanical oscillators. Work in the optical domain has revolved around millimetre- or micrometre-scale structures using the radiation pressure force. By comparison, in microwave devices, low-loss superconducting structures have been used for gradient-force-mediated coupling to a nanomechanical oscillator of picogram mass. Here we describe measurements of an optical system consisting of a pair of specially patterned nanoscale beams in which optical and mechanical energies are simultaneously localized to a cubic-micron-scale volume, and for which large per-photon optical gradient forces are realized. The resulting scale of the per-photon force and the mass of the structure enable the exploration of cavity optomechanical regimes in which, for example, the mechanical rigidity of the structure is dominantly provided by the internal light field itself. In addition to precision measurement and sensitive force detection, nano-optomechanics may find application in reconfigurable and tunable photonic systems, light-based radio-frequency communication and the generation of giant optical nonlinearities for wavelength conversion and optical buffering.

Centrifugal force: a few surprises

International Nuclear Information System (INIS)

Abramowicz, M.A.; Max-Planck-Institut fuer Physik und Astrophysik, Garching

1990-01-01

The need for a rather fundamental revision in understanding of the nature of the centrifugal force is discussed. It is shown that in general relativity (and contrary to the situation in Newtonian theory) rotation of a reference frame is a necessary but not sufficient condition for the centrifugal force to appear. A sufficient condition for its appearance, in the instantaneously corotating reference frame of a particle, is that the particle motion in space (observed in the global rest frame) differs from a photon trajectory. The direction of the force is the same as that of the gradient of the effective potential for photon motion. In some cases, the centrifugal force will attract towards the axis of rotation. (author)

Insole optical fiber Bragg grating sensors network for dynamic vertical force monitoring.

Science.gov (United States)

Domingues, Maria Fátima; Tavares, Cátia; Leitão, Cátia; Frizera-Neto, Anselmo; Alberto, Nélia; Marques, Carlos; Radwan, Ayman; Rodriguez, Jonathan; Postolache, Octavian; Rocon, Eduardo; André, Paulo; Antunes, Paulo

2017-09-01

In an era of unprecedented progress in technology and increase in population age, continuous and close monitoring of elder citizens and patients is becoming more of a necessity than a luxury. Contributing toward this field and enhancing the life quality of elder citizens and patients with disabilities, this work presents the design and implementation of a noninvasive platform and insole fiber Bragg grating sensors network to monitor the vertical ground reaction forces distribution induced in the foot plantar surface during gait and body center of mass displacements. The acquired measurements are a reliable indication of the accuracy and consistency of the proposed solution in monitoring and mapping the vertical forces active on the foot plantar sole, with a sensitivity up to 11.06 ?? pm / N . The acquired measurements can be used to infer the foot structure and health condition, in addition to anomalies related to spine function and other pathologies (e.g., related to diabetes); also its application in rehabilitation robotics field can dramatically reduce the computational burden of exoskeletons’ control strategy. The proposed technology has the advantages of optical fiber sensing (robustness, noninvasiveness, accuracy, and electromagnetic insensitivity) to surpass all drawbacks verified in traditionally used sensing systems (fragility, instability, and inconsistent feedback).

Insole optical fiber Bragg grating sensors network for dynamic vertical force monitoring

Science.gov (United States)

Domingues, Maria Fátima; Tavares, Cátia; Leitão, Cátia; Frizera-Neto, Anselmo; Alberto, Nélia; Marques, Carlos; Radwan, Ayman; Rodriguez, Jonathan; Postolache, Octavian; Rocon, Eduardo; André, Paulo; Antunes, Paulo

2017-09-01

In an era of unprecedented progress in technology and increase in population age, continuous and close monitoring of elder citizens and patients is becoming more of a necessity than a luxury. Contributing toward this field and enhancing the life quality of elder citizens and patients with disabilities, this work presents the design and implementation of a noninvasive platform and insole fiber Bragg grating sensors network to monitor the vertical ground reaction forces distribution induced in the foot plantar surface during gait and body center of mass displacements. The acquired measurements are a reliable indication of the accuracy and consistency of the proposed solution in monitoring and mapping the vertical forces active on the foot plantar sole, with a sensitivity up to 11.06 pm/N. The acquired measurements can be used to infer the foot structure and health condition, in addition to anomalies related to spine function and other pathologies (e.g., related to diabetes); also its application in rehabilitation robotics field can dramatically reduce the computational burden of exoskeletons' control strategy. The proposed technology has the advantages of optical fiber sensing (robustness, noninvasiveness, accuracy, and electromagnetic insensitivity) to surpass all drawbacks verified in traditionally used sensing systems (fragility, instability, and inconsistent feedback).

Quantitative measurements of electromechanical response with a combined optical beam and interferometric atomic force microscope

Energy Technology Data Exchange (ETDEWEB)

Labuda, Aleksander; Proksch, Roger [Asylum Research an Oxford Instruments Company, Santa Barbara, California 93117 (United States)

2015-06-22

An ongoing challenge in atomic force microscope (AFM) experiments is the quantitative measurement of cantilever motion. The vast majority of AFMs use the optical beam deflection (OBD) method to infer the deflection of the cantilever. The OBD method is easy to implement, has impressive noise performance, and tends to be mechanically robust. However, it represents an indirect measurement of the cantilever displacement, since it is fundamentally an angular rather than a displacement measurement. Here, we demonstrate a metrological AFM that combines an OBD sensor with a laser Doppler vibrometer (LDV) to enable accurate measurements of the cantilever velocity and displacement. The OBD/LDV AFM allows a host of quantitative measurements to be performed, including in-situ measurements of cantilever oscillation modes in piezoresponse force microscopy. As an example application, we demonstrate how this instrument can be used for accurate quantification of piezoelectric sensitivity—a longstanding goal in the electromechanical community.

Particle force model effects in a shock-driven multiphase instability

Science.gov (United States)

Black, W. J.; Denissen, N.; McFarland, J. A.

2018-05-01

This work presents simulations on a shock-driven multiphase instability (SDMI) at an initial particle volume fraction of 1% with the addition of a suite of particle force models applicable in dense flows. These models include pressure-gradient, added-mass, and interparticle force terms in an effort to capture the effects neighboring particles have in non-dilute flow regimes. Two studies are presented here: the first seeks to investigate the individual contributions of the force models, while the second study focuses on examining the effect of these force models on the hydrodynamic evolution of a SDMI with various particle relaxation times (particle sizes). In the force study, it was found that the pressure gradient and interparticle forces have little effect on the instability under the conditions examined, while the added-mass force decreases the vorticity deposition and alters the morphology of the instability. The relaxation-time study likewise showed a decrease in metrics associated with the evolution of the SDMI for all sizes when the particle force models were included. The inclusion of these models showed significant morphological differences in both the particle and carrier species fields, which increased as particle relaxation times increased.

Color gradients in the coma of P/Halley

International Nuclear Information System (INIS)

Meech, K.

1988-01-01

Some important information relevant to the understanding of the gas/dust dynamics near the surface of a comet nucleus concerns knowledge of the grain composition and scattering properties as well as the particle size distribution of dust in the coma. Ground based measurements of light scattered from the dust comae can provide some information about the physical grain properties, in particular about the mean optically dominant grain size. Optical spectra of continua of nine comets presented by Jewitt and Meech, 1986, show that all of the scattered light is reddened with respect to the Sun. There is significant scatter in the amount of reddening seen for different comets. In the near IF regions, the reddening decreases until near 2 to 3 micrometers where the reflectivity is nearly neutral. It is of particular interest to see if there are any observable changes in the grain size distribution during outburst. Although no coma colar changes were observed during the Nov. 1985 outbursts, a color gradient within the coma has been observed in Halley. Radial color gradients in J, H, and K images of Halley as reported by Campins have not been observed by the author

Regulation of dextransucrase secretion by proton motive force in Leuconostoc mesenteroides

International Nuclear Information System (INIS)

Otts, D.R.

1987-01-01

The relationship between proton motive force and the secretion of the enzyme dextransucrase in Leuconostoc mesenteroides was investigated. The transmembrane pH gradient was determined by measurement of the uptake of radiolabeled benzoate or methylamine while the membrane potential was determined by measurement of the uptake of radiolabeled tetraphenylphosphonium bromide. Leuconostoc mesenteroides was able to maintain a constant proton motive force of -130 mV when grown in fermenters at constant pH while a value of -140 mV was determined from concentrated cell suspensions. The contribution of the membrane potential and transmembrane pH gradient to the proton motive force varied depending on the cation concentration and pH of the medium. The results of this study strongly indicate that dextransucrase secretion Leuconostoc mesenteroides is dependent on the presence of a proton gradient across the cytoplasmic membrane. The results further suggest that dextransucrase secretion is coupled to proton influx into the cell

3D characterization of the forces in optical traps based on counter-propagation beams shaped by a spatial light modulator

DEFF Research Database (Denmark)

Kristensen, M. V.; Lindballe, T.; Kylling, A.

2010-01-01

An experimental characterization of the 3D forces, acting on a trapped polystyrene bead in a counter-propagating beam geometry, is reported. Using a single optical trap with a large working distance (in the BioPhotonics Workstation), we simultaneously measure the transverse and longitudinal...... trapping force constants. Two different methods were used: The Drag force method and the Equipartition method. We show that the counterpropagating beams traps are simple harmonic for small displacements. The force constants reveal a transverse asymmetry as - = 9.7 pN/µm and + = 11.3 pN/µm (at a total laser...... power of 2x35 mW) for displacements in opposite directions. The Equipartition method is limited by mechanical noise and is shown to be applicable only when the total laser power in a single 10 µm counter-propagating trap is below 2x20 mW....

Near field plasmonic gradient effects on high vacuum tip-enhanced Raman spectroscopy.

Science.gov (United States)

Fang, Yurui; Zhang, Zhenglong; Chen, Li; Sun, Mengtao

2015-01-14

Near field gradient effects in high vacuum tip-enhanced Raman spectroscopy (HV-TERS) are a recent developing ultra-sensitive optical and spectral analysis technology on the nanoscale, based on the plasmons and plasmonic gradient enhancement in the near field and under high vacuum. HV-TERS can not only be used to detect ultra-sensitive Raman spectra enhanced by surface plasmon, but also to detect clear molecular IR-active modes enhanced by strongly plasmonic gradient. Furthermore, the molecular overtone modes and combinational modes can also be experimentally measured, where the Fermi resonance and Darling-Dennison resonance were successfully observed in HV-TERS. Theoretical calculations using electromagnetic field theory firmly supported experimental observation. The intensity ratio of the plasmon gradient term over the linear plasmon term can reach values greater than 1. Theoretical calculations also revealed that with the increase in gap distance between tip and substrate, the decrease in the plasmon gradient was more significant than the decrease in plasmon intensity, which is the reason that the gradient Raman can be only observed in the near field. Recent experimental results of near field gradient effects on HV-TERS were summarized, following the section of the theoretical analysis.

Polarization-dependent tunneling of light in gradient optics

Czech Academy of Sciences Publication Activity Database

Shvartsburg, A. B.; Kuzmiak, Vladimír; Petite, G.

2007-01-01

Roč. 76, č. 1 (2007), 016603.1-01663.11 ISSN 1539-3755 R&D Projects: GA MŠk(CZ) OC P11.001 Institutional research plan: CEZ:AV0Z20670512 Keywords : wave propagation * tunnelling Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.483, year: 2007

A nonsmooth nonlinear conjugate gradient method for interactive contact force problems

DEFF Research Database (Denmark)

Silcowitz, Morten; Abel, Sarah Maria Niebe; Erleben, Kenny

2010-01-01

of a nonlinear complementarity problem (NCP), which can be solved using an iterative splitting method, such as the projected Gauss–Seidel (PGS) method. We present a novel method for solving the NCP problem by applying a Fletcher–Reeves type nonlinear nonsmooth conjugate gradient (NNCG) type method. We analyze...... and present experimental convergence behavior and properties of the new method. Our results show that the NNCG method has at least the same convergence rate as PGS, and in many cases better....

Beyond-proximity-force-approximation Casimir force between two spheres at finite temperature

Science.gov (United States)

Bimonte, Giuseppe

2018-04-01

A recent experiment [J. L. Garrett, D. A. T. Somers, and J. N. Munday, Phys. Rev. Lett. 120, 040401 (2018), 10.1103/PhysRevLett.120.040401] measured for the first time the gradient of the Casimir force between two gold spheres at room temperature. The theoretical analysis of the data was carried out using the standard proximity force approximation (PFA). A fit of the data, using a parametrization of the force valid for the sphere-plate geometry, was used by the authors to place a bound on deviations from PFA. Motivated by this work, we compute the Casimir force between two gold spheres at finite temperature. The semianalytic formula for the Casimir force that we construct is valid for all separations, and can be easily used to interpret future experiments in both the sphere-plate and sphere-sphere configurations. We describe the correct parametrization of the corrections to PFA for two spheres that should be used in data analysis.

Optically directed molecular transport and 3D isoelectric positioning of amphoteric biomolecules

International Nuclear Information System (INIS)

Hafeman, Dean G.; Harkins, James B.; Witkowski, Charles E. II; Lewis, Nathan S.; Brown, Gilbert M.; Warmack, Robert J. Bruce; Thundat, Thomas George

2006-01-01

We demonstrate the formation of charged molecular packets and their transport within optically created electrical force-field traps in a pH-buffered electrolyte. We call this process photoelectrophoretic localization and transport (PELT). The electrolyte is in contact with a photoconductive semiconductor electrode and a counterelectrode that are connected through an external circuit. A light beam directed to coordinates on the photoconductive electrode surface produces a photocurrent within the circuit and electrolyte. Within the electrolyte, the photocurrent creates localized force-field traps centered at the illuminated coordinates. Charged molecules, including polypeptides and proteins, electrophoretically accumulate into the traps and subsequently can be transported in the electrolyte by moving the traps over the photoconductive electrode in response to movement of the light beam. The molecules in a single trap can be divided into aliquots, and the aliquots can be directed along multiple routes simultaneously by using multiple light beams. This photoelectrophoretic transport of charged molecules by PELT resembles the electrostatic transport of electrons within force-field wells of solid-state charge-coupled devices. The molecules, however, travel in a liquid electrolyte rather than a solid. Furthermore, we have used PELT to position amphoteric biomolecules in three dimensions. A 3D pH gradient was created in an electrolyte medium by controlling the illumination position on a photoconductive anode where protons were generated electrolytically. Photoelectrophoretic transport of amphoteric molecules through the pH gradient resulted in accumulation of the molecules at their apparent 3D isoelectric coordinates in the medium.

A flexoelectric theory with rotation gradient effects for elastic dielectrics

International Nuclear Information System (INIS)

Anqing, Li; Shenjie, Zhou; Lu, Qi; Xi, Chen

2016-01-01

In this paper, a general flexoelectric theory in the framework of couple stress theory is proposed for isotropic dielectrics, in which the rotation gradient and the polarization gradient are involved to represent the nonlocal mechanical and electrical effects, respectively. The present flexoelectric theory shows only the anti-symmetric part of rotation gradient can induce polarization, while the symmetric part of rotation gradient cannot induce polarization in isotropic dielectrics. The electrostatic stress is obtained naturally in the governing equations and boundary conditions in terms of the variational principle, which is composed of two parts: the Maxwell stress corresponding to the polarization and the remainder relating to the polarization gradient. The current theory is able to account for the effects of size, direct and inverse flexoelectricities, and electrostatic force. To illustrate this theory, a simple application of Bernoulli–Euler cantilever beam is discussed. The numerical results demonstrate neither the higher-order constant l 1 nor the higher-order constant l 2 associated with the symmetric and anti-symmetric parts of rotation gradient, respectively, can be ignored in the flexoelectric theory. In addition, the induced deflection increases as the increase of the flexoelectric coefficient. The polarization is no longer constant and the potential is no longer linear along the thickness direction of beam because of the influence of polarization gradient. (paper)

Physical Limitations of Empirical Field Models: Force Balance and Plasma Pressure

International Nuclear Information System (INIS)

Sorin Zaharia; Cheng, C.Z.

2002-01-01

In this paper, we study whether the magnetic field of the T96 empirical model can be in force balance with an isotropic plasma pressure distribution. Using the field of T96, we obtain values for the pressure P by solving a Poisson-type equation (gradient) 2 P = (gradient) · (J x B) in the equatorial plane, and 1-D profiles on the Sun-Earth axis by integrating (gradient)P = J x B. We work in a flux coordinate system in which the magnetic field is expressed in terms of Euler potentials. Our results lead to the conclusion that the T96 model field cannot be in equilibrium with an isotropic pressure. We also analyze in detail the computation of Birkeland currents using the Vasyliunas relation and the T96 field, which yields unphysical results, again indicating the lack of force balance in the empirical model. The underlying reason for the force imbalance is likely the fact that the derivatives of the least-square fitted model B are not accurate predictions of the actual magnetospheric field derivatives. Finally, we discuss a possible solution to the problem of lack of force balance in empirical field models

Voltammetry under a Controlled Temperature Gradient

Directory of Open Access Journals (Sweden)

Jan Krejci, Jr.

2010-07-01

Full Text Available Electrochemical measurements are generally done under isothermal conditions. Here we report on the application of a controlled temperature gradient between the working electrode surface and the solution. Using electrochemical sensors prepared on ceramic materials with extremely high specific heat conductivity, the temperature gradient between the electrode and solution was applied here as a second driving force. This application of the Soret phenomenon increases the mass transfer in the Nernst layer and enables more accurate control of the electrode response enhancement by a combination of diffusion and thermal diffusion. We have thus studied the effect of Soret phenomenon by cyclic voltammetry measurements in ferro/ferricyanide. The time dependence of sensor response disappears when applying the Soret phenomenon, and the complicated shape of the cyclic voltammogram is replaced by a simple exponential curve. We have derived the Cotrell-Soret equation describing the steady-state response with an applied temperature difference.

Stationary flow in magnetic tubes of force

International Nuclear Information System (INIS)

Engvold, O.; Jensen, E.

1976-01-01

For one particular set of boundary conditions Pikel'ner obtained a stationary solution displaying a condensation, which he applied to quiescent prominences. Calculations in the stationary case for a range of parameters have been carried out, after some modifications of the basic equations. These modifications involved a complete non-LTE formulation of the ionization equilibrium, an improved radiative loss-function and more accurate values of the thermodynamic parameters. The calculations were carried out for a hydrogen helium mixture with B = 10 and for a pure hydrogen gas. The solutions were terminated where the optical thickness in lyα along the tube exceeded unity, corresponding to T approx.equal to 20 000K. The solutions are strongly dependent upon the geometry of the tube of force. Condensations may be made to appear on the ascending as well as on the descending branch of the magnetic arch by varying the parameters. Solutions also depend strongly upon the energy input into the tube at the footpoint, mainly determined by the injection velocity and the starting value of the temperature gradient. The radiative loss is of less importance for the values of the gas pressure close to the Pikel'ner case. Recent observational data indicate gas pressure in the chromosphere corona transition region as much as 4 times the boundary pressure assumed by Pikel'ner. Such a high initial pressure, however, produce no condensation. In the temperature range 1.2x10 5 K > T > 5x10 4 K the temperature gradients in the condensations are in fair agreement with observations of the CIII lines in the EUV-region. For higher temperatures 5x10 5 K > T > 2x10 5 K our temperature gradients are much smaller than those indicated by observations. (Auth.)

A method for the on-site determination of prestressing forces using long-gauge fiber optic strain sensors

International Nuclear Information System (INIS)

Abdel-Jaber, H; Glisic, B

2014-01-01

Structural health monitoring (SHM) consists of the continuous or periodic measurement of structural parameters and their analysis with the aim of deducing information about the performance and health condition of a structure. The significant increase in the construction of prestressed concrete bridges motivated this research on an SHM method for the on-site determination of the distribution of prestressing forces along prestressed concrete beam structures. The estimation of the distribution of forces is important as it can give information regarding the overall performance and structural integrity of the bridge. An inadequate transfer of the designed prestressing forces to the concrete cross-section can lead to a reduced capacity of the bridge and consequently malfunction or failure at lower loads than predicted by design. This paper researches a universal method for the determination of the distribution of prestressing forces along concrete beam structures at the time of transfer of the prestressing force (e.g., at the time of prestressing or post-tensioning). The method is based on the use of long-gauge fiber optic sensors, and the sensor network is similar (practically identical) to the one used for damage identification. The method encompasses the determination of prestressing forces at both healthy and cracked cross-sections, and for the latter it can yield information about the condition of the cracks. The method is validated on-site by comparison to design forces through the application to two structures: (1) a deck-stiffened arch and (2) a curved continuous girder. The uncertainty in the determination of prestressing forces was calculated and the comparison with the design forces has shown very good agreement in most of the structures’ cross-sections, but also helped identify some unusual behaviors. The method and its validation are presented in this paper. (papers)

Numerical study of divertor plasma transport with thermal force due to temperature gradient

International Nuclear Information System (INIS)

Ohtsu, Shigeki; Tanaka, Satoru; Yamawaki, Michio

1992-01-01

A one-dimensional, steady state divertor plasma model is developed in order to study the carbon impurity transport phenomena considering thermal force. The divertor plasma is composed of four regions in terms of momentum transport between hydrogen and carbon impurity: Momentum transferring region, equilibrium region, hydrogen recycling region and carbon recycling region. In the equilibrium region where the friction force is counterbalanced by the thermal force, the localization of carbon impurity occurs. The sufficient condition to avoid the reverse of carbon velocity due to the thermal force is evaluated. (orig.)

Fluvial signatures of modern and paleo orographic rainfall gradients

Science.gov (United States)

Schildgen, Taylor; Strecker, Manfred

2016-04-01

The morphology of river profiles is intimately linked to both climate and tectonic forcing. While much interest recently has focused on how river profiles can be inverted to derive uplift histories, here we show how in regions of strong orographic rainfall gradients, rivers may primarily record spatial patterns of precipitation. As a case study, we examine the eastern margin of the Andean plateau in NW Argentina, where the outward (eastward) growth of a broken foreland has led to a eastward shift in the main orographic rainfall gradient over the last several million years. Rivers influenced by the modern rainfall gradient are characterized by normalized river steepness values in tributary valleys that closely track spatial variations in rainfall, with higher steepness values in drier areas and lower steepness values in wetter areas. The same river steepness pattern has been predicted in landscape evolution models that apply a spatial gradient in rainfall to a region of uniform erosivity and uplift rate (e.g., Han et al., 2015). Also, chi plots from river networks on individual ranges affected by the modern orographic rainfall reveal patterns consistent with assymmetric precipitation across the range: the largest channels on the windward slopes are characterized by capture, while the longest channels on the leeward slopes are dominated by beheadings. Because basins on the windward side both lengthen and widen, tributary channels in the lengthening basins are characterized by capture, while tributary channels from neighboring basins on the windward side are dominated by beheadings. These patterns from the rivers influenced by the modern orographic rainfall gradient provide a guide for identifying river morphometric signatures of paleo orographic rainfall gradients. Mountain ranges to the west of the modern orographic rainfall have been interpreted to mark the location of orographic rainfall in the past, but these ranges are now in spatially near-uniform semi-arid to

Optical trapping of carbon nanotubes and graphene

Directory of Open Access Journals (Sweden)

S. Vasi

2011-09-01

Full Text Available We study optical trapping of nanotubes and graphene. We extract the distribution of both centre-of-mass and angular fluctuations from three-dimensional tracking of these optically trapped carbon nanostructures. The optical force and torque constants are measured from auto and cross-correlation of the tracking signals. We demonstrate that nanotubes enable nanometer spatial, and femto-Newton force resolution in photonic force microscopy by accurately measuring the radiation pressure in a double frequency optical tweezers. Finally, we integrate optical trapping with Raman and photoluminescence spectroscopy demonstrating the use of a Raman and photoluminescence tweezers by investigating the spectroscopy of nanotubes and graphene flakes in solution. Experimental results are compared with calculations based on electromagnetic scattering theory.

Effects of high-gradient magnetic fields on living cell machinery

Czech Academy of Sciences Publication Activity Database

Zablotskyy, V.; Lunov, O.; Kubinová, Šárka; Polyakova, T.; Syková, Eva; Dejneka, A.

2016-01-01

Roč. 49, č. 2016 (2016), s. 493003 ISSN 0022-3727 R&D Projects: GA MŠk(CZ) LO1309 Institutional support: RVO:68378041 Keywords : living cell * magnetic gradient force * cell mechanics * stem cell * magnetic field Subject RIV: FP - Other Medical Disciplines Impact factor: 2.588, year: 2016

Constraints on spatially oscillating sub-mm forces from the Stanford Optically Levitated Microsphere Experiment data

Science.gov (United States)

Antoniou, I.; Perivolaropoulos, L.

2017-11-01

A recent analysis by one of the authors [L. Perivolaropoulos, Phys. Rev. D 95, 084050 (2017), 10.1103/PhysRevD.95.084050] has indicated the presence of a 2 σ signal of spatially oscillating new force residuals in the torsion balance data of the Washington experiment. We extend that study and analyze the data of the Stanford Optically Levitated Microsphere Experiment (SOLME) [A. D. Rider et al., Phys. Rev. Lett. 117, 101101 (2016), 10.1103/PhysRevLett.117.101101] (kindly provided by A. D. Rider et al.) searching for sub-mm spatially oscillating new force signals. We find a statistically significant oscillating signal for a force residual of the form F (z )=α cos (2/π λ z +c ) where z is the distance between the macroscopic interacting masses (levitated microsphere and cantilever). The best fit parameter values are α =(1.1 ±0.4 )×10-17N , λ =(35.2 ±0.6 ) μ m . Monte Carlo simulation of the SOLME data under the assumption of zero force residuals has indicated that the statistical significance of this signal is at about 2 σ level. The improvement of the χ2 fit compared to the null hypothesis (zero residual force) corresponds to Δ χ2=13.1 . There are indications that this previously unnoticed signal is indeed in the data but is most probably induced by a systematic effect caused by diffraction of non-Gaussian tails of the laser beam. Thus the amplitude of this detected signal can only be useful as an upper bound to the amplitude of new spatially oscillating forces on sub-mm scales. In the context of gravitational origin of the signal emerging from a fundamental modification of the Newtonian potential of the form Veff(r )=-G M/r (1 +αOcos (2/π λ r +θ ))≡VN(r )+Vosc(r ) , we evaluate the source integral of the oscillating macroscopically induced force. If the origin of the SOLME oscillating signal is systematic, the parameter αO is bounded as αOchameleon oscillating potentials etc.).

Dynamics of an optically confined nanoparticle diffusing normal to a surface.

Science.gov (United States)

Schein, Perry; O'Dell, Dakota; Erickson, David

2016-06-01

Here we measure the hindered diffusion of an optically confined nanoparticle in the direction normal to a surface, and we use this to determine the particle-surface interaction profile in terms of the absolute height. These studies are performed using the evanescent field of an optically excited single-mode silicon nitride waveguide, where the particle is confined in a height-dependent potential energy well generated from the balance of optical gradient and surface forces. Using a high-speed cmos camera, we demonstrate the ability to capture the short time-scale diffusion dominated motion for 800-nm-diam polystyrene particles, with measurement times of only a few seconds per particle. Using established theory, we show how this information can be used to estimate the equilibrium separation of the particle from the surface. As this measurement can be made simultaneously with equilibrium statistical mechanical measurements of the particle-surface interaction energy landscape, we demonstrate the ability to determine these in terms of the absolute rather than relative separation height. This enables the comparison of potential energy landscapes of particle-surface interactions measured under different experimental conditions, enhancing the utility of this technique.

Surface complexation modeling of groundwater arsenic mobility: Results of a forced gradient experiment in a Red River flood plain aquifer, Vietnam

DEFF Research Database (Denmark)

Jessen, Søren; Postma, Dieke; Larsen, Flemming

2012-01-01

, suggesting a comparable As(III) affinity of Holocene and Pleistocene aquifer sediments. A forced gradient field experiment was conducted in a bank aquifer adjacent to a tributary channel to the Red River, and the passage in the aquifer of mixed groundwater containing up to 74% channel water was observed......Three surface complexation models (SCMs) developed for, respectively, ferrihydrite, goethite and sorption data for a Pleistocene oxidized aquifer sediment from Bangladesh were used to explore the effect of multicomponent adsorption processes on As mobility in a reduced Holocene floodplain aquifer......(III) while PO43− and Fe(II) form the predominant surface species. The SCM for Pleistocene aquifer sediment resembles most the goethite SCM but shows more Si sorption. Compiled As(III) adsorption data for Holocene sediment was also well described by the SCM determined for Pleistocene aquifer sediment...

FDTD simulations of forces on particles during holographic assembly.

Science.gov (United States)

Benito, David C; Simpson, Stephen H; Hanna, Simon

2008-03-03

We present finite-difference time-domain (FDTD) calculations of the forces and torques on dielectric particles of various shapes, held in one or many Gaussian optical traps, as part of a study of the physical limitations involved in the construction of micro- and nanostructures using a dynamic holographic assembler (DHA). We employ a full 3-dimensional FDTD implementation, which includes a complete treatment of optical anisotropy. The Gaussian beams are sourced using a multipole expansion of a fifth order Davis beam. Force and torques are calculated for pairs of silica spheres in adjacent traps, for silica cylinders trapped by multiple beams and for oblate silica spheroids and calcite spheres in both linearly and circularly polarized beams. Comparisons are drawn between the magnitudes of the optical forces and the Van der Waals forces acting on the systems. The paper also considers the limitations of the FDTD approach when applied to optical trapping.

Anti-drift and auto-alignment mechanism for an astigmatic atomic force microscope system based on a digital versatile disk optical head.

Science.gov (United States)

Hwu, E-T; Illers, H; Wang, W-M; Hwang, I-S; Jusko, L; Danzebrink, H-U

2012-01-01

In this work, an anti-drift and auto-alignment mechanism is applied to an astigmatic detection system (ADS)-based atomic force microscope (AFM) for drift compensation and cantilever alignment. The optical path of the ADS adopts a commercial digital versatile disc (DVD) optical head using the astigmatic focus error signal. The ADS-based astigmatic AFM is lightweight, compact size, low priced, and easy to use. Furthermore, the optical head is capable of measuring sub-atomic displacements of high-frequency AFM probes with a sub-micron laser spot (~570 nm, FWHM) and a high-working bandwidth (80 MHz). Nevertheless, conventional DVD optical heads suffer from signal drift problems. In a previous setup, signal drifts of even thousands of nanometers had been measured. With the anti-drift and auto-alignment mechanism, the signal drift is compensated by actuating a voice coil motor of the DVD optical head. A nearly zero signal drift was achieved. Additional benefits of this mechanism are automatic cantilever alignment and simplified design.

Investigation into local cell mechanics by atomic force microscopy mapping and optical tweezer vertical indentation.

Science.gov (United States)

Coceano, G; Yousafzai, M S; Ma, W; Ndoye, F; Venturelli, L; Hussain, I; Bonin, S; Niemela, J; Scoles, G; Cojoc, D; Ferrari, E

2016-02-12

Investigating the mechanical properties of cells could reveal a potential source of label-free markers of cancer progression, based on measurable viscoelastic parameters. The Young's modulus has proved to be the most thoroughly studied so far, however, even for the same cell type, the elastic modulus reported in different studies spans a wide range of values, mainly due to the application of different experimental conditions. This complicates the reliable use of elasticity for the mechanical phenotyping of cells. Here we combine two complementary techniques, atomic force microscopy (AFM) and optical tweezer microscopy (OTM), providing a comprehensive mechanical comparison of three human breast cell lines: normal myoepithelial (HBL-100), luminal breast cancer (MCF-7) and basal breast cancer (MDA-MB-231) cells. The elastic modulus was measured locally by AFM and OTM on single cells, using similar indentation approaches but different measurement parameters. Peak force tapping AFM was employed at nanonewton forces and high loading rates to draw a viscoelastic map of each cell and the results indicated that the region on top of the nucleus provided the most meaningful results. OTM was employed at those locations at piconewton forces and low loading rates, to measure the elastic modulus in a real elastic regime and rule out the contribution of viscous forces typical of AFM. When measured by either AFM or OTM, the cell lines' elasticity trend was similar for the aggressive MDA-MB-231 cells, which were found to be significantly softer than the other two cell types in both measurements. However, when comparing HBL-100 and MCF-7 cells, we found significant differences only when using OTM.

Transport in Halobacterium Halobium: Light-Induced Cation-Gradients, Amino Acid Transport Kinetics, and Properties of Transport Carriers

Science.gov (United States)

Lanyi, Janos K.

1977-01-01

Cell envelope vesicles prepared from H. halobium contain bacteriorhodopsin and upon illumination protons are ejected. Coupled to the proton motive force is the efflux of Na(+). Measurements of Na-22 flux, exterior pH change, and membrane potential, Delta(psi) (with the dye 3,3'-dipentyloxadicarbocyanine) indicate that the means of Na(+) transport is sodium/proton exchange. The kinetics of the pH changes and other evidence suggests that the antiport is electrogenic (H(+)/Na(++ greater than 1). The resulting large chemical gradient for Na(+) (outside much greater than inside), as well as the membrane potential, will drive the transport of 18 amino acids. The I9th, glutamate, is unique in that its accumulation is indifferent to Delta(psi): this amino acid is transported only when a chemical gradient for Na(+) is present. Thus, when more and more NaCl is included in the vesicles glutamate transport proceeds with longer and longer lags. After illumination the gradient of H+() collapses within 1 min, while the large Na(+) gradient and glutamate transporting activity persists for 10- 15 min, indicating that proton motive force is not necessary for transport. A chemical gradient of Na(+), arranged by suspending vesicles loaded with KCl in NaCl, drives glutamate transport in the dark without other sources of energy, with V(sub max) and K(sub m) comparable to light-induced transport. These and other lines of evidence suggest that the transport of glutamate is facilitated by symport with Na(+), in an electrically neutral fashion, so that only the chemical component of the Na(+) gradient is a driving force.

Optical Manipulation System Using a Plurality of Optical Traps

DEFF Research Database (Denmark)

2006-01-01

The present invention relates to an optical manipulation system (10) for generation of a plurality of optical traps for manipulation of micro-objects including nano-objects using electromagnetic radiation forces in a micro-object manipulation volume (14), the system comprising a spatially modulat...

Fundamentals of negative refractive index optical trapping: forces and radiation pressures exerted by focused Gaussian beams using the generalized Lorenz-Mie theory.

Science.gov (United States)

Ambrosio, Leonardo A; Hernández-Figueroa, Hugo E

2010-11-04

Based on the generalized Lorenz-Mie theory (GLMT), this paper reveals, for the first time in the literature, the principal characteristics of the optical forces and radiation pressure cross-sections exerted on homogeneous, linear, isotropic and spherical hypothetical negative refractive index (NRI) particles under the influence of focused Gaussian beams in the Mie regime. Starting with ray optics considerations, the analysis is then extended through calculating the Mie coefficients and the beam-shape coefficients for incident focused Gaussian beams. Results reveal new and interesting trapping properties which are not observed for commonly positive refractive index particles and, in this way, new potential applications in biomedical optics can be devised.

Quantitative optical trapping and optical manipulation of micro-sized objects

Directory of Open Access Journals (Sweden)

Rania Sayed

2017-10-01

Full Text Available An optical tweezers technique is used for ultraprecise micromanipulation to measure positions of micrometer scale objects with a precision down to the nanometer scale. It consists of a high performance research microscope with motorized scanning stage and sensitive position detection system. Up to 10 traps can be used quasi-simultaneously. Non photodamage optical trapping of Escherichia coli (E. coli bacteria cells of 2 µm in length, as an example of motile bacteria, has been shown in this paper. Also, efficient optical trapping and rotation of polystyrene latex particles of 3 µm in diameter have been studied, as an optical handle for the pick and place of other tiny objects. A fast galvoscanner is used to produce multiple optical traps for manipulation of micro-sized objects and optical forces of these trapped objects quantified and measured according to explanation of ray optics regime. The diameter of trapped particle is bigger than the wavelength of the trapping laser light. The force constant (k has been determined in real time from the positional time series recorded from the trapped object that is monitored by a CCD camera through a personal computer.

Space-charge limits on the transport of ion beams in a long alternating gradient system

International Nuclear Information System (INIS)

Tiefenback, M.G.

1986-11-01

We have experimentally studied the space-charge-dominated transport of ion beams in an alternating-gradient channel, without acceleration. We parameterize the focusing strength in terms of the zero-current ''betatron'' oscillation phase advance rate, σ 0 (degrees per focusing period). We have investigated the conditions for ''stability'', defined as the constancy of the total current and phase space area of the beam during transport. We find that the beam may be transported with neither loss of current nor growth in phase area if σ 0 0 . In this regime, the space-charge repulsive force can counter 98-99% of the externally applied focusing field, and the oscillation frequency of the beam particles can be depressed by self-forces to almost a factor of 10 below the zero-current value, limited only by the optical quality of our ion source. For σ 0 > 90 0 , we find that collective interactions bound the maintainable density of the beam, and we present a simple, semi-empirical characterization for stability, within our ability to distinguish the growth rate from zero in our apparatus. Our channel comprises 87 quadrupole lenses, 5 of which are used to prepare the beam for injection into the non-azimuthally-symmetric focusing channel

On the solution of the Hartree-Fock-Bogoliubov equations by the conjugate gradient method

International Nuclear Information System (INIS)

Egido, J.L.; Robledo, L.M.

1995-01-01

The conjugate gradient method is formulated in the Hilbert space for density and non-density dependent Hamiltonians. We apply it to the solution of the Hartree-Fock-Bogoliubov equations with constraints. As a numerical application we show calculations with the finite range density dependent Gogny force. The number of iterations required to reach convergence is reduced by a factor of three to four as compared with the standard gradient method. (orig.)

Thomas Young's contributions to geometrical optics.

Science.gov (United States)

Atchison, David A; Charman, W Neil

2011-07-01

In addition to his work on physical optics, Thomas Young (1773-1829) made several contributions to geometrical optics, most of which received little recognition in his time or since. We describe and assess some of these contributions: Young's construction (the basis for much of his geometric work), paraxial refraction equations, oblique astigmatism and field curvature, and gradient-index optics. © 2011 The Authors. Clinical and Experimental Optometry © 2011 Optometrists Association Australia.

Force detection of nuclear magnetic resonance

International Nuclear Information System (INIS)

Rugar, D.; Zueger, O.; Hoen, S.; Yannoni, C.S.; Vieth, H.M.; Kendrick, R.D.

1994-01-01

Micromechanical sensing of magnetic force was used to detect nuclear magnetic resonance with exceptional sensitivity and spatial resolution. With a 900 angstrom thick silicon nitride cantilever capable of detecting subfemtonewton forces, a single shot sensitivity of 1.6 x 10 13 protons was achieved for an ammonium nitrate sample mounted on the cantilever. A nearby millimeter-size iron particle produced a 600 tesla per meter magnetic field gradient, resulting in a spatial resolution of 2.6 micrometers in one dimension. These results suggest that magnetic force sensing is a viable approach for enhancing the sensitivity and spatial resolution of nuclear magnetic resonance microimaging

Nucleation in Synoptically Forced Cirrostratus

Science.gov (United States)

Lin, R.-F.; Starr, D. OC.; Reichardt, J.; DeMott, P. J.

2004-01-01

Formation and evolution of cirrostratus in response to weak, uniform and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied here, nucleation is first activated in the prescribed moist layer. A continuous cloud-top nucleation zone with a depth depending on the vertical humidity gradient and one of the nucleation parameters is developed afterward. For the heterogeneous nucleation cases, intermittent nucleation zones in the mid-upper portion of the cloud form where the relative humidity is on the rise, because existent ice crystals do not uptake excess water vapor efficiently, and ice nuclei (IN) are available. Vertical resolution as fine as 1 m is required for realistic simulation of the homogeneous-freezing-only scenario, while the model resolution requirement is more relaxed in the cases where heterogeneous nucleation dominates. Bulk microphysical and optical properties are evaluated and compared. Ice particle number flux divergence, which is due to the vertical gradient of the gravity-induced particle sedimentation, is constantly and rapidly changing the local ice number concentration, even in the nucleation zone. When the depth of the nucleation zone is shallow, particle number concentration decreases rapidly as ice particles grow and sediment away from the nucleation zone. When the depth of the nucleation zone is large, a region of high ice number concentration can be sustained. The depth of nucleation zone is an important parameter to be considered in parametric treatments of ice cloud generation.

Spherical gradient-index lenses as perfect imaging and maximum power transfer devices.

Science.gov (United States)

Gordon, J M

2000-08-01

Gradient-index lenses can be viewed from the perspectives of both imaging and nonimaging optics, that is, in terms of both image fidelity and achievable flux concentration. The simple class of gradient-index lenses with spherical symmetry, often referred to as modified Luneburg lenses, is revisited. An alternative derivation for established solutions is offered; the method of Fermat's strings and the principle of skewness conservation are invoked. Then these nominally perfect imaging devices are examined from the additional vantage point of power transfer, and the degree to which they realize the thermodynamic limit to flux concentration is determined. Finally, the spherical gradient-index lens of the fish eye is considered as a modified Luneburg lens optimized subject to material constraints.

Improving fiber-optic laser beam delivery by incorporating GRADIUM optics

International Nuclear Information System (INIS)

Hunter, B.V.; Leong, K.H.

1997-01-01

The performance of a fiber-optic laser beam delivery system strongly depends on the fiber and the optics used to image the fiber face on the workpiece. We have compared off-the-shelf homogenous (BK7) and GRADIUM (axial-gradient) singlets to determine what improvement the GRADIUM offers in practice to the typical laser user. The realized benefit for this application, although significant, is much smaller than would be realized by a conventional imaging application. The figure of merit for laser-based materials processing is the 86% energy-enclosure radius, which is not directly supported by commerical ray-tracing software. Therefore empirical rules of thumb are presented to understand when GRADIUM (or any other well-corrected optics) will yield meaningful improvement to the beam delivery system. copyright 1997 Optical Society of America

Strain gradient drives shear banding in metallic glasses

Science.gov (United States)

Tian, Zhi-Li; Wang, Yun-Jiang; Chen, Yan; Dai, Lan-Hong

2017-09-01

Shear banding is a nucleation-controlled process in metallic glasses (MGs) involving multiple temporal-spatial scales, which hinders a concrete understanding of its structural origin down to the atomic scale. Here, inspired by the morphology of composite materials, we propose a different perspective of MGs as a hard particle-reinforced material based on atomic-scale structural heterogeneity. The local stable structures indicated by a high level of local fivefold symmetry (L5FS) act as hard "particles" which are embedded in the relatively soft matrix. We demonstrate this concept by performing atomistic simulations of shear banding in CuZr MG. A shear band is prone to form in a sample with a high degree of L5FS which is slowly quenched from the liquid. An atomic-scale analysis on strain and the structural evolution reveals that it is the strain gradient effect that has originated from structural heterogeneity that facilitates shear transformation zones (STZs) to mature shear bands. An artificial composite model with a high degree of strain gradient, generated by inserting hard MG strips into a soft MG matrix, demonstrates a great propensity for shear banding. It therefore confirms the critical role strain gradient plays in shear banding. The strain gradient effect on shear banding is further quantified with a continuum model and a mechanical instability analysis. These physical insights might highlight the strain gradient as the hidden driving force in transforming STZs into shear bands in MGs.

Ponderomotive force, magnetic fields and hydrodynamics of laser produced plasmas

International Nuclear Information System (INIS)

Bobin, J.-L.; Wee Woo; Degroot, J.-S.

1977-01-01

Nonlinear effects deeply change the structure of a laser driven plasma flow. For high intensities, the radiation pressure should be taken into account. It acts through a ponderomotive force proportional to the electron density and to the gradient of the mean electric field energy density of the incident wave. Static magnetic fields originate from a term in the ponderomotive force which includes radiation absorption and whose curl is non zero. The basic properties of the structure are determined analytically in the absence of thermal conductivity and magnetic fields: steep density gradient close to the cut-off density, shelf at lower densities. The conditions of a steady state regime are set up. The isothermal case is specially investigated. It is shown that the cavities which are created in a motionless plasma may disappear due to the onset of a flow. Regions in which electromagnetic forces arising from the static field compensate the ponderomotive force are determined. The subsequent effects on the flow itself are studied [fr

Three-dimensional imaging and force characterization of multiple trapped particles in low NA counterpropagating optical traps

DEFF Research Database (Denmark)

Lindballe, T. B.; Kristensen, M. V.; Kylling, A. P.

2011-01-01

from two orthogonal views and used to determine the stiffness along all three spatial directions through power spectrum analysis and the equipartition method. For the case of three trapped beads we measure the dependence of the force constants on the counterpropagating beams waist separation....... The maximal transverse stiffnesses, is about 0.1 pN/mm per mW at a beam waist separation of 67 mm whereas the longitudinal stiffness is approximately 20 times lower. The experimental findings are in reasonable agreement with a recent physical-geometric optics calculation....

The Use of Remote Sensing to Resolve the Aerosol Radiative Forcing

Science.gov (United States)

Kaufman, Y. J.; Tanre, D.; Remer, Lorraine

1999-01-01

Satellites are used for remote sensing of aerosol optical thickness and optical properties in order to derive the aerosol direct and indirect radiative forcing of climate. Accuracy of the derived aerosol optical thickness is used as a measure of the accuracy in deriving the aerosol radiative forcing. Several questions can be asked to challenge this concept. Is the accuracy of the satellite-derived aerosol direct forcing limited to the accuracy of the measured optical thickness? What are the spectral bands needed to derive the total aerosol forcing? Does most of the direct or indirect aerosol forcing of climate originate from regions with aerosol concentrations that are high enough to be detected from space? What should be the synergism ground-based and space-borne remote sensing to solve the problem? We shall try to answer some of these questions, using AVIRIS airborne measurements and simulations.

Sensitive Detection of Small Particles in Fluids Using Optical Fiber Tip with Dielectrophoresis

Directory of Open Access Journals (Sweden)

Yi-Hsin Tai

2016-02-01

Full Text Available This work presents using a tapered fiber tip coated with thin metallic film to detect small particles in water with high sensitivity. When an AC voltage applied to the Ti/Al coated fiber tip and indium tin oxide (ITO substrate, a gradient electric field at the fiber tip induced attractive/repulsive force to suspended small particles due to the frequency-dependent dielectrophoresis (DEP effect. Such DEP force greatly enhanced the concentration of the small particles near the tip. The increase of the local concentration also increased the scattering of surface plasmon wave near the fiber tip. Combined both DEP effect and scattering optical near-field, we show the detection limit of the concentration for 1.36 μm polystyrene beads can be down to 1 particle/mL. The detection limit of the Escherichia coli (E. coli bacteria was 20 CFU/mL. The fiber tip sensor takes advantages of ultrasmall volume, label-free and simple detection system.

Spectroscopic ellipsometric modeling of a Bi–Te–Se write layer of an optical data storage device as guided by atomic force microscopy, scanning electron microscopy, and X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Wang, Hao; Madaan, Nitesh; Bagley, Jacob; Diwan, Anubhav [Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602 (United States); Liu, Yiqun [Department of Chemistry, Lehigh University, Bethlehem, PA 18015 (United States); Davis, Robert C. [Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602 (United States); Lunt, Barry M. [Department of Information Technology, Brigham Young University, Provo, UT 84602 (United States); Smith, Stacey J., E-mail: ssmith@chem.byu.edu [Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602 (United States); Linford, Matthew R., E-mail: mrlinford@chem.byu.edu [Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602 (United States)

2014-10-31

Conventional magnetic tape is the most widely used medium for archival data storage. However, data stored on it need to be migrated every ca. 5 years. Recently, optical discs that store information for hundreds, or even more than 1000 years, have been introduced to the market. We recently proposed that technology in these optical discs be used to make an optical tape that would show greater permanence than its magnetic counterpart. Here we provide a detailed optical characterization of a sputtered thin film of bismuth, tellurium, and selenium (BTS) that is a proposed data storage layer for these devices. The methodology described herein should be useful in the future development of related materials. Spectroscopic ellipsometry (SE) data are obtained using interference enhancement, and the modeling of this data is guided by results from atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray reflectivity (XRR). By AFM, ca. 40 nm BTS films show ca. 10 nm roughness. SEM images also suggest considerable roughness in the films and indicate that they are composed of 13.1 ± 5.9 nm grains. XRD confirms that the films are crystalline and predicts a grain size of 17 ± 2 nm. XRD results are consistent with the composition of the films — a mildly oxidized BTS material. Three models of increasing complexity are investigated to explain the SE data. The first model consists of a smooth, homogeneous BTS film. The second model adds a roughness layer to the previous model. The third model also has two layers. The bottom layer is modeled as a mixture of BTS and void using a Bruggeman effective medium approximation. The upper layer is similarly modeled, but with a gradient. The first model was unable to adequately model the SE data. The second model was an improvement — lower MSE (4.4) and good agreement with step height measurements. The third model was even better — very low MSE (2.6) and good agreement with AFM results. The

Multigrid preconditioned conjugate-gradient method for large-scale wave-front reconstruction.

Science.gov (United States)

Gilles, Luc; Vogel, Curtis R; Ellerbroek, Brent L

2002-09-01

We introduce a multigrid preconditioned conjugate-gradient (MGCG) iterative scheme for computing open-loop wave-front reconstructors for extreme adaptive optics systems. We present numerical simulations for a 17-m class telescope with n = 48756 sensor measurement grid points within the aperture, which indicate that our MGCG method has a rapid convergence rate for a wide range of subaperture average slope measurement signal-to-noise ratios. The total computational cost is of order n log n. Hence our scheme provides for fast wave-front simulation and control in large-scale adaptive optics systems.

Designing an experiment to measure cellular interaction forces

Science.gov (United States)

McAlinden, Niall; Glass, David G.; Millington, Owain R.; Wright, Amanda J.

2013-09-01

Optical trapping is a powerful tool in Life Science research and is becoming common place in many microscopy laboratories and facilities. The force applied by the laser beam on the trapped object can be accurately determined allowing any external forces acting on the trapped object to be deduced. We aim to design a series of experiments that use an optical trap to measure and quantify the interaction force between immune cells. In order to cause minimum perturbation to the sample we plan to directly trap T cells and remove the need to introduce exogenous beads to the sample. This poses a series of challenges and raises questions that need to be answered in order to design a set of effect end-point experiments. A typical cell is large compared to the beads normally trapped and highly non-uniform - can we reliably trap such objects and prevent them from rolling and re-orientating? In this paper we show how a spatial light modulator can produce a triple-spot trap, as opposed to a single-spot trap, giving complete control over the object's orientation and preventing it from rolling due, for example, to Brownian motion. To use an optical trap as a force transducer to measure an external force you must first have a reliably calibrated system. The optical trapping force is typically measured using either the theory of equipartition and observing the Brownian motion of the trapped object or using an escape force method, e.g. the viscous drag force method. In this paper we examine the relationship between force and displacement, as well as measuring the maximum displacement from equilibrium position before an object falls out of the trap, hence determining the conditions under which the different calibration methods should be applied.

Pose control of the chain composed of magnetic particles using external uniform and gradient magnetic fields

International Nuclear Information System (INIS)

Zhou, J. F.; Shao, C. L.; Gu, B. Q.

2016-01-01

Magnetic particles (MPs) are known to respond to a magnetic field and can be moved by magnetic force, which make them good carriers in bioengineering and pharmaceutical engineering. In this paper, a pose control method for the straight chain composed of MPs is proposed, and the chain with one pose can be moved to another position with another pose using alternately employed uniform and gradient magnetic fields. Based on computer simulations, it is revealed that in the uniform magnetic field, the MPs form a straight chain with the same separation space along the field lines, and once the uniform magnetic field rotates, the chain also rotates with the field. In the gradient magnetic field, the MPs move toward the higher field so that the translation of the chain can be realized. The simulation results indicate that while the uniform magnetic field is rotating, there exists certain hysteresis between the chain and the field, and the chain is not straight anymore. So the uniform magnetic field should rest at the target angle for a period to make the chain fully relax to be straight. For nanoMP, its magnetic moment directly determines the gradient magnetic force which is much smaller than the dipole–dipole force among MPs. Therefore, the translation of the chain is much more time-consuming than rotation. To enlarge the translational velocity, it is suggested to increase the size of MPs or the magnetic field gradient

Diurnal and seasonal characteristics of the optical properties and direct radiative forcing of different aerosol components in Seoul megacity.

Science.gov (United States)

Song, Sang-Keun; Shon, Zang-Ho; Park, Yeon-Hee

2017-12-01

The temporal variations (diurnal and seasonal) of the optical properties and direct aerosol radiative forcing (DARF) of different aerosol components (water-soluble, insoluble, black carbon (BC), and sea-salt) were analyzed using the hourly resolution data (PM 2.5 ) measured at an urban site in Seoul, Korea during 2010, based on a modeling approach. In general, the water-soluble component was predominant over all other components (with a higher concentration) in terms of its impact on the optical properties (except for absorbing BC) and DARF. The annual mean aerosol optical depth (AOD, τ) at 500nm for the water-soluble component was 0.38±0.07 (0.06±0.01 for BC). The forcing at the surface (DARF SFC ) and top of the atmosphere (DARF TOA ), and in the atmosphere (DARF ATM ) for most aerosol components (except for BC) during the daytime were highest in spring and lowest in late fall or early winter. The maximum DARF SFC occurred in the morning during most seasons (except for the water-soluble components showing peaks in the afternoon or noon in summer, fall, or winter), while the maximum DARF TOA occurred in the morning during spring and/or winter and in the afternoon during summer and/or fall. The estimated DARF SFC and DARF ATM of the water-soluble component were in the range of -49 to -84Wm -2 and +10 to +22Wm -2 , respectively. The DARF SFC and DARF ATM of BC were -26 to -39Wm -2 and +32 to +51Wm -2 , respectively, showing highest in summer and lowest in spring, with morning peaks regardless of the season. This positive DARF ATM of BC in this study area accounted for approximately 64% of the total atmospheric aerosol forcing due to strong radiative absorption, thus increasing atmospheric heating by 2.9±1.2Kday -1 (heating rate efficiency of 39K day -1 τ -1 ) and then causing further atmospheric warming. Copyright © 2017 Elsevier B.V. All rights reserved.

RACORO continental boundary layer cloud investigations: 1. Case study development and ensemble large-scale forcings

Science.gov (United States)

Vogelmann, Andrew M.; Fridlind, Ann M.; Toto, Tami; Endo, Satoshi; Lin, Wuyin; Wang, Jian; Feng, Sha; Zhang, Yunyan; Turner, David D.; Liu, Yangang; Li, Zhijin; Xie, Shaocheng; Ackerman, Andrew S.; Zhang, Minghua; Khairoutdinov, Marat

2015-06-01

Observation-based modeling case studies of continental boundary layer clouds have been developed to study cloudy boundary layers, aerosol influences upon them, and their representation in cloud- and global-scale models. Three 60 h case study periods span the temporal evolution of cumulus, stratiform, and drizzling boundary layer cloud systems, representing mixed and transitional states rather than idealized or canonical cases. Based on in situ measurements from the Routine AAF (Atmospheric Radiation Measurement (ARM) Aerial Facility) CLOWD (Clouds with Low Optical Water Depth) Optical Radiative Observations (RACORO) field campaign and remote sensing observations, the cases are designed with a modular configuration to simplify use in large-eddy simulations (LES) and single-column models. Aircraft measurements of aerosol number size distribution are fit to lognormal functions for concise representation in models. Values of the aerosol hygroscopicity parameter, κ, are derived from observations to be 0.10, which are lower than the 0.3 typical over continents and suggestive of a large aerosol organic fraction. Ensemble large-scale forcing data sets are derived from the ARM variational analysis, European Centre for Medium-Range Weather Forecasts, and a multiscale data assimilation system. The forcings are assessed through comparison of measured bulk atmospheric and cloud properties to those computed in "trial" large-eddy simulations, where more efficient run times are enabled through modest reductions in grid resolution and domain size compared to the full-sized LES grid. Simulations capture many of the general features observed, but the state-of-the-art forcings were limited at representing details of cloud onset, and tight gradients and high-resolution transients of importance. Methods for improving the initial conditions and forcings are discussed. The cases developed are available to the general modeling community for studying continental boundary clouds.

RACORO Continental Boundary Layer Cloud Investigations: 1. Case Study Development and Ensemble Large-Scale Forcings

Science.gov (United States)

Vogelmann, Andrew M.; Fridlind, Ann M.; Toto, Tami; Endo, Satoshi; Lin, Wuyin; Wang, Jian; Feng, Sha; Zhang, Yunyan; Turner, David D.; Liu, Yangang;

Density gradient in SiO 2 films on silicon as revealed by positron annihilation spectroscopy

Science.gov (United States)

Revesz, A. G.; Anwand, W.; Brauer, G.; Hughes, H. L.; Skorupa, W.

2002-06-01

Positron annihilation spectroscopy of thermally grown and deposited SiO 2 films on silicon shows in a non-destructive manner that these films have a gradient in their density. The gradient is most pronounced for the oxide grown in dry oxygen. Oxidation in water-containing ambient results in an oxide with reduced gradient, similarly to the gradient in the deposited oxide. These observations are in accordance with earlier optical and other studies using stepwise etching or a set of samples of varying thickness. The effective oxygen charge, which is very likely one of the reasons for the difference in the W parameters of silica glass and quartz crystal, could be even higher at some localized configurations in the SiO 2 films resulting in increased positron trapping.

Effects of ponderomotive forces and space-charge field on laser plasma hydrodynamics

International Nuclear Information System (INIS)

Cang Yu; Lu Xin; Wu Huichun; Zhang Jie

2005-01-01

Using a two-fluid two-temperature hydrodynamic code, authors studied the hydrodynamics in the interaction of intense (10 15 W/cm 2 ) ultrashort (150 fs) laser pulses and linear density plasmas. The simulation results show the ponderomotive force effect on the formation of the electron density ripples in under-dense region, such ripples increase the reflection of the laser pulse, and on the separation of the plasma in critical surface. Quasi-electroneutrality is not suitable in this case because of the different ponderomotive force and the gradient of thermal-pressure for ions and electrons. Ions are moved by the electrostatic force. Comparing with the simulation results from one-fluid two-temperature code, authors find that under strong ponderomotive force and gradient of thermo-pressure, two-fluid code is more suitable to simulate the hydrodynamics of plasmas. (authors)

Three gradients and the perception of flat and curved surfaces.

Science.gov (United States)

Cutting, J E; Millard, R T

1984-06-01

Researchers of visual perception have long been interested in the perceived slant of a surface and in the gradients that purportedly specify it. Slant is the angle between the line of sight and the tangent to the planar surface at any point, also called the surface normal. Gradients are the sources of information that grade, or change, with visual angle as one looks from one's feet upward to the horizon. The present article explores three gradients--perspective, compression, and density--and the phenomenal impression of flat and curved surfaces. The perspective gradient is measured at right angles to the axis of tilt at any point in the optic array; that is, when looking down a hallway at the tiles of a floor receding in the distance, perspective is measured by the x-axis width of each tile projected on the image plane orthogonal to the line of sight. The compression gradient is the ratio of y/x axis measures on the projected plane. The density gradient is measured by the number of tiles per unit solid visual angle. For flat surfaces and many others, perspective and compression gradients decrease with distance, and the density gradient increases. We discuss the manner in which these gradients change for various types of surfaces. Each gradient is founded on a different assumption about textures on the surfaces around us. In Experiment 1, viewers assessed the three-dimensional character of projections of flat and curved surfaces receding in the distance. They made pairwise judgments of preference and of dissimilarity among eight stimuli in each of four sets. The presence of each gradient was manipulated orthogonally such that each stimulus had zero, one, two, or three gradients appropriate for either a flat surface or a curved surface. Judgments were made were made for surfaces with both regularly shaped and irregularly shaped textures scattered on them. All viewer assessment were then scaled in one dimension. Multiple correlation and regression on the scale values

Effects of coating on the optical trapping efficiency of microspheres via geometrical optics approximation.

Science.gov (United States)

Park, Bum Jun; Furst, Eric M

2014-09-23

We present the optical trapping forces that are generated when a single laser beam strongly focuses on a coated dielectric microsphere. On the basis of geometrical optics approximation (GOA), in which a particle intercepts all of the rays that make up a single laser beam, we calculate the trapping forces with varying coating thickness and refractive index values. To increase the optical trapping efficiency, the refractive index (n(b)) of the coating is selected such that n(a) < n(b) < n(c), where na and nc are the refractive indices of the medium and the core material, respectively. The thickness of the coating also increases trapping efficiency. Importantly, we find that trapping forces for the coated particles are predominantly determined by two rays: the incident ray and the first refracted ray to the medium.

Thermal-gradient migration of brine inclusions in salt crystals

International Nuclear Information System (INIS)

Yagnik, S.K.

1982-09-01

It has been proposed that high-level nuclear waste be disposed in a geologic repository. Natural-salt deposits, which are being considered for this purpose, contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive-decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In this work, thermal gradient migration of both all-liquid and gas-liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot-stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusions were found to be dependent on temperature, temperature gradient, and inclusion shape and size. The velocities were also dictated by the interfacial mass transfer resistance at brine/solid interface. This interfacial resistance depends on the dislocation density in the crystal, which in turn, depends on the axial compressive loading of the crystal. At low axial loads, the dependence between the velocity and temperature gradient is non-linear.At high axial loads, however, the interfacial resistance is reduced and the migration velocity depends linearly on the temperature gradient. All-liquid inclusions filled with mixed brines were also studied. For gas-liquid inclusions, three different gas phases (helium, air and argon) were compared. Migration studies were also conducted on single crystallites of natural salt as well as in polycrystalline natural salt samples. The behavior of the inclusions at large angle grain boundaries was observed. 35 figures, 3 tables

Thermal gradient migration of brine inclusions in salt crystals

International Nuclear Information System (INIS)

Yagnik, S.K.

1982-01-01

Natural salt deposits, which are being considered for high-level nuclear wastes repositories, contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine (the all-liquid inclusions) migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In the present work, thermal gradient migration of both all-liquid and gas-liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot-stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusions were found to be dependent on temperature, temperature gradient, and inclusion shape and size. The velocities were also dictated by the interfacial mass transfer resistance at brine/solid interface. This interfacial resistance depends on the dislocation density in the crystal, which in turn, depends on the axial compressive loading of the crystal. At low axial loads, the dependence between the velocity and temperature gradient is nonlinear. At high axial loads, however, the interfacial resistance is reduced and the migration velocity depends linearly on the temperature gradient. All-liquid inclusions filled with mixed brines were also studied. For gas-liquid inclusions, three different gas phases (helium, air and argon) were compared. Migration studies were also conducted on single crystallites of natural salt as well as in polycrystalline natural salt samples. The behavior of the inclusions at large angle grain boudaries was observed

On deriving the Maxwell stress tensor method for calculating the optical force and torque on an object in harmonic electromagnetic fields

Science.gov (United States)

Ye, Qian; Lin, Haoze

2017-07-01

Though extensively used in calculating optical force and torque acting on a material object illuminated by laser, the Maxwell stress tensor (MST) method follows the electromagnetic linear and angular momentum balance that is usually derived in most textbooks for a continuous volume charge distribution in free space, if not resorting to the application of Noether’s theorem in electrodynamics. To cast the conservation laws into a physically appealing form involving the current densities of linear and angular momentum, on which the MST method is based, the divergence theorem is employed to transform a volume integral into a surface integral. When a material object of finite volume is put into the field, it brings about a discontinuity of field across its surface, due to the presence of induced surface charge and surface current. Ambiguity arises among students in whether the divergence theorem can still be directly used without any justification. By taking into account the effect of the induced surface charge and current, we present a simple pedagogical derivation for the MST method for calculating the optical force and torque on an object immersed in monochromatic optical field, without resorting to Noether’s theorem. Although the results turn out to be identical to those given in the standard textbooks, our derivation avoids the direct use of the divergence theorem on a discontinuous function.

On deriving the Maxwell stress tensor method for calculating the optical force and torque on an object in harmonic electromagnetic fields

International Nuclear Information System (INIS)

Ye, Qian; Lin, Haoze

2017-01-01

Though extensively used in calculating optical force and torque acting on a material object illuminated by laser, the Maxwell stress tensor (MST) method follows the electromagnetic linear and angular momentum balance that is usually derived in most textbooks for a continuous volume charge distribution in free space , if not resorting to the application of Noether’s theorem in electrodynamics. To cast the conservation laws into a physically appealing form involving the current densities of linear and angular momentum, on which the MST method is based, the divergence theorem is employed to transform a volume integral into a surface integral. When a material object of finite volume is put into the field, it brings about a discontinuity of field across its surface, due to the presence of induced surface charge and surface current. Ambiguity arises among students in whether the divergence theorem can still be directly used without any justification. By taking into account the effect of the induced surface charge and current, we present a simple pedagogical derivation for the MST method for calculating the optical force and torque on an object immersed in monochromatic optical field, without resorting to Noether’s theorem. Although the results turn out to be identical to those given in the standard textbooks, our derivation avoids the direct use of the divergence theorem on a discontinuous function. (paper)

The influence of ALN-Al gradient material gradient index on ballistic performance

International Nuclear Information System (INIS)

Wang Youcong; Liu Qiwen; Li Yao; Shen Qiang

2013-01-01

Ballistic performance of the gradient material is superior to laminated material, and gradient materials have different gradient types. Using ls-dyna to simulate the ballistic performance of ALN-AL gradient target plates which contain three gradient index (b = 1, b = 0.5, b = 2). Through Hopkinson bar numerical simulation to the target plate materials, we obtained the reflection stress wave and transmission stress wave state of gradient material to get the best gradient index. The internal stress state of gradient material is simulated by amplification processing of the target plate model. When the gradient index b is equal to 1, the gradient target plate is best of all.

Shear force distance control in a scanning near-field optical microscope: in resonance excitation of the fiber probe versus out of resonance excitation

International Nuclear Information System (INIS)

Lapshin, D.A.; Letokhov, V.S.; Shubeita, G.T.; Sekatskii, S.K.; Dietler, G.

2004-01-01

The experimental results of the direct measurement of the absolute value of interaction force between the fiber probe of a scanning near-field optical microscope (SNOM) operated in shear force mode and a sample, which were performed using combined SNOM-atomic force microscope setup, are discussed for the out-of-resonance fiber probe excitation mode. We demonstrate that the value of the tapping component of the total force for this mode at typical dither amplitudes is of the order of 10 nN and thus is quite comparable with the value of this force for in resonance fiber probe excitation mode. It is also shown that for all modes this force component is essentially smaller than the usually neglected static attraction force, which is of the order of 200 nN. The true contact nature of the tip-sample interaction during the out of resonance mode is proven. From this, we conclude that such a detection mode is very promising for operation in liquids, where other modes encounter great difficulties

Hydrodynamic Forces from Steep Waves in Rivers

Energy Technology Data Exchange (ETDEWEB)

Loevoll, A.

1996-12-31

The reservoir behind a hydroelectric power production dam has an enormous potential for destruction in case of a dam break. The present doctoral thesis evaluates the hydrodynamic forces from steep waves in rivers. In the laboratory, forces on a structure shaped as a vertical cylinder of rectangular cross section were measured, and the threshold condition for the bed sediment was investigated. A wave parameter {alpha} is introduced to describe the gradient of a wave front. The flow condition in the flume was reproduced by a 3-D numerical model. For various values of the wave parameter the forces were measured and compared to the drag force calculated from measured depth and velocity. From these comparisons the hydrodynamic force can be calculated as drag only, even in the case of a breaking wave front. The contribution from inertia relative to drag depends on the size of the structure. For larger structures the contributions may be important in steep waves. To study the initiation of motion (of sediments) under unsteady flow, waves of various parameter values were passed over a gravel covered bed. The initiation of motion starts before the peak of the wave, and is given by Shield`s relation if the friction slope is applied. No dependence upon the wave gradient was found. A relation was established which gives the critical shear stress if the friction slope is estimated by the bottom slope. 65 refs., 41 figs., 10 tabs.

Hydrodynamic Forces from Steep Waves in Rivers

International Nuclear Information System (INIS)

Loevoll, A.

1996-01-01

The reservoir behind a hydroelectric power production dam has an enormous potential for destruction in case of a dam break. The present doctoral thesis evaluates the hydrodynamic forces from steep waves in rivers. In the laboratory, forces on a structure shaped as a vertical cylinder of rectangular cross section were measured, and the threshold condition for the bed sediment was investigated. A wave parameter α is introduced to describe the gradient of a wave front. The flow condition in the flume was reproduced by a 3-D numerical model. For various values of the wave parameter the forces were measured and compared to the drag force calculated from measured depth and velocity. From these comparisons the hydrodynamic force can be calculated as drag only, even in the case of a breaking wave front. The contribution from inertia relative to drag depends on the size of the structure. For larger structures the contributions may be important in steep waves. To study the initiation of motion (of sediments) under unsteady flow, waves of various parameter values were passed over a gravel covered bed. The initiation of motion starts before the peak of the wave, and is given by Shield's relation if the friction slope is applied. No dependence upon the wave gradient was found. A relation was established which gives the critical shear stress if the friction slope is estimated by the bottom slope. 65 refs., 41 figs., 10 tabs

Optical tweezers principles and applications

CERN Document Server

Jones, Philip; Volpe, Giovanni

2015-01-01

Combining state-of-the-art research with a strong pedagogic approach, this text provides a detailed and complete guide to the theory, practice and applications of optical tweezers. In-depth derivation of the theory of optical trapping and numerical modelling of optical forces are supported by a complete step-by-step design and construction guide for building optical tweezers, with detailed tutorials on collecting and analysing data. Also included are comprehensive reviews of optical tweezers research in fields ranging from cell biology to quantum physics. Featuring numerous exercises and problems throughout, this is an ideal self-contained learning package for advanced lecture and laboratory courses, and an invaluable guide to practitioners wanting to enter the field of optical manipulation. The text is supplemented by www.opticaltweezers.org, a forum for discussion and a source of additional material including free-to-download, customisable research-grade software (OTS) for calculation of optical forces, dig...

Optical detection of ultrasound from optically rough surfaces using a custom CMOS sensor

International Nuclear Information System (INIS)

Achamfuo-Yeboah, S O; Light, R A; Sharpies, S D

2015-01-01

The optical detection of ultrasound from optically rough surfaces is severely limited when using a conventional interferometric or optical beam deflection (OBD) setup because the detected light is speckled. This means that complicated and expensive setups are required to detect ultrasound optically on rough surfaces. We present a CMOS integrated circuit that can detect laser ultrasound in the presence of speckle. The detector circuit is based on the simple knife edge detector. It is self-adapting and is fast, inxepensive, compact and robust. The CMOS circuit is implemented as a widefield array of 32×32 pixels. At each pixel the received light is compared with an adjacent pixel in order to determine the local light gradient. The result of this comparison is stored and used to connect each pixel to the positive or negative gradient output as appropriate (similar to a balanced knife edge detector). The perturbation of the surface due to ultrasound preserves the speckle distribution whilst deflecting it. The spatial disturbance of the speckle pattern due to the ultrasound is detected by considering each pair of pixels as a knife edge detector. The sensor can adapt itself to match the received optical speckle pattern in less than 0.1 μs, and then detect the ultrasound within 0.5 μs of adaptation. This makes it possible to repeatedly detect ultrasound from optically rough surfaces very quickly. The detector is capable of independent operation controlled by a local microcontroller, or it may be connected to a computer for more sophisticated configuration and control. We present the theory of its operation and discuss results validating the concept and operation of the device. We also present preliminary results from an improved design which grants a higher bandwidth, allowing for optical detection of higher frequency ultrasound

Wide-field schematic eye models with gradient-index lens.

Science.gov (United States)

Goncharov, Alexander V; Dainty, Chris

2007-08-01

We propose a wide-field schematic eye model, which provides a more realistic description of the optical system of the eye in relation to its anatomical structure. The wide-field model incorporates a gradient-index (GRIN) lens, which enables it to fulfill properties of two well-known schematic eye models, namely, Navarro's model for off-axis aberrations and Thibos's chromatic on-axis model (the Indiana eye). These two models are based on extensive experimental data, which makes the derived wide-field eye model also consistent with that data. A mathematical method to construct a GRIN lens with its iso-indicial contours following the optical surfaces of given asphericity is presented. The efficiency of the method is demonstrated with three variants related to different age groups. The role of the GRIN structure in relation to the lens paradox is analyzed. The wide-field model with a GRIN lens can be used as a starting design for the eye inverse problem, i.e., reconstructing the optical structure of the eye from off-axis wavefront measurements. Anatomically more accurate age-dependent optical models of the eye could ultimately help an optical designer to improve wide-field retinal imaging.

Coherent Bichromatic Force Deflection of Molecules

Science.gov (United States)

Kozyryev, Ivan; Baum, Louis; Aldridge, Leland; Yu, Phelan; Eyler, Edward E.; Doyle, John M.

2018-02-01

We demonstrate the effect of the coherent optical bichromatic force on a molecule, the polar free radical strontium monohydroxide (SrOH). A dual-frequency retroreflected laser beam addressing the X˜2Σ+↔A˜2Π1 /2 electronic transition coherently imparts momentum onto a cryogenic beam of SrOH. This directional photon exchange creates a bichromatic force that transversely deflects the molecules. By adjusting the relative phase between the forward and counterpropagating laser beams we reverse the direction of the applied force. A momentum transfer of 70 ℏk is achieved with minimal loss of molecules to dark states. Modeling of the bichromatic force is performed via direct numerical solution of the time-dependent density matrix and is compared with experimental observations. Our results open the door to further coherent manipulation of molecular motion, including the efficient optical deceleration of diatomic and polyatomic molecules with complex level structures.

Shape-dependent orientation of thermophoretic forces in microsystems

KAUST Repository

Li, Qi

2013-09-24

It is generally acknowledged that the direction of the thermophoretic force acting on microparticles is largely determined by the imposed temperature gradient, and the shape of the microparticle has little influence on its direction. We show that one type of thermophoretic force, emerged due to the advent of microfabrication techniques, is highly sensitive to object shape, and it is feasible to tune force orientation via proper shape design. We reveal the underlying mechanism by an asymptotic analysis of the Boltzmann equation and point out the reason why the classical thermophoretic force is insensitive to the particle shape, but the force in microsystems is. The discovered phenomenon could find its applications in methods for microparticle manipulation and separation.

Shape-dependent orientation of thermophoretic forces in microsystems

KAUST Repository

Li, Qi; Liang, Tengfei; Ye, Wenjing

2013-01-01

It is generally acknowledged that the direction of the thermophoretic force acting on microparticles is largely determined by the imposed temperature gradient, and the shape of the microparticle has little influence on its direction. We show that one type of thermophoretic force, emerged due to the advent of microfabrication techniques, is highly sensitive to object shape, and it is feasible to tune force orientation via proper shape design. We reveal the underlying mechanism by an asymptotic analysis of the Boltzmann equation and point out the reason why the classical thermophoretic force is insensitive to the particle shape, but the force in microsystems is. The discovered phenomenon could find its applications in methods for microparticle manipulation and separation.

Plasma membrane temperature gradients and multiple cell permeabilization induced by low peak power density femtosecond lasers

Directory of Open Access Journals (Sweden)

Allen L. Garner

2016-03-01

Full Text Available Calculations indicate that selectively heating the extracellular media induces membrane temperature gradients that combine with electric fields and a temperature-induced reduction in the electropermeabilization threshold to potentially facilitate exogenous molecular delivery. Experiments by a wide-field, pulsed femtosecond laser with peak power density far below typical single cell optical delivery systems confirmed this hypothesis. Operating this laser in continuous wave mode at the same average power permeabilized many fewer cells, suggesting that bulk heating alone is insufficient and temperature gradients are crucial for permeabilization. This work suggests promising opportunities for a high throughput, low cost, contactless method for laser mediated exogenous molecule delivery without the complex optics of typical single cell optoinjection, for potential integration into microscope imaging and microfluidic systems.

The Effect of Large Scale Salinity Gradient on Langmuir Turbulence

Science.gov (United States)

Fan, Y.; Jarosz, E.; Yu, Z.; Jensen, T.; Sullivan, P. P.; Liang, J.

2017-12-01

Langmuir circulation (LC) is believed to be one of the leading order causes of turbulent mixing in the upper ocean. It is important for momentum and heat exchange across the mixed layer (ML) and directly impact the dynamics and thermodynamics in the upper ocean and lower atmosphere including the vertical distributions of chemical, biological, optical, and acoustic properties. Based on Craik and Leibovich (1976) theory, large eddy simulation (LES) models have been developed to simulate LC in the upper ocean, yielding new insights that could not be obtained from field observations and turbulent closure models. Due its high computational cost, LES models are usually limited to small domain sizes and cannot resolve large-scale flows. Furthermore, most LES models used in the LC simulations use periodic boundary conditions in the horizontal direction, which assumes the physical properties (i.e. temperature and salinity) and expected flow patterns in the area of interest are of a periodically repeating nature so that the limited small LES domain is representative for the larger area. Using periodic boundary condition can significantly reduce computational effort in problems, and it is a good assumption for isotropic shear turbulence. However, LC is anisotropic (McWilliams et al 1997) and was observed to be modulated by crosswind tidal currents (Kukulka et al 2011). Using symmetrical domains, idealized LES studies also indicate LC could interact with oceanic fronts (Hamlington et al 2014) and standing internal waves (Chini and Leibovich, 2005). The present study expands our previous LES modeling investigations of Langmuir turbulence to the real ocean conditions with large scale environmental motion that features fresh water inflow into the study region. Large scale gradient forcing is introduced to the NCAR LES model through scale separation analysis. The model is applied to a field observation in the Gulf of Mexico in July, 2016 when the measurement site was impacted by

Optical tweezers and paradoxes in electromagnetism

International Nuclear Information System (INIS)

Pfeifer, Robert N C; Nieminen, Timo A; Heckenberg, Norman R; Rubinsztein-Dunlop, Halina

2011-01-01

The widespread application of optical forces and torques has contributed to renewed interest in the fundamentals of the electromagnetic force and torque, including long-standing paradoxes such as the Abraham–Minkowski controversy and the angular momentum density of a circularly polarized plane wave. We discuss the relationship between these electromagnetic paradoxes and optical tweezers. In particular, consideration of possible optical tweezers experiments to attempt to resolve these paradoxes strongly suggests that they are beyond experimental resolution, yielding identical observable results in all cases

Cartilage microindentation using cylindrical and spherical optical fiber indenters with integrated Bragg gratings as force sensors

Science.gov (United States)

Marchi, G.; Canti, O.; Baier, V.; Micallef, W.; Hartmann, B.; Alberton, P.; Aszodi, A.; Clausen-Schaumann, H.; Roths, J.

2018-02-01

Fiber optic microindentation sensors that have the potential to be integrated into arthroscopic instruments and to allow localizing degraded articular cartilage are presented in this paper. The indenters consist of optical fibers with integrated Bragg gratings as force sensors. In a basic configuration, the tip of the fiber optic indenter consists of a cleaved fiber end, forming a cylindrical flat punch indenter geometry. When using this indenter geometry, high stresses at the edges of the cylinder are present, which can disrupt the tissue structure. This is avoided with an improved version of the indenter. A spherical indenter tip that is formed by melting the end of the glass fiber. The spherical fiber tip shows the additional advantage of strongly reducing reflections from the fiber end. This allows a reduction of the length of the fiber optic sensor element from 65 mm of the flat punch type to 27 mm of the spherical punch. In order to compare the performance of both indenter types, in vitro stress-relaxation indentation experiments were performed on bovine articular cartilage with both indenter types, to assess biomechanical properties of bovine articular cartilage. For indentation depths between 60 μm and 300 μm, the measurements with both indenter types agreed very well with each other. This shows that both indenter geometries are suitable for microindentation measuremnts . The spherical indenter however has the additional advantage that it minimizes the risk to damage the surface of the tissue and has less than half dimensions than the flat indenter.

Entropy Generation in Steady Laminar Boundary Layers with Pressure Gradients

Directory of Open Access Journals (Sweden)

Donald M. McEligot

2014-07-01

Full Text Available In an earlier paper in Entropy [1] we hypothesized that the entropy generation rate is the driving force for boundary layer transition from laminar to turbulent flow. Subsequently, with our colleagues we have examined the prediction of entropy generation during such transitions [2,3]. We found that reasonable predictions for engineering purposes could be obtained for flows with negligible streamwise pressure gradients by adapting the linear combination model of Emmons [4]. A question then arises—will the Emmons approach be useful for boundary layer transition with significant streamwise pressure gradients as by Nolan and Zaki [5]. In our implementation the intermittency is calculated by comparison to skin friction correlations for laminar and turbulent boundary layers and is then applied with comparable correlations for the energy dissipation coefficient (i.e., non-dimensional integral entropy generation rate. In the case of negligible pressure gradients the Blasius theory provides the necessary laminar correlations.

Patterned gradient surface for spontaneous droplet transportation and water collection: simulation and experiment

International Nuclear Information System (INIS)

Tan, Xianhua; Zhu, Yiying; Shi, Tielin; Tang, Zirong; Liao, Guanglan

2016-01-01

We demonstrate spontaneous droplet transportation and water collection on wedge-shaped gradient surfaces consisting of alternating hydrophilic and hydrophobic regions. Droplets on the surfaces are modeled and simulated to analyze the Gibbs free energy and free energy gradient distributions. Big half-apex angle and great wettability difference result in considerable free energy gradient, corresponding to large driving force for spontaneous droplet transportation, thus causing the droplets to move towards the open end of the wedge-shaped hydrophilic regions, where the Gibbs free energy is low. Gradient surfaces are then fabricated and tested. Filmwise condensation begins on the hydrophilic regions, forming wedge-shaped tracks for water collection. Dropwise condensation occurs on the hydrophobic regions, where the droplet size distribution and departure diameters are controlled by the width of the regions. Condensate water from both the hydrophilic and hydrophobic regions are collected directionally to the open end of the wedge-shaped hydrophilic regions, agreeing with the simulations. Directional droplet transport and controllable departure diameters make the branched gradient surfaces more efficient than smooth surfaces for water collection, which proves that gradient surfaces are potential in water collection, microfluidic devices, anti-fogging and self-cleaning. (paper)

Near field plasmon and force microscopy

NARCIS (Netherlands)

de Hollander, R.B.G.; van Hulst, N.F.; Kooyman, R.P.H.

1995-01-01

A scanning plasmon near field optical microscope (SPNM) is presented which combines a conventional far field surface plasmon microscope with a stand-alone atomic force microscope (AFM). Near field plasmon and force images are recorded simultaneously both with a lateral resolution limited by the

A high-gradient high-duty-factor Rf photo-cathode electron gun

International Nuclear Information System (INIS)

Rimmer, Robert A.; Hartman, Neal; Lidia, Steven M.; Wang, Shaoheng

2002-01-01

We describe the analysis and preliminary design of a high-gradient, high-duty factor RF photocathode gun. The gun is designed to operate at high repetition rate or CW, with high gradient on the cathode surface to minimize emittance growth due to space charge forces at high bunch charge. The gun may also be operated in a solenoidal magnetic field for emittance compensation. The design is intended for use in short-pulse, high-charge, and high-repetition rate applications such as linac based X-ray sources. We present and compare the results of gun simulations using different codes, as well as RF and thermal analysis of the structure

A high-gradient high-duty-factor RF photo-cathode electron gun

International Nuclear Information System (INIS)

Rimmer, Robert; Hartman, N.; Lidia, S.; Wang, S.H.

2002-01-01

We describe the analysis and preliminary design of a high-gradient, high-duty factor RF photocathode gun. The gun is designed to operate at high repetition rate or CW, with high gradient on the cathode surface to minimize emittance growth due to space charge forces at high bunch charge. The gun may also be operated in a solenoidal magnetic field for emittance compensation. The design is intended for use in short-pulse, high-charge, and high-repetition rate applications such as linac based X-ray sources. We present and compare the results of gun simulations using different codes, as well as RF and thermal analysis of the structure

Diverse Expected Gradient Active Learning for Relative Attributes.

Science.gov (United States)

You, Xinge; Wang, Ruxin; Tao, Dacheng

2014-06-02

The use of relative attributes for semantic understanding of images and videos is a promising way to improve communication between humans and machines. However, it is extremely labor- and time-consuming to define multiple attributes for each instance in large amount of data. One option is to incorporate active learning, so that the informative samples can be actively discovered and then labeled. However, most existing active-learning methods select samples one at a time (serial mode), and may therefore lose efficiency when learning multiple attributes. In this paper, we propose a batch-mode active-learning method, called Diverse Expected Gradient Active Learning (DEGAL). This method integrates an informativeness analysis and a diversity analysis to form a diverse batch of queries. Specifically, the informativeness analysis employs the expected pairwise gradient length as a measure of informativeness, while the diversity analysis forces a constraint on the proposed diverse gradient angle. Since simultaneous optimization of these two parts is intractable, we utilize a two-step procedure to obtain the diverse batch of queries. A heuristic method is also introduced to suppress imbalanced multi-class distributions. Empirical evaluations of three different databases demonstrate the effectiveness and efficiency of the proposed approach.

Effects of high-gradient magnetic fields on living cell machinery

Czech Academy of Sciences Publication Activity Database

Zablotskyy, Vitaliy A.; Lunov, Oleg; Kubinová, Šárka; Polyakova, Tetyana; Syková, E.; Dejneka, Alexandr

2016-01-01

Roč. 49, č. 49 (2016), s. 1-23, č. článku 493003. ISSN 0022-3727 R&D Projects: GA MŠk LO1409 Grant - others:FUNBIO(XE) CZ.2.16/3.1.00/21568 Institutional support: RVO:68378271 Keywords : living cell * magnetic gradient force * cell mechanics * stem cell * magnetic field Subject RIV: BO - Biophysics Impact factor: 2.588, year: 2016

Servo control of an optical trap.

Science.gov (United States)

Wulff, Kurt D; Cole, Daniel G; Clark, Robert L

2007-08-01

A versatile optical trap has been constructed to control the position of trapped objects and ultimately to apply specified forces using feedback control. While the design, development, and use of optical traps has been extensive and feedback control has played a critical role in pushing the state of the art, few comprehensive examinations of feedback control of optical traps have been undertaken. Furthermore, as the requirements are pushed to ever smaller distances and forces, the performance of optical traps reaches limits. It is well understood that feedback control can result in both positive and negative effects in controlled systems. We give an analysis of the trapping limits as well as introducing an optical trap with a feedback control scheme that dramatically improves an optical trap's sensitivity at low frequencies.

Centipede assemblages along an urbanization gradient in the city of Heraklion, Crete (Greece

Directory of Open Access Journals (Sweden)

Gabriella Papastefanou

2015-06-01

Full Text Available Global urbanization is a major force that causes alteration and loss of natural habitats. Urban ecosystems are strongly affected by humans and there is a gradient of decreasing human influence from city centers to natural habitats. To study ecological changes along this continuum, researchers introduced the urban-rural gradient approach. The responses of centipedes to an urbanization gradient (urban-suburban-rural areas were studied using pitfall traps in and near the city of Heraklion, in the island of Crete, Greece, from November 2010 to November 2011. Our results do not support the intermediate disturbance hypothesis, in which suburban areas located in the transitional zone between urban and rural habitats failed to indicate significant increase in terms of species richness and diversity.

Microfluidic high gradient magnetic cell separation

Science.gov (United States)

Inglis, David W.; Riehn, Robert; Sturm, James C.; Austin, Robert H.

2006-04-01

Separation of blood cells by native susceptibility and by the selective attachment of magnetic beads has recently been demonstrated on microfluidic devices. We discuss the basic principles of how forces are generated via the magnetic susceptibility of an object and how microfluidics can be combined with micron-scale magnetic field gradients to greatly enhance in principle the fractionating power of magnetic fields. We discuss our efforts and those of others to build practical microfluidic devices for the magnetic separation of blood cells. We also discuss our attempts to integrate magnetic separation with other microfluidic features for developing handheld medical diagnostic tools.

Drift forces on vacancies and interstitials in alloys with radiation-induced segregation

International Nuclear Information System (INIS)

Wolfer, W.G.

1983-01-01

Radiation-induced segregation in alloys leads to compositional gradients around point defect sinks such as voids and dislocations. These compositional gradients in turn affect the drift forces on both interstitials and vacancies and thereby modify the bias. Linear irreversible thermodynamics is employed to derive the total drift force on interstitials and vacancies in substitutional binary alloys. The obtained results are evaluated for binary Fe-Ni alloys. It is shown that radiation-induced segregation produces new drift forces which can be of the same order of magnitude as the stress-induced drift force produced by edge dislocations in an alloy with uniform composition. Hence, segregation results in a significant modification of the bias for void nucleation and swelling. The additional drift forces on interstitials and vacancies are due to the compositional dependence of the formation and migration energies; due to the dependence of the point defect's strain energy on the local elastic properties; due to a coherency strain field caused by lattice parameter variations; and finally due to the Kirkendall force produced by the difference in tracer mobilities. Estimates of these forces given for Fe-Ni alloys indicate that the Kirkendall force is small compared to the other segregation-induced forces on interstitials. In contrast, the Kirkendall force seems to be the dominant one for vacancies. (orig.)

Disaggregation and separation dynamics of magnetic particles in a microfluidic flow under an alternating gradient magnetic field

Science.gov (United States)

Cao, Quanliang; Li, Zhenhao; Wang, Zhen; Qi, Fan; Han, Xiaotao

2018-05-01

How to prevent particle aggregation in the magnetic separation process is of great importance for high-purity separation, while it is a challenging issue in practice. In this work, we report a novel method to solve this problem for improving the selectivity of size-based separation by use of a gradient alternating magnetic field. The specially designed magnetic field is capable of dynamically adjusting the magnetic field direction without changing the direction of magnetic gradient force acting on the particles. Using direct numerical simulations, we show that particles within a certain center-to-center distance are inseparable under a gradient static magnetic field since they are easy aggregated and then start moving together. By contrast, it has been demonstrated that alternating repulsive and attractive interaction forces between particles can be generated to avoid the formation of aggregations when the alternating gradient magnetic field with a given alternating frequency is applied, enabling these particles to be continuously separated based on size-dependent properties. The proposed magnetic separation method and simulation results have the significance for fundamental understanding of particle dynamic behavior and improving the separation efficiency.

Updating optical pseudoinverse associative memories.

Science.gov (United States)

Telfer, B; Casasent, D

1989-07-01

Selected algorithms for adding to and deleting from optical pseudoinverse associative memories are presented and compared. New realizations of pseudoinverse updating methods using vector inner product matrix bordering and reduced-dimensionality Karhunen-Loeve approximations (which have been used for updating optical filters) are described in the context of associative memories. Greville's theorem is reviewed and compared with the Widrow-Hoff algorithm. Kohonen's gradient projection method is expressed in a different form suitable for optical implementation. The data matrix memory is also discussed for comparison purposes. Memory size, speed and ease of updating, and key vector requirements are the comparison criteria used.

Great bowerbirds create theaters with forced perspective when seen by their audience.

Science.gov (United States)

Endler, John A; Endler, Lorna C; Doerr, Natalie R

2010-09-28

Birds in the infraorder Corvida [1] (ravens, jays, bowerbirds) are renowned for their cognitive abilities [2-4], which include advanced problem solving with spatial inference [4-8], tool use and complex constructions [7-10], and bowerbird cognitive ability is associated with mating success [11]. Great bowerbird males construct bowers with a long avenue from within which females view the male displaying over his bower court [10]. This predictable audience viewpoint is a prerequisite for forced (altered) visual perspective [12-14]. Males make courts with gray and white objects that increase in size with distance from the avenue entrance. This gradient creates forced visual perspective for the audience; court object visual angles subtended on the female viewer's eye are more uniform than if the objects were placed at random. Forced perspective can yield false perception of size and distance [12, 15]. After experimental reversal of their size-distance gradient, males recovered their gradients within 3 days, and there was little difference from the original after 2 wks. Variation among males in their forced-perspective quality as seen by their female audience indicates that visual perspective is available for use in mate choice, perhaps as an indicator of cognitive ability. Regardless of function, the creation and maintenance of forced visual perspective is clearly important to great bowerbirds and suggests the possibility of a previously unknown dimension of bird cognition. Copyright © 2010 Elsevier Ltd. All rights reserved.

The proton motive force generated in Leuconostoc oenos by L-malate fermentation

NARCIS (Netherlands)

Salema, Madalena; Lolkema, Juke S.; San Romão, M.V.; Loureiro Dias, Maria C.

In cells of Leuconostoc oenos, the fermentation of L-malic acid generates both a transmembrane pH gradient, inside alkaline, and an electrical potential gradient, inside negative. In resting cells, the proton motive force ranged from -170 mV to -88 mV between pH 3.1 and 5.6 in the presence of

System modelling of a lateral force microscope

International Nuclear Information System (INIS)

Michal, Guillaume; Lu, Cheng; Kiet Tieu, A

2008-01-01

To quantitatively analyse lateral force microscope measurements one needs to develop a model able to relate the photodiode signal to the force acting on the tip apex. In this paper we focus on the modelling of the interaction between the cantilever and the optical chain. The laser beam is discretized by a set of rays which propagates in the system. The analytical equation of a single ray's position on the optical sensor is presented as a function of the reflection's state on top of the cantilever. We use a finite element analysis on the cantilever to connect the optical model with the force acting on the tip apex. A first-order approximation of the constitutive equations are derived along with a definition of the system's crosstalk. Finally, the model is used to analytically simulate the 'wedge method' in the presence of crosstalk in 2D. The analysis shows how the torsion loop and torsion offset signals are affected by the crosstalk.

THE ORIGIN OF COLOR GRADIENTS IN EARLY-TYPE SYSTEMS AND THEIR COMPACTNESS AT HIGH-z

International Nuclear Information System (INIS)

La Barbera, F.; De Carvalho, R. R.

2009-01-01

In this Letter, we present mean optical+NIR color gradient estimates for 5080 early-type galaxies (ETGs) in the grizY JHK wavebands of the Sloan Digital Sky Survey plus the UKIRT Infrared Deep Sky Survey. The color gradient is estimated as the logarithmic slope of the radial color profile in ETGs. With such a large sample size, we study the variation of the mean color gradient as a function of waveband with unprecedented accuracy. We find that (1) color gradients are mainly due, on average, to a metallicity variation of about -0.4 dex per decade in galaxy radius; and (2) a small, but significant, positive age gradient is present, on average, in ETGs, with the inner stellar population being slightly younger, by ∼0.1 dex per radial decade, than the outer one. Also, we show that the presence of a positive mean age gradient in ETGs, as found in the present study, implies their effective radius to be smaller at high-z, consistent with observations.

Arginine promotes Proteus mirabilis motility and fitness by contributing to conservation of the proton gradient and proton motive force.

Science.gov (United States)

Armbruster, Chelsie E; Hodges, Steven A; Smith, Sara N; Alteri, Christopher J; Mobley, Harry L T

2014-10-01

Swarming contributes to Proteus mirabilis pathogenicity by facilitating access to the catheterized urinary tract. We previously demonstrated that 0.1-20 mmol/L arginine promotes swarming on normally nonpermissive media and that putrescine biosynthesis is required for arginine-induced swarming. We also previously determined that arginine-induced swarming is pH dependent, indicating that the external proton concentration is critical for arginine-dependent effects on swarming. In this study, we utilized survival at pH 5 and motility as surrogates for measuring changes in the proton gradient (ΔpH) and proton motive force (μH(+) ) in response to arginine. We determined that arginine primarily contributes to ΔpH (and therefore μH(+) ) through the action of arginine decarboxylase (speA), independent of the role of this enzyme in putrescine biosynthesis. In addition to being required for motility, speA also contributed to fitness during infection. In conclusion, consumption of intracellular protons via arginine decarboxylase is one mechanism used by P. mirabilis to conserve ΔpH and μH(+) for motility. © 2014 The Authors. MicrobiologyOpen published by John Wiley & Sons Ltd.

Combining Step Gradients and Linear Gradients in Density.

Science.gov (United States)

Kumar, Ashok A; Walz, Jenna A; Gonidec, Mathieu; Mace, Charles R; Whitesides, George M

2015-06-16

Combining aqueous multiphase systems (AMPS) and magnetic levitation (MagLev) provides a method to produce hybrid gradients in apparent density. AMPS—solutions of different polymers, salts, or surfactants that spontaneously separate into immiscible but predominantly aqueous phases—offer thermodynamically stable steps in density that can be tuned by the concentration of solutes. MagLev—the levitation of diamagnetic objects in a paramagnetic fluid within a magnetic field gradient—can be arranged to provide a near-linear gradient in effective density where the height of a levitating object above the surface of the magnet corresponds to its density; the strength of the gradient in effective density can be tuned by the choice of paramagnetic salt and its concentrations and by the strength and gradient in the magnetic field. Including paramagnetic salts (e.g., MnSO4 or MnCl2) in AMPS, and placing them in a magnetic field gradient, enables their use as media for MagLev. The potential to create large steps in density with AMPS allows separations of objects across a range of densities. The gradients produced by MagLev provide resolution over a continuous range of densities. By combining these approaches, mixtures of objects with large differences in density can be separated and analyzed simultaneously. Using MagLev to add an effective gradient in density also enables tuning the range of densities captured at an interface of an AMPS by simply changing the position of the container in the magnetic field. Further, by creating AMPS in which phases have different concentrations of paramagnetic ions, the phases can provide different resolutions in density. These results suggest that combining steps in density with gradients in density can enable new classes of separations based on density.

Acoustic interaction forces between small particles in an ideal fluid

DEFF Research Database (Denmark)

Silva, Glauber T.; Bruus, Henrik

2014-01-01

We present a theoretical expression for the acoustic interaction force between small spherical particles suspended in an ideal fluid exposed to an external acoustic wave. The acoustic interaction force is the part of the acoustic radiation force on one given particle involving the scattered waves...... from the other particles. The particles, either compressible liquid droplets or elastic microspheres, are considered to be much smaller than the acoustic wavelength. In this so-called Rayleigh limit, the acoustic interaction forces between the particles are well approximated by gradients of pair...

Significance of human retinal optic disk localization in various retinal eye diseases

International Nuclear Information System (INIS)

Basit, A.

2011-01-01

Optic Disk is one of the prominent features in human fundus images. Automatic localization and segmentation of optic disk can help in early diagnosis of diabetic retinopathies and preventing vision loss. In this paper robust method for optic disk detection and extraction of optic disk boundary is proposed based on morphological operations, smoothing filters and markers controlled watershed transform. This method has shown significant improvements in terms of detection and boundaries extraction of optic disk. This method used two types of markers: internal marker and external marker. These markers first modified the gradient magnitude image and then watershed transformation is applied on this modified gradient magnitude image for boundary extraction. The proposed method has optic disk detection success rate of 100% for Shifa and 87.6% for DIARETDB1 databases. Proposed method achieved average overlap of 51.19% for DIARETDB1 database and 73.98% for Shifa database which is higher than currents methods. Experimental results clearly demonstrate an efficient performance of the proposed algorithm. (author)

Scanning probe and optical tweezer investigations of biomolecular interactions

International Nuclear Information System (INIS)

Rigby-Singleton, Shellie

2002-01-01

A complex array of intermolecular forces controls the interactions between and within biological molecules. The desire to empirically explore the fundamental forces has led to the development of several biophysical techniques. Of these, the atomic force microscope (AFM) and the optical tweezers have been employed throughout this thesis to monitor the intermolecular forces involved in biomolecular interactions. The AFM is a well-established force sensing technique capable of measuring biomolecular interactions at a single molecule level. However, its versatility has not been extrapolated to the investigation of a drug-enzyme complex. The energy landscape for the force induced dissociation of the DHFR-methotrexate complex was studied. Revealing an energy barrier to dissociation located ∼0.3 nm from the bound state. Unfortunately, the AFM has a limited range of accessible loading rates and in order to profile the complete energy landscape alternative force sensing instrumentation should be considered, for example the BFP and optical tweezers. Thus, this thesis outlines the development and construction an optical trap capable of measuring intermolecular forces between biomolecules at the single molecule level. To demonstrate the force sensing abilities of the optical set up, proof of principle measurements were performed which investigate the interactions between proteins and polymer surfaces subjected to varying degrees of argon plasma treatment. Complementary data was gained from measurements performed independently by the AFM. Changes in polymer resistance to proteins as a response to changes in polymer surface chemistry were detected utilising both AFM and optical tweezers measurements. Finally, the AFM and optical tweezers were employed as ultrasensitive biosensors. Single molecule investigations of the antibody-antigen interaction between the cardiac troponin I marker and its complementary antibody, reveals the impact therapeutic concentrations of heparin have

Design and performance of a high-resolution frictional force microscope with quantitative three-dimensional force sensitivity

International Nuclear Information System (INIS)

Dienwiebel, M.; Kuyper, E. de; Crama, L.; Frenken, J.W.M.; Heimberg, J.A.; Spaanderman, D.-J.; Glatra van Loon, D.; Zijlstra, T.; Drift, E. van der

2005-01-01

In this article, the construction and initial tests of a frictional force microscope are described. The instrument makes use of a microfabricated cantilever that allows one to independently measure the lateral forces in X and Y directions as well as the normal force. We use four fiber-optic interferometers to detect the motion of the sensor in three dimensions. The properties of our cantilevers allow easy and accurate normal and lateral force calibration, making it possible to measure the lateral force on a fully quantitative basis. First experiments on highly oriented pyrolytic graphite demonstrate that the microscope is capable of measuring lateral forces with a resolution down to 15 pN

On the influence of cloud fraction diurnal cycle and sub-grid cloud optical thickness variability on all-sky direct aerosol radiative forcing

International Nuclear Information System (INIS)

Min, Min; Zhang, Zhibo

2014-01-01

The objective of this study is to understand how cloud fraction diurnal cycle and sub-grid cloud optical thickness variability influence the all-sky direct aerosol radiative forcing (DARF). We focus on the southeast Atlantic region where transported smoke is often observed above low-level water clouds during burning seasons. We use the CALIOP observations to derive the optical properties of aerosols. We developed two diurnal cloud fraction variation models. One is based on sinusoidal fitting of MODIS observations from Terra and Aqua satellites. The other is based on high-temporal frequency diurnal cloud fraction observations from SEVIRI on board of geostationary satellite. Both models indicate a strong cloud fraction diurnal cycle over the southeast Atlantic region. Sensitivity studies indicate that using a constant cloud fraction corresponding to Aqua local equatorial crossing time (1:30 PM) generally leads to an underestimated (less positive) diurnal mean DARF even if solar diurnal variation is considered. Using cloud fraction corresponding to Terra local equatorial crossing time (10:30 AM) generally leads overestimation. The biases are a typically around 10–20%, but up to more than 50%. The influence of sub-grid cloud optical thickness variability on DARF is studied utilizing the cloud optical thickness histogram available in MODIS Level-3 daily data. Similar to previous studies, we found the above-cloud smoke in the southeast Atlantic region has a strong warming effect at the top of the atmosphere. However, because of the plane-parallel albedo bias the warming effect of above-cloud smoke could be significantly overestimated if the grid-mean, instead of the full histogram, of cloud optical thickness is used in the computation. This bias generally increases with increasing above-cloud aerosol optical thickness and sub-grid cloud optical thickness inhomogeneity. Our results suggest that the cloud diurnal cycle and sub-grid cloud variability are important factors

Immersion transmission ellipsometry (ITE) for the determination of orientation gradients in photoalignment layers

Science.gov (United States)

Jung, C. C.; Stumpe, J.

2014-09-01

The capability of the method of immersion transmission ellipsometry (ITE) (Jung et al. Int Patent WO, 2004/109260) to not only determine three-dimensional refractive indices in anisotropic thin films (which was already possible in the past), but even their gradients along the z-direction (perpendicular to the film plane) is investigated in this paper. It is shown that the determination of orientation gradients in deep-sub-μm films becomes possible by applying ITE in combination with reflection ellipsometry. The technique is supplemented by atomic force microscopy for measuring the film thickness. For a photo-oriented thin film, no gradient was found, as expected. For a photo-oriented film, which was subsequently annealed in a nematic liquid crystalline phase, an order was found similar to the one applied in vertically aligned nematic displays, with a tilt angle varying along the z-direction. For fresh films, gradients were only detected for the refractive index perpendicular to the film plane, as expected.

Microstructure actuation and gas sensing by the Knudsen thermal force

Energy Technology Data Exchange (ETDEWEB)

Strongrich, Andrew; Alexeenko, Alina, E-mail: alexeenk@purdue.edu [School of Aeronautics and Astronautics and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)

2015-11-09

The generation of forces and moments on structures immersed in rarefied non-isothermal gas flows has received limited practical implementation since first being discovered over a century ago. The formation of significant thermal stresses requires both large thermal gradients and characteristic dimensions which are comparable to the gas molecular mean free path. For macroscopic geometries, this necessitates impractically high temperatures and very low pressures. At the microscale, however, these conditions are easily achieved, allowing the effects to be exploited, namely, for gas-property sensing and microstructure actuation. In this letter, we introduce and experimentally evaluate performance of a microelectromechanical in-plane Knudsen radiometric actuator, a self-contained device having Knudsen thermal force generation, sensing, and tuning mechanisms integrated onto the same platform. Sensitivity to ambient pressure, temperature gradient, as well as gas composition is demonstrated. Results are presented in terms of a non-dimensional force coefficient, allowing measurements to be directly compared to the previous experimental and computational data on out-of-plane cantilevered configurations.

How to measure load-dependent kinetics of individual motor molecules without a force clamp

DEFF Research Database (Denmark)

Sung, J.; Mortensen, Kim; Spudich, J.A.

2017-01-01

Single-molecule force spectroscopy techniques, including optical trapping, magnetic trapping, and atomic force microscopy, have provided unprecedented opportunities to understand biological processes at the smallest biological length scales. For example, they have been used to elucidate the molec......Single-molecule force spectroscopy techniques, including optical trapping, magnetic trapping, and atomic force microscopy, have provided unprecedented opportunities to understand biological processes at the smallest biological length scales. For example, they have been used to elucidate...... functions at the single molecule level, such as conformational changes and force-generation of individual motor proteins or force-dependent kinetics in molecular interactions. Here, we describe a new method, “Harmonic Force Spectroscopy (HFS).” With a conventional dual-beam optical trap and a simple...... concepts, experimental setup, step-by-step experimental protocol, theory, data analysis, and results....

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

Science.gov (United States)

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

2012-02-01

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.

A STUDY OF SOLAR PHOTOSPHERIC TEMPERATURE GRADIENT VARIATION USING LIMB DARKENING MEASUREMENTS

Energy Technology Data Exchange (ETDEWEB)

Criscuoli, Serena [National Solar Observatory, Boulder, CO 80303 (United States); Foukal, Peter [192 Willow Road, Nahant, MA 01908 (United States)

2017-01-20

The variation in area of quiet magnetic network measured over the sunspot cycle should modulate the spatially averaged photospheric temperature gradient, since temperature declines with optical depth more gradually in magnetic flux tube atmospheres. Yet, limb darkening measurements show no dependence upon activity level, even at an rms precision of 0.04%. We study the sensitivity of limb darkening to changes in area filling factor using a 3D MHD model of the magnetized photosphere. The limb darkening change expected from the measured 11-year area variation lies below the level of measured limb darkening variations, for a reasonable range of magnetic flux in quiet network and internetwork regions. So the remarkably constant limb darkening observed over the solar activity cycle is not inconsistent with the measured 11-year change in area of quiet magnetic network. Our findings offer an independent constraint on photospheric temperature gradient changes reported from measurements of the solar spectral irradiance from the Spectral Irradiance Monitor, and recently, from wavelength-differential spectrophotometry using the Solar Optical Telescope aboard the HINODE spacecraft.

Design of LED projector based on gradient-index lens

Science.gov (United States)

Qian, Liyong; Zhu, Xiangbing; Cui, Haitian; Wang, Yuanhang

2018-01-01

In this study, a new type of projector light path is designed to eliminate the deficits of existing projection systems, such as complex structure and low collection efficiency. Using a three-color LED array as the lighting source, by means of the special optical properties of a gradient-index lens, the complex structure of the traditional projector is simplified. Traditional components, such as the color wheel, relay lens, and mirror, become unnecessary. In this way, traditional problems, such as low utilization of light energy and loss of light energy, are solved. With the help of Zemax software, the projection lens is optimized. The optimized projection lens, LED, gradient-index lens, and digital micromirror device are imported into Tracepro. The ray tracing results show that both the utilization of light energy and the uniformity are improved significantly.

Design and Fabrication of Large Diameter Gradient-Index Lenses for Dual-Band Visible to Short-Wave Infrared Imaging Applications

Science.gov (United States)

Visconti, Anthony Joseph

The fabrication of gradient-index (GRIN) optical elements is quite challenging, which has traditionally restricted their use in many imaging systems; consequently, commercial-level GRIN components usually exist in one particular market or niche application space. One such fabrication technique, ion exchange, is a well-known process used in the chemical strengthening of glass, the fabrication of waveguide devices, and the production of small diameter GRIN optical relay systems. However, the manufacturing of large diameter ion-exchanged GRIN elements has historically been limited by long diffusion times. For example, the diffusion time for a 20 mm diameter radial GRIN lens in commercially available ion exchange glass for small diameter relays, is on the order of a year. The diffusion time can be dramatically reduced by addressing three key ion exchange process parameters; the composition of the glass, the diffusion temperature, and the composition of the salt bath. Experimental work throughout this thesis aims to (1) scale up the ion exchange diffusion process to 20 mm diameters for a fast-diffusing titania silicate glass family in both (2) sodium ion for lithium ion (Na+ for Li+) and lithium ion for sodium ion (Li+ for Na+) exchange directions, while (3) utilizing manufacturing friendly salt bath compositions. In addition, optical design studies have demonstrated that an important benefit of gradient-index elements in imaging systems is the added degree of freedom introduced with a gradient's optical power. However, these studies have not investigated the potential usefulness of GRIN materials in dual-band visible to short-wave infrared (vis-SWIR) imaging systems. The unique chromatic properties of the titania silicate ion exchange glass become a significant degree of freedom in the design process for these color-limited, broadband imaging applications. A single GRIN element can replace a cemented doublet or even a cemented triplet, without loss in overall system

Momentum-weighted conjugate gradient descent algorithm for gradient coil optimization.

Science.gov (United States)

Lu, Hanbing; Jesmanowicz, Andrzej; Li, Shi-Jiang; Hyde, James S

2004-01-01

MRI gradient coil design is a type of nonlinear constrained optimization. A practical problem in transverse gradient coil design using the conjugate gradient descent (CGD) method is that wire elements move at different rates along orthogonal directions (r, phi, z), and tend to cross, breaking the constraints. A momentum-weighted conjugate gradient descent (MW-CGD) method is presented to overcome this problem. This method takes advantage of the efficiency of the CGD method combined with momentum weighting, which is also an intrinsic property of the Levenberg-Marquardt algorithm, to adjust step sizes along the three orthogonal directions. A water-cooled, 12.8 cm inner diameter, three axis torque-balanced gradient coil for rat imaging was developed based on this method, with an efficiency of 2.13, 2.08, and 4.12 mT.m(-1).A(-1) along X, Y, and Z, respectively. Experimental data demonstrate that this method can improve efficiency by 40% and field uniformity by 27%. This method has also been applied to the design of a gradient coil for the human brain, employing remote current return paths. The benefits of this design include improved gradient field uniformity and efficiency, with a shorter length than gradient coil designs using coaxial return paths. Copyright 2003 Wiley-Liss, Inc.

In Situ Gold Nanoparticle Gradient Formation in a 3D Meso- and Macroporous Polymer Matrix.

Science.gov (United States)

Penders, Jelle; Rajasekharan, Anand K; Hulander, Mats; Andersson, Martin

2017-08-01

Herein, the development and characterization of a 3D gradient structure of gold nanoparticles is described. The gradient of gold nanoparticles is made in situ in a macroporous nonionic block copolymer hydrogel matrix, through gold ion diffusion control. The polymer provides a matrix for diffusion of gold ions, acts as a template for controlling nanoparticle growth, and facilitates the in situ reduction of gold ions to gold nanoparticles. A clear gradient in gold nanoparticles is observed across the 3D space of the polymer matrix using scanning electron microscopy, fluorescence microscopy, atomic force microscopy, and thermogravimetric analysis. The particle gradient is further functionalized with both hydrophobic and hydrophilic groups via thiol-gold linkage to demonstrate the ability to form gradients with different chemical functionalities. Using additive manufacturing, the polymer can also be printed as a porous network with possible applications for 3D cell culturing in, e.g., biomaterials research. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Generalizing optical geometry

International Nuclear Information System (INIS)

Jonsson, Rickard; Westman, Hans

2006-01-01

We show that by employing the standard projected curvature as a measure of spatial curvature, we can make a certain generalization of optical geometry (Abramowicz M A and Lasota J-P 1997 Class. Quantum Grav. A 14 23-30). This generalization applies to any spacetime that admits a hypersurface orthogonal shearfree congruence of worldlines. This is a somewhat larger class of spacetimes than the conformally static spacetimes assumed in standard optical geometry. In the generalized optical geometry, which in the generic case is time dependent, photons move with unit speed along spatial geodesics and the sideways force experienced by a particle following a spatially straight line is independent of the velocity. Also gyroscopes moving along spatial geodesics do not precess (relative to the forward direction). Gyroscopes that follow a curved spatial trajectory precess according to a very simple law of three-rotation. We also present an inertial force formalism in coordinate representation for this generalization. Furthermore, we show that by employing a new sense of spatial curvature (Jonsson R 2006 Class. Quantum Grav. 23 1)) closely connected to Fermat's principle, we can make a more extensive generalization of optical geometry that applies to arbitrary spacetimes. In general this optical geometry will be time dependent, but still geodesic photons move with unit speed and follow lines that are spatially straight in the new sense. Also, the sideways experienced (comoving) force on a test particle following a line that is straight in the new sense will be independent of the velocity

Observations of wave-induced pore pressure gradients and bed level response on a surf zone sandbar

Science.gov (United States)

Anderson, Dylan; Cox, Dan; Mieras, Ryan; Puleo, Jack A.; Hsu, Tian-Jian

2017-06-01

Horizontal and vertical pressure gradients may be important physical mechanisms contributing to onshore sediment transport beneath steep, near-breaking waves in the surf zone. A barred beach was constructed in a large-scale laboratory wave flume with a fixed profile containing a mobile sediment layer on the crest of the sandbar. Horizontal and vertical pore pressure gradients were obtained by finite differences of measurements from an array of pressure transducers buried within the upper several centimeters of the bed. Colocated observations of erosion depth were made during asymmetric wave trials with wave heights between 0.10 and 0.98 m, consistently resulting in onshore sheet flow sediment transport. The pore pressure gradient vector within the bed exhibited temporal rotations during each wave cycle, directed predominantly upward under the trough and then rapidly rotating onshore and downward as the wavefront passed. The magnitude of the pore pressure gradient during each phase of rotation was correlated with local wave steepness and relative depth. Momentary bed failures as deep as 20 grain diameters were coincident with sharp increases in the onshore-directed pore pressure gradients, but occurred at horizontal pressure gradients less than theoretical critical values for initiation of the motion for compact beds. An expression combining the effects of both horizontal and vertical pore pressure gradients with bed shear stress and soil stability is used to determine that failure of the bed is initiated at nonnegligible values of both forces.type="synopsis">type="main">Plain Language SummaryThe pressure gradient present within the seabed beneath breaking waves may be an important physical mechanism transporting sediment. A large-scale laboratory was used to replicate realistic surfzone conditions in controlled tests, allowing for horizontal and vertical pressure gradient magnitudes and the resulting sediment bed response to be observed with precise instruments

Paleo-channel deposition of natural uranium at a US Air Force landfill

International Nuclear Information System (INIS)

Young, Carl; Weismann, Joseph; Caputo, Daniel

2007-01-01

Available in abstract form only. Full text of publication follows: The US Air Force sought to identify the source of radionuclides that were detected in groundwater surrounding a closed solid waste landfill at the former Lowry Air Force Base in Denver, Colorado, USA. Gross alpha, gross beta, and uranium levels in groundwater were thought to exceed US drinking water standards and down-gradient concentrations exceeded up-gradient concentrations. Our study has concluded that the elevated radionuclide concentrations are due to naturally-occurring uranium in the regional watershed and that the uranium is being released from paleo-channel sediments beneath the site. Groundwater samples were collected from monitor wells, surface water and sediments over four consecutive quarters. A list of 23 radionuclides was developed for analysis based on historical landfill records. Concentrations of major ions and metals and standard geochemical parameters were analyzed. The only radionuclide found to be above regulatory standards was uranium. A search of regional records shows that uranium is abundant in the upstream drainage basin. Analysis of uranium isotopic ratios shows that the uranium has not been processed for enrichment nor is it depleted uranium. There is however slight enrichment in the U-234:U- 238 activity ratio, which is consistent with uranium that has undergone aqueous transport. Comparison of up-gradient versus down-gradient uranium concentrations in groundwater confirms that higher uranium concentrations are found in the down-gradient wells. The US drinking water standard of 30 μg/L for uranium was exceeded in some of the up-gradient wells and in most of the down-gradient wells. Several lines of evidence indicate that natural uranium occurring in streams has been preferentially deposited in paleo-channel sediments beneath the site, and that the paleo-channel deposits are causing the increased uranium concentrations in down-gradient groundwater compared to up-gradient

A Thermo-Optic Propagation Modeling Capability.

Energy Technology Data Exchange (ETDEWEB)

Schrader, Karl; Akau, Ron

2014-10-01

A new theoretical basis is derived for tracing optical rays within a finite-element (FE) volume. The ray-trajectory equations are cast into the local element coordinate frame and the full finite-element interpolation is used to determine instantaneous index gradient for the ray-path integral equation. The FE methodology (FEM) is also used to interpolate local surface deformations and the surface normal vector for computing the refraction angle when launching rays into the volume, and again when rays exit the medium. The method is implemented in the Matlab(TM) environment and compared to closed- form gradient index models. A software architecture is also developed for implementing the algorithms in the Zemax(TM) commercial ray-trace application. A controlled thermal environment was constructed in the laboratory, and measured data was collected to validate the structural, thermal, and optical modeling methods.

Calibration of optically trapped nanotools

Energy Technology Data Exchange (ETDEWEB)

Carberry, D M; Simpson, S H; Grieve, J A; Hanna, S; Miles, M J [H H Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Wang, Y; Schaefer, H; Steinhart, M [Institute for Chemistry, University of Osnabrueck, Osnabrueck (Germany); Bowman, R; Gibson, G M; Padgett, M J, E-mail: m.j.miles@bristol.ac.uk [SUPA, Department of Physics and Astronomy, University of Glasgow, Science Road, Glasgow G12 8QQ (United Kingdom)

2010-04-30

Holographically trapped nanotools can be used in a novel form of force microscopy. By measuring the displacement of the tool in the optical traps, the contact force experienced by the probe can be inferred. In the following paper we experimentally demonstrate the calibration of such a device and show that its behaviour is independent of small changes in the relative position of the optical traps. Furthermore, we explore more general aspects of the thermal motion of the tool.

Micromanipulation and microfabrication for optical microrobotics

DEFF Research Database (Denmark)

Palima, Darwin; Bañas, Andrew Rafael; Vizsnyiczai, Gaszton

2012-01-01

Robotics can use optics feedback in vision-based control of intelligent robotic guidance systems. With light’s miniscule momentum, shrinking robots down to the microscale regime creates opportunities for exploiting optical forces and torques in microrobotic actuation and control. Indeed...... of the trapped microstructure that can be achieved when using static traps in the BWS. This can be generalized, in the future, towards a structural shaping optimization strategy for optimally controlling microstructures to complement approaches based on lightshaping. We also show that light channeled...... to microfabricated, free-standing waveguides can be used not only to redirect light for targeted delivery of optical energy but can also for targeted delivery of optical force, which can serve to further extend the manipulation arms in optical robotics. Moreover, light deflection with waveguide also creates a recoil...

Optical tractor Bessel polarized beams

International Nuclear Information System (INIS)

Mitri, F.G.; Li, R.X.; Guo, L.X.; Ding, C.Y.

2017-01-01

Axial and transverse radiation force cross-sections of optical tractor Bessel polarized beams are theoretically investigated for a dielectric sphere with particular emphasis on the beam topological charge (or order), half-cone angle and polarization. The angular spectrum decomposition method (ASDM) is used to derive the non-paraxial electromagnetic (EM) field components of the Bessel beams. The multipole expansion method using vector spherical harmonics is utilized and appropriate beam-shape coefficients are derived in order to compute the radiation force cross-sections. The analysis has no limitation to a particular range of frequencies such that the Rayleigh, Mie or geometrical optics regimes can all be considered effectively using the present rigorous formalism. The focus of this investigation is to identify some of the tractor beam conditions so as to achieve retrograde motion of a dielectric sphere located arbitrarily in space. Numerical computations for the axial and transverse radiation force cross-sections are presented for linear, right-circular, radial, azimuthal and mixed polarizations of the individual plane waves forming the Bessel beams of zeroth- and first-order (with positive or negative helicity), respectively. As the sphere shifts off the beam's axis, the axial pulling (tractor) force is weakened. Moreover, the transverse radiation force cross-section field changes with the sphere's size factor ka (where k is the wavenumber and a is the sphere radius). Both stable and unstable equilibrium regions around the beam's axis are found, depending on the choice of ka and the half-cone angle α_0. These results are particularly important in the development of emergent technologies for the photophoretic assembly of optically-engineered (meta)materials with designed properties using optical tractor (vortex) beams, particle manipulation, levitation and positioning, and other applications. - Highlights: • Optical tractor Bessel polarized beams are

Design and Performance of Property Gradient Ternary Nitride Coating Based on Process Control.

Science.gov (United States)

Yan, Pei; Chen, Kaijie; Wang, Yubin; Zhou, Han; Peng, Zeyu; Jiao, Li; Wang, Xibin

2018-05-09

Surface coating is an effective approach to improve cutting tool performance, and multiple or gradient coating structures have become a common development strategy. However, composition mutations at the interfaces decrease the performance of multi-layered coatings. The key mitigation technique has been to reduce the interface effect at the boundaries. This study proposes a structure design method for property-component gradient coatings based on process control. The method produces coatings with high internal cohesion and high external hardness, which could reduce the composition and performance mutations at the interface. A ZrTiN property gradient ternary nitride coating was deposited on cemented carbide by multi-arc ion plating with separated Ti and Zr targets. The mechanical properties, friction behaviors, and cutting performances were systematically investigated, compared with a single-layer coating. The results indicated that the gradient coating had better friction and wear performance with lower wear rate and higher resistance to peeling off during sliding friction. The gradient coating had better wear and damage resistance in cutting processes, with lower machined surface roughness Ra. Gradient-structured coatings could effectively inhibit micro crack initiation and growth under alternating force and temperature load. This method could be extended to similar ternary nitride coatings.

Atomic force microscopy for the determination of refractive index profiles of optical fibres and waveguides: a quantitative study

International Nuclear Information System (INIS)

Huntington, S.T.; Mulvaney, P.; Roberts, K.A.

1997-01-01

The use of preferential etching and atomic force microscopy to measure refractive index profiles of optical fibres is investigated. Both the etch rate and the position of lateral features are shown to be independent of etch time. An elliptical core fibre has been studied and the resultant profile found to be in qualitative agreement with the preform index profile. It is shown, however, that the ellipticity of the core has changed during the drawing process. The method has been extended to fluorine and germanium doped planar waveguides and the results correlated with the fabrication process

Passive force balancing of an active magnetic regenerative liquefier

Science.gov (United States)

Teyber, R.; Meinhardt, K.; Thomsen, E.; Polikarpov, E.; Cui, J.; Rowe, A.; Holladay, J.; Barclay, J.

2018-04-01

Active magnetic regenerators (AMR) have the potential for high efficiency cryogen liquefaction. One active magnetic regenerative liquefier (AMRL) configuration consists of dual magnetocaloric regenerators that reciprocate in a persistent-mode superconducting solenoid. Issues with this configuration are the spatial and temporal magnetization gradients that induce large magnetic forces and winding currents. To solve the coupled problem, we present a force minimization approach using passive magnetic material to balance a dual-regenerator AMR. A magnetostatic model is developed and simulated force waveforms are compared with experimental measurements. A genetic algorithm identifies force-minimizing passive structures with virtually ideal balancing characteristics. Implementation details are investigated which affirm the potential of the proposed methodology.

Force estimation from OCT volumes using 3D CNNs.

Science.gov (United States)

Gessert, Nils; Beringhoff, Jens; Otte, Christoph; Schlaefer, Alexander

2018-05-04

Estimating the interaction forces of instruments and tissue is of interest, particularly to provide haptic feedback during robot-assisted minimally invasive interventions. Different approaches based on external and integrated force sensors have been proposed. These are hampered by friction, sensor size, and sterilizability. We investigate a novel approach to estimate the force vector directly from optical coherence tomography image volumes. We introduce a novel Siamese 3D CNN architecture. The network takes an undeformed reference volume and a deformed sample volume as an input and outputs the three components of the force vector. We employ a deep residual architecture with bottlenecks for increased efficiency. We compare the Siamese approach to methods using difference volumes and two-dimensional projections. Data were generated using a robotic setup to obtain ground-truth force vectors for silicon tissue phantoms as well as porcine tissue. Our method achieves a mean average error of [Formula: see text] when estimating the force vector. Our novel Siamese 3D CNN architecture outperforms single-path methods that achieve a mean average error of [Formula: see text]. Moreover, the use of volume data leads to significantly higher performance compared to processing only surface information which achieves a mean average error of [Formula: see text]. Based on the tissue dataset, our methods shows good generalization in between different subjects. We propose a novel image-based force estimation method using optical coherence tomography. We illustrate that capturing the deformation of subsurface structures substantially improves force estimation. Our approach can provide accurate force estimates in surgical setups when using intraoperative optical coherence tomography.

Polarization effects in polymer FBGs: study and use for transverse force sensing

DEFF Research Database (Denmark)

Hu, Xuehao; Saez-Rodriguez, David; Marques, Carlos

2015-01-01

Bragg gratings photo-inscribed in polymer optical fibers (POFs) are more sensitive to temperature and pressure than their silica counterparts, because of their larger thermo-optic coefficient and smaller Young's modulus. Polymer optical fiber Bragg gratings (POFBGs) are most often photo-written i...... the PDL response of FBGs manufactured in step-index POFs. As the force induced birefringence adds to the photo-induced one, a force dependent evolution of the PDL maximum value was noticed, with a good temperature-insensitivity. (C) 2015 Optical Society of America...

Effects of high-gradient magnetic fields on living cell machinery

International Nuclear Information System (INIS)

Zablotskii, V; Lunov, O; Kubinova, S; Polyakova, T; Dejneka, A; Sykova, E

2016-01-01

A general interest in biomagnetic effects is related to fundamental studies of the influence of magnetic fields on living objects on the cellular and whole organism levels. Emerging technologies offer new directions for the use of high-gradient magnetic fields to control cell machinery and to understand the intracellular biological processes of the emerging field of nanomedicine. In this review we aim at highlighting recent advances made in identifying fundamental mechanisms by which magnetic gradient forces act on cell fate specification and cell differentiation. The review also provides an analysis of the currently available magnetic systems capable of generating magnetic fields with spatial gradients of up to 10 MT m −1 , with the focus on their suitability for use in cell therapy. Relationships between experimental factors and underlying biophysical mechanisms and assumptions that would ultimately lead to a deeper understanding of cell machinery and the development of more predictive models for the evaluation of the effects of magnetic fields on cells, tissue and organisms are comprehensively discussed. (topical review)

Nanomaterials for in vivo imaging of mechanical forces and electrical fields

Science.gov (United States)

Mehlenbacher, Randy D.; Kolbl, Rea; Lay, Alice; Dionne, Jennifer A.

2018-02-01

Cellular signalling is governed in large part by mechanical forces and electromagnetic fields. Mechanical forces play a critical role in cell differentiation, tissue organization and diseases such as cancer and heart disease; electrical fields are essential for intercellular communication, muscle contraction, neural signalling and sensory perception. Therefore, quantifying a biological system's forces and fields is crucial for understanding physiology and disease pathology and for developing medical tools for repair and recovery. This Review highlights advances in sensing mechanical forces and electrical fields in vivo, focusing on optical probes. The emergence of biocompatible optical probes, such as genetically encoded voltage indicators, molecular rotors, fluorescent dyes, semiconducting nanoparticles, plasmonic nanoparticles and lanthanide-doped upconverting nanoparticles, offers exciting opportunities to push the limits of spatial and temporal resolution, stability, multi-modality and stimuli sensitivity in bioimaging. We further discuss the materials design principles behind these probes and compare them across various metrics to facilitate sensor selection. Finally, we examine which advances are necessary to fully unravel the role of mechanical forces and electrical fields in vivo, such as the ability to probe the vectorial nature of forces, the development of combined force and field sensors, and the design of efficient optical actuators.

Optic disc detection and boundary extraction in retinal images.

Science.gov (United States)

Basit, A; Fraz, Muhammad Moazam

2015-04-10

With the development of digital image processing, analysis and modeling techniques, automatic retinal image analysis is emerging as an important screening tool for early detection of ophthalmologic disorders such as diabetic retinopathy and glaucoma. In this paper, a robust method for optic disc detection and extraction of the optic disc boundary is proposed to help in the development of computer-assisted diagnosis and treatment of such ophthalmic disease. The proposed method is based on morphological operations, smoothing filters, and the marker controlled watershed transform. Internal and external markers are used to first modify the gradient magnitude image and then the watershed transformation is applied on this modified gradient magnitude image for boundary extraction. This method has shown significant improvement over existing methods in terms of detection and boundary extraction of the optic disc. The proposed method has optic disc detection success rate of 100%, 100%, 100% and 98.9% for the DRIVE, Shifa, CHASE_DB1, and DIARETDB1 databases, respectively. The optic disc boundary detection achieved an average spatial overlap of 61.88%, 70.96%, 45.61%, and 54.69% for these databases, respectively, which are higher than currents methods.

Design Studies of Nb3Sn High-Gradient Quadrupole Models for LARP

International Nuclear Information System (INIS)

Andreev, Nikolai; Caspi, Shlomo; Dietderich, Daniel; Ferracin, Paolo; Ghosh, Arup; Kashikhin, Vadim; Lietzke, Al; Novitski, Igor; Zlobin, Alexander; McInturff, Alfred; Sabbi, GianLuca

2007-01-01

Insertion quadrupoles with large aperture and high gradient are required to achieve the luminosity upgrade goal of 10 35 cm -2 s -1 at the Large Hadron Collider (LHC). In 2004, the US Department of Energy established the LHC Accelerator Research Program (LARP) to develop a technology base for the upgrade. Nb 3 Sn conductor is required in order to operate at high field and with sufficient temperature margin. We report here on the conceptual design studies of a series of 1 m long 'High-gradient Quadrupoles' (HQ) that will explore the magnet performance limits in terms of peak fields, forces and stresses. The HQ design is expected to provide coil peak fields of more than 15 T, corresponding to gradients above 300 T/m in a 90 mm bore. Conductor requirements, magnetic, mechanical and quench protection issues for candidate HQ designs will be presented and discussed

Optical neutron polarizers

International Nuclear Information System (INIS)

Hayter, J.B.

1990-01-01

A neutron wave will be refracted by an appropriately varying potential. Optical neutron polarizers use spatially varying, spin- dependent potentials to refract neutrons of opposite spin states into different directions, so that an unpolarized beam will be split into two beams of complementary polarization by such a device. This paper will concentrate on two methods of producing spin-dependent potentials which are particularly well-suited to polarizing cold neutron beams, namely thin-film structures and field-gradient techniques. Thin-film optical devices, such as supermirror multilayer structures, are usually designed to deviate only one spin-state, so that they offer the possibility of making insertion (transmission) polarizers. Very good supermirrors may now be designed and fabricated, but it is not always straightforward to design mirror-based devices which are useful in real (divergent beam) applications, and some practical configurations will be discussed. Field-gradient devices, which are usually based on multipolar magnets, have tended to be too expensive for general use, but this may change with new developments in superconductivity. Dipolar and hexapolar configurations will be considered, with emphasis on the focusing characteristics of the latter. 21 refs., 7 figs

Physisorbed Polymer-Tethered Lipid Bilayer with Lipopolymer Gradient

Directory of Open Access Journals (Sweden)

Christoph A. Naumann

2012-11-01

Full Text Available Physisorbed polymer-tethered lipid bilayers consisting of phospholipids and lipopolymers represent an attractive planar model membrane platform, in which bilayer fluidity and membrane elastic properties can be regulated through lipopolymer molar concentration. Herein we report a method for the fabrication of such a planar model membrane system with a lateral gradient of lipopolymer density. In addition, a procedure is described, which leads to a sharp boundary between regions of low and high lipopolymer molar concentrations. Resulting gradients and sharp boundaries are visualized on the basis of membrane buckling structures at elevated lipopolymer concentrations using epifluorescence microscopy and atomic force microscopy. Furthermore, results from spot photobleaching experiments are presented, which provide insight into the lipid lateral fluidity in these model membrane architectures. The presented experimental data highlight a planar, solid-supported membrane characterized by fascinating length scale-dependent dynamics and elastic properties with remarkable parallels to those observed in cellular membranes.

Analysis of the electrolyte convection inside the concentration boundary layer during structured electrodeposition of copper in high magnetic gradient fields.

Science.gov (United States)

König, Jörg; Tschulik, Kristina; Büttner, Lars; Uhlemann, Margitta; Czarske, Jürgen

2013-03-19

To experimentally reveal the correlation between electrodeposited structure and electrolyte convection induced inside the concentration boundary layer, a highly inhomogeneous magnetic field, generated by a magnetized Fe-wire, has been applied to an electrochemical system. The influence of Lorentz and magnetic field gradient force to the local transport phenomena of copper ions has been studied using a novel two-component laser Doppler velocity profile sensor. With this sensor, the electrolyte convection within 500 μm of a horizontally aligned cathode is presented. The electrode-normal two-component velocity profiles below the electrodeposited structure show that electrolyte convection is induced and directed toward the rim of the Fe-wire. The measured deposited structure directly correlates to the observed boundary layer flow. As the local concentration of Cu(2+) ions is enhanced due to the induced convection, maximum deposit thicknesses can be found at the rim of the Fe-wire. Furthermore, a complex boundary layer flow structure was determined, indicating that electrolyte convection of second order is induced. Moreover, the Lorentz force-driven convection rapidly vanishes, while the electrolyte convection induced by the magnetic field gradient force is preserved much longer. The progress for research is the first direct experimental proof of the electrolyte convection inside the concentration boundary layer that correlates to the deposited structure and reveals that the magnetic field gradient force is responsible for the observed structuring effect.

Monitoring ligand-receptor interactions by photonic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Jeney, Sylvia [M E Mueller Institute for Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, Basel, 4056 (Switzerland); Mor, Flavio; Forro, Laszlo [Laboratory of Complex Matter Physics (LPMC), Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Koszali, Roland [Institute for Information and Communication Technologies (IICT), University of Applied Sciences of Western Switzerland (HEIG-VD), Rue Galilee 15, CH 1401 Yverdon-les-bains (Switzerland); Moy, Vincent T, E-mail: sylvia.jeney@unibas.ch, E-mail: vmoy@miami.edu [Department of Physiology and Biophysics, University of Miami Miller School of Medicine, 1600 NW 10th Avenue, Miami, FL 33136 (United States)

2010-06-25

We introduce a method for the acquisition of single molecule force measurements of ligand-receptor interactions using the photonic force microscope (PFM). Biotin-functionalized beads, manipulated with an optical trap, and a streptavidin-functionalized coverslip were used to measure the effect of different pulling forces on the lifetime of individual streptavidin-biotin complexes. By optimizing the design of the optical trap and selection of the appropriate bead size, pulling forces in excess of 50 pN were achieved. Based on the amplitude of three-dimensional (3D) thermal position fluctuations of the attached bead, we were able to select for a bead-coverslip interaction that was mediated by a single streptavidin-biotin complex. Moreover, the developed experimental system was greatly accelerated by automation of data acquisition and analysis. In force-dependent kinetic measurements carried out between streptavidin and biotin, we observed that the streptavidin-biotin complex exhibited properties of a catch bond, with the lifetime increasing tenfold when the pulling force increased from 10 to 20 pN. We also show that silica beads were more appropriate than polystyrene beads for the force measurements, as tethers, longer than 200 nm, could be extracted from polystyrene beads.

Monitoring ligand-receptor interactions by photonic force microscopy

International Nuclear Information System (INIS)

Jeney, Sylvia; Mor, Flavio; Forro, Laszlo; Koszali, Roland; Moy, Vincent T

2010-01-01

We introduce a method for the acquisition of single molecule force measurements of ligand-receptor interactions using the photonic force microscope (PFM). Biotin-functionalized beads, manipulated with an optical trap, and a streptavidin-functionalized coverslip were used to measure the effect of different pulling forces on the lifetime of individual streptavidin-biotin complexes. By optimizing the design of the optical trap and selection of the appropriate bead size, pulling forces in excess of 50 pN were achieved. Based on the amplitude of three-dimensional (3D) thermal position fluctuations of the attached bead, we were able to select for a bead-coverslip interaction that was mediated by a single streptavidin-biotin complex. Moreover, the developed experimental system was greatly accelerated by automation of data acquisition and analysis. In force-dependent kinetic measurements carried out between streptavidin and biotin, we observed that the streptavidin-biotin complex exhibited properties of a catch bond, with the lifetime increasing tenfold when the pulling force increased from 10 to 20 pN. We also show that silica beads were more appropriate than polystyrene beads for the force measurements, as tethers, longer than 200 nm, could be extracted from polystyrene beads.