Browsing by Subject "physics, fluids & plasmas"

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Antibody-Independent Isolation of Circulating Tumor Cells by Continuous-Flow Dielectrophoresis
(2013-01) Shim, Sangjo; Stemke-Hale, Katherine; Tsimberidou, Apostolia M.; Noshari, Jamileh; Anderson, Thomas E.; Gascoyne, Peter R. C.; Shim, Sangjo; Noshari, Jamileh; Anderson, Thomas E.; Gascoyne, Peter R. C.
Circulating tumor cells (CTCs) are prognostic markers for the recurrence of cancer and may carry molecular information relevant to cancer diagnosis. Dielectrophoresis (DEP) has been proposed as a molecular marker-independent approach for isolating CTCs from blood and has been shown to be broadly applicable to different types of cancers. However, existing batch-mode microfluidic DEP methods have been unable to process 10 ml clinical blood specimens rapidly enough. To achieve the required processing rates of 106 nucleated cells/min, we describe a continuous flow microfluidic processing chamber into which the peripheral blood mononuclear cell fraction of a clinical specimen is slowly injected, deionized by diffusion, and then subjected to a balance of DEP, sedimentation and hydrodynamic lift forces. These forces cause tumor cells to be transported close to the floor of the chamber, while blood cells are carried about three cell diameters above them. The tumor cells are isolated by skimming them from the bottom of the chamber while the blood cells flow to waste. The principles, design, and modeling of the continuous-flow system are presented. To illustrate operation of the technology, we demonstrate the isolation of circulating colon tumor cells from clinical specimens and verify the tumor origin of these cells by molecular analysis. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4774304]
Application Of Detuned Laser Beatwave For Generation Of Few-Cycle Electromagnetic Pulses
(2004-12) Kalmykov, S.; Shvets, G.; Shvets, Gennady; Kalmykov, Sergey
An approach to compressing high-power laser beams in plasmas via coherent Raman sideband generation is described. The technique requires two beams: a pump and a probe detuned by a near-resonant frequency Omega < omega(p). The two laser beams drive a high-amplitude electron plasma wave (EPW) which modifies the refractive index of plasma so as to produce a periodic phase modulation of the incident laser with the laser beat period tau(b) = 2pi/Omega. After propagation through plasma, the original laser beam breaks into a train of chirped beatnotes (each of duration tau(b)). The chirp is positive (the longer-wavelength sidebands are advanced in time) when Omega < omega(p) and negative otherwise. Finite group velocity dispersion (GVD) of radiation in plasma can compress the positively chirped beatnotes to a few-laser-cycle duration thus creating in plasma a sequence of sharp electromagnetic spikes separated in time by tau(b). Driven EPW strongly couples the laser sidebands and thus reduces the effect of GVD. Compression of the chirped beatnotes can be implemented in a separate plasma of higher density, where the laser sidebands become uncoupled.
Design And Fabrication Of A Surface-Wave Accelerator Based On Silicon Carbide
(2004-12) Shvets, G.; Kalmykov, S.; Shvets, Gennady; Kalmykov, Sergey
The principles and electromagnetic simulations of a novel accelerating structure are described. The structure is planar, consisting of two plates of silicon carbide (SiC) separated by a vacuum gap. Charged particle bunches are accelerated in the vacuum gap by the surface electromagnetic waves (phonon polaritons) localized near the vacuum/SiC interface. The structure can be powered by a carbon dioxide (CO2) laser with the wavelength lambda(0) approximate to 10.6mum. The operating wavelength is dictated by the frequency-dependent dielectric permittivity epsilon(omega) of SiC which is negative for the frequencies in the CO2 tunability range. The resulting accelerator can support accelerating fields well in excess of 1 GeV/m without breakdown, and provide the path to compact and inexpensive particle accelerators. The challenge of coupling radiation into a very narrow (a few microns) vacuum gap is resolved by designing a coupling grating on the top surface of a Si wafer, and attaching a thin SiC film to the bottom of the wafer. Preliminary fabrication results are reported.
Development Of 873 nm Raman Seed Pulse For Raman-Seeded Laser Wakefield Acceleration
(2004-12) Grigsby, F.; Peng, D.; Downer, M. C.; Grigsby, F.; Peng, D.; Downer, M. C.
By using a Raman-shifted seed pulse coincident with a main driving pulse. laser wakefields can be generated with sub-relativistic intensity, coherent control and high repetition rate in the self-modulated regime. Experimentally, the generation of a chirped Stokes laser pulse by inserting a solid state Raman shifter, Ba(NO3)(2), into a CPA system before the compressor (to suppress self-phase modulation) will be described. We will also report on design. modeling and experimental demonstration of a novel compressor for the Stokes pulse that uses a mismatched grating pair to achieve a near transform-limited seed pulse. Finally, we will describe the design. simulation and current status of Raman-seeded LWFA experiments that use this novel source..
Dielectrophoresis has Broad Applicability to Marker-Free Isolation of Tumor Cells from Blood by Microfluidic Systems
(2013-01) Shim, Sangjo; Stemke-Hale, Katherine; Noshari, Jamileh; Becker, Frederick F.; Gascoyne, Peter R. C.; Shim, Sangjo
The number of circulating tumor cells (CTCs) found in blood is known to be a prognostic marker for recurrence of primary tumors, however, most current methods for isolating CTCs rely on cell surface markers that are not universally expressed by CTCs. Dielectrophoresis (DEP) can discriminate and manipulate cancer cells in microfluidic systems and has been proposed as a molecular marker-independent approach for isolating CTCs from blood. To investigate the potential applicability of DEP to different cancer types, the dielectric and density properties of the NCI-60 panel of tumor cell types have been measured by dielectrophoretic field-flow fractionation (DEP-FFF) and compared with like properties of the subpopulations of normal peripheral blood cells. We show that all of the NCI-60 cell types, regardless of tissue of origin, exhibit dielectric properties that facilitate their isolation from blood by DEP. Cell types derived from solid tumors that grew in adherent cultures exhibited dielectric properties that were strikingly different from those of peripheral blood cell subpopulations while leukemia-derived lines that grew in non-adherent cultures exhibited dielectric properties that were closer to those of peripheral blood cell types. Our results suggest that DEP methods have wide applicability for the surface-marker independent isolation of viable CTCs from blood as well as for the concentration of leukemia cells from blood. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4774307]
Drift Wave Turbulence
(2008-05) Horton, W.; Kim, J. H.; Asp, E.; Hoang, T.; Watanabe, T. H.; Sugama, H.; Horton, W.; Kim, J. H.
Drift waves occur universally in magnetized plasmas producing the dominant mechanism for transport of particles, energy and momentum across magnetic field lines. A wealth of information obtained from laboratory experiments for plasma confinement is reviewed for drift waves driven unstable by density gradients, temperature gradients and trapped particle effects. The modern understanding of origin of the scaling laws for Bohm and gyro-Bohm transport fluxes is discussed. The role of sheared flows and magnetic shear in reducing the transport fluxes is discussed and illustrated with large scale computer simulations. Plasmas turbulence models are derived with reduced magnetized fluid descriptions. The types of theoretical descriptions reviewed include weak turbulence theory and anisotropic Kolmogorov-hke spectral indices, and the mixing length. A number of standard turbulent diffusivity formulas are given for the various space-time scales of the drift-wave turbulent mixing.
DSMC Modeling Of Gasdynamics, Radiation And Fine Particulates In Ionian Volcanic Jets
(2003-05) Zhang, J.; Goldstein, D. B.; Varghese, P. L.; Gimelshein, N. E.; Gimelshein, S. F.; Levin, D. A.; Trafton, L.; Zhang, J.; Goldstein, D. B.; Varghese, P. L.; Trafton, L.
Electron Temperature Gradient Mode Transport
(2008-05) Horton, W.; Kim, J. H.; Hoang, G. T.; Park, H.; Kaye, S. M.; LeBlanc, B. P.; Horton, W.; Kim, J. H.
Anomalous electron thermal losses plays a central role in the history of the controlled fusion program being the first and most persistent form of anomalous transport across all toroidal magnetic confinement devices. In the past decade the fusion program has made analysis and simulations of electron transport a high priority with the result of a clearer understanding of the phenomenon, yet still incomplete. Electron thermal transport driven by the electron temperature gradient is examined in detail from theory, simulation and power balance studies in tokamaks with strong auxiliary heating.
Emittance Control In Laser Wakefield Accelerator
(2001-05) Cheshkov, S.; Tajima, T.; Chiu, C.; Breitling, F.; Cheshkov, S.; Tajima, T.; Chiu, C.; Breitling, F.
In this paper we summarize our recent effort and results in theoretical study of the emittance issues of multistaged Laser Wakefield Accelerator (LWFA) in TeV energy range, In such an energy regime the luminosity and therefore the emittance requirements become very stringent and tantamount to the success or failure of such an accelerator. The system of such a machine is very sensitive to jitters due to misalignment between the beam and the wakefield. In particular, the effect of jitters in the presence of a strong focusing wakefield and initial longitudinal phase space spread of the beam leads to severe transverse emittance degradation of the beam. To improve the emittance we introduce several methods: a mitigated wakefield focusing by working with a plasma channel, an approximately synchronous acceleration in a superunit setup, the >horn> model based on exactly synchronous acceleration achieved through plasma density variation and lastly an algorithm based on minimization of the final beam emittance to actively control the stage displacement of such an accelerator.
Femtosecond Pump-Probe Diagnostics Of Preformed Plasma Channels
(2004-12) Zgadzaj, R.; Gaul, E. W.; Matlis, N. H.; Shvets, G.; Debus, A.; Downer, M. C.; Zgadzaj, R.; Gaul, E. W.; Matlis, N. H.; Shvets, G.; Debus, A.; Downer, M. C.
We report on recent ultrafast pump-probe experiments 28 in He plasma waveguides using 800 nm, 80 fs pump pulses of 0.2 x 1018 W/cm2 peak guided intensity, and single orthogonally-polarized 800 nm probe pulses with similar to0.1% of pump intensity. The main results are: (1) We observe frequency-domain interference between the probe and a weak, depolarized component of the pump that differs substantially in mode shape from the injected pump pulse; (2) we observe spectral blue-shifts in the transmitted probe that are not evident in the transmitted pump. The evidence indicates that pump depolarization and probe blue-shifts both originate near the channel entrance.
High Intensity Femtosecond Xuv Pulse Interactions With Atomic Clusters
(2009-09) Hoffmann, K.; Murphy, B.; Keto, J.; Ditmire, T.; Hoffmann,K.; Murphy, B.; Keto, J.; Ditmire, T.
The interactions of large xenon clusters irradiated by intense, femtosecond extreme-ultraviolet pulses at a wavelength of 38 nm have been studied. Using high harmonic generation from a 35 fs near-infrared terawatt laser, clusters have been irradiated by XUV pulses of 10(11) W/cm(2) intensity. Charge states up to Xe(8+) are observed, states well above that produced by single atom illumination, indicating that plasma continuum lowering is important. Furthermore the kinetic energy distribution of the exploding ions is consistent with a quasineutral hydrodynamic expansion, rather than a Coulomb explosion.
Improvement Of A Discrete Velocity Boltzmann Equation Solver With Arbitrary Post-Collision Velocities
(2009-12) Morris, A. B.; Varghese, P. L.; Goldstein, D. B.; Morris, A. B.; Varghese, P. L.; Goldstein, D. B.
We present a discrete velocity scheme which solves the Boltzmann equation and show numerical results for homogeneous relaxation problems. Although direct simulation of the Boltzmann equation can be efficient for transient problems, computational costs have restricted its use. A velocity interpolation algorithm enables us to select post-collision velocity pairs not restricted to those that lie precisely on the grid. This allows efficient evaluation of the replenishing part of the collision integral with reasonable accuracy. In previous work [1] the scheme was demonstrated with the depleting terms evaluated exactly, which made the method of O(N(2)) where N is the number of grid points in the velocity space. In order to reduce the computational cost, we have developed an acceptance-rejection scheme to enable more efficient evaluation of the depleting term. We show that the total collision integral can be evaluated accurately in combination with the mapping scheme for the replenishing term. To improve our scheme, we study the error and computational time associated with the number of depleting and replenishing points. We predict the correct relaxation rate for the Bobylev-Krook-Wu distribution and obtain exact conservation of mass, momentum, and energy. Comparisons between computed and reference solutions are shown as well, demonstrating the correct relaxation rate and dependence of error on parameters in the computational scheme.
Io'S Atmospheric Freeze-Out Dynamics In The Presence Of A Non-Condensable Species
(2009-12) Moore, C. H.; Goldstein, D. B.; Varghese, P. L.; Trafton, L. M.; Stewart, B. D.; Walker, A. C.; Moore, C. H.; Goldstein, D. B.; Varghese, P. L.; Trafton, L. M.; Stewart, B. D.; Walker, A. C.
One dimensional direct simulation Monte Carlo (DSMC) simulations are used to examine the effect of a trace non-condensable species on the freeze-out dynamics of Io's sulfur dioxide sublimation atmosphere during eclipse and egress. Due to finite ballistic times, essentially no collapse occurs during the first 10 minutes of eclipse at altitudes above similar to 100 km, and hence immediately after ingress auroral emission morphology above 100 km should resemble that of the immediate pre-eclipse state. In the absence of a non-condensable species the sublimation SO2 atmosphere will freeze-out (collapse) during eclipse as the surface temperature drops. However, rapid collapse is prevented by the presence of even a small amount of a perfect non-condensable species due to the formation of a static diffusion layer several mean free paths thick near the surface. The higher the non-condensable mole fraction, the longer the collapse time. The effect of a weakly condensable gas species (non-zero sticking/reaction coefficient) was examined since real gas species may not be perfectly non-condensable at realistic surface temperatures. It is found that even a small sticking coefficient dramatically reduces the effect of the diffusion layer on the dynamics. If the sticking coefficient of the non-condensable exceeds similar to 0.25 the collapse dynamics are effectively the same as if there was no non-condensable present. This sensitivity results because the loss of non-condensable to the surface reduces the effective diffusion layer size and the formation of an effective diffusion layer requires that the layer be stationary which does not occur if the surface is a sink. As the surface temperature increases during egress from eclipse the sublimating SO2 gas pushes the non-condensable diffusion layer up to higher altitudes once it becomes dense enough to be collisional. This vertical species stratification should alter the auroral emissions after egress.
LWFA With Low Energy Raman Seeded Pulses
(2004-12) Fomyts'kyi, M.; Chiu, C.; Downer, M.; Grigsby, F.; Fomyts’kyi, Mykhailo; Chiu, Charles; Downer, Michael; Grigsby, Franklin
Analytical and numerical calculations of plasma wakefield excitation and particle acceleration by Raman seeded laser pulse in self-modulation regime are presented. We derive energy threshold for self-modulation of diffraction-limited pulses. The parameter range where the Raman seeded amplitude plays an important role is investigated. We show that the seeded amplitude provides a coherent control mechanism for the phase of the wakefield wave. We show that with the use of Raman seed self-modulated wakefield acceleration is achievable for the pulses of intensities much lower than those typically used in the experiments. In particular, our 2D particle-in-cell simulations show that 30 mJ pulse combined with Raman seeded pulse, which is 1% in intensity of the main pulse is capable of generating similar to1 nC of relativistic electrons.
Microfluidic Enrichment of Small Proteins from Complex Biological Mixture on Nanoporous Silica Chip
(2011-03) Hu, Ye; Gopal, Ashwini; Lin, Kevin; Peng, Yang; Tasciotti, Ennio; Zhang, Xiojing John; Ferrari, Mauro; Gopal, Ashwini; Lin, Kevin; Zhang, Xiojing John
The growing field of miniaturized diagnostics is hindered by a lack of pre-analysis treatments that are capable of processing small sample volumes for the detection of low concentration analytes in a high-throughput manner. This letter presents a novel, highly efficient method for the extraction of low-molecular weight (LMW) proteins from biological fluids, represented by a mixture of standard proteins, using integrated microfluidic systems. We bound a polydimethylsiloxane layer patterned with a microfluidic channel onto a well-defined nanoporous silica substrate. Using rapid, pressure-driven fractionation steps, this system utilizes the size-exclusion properties of the silica nanopores to remove high molecular weight proteins while simultaneously isolating and enriching LMW proteins present in the biological sample. The introduction of the microfluidic component offers important advantages such as high reproducibility, a simple user interface, controlled environment, the ability to process small sample volumes, and precise quantification. This solution streamlines high-throughput proteomics research on many fronts and may find broad acceptance and application in clinical diagnostics and point of care detection. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3528237]
Minority Ion Measurements During ICRF Experiments In Alcator C-Mod
(2011-12) Liao, K. T.; Rowan, W. L.; Bespamyatnov, I. O.; Wukitch, S. J.; Lin, Y.; Bader, A.; Tsujii, N.; Alcator, C. Mod Team; Liao, K. T.; Rowan, W. L.; Bespamyatnov, I. O.
ICRF is the primary auxiliary heating in C-Mod where both H or He-3 minority and mode conversion regimes are utilized. For transport analysis, the power deposition profile is critical and measuring the resulting fast ion distribution provides a direct means to constrain and validate ICRF simulations used to calculate power deposition. In mode conversion, measurement of the minority ion density, temperature, and velocity profiles is critical for the wave physics and may provide some insight into the fundamental physics of flow drive. Using active charge exchange, the He+1 4686 angstrom or H 6563 angstrom line is observed to find whether fast ion and relevant thermal ion measurements are practical. Results of these experiments yield fast ion and thermal ion measurements in D(He). A new analysis technique to extract information from high noise fast ion spectra is developed. A development path for improved D(He-3) and D(H) is indicated.
Modeling Io'S Sublimation-Driven Atmosphere: Gas Dynamics And Radiation Emission
(2009-12) Walker, A. C.; Gratiy, S. L.; Levin, D. A.; Goldstein, D. B.; Varghese, P. L.; Trafton, L. M.; Moore, C. H.; Stewart, B.; Walker, A. C.; Goldstein, D. B.; Varghese, P. L.; Trafton, L. M.; Moore, C. H.; Stewart, B.
Io's sublimation-driven atmosphere is modeled using the direct simulation Monte Carlo method. These rarefied gas dynamics simulations improve upon earlier models by using a three-dimensional domain encompassing the entire planet computed in parallel. The effects of plasma impact heating, planetary rotation, and inhomogeneous surface frost are investigated. Circumplanetary flow is predicted to develop from the warm subsolar region toward the colder night-side. The non-equilibrium thermal structure of the atmosphere, including vibrational and rotational temperatures, is also presented. Io's rotation leads to an asymmetric surface temperature distribution which is found to strengthen circumplanetary flow near the dusk terminator. Plasma heating is found to significantly inflate the atmosphere on both day- and night-sides. The plasma energy flux also causes high temperatures at high altitudes but permits relatively cooler temperatures at low altitudes near the dense subsolar point due to plasma energy depletion. To validate the atmospheric model, a radiative transfer model was developed utilizing the backward Monte Carlo method. The model allows the calculation of the atmospheric radiation from emitting/absorbing and scattering gas using an arbitrary scattering law and art arbitrary surface reflectivity. The model calculates the spectra in the v, vibrational band of SO(2) which are then compared to the observational data.
Modeling The Vapor And Dust Dynamics Due To The Impact Of The Lcross Spacecraft On The Moon
(2009-12) Goldstein, D. B.; Summy, D.; Colaprete, A.; Varghese, P. L.; Trafton, L. M.; Goldstein, D. B.; Summy, D.
The implications of possibly large volatile reservoirs on the Moon are significant for the future of manned activity there and for space science and exploration in general. In autumn of 2008 NASA will launch the LCROSS mission to impact two spacecraft into a permanently shadowed crater-a cold trap - at the south pole of the Moon. The lead spacecraft will excavate its own several meter crater. The process will be observed by the following smaller vehicle and by orbiting and Earth-based instruments in hopes of observing the release of volatiles-predominantly water -- from the lunar soil. The following vehicle will then impact as well. We examine the plausible vapor dynamics following the impacts and concentrate on the observability of the gas from Earth or lunar orbit. In the free-molecular computational model of the vapor motion, water and OH molecules move ballistically, have a temperature-dependent surface residence time, and are subject to photo-dissociation and ionization losses. Sunlight shadowing, separation of the vapor from the dust grains, dust thermodynamics and different impact plume models are considered.
On Hamiltonian And Action Principle Formulations Of Plasma Dynamics
(2009-11) Morrison, P. J.; Morrison, P.J.
A general discussion of Hamiltonian and action principle formulations for fluid and plasma models is given. A procedure, based on Hamilton's principle of mechanics but adapted for continua, for the construction of action principles for fluid and kinetic models is given. The transformation from action principles in terms of the Lagrangian variable description to the Eulerian variable description in terms of noncanonical Poisson brackets is described. Two examples are developed: ideal MHD and Braginskii's fluid model with gyroviscosity.
Optimization Of Laser Wakefield Acceleration
(2001) Rundquist, A. R.; LeBlanc, S. P.; Gaul, E. W.; Cheshkov, S.; Grigsby, F. B.; Tajima, T. T.; Downer, M. C.; Rundquist, A. R.; LeBlanc, S. P.; Gaul, E. W.; Cheshkov, S.; Grigsby, F. B.; Tajima, T. T.; Downer, M. C.
Using an evolutionary strategy algorithm, we optimize the generalized transformer ration of a laser wakefield accelerator. The algorithm tests several realistic pulse shapes by integrating the fluid wakefield differential equation and it converges to the shape that most efficiently produces a strong accelerating gradient while experiencing minimal distortion.