Experimental investigation of electron guns for THz microwave vacuum amplifiers

NASA Astrophysics Data System (ADS)

Burtsev, A. A.; Grigor'ev, Yu. A.; Navrotsky, I. A.; Rogovin, V. I.; Sakhadzhi, G. V.; Shumikhin, K. V.

2016-05-01

Single-sheet and multiple beam electron emitters based on thermionic minicathodes for terahertz traveling-wave tubes have been studied. Data are presented for impregnated blade thermionic cathode with dimensions 0.1 × 0.7 mm and a maximum current density of 114 A/cm2 in a pulsed mode. A variant of the five-beam electron gun with 0.25-mm-diameter cylindrical minicathodes in cells of a control grid is proposed that provides a current density of 85.5 A/cm2 at a grid potential of 900-1000 V.

Tubular graphite cones.

PubMed

Zhang, Guangyu; Jiang, Xin; Wang, Enge

2003-04-18

We report the synthesis of tubular graphite cones using a chemical vapor deposition method. The cones have nanometer-sized tips, micrometer-sized roots, and hollow interiors with a diameter ranging from about 2 to several tens of nanometers. The cones are composed of cylindrical graphite sheets; a continuous shortening of the graphite layers from the interior to the exterior makes them cone-shaped. All of the tubular graphite cones have a faceted morphology. The constituent graphite sheets have identical chiralities of a zigzag type across the entire diameter, imparting structural control to tubular-based carbon structures. The tubular graphite cones have potential for use as tips for scanning probe microscopy, but with greater rigidity and easier mounting than currently used carbon nanotubes.

Packing of flexible 2D materials in vesicles

NASA Astrophysics Data System (ADS)

Zou, Guijin; Yi, Xin; Zhu, Wenpeng; Gao, Huajian

2018-06-01

To understand the mechanics of cellular packing of two-dimensional (2D) materials, we perform systematic molecular dynamics simulations and theoretical analysis to investigate the packing of a flexible circular sheet in a spherical vesicle and the 2D packing problem of a strip in a cylindrical vesicle. Depending on the system dimensions and the bending rigidity ratio between the confined sheet and the vesicle membrane, a variety of packing morphologies are observed, including a conical shape, a shape of three-fold symmetry, a cylindrically curved shape, an axisymmetrically buckled shape, as well as the initial circular shape. A set of buckling analyses lead to phase diagrams of the packing morphologies of the encapsulated sheets. These results may have important implications on the mechanism of intracellular packing and toxicity of 2D materials.

Scattering of Airy elastic sheets by a cylindrical cavity in a solid.

PubMed

Mitri, F G

2017-11-01

The prediction of the elastic scattering by voids (and cracks) in materials is an important process in structural health monitoring, phononic crystals, metamaterials and non-destructive evaluation/imaging to name a few examples. Earlier analytical theories and numerical computations considered the elastic scattering by voids in plane waves of infinite extent. However, current research suggesting the use of (limited-diffracting, accelerating and self-healing) Airy acoustical-sheet beams for non-destructive evaluation or imaging applications in elastic solids requires the development of an improved analytical formalism to predict the scattering efficiency used as a priori information in quantitative material characterization. Based on the definition of the time-averaged scattered power flow density, an analytical expression for the scattering efficiency of a cylindrical empty cavity (i.e., void) encased in an elastic medium is derived for compressional and normally-polarized shear-wave Airy beams. The multipole expansion method using cylindrical wave functions is utilized. Numerical computations for the scattering energy efficiency factors for compressional and shear waves illustrate the analysis with particular emphasis on the Airy beam parameters and the non-dimensional frequency, for various elastic materials surrounding the cavity. The ratio of the compressional to the shear wave speed stimulates the generation of elastic resonances, which are manifested as a series of peaks in the scattering efficiency plots. The present analysis provides an improved method for the computations of the scattering energy efficiency factors using compressional and shear-wave Airy beams in elastic materials as opposed to plane waves of infinite extent. Copyright © 2017 Elsevier B.V. All rights reserved.

An Al-doped ZnO electrode grown by highly efficient cylindrical rotating magnetron sputtering for low cost organic photovoltaics

NASA Astrophysics Data System (ADS)

Park, Jun-Hyuk; Ahn, Kyung-Jun; Park, Kang-Il; Na, Seok-In; Kim, Han-Ki

2010-03-01

We report the characteristics of Al-doped zinc oxide (AZO) films prepared by a highly efficient cylindrical rotating magnetron sputtering (CRMS) system for use as a transparent conducting electrode in cost-efficient bulk hetero-junction organic solar cells (OSCs). Using a rotating cylindrical type cathode with an AZO target, whose usage was above 80%, we were able to obtain a low cost and indium free AZO electrode with a low sheet resistance of ~4.59 Ω/sq, a high transparency of 85% in the visible wavelength region and a work function of 4.9 eV at a substrate temperature of 230 °C. Moreover, the neutral poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) based OSC fabricated on the CRMS-grown AZO electrode at 230 °C showed an open circuit voltage of 0.5 V, a short circuit current of 8.94 mA cm-2, a fill factor of 45% and power conversion efficiency of 2.01%, indicating that CRMS is a promising cost-efficient AZO deposition technique for low cost OSCs.

Free-edge effects in a cylindrical sandwich panel with a flexible core and laminated composite face sheets

NASA Astrophysics Data System (ADS)

Afshin, M.; Sadighi, M.; Shakeri, M.

2010-12-01

In the present study, the static response of cylindrical sandwich panels with a flexible core is investigated. The face sheets are considered as composite laminates with a cross-ply lay-up and the core as a flexible elastic medium. The flexibility of the low-strength core leads to high stress concentrations in terms of peeling stresses between the face sheets and the core at edges of the sandwich panel. To take into account the compressibility of the core and to determine the free-edge stresses of sandwich structures accurately, the Reddy layerwise theory (LWT) is used in this paper. The paper outlines the mathematical formulation, along with a numerical study, of a cylindrical sandwich panel with two simply supported and two free edges under a transverse load. The formulation includes the derivation of field equations along with boundary conditions. A Levy-type solution procedure is performed to determine the distributions of stresses and strains. In the numerical study, first a comparison is made with results from the commercial finite-element software ANSYS to verify the LWT results. Finally, a parametric study is conducted, and the effect caused by varying different parameters, such as the radii of curvature and the core to face sheet thickness ratio, on the results are investigated. The results obtained demonstrate a good agreement between LWT and FEM solutions and show increasing interlaminar stresses in the free edge of the sandwich panel

Three-Dimensional Spherical Models of Convection in the Earth's Mantle.

PubMed

Bercovici, D; Schubert, G; Glatzmaier, G A

1989-05-26

Three-dimensional, spherical models of mantle convection in the earth reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of mantle circulation. Thus, subduction zones and descending sheetlike slabs in the mantle are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs, which are cooler than the surrounding mantle. Cylindrical mantle plumes that cause hotspots such as Hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large-scale mantle circulation. Active sheetlike upwellings that could be associated with mid-ocean ridges did not develop in the model simulations, a result that is in agreement with evidence suggesting that ridges are passive phenomena resulting from the tearing of surface plates by the pull of descending slabs.

Calculation of load distribution in stiffened cylindrical shells

NASA Technical Reports Server (NTRS)

Ebner, H; Koller, H

1938-01-01

Thin-walled shells with strong longitudinal and transverse stiffening (for example, stressed-skin fuselages and wings) may, under certain simplifying assumptions, be treated as static systems with finite redundancies. In this report the underlying basis for this method of treatment of the problem is presented and a computation procedure for stiffened cylindrical shells with curved sheet panels indicated. A detailed discussion of the force distribution due to applied concentrated forces is given, and the discussion illustrated by numerical examples which refer to an experimentally determined circular cylindrical shell.

Particle-in-cell simulations of magnetically driven reconnection using laser-powered capacitor coils

NASA Astrophysics Data System (ADS)

Huang, Kai; Lu, Quanming; Gao, Lan; Ji, Hantao; Wang, Xueyi; Fan, Feibin

2018-05-01

In this paper, we propose an experimental scheme to fulfill magnetically driven reconnections. Here, two laser beams are focused on a capacitor-coil target and then strong currents are wired in two parallel circular coils. Magnetic reconnection occurs between the two magnetic bubbles created by the currents in the two parallel circular coils. A two-dimensional particle-in-cell simulation model in the cylindrical coordinate is used to investigate such a process, and the simulations are performed in the (r ,z ) plane. The results show that with the increase of the currents in the two coils, the associated magnetic bubbles expand and a current sheet is formed between the two bubbles. Magnetic reconnection occurs when the current sheet is sufficiently thin. A quadrupole structure of the magnetic field in the θ direction ( Bθ ) is generated in the diffusion region and a strong electron current along the r direction ( Je r ) is also formed due to the existence of the high-speed electron flow away from the X line in the center of the outflow region. Because the X line is a circle along the θ direction, the convergence of the plasma flow around r =0 will lead to the asymmetry of Je r and Bθ between the two outflow regions of magnetic reconnection.

Bipolar battery plate

NASA Technical Reports Server (NTRS)

Rowlette, John J. (Inventor)

1987-01-01

A liquid-impermeable plate (10) having through-plate conductivity with essentially zero resistance comprises an insulator sheet (12) having a series of spaced perforations (14) each of which contains a metal element (16) sealingly received into the perforation (14). A low-cost plate can readily be manufactured by punching a thermoplastic sheet (40) such as polypropylene with a punching tool (52), filling the apertures with led spheres (63) having a diameter smaller than the holes (50) but larger than the thickness of the sheet, sweeping excess spheres (62) off the sheet with a doctor blade (60) and then pressing a heated platen (74) onto the sheet to swage the spheres into a cylindrical shape and melt the surrounding resin to form a liquid-impermeable collar (4) sealing the metal into the sheet.

Bipolar battery plate

NASA Technical Reports Server (NTRS)

Rowlette, John J. (Inventor)

1985-01-01

A liquid-impermeable plate (10) having throughplate conductivity with essentially zero resistance comprises an insulator sheet (12) having a series of spaced perforations (14) each of which contains a metal element (16) sealingly received into the perforation (14). A low-cost plate can readily be manufactured by punching a thermoplastic sheet (40) such as polypropylene with a punching tool (52), filling the apertures with lead spheres (63) having a diameter smaller than the holes (50) but larger than the thickness of the sheet, sweeping excess spheres (62) off the sheet with a doctor blade (60) and then pressing a heated platen (74) onto the sheet to swage the spheres into a cylindrical shape and melt the surrounding resin to form a liquid-impermeable collar (4) sealing the metal into the sheet.

Resonant coupling through a slot to a loaded cylindrical cavity: Experimental results

NASA Astrophysics Data System (ADS)

Norgard, John D.; Sega, Ronald M.

1990-03-01

The effect of cavity geometry on the energy coupled through a slot aperture is investigated through the use of planar mappings of the internal cavity field. A copper cylinder, closed at both ends, is constructed with copper mesh sections incorporated at the ends of the cylinder and in the cylinder wall opposite a thin slot aperture placed in the wall. The frequencies used for testing are 2 to 4 GHz. Internal field mapping is accomplished by placing thin carbon-loaded sheets in the plane of interest and recording the digitized temperature distribution using an infrared scanning system. The sheets are calibrated such that the temperature data is transformed to current densities or electric field strengths. Using several positions for the detection material, a three-dimensional field profile is obtained. The onset of the internal cavity resonance is studied as it is related to the energy coupled through small apertures.

Ringin' the water bell: dynamic modes of curved fluid sheets

NASA Astrophysics Data System (ADS)

Kolinski, John; Aharoni, Hillel; Fineberg, Jay; Sharon, Eran

2015-11-01

A water bell is formed by fluid flowing in a thin, coherent sheet in the shape of a bell. Experimentally, a water bell is created via the impact of a cylindrical jet on a flat surface. Its shape is set by the splash angle (the separation angle) of the resulting cylindrically symmetric water sheet. The separation angle is altered by adjusting the height of a lip surrounding the impact point, as in a water sprinkler. We drive the lip's height sinusoidally, altering the separation angle, and ringin' the water bell. This forcing generates disturbances on the steady-state water bell that propagate forward and backward in the fluid's reference frame at well-defined velocities, and interact, resulting in the emergence of an interference pattern unique to each steady-state geometry. We analytically model these dynamics by linearizing the amplitude of the bell's response about the underlying curved geometry. This simple model predicts the nodal structure over a wide range of steady-state water bell configurations and driving frequencies. Due to the curved water bell geometry, the nodal structure is quite complex; nevertheless, the predicted nodal structure agrees extremely well with the experimental data. When we drive the bell beyond perturbative separation angles, the nodal locations surprisingly persist, despite the strikingly altered underlying water bell shape. At extreme driving amplitudes the water sheet assumes a rich variety of tortuous, non-convex shapes; nevertheless, the fluid sheet remains intact.

Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL

NASA Astrophysics Data System (ADS)

Furno, I.; Intrator, T.; Hemsing, E.; Hsu, S.; Lapenta, G.; Abbate, S.

2004-12-01

Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (Bθ ≤ 100 Gauss, L=90 cm, r≤3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / Bθ > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t≤ 20 τ Alfv´ {e}n), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

Relaxation of flux ropes and magnetic reconnection in the Reconnection Scaling Experiment at LANL

NASA Astrophysics Data System (ADS)

Furno, Ivo

2004-11-01

Magnetic reconnection and plasma relaxation are studied in the Reconnection Scaling Experiment (RSX) with current carrying plasma columns (magnetic flux ropes). Using plasma guns, multiple flux ropes (B_pol < 100 Gauss, L=90 cm, r < 3 cm) are generated in a three-dimensional (3D) cylindrical geometry and are observed to evolve dynamically during the injection of magnetic helicity. Detailed evolution of electron density, temperature, plasma potential and magnetic field structures is reconstructed experimentally and visible light emission is captured with a fast-gated, intensified CCD camera to provide insight into the global flux rope dynamics. Experiments with two flux ropes in collisional plasmas and in a strong axial guide field (Bz / B_pol > 10) suggest that magnetic reconnection plays an important role in the initial stages of flux rope evolution. During the early stages of the applied current drive (t < 20τ_Alfven), the flux ropes are observed to twist, partially coalesce and form a thin current sheet with a scale size comparable to that of the ion sound gyro-radius. Here, non-ideal terms in a generalized Ohm's Law appear to play a significant role in the 3D reconnection process as shown by the presence of a strong axial pressure gradient in the current sheet. In addition, a density perturbation with a structure characteristic of a kinetic Alfvén wave is observed to propagate axially in the current layer, anti-parallel to the induced sheet current. Later in the evolution, when a sufficient amount of helicity is injected into the system, a critical threshold for the kink instability is exceeded and the helical twisting of each individual flux rope can dominate the dynamics of the system. This may prevent the complete coalescence of the flux ropes.

Experimental formability analysis of bondal sandwich sheet

NASA Astrophysics Data System (ADS)

Kami, Abdolvahed; Banabic, Dorel

2018-05-01

Metal/polymer/metal sandwich sheets have recently attracted the interests of industries like automotive industry. These sandwich sheets have superior properties over single-layer metallic sheets including good sound and vibration damping and light weight. However, the formability of these sandwich sheets should be enhanced which requires more research. In this paper, the formability of Bondal sheet (DC06/viscoelastic polymer/DC06 sandwich sheet) was studied through different types of experiments. The mechanical properties of Bondal were determined by uniaxial tensile tests. Hemispherical punch stretching and hydraulic bulge tests were carried out to determine the forming limit diagram (FLD) of Bondal. Furthermore, cylindrical and square cup drawing tests were performed in dry and oil lubricated conditions. These tests were conducted at different blank holding forces (BHFs). An interesting observation about Bondal sheet deep drawing was obtaining of higher drawing depths at dry condition in comparison with oil-lubricated condition.

Engineering tubular bone using mesenchymal stem cell sheets and coral particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geng, Wenxin; Ma, Dongyang; Yan, Xingrong

Highlights: • We developed a novel engineering strategy to solve the limitations of bone grafts. • We fabricated tubular constructs using cell sheets and coral particles. • The composite constructs showed high radiological density and compressive strength. • These characteristics were similar to those of native bone. -- Abstract: The development of bone tissue engineering has provided new solutions for bone defects. However, the cell-scaffold-based approaches currently in use have several limitations, including low cell seeding rates and poor bone formation capacity. In the present study, we developed a novel strategy to engineer bone grafts using mesenchymal stem cell sheetsmore » and coral particles. Rabbit bone marrow mesenchymal stem cells were continuously cultured to form a cell sheet with osteogenic potential and coral particles were integrated into the sheet. The composite sheet was then wrapped around a cylindrical mandrel to fabricate a tubular construct. The resultant tubular construct was cultured in a spinner-flask bioreactor and subsequently implanted into a subcutaneous pocket in a nude mouse for assessment of its histological characteristics, radiological density and mechanical property. A similar construct assembled from a cell sheet alone acted as a control. In vitro observations demonstrated that the composite construct maintained its tubular shape, and exhibited higher radiological density, compressive strength and greater extracellular matrix deposition than did the control construct. In vivo experiments further revealed that new bone formed ectopically on the composite constructs, so that the 8-week explants of the composite sheets displayed radiological density similar to that of native bone. These results indicate that the strategy of using a combination of a cell sheet and coral particles has great potential for bone tissue engineering and repairing bone defects.« less

Radial-rotation profile forming: A new processing technology of incremental sheet metal forming

NASA Astrophysics Data System (ADS)

Laue, Robert; Härtel, Sebastian; Awiszus, Birgit

2018-05-01

Incremental forming processes (i.e., spinning) of sheet metal blanks into cylindrical cups are suitable for lower lot sizes. The produced cups were frequently used as preforms to produce workpieces in further forming steps with additional functions like profiled hollow parts [1]. The incremental forming process radial-rotation profile forming has been developed to enable the production of profiled hollow parts with low sheet thinning and good geometrical accuracy. The two principal forming steps are the production of the preform by rotational swing-folding [2] and the subsequent radial profiling of the hollow part in one clamping position. The rotational swing-folding process is based on a combination of conventional spinning and swing-folding. Therefore, a round blank rotates on a profiled mandrel and due to the swinging of a cylindrical forming tool, the blank is formed to a cup with low sheet thinning. In addition, thickening results at the edge of the blank and wrinkling occurs. However, the wrinkles are formed into the indentation of the profiled mandrel and can be reshaped as an advantage in the second process step, the radial profiling. Due to the rotation and continuous radial feed of a profiled forming tool to the profiled mandrel, the axial profile is formed in the second process step. Because of the minor relative movement in axial direction between tool and blank, low sheet thinning occurs. This is an advantage of the principle of the process.

Thin Film Electrodes for Rare Event Detectors

NASA Astrophysics Data System (ADS)

Odgers, Kelly; Brown, Ethan; Lewis, Kim; Giordano, Mike; Freedberg, Jennifer

2017-01-01

In detectors for rare physics processes, such as neutrinoless double beta decay and dark matter, high sensitivity requires careful reduction of backgrounds due to radioimpurities in detector components. Ultra pure cylindrical resistors are being created through thin film depositions onto high purity substrates, such as quartz glass or sapphire. By using ultra clean materials and depositing very small quantities in the films, low radioactivity electrodes are produced. A new characterization process for cylindrical film resistors has been developed through analytic construction of an analogue to the Van Der Pauw technique commonly used for determining sheet resistance on a planar sample. This technique has been used to characterize high purity cylindrical resistors ranging from several ohms to several tera-ohms for applications in rare event detectors. The technique and results of cylindrical thin film resistor characterization will be presented.

DIFFUSION PUMP

DOEpatents

Levenson, L.

1963-09-01

A high-vacuum diffusion pump is described, featuring a novel housing geometry for enhancing pumping speed. An upright, cylindrical lower housing portion is surmounted by a concentric, upright, cylindrical upper housing portion of substantially larger diameter; an uppermost nozzle, disposed concentrically within the upper portion, is adapted to eject downwardly a conical sheet of liquid outwardly to impinge upon the uppermost extremity of the interior wall of the lower portion. Preferably this nozzle is mounted upon a pedestal rising coaxially from within the lower portion and projecting up into said upper portion. (AEC)

Curved cap corrugated sheet

NASA Technical Reports Server (NTRS)

Davis, R. C.; Bales, T. T.; Royster, D. M.; Jackson, L. R. (Inventor)

1984-01-01

The report describes a structure for a strong, lightweight corrugated sheet. The sheet is planar or curved and includes a plurality of corrugation segments, each segment being comprised of a generally U-shaped corrugation with a part-cylindrical crown and cap strip, and straight side walls and with secondary corrugations oriented at right angles to said side walls. The cap strip is bonded to the crown and the longitudinal edge of said cap strip extends beyond edge at the intersection between said crown and said side walls. The high strength relative to weight of the structure makes it desirable for use in aircraft or spacecraft.

Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet

NASA Astrophysics Data System (ADS)

Hamrin, M.; Norqvist, P.; Marghitu, O.; Vaivads, A.; Klecker, B.; Kistler, L. M.; Dandouras, I.

2009-11-01

In this article, and in a companion paper by Hamrin et al. (2009) [Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs) in Earth's plasma sheet. From more than 80 Cluster plasma sheet crossings (660 h data) at the altitude of about 15-20 RE in the summer and fall of 2001, we have identified 116 Concentrated Load Regions (CLRs) and 35 Concentrated Generator Regions (CGRs). By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have estimated typical values of the scale size and life time of the CLRs and the CGRs. We find that a majority of the observed ECRs are rather stationary in space, but varying in time. Assuming that the ECRs are cylindrically shaped and equal in size, we conclude that the typical scale size of the ECRs is 2 RE≲ΔSECR≲5 RE. The ECRs hence occupy a significant portion of the mid altitude plasma sheet. Moreover, the CLRs appear to be somewhat larger than the CGRs. The life time of the ECRs are of the order of 1-10 min, consistent with the large scale magnetotail MHD simulations of Birn and Hesse (2005). The life time of the CGRs is somewhat shorter than for the CLRs. On time scales of 1-10 min, we believe that ECRs rise and vanish in significant regions of the plasma sheet, possibly oscillating between load and generator character. It is probable that at least some of the observed ECRs oscillate energy back and forth in the plasma sheet instead of channeling it to the ionosphere.

Software Method for Computed Tomography Cylinder Data Unwrapping, Re-slicing, and Analysis

NASA Technical Reports Server (NTRS)

Roth, Don J.

2013-01-01

A software method has been developed that is applicable for analyzing cylindrical and partially cylindrical objects inspected using computed tomography (CT). This method involves unwrapping and re-slicing data so that the CT data from the cylindrical object can be viewed as a series of 2D sheets (or flattened onion skins ) in addition to a series of top view slices and 3D volume rendering. The advantages of viewing the data in this fashion are as follows: (1) the use of standard and specialized image processing and analysis methods is facilitated having 2D array data versus a volume rendering; (2) accurate lateral dimensional analysis of flaws is possible in the unwrapped sheets versus volume rendering; (3) flaws in the part jump out at the inspector with the proper contrast expansion settings in the unwrapped sheets; and (4) it is much easier for the inspector to locate flaws in the unwrapped sheets versus top view slices for very thin cylinders. The method is fully automated and requires no input from the user except proper voxel dimension from the CT experiment and wall thickness of the part. The software is available in 32-bit and 64-bit versions, and can be used with binary data (8- and 16-bit) and BMP type CT image sets. The software has memory (RAM) and hard-drive based modes. The advantage of the (64-bit) RAM-based mode is speed (and is very practical for users of 64-bit Windows operating systems and computers having 16 GB or more RAM). The advantage of the hard-drive based analysis is one can work with essentially unlimited-sized data sets. Separate windows are spawned for the unwrapped/re-sliced data view and any image processing interactive capability. Individual unwrapped images and un -wrapped image series can be saved in common image formats. More information is available at http://www.grc.nasa.gov/WWW/OptInstr/ NDE_CT_CylinderUnwrapper.html.

A light sheet confocal microscope for image cytometry with a variable linear slit detector

NASA Astrophysics Data System (ADS)

Hutcheson, Joshua A.; Khan, Foysal Z.; Powless, Amy J.; Benson, Devin; Hunter, Courtney; Fritsch, Ingrid; Muldoon, Timothy J.

2016-03-01

We present a light sheet confocal microscope (LSCM) capable of high-resolution imaging of cell suspensions in a microfluidic environment. In lieu of conventional pressure-driven flow or mechanical translation of the samples, we have employed a novel method of fluid transport, redox-magnetohydrodynamics (redox-MHD). This method achieves fluid motion by inducing a small current into the suspension in the presence of a magnetic field via electrodes patterned onto a silicon chip. This on-chip transportation requires no moving parts, and is coupled to the remainder of the imaging system. The microscopy system comprises a 450 nm diode 20 mW laser coupled to a single mode fiber and a cylindrical lens that converges the light sheet into the back aperture of a 10x, 0.3 NA objective lens in an epi-illumination configuration. The emission pathway contains a 150 mm tube lens that focuses the light onto the linear sensor at the conjugate image plane. The linear sensor (ELiiXA+ 8k/4k) has three lateral binning modes which enables variable detection aperture widths between 5, 10, or 20 μm, which can be used to vary axial resolution. We have demonstrated redox-MHD-enabled light sheet microscopy in suspension of fluorescent polystyrene beads. This approach has potential as a high-throughput image cytometer with myriad cellular diagnostic applications.

Cylindrical Organic Solar Cells with Carbon Nanotube Charge Collectors

NASA Astrophysics Data System (ADS)

Zakhidov, Dante; Lou, Raymond; Ravi, Nav; Mielczarek, Kamil; Cook, Alexander

2009-10-01

Traditional organic photovoltaic devices (OPV) are built on a flat glass substrates coated by ITO. The maximum area covered by the solar cells is limited to a two dimensional plane. Moreover the light absorption is not maximized for a very thin photoactive layer. We suggest here a cylindrical design which has a vertical structure of optical fiber coated by OPV, with light incident from the side and from edge. The sunlight, entering via a smaller area is captured into optical fiber, which allows more sunlight to be absorbed by a cylindrical OPV overcoating with multiple reflections inside the optical fiber. Instead of using brittle ITO as a hole collecting layer in the cylindrical OPV, transparent sheets of multi-walled carbon nanotubes are applied. Their highly conductive nature and 3-D collection of carriers from the P3HT/PCBM photoactive layer allows for increased efficiency over a planar geometry while keeping the device transparent. Aluminum is used as the electron collecting layer and as a cylindrical mirror. [4pt] [1] Ulbricht, et.al, phys. stat. sol. (b) 243, No. 13, 3528 - 3532 (2006) / DOI 10.1002/pssb.200669181

Impinging jets atomization

NASA Technical Reports Server (NTRS)

Ibrahim, E. A.; Przekwas, A. J.

1991-01-01

An analysis of the characteristics of the spray produced by an impinging-jet injector is presented. Predictions of the spray droplet size and distribution are obtained through studying the formation and disintegration of the liquid sheet formed by the impact of two cylindrical jets of the same diameter and momentum. Two breakup regimes of the sheet are considered depending on Weber number, with transition occurring at Weber numbers between 500 and 2000. In the lower Weber number regime, the breakup is due to Taylor cardioidal waves, while at Weber number higher than 2000, the sheet disintegration is by the growth of Kelvin-Helmholtz instability waves. Theoretical expressions to predict the sheet thickness and shape are derived for the low Weber number breakup regime. An existing mathematical analysis of Kelvin-Helmholtz instability of radially moving liquid sheets is adopted in the predictions of resultant drop sizes by sheet breakup at Weber numbers greater than 2000. Comparisons of present theoretical results with experimental measurements and empirical correlations reported in the literature reveal favorable agreement.

Metabolome-mediated biocryomorphic evolution promotes carbon fixation in Greenlandic cryoconite holes.

PubMed

Cook, Joseph M; Edwards, Arwyn; Bulling, Mark; Mur, Luis A J; Cook, Sophie; Gokul, Jarishma K; Cameron, Karen A; Sweet, Michael; Irvine-Fynn, Tristram D L

2016-12-01

Microbial photoautotrophs on glaciers engineer the formation of granular microbial-mineral aggregates termed cryoconite which accelerate ice melt, creating quasi-cylindrical pits called 'cryoconite holes'. These act as biogeochemical reactors on the ice surface and provide habitats for remarkably active and diverse microbiota. Evolution of cryoconite holes towards an equilibrium depth is well known, yet interactions between microbial activity and hole morphology are currently weakly addressed. Here, we experimentally perturbed the depths and diameters of cryoconite holes on the Greenland Ice Sheet. Cryoconite holes responded by sensitively adjusting their shapes in three dimensions ('biocryomorphic evolution') thus maintaining favourable conditions for net autotrophy at the hole floors. Non-targeted metabolomics reveals concomitant shifts in cyclic AMP and fucose metabolism consistent with phototaxis and extracellular polymer synthesis indicating metabolomic-level granular changes in response to perturbation. We present a conceptual model explaining this process and suggest that it results in remarkably robust net autotrophy on the Greenland Ice Sheet. We also describe observations of cryoconite migrating away from shade, implying a degree of self-regulation of carbon budgets over mesoscales. Since cryoconite is a microbe-mineral aggregate, it appears that microbial processes themselves form and maintain stable autotrophic habitats on the surface of the Greenland ice sheet. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Equivalent-Continuum Modeling With Application to Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Odegard, Gregory M.; Gates, Thomas S.; Nicholson, Lee M.; Wise, Kristopher E.

2002-01-01

A method has been proposed for developing structure-property relationships of nano-structured materials. This method serves as a link between computational chemistry and solid mechanics by substituting discrete molecular structures with equivalent-continuum models. It has been shown that this substitution may be accomplished by equating the vibrational potential energy of a nano-structured material with the strain energy of representative truss and continuum models. As important examples with direct application to the development and characterization of single-walled carbon nanotubes and the design of nanotube-based devices, the modeling technique has been applied to determine the effective-continuum geometry and bending rigidity of a graphene sheet. A representative volume element of the chemical structure of graphene has been substituted with equivalent-truss and equivalent continuum models. As a result, an effective thickness of the continuum model has been determined. This effective thickness has been shown to be significantly larger than the interatomic spacing of graphite. The effective thickness has been shown to be significantly larger than the inter-planar spacing of graphite. The effective bending rigidity of the equivalent-continuum model of a graphene sheet was determined by equating the vibrational potential energy of the molecular model of a graphene sheet subjected to cylindrical bending with the strain energy of an equivalent continuum plate subjected to cylindrical bending.

A Novel Automated Method for Analyzing Cylindrical Computed Tomography Data

NASA Technical Reports Server (NTRS)

Roth, D. J.; Burke, E. R.; Rauser, R. W.; Martin, R. E.

2011-01-01

A novel software method is presented that is applicable for analyzing cylindrical and partially cylindrical objects inspected using computed tomography. This method involves unwrapping and re-slicing data so that the CT data from the cylindrical object can be viewed as a series of 2-D sheets in the vertical direction in addition to volume rendering and normal plane views provided by traditional CT software. The method is based on interior and exterior surface edge detection and under proper conditions, is FULLY AUTOMATED and requires no input from the user except the correct voxel dimension from the CT scan. The software is available from NASA in 32- and 64-bit versions that can be applied to gigabyte-sized data sets, processing data either in random access memory or primarily on the computer hard drive. Please inquire with the presenting author if further interested. This software differentiates itself in total from other possible re-slicing software solutions due to complete automation and advanced processing and analysis capabilities.

High-fidelity large area nano-patterning of silicon with femtosecond light sheet

NASA Astrophysics Data System (ADS)

Sidhu, Mehra S.; Munjal, Pooja; Singh, Kamal P.

2018-01-01

We employ a femtosecond light sheet generated by a cylindrical lens to rapidly produce high-fidelity nano-structures over large area on silicon surface. The Fourier analysis of electron microscopy images of the laser-induced surface structures reveals sharp peaks indicating good homogeneity. We observed an emergence of second-order spatial periodicity on increasing the scan speed. Our reliable approach may rapidly nano-pattern curved solid surfaces and tiny objects for diverse potential applications in optical devices, structural coloring, plasmonic substrates and in high-harmonic generation.

Electrical Oscillations in Two-Dimensional Microtubular Structures

PubMed Central

Cantero, María del Rocío; Perez, Paula L.; Smoler, Mariano; Villa Etchegoyen, Cecilia; Cantiello, Horacio F.

2016-01-01

Microtubules (MTs) are unique components of the cytoskeleton formed by hollow cylindrical structures of αβ tubulin dimeric units. The structural wall of the MT is interspersed by nanopores formed by the lateral arrangement of its subunits. MTs are also highly charged polar polyelectrolytes, capable of amplifying electrical signals. The actual nature of these electrodynamic capabilities remains largely unknown. Herein we applied the patch clamp technique to two-dimensional MT sheets, to characterize their electrical properties. Voltage-clamped MT sheets generated cation-selective oscillatory electrical currents whose magnitude depended on both the holding potential, and ionic strength and composition. The oscillations progressed through various modes including single and double periodic regimes and more complex behaviours, being prominent a fundamental frequency at 29 Hz. In physiological K+ (140 mM), oscillations represented in average a 640% change in conductance that was also affected by the prevalent anion. Current injection induced voltage oscillations, thus showing excitability akin with action potentials. The electrical oscillations were entirely blocked by taxol, with pseudo Michaelis-Menten kinetics and a KD of ~1.29 μM. The findings suggest a functional role of the nanopores in the MT wall on the genesis of electrical oscillations that offer new insights into the nonlinear behaviour of the cytoskeleton. PMID:27256791

Three-dimensional shape transformations of hydrogel sheets induced by small-scale modulation of internal stresses

NASA Astrophysics Data System (ADS)

Wu, Zi Liang; Moshe, Michael; Greener, Jesse; Therien-Aubin, Heloise; Nie, Zhihong; Sharon, Eran; Kumacheva, Eugenia

2013-03-01

Although Nature has always been a common source of inspiration in the development of artificial materials, only recently has the ability of man-made materials to produce complex three-dimensional (3D) structures from two-dimensional sheets been explored. Here we present a new approach to the self-shaping of soft matter that mimics fibrous plant tissues by exploiting small-scale variations in the internal stresses to form three-dimensional morphologies. We design single-layer hydrogel sheets with chemically distinct, fibre-like regions that exhibit differential shrinkage and elastic moduli under the application of external stimulus. Using a planar-to-helical three-dimensional shape transformation as an example, we explore the relation between the internal architecture of the sheets and their transition to cylindrical and conical helices with specific structural characteristics. The ability to engineer multiple three-dimensional shape transformations determined by small-scale patterns in a hydrogel sheet represents a promising step in the development of programmable soft matter.

Controlled bending and folding of a bilayer structure consisting of a thin stiff film and a heat shrinkable polymer sheet

NASA Astrophysics Data System (ADS)

Cui, Jianxun; Adams, John G. M.; Zhu, Yong

2018-05-01

Bending pre-designed flat sheets into three-dimensional (3D) structures is attracting much interest, as it provides a simple approach to make 3D devices. Here we report controlled bending and folding of a bilayer structure consisting of a heat shrinkable polymer sheet and a thin stiff film (not thermally responsive). Upon heating, the prestrained polymer sheet shrinks, leading to bending or folding of the bilayer. We studied the effect of relative dimensions of the two layers on the bending behavior and demonstrated the transition from longitudinal bending to transverse bending of the bilayer strip. Transverse bending was utilized to fold origami structures, including several flat letters, a crane, and a corrugated metal sheet via Miura-ori folding. We developed a method to further control the bending orientation based on bio-inspired anisotropic bending stiffness. By bending the metal foil in different orientations, several structures were obtained, including cylindrical surfaces and left-handed/right-handed helical structures.

Spray From a Rolling Tire: Mechanics of Droplet Formation

NASA Astrophysics Data System (ADS)

Plocher, Dennis; Browand, Fred

2010-11-01

The spray pattern immediately behind a single-groove tire rolling on a wet surface is produced in the laboratory using a specially designed tire spray simulator. The spray development is examined using high speed video. Water from the groove forms a liquid sheet as the tire-tread lifts away from the surface. The sheet is not of uniform thickness, but it remains attached to the tread. The thinner portions of the sheet become even thinner as the tire rotates, and eventually break to produce holes near the tire surface. The holes grow as the sheet margins surrounding the holes retract into the thicker portions of the sheet which become roughly cylindrical "ligaments" aligned at right angles to the direction of spray motion. The ligaments break into large droplets via a Rayleigh instability. The smallest droplets form when the margins of two holes collide. As Weber number, We = ρU^2w/2σ , based on tire groove half width, w/2, varies by a factor of 25, the sheet-ligament structure persists, but ligaments become less organized, and more small droplets appear in the pattern.

Turbulent magnetic fluctuations in laboratory reconnection

NASA Astrophysics Data System (ADS)

Von Stechow, Adrian; Grulke, Olaf; Klinger, Thomas

2016-07-01

The role of fluctuations and turbulence is an important question in astrophysics. While direct observations in space are rare and difficult dedicated laboratory experiments provide a versatile environment for the investigation of magnetic reconnection due to their good diagnostic access and wide range of accessible plasma parameters. As such, they also provide an ideal chance for the validation of space plasma reconnection theories and numerical simulation results. In particular, we studied magnetic fluctuations within reconnecting current sheets for various reconnection parameters such as the reconnection rate, guide field, as well as plasma density and temperature. These fluctuations have been previously interpreted as signatures of current sheet plasma instabilities in space and laboratory systems. Especially in low collisionality plasmas these may provide a source of anomalous resistivity and thereby contribute a significant fraction of the reconnection rate. We present fluctuation measurements from two complementary reconnection experiments and compare them to numerical simulation results. VINETA.II (Greifswald, Germany) is a cylindrical, high guide field reconnection experiment with an open field line geometry. The reconnecting current sheet has a three-dimensional structure that is predominantly set by the magnetic pitch angle which results from the superposition of the guide field and the in-plane reconnecting field. Within this current sheet, high frequency magnetic fluctuations are observed that correlate well with the local current density and show a power law spectrum with a spectral break at the lower hybrid frequency. Their correlation lengths are found to be extremely short, but propagation is nonetheless observed with high phase velocities that match the Whistler dispersion. To date, the experiment has been run with an external driving field at frequencies higher than the ion cyclotron frequency f_{ci}, which implies that the EMHD framework applies. Recent machine upgrades allow the inclusion of ion dynamics by reducing the drive frequency below f_{ci}. Two numerical codes (EMHD and hybrid, respectively) have been developed at the Max Planck Institute for solar physics and are used to investigate instability mechanisms and scaling laws for the observed results. MRX (PPPL. Princeton) is a zero to medium guide field, toroidal reconnection experiment. Despite the differing plasma parameters, the qualitative magnetic fluctuation behavior (amplitude profiles, spectra and propagation properties) is comparable to VINETA.II. Results from a new measurement campaign at several different guide fields provides partial overlap with VINETA.II guide field ratios and thereby extends the accessible parameter space of our studies.

Self-assembly of peptide-amphiphile nanofibers under physiological conditions

DOEpatents

Stupp, Samuel I [Chicago, IL; Hartgerink, Jeffrey D [Pearland, TX; Beniash, Elia [Auburndale, MA

2011-11-22

The present invention provides a method of promoting neuron growth and development by contacting cells with a peptide amphiphile molecule in an aqueous solution in the presence of a metal ion. According to the method, the peptide amphiphile forms a cylindrical micellar nanofiber composed of beta-sheets, which promote neuron growth and development.

Effect of Evolutionary Anisotropy on Earing Prediction in Cylindrical Cup Drawing

NASA Astrophysics Data System (ADS)

Choi, H. J.; Lee, K. J.; Choi, Y.; Bae, G.; Ahn, D.-C.; Lee, M.-G.

2017-05-01

The formability of sheet metals is associated with their planar anisotropy, and finite element simulations have been applied to the sheet metal-forming process by describing the anisotropic behaviors using yield functions and hardening models. In this study, the evaluation of anisotropic constitutive models was performed based on the non-uniform height profile or earing in circular cylindrical cup drawing. Two yield functions, a quadratic Hill1948 and a non-quadratic Yld2000-2d model, were used under non-associated and associated flow rules, respectively, to simultaneously capture directional differences in yield stress and r value. The effect of the evolution of anisotropy on the earing prediction was also investigated by employing simplified equivalent plastic strain rate-dependent anisotropic coefficients. The computational results were in good agreement with experiments when the proper choice of the yield function and flow rule, which predicts the planar anisotropy, was made. Moreover, the accuracy of the earing profile could be significantly enhanced if the evolution of anisotropy between uniaxial and biaxial stress states was additionally considered.

A Hierarchical MFI Zeolite with a Two-Dimensional Square Mesostructure.

PubMed

Shen, Xuefeng; Mao, Wenting; Ma, Yanhang; Xu, Dongdong; Wu, Peng; Terasaki, Osamu; Han, Lu; Che, Shunai

2018-01-15

A conceptual design and synthesis of ordered mesoporous zeolites is a challenging research subject in material science. Several seminal articles report that one-dimensional (1D) mesostructured lamellar zeolites are possibly directed by sheet-assembly of surfactants, which collapse after removal of intercalated surfactants. However, except for one example of two-dimensional (2D) hexagonal mesoporous zeolite, no other zeolites with ordered 2D or three-dimensional (3D) mesostructures have been reported. An ordered 2D mesoporous zeolite can be templated by a cylindrical assembly unit with specific interactions in the hydrophobic part. A template molecule with azobenzene in the hydrophobic tail and diquaternary ammonium in the hydrophilic head group directs hierarchical MFI zeolite with a 2D square mesostructure. The material has an elongated octahedral morphology, and quaternary, ordered, straight, square channels framed by MFI thin sheets expanded along the a-c planes and joined with 90° rotations. The structural matching between the cylindrical assembly unit and zeolite framework is crucial for mesostructure construction. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The heliospheric sector boundary as a distented magnetic cloud

NASA Technical Reports Server (NTRS)

Crooker, N. U.; Intriligator, D. S.

1995-01-01

A magnetic cloud was detected both near Earth and by Pioneer 11 located 43 deg east of Earth at 4.8 AU. The magnetic field within the cloud rotated smoothly from toward to away polarity, marking sector boundary passage. Interpreted as a flux rope, the cloud had a vertical axis, implying that its cylindrical cross-section in the ecliptic plane was distended along the sector boundary by at least 43, forming an extensive occlusion in the heliospheric current sheet. At 1 AU the cloud had plasma signatures typical of a fast coronal mass ejection with low temperature and a leading shock. In contrast, at 4.8 AU, only the cloud signature remained. Its radial dimension was the same at both locations, consistent with little expansion beyond 1 AU. Energetic particle data at 4.8 AU show high fluxes preceding the cloud but not extending forward to the corotating shock that marked entry into the interaction region containing the cloud. The streaming direction was antisunward, consistent with possible acceleration in a low-beta region of field line draping around the cloud's western (upstream) end. The fluxes dropped upon entry into the cloud and became essentially isotropic one third of the way through it. On the basis of sector boundary characteristics published in the past, we suggest that distended clouds may be common heliospheric current sheet occlusions.

Solar array deployment from a spinning spacecraft

NASA Technical Reports Server (NTRS)

Carlin, A. H.; Gardner, J. B.; Lassen, H. A.

1974-01-01

Cylindrical drum, wrapped with flexible solar array of solar cells mounted on Mylar sheet, is held by two end-fittings with cable (under tension) passing through axel of drum. Drum is held to end-fittings by axial cable through drum axel; drum is released for deployment when cable is cut at each end and end-fittings spring outward.

Spiraling Cracks in Thin Sheets

NASA Astrophysics Data System (ADS)

Romero, Victor; Roman, Benoit; Cerda, Enrique

2008-03-01

A wide kind of everyday-life industrial products come in a thin package that needs to be torn open by the user, and the opening is not always easy. We built a simple setup to study crack propagation in thin sheets coupled with large out-of-plane displacement : A cylindrical tool is inserted in a straight incision in a thin sheet, and is pushed against the sheet perpendicularly to that incision, eventually propagating a crack. When the blunt tool is continually pushed against the lip, we found that the crack follows a very robust spiraling path. Experiments may be interpreted in terms of ``Spira Mirabilis'' (logarithmic spiral). Starting with crack theory argument, we will show that the early behavior of the cut path follows a portion of a logathmic spiral, and that the path tends to another spiral with a different pitch as the crack adds more turns. Our crack experiment illustrates the fact that thin sheets mechanics is deeply connected to geometry, and finally spirals characteristics allow us to measure material crack properties of the thin layer used.

Selectable light-sheet uniformity using tuned axial scanning

PubMed Central

Duocastella, Martí; Arnold, Craig B.; Puchalla, Jason

2016-01-01

Light-sheet fluorescence microscopy (LSFM) is an optical sectioning technique capable of rapid three-dimensional (3D) imaging of a wide range of specimens with reduced phototoxicity and superior background rejection. However, traditional light-sheet generation approaches based on elliptical or circular Gaussian beams suffer an inherent trade-off between light-sheet thickness and area over which this thickness is preserved. Recently, an increase in light-sheet uniformity was demonstrated using rapid biaxial Gaussian beam scanning along the lateral and beam propagation directions. Here we apply a similar scanning concept to an elliptical beam generated by a cylindrical lens. In this case, only z-scanning of the elliptical beam is required and hence experimental implementation of the setup can be simplified. We introduce a simple dimensionless uniformity statistic to better characterize scanned light-sheets and experimentally demonstrate custom tailored uniformities up to a factor of 5 higher than those of un-scanned elliptical beams. This technique offers a straightforward way to generate and characterize a custom illumination profile that provides enhanced utilization of the detector dynamic range and field of view, opening the door to faster and more efficient 2D and 3D imaging. PMID:28132409

Transverse field focused system

DOEpatents

Anderson, Oscar A.

1986-01-01

A transverse field focused (TFF) system for transport or acceleration of an intense sheet beam of negative ions in which a serial arrangement of a plurality of pairs of concentric cylindrical-arc electrodes is provided. Acceleration of the sheet beam can be achieved by progressively increasing the mean electrode voltage of successive electrode pairs. Because the beam is curved by the electrodes, the system can be designed to transport the beam through a maze passage which is baffled to prevent line of sight therethrough. Edge containment of the beam can be achieved by shaping the side edges of the electrodes to produce an electric force vector directed inwardly from the electrode edges.

Heat transfer studies on the liquid droplet radiator

NASA Technical Reports Server (NTRS)

Mattick, A. T.; Nelson, M.

1987-01-01

This paper examines radiation transfer in the droplet sheet of a liquid droplet radiator including non-isotropic scattering by the droplets. Non-isotropic scattering becomes significant for small droplets (diameter less than 0.1 mm) and for low emissivity liquids. For droplets with an emittance of 0.1 and for a droplet sheet optical depth or 5, the radiated power varies by about 12 percent, depending on whether scattering is predominantly forward or backward. An experimental measurement of the power emitted by a cylindrical cloud of heated droplets of silicone fluid is also reported. The measured cloud emissivity correlates, within experimental error, with the analytical model.

Effect of Hydraulic Pressure on Warm Hydro Mechanical Deep Drawing of Magnesium Alloy Sheet

NASA Astrophysics Data System (ADS)

Liu, Wei; Wu, Linzhi; Yuan, Shijian

The uniaxial tensile test and hydraulic bulging test of AZ31 magnesium alloy sheets were applied to study the influence of temperature on the material properties and obtain the forming limit curves at different temperatures. Numerical simulations of warm hydro mechanical deep drawing were carried out to investigate the effect of hydraulic pressure on the formability of a cylindrical cup, and the simplified hydraulic pressure profiles were used to simulate the loading procedure of hydraulic pressure. The optimal hydraulic pressure at different temperatures were given and verified by experimental studies at temperature 100°C and 170V.

NASA Ares 1 Crew Launch Vehicle Upper Stage Configuration Selection Process

NASA Technical Reports Server (NTRS)

Cook, Jerry R.

2006-01-01

The Upper Stage Element of NASA s Ares I Crew Launch Vehicle (CLV) is a "clean-sheet" approach that is being designed and developed in-house, with Element management at MSFC. The USE concept is a self-supporting cylindrical structure, approximately 115 long and 216" in diameter. While the Reusable Solid Rocket Booster (RSRB) design has changed since the CLV inception, the Upper Stage Element design has remained essentially a clean-sheet approach. Although a clean-sheet upper stage design inherently carries more risk than a modified design, it does offer many advantages: a design for increased reliability; built-in extensibility to allow for commonality/growth without major redesign; and incorporation of state-of-the-art materials, hardware, and design, fabrication, and test techniques and processes to facilitate a potentially better, more reliable system.

Electric field induced sheeting and breakup of dielectric liquid jets

NASA Astrophysics Data System (ADS)

Khoshnevis, Ahmad; Tsai, Scott S. H.; Esmaeilzadeh, Esmaeil

2014-01-01

We report experimental observations of the controlled deformation of a dielectric liquid jet subjected to a local high-voltage electrostatic field in the direction normal to the jet. The jet deforms to the shape of an elliptic cylinder upon application of a normal electrostatic field. As the applied electric field strength is increased, the elliptic cylindrical jet deforms permanently into a flat sheet, and eventually breaks-up into droplets. We interpret this observation—the stretch of the jet is in the normal direction to the applied electric field—qualitatively using the Taylor-Melcher leaky dielectric theory, and develop a simple scaling model that predicts the critical electric field strength for the jet-to-sheet transition. Our model shows a good agreement with experimental results, and has a form that is consistent with the classical drop deformation criterion in the Taylor-Melcher theory. Finally, we statistically analyze the resultant droplets from sheet breakup, and find that increasing the applied electric field strength improves droplet uniformity and reduces droplet size.

Springback evaluation of friction stir welded TWB automotive sheets

NASA Astrophysics Data System (ADS)

Kim, Junehyung; Lee, Wonoh; Chung, Kyung-Hwan; Kim, Daeyong; Kim, Chongmin; Okamoto, Kazutaka; Wagoner, R. H.; Chung, Kwansoo

2011-02-01

Springback behavior of automotive friction stir welded TWB (tailor welded blank) sheets was experimentally investigated and the springback prediction capability of the constitutive law was numerically validated. Four automotive sheets, aluminum alloy 6111-T4, 5083-H18, 5083-O and dual-phase DP590 steel sheets, each having one or two different thicknesses, were considered. To represent mechanical properties, the modified Chaboche type combined isotropic-kinematic hardening law was utilized along with the non-quadratic orthogonal anisotropic yield function, Yld2000-2d, while the anisotropy of the weld zone was ignored for simplicity. For numerical simulations, mechanical properties previously characterized [1] were applied. For validation purposes, three springback tests including the unconstrained cylindrical bending, 2-D draw bending and OSU draw-bend tests were carried out. The numerical method performed reasonably well in analyzing all verification tests and it was confirmed that the springback of TWB as well as of base samples is significantly affected by the ratio of the yield stress with respect to Young's modulus and thickness.

Folding to Curved Surfaces: A Generalized Design Method and Mechanics of Origami-based Cylindrical Structures.

PubMed

Wang, Fei; Gong, Haoran; Chen, Xi; Chen, C Q

2016-09-14

Origami structures enrich the field of mechanical metamaterials with the ability to convert morphologically and systematically between two-dimensional (2D) thin sheets and three-dimensional (3D) spatial structures. In this study, an in-plane design method is proposed to approximate curved surfaces of interest with generalized Miura-ori units. Using this method, two combination types of crease lines are unified in one reprogrammable procedure, generating multiple types of cylindrical structures. Structural completeness conditions of the finite-thickness counterparts to the two types are also proposed. As an example of the design method, the kinematics and elastic properties of an origami-based circular cylindrical shell are analysed. The concept of Poisson's ratio is extended to the cylindrical structures, demonstrating their auxetic property. An analytical model of rigid plates linked by elastic hinges, consistent with numerical simulations, is employed to describe the mechanical response of the structures. Under particular load patterns, the circular shells display novel mechanical behaviour such as snap-through and limiting folding positions. By analysing the geometry and mechanics of the origami structures, we extend the design space of mechanical metamaterials and provide a basis for their practical applications in science and engineering.

Folding to Curved Surfaces: A Generalized Design Method and Mechanics of Origami-based Cylindrical Structures

NASA Astrophysics Data System (ADS)

Wang, Fei; Gong, Haoran; Chen, Xi; Chen, C. Q.

2016-09-01

Origami structures enrich the field of mechanical metamaterials with the ability to convert morphologically and systematically between two-dimensional (2D) thin sheets and three-dimensional (3D) spatial structures. In this study, an in-plane design method is proposed to approximate curved surfaces of interest with generalized Miura-ori units. Using this method, two combination types of crease lines are unified in one reprogrammable procedure, generating multiple types of cylindrical structures. Structural completeness conditions of the finite-thickness counterparts to the two types are also proposed. As an example of the design method, the kinematics and elastic properties of an origami-based circular cylindrical shell are analysed. The concept of Poisson’s ratio is extended to the cylindrical structures, demonstrating their auxetic property. An analytical model of rigid plates linked by elastic hinges, consistent with numerical simulations, is employed to describe the mechanical response of the structures. Under particular load patterns, the circular shells display novel mechanical behaviour such as snap-through and limiting folding positions. By analysing the geometry and mechanics of the origami structures, we extend the design space of mechanical metamaterials and provide a basis for their practical applications in science and engineering.

Folding to Curved Surfaces: A Generalized Design Method and Mechanics of Origami-based Cylindrical Structures

PubMed Central

Wang, Fei; Gong, Haoran; Chen, Xi; Chen, C. Q.

2016-01-01

Origami structures enrich the field of mechanical metamaterials with the ability to convert morphologically and systematically between two-dimensional (2D) thin sheets and three-dimensional (3D) spatial structures. In this study, an in-plane design method is proposed to approximate curved surfaces of interest with generalized Miura-ori units. Using this method, two combination types of crease lines are unified in one reprogrammable procedure, generating multiple types of cylindrical structures. Structural completeness conditions of the finite-thickness counterparts to the two types are also proposed. As an example of the design method, the kinematics and elastic properties of an origami-based circular cylindrical shell are analysed. The concept of Poisson’s ratio is extended to the cylindrical structures, demonstrating their auxetic property. An analytical model of rigid plates linked by elastic hinges, consistent with numerical simulations, is employed to describe the mechanical response of the structures. Under particular load patterns, the circular shells display novel mechanical behaviour such as snap-through and limiting folding positions. By analysing the geometry and mechanics of the origami structures, we extend the design space of mechanical metamaterials and provide a basis for their practical applications in science and engineering. PMID:27624892

Premixed flames in closed cylindrical tubes

NASA Astrophysics Data System (ADS)

Metzener, Philippe; Matalon, Moshe

2001-09-01

We consider the propagation of a premixed flame, as a two-dimensional sheet separating unburned gas from burned products, in a closed cylindrical tube. A nonlinear evolution equation, that describes the motion of the flame front as a function of its mean position, is derived. The equation contains a destabilizing term that results from the gas motion induced by thermal expansion and has a memory term associated with vorticity generation. Numerical solutions of this equation indicate that, when diffusion is stabilizing, the flame evolves into a non-planar form whose shape, and its associated symmetry properties, are determined by the Markstein parameter, and by the initial data. In particular, we observe the development of convex axisymmetric or non-axisymmetric flames, tulip flames and cellular flames.

Magnetic Configurations of the Tilted Current Sheets and Dynamics of Their Flapping in Magnetotail

NASA Astrophysics Data System (ADS)

Shen, C.; Rong, Z. J.; Li, X.; Dunlop, M.; Liu, Z. X.; Malova, H. V.; Lucek, E.; Carr, C.

2009-04-01

Based on multiple spacecraft measurements, the geometrical structures of tilted current sheet and tail flapping waves have been analyzed and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1) The magnetic field lines (MFLs) are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the magnetic equatorial plane, while the tilted current sheet may lean severely to the dawn or dusk side. (2) The tilted current sheet may become very thin, its half thickness is generally much less than the minimum radius of the curvature of the MFLs. (3) In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4) In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail thick current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1RE, while the neutral sheet may be very thin, with its half thickness being several tenths ofRE. During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45

Uncertainties in cylindrical anode current inferences on pulsed power drivers

NASA Astrophysics Data System (ADS)

Porwitzky, Andrew; Brown, Justin

2018-06-01

For over a decade, velocimetry based techniques have been used to infer the electrical current delivered to dynamic materials properties experiments on pulsed power drivers such as the Z Machine. Though originally developed for planar load geometries, in recent years, inferring the current delivered to cylindrical coaxial loads has become a valuable diagnostic tool for numerous platforms. Presented is a summary of uncertainties that can propagate through the current inference technique when applied to expanding cylindrical anodes. An equation representing quantitative uncertainty is developed which shows the unfold method to be accurate to a few percent above 10 MA of load current.

Ice Action on Pairs of Cylindrical and Conical Structures,

DTIC Science & Technology

1983-09-01

correlation because the forces generated ficult to pick a distinct peak in the autospectra for between the structure and the ice sheet are af- the...against two conical structures ...... 20 24. Normalized maximum ice force versus ice velocity ................. 20 25. Normalized initial peak force...versus ice velocity .................. 21 26. Ratio of initial peak ice force to theoretical ice force versus ratio of center-to-center distance

Strain tensor selection and the elastic theory of incompatible thin sheets.

PubMed

Oshri, Oz; Diamant, Haim

2017-05-01

The existing theory of incompatible elastic sheets uses the deviation of the surface metric from a reference metric to define the strain tensor [Efrati et al., J. Mech. Phys. Solids 57, 762 (2009)JMPSA80022-509610.1016/j.jmps.2008.12.004]. For a class of simple axisymmetric problems we examine an alternative formulation, defining the strain based on deviations of distances (rather than distances squared) from their rest values. While the two formulations converge in the limit of small slopes and in the limit of an incompressible sheet, for other cases they are found not to be equivalent. The alternative formulation offers several features which are absent in the existing theory. (a) In the case of planar deformations of flat incompatible sheets, it yields linear, exactly solvable, equations of equilibrium. (b) When reduced to uniaxial (one-dimensional) deformations, it coincides with the theory of extensible elastica; in particular, for a uniaxially bent sheet it yields an unstrained cylindrical configuration. (c) It gives a simple criterion determining whether an isometric immersion of an incompatible sheet is at mechanical equilibrium with respect to normal forces. For a reference metric of constant positive Gaussian curvature, a spherical cap is found to satisfy this criterion except in an arbitrarily narrow boundary layer.

Strain tensor selection and the elastic theory of incompatible thin sheets

NASA Astrophysics Data System (ADS)

Oshri, Oz; Diamant, Haim

2017-05-01

The existing theory of incompatible elastic sheets uses the deviation of the surface metric from a reference metric to define the strain tensor [Efrati et al., J. Mech. Phys. Solids 57, 762 (2009), 10.1016/j.jmps.2008.12.004]. For a class of simple axisymmetric problems we examine an alternative formulation, defining the strain based on deviations of distances (rather than distances squared) from their rest values. While the two formulations converge in the limit of small slopes and in the limit of an incompressible sheet, for other cases they are found not to be equivalent. The alternative formulation offers several features which are absent in the existing theory. (a) In the case of planar deformations of flat incompatible sheets, it yields linear, exactly solvable, equations of equilibrium. (b) When reduced to uniaxial (one-dimensional) deformations, it coincides with the theory of extensible elastica; in particular, for a uniaxially bent sheet it yields an unstrained cylindrical configuration. (c) It gives a simple criterion determining whether an isometric immersion of an incompatible sheet is at mechanical equilibrium with respect to normal forces. For a reference metric of constant positive Gaussian curvature, a spherical cap is found to satisfy this criterion except in an arbitrarily narrow boundary layer.

Magnetic configurations of the tilted current sheets in magnetotail

NASA Astrophysics Data System (ADS)

Shen, C.; Rong, Z. J.; Li, X.; Dunlop, M.; Liu, Z. X.; Malova, H. V.; Lucek, E.; Carr, C.

2008-11-01

In this research, the geometrical structures of tilted current sheet and tail flapping waves have been analysed based on multiple spacecraft measurements and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1) The magnetic field lines (MFLs) in the tilted current sheet are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the equatorial plane, while the normal of the tilted current sheet leans severely to the dawn or dusk side. (2) The tilted current sheet may become very thin, the half thickness of its neutral sheet is generally much less than the minimum radius of the curvature of the MFLs. (3) In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4) In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1 RE, while the neutral sheet may be very thin, with its half thickness being several tenths of RE. During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45°. The phase velocities of these flapping waves are several tens km/s, while their periods and wavelengths are several tens of minutes, and several earth radii, respectively. These tail flapping events generally last several hours and occur during quiet periods or periods of weak magnetospheric activity.

An advanced constitutive model in the sheet metal forming simulation: the Teodosiu microstructural model and the Cazacu Barlat yield criterion

NASA Astrophysics Data System (ADS)

Alves, J. L.; Oliveira, M. C.; Menezes, L. F.

2004-06-01

Two constitutive models used to describe the plastic behavior of sheet metals in the numerical simulation of sheet metal forming process are studied: a recently proposed advanced constitutive model based on the Teodosiu microstructural model and the Cazacu Barlat yield criterion is compared with a more classical one, based on the Swift law and the Hill 1948 yield criterion. These constitutive models are implemented into DD3IMP, a finite element home code specifically developed to simulate sheet metal forming processes, which generically is a 3-D elastoplastic finite element code with an updated Lagrangian formulation, following a fully implicit time integration scheme, large elastoplastic strains and rotations. Solid finite elements and parametric surfaces are used to model the blank sheet and tool surfaces, respectively. Some details of the numerical implementation of the constitutive models are given. Finally, the theory is illustrated with the numerical simulation of the deep drawing of a cylindrical cup. The results show that the proposed advanced constitutive model predicts with more exactness the final shape (medium height and ears profile) of the formed part, as one can conclude from the comparison with the experimental results.

Strength and Formability Improvement of Al-Cu-Mn Aluminum Alloy Complex Parts by Thermomechanical Treatment with Sheet Hydroforming

NASA Astrophysics Data System (ADS)

Chen, Yi-Zhe; Liu, Wei; Yuan, Shi-Jian

2015-05-01

Normally, the strength and formability of aluminum alloys can be increased largely by severe plastic deformation and heat treatment. However, many plastic deformation processes are more suitable for making raw material, not for formed parts. In this article, an experimental study of the thermomechanical treatment by using the sheet hydroforming process was developed to improve both mechanical strength and formability for aluminum alloys in forming complex parts. The limiting drawing ratio, thickness, and strain distribution of complex parts formed by sheet hydroforming were investigated to study the formability and sheet-deformation behavior. Based on the optimal formed parts, the tensile strength, microhardness, grain structure, and strengthening precipitates were analyzed to identify the strengthening effect of thermomechanical treatment. The results show that in the solution state, the limiting drawing ratio of cylindrical parts could be increased for 10.9% compared with traditional deep drawing process. The peak values of tensile stress and microhardness of formed parts are 18.0% and 12.5% higher than that in T6 state. This investigation shows that the thermomechanical treatment by sheet hydroforming is a potential method for the products manufacturing of aluminum alloy with high strength and good formability.

Cartilage repair using mesenchymal stem cell (MSC) sheet and MSCs-loaded bilayer PLGA scaffold in a rabbit model.

PubMed

Qi, Yiying; Du, Yi; Li, Weixu; Dai, Xuesong; Zhao, Tengfei; Yan, Weiqi

2014-06-01

The integration of regenerated cartilage with surrounding native cartilage is a major challenge for the success of cartilage tissue-engineering strategies. The purpose of this study is to investigate whether incorporation of the power of mesenchymal stem cell (MSC) sheet to MSCs-loaded bilayer poly-(lactic-co-glycolic acid) (PLGA) scaffolds can improve the integration and repair of cartilage defects in a rabbit model. Rabbit bone marrow-derived MSCs were cultured and formed cell sheet. Full-thickness cylindrical osteochondral defects (4 mm in diameter, 3 mm in depth) were created in the patellar groove of 18 New Zealand white rabbits and the osteochondral defects were treated with PLGA scaffold (n = 6), PLGA/MSCs (n = 6) or MSC sheet-encapsulated PLGA/MSCs (n = 6). After 6 and 12 weeks, the integration and tissue response were evaluated histologically. The MSC sheet-encapsulated PLGA/MCSs group showed significantly more amounts of hyaline cartilage and higher histological scores than PLGA/MSCs group and PLGA group (P < 0.05). In addition, the MSC sheet-encapsulated PLGA/MCSs group showed the best integration between the repaired cartilage and surrounding normal cartilage and subchondral bone compared to other two groups. The novel method of incorporation of MSC sheet to PLGA/MCSs could enhance the ability of cartilage regeneration and integration between repair cartilage and the surrounding cartilage. Transplantation of autologous MSC sheet combined with traditional strategies or cartilage debris might provide therapeutic opportunities for improving cartilage regeneration and integration in humans.

Thin current sheets observation by MMS during a near-Earth's magnetotail reconnection event

NASA Astrophysics Data System (ADS)

Nakamura, R.; Varsani, A.; Nakamura, T.; Genestreti, K.; Plaschke, F.; Baumjohann, W.; Nagai, T.; Burch, J.; Cohen, I. J.; Ergun, R.; Fuselier, S. A.; Giles, B. L.; Le Contel, O.; Lindqvist, P. A.; Magnes, W.; Schwartz, S. J.; Strangeway, R. J.; Torbert, R. B.

2017-12-01

During summer 2017, the four spacecraft of the Magnetospheric Multiscale (MMS) mission traversed the nightside magnetotail current sheet at an apogee of 25 RE. They detected a number of flow reversal events suggestive of the passage of the reconnection current sheet. Due to the mission's unprecedented high-time resolution and spatial separation well below the ion scales, structure of thin current sheets is well resolved both with plasma and field measurements. In this study we examine the detailed structure of thin current sheets during a flow reversal event from tailward flow to Earthward flow, when MMS crossed the center of the current sheet . We investigate the changes in the structure of the thin current sheet relative to the X-point based on multi-point analysis. We determine the motion and strength of the current sheet from curlometer calculations comparing these with currents obtained from the particle data. The observed structures of these current sheets are also compared with simulations.

Growth patterns for shape-shifting elastic bilayers.

PubMed

van Rees, Wim M; Vouga, Etienne; Mahadevan, L

2017-10-31

Inspired by the differential-growth-driven morphogenesis of leaves, flowers, and other tissues, there is increasing interest in artificial analogs of these shape-shifting thin sheets made of active materials that respond to environmental stimuli such as heat, light, and humidity. But how can we determine the growth patterns to achieve a given shape from another shape? We solve this geometric inverse problem of determining the growth factors and directions (the metric tensors) for a given isotropic elastic bilayer to grow into a target shape by posing and solving an elastic energy minimization problem. A mathematical equivalence between bilayers and curved monolayers simplifies the inverse problem considerably by providing algebraic expressions for the growth metric tensors in terms of those of the final shape. This approach also allows us to prove that we can grow any target surface from any reference surface using orthotropically growing bilayers. We demonstrate this by numerically simulating the growth of a flat sheet into a face, a cylindrical sheet into a flower, and a flat sheet into a complex canyon-like structure.

Growth patterns for shape-shifting elastic bilayers

PubMed Central

van Rees, Wim M.; Vouga, Etienne; Mahadevan, L.

2017-01-01

Inspired by the differential-growth-driven morphogenesis of leaves, flowers, and other tissues, there is increasing interest in artificial analogs of these shape-shifting thin sheets made of active materials that respond to environmental stimuli such as heat, light, and humidity. But how can we determine the growth patterns to achieve a given shape from another shape? We solve this geometric inverse problem of determining the growth factors and directions (the metric tensors) for a given isotropic elastic bilayer to grow into a target shape by posing and solving an elastic energy minimization problem. A mathematical equivalence between bilayers and curved monolayers simplifies the inverse problem considerably by providing algebraic expressions for the growth metric tensors in terms of those of the final shape. This approach also allows us to prove that we can grow any target surface from any reference surface using orthotropically growing bilayers. We demonstrate this by numerically simulating the growth of a flat sheet into a face, a cylindrical sheet into a flower, and a flat sheet into a complex canyon-like structure. PMID:29078336

Engineering Vascularized Bone Grafts by Integrating a Biomimetic Periosteum and β-TCP Scaffold

PubMed Central

2015-01-01

Treatment of large bone defects using synthetic scaffolds remain a challenge mainly due to insufficient vascularization. This study is to engineer a vascularized bone graft by integrating a vascularized biomimetic cell-sheet-engineered periosteum (CSEP) and a biodegradable macroporous beta-tricalcium phosphate (β-TCP) scaffold. We first cultured human mesenchymal stem cells (hMSCs) to form cell sheet and human umbilical vascular endothelial cells (HUVECs) were then seeded on the undifferentiated hMSCs sheet to form vascularized cell sheet for mimicking the fibrous layer of native periosteum. A mineralized hMSCs sheet was cultured to mimic the cambium layer of native periosteum. This mineralized hMSCs sheet was first wrapped onto a cylindrical β-TCP scaffold followed by wrapping the vascularized HUVEC/hMSC sheet, thus generating a biomimetic CSEP on the β-TCP scaffold. A nonperiosteum structural cell sheets-covered β-TCP and plain β-TCP were used as controls. In vitro studies indicate that the undifferentiated hMSCs sheet facilitated HUVECs to form rich capillary-like networks. In vivo studies indicate that the biomimetic CSEP enhanced angiogenesis and functional anastomosis between the in vitro preformed human capillary networks and the mouse host vasculature. MicroCT analysis and osteocalcin staining show that the biomimetic CSEP/β-TCP graft formed more bone matrix compared to the other groups. These results suggest that the CSEP that mimics the cellular components and spatial configuration of periosteum plays a critical role in vascularization and osteogenesis. Our studies suggest that a biomimetic periosteum-covered β-TCP graft is a promising approach for bone regeneration. PMID:24858072

Transmission of sound across a vortex layer enclosing a cylindrical column of jet

NASA Technical Reports Server (NTRS)

Luh, R.; Chao, C. C.

1982-01-01

An approximate solution to the problem of transmission of sound across a cylindrical vortex was obtained. Results are considerably different from the plane vortex sheet case because of the added role played by the curvature of the jet. In comparison with the plane case, the specularly transmitted waves are more complex and require some numerical integration. Resonance waves are identically predicted for M 2, but there is also a wave field whose modified effect appears to extend the region of resonance just as the instability waves cover a region in space and time. The instability waves are predicted to exist for all Mach numbers but vanish for wavelengths that are large compared to the jet radius. The region of propagation is similarly wavelength dependent.

Continuous development of current sheets near and away from magnetic nulls

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Sanjay; Bhattacharyya, R.

2016-04-15

The presented computations compare the strength of current sheets which develop near and away from the magnetic nulls. To ensure the spontaneous generation of current sheets, the computations are performed congruently with Parker's magnetostatic theorem. The simulations evince current sheets near two dimensional and three dimensional magnetic nulls as well as away from them. An important finding of this work is in the demonstration of comparative scaling of peak current density with numerical resolution, for these different types of current sheets. The results document current sheets near two dimensional magnetic nulls to have larger strength while exhibiting a stronger scalingmore » than the current sheets close to three dimensional magnetic nulls or away from any magnetic null. The comparative scaling points to a scenario where the magnetic topology near a developing current sheet is important for energetics of the subsequent reconnection.« less

A comparison of coronal and interplanetary current sheet inclinations

NASA Technical Reports Server (NTRS)

Behannon, K. W.; Burlaga, L. F.; Hundhausen, A. J.

1983-01-01

The HAO white light K-coronameter observations show that the inclination of the heliospheric current sheet at the base of the corona can be both large (nearly vertical with respect to the solar equator) or small during Cararington rotations 1660 - 1666 and even on a single solar rotation. Voyager 1 and 2 magnetic field observations of crossing of the heliospheric current sheet at distances from the Sun of 1.4 and 2.8 AU. Two cases are considered, one in which the corresponding coronameter data indicate a nearly vertical (north-south) current sheet and another in which a nearly horizontal, near equatorial current sheet is indicated. For the crossings of the vertical current sheet, a variance analysis based on hour averages of the magnetic field data gave a minimum variance direction consistent with a steep inclination. The horizontal current sheet was observed by Voyager as a region of mixed polarity and low speeds lasting several days, consistent with multiple crossings of a horizontal but irregular and fluctuating current sheet at 1.4 AU. However, variance analysis of individual current sheet crossings in this interval using 1.92 see averages did not give minimum variance directions consistent with a horizontal current sheet.

Eddy Current System and Method for Crack Detection

NASA Technical Reports Server (NTRS)

Wincheski, Russell A. (Inventor); Simpson, John W. (Inventor)

2012-01-01

An eddy current system and method enables detection of sub-surface damage in a cylindrical object. The invention incorporates a dual frequency, orthogonally wound eddy current probe mounted on a stepper motor-controlled scanning system. The system is designed to inspect for outer surface damage from the interior of the cylindrical object.

Ohm's law for a current sheet

NASA Technical Reports Server (NTRS)

Lyons, L. R.; Speiser, T. W.

1985-01-01

The paper derives an Ohm's law for single-particle motion in a current sheet, where the magnetic field reverses in direction across the sheet. The result is considerably different from the resistive Ohm's law often used in MHD studies of the geomagnetic tail. Single-particle analysis is extended to obtain a self-consistency relation for a current sheet which agrees with previous results. The results are applicable to the concept of reconnection in that the electric field parallel to the current is obtained for a one-dimensional current sheet with constant normal magnetic field. Dissipated energy goes directly into accelerating particles within the current sheet.

THE DYNAMICAL GENERATION OF CURRENT SHEETS IN ASTROPHYSICAL PLASMA TURBULENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howes, Gregory G.

2016-08-20

Turbulence profoundly affects particle transport and plasma heating in many astrophysical plasma environments, from galaxy clusters to the solar corona and solar wind to Earth's magnetosphere. Both fluid and kinetic simulations of plasma turbulence ubiquitously generate coherent structures, in the form of current sheets, at small scales, and the locations of these current sheets appear to be associated with enhanced rates of dissipation of the turbulent energy. Therefore, illuminating the origin and nature of these current sheets is critical to identifying the dominant physical mechanisms of dissipation, a primary aim at the forefront of plasma turbulence research. Here, we presentmore » evidence from nonlinear gyrokinetic simulations that strong nonlinear interactions between counterpropagating Alfvén waves, or strong Alfvén wave collisions, are a natural mechanism for the generation of current sheets in plasma turbulence. Furthermore, we conceptually explain this current sheet development in terms of the nonlinear dynamics of Alfvén wave collisions, showing that these current sheets arise through constructive interference among the initial Alfvén waves and nonlinearly generated modes. The properties of current sheets generated by strong Alfvén wave collisions are compared to published observations of current sheets in the Earth's magnetosheath and the solar wind, and the nature of these current sheets leads to the expectation that Landau damping of the constituent Alfvén waves plays a dominant role in the damping of turbulently generated current sheets.« less

Triggering of explosive reconnection in a thick current sheet via current sheet compression: Less current sheet thinning, more temperature anisotropy

NASA Astrophysics Data System (ADS)

Shimizu, K.; Shinohara, I.; Fujimoto, M.

2016-12-01

Two-dimensional kinetic simulations of compression of thick current sheets are performed to see how it can lead to triggering of explosive magnetic reconnection. The current sheet under study is simply in a Harris-like anti-paralell and symmetric geometry. A one-dimensional pre-study shows that the compression is more effective to make the plasma anisotropy than to thin the current sheet width. When the lobe magnetic field is amplified by a factor of 2, the plasma temperature anisotropy inside the current sheet reaches 2 but the current sheet thickness is reduced only by 1/sqrt(2). If a current sheet thickness needs to be comparable to the ion inertial scale for reconnection triggering take place, as is widely and frequently mentioned in the research community, the initial thickness cannot be more than a few ion scale for reconnection to set-in. On the other hand, the temperature anisotropy of 2 can be significant for the triggering problem. Two-dimensional simulations show explosive magnetic reconnection to take place even when the initial current sheet thickness more than an order of magnitude thicker than the ion scale, indicating the resilient triggering drive supplied by the temperature anisotropy. We also discuss how the reconnection triggering capability of the temperature anisotropy boosted tearing mode for thick current sheets compares with the instabilities in the plane orthogonal to the reconnecting field.

Shaping-lathe roundup machine is key to profitable manufacturing of composite sheathing panels in Massachusetts or Maine

Treesearch

N. Springate; I. Plough; P. Koch

1978-01-01

A process is described in which a shaping-lathe headrig produces flakes of optimum geometry while rounding 8-foot peeler bolts to their maximum cylindrical diameter. The cylinders are then passed, at a rate of 5 to 7 per minute, to a veneer lathe for production of continuoua veneer, which is subsequently clipped into 4- by 8-foot sheets. Veneer cores are flaked in a...

Shaping-lathe roundup machine is key to profitable manufacture of composite sheathing panels in Massachusetts or Maine

Treesearch

Norman Springate; Peter Koch; Irving Plough

1978-01-01

A process is described in which a shaping-lathe headrig produces flakes of optimum geometry while rounding 8-foot peeler bolts to their maximum cylindrical diameter. The cylinder are then passed, at a rate of 5 to 7 per minute, to a veneer lathe for production of continuous veneer, which is Subsequently clipped into 4- by 8-foot sheet.. Veneer cores are flaked in a...

Structural characterization of toxic oligomers that are kinetically trapped during α-synuclein fibril formation

PubMed Central

Chen, Serene W.; Drakulic, Srdja; Deas, Emma; Ouberai, Myriam; Aprile, Francesco A.; Arranz, Rocío; Ness, Samuel; Roodveldt, Cintia; Guilliams, Tim; De-Genst, Erwin J.; Klenerman, David; Wood, Nicholas W.; Knowles, Tuomas P.J.; Alfonso, Carlos; Rivas, Germán; Abramov, Andrey Y.; Valpuesta, José María; Dobson, Christopher M.; Cremades, Nunilo

2015-01-01

We describe the isolation and detailed structural characterization of stable toxic oligomers of α-synuclein that have accumulated during the process of amyloid formation. Our approach has allowed us to identify distinct subgroups of oligomers and to probe their molecular architectures by using cryo-electron microscopy (cryoEM) image reconstruction techniques. Although the oligomers exist in a range of sizes, with different extents and nature of β-sheet content and exposed hydrophobicity, they all possess a hollow cylindrical architecture with similarities to certain types of amyloid fibril, suggesting that the accumulation of at least some forms of amyloid oligomers is likely to be a consequence of very slow rates of rearrangement of their β-sheet structures. Our findings reveal the inherent multiplicity of the process of protein misfolding and the key role the β-sheet geometry acquired in the early stages of the self-assembly process plays in dictating the kinetic stability and the pathological nature of individual oligomeric species. PMID:25855634

High-latitude Conic Current Sheets in the Solar Wind

NASA Astrophysics Data System (ADS)

Khabarova, Olga V.; Malova, Helmi V.; Kislov, Roman A.; Zelenyi, Lev M.; Obridko, Vladimir N.; Kharshiladze, Alexander F.; Tokumaru, Munetoshi; Sokół, Justyna M.; Grzedzielski, Stan; Fujiki, Ken'ichi

2017-02-01

We provide observational evidence for the existence of large-scale cylindrical (or conic-like) current sheets (CCSs) at high heliolatitudes. Long-lived CCSs were detected by Ulysses during its passages over the South Solar Pole in 1994 and 2007. The characteristic scale of these tornado-like structures is several times less than a typical width of coronal holes within which the CCSs are observed. CCS crossings are characterized by a dramatic decrease in the solar wind speed and plasma beta typical for predicted profiles of CCSs. Ulysses crossed the same CCS at different heliolatitudes at 2-3 au several times in 1994, as the CCS was declined from the rotation axis and corotated with the Sun. In 2007, a CCS was detected directly over the South Pole, and its structure was strongly highlighted by the interaction with comet McNaught. Restorations of solar coronal magnetic field lines reveal the occurrence of conic-like magnetic separators over the solar poles in both 1994 and 2007. Such separators exist only during solar minima. Interplanetary scintillation data analysis confirms the presence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. Energetic particle flux enhancements up to several MeV/nuc are observed at edges of the CCSs. We built simple MHD models of a CCS to illustrate its key features. The CCSs may be formed as a result of nonaxiality of the solar rotation axis and magnetic axis, as predicted by the Fisk-Parker hybrid heliospheric magnetic field model in the modification of Burger and coworkers.

High-latitude Conic Current Sheets in the Solar Wind

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khabarova, Olga V.; Obridko, Vladimir N.; Kharshiladze, Alexander F.

We provide observational evidence for the existence of large-scale cylindrical (or conic-like) current sheets (CCSs) at high heliolatitudes. Long-lived CCSs were detected by Ulysses during its passages over the South Solar Pole in 1994 and 2007. The characteristic scale of these tornado-like structures is several times less than a typical width of coronal holes within which the CCSs are observed. CCS crossings are characterized by a dramatic decrease in the solar wind speed and plasma beta typical for predicted profiles of CCSs. Ulysses crossed the same CCS at different heliolatitudes at 2–3 au several times in 1994, as the CCSmore » was declined from the rotation axis and corotated with the Sun. In 2007, a CCS was detected directly over the South Pole, and its structure was strongly highlighted by the interaction with comet McNaught. Restorations of solar coronal magnetic field lines reveal the occurrence of conic-like magnetic separators over the solar poles in both 1994 and 2007. Such separators exist only during solar minima. Interplanetary scintillation data analysis confirms the presence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. Energetic particle flux enhancements up to several MeV/ nuc are observed at edges of the CCSs. We built simple MHD models of a CCS to illustrate its key features. The CCSs may be formed as a result of nonaxiality of the solar rotation axis and magnetic axis, as predicted by the Fisk–Parker hybrid heliospheric magnetic field model in the modification of Burger and coworkers.« less

Wave-induced drift of large floating sheets

NASA Astrophysics Data System (ADS)

Christensen, K. H.; Weber, J. E.

In this article we study the wave-induced drift of large, flexible shallow floating objects, referred to as sheets. When surface waves propagate through a sheet, they provide a mean stress on the sheet, resulting in a mean drift. In response, the sheet generates an Ekman current. The drift velocity of the sheet is determined by (i) the wave-induced stress, (ii) the viscous stress due to the Ekman current, and (iii) the Coriolis force. The sheet velocity and the current beneath the sheet are determined for constant and depth-varying eddy viscosities.

Time Evolution of the Macroscopic Characteristics of a Thin Current Sheet in the Course of Its Formation in the Earth's Magnetotail

NASA Astrophysics Data System (ADS)

Domrin, V. I.; Malova, H. V.; Popov, V. Yu.

2018-04-01

A numerical model is developed that allows tracing the time evolution of a current sheet from a relatively thick current configuration with isotropic distributions of the pressure and temperature in an extremely thin current sheet, which plays a key role in geomagnetic processes. Such a configuration is observed in the Earth's magnetotail in the stage preceding a large-scale geomagnetic disturbance (substorm). Thin current sheets are reservoirs of the free energy released during geomagnetic disturbances. The time evolution of the components of the pressure tensor caused by changes in the structure of the current sheet is investigated. It is shown that the pressure tensor in the current sheet evolves in two stages. In the first stage, a current sheet with a thickness of eight to ten proton Larmor radii forms. This stage is characterized by the plasma drift toward the current sheet and the Earth and can be described in terms of the Chu-Goldberger-Low approximation. In the second stage, an extremely thin current sheet with an anisotropic plasma pressure tensor forms, due to which the system is maintained in an equilibrium state. Estimates of the characteristic time of the system evolution agree with available experimental data.

Production of radially and azimuthally polarized polychromatic beams

NASA Astrophysics Data System (ADS)

Shoham, A.; Vander, R.; Lipson, S. G.

2006-12-01

We describe a system that efficiently provides radially or azimuthally polarized radiation from a randomly polarized source. It is constructed from two conical reflectors and a cylindrical sheet of polarizing film. Envisaged applications include a microscope illuminator for high-resolution surface plasmon resonance microscopy, illumination for high-resolution microlithography, and efficient coupling of a laser source to hollow optical fibers. The angular coherence function of light polarized by the device was measured to evaluate its usefulness for these applications.

Design and assessment of a wrapped cylindrical Ca-P AZ31 Mg alloy for critical-size ulna defect repair.

PubMed

Smith, Montserrat Rabago; Atkinson, Patrick; White, Désirée; Piersma, Tyler; Gutierrez, Gloria; Rossini, Gianny; Desai, Sapna; Wellinghoff, Stephen; Yu, Hui; Cheng, Xingguo

2012-01-01

Recently, magnesium has been investigated as a promising bioresorbable orthopedic biomaterial. Its mechanical properties are very similar to natural bone, making it appropriate for load-bearing orthopedic fracture repair applications. However, significant hurdles remain regarding the design of practical implants and methods to control degradation and enhance biocompatibility. Although attempts have been made to hinder magnesium's rapid corrosion via alloying and coating, these studies have used solid monoliths. In an effort to reduce the amount of alloy used for implantation in a shape that mimics cortical bone shape, this study used a thin sheet of Mg AZ31 which was rolled into hollow cylindrical scaffolds. The scaffold was coated with different amounts of Ca-P; this implant demonstrated slowed corrosion in simulated body fluid (SBF) as well as enhanced biocompatibility for mesenchymal stem cells (MSC). In vivo implantation of magnesium alloy scaffold adjacent to the rat femur showed significant biointegration with further deposition of complex Mg-Ca phosphates/carbonates typical of natural bone. Finally, the implant was placed in a critical-size ulna defect in live rabbits, which lead to radiographic union and partial restoration of biomechanical strength in the defect. This study demonstrated that a thin sheet of coated Mg alloy that was spirally wrapped wound be a promising orthopedic biomaterial for bone repair. Copyright © 2011 Wiley Periodicals, Inc.

THEMIS two‐point measurements of the cross‐tail current density: A thick bifurcated current sheet in the near‐Earth plasma sheet

PubMed Central

2015-01-01

Abstract The basic properties of the near‐Earth current sheet from 8 RE to 12 RE were determined based on Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations from 2007 to 2013. Ampere's law was used to estimate the current density when the locations of two spacecraft were suitable for the calculation. A total of 3838 current density observations were obtained to study the vertical profile. For typical solar wind conditions, the current density near (off) the central plane of the current sheet ranged from 1 to 2 nA/m2 (1 to 8 nA/m2). All the high current densities appeared off the central plane of the current sheet, indicating the formation of a bifurcated current sheet structure when the current density increased above 2 nA/m2. The median profile also showed a bifurcated structure, in which the half thickness was about 3 RE. The distance between the peak of the current density and the central plane of the current sheet was 0.5 to 1 RE. High current densities above 4 nA/m2 were observed in some cases that occurred preferentially during substorms, but they also occurred in quiet times. In contrast to the commonly accepted picture, these high current densities can form without a high solar wind dynamic pressure. In addition, these high current densities can appear in two magnetic configurations: tail‐like and dipolar structures. At least two mechanisms, magnetic flux depletion and new current system formation during the expansion phase, other than plasma sheet compression are responsible for the formation of the bifurcated current sheets. PMID:27722039

Ring current dynamics and plasma sheet sources. [magnetic storms

NASA Technical Reports Server (NTRS)

Lyons, L. R.

1984-01-01

The source of the energized plasma that forms in geomagnetic storm ring currents, and ring current decay are discussed. The dominant loss processes for ring current ions are identified as charge exchange and resonant interactions with ion-cyclotron waves. Ring current ions are not dominated by protons. At L4 and energies below a few tens of keV, O+ is the most abundant ion, He+ is second, and protons are third. The plasma sheet contributes directly or indirectly to the ring current particle population. An important source of plasma sheet ions is earthward streaming ions on the outer boundary of the plasma sheet. Ion interactions with the current across the geomagnetic tail can account for the formation of this boundary layer. Electron interactions with the current sheet are possibly an important source of plasma sheet electrons.

Structure and Dynamics of Current Sheets in 3D Magnetic Fields with the X-line

NASA Astrophysics Data System (ADS)

Frank, Anna G.; Bogdanov, S. Yu.; Bugrov, S. G.; Markov, V. S.; Dreiden, G. V.; Ostrovskaya, G. V.

2004-11-01

Experimental results are presented on the structure of current sheets formed in 3D magnetic fields with singular lines of the X-type. Two basic diagnostics were used with the device CS - 3D: two-exposure holographic interferometry and magnetic measurements. Formation of extended current sheets and plasma compression were observed in the presence of the longitudinal magnetic field component aligned with the X-line. Plasma density decreased and the sheet thickness increased with an increase of the longitudinal component. We succeeded to reveal formation of the sheets taking unusual shape, namely tilted and asymmetric sheets, in plasmas with the heavy ions. These current sheets were obviously different from the planar sheets formed in 2D magnetic fields, i.e. without longitudinal component. Analysis of typical plasma parameters made it evident that plasma dynamics and current sheet evolution should be treated on the base of the two-fluid approach. Specifically it is necessary to take into account the Hall currents in the plane perpendicular to the X-line, and the dynamic effects resulting from interaction of the Hall currents and the 3D magnetic field. Supported by RFBR, grant 03-02-17282, and ISTC, project 2098.

Magnetic reconnection during eruptive magnetic flux ropes

NASA Astrophysics Data System (ADS)

Mei, Z. X.; Keppens, R.; Roussev, I. I.; Lin, J.

2017-08-01

Aims: We perform a three-dimensional (3D) high resolution numerical simulation in isothermal magnetohydrodynamics to study the magnetic reconnection process in a current sheet (CS) formed during an eruption of a twisted magnetic flux rope (MFR). Because the twist distribution violates the Kruskal-Shafranov condition, the kink instability occurs, and the MFR is distorted. The centre part of the MFR loses its equilibrium and erupts upward, which leads to the formation of a 3D CS underneath it. Methods: In order to study the magnetic reconnection inside the CS in detail, mesh refinement has been used to reduce the numerical diffusion and we estimate a Lundquist number S = 104 in the vicinity of the CS. Results: The refined mesh allows us to resolve fine structures inside the 3D CS: a bifurcating sheet structure signaling the 3D generalization of Petschek slow shocks, some distorted-cylindrical substructures due to the tearing mode instabilities, and two turbulence regions near the upper and the lower tips of the CS. The topological characteristics of the MFR depend sensitively on the observer's viewing angle: it presents as a sigmoid structure, an outwardly expanding MFR with helical distortion, or a flare-CS-coronal mass ejection symbiosis as in 2D flux-rope models when observed from the top, the front, or the side. The movie associated to Fig. 2 is available at http://www.aanda.org

ISEE-1 and 2 observations of field-aligned currents in the distant midnight magnetosphere

NASA Technical Reports Server (NTRS)

Elphic, R. C.; Kelly, T. J.; Russell, C. T.

1985-01-01

Magnetic field measurements obtained in the nightside magnetosphere by the co-orbiting ISEE-1 and 2 spacecraft have been examined for signatures of field-aligned currents (FAC). Such currents are found on the boundary of the plasma sheet both when the plasma sheet is expanding and when it is thinning. Evidence is often found for the existence of waves on the plasma sheet boundary, leading to multiple crossings of the FAC sheet. At times the boundary layer FAC sheet orientation is nearly parallel to the X-Z GSM plane, suggesting 'protrusions' of plasma sheet into the lobes. The boundary layer current polarity is, as expected, into the ionosphere in the midnight to dawn local time sector, and outward near dusk. Current sheet thicknesses and velocities are essentially independent of plasma sheet expansion or thinning, having typical values of 1500 km and 20-40 km/s respectively. Characteristic boundary layer current densities are about 10 nanoamps per square meter.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erkaev, N. V.; Siberian Federal University, Krasnoyarsk; Semenov, V. S.

A new kind of magnetohydrodynamic instability and waves are analyzed for a current sheet in the presence of a small normal magnetic field component varying along the sheet. These waves and instability are related to the existence of two gradients of the tangential (B{sub {tau}}) and normal (B{sub n}) magnetic field components along the normal ({nabla}{sub n}B{sub {tau}}) and tangential ({nabla}{sub {tau}}B{sub n}) directions with respect to the current sheet. The current sheet can be stable or unstable if the multiplication of two magnetic gradients is positive or negative. In the stable region, the kinklike wave mode is interpreted asmore » so-called flapping waves observed in Earth's magnetotail current sheet. The kink wave group velocity estimated for the Earth's current sheet is of the order of a few tens of kilometers per second. This is in good agreement with the observations of the flapping motions of the magnetotail current sheet.« less

A Description of Local Time Asymmetries in the Kronian Current Sheet

NASA Astrophysics Data System (ADS)

Nickerson, J. S.; Hansen, K. C.; Gombosi, T. I.

2012-12-01

Cassini observations imply that Saturn's magnetospheric current sheet is displaced northward above the rotational equator [C.S. Arridge et al., Warping of Saturn's magnetospheric and magnetotail current sheets, Journal of Geophysical Research, Vol. 113, August 2008]. Arridge et al. show that this hinging of the current sheet above the equator occurs over the noon, midnight, and dawn local time sectors. They present an azimuthally independent model to describe this paraboloid-like geometry. We have used our global MHD model, BATS-R-US/SWMF, to study Saturn's magnetospheric current sheet under various solar wind dynamic pressure and solar zenith angle conditions. We show that under reasonable conditions the current sheet does take on the basic shape of the Arridge model in the noon, midnight, and dawn sectors. However, the hinging distance parameter used in the Arridge model is not a constant and does in fact vary in Saturn local time. We recommend that the Arridge model should be adjusted to account for this azimuthal dependence. Arridge et al. does not discuss the shape of the current sheet in the dusk sector due to an absence of data but does presume that the current sheet will assume the same geometry in this region. On the contrary, our model shows that this is not the case. On the dusk side the current sheet hinges (aggressively) southward and cannot be accounted for by the Arridge model. We will present results from our simulations showing the deviation from axisymmetry and the general behavior of the current sheet under different conditions.

High-resolution simulations of unstable cylindrical gravity currents undergoing wandering and splitting motions in a rotating system

NASA Astrophysics Data System (ADS)

Dai, Albert; Wu, Ching-Sen

2018-02-01

High-resolution simulations of unstable cylindrical gravity currents when wandering and splitting motions occur in a rotating system are reported. In this study, our attention is focused on the situation of unstable rotating cylindrical gravity currents when the ratio of Coriolis to inertia forces is larger, namely, 0.5 ≤ C ≤ 2.0, in comparison to the stable ones when C ≤ 0.3 as investigated previously by the authors. The simulations reproduce the major features of the unstable rotating cylindrical gravity currents observed in the laboratory, i.e., vortex-wandering or vortex-splitting following the contraction-relaxation motion, and good agreement is found when compared with the experimental results on the outrush radius of the advancing front and on the number of bulges. Furthermore, the simulations provide energy budget information which could not be attained in the laboratory. After the heavy fluid is released, the heavy fluid collapses and a contraction-relaxation motion is at work for approximately 2-3 revolutions of the system. During the contraction-relaxation motion of the heavy fluid, the unstable rotating cylindrical gravity currents behave similar to the stable ones. Towards the end of the contraction-relaxation motion, the dissipation rate in the system reaches a local minimum and a quasi-geostrophic equilibrium state is reached. After the quasi-geostrophic equilibrium state, vortex-wandering or vortex-splitting may occur depending on the ratio of Coriolis to inertia forces. The vortex-splitting process begins with non-axisymmetric bulges and, as the bulges grow, the kinetic energy increases at the expense of decreasing potential energy in the system. The completion of vortex-splitting is accompanied by a local maximum of dissipation rate and a local maximum of kinetic energy in the system. A striking feature of the unstable rotating cylindrical gravity currents is the persistent upwelling and downwelling motions, which are observed for both the vortex-wandering and vortex-splitting motions and were not previously documented for such flows. Depending on the Reynolds number, the bulges around the circumference of the unstable rotating cylindrical gravity currents may or may not develop into cutoff distinct circulations. The number of bulges is seen to be dependent on the ratio of Coriolis to inertia forces but independent of the Reynolds number for the range of Reynolds number considered in this study.

Why S, Not X, Marks the Spot for CME/Flare Eruptions

NASA Technical Reports Server (NTRS)

Moore, Ronald L.; Sterling, Alphonse; Gary, Allen; Cirtain, Jonathan; Falconer, David

2010-01-01

For any major CME/flare eruption: I. The field that erupts is an arcade in which the interior is greatly sheared and twisted. Most of the free magnetic energy to be released: a) Is in the shear and twist of the interior field. b) Is Not due to a big current sheet. The eruption is unleashed by reconnection at a growing current sheet. The current sheet is still little when the reconnection turns on. The unleashed eruption then makes the current sheet much bigger by building it up faster than the reconnection can tear it down. II. Most X-ray jets work the opposite way: a) Tapped free energy is in the field of a pre-jet current sheet. b) Current sheet built by small arcade emerging into ambient field. c) Current sheet still much smaller than the arcade when reconnection turns on and tears it down, producing a jet. III. These rules reflect the low-beta condition in the eruptive magnetic field

Effects of electron pressure anisotropy on current sheet configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Artemyev, A. V., E-mail: aartemyev@igpp.ucla.edu; Angelopoulos, V.; Runov, A.

2016-09-15

Recent spacecraft observations in the Earth's magnetosphere have demonstrated that the magnetotail current sheet can be supported by currents of anisotropic electron population. Strong electron currents are responsible for the formation of very thin (intense) current sheets playing the crucial role in stability of the Earth's magnetotail. We explore the properties of such thin current sheets with hot isotropic ions and cold anisotropic electrons. Decoupling of the motions of ions and electrons results in the generation of a polarization electric field. The distribution of the corresponding scalar potential is derived from the electron pressure balance and the quasi-neutrality condition. Wemore » find that electron pressure anisotropy is partially balanced by a field-aligned component of this polarization electric field. We propose a 2D model that describes a thin current sheet supported by currents of anisotropic electrons embedded in an ion-dominated current sheet. Current density profiles in our model agree well with THEMIS observations in the Earth's magnetotail.« less

Electronic quantum confinement in cylindrical potential well

NASA Astrophysics Data System (ADS)

Baltenkov, Arkadiy S.; Msezane, Alfred Z.

2016-04-01

The effects of quantum confinement on the momentum distribution of electrons confined within a cylindrical potential well have been analyzed. The motivation is to understand specific features of the momentum distribution of electrons when the electron behavior is completely controlled by the parameters of a non-isotropic potential cavity. It is shown that studying the solutions of the wave equation for an electron confined in a cylindrical potential well offers the possibility to analyze the confinement behavior of an electron executing one- or two-dimensional motion in the three-dimensional space within the framework of the same mathematical model. Some low-lying electronic states with different symmetries have been considered and the corresponding wave functions have been calculated; the behavior of their nodes and their peak positions with respect to the parameters of the cylindrical well has been analyzed. Additionally, the momentum distributions of electrons in these states have been calculated. The limiting cases of the ratio of the cylinder length H and its radius R0 have been considered; when the cylinder length H significantly exceeds its radius R0 and when the cylinder radius is much greater than its length. The cylindrical quantum confinement effects on the momentum distribution of electrons in these potential wells have been analyzed. The possible application of the results obtained here for the description of the general features in the behavior of electrons in nanowires with metallic type of conductivity (or nanotubes) and ultrathin epitaxial films (or graphene sheets) are discussed. Possible experiments are suggested where the quantum confinement can be manifested. Contribution to the Topical Issue "Atomic Cluster Collisions (7th International Symposium)", edited by Gerardo Delgado Barrio, Andrey Solov'Yov, Pablo Villarreal, Rita Prosmiti.

Current Sheet Formation in a Conical Theta Pinch Faraday Accelerator with Radio-frequency Assisted Discharge

NASA Technical Reports Server (NTRS)

Polzin, Kurt A.; Hallock, Ashley K.; Choueiri, Edgar Y.

2008-01-01

Data from an inductive conical theta pinch accelerator are presented to gain insight into the process of inductive current sheet formation in the presence of a preionized background gas produced by a steady-state RF-discharge. The presence of a preionized plasma has been previously shown to allow for current sheet formation at lower discharge voltages and energies than those found in other pulsed inductive accelerator concepts, leading to greater accelerator efficiencies at lower power levels. Time-resolved magnetic probe measurements are obtained for different background pressures and pulse energies to characterize the effects of these parameters on current sheet formation. Indices are defined that describe time-resolved current sheet characteristics, such as the total current owing in the current sheet, the time-integrated total current ('strength'), and current sheet velocity. It is found that for a given electric field strength, maximums in total current, strength, and velocity occur for one particular background pressure. At other pressures, these current sheet indices are considerably smaller. The trends observed in these indices are explained in terms of the principles behind Townsend breakdown that lead to a dependence on the ratio of the electric field to the background pressure. Time-integrated photographic data are also obtained at the same experimental conditions, and qualitatively they compare quite favorably with the time-resolved magnetic field data.

Energized Oxygen : Speiser Current Sheet Bifurcation

NASA Astrophysics Data System (ADS)

George, D. E.; Jahn, J. M.

2017-12-01

A single population of energized Oxygen (O+) is shown to produce a cross-tail bifurcated current sheet in 2.5D PIC simulations of the magnetotail without the influence of magnetic reconnection. Treatment of oxygen in simulations of space plasmas, specifically a magnetotail current sheet, has been limited to thermal energies despite observations of and mechanisms which explain energized ions. We performed simulations of a homogeneous oxygen background, that has been energized in a physically appropriate manner, to study the behavior of current sheets and magnetic reconnection, specifically their bifurcation. This work uses a 2.5D explicit Particle-In-a-Cell (PIC) code to investigate the dynamics of energized heavy ions as they stream Dawn-to-Dusk in the magnetotail current sheet. We present a simulation study dealing with the response of a current sheet system to energized oxygen ions. We establish a, well known and studied, 2-species GEM Challenge Harris current sheet as a starting point. This system is known to eventually evolve and produce magnetic reconnection upon thinning of the current sheet. We added a uniform distribution of thermal O+ to the background. This 3-species system is also known to eventually evolve and produce magnetic reconnection. We add one additional variable to the system by providing an initial duskward velocity to energize the O+. We also traced individual particle motion within the PIC simulation. Three main results are shown. First, energized dawn- dusk streaming ions are clearly seen to exhibit sustained Speiser motion. Second, a single population of heavy ions clearly produces a stable bifurcated current sheet. Third, magnetic reconnection is not required to produce the bifurcated current sheet. Finally a bifurcated current sheet is compatible with the Harris current sheet model. This work is the first step in a series of investigations aimed at studying the effects of energized heavy ions on magnetic reconnection. This work differs significantly from previous investigations involving heavy ions in that they are energized as opposed to being simply thermal. This is a variation based firmly on published in-situ measurements. It also differs in that a complete population is used as opposed to simply test particles in a magnetic field model.

Analysis of Magnetic Flux Rope Chains Embedded in Martian Current Sheets Using MAVEN Data

NASA Astrophysics Data System (ADS)

Bowers, C. F.; DiBraccio, G. A.; Brain, D.; Hara, T.; Gruesbeck, J.; Espley, J. R.; Connerney, J. E. P.; Halekas, J. S.

2017-12-01

The magnetotail of Mars is formed as the interplanetary magnetic field (IMF) drapes around the planet's conducting ionosphere and localized crustal magnetic fields. In this scenario, a cross-tail current sheet separates the sunward and anti-sunward tail lobes. This tail current sheet is a highly dynamic region where magnetic reconnection is able to occur between the oppositely oriented fields. Magnetic flux ropes, a by-product of magnetic reconnection in the tail or in the ionosphere characterized by their helical outer wraps and strong axial core field, are commonly observed in the Martian magnetotail. An initial study using Mars Global Surveyor measurements reported a chain of flux ropes in the tail. During this event, 3 flux ropes were observed during a single traversal of the tail current sheet with a duration of 4 minutes. Here, we perform a statistical survey of these chain-of-flux-rope events to characterize their occurrence in the tail current sheet using Mars Atmosphere and Volatile EvolutioN (MAVEN) data. We implement the well-established technique of Minimum Variance Analysis to confirm the helical structure of the flux ropes and also determine local current sheet orientation. Thorough visual examination of more than 1600 orbits has resulted in the identification of 784 tail current sheet traversals. We determine the current sheet thickness to be on the order of 100-1000 km. From these current sheet observations, a subset of 30 events include embedded chain of flux ropes within the current sheet structure. We find that 87% of these flux rope chain events are identified in the southern latitude regions of Mars, associated with crustal fields. Their location suggests that magnetic reconnection occurring near crustal fields may be the source of these flux ropes. These statistical measurements of both current sheets and associated flux rope chains provide information about the complex magnetospheric dynamics at Mars, and how these dynamics affect atmospheric loss to space.

Effect of Inductive Coil Geometry and Current Sheet Trajectory of a Conical Theta Pinch Pulsed Inductive Plasma Accelerator

NASA Technical Reports Server (NTRS)

Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.

2011-01-01

Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration that accompanies the radial compression of the plasma in conical theta pinches.

The Influence of the Inner Topology of Cooling Units on the Performance of Automotive Exhaust-Based Thermoelectric Generators

NASA Astrophysics Data System (ADS)

Zhu, D. C.; Su, C. Q.; Deng, Y. D.; Wang, Y. P.; Liu, X.

2017-11-01

Automotive exhaust-based thermoelectric generators are currently a hot topic in energy recovery. The waste heat of automotive exhaust gas can be converted into electricity by means of thermoelectric modules. Generally, inserting fins into the cooling unit contributes to enhancing the heat transfer for a higher power output. However, the introduction of fins will result in a pressure drop in the cooling system. In current research, in order to enhance the heat transfer and avoid a large pressure drop, a cooling unit with cylindrical grooves on the interior surface was proposed. To evaluate the performance of the cylindrical grooves, different inner topologies, including a smooth interior surface,a smooth interior surface with inserted fins and an interior surface with cylindrical grooves, were compared. The results revealed that compared with the smooth interior surface, the smooth interior surface with inserted fins and the interior surface with cylindrical grooves both enhanced the heat transfer, but the interior surface with cylindrical grooves obtained a lower pressure drop. To improve the performance of the cylindrical grooves, different groove-depth ratios were tried, and the results showed that a groove-depth ratio of 0.081 could provide the best overall performance.

The Influence of the Inner Topology of Cooling Units on the Performance of Automotive Exhaust-Based Thermoelectric Generators

NASA Astrophysics Data System (ADS)

Zhu, D. C.; Su, C. Q.; Deng, Y. D.; Wang, Y. P.; Liu, X.

2018-06-01

Automotive exhaust-based thermoelectric generators are currently a hot topic in energy recovery. The waste heat of automotive exhaust gas can be converted into electricity by means of thermoelectric modules. Generally, inserting fins into the cooling unit contributes to enhancing the heat transfer for a higher power output. However, the introduction of fins will result in a pressure drop in the cooling system. In current research, in order to enhance the heat transfer and avoid a large pressure drop, a cooling unit with cylindrical grooves on the interior surface was proposed. To evaluate the performance of the cylindrical grooves, different inner topologies, including a smooth interior surface,a smooth interior surface with inserted fins and an interior surface with cylindrical grooves, were compared. The results revealed that compared with the smooth interior surface, the smooth interior surface with inserted fins and the interior surface with cylindrical grooves both enhanced the heat transfer, but the interior surface with cylindrical grooves obtained a lower pressure drop. To improve the performance of the cylindrical grooves, different groove-depth ratios were tried, and the results showed that a groove-depth ratio of 0.081 could provide the best overall performance.

Distribution of Region 1 and 2 currents in the quietand substorm time plasma sheetfrom THEMIS observations

NASA Astrophysics Data System (ADS)

Liu, J.; Angelopoulos, V.; Chu, X.; McPherron, R. L.

2016-12-01

Although Earth's Region 1 and 2 currents are related to activities such as substorm initiation, their magnetospheric origin remains unclear. Utilizing the triangular configuration of THEMIS probes at 8-12 RE downtail, we seek the origin of nightside Region 1 and 2 currents. The triangular configuration allows a curlometer-like technique which do not rely on active-time boundary crossings, so we can examine the current distribution in quiet times as well as active times. Our statistical study reveals that both Region 1 and 2 currents exist in the plasma sheet during quiet and active times. Especially, this is the first unequivocal, in-situ evidence of the existence of Region 2 currents in the plasma sheet. Farther away from the neutral sheet than the Region 2 currents lie the Region 1 currents which extend at least to the plasma sheet boundary layer. At geomagnetic quiet times, the separation between the two currents is located 2.5 RE from the neutral sheet. These findings suggest that the plasma sheet is a source of Region 1 and 2 currents regardless of geomagnetic activity level. During substorms, the separation between Region 1 and 2 currents migrates toward (away from) the neutral sheet as the plasma sheet thins (thickens). This migration indicates that the deformation of Region 1 and 2 currents is associated with redistribution of FAC sources in the magnetotail. In some substorms when the THEMIS probes encounter a dipolarization, a substorm current wedge (SCW) can be inferred from our technique, and it shows a distinctively larger current density than the pre-existing Region 1 currents. This difference suggests that the SCW is not just an enhancement of the pre-existing Region 1 current; the SCW and the Region 1 currents have different sources.

Cross-tail current - Resonant orbits

NASA Technical Reports Server (NTRS)

Kaufmann, Richard L.; Lu, Chen

1993-01-01

A technique to generate self-consistent 1D current sheets is described. Groups of monoenergetic protons were followed in a modified Harris magnetic field. This sample current sheet is characterized by resonant quasi-adiabatic orbits. The magnetic moment of a quasi-adiabatic ion which is injected from outside a current sheet changes substantially during the orbit but returns to almost its initial value by the time the ion leaves. Several ion and electron groups were combined to produce a plasma sheet in which the charged particles carry the currents needed to generate the magnetic field in which the orbits were traced. An electric field also is required to maintain charge neutrality. Three distinct orbit types, one involving untrapped ions and two composed of trapped ions, were identified. Limitations associated with the use of a 1D model also were investigated; it can provide a good physical picture of an important component of the cross-tail current, but cannot adequately describe any region of the magnetotail in which the principal current sheet is separated from the plasma sheet boundary layer by a nearly isotropic outer position of the central plasma sheet.

Construction of osteochondral-like tissue graft combining β-tricalcium phosphate block and scaffold-free centrifuged chondrocyte cell sheet.

PubMed

Niyama, Kouhei; Ide, Naoto; Onoue, Kaori; Okabe, Takahiro; Wakitani, Shigeyuki; Takagi, Mutsumi

2011-09-01

The combination of a β-tricalcium phosphate (βTCP) block with a scaffold-free chondrocyte sheet formed by the centrifugation of chondrocytes in a well was investigated with the aim of constructing an osteochondral-like structure. Human and porcine articular cartilage chondrocytes were respectively centrifuged in a 96-well plate or cell culture insert (0.32 cm(2)) that was set in a 24-well plate, cultivated in the respective vessel for 3 weeks, and the cell sheets were harvested. In some cases, a cylindrical βTCP block (diameter 5 mm, height 3 mm) was placed on the sheet on days 1-7. The sheet size, cell number, and sulfated glycosaminoglycan accumulation were determined. The use of a 96-well plate for not suspension but adhesion culture and the initial centrifugation of a well containing cells were crucial to obtaining a uniformly thick cell sheet. The glycosaminoglycan density of the harvested cell sheet was comparable to that of the pellet culture. An inoculum cell number of more than 31 × 10(5) cells tended to result in a curved cell sheet. Culture involving 18.6 × 10(5) cells and the 96-well plate for adhesion culture showed no curving of the cell sheet (thickness of 0.85 mm), and these were found to be the best of the culture conditions tested. The timing of the addition of a βTCP block to the cell sheet (1-7 days) markedly affected the balance between the thickness of cell sheet parts on and in the βTCP block. Centrifugation and subsequent cultivation of chondrocytes (18.6 × 10(5) cells) in a 96-well plate for adhesion culture led to the production of a scaffold-free cartilage-like cell sheet with a thickness of 0.85 mm. A combined osteochondral-like structure was produced by putting a βTCP block on the cell sheet. The thickness of the cell sheet on the βTCP block and the binding strength between the cell sheet and the βTCP block could be optimized by adjusting the inoculum cell number and timing of βTCP block addition.

Kinetic Studies of Thin Current Sheets at Magnetosheath Jets

NASA Astrophysics Data System (ADS)

Eriksson, E.; Vaivads, A.; Khotyaintsev, Y. V.; Graham, D. B.; Yordanova, E.; Hietala, H.; Markidis, S.; Giles, B. L.; Andre, M.; Russell, C. T.; Le Contel, O.; Burch, J. L.

2017-12-01

In near-Earth space one of the most turbulent plasma environments is the magnetosheath (MSH) downstream of the quasi-parallel shock. The particle acceleration and plasma thermalization processes there are still not fully understood. Regions of strong localized currents are believed to play a key role in those processes. The Magnetospheric Multiscale (MMS) mission has sufficiently high cadence to study these processes in detail. We present details of studies of two different events that contain strong current regions inside the MSH downstream of the quasi-parallel shock. In both cases the shape of the current region is in the form of a sheet, however they show internal 3D structure on the scale of the spacecraft separation (15 and 20 km, respectively). Both current sheets have a normal magnetic field component different from zero indicating that the regions at the different sides of the current sheets are magnetically connected. Both current sheets are boundaries between two different plasma regions. Furthermore, both current sheets are observed at MSH jets. These jets are characterized by localized dynamic pressure being larger than the solar wind dynamic pressure. One current sheet does not seem to be reconnecting while the other shows reconnection signatures. Inside the non-reconnecting current sheet we observe locally accelerated electron beams along the magnetic field. At energies above the beam energy we observe a loss cone consistent with part of the hot MSH-like electrons escaping into the colder solar wind-like plasma. This suggests that the acceleration process within this current sheet is similar to the one that occurs at the bow shock, where electron beams and loss cones are also observed. Therefore, we conclude that electron beams observed in the MSH do not have to originate from the bow shock, but can also be generated locally inside the MSH. The reconnecting current sheet also shows signs of thermalization and electron acceleration processes that are discussed in detail.

Spectral and Imaging Observations of a Current Sheet Region in a Small-scale Magnetic Reconnection Event

NASA Astrophysics Data System (ADS)

Xue, Zhike; Yan, Xiaoli; Yang, Liheng; Wang, Jincheng; Feng, Song; Li, Qiaoling; Ji, Kaifan; Zhao, Li

2018-05-01

We report a possible current sheet region associated with a small-scale magnetic reconnection event by using the spectral and imaging observations of the Interface Region Imaging Spectrograph (IRIS) and the magnetograms obtained by the Solar Dynamics Observatory on 2016 August 08. The length and width of the current sheet region are estimated to be from 1.4 ± 0.1 Mm to 3.0 ± 0.3 Mm and from 0.34 ± 0.01 Mm to 0.64 ± 0.09 Mm, respectively. The evolutions of the length of the current sheet region are positively correlated with that of the width. These measurements are among the smallest reported. When the IRIS slit scans the current sheet region, the spectroscopic observations show that the Si IV line is broadened in the current sheet region and the plasma has a blueshifted feature at the middle and a redshifted feature at the ends of the current sheet region. The maximum measured blueshifted and redshifted Doppler velocities are ‑20.8 ± 0.9 and 34.1 ± 0.4 km s‑1, respectively. Additionally, the electron number densities of the plasma in the current sheet region are computed to be around 1011 cm‑3 based on the spectrums of the two O IV lines. The emergence, movement, and cancellation of a small sunspot with negative polarity are observed during the formation and shift of the current sheet region. We suggest that the occurrence and evolution of the magnetic reconnection are driven by the movement of the small sunspot in the photosphere.

On the mechanism of elasto-inertial turbulence.

PubMed

Dubief, Yves; Terrapon, Vincent E; Soria, Julio

2013-11-01

Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Q a isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Q a cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number ( Wi , ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi . EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows observed in some polymeric flows.

On the mechanism of elasto-inertial turbulence

NASA Astrophysics Data System (ADS)

Dubief, Yves; Terrapon, Vincent E.; Soria, Julio

2013-11-01

Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Qa isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Qa cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number (Wi, ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi. EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows observed in some polymeric flows.

On the mechanism of elasto-inertial turbulence

PubMed Central

Dubief, Yves; Terrapon, Vincent E.; Soria, Julio

2013-01-01

Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Qa isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Qa cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number (Wi, ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi. EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows observed in some polymeric flows. PMID:24170968

Airy acoustical-sheet spinner tweezers

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2016-09-01

The Airy acoustical beam exhibits parabolic propagation and spatial acceleration, meaning that the propagation bending angle continuously increases before the beam trajectory reaches a critical angle where it decays after a propagation distance, without applying any external bending force. As such, it is of particular importance to investigate its properties from the standpoint of acoustical radiation force, spin torque, and particle dynamics theories, in the development of novel particle sorting techniques and acoustically mediated clearing systems. This work investigates these effects on a two-dimensional (2D) circular absorptive structure placed in the field of a nonparaxial Airy "acoustical-sheet" (i.e., finite beam in 2D), for potential applications in surface acoustic waves and acousto-fluidics. Based on the characteristics of the acoustic field, the beam is capable of manipulating the circular cylindrical fluid cross-section and guides it along a transverse or parabolic trajectory. This feature of Airy acoustical beams could lead to a unique characteristic in single-beam acoustical tweezers related to acoustical sieving, filtering, and removal of particles and cells from a section of a small channel. The analysis developed here is based on the description of the nonparaxial Airy beam using the angular spectrum decomposition of plane waves in close association with the partial-wave series expansion method in cylindrical coordinates. The numerical results demonstrate the ability of the nonparaxial Airy acoustical-sheet beam to pull, propel, or accelerate a particle along a parabolic trajectory, in addition to particle confinement in the transverse direction of wave propagation. Negative or positive radiation force and spin torque causing rotation in the clockwise or the anticlockwise direction can occur depending on the nondimensional parameter ka (where k is the wavenumber and a is the radius) and the location of the cylinder in the beam. Applications in acoustic levitation, long-distance particle transport and manipulation, as well as acousto-fluidics directly benefit from the results of this analysis.

Hypersonic Magneto-Fluid-Dynamic Compression in Cylindrical Inlet

NASA Technical Reports Server (NTRS)

Shang, Joseph S.; Chang, Chau-Lyan

2007-01-01

Hypersonic magneto-fluid-dynamic interaction has been successfully performed as a virtual leading-edge strake and a virtual cowl of a cylindrical inlet. In a side-by-side experimental and computational study, the magnitude of the induced compression was found to be depended on configuration and electrode placement. To better understand the interacting phenomenon the present investigation is focused on a direct current discharge at the leading edge of a cylindrical inlet for which validating experimental data is available. The present computational result is obtained by solving the magneto-fluid-dynamics equations at the low magnetic Reynolds number limit and using a nonequilibrium weakly ionized gas model based on the drift-diffusion theory. The numerical simulation provides a detailed description of the intriguing physics. After validation with experimental measurements, the computed results further quantify the effectiveness of a magnet-fluid-dynamic compression for a hypersonic cylindrical inlet. At a minuscule power input to a direct current surface discharge of 8.14 watts per square centimeter of electrode area produces an additional compression of 6.7 percent for a constant cross-section cylindrical inlet.

Magnetic field configurations on thruster performance in accordance with ion beam characteristics in cylindrical Hall thruster plasmas

NASA Astrophysics Data System (ADS)

Kim, Holak; Choe, Wonho; Lim, Youbong; Lee, Seunghun; Park, Sanghoo

2017-03-01

Magnetic field configuration is critical in Hall thrusters for achieving high performance, particularly in thrust, specific impulse, efficiency, etc. Ion beam features are also significantly influenced by magnetic field configurations. In two typical magnetic field configurations (i.e., co-current and counter-current configurations) of a cylindrical Hall thruster, ion beam characteristics are compared in relation to multiply charged ions. Our study shows that the co-current configuration brings about high ion current (or low electron current), high ionization rate, and small plume angle that lead to high thruster performance.

Intermittent magnetic reconnection in TS-3 merging experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ono, Y.; Hayashi, Y.; Ii, T.

2011-11-15

Ejection of current sheet with plasma mass causes impulsive and intermittent magnetic reconnection in the TS-3 spherical tokamak (ST) merging experiment. Under high guide toroidal field, the sheet resistivity is almost classical due to the sheet thickness much longer than the ion gyroradius. Large inflow flux and low current-sheet resistivity result in flux and plasma pileup followed by rapid growth of the current sheet. When the pileup exceeds a critical limit, the sheet is ejected mechanically from the squeezed X-point area. The reconnection (outflow) speed is slow during the flux/plasma pileup and is fast during the ejection, suggesting that intermittentmore » reconnection similar to the solar flare increases the averaged reconnection speed. These transient effects enable the merging tokamaks to have the fast reconnection as well as the high-power reconnection heating, even when their current-sheet resistivity is low under high guide field.« less

Non-Evolutionarity of a Reconnecting Current Sheet as a Cause of Its Splitting into MHD Shocks

NASA Astrophysics Data System (ADS)

Markovsky, S. A.; Somov, B. V.

1995-04-01

Numerical simulations of the magnetic reconnection process in a current sheet show that, in some cases, MHD shocks appear to be attached to edges of the sheet. The appearance of the shocks may be considered to be a result of splitting of the sheet. In the present paper we suppose that this splitting takes place in consequence of non-evolutionarity of the reconnecting current sheet as a discontinuity. The problem of time evolution of small perturbations does not have a unique solution for a non-evolutionary discontinuity, and it splits into other (evolutionary) discontinuities. Such an approach allows us to determine conditions under which the splitting of the-sheet occurs. The main difficulty of this approach is that a current sheet is not reduced to a classified 1D discontinuity, because inhomogeneity of flow velocity inside the sheet is two-dimensional. To formulate the non-evolutionarity problem, we solve the linear MHD equations inside and outside the sheet and deduce linearized 1D boundary conditions at its surface. We show that for large enough conductivity, small perturbations exist which interact with the sheet as with a discontinuity. Then we obtain a non-evolutionarity criterion, with respect to these perturbations, in the form of a restriction on the flow velocity across the surface of the sheet.

Dynamo-driven plasmoid formation from a current-sheet instability

DOE PAGES

Ebrahimi, F.

2016-12-15

Axisymmetric current-carrying plasmoids are formed in the presence of nonaxisymmetric fluctuations during nonlinear three-dimensional resistive MHD simulations in a global toroidal geometry. In this study, we utilize the helicity injection technique to form an initial poloidal flux in the presence of a toroidal guide field. As helicity is injected, two types of current sheets are formed from the oppositely directed field lines in the injector region (primary reconnecting current sheet), and the poloidal flux compression near the plasma edge (edge current sheet). We first find that nonaxisymmetric fluctuations arising from the current-sheet instability isolated near the plasma edge have tearingmore » parity but can nevertheless grow fast (on the poloidal Alfven time scale). These modes saturate by breaking up the current sheet. Second, for the first time, a dynamo poloidal flux amplification is observed at the reconnection site (in the region of the oppositely directed magnetic field). This fluctuation-induced flux amplification increases the local Lundquist number, which then triggers a plasmoid instability and breaks the primary current sheet at the reconnection site. Finally, the plasmoids formation driven by large-scale flux amplification, i.e., a large-scale dynamo, observed here has strong implications for astrophysical reconnection as well as fast reconnection events in laboratory plasmas.« less

Spontaneous formation of electric current sheets and the origin of solar flares

NASA Technical Reports Server (NTRS)

Low, B. C.; Wolfson, R.

1988-01-01

It is demonstrated that the continuous boundary motion of a sheared magnetic field in a tenuous plasma with an infinite electrical conductivity can induce the formation of multiple electric current sheets in the interior plasma. In response to specific footpoint displacements, the quadrupolar magnetic field considered is shown to require the formation of multiple electric current sheets as it achieves a force-free state. Some of the current sheets are found to be of finite length, running along separatrix lines of force which separate lobes of magnetic flux. It is suggested that current sheets in the form of infinitely thin magnetic shear layers may be unstable to resistive tearing, a process which may have application to solar flares.

Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet.

PubMed

Bons, Paul D; Jansen, Daniela; Mundel, Felicitas; Bauer, Catherine C; Binder, Tobias; Eisen, Olaf; Jessell, Mark W; Llorens, Maria-Gema; Steinbach, Florian; Steinhage, Daniel; Weikusat, Ilka

2016-04-29

The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier.

Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet

NASA Astrophysics Data System (ADS)

Bons, Paul D.; Jansen, Daniela; Mundel, Felicitas; Bauer, Catherine C.; Binder, Tobias; Eisen, Olaf; Jessell, Mark W.; Llorens, Maria-Gema; Steinbach, Florian; Steinhage, Daniel; Weikusat, Ilka

2016-04-01

The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier.

LSA Large Area Silicon Sheet Task Continuous Czochralski Process Development

NASA Technical Reports Server (NTRS)

Rea, S. N.

1979-01-01

A commercial Czochralski crystal growing furnace was converted to a continuous growth facility by installation of a small, in-situ premelter with attendant silicon storage and transport mechanisms. Using a vertical, cylindrical graphite heater containing a small fused quartz test tube linear from which the molten silicon flowed out the bottom, approximately 83 cm of nominal 5 cm diamter crystal was grown with continuous melt addition furnished by the test tube premelter. High perfection crystal was not obtained, however, due primarily to particulate contamination of the melt. A major contributor to the particulate problem was severe silicon oxide buildup on the premelter which would ultimately drop into the primary melt. Elimination of this oxide buildup will require extensive study and experimentation and the ultimate success of continuous Czochralski depends on a successful solution to this problem. Economically, the continuous Czochralski meets near-term cost goals for silicon sheet material.

Wavelength selection in the crown splash

NASA Astrophysics Data System (ADS)

Zhang, Li V.; Brunet, Philippe; Eggers, Jens; Deegan, Robert D.

2010-12-01

The impact of a drop onto a liquid layer produces a splash that results from the ejection and dissolution of one or more liquid sheets, which expand radially from the point of impact. In the crown splash parameter regime, secondary droplets appear at fairly regularly spaced intervals along the rim of the sheet. By performing many experiments for the same parameter values, we measure the spectrum of small-amplitude perturbations growing on the rim. We show that for a range of parameters in the crown splash regime, the generation of secondary droplets results from a Rayleigh-Plateau instability of the rim, whose shape is almost cylindrical. In our theoretical calculation, we include the time dependence of the base state. The remaining irregularity of the pattern is explained by the finite width of the Rayleigh-Plateau dispersion relation. Alternative mechanisms, such as the Rayleigh-Taylor instability, can be excluded for the experimental parameters of our study.

Development of a prototype regenerable carbon dioxide absorber for portable life support systems. [for astronaut EVA

NASA Technical Reports Server (NTRS)

Onischak, M.; Baker, B.

1977-01-01

The design and development of a prototype carbon dioxide absorber using potassium carbonate (K2CO3) is described. Absorbers are constructed of thin, porous sheets of supported K2CO3 that are spirally wound to form a cylindrical reactor. Axial gas passages are formed between the porous sheets by corrugated screen material. Carbon dioxide and water in an enclosed life support system atmosphere react with potassium carbonate to form potassium bicarbonate. The potassium carbonate is regenerated by heating the potassium bicarbonate to 150 C at ambient pressure. The extravehicular mission design conditions are for one man for 8 h. Results are shown for a subunit test module investigating the effects of heat release, length-to-diameter ratio, and active cooling upon performance. The most important effect upon carbon dioxide removal is the temperature of the potassium carbonate.

Hollow Fiber Spacesuit Water Membrane Evaporator Development and Testing for Advanced Spacesuits

NASA Technical Reports Server (NTRS)

Bue, Grant C.; Trevino, Luis; Tsioulos, Gus; Settles, Joseph; Colunga, Aaron; Vogel, Matthew; Vonau, Walt

2010-01-01

Grant Bue and Matthew Vogel presented the two types of Spacesuit Water Membrane Evaporators (SWME) that were developed based on hydrophobic microporous membranes. One type, the Sheet Membrane (SaM) SWME, is composed of six concentric Teflon sheet membranes fixed on cylindrical-supporting screens to form three concentric annular water channels. Those water channels are surrounded by vacuum passages to draw off the water vapor that passes through the membrane. The other type, the Hollow Fiber (HoFi) SWME, is composed of more than 14,000 tubes. Water flows through the tubes and water vapor passes through the tube wall to the shell side that vents to the vacuum of space. Both SWME types have undergone testing to baseline the performance at predicted operating temperatures and flow rates; the units also have been subjected to contamination testing and other conditions to test resiliency.

Two-dimensional potential double layers and discrete auroras

NASA Technical Reports Server (NTRS)

Kan, J. R.; Lee, L. C.; Akasofu, S.-I.

1979-01-01

This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc and with the formation of the inverted V precipitation region. The former is embedded in the latter, and both are associated with field-aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two-dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter solutions are obtained in which the field-aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter solutions are obtained in which the potential drop is confined to a distance on the order of the Debye length. The electric field in the two-dimensional double-layer model is the zeroth-order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first-order field due to current instabilities or turbulences. The maximum potential in the two-dimensional double-layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.

Current Sheet Properties and Dynamics During Sympathetic Breakout Eruptions

NASA Astrophysics Data System (ADS)

Lynch, B. J.; Edmondson, J. K.

2013-12-01

We present the continued analysis of the high-resolution 2.5D MHD simulations of sympathetic magnetic breakout eruptions from a pseudostreamer source region. We examine the generation of X- and O-type null points during the current sheet tearing and track the magnetic island formation and evolution during periods of reconnection. The magnetic breakout eruption scenario forms an overlying 'breakout' current sheet that evolves slowly and removes restraining flux from above the sheared field core that will eventually become the center of the erupting flux rope-like structure. The runaway expansion from the expansion-breakout reconnection positive feedback enables the formation of the second, vertical/radial current sheet underneath the rising sheared field core as in the standard CHSKP eruptive flare scenario. We will examine the flux transfer rates through the breakout and flare current sheets and compare the properties of the field and plasma inflows into the current sheets and the reconnection jet outflows into the flare loops and flux rope ejecta.

Fluctuation dynamics in reconnecting current sheets

NASA Astrophysics Data System (ADS)

von Stechow, Adrian; Grulke, Olaf; Ji, Hantao; Yamada, Masaaki; Klinger, Thomas

2015-11-01

During magnetic reconnection, a highly localized current sheet forms at the boundary between opposed magnetic fields. Its steep perpendicular gradients and fast parallel drifts can give rise to a range of instabilities which can contribute to the overall reconnection dynamics. In two complementary laboratory reconnection experiments, MRX (PPPL, Princeton) and VINETA.II (IPP, Greifswald, Germany), magnetic fluctuations are observed within the current sheet. Despite the large differences in geometries (toroidal vs. linear), plasma parameters (high vs. low beta) and magnetic configuration (low vs. high magnetic guide field), similar broadband fluctuation characteristics are observed in both experiments. These are identified as Whistler-like fluctuations in the lower hybrid frequency range that propagate along the current sheet in the electron drift direction. They are intrinsic to the localized current sheet and largely independent of the slower reconnection dynamics. This contribution characterizes these magnetic fluctuations within the wide parameter range accessible by both experiments. Specifically, the fluctuation spectra and wave dispersion are characterized with respect to the magnetic topology and plasma parameters of the reconnecting current sheet.

Lab Experiments Probe Interactions Between Dilute Pyroclastic Density Currents and 3D Barriers

NASA Astrophysics Data System (ADS)

Fauria, K.; Andrews, B. J.; Manga, M.

2014-12-01

We conducted scaled laboratory experiments of unconfined dilute pyroclastic density currents (PDCs) to examine interactions between three - dimensional obstacles and dilute PDCs. While it is known that PDCs can surmount barriers by converting kinetic energy into potential energy, the signature of topography on PDC dynamics is unclear. To examine the interplay between PDCs and topography, we turbulently suspended heated and ambient-temperature 20 μm talc powder in air within an 8.5 x 6.1 x 2.6 m tank. Experimental parameters (Froude number, densimetric and thermal Richardson number, particle Stokes and Settling numbers) were scaled such that the experimental currents were dynamically similar to natural PCS. The Reynolds number, however, is much smaller than in natural currents, but still large enough for the flows to be turbulent. We placed cylindrical and ridge-like objects in the path of the currents, illuminated the currents with orthogonal laser sheets, and recorded each experiment with high definition cameras. We observed currents surmounting ridge-like barriers (barrier height = current height). Slanted ridges redirected the currents upward and parallel to the upstream face of the ridges (~45° from horizontal). Down stream of the slanted ridges, ambient-temperature currents reattached to the floor. By comparison, hot currents reversed buoyancy and lifted off. These observations suggest that obstacles enhance air entrainment, a process key to affecting runout distance and the depletion of fine particles in ignimbrites. Moreover, we observed vortex shedding in the wake of cylinders. Our experiments demonstrate that barriers of various shapes affect PDC dynamics and can shorten PDC runout distances. Understanding the effects of topography on PDCs is required for interpreting many deposits because processes such as vortex shedding and topographically-induced changes in turbulent length scales and entrainment likely leave depositional signatures.

Comparing Sources of Storm-Time Ring Current O+

NASA Astrophysics Data System (ADS)

Kistler, L. M.

2015-12-01

The first observations of the storm-time ring current composition using AMPTE/CCE data showed that the O+ contribution to the ring current increases significantly during storms. The ring current is predominantly formed from inward transport of the near-earth plasma sheet. Thus the increase of O+ in the ring current implies that the ionospheric contribution to the plasma sheet has increased. The ionospheric plasma that reaches the plasma sheet can come from both the cusp and the nightside aurora. The cusp outflow moves through the lobe and enters the plasma sheet through reconnection at the near-earth neutral line. The nightside auroral outflow has direct access to nightside plasma sheet. Using data from Cluster and the Van Allen Probes spacecraft, we compare the development of storms in cases where there is a clear input of nightside auroral outflow, and in cases where there is a significant cusp input. We find that the cusp input, which enters the tail at ~15-20 Re becomes isotropized when it crosses the neutral sheet, and becomes part of the hot (>1 keV) plasma sheet population as it convects inward. The auroral outflow, which enters the plasma sheet closer to the earth, where the radius of curvature of the field line is larger, does not isotropize or become significantly energized, but remains a predominantly field aligned low energy population in the inner magnetosphere. It is the hot plasma sheet population that gets accelerated to high enough energies in the inner magnetosphere to contribute strongly to the ring current pressure. Thus it appears that O+ that enters the plasma sheet further down the tail has a greater impact on the storm-time ring current than ions that enter closer to the earth.

A 2D analytical cylindrical gate tunnel FET (CG-TFET) model: impact of shortest tunneling distance

NASA Astrophysics Data System (ADS)

Dash, S.; Mishra, G. P.

2015-09-01

A 2D analytical tunnel field-effect transistor (FET) potential model with cylindrical gate (CG-TFET) based on the solution of Laplace’s equation is proposed. The band-to-band tunneling (BTBT) current is derived by the help of lateral electric field and the shortest tunneling distance. However, the analysis is extended to obtain the subthreshold swing (SS) and transfer characteristics of the device. The dependency of drain current, SS and transconductance on gate voltage and shortest tunneling distance is discussed. Also, the effect of scaling the gate oxide thickness and the cylindrical body diameter on the electrical parameters of the device is analyzed.

Electromagnetic augmentation for casting of thin metal sheets

DOEpatents

Hull, John R.

1989-01-01

Thin metal sheets are cast by magnetically levitating molten metal deposited in a mold within a ferromagnetic yoke and between AC conducting coils and linearly displacing the magnetically levitated liquid metal while it is being cooled by the water-cooled walls of the mold to form a solid metal sheet. A conducting shield is electrically coupled to the molten metal sheet to provide a return path for eddy currents induced in the metal sheet by the current in the AC conducting coils. In another embodiment, a DC conducting coil is coupled to the metal sheet for providing a direct current therein which interacts with the magnetic field to levitate the moving metal sheet. Levitation of the metal sheet in both molten and solid forms reduces its contact pressure with the mold walls while maintaining sufficient engagement therebetween to permit efficient conductive cooling by the mold through which a coolant fluid may be circulated. The magnetic fields associated with the currents in the aforementioned coils levitate the molten metal sheet while the mold provides for its lateral and vertical confinement. A leader sheet having electromagnetic characteristics similar to those of the molten metal sheet is used to start the casing process and precedes the molten metal sheet through the yoke/coil arrangement and mold and forms a continuous sheet therewith. The yoke/coil arrangement may be either U-shaped with a single racetrack coil or may be rectangular with a pair of spaced, facing bedstead coils.

A coronal magnetic field model with horizontal volume and sheet currents

NASA Technical Reports Server (NTRS)

Zhao, Xuepu; Hoeksema, J. Todd

1994-01-01

When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside the source surface or by limiting the interaction to thin current sheets between oppositely directed field regions. Yet observations and numerical Magnetohydrodynamic (MHD) calculations suggest the presence of non-force-free volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the magnetostatic equilibria developed by Bogdan and Low and the current-sheet modeling technique developed by Schatten. The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coro nal helmet structures better than the current-sheet model.

Dynamic Harris current sheet thickness from Cluster current density and plasma measurements

NASA Technical Reports Server (NTRS)

Thompson, S. M.; Kivelson, M. G.; Khurana, K. K.; McPherron, R. L.; Weygand, J. M.; Balogh, A.; Reme, H.; Kistler, L. M.

2005-01-01

We use the first accurate measurements of current densities in the plasma sheet to calculate the half-thickness and position of the current sheet as a function of time. Our technique assumes a Harris current sheet model, which is parameterized by lobe magnetic field B(o), current sheet half-thickness h, and current sheet position z(sub o). Cluster measurements of magnetic field, current density, and plasma pressure are used to infer the three parameters as a function of time. We find that most long timescale (6-12 hours) current sheet crossings observed by Cluster cannot be described by a static Harris current sheet with a single set of parameters B(sub o), h, and z(sub o). Noting the presence of high-frequency fluctuations that appear to be superimposed on lower frequency variations, we average over running 6-min intervals and use the smoothed data to infer the parameters h(t) and z(sub o)(t), constrained by the pressure balance lobe magnetic field B(sub o)(t). Whereas this approach has been used in previous studies, the spatial gnuhen& now provided by the Cluster magnetometers were unavailable or not well constrained in earlier studies. We place the calculated hdf&cknessa in a magnetospheric context by examining the change in thickness with substorm phase for three case study events and 21 events in a superposed epoch analysis. We find that the inferred half-thickness in many cases reflects the nominal changes experienced by the plasma sheet during substorms (i.e., thinning during growth phase, thickening following substorm onset). We conclude with an analysis of the relative contribution of (Delta)B(sub z)/(Delta)X to the cross-tail current density during substorms. We find that (Delta)B(sub z)/(Delta)X can contribute a significant portion of the cross-tail c m n t around substorm onset.

COLD TRAP

DOEpatents

Milleron, N.

1963-03-12

An improved linear-flow cold trap is designed for highvacuum applications such as mitigating back migration of diffusion pump oil moiecules. A central pot of liquid nitrogen is nested within and supported by a surrounding, vertical, helical coil of metai sheet, all enveloped by a larger, upright, cylindrical, vacuum vessel. The vertical interstices between successive turns of the coil afford lineal, axial, high-vacuum passages between open mouths at top and bottom of said vessel, while the coil, being cold by virtue of thermal contact of its innermost turn with the nitrogen pot, affords expansive proximate condensation surfaces. (AEC)

Optical elements formed by compressed gases: Analysis and potential applications

NASA Technical Reports Server (NTRS)

Howes, W. L.

1986-01-01

Spherical, cylindrical, and conical shock waves are optically analogous to gas lenses. The geometrical optics of these shock configurations are analyzed as they pertain to flow visualization instruments, particularly the rainbow schlieren apparatus and single-pass interferometers. It is proposed that a lens or mirror formed by gas compressed between plastic sheets has potential as a fluid visualization test object; as the objective mirror in a very large space-based telescope, communication antenna, or energy collector; as the objective mirror in inexpensive commercial telescopes; and as a component in fluid visualization apparatuses.

Extreme energetic particle decreases near geostationary orbit - A manifestation of current diversion within the inner plasma sheet

NASA Technical Reports Server (NTRS)

Baker, D. N.; Mcpherron, R. L.

1990-01-01

A qualitative model of magnetic field reconfiguration as might result from neutral line formation in the central plasma sheet late in a substorm growth phase is considered. It is suggested that magnetic reconnection probably begins before the substorm expansion phase and that cross-tail current is enhanced across the plasma sheet both earthward and tailward of a limited region near the neutral line. Such an enhanced cross-tail current earthward of the original X line region may contribute to thinning the plasma sheet substantially, and this would in turn affect the drift currents in that location, thus enhancing the current even closer toward the earth. In this way a redistribution and progressive diversion of normal cross-tail current throughout much of the inner portion of the plasma sheet could occur. The resulting intensified current, localized at the inner edge of the plasma sheet, would lead to a very thin plasma confinement region. This would explain the very taillike field and extreme particle dropouts often seen late in substorm growth phases.

Evolution of three-dimensional relativistic current sheets and development of self-generated turbulence

NASA Astrophysics Data System (ADS)

Takamoto, M.

2018-05-01

In this paper, the temporal evolution of three-dimensional relativistic current sheets in Poynting-dominated plasma is studied for the first time. Over the past few decades, a lot of efforts have been conducted on studying the evolution of current sheets in two-dimensional space, and concluded that sufficiently long current sheets always evolve into the so-called plasmoid chain, which provides a fast reconnection rate independent of its resistivity. However, it is suspected that plasmoid chain can exist only in the case of two-dimensional approximation, and would show transition to turbulence in three-dimensional space. We performed three-dimensional numerical simulation of relativistic current sheet using resistive relativistic magnetohydrodynamic approximation. The results showed that the three-dimensional current sheets evolve not into plasmoid chain but turbulence. The resulting reconnection rate is 0.004, which is much smaller than that of plasmoid chain. The energy conversion from magnetic field to kinetic energy of turbulence is just 0.01 per cent, which is much smaller than typical non-relativistic cases. Using the energy principle, we also showed that the plasmoid is always unstable for a displacement in the opposite direction to its acceleration, probably interchange-type instability, and this always results in seeds of turbulence behind the plasmoids. Finally, the temperature distribution along the sheet is discussed, and it is found that the sheet is less active than plasmoid chain. Our finding can be applied for many high-energy astrophysical phenomena, and can provide a basic model of the general current sheet in Poynting-dominated plasma.

Electromagnetic augmentation for casting of thin metal sheets

DOEpatents

Hull, J.R.

1987-10-28

Thin metal sheets are cast by magnetically levitating molten metal deposited in a model within a ferromagnetic yoke and between AC conducting coils and linearly displacing the magnetically levitated liquid metal while it is being cooled by the water-cooled walls of the mold to form a solid metal sheet. A conducting shield is electrically coupled to the molten metal sheet to provide a return path for eddy currents induced in the metal sheet by the current in the AC conducting coils. In another embodiment, a DC conducting coil is coupled to the metal sheet for providing a direct current therein which interacts with the magnetic field to levitate the moving metal sheet. Levitation of the metal sheet in both molten and solid forms reduces its contact pressure with the mold walls while maintaining sufficient engagement therebetween to permit efficient conductive cooling by the mold through which a coolant fluid may be circulated. 8 figs.

Design and Construction of a Small Vacuum Furnace

NASA Astrophysics Data System (ADS)

Peawbang, P.; Thedsakhulwong, A.

2017-09-01

The purpose of this research is designed and constructed of a small vacuum furnace. A cylindrical graphite was chosen as the material of the furnace, the cylinder aluminium and copper sheets were employed to prevent the heat radiation that transfers from the furnace to the chamber wall. A rotary pump used, the pressure of graphite furnace can be pumped up to 30 mTorr and heated up to 700 °C driving by wire and the temperature of the chamber wall is relatively remained too low. In addition, heat loss obtained from the graphite furnace by conduction, convection, and radiation were analyzed. The dominating heat loss was found to be caused by the blackbody radiation, which can thus be used to estimate the relationship between graphite furnace temperature and the drive power needed. The cylindrical graphite furnace has an inner diameter of 44 mm, the outer diameter of 60 mm and 45 mm in height, the 355.5 W of power is needed to drive the furnace to 700 °C.

Phenomenological Model of Current Sheet Canting in Pulsed Electromagnetic Accelerators

NASA Technical Reports Server (NTRS)

Markusic, Thomas; Choueiri, E. Y.

2003-01-01

The phenomenon of current sheet canting in pulsed electromagnetic accelerators is the departure of the plasma sheet (that carries the current) from a plane that is perpendicular to the electrodes to one that is skewed, or tipped. Review of pulsed electromagnetic accelerator literature reveals that current sheet canting is a ubiquitous phenomenon - occurring in all of the standard accelerator geometries. Developing an understanding of current sheet canting is important because it can detract from the propellant sweeping capabilities of current sheets and, hence, negatively impact the overall efficiency of pulsed electromagnetic accelerators. In the present study, it is postulated that depletion of plasma near the anode, which results from axial density gradient induced diamagnetic drift, occurs during the early stages of the discharge, creating a density gradient normal to the anode, with a characteristic length on the order of the ion skin depth. Rapid penetration of the magnetic field through this region ensues, due to the Hall effect, leading to a canted current front ahead of the initial current conduction channel. In this model, once the current sheet reaches appreciable speeds, entrainment of stationary propellant replenishes plasma in the anode region, inhibiting further Hall-convective transport of the magnetic field; however, the previously established tilted current sheet remains at a fairly constant canting angle for the remainder of the discharge cycle, exerting a transverse J x B force which drives plasma toward the cathode and accumulates it there. This proposed sequence of events has been incorporated into a phenomenological model. The model predicts that canting can be reduced by using low atomic mass propellants with high propellant loading number density; the model results are shown to give qualitative agreement with experimentally measured canting angle mass dependence trends.

Criticality and turbulence in a resistive magnetohydrodynamic current sheet

NASA Astrophysics Data System (ADS)

Klimas, Alexander J.; Uritsky, Vadim M.

2017-02-01

Scaling properties of a two-dimensional (2d) plasma physical current-sheet simulation model involving a full set of magnetohydrodynamic (MHD) equations with current-dependent resistivity are investigated. The current sheet supports a spatial magnetic field reversal that is forced through loading of magnetic flux containing plasma at boundaries of the simulation domain. A balance is reached between loading and annihilation of the magnetic flux through reconnection at the current sheet; the transport of magnetic flux from boundaries to current sheet is realized in the form of spatiotemporal avalanches exhibiting power-law statistics of lifetimes and sizes. We identify this dynamics as self-organized criticality (SOC) by verifying an extended set of scaling laws related to both global and local properties of the current sheet (critical susceptibility, finite-size scaling of probability distributions, geometric exponents). The critical exponents obtained from this analysis suggest that the model operates in a slowly driven SOC state similar to the mean-field state of the directed stochastic sandpile model. We also investigate multiscale correlations in the velocity field and find them numerically indistinguishable from certain intermittent turbulence (IT) theories. The results provide clues on physical conditions for SOC behavior in a broad class of plasma systems with propagating instabilities, and suggest that SOC and IT may coexist in driven current sheets which occur ubiquitously in astrophysical and space plasmas.

Criticality and turbulence in a resistive magnetohydrodynamic current sheet.

PubMed

Klimas, Alexander J; Uritsky, Vadim M

2017-02-01

Scaling properties of a two-dimensional (2d) plasma physical current-sheet simulation model involving a full set of magnetohydrodynamic (MHD) equations with current-dependent resistivity are investigated. The current sheet supports a spatial magnetic field reversal that is forced through loading of magnetic flux containing plasma at boundaries of the simulation domain. A balance is reached between loading and annihilation of the magnetic flux through reconnection at the current sheet; the transport of magnetic flux from boundaries to current sheet is realized in the form of spatiotemporal avalanches exhibiting power-law statistics of lifetimes and sizes. We identify this dynamics as self-organized criticality (SOC) by verifying an extended set of scaling laws related to both global and local properties of the current sheet (critical susceptibility, finite-size scaling of probability distributions, geometric exponents). The critical exponents obtained from this analysis suggest that the model operates in a slowly driven SOC state similar to the mean-field state of the directed stochastic sandpile model. We also investigate multiscale correlations in the velocity field and find them numerically indistinguishable from certain intermittent turbulence (IT) theories. The results provide clues on physical conditions for SOC behavior in a broad class of plasma systems with propagating instabilities, and suggest that SOC and IT may coexist in driven current sheets which occur ubiquitously in astrophysical and space plasmas.

Structure of the Magnetotail Current Sheet

NASA Technical Reports Server (NTRS)

Larson, Douglas J.; Kaufmann, Richard L.

1996-01-01

An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(sub E) less than x less than - 14 R(sub E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

Structure of the Magnetotail Current Sheet

NASA Technical Reports Server (NTRS)

Larson, Douglas J.; Kaufmann, Richard L.

1996-01-01

An orbit tracing technique was used to generate current sheets for three magnetotail models. Groups of ions were followed to calculate the resulting cross-tail current. Several groups then were combined to produce a current sheet. The goal is a model in which the ions and associated electrons carry the electric current distribution needed to generate the magnetic field B in which ion orbits were traced. The region -20 R(E) less than x less than -14 R(E) in geocentric solar magnetospheric coordinates was studied. Emphasis was placed on identifying the categories of ion orbits which contribute most to the cross-tail current and on gaining physical insight into the manner by which the ions carry the observed current distribution. Ions that were trapped near z = 0, ions that magnetically mirrored throughout the current sheet, and ions that mirrored near the Earth all were needed. The current sheet structure was determined primarily by ion magnetization currents. Electrons of the observed energies carried relatively little cross-tail current in these quiet time current sheets. Distribution functions were generated and integrated to evaluate fluid parameters. An earlier model in which B depended only on z produced a consistent current sheet, but it did not provide a realistic representation of the Earth's middle magnetotail. In the present study, B changed substantially in the x and z directions but only weakly in the y direction within our region of interest. Plasmas with three characteristic particle energies were used with each of the magnetic field models. A plasma was found for each model in which the density, average energy, cross-tail current, and bulk flow velocity agreed well with satellite observations.

Current-sheet formation in two-dimensional coronal fields

NASA Astrophysics Data System (ADS)

Billinghurst, M. N.; Craig, I. J. D.; Sneyd, A. D.

1993-11-01

The formation of current sheets by shearing motions in line-tied twin-lobed fields is examined. A general analytic argument shows that current sheets form along the fieldline bounding the two lobes in the case of both symmetric and asymmetric footpoint motions. In the case of strictly antisymmetric motions however no current sheets can form. These findings are reinforced by magnetic relaxation experiments involving sheared two-lobed fields represented by Clebsh variables. It is pointed out that, although current singularites cannot be expected to form when the line-tying assumption is relaxed, the two-lobed geometry is still consistent with the formation of highly localised currents - and strong resistive dissipation - along field lines close to the bounding fieldline.

Gate simulation of Compton Ar-Xe gamma-camera for radionuclide imaging in nuclear medicine

NASA Astrophysics Data System (ADS)

Dubov, L. Yu; Belyaev, V. N.; Berdnikova, A. K.; Bolozdynia, A. I.; Akmalova, Yu A.; Shtotsky, Yu V.

2017-01-01

Computer simulations of cylindrical Compton Ar-Xe gamma camera are described in the current report. Detection efficiency of cylindrical Ar-Xe Compton camera with internal diameter of 40 cm is estimated as1-3%that is 10-100 times higher than collimated Anger’s camera. It is shown that cylindrical Compton camera can image Tc-99m radiotracer distribution with uniform spatial resolution of 20 mm through the whole field of view.

Current-induced three-dimensional domain wall propagation in cylindrical NiFe nanowires

NASA Astrophysics Data System (ADS)

Wong, D. W.; Purnama, I.; Lim, G. J.; Gan, W. L.; Murapaka, C.; Lew, W. S.

2016-04-01

We report on the magnetization configurations in single NiFe cylindrical nanowires grown by template-assisted electrodeposition. Angular anisotropic magnetoresistance measurements reveal that a three-dimensional helical domain wall is formed naturally upon relaxation from a saturated state. Micromagnetic simulations support the helical domain wall properties and its reversal process, which involves a splitting of the clockwise and anticlockwise vortices. When a pulsed current is applied to the nanowire, the helical domain wall propagation is observed with a minimum current density needed to overcome its intrinsic pinning.

Current distribution on a cylindrical antenna with parallel orientation in a lossy magnetoplasma

NASA Technical Reports Server (NTRS)

Klein, C. A.; Klock, P. W.; Deschamps, G. A.

1972-01-01

The current distribution and impedance of a thin cylindrical antenna with parallel orientation to the static magnetic field of a lossy magnetoplasma is calculated with the method of moments. The electric field produced by an infinitesimal current source is first derived. Results are presented for a wide range of plasma parameters. Reasonable answers are obtained for all cases except for the overdense hyperbolic case. A discussion of the numerical stability is included which not only applies to this problem but other applications of the method of moments.

Self-rolling up micro 3D structures using temperature-responsive hydrogel sheet

NASA Astrophysics Data System (ADS)

Iwata, Y.; Miyashita, S.; Iwase, E.

2017-12-01

This paper proposes a micro self-folding using a self-rolling up deformation. In the fabrication method at micro scale, self-folding is an especially useful method of easily fabricating complex three-dimensional (3D) structures from engineered two-dimensional (2D) sheets. However, most self-folded structures are limited to 3D structures with a hollow region. Therefore, we made 3D structures with a small hollow region by self-rolling up a 2D sheet consisting of SU-8 and a temperature-responsive hybrid hydrogel of poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM-AAc). The temperature-responsive hydrogel can provide repetitive deformation, which is a good feature for micro soft robots or actuators, using hydrogel shrinking and swelling. Our micro self-rolling up method is a self-folding method for a 3D structure performed by rolling up a 2D flat sheet, like making a croissant, through continuous self-folding. We used our method to fabricate 3D structures with a small hollow region, such as cylindrical, conical, and croissant-like ellipsoidal structures, and 3D structures with a hollow region, such as spiral shapes. All the structures showed repetitive deformation, forward rolling up in 20 °C cold water and backward rolling up in 40 °C hot water. The results demonstrate that self-rolling up deformation can be useful in the field of micro soft devices.

Coupling between Mercury and its nightside magnetosphere: Cross-tail current sheet asymmetry and substorm current wedge formation

NASA Astrophysics Data System (ADS)

Poh, Gangkai; Slavin, James A.; Jia, Xianzhe; Raines, Jim M.; Imber, Suzanne M.; Sun, Wei-Jie; Gershman, Daniel J.; DiBraccio, Gina A.; Genestreti, Kevin J.; Smith, Andy W.

2017-08-01

We analyzed MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma measurements taken during 319 crossings of Mercury's cross-tail current sheet. We found that the measured BZ in the current sheet is higher on the dawnside than the duskside by a factor of ≈3 and the asymmetry decreases with downtail distance. This result is consistent with expectations based upon MHD stress balance. The magnetic fields threading the more stretched current sheet in the duskside have a higher plasma beta than those on the dawnside, where they are less stretched. This asymmetric behavior is confirmed by mean current sheet thickness being greatest on the dawnside. We propose that heavy planetary ion (e.g., Na+) enhancements in the duskside current sheet provides the most likely explanation for the dawn-dusk current sheet asymmetries. We also report the direct measurement of Mercury's substorm current wedge (SCW) formation and estimate the total current due to pileup of magnetic flux to be ≈11 kA. The conductance at the foot of the field lines required to close the SCW current is found to be ≈1.2 S, which is similar to earlier results derived from modeling of Mercury's Region 1 field-aligned currents. Hence, Mercury's regolith is sufficiently conductive for the current to flow radially then across the surface of Mercury's highly conductive iron core. Mercury appears to be closely coupled to its nightside magnetosphere by mass loading of upward flowing heavy planetary ions and electrodynamically by field-aligned currents that transfer momentum and energy to the nightside auroral oval crust and interior. Heavy planetary ion enhancements in Mercury's duskside current sheet provide explanation for cross-tail asymmetries found in this study. The total current due to the pileup of magnetic flux and conductance required to close the SCW current is found to be ≈11 kA and 1.2 S. Mercury is coupled to magnetotail by mass loading of heavy ions and field-aligned currents driven by reconnection-related fast plasma flow.

The ultimate intrinsic signal-to-noise ratio of loop- and dipole-like current patterns in a realistic human head model.

PubMed

Pfrommer, Andreas; Henning, Anke

2018-03-13

The ultimate intrinsic signal-to-noise ratio (UISNR) represents an upper bound for the achievable SNR of any receive coil. To reach this threshold a complete basis set of equivalent surface currents is required. This study systematically investigated to what extent either loop- or dipole-like current patterns are able to reach the UISNR threshold in a realistic human head model between 1.5 T and 11.7 T. Based on this analysis, we derived guidelines for coil designers to choose the best array element at a given field strength. Moreover, we present ideal current patterns yielding the UISNR in a realistic body model. We distributed generic current patterns on a cylindrical and helmet-shaped surface around a realistic human head model. We excited electromagnetic fields in the human head by using eigenfunctions of the spherical and cylindrical Helmholtz operator. The electromagnetic field problem was solved by a fast volume integral equation solver. At 7 T and above, adding curl-free current patterns to divergence-free current patterns substantially increased the SNR in the human head (locally >20%). This was true for the helmet-shaped and the cylindrical surface. On the cylindrical surface, dipole-like current patterns had high SNR performance in central regions at ultra-high field strength. The UISNR increased superlinearly with B0 in most parts of the cerebrum but only sublinearly in the periphery of the human head. The combination of loop and dipole elements could enhance the SNR performance in the human head at ultra-high field strength. © 2018 International Society for Magnetic Resonance in Medicine.

A case study of magnetotail current sheet disruption and diversion

NASA Technical Reports Server (NTRS)

Lui, A. T. Y.; Lopez, R. E.; Krimigis, S. M.; Mcentire, R. W.; Zanetti, L. J.

1988-01-01

On June 1, 1985 the AMPTE/CCE spacecraft (at a geocentric distance of about 8.8 earth radii at the midnight neutral sheet region) observed a dispersionless energetic particle injection and an increase in magnetic field magnitude, which are features commonly attributed to disruption of the near-earth cross-tail current sheet during substorm expansion onsets. An analysis based on high time-resolution measurements from the magnetometer and the energetic particle detector indicates that the current sheet disruption region exhibited localized (less than 1 earth radius) and transient (less than 1 min) particle intensity enhancements, accompanied by complex magnetic field changes with occasional development of a southward magnetic field component. Similar features are seen in other current disruption/diversion events observed by the CCE. The present analysis suggests that the current disruption region is quite turbulent, similar to laboratory experiments on current sheet disruption, with signatures unlike those expected from an X-type neutral line configuration. No clear indication of periodicity in any magnetic field parameter is discernible for this current disruption event.

Tearing Instability of a Current Sheet Forming by Sheared Incompressible Flow

NASA Astrophysics Data System (ADS)

Tolman, Elizabeth; Loureiro, Nuno; Uzdensky, Dmitri

2017-10-01

Sweet-Parker current sheets are unstable to the tearing mode, suggesting they will not form in physical systems. Understanding magnetic reconnection thus requires study of the stability of a current sheet as it forms. Such formation can occur as a result of sheared, sub-Alfvénic incompressible flows into and along the sheet. This work presents an analysis of how tearing perturbations behave in a current sheet forming under the influence of such flows, beginning with a phase when the growth rate of the tearing mode is small and the behavior of perturbations is primarily governed by ideal MHD. Later, after the tearing growth rate becomes significant relative to the time scale of the driving flows, the flows cause a slight reduction in the tearing growth rate and wave vector of the dominant mode. Once the tearing mode enters the nonlinear regime, the flows accelerate the tearing growth slightly; during X-point collapse, the flows have negligible effect on the system behavior. This analysis allows greater understanding of reconnection in evolving systems and increases confidence in the application of tools developed in time-independent current sheets to changing current sheets. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship.

Particle Acceleration and Heating by Turbulent Reconnection

NASA Astrophysics Data System (ADS)

Vlahos, Loukas; Pisokas, Theophilos; Isliker, Heinz; Tsiolis, Vassilis; Anastasiadis, Anastasios

2016-08-01

Turbulent flows in the solar wind, large-scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains “turbulent reconnection.” We constructed a 2D grid on which a number of randomly chosen grid points are acting as scatterers (I.e., magnetic clouds or current sheets). Our goal is to examine how test particles respond inside this large-scale collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, and their escape time distribution. We have developed a new method to estimate the transport coefficients from the dynamics of the interaction of the particles with the scatterers. Replacing the “magnetic clouds” with current sheets, we have proven that the energization processes can be more efficient depending on the strength of the effective electric fields inside the current sheets and their statistical properties. Using the estimated transport coefficients and solving the Fokker-Planck (FP) equation, we can recover the energy distribution of the particles only for the stochastic Fermi process. We have shown that the evolution of the particles inside a turbulent reconnecting volume is not a solution of the FP equation, since the interaction of the particles with the current sheets is “anomalous,” in contrast to the case of the second-order Fermi process.

PARTICLE ACCELERATION AND HEATING BY TURBULENT RECONNECTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vlahos, Loukas; Pisokas, Theophilos; Isliker, Heinz

2016-08-10

Turbulent flows in the solar wind, large-scale current sheets, multiple current sheets, and shock waves lead to the formation of environments in which a dense network of current sheets is established and sustains “turbulent reconnection.” We constructed a 2D grid on which a number of randomly chosen grid points are acting as scatterers (i.e., magnetic clouds or current sheets). Our goal is to examine how test particles respond inside this large-scale collection of scatterers. We study the energy gain of individual particles, the evolution of their energy distribution, and their escape time distribution. We have developed a new method tomore » estimate the transport coefficients from the dynamics of the interaction of the particles with the scatterers. Replacing the “magnetic clouds” with current sheets, we have proven that the energization processes can be more efficient depending on the strength of the effective electric fields inside the current sheets and their statistical properties. Using the estimated transport coefficients and solving the Fokker–Planck (FP) equation, we can recover the energy distribution of the particles only for the stochastic Fermi process. We have shown that the evolution of the particles inside a turbulent reconnecting volume is not a solution of the FP equation, since the interaction of the particles with the current sheets is “anomalous,” in contrast to the case of the second-order Fermi process.« less

Current sheet characteristics of a parallel-plate electromagnetic plasma accelerator operated in gas-prefilled mode

NASA Astrophysics Data System (ADS)

Liu, Shuai; Huang, Yizhi; Guo, Haishan; Lin, Tianyu; Huang, Dong; Yang, Lanjun

2018-05-01

The axial characteristics of a current sheet in a parallel-plate electromagnetic plasma accelerator operated in gas-prefilled mode are reported. The accelerator is powered by a fourteen stage pulse forming network. The capacitor and inductor in each stage are 1.5 μF and 300 nH, respectively, and yield a damped oscillation square wave of current with a pulse width of 20.6 μs. Magnetic probes and photodiodes are placed at various axial positions to measure the behavior of the current sheet. Both magnetic probe and photodiode signals reveal a secondary breakdown when the current reverses the direction. An increase in the discharge current amplitude and a decrease in pressure lead to a decrease in the current shedding factor. The current sheet velocity and thickness are nearly constant during the run-down phase under the first half-period of the current. The current sheet thicknesses are typically in the range of 25 mm to 40 mm. The current sheet velocities are in the range of 10 km/s to 45 km/s when the discharge current is between 10 kA and 55 kA and the gas prefill pressure is between 30 Pa and 800 Pa. The experimental velocities are about 75% to 90% of the theoretical velocities calculated with the current shedding factor. One reason for this could be that the idealized snowplow analysis model ignores the surface drag force.

Gamma compensated, self powered neutron detector

DOEpatents

Brown, Donald P.

1977-01-01

An improved, self-powered, gamma compensated, neutron detector having two electrically conductive concentric cylindrical electrodes and a central rod emitter formed from a material which emits beta particles when bombarded by neutrons. The outer electrode and emitter are maintained at a common potential and the neutron representative current is furnished at the inner cylindrical electrode which serves as a collector. The two concentric cylindrical electrodes are designed to exhibit substantially equal electron emission induced by Compton scattering under neutron bombardment to supply the desired gamma compensation.

Structure of the Jovian Magnetodisk Current Sheet: Initial Galileo Observations

NASA Technical Reports Server (NTRS)

Russell, C. T.; Huddleston, D. E.; Khurana, K. K.; Kivelson, M. G.

2001-01-01

The ten-degree tilt of the Jovian magnetic dipole causes the magnetic equator to move back and forth across Jupiter's rotational equator and tile Galileo orbit that lies therein. Beyond about 24 Jovian radii, the equatorial current sheet thins and tile magnetic structure changes from quasi-dipolar into magnetodisk-like with two regions of nearly radial but antiparallel magnetic field separated by a strong current layer. The magnetic field at the center of the current sheet is very weak in this region. Herein we examine tile current sheet at radial distances from 24 55 Jovian radii. We find that the magnetic structure very much resembles tile structure seen at planetary magnetopause and tail current sheet crossings. Tile magnetic field variation is mainly linear with little rotation of the field direction, At times there is almost no small-scale structure present and the normal component of the magnetic field is almost constant through the current sheet. At other times there are strong small-scale structures present in both the southward and northward directions. This small-scale structure appears to grow with radial distance and may provide the seeds for tile explosive reconnection observed at even greater radial distances oil tile nightside. Beyond about 40 Jovian radii, the thin current sheet also appears to be almost constantly in oscillatory motion with periods of about 10 min. The amplitude of these oscillations also appears to grow with radial distance. The source of these fluctuations may be dynamical events in tile more distant magnetodisk.

Self-consistent current sheet structures in the quiet-time magnetotail

NASA Technical Reports Server (NTRS)

Holland, Daniel L.; Chen, James

1993-01-01

The structure of the quiet-time magnetotail is studied using a test particle simulation. Vlasov equilibria are obtained in the regime where v(D) = E(y) c/B(z) is much less than the ion thermal velocity and are self-consistent in that the current and magnetic field satisfy Ampere's law. Force balance between the plasma and magnetic field is satisfied everywhere. The global structure of the current sheet is found to be critically dependent on the source distribution function. The pressure tensor is nondiagonal in the current sheet with anisotropic temperature. A kinetic mechanism is proposed whereby changes in the source distribution results in a thinning of the current sheet.

Transformer current sensor for superconducting magnetic coils

DOEpatents

Shen, S.S.; Wilson, C.T.

1985-04-16

The present invention is a current transformer for operating currents larger than 2kA (two kiloamps) that is capable of detecting a millivolt level resistive voltage in the presence of a large inductive voltage. Specifically, the present invention includes substantially cylindrical primary turns arranged to carry a primary current and substantially cylindrical secondary turns arranged coaxially with and only partially within the primary turns, the secondary turns including an active winding and a dummy winding, the active and dummy windings being coaxial, longitudinally separated and arranged to mutually cancel voltages excited by commonly experienced magnetic fields, the active winding but not the dummy winding being arranged within the primary turns.

Distribution of leakage currents in the cylindrical and conical sections of the magnetically insulated transmission line of the Angara-5-1 facility in experiments with wire arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grabovski, E. V.; Gribov, A. N.; Samokhin, A. A.

2016-08-15

Current leakages in the magnetically insulated transmission lines (MITL) impose restrictions on the transmission of electromagnetic pulses to the load in high-power electrophysical facilities. The multimodule Angara-5-1 facility with an output electric power of up to 6 TW is considered. In this work, the experimental and calculated profiles of leakage currents in two sections of the line are compared when the eight-module facility is loaded by a wire array. The azimuthal distribution of the current in the cylindrical section of the MITL is also considered.

Large-current-controllable carbon nanotube field-effect transistor in electrolyte solution

NASA Astrophysics Data System (ADS)

Myodo, Miho; Inaba, Masafumi; Ohara, Kazuyoshi; Kato, Ryogo; Kobayashi, Mikinori; Hirano, Yu; Suzuki, Kazuma; Kawarada, Hiroshi

2015-05-01

Large-current-controllable carbon nanotube field-effect transistors (CNT-FETs) were fabricated with mm-long CNT sheets. The sheets, synthesized by remote-plasma-enhanced CVD, contained both single- and double-walled CNTs. Titanium was deposited on the sheet as source and drain electrodes, and an electrolyte solution was used as a gate electrode (solution gate) to apply a gate voltage to the CNTs through electric double layers formed around the CNTs. The drain current came to be well modulated as electrolyte solution penetrated into the sheets, and one of the solution gate CNT-FETs was able to control a large current of over 2.5 A. In addition, we determined the transconductance parameter per tube and compared it with values for other CNT-FETs. The potential of CNT sheets for applications requiring the control of large current is exhibited in this study.

Observational support for the current sheet catastrophe model of substorm current disruption

NASA Technical Reports Server (NTRS)

Burkhart, G. R.; Lopez, R. E.; Dusenbery, P. B.; Speiser, T. W.

1992-01-01

The principles of the current sheet catastrophe models are briefly reviewed, and observations of some of the signatures predicted by the theory are presented. The data considered here include AMPTE/CCE observations of fifteen current sheet disruption events. According to the model proposed here, the root cause of the current disruption is some process, as yet unknown, that leads to an increase in the k sub A parameter. Possible causes for the increase in k sub A are discussed.

Nonlinear evolution of three-dimensional instabilities of thin and thick electron scale current sheets: Plasmoid formation and current filamentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Neeraj; Büchner, Jörg; Max Planck Institute for Solar System Research, Justus-Von-Liebig-Weg-3, Göttingen

Nonlinear evolution of three dimensional electron shear flow instabilities of an electron current sheet (ECS) is studied using electron-magnetohydrodynamic simulations. The dependence of the evolution on current sheet thickness is examined. For thin current sheets (half thickness =d{sub e}=c/ω{sub pe}), tearing mode instability dominates. In its nonlinear evolution, it leads to the formation of oblique current channels. Magnetic field lines form 3-D magnetic spirals. Even in the absence of initial guide field, the out-of-reconnection-plane magnetic field generated by the tearing instability itself may play the role of guide field in the growth of secondary finite-guide-field instabilities. For thicker current sheetsmore » (half thickness ∼5 d{sub e}), both tearing and non-tearing modes grow. Due to the non-tearing mode, current sheet becomes corrugated in the beginning of the evolution. In this case, tearing mode lets the magnetic field reconnect in the corrugated ECS. Later thick ECS develops filamentary structures and turbulence in which reconnection occurs. This evolution of thick ECS provides an example of reconnection in self-generated turbulence. The power spectra for both the thin and thick current sheets are anisotropic with respect to the electron flow direction. The cascade towards shorter scales occurs preferentially in the direction perpendicular to the electron flow.« less

Collisionless current sheet equilibria

NASA Astrophysics Data System (ADS)

Neukirch, T.; Wilson, F.; Allanson, O.

2018-01-01

Current sheets are important for the structure and dynamics of many plasma systems. In space and astrophysical plasmas they play a crucial role in activity processes, for example by facilitating the release of magnetic energy via processes such as magnetic reconnection. In this contribution we will focus on collisionless plasma systems. A sensible first step in any investigation of physical processes involving current sheets is to find appropriate equilibrium solutions. The theory of collisionless plasma equilibria is well established, but over the past few years there has been a renewed interest in finding equilibrium distribution functions for collisionless current sheets with particular properties, for example for cases where the current density is parallel to the magnetic field (force-free current sheets). This interest is due to a combination of scientific curiosity and potential applications to space and astrophysical plasmas. In this paper we will give an overview of some of the recent developments, discuss their potential applications and address a number of open questions.

Four large-scale field-aligned current systmes in the dayside high-latitude region

NASA Technical Reports Server (NTRS)

Ohtani, S.; Potemra, T. A.; Newell, P.T.; Zanetti, L. J.; Iijima, T.; Watanabe, M.; Blomberg, L. G.; Elphinstone, R. D.; Murphree, J. S.; Yamauchi, M.

1995-01-01

A system of four current sheets of large-scale field-aligned currents (FACs) was discovered in the data set of simultaneous Viking and Defense Meteorological Satellire Program-F7 (DMSP-F7) crossing of the dayside high-latitude region. This paper reports four examples of this system that were observed in the prenoon sector. The flow polarities of FACs are upward, downward, upward, and downward, from equatorward to poleward. The lowest-latitude upward current is flowing mostly in the central plasma sheet (CPS) precipitation region, often overlapping with the boundary plasma sheet (BPS) at its poleward edge, andis interpreted as a region 2 current. The pair of downward and upward FACs in the middle of te structure are collocated with structured electron precipitation. The precipitation of high-energy (greater than 1 keV) electrons is more intense in the lower-latitude downward current sheet. The highest-latitude downward flowing current sheet is located in a weak, low-energy particle precipitation region, suggesting that this current is flowing on open field lines. Simulaneous observations in the postnoon local time sector reveal the standard three-sheet structure of FACs, sometimes described as region 2, region 1, and mantle (referred to the midday region O) currents. A high correlation was found between the occurrence of the four FAC sheet structure and negative interplanetary magnetic field (IMF) B(sub Y). We discuss the FAC structurein terms of three types of convection cells: the merging, viscous, andlobe cells. During strongly negative IMF B(sub Y), two convection reversals exist in the prenoon sector; one is inside the viscous cell, and the other is between the viscous cell and the lobe cell. This structure of convection flow is supported by the Viking electric field and auroral UV image data. Based on the convection pattern, the four FAC sheet structure is interpreted as the latitude overlap of midday and morning FAC systems. We suggest that the for-current sheet structure is common in a certain prenoon localtime sector during strongly negative IMF B(sub Y).

Current sheet formation in a sheared force-free-magnetic field. [in sun

NASA Technical Reports Server (NTRS)

Wolfson, Richard

1989-01-01

This paper presents the results of a study showing how continuous shearing motion of magnetic footpoints in a tenuous, infinitely conducting plasma can lead to the development of current sheets, despite the absence of such sheets or even of neutral points in the initial state. The calculations discussed here verify the earlier suggestion by Low and Wolfson (1988) that extended current sheets should form due to the shearing of a force-free quadrupolar magnetic field. More generally, this work augments earlier studies suggesting that the appearance of discontinuities - current sheets - may be a necessary consequence of the topological invariance imposed on the magnetic field geometry of an ideal MHD system by virtue of its infinite conductivity. In the context of solar physics, the work shows how the gradual and continuous motion of magnetic footpoints at the solar photosphere may lead to the buildup of magnetic energy that can then be released explosively when finite conductivity effects become important and lead to the rapid dissipation of current sheets. Such energy release may be important in solar flares, coronal mass ejections, and other eruptive events.

Ionospheric control of the dawn-dusk asymmetry of the Mars magnetotail current sheet

NASA Astrophysics Data System (ADS)

Liemohn, Michael W.; Xu, Shaosui; Dong, Chuanfei; Bougher, Stephen W.; Johnson, Blake C.; Ilie, Raluca; De Zeeuw, Darren L.

2017-06-01

This study investigates the role of solar EUV intensity at controlling the location of the Mars magnetotail current sheet and the structure of the lobes. Four simulation results are examined from a multifluid magnetohydrodynamic model. The solar wind and interplanetary magnetic field (IMF) conditions are held constant, and the Mars crustal field sources are omitted from the simulation configuration. This isolates the influence of solar EUV. It is found that solar maximum conditions, regardless of season, result in a Venus-like tail configuration with the current sheet shifted to the -Y (dawnside) direction. Solar minimum conditions result in a flipped tail configuration with the current sheet shifted to the +Y (duskside) direction. The lobes follow this pattern, with the current sheet shifting away from the larger lobe with the higher magnetic field magnitude. The physical process responsible for this solar EUV control of the magnetotail is the magnetization of the dayside ionosphere. During solar maximum, the ionosphere is relatively strong and the draped IMF field lines quickly slip past Mars. At solar minimum, the weaker ionosphere allows the draped IMF to move closer to the planet. These lower altitudes of the closest approach of the field line to Mars greatly hinder the day-to-night flow of magnetic flux. This results in a buildup of magnetic flux in the dawnside lobe as the S-shaped topology on that side of the magnetosheath extends farther downtail. The study demonstrates that the Mars dayside ionosphere exerts significant control over the nightside induced magnetosphere of that planet.