Note: This page contains sample records for the topic halbach magnet array from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

Halbach array motor/generators: A novel generalized electric machine  

SciTech Connect

In August 1979, Halbach submitted a paper entitled ``Design of Permanent Multipole Magnets with Oriented Rare Earth Cobalt Material.`` In this paper, he presented a novel method of generating multipole magnetic fields using non-intuitive geometrical arrangements of permanent magnets. In subsequent publications, he further defined these concepts. Of particular interest to one of the authors (RFP) was the special magnet array that generated a uniform dipole field. In 1990 Post proposed the construction of an electric machine (a motor/generator) using a dipole field based on Klaus Halbach`s array of permanent magnets. He further proposed that such a system should be employed as an integral part of ``an electromechanical battery`` (EMB), i.e., a modular flywheel system to be used as a device for storing electrical energy, as an alternative to the electrochemical storage battery. This paper reviews Halbach`s theory for the generation of a dipole field using an array of permanent magnet bars, presents a simple analysis of a family of novel ``ironless`` electric machines designed using the dipole Halbach array, and describes the results obtained when they were tested in the laboratory.

Merritt, B.T.; Post, R.F.; Dreifuerst, G.R.; Bender, D.A.

1994-10-28

2

Development and Testing of an Axial Halbach Magnetic Bearing.  

National Technical Information Service (NTIS)

The NASA Glenn Research Center has developed and tested a revolutionary Axial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic thrust bearing utilizing Halbach arrays for all-electric flight, and many other ...

D. J. Eichenberg C. A. Gallo W. K. Thompson

2006-01-01

3

Development and Testing of a Radial Halbach Magnetic Bearing.  

National Technical Information Service (NTIS)

The NASA John H. Glenn Research Center has developed and tested a revolutionary Radial Halbach Magnetic Bearing. The objective of this work is to develop a viable non-contact magnetic bearing utilizing Halbach arrays for all-electric flight, and many othe...

C. A. Gallo D. J. Eichenberg W. K. Thompson

2006-01-01

4

The use of a linear Halbach array combined with a step-SPLITT channel for continuous sorting of magnetic species  

NASA Astrophysics Data System (ADS)

The Quadrupole Magnetic Sorter (QMS), employing an annular flow channel concentric with the aperture of a quadrupole magnet, is well established for cell and particle separations. Here we propose a magnetic particle separator comprising a linear array of cylindrical magnets, analogous to the array proposed by Klaus Halbach, mated to a substantially improved form of a parallel plate SPLITT channel, known as the step-SPLITT channel. While the magnetic force and throughput are generally lower than for the QMS, the new separator has advantages in ease of fabrication and the ability to vary the magnetic force to suit the separands. Preliminary experiments yield results consistent with prediction and show promise regarding future separations of cells of biomedical interest.

Hoyos, Mauricio; Moore, Lee; Williams, P. Stephen; Zborowski, Maciej

2011-05-01

5

A two-pole Halbach permanent magnet guideway for high temperature superconducting Maglev vehicle  

Microsoft Academic Search

In order to improve the levitation performance of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle, a two-pole Halbach array’s permanent magnet guideway (PMG) is proposed, which is called as Halbach PMG. The finite element method (FEM) calculations indicate that Halbach PMG has a wider high-field region than the present PMG of equal PM’s transverse section. The levitation force

H. Jing; J. Wang; S. Wang; L. Wang; L. Liu; J. Zheng; Z. Deng; G. Ma; Y. Zhang; J. Li

2007-01-01

6

Halbach array DC motor/generator  

SciTech Connect

A new configuration of DC motor/generator is based on a Halbach array of permanent magnets. This motor does not use ferrous materials so that the only losses are winding losses and losses due to bearings and windage. An "inside-out" design is used as compared to a conventional motor/generator design. The rotating portion, i.e., the rotor, is on the outside of the machine. The stationary portion, i.e., the stator, is formed by the inside of the machine. The rotor contains an array of permanent magnets that provide a uniform field. The windings of the motor are placed in or on the stator. The stator windings are then "switched" or "commutated" to provide a DC motor/generator much the same as in a conventional DC motor. The commutation can be performed by mechanical means using brushes or by electronic means using switching circuits. The invention is useful in electric vehicles and adjustable speed DC drives.

Merritt, Bernard T. (Livermore, CA); Dreifuerst, Gary R. (Livermore, CA); Post, Richard F. (Walnut Creek, CA)

1998-01-01

7

Halbach array DC motor/generator  

DOEpatents

A new configuration of DC motor/generator is based on a Halbach array of permanent magnets. This motor does not use ferrous materials so that the only losses are winding losses and losses due to bearings and windage. An ``inside-out`` design is used as compared to a conventional motor/generator design. The rotating portion, i.e., the rotor, is on the outside of the machine. The stationary portion, i.e., the stator, is formed by the inside of the machine. The rotor contains an array of permanent magnets that provide a uniform field. The windings of the motor are placed in or on the stator. The stator windings are then ``switched`` or ``commutated`` to provide a DC motor/generator much the same as in a conventional DC motor. The commutation can be performed by mechanical means using brushes or by electronic means using switching circuits. The invention is useful in electric vehicles and adjustable speed DC drives. 17 figs.

Merritt, B.T.; Dreifuerst, G.R.; Post, R.F.

1998-01-06

8

Halbach array superconducting magnetic bearing for a flywheel energy storage system  

Microsoft Academic Search

In order to develop a new magnetic bearing set for a flywheel energy storage prototype, it was designed and simulated some configurations of Permanent Magnetic Bearings (PMB) and Superconducting Magnetic Bearings (SMB). The bearings were assembled with Nd-Fe-B permanent magnets and the simulations were carried out with the Finite Element Method (FEM). The PMB was designed to reduce the load

Guilherme G. Sotelo; Antonio C. Ferreira

2005-01-01

9

Halbach array motor/generators: A novel generalized electric machine.  

National Technical Information Service (NTIS)

In August 1979, Halbach submitted a paper entitled ''Design of Permanent Multipole Magnets with Oriented Rare Earth Cobalt Material.'' In this paper, he presented a novel method of generating multipole magnetic fields using non-intuitive geometrical arran...

B. T. Merritt R. F. Post G. R. Dreifuerst D. A. Bender

1994-01-01

10

Analysis on electric power consumption characteristics of cylindrical linear oscillatory actuator with Halbach permanent magnet array mover under electromechanical resonance frequency  

NASA Astrophysics Data System (ADS)

This paper deals with electric power consumption characteristics of cylindrical linear oscillatory actuator with Halbach permanent magnet array mover under electromechanical resonance frequency. The control parameters such as back-emf constant, torque constant, resistance, and inductance are obtained from characteristic equations and experimental results. Then, the voltage equation and mechanical motion equation after deriving control parameters are proposed by impedance modeling considering mechanical component, and theoretical resonance frequency is predicted by impedance modeling. Finally, dynamic simulation and experimental results are presented for drive characteristics such as current, power factor, and displacement according to the various values of frequency, and this paper find that the current and electric power consumed in linear actuator have the minimum value at the resonance frequency.

Ko, Kyoung-Jin; Jang, Seok-Myeong; Choi, Ji-Hwan; Choi, Jang-Young; Sung, So-Young; Park, Young-Tae

2011-04-01

11

Magnet arrays for synchronous machines  

Microsoft Academic Search

The authors demonstrate that the Halbach array is highly applicable for magnetic excitation in synchronous machines. To this end, they present the geometry of Halbach arrays in Cartesian, polar, and cylindrical coordinates. They also present the design of a Cartesian linear motor which has been optimized for use in conjunction with a class of high-precision magnetic suspension stages for photolithography.

David L. Trumper; Mark E. Williams; Tiep H. Nguyen

1993-01-01

12

Intensity distribution of strong magnetic fields created by opposing linear Halbach assemblies of permanent magnets  

NASA Astrophysics Data System (ADS)

The work is devoted to the geometrical configuration of permanent magnets on the basis of opposing geometrically linear assemblies (e.g. Halbach arrays) for the generation of strong magnetic fields, which have been theoretically modeled and experimentally verified. The implementation of these opposing assemblies using NdFeB magnets of a total weight of 3.75 kg provided a value of magnetic induction in the middle of an air gap of a width of 20 mm that was higher by 56% in comparison with the simplest possible design. When the air gap width was 3 mm, the induction reached a value of 2.16 T, which represents an increase of more than 100%. Simultaneously, however, unlike in the simplest possible parallel configuration, opposing Halbach assemblies have shown, in the middle of an air gap, a significant decrease of the magnetic induction values when passing from the middle of the assemblies in the direction parallel to the x-axis.

Žežulka, Václav; Pištora, Jaromír; Les?ák, Michal; Straka, Pavel; Ciprian, Dalibor; Foukal, Jaroslav

2013-11-01

13

Laboratory Scale Prototype of a Low-Speed Electrodynamic Levitation System Based on a Halbach Magnet Array  

ERIC Educational Resources Information Center

|In this paper we analyse the behaviour of a small-scale model of a magnetic levitation system based on the Inductrack concept. Drag and lift forces acting on our prototype, moving above a continuous copper track, are studied analytically following a simple low-speed approach. The experimental results are in good agreement with the theoretical…

Iniguez, J.; Raposo, V.

2009-01-01

14

Laboratory scale prototype of a low-speed electrodynamic levitation system based on a Halbach magnet array  

Microsoft Academic Search

In this paper we analyse the behaviour of a small-scale model of a magnetic levitation system based on the Inductrack concept. Drag and lift forces acting on our prototype, moving above a continuous copper track, are studied analytically following a simple low-speed approach. The experimental results are in good agreement with the theoretical calculations. 3D-numerical simulations are also used to

J. Íñiguez; V. Raposo

2009-01-01

15

Comparative study of electromagnetic performance of alternative Halbach and conventional radially magnetized permanent magnet brushless motors  

Microsoft Academic Search

In this paper, the static and dynamic electromagnetic performance, including the airgap field distribution, the back-emf waveform, the cogging torque, and the torque-speed characteristic and the efficiency, of three alternative Halbach permanent magnet brushless motors, employing anisotropic bonded NdFeB Halbach cylinder with and without rotor back-iron, as well as segmented Halbach cylinder with sintered NdFeB magnets, are compared by finite

Z. Q. Zhu; Z. P. Xia; D. Howe

2008-01-01

16

Magnetomechanics of internal-dipole, Halbach-array motor/generators.  

SciTech Connect

The magnetomechanical behavior of internal-dipole, Halbach-type magnet arrays is analyzed for application as a motor/generator (M/G) with an energy-storage flywheel that is suspended by low-stiffness bearings. Scaling laws for the maximization of torque are derived as a function of geometry. The optimal geometry is relatively insensitive to gap and stator design and occurs approximately at a ratio of inner to outer diameter of the array of 0.8. Values are found for the angular extent of each phase of the stator coil that minimize the stiffness. The negative stiffness of the internal-dipole array is calculated for several manufacturable configurations and is shown to provide an upper limit on the available torque of the M/G according to the positive stiffness of the bearings. Experimental results are reported for an internal-dipole array used as a M/G for a flywheel suspended by a bearing consisting of a permanent-magnet assembly levitated over an array of high-temperature superconductors. Results show that the system is stable and that idling losses are low.

Hull, J. R.; Turner, L. R.; Energy Technology

2000-07-01

17

Design of magnet arrays for permanent magnetic linear motor  

Microsoft Academic Search

An iron-less single side permanent magnetic linear motor structure is presented, and two-dimensional analytical formulae for\\u000a its magnetic field are deduced to design the types of magnetic arrays, the thickness of permanent magnet, and the duty ratio\\u000a of magnet arrays, etc. With certain design parameters, conventional arrays are used instead of a piecewise Halbach arrays,\\u000a and the machining and assembling

Junhong Mao; Junhang Luo; Qiang Jiang; Youbai Xie

2008-01-01

18

Art and science of magnet design: Selected notes of Klaus Halbach. Volume 2.  

National Technical Information Service (NTIS)

This volume contains a compilation of 57 notes written by Dr. Klaus Halbach selected from his collection of over 1650 such documents. It provides an historic snapshot of the evolution of magnet technology and related fields as the notes range from as earl...

1995-01-01

19

Recent Development of Halbach Permanent Magnet Machines and Applications  

Microsoft Academic Search

Halbach magnetised PM brushless machines are novel in that their magnetisation is self-shielding. They offer many attractive features, such as sinusoidal airgap field distribution and back-emf waveform, negligible cogging torque, potentially high airgap flux density and no need of rotor back-iron. Hence, they have recently attracted many research and development interests and extensive exploitation for their applications. This paper starts

Z. Q. Zhu

2007-01-01

20

The art and science of magnet design: Selected notes of Klaus Halbach, volume 2  

NASA Astrophysics Data System (ADS)

This volume contains a compilation of 57 notes written by Dr. Klaus Halbach selected from his collection of over 1650 such documents. It provides an historic snapshot of the evolution of magnet technology and related fields as the notes range from as early as 1965 to the present, and is intended to show the breadth of Dr. Halbach's interest and ability that have long been an inspiration to his many friends and colleagues. As Halbach is an experimental physicist whose scientific interests span many areas, and who does his most innovative work with pencil and paper rather than at the workbench or with a computer, the vast majority of the notes in this volume were handwritten and their content varies greatly--some reflect original work or work for a specific project, while others are mere clarifications of mathematical calculations or design specifications. As the authors converted the notes to electronic form, some were superficially edited and corrected, while others were extensively re-written to reflect current knowledge and notation. The notes are organized under five categories which reflect their primary content: Beam Position Monitors, (bpm), Current Sheet Electron Magnets (csem), Magnet Theory, (thry), Undulators and Wigglers (u-w), and Miscellaneous (misc). Within the category, they are presented chronologically starting from the most recent note and working backwards in time.

1995-02-01

21

A portable Halbach magnet that can be opened and closed without force: the NMR-CUFF.  

PubMed

Portable equipment for nuclear magnetic resonance (NMR) is becoming increasingly attractive for use in a variety of applications. One of the main scientific challenges in making NMR portable is the design of light-weight magnets that possess a strong and homogeneous field. Existing NMR magnets can provide such magnetic fields, but only for small samples or in small regions, or are rather heavy. Here we show a simple yet elegant concept for a Halbach-type permanent magnet ring, which can be opened and closed with minimal mechanical force. An analytical solution for an ideal Halbach magnet shows that the magnetic forces cancel if the structure is opened at an angle of 35.3° relative to its poles. A first prototype weighed only 3.1 kg, and provided a flux density of 0.57 T with a homogeneity better than 200 ppm over a spherical volume of 5mm in diameter without shimming. The force needed to close it was found to be about 20 N. As a demonstration, intact plants were imaged and water (xylem) flow measured. Magnets of this type (NMR-CUFF = Cut-open, Uniform, Force Free) are ideal for portable use and are eminently suited to investigate small or slender objects that are part of a larger or immobile whole, such as branches on a tree, growing fruit on a plant, or non-metallic tubing in industrial installations. This new concept in permanent-magnet design enables the construction of openable, yet strong and homogeneous magnets, which aside from use in NMR or MRI could also be of interest for applications in accelerators, motors, or magnetic bearings. PMID:21036637

Windt, Carel W; Soltner, Helmut; van Dusschoten, Dagmar; Blümler, Peter

2010-10-30

22

Tubular modular permanent-magnet machines equipped with quasi-Halbach magnetized magnets-part I: magnetic field distribution, EMF, and thrust force  

Microsoft Academic Search

This paper describes the analysis, design, and experimental characterization of three-phase tubular modular permanent-magnet machines equipped with quasi-Halbach magnetized magnets. It identifies feasible slot\\/pole number combinations and discusses their relative merits. It establishes an analytical expression for the open-circuit magnetic field distribution, formulated in the cylindrical coordinate system. The expression has been verified by finite-element analysis. The analytical solution allows

Jiabin Wang; David Howe

2005-01-01

23

Art and science of magnet design: A Festschrift in honor of Klaus Halbach. Volume 1.  

National Technical Information Service (NTIS)

This is a collection of technical papers and personal remembrances written expressly for the Halbach Symposium and dedicated to Klaus Halbach. The topics presented offer a hint of the diversity of Klaus's scientific career. Most of the papers deal with ma...

J. Cross

1995-01-01

24

The Inductrack: a simpler approach to magnetic levitation  

Microsoft Academic Search

Arising out of research at the Lawrence Livermore National Laboratory on passive magnetic bearings, a new magnetic levitation system, the Inductrack, has been developed and tested at model scale. The system employs special arrays of permanent magnets (Halbach arrays) on the moving car. The magnetic field from the arrays induces repelling currents in a close-packed array of shorted circuits in

Richard F. Post; D. D. Ryutov

2000-01-01

25

The application of Halbach cylinders to brushless ac servo motors  

SciTech Connect

Halbach cylinders are applied to brushless ac servo motors. It is shown that a sinusoidal back-emf waveform and a low cogging torque can be achieved without recourse to conventional design features such as distributed windings and/or stator/rotor skew. A technique for imparting a multipole Halbach magnetization distribution on an isotropic permanent magnet cylinder is described, and it is shown that the torque capability of a Halbach ac servo motor can be up to 33% higher than conventional brushless permanent magnet ac motors.

Atallah, K.; Howe, D. [Univ. of Sheffield (United Kingdom). Dept. of Electronic and Electrical Engineering

1998-07-01

26

A permanent magnet tubular linear generator for wave energy conversion  

NASA Astrophysics Data System (ADS)

A novel three-phase permanent magnet tubular linear generator (PMTLG) with Halbach array is proposed for the sea wave energy conversion. Non-linear axi-symmetrical finite element method (FEM) is implemented to calculate the magnetic fields along air-gap for different Halbach arrays of PMTLGs. The PMTLG characteristics are analyzed and the simulation results are validated by the experiment. An assistant tooth is implemented to greatly minimize the end and cogging effects which cause the oscillatory detent force.

Yu, Haitao; Liu, Chunyuan; Yuan, Bang; Hu, Minqiang; Huang, Lei; Zhou, Shigui

2012-04-01

27

Coherent magnetic semiconductor nanodot arrays  

PubMed Central

In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors. Up to now, lack of reliable methods to obtain high-quality MnGe nanostructures with a desired shape and a good controllability has been a barrier to make these materials practically applicable for spintronic devices. Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility. Magnetotransport experiments reveal that the nanodot arrays possess giant magneto-resistance associated with geometrical effects. The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation.

2011-01-01

28

Magnetic resonance measurements of polar sea ice  

Microsoft Academic Search

A Nuclear Magnetic Resonance (NMR) sensor system has been developed to measure the brine fraction profile of polar sea ice. The system is based on a 0.3 T Halbach permanent magnet array and has significantly more sensitivity than earlier Earth's field NMR systems deployed in Antarctica. Brine fraction experiments were performed in November 2009 near Ross Island, Antarctica and the

Robin Dykstra; Achim Gadke

2011-01-01

29

Magnetic nanocap arrays with tilted magnetization  

NASA Astrophysics Data System (ADS)

In modern magnetic recording materials the ``superparamagnetic effect'' has become increasingly important as new magnetic hard disk drive products are designed for higher storage densities. In this regard, patterned media [1], where two-dimensional arrays of nanostructures are used, is one of the concepts that might provide the required areal density in future magnetic recording devices. However, also nanostructure arrays will ultimately need high anisotropy material such as L10-FePt to provid enough thermal stability and thus much higher writing fields than currently obtainable from perpendicular magnetic recording heads. One proposed solution to this problem is the use of tilted magnetic recording media [2]. The basic idea is to tilt the easy axis of the magnetic medium from the perpendicular direction to 45 degree. In this case, the switching field will be reduced by a foctor of two in the Stoner-Wohlfarth limit. Recently, this approach was realized by oblique film deposition onto arrays of self-assembled spherical particles [3-5]. In this presentation, recent results on different film systems including Co/Pt multilayers, FePt and CoPtCr-SiO2 alloys which have been deposited onto SiO2 particle monolayers will be presented. It turned out that by tuning the growth conditions single domain nanocaps with enhanced magnetic coercivity and tilted anisostropy axis can be achieved even for particle sizes below 50 nm. [4pt] [1] B. D. Terris and T. Thomson, J. Phys. D: Appl. Phys. 38 (2005) R199 [0pt] [2] J.-P. Wang, Nat. Mater. 4, 191 (2005). [0pt] [3] M. Albrecht et al., Nat. Mater. 4, 203 (2005). [0pt] [4] T. Ulbrich et al., Phys. Rev. Lett. 96 (2006) 077202. [0pt] [5] D. Makarov et al., Appl. Phys. Lett. 93, 153112 (2008).

Albrecht, Manfred

2009-03-01

30

Magnetic properties of hexagonal ferrite dot arrays  

Microsoft Academic Search

Patterned magnetic media have been considered as one of the promising candidates for future ultra-high-density magnetic recording. In this paper, a new kind of patterned medium based on hexagonal ferrite have been studied. We have successfully fabricated strontium ferrite dot arrays by electron beam lithography. Their magnetic properties are evaluated by magnetic force microscopy (MFM) and superconducting quantum interference device

Xiaoxi Liu; Akimitsu Morisako

2006-01-01

31

CHIP-SIZE MAGNETIC SENSOR ARRAYS  

Microsoft Academic Search

Arrays of micron-sized magnetic sensors and sensor spacing on a single chip can be used to detect very small magnetic fields with high spatial resolution. These very small magnetic fields, or changes in magnetic fields, are associated with magnetic biosensors, non-destructive test\\/ inspection\\/evaluation, document validation including currency and credit cards and magnetic imaging. By using a silicon substrate, the signal

Carl H. Smith; Robert W. Schneider

2002-01-01

32

Note: Manipulation of supersonic atomic beams with static magnetic fields.  

PubMed

The inhomogeneous magnetic field of a permanent-magnet planar Halbach array is used to either deflect or to specularly reflect a supersonic beam of neutral atoms. Metastable neon and helium beams are tested to experimentally evaluate the performance of this array in a range of configurations. Results are compared with numerical simulations and the device is presented as a high precision tool for the manipulation of neutral atom beams. PMID:24028135

Gardner, Jamie; Castillo-Garza, Rodrigo; Raizen, Mark G

2013-09-01

33

Magnetic Nanoparticle Arrays prepared via Coaxial Electrospinning  

NASA Astrophysics Data System (ADS)

One dimensional nanoparticle (1D NP) arrays display strong anisotropy in their physical properties making them interesting from a fundamental as well as applications perspective. 1D arrays of Fe3O4 nanoparticles have been constructed by encapsulating magnetite nanoparticles within Poly(ethylene oxide) nanofibers, by a modified solution spinning process. Electrospinning is a facile process for creating 1D nanostructures and a simple modification to the process renders a coaxial delivery mechanism that facilitates the construction of nanoparticle arrays. These hybrid 1D nanomaterials were structurally characterized by electron microscopy and the magnetic characteristics of these fiber encapsulated particle arrays were studied using vibrating sample magnetometry. Anisotropic magnetic behavior along different orthogonal axes (parallel and perpendicular) was observed even at room temperature with an appreciable increase in coercivity in the perpendicular configuration. Experimental work is underway to use these particle arrays as precursor materials for the creation of magnetite nanorods.

Sharma, Nikhil; Jaffari, Hassnain; Shah, Ismat; Pochan, Darrin

2009-03-01

34

A CMOS rotary encoder using magnetic sensor arrays  

Microsoft Academic Search

A new type of small magnetic rotary encoder is presented. The device detects the magnetic field of a permanent magnet attached to the end of the rotating shaft using complementary metal-oxide semiconductor (CMOS) magnetic sensors [magnetic field effect transistor (MAGFET) arrays] set in a square arrangement. The sensor array is integrated onto a CMOS chip along with angle-detection circuits, leading

Kazuhiro Nakano; Toru Takahashi; Shoji Kawahito

2005-01-01

35

Colocated Magnetic Loop, Electric Dipole Array Antenna (Preliminary Results).  

National Technical Information Service (NTIS)

We present a detailed electromagnetic analysis of an electrically small colocated electric dipole and magnetic loop antenna array. This antenna is the simplest example of the Grimes multipole class of antenna arrays. We have determined that since the inte...

P. L. Overfelt D. R. Bowling D. J. White

1994-01-01

36

Assembly of ordered magnetic microsphere arrays  

NASA Astrophysics Data System (ADS)

We have developed a straightforward technique to assemble ordered arrays of magnetic microspheres on patterned thin Permalloy (Py) films deposited on the surface of a silicon wafer. Droplets containing micrometer-sized carboxyl paramagnetic microspheres are placed on a horizontally oriented wafer. The field produced by a permanent magnet placed under the wafer is rendered inhomogeneous by the patterned Py features and the resulting field gradients attract and hold the paramagnetic microspheres to these features. While the magnetic microspheres are being attracted to and secured on the pattered Permalloy features, a horizontal flow is created by a pipette, which also removes loose (unsecured) microspheres. By applying this technique to a cocktail of individually functionalized microspheres, a sensor could be realized, which will screen, in parallel, for a large number of targets per unit area. The ability to resolve individual microspheres is close to 100%. A desirable feature is that the substrate is reusable; removing the magnet allows an existing batch of microspheres, which may have lost sensitivity due to environmental exposure, to be flushed from the substrate and replaced with a new batch. The technique complements existing approaches in the field of microarrays widely used in immunoassay, DNA fragment detection, pathogen detection, and other applications in functional genomics and diagnostics.

Xu, Wanling; Ketterson, John

2008-08-01

37

Design and testing of a four-phase fault-tolerant permanent-magnet machine for an engine fuel pump  

Microsoft Academic Search

This paper discusses the design and testing of an aircraft electric fuel pump drive. The drive is a modular, four-phase, fault-tolerant system which is designed to meet the specification with a fault in any one of the phases. The motor employed has a permanent-magnet rotor with the magnets arranged in a Halbach array to maximize the air-gap flux density. Exceptionally

Barrie C. Mecrow; Alan G. Jack; David J. Atkinson; Simon R. Green; Glynn J. Atkinson; Andrew King; Brian Green

2004-01-01

38

Vector Potential and Stored Energy of a Quadrupole Magnet Array  

SciTech Connect

The vector potential, magnetic field and stored energy of a quadrupole magnet array are derived. Each magnet within the array is a current sheet with a current density proportional to the azimuthal angle 2{theta} and the longitudinal periodicity (2m-1){pi}/L. Individual quadrupoles within the array are oriented in a way that maximizes the field gradient The array does not have to be of equal spacing and can be of a finite size, however when the array is equally spaced and is of infinite size the solution can be simplified. We note that whereas, in a single quadrupole magnet with a current density proportional to cos2{theta} the gradient is pure, such purity is not preserved in a quadrupole array.

Caspi, S.

1999-03-15

39

Arrays of carbon nanoscrolls as deep subwavelength magnetic metamaterials  

NASA Astrophysics Data System (ADS)

We demonstrate theoretically that an array of carbon nanoscrolls acts as a hyperbolic magnetic metamaterial in the terahertz regime with genuine subwavelength operation corresponding to a wavelength-to-structure ratio of about 200. Due to the low sheet resistance of graphene, the electromagnetic losses in an array of carbon nanoscrolls are almost negligible, offering a very sharp magnetic resonance of extreme positive and negative values of the effective magnetic permeability. The latter property leads to superior imaging properties for arrays of carbon nanoscrolls which can operate as magnetic endoscopes in the terahertz range where magnetic materials are scarce. Our optical modeling is supplemented with ab initio density functional calculations of the self-winding of a single layer of graphene onto a carbon nanotube so as to form a carbon nanoscroll. The latter process is viewed as a means to realize ordered arrays of carbon nanoscrolls in the laboratory based on arrays of aligned carbon nanotubes which are now routinely fabricated.

Yannopapas, Vassilios; Tzavala, Marilena; Tsetseris, Leonidas

2013-10-01

40

A CMOS smart rotary encoder using magnetic sensor arrays  

Microsoft Academic Search

This paper presents a new concept of small magnetic rotary encoders. The magnetic field induced by a rotatable magnet is detected by integrated CMOS magnetic sensors (MAGFETs) arranged in a square form. This magnetic sensor array is integrated on a CMOS chip with angle detection circuits, leading to the realization of a small-size and cost-effective rotary encoder. Commonly-used magnetic encoders

Kazuhiro Nakano; Toru Takahashi; Shoji Kawahito

2003-01-01

41

Model Based Commutation Containing Edge Coils for a Moving Magnet Planar Actuator  

NASA Astrophysics Data System (ADS)

An extension of a special analytical commutation method for long-stroke magnetically levitated moving magnet type planar actuators is presented. It enables the use of coils that are influenced by the end-effect of the Halbach magnet array. They are located near the edge of the magnet array and are referred to as edge coils. The method adds those coils to the commutation correcting for the end-effect by modeling it as a multiplicative error in the commutation. As a result thermal losses are decreased while the error in the commutation is kept in the same order of magnitude. Experiments support the results.

Achterberg, J.; Rovers, J. M. M.; Lierop, C. M. M. Van; Jansen, J. W.; Bosch, P. P. J. Van Den; Lomonova, E. A.

42

VERY DENSE MAGNETIC SENSOR ARRAYS FOR PRECISION MEASUREMENT AND DETECTION  

Microsoft Academic Search

Very dense arrays of micron-sized magnetic sensors combined with micron sensor spacing on a single chip can detect very small magnetic fields with high spatial resolution. These changes in magnetic fields are in the milligauss range, approximately 500 times less than Earth's field, and are required for magnetic biosensors, non- destructive test\\/inspection\\/evaluation, precision position measurement, document validation and magnetic imaging

Carl H. Smith; Robert W. Schneider

2003-01-01

43

A magnetic microstirrer and array for microfluidic mixing  

Microsoft Academic Search

We report the development of a micromachined magnetic-bar micromixer for microscale fluid mixing in biological laboratory-on-a-chip applications. The mixer design is inspired by large scale magnetic bar mixers. A rotating magnetic field causes a single magnetic bar or an array of them to rotate rapidly within a fluid environment. A fabrication process of the magnetic bar mixer is developed. Results

Liang-Hsuan Lu; Kee Suk Ryu; Chang Liu

2002-01-01

44

Magnetic anisotropy transformation of Co-Fe-B nanowire arrays synthesized under the magnetic field  

NASA Astrophysics Data System (ADS)

The effects of magnetic field on the magnetic anisotropy of amorphous Co-Fe-B nanowire arrays during the electroless plating process have been investigated. The results show that the easy magnetization direction of the Co-Fe-B nanowire array rotated from in-plane to out-of-plane with the applied magnetic field increasing. A mechanism based on the variation of atomic short-range ordering induced by the applied magnetic field is proposed to interpret this unique anisotropy transformation.

Liu, Z.; Li, W. L.; Jin, P. P.; Fei, W. D.

2013-11-01

45

Eddy-current testing by flexible microloop magnetic sensor array  

Microsoft Academic Search

A flexible microloop magnetic sensor array has been developed for nondestructive evaluation in nuclear power plants and its fundamental characteristics have been investigated. A flexible micro-eddy current testing (micro-ECT) probe consists of a pancake-type exciting coil of the diameter of 3.2 ?m and a flexible microloop magnetic sensor array with an area of 14×14 mm2 and a thickness of 125

Mitsuru Uesaka; Kazumi Hakuta; Kenzo Miya; Kazuhiko Aoki; Ayumu Takahashi

1998-01-01

46

Design and analysis of magnetically-drive actuator applied for linear compressor  

Microsoft Academic Search

A novel Magnetically Levitated Linear Actuator (MLLA), mainly consisting of a Halbach magnetized moving-magnet armature, a cylindrical frame, a rod and electromagnetic (EM) poles, is presented and analyzed for linear compressors applications. The Halbach magnetized armature naturally generates a periodically distributed magnetic field which is interacted with that induced by the EM poles. Therefore, an axially reciprocating thrust force is

Nan-Chyuan Tsai; Chao-Wen Chiang

2010-01-01

47

Fabrication, characterization and applications of magnetic nanowire arrays  

NASA Astrophysics Data System (ADS)

Fe-Co-Ni ternary alloy nanowire arrays 32--106 nm in diameter are fabricated within nanoporous alumina membranes using 15 Vrms alternating current electrodeposition at frequencies of 50, 250, 500, 750, and 1000 Hz. The alumina membranes, 10--15 microns thick, are synthesized by anodization of aluminum foil using a two-step technique to increase pore uniformity. The alumina membrane structure is tailored with the end aim being uniform magnetic nanowire electrodeposition. Using an electrodeposition frequency of 1000 Hz, 15 Vrms, consistently and repeatably yield nanowire arrays over membranes several cm2 in extent. Electrochemical Impedance Spectroscopy (EIS) is used to explain the effects of AC electrodeposition frequency. The impedance of the residual alumina barrier layer, separating the underlying aluminum metal and the nanoporous membrane, decreases drastically with electrodeposition frequency facilitating uniform pore-filling of samples several cm2 in area. The magnetic coercivity and hysteresis loop squareness-ratio (Mr/Ms) were studied as functions of electrolyte composition, nanowire diameter, and nanowire aspect ratio. Anodic polarization studies on thin films having alloy compositions identical to the nanowires display excellent corrosion resistance properties. Two potential applications of the nanowire arrays are investigated. Iron nanowire arrays, oriented perpendicular to the substrate, are fabricated by electrodeposition of iron in nanoporous alumina membranes, followed by precise wet etching of the alumina membrane to partially expose the nanowire array. It is shown that oxidation of standing iron nanowire arrays, at 600°C in an oxygen ambient leads to standing alpha-Fe2O3 (hematite) nanowire arrays. These hematite nanowire arrays show a distinct photocurrent response and can be used as photocatalysts. Second, protein adsorption studies on standing Fe-Co-Ni nanowire arrays and flat Fe-Co-Ni thin films show that nanowire array morphology leads to attenuation of protein adsorption. Since protein adsorption is the first step in the biofouling process magnetic nanowire arrays can potentially find applications as non-biofouling surfaces. Placing magnetic nanowire arrays in a sinusoidally varying magnetic field leads to their oscillation that further reduces protein adsorption in comparison to stationary nanowire arrays.

Sharma, Gaurav

48

Selective actuation of arrays of carbon nanotubes using magnetic resonance.  

PubMed

We introduce the use of ferromagnetic resonance (FMR) to actuate mechanical resonances in as grown arrays of carbon nanotubes (CNTs) loaded with Ni particles (Ni-CNTs). This contactless method is closely related to the magnetic resonance force microscopy technique and provides spatial selectivity of actuation along the array. The Ni-CNT arrays are grown by chemical vapor deposition and are composed of homogeneous CNTs with uniform length (~600 nm) and almost equal diameter (~20 nm), which are loaded with Ni catalyst particles at their tips due to the tip growth mode. The vibrations of the Ni-CNTs are actuated by relying on the driving force that appears due to the FMR excited at about 2 GHz in the Ni particles (diameter ~100 nm). The Ni-CNT oscillations (frequency ~40 MHz) are detected mechanically by atomic force microscopy. The acquired oscillation images of the Ni-CNT uniform array reveal clear maxima in the spatial distribution of the oscillation amplitudes. We attribute these maxima to the "sensitive slices", i.e., the spatial regions of the Ni-CNT array where the FMR condition is met. Similar to magnetic resonance imaging, the sensitive slice is determined by the magnetic field gradient and moves along the Ni-CNT array as the applied magnetic field is ramped. Our excitation method does not require the presence of any additional microfabricated electrodes or coils near the CNTs and is particularly advantageous in cases where the traditional electrical actuation methods are not effective or cannot be implemented. The remote actuation can be effectively implemented also for arrays of other magnetic nanomechanical resonators. PMID:23742039

Volodin, Alexander; Santini, Claudia A; De Gendt, Stefan; Vereecken, Philippe M; Van Haesendonck, Chris

2013-06-06

49

Magnetic composite electrodeposition of micro-array magnets for MEMS actuators  

Microsoft Academic Search

This paper reports a new magnetic composite material deposition technique called magnetic composite electrodeposition (MCE). Thin films and micro-arrays of a composite matrix consisting of magnetic particles and a ferromagnetic alloy have been fabricated based on composite electroplating techniques. The magnetic particle selected is a barium ferrite magnet (BaFe12O19) and the ferromagnetic matrix is a pulse-reverse electrodeposited CoNiP alloy. The

S. Guan; B. J. Nelson

2004-01-01

50

Calibration of magnetic gradient tensor measurement array in magnetic anomaly detection  

NASA Astrophysics Data System (ADS)

Magnetic anomaly detection based on magnetic gradient tensor has become more and more important in civil and military applications. Compared with methods based on magnetic total field or components measurement, magnetic gradient tensor has some unique advantages. Usually, a magnetic gradient tensor measurement array is constituted by four three-axis magnetometers. The prominent problem of magnetic gradient tensor measurement array is the misalignment of sensors. In order to measure the magnetic gradient tensor accurately, it is quite essential to calibrate the measurement array. The calibration method, which is proposed in this paper, is divided into two steps. In the first step, each sensor of the measurement array should be calibrated, whose error is mainly caused by constant biases, scale factor deviations and nonorthogonality of sensor axes. The error of measurement array is mainly caused by the misalignment of sensors, so that triplets' deviation in sensors array coordinates is calibrated in the second step. In order to verify the effectiveness of the proposed method, simulation was taken and the result shows that the proposed method improves the measurement accuracy of magnetic gradient tensor greatly.

Chen, Jinfei; Zhang, Qi; Pan, Mengchun; Weng, Feibing; Chen, Dixiang; Pang, Hongfeng

2013-01-01

51

Collective modes in quantum-dot arrays in magnetic fields  

Microsoft Academic Search

We study collective excitations in a model array of parabolically confined quantum dots in an applied magnetic field. Treating the interactions between electrons on the same dot exactly and those between electrons on different dots in a simple approximation, we find that the Hamiltonian separates into a term involving center-of-mass coordinates of the electrons on each dot and a term

Jed Dempsey; N. F. Johnson; L. Brey; B. I. Halperin

1990-01-01

52

Parallel arrays of microtubles formed in electric and magnetic fields  

Microsoft Academic Search

The influence of electric and magnetic fields on microtubule assembly in vitro was studied. Both types of field caused alignment of microtubules in parallel arrays, as demonstrated by electron micrographs. These Iindings suggest a possible role of microtubules in the biological effects of exogenous as well as endogenous

Peter M. Vassilev; Reni T. Dronzine; Maria P. Vassileva; Georgi A. Georgiev

1982-01-01

53

Controlling magnetic flux motion by arrays of zigzag-arranged magnetic bars  

NASA Astrophysics Data System (ADS)

Recent advances in manufacturing arrays of artificial pinning sites, i.e., antidots, blind holes and magnetic dots, allowed an effective control of magnetic flux in superconductors. An array of magnetic bars deposited on top of a superconducting film was shown to display different pinning regimes depending on the direction of the in-plane magnetization of the bars. Changing the sign of their magnetization results in changes in the induced magnetic pinning potentials. By numerically solving the time-dependent Ginzburg-Landau equations in a superconducting film with periodic arrays of zigzag-arranged magnetic bars, we revealed various flux dynamics regimes. In particular, we demonstrate flux pinning and flux flow, depending on the direction of the magnetization of the magnetic bars. Remarkably, the revealed different flux-motion regimes are associated with different mechanisms of vortex-antivortex dynamics. For example, we found that for an ‘antiparallel’ configuration of magnetic bars this dynamics involves a repeating vortex-antivortex generation and annihilation. We show that the depinning transition and the onset of flux flow can be manipulated by the magnetization of the bars and the geometry of the array. This provides an effective control of the depinning critical current that can be useful for possible fluxonics applications.

Kapra, A. V.; Misko, V. R.; Peeters, F. M.

2013-02-01

54

Emerging magnetic stability in atomically assembled spin arrays  

NASA Astrophysics Data System (ADS)

Magnetic stability is usually created by the interaction of a large ensemble of atomically small magnetic moments that are themselves unstable. We make use of the Scanning Tunneling Microscope's ability to move individual atoms and construct arrays of interacting spins. Owed to their smallness, the magnetic states of these spin arrays are quantized and we probe their energies by inelastic electron tunneling spectroscopy [1]. To gain access to the equally important dynamical properties we employ an all-electronic pump-probe measurement scheme with which we follow the evolution between the spin states at nanosecond speed [2]. The combination of energetic and dynamical information allows identification of the relevant spin interaction and spin relaxation mechanisms at the atomic level. We design arrangements of atoms that suppress quantum tunneling of magnetization and drastically stabilize different spin configurations. Tracing the emergence of magnetic stability in the progression from individual atoms to arrays of spins points to new avenues for spintronic applications at atomic dimensions. [4pt] [1] A. J. Heinrich, J. A. Gupta, C. P. Lutz, D. M. Eigler, Science 306 466 (2004).[0pt] [2] S. Loth, M. Etzkorn, C. P. Lutz, D. M. Eigler, A. J. Heinrich, Science 329 1628 (2010).

Loth, Sebastian; Baumann, Susanne; Lutz, Christopher P.; Eigler, D. M.; Heinrich, Andreas J.

2012-02-01

55

Analysis and design optimization of ironless linear permanent magnet synchronous motors with non-overlapping concentrated windings for ultra-precision positioning system  

NASA Astrophysics Data System (ADS)

This paper presents the electromagnetic design of Ironless permanent magnet linear synchronous motor with non-overlapping concentrated windings based on the Equivalent Magnetizing Current(EMC) method. For one such motor structure we give analytical formulae for its magnetic field and thrust density and analyze to improve air-gap flux density and thrust density by varying motor design parameters. In order to minimize thrust ripple and improve thrust density, we analyze the superiority of ILPMLSM with Halbach magnet array and fractional-slot concentrated winding. The validity of the proposed technique is confirmed with 2-D Finite Element (FE) analysis.

Li, Liyi; Tang, Yongbin; Liu, Jiaxi; Chen, Qiming

2013-01-01

56

Angular resonant absorption curves in magnetic nanowire arrays  

NASA Astrophysics Data System (ADS)

We systematically probed the dynamics of two-dimensional Ni80Fe20 nanowire arrays with different strengths of interwire interactions using angular dependent microwave absorption spectroscopy. The experimental results are analyzed in terms of a graphical representation of the resonant absorption data through a critical-curve-like approach. This representation has the advantage of offering a direct and complete visual representation of anisotropy, interactions, and magnetization dynamics effects in nanomagnet arrays. In the paper, the connection between the proposed image of polar resonant absorption curves and the static switching field critical curves is substantiated using both macrospin and fully micromagnetic simulation approaches.

Cimpoesu, Dorin; Ding, Junjia; Stoleriu, Laurentiu; Adeyeye, Adekunle; Stancu, Alexandru; Spinu, Leonard

2013-06-01

57

Microfabricated atomic vapor cell arrays for magnetic field measurements  

SciTech Connect

We describe a method for charging atomic vapor cells with cesium and buffer gas. By this, it is possible to adjust the buffer gas pressure in the cells with good accuracy. Furthermore, we present a new design of microfabricated vapor cell arrays, which combine silicon wafer based microfabrication and ultrasonic machining to achieve the arrays of thermally separated cells with 50 mm{sup 3} volume. With cells fabricated in the outlined way, intrinsic magnetic field sensitivities down to 300 fT/Hz{sup 1/2} are reached.

Woetzel, S.; Schultze, V.; IJsselsteijn, R.; Schulz, T.; Anders, S.; Stolz, R.; Meyer, H.-G. [Institute of Photonic Technology, Albert-Einstein-Str. 9, D-07745 Jena (Germany)

2011-03-15

58

Bistability in a superconducting Al thin film induced by arrays of Fe-nanodot magnetic vortices.  

PubMed

A hybrid system, consisting of an array of Fe nanodots covered by a superconducting Al thin film, exhibits very unusual magnetotransport, including a giant hysteretic magnetoresistance with different reversible or irreversible regimes related to the magnetic state of the array. These effects originate from the magnetic fields produced by magnetic nanodots in the "magnetic vortex state." This is a unique model system in which properties of a magnetic array are transferred into the superconductor. PMID:18233315

Villegas, J E; Li, C-P; Schuller, Ivan K

2007-11-28

59

Formation of nanostructured arrays through magnetic ramp compression  

NASA Astrophysics Data System (ADS)

Recently, pressure-driven assembly of spherical nanoparticles and formation of one to three dimensional, nanostructured arrays have been demonstrated using diamond anvil cells. Extending the pressure-driven assembly of nanostructured arrays from static diamond anvil cells to dynamic compression techniques has been studied. Shock compression would be unsuitable for synthesis of nanostructures because the evaluated temperatures of shock states would induce melting of nanoparticles. However, magnetic ramp compression has been demonstrated to produce smooth, shockless loading with low temperature states suitable for nanostructure synthesis. Experiments have been performed on the Veloce pulsed power generator to ramp compress nanoparticles into nanostructured arrays, which utilizes a soft-recovery assembly to retrieve formed nanostructure samples. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Hickman, Randy J.; Ao, Tommy; Wise, Jack L.; Fan, Hongyou

2011-06-01

60

Micro Eddy Current Testing by micro magnetic sensor array  

SciTech Connect

A micro Eddy Current Testing (ECT) system for planar thin specimens made of INCONEL 600 with flaws was proposed and developed. A micro ECT probe used here consists of a conventional pancake-type coil as an exciting coil and a micro magnetic sensor array as a set of pickup coils. Magnetic field perturbation due to a flaw was measured with high spatial resolution and signal-to-noise (S/N) ratio. The measured signals from the array were compared with numerical results obtained by a three-dimensional A-[phi] code. It was confirmed that the Micro ECT system has the potential to evaluate the length and depth of a flaw with better accuracy than that of a conventional pancake-type ECT in the stream generator tubings in a pressurized water nuclear reactor.

Uesaka, Mitsuru; Nakanishi, Takahiro; Miya, Kenzo (Univ. of Tokyo, Ibaraki (Japan). Nuclear Engineering Research Lab.); Komatsu, Hidenobu; Aoki, Kazuhiko (Nuclear Fuel Industries, Ltd., Osaka (Japan)); Kasai, Kazuo (Sumitomo Precision Co. Ltd., Hyogo (Japan))

1995-01-01

61

Fabrication of magnetic nanodot arrays using ultrathin alumina membrane (UTAM)  

NASA Astrophysics Data System (ADS)

Fabrication of ultrathin alumina membranes were carried out using two step anodization from high purity aluminum foil. This membrane provides highly ordered nano pores with diameter of 80 nm and intra-pore distance of the order 110 nm. The membrane with thickness < 100 nm was used as a evaporation mask for the growth of magnetic nanodot arrays of Co, SmCo5 and CoPt on Si substrates. The structural investigations were carried out using Field Emission Scanning Electron Microscopy (FESEM). The elemental composition of nanodot arrays was confirmed using Energy Dispersive X-Ray (EDX) analysis. Magnetic characterizations were carried out to study the in-plane and out of-plane hysteresis behaviors and the coercive fields. The present novel two-step anodization approach is simple, efficient, and provides an inexpensive non-lithographic method to produce high density nano-structured materials for wide range of applications in nanotechnology and spintronics.

Chowdhury, P.; Sellarajan, S. Boominatha; Krishnan, M.; Barshilia, H. C.

2012-06-01

62

Magnetic Sense Coil Array for the FAMU Spheromak  

NASA Astrophysics Data System (ADS)

First plasmas in the Florida A&M Spheromak are expected in 2012. Here we describe the design, construction, and calibration of a magnetic sense coil array that will provide measurements of the edge poloidal and toroidal magnetic field fluctuations in the spheromak. The electrostatically shielded coils are mounted flush with the inner edge of the vacuum chamber. Custom differential amplifiers, based on designs by the MST group at the University of Wisconsin-Madison, enable fluctuation measurements up to frequencies of 2 MHz.

Vandervort, Robert; Keesee, Amy; Lusk, Greg; Reynolds, Eric; Scime, Earl

2012-10-01

63

Magnetic properties of strip-like Josephson-junction arrays  

NASA Astrophysics Data System (ADS)

Zero-field-cooled (ZFC) and field-cooled (FC) magnetic properties of strip-like Josephson-junction (JJ) arrays with very strong demagnetizing effects are calculated from basic laws. Similar to slab-like JJ arrays without considering demagnetizing effects, a vortex state evolves to a critical state (CS) with increasing maximum JJ currents in the ZFC case, and a vortex state always remains with a negative low-field susceptibility in the FC case. However, the strong demagnetizing effects cause qualitative changes in the CS, where the overall feature of the field and current profiles turns out to be similar to that in type-II superconducting strips, but not like the ordinary Bean CS in slab-like JJ arrays, the CS current profile is never flat and the critical current is no longer a step function of the maximum JJ current as in slab-like JJ arrays. The calculated results of different types of JJ arrays indicate that although the intergranular CS in granular superconductors may have a common origin, the discovered paramagnetic Meissner effect in them is still difficult to explain.

Chen, D.-X.; Moreno, J. J.; Hernando, A.; Sanchez, A.

2000-07-01

64

Magnetic screening in proximity effect Josephson-junction arrays  

NASA Astrophysics Data System (ADS)

The modulation with magnetic field of the sheet inductance measured on proximity effect Josephson-junction arrays (JJAs) is progressively vanishing on lowering the temperature, leading to a low-temperature field-independent response. This behaviour is consistent with the decrease of the two-dimensional penetration length below the lattice parameter. Low-temperature data are quantitatively compared with theoretical predictions based on the XY model in the absence of thermal fluctuations. The results show that the description of a JJA within the XY model is incomplete and the system is put well beyond the weak screening limit which is usually assumed in order to invoke the well-known frustrated XY model describing classical Josephson-junction arrays.

Tesei, M.; Théron, R.

2009-03-01

65

Probing arrays of circular magnetic microdots by ferromagnetic resonance.  

SciTech Connect

X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions.

Kakazei, G. N.; Mewes, T.; Wigen, P. E.; Hammel, P. C.; Slavin, A. N.; Pogorelov, Y. G.; Costa, M. D.; Golub, V. O.; Guslienko, K. Y.; Novosad, V. (Materials Science Division); (Univ. of Porto); (National Academy of Sciences Ukraine); (Univ. of Alabama); (Ohio State Univ.); (Oakland Univ.)

2008-06-01

66

Probing arrays of circular magnetic microdots by ferromagnetic resonance.  

PubMed

X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions. PMID:18681017

Kakazei, G N; Mewes, T; Wigen, P E; Hammel, P C; Slavin, A N; Pogorelov, Yu G; Costa, M D; Golub, V O; Guslienko, K Yu; Novosad, V

2008-06-01

67

A superconducting quadrupole magnet array for a heavy ion fusion driver  

SciTech Connect

A multi-channel quadrupole array has been proposed to increase beam intensity and reduce space charge effects in a Heavy Ion Fusion Driver. A single array unit composed of several quadrupole magnets, each with its own beam line, will be placed within a ferromagnetic accelerating core whose cost is directly affected by the array size. A large number of focusing arrays will be needed along the accelerating path. The use of a superconducting quadrupole magnet array will increase the field and reduce overall cost. We report here on the design of a compact 3 x 3 superconducting quadrupole magnet array. The overall array diameter and length including the cryostat is 900 x 700 mm. Each of the 9 quadrupole magnets has a 78 mm warm bore and an operating gradient of 50 T/m over an effective magnetic length of 320 mm.

Caspi, S.; Bangerter, r.; Chow, K.; Faltens, A.; Gourley, S.; Hinkins, R.; Gupta, R.; Lee, E.; McInturff, A.; Scanlan, R.; Taylor, C.; Wolgast, D.

2000-06-27

68

Nanofabrication of two-dimensional arrays of magnetite particles for fundamental rock magnetic studies  

Microsoft Academic Search

Magnetic measurements of samples with precisely controlled magnetic mineralogy, grain size, and interparticle spacing are needed to provide crucial experimental rock magnetic underpinning for paleomagnetic studies. We report a novel nanofabrication method for producing two-dimensional arrays of cylindrical synthetic magnetite particles with well-defined composition, particle size, and interparticle spacing. The samples are fabricated by writing dot arrays with electron beam

David Krása; Chris D. W. Wilkinson; Nikolaj Gadegaard; Xiang Kong; Haiping Zhou; Andrew P. Roberts; Adrian R. Muxworthy; Wyn Williams

2009-01-01

69

Static and dynamic magnetic properties of densely packed magnetic nanowire arrays  

NASA Astrophysics Data System (ADS)

The static and dynamic magnetic properties of magnetic nanowire arrays with high packing density (>0.4) and wire diameter much greater than the exchange length have been studied by static and time-resolved magneto-optical Kerr effect measurements and micromagnetic simulations. The nanowires were formed by electrodeposition within a nanoporous template such that their symmetry axes lay normal to the plane of the substrate. A quantitative and systematic investigation has been made of the static and dynamic properties of the array, which lie between the limiting cases of a single wire and a continuous ferromagnetic thin film. In particular, the competition between anisotropies associated with the shape of the individual nanowires and that of the array as a whole has been studied. Measured and simulated hysteresis loops are largely anhysteretic with zero remanence, and the micromagnetic configuration is such that the net magnetization vanishes in directions orthogonal to the applied field. Simulations of the remanent state reveal antiferromagnetic alignment of the magnetization in adjacent nanowires and the formation of vortex flux closure structures at the ends of each nanowire. The excitation spectra obtained from experiment and micromagnetic simulations are in qualitative agreement for magnetic fields applied both parallel and perpendicular to the axes of the nanowires. For the field parallel to the nanowire axes, there is also good quantitative agreement between experiment and simulation. The resonant frequencies are initially found to decrease as the applied field is increased from remanence. This is the result of a change of mode profile within the plane of the array from nonuniform to uniform as the ground state evolves with increasing applied field. Quantitative differences between experimental and simulated spectra are observed when the field is applied perpendicular to the nanowire axes. The dependence of the magnetic excitation spectra upon the array packing density is explored, and dispersion curves for spin waves propagating within the array parallel to the nanowire axis are presented. Finally, a tunneling of end modes through the middle region of the nanowires was observed. The tunneling is more efficient for wires forming densely packed arrays, as a result of the extended penetration of the dynamic demagnetizing fields into the middle of the wires and due to the lowering of the tunneling barrier by the static demagnetizing field of the array.

Dmytriiev, O.; Al-Jarah, U. A. S.; Gangmei, P.; Kruglyak, V. V.; Hicken, R. J.; Mahato, B. K.; Rana, B.; Agrawal, M.; Barman, A.; Mátéfi-Tempfli, M.; Piraux, L.; Mátéfi-Tempfli, S.

2013-05-01

70

Optical spins and nano-antenna array for magnetic therapy.  

PubMed

Magnetic therapy is an alternative medicine practice involving the use of magnetic fields subjected to certain parts of the body and stimulates healing from a range of health problems. In this paper, an embedded nano-antenna system using the optical spins generated from a particular configuration of microrings (PANDA) is proposed. The orthogonal solitons pairs corresponding to the left-hand and right-hand optical solitons (photons) produced from dark-bright soliton conversion can be simultaneously detected within the system at the output ports. Two possible spin states which are assigned as angular momentum of either +? or -? will be absorbed by an object whenever this set of orthogonal solitons is imparted to the object. Magnetic moments could indeed arise from the intrinsic property of spins. By controlling some important parameters of the system such as soliton input power, coupling coefficients and sizes of rings, output signals from microring resonator system can be tuned and optimized to be used as magnetic therapy array. PMID:23686955

Thammawongsa, N; Mitatha, S; Yupapin, P P

2013-05-15

71

Resonance properties of bi-component arrays of magnetic dots magnetized perpendicular to their planes  

NASA Astrophysics Data System (ADS)

The spin wave spectrum of dense arrays of rectangular elements periodically arranged in a two-dimensional magnonic crystal with a complex unit cell and magnetized perpendicularly to the array plane has been characterized using broadband ferromagnetic resonance (FMR) spectroscopy. The crystal's unit cell consists of non-collinear orientations of constituting elongated rectangular elements. We found that only one mode is excited in the perpendicular-to-plane FMR in complete magnetic saturation. We also conducted out-of-plane angle resolved measurements of the FMR resonance field. We observe splitting of the singlet observed for the perfect perpendicular-to-plane orientation of the applied field into a doublet upon a tilt of the field from this orientation. The splitting of the singlet into a doublet is explained as an experimental evidence of dipole coupling of the elements on the arrays. Our experimental observations are in good agreement with the theory we developed to describe the magnetization dynamics on this periodic array.

Kostylev, Mikhail; Zhong, Shudan; Ding, Junjia; Adeyeye, Adekunle O.

2013-09-01

72

Magnetic wire trap arrays for biomarker-based molecular detection  

NASA Astrophysics Data System (ADS)

Submicrometer-scale magnetic devices built on chip-based platforms have recently been shown to present opportunities for new particle trapping and manipulation technologies. Meanwhile, advances in nanoparticle fabrication allow for the building of custom-made particles with precise control of their size, composition, and other properties such as magnetism, fluorescence, and surface biomarker characteristics. In particular, carefully tailored surface biomarkers facilitate precise binding to targeted molecules, self-actuated construction of hybrid structures, and fluorescence-based detection schemes. Based on these progresses, we present an on-chip detection mechanism for molecules with known surface markers. Hybrid nanostructures consisting of micelle nanoparticles, fluorescent quantum dots, and superparamagnetic iron oxide nanoparticles are used to detect proteins or DNA molecules. The target is detected by the magnetic and fluorescent functionalities of the composite nanostructure, whereas in the absence of the target these signals are not present. Underlying this approach is the simultaneous manipulation via ferromagnetic zigzag nanowire arrays and imaging via quantum dot excitation. This chip-based detection technique could provide a powerful, low cost tool for ultrasensitive molecule detection with ramifications in healthcare diagnostics and small-scale chemical synthesis.

Vieira, Gregory; Mahajan, Kalpesh; Ruan, Gang; Winter, Jessica; Sooryakumar, R.

2012-02-01

73

A Mobile Ferromagnetic Shape Detection Sensor Using a Hall Sensor Array and Magnetic Imaging  

PubMed Central

This paper presents a Mobile Hall Sensor Array system for the shape detection of ferromagnetic materials that are embedded in walls or floors. The operation of the Mobile Hall Sensor Array system is based on the principle of magnetic flux leakage to describe the shape of the ferromagnetic material. Two permanent magnets are used to generate the magnetic flux flow. The distribution of magnetic flux is perturbed as the ferromagnetic material is brought near the permanent magnets and the changes in magnetic flux distribution are detected by the 1-D array of the Hall sensor array setup. The process for magnetic imaging of the magnetic flux distribution is done by a signal processing unit before it displays the real time images using a netbook. A signal processing application software is developed for the 1-D Hall sensor array signal acquisition and processing to construct a 2-D array matrix. The processed 1-D Hall sensor array signals are later used to construct the magnetic image of ferromagnetic material based on the voltage signal and the magnetic flux distribution. The experimental results illustrate how the shape of specimens such as square, round and triangle shapes is determined through magnetic images based on the voltage signal and magnetic flux distribution of the specimen. In addition, the magnetic images of actual ferromagnetic objects are also illustrated to prove the functionality of Mobile Hall Sensor Array system for actual shape detection. The results prove that the Mobile Hall Sensor Array system is able to perform magnetic imaging in identifying various ferromagnetic materials.

Misron, Norhisam; Shin, Ng Wei; Shafie, Suhaidi; Marhaban, Mohd Hamiruce; Mailah, Nashiren Farzilah

2011-01-01

74

Microwave studies of magnetic anisotropy of Co nanowire arrays  

NASA Astrophysics Data System (ADS)

The effect of magnetocrystalline anisotropy and dipolar interactions in Co nanowire arrays is studied by ferromagnetic resonance (FMR). Microwave measurements performed by the microstripline method are reported for two series of crystalline hcp Co (with the c axis nominally perpendicular [Co(c?)] and parallel to the wires [Co(c?)]) and an amorphous alloy with Co as the main component-Co94Fe5B1. Extrapolation of the high field linear part of the resonance curve (frequency versus dc field) permitted an evaluation of the effective anisotropy fields for saturated samples, as well as of the intrinsic fields HK, showing that the great differences between the three series are due to the magnetocrystalline anisotropy. The HK values for the two series of Co are discussed in terms of a model which accounts for the effect of the distributions of the c axis orientation in systems of uniaxial ferromagnets. The observed dependence of the effective anisotropy fields on the array geometry (wire length and diameter) is interpreted in terms of the interwire dipolar interactions and found to be in agreement with theoretical predictions based on a micromagnetic model. The fact that the resonance frequencies at Hdc=0 are geometry dependent shows that magnetostatic interactions are still significant at remanence. A second series of FMR experiments was performed at constant frequency (38 GHz), with the purpose of obtaining the angle dependence of the resonance field. These experiments provided an alternative method for the evaluation of the effective anisotropy field. The angle dependence of the resonance field for Co(c?) fitted the simplest equation for magnets with uniaxial anisotropy, obtained considering only the first order term in the expression of the magnetocrystalline energy as a function of the magnetization orientation. The same is not true for Co(c?), which required inclusion of a second order term.

Sklyuyev, A.; Ciureanu, M.; Akyel, C.; Ciureanu, P.; Yelon, A.

2009-01-01

75

Magnetic imaging of ferromagnetic shape with Mobile Hall Sensor Array system  

Microsoft Academic Search

The Mobile Hall Sensor Array system is a dynamic moving device capable of ferromagnetic shape evaluation based on the magnetic flux leakage testing principle. The device consists of a linearly integrated 1-D Hall Sensor array to detect magnetic field changes on a ferromagnetic shape under evaluation. The signal processing application software residing on a computer is developed for the Hall

M. Norhisam; N. Wei Shin; M. Hamiruce Marhaban; S. Suhaidi

2011-01-01

76

APPLICATION OF DFA METHOD TO MAGNETIC FIELD DATA FROM SEGMA ARRAY  

Microsoft Academic Search

We apply DFA method to magnetic field data from SEGMA array for the period August 2004 - February 2005. The SEGMA meridional array is a set of stations mainly localized in the Adriatic region (at a longi tude of about 10-16° E) and devoted to magnetic field measurements in the ULF frequency range. We study the fluctuation function and the

M. Chamati; P. Nenovski; M. Vellante; U. Villante; K. Schwingenschuh; M. Boudjada; V. Wesztergom

2009-01-01

77

Two-dimensional field-sensing map and magnetic anisotropy dispersion in magnetic tunnel junction arrays  

NASA Astrophysics Data System (ADS)

Due to the inherent disorder in local structures, anisotropy dispersion exists in almost all systems that consist of multiple magnetic tunnel junctions (MTJs). Aided by micromagnetic simulations based on the Stoner-Wohlfarth (S-W) model, we used a two-dimensional field-sensing map to study the effect of anisotropy dispersion in MTJ arrays. First, we recorded the field sensitivity value of an MTJ array as a function of the easy- and hard-axis bias fields, and then extracted the anisotropy dispersion in the array by comparing the experimental sensitivity map to the simulated map. Through a mean-square-error-based image processing technique, we found the best match for our experimental data, and assigned a pair of dispersion numbers (anisotropy angle and anisotropy constant) to the array. By varying each of the parameters one at a time, we were able to discover the dependence of field sensitivity on magnetoresistance ratio, coercivity, and magnetic anisotropy dispersion. The effects from possible edge domains are also discussed to account for a correction term in our analysis of anisotropy angle distribution using the S-W model. We believe this model is a useful tool for monitoring the formation and evolution of anisotropy dispersion in MTJ systems, and can facilitate better design of MTJ-based devices.

Zhang, Wenzhe; Xiao, Gang; Carter, Matthew J.

2011-04-01

78

Resonance modes in arrays of interacting ferromagnetic nanowires subjected to a transverse static magnetic field  

NASA Astrophysics Data System (ADS)

We report the measurement and modeling of two ferromagnetic resonance (FMR) modes in an array of amorphous CoFeB ferromagnetic nanowires with the applied static magnetic field transverse to the nanowire axes. The two modes are observed below saturation and are excited independently by the components of the microwave magnetic field parallel and perpendicular to the static field. We model the magnetization dynamics of the array as arising from the response of two interacting populations of wires magnetized mirror-symmetrically to each other relative to the plane of the array. The theory is well supported by experimental results obtained from vibrating sample magnetometer and shorted waveguide FMR measurements.

Boucher, Vincent; Lacroix, Christian; Carignan, Louis-Philippe; Yelon, Arthur; Ménard, David

2011-03-01

79

Dipolar interactions in two- and three-dimensional magnetic nanoparticle arrays  

NASA Astrophysics Data System (ADS)

Uniform, organically functionalized, 8.5-nm-diameter nanocrystals of Fe3O4 were synthesized and assembled into close-packed monolayer as well as multilayer arrays using the Langmuir-Blodgett technique. The ac and dc magnetic susceptibility measurements on arrays in comparison with isolated particles indicate strong dipolar interactions and a spin-glass-like slowing down of relaxation times. Differences in magnetic characteristics between monolayer to multilayer arrays were observed, such as larger remanent magnetization and a higher blocking temperature in the two-dimensional system.

Poddar, Pankaj; Telem-Shafir, Tamar; Fried, Tcipi; Markovich, Gil

2002-08-01

80

``Optical'' soft x-ray arrays for fluctuation diagnostics in magnetic fusion energy experiments  

Microsoft Academic Search

We are developing large pixel count, fast (>=100 kHz) and continuously sampling soft x-ray (SXR) array for the diagnosis of magnetohydrodynamics (MHD) and turbulent fluctuations in magnetic fusion energy plasmas. The arrays are based on efficient scintillators, high thoughput multiclad fiber optics, and multichannel light amplification and integration. Compared to conventional x-ray diode arrays, such systems can provide vastly increased

L. F. Delgado-Aparicio; D. Stutman; K. Tritz; M. Finkenthal; R. Kaita; L. Roquemore; D. Johnson; R. Majeski

2004-01-01

81

Coherent inelastic light scattering from a microwave-excited array of magnetic particles.  

PubMed

Inelastic light scattering from an array of Permalloy particles driven by a microwave magnetic field is shown to be a coherent phenomenon in which the scattered radiation is observed only at diffraction angles corresponding to the reciprocal lattice of the array. The results are explained in terms of the phase coherence of the inelastically scattered light by each of the particles. PMID:16486893

Grimsditch, M; Fradin, F Y; Ji, Y; Hoffmann, A; Camley, R E; Metlushko, V; Novosad, V

2006-01-31

82

Fabrication of Microstructured Magnetic Arrays Using Si3N4 Membrane Mask  

Microsoft Academic Search

We present a novel technique for the fabrication of microstructured magnetic thin film arrays without standard lithography process. The patterned magnetic arrays in the scale of micrometers have been fabricated by thermal evaporation through Si3N4 membrane mask. First, a standard photolithography together with wet etching was used for making Si3N4 membrane. A commercial scanning electron microscope modified for direct writing

J. Y. Ou

2005-01-01

83

LOW-COST CURRENT TRANSDUCER BASED ON CIRCULAR ARRAY OF MAGNETIC SENSORS  

Microsoft Academic Search

A Low-cost current transducer based on circular array of magnetic sensors is proposed as a valid alternative to traditional current transformers for high-current industrial applications in poly-phase systems of conductors. Since the accuracy of a circular array can be limited by the effects of magnetic fields of nearby phases and by those of eddy currents in the conductors, a new

Angelo Manara; Luca Di Rienzo; Roberto Ottoboni

2001-01-01

84

Electroless synthesis of large scale Co Zn P nanowire arrays and the magnetic behaviour  

NASA Astrophysics Data System (ADS)

Co Zn P nanowire arrays have been synthesized by electroless deposition in an anodic alumina membrane (AAM). The images of Co Zn P nanowire arrays and single nanowires are obtained by both scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that Co Zn P nanowire arrays are amorphous in structure. The hysteresis loops characterized by a vibrating sample magnetometer (VSM) show that the easily magnetized direction of Co Zn P nanowire arrays is parallel to the nanowire arrays and that there exhibits clearly a magnetic anisotropy as a result of the shape anisotropy.

Yuan, Xiaoyou; Du, Chunsheng; Sun, Gang; Pan, Ning

2007-03-01

85

Understanding magnetic properties of arrays of small FePt dots with perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

FePt dot arrays with dot size down to 15 nm are fabricated by film annealing and patterning. The array coercivity shows an increase with dot size decreasing from 100 to 30 nm, and a slight reduction for the 15 nm dot sample. Annealing these dot arrays at higher temperatures results in large enhancements in the coercivities, except the 15 nm dot array where the coercivity increases a little. Micromagnetic models of a 15 nm FePt dot with uniform and nonuniform edges of soft magnetic defects and with inside defects are calculated to reveal the microstructure origins of the dot magnetic properties. It is found that the volume fraction of the L10-phase FePt with perpendicular c-axis orientation is about 50% in the dot and the switching field distribution of the dot array can be influenced significantly by the defect arrangement in the dots.

Yan, Z. J.; Takahashi, S.; Hasegawa, T.; Ishio, S.; Kondo, Y.; Ariake, J.; Xue, D. S.

2012-11-01

86

Influence of soft magnetic materials on the design and performance of tubular permanent magnet machines  

Microsoft Academic Search

This paper investigates the influence of the choice of soft magnetic material on the performance of a tubular permanent magnet machine, and quantifies the relative merits of silicon iron laminations and soft magnetic composites (SMCs). The machine is equipped with a modular stator winding and employs a quasi-Halbach magnetized moving-magnet armature. It is shown that, despite its poorer space utilization,

Jiabin Wang; David Howe

2005-01-01

87

Optimization of magnetic sensor arrays for current measurement based on swarm intelligence and D-optimality  

Microsoft Academic Search

Purpose – The purpose of this paper is to improve the accuracy of innovative current transducers based on magnetic sensor arrays. Design\\/methodology\\/approach – The positions and the orientations of the magnetic sensors are optimized. The objective function is defined according to D-optimality theory and the optimization problem solved using particle swarm optimization (PSO). Findings – PSO is shown to be

Z. Zhang; L. Di Rienzo

2009-01-01

88

Conditions for the spin wave nonreciprocity in an array of dipolarly coupled magnetic nanopillars  

NASA Astrophysics Data System (ADS)

It is demonstrated that collective spin waves (SWs) propagating in complex periodic arrays of dipolarly coupled magnetic nanopillars existing in a saturated (single-domain) ground state in a zero bias magnetic field could be nonreciprocal. To guarantee the SW nonreciprocity, two conditions should be fulfilled: (i) existence of a nonzero out-of-plane component of the pillars' static magnetization and (ii) a complex periodicity of array's ground state with at least two elements per a primitive cell, if the elements are different, and at least three elements per a primitive cell, if the elements are identical.

Verba, Roman; Tiberkevich, Vasil; Bankowski, Elena; Meitzler, Thomas; Melkov, Gennadiy; Slavin, Andrei

2013-08-01

89

Multisegmented Magnet Array on Voice Coil Motor in Rotating Data Storage Devices  

NASA Astrophysics Data System (ADS)

The swing-arm-type voice coil motor (VCM) is widely used as an actuator in rotating data storage devices. Recently, it has been found that to achieve a faster data transfer rate and a higher data storage areal density, a high performance actuator is required. Moreover, a small form factor has become desirable for portable devices. In this paper, a novel magnetic circuit of VCM with multisegmented magnet array (MSMA) is proposed. Both the magnetic circuits of the conventional VCM and the MSMA VCM are optimized using the 3D finite element method. Sample magnetic circuits are fabricated with optimally designed parameters and a comparative analysis is carried out. The performances of magnetic circuits are evaluated and the experimental results prove the effectiveness of the proposed magnet array.

Jeong, Jaehwa; Lee, Moon G.; Lee, Jun-Hee; Yoon, Hyoung-Kil; Gweon, Dae-Gab

2004-04-01

90

The Inductrack Approach to Magnetic Levitation  

Microsoft Academic Search

Concepts developed during research on passive magnetic bearing systems at the Lawrence Livermore National Laboratory gave rise to a new approach to magnetic levitation, the Inductrack. A passive induced-current system employing permanent magnets on the moving vehicle, the Inductrack maximizes levitation forces by a combination of two elements. First, the permanent magnets on the vehicle are arranged in a ''Halbach

R. F. Post; D. D. Ryutov

2000-01-01

91

Highly stable and finely tuned magnetic fields generated by permanent magnet assemblies.  

PubMed

Permanent magnetic materials are the only magnetic source that can be used to generate magnetic fields without power consumption or maintenance. Such stand-alone magnets are very attractive for many scientific and engineering areas, but they suffer from poor temporal field stability, which arises from the strong sensitivity of the magnetic materials and mechanical support to temperature variation. In this work, we describe a highly efficient method useful to cancel the temperature coefficient of permanent magnet assemblies in a passive and accurate way. It is based on the combination of at least two units made of magnetic materials with different temperature coefficients arranged in such a way that the ratio of the fields generated by each unit matches the ratio of their effective temperature coefficients defined by both the magnetic and mechanical contributions. Although typically available magnetic materials have negative temperature coefficients, the cancellation is achieved by aligning the fields generated by each unit in the opposite direction. We demonstrate the performance of this approach by stabilizing the field generated by a dipolar Halbach magnet, recently proposed to achieve high field homogeneity. Both the field drift and the homogeneity are monitored via nuclear magnetic resonance spectroscopy experiments. The results demonstrate the compatibility of the thermal compensation approach with existing strategies useful to fine-tune the spatial dependence of the field generated by permanent magnet arrays. PMID:23683185

Danieli, E; Perlo, J; Blümich, B; Casanova, F

2013-04-30

92

Nonlithographic fabrication of 25 nm magnetic nanodot arrays with perpendicular anisotropy over a large area  

SciTech Connect

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm{sup 2} coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO{sub 2} dot arrays formed on a Si wafer. At first, arrays of the SiO{sub 2} dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO{sub 2} dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO{sub 2} dots are about 24, 43, and 17 nm, respectively. Then (Co(0.4 nm)/Pt(0.08 nm)){sub 8} MLs with a 3 nm Pt buffer layer is deposited onto the SiO{sub 2} dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO{sub 2} substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner-Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array.

Rahman, M. Tofizur; Shams, Nazmun N.; Lai, C.-H. [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

2009-04-01

93

Magnetization reversal measurements in Gd/Fe multilayer antidot arrays by vector magnetometry using x-ray magnetic circular dichroism  

NASA Astrophysics Data System (ADS)

Fe K-edge x-ray magnetic circular dichroism (XMCD) was used as vector magnetometry to measure the magnetization rotation while field cycling Gd/Fe multilayer antidot arrays through a hysteresis loop. The measured XMCD hysteresis curves were then compared quantitatively with micromagnetic calculations to reconstruct the microscopic magnetization configurations. The best fit reveals the existence of three types of characteristic domains: two that rotate coherently during magnetization reversal and one that is strongly pinned. The behavior is explained by a simple three-domain energy model, including a phenomenological ansatz for a shape-induced demagnetization energy contribution.

Lee, D. R.; Choi, Y.; You, C.-Y.; Lang, J. C.; Haskel, D.; Srajer, G.; Metlushko, V.; Ilic, B.; Bader, S. D.

2002-12-01

94

Magnetic induction measurements with a six channel coil array for vital parameter monitoring.  

PubMed

Vital parameter monitoring on neonatal intensive care units is essential but very stressful for patients during daily routine care. For contact-less monitoring of breathing and heart activity, magnetic induction measurements are applicable in research scenarios. For monitoring both vital parameters in newborn intensive care wards, we developed a Multi Channel Simultaneous Magnetic Induction Measurement System (MUSIMITOS2+). In this article we now evaluate the technical requirements of a coil array for vital parameter monitoring and finally present a multichannel coil array with 6 excitation and measurement channels combined as axial gradiometers for the specific measurement scenario. This array will be stored underneath the child. As a test case we will present data of a animal trial with the described coil array and the measurement device MUSIMITOS2+. PMID:23365964

Cordes, Axel; Heimann, Konrad; Leonhardt, Steffen

2012-01-01

95

Laser induced ultrafast magnetization reorientation in two dimensional arrays of Fe nanoparticles  

NASA Astrophysics Data System (ADS)

We report on our recent study of ultrafast demagnetization and reorientation dynamics induced by femtosecond optical pulses in two dimensional arrays of magnetic nanoparticles. The transient Faraday rotation signal and magnetic hysteresis loops were acquired with a probe beam following excitation by pump pulses in the 50-nm Fe nanoparticle arrays. We observed rapid change and recovery of magnetization hysteresis loops of about 50 fs along with excitation of 50 fs optical pulses under Voigt geometry. The processes are consistent with the ultrafast coherent magnetic responses of the sample and clearly show that the mechanisms of optomagnetic interactions do not rely on laser-induced heating but have a nonthermal origin. Our results clearly show the feasibility of ultrafast optical control of both the magnetization and the magnetocrystalline anisotropy.

Cevher, Zehra; Gong, Yu; Lai, Wei; Ren, Yuhang; Kim, C.; Delikanli, S.; Zeng, Hao

2010-03-01

96

Phase Dynamics and Magnetic Field Response of Proximity-Coupled Superconductor Arrays  

Microsoft Academic Search

We have fabricated and measured electrical transport properties of arrays of proximity-coupled superconductor islands as a function of temperature, magnetic field, and bias current for several geometries. The weakly-coupled arrays, a physical realization of the frustrated XY-model, show interesting behavior relating to phase coherence, fluctuations, and dynamics. Our samples display a broad transition to zero-resistance at a field-dependent temperature T_{rm

Kendall Norris Springer

1988-01-01

97

Magnetic properties of ferromagnetic nanowire arrays: Theory and experiment  

NASA Astrophysics Data System (ADS)

Magnetic nanowires are good candidates for microwave filters, sensors and data storage applications. An investigation of magnetic properties of single-component nanowires as a function of diameter and aspect ratio is performed in this work. Nickel nanowire (with 15 and 100 nm diameter and 6000 nm length) are grown with electrodeposition in polycarbonates templates. Two reversal modes (coherent and curling) are studied versus nanowire diameter. Magnetostatic interaction among wires and its effect on nanowire magnetic properties is also studied. Using vibrating magnetometer (VSM) and X-band ferromagnetic resonance (FMR) experiments at room temperature we infer that the interaction field Hc value may vary significantly and may cause a change of magnetic easy axis orientation along geometrical wire axis (for large diameter) to an easy magnetic plane perpendicular to the nanowire axis (for small diameter).

Ghaddar, A.; Gloaguen, F.; Gieraltowski, J.

2010-01-01

98

Development of flexible array eddy current probes for complex geometries and inspection of magnetic parts using magnetic sensors  

NASA Astrophysics Data System (ADS)

Eddy Current Technique is a powerful method of inspection of metal parts. When size of flaws decreases, inspection areas become hardly accessible or material is magnetic, traditional winding coil probes are less efficient. Thanks to new CIVA simulation tools, we have designed and optimized advanced EC probes: flexible EC probe based on micro-coil arrays and EC probe with magnetic sensors, including specific electronics.

Marchand, B.; Decitre, J.-M.; Sergeeva-Chollet, N.; Skarlatos, A.

2013-01-01

99

Least Squares Magnetic-Field Optimization for Portable Nuclear Magnetic Resonance Magnet Design  

SciTech Connect

Single-sided and mobile nuclear magnetic resonance (NMR) sensors have the advantages of portability, low cost, and low power consumption compared to conventional high-field NMR and magnetic resonance imaging (MRI) systems. We present fast, flexible, and easy-to-implement target field algorithms for mobile NMR and MRI magnet design. The optimization finds a global optimum ina cost function that minimizes the error in the target magnetic field in the sense of least squares. When the technique is tested on a ring array of permanent-magnet elements, the solution matches the classical dipole Halbach solution. For a single-sided handheld NMR sensor, the algorithm yields a 640 G field homogeneous to 16 100 ppm across a 1.9 cc volume located 1.5 cm above the top of the magnets and homogeneous to 32 200 ppm over a 7.6 cc volume. This regime is adequate for MRI applications. We demonstrate that the homogeneous region can be continuously moved away from the sensor by rotating magnet rod elements, opening the way for NMR sensors with adjustable"sensitive volumes."

Paulsen, Jeffrey L; Franck, John; Demas, Vasiliki; Bouchard, Louis-S.

2008-03-27

100

Magnetic flux pinning in superconductors with hyperbolic-tessellation arrays of pinning sites  

NASA Astrophysics Data System (ADS)

We study magnetic flux interacting with arrays of pinning sites (APSs) placed on vertices of hyperbolic tessellations (HTs). We show that, due to the gradient in the density of pinning sites, HT APSs are capable of trapping vortices for a broad range of applied magnetic fluxes. Thus, the penetration of magnetic field in HT APSs is essentially different from the usual scenario predicted by the Bean model. We demonstrate that, due to the enhanced asymmetry of the surface barrier for vortex entry and exit, this HT APS could be used as a “capacitor” to store magnetic flux.

Misko, V. R.; Nori, Franco

2012-05-01

101

Analysis of Lightning Induced Magnetic Field Penetration Through Protective Metal Screens Using an Equivalent Magnetic Dipole Moment Representation of an Array of Elliptic Apertures.  

National Technical Information Service (NTIS)

This investigation analyzed lightning induced magnetic field penetration through protective metal screens using an equivalent magnetic dipole moment representation of an array of elliptic apertures. Two metal screens with differing aperture sizes were mod...

J. L. O'Neal

1986-01-01

102

High sensitivity, inductively coupled miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows  

Microsoft Academic Search

A modified {dot {ital B}} circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment [R. M. Mayo {ital et} {ital al}., Plasma Sources Sci. Technol. {bold 4}, 47 (1995)] at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow

D. C. Black; R. M. Mayo

1996-01-01

103

High sensitivity, inductively coupled miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows  

Microsoft Academic Search

A modified B˙ circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment [R. M. Mayo etal., Plasma Sources Sci. Technol. 4, 47 (1995)] at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow laboratory study of magnetogasdynamics with particular

D. C. Black; R. M. Mayo

1996-01-01

104

Effect of spatially asymmetric dipolar interactions in the magnetization reversal of closely spaced ferromagnetic nanoisland arrays  

NASA Astrophysics Data System (ADS)

The magnetization reversal process of interacting elongated nanoislands is presented here. The magnetization reversal has been investigated by means of magneto-optical Kerr effect magnetometry, analyzing the beams reflected and diffracted by the array, magnetic force microscopy, and micromagnetic simulations. The nanoislands have an aspect ratio of 4.2 and are arranged in chiral square units forming a checkerboard array. Due to this particular arrangement, each island is subjected to a spatially asymmetric dipolar interaction field. We found that for certain directions of the applied field this specific character of the dipolar interaction affects the reversal process profoundly. In these cases the magnetization reversal takes places via the nucleation and displacement of a vortex state in two of the four nanoislands in every square unit, at variance with single domain rotation process generally observed for other directions of the applied field.

Porro, J. M.; Berger, A.; Grimsditch, M.; Metlushko, V.; Ilic, B.; Vavassori, P.

2012-04-01

105

Formation of a Cobalt Magnetic Dot Array via Block Copolymer Lithography  

Microsoft Academic Search

Single-domain cobalt dot arrayswith high magnetic particle density, patterned over large areas (e.g., 10 cm diameter wafers) are fabricated by self-assembled block copolymer lithography, using a polystyrene-poly(ferrocenyldimethylsilane) copolymer as a template. By varying the copolymer type and etching conditions the magnetic properties can be tuned. The Figure shows a typical array of Co dots with tungsten caps obtained via this

J. Y. Cheng; C. A. Ross; V. Z.-H. Chan; E. L. Thomas; R. G. H. Lammertink; G. Julius Vancso

2001-01-01

106

Non Destructive Testing with GMR Magnetic Sensor Arrays  

Microsoft Academic Search

The inspection of material used in aerospace, nuclear or transport industry is a critical issue for the safety of components exposed to stress or\\/and corrosion. The industry claims for faster, more sensitive and cost-effective techniques. Technologies based on magnetic sensor with high sensitivity such as giant magneto- resistance (GMR) may be a good solution to improve the performances of the

F. VACHER; C. GILLES-PASCAUD; J. M. DECITRE; C. FERMON; M. PANNETIER

2006-01-01

107

A magnetic type tactile sensor using a two-dimensional array of inductors  

Microsoft Academic Search

A novel tactile sensor based on electromagnetic induction that can detect slippage in addition to three-axis force is proposed. The structure of this sensor is simple, and the sensor, which is essentially a displacement gauge, consists of a two-dimensional array of inductors and an elastic body containing a permanent magnet. Formulas to transform the output voltage of the proposed sensor

Satoru Takenawa

2009-01-01

108

Measurements of the cosmological evolution of magnetic fields with the Square Kilometre Array  

Microsoft Academic Search

We investigate the potential of the Square Kilometre Array (SKA) for measuring the magnetic fields in clusters of galaxies via Faraday rotation of background polarized sources. The populations of clusters and radio sources are derived from an analytical cosmological model, combined with an extrapolation of current observational constraints. We adopt an empirical model for the Faraday screen in individual clusters,

Martin Krause; Paul Alexander; Rosie Bolton; Jörn Geisbüsch; David A. Green; Julia Riley

2009-01-01

109

Dispersion Diagram Characteristics of Periodic Array of Dielectric and Magnetic Materials Based Spheres  

Microsoft Academic Search

In this paper, the characteristics of electromagnetic (EM) waves supported by three dimensional (3D) periodic arrays of dielectric and magneto-dielectric spheres are theoretically investigated. The sphere particles have the potential to offer electric and magnetic dipole modes, where their novel arrangements engineer desired metamaterial performance. A full wave spherical modal analysis is applied to express the electromagnetic fields in terms

Shabnam Ghadarghadr; Hossein Mosallaei

2009-01-01

110

Laser induced nanobump array on magnetic glass disk for low flying height application  

Microsoft Academic Search

Laser processing has found an important application in the hard disk drive (HDD) industry to fabricate bumps for screen testing of the manufactured magnetic disk media prior to HDD assembly. The flying height of the head slider needs to be calibrated by a specifically designed bump array. With areal density of HDD already exceeds 100Gbits\\/in2, the head slider flies at

W J Wang; G H Lim; W D Song; K D Ye; J Zhou; M H Hong; B Liu

2007-01-01

111

Determination of the plasma velocity in an imploding wire array from magnetic field measurements by a gradient probe  

NASA Astrophysics Data System (ADS)

A method for measuring the gradient of the magnetic field in the plasma of an imploding wire array is described. Results from measurements of the magnitude and gradient of the magnetic field in a tungsten wire array on the Angara-5-1 facility at currents of ˜3 MA are presented. A novel method for calculating the velocity of the current-carrying plasma in the framework of MHD equations from data on the magnitude and gradient of the magnetic field at a certain point inside the array is proposed. It is demonstrated that a gradient magnetic probe can be used to investigate the plasma current sheath in plasma focus facilities.

Grabovski, E. V.; Mitrofanov, K. N.; Koshelev, A. Yu.; Samokhin, A. A.; Aleksandrov, V. V.; Gritsuk, A. N.; Laukhin, Ya. N.; Oleinik, G. M.; Frolov, I. N.

2011-07-01

112

Asymmetric magnetization reversal process in Co nanohill arrays  

SciTech Connect

Co thin films deposited by sputtering onto nanostructured polymer [poly(methyl methacrylate)] were prepared following replica-antireplica process based on porous alumina membrane. In addition, different capping layers were deposited onto Co nanohills. Morphological and compositional analysis was performed by atomic force microscopy and x-ray photoemission spectroscopy techniques to obtain information about the surface characteristics. The observed asymmetry in the magnetization reversal process at low temperatures is ascribed to the exchange bias generated by the ferromagnetic-antiferromagnetic interface promoted by the presence of Co oxide detected in all the samples. Especially relevant is the case of the Cr capping, where an enhanced magnetic anisotropy in the Co/Cr interface is deduced.

Rosa, W. O.; Martinez, L.; Jaafar, M.; Asenjo, A.; Vazquez, M. [Instituto de Ciencias de Materiales de Madrid, CSIC Sor Juana Ines de la Cruz 3, Cantoblanco, Madrid 28049 (Spain)

2009-11-15

113

Synthesis and magnetic properties of large-area ferromagnetic cylindrical nanoshell and nanocup arrays  

NASA Astrophysics Data System (ADS)

Large-area arrays of magnetic Ni80Fe20 cylindrical nanoshells, nanocups, and perforated nanocups were synthesized using oblique deposition into topographical templates patterned using laser interference lithography. The geometry of the template and the tilt angle of the sample during deposition provide versatile control over the final geometry and dimension of nanostructures with thickness below 10 nm. Decreasing shell thickness led to a magnetization switching path between onion (bidomain) and reverse onion states, bypassing the vortex (flux-closed) state. The variation of magnetization reversal processes with geometry was characterized using vibrating sample magnetometry, and the results were in good agreement with micromagnetic simulations.

Wang, Z.; Shimon, G.; Liu, X.; Thompson, C. V.; Ross, C. A.; Choi, W. K.; Adeyeye, A. O.

2013-06-01

114

Pulse electrodeposition and electrochemical quartz crystal microbalance techniques for high perpendicular magnetic anisotropy cobalt nanowire arrays  

SciTech Connect

This research is focused on the development of pulse electrodeposition techniques to fabricate a high-density array of vertically oriented, high-magnetic anisotropy cobalt nanowires using a porous polymer film template. This type of array is a competitive candidate for future perpendicular magnetic media capable of storage densities exceeding 1 Terabit/in.{sup 2} The polymer template, derived from a self-assembling P(S-b-MMA) diblock copolymer film, provides precise control over the nanowire diameter (15 nm) and interwire spacing (24 nm), whereas nanowire length (typically 50 to 1000 nm) is controlled accurately with the aid of real-time electrochemical quartz crystal monitoring. Pulse and pulse-reversed electrodeposition techniques, as compared to dc, are shown to significantly enhance the perpendicular magnetic anisotropy of the magnetic nanowire array and ultimately result in coercivity as large as 2.7 kOe at 300 K. Magnetic and structural characterizations suggest that these properties arise from an improved degree of magnetocrystalline anisotropy (due to c-axis oriented crystal growth and improvements in crystal quality) that strongly supplements the basic shape anisotropy of the nanowires. Low temperature magnetometry is used to investigate exchange bias effects due to the incorporation of CoO antiferromagnetic impurities during the electrodeposition process and subsequent Co oxidation in air.

Ursache, Andrei; Goldbach, James T.; Russell, Thomas P.; Tuominen, Mark T. [Department of Physics, University of Massachusetts, 666 N Pleasant St., Hasbrouck Lab, Room 411, Amherst, Massachusetts 01003 (United States); Department of Polymer Science and Engineering, University of Massachusetts, 120 Governors Drive Amherst, Massachusetts 01003 (United States); Department of Physics, University of Massachusetts, 666 N Pleasant St., Hasbrouck Lab, Room 411, Amherst, Massachusetts 01003 (United States)

2005-05-15

115

Pulse electrodeposition and electrochemical quartz crystal microbalance techniques for high perpendicular magnetic anisotropy cobalt nanowire arrays  

NASA Astrophysics Data System (ADS)

This research is focused on the development of pulse electrodeposition techniques to fabricate a high-density array of vertically oriented, high-magnetic anisotropy cobalt nanowires using a porous polymer film template. This type of array is a competitive candidate for future perpendicular magnetic media capable of storage densities exceeding 1 Terabit/in.2 The polymer template, derived from a self-assembling P(S-b-MMA) diblock copolymer film, provides precise control over the nanowire diameter (15 nm) and interwire spacing (24 nm), whereas nanowire length (typically 50 to 1000 nm) is controlled accurately with the aid of real-time electrochemical quartz crystal monitoring. Pulse and pulse-reversed electrodeposition techniques, as compared to dc, are shown to significantly enhance the perpendicular magnetic anisotropy of the magnetic nanowire array and ultimately result in coercivity as large as 2.7 kOe at 300 K. Magnetic and structural characterizations suggest that these properties arise from an improved degree of magnetocrystalline anisotropy (due to c-axis oriented crystal growth and improvements in crystal quality) that strongly supplements the basic shape anisotropy of the nanowires. Low temperature magnetometry is used to investigate exchange bias effects due to the incorporation of CoO antiferromagnetic impurities during the electrodeposition process and subsequent Co oxidation in air.

Ursache, Andrei; Goldbach, James T.; Russell, Thomas P.; Tuominen, Mark T.

2005-05-01

116

Time Evolution of the Magnetic Field Topology of Cylindrical Wire Array Z-Pinches  

NASA Astrophysics Data System (ADS)

We study the influence of the magnetic field topology and the global field penetration time on the ablation plasma dynamics of individual wires in wire array Z-pinches. Knowledge of the magnetic field configuration is necessary for understanding the ablation plasma acceleration process near the wires and the validity of constant ablation velocity approximation as applied to the 1 MA COBRA pulsed power generator. Three-dimensional resistive MHD simulation results suggest that a change in the global magnetic field topology is critical to initiating inward flow of the ablation plasmas. These simulation results are investigated experimentally by using B-dot probes to track the evolution of the field topology over time for small wire number cylindrical arrays on COBRA. This research was supported by the Stewardship Sciences Academic Alliances program of the National Nuclear Security Administration under DOE Cooperative agreement DE-FC03-02NA00057.

Martin, Matthew; Greenly, John; Seyler, Charles

2007-11-01

117

Permanent-magnet helicon sources and arrays: A new type of rf plasma  

NASA Astrophysics Data System (ADS)

Helicon discharges are known for their ability to produce high densities of partially ionized plasma, their efficiency arising from an unusual mechanism of rf coupling. However, the requirement of a dc magnetic field has prevented their wide acceptance in industry. The use of permanent magnets greatly simplifies helicon sources, and arrays of small sources extend the use of helicons to the processing of large substrates. An eight-tube array was designed and constructed, and its density uniformity measured in a 53×165 cm2 chamber. Three innovations involved (a) the remote field of ring magnets, (b) a low-field density peak, and (c) rf power distribution. High-density plasmas uniform over large areas requires compatibility in all three areas.

Chen, Francis F.; Torreblanca, Humberto

2009-05-01

118

The Magnetic Spectrometer PRISMA Combined With Large Gamma Arrays  

SciTech Connect

The large solid angle magnetic spectrometer for heavy ions PRISMA was operated at LNL in conjunction with the highly efficient CLARA set-up up to the end of March 2008. The AGATA Demonstrator is being mounted around the target area of PRISMA replacing the CLARA set-up. It will allow to carry out nuclear structure and reaction mechanism studies with better resolution and higher statistics. New detectors for light ions and slow moving heavy ions have been designed for the focal plane of the spectrometer.

Fioretto, E.; Corradi, L.; Stefanini, A. M.; De Angelis, G.; Gadea, A.; Napoli, D. R.; Recchia, F.; Silvestri, R.; Valiente-Dobon, J. J. [INFN-Laboratori Nazionali di Legnaro, Viale dell'Universita 2, Legnaro (PD), 35020 (Italy); Beghini, S.; Bazzacco, D.; Farnea, E.; Mason, P.; Menegazzo, R.; Ur, C. A. [INFN Sez. di Padova, Via Marzolo 4, Padova, 35131 (Italy); Montagnoli, G.; Scarlassara, F.; Guiot, B.; Lenzi, S. M.; Lunardi, S. [Dipartimento di Fisica dell'Universita di Padova, Via Marzolo 4, Padova, 35131 (Italy); INFN Sez. di Padova, Via Marzolo 4, Padova, 35131 (Italy)] (and others)

2009-03-04

119

Reentrant quantum phase transitions in two capacitively coupled Josephson arrays in perpendicular magnetic fields  

SciTech Connect

We have studied the phase diagram structure of two capacitively coupled Josephson junction arrays as a function of their charging energy E{sub c}, Josephson coupling energy E{sub J}, and a homogeneous perpendicular magnetic field. The arrays are coupled via a site interaction capacitance, C{sub int}=C{sub inter}/C{sub m}, with C{sub inter} as the interlayer mutual capacitance and C{sub m} as the intralayer mutual capacitance defined as the nearest neighbor grain mutual capacitance. The parameter that measures the competition between thermal and quantum fluctuations in the ith array (i=1,2) is {alpha}{sub i}{identical_to}E{sub c{sub i}}/E{sub J{sub i}}. The phase structure of the system is dominated by the thermally induced and magnetically induced vortices as well as intergrain charge induced excitations. We have studied the capacitively coupled array behavior when one of them is in the vortex dominated regime, and the other in the quantum charge dominated regime. We determined the different possible phase boundaries by carrying out extensive quantum path integral Monte Carlo calculations of the helicity modulus {upsilon}{sub 1,2}({alpha},f) and the inverse dielectric constant {epsilon}{sub 1,2}{sup -1}({alpha},f) for each array as a function of temperature, interlayer capacitance C{sub int}, quantum parameter {alpha}, and frustration values f{identical_to}({phi}/{phi}{sub 0})=1/2 and f=1/3. Here, {phi} is the total flux in a plaquette and {phi}{sub 0} is the quantum of flux. We found an intermediate temperature range when array 1 is in the semiclassical regime ({alpha}{sub 1}=0.5) and array 2 is in the quantum regime with 1.25{<=}{alpha}{sub 2}<2, in which {upsilon}{sub 2}(T,{alpha},f=1/2)>0 and then goes down to zero while {epsilon}{sub 2}{sup -1}(T,{alpha},f=1/2) increases from zero up to a finite value. This behavior is similar to the one previously found for unfrustrated capacitively coupled arrays. However, for {alpha}{sub 2}=2.0, a reentrant transition in {upsilon}{sub 2}(T,{alpha},f=1/2) occurs at intermediate temperatures for C{sub int}=0.782 61, 1.043 48, and 1.304 35. For smaller values of the interlayer capacitance no phase coherence was found in array 2. This suggest that the increase between the array capacitive coupling induces a normal-superconducting-normal (N-SC-N) reentrant phase transition. For values of {alpha}{sub 2}>2.0, the quantum array only exhibits an insulating phase, while the semiclassical array shows a superconducting behavior. In contrast, for phase frustration, f=1/3, we found that when array 2 is in the full quantum regime, 2{<=}{alpha}{sub 2}{<=}4, the semiclassical array is the one that shows a reentrant N-SC-N behavior at relatively low temperatures. This reentrance in the coupled array behavior is a manifestation of the gauge invariant capacitive interaction and the duality relation between vortices, in the semiclassical array, and charges in the quantum-fluctuation dominated array. We find that the phase diagrams for f=1/2 and f=1/3 are very different in nature.

Ramirez-Santiago, Guillermo; Jose, Jorge V. [Departamento de Fisica-Quimica, Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apartado Postal 20-364, Mexico, 01000, Distrito Federal (Mexico); Department of Physics, Fronczak Hall, University at Buffalo, State University of New York, Buffalo, New York 14260-1500 (United States)

2008-02-01

120

MagArray Biochips for Protein and DNA Detection with Magnetic Nanotags: Design, Experiment, and Signal-to-Noise Ratio  

NASA Astrophysics Data System (ADS)

MagArray™ chips contain arrays of magnetic sensors, which can be used to detect surface binding reactions of biological molecules that have been labeled with 10 to 100 nm sized magnetic particles. Although MagArray chips are in some ways similar to fluorescence-based DNA array chips, the use of magnetic labeling tags leads to many distinct advantages, such as better background rejection, no label bleaching, inexpensive chip readers, potentially higher sensitivity, ability to measure multiple binding reactions in homogeneous assays simultaneously and in real-time, and seamless integration with magnetic separation techniques. So far, the technology of MagArray chips has been successfully used to perform quantitative analytic bioassays of both protein and nucleic acid targets. The potential of this technology, especially for point-of-care testing (POCT) and portable molecular diagnostics, appears promising, and it is likely that this technology will see significant further performance gains in the near future.

Osterfeld, Sebastian J.; Wang, Shan X.

121

Off-axis electron holography of magnetic nanowires and chains, rings, and planar arrays of magnetic nanoparticles  

Microsoft Academic Search

A selection of recent results illustrating the application of off-axis electron holog- raphy to the study of magnetic microstructure in closely-spaced nanoparticles and nanowires is reviewed. Examples are taken from the characterization of FeNi nanoparticle chains, Co nanopar- ticle rings, two-dimensional arrays of naturally occurring magnetite crystals in minerals, and single crystalline Co nanowires. Approaches that can be used to

Rafal E. Dunin-Borkowski; Takeshi Kasama; Alexander Wei; Steven L. Tripp; Etienne Snoeck; Richard J. Harrison; Andrew Putnis

2004-01-01

122

Numerical Study of a Crossed Loop Coil Array for Parallel Magnetic Resonance Imaging  

SciTech Connect

A coil design has been recently proposed by Temnikov (Instrum Exp Tech. 2005;48;636-637), with higher experimental signal-to-noise ratio than that of the birdcage coil. It is also claimed that it is possible to individually tune it with a single chip capacitor. This coil design shows a great resemble to the gradiometer coil. These results motivated us to numerically simulate a three-coil array for parallel magnetic resonance imaging and in vivo magnetic resonance spectroscopy with multi nuclear capability. The magnetic field was numerical simulated by solving Maxwell's equations with the finite element method. Uniformity profiles were calculated at the midsection for one single coil and showed a good agreement with the experimental data. Then, two more coils were added to form two different coil arrays: coil elements were equally distributed by an angle of a 30 deg. angle. Then, uniformity profiles were calculated again for all cases at the midsection. Despite the strong interaction among all coil elements, very good field uniformity can be achieved. These numerical results indicate that this coil array may be a good choice for magnetic resonance imaging parallel imaging.

Hernandez, J.; Solis, S. E.; Rodriguez, A. O. [Centro de Investigacion e Instrumentacion e Imagenoloia Medica, Universidad Autonoma Metropolitana Iztapalapa, Mexico DF 09340 (Mexico)

2008-08-11

123

Numerical Study of a Crossed Loop Coil Array for Parallel Magnetic Resonance Imaging  

NASA Astrophysics Data System (ADS)

A coil design has been recently proposed by Temnikov (Instrum Exp Tech. 200548636-637), with higher experimental signal-to-noise ratio than that of the birdcage coil. It is also claimed that it is possible to individually tune it with a single chip capacitor. This coil design shows a great resemble to the gradiometer coil. These results motivated us to numerically simulate a three-coil array for parallel magnetic resonance imaging and in vivo magnetic resonance spectroscopy with multi nuclear capability. The magnetic field was numerical simulated by solving Maxwell's equations with the finite element method. Uniformity profiles were calculated at the midsection for one single coil and showed a good agreement with the experimental data. Then, two more coils were added to form two different coil arrays: coil elements were equally distributed by an angle of a 30° angle. Then, uniformity profiles were calculated again for all cases at the midsection. Despite the strong interaction among all coil elements, very good field uniformity can be achieved. These numerical results indicate that this coil array may be a good choice for magnetic resonance imaging parallel imaging.

Hernández, J.; Solis, S. E.; Rodriguez, A. O.

2008-08-01

124

Magnetic properties of Ni-Fe nanowire arrays: effect of template material and deposition conditions  

SciTech Connect

The objective of this work is to study the magnetic properties of arrays of Ni-Fe nanowires electrodeposited in different template materials such as porous silicon, polycarbonate and alumina. Magnetic properties were studied as a function of template material, applied magnetic field (parallel and perpendicular) during deposition, wire length, as well as magnetic field orientation during measurement. The results show that application of magnetic field during deposition strongly influences the c-axis preferred orientation growth of Ni-Fe nanowires. The samples with magnetic field perpendicular to template plane during deposition exhibits strong perpendicular anisotropy with greatly enhanced coercivity and squareness ratio, particularly in Ni-Fe nanowires deposited in polycarbonate templates. In case of polycarbonate template, as magnetic field during deposition increases, both coercivity and squareness ratio also increase. The wire length dependence was also measured for polycarbonate templates. As wire length increases, coercivity and squarness ratio decrease, but saturation field increases. Such magnetic behavior (dependence on template material, magnetic field, wire length) can be qualitatively explained by preferential growth phenomena, dipolar interactions among nanowires, and perpendicular shape anisotropy in individual nanowires.

Singleton, John [Los Alamos National Laboratory; Aravamudhan, Shyan [U OF SOUTH FL; Goddard, Paul A [U OF OXFORD; Bhansali, Shekhar [U OF SOUTH FL

2008-01-01

125

Analysis of lightning induced magnetic field penetration through protective metal screens using an equivalent magnetic dipole moment representation of an array of elliptic apertures  

Microsoft Academic Search

This investigation analyzed lightning induced magnetic field penetration through protective metal screens using an equivalent magnetic dipole moment representation of an array of elliptic apertures. Two metal screens with differing aperture sizes were modeled. Experiments, using lightning level currents, measured the magnetic field penetration through each screen. A comparison of model versus experimental results was performed. The effect of decreasing

James L. Oneal

1986-01-01

126

A fully automated in vitro diagnostic system based on magnetic tunnel junction arrays and superparamagnetic particles  

NASA Astrophysics Data System (ADS)

A fully automated in vitro diagnostic (IVD) system for diagnosing acute myocardial infarction was developed using high sensitivity MTJ array as sensors and nano-magnetic particles as tags. On the chip is an array of 12 × 106 MTJ devices integrated onto a 3 metal layer CMOS circuit. The array is divided into 48 detection areas, therefore 48 different types of bio targets can be analyzed simultaneously if needed. The chip is assembled with a micro-fluidic cartridge which contains all the reagents necessary for completing the assaying process. Integrated with electrical, mechanical and micro-fluidic pumping devices and with the reaction protocol programed in a microprocessor, the system only requires a simple one-step analyte application procedure to operate and yields results of the three major AMI bio-markers (cTnI, MYO, CK-MB) in 15 mins.

Lian, Jie; Chen, Si; Qiu, Yuqin; Zhang, Suohui; Shi, Stone; Gao, Yunhua

2012-04-01

127

Magnetic properties of Fe20 Ni80 antidots: Pore size and array disorder  

NASA Astrophysics Data System (ADS)

Magnetic properties of nanoscale Fe20Ni80 antidot arrays with different hole sizes prepared on top of nanoporous alumina membranes have been studied by means of magnetometry and micromagnetic simulations. The results show a significant increase of the coercivity as well as a reduction of the remanence of the antidot arrays, as compared with their parent continuous film, which depends on the hole size introduced in the Fe20Ni80 thin film. When the external field is applied parallel to the antidots, the reversal of magnetization is achieved by free-core vortex propagation, whereas when the external field is applied perpendicular to the antidots, the reversal occurs through a process other than the coherent rotation (a maze-like pattern). Besides, in-plane hysteresis loops varying the angle show that the degree of disorder in the sample breaks the expected hexagonal symmetry.

Palma, J. L.; Gallardo, C.; Spinu, L.; Vargas, J. M.; Dorneles, L. S.; Denardin, J. C.; Escrig, J.

2013-10-01

128

SQUID (superconducting quantum interference device) arrays for simultaneous magnetic measurements: Calibration and source localization performance  

NASA Astrophysics Data System (ADS)

Recently developed small arrays of SQUID-based magnetic sensors can, if appropriately placed, locate the position of a confined biomagnetic source without moving the array. The authors present a technique with a relative accuracy of about 2 percent for calibrating such sensors having detection coils with the geometry of a second-order gradiometer. The effects of calibration error and magnetic noise on the accuracy of locating an equivalent current dipole source in the human brain are investigated for 5- and 7-sensor probes and for a pair of 7-sensor probes. With a noise level of 5 percent of peak signal, uncertainties of about 20 percent in source strength and depth for a 5-sensor probe are reduced to 8 percent for a pair of 7-sensor probes, and uncertainties of about 15 mm in lateral position are reduced to 1 mm, for the configuration considered.

Kaufman, Lloyd; Williamson, Samuel J.; Costaribeiro, P.

1988-02-01

129

Development of 3-D magnetic nano-arrays by electrodeposition into mesoporous silica  

Microsoft Academic Search

The development of periodic nanostructures fabricated by self-assembly of surfactants and block co-polymers has opened up the possibility of generating periodic magnetic nanostructures of types not accessible by self-assembly of nano-particles. The fabrication of mesoporous silica thin films around self-assembled block co-polymers is well established. Common structures for such films are SBA-15 which consists of hexagonal arrays of cylindrical pores

R. Campbell; J. Manning; M. G. Bakker; X. Li; D. R. Lee; J. Wang

2006-01-01

130

Preparation and characterization of highly ordered vanadium iron cyanide molecular magnet nanowire arrays  

Microsoft Academic Search

Highly ordered vanadium-iron cyanide molecular magnet nanowire arrays have been prepared for the first time using an electrodepositing technology with two-step anodized anodic aluminium oxide films. Selectable diameters and lengths of the nanowires can be obtained by controlling the diameters of the nanopores in the anodic aluminium oxide films and the electrodepositing time, respectively. X-ray diffraction and transmission electron microscopy

Pingheng Zhou; Desheng Xue; Haiqing Luo; Jinli Yao; Huigang Shi

2004-01-01

131

Covalent binding of streptavidin on gold magnetic nanoparticles for bead array fabrication.  

PubMed

In this study, we report the chemical synthesis and functionalization of streptavidin coated gold magnetic nanoparticles (GMNPs) and the immobilization of single-stranded biotinylated oligonucleotides onto these particles. By using covalent interaction or physical adsorption, two kinds of streptavidin coated GMNPs (SA-GMNPs) were prepared. The quantity and stability of streptavidin bound to the GMNPs using different methods were determined by UV-Vis spectrometer. The results indicated that by physical absorption the GMNPs can capture more streptavidin, the SA-GMNPs with either physical adsorption or covalent reaction were both stable in PBS buffer. In contrast, SA-GMNPs with covalent reaction was stable in SDS buffer, while most of the SA-GMNPs by physical adsorption would be eluted from the particles in SDS buffer. Therefore, the SA-GMNPs by covalent immobilization were more suitable for fabrication of bead array. To evaluate the binding efficiency and capacity of DNA on SA-GMNPs, the capture of biotinylated oligonucleotide or PCR products on SA-GMNPs at different concentrations were examined. A magnetic beads array was fabricated by immobilizing DNA-MNPs complexes onto a glass slide using a magnetic field. The synthesized DNA targets with different concentrations were detected with a detection limit of approximately 0.05 nM, indicating the potential application of this MNPs array to high-throughput DNA detection. PMID:21125822

Li, Song; Liu, Hongna; He, Nongyue

2010-08-01

132

A thin wire array and magnetic host structure with n<0  

NASA Astrophysics Data System (ADS)

Construction of artificial media possessing a negative index of refraction can be simplified by using a nonconducting ferrimagnetic host medium to provide a negative permeability and an array of conducting wires to provide a negative permittivity. The interaction between the ferrimagnet and the wire array, which destroys the negative permittivity of the wire array, can be overcome by cladding the wires with an insulating, nonmagnetic jacket. Calculations of the propagation constants and transmission coefficients for a square array of cladded wires in a ferrimagnetic host are presented. The calculations are near exact for wavelengths significantly greater than the lattice parameter of the wire array. For wires a few microns in diameter, a lattice constant of 0.8 mm, and an appropriate ferrimagnetic host in a biasing magnetic field, a transmission band 0.5 GHz wide centered near 16 GHz exhibits a negative index of refraction. Losses in the ferrimagnet and impedance mismatch to vacuum limit the peak transmission amplitude ratio through a slab 3.0 cm thick to ~3%.

Dewar, G.

2005-05-01

133

Dynamic performance of a permanent magnet brushless DC motor powered by a PV array for water pumping  

Microsoft Academic Search

The dynamic performance of a permanent magnet brushless DC (PMBDC) motor connected to photovoltaic (PV) array through an inverter is analyzed. The mathematical models of PV array, inverter\\/motor and controller are developed. The photovoltaic array is represented by an equivalent circuit whose parameters are computed using experimentally determined current-voltage (I–V) characteristics. The necessary computer algorithm is developed to analyze the

C. L. Putta Swamy; B. Singh

1995-01-01

134

Rotatable Magnetron Sputtering of Aluminium in Continuous and High Power Pulse Modes Using Different Strength Magnetic Arrays  

Microsoft Academic Search

This paper reports preliminary results of industrial size (152mm target O.D.) rotatable magnetron sputtering of Al target in Direct Current (DC) and High Power Impulse Magnetron Sputtering (HIPIMS) modes using two standard commercially available magnetic arrays: standard strength array (as used for DC and AC processing) and a lower strength ‘RF’ array [i.e. as used for radio frequency (RF) magnetron

Martynas Audronis; Victor Bellido-Gonzalez; Robert Brown

135

Rotatable magnetron sputtering of aluminium in continuous and high power pulse modes using different strength magnetic arrays  

Microsoft Academic Search

This paper reports preliminary results of industrial size (152mm target O.D.) rotatable magnetron sputtering of Al target in direct current (DC) and High Power Impulse Magnetron Sputtering (HIPIMS) modes using two standard commercially available magnetic arrays: standard strength array (as used for DC and AC processing) and a lower strength ‘RF’ array [i.e. as used for radio frequency (RF) magnetron

Martynas Audronis; Victor Bellido-Gonzalez; Robert Brown

136

Morphology dependent magnetic properties of two-dimensional alpha-Fe2O3 ordered nanostructured arrays.  

PubMed

Magnetic properties of two-dimensional alpha-Fe2O3 ordered bowl-like pore and ring arrays, fabricated by solution-dipping on a colloidal monolayer, were studied. All the alpha-Fe2O3 nanostructured arrays exhibit weak ferromagnetic properties at room temperature, while the hysteresis loops strongly depend on the morphology of the arrays. Some novel magnetic properties, such as plateau regions and jumps in hysteresis loops, have been observed for the ring and bowl-like pore arrays at room temperature, respectively. The morphology-dependent magnetic properties will exhibit the potential applications in nanodevices, such as giant magnetoresistance spin-valve devices and magnetic data storage. PMID:19452957

Li, Zhigang; Cai, Weiping; Duan, Guotao; Zeng, Haibo; Liu, Peisheng

2009-05-01

137

MAGNETIC INDUCTION MAPPING IN TEM OF MICRO AND NANO PATTERNED CO/NI ARRAYS.  

SciTech Connect

Understanding magnetic structures and properties of patterned magnetic films at nanometer length-scale is the area of immense technological and fundamental scientific importance. The patterned magnetic films can be used for magnetic sensing . applications, magnetic recording, magnetoelectronics, microactuators and hybrid magneto-superconducting devices. The optimization of film properties is crucially dependent on the understanding of their magnetic properties, which in turn, become sensitive to the specific geometry and, hence, magnetic configurations of a given system when the elements diminish in size. Recent progress in the field of noninterferometric phase retrieval brings the ordinary Fresnel microscopy to a new quantitative level, capable of recovering both the amplitude and phase of the object from the experimental images [1,2], and thus induction mapping of small magnetic elements with known geometry ranging from micro- to few nanometers in size. The key concept behind this approach is the improvement of phase recovery algorithm derived from the transport-of-intensity (TIE) equation with a fast-solution via Fourier transform. A number of quantitative in-situ TEM magnetization experiments can be realized now with the help of magnetic-field calibrated microscope (see, for example [3]). To demonstrate the practical use of the new approach in TEM magnetic imaging with nanoscale resolution we have prepared several films directly on 3mm TEM-grids: (a) square-patterned magnetic films of Co islands with size of 6 pm (Fig. 1), and (b) nano-patterned arrays of Ni-nanodots (Fig.2) with lateral size about 40nm. The Co-films were prepared in UHV system by electron-beam evaporation of Co through an appropriate mask onto 30-nm-thick Si{sub 3}N{sub 4} membrane. The thickness of magnetic elements was approximately 40 nm as determined by EELS. The array of Ni-nanodots on a carbon membrane was prepared by electron-beam TEM-nanolithography followed by oblique angle deposition. Both types of the patterned arrays for Co and Ni films have been characterized by the TEM/ED methods. They were found to have a polycrystalline microstructure with the average crystallite size {approx}10 and 7 nm respectively. The Co films consisted of mixture of cubic and hcp phases. To experimentally check the sensitivity of TIE-recovered phase information to local magnetic configurations a set of in-focus and out-of-focus images was recorded on CCD (llarlk) during the in-situ magnetizing experiments in JEOL3000F microscope at different magnifications using the Gatan Imaging Filter (GIF) as function of applied field (H) and/or specimen tilt angle ({var_phi}) under constant external field. The results of the image processing (Figs.1-2), strongly suggest that TIE-phase retrieval method is a powerful tool suitable for local induction mapping B(x,y) of in-plane magnetization of magnetic elements down to few nanometers scale. The method is fast, robust, insensitive to noise, does not require the holographic equipment, and can be applied to a wide class of objects. The quantitative results can be obtained for films of known or uniform thickness.

VOLKOV,V.V.; ZHU,Y.; MALAC,M.; LAU,J.W.; SCHOFIELD,M.A.

2002-08-04

138

2D to 3D crossover of the magnetic properties in ordered arrays of iron oxide nanocrystals.  

PubMed

The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain ?-Fe(2)O(3) spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC) simulations. Using the structural information of the arrays obtained from grazing incidence small-angle X-ray scattering and scanning electron microscopy together with the experimentally determined values for the saturation magnetization and magnetic anisotropy of the nanoparticles, we show that MC simulations can reproduce the thickness-dependent magnetic behavior. The magnetic dipolar particle interactions induce a ferromagnetic coupling that increases in strength with decreasing thickness of the array. The 2D to 3D transition in the magnetic properties is mainly driven by a change in the orientation of the magnetic vortex states with increasing thickness, becoming more isotropic as the thickness of the array increases. Magnetic anisotropy prevents long-range ferromagnetic order from being established at low temperature and the nanoparticle magnetic moments instead freeze along directions defined by the distribution of easy magnetization directions. PMID:23238262

Faure, Bertrand; Wetterskog, Erik; Gunnarsson, Klas; Josten, Elisabeth; Hermann, Raphaël P; Brückel, Thomas; Andreasen, Jens Wenzel; Meneau, Florian; Meyer, Mathias; Lyubartsev, Alexander; Bergström, Lennart; Salazar-Alvarez, German; Svedlindh, Peter

2012-12-13

139

Measurements of the cosmological evolution of magnetic fields with the Square Kilometre Array  

NASA Astrophysics Data System (ADS)

We investigate the potential of the Square Kilometre Array (SKA) for measuring the magnetic fields in clusters of galaxies via Faraday rotation of background polarized sources. The populations of clusters and radio sources are derived from an analytical cosmological model, combined with an extrapolation of current observational constraints. We adopt an empirical model for the Faraday screen in individual clusters, gauged to observations of nearby clusters and extrapolate the polarization properties for the radio source population from the National Radio Astronomy Observatory Very Large Array Sky Survey. We find that about 10 per cent of the sky is covered by a significant extragalactic Faraday screen. Most of it has rotation measures between 10 and 100 rad m-2. We argue that the cluster centres should have up to about 5000 rad m-2. We show that the proposed mid frequency aperture array of the SKA as well as the lowest band of the SKA dish array are well suited to make measurements for most of these rotation measure values, typically requiring a signal-to-noise ratio of 10. We calculate the spacing of sources forming a grid for the purpose of measuring foreground rotation measures: it reaches a spacing of 36 arcsec for a 100 h SKA observation per field. We also calculate the statistics for background rotation measure (RM) measurements in clusters of galaxies. We find that a first phase of the SKA would allow us to take stacking experiments out to high redshifts (>1), and provide improved magnetic field structure measurements for individual nearby clusters. The full SKA aperture array would be able to make very detailed magnetic field structure measurements of clusters with more than 100 background sources per cluster up to a redshift of 0.5 and more than 1000 background sources per cluster for nearby clusters, and could for reasonable assumptions about future measurements of electron densities in high-redshift clusters constrain the power-law index for the magnetic field evolution to better than ?m = 0.4, if the magnetic field in clusters should follow B ~ (1 + z)m.

Krause, Martin; Alexander, Paul; Bolton, Rosie; Geisbüsch, Jörn; Green, David A.; Riley, Julia

2009-12-01

140

Ambient-temperature passive magnetic bearings: Theory and design equations  

SciTech Connect

Research has been underway at the Lawrence Livermore National Laboratory to build a theoretical and experimental base for the design of ambient-temperature passive magnetic bearings for a variety of possible applications. in the approach taken the limitations imposed by Earnshaw`s theorem with respect to the stability of passive magnetic bearing systems employing axially symmetric permanent-magnet elements are overcome by employing special combinations of elements, as follows: Levitating and restoring forces are provided by combinations of permanent-magnet-excited elements chosen to provide positive stiffnesses (negative force derivatives) for selected displacements (i.e., those involving translations or angular displacement of the axis of rotation). As dictated by Eamshaw`s theorem, any bearing system thus constructed will be statically unstable for at least one of the remaining possible displacements. Stabilization against this displacement is accomplished by using periodic arrays (`Halbach arrays`) of permanent magnets to induce currents in close-packed inductively loaded circuits, thereby producing negative force derivatives stabilizing the system while in rotation. Disengaging mechanical elements stabilize the system when at rest and when below a low critical speed. The paper discusses theory and equations needed for the design of such systems.

Post, R.F.; Ryutov, D.D.

1997-12-30

141

Coupled microstructural and magnetic transition in Co-doped Ni nano-arrays  

NASA Astrophysics Data System (ADS)

A superparamagnetic (SM) to ferromagnetic (FM) phase transition was investigated in Co-doped (~6%) electroless plated Ni arrays. The introduction of Co altered the microstructure of the Ni arrays from nanocrystalline to polycrystalline, resulting in a SM-->FM transition. This Co-induced magnetic phase transition is similar to that observed after heat treatment of undoped samples [C. M. Liu, Y. C. Tseng, C. Chen, M. C. Hsu, T. Y. Chao, and Y. T. Cheng, Nanotechnology 20, 415703 (2009); C. C. Huang, C. C. Lo, Y. C. Tseng, C. M. Liu, and C. Chen, J. Appl. Phys. 109, 113905 (2011)]. The role of Co dopant was identified electronically using x-ray magnetic spectroscopy, revealing that the transition modified the Ni host's electronic structure and enhanced its moment by effectively spin-polarizing the Ni 3d conduction band. This was distinctly different than in the heat treatment case, which underwent an electronically independent phase transition. The element-specific magnetic hysteresis of Co and Ni was also probed, which showed that the two elements were magnetically coupled.

Yang, Chao-Yao; Huang, Chun-Chao; Tseng, Yuan-Chieh; Liu, Chien-Min; Chen, Chih; Lin, Hong-Ji

2011-10-01

142

Magnetic anisotropy in CoNi nanowire arrays: Analytical calculations and experiments  

NASA Astrophysics Data System (ADS)

Ordered arrays of CoxNi1-x nanowires (0magnetic properties (e.g., hysteresis curves and their parameters as well as first-order reversal curve analysis), paying particular attention to their angular dependence. It is confirmed that the crystal phase of nanowires with length 2.5 ?m and diameter 35 nm shifts from hcp to fcc as the Ni content increases. That results in a significant modification of the magnetization process and, accordingly, of the magnetic properties of the array. Analytical calculations of the angular dependence of the coercivity allow us to confirm that the magnetization reversal is mostly ascribed to the propagation of a transverse domain wall. Fitting of the experiment to these calculations indicates the presence of a transverse crystalline anisotropy (ascribed to the hcp phase) in Co wires, while this changes to an axial anisotropy (fcc phase) as the Ni content increases.

Vivas, L. G.; Vazquez, M.; Escrig, J.; Allende, S.; Altbir, D.; Leitao, D. C.; Araujo, J. P.

2012-01-01

143

Size effects in ordered arrays of magnetic nanotubes: Pick your reversal mode  

NASA Astrophysics Data System (ADS)

Ordered arrays of magnetic nanotubes are prepared by combining a porous template (anodic alumina) with a self-limiting gas-solid chemical reaction (atomic layer deposition). The geometric parameters can thus be tuned accurately (tube length of 1-50 ?m, diameter of 20-150 nm, and wall thickness of 1-40 nm), which enables one to systematically study how confinement and anisotropy effects affect the magnetic properties. In particular, the wall thickness of such ordered Fe3O4 nanotubes has a nonmonotonic influence on their coercive field. Theoretical models reproduce the size effects that are experimentally observed and interpret them as originating from a crossover between two distinct modes of magnetization reversal.

Bachmann, Julien; Escrig, Juan; Pitzschel, Kristina; Moreno, Josep M. Montero; Jing, Jing; Görlitz, Detlef; Altbir, Dora; Nielsch, Kornelius

2009-04-01

144

FAST TRACK COMMUNICATION: Gyration mode splitting in magnetostatically coupled magnetic vortices in an array  

NASA Astrophysics Data System (ADS)

We present the experimental observation of gyration mode splitting by the time-resolved magneto-optical Kerr effect in an array consisting of magnetostatically coupled Ni81Fe19 discs of 1 µm diameter, 50 nm thickness and inter-disc separations varying between 150 and 270 nm. A splitting of the vortex core gyration mode is observed when the inter-disc separation is 200 nm or less and the splitting is controllable by a bias magnetic field. The observed mode splitting is interpreted by micromagnetic simulations as the normal modes of the vortex cores analogous to the coupled classical oscillators. The splitting depends upon the strength of the inter-disc magnetostatic coupling mediated by magnetic side charges, which depends strongly on the magnetic ground states of the samples.

Barman, Anjan; Barman, Saswati; Kimura, T.; Fukuma, Y.; Otani, Y.

2010-10-01

145

Neutralization of space charge in magnetic field by electrons supplied from silicon based field emitter arrays  

NASA Astrophysics Data System (ADS)

Neutralization of the space charge in a magnetic field by the electrons supplied from a silicon based field emitter array (Si-FEA) was experimentally investigated. In this report, we have studied the trajectory of electrons emitted from a Si-FEA. The relationship between these electrons and diverging ion beam was experimentally studied. As a result, we have found that both the emitting position and the energy of the electrons were important to neutralize the diverging ion beam. In case the magnetic field was stronger than 15 mT, the electrons were trapped by the magnetic field and so removed from the ion beam, as the result, the ion beam was diverged. Ion beam neutralization was well done using low energy electrons less than 5 eV.

Daimaru, Tomohiro; Sakai, Shigeki; Gotoh, Yasuhito

2012-11-01

146

The domain formation in Fe/Ni/Fe nanoscale magnetic antidot arrays  

NASA Astrophysics Data System (ADS)

In this paper we report the superconducting quantum interference device (SQUID) and magnetic force microscope (MFM) measurements of magnetic multilayer nanoscale antidot samples. The systems used consist of Fe(60 A?)/Ni(90 A?)/Fe(60 A?) (FeNiFe) multilayer antidots with hexagonal lattice fabricated on nanochannel glass (NCG) substrates with antidot diameters of 260, 362, 530, and 800 nm. The results indicate that the domain structure is commensurate with the holes due to the pinning effect of the antidots. This pinning effect is inversely proportional to the diameter of the antidots. The field dependent MFM data show that the hexagonal antidot lattice induces a weak anisotropy with the magnetic easy axis along the nearest neighbor direction. The unit cell in the antidot arrays could be used for data storage.

Cheng, Ruihua; Rosenberg, A.; McIlroy, D. N.; Holman, Z.; Zhang, D.; Kranov, Y.

2012-03-01

147

A Novel SNPs Detection Method Based on Gold Magnetic Nanoparticles Array and Single Base Extension  

PubMed Central

To fulfill the increasing need for large-scale genetic research, a high-throughput and automated SNPs genotyping method based on gold magnetic nanoparticles (GMNPs) array and dual-color single base extension has been designed. After amplification of DNA templates, biotinylated extension primers were captured by streptavidin coated gold magnetic nanoparticle (SA-GMNPs). Next a solid-phase, dual-color single base extension (SBE) reaction with the specific biotinylated primer was performed directly on the surface of the GMNPs. Finally, a “bead array” was fabricated by spotting GMNPs with fluorophore on a clean glass slide, and the genotype of each sample was discriminated by scanning the “bead array”. MTHFR gene C677T polymorphism of 320 individual samples were interrogated using this method, the signal/noise ratio for homozygous samples were over 12.33, while the signal/noise ratio for heterozygous samples was near 1. Compared with other dual-color hybridization based genotyping methods, the method described here gives a higher signal/noise ratio and SNP loci can be identified with a high level of confidence. This assay has the advantage of eliminating the need for background subtraction and direct analysis of the fluorescence values of the GMNPs to determine their genotypes without the necessary procedures for purification and complex reduction of PCR products. The application of this strategy to large-scale SNP studies simplifies the process, and reduces the labor required to produce highly sensitive results while improving the potential for automation.

Li, Song; Liu, Hongna; Jia, Yingying; Deng, Yan; Zhang, Liming; Lu, Zhuoxuan; He, Nongyue

2012-01-01

148

High sensitivity, inductively coupled miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows  

SciTech Connect

A modified {dot {ital B}} circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment [R. M. Mayo {ital et} {ital al}., Plasma Sources Sci. Technol. {bold 4}, 47 (1995)] at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow laboratory study of magnetogasdynamics with particular emphasis on the importance of the Hall effect [D. C. Black {ital et} {ital al}., Phys. Plasma {bold 1}, 3115 (1994)] and plasma microinstabilities [R. M. Mayo {ital et} {ital al}., Phys. Plasma {bold 2}, 337 (1995)] to plasma transport in coaxial plasma sources. The miniature magnetic probe array consists of ten spatially separated coils wound on an Acetal form of dimensions 2.38 cm by 0.32 cm by 0.32 cm. At five positions, with roughly 0.32 cm separation, two mutually perpendicular coils are wound to measure the magnetic field in the {cflx {theta}} and {cflx {ital z}} directions. The modification to the signal processing circuitry consists of the use of a step-up transformer to boost the probe signal prior to filtering and acquiring the signal at the data acquisition system. This additional means of amplifying the signal allows for reduction in the size of the probe, and thus helps minimize the perturbing effect of the magnetic probe on the plasma. An additional advantage of using a signal transformer is that it provides electrical isolation between the experiment and the data acquisition system. {copyright} {ital 1996 American Institute of Physics.}

Black, D.C.; Mayo, R.M. [Department of Nuclear Engineering, North Carolina State University, Raleigh, North Carolina 27695-7909 (United States)

1996-04-01

149

Ion Beam Stabilization of FePt Nanoparticle Arrays for Magnetic Storage Media  

SciTech Connect

The authors describe the use of ion beam induced crosslinking to harden the organic matrix material of self-assembled arrays of monodisperse (4 nm) FePt nanoparticles, providing diamondlike carbon barriers to inhibit agglomeration of the nanoparticles under heat treatment. Such stabilization is necessary for the particles to survive the > 500 C annealing required for growth of the fct L 1{sub 0} phase of FePt, whose magnetic anisotropy is necessary for application of such arrays for high density perpendicular recording. Selective area irradiation of continuous nanoparticle coatings, using ion beams patterned over a full disk by stencil mask or with ion projection optics, followed by dissolution of the unexposed coating, is proposed as a means of fabricating extended bit patterns consisting of isolated islands of FePt nanoparticles, with characteristic dimensions of tens of nanometers.

Toney, Michael F

2003-07-31

150

Spectral gap of shear Alfvén waves in a periodic array of magnetic mirrors  

NASA Astrophysics Data System (ADS)

A multiple magnetic mirror array is formed at the Large Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)] to study axial periodicity-influenced Alfvén spectra. Shear Alfvén waves (SAW) are launched by antennas inserted in the LAPD plasma and diagnosed by B-dot probes at many axial locations. Alfvén wave spectral gaps and continua are formed similar to wave propagation in other periodic media due to the Bragg effect. The measured width of the propagation gap increases with the modulation amplitude as predicted by the solutions to Mathieu's equation. A two-dimensional finite-difference code modeling SAW in a mirror array configuration shows similar spectral features. Machine end-reflection conditions and damping mechanisms including electron-ion Coulomb collision and electron Landau damping are important for simulation.

Zhang, Yang; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Chen, Guangye; Breizman, B. N.; Vincena, S.; Carter, T.; Leneman, D.; Gekelman, W.; Pribyl, P.; Brugman, B.

2008-01-01

151

Spectral Gap of Shear Alfv'en Waves in a Periodic Array of Magnetic Mirrors  

NASA Astrophysics Data System (ADS)

A multiple magnetic mirror array is formed at the LArge Plasma Device (LAPD), to study axial periodicity-influenced Alfv'en spectra. Shear Alfv'en Waves (SAW) are launched by antennas inserted in the LAPD plasma. From radial wave field scans with B-dot probes at many axial locations, SAW standing-wave formation and wave refraction in mirror cell(s) are observed. Alfv'en wave spectral gaps and continua are formed similar to wave propagation in other periodic media due to the Bragg effect. The width of the propagation gap scales with the modulation amplitude according to the solutions of Mathieu's equation. A 2-D finite-difference code modeling SAW in a mirror array configuration shows similar spectral features. Machine end-reflection conditions and damping mechanisms including electron-ion Coulomb collision and electron Landau damping are important for simulation.

McWilliams, Roger; Zhang, Yang; Heidbrink, William; Boehmer, Heinz; Chen, Guangye; Breizman, Boris; Vincena, Stephen; Carter, Troy; Leneman, David; Gekelman, Walter; Brugman, Brian

2007-11-01

152

A Gravito-Magnetic Trap for Measuring the Neutron Lifetime using Ultracold Neutrons  

NASA Astrophysics Data System (ADS)

There continues to be a significant discrepancy amongst the most precise measurements of the neutron lifetime. To help resolve this, the lifetime experiment at the Los Alamos Neutron Science Center (LANSCE) will use polarized ultracold neutrons (UCN) trapped by gravity in an asymmetric compound toroidal trap made of permanent magnets arranged in a high field gradient configuration called a Halbach array. Progress has been made on constructing the LANL experiment which removes marginally trapped UCN, a problematic systematic effect in previous measurements, with a compound toroid and a rippled multipole field that can quickly reduce the fraction of phase space of the trap that is quasi-bound, decreasing the probability that UCN escape or have material interactions during the lifetime measuring period.

Hickerson, Kevin

2009-10-01

153

Synthesis and Magnetism of High Curie Temperature Prussian Blue Analogue Molecular Nanomagnet-Chromium Cyanide Molecule Nanowire Arrays  

Microsoft Academic Search

The goal to synthesize molecular nanomagnets that exhibit spontaneous magnetic ordering close to room temperature might enable one to apply them in the fields of magnetic memory devices and microelectronics. Chromium cyanide molecule nanowire arrays with diameters of about 50 nm and lengths up to 4mum have been synthesized by an electrodepositing technology based on anodizing anodic aluminum oxide films.

Pingheng Zhou; Desheng Xue; Jinli Yao

2009-01-01

154

Electrodeposition and magnetic properties of ternary Fe-Co-Ni alloy nanowire arrays with high squareness ratio  

NASA Astrophysics Data System (ADS)

Highly-ordered ternary Fe-Co-Ni alloy nanowire arrays with diameters of about 50 nm have been fabricated by alternating current (AC) electrodeposition into the nanochannels of porous anodic aluminum oxide templates. SEM and TEM results indicate that the alloy nanowires are highly ordered. XRD and HRTEM results show that the ternary FeCoNi alloy nanowires are polycrystalline, with HCP-FCC dual phase structure. Magnetic measurements demonstrate that the ternary alloy nanowire arrays have an obvious magnetic anisotropy with an easy magnetization direction being parallel to the nanowire arrays. Along the easy magnetization direction, the coercivity (H c ) and squareness ratio (S) increase as the annealing temperature increases, and reach a maximum level (H c = 1337 Oe, S = 0.96) at 300 °C.

Fu, P.; Chen, G.; Xu, Y.; Cai, P.; Wang, X. H.

2012-09-01

155

Standing-wave excited soft x-ray photoemission microscopy: application to Co microdot magnetic arrays  

SciTech Connect

We demonstrate the addition of depth resolution to the usual two-dimensional images in photoelectron emission microscopy (PEEM), with application to a square array of circular magnetic Co microdots. The method is based on excitation with soft x-ray standing-waves generated by Bragg reflection from a multilayer mirror substrate. Standing wave is moved vertically through sample simply by varying the photon energy around the Bragg condition. Depth-resolved PEEM images were obtained for all of the observed elements. Photoemission intensities as functions of photon energy were compared to x-ray optical calculations in order to quantitatively derive the depth-resolved film structure of the sample.

Gray, Alexander; Kronast, Florian; Papp, Christian; Yang, See-Hun; Cramm, Stefan; Krug, Ingo P.; Salmassi, Farhad; Gullikson, Eric M.; Hilken, Dawn L.; Anderson, Erik H.; Fischer, Peter; Durr, Hermann A.; Schneider, Claus M.; Fadley, Charles S.

2010-10-29

156

The ENIGMA project: a ground-based magnetic array for space research  

NASA Astrophysics Data System (ADS)

National Observatory of Athens (NOA) currently operates ENIGMA (HellENIc GeoMagnetic Array), an array of 4 ground-based magnetometer stations in the area of south-eastern Europe (central and southern Greece). The current stations are latitudinally equi-spaced between 30° and 33° corrected geomagnetic latitude. In the near future another station will be installed in Macedonia or Thrace, and there are plans for the installation of an additional station in Crete by mid-2010. One of the primary research objectives assigned to ENIGMA is the study of geomagnetic field line resonances (FLRs). The latter is a well-established phenomenon taking place in the Earth's magnetosphere. It can be pictured as the formation of standing magnetohydrodynamic waves on magnetic field lines with fixed ends at the conjugate ionospheres. An interesting option in this field of research would be to compare ultra-low-frequency (ULF) wave observations in space made by ESA's Cluster mission and on the ground acquired by these mid-to-low-latitude ground-based observation sites of the Earth's magnetic field. Cluster has a high inclination orbit; insofar studies at high latitudes are more justified for direct interactions along the magnetic field lines. So, for a Cluster-ENIGMA study one has to expect some indirect, somehow related reactions with propagations perpendicular to the B-field. The Cluster-ENIGMA study can serve as a pilot-study for the upcoming Swarm mission of ESA. The Swarm constellation of spacecraft will allow, for the first time, the unique determination of the near-Earth field aligned currents, which connect various regions of the magnetosphere with the ionosphere and can be regarded as a complement to the Cluster mission.

Daglis, I. A.; Balasis, G.; Anastasiadis, A.; Ganas, A.; Melis, N.; Baumjohann, W.; Magnes, W.; Mandea, M.; Lesur, V.; Korte, M.

2010-05-01

157

Broadband Magnetic Resonance Measurements on Periodic Patterned Disc and Hole Arrays  

NASA Astrophysics Data System (ADS)

We have made broadband ferromagnetic resonance measurements on patterned permalloy arrays consisting of circular dots (discs) and both square and circular anti-dots (holes). We employ a transmission meander line approach as opposed to a resonant cavity technique, and cover the frequency range 10MHz to 20GHz. Experiments are performed at a fixed frequency by sweeping the field (through positive and negative values) and at a fixed field while varying the frequency; both magnetic field and frequency modulation are employed to suppress noise and background effects. Experiments on hole arrays show two dominant resonances which from their symmetry appear to be standing spin waves centered at the X- points of the square Brillouin zone. Low field measurements on disc arrays where the field is swept over varying ranges in the region where the sample is hysteretic while tracking the history dependent disappearance and reappearance of the uniform FMR mode, allows a determination of the phase boundaries separating the single and double vortex states, and are in agreement with simulations by Rivkin.

Sklenar, J.; Bhat, V. S.; Delong, L.; Metlushko, V.; Tsai, C. C.; Chernyashevskyy, O.; Rivkin, K.; Ketterson, J. B.

2011-03-01

158

Hign acceleration with a rotating radiofrequency coil array (RRFCA) in parallel magnetic resonance imaging (MRI).  

PubMed

This study explores the performance of a novel hybrid technology, in which the recently introduced rotating RF coil (RRFC) was combined with the principles of Parallel Imaging (PI) to improve the quality and speed of magnetic resonance (MR) images. To evaluate the system, a low-density naturally-decoupled 4-channel rotating radiofrequency coil array (RRFCA) was modelled and investigated. The traditional SENSitivity Encoding (SENSE) reconstruction method and the means of calculating the geometry factor distribution (g map) were adapted to take into account the transient sensitivity encoding. It was found from simulations at 3T that, continuous rotating motion considerably enhanced the coil sensitivity encoding capability, making higher reduction factors in scan time possible. The sensitivity encoding capability can be further improved by choosing an optimal speed of array rotation. Compared to traditional phased-array coils (PACs) with twice as many coil elements, the RRFCA demonstrated clear advantages in terms of quality of reconstruction and superior noise behaviour in all the cases investigated in this initial study. PMID:23366087

Li, Mingyan; Jin, Jin; Trakic, Adnan; Liu, Feng; Weber, Ewald; Li, Yu; Crozier, Stuart

2012-01-01

159

Transport measurements on a thin Nb film with square array of nanoscale magnetic dots.  

NASA Astrophysics Data System (ADS)

Transport measurements (R vs. T, R vs. B, and V-I characteristics) were made on a thin Nb film deposited on top of a square array of nanoscale magnetic dots [1]. These measurements established that in many ways this system behaved like a Josephson junction array (JJA). We hypothesized that the stray magnetic field of the dots reduced the superconductivity in the Nb film in such a way as to make the film a superconductor-weaker superconductor-superconductor (S-S-S) JJA. Studies of the VIs in the presence of a radio frequency (rf) signal revealed the appearance of Shapiro steps in the VI's. The voltage location at which the steps occurred follow the Josephson relation Vn=n*N*(h/2)*?, where n=1,2,3, etc, N is the number of junctions along the current direction, and ? is the frequency of the rf signal. Sample provided by Dr. Axel Hoffmann from Argonne National Laboratory and Dr. Ivan K. Schuller from UCSD. [1] J. I. Martin, Y. Jaccard, A. Hoffmann, J. Nogues, J. M. George, J. I. Vicent, and I. K. Schuller, J. Appl. Physics. 84, 411 (1998)

Gómez, Luis B.; Mast, David B.

2002-03-01

160

Non-lift-off block copolymer lithography of 25 nm magnetic nanodot arrays.  

PubMed

Although nanolithographic techniques based on self-assembled block copolymer templates offer tremendous potential for fabrication of large-area nanostructure arrays, significant difficulties arise with both the lift-off and etch processes typically used for pattern transfer. These become progressively more important in the limit of extreme feature sizes. The few techniques that have been developed to avoid these issues are quite complex. Here, we demonstrate successful execution of a nanolithographic process based on solvent annealed, cylinder-forming, easily degradable, polystyrene-b-polylactide block copolymer films that completely avoids lift-off in addition to the most challenging aspects of etching. We report a "Damascene-type" process that overfills the polystyrene template with magnetic metal, employs ion beam milling to planarize the metal surface down to the underlying polystyrene template, then exploits the large etch rate contrast between polystyrene and typical metals to generate pattern reversal of the original template into the magnetic metal. The process is demonstrated via formation of a large-area array of 25 nm diameter ferromagnetic Ni(80)Fe(20) nanodots with hexagonally close-packed order. Extensive microscopy, magnetometry, and electrical measurements provide detailed characterization of the pattern formation. We argue that the approach is generalizable to a wide variety of materials, is scalable to smaller feature sizes, and critically, minimizes etch damage, thus preserving the essential functionality of the patterned material. PMID:21830808

Baruth, A; Rodwogin, Marc D; Shankar, A; Erickson, M J; Hillmyer, Marc A; Leighton, C

2011-08-25

161

Harmonic magnetic field reconstruction from external sensor arrays on HBT-EP  

NASA Astrophysics Data System (ADS)

In the vacuum region surrounding a toroidal plasma, it is natural to decompose the perturbed magnetic field in terms of an orthogonal representation of the magnetic scalar potential. In HBT-EP, the relatively thin radial region between the conducting wall and the plasma surface is large-aspect ratio (R/a˜6), and as a first approximation we expand the perturbed magnetic field in a cylindrical representation, as B=?m,n??m,n, where ?m,n=?m,n(r)e^i(m?-n). Because HBT-EP has more than 200 magnetic sensors distributed in both toroidal and poloidal arrays, we have been able to reconstruct the perturbed vacuum field harmonic amplitudes, ?m,n as a function of time under a variety of conditions, including variations of the plasma equilibrium and the magnitude of applied error fields. Using these harmonic amplitudes, we describe how to compute the Maxwell stress tensor in the vacuum region and to estimate the net torque on the plasma exerted by the surrounding resistive wall and error field coils.

Peng, Q.; Rath, N.; Levesque, J. P.; Byrne, P. J.; Shiraki, D.; Cole, A.; Mauel, M. E.; Navratil, G. A.

2012-10-01

162

Scintillation detectors for operation in high magnetic fields: Recent developments based on arrays of avalanche microchannel photodiodes  

NASA Astrophysics Data System (ADS)

The development of scintillation detectors to be used in a high-magnetic-field environment requires novel photodetectors to substitute photomultiplier tubes (PMTs). Avalanche microchannel photodiodes (AMPDs) are competitive to PMTs in terms of gain and photon detection efficiency, and they are insensitive to magnetic fields. But the small active area of an AMPD (typically from 1 to 10mm) could restrict the field of applications for such a photosensor. In this work we demonstrate that the above restriction can be, to a certain extent, overcome by using AMPD arrays: based on an array of four (1×1mm) AMPDs we built scintillation detectors with promising characteristics.

Scheuermann, R.; Stoykov, A.; Renker, D.; Sadygov, Z.; Mehtieva, R.; Dovlatov, A.; Zhuk, V.

2007-10-01

163

Formations of magnetic vortices in a chain array of triangle Py dots and an isosceles triangle Py dot  

NASA Astrophysics Data System (ADS)

We have studied the magnetic domain structures in a magneto-statically-coupled chain array of the triangle dots and an isosceles triangle dot by means of magnetic force microscopy (MFM). Despite the strong magneto-static interaction in the chain array of the dots, each triangle dot takes a single vortex structure. The chirality of each dot is found to behave similarly to that for the isolated triangle dot. We also demonstrated that single-vortex and double-vortex structures with the desired chiralities can be stabilized in an isosceles triangle dot.

Miyata, M.; Kiseki, K.; Yakata, S.; Wada, H.; Kimura, T.

2012-04-01

164

Room- and low-temperature magnetic properties of 2-D magnetite particle arrays  

NASA Astrophysics Data System (ADS)

Palaeomagnetic observations are being used in increasingly sophisticated geological and geophysical interpretations. It is therefore important to test the theories behind palaeomagnetic recording by rocks, and this can only be achieved using samples containing precisely controlled magnetic mineralogy, grain size and interparticle spacing, the last of which controls the degree of magnetostatic interactions within the samples. Here we report the room- and low temperature magnetic behaviour of a set of samples produced by the nano-scale patterning technique electron beam lithography. The samples consist of 2-D arrays of near-identical magnetite dots of various sizes, geometries and spatial configurations, with dot sizes from ranging from near the single domain threshold of 74-333 nm. We have made a series of magnetic measurements including hysteresis, first-order-reversal curve measurements and remanence acquisition, many as a function of temperature between 20 and 300 K, to quantify the samples’ behaviour to routine palaeomagnetic measurement procedures. We have also examined the behaviour of saturation isothermal remanences (SIRM) to cooling and warming cycling of the sample below room temperature. In addition, we investigated the samples’ responses to alternating-field demagnetization of room temperature induced SIRM, anhysteretic remanent magnetization (ARM) and partial ARM. ARM was used as a non-heating analogue for natural thermoremanence. Given the 2-D spatial distribution of the samples, in all the experiments we conducted both in-plane and out-of-plane measurements. Generally, the samples were found to display pseudo-single-domain hysteresis characteristics, but were found to be reliable recorders of weak-field remanences like ARM. For the closely packed samples, the samples’ magnetic response was highly dependent on measurement orientation.

Krása, David; Muxworthy, Adrian R.; Williams, Wyn

2011-04-01

165

Magnetic design of trim excitations for the advanced light source storage ring sextupole  

SciTech Connect

The Advanced Light Source (ALS) storage ring sextupole is a unique multi-purpose magnet. It is designed to operate as a sextupole with three auxiliary trim modes: horizontal steering, vertical steering, and skew quadrupole. A perturbation theory for iron-dominated magnets developed by Klaus Halbach provides the basis for this design. The three trim excitations are produced by violating sextupole symmetry and are thus perturbations of the normal sextupole excitation. The magnet was designed such that all four modes are decoupled and can be excited independently. This paper discusses the use of Halbach`s perturbation theory to design the trim functions and to evaluate the primary asymmetry in the sextupole mode, namely, a gap in the return yoke to accommodate the vacuum chamber.

Marks, S.

1995-06-01

166

Magnetic design of trim excitations for the Advanced Light Source storage ring sextupole  

SciTech Connect

The Advanced Light Source (ALS) storage ring sextupole is a unique multi-purpose magnet. It is designed to operate as a sextupole with three auxiliary trim modes: horizontal steering, vertical steering, and skew quadrupole. A perturbation theory for iron-dominated magnets developed by Klaus Halbach provides the basis for this design. The three trim excitations are produced by violating sextupole symmetry and are thus perturbations of the normal sextupole excitation. The magnet was designed such that all four modes are decoupled and can be excited independently. This paper discusses the use of Halbach`s perturbation theory to design the trim functions and to evaluate the primary asymmetry in the sextupole mode, namely, a gap in the return yoke to accommodate the vacuum chamber.

Marks, S. [Lawrence Berkeley Lab., CA (United States)

1996-07-01

167

Correlations among magnetic, electrical and magneto-transport properties of NiFe nanohole arrays  

NASA Astrophysics Data System (ADS)

In this work, we use anodic aluminum oxide (AAO) templates to build NiFe magnetic nanohole arrays. We perform a thorough study of their magnetic, electrical and magneto-transport properties (including the resistance R(T), and magnetoresistance MR(T)), enabling us to infer the nanohole film morphology, and the evolution from granular to continuous film with increasing thickness. In fact, different physical behaviors were observed to occur in the thickness range of the study (2 nm < t < 100 nm). For t < 10 nm, an insulator-to-metallic crossover was visible in R(T), pointing to a granular film morphology, and thus being consistent with the presence of electron tunneling mechanisms in the magnetoresistance. Then, for 10 nm < t < 50 nm a metallic R(T) allied with a larger anisotropic magnetoresistance suggests the onset of morphological percolation of the granular film. Finally, for t > 50 nm, a metallic R(T) and only anisotropic magnetoresistance behavior were obtained, characteristic of a continuous thin film. Therefore, by combining simple low-cost bottom-up (templates) and top-down (sputtering deposition) techniques, we are able to obtain customized magnetic nanostructures with well-controlled physical properties, showing nanohole diameters smaller than 35 nm.

Leitao, D. C.; Ventura, J.; Teixeira, J. M.; Sousa, C. T.; Pinto, S.; Sousa, J. B.; Michalik, J. M.; De Teresa, J. M.; Vazquez, M.; Araujo, J. P.

2013-02-01

168

Probing cellular traction forces with magnetic nanowires and microfabricated force sensor arrays  

NASA Astrophysics Data System (ADS)

In this paper, the use of magnetic nanowires for the study of cellular response to force is demonstrated. High-aspect ratio Ni rods with diameter 300 nm and lengths up to 20 ?m were bound to or internalized by pulmonary artery smooth muscle cells (SMCs) cultured on arrays of flexible micropost force sensors. Forces and torques were applied to the cells by driving the nanowires with AC magnetic fields in the frequency range 0.1-10 Hz, and the changes in cellular contractile forces were recorded with the microposts. These local stimulations yield global force reinforcement of the cells’ traction forces, but this contractile reinforcement can be effectively suppressed upon addition of a calcium channel blocker, ruthenium red, suggesting the role of calcium channels in the mechanical response. The responsiveness of the SMCs to actuation depends on the frequency of the applied stimulation. These results show that the combination of magnetic nanoparticles and micropatterned, flexible substrates can provide new approaches to the study of cellular mechanotransduction.

Lin, Yi-Chia; Kramer, Corinne M.; Chen, Christopher S.; Reich, Daniel H.

2012-02-01

169

Precision formed micro magnets: LDRD project summary report  

SciTech Connect

A microfabrication process is described that provides for the batch realization of miniature rare earth based permanent magnets. Prismatic geometry with features as small as 5 microns, thicknesses up through several hundred microns and with submicron tolerances may be accommodated. The processing is based on a molding technique using deep x-ray lithography as a means to generate high aspect-ratio precision molds from PMMA (poly methyl methacrylate) used as an x-ray photoresist. Subsequent molding of rare-earth permanent magnet (REPM) powder combined with a thermosetting plastic binder may take place directly in the PMMA mold. Further approaches generate an alumina form replicated from the PMMA mold that becomes an intermediate mold for pressing higher density REPM material and allows for higher process temperatures. Maximum energy products of 3--8 MGOe (Mega Gauss Oersted, 1 MGOe = 100/4{pi} kJ/m{sup 3}) are obtained for bonded isotropic forms of REPM with dimensions on the scale of 100 microns and up to 23 MGOe for more dense anisotropic REPM material using higher temperature processing. The utility of miniature precision REPMs is revealed by the demonstration of a miniature multipole brushless DC motor that possesses a pole-anisotropic rotor with dimensions that would otherwise prohibit multipole magnetization using a multipole magnetizing fixture at this scale. Subsequent multipole assembly also leads to miniaturized Halbach arrays, efficient magnetic microactuators, and mechanical spring-like elements which can offset miniaturized mechanical scaling behavior.

CHRISTENSON,TODD R.; GARINO,TERRY J.; VENTURINI,EUGENE L.

2000-02-01

170

Enhanced Asymmetric Magnetization Reversal in Nanoscale Co\\/CoO Arrays: Competition between Exchange Bias and Magnetostatic Coupling  

Microsoft Academic Search

Magnetization reversal was studied in square arrays of square Co\\/CoO dots with lateral size varying between 200 and 900nm. While reference nonpatterned Co\\/CoO films show the typical shift and increased width of the hysteresis loop due to exchange bias, the patterned samples reveal a pronounced size dependence. In particular, an anomaly appears in the upper branch of the magnetization cycle

E. Girgis; R. D. Portugal; H. Loosvelt; M. J. van Bael; I. Gordon; M. Malfait; K. Temst; C. van Haesendonck; L. H. Leunissen; R. Jonckheere

2003-01-01

171

Development of novel techniques to study the magnetic field evolution in wire array Z-pinches and X pinches  

Microsoft Academic Search

Understanding the magnetic field topology in wire-array Z-pinches is of great significance for their ultimate application to stockpile stewardship and inertial confinement fusion. We have developed and tested several novel techniques involving material-based sensors to measure magnetic fields as a function of space and time in high energy density plasmas on pulsed power machines. We first briefly introduce a technique

Wasif Syed

2010-01-01

172

Giant positive magnetoresistance of Bi nanowire arrays in high magnetic fields  

SciTech Connect

We have studied the magnetoresistance of electrodeposited Bi wires with diameters between 200 nm and 2 {mu}m in magnetic fields up to B=55T. In zero field, the resistance increases with decreasing temperature, indicating that the mean free path is strongly influenced by the nanowire geometry. The high-field magnetoresistance shows strong dependence on field orientation; typically 200{percent} for B parallel to the wires, and 600{percent}{endash}800{percent} for B perpendicular to the wires. The perpendicular magnetoresistance is well described by a modified two-current model which suggests that the high-field response of the arrays is fairly insensitive to the wire diameter, and is dominated by bulk properties of Bi. {copyright} {ital 1999 American Institute of Physics.}

Hong, K.; Yang, F.Y.; Liu, K.; Reich, D.H.; Searson, P.C.; Chien, C.L. [The Johns Hopkins University, Baltimore, Maryland 21218 (United States); Balakirev, F.F.; Boebinger, G.S. [Bell Laboratories, Lucent Technologies, 700 Mountain Avenue, Murray Hill, New Jersey 07974 (United States)]|[Los Alamos National Laboratory, MS E534, Los Alamos, New Mexico 87545 (United States)

1999-04-01

173

Size and space controlled hexagonal arrays of superparamagnetic iron oxide nanodots: magnetic studies and application  

PubMed Central

Highly dense hexagonally arranged iron oxide nanodots array were fabricated using PS-b-PEO self-assembled patterns. The copolymer molecular weight, composition and choice of annealing solvent/s allows dimensional and structural control of the nanopatterns at large scale. A mechanism is proposed to create scaffolds through degradation and/or modification of cylindrical domains. A methodology based on selective metal ion inclusion and subsequent processing was used to create iron oxide nanodots array. The nanodots have uniform size and shape and their placement mimics the original self-assembled nanopatterns. For the first time these precisely defined and size selective systems of ordered nanodots allow careful investigation of magnetic properties in dimensions from 50?nm to 10?nm, which delineate the nanodots are superparamagnetic, well-isolated and size monodispersed. This diameter/spacing controlled iron oxide nanodots systems were demonstrated as a resistant mask over silicon to fabricate densely packed, identical ordered, high aspect ratio silicon nanopillars and nanowire features.

Ghoshal, Tandra; Maity, Tuhin; Senthamaraikannan, Ramsankar; Shaw, Matthew T.; Carolan, Patrick; Holmes, Justin D.; Roy, Saibal; Morris, Michael A.

2013-01-01

174

Size and space controlled hexagonal arrays of superparamagnetic iron oxide nanodots: magnetic studies and application.  

PubMed

Highly dense hexagonally arranged iron oxide nanodots array were fabricated using PS-b-PEO self-assembled patterns. The copolymer molecular weight, composition and choice of annealing solvent/s allows dimensional and structural control of the nanopatterns at large scale. A mechanism is proposed to create scaffolds through degradation and/or modification of cylindrical domains. A methodology based on selective metal ion inclusion and subsequent processing was used to create iron oxide nanodots array. The nanodots have uniform size and shape and their placement mimics the original self-assembled nanopatterns. For the first time these precisely defined and size selective systems of ordered nanodots allow careful investigation of magnetic properties in dimensions from 50?nm to 10?nm, which delineate the nanodots are superparamagnetic, well-isolated and size monodispersed. This diameter/spacing controlled iron oxide nanodots systems were demonstrated as a resistant mask over silicon to fabricate densely packed, identical ordered, high aspect ratio silicon nanopillars and nanowire features. PMID:24072037

Ghoshal, Tandra; Maity, Tuhin; Senthamaraikannan, Ramsankar; Shaw, Matthew T; Carolan, Patrick; Holmes, Justin D; Roy, Saibal; Morris, Michael A

2013-09-27

175

Structure and magnetic properties of Fe96- x Zr x B4 nanowire arrays  

NASA Astrophysics Data System (ADS)

Fe96- x Zr x B4 (1< x<12) nanowires were prepared by electrodepositing into anodic aluminum oxide templates. The diameter of nanowires used is 100 nm and the aspect ratio is 75. The structure of the nanowire arrays was studied by selected area electron diffraction, X-ray diffraction and Mössbauer spectrometer. The phase structure of Fe96- x Zr x B4 nanowires is changed from a crystalline phase to a homogenous amorphous phase with the increasing of Zr content. The Fe96- x Zr x B4 nanowires are composed of ?-Fe-like and Zr-rich FeZrB phases. With the increasing of Zr composition, the atoms of Fe site in both phases are more disorderly, and the ?-Fe-like phase decreasing with the FeZrB phase increasing. The anisotropy of Fe96- x Zr x B4 nanowires becomes more obvious with the increasing of Zr content, and the easy magnetizing axis is parallel to the nanowire arrays.

Fu, JunLi; Zhu, Min; Wang, WenZhong; Xue, DeSheng

2013-10-01

176

Electromagnetic vibration energy harvesting with high power density using a magnet array  

NASA Astrophysics Data System (ADS)

Electromagnetic vibration energy harvesters have been widely used to convert the vibration energy into electricity. However, one of the main challenges of using electromagnetic vibration energy harvesters is that they are usually in very large size with low power density. In this paper, a new type of electromagnetic vibration energy harvester with remarkably high power density is developed. By putting the strong rare-earth magnets in alternating directions and using high-magnetic-conductive casing, magnetic flux density up to 0.9T are obtained. This configuration also has a small current loop with less electrical reluctance, which further increases the high power density when the coil is designed to follow the current loop. The prototype, the size of which is 142x140x86 mm3, can provided up to 727Ns/m damping coefficient, which means 428 kNs/m4 damping density when it is shunt with 70? external resistive load which is set to the same as the internal resistor of the harvester to achieve maximum power. The corresponding power density is 725 ?W/cm3 at 15HZ harmonic force excitation of 2.54mm peak-to-peak amplitude. When shot-circuited, 1091Ns/m damping coefficient and 638 kNs/m4 damping density is achieved. The effectiveness of this novel vibration energy harvester is shown both by FEA and experiments. The eddy current damper is also discussed in this paper for comparison. The proposed configuration of the magnet array can also be extended for both micro-scale and large-scale energy harvesting applications, such as vibration energy harvesting from tall buildings, long bridges and railways.

Tang, Xiudong; Lin, Teng; Zuo, Lei

2012-03-01

177

Development of a high sensitivity, inductively coupled, miniature magnetic probe array for detailed measurement of time varying magnetic field profiles in plasma flows  

Microsoft Academic Search

A modified B˙ circuit design has been implemented as part of a miniature magnetic probe array for the Coaxial Plasma Source experiment at the North Carolina State University. This facility is currently being used for the generation of energetic plasma flows to allow laboratory study of magnetogasdynamics with particular emphasis on the importance of the Hall effect to plasma transport

D. C. Black; R. M. Mayo

1995-01-01

178

A digital magnetic resonance imaging spectrometer using digital signal processor and field programmable gate array  

NASA Astrophysics Data System (ADS)

A digital spectrometer for low-field magnetic resonance imaging is described. A digital signal processor (DSP) is utilized as the pulse programmer on which a pulse sequence is executed as a subroutine. Field programmable gate array (FPGA) devices that are logically mapped into the external addressing space of the DSP work as auxiliary controllers of gradient control, radio frequency (rf) generation, and rf receiving separately. The pulse programmer triggers an event by setting the 32-bit control register of the corresponding FPGA, and then the FPGA automatically carries out the event function according to preset configurations in cooperation with other devices; accordingly, event control of the spectrometer is flexible and efficient. Digital techniques are in widespread use: gradient control is implemented in real-time by a FPGA; rf source is constructed using direct digital synthesis technique, and rf receiver is constructed using digital quadrature detection technique. Well-designed performance is achieved, including 1 ?s time resolution of the gradient waveform, 1 ?s time resolution of the soft pulse, and 2 MHz signal receiving bandwidth. Both rf synthesis and rf digitalization operate at the same 60 MHz clock, therefore, the frequency range of transmitting and receiving is from DC to ~27 MHz. A majority of pulse sequences have been developed, and the imaging performance of the spectrometer has been validated through a large number of experiments. Furthermore, the spectrometer is also suitable for relaxation measurement in nuclear magnetic resonance field.

Liang, Xiao; Binghe, Sun; Yueping, Ma; Ruyan, Zhao

2013-05-01

179

A digital magnetic resonance imaging spectrometer using digital signal processor and field programmable gate array.  

PubMed

A digital spectrometer for low-field magnetic resonance imaging is described. A digital signal processor (DSP) is utilized as the pulse programmer on which a pulse sequence is executed as a subroutine. Field programmable gate array (FPGA) devices that are logically mapped into the external addressing space of the DSP work as auxiliary controllers of gradient control, radio frequency (rf) generation, and rf receiving separately. The pulse programmer triggers an event by setting the 32-bit control register of the corresponding FPGA, and then the FPGA automatically carries out the event function according to preset configurations in cooperation with other devices; accordingly, event control of the spectrometer is flexible and efficient. Digital techniques are in widespread use: gradient control is implemented in real-time by a FPGA; rf source is constructed using direct digital synthesis technique, and rf receiver is constructed using digital quadrature detection technique. Well-designed performance is achieved, including 1 ?s time resolution of the gradient waveform, 1 ?s time resolution of the soft pulse, and 2 MHz signal receiving bandwidth. Both rf synthesis and rf digitalization operate at the same 60 MHz clock, therefore, the frequency range of transmitting and receiving is from DC to ~27 MHz. A majority of pulse sequences have been developed, and the imaging performance of the spectrometer has been validated through a large number of experiments. Furthermore, the spectrometer is also suitable for relaxation measurement in nuclear magnetic resonance field. PMID:23742570

Liang, Xiao; Binghe, Sun; Yueping, Ma; Ruyan, Zhao

2013-05-01

180

Preparation and characterization of highly ordered vanadium iron cyanide molecular magnet nanowire arrays  

NASA Astrophysics Data System (ADS)

Highly ordered vanadium-iron cyanide molecular magnet nanowire arrays have been prepared for the first time using an electrodepositing technology with two-step anodized anodic aluminium oxide films. Selectable diameters and lengths of the nanowires can be obtained by controlling the diameters of the nanopores in the anodic aluminium oxide films and the electrodepositing time, respectively. X-ray diffraction and transmission electron microscopy measurement results show that the vanadium-iron cyanide nanowires are straight, continuous, and highly crystalline with a face-centred cubic cubic structure of a = 10.14 Å. The x-ray photoelectron system, Mössbauer spectrum and infrared spectrum measurement results indicate that the oxidation state of the metal ions in the vanadium-iron nanowires can be expressed as V4+-CN-Fe2+. The hysteresis loop of the vanadium-iron cyanide nanowires at 1.9 K indicates that there are magnetic exchange interactions between vanadium and iron ions in the nanowires.

Zhou, Pingheng; Xue, Desheng; Luo, Haiqing; Yao, Jinli; Shi, Huigang

2004-01-01

181

Synthesis and Magnetism of High Curie Temperature Prussian Blue Analogue Molecular Nanomagnet-Chromium Cyanide Molecule Nanowire Arrays  

NASA Astrophysics Data System (ADS)

The goal to synthesize molecular nanomagnets that exhibit spontaneous magnetic ordering close to room temperature might enable one to apply them in the fields of magnetic memory devices and microelectronics. Chromium cyanide molecule nanowire arrays with diameters of about 50 nm and lengths up to 4?m have been synthesized by an electrodepositing technology based on anodizing anodic aluminum oxide films. Characterization measurements show that the oxidation state of the chromium ions in the chromium cyanide nanowires can be expressed as Cr^3+--CN--Cr^3+. Magnetic properties measurements indicate that the Curie temperature of chromium cyanide nanowire is 200 K, which is closer room temperature compared with current molecular nanomagnet systems.

Zhou, Pingheng; Xue, Desheng; Yao, Jinli

2009-03-01

182

Optimal Design of Rotary-Type Voice Coil Motor Using Multisegmented Magnet Array for Small Form Factor Optical Disk Drive  

NASA Astrophysics Data System (ADS)

For a small form factor optical disk drive (SFFODD), a high-performance actuator satisfying the requirements for small size, high speed, and low-power consumption simultaneously is required. In this paper, we propose a rotary-type voice coil motor (VCM) using a multisegmented magnet array (MSMA) for the SFFODD. The VCM is designed to move the entire system including miniaturized optical components, which are necessary in reading and writing data. To increase the actuating force of the VCM, the MSMA, a novel magnetic circuit, is adopted because it can provide a higher flux density than a conventional magnet array in the rotary-type VCM. To obtain the best performance from the VCM in the limit of actuator size, design optimization is performed. The manufactured actuator with optimally designed parameters is described and the potential performance of track seeking is evaluated and presented.

Jeong, Jaehwa; Gweon, Dae-Gab

2007-05-01

183

Thiol-capped ZnO nanowire/nanotube arrays with tunable magnetic properties at room temperature.  

PubMed

The present study reports room-temperature ferromagnetic behaviors in three-dimensional (3D)-aligned thiol-capped single-crystalline ZnO nanowire (NW) and nanotube (NT) arrays as well as polycrystalline ZnO NT arrays. Besides the observation of height-dependent saturation magnetization, a much higher M(s) of 166 microemu cm(-2) has been found in NTs compared to NWs (36 microemu cm(-2)) due to larger surface area in ZnO NTs, indicating morphology-dependent magnetic properties in ZnO NW/NT systems. Density functional calculations have revealed that the origin of ferromagnetism is mainly attributed to spin-polarized 3p electrons in S sites and, therefore, has a strong correlation with Zn-S bond anisotropy. The preferential magnetization direction of both single-crystalline NTs and NWs lies perpendicular to the tube/wire axis due to the aligned high anisotropy orientation of the Zn-S bonds on the lateral (100) face of ZnO NWs and NTs. Polycrystalline ZnO NTs, however, exhibit a preferential magnetization direction parallel to the tube axis which is ascribed to shape anisotropy dominating the magnetic response. Our results demonstrate the interplay of morphology, dimensions, and crystallinity on spin alignment and magnetic anisotropy in a 3D semiconductor nanosystem with interfacial magnetism. PMID:20028113

Deng, Su-Zi; Fan, Hai-Ming; Wang, Miao; Zheng, Min-Rui; Yi, Jia-Bao; Wu, Rong-Qin; Tan, Hui-Ru; Sow, Chorng-Haur; Ding, Jun; Feng, Yuan-Ping; Loh, Kian-Ping

2010-01-26

184

Giant magnetoresistance sensors. 1. Internally calibrated readout of scanned magnetic arrays.  

PubMed

This paper describes efforts aimed at setting the stage for the application of giant magnetoresistance sensor (GMRs) networks as readers for quantification of biolytes selectively captured and then labeled with superparamagnetic particles on a scanned chip-scale array. The novelty and long-range goal of this research draws from the potential development of a card-swipe instrument through which an array of micrometer-sized, magnetically tagged addresses (i.e., a sample stick) can be interrogated in a manner analogous to a credit card reader. This work describes the construction and testing of a first-generation instrument that uses a GMR sensor network to read the response of a "simulated" sample stick. The glass sample stick is composed of 20-nm-thick films of permalloy that have square or rectangular lateral footprints of up to a few hundred micrometers. Experiments were carried out to gain a fundamental understanding of the dependence of the GMR response on the separation between, and planarity of, the scanned sample stick and sensor. Results showed that the complex interplay between these experimentally controllable variables strongly affect the shape and magnitude of the observed signal and, ultimately, the limit of detection. This study also assessed the merits of using on-sample standards as internal references as a facile means to account for small variations in the gap between the sample stick and sensor. These findings were then analyzed to determine various analytical figures of merit (e.g., limit of detection in terms of the amount of magnetizable material on each address) for this readout strategy. An in-depth description of the first-generation test equipment is presented, along with a brief discussion of the potential widespread applicability of the concept. PMID:18826239

Nordling, John; Millen, Rachel L; Bullen, Heather A; Porter, Marc D; Tondra, Mark; Granger, Michael C

2008-10-01

185

Spacing-dependent dipolar interactions in dendronized magnetic iron oxide nanoparticle 2D arrays and powders  

NASA Astrophysics Data System (ADS)

Self-assembly of nanoparticles (NPs) into tailored structures is a promising strategy for the production and design of materials with new functions. In this work, 2D arrays of iron oxide NPs with interparticle distances tuned by grafting fatty acids and dendritic molecules at the NPs surface have been obtained over large areas with high density using the Langmuir-Blodgett technique. The anchoring agent of molecules and the Janus structure of NPs are shown to be key parameters driving the deposition. Finally the influence of interparticle distance on the collective magnetic properties in powders and in monolayers is clearly demonstrated by DC and AC SQUID measurements. The blocking temperature TB increases as the interparticle distance decreases, which is consistent with the fact that dipolar interactions are responsible for this increase. Dipolar interactions are found to be stronger for particles assembled in thin films compared to powdered samples and may be described by using the Vogel Fulcher model.Self-assembly of nanoparticles (NPs) into tailored structures is a promising strategy for the production and design of materials with new functions. In this work, 2D arrays of iron oxide NPs with interparticle distances tuned by grafting fatty acids and dendritic molecules at the NPs surface have been obtained over large areas with high density using the Langmuir-Blodgett technique. The anchoring agent of molecules and the Janus structure of NPs are shown to be key parameters driving the deposition. Finally the influence of interparticle distance on the collective magnetic properties in powders and in monolayers is clearly demonstrated by DC and AC SQUID measurements. The blocking temperature TB increases as the interparticle distance decreases, which is consistent with the fact that dipolar interactions are responsible for this increase. Dipolar interactions are found to be stronger for particles assembled in thin films compared to powdered samples and may be described by using the Vogel Fulcher model. Electronic supplementary information (ESI) available: TEM images and size distribution of NP@L1 and NP@L2; infrared spectra of functionalized nanoparticles; size distribution determined by Dynamic Light Scattering (DLS) measurements; SEM images of a monolayer obtained by the Langmuir-Blodgett technique of iron oxide NPs synthesized by the thermal decomposition method and then coated with phosphonate dendrimers NP@L3P and carboxylate dendrimers NP@L3C. See DOI: 10.1039/c2nr32117c

Fleutot, Solenne; Nealon, Gareth L.; Pauly, Matthias; Pichon, Benoit P.; Leuvrey, Cédric; Drillon, Marc; Gallani, Jean-Louis; Guillon, Daniel; Donnio, Bertrand; Begin-Colin, Sylvie

2013-01-01

186

Parallel magnetic resonance imaging with localized arrays and Sinc interpolation (PILARS)  

Microsoft Academic Search

Large arrays with localized coil sensitivity make it possible to use parallel imaging to significantly accelerate MR imaging speed. However, the need for auto calibration signals limits the actual acceleration factors achievable with large arrays. This paper presents a novel method for parallel imaging with large arrays. The method uses Sinc kernels for k-space data interpolation that only requires one

Shuo Feng; Jim Ji

2011-01-01

187

Analysis and design of magnetic mesa-structure array for ensemble detection applications of nuclear spins  

Microsoft Academic Search

Micro\\/nano fabrication of magnetic materials is becoming a crucial technology for future magnetic systems\\/devices such as high-density magnetic recording heads, high-density patterned media, magnetic quantum devices, and micro\\/nano magnetic smart systems, etc. In our previous work, NiFe alloy with the highest saturation magnetic-flux density was selected as the micro-magnet for detecting the feasibility of all- silicon quantum computer. The micro-magnet

Xiaoqiang Li; Dong F. Wang; Ryutaro Maeda

2011-01-01

188

Design and Experimental Verification of a Linear Permanent Magnet Generator for a Free-Piston Energy Converter  

Microsoft Academic Search

This paper discusses issues that are pertinent to the design of a linear permanent magnet generator for application in a free-piston energy converter. To achieve the required high power density, high efficiency, and low moving mass, a tubular machine equipped with a modular stator winding and a quasi-Halbach magnetized armature is employed. It is shown that the machine design can

Jiabin Wang; David Howe; Hector Zelaya-De La Parra; Waqas M. Arshad

2007-01-01

189

A novel automated assay with dual-color hybridization for single-nucleotide polymorphisms genotyping on gold magnetic nanoparticle array.  

PubMed

A high-throughput and cost-effective single-nucleotide polymorphism (SNP) genotyping method based on a gold magnetic nanoparticle (GMNP) array with dual-color hybridization has been designed. Biotinylated single-strand polymerase chain reaction (PCR) products containing the SNP locus were captured by the GMNPs that were coated with streptavidin. The GMNP array was fabricated by immobilizing single-stranded DNA (ssDNA)-GMNP complexes onto a glass slide using a magnetic field, and SNPs were identified with dual-color fluorescence hybridization. Three different SNP loci from 24 samples were genotyped successfully using this platform. This procedure allows the user to directly analyze the bead fluorescence to determine the SNP genotype, and it eliminates the need for background subtraction for signal determination. This method also bypasses tedious PCR purification and concentration procedures, and it facilitates large-scale SNP studies by using a method that is highly sensitive, simple, labor-saving, and potentially automatable. PMID:20507822

Li, Song; Liu, Hongna; Liu, Lishang; Tian, Lan; He, Nongyue

2010-05-25

190

Remanent magnetization states and interactions in square arrays of 100-nm cobalt dots measured using transmission electron microscopy  

NASA Astrophysics Data System (ADS)

Large area square arrays of circular cobalt dots, nominally 100 nm in diameter and 20 nm in thickness, were patterned using interference lithography. Magnetic remanent states were measured using off-axis electron holography in the transmission electron microscope (TEM). The results show that the dots are mostly single domain, although vortex states and multidomain configurations are occasionally observed. Significant magnetic interactions between adjacent dots result in variations in their magnetization direction away from the direction of the applied field. The suitability of such dots for data storage applications is discussed. Quantitative magnetic phase measurements were also obtained by applying the transport of intensity equation to images acquired using the Fresnel mode of Lorentz microscopy in the TEM. The consistency between the electron holography and transport of intensity equation (TIE) results is assessed.

Bromwich, T. J.; Kohn, A.; Petford-Long, A. K.; Kasama, T.; Dunin-Borkowski, R. E.; Newcomb, S. B.; Ross, C. A.

2005-09-01

191

Enhanced magnetic performance of metal-organic nanowire arrays by FeCo/polypyrrole co-electrodeposition  

NASA Astrophysics Data System (ADS)

FeCo/polypyrrole (PPy) composite nanowire array, which shows enhanced magnetic remanence and coercivity along the nanowires, was fabricated by AC electrodeposition using anodic aluminum oxide templates. High resolution transmission electron microscopy shows that PPy grows on the surface of FeCo nanowires forming a coaxial nanowire structure, with a coating layer of about 4 nm. It suggests that the decreased dipolar interaction due to the reduced nanowire diameters is responsible for the enhancement of magnetic performance. The possible mechanism of this coating may be that PPy is inclined to nucleate along the pore wall of the templates.

Luo, X. J.; Xia, W. B.; Gao, J. L.; Zhang, S. Y.; Li, Y. L.; Tang, S. L.; Du, Y. W.

2013-05-01

192

A fast integral equation method for simulating high-field radio frequency coil arrays in magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

A fast full-wave numerical approach was developed for simulating high-field multi-channel radio-frequency (RF) receive coil arrays in magnetic resonance imaging. To improve the efficiency, the impedance matrix was compressed by a multilevel adaptive cross approximation method. Furthermore, careful organization of multiple coil simulations was applied so that the impedance matrix associated with biological subjects is constructed and pre-conditioned only once. Numerical examples demonstrate the efficacy of the proposed approach for RF coil simulations.

Wang, Shumin; de Zwart, Jacco A.; Duyn, Jeff H.

2011-05-01

193

A compact Hall-effect sensor array for the detection and imaging of single magnetic beads in biomedical assays  

Microsoft Academic Search

A 64-unit Hall-effect sensor array capable of detecting magnetic beads is implemented in 0.18 ?m CMOS process. Two Hall sensor implementations, one using n-wells and another using MOS transistors, are analyzed. The n-well implementation can detect a single 4.5 ?m bead in .5 ms with a probability of error below 1% while the MOS implementation takes 2.5 ms to detect

K. Skucha; P. Liu; M. Megens; J. Kim; B. Boser

2011-01-01

194

Small angle x-ray and neutron scattering study of disordered and three dimensional-ordered magnetic protein arrays  

NASA Astrophysics Data System (ADS)

The magnetic nanoparticles of Fe3O4-?-Fe2O3 grown inside the cavity of globular proteins (apoferritin)-magnetoferritin proved to be a useful model system for studying the fundamental effects of magnetostatic interactions in nanoparticle assemblies. In this work the main focus is on structural characterization of such new nanocomposites by small angle x-ray scattering (SAXS) and small angle neutron scattering to evaluate interparticle separation (center to center) in two types of assemblies: three dimensional periodic arrays and disordered (amorphous) assemblies. Straightforward analysis of the face-centered cubic pattern of periodic arrays revealed that the interparticle spacing is 9.9 nm, whereas the SAXS pattern of disordered assembly reveals three correlation lengths, one of which is 10.5 nm and corresponds to the interparticle (center-to-center) nearest neighbor distance. The magnetic behaviors of the two systems are distinctly different. Given that the interparticle separation differs by only ~0.6 nm, the main structural factor contributing to the observed differences in magnetic properties is likely to be the array order.

Kasyutich, O.; Tatchev, D.; Hoell, A.; Ogrin, F.; Dewhurst, C.; Schwarzacher, W.

2009-04-01

195

Dynamics of nano-scale magnetic vortices in ferromagnetic dot arrays  

Microsoft Academic Search

We investigate analytically and numerically the dynamics of magnetostatically coupled vortices in ferromagnetic dot arrays. Eigenfrequencies of rotational motion of vortex core in two nano-dots are calculated by using the rigid vortex model and Thiele's equation where collective degrees of freedom describe the motion of each vortex core. We further extend the model to array of magnetostatically coupled N×N dots

J. Shibata; K. Shigeto; Y. Otani

2004-01-01

196

High-Density, Low-Mating-Force, Magnetically-Coupled, Percutaneous Connector for Implanted Electrode Arrays  

Microsoft Academic Search

As the fields of neuroscience and neural engineering have advanced, chronic implantable microelectrode arrays with 16 to 256 active channels have reached widespread use. However, implanted connector systems for these arrays have not received much attention and are a common source of experiment failure and irregularities. Intermittent connections, unreliable mechanical coupling, contamination, breaks and failures of materials, and high mating

C. F. Smith; K. S. Guillory

2007-01-01

197

Research on ambient temperature passive magnetic bearings at the Lawrence Livermore National Laboratory  

SciTech Connect

Research performed at the Lawrence Livermore National Laboratory on the equilibrium and stability of a new class of ambient-temperature passive bearing systems is described. The basic concepts involved are: (1) Stability of the rotating system is only achieved in the rotating state. That is, disengaging mechanical systems are used to insure stable levitation at rest (when Earnshaw`s theorem applies). (2) Stable levitation by passive magnetic elements can be achieved if the vector sum of the force derivatives of the several elements of the system is net negative (i.e. restoring) for axial, transverse, and tilt-type perturbations from equilibrium. To satisfy the requirements of (2) using only permanent magnet elements we have employed periodic ``Halbach arrays.`` These interact with passive inductive loaded circuits and act as stabilizers, with the primary forces arising from axially symmetric permanent-magnet elements. Stabilizers and other elements needed to create compact passive magnetic bearing systems have been constructed. Novel passive means for stabilizing classes of rotor-dynamic instabilities in such systems have also been investigated.

Post, R.F.; Ryitov, D.D.` Smith, J.R.; Tung, L.S.

1997-04-01

198

Spectral properties of electromotive force induced by periodic magnetization reversal of arrays of coupled magnetic glass-covered microwires  

NASA Astrophysics Data System (ADS)

In this paper we present the calculated spectra of signals originating from the magnetization reversal of a system of two identical bistable magnetic moments. We show that in contrast to the spectrum characteristic of magnetization reversal in any common ferromagnetic material, the amplitude of the harmonics in the calculated spectra can change periodically. Also, we present experimental spectra of signals induced by the magnetization reversal of two magnetically coupled glass-covered. Periodic variation of the harmonics amplitude predicted by the calculations was observed in the experimental spectra.

Rodionova, V.; Ilyn, M.; Ipatov, M.; Zhukova, V.; Perov, N.; Zhukov, A.

2012-04-01

199

Fabrication of Ni–W–P nanowire arrays by electroless deposition and magnetic studies  

Microsoft Academic Search

Ni–W–P alloy nanowire arrays have been fabricated by electroless deposition in an anodic alumina membrane. The images of Ni–W–P nanowire arrays and single nanowires are obtained by scanning electron microscope and transmission electron microscope, respectively. Selected area electron diffraction, X-ray diffraction (XRD) and energy dispersive spectra are employed to study the morphology and chemical composition of the nanowires. The results

X. Y. Yuan; T. Xie; G. S. Wu; Y. Lin; G. W. Meng; L. D. Zhang

2004-01-01

200

A fast integral equation method for simulating high-field radio frequency coil arrays in magnetic resonance imaging.  

PubMed

A fast full-wave numerical approach was developed for simulating high-field multi-channel radio-frequency (RF) receive coil arrays in magnetic resonance imaging. To improve the efficiency, the impedance matrix was compressed by a multilevel adaptive cross approximation method. Furthermore, careful organization of multiple coil simulations was applied so that the impedance matrix associated with biological subjects is constructed and pre-conditioned only once. Numerical examples demonstrate the efficacy of the proposed approach for RF coil simulations. PMID:21464529

Wang, Shumin; de Zwart, Jacco A; Duyn, Jeff H

2011-04-05

201

An 11-channel radio frequency phased array coil for magnetic resonance guided high-intensity focused ultrasound of the breast.  

PubMed

In this study, a radio frequency phased array coil was built to image the breast in conjunction with a magnetic resonance guided high-intensity focused ultrasound (MRgHIFU) device designed specifically to treat the breast in a treatment cylinder with reduced water volume. The MRgHIFU breast coil was comprised of a 10-channel phased array coil placed around an MRgHIFU treatment cylinder where nearest-neighbor decoupling was achieved with capacitive decoupling in a shared leg. In addition a single loop coil was placed at the chest wall making a total of 11 channels. The radio frequency coil array design presented in this work was chosen based on ease of implementation, increased visualization into the treatment cylinder, image reconstruction speed, temporal resolution, and resulting signal-to-noise ratio profiles. This work presents a dedicated 11-channel coil for imaging of the breast tissue in the MRgHIFU setup without obstruction of the ultrasound beam and, specifically, compares its performance in signal-to-noise, overall imaging time, and temperature measurement accuracy to that of the standard single chest-loop coil typically used in breast MRgHIFU. PMID:22431301

Minalga, E; Payne, A; Merrill, R; Todd, N; Vijayakumar, S; Kholmovski, E; Parker, D L; Hadley, J R

2012-03-16

202

Nonlinear oscillations of magnetization for ferromagnetic particles in the vortex state and their ordered arrays  

SciTech Connect

The dynamics of magnetization oscillations with a considerable amplitude and a radial symmetry in small ferromagnetic particles in the form of a thin disk with a magnetic vortex has been investigated. The collective variables that describe radially symmetric oscillations of the magnetization dynamics for particles in the vortex state are introduced, and the dependence of the particle energy is studied as a function of these variables. The analytical expressions describing the frequency of magnetization oscillations with a radial symmetry, including nonlinear oscillations, are derived using the collective variables. It is shown that the presence of a magnetic field oriented perpendicular to the particle plane reduces the oscillation frequency and can lead to hybridization of this mode with other modes of spin oscillations, including the mode of translational oscillations of the vortex core. The soliton solutions describing the propagation of collective oscillations along the chain of magnetic particles are found.

Galkin, A. Yu.; Ivanov, B. A., E-mail: bivanov@i.com.u [National Academy of Sciences of Ukraine, Ministry of Education and Science, Institute of Magnetism (Ukraine)

2009-07-15

203

Nonlinear oscillations of magnetization for ferromagnetic particles in the vortex state and their ordered arrays  

NASA Astrophysics Data System (ADS)

The dynamics of magnetization oscillations with a considerable amplitude and a radial symmetry in small ferromagnetic particles in the form of a thin disk with a magnetic vortex has been investigated. The collective variables that describe radially symmetric oscillations of the magnetization dynamics for particles in the vortex state are introduced, and the dependence of the particle energy is studied as a function of these variables. The analytical expressions describing the frequency of magnetization oscillations with a radial symmetry, including nonlinear oscillations, are derived using the collective variables. It is shown that the presence of a magnetic field oriented perpendicular to the particle plane reduces the oscillation frequency and can lead to hybridization of this mode with other modes of spin oscillations, including the mode of translational oscillations of the vortex core. The soliton solutions describing the propagation of collective oscillations along the chain of magnetic particles are found.

Galkin, A. Yu.; Ivanov, B. A.

2009-07-01

204

Strongly Enhanced Pinning of Magnetic Vortices in Type-II Superconductors by Conformal Crystal Arrays  

NASA Astrophysics Data System (ADS)

Conformal crystals are nonuniform structures created by a conformal transformation of regular two-dimensional lattices. We show that gradient-driven vortices interacting with a conformal pinning array exhibit substantially stronger pinning effects over a much larger range of field than found for random or periodic pinning arrangements. The pinning enhancement is partially due to matching of the critical flux gradient with the pinning gradient, but the preservation of local ordering in the conformally transformed hexagonal lattice and the arching arrangement of the pinning also play crucial roles. Our results can be generalized to a wide class of gradient-driven interacting particle systems such as colloids on optical trap arrays.

Ray, D.; Olson Reichhardt, C. J.; Jankó, B.; Reichhardt, C.

2013-06-01

205

Study on the structures and magnetic properties of Ni, Co-Al{sub 2}O{sub 3} electrodeposited nanowire arrays  

SciTech Connect

We report on the direct electrodeposition of nickel and cobalt nanowire arrays within the nanopores of ordered porous alumina films prepared by a two-step anodization. SEM and TEM images reveal that the pore arrays are regularly arranged throughout the alumina film. X-ray diffraction and TEM analysis show that the nickel and cobalt nanowires are single crystalline with highly preferential orientation. The aspect ratio of nanowires is over 300. M-H hysteresis loops determined by VSM indicate that the nanowire arrays obtained possess obvious magnetic anisotropy. Because of proper square ratio and coercivity the nanowire arrays of nickel seem to be more suitable candidates for perpendicular magnetic recording medium than those of cobalt.

Xu Jinxia; Huang Xinming; Xie Guozhi; Fang Yonghao; Liu Dazhi

2004-05-05

206

Ion Beam Stabilization of FePt Nanoparticle Arrays for Magnetic Storage Media.  

National Technical Information Service (NTIS)

We describe the use of ion beam induced crosslinking to harden the organic matrix material of self-assembled arrays of monodisperse (4 nm) FePt nanoparticles, providing Diamondlike Carbon barriers to inhibit agglomeration of the nanoparticles under heat t...

J. E. E. Baglin S. Sun A. J. Kellock T. Thomson M. F. Toney B. D. Terris C. B. Murray

2003-01-01

207

Physical realization of magnetic walls using finite-thickness 3D printed arrays  

Microsoft Academic Search

Perfect magnetic conductors (PMC) have been useful in electromagnetics for many years as subsidiary hypothetical surfaces in conjunction with formal dualities between dielectric and magnetic currents and vector potentials. This in turn helped formulating equivalence theorems and solving many scattering problems involving either a single scatterer in a solvable background (aperture in waveguiding structures) or many scatterers in highly symmetrical

H. Contopanagos; C. Kyriazidou; W. Merrill; N. G. Alexopoulos

1999-01-01

208

Complete numerical description of nonlocal quantum diffusion in an array of magnetic-flux vortices  

Microsoft Academic Search

A hybrid experimental system in which the inhomogeneous magnetic-field distribution near a superconducting gate layer is projected down onto the two-dimensional electron gas beneath it has been the subject of a large number of recent investigations. Studies have focused on both the transport of carriers in such a ``magnetic'' mesoscopic system as well as the dynamics of vortices in the

S. J. Bending

1994-01-01

209

Detection and localization of improvised explosive devices based on 3-axis magnetic sensor array system  

Microsoft Academic Search

The detection and localization of improvised explosive devices(IEDs) on the roadside is a new subject encountered in the struggle against terrorism. A novel detection and localization method was proposed for IEDs based on magnetic signals. Since most of the IEDs have the ferromagnetic properties, the magnetic field produced around the body by the IED can be detected by 3-axis fluxgate

Renhao Liu; Hua Wang

2010-01-01

210

Study of the magnetic interaction of a 4-coil array and copper shielding with a PET/MRI using the finite-element method.  

PubMed

The effect of the shielding in a PET-MRI system was numerically estimated by calculating the RF magnetic field, B1, produced by a coil array of 4 independent elements at the resonant frequency of 171 MHz (4T for protons). The array coil is located inside a ?PET camera to simultaneously acquire PET and MR images of a rat brain. Profiles showed a good uniformity despite the shielding that is interacting between the coil array and the ?PET camera. These limitations are currently being dealt with the fabrication of a birdcage coil design. PMID:21097202

Solis, S E; Rodriguez, A O; Tomasi, D

2010-01-01

211

Ambient-Temperature Passive Magnetic Bearings for Flywheel Energy Storage Systems  

SciTech Connect

Based on prior work at the Lawrence Livermore National Laboratory ambient-temperature passive magnetic bearings are being adapted for use in high-power flywheel energy storage systems developed at the Trinity Flywheel Power company. En route to this goal specialized test stands have been built and computer codes have been written to aid in the development of the component parts of these bearing systems. The Livermore passive magnetic bearing system involves three types of elements, as follows: (1) Axially symmetric levitation elements, energized by permanent magnets., (2) electrodynamic ''stabilizers'' employing axially symmetric arrays of permanent magnet bars (''Halbach arrays'') on the rotating system, interacting with specially wound electrically shorted stator circuits, and, (3) eddy-current-type vibration dampers, employing axially symmetric rotating pole assemblies interacting with stationary metallic discs. The theory of the Livermore passive magnetic bearing concept describes specific quantitative stability criteria. The satisfaction of these criteria will insure that, when rotating above a low critical speed, a bearing system made up of the three elements described above will be dynamically stable. That is, it will not only be stable for small displacements from equilibrium (''Earnshaw-stable''), but will also be stable against whirl-type instabilities of the types that can arise from displacement-dependent drag forces, or from mechanical-hysteritic losses that may occur in the rotor. Our design problem thus becomes one of calculating and/or measuring the relevant stiffnesses and drag coefficients of the various elements and comparing our results with the theory so as to assure that the cited stability criteria are satisfied.

Bender, D.; Post, R.

2000-05-26

212

Gas-assisted growth of boron-doped nickel nanotube arrays: rapid synthesis, growth mechanisms, tunable magnetic properties, and super-efficient reduction of 4-nitrophenol  

NASA Astrophysics Data System (ADS)

Highly ordered noncrystalline boron-doped nickel nanotube arrays are rapidly synthesized within 150 s by template-based electroless deposition. The as-prepared nanotubes have tunable magnetic properties and exhibit super efficient catalytic activity (~70 s) for the reduction of 4-nitrophenol.Highly ordered noncrystalline boron-doped nickel nanotube arrays are rapidly synthesized within 150 s by template-based electroless deposition. The as-prepared nanotubes have tunable magnetic properties and exhibit super efficient catalytic activity (~70 s) for the reduction of 4-nitrophenol. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr00411b

Li, Xiang-Zi; Wu, Kong-Lin; Ye, Yin; Wei, Xian-Wen

2013-04-01

213

Magnetic properties of arrays of cobalt nanoparticles on the CaF2(110)/Si(001) surface  

NASA Astrophysics Data System (ADS)

The Co/CaF2/Si(001) heterostructures with the corrugated (110) surface of the CaF2 buffer layer have been grown by molecular beam epitaxy. The structures are nanoparticle arrays of single-crystal Co, mostly of the cubic fcc modification. The behavior of the magnetic hysteresis loops as a function of the density of coverage of the substrate by cobalt islands, the island size, and the temperature is studied using the magnetooptical technique. At low coverage densities, where the effective cobalt film thickness d eff is less than the critical value d {eff/ c }, the magnetic structure of the films at T = 294 K can be visualized as an ensemble of superparamagnetic, weakly interacting nanoparticles and is characterized by small values of the coercive field H c and the remanent magnetization M rem. A decrease in the temperature leads to a strong increase in H c and M rem, which is associated with the transition of the islands to the blocked state. The blocking temperature of the structures is T b ˜ 280 K. The magnetic anisotropy parameter K and the saturation magnetization M s of the islands depend on the growth temperature of cobalt T Co. An increase in the coverage density above the critical thickness d {iff/ c } at T = 294 K brings about a strong increase in H c and M rem and the appearance of a hysteresis loop anisotropy originating from the corrugated structure of the CaF2 buffer layer. The experimental results are compared with the model of an ensemble of noninteracting superparamagnetic particles.

Krichevtsov, B. B.; Gastev, S. V.; Il'Yushchenkov, D. S.; Kaveev, A. K.; Sokolov, N. S.

2009-01-01

214

Contrasting vortex-gyration dispersions for different lattice bases in one-dimensional magnetic vortex arrays  

NASA Astrophysics Data System (ADS)

We performed micromagnetic numerical and analytical calculations in studying the effects of change in the primitive unit cells of one-dimensional (1D) vortex arrays on collective vortex-gyration dispersion. As the primitive basis, we consider alternating constituent materials (NiMnSb vs. Permalloy) and alternating dimensions including constituent disk diameter and thickness. In the simplest case, that of one vortex-state disk of given dimensions and single material in the primitive cell, only a single branch of collective vortex-gyration dispersion appears. By contrast, two constituent disks' different alternating materials, thicknesses, and diameters yield characteristic two-branch dispersions, the band widths and gaps of which differ in each case. This work offers not only an efficient means of manipulating collective vortex-gyration band structures but also a foundation for the development of a rich variety of 1D or 2D magnonic crystals and their band structures based on dipolar-coupled-vortex arrays.

Han, Dong-Soo; Jeong, Han-Byeol; Kim, Sang-Koog

2013-09-01

215

Magnetic properties of magnetite arrays produced by the method of electron beam lithography  

NASA Astrophysics Data System (ADS)

Arrays of magnetite particles in the submicron range (0.1-4.0 µm) have been produced. A novel method involving the utilisation of Electron Beam Lithography techniques often employed in the engineering design of integrated circuits of microchips was used. The fabrication process involved first producing arrays of iron (Fe) particles and then converting them to magnetite (Fe3O4) by thermal treatment. The fabricated magnetite particles have well controlled parameters including inter-particle spacing, an impossible task to achieve using artificially produced powders often employed in rockmagnetic studies. Two methods of converting Fe to Fe3O4 by annealing were used. One method led to Fe3O4 grains with high coercivities, typical of stressed grains and the other low coercivities in agreement with those for laboratory grown crystals. The crystal unit cell edge. Curie temperature, and saturation isothermal remanent magnetisation (SIRM) intensity observed at the Verwey transition are all consistent with stoichiometric magnetite.

King, James G.; Williams, Wyn; Wilkinson, C. D. W.; McVitie, Stephen; Chapman, John N.

216

Synthesis and magnetic properties of Cu-doped ZnO nanowire arrays  

Microsoft Academic Search

Arrays of Cu-doped ZnO nanowires were successfully fabricated by electrodeposition of Zn2+ and Cu2+ into anodic aluminum oxide template and post-oxidation annealing in air atmosphere. The transmission electron microscopy result shows that the nanowires are uniform, about 100nm in diameter and with the aspect ratio of up to 40. Selected area electron diffraction and X-ray diffraction results indicate that the

D. Q. Gao; D. S. Xue; Y. Xu; Z. J. Yan; Z. H. Zhang

2009-01-01

217

Cell behavior observation and gene expression analysis of melanoma associated with stromal fibroblasts in a three-dimensional magnetic cell culture array.  

PubMed

A three-dimensional (3D) multicellular tumor spheroid culture array has been fabricated using a magnetic force-based cell patterning method, analyzing the effect of stromal fibroblast on the invasive capacity of melanoma. Formation of spheroids was observed when array-like multicellular patterns of melanoma were developed using a pin-holder device made of magnetic soft iron and an external magnet, which enables the assembly of the magnetically labeled cells on the collagen gel-coated surface as array-like cell patterns. The interaction of fibroblast on the invasion of melanoma was investigated using three types of cell interaction models: (i) fibroblasts were magnetically labeled and patterned together in array with melanoma spheroids (direct-interaction model), (ii) fibroblasts coexisting in the upper collagen gel (indirect-interaction model) of melanoma spheroids, and (iii) fibroblast-sheets coexisting under melanoma spheroids (fibroblast-sheet model). The fibroblast-sheet model has largely increased the invasive capacity of melanoma, and the promotion of adhesion, migration, and invasion were also observed. In the fibroblast-sheet model, the expression of IL-8 and MMP-2 increased by 24-fold and 2-fold, respectively, in real time RT-PCR compared to the absence of fibroblasts. The results presented in this study demonstrate the importance of fibroblast interaction to invasive capacity of melanoma in the 3D in vitro bioengineered tumor microenvironment. PMID:23073999

Okochi, Mina; Matsumura, Taku; Yamamoto, And Shuhei; Nakayama, Eiichi; Jimbow, Kowichi; Honda, Hiroyuki

2012-11-21

218

Magnetic and magnetotransport properties of arrays of nanostructured antidots obtained by self-assembling polystyrene nanosphere lithography  

SciTech Connect

A well-ordered nanopatterned structure has been obtained in sputtered magnetic thin films by self-assembling of polystyrene nanospheres. Arrays of holes in Co, Ni, and Ni{sub 80}Fe{sub 20} films having a mean size ranging in the interval of 200-400 nm depending on the experimental condition have been prepared. Sample microstructure has been studied by scanning electron microscopy and atomic force microscopy. Room-temperature hysteresis loops have been measured in the parallel and perpendicular configuration (H{sub max}=20 kOe). Magnetoresistance (MR) measurements have been performed by means of a standard four-contact technique at several angles between the current and the magnetic field (H{sub max}=70 kOe) in the temperature interval of 4-200 K. An anisotropic MR effect has been observed in all compositions independent on the hole mean dimension. The role on magnetic and magnetotransport properties of either sample microstructure or composition has been studied in such patterned structures.

Tiberto, Paola; Boarino, Luca; Celegato, Federica; Coiesson, Marco; De Leo, Natascia; Vinai, Franco [INRIM, Strada delle Cacce 91, Torino I-10135 (Italy); Allia, Paolo [DISMIC, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 1-10129 (Italy)

2010-05-15

219

Reliability of Signal Propagation in Magnetostatically Coupled Arrays of Magnetic Nanoelements  

NASA Astrophysics Data System (ADS)

Nanomagnetic logic (NML) has promise as a low-power, non-volatile, and radiation resistant alternative to CMOS-based computational devices. Lines of magnetostatically coupled magnetic nano-elements (NEs) propagate information, and the intersections between lines form logic gates. We present simulations and experiments exploring the reliability of signal propagation in NML devices composed of lines of nominally rectangular permalloy NEs, typically 90x60 nm^2 in size. An external magnetic field sets the magnetic state of an input bit and also resets each of the NEs' magnetizations along their hard axis direction. As the field is reduced to zero the input state propagates along the line of NEs as they successively relax into one of two equilibrium states. The state of the NEs is probed by (i) a magnetic tunnel junction sensing device integrated with the output NE and (ii) magnetic force microscopy imaging. We conclude that signal propagation is inherently unreliable both through variations in fabrication of the NEs and due to the innate lack of directionality of the flow of information. We demonstrate an alternative clocking method where a domain wall passing underneath an NML device clocks each NE sequentially, thereby increasing the success of signal propagation.

van Mourik, Reinier; Gao, Li; Hughes, Brian; Rettner, Charles; Koopmans, Bert; Parkin, Stuart

2013-03-01

220

Giant magenetoresistive sensors. 2. Detection of biorecognition events at self-referencing and magnetically tagged arrays.  

PubMed

Microfabricated devices formed from alternating layers of magnetic and nonmagnetic materials at combined thicknesses of a few hundred nanometers exhibit a phenomenon known as the giant magnetoresistance effect. Devices based on this effect are known as giant magnetoresistive (GMR) sensors. The resistance of a GMR is dependent on the strength of an external magnetic field, which has resulted in the widespread usage of such platforms in high-speed, high-data density storage drives. The same attributes (i.e., sensitivity, small size, and speed) are also important embodiments of many types of bioanalytical sensors, pointing to an intriguing opportunity via an integration of GMR technology, magnetic labeling strategies, and biorecognition elements (e.g., antibodies). This paper describes the utilization of GMRs for the detection of streptavidin-coated magnetic particles that are selectively captured by biotinylated gold addresses on a 2 x 0.3 cm sample stick. A GMR sensor network reads the addresses on a sample stick in a manner that begins to emulate that of a "card-swipe" system. This study also takes advantage of on-sample magnetic addresses that function as references for internal calibration of the GMR response and as a facile means to account for small variations in the gap between the sample stick and sensor. The magnetic particle surface coverage at the limit of detection was determined to be approximately 2%, which corresponds to approximately 800 binding events over the 200 x 200 microm capture address. These findings, along with the potential use of streptavidin-coated magnetic particles as a universal label for antigen detection in, for example, heterogeneous assays, are discussed. PMID:18826241

Millen, Rachel L; Nordling, John; Bullen, Heather A; Porter, Marc D; Tondra, Mark; Granger, Michael C

2008-10-01

221

A novel single nucleotide polymorphisms detection sensors based on magnetic nanoparticles array and dual-color single base extension.  

PubMed

To fulfill the increasing need for large-scale genetic research, a high-throughput and automated SNPs genotyping method based on gold coated magnetic nanoparticles (GMNPs) array and dual-color single base extension has been designed. Biotinylated single base extension primer were captured onto the GMNPs coated with streptavidin. Dual-color fluorescence single base extension was employed as a tool for SNPs identification, and then a "bead array" was fabricated by spotting GMNPs with fluorophore on the glass slide. Using this platform, MTHFR gene C677T locus from 12 samples was genotyped. The results showed that all homozygous samples gave a signal/noise ratio over 30, and the fluorescent intensities ratios of heterozygote samples were around 1. With advantages to defeat the background subtract feature and read-out the fluorescence values of the GMNPs directly to determine their genotypes, without the necessary procedures for purification and complex reduction of PCR products, the application of this strategy to large-scale SNP studies will be simple, labor-saving, high sensitive and potential for automation. PMID:21125888

Liu, Hongna; Li, Song; Tian, Lan; Liu, Lishang; He, Nongyue

2010-08-01

222

Accelerated cardiac magnetic resonance imaging in the mouse using an eight-channel array at 9.4 Tesla.  

PubMed

MRI has become an important tool to noninvasively assess global and regional cardiac function, infarct size, or myocardial blood flow in surgically or genetically modified mouse models of human heart disease. Constraints on scan time due to sensitivity to general anesthesia in hemodynamically compromised mice frequently limit the number of parameters available in one imaging session. Parallel imaging techniques to reduce acquisition times require coil arrays, which are technically challenging to design at ultrahigh magnetic field strengths. This work validates the use of an eight-channel volume phased-array coil for cardiac MRI in mice at 9.4 T. Two- and three-dimensional sequences were combined with parallel imaging techniques and used to quantify global cardiac function, T(1)-relaxation times and infarct sizes. Furthermore, the rapid acquisition of functional cine-data allowed for the first time in mice measurement of left-ventricular peak filling and ejection rates under intravenous infusion of dobutamine. The results demonstrate that a threefold accelerated data acquisition is generally feasible without compromising the accuracy of the results. This strategy may eventually pave the way for routine, multiparametric phenotyping of mouse hearts in vivo within one imaging session of tolerable duration. PMID:20740650

Schneider, Jürgen E; Lanz, Titus; Barnes, Hannah; Stork, Lee-Anne; Bohl, Steffen; Lygate, Craig A; Ordidge, Roger J; Neubauer, Stefan

2011-01-01

223

A CMOS magnetic microbead-based capacitive biosensor array with on-chip electromagnetic manipulation.  

PubMed

Magnetic microbeads are widely used in biotechnology and biomedical research for manipulation and detection of cells and biomolecules. Most lab-on-chip systems capable of performing manipulation and detection require external instruments to perform one of the functions, leading to increased size and cost. This work aims at developing an integrated platform to perform these two functions by implementing electromagnetic microcoils and capacitive biosensors on a CMOS (complementary metal oxide semiconductor) chip. Compared to most magnetic-type sensors, our detection method requires no externally applied magnetic fields and the associated fabrication is less complicated. In our experiment, microbeads coated with streptavidin were driven to the sensors in the center of microcoils with functionalized anti-streptavidin antibody. Detection of a single microbead was successfully demonstrated using a capacitance-to-frequency readout. The average capacitance changes for the experimental and control groups were -5.3 fF and -0.2 fF, respectively. PMID:23454336

Chang, An-Yu; Lu, Michael S-C

2013-01-29

224

[Expansion of sensitivity area for magnetic resonance imaging of the hand using parallel-array coil].  

PubMed

It is difficult for Rheumatoid Arthritis (RA) patients to remain in a strenuous position for a long time during examinations. The field of view (FOV): 250 mm is needed for hand examinations from the wrist to the finger. Two channel phased array coils are effective to use when examinations of the 'off center' are taken for the upper and lower extremities. The area of the array coils' sensitivity can be expanded by shifting both coil elements 40-60% in the opposite direction of the element's diameter. This method is given credibility due to the increased signal-to-noise ratio (SNR) in the peripheral regions (shifted directions), but loses value in the central area, as indicated by the decrease in SNR. This was confirmed in the image of the hand using visual assessment including the fat suppression technique. It was verified that the sensitivity area was expanded using Scheffe's method of paired comparison (Ura's modified method). An application at the other regions of the body can be expected to be used in the case of using parallel positioned coils during clinical situation. PMID:23089837

Takatsu, Yasuo; Yamamura, Kenichirou; Miyati, Tosiaki; Kimura, Tetsuya; Ueyama, Tsuyoshi; Ishikuro, Akihiro

2012-01-01

225

Structure and magnetic properties of three-dimensional (La,Sr)MnO{sub 3} nanofilms on ZnO nanorod arrays  

SciTech Connect

Three-dimensional (3D) cubic perovskite (La,Sr)MnO{sub 3} (LSMO) nanofilms have been deposited on ZnO nanorod arrays with controlled dimensionality and crystallinity by radio frequency (rf) magnetron sputtering and post thermal annealing. Compared to the two-dimensional (2D) LSMO nanofilm on flat Si, the structure and magnetic properties of 3D LSMO nanofilms on ZnO nanorod arrays have a strong anisotropic morphology and thickness dependence. Ferromagnetic property has been observed in both 2D and 3D LSMO nanofilms while a ferromagnetic-superparamagnetic transition was revaled in 3D LSMO nanofilms on ZnO nanorod array with decreasing nanofilm thickness, due to a large surface dispersion effect. The LSMO/ZnO nanofilm/nanorod structures could open up new avenues for intriguing magnetic properties studies and applications of nanoscale perovskites.

Gao Haiyong; Gao Puxian; Shimpi, Paresh; Guo Yanbing; Cai Wenjie; Lin Huijan [Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136 (United States); Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269-3136 (United States); Staruch, M. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States); Jain, Menka [Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136 (United States); Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States)

2011-03-21

226

Gas-assisted growth of boron-doped nickel nanotube arrays: rapid synthesis, growth mechanisms, tunable magnetic properties, and super-efficient reduction of 4-nitrophenol.  

PubMed

Highly ordered noncrystalline boron-doped nickel nanotube arrays are rapidly synthesized within 150 s by template-based electroless deposition. The as-prepared nanotubes have tunable magnetic properties and exhibit super efficient catalytic activity (?70 s) for the reduction of 4-nitrophenol. PMID:23546439

Li, Xiang-Zi; Wu, Kong-Lin; Ye, Yin; Wei, Xian-Wen

2013-04-02

227

A Linear Permanent Magnet Generator for a Free-Piston Energy Converter  

Microsoft Academic Search

This paper discusses the issues that are pertinent to the design of a linear permanent magnet generator for application in a free-piston energy converter. To achieve the required high power density, high efficiency and low moving mass, a tubular machine equipped with modular windings and quasi-Halbach magnetization is considered to be the most appropriate. Analytical expressions for predicting the open-circuit

Jiabin Wang; David Howe

2005-01-01

228

Bulk properties, structure and pinning of magnetic flux-line arrays in high-temperature superconductors  

Microsoft Academic Search

A serious impediment to many potential applications of the high-Tsb{c} copper oxide superconductors is the relative ease with which magnetic flux-lines move within these materials, thereby producing finite electrical resistance. To devise methods for rigidly fixing flux-lines in these materials, which is necessary to achieve a truly superconducting state, requires an understanding of their fundamental structural properties. The most direct

Zhen Yao

1997-01-01

229

Modulation theory in PT-symmetric magnetic metamaterial arrays in the continuum limit  

NASA Astrophysics Data System (ADS)

We present results on the dynamics of split-ring dimers having both gain and loss in one-dimensional nonlinear parity-time- (PT-)symmetric magnetic metamaterials. For the long-wave (continuum) limit approximation and in the weakly nonlinear limit, we show analytic results on the existence of gap soliton solutions and on symmetry-breaking phenomenon at a critical value of the gain or loss term.

Wang, Danhua; Aceves, Alejandro B.

2013-10-01

230

A primary field compensation scheme for planar array magnetic induction tomography  

Microsoft Academic Search

In biomedical magnetic induction tomography (MIT), measurement precision may be improved by incorporating some form of primary field compensation\\/cancellation scheme. Schemes which have been described previously include gradiometric approaches and the use of 'back-off' coils. In each of these methods, however, the primary field cancellation was achieved only for a single transmitter\\/receiver combination. For the purpose of imaging, it would

S. Watson; A. Morris; R. J. Williams; H. Griffiths; W. Gough

2004-01-01

231

Magnetization reversal of stripe arrays: comparison of PNR and MOKE results  

NASA Astrophysics Data System (ADS)

In order to minimize stray field energies, lateral structures often show a variety of domain configurations. A method which is very suitable for studying different remagnetization processes is polarized neutron reflectivity (PNR) because it can distinguish between reversal via coherent rotation or domain nucleation and wall movement. Furthermore, by applying PNR to lateral structures it is possible to perform measurements at Bragg peaks from the artificial periodicity and therefore filter out correlation effects between indivdiual magnetic units during reversal. We have studied the magnetization reversal of laterally structured CoFe films by PNR and compared the results to longitudinal MOKE measurements with the field applied in longitudinal and in transverse orientation [1]. In addition, Kerr-microscopy was used for visualizing the domain state at different field values. The parameters of the CoFe stripes were chosen such that a strong two-fold shape anisotropy is present in the polycrystalline stripes. By varying the width of the stripes the magnetic anisotropy can be changed. Consequently we observe more complex domain configurations for stripes with larger widths than for those with smaller widths. Neutron spin-flip scattering also indicates inhomogeneous stray fields most likely due to dipole-dipole interaction between the stripes. We acknowledge founding by DFG, SFB 491 and BMBF 032AE8BO [1] K. Theis-Bröhl, T. Schmitte, V. Leiner, H. Zabel, K. Rott, H. Brueckl, and J. McCord, Phys. Rev. B 67 (2003)

Zabel, Hartmut

2003-03-01

232

Seismo-magnetic multi-point ULF studies before the 2009 L'Aquila earthquake using the South European GeoMagnetic Array  

NASA Astrophysics Data System (ADS)

A strong earthquake (Ml=5.8, Mw=6.3) hit L'Aquila (Central Italy, Abruzzo region, LT=UT+1) on April 6, 2009, 01:32 UT, causing more than 300 deaths. We present a seismo-magnetic analysis of local ULF measurements for the time period one year before the main stroke. As part of the South European GeoMagnetic Array (SEGMA) the evaluated station L'Aquila in closest distance to the epicentre of the main seismic event is ~ 6 km. We consider three further SEGMA stations: Castello Tesino, Ranchio (both Italy) and Nagycenk (Hungary) for comparison and the Kp geomagnetic index to distinguish local- , global- and geomagnetic effects. Further local seismic activities are respected. The instrumentation consists of fluxgate magnetometers with a sampling frequency of 1 Hz. Concerning signal processing the standardized polarization method was applied based on the ratio between the vertical and horizontal power spectral density. A frequency band from 10-100 mHz focused on 10-15 mHz was used during the nighttime period from 22.00 - 02.00 UT. The polarization analysis was introduced and applied for previous seismic events by Hayakawa et al., GRL, 23, 241, 1996.; Molchanov et al., GRL, 19, 1495, 1992.; Prattes et al., NHESS, 2008. A sophisticated method was performed by Ida, et al, NHESS, 2008. With these calculations we expect clearer precursor signatures and they could contribute to EQ forecast. The results are explained using a simple source magnetic dipole model near the EQ focus. The results obtained are explained by the attenuation in the electrical conductive lithosphere.

Prattes, G.; Schwingenschuh, K.; Eichelberger, H.; Besser, B.; Magnes, W.; Stachel, M.; Vellante, M.; Villante, U.; Nenovski, P.

2010-05-01

233

Magnetic measurements using array of integrated Hall sensors on the CASTOR tokamak.  

PubMed

We have performed the first tests of "integrated" Hall sensors (IHSs) in a tokamak in-vessel environment. IHS combines the sensing element together with the complex electronic circuitry on a single small chip. The on-chip integrated circuits provide stabilization of the supply voltage, output amplification, noise suppression, and elimination of temperature dependencies. Eight IHSs of A1322LUA type produced by Allegro MicroSystems, Inc. were mounted on a stainless steel ring symmetrically encircling the CASTOR plasmas in poloidal direction 10 mm outside the limiter radius. IHSs were oriented such that they measure the horizontal and vertical magnetic fields. We found out that these sensors qualify for in-vessel use of small to middle sized fusion devices where the radiation is not an issue and the temperature below 150 degrees C can be guaranteed. The main advantages over the traditional pickup coils are the smaller size and more straightforward interpretation of output without the need of rather cumbersome integration and drift removal procedure associated with the use of inductive loops. We successfully exploited the sensors for determination of vertical plasma displacement on CASTOR. This new diagnostic helped us to shed more light into long term observed discrepancy on CASTOR between vertical plasma displacement as deduced by standard magnetic and by nonmagnetic diagnostics (Langmuir probes, bolometers). PMID:19044607

Duran, Ivan; Hronová, Olena; Stöckel, Jan; Sentkerestiová, Jana; Havlicek, Josef

2008-10-01

234

Magnetic measurements using array of integrated Hall sensors on the CASTOR tokamak  

SciTech Connect

We have performed the first tests of 'integrated' Hall sensors (IHSs) in a tokamak in-vessel environment. IHS combines the sensing element together with the complex electronic circuitry on a single small chip. The on-chip integrated circuits provide stabilization of the supply voltage, output amplification, noise suppression, and elimination of temperature dependencies. Eight IHSs of A1322LUA type produced by Allegro MicroSystems, Inc. were mounted on a stainless steel ring symmetrically encircling the CASTOR plasmas in poloidal direction 10 mm outside the limiter radius. IHSs were oriented such that they measure the horizontal and vertical magnetic fields. We found out that these sensors qualify for in-vessel use of small to middle sized fusion devices where the radiation is not an issue and the temperature below 150 deg. C can be guaranteed. The main advantages over the traditional pickup coils are the smaller size and more straightforward interpretation of output without the need of rather cumbersome integration and drift removal procedure associated with the use of inductive loops. We successfully exploited the sensors for determination of vertical plasma displacement on CASTOR. This new diagnostic helped us to shed more light into long term observed discrepancy on CASTOR between vertical plasma displacement as deduced by standard magnetic and by nonmagnetic diagnostics (Langmuir probes, bolometers)

Duran, Ivan; Hronova, Olena; Stoeckel, Jan [Association EURATOM/IPP.CR, Institute of Plasma Physics AS CR, v. v. i., Za Slovankou 3, 182 00 Praha 8 (Czech Republic); Sentkerestiova, Jana [Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Brehova 7, 115 19 Praha 1 (Czech Republic); Havlicek, Josef [Association EURATOM/IPP.CR, Institute of Plasma Physics AS CR, v. v. i., Za Slovankou 3, 182 00 Praha 8 (Czech Republic); Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Praha 2 (Czech Republic)

2008-10-15

235

Comparison of Pelvic Phased-Array versus Endorectal Coil Magnetic Resonance Imaging at 3 Tesla for Local Staging of Prostate Cancer  

PubMed Central

Purpose Several studies have demonstrated the superiority of endorectal coil magnetic resonance imaging (MRI) over pelvic phased-array coil MRI at 1.5 Tesla for local staging of prostate cancer. However, few have studied which evaluation is more accurate at 3 Tesla MRI. In this study, we compared the accuracy of local staging of prostate cancer using pelvic phased-array coil or endorectal coil MRI at 3 Tesla. Materials and Methods Between January 2005 and May 2010, 151 patients underwent radical prostatectomy. All patients were evaluated with either pelvic phased-array coil or endorectal coil prostate MRI prior to surgery (63 endorectal coils and 88 pelvic phased-array coils). Tumor stage based on MRI was compared with pathologic stage. We calculated the specificity, sensitivity and accuracy of each group in the evaluation of extracapsular extension and seminal vesicle invasion. Results Both endorectal coil and pelvic phased-array coil MRI achieved high specificity, low sensitivity and moderate accuracy for the detection of extracapsular extension and seminal vesicle invasion. There were statistically no differences in specificity, sensitivity and accuracy between the two groups. Conclusion Overall staging accuracy, sensitivity and specificity were not significantly different between endorectal coil and pelvic phased-array coil MRI.

Kim, Bum Soo; Kim, Tae-Hwan; Kwon, Tae Gyun

2012-01-01

236

Constraining weak intergalactic magnetic fields: prospects for the Cherenkov Telescope Array  

NASA Astrophysics Data System (ADS)

In recent years the possibility of constraining weak intergalactic magnetic fields (IGMFs) has emerged through simultaneous spectral observations of blazars at very high energies (VHE) utilizing data from the Fermi Gamma Ray Space Telescope and the ground-based imaging atmospheric Cherenkov Telescopes (IACTs). In this submission we explore the capabilities of Fermi and CTA to advance such studies through the potential detection of gamma-ray halos around AGN and detection of delayed VHE radiation decaying after intense VHE flares of Flat Spectrum Radio Quasars (FSRQs), which have recently been observed from such astrophysical objects. CTA will be an effective tool for constraining the properties of the IGMF, due to its vastly increased collecting area, improved angular resolution, and wide field of view, all of which enhance its capability for the study of VHE transients and astrophysical source morphology.

Vassiliev, Vladimir; Arlen, Timothy

2012-07-01

237

Development of a Magnetic Electrochemical Bar Code Array for Point Mutation Detection in the H5N1 Neuraminidase Gene  

PubMed Central

Since its first official detection in the Guangdong province of China in 1996, the highly pathogenic avian influenza virus of H5N1 subtype (HPAI H5N1) has reportedly been the cause of outbreaks in birds in more than 60 countries, 24 of which were European. The main issue is still to develop effective antiviral drugs. In this case, single point mutation in the neuraminidase gene, which causes resistance to antiviral drug and is, therefore, subjected to many studies including ours, was observed. In this study, we developed magnetic electrochemical bar code array for detection of single point mutations (mismatches in up to four nucleotides) in H5N1 neuraminidase gene. Paramagnetic particles Dynabeads® with covalently bound oligo (dT)25 were used as a tool for isolation of complementary H5N1 chains (H5N1 Zhejin, China and Aichi). For detection of H5N1 chains, oligonucleotide chains of lengths of 12 (+5 adenine) or 28 (+5 adenine) bp labeled with quantum dots (CdS, ZnS and/or PbS) were used. Individual probes hybridized to target molecules specifically with efficiency higher than 60%. The obtained signals identified mutations present in the sequence. Suggested experimental procedure allows obtaining further information from the redox signals of nucleic acids. Moreover, the used biosensor exhibits sequence specificity and low limits of detection of subnanogram quantities of target nucleic acids.

Krejcova, Ludmila; Hynek, David; Kopel, Pavel; Merlos Rodrigo, Miguel Angel; Adam, Vojtech; Hubalek, Jaromir; Babula, Petr; Trnkova, Libuse; Kizek, Rene

2013-01-01

238

Development of a magnetic electrochemical bar code array for point mutation detection in the H5N1 neuraminidase gene.  

PubMed

Since its first official detection in the Guangdong province of China in 1996, the highly pathogenic avian influenza virus of H5N1 subtype (HPAI H5N1) has reportedly been the cause of outbreaks in birds in more than 60 countries, 24 of which were European. The main issue is still to develop effective antiviral drugs. In this case, single point mutation in the neuraminidase gene, which causes resistance to antiviral drug and is, therefore, subjected to many studies including ours, was observed. In this study, we developed magnetic electrochemical bar code array for detection of single point mutations (mismatches in up to four nucleotides) in H5N1 neuraminidase gene. Paramagnetic particles Dynabeads® with covalently bound oligo (dT)?? were used as a tool for isolation of complementary H5N1 chains (H5N1 Zhejin, China and Aichi). For detection of H5N1 chains, oligonucleotide chains of lengths of 12 (+5 adenine) or 28 (+5 adenine) bp labeled with quantum dots (CdS, ZnS and/or PbS) were used. Individual probes hybridized to target molecules specifically with efficiency higher than 60%. The obtained signals identified mutations present in the sequence. Suggested experimental procedure allows obtaining further information from the redox signals of nucleic acids. Moreover, the used biosensor exhibits sequence specificity and low limits of detection of subnanogram quantities of target nucleic acids. PMID:23860384

Krejcova, Ludmila; Hynek, David; Kopel, Pavel; Rodrigo, Miguel Angel Merlos; Adam, Vojtech; Hubalek, Jaromir; Babula, Petr; Trnkova, Libuse; Kizek, Rene

2013-07-15

239

Development of a miniature permanent magnetic circuit for nuclear magnetic resonance chip  

NASA Astrophysics Data System (ADS)

The existing researches of miniature magnetic circuits focus on the single-sided permanent magnetic circuits and the Halbach permanent magnetic circuits. In the single-sided permanent magnetic circuits, the magnetic flux density is always very low in the work region. In the Halbach permanent magnetic circuits, there are always great difficulties in the manufacturing and assembly process. The static magnetic flux density required for nuclear magnetic resonance(NMR) chip is analyzed based on the signal noise ratio(SNR) calculation model, and then a miniature C-shaped permanent magnetic circuit is designed as the required magnetic flux density. Based on Kirchhoff's law and magnetic flux refraction principle, the concept of a single shimming ring is proposed to improve the performance of the designed magnetic circuit. Using the finite element method, a comparative calculation is conducted. The calculation results demonstrate that the magnetic circuit improved with a single shimming has higher magnetic flux density and better magnetic field homogeneity than the one improved with no shimming ring or double shimming rings. The proposed magnetic circuit is manufactured and its experimental test platform is also built. The magnetic flux density measured in the work region is 0.7 T, which is well coincided with the theoretical design. The spatial variation of the magnetic field is within the range of the instrument error. At last, the temperature dependence of the magnetic flux density produced by the proposed magnetic circuit is investigated through both theoretical analysis and experimental study, and a linear functional model is obtained. The proposed research is crucial for solving the problem in the application of NMR-chip under different environmental temperatures.

Lu, Rongsheng; Yi, Hong; Wu, Weiping; Ni, Zhonghua

2013-07-01

240

A review of new wire arrays with open and closed magnetic configurations at the 1.6 MA Zebra generator for radiative properties and opacity effects  

NASA Astrophysics Data System (ADS)

The studies emphasize investigation of plasma formation, implosion, and radiation features as a function of two load configurations: compact multi-planar and cylindrical wire arrays. Experiments with different Z-pinch loads were performed on 1.6 MA, 100 ns, Zebra generator at University of Nevada, Reno. The multi-planar wire arrays (PWAs) were studied in open and closed configurations with Al, Cu, brass, Mo and W wires. In the open magnetic configurations (single, double, triple PWAs) magnetic fields are present inside the arrays from the beginning of discharge, while in closed configurations (prism-like PWA) the global magnetic field is excluded inside before plasma flow occurs. The new prism-like PWA allows high flexibility in control of implosion dynamics and precursor formation. The spectral modeling, magneto-hydrodynamic (MHD) and wire ablation dynamic model (WADM) codes were used to describe the plasma evolution and plasma parameters. Experimentally observed electron temperature and density in multiple bright spots reached 1.4 keV and 5 × 10 21 cm -3, respectively. Two types of bright spots were observed. With peak currents up to 1.3 MA opacity effects became more pronounced and led to a limiting of the X-ray yields from compact cylindrical arrays. Despite different magnetic energy to plasma coupling mechanisms early in the implosion a comparison of compact double PWA and cylindrical WA results indicates that during the stagnation stage the same plasma heating mechanism may occur. The double PWA was found to be the best radiator tested at University scale 1 MA generator. It is characterized by a combination of larger yield and power, mm-scale size, and provides the possibility of radiation pulse shaping. Further, the newer configuration, the double PWA with skewed wires, was tested and showed the possibility of a more effective X-ray generation.

Kantsyrev, V. L.; Safronova, A. S.; Esaulov, A. A.; Williamson, K. M.; Shrestha, I.; Yilmaz, F.; Osborne, G. C.; Weller, M. E.; Ouart, N. D.; Shlyaptseva, V. V.; Rudakov, L. I.; Chuvatin, A. S.; Velikovich, A. L.

2009-09-01

241

Surface potential and magnetic properties of La0.7Sr0.3MnO3 periodic arrays fabricated by direct electron beam writing  

Microsoft Academic Search

It is demonstrated that magnetic periodic arrays can be easily fabricated from direct writing water developable La0.7Sr0.3MnO3 electron beam resist. Two unique features of our approach are (1) the patterned La0.7Sr0.3MnO3 resist film can be developed using nontoxic and environmentally friendly pure water and (2) either positive or negative patterns can be fabricated depending on the dosage of electron beam.

Ming-Chung Wu; Yi-Jen Wu; Yu-Ching Huang; Chih-Min Chuang; Kuo-Chung Cheng; Ching-Fuh Lin; Yang-Fang Chen; Wei-Fang Su

2008-01-01

242

The reliability of the seismo-magnetic method derived from ULF/ELF observations by the South European Geomagnetic Array (SEGMA)  

NASA Astrophysics Data System (ADS)

In the frame of the South European GeoMagnetic Array (SEGMA) project magnetic field variations are studied in the frequency range from several milli-Hz to several Hz. The fluxgate and induction coil magnetometers are located in Italy, Bulgaria and Hungary. The scientific objectives comprises field-line resonances, space weather phenomena and seismo-magnetic (SM) studies. In our present study on the reliability of the seismo-magnetic method we emphasize on the influence of external non-seismic sources on the quality of seismo-magnetic studies. External magnetic sources include lightning, power lines, railway and traffic as well as geomagnetic variations of magnetospheric origin. We observe anomalies of the ratio of the vertical to horizontal magnetic field component in the ultra/extreme-low-frequency (ULF/ELF) frequency range up to several Hz [2]. These signals can be produced in the lithosphere near a seismic active region and are interpreted as earthquake precursors. In order to differentiate geomagnetic from seismo-magnetic fluctuations, we use mainly observations around midnight because the night time geomagnetic fluctuations are much smaller than during day time. The SEGMA network provides the unique opportunity to use multipoint observations, which are also useful to distinguish local from global phenomena. In order to get undisturbed magnetic field observations, the stations are located outside populated areas [2]. The electrical conductivity of the soil in the vicinity of magnetometers on the terrestrial surface is a further source for interferences. This type of disturbances caused by induced electrical currents can be minimized either by a careful selection of the magnetometer site ans/or by the measurement of the conductivity profile in the vicinity of the instrument site. In the frame of the investigation of the April 6, 2009 L'Aquila earthquake magneto-telluric methods have been used to measure the conductivity profile near the epicenter of the earthquake and thus correct the observed magnetic field fluctuations [1]. A further interference source which can reduce the sensitivity of the seismo-magnetic methods (SM) is the mechanical vibration of the magnetometer sensors. We present a SM reliability number taking into account all above mentioned interference sources. The SM number can be used to improve the sensitivity of the seismo-magnetic method. References [1] G. Prattes, et al.: Ultra Low Frequency (ULF) European multi station magnetic field analysis before and during the 2009 earthquake at L'Aquila regarding regional geotechnical information, Nat. Hazards Earth Syst. Sci., 11, 1959-1968, 2011 [2] K. Schwingenschuh, et al.: 'Clean' observations of magnetic field fluctuations on planetary surfaces, Aerospace EMC, 2012 Proceedings ESA Workshop on 21-23 May 2012, 4 p., 2012.

Schwingenschuh, Konrad; Prattes, Gustav; Eichelberger, Hans Ulrich; Magnes, Werner; Berghofer, Gerhard; Aydogar, Özer; Besser, Bruno P.; Boudjada, Mohammed; Stangl, Günter; Zhang, Tie Long; Wolbang, Daniel; Vellante, Massimo; Villante, Umberto; Rozhnoi, Alexander; Solovieva, Maria; Nenovski, Petko; Veztergom, Victor; Szendr?i, Judith

2013-04-01

243

Controllable growth and magnetic characterization of electrodeposited nanocrystalline Ni–P alloy nanotube and nanowire arrays inside AAO template  

Microsoft Academic Search

The highly ordered Ni–P alloy nanotube and nanowire arrays with high aspect-ratio have been successfully synthesized inside porous anodic aluminum oxide (AAO) membranes by self-assembly electrodeposition at different current densities. The as-synthesized Ni–P alloy arrays have the amorphous phase structure with nanograin of crystalline Ni. The length and outer diameter predominantly determined by the deposition time and pore diameter of

Jingjun Liu; Feng Wang; Junyun Zhai; Jing Ji

2010-01-01

244

The characterization of nitrogen content, diamond-like carbon field emission arrays using a magnetic filtered arc method  

Microsoft Academic Search

Uniform and large area pyramid-shape diamond-like carbon (DLC) field emission arrays are successfully deposited using the filtered arc deposition (FAD) system. Nitrogen gas serves as the dopant source to deposit the diamond-like carbon films on the inverted pyramid-shape SiO2 substrates. Experimental results indicate that the current-voltage (I–V) value of field emission arrays is closely related to the diamond-like carbon film

C.-F Chen; C.-H Shen; C.-L Lin

2000-01-01

245

Tuning the magnetic anisotropy of Co-Ni nanowires: comparison between single nanowires and nanowire arrays in hard-anodic aluminum oxide membranes.  

PubMed

Co(x)Ni(1-x) alloy nanowires with varying Co content (0 ? x ? 0.95), having a diameter of 130 nm and length of around 20 ?m, are synthesized by template-assisted electrodeposition into the nanopores of SiO(2) conformal coated hard-anodic aluminum oxide membranes. The magneto-structural properties of both single isolated nanowires and hexagonally ordered nanowire arrays of Co-Ni alloys are systematically studied by means of magneto-optical Kerr effect magnetometry and vibrating sample magnetometry, respectively, allowing us to compare different alloy compositions and to distinguish between the magnetostatic and magnetocrystalline contributions to the effective magnetic anisotropy for each system. The excellent tunable soft magnetic properties and magnetic bistability exhibited by low Co content Co-Ni nanowires indicate that they might become the material of choice for the development of nanostructured magnetic systems and devices as an alternative to Fe-Ni alloy based systems, being chemically more robust. Furthermore, Co contents higher than 51 at.% allow us to modify the magnetic behavior of Co-rich nanowires by developing well controlled magnetocrystalline anisotropy, which is desirable for data storage applications. PMID:23095457

Vega, V; Böhnert, T; Martens, S; Waleczek, M; Montero-Moreno, J M; Görlitz, D; Prida, V M; Nielsch, K

2012-10-24

246

P1–15: Patterning of high density magnetic nanodot arrays by imprint lithography with hole tone template  

Microsoft Academic Search

Nanoimprint Lithography presents unique opportunities for high density patterning due to its advantages of sub-10nm resolution capability and high throughput. Imprint and pattern transfer with Pillar tone template were widely studies recently. However, there are several critical issues that still remain very challenging, including fabrication of pillar templates and pattern reverse from imprint holes to nano dots array at high

Yuan Xu; Wei Hu; Xiaomin Yang; Zhaohui Fan; Justin Hwu; Koichi Wago; David Kuo

2010-01-01

247

Observations of magnetic fields in the Milky Way and in nearby galaxies with a Square Kilometre Array  

Microsoft Academic Search

The role of magnetic fields in the dynamical evolution of galaxies and of the interstellar medium (ISM) is not well understood, mainly because such fields are difficult to directly observe. Radio astronomy provides the best tools to measure magnetic fields: synchrotron radiation traces fields illuminated by cosmic-ray electrons, while Faraday rotation and Zeeman splitting allow us to detect fields in

R. Beck; B. M. Gaensler

2004-01-01

248

Magnetic Forces Simulation of Bulk HTS over Permanent Magnetic Railway with Numerical Method  

NASA Astrophysics Data System (ADS)

Magnetic levitation forces of bulk high temperature superconductor (HTS) above two types permanent magnet railway (PMR) is simulated using finite element method (FEM). The models are formulated by H-formulation and resolving codes is developed using Finite Element Program Generator (FEPG). The E- J power law is used to describe the electrical field vs. current density nonlinear characteristic of HTS. The applied magnetic fields induced by the PMR are calculated by the standard analysis method with the equivalent surface current model. By the method, the calculation formulation of magnetic fields generated by Halbach PMR and symmetrical PMR is derived respectively. The simulation results show that the finite element dynamic mesh rebuilding problem of HTS magnetic levitation transportation system comprised of bulk HTS and PMR can be easily avoided by the methods.

Lu, Yiyun; Zhuang, Shujun

2012-10-01

249

High-order optics of multipole magnets  

SciTech Connect

We have developed a new capability to compute third and fifth order Lie algebraic transfer maps for a family of realistic multipole magnets, including dipoles. The general Hamiltonian is expanded symbolically to arbitrary order. The vector potential off axis, for a given multipole symmetry, is determined from the appropriate magnetic field gradients and their longitudinal derivatives on axis. Subroutines to compute the required gradients are available for Halbach REC quadrupoles, and for general multipoles, with the current distribution on a cylindrical surface specified by a shape function. This function can be supplied by the user, or selected from internal options. Both the reference trajectory, and the map about it are calculated by numerical integration through the general magnetic field, using modular GENMAP software. This allows the calculation of curved reference trajectories in a general dipole magnet, as well as offset reference trajectories needed for misalignment tolerance studies. These new calculational capabilities have been added to the MARYLIE Lie Algebraic beam optics design code.

Walstrom, P.; Neri, F.; Mottershead, T.

1990-01-01

250

Time-domain study of spin-wave dynamics in two-dimensional arrays of bi-component magnetic structures  

NASA Astrophysics Data System (ADS)

Spin-waves in single Ni80Fe20 (Py) and Co bi-component units embedded in two-dimensional arrays thereof are investigated by all-optical time-resolved magneto-optical Kerr effect microscope. Two bands of modes observed for the bias field applied along the long-axis of the bi-component unit convert into four distinct bands, and the mode frequencies change significantly as the field is rotated to the short-axis. Micromagnetic simulations reproduce the experimental results, and comparison with single Py and Co elements and single bi-component unit reveals significant variations of mode frequencies and mode profiles, indicating opportunities for magnonic band engineering in this type of bi-component arrays.

Saha, Susmita; Barman, Saswati; Ding, Junjia; Adeyeye, Adekunle O.; Barman, Anjan

2013-06-01

251

Synthesis and Magnetic Properties of FePt Fe3Pt Nanowire Arrays Embedded in Anodic Alumina Membranes  

Microsoft Academic Search

FePt Fe3Pt nanowire arrays embedded in the nanochannels of anodic alumina membranes (AAM) were successfully fabricated by electrodeposition. X-ray diffraction (XRD) pattern indicates that the crystallites of FePt Fe3Pt nanowires embedded in AAM are face centered cubic structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that the diameter and the length of nanowires are about 60 nm

Yantao Pang; Baojin Zhang; Junqing Zhao; Jie Wang; Yanqi Wu

2012-01-01

252

An improved permanent magnet quadrupole design with larger good field region for high intensity proton linacs  

NASA Astrophysics Data System (ADS)

The Low Energy High Intensity Proton Accelerator (LEHIPA), being developed at the Bhabha Atomic Research Centre (BARC) will produce a 20 MeV, 30 mA, continuous wave (CW) proton beam. At these low velocities, space-charge forces dominate, and could lead to larger beam sizes and beam halos. Hence in the design of the focusing lattice of the LEHIPA drift tube linac (DTL) using permanent magnet quadrupoles (PMQs), a larger good field region is preferred. Here we study, using the two dimensional (2D) and three dimensional (3D) simulation codes PANDIRA and RADIA, four different types of cylindrical PMQ designs: 16-segment trapezoidal Halbach configuration, bullet-nosed geometry and 8- and 16-segment rectangular geometries. The trapezoidal Halbach geometry is used in a variety of accelerators since it provides very high field gradients in small bores, while the bullet-nosed geometry, which is a combination of the trapezoidal and rectangular designs, is used in some DTLs. This study shows that a larger good field region is possible in the 16-segment rectangular design as compared to the Halbach and bullet-nosed designs, making it more attractive for high-intensity proton linacs. An improvement in good-field region by ˜16% over the Halbach design is obtained in the optimized 16-segment rectangular design, although the field gradient is lower by ˜20%. Tolerance studies show that the rectangular segment PMQ design is substantially less sensitive to the easy axis orientation errors and hence will be a better choice for DTLs.

Mathew, Jose V.; Rao, S. V. L. S.; Krishnagopal, S.; Singh, P.

2013-11-01

253

Magnetism.  

National Technical Information Service (NTIS)

This program describes magnets and magnetic materials by pointing out the characteristics of the magnetic field, the molecular arrangement of magnetized and unmagnetized metals, the laws of attraction and repulsion, and the factors that affect the amount ...

1972-01-01

254

Hard modeling methods for the curve resolution of data from liquid chromatography with a diode array detector and on-flow liquid chromatography with nuclear magnetic resonance spectroscopy.  

PubMed

Hard modeling methods have been performed on data from high-performance liquid chromatography with a diode array detector (LC-DAD) and on-flow liquid chromatography with 1H nuclear magnetic spectroscopy (LC-NMR). Four methods have been used to optimize parameters to model concentration profiles, three of which belong to classical optimization methods (the simplex method of Nelder-Mead, sequential quadratic programming approach, and Levenberg-Marquardt method), and the fourth is the application of genetic algorithms using real-value encoding. Only classical methods worked well for LC-DAD data, while all of the methods produced good results when LC-NMR data were divided into small spectral windows of peak clusters and parameters were optimized over each window. PMID:16711734

Wasim, Mohammad; Brereton, Richard G

255

Use of a SQUID array to detect T-cells with magnetic nanoparticles in determining transplant rejection  

NASA Astrophysics Data System (ADS)

Acute rejection in organ transplant is signaled by the proliferation of T-cells that target and kill the donor cells requiring painful biopsies to detect rejection onset. An alternative non-invasive technique is proposed using a multi-channel superconducting quantum interference device (SQUID) magnetometer to detect T-cell lymphocytes in the transplanted organ labeled with magnetic nanoparticles conjugated to antibodies specifically attached to lymphocytic ligand receptors. After a magnetic field pulse, the T-cells produce a decaying magnetic signal with a characteristic time of the order of a second. The extreme sensitivity of this technique, 105 cells, can provide early warning of impending transplant rejection and monitor immune-suppressive chemotherapy.

Flynn, Edward R.; Bryant, H. C.; Bergemann, Christian; Larson, Richard S.; Lovato, Debbie; Sergatskov, Dmitri A.

2007-04-01

256

Surface potential and magnetic properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} periodic arrays fabricated by direct electron beam writing  

SciTech Connect

It is demonstrated that magnetic periodic arrays can be easily fabricated from direct writing water developable La{sub 0.7}Sr{sub 0.3}MnO{sub 3} electron beam resist. Two unique features of our approach are (1) the patterned La{sub 0.7}Sr{sub 0.3}MnO{sub 3} resist film can be developed using nontoxic and environmentally friendly pure water and (2) either positive or negative patterns can be fabricated depending on the dosage of electron beam. The mechanism of the dual function characteristic of the resist was studied using Kelvin probe microscope. The surface potential of patterned La{sub 0.7}Sr{sub 0.3}MnO{sub 3} resist increases with increasing electron beam dosage due to the changes of resist composition. The formations of periodic magnetic arrays were confirmed by the studies of scanning electron microscope and magnetic force microscope. The magnetization of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} can be enhanced by postsintering the sample at 900 deg. C after electron beam irradiation. We have therefore provided a one-step, simple, and convenient alternative technique for the fabrication of nanoscale magnetic patterns, which form the building blocks for the study of physical properties in periodic magnetic arrays.

Wu, M.-C.; Wu, Y.-J.; Huang, Y.-C.; Chuang, C.-M. [Department of Materials Science and Engineering, National Taiwan University, Taipei 106-17, Taiwan (China); Cheng, K.-C. [Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 106-08, Taiwan (China); Lin, C.-F. [Graduate Institute of Electro-optical Engineering and Department of Electrical Engineering, National Taiwan University, Taipei 106-17, Taiwan (China); Chen, Y.-F. [Department of Physics, National Taiwan University, Taipei 106-17, Taiwan (China); Center for Condensed Matter Sciences, National Taiwan University, Taipei 106-17, Taiwan (China); Su, W.-F. [Department of Materials Science and Engineering, National Taiwan University, Taipei 106-17, Taiwan (China); Center for Condensed Matter Sciences, National Taiwan University, Taipei 106-17, Taiwan (China)

2008-07-15

257

Simulations of electron trajectories under the influence of an array of permanent magnets in a compact ion source  

NASA Astrophysics Data System (ADS)

Trajectories of electrons emitted from a filament in a discharge ion source are computer simulated in order to investigate their behavior under the influence of different magnetic fields. These calculations allowed a better understanding of the high efficiency obtained in a recently developed compact ion source.

Somacal, H.; Huck, H.; di Gregorio, D. E.; Fernández Niello, J. O.; Igarzábal, M.

2002-09-01

258

A magnetic quadrupole from rectangular permanent magnets  

NASA Astrophysics Data System (ADS)

An analytical model of iron-free pure permanent magnet (PPM) quadrupole consisting of rectangular magnets is presented. Its strength is tunable via the retraction of four magnet arms so that it can be axially compact also. Its working principle is given by a theory of ideal rectangular PPM quadrupole developed from the theory of planar PPM undulators. It is simple to build and tune for minimization of the undesired higher harmonics arising in practice. It has demagnetizing fields limited to the linear region of the B-H curve. Its field quality is not degraded by anisotropic nonunit permeability of rare-earth alloys (like NdFeB, SmCo). Its parameters are suitable between ultra-compact high-gradient Halbach quadrupoles and low-gradient-medium-aperture iron pole current-fed quadrupoles. It can be suitable for applications like focussing inside a free electron laser cavity, horizontal focussing between contiguous undulators in XFELs or final focussing in scattering experiments.

Biswas, B.

2009-07-01

259

Systolic arrays  

SciTech Connect

Selected Contents of this book are: Efficient Systolic Arrays for the Solution of Toeplitz Systems, The Derivation and Utilization of Bit Level Systolic Array Architectures, an Efficient Systolic Array for Distance Computation Required in a Video-Codec Based Motion-Detection, On Realizations of Least-Squares Estimation and Kalman Filtering by Systolic Arrays, and Comparison of Systolic and SIMD Architectures for Computer Vision Computations.

Moore, W.R.; McCabe, A.P.H.; Vrquhart, R.B.

1987-01-01

260

Nanocylinder arrays  

DOEpatents

Pathways to rapid and reliable fabrication of nanocylinder arrays are provided. Simple methods are described for the production of well-ordered arrays of nanopores, nanowires, and other materials. This is accomplished by orienting copolymer films and removing a component from the film to produce nanopores, that in turn, can be filled with materials to produce the arrays. The resulting arrays can be used to produce nanoscale media, devices, and systems.

Tuominen, Mark (Shutesbury, MA); Schotter, Joerg (Bielefeld, DE); Thurn-Albrecht, Thomas (Freiburg, DE); Russell, Thomas P. (Amherst, MA)

2009-08-11

261

Method and apparatus for control of a magnetic structure  

SciTech Connect

A method and apparatus for independently adjusting the spacing between opposing magnet arrays in charged particle based light sources. Adjustment mechanisms between each of the magnet arrays and the supporting structure allow the gap between the two magnet arrays to be independently adjusted. In addition, spherical bearings in the linkages to the magnet arrays permit the transverse angular orientation of the magnet arrays to also be adjusted. The opposing magnet arrays can be supported above the ground by the structural support. 4 figs.

Challenger, M.P.; Valla, A.S.

1996-06-18

262

AC current rectification in Nb films with or without symmetrical Nb/Ni periodic pinning arrays in perpendicular magnetic field  

NASA Astrophysics Data System (ADS)

Rectification of AC current has been observed in plain superconducting Nb films and in Nb/Ni films with symmetric periodic pinning centers. The rectified DC voltage appears for various sample geometries (cross or strip) both along and transverse to the alternating current direction, is nearly anti-symmetric with perpendicular magnetic field and strongly dependent on temperature below Tc. Analyses of the data at different temperatures, drive frequencies from 100kHz to 150MHz and at the different sample sides [1] shows that not far below Tc the rectification phenomena can be understood in terms of generation of electric fields due to local excess of critical current. Further below Tc anisotropic pinning effects could also contribute to the rectification. [1] F.G.Aliev, et al., Cond. Mat.405656. Supported by Comunidad Autonoma de Madrid -CAM/07N/0050/2002

Pryadun, Vladimir

2005-03-01

263

Chemical identification strategies using liquid chromatography-photodiode array-solid-phase extraction-nuclear magnetic resonance/mass spectrometry.  

PubMed

The identification of metabolites in biochemical studies is a major bottleneck in the proliferating field of metabolomics. In particular in plant metabolomics, given the diversity and abundance of endogenous secondary metabolites in plants, the identification of these is not only challenging but also essential to understanding their biological role in the plant, and their value to quality and nutritional attributes as food crops. With the new generation of analytical technologies, in which liquid chromatography (LC)-mass spectrometry (MS) and nuclear magnetic resonance (NMR) play a pioneering role, profiling metabolites in complex extracts is feasible at high throughput. However, the identification of key metabolites remains a limitation given the analytical effort necessary for traditional structural elucidation strategies. The hyphenation of LC-solid phase extraction (SPE)-NMR is a powerful analytical platform for isolating and concentrating metabolites for unequivocal identification by NMR measurements. The combination with LC-MS is a relatively straightforward approach to obtaining all necessary information for structural elucidation. Using this set-up, we could, as an example, readily identify five related glycosylated phenolic acids present in broccoli (Brassica oleracea, group Italica, cv Monaco): 1,2-di-O-E-sinapoyl-?-gentiobiose, 1-O-E-sinapoyl-2-O-E-feruloyl-?-gentiobiose, 1,2-di-O-E-feruloyl-?-gentiobiose, 1,2,2'-tri-O-E-sinapoyl-?-gentiobiose, and 1,2'-di-O-E-sinapoyl-2-O-E-feruloyl-?-gentiobiose. PMID:22351183

Moco, Sofia; Vervoort, Jacques

2012-01-01

264

Magnetism  

NSDL National Science Digital Library

This webpage is part of the University Corporation for Atmospheric Research (UCAR) Windows to the Universe program. It describes the nature and configuration of magnetic fields, which are the result of moving electric charges, including how they cause magnetic objects to orient themselves along the direction of the magnetic force points, which are illustrated as lines. Magnetic field lines by convention point outwards at the north magnetic pole and inward at the south magnetic pole. The site features text, scientific illustrations and an animation. Text and vocabulary are selectable for the beginning, intermediate, or advanced reader.

Team, University C.

2007-12-12

265

Polarization Dependence of Readout Signals from Periodic One-Dimensional Arrays of Magnetic Domains in Magneto-Optical Media and Crystalline-Amorphous Line Pairs in PhaseChange Media of Optical Recording  

Microsoft Academic Search

Polarization dependence of signals from periodic one-dimensional arrays of magnetic domains in magneto-optical (MO) media and crystalline domains in amorphous phase-change (PC) media has been studied by theoretical calculation and experiment. The MO signal in the small-period regime depends on the direction of incident polarization. The relative strength of theE || and E signals changes depending on the period of

Rongguang Liang; Lifeng Li; Kimihiro Saito; Masud Mansuripur

2001-01-01

266

An experimental investigation of the improvement in the reception of TM (Transverse Magnetic)-polarized LF (Low-Frequency) waves with a two-element spaced array  

Microsoft Academic Search

For this study, a 2-element spaced array antenna system was developed and tested. This array consisted of two well-spaced vertical loops combined with a microwave link. The array was tested to show improvements in signal-to-noise ratio over omnidirectional antennas, using received transmissions from an aircraft towing a long wire antenna. Gains in signal-to-noise ratio of up to 12.8 dB were

F. M. Tingley; R. C. Kahler

1984-01-01

267

An experimental investigation of the improvement in the reception of TM (Transverse Magnetic)-polarized LF (Low-Frequency) waves with a two-element spaced array  

NASA Astrophysics Data System (ADS)

For this study, a 2-element spaced array antenna system was developed and tested. This array consisted of two well-spaced vertical loops combined with a microwave link. The array was tested to show improvements in signal-to-noise ratio over omnidirectional antennas, using received transmissions from an aircraft towing a long wire antenna. Gains in signal-to-noise ratio of up to 12.8 dB were demonstrated.

Tingley, F. M.; Kahler, R. C.

1984-05-01

268

Array capabilities and future arrays  

SciTech Connect

Early results from the new third-generation instruments GAMMASPHERE and EUROGAM are confirming the expectation that such arrays will have a revolutionary effect on the field of high-spin nuclear structure. When completed, GAMMASHPERE will have a resolving power am order of magnitude greater that of the best second-generation arrays. When combined with other instruments such as particle-detector arrays and fragment mass analysers, the capabilites of the arrays for the study of more exotic nuclei will be further enhanced. In order to better understand the limitations of these instruments, and to design improved future detector systems, it is important to have some intelligible and reliable calculation for the relative resolving power of different instrument designs. The derivation of such a figure of merit will be briefly presented, and the relative sensitivities of arrays currently proposed or under construction presented. The design of TRIGAM, a new third-generation array proposed for Chalk River, will also be discussed. It is instructive to consider how far arrays of Compton-suppressed Ge detectors could be taken. For example, it will be shown that an idealised {open_quote}perfect{close_quotes} third-generation array of 1000 detectors has a sensitivity an order of magnitude higher again than that of GAMMASPHERE. Less conventional options for new arrays will also be explored.

Radford, D.

1993-10-01

269

DNA Arrays  

NSDL National Science Digital Library

This animation from Cold Spring Harbor Laboratory's Dolan DNA Learning Center presents DNA arrays. The animation contains information on Pat Brown's discovery and the purpose of DNA arrays to study gene expression as well as its role in the development of pharmacogenomic treatment for diseases such as cancer.

2012-04-10

270

Enthalpy arrays  

NASA Astrophysics Data System (ADS)

We report the fabrication of enthalpy arrays and their use to detect molecular interactions, including protein-ligand binding, enzymatic turnover, and mitochondrial respiration. Enthalpy arrays provide a universal assay methodology with no need for specific assay development such as fluorescent labeling or immobilization of reagents, which can adversely affect the interaction. Microscale technology enables the fabrication of 96-detector enthalpy arrays on large substrates. The reduction in scale results in large decreases in both the sample quantity and the measurement time compared with conventional microcalorimetry. We demonstrate the utility of the enthalpy arrays by showing measurements for two protein-ligand binding interactions (RNase A + cytidine 2'-monophosphate and streptavidin + biotin), phosphorylation of glucose by hexokinase, and respiration of mitochondria in the presence of 2,4-dinitrophenol uncoupler.

Torres, Francisco E.; Kuhn, Peter; de Bruyker, Dirk; Bell, Alan G.; Wolkin, Michal V.; Peeters, Eric; Williamson, James R.; Anderson, Gregory B.; Schmitz, Gregory P.; Recht, Michael I.; Schweizer, Sandra; Scott, Lincoln G.; Ho, Jackson H.; Elrod, Scott A.; Schultz, Peter G.; Lerner, Richard A.; Bruce, Richard H.

2004-06-01

271

Magnetism  

NSDL National Science Digital Library

This overview of magnetism provides a brief history prior to 1600 and continues with the work of William Gilbert, Hans Christian Oersted, and Andre-Marie Ampere in describing and exploring the magnetosphere and learning the role that electric current plays in producing magnetism. Magnetic field lines are then discussed, citing the work of Michael Faraday. The work of James Clerk Maxwell and Heinrich Hertz is mentioned in a discussion of the relationship of light waves and radio waves as part of the electromagnetic spectrum.

Stern, David

272

Surface potential and magnetic properties of La{sub 0.7}Sr{sub 0.3}MnO periodic arrays fabricated by direct electron beam writing  

Microsoft Academic Search

It is demonstrated that magnetic periodic arrays can be easily fabricated from direct writing water developable La{sub 0.7}Sr{sub 0.3}MnO electron beam resist. Two unique features of our approach are (1) the patterned La{sub 0.7}Sr{sub 0.3}MnO resist film can be developed using nontoxic and environmentally friendly pure water and (2) either positive or negative patterns can be fabricated depending on the

M.-C. Wu; Y.-J. Wu; Y.-C. Huang; C.-M. Chuang; K.-C. Cheng; C.-F. Lin; Y.-F. Chen; W.-F. Su

2008-01-01

273

MAGNETS  

DOEpatents

This patent relates to nmgnets used in a calutron and more particularly to means fur clamping an assembly of magnet coils and coil spacers into tightly assembled relation in a fluid-tight vessel. The magnet comprises windings made up of an assembly of alternate pan-cake type coils and spacers disposed in a fluid-tight vessel. At one end of the tank a plurality of clamping strips are held firmly against the assembly by adjustable bolts extending through the adjacent wall. The foregoing arrangement permits taking up any looseness which may develop in the assembly of coils and spacers.

Hofacker, H.B.

1958-09-23

274

Metamaterial-Substrate Antenna Array for MIMO Communication System  

Microsoft Academic Search

We demonstrate how a magnetic permeability enhanced metamaterial can enhance the antenna array of a multiple-input multiple-output(MIMO) communication system. The performance of a rectangular patch antenna array on a metamaterial substrate was studied relative to a similar array constructed on a conventional FR4 substrate. Differently spaced arrays were analytically compared using array correlation coefficients and mean effective gain as performance

Prathaban Mookiah; Kapil R. Dandekar

2009-01-01

275

Sonar Arrays and Array Processing  

NASA Astrophysics Data System (ADS)

Arrays of hydrophones have been part of Navy sonar systems for over fifty years now. They are used both passively and actively and now are quite sophisticated. These arrays were used in fixed configuration such as the SOSUS system and towed arrays deployed from surface ships and submarines. One can assert that these arrays were a key factor in winning the cold war. Similarly, medical ultrasonics have used many of the techniques initially developed for sonar systems save four orders of magnitude in frequency. The major area where modern sonars differ involves the use of adaptive array processing whereby one usually needs to localize a weak signal in the presence of strong interference in a nonstationary environment. Most of the recent literature concerns advancing these techniques especially making them more robust to environmental uncertainties including calibration and properties of the ocean. This presentation will give an overview of the state of the art in sonar and hopefully establish a few points of relevance with nondestructive testing.

Baggeroer, A. B.

2005-04-01

276

Magnetic Cusp Configuration of the SPL Plasma Generator  

SciTech Connect

The Superconducting Proton Linac (SPL) is a novel linear accelerator concept currently studied at CERN. As part of this study, a new Cs-free, RF-driven external antenna H{sup -} plasma generator has been developed to withstand an average thermal load of 6 kW. The magnetic configuration of the new plasma generator includes a dodecapole cusp field and a filter field separating the plasma heating and H{sup -} production regions. Ferrites surrounding the RF antenna serve in enhancing the coupling of the RF to the plasma. Due to the space requirements of the plasma chamber cooling circuit, the cusp magnets are pushed outwards compared to Linac4 and the cusp field strength in the plasma region is reduced by 40% when N-S magnetized magnets are used. The cusp field strength and plasma confinement can be improved by replacing the N-S magnets with offset Halbach elements of which each consists of three magnetic sub-elements with different magnetization direction. A design challenge is the dissipation of RF power induced by eddy currents in the cusp and filter magnets which may lead to overheating and demagnetization. In view of this, a copper magnet cage has been developed that shields the cusp magnets from the radiation of the RF antenna.

Kronberger, Matthias; Chaudet, Elodie; Favre, Gilles; Lettry, Jacques; Kuechler, Detlef; Moyret, Pierre; Paoluzzi, Mauro; Prever-Loiri, Laurent; Schmitzer, Claus; Scrivens, Richard; Steyaert, Didier [CERN, 385 Route de Meyrin, 1211 Geneva (Switzerland)

2011-09-26

277

Coupling a CLOVER detector array with the PRISMA magnetic spectrometer. Investigation of moderately neutron-rich nuclei populated by multinucleon transfer and deep inelastic collisions  

NASA Astrophysics Data System (ADS)

. Following the commissioning of the PRISMA large-acceptance spectrometer, installed at the Laboratori Nazionali di Legnaro (LNL), an international nuclear-structure collaboration has started to develop a large ? -ray setup to be installed in the target position of the spectrometer. The array is based on the EUROBALL composite CLOVER detectors. In this contribution the CLOVER detector array is described and its expected performance figures discussed. This new setup, by using the high-intensity heavy-ion beams provided by the LNL ALPI linac, will push the study of nuclear structure towards moderately neutron-rich nuclei by means of quasi-elastic and deep inelastic reactions.

EUROBALL and PRISMA-2 Collaboration; Gadea, A.; Napoli, D. R.; de Angelis, G.; Menegazzo, R.; Stefanini, A. M.; Corradi, L.; Axiotis, M.; Berti, L.; Fioretto, E.; Kroell, T.; Latina, A.; Marginean, N.; Maron, G.; Martinez, T.; Rosso, D.; Rusu, C.; Toniolo, N.; Szilner, S.; Trotta, M.; Bazzacco, D.; Beghini, S.; Bellato, M.; Brandolini, F.; Farnea, E.; Isocrate, R.; Lenzi, S. M.; Lunardi, S.; Montagnoli, G.; Pavan, P.; Rossi Alvarez, C.; Scarlassara, F.; Ur, C.; Blasi, N.; Bracco, A.; Camera, F.; Leoni, S.; Million, B.; Pignanelli, M.; Pollarolo, G.; DeRosa, A.; Inglima, G.; La Commara, M.; La Rana, G.; Pierroutsakou, D.; Romoli, M.; Sandoli, M.; Bizzeti, P. G.; Bizzeti-Sona, A. M.; Lo Bianco, G.; Petrache, C. M.; Zucchiatti, A.; Cocconi, P.; Quintana, B.; Beck, Ch; Curien, D.; Duchene, G.; Haas, F.; Medina, P.; Papka, P.; Durell, J.; Freeman, S. J.; Smith, A.; Varley, B.; Fayz, K.; Pucknell, V.; Simpson, J.; Gelletly, W.; Regan, P.

2003-04-01

278

Nanocap arrays of granular CoCrPt:SiO2 films on silica particles: tailoring of the magnetic properties by Co + irradiation  

NASA Astrophysics Data System (ADS)

An approach for tailoring the magnetic properties by ion irradiation of granular perpendicular CoCrPt:SiO2 films grown on silica particles with sizes down to 10 nm was investigated. The as-prepared samples reveal an intriguing scaling dependence of the coercive field and remnant magnetization: both parameters are found to decrease with decreasing particle size. However, Co + irradiation at a low fluence of 0.5 × 1014 cm - 2 already results in an opposite scaling behavior. It is assumed that this modification is due to the enhancement of the intergranular magnetic exchange coupling of the granular CoCrPt:SiO2 film initiated by Co + irradiation resulting in a modified reversal behavior. Further increase of the irradiation fluence beyond 1.6 × 1014 ions cm - 2 leads to a degradation of the magnetic layer properties, lowering the remnant magnetization and the coercive field in the easy-axis direction. Moreover, the local magnetic properties of the samples were analyzed by magnetic force microscopy revealing magnetic multi-domain cap structures.

Krone, P.; Brombacher, C.; Makarov, D.; Lenz, K.; Ball, D.; Springer, F.; Rohrmann, H.; Fassbender, J.; Albrecht, M.

2010-09-01

279

Trapped magnetic field profiles of arrays of (Gd,Y)Ba2Cu3Ox superconductor tape in different stacking configurations  

NASA Astrophysics Data System (ADS)

Trapped magnetic field profiles were investigated in thin film (Gd,Y)Ba2Cu3Ox superconducting tapes stacked in different configurations consisting of three 12 mm wide, 36 mm long tapes per layer. The trapped magnetic field values were found to increase monotonically with the increasing number of tape layers in the stack. A crisscross arrangement of the tapes was found to yield a more uniform trapped-field profile than a straight arrangement of the tapes. Furthermore, the decay rate of the trapped magnetic field as a function of distance from the tape stack surface was found to be lower in the crisscross arrangement.

Selva, Kavita; Majkic, Goran

2013-11-01

280

DTU Space magnetometer array  

NASA Astrophysics Data System (ADS)

DTU Space is monitoring the Earth's magnetic field with a network of ground stations in Greenland, Denmark, and the South Atlantic. An array with 17 stations at coastal locations is operated in Greenland. All stations provide full vector geomagnetic field variations with 1 Hz resolution, and 5 stations are geomagnetic observatories and calibrated to INTERMAGNET standards. The magnetometer array is listed as an asset for the ESA's Space Situational Awareness (SSA) program and it is an integral part in the EU FP7 project ESPAS. The outstanding location of the magnetometer array reaching from the geomagnetic pole over the auroral and subauroral region, and one observatory in the South Atlantic Anomaly region makes it useful for Space Weather applications and Space Physics investigations. The observatory in Narsarsuaq (NAQ) is one of 12 stations contributing to the auroral electrojet index distributed by the WDC Kyoto. However, even for low indices AE < 100 we found considerable geomagnetic disturbances northward of NAQ station that can be attributed to auroral electrojet activity. The distribution in local time and latitude of such disturbances will be presented and discussed in this paper.

Stolle, C.; Matzka, J.; Sarauw, E.; Pedersen, L. W.

2012-04-01

281

A 10 ns read and write non-volatile memory array using a magnetic tunnel junction and FET switch in each cell  

Microsoft Academic Search

Magnetic random access memory (MRAM) offers an alternative approach to fast low-power non-volatile VLSI memory. MRAM has been pursued for more than 10 years as a robust non-volatile memory for space applications. The magnetic tunnel junction (MTJ) MRAM is dramatically different and achieves four orders of magnitude better bandwidth to sense power ratio by utilizing a high resistance and high

Roy Scheuerlein; William Gallagher; Stuart Parkin; Alex Lee; Sam Ray; Ray Robertazzi; William Reohr

2000-01-01

282

Design of a permanent magnet with a mechanical sweep suitable for variable-temperature continuous-wave and pulsed EPR spectroscopy.  

PubMed

A magnetic system is introduced which consists of three nested rings of permanent magnets of a Halbach dipolar layout and is capable for EPR spectroscopy. Two of the rings can be rotated independently to adjust the magnetic flux in the center and even allow for mechanical field sweeps. The presented prototype achieves a magnetic flux range of 0.0282-0.3013T with a minimal sweep of 0.15mT and homogeneity of about 10(-3). First applications with CW and pulsed Mims ENDOR as well as ESEEM experiments on a sample of a glycine single crystal doped with 1% copper nitrate demonstrate that flux range, sweep accuracy and homogeneity of this prototype is sufficient for EPR experiments on most solid samples. Together with a recently improved design magnets can be build which could serve as compact and easily transportable replacement of standard electromagnets with negligible consumption of power or coolants. PMID:19299174

Bauer, C; Raich, H; Jeschke, G; Blümler, P

2009-02-27

283

Array tomography.  

PubMed

In array tomography ordered, ribbon-like assemblies of ultrathin serial sections are deposited on a solid substrate and imaged afterwards. The resulting images are then aligned and reconstructed into a three-dimensional representation of the object. Depending on the preparation and labelling regime, different imaging modalities can be applied. When using light microscopy, the labelling with fluorescent markers would be the obvious choice, whereas the imaging in a scanning electron microscope would require impregnation with heavy metals. Depending on preparative constraints, the combination of diverse imaging modalities or truly correlative imaging is possible. PMID:24111814

Wacker, I; Schroeder, R R

2013-09-20

284

The Square Kilometre Array  

NASA Astrophysics Data System (ADS)

The Square Kilometre Array (SKA) is the future centimeter- and meter-wavelength telescope with a sensitivity about 50 times higher than present instruments. Its Key Science Projects are (a) Astrobiology including planetary formation within protoplanetary disks; (b) Testing theories of gravitation using an array of pulsars to search for gravitational waves and relativistic binaries to probe the strong-field regime; (c) The origin and evolution of cosmic magnetism, both within the Galaxy and in intergalactic space, via an all-sky grid of magnetic field measurements; (d) The end of the Dark Ages, involving searches for a neutral hydrogen signature, the first supermassive black holes, and the first metal-rich systems; and (e) A hydrogen census to a redshift z greater than or equal to 1 from which to study the evolution of galaxies, dark matter, and dark energy. The SKA will operate at wavelengths from 1.2 cm to 3 m (0.1-25 GHz), providing milliarcsecond resolution at the shortest wavelengths. Its instantaneous field of view will be about 1° (20 cm wavelength), with many simultaneous beams on the sky. The Reference Design is composed of a large number of small dish antennas, building upon an original US proposal. In order to obtain these capabilities at a reasonable cost, significant engineering investments are being made in antennas, wideband feeds and receivers, and signal processing; aperture arrays (phased feeds) are also being investigated in Europe for the lower frequencies. Candidate sites are in Argentina, Australia, China, and South Africa, with a short list of acceptable sites anticipated late in 2006.

Terzian, Yervant; Lazio, Joseph

2006-07-01

285

Anisotropy of the critical temperature of a superconducting niobium thin film with an array of nanoscale holes in an external magnetic field  

NASA Astrophysics Data System (ADS)

We report on magnetotransport experiments investigating the effect of a regular array of nanoscale holes on the anisotropic response in the transition temperature of a superconducting niobium thin film. We find that the angle dependence of the critical temperature exhibits two strong anisotropic effects: Little-Parks oscillations whose period varies with field direction and a smooth background arising from one-dimensional confinement by the finite lateral space between neighboring holes. The two components of the anisotropy are intrinsically linked and appear in concert with one superimposed on top of the other.

Latimer, M. L.; Xiao, Z. L.; Hua, J.; Joshi-Imre, A.; Wang, Y. L.; Divan, R.; Kwok, W. K.; Crabtree, G. W.

2013-01-01

286

Piezoelectric Volumetric Array.  

National Technical Information Service (NTIS)

A three-dimensional array of acoustic sensors. The array can be used for both the transmission and reception of acoustic signals. The array comprises electroplated piezoelectric polymer layers that are laminated with a non- conductive epoxy to form indivi...

K. C. Benjamin

2002-01-01

287

Ultrawide Bandwidth 2 $\\\\,\\\\times\\\\,$2 Microstrip Patch Array Antenna Using Electromagnetic BandGap Structure (EBG)  

Microsoft Academic Search

Four types of EBG structures are proposed and used in the design of a patch antenna array to improve the bandwidth, gain and reduce the overall array size. The four ground plane designs for the 2 2 microstrip patch antenna array (MPAA) are; spiral artificial magnetic conductor (SAMC) ground plane, an SAMC embedded with a large spiral artificial magnetic conductor

Dalia Nashaat; Hala A. Elsadek; Esmat A. Abdallah; Magdy F. Iskander; Hadia M. Elhenawy

2011-01-01

288

Diode Laser Arrays  

NASA Astrophysics Data System (ADS)

Contributors; 1. Monolithic phase-locked semiconductor laser arrays D. Botez; 2. High power coherent, semiconductor laser master oscillator power amplifiers and amplifier arrays D. F. Welch and D. G. Mehuys; 3. Microoptical components applied to incoherent and coherent laser arrays J. R. Leger; 4. Modeling of diode laser arrays G. R. Hadley; 5. Dynamics of coherent semiconductor laser arrays H. G. Winfuland and R. K. Defreez; 6. High average power semiconductor laser arrays and laser array packaging with an emphasis for pumping solid state lasers R. Solarz; 7. High power diode laser arrays and their reliability D. R. Scifres and H. H. Kung; 8. Strained layer quantum well heterostructure laser arrays J. J. Coleman; 9. Vertical cavity surface emitting laser arrays C. J. Chang-Hasnain; 10. Individually addressed arrays of diode lasers D. Carlin.

Botez, Dan; Scifres, Don R.

2005-11-01

289

Designs for a Microfabricated Magnetic Sifter  

Microsoft Academic Search

A microfabricated magnetic sifter has been designed and fabricated for applications in biological sample preparation. The device enables high-throughput, high-gradient magnetic separation of magnetic nanoparticles by utilizing parallel fluid flow through a dense array (~500 \\/mm2 ) of micropatterned slots in a magnetically soft membrane. Finite element models have been carried out to map the magnetic field and magnetic field

Christopher M. Earhart; Evelyn M. Nguyen; Robert J. Wilson; Y. Andrew Wang; Shan X. Wang

2009-01-01

290

Fabrication of electromagnetic micromirror array  

NASA Astrophysics Data System (ADS)

This paper describes the design, fabrication and experiments of a micromirror array driven by electromagnetic force for right angle beam reflection to the vertical direction of the substrate. The device was fabricated using aluminum surface micromachining combined with nickel electroplating. The micromirror has couple of torsional springs enough long for 45 degree rotation, which angular deflection is necessary for right angle beam reflection. Also micromirror has a magnetic material for electromagnetic operation, and it has a mechanical stopper for angular deflection control. The main structural material is evaporated aluminum, and magnetic material is electroplated nickel. Thick photoresist is used as a sacrificial layer, and it is removed by oxygen plasma process. Electromagnetic characteristics were measured to find that about 10kA/m magnetic field intensity is needed for 45 degrees angular deflection. 25V to approximately 50V clamping voltage is required for selectively operation between the array within the external magnetic field. The dynamic response measurement was fulfilled using He-Ne laser and position sensitive diode (PSD). The lapsed time to reach 45 degrees is less than 0.5ms. But upward spring bending prevents the stopper from touching the substrate, so some oscillations corresponding to natural response is observed.

Jang, YunHo; Kim, Yong-Kweon

2001-09-01

291

EVOLUTION OF MAGNETIC FIELDS IN HIGH MASS STAR FORMATION: SUBMILLIMETER ARRAY DUST POLARIZATION IMAGE OF THE ULTRACOMPACT H II REGION G5.89-0.39  

SciTech Connect

We report high angular resolution (3'') Submillimeter Array (SMA) observations of the molecular cloud associated with the Ultracompact H II region G5.89 - 0.39. Imaged dust continuum emission at 870 {mu}m reveals significant linear polarization. The position angles (P.A.s) of the polarization vary enormously but smoothly in a region of 2 x 10{sup 4} AU. Based on the distribution of the P.A.s and the associated structures, the polarized emission can be separated roughly into two components. The component 'x' is associated with a well-defined dust ridge at 870 {mu}m, and is likely tracing a compressed B field. The component 'o' is located at the periphery of the dust ridge and is probably from the original B field associated with a pre-existing extended structure. The global B field morphology in G5.89, as inferred from the P.A.s, is clearly disturbed by the expansion of the H II region and the molecular outflows. Using the Chandrasekhar-Fermi method, we estimate from the smoothness of the field structures that the B field strength in the plane of sky can be no more than 2-3 mG. We then compare the energy densities in the radiation, the B field, and the mechanical motions as deduced from the C{sup 17}O 3-2 line emission. We conclude that the B field structures are already overwhelmed and dominated by the radiation, outflows, and turbulence from the newly formed massive stars.

Tang, Y.-W. [Department of Physics, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan (China); Ho, Paul T. P.; Rao, Ramprasad; Koch, Patrick; Lai, Shih-Ping [Academia Sinica Institute of Astronomy and Astrophysics, P. B. Box 23-141, Taipei 10617, Taiwan (China); Girart, Josep Miquel [Institut de Ciencies de l' Espai (CSIC-IEEC), Campus UAB, Facultat de Ciencies, Torre C5-parell 2, 08193 Bellaterra, Catalunya (Spain)

2009-04-20

292

Prostate and lymph node proton magnetic resonance (MR) spectroscopic imaging with external array coils at 3 T to detect recurrent prostate cancer after radiation therapy.  

PubMed

In a patient suspected of having recurrent prostate cancer after radiation therapy, we demonstrate the feasibility of noninvasive proton magnetic resonance spectroscopic (1H-MRS) imaging of the prostate and a lymph node at 3 T using a matrix of external surface coils. Written informed consent was obtained from the patient. With 1H-MRS imaging, high choline with low citrate signal was observed in the prostate, and in the lymph node a signal of choline-containing compounds was identified. The tissue level of the compounds in the enlarged lymph node was estimated to be 8.1 mmol/kg water. Subsequent histopathological analysis of systematic transrectal ultrasound-guided prostate biopsy and computed tomography-guided biopsy of the lymph node confirmed the presence of prostate cancer in both. PMID:17507814

Heijmink, Stijn W T P J; Scheenen, Tom W J; Fütterer, Jurgen J; Klomp, Dennis W J; Heesakkers, Roel A M; Hulsbergen-van de Kaa, Christina A; van Lin, Emile N J Th; Heerschap, Arend; Barentsz, Jelle O

2007-06-01

293

Integration of magnetic solid phase fishing and off-line two-dimensional high-performance liquid chromatography-diode array detector-mass spectrometry for screening and identification of human serum albumin binders from Radix Astragali.  

PubMed

Radix Astragali is one of the most popular traditional medicinal herb and healthy dietary supplement. Isoflavonoids and astragalosides are the main bioactive ingredients. However, the systematic bioactive component analysis is inadequate so far. Then a facile method based on Fe3O4@SiO2-human serum albumin (Fe3O4@SiO2-HSA) magnetic solid phase fishing integrated with two-dimensional high-performance liquid chromatography-diode array detector-mass spectrometry (2D HPLC-DAD-MS(n)) was developed to fish out and identify HSA binders from Radix Astragali. The immobilized HSA displayed a high stability with 96.2% retained after ten consecutive cycles. 2D HPLC system (size exclusion chromatography×reversed phase chromatography, SEC×RP) were developed and optimised. Forty-seven bioactive compounds including thirty-four isoflavonoids and thirteen astragalosides were screened and identified or tentatively deduced based on their retention time, ultraviolet (UV), accurate molecular weight and diagnostic fragment ions. The results indicated that the integrated method could be widely applied for systematical fishing and identification of bioactive compounds, especially for low-abundance and overlapped compounds, from complex mixtures. PMID:24176313

Zhang, Yuping; Nie, Mingkun; Shi, Shuyun; You, Qingping; Guo, Junfang; Liu, Liangliang

2013-09-13

294

Magnetic multipole redirector of moving plasmas  

DOEpatents

A method and apparatus for redirecting moving plasma streams using a multiple array of magnetic field generators (e.g., permanent magnets or current bearing wires). Alternate rows of the array have opposite magnetic field directions. A fine wire mesh may be employed to focus as well as redirect the plasma.

Crow, James T. (Albuquerque, NM); Mowrer, Gary R. (Cedar Crest, NM)

1999-01-01

295

Piezoelectric Volumetric Array  

NASA Astrophysics Data System (ADS)

A three-dimensional array of acoustic sensors. The array can be used for both the transmission and reception of acoustic signals. The array comprises electroplated piezoelectric polymer layers that are laminated with a non-conductive epoxy to form individual multi-layer array transducer elements. Circuit support layer layers are incorporated between the multi-layer array transducer elements. Because of the three-dimensional configuration of the array, logical transducers can be created from multiple transducer elements, and transmission and reception of acoustic signals in any direction can be realized.

Benjamin, Kim C.

2002-09-01

296

Mutual Coupling Effects in Antenna Arrays, Volume 1.  

National Technical Information Service (NTIS)

Mutual coupling between rectangular apertures in a finite antenna array, in an infinite ground plane, is analyzed using the vector potential approach. The method of moments is used to solve the equations that result from setting the tangential magnetic fi...

R. E. Collin

1986-01-01

297

Drag Current Reversal in Capacitively Coupled Arrays of Small Josephson Junctions  

NASA Astrophysics Data System (ADS)

The current-voltage characteristics of two long capacitively coupled one-dimensional arrays of small Josephson junctions were measured, where the coupling capacitance was comparable with the capacitance of the junction. The current in both arrays was simultaneously measured at various applied magnetic fields with the voltage applied to only one of the arrays. The current was induced in the unbiased array beyond the threshold voltage for the Coulomb blockade of the biased array. The direction of the induced current is the same as that of the current in the other array when the applied magnetic field is small and Cooper-pair tunneling is dominant, while it changes to the opposite direction when the applied magnetic field is large and single-electron tunneling is dominant. This suggests that the current induction mechanism between arrays of small Josephson junctions is substantially different from that in arrays of small normal tunnel junctions.

Shimada, Hiroshi; Ishida, Chihiro; Mizugaki, Yoshinao

2012-11-01

298

Effects of array arrangements in nano-patterned thin film media  

NASA Astrophysics Data System (ADS)

In this work, the effect of different arrays arrangements on the magnetic behaviour of patterned thin film media is simulated. The modeled films consist of 80×80 cobalt grains of uniform diameter (20 nm) distributed into two different array arrangement: hexagonal (triangular) or square arrays. In addition to that, for each array arrangement, two cases of anisotropy orientations, random and textured films are considered. For both array arrangements and media orientations, hysteresis loops at different array separation (d) were simulated. Predictions show that for closely packed films, the shearing effects on the magnetization loop are much larger for the square array arrangement than the hexagonal one. According to these predictions, the bit switching field distribution in interacting 2D systems is much narrower for the hexagonal array arrangement. This result could be very important for high-density magnetic recording where a narrow bit switching field distribution is required.

El-Hilo, M.

2010-05-01

299

Adaptive Arrays and Tracking.  

National Technical Information Service (NTIS)

Adaptive arrays and tracking share many concepts mathematical tools, practical issues, and algorithms. For example, ill-conditioning of the sample covariance matrix for adaptive arrays and ill-conditioning of the covariance matrix in a Kalman filter are b...

F. E. Daum

2004-01-01

300

VLF Loop Array Antenna.  

National Technical Information Service (NTIS)

The report describes a directional loop array antenna for very low frequency (VLF) reception. The array comprises four closely spaced loop antennas forming a unidirectional reception pattern with a main beam of less than 43 deg between half power points. ...

E. W. Seeley

1978-01-01

301

Advanced Vertical Array Beamformer.  

National Technical Information Service (NTIS)

The advanced vertical array beamformer signal processor accomplishes acoustic beamforming of an underwater vertical array used in shallow water utilizing matched beam processing to suppress generated noise and/or ship radiated noise thereby increasing the...

T. C. Yang J. A. Mobbs

1998-01-01

302

Angular dependence of the magnetoresistance in nanoparticle arrays.  

PubMed

The interplay between the ferromagnetism and the charging effects strongly affects the electron transport through nanoparticle arrays when they are placed between two ferromagnetic electrodes with collinear magnetizations. There are oscillations in the current for the parallel orientation of magnetizations, and large values of the tunneling magnetoresistance (TMR). We analyze the transport properties in nanoparticle arrays for the case of noncollinear magnetizations. We show that the I-V and TMR curves strongly depend on the angle ? between the magnetization orientations of both electrodes. Large values of TMR are obtained for several values of ?. PMID:24072186

Estévez, V; Guslienko, K Y

2013-09-26

303

Magnetic composite electroplating for depositing micromagnets  

Microsoft Academic Search

This paper reports a novel magnetic composite materials deposition technique called magnetic composite electroplating (MCE). Thin films and micromagnets arrays of a composite matrix consisting of magnetic particles and a ferromagnetic alloy have been fabricated based on this technique. In a typical MCE process, magnetic particles are electrochemically and mechanically embedded into electroplated ferromagnetic thin films to form a magnetic

Shan Guan; Bradley J. Nelson

2006-01-01

304

Soft-edged magnet models for higher-order beam-optics map codes  

SciTech Connect

Continuously varying surface and volume source-density distributions are used to model magnetic fields inside of cylindrical volumes. From these distributions, a package of subroutines computes on-axis generalized gradients and their derivatives at arbitrary points on the magnet axis for input to the numerical map-generating subroutines of the Lie-algebraic map code Marylie. In the present version of the package, the magnet menu includes: 1. cylindrical current-sheet or radially thick current distributions with either open boundaries or with a surrounding cylindrical boundary with normal field lines (which models high-permeability iron), 2. Halbach-type permanent mutipole magnets, either as sheet magnets or as radially thick magnets, 3. modeling of arbitrary fields inside a cylinder by use of a fictitious current sheet. The subroutines provide on-axis gradients and their z derivatives to essentially arbitrary order, although in the present 3rd and 5th order Marylie only the 0th through 6th derivatives are needed. The formalism is especially useful in beam-optics applications, such as magnetic lenses, where realistic treatment of fringefield effects is needed.

Walstrom, P. L. (Peter L.)

2002-01-01

305

Portable Phased Array Applications  

Microsoft Academic Search

This paper describes several in-service application s for portable phased arrays. OmniScan is new categ ory of instrument using ultrasonic phased arrays, as well as other technologies (conventional ultrasonics, TO FD, eddy current arrays etc.). Portable phased arrays can op erate in manual, semi-automated (i.e. encoded) or f ully automated modes, though most of the applications to date have been

Michael Moles

306

Micromachined pipette arrays  

Microsoft Academic Search

The design and characterization of batch fabricated metallic micromachined pipette arrays is described. The process used to fabricate the micromachined pipette arrays (MPA) includes p + etch-stop membrane technology anisotropic etching of silicon in potassium hydroxide, sacrificial thick photoresist micromolding technology, and electrodeposition. Arrays of one to ten pipettes have been fabricated using nickel as the structural material and palladium

Ian Papautsky; John Brazzle; Harold Swerdlow; Robert Weiss; A. Bruno Frazier

2000-01-01

307

The HELIOS silicon detector array  

NASA Astrophysics Data System (ADS)

A prototype detector array has been constructed for use in the Helical Orbit Spectrometer (HELIOS) at the ATLAS facility at Argonne National Laboratory. HELIOS is a high-resolution spectrometer for use in studying reactions in inverse kinematics on hydrogen or helium targets. HELIOS consists of a large bore, 3T superconducting solenoid oriented with the magnetic and beam axes aligned. The detector array is comprised of four modules each with six 1.2 x 5.6cm position sensitive silicon detectors. On each module, the detectors were affixed with conductive epoxy and wire bonded to custom made multi-layer printed circuit boards. To keep the radial extent of the detectors to a minimum, the modules were assembled on a hollow 1.6 x 1.6 x 68.8 cm aluminum rail centered on the beam axis located upstream from the target. To characterize the timing, position, and energy resolutions, the detectors were evaluated at the Western Michigan University Accelerator Laboratory using elastic proton-proton scattering. The construction, assembly and preliminary testing of the array will be discussed.

Marley, S. T.

2008-10-01

308

Intracavitary ultrasound phased arrays for thermal therapies  

NASA Astrophysics Data System (ADS)

Currently, the success of hyperthermia and thermal surgery treatments is limited by the technology used in the design and fabrication of clinical heating devices and the completeness of the thermometry systems used for guidance. For both hyperthermia and thermal surgery, electrically focused ultrasound generated by phased arrays provides a means of controlling localized energy deposition in body tissues. Intracavitary applicators can be used to bring the energy source close to a target volume, such as the prostate, thereby minimizing normal tissue damage. The work performed in this study was aimed at improving noninvasive prostate thermal therapies and utilized three research approaches: (1) Acoustic, thermal and optimization simulations, (2) Design and fabrication of multiple phased arrays, (3) Ex vivo and in vivo experimental testing of the heating capabilities of the phased arrays. As part of this study, a novel aperiodic phased array design was developed which resulted in a 30- 45% reduction in grating lobe levels when compared to conventional phased arrays. Measured acoustic fields generated by the constructed aperiodic arrays agreed closely with the fields predicted by the theoretical simulations and covered anatomically appropriate ranges. The power capabilities of these arrays were demonstrated to be sufficient for the purposes of hyperthermia and thermal surgery. The advantage of using phased arrays in place of fixed focus transducers was shown by demonstrating the ability of electronic scanning to increase the size of the necrosed tissue volume while providing a more uniform thermal dose, which can ultimately reduce patient treatment times. A theoretical study on the feasibility of MRI (magnetic resonance imaging) thermometry for noninvasive temperature feedback control was investigated as a means to improve transient and steady state temperature distributions achieved in hyperthermia treatments. MRI guided ex vivo and in vivo experiments demonstrated that the heating capabilities of the constructed phased arrays were adequate for hyperthermia and thermal surgery treatments. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253- 1690.)

Hutchinson, Erin

309

IMPROVEMENT OF SYNCHRONOUS AND ASYNCHRONOUS MOTOR DRIVE SYSTEMS SUPPLIED BY PHOTOVOLTAIC ARRAYS WITH FREQUENCY CONTROL  

Microsoft Academic Search

The dynamic performances of a permanent magnet synchronous motor (PMSM) and an asynchronous motor (ASM) con- nected to a photovoltaic (PV) array through an inverter are analyzed. The mathematical models of PV array, inverter\\/motor and controller are developed. The photovoltaic array is represented by an equivalent circuit whose parameters are computed using experimentally determined current-voltage (I ¡V ) characteristics. The

Laid Zarour; Rachid Chenni; Abdelhalim Borni; Aissa Bouzid

2008-01-01

310

Double ferromagnetic resonance in nanowire arrays  

NASA Astrophysics Data System (ADS)

Microstrip line measurements are used to determine the frequency dependent microwave response of 40 nm diameter CoFeB ferromagnetic nanowire arrays, with external static applied field parallel to the nanowire axis. The ferromagnetic resonance (FMR) response of the wires is obtained for applied fields below and above magnetization saturation. For applied magnetic fields above saturation, a single FMR peak is observed, while below saturation, two sets of peaks are obtained. The two FMR peaks below saturation are associated with two magnetization populations, one for nanowires with upward magnetization and one with downward magnetization. A model based on a Maxwell-Garnett homogenization procedure has been established and used to predict the frequency response of the FMR peaks. There is good agreement between the model and experimental results.

Carignan, Louis-Philippe; Boucher, Vincent; Kodera, Toshiro; Caloz, Christophe; Yelon, Arthur; Ménard, David

2009-08-01

311

Highly stable signal propagation in a consecutively tuned nanomagnet array  

NASA Astrophysics Data System (ADS)

A key function of magnetic quantum-dot cellular automata (MQCA) is signal propagation in the nanomagnet array, for which a clocking field is required. However, the misalignment of the clocking field and the resultant low stability for signal propagation is one of the main challenges for its application. Here, we modeled and fabricated a progressively shape-tuned nanomagnet array combined with a reversal clocking field with progressively reduced amplitude. Based on micromagnetic simulations, Fe nanomagnet arrays were fabricated by electron beam lithography and their magnetization states characterized by magnetic force microscopy demonstrated correct signal propagation against clocking field misalignment up to +/-5°. Furthermore, cascade-like signal propagation was observed. This novel design provides high stability and directional control in signal propagation within the nanomagnet array and potentially paves the way for addressing the misalignment issue in MQCA structures.

Li, Zheng; Krishnan, Kannan M.

2013-05-01

312

Simple configurable systolic array  

NASA Astrophysics Data System (ADS)

In this paper, a simple configurable systolic array structure for signal processing is proposed. This array is configurable not only for its dimension, but also for different kinds of signal processing algorithms. The basic connection pattern used is a spiral structure. Through a carefully designed switch, a desired array dimension can be easily configured. The configurability for various kinds of signal processing operations is achieved by designing a simple configurable processing element whose configuration is set by a control signal. This systolic array can be applied to the following areas: matrix multiplication, FIR filtering, convolution and correlation, DFT and IDFT. Examples are included to demonstrate how to use the systolic array for each of these operations. With some modification of the PE structure, more applications in signal processing could be expected. This systolic array design gives a good trade-off among simplicity, modularity, flexibility and configurability.

Fan, Yiping; Thompson, Wiley E.

1996-06-01

313

Sorting white blood cells in microfabricated arrays  

NASA Astrophysics Data System (ADS)

Fractionating white cells in microfabricated arrays presents the potential for detecting cells with abnormal adhesive or deformation properties. A possible application is separating nucleated fetal red blood cells from maternal blood. Since fetal cells are nucleated, it is possible to extract genetic information about the fetus from them. Separating fetal cells from maternal blood would provide a low cost noninvasive prenatal diagnosis for genetic defects, which is not currently available. We present results showing that fetal cells penetrate further into our microfabricated arrays than adult cells, and that it is possible to enrich the fetal cell fraction using the arrays. We discuss modifications to the array which would result in further enrichment. Fetal cells are less adhesive and more deformable than adult white cells. To determine which properties limit penetration, we compared the penetration of granulocytes and lymphocytes in arrays with different etch depths, constriction size, constriction frequency, and with different amounts of metabolic activity. The penetration of lymphocytes and granulocytes into constrained and unconstrained arrays differed qualitatively. In constrained arrays, the cells were activated by repeated shearing, and the number of cells stuck as a function of distance fell superexponentially. In unconstrained arrays the number of cells stuck fell slower than an exponential. We attribute this result to different subpopulations of cells with different sticking parameters. We determined that penetration in unconstrained arrays was limited by metabolic processes, and that when metabolic activity was reduced penetration was limited by deformability. Fetal cells also contain a different form of hemoglobin with a higher oxygen affinity than adult hemoglobin. Deoxygenated cells are paramagnetic and are attracted to high magnetic field gradients. We describe a device which can separate cells using 10 ?m magnetic wires to deflect the paramagnetic cells. We present preliminary results from a test system that separates paramagnetic beads from latex beads. The separation is limited by our ability to produce the high field gradients which are necessary to separate cells according to their hemoglobin content, and we present estimates of the magnetic gradients we achieved.

Castelino, Judith Andrea Rose

314

Spin and charge polarization in quantum dot arrays  

Microsoft Academic Search

The role of spin and charge distribution in a planar semiconductor quantum dot array (square geometry) with two electrons is studied in the presence of a driver cell and magnetic nanoparticles located near two quantum dots providing a local magnetic field. We use an extended Hubbard model to describe the electrons in the cell, taking into account intra and intercell

F. Rojas; E. Cota; F. Mireles; S. E. Ulloa

2005-01-01

315

Compact Suffix Array  

Microsoft Academic Search

\\u000a Suffix array is a data structure that can be used to index a large text file so that queries of its content can be answered quickly. Basically\\u000a a suffix array is an array of all suffixes of the text in the lexicographic order. Whether or not a word occurs in the text\\u000a can be answered in logarithmic time by binary

Veli Mäkinen

2000-01-01

316

Compressed Compact Suffix Arrays  

Microsoft Academic Search

\\u000a The compact suffix array (CSA) is a space-efficient full-text index, which is fast in practice to search for patterns in a static text. Compared to\\u000a other compressed suffix arrays (Grossi and Vitter, Sadakane, Ferragina and Manzini), the CSA is significantly larger (2.7 times the text size, as opposed\\u000a to 0.6–0.8 of compressed suffix arrays). The space of the CSA includes

Veli Mäkinen; Gonzalo Navarro

2004-01-01

317

Spherical Wire-Array Implosion Experiments  

NASA Astrophysics Data System (ADS)

The results of the first spherical wire array z-pinch implosion experiments are presented. Arrays were driven by the MAGPIE generator (1MA, 240ns) and consisted of 8x25?m aluminium wires forming the lines of longitude of a sphere with an equatorial diameter of 21mm. Plasma dynamics around each pole of the spherical array are comparable to those observed in radial wire array z-pinch experiments. The smaller radius at the poles produces a higher magnetic field than at the equator, leading to a higher rate of ablation of the wires into plasma. The ablated plasma from each pole forms a jet; and the jets from the poles collide near the centre of the sphere to produce a high-density precursor plasma. Later in time the array implodes, with a pair of plasma bubbles being launched from the poles towards the centre of the array, driving a pair of shock waves onto the precursor plasma. This research was sponsored by Sandia National Laboratories Albuquerque, the SSAA program of NNSA under DOE Cooperative Agreement DE-FC03-02NA00057.

Hall, G. N.; Ciardi, A.; Palmer, J. B. A.

2005-10-01

318

The Magnetic Properties Experiments on Mars Pathfinder  

NASA Astrophysics Data System (ADS)

A remarkable result from the Viking missions was the discovery that the Martian soil is highly magnetic, in the sense that the soil is attracted by permanent magnets. Both the strong and weak magnets on the Viking landers were saturated with dust throughout the mission. Appropriate limits for the spontaneous magnetization sigma_S were advanced: 1 Am(2) (kg soil)(-1) < sigma_S < 7 Am(2) (kg soil)(-1) . The essential difference between the Magnet Arrays for Mars Pathfinder and the Viking Magnetic Properties Experiment is that Magnet Arrays on Pathfinder will include magnets of lower strengths that the weakest Viking magnet. The five magnets consist of small ring magnets concentric with oppositely polarized cylindrical magnets. The outer diameter of the ring magnets is 18 mm. Discrete (single phase) particles of strongly magnetic minerals (gamma -Fe2O3 or Fe3O4) will stick to all five magnets, while composite (multiphase) particles will stick preferentially to the strongest magnets. Two Magnet Arrays are placed on the Pathfinder lander, with a distance of 1180 and 1450 mm, respectively, from the Imager for Mars Pathfinder (IMP). The magnets will attract airborne dust, and the dust on the magnets will be periodically viewed by the IMP. The images transmitted to Earth are the data on which conclusions on the magnetic properties of the dust will be based. Besides the Magnet Arrays the Pathfinder lander carries two other types of magnets. The Tip Plate Magnet is placed at a distance of 10 cm from the IMP, and thus allows a rather high resolution imaging of the dust clinging to the magnet. The Ramp Magnets are placed near the end of the ramps by which the micro-rover will descend to the surface. The dust on the Ramp Magnets will be studied by the APX-spectrometer of the micro-rover.

Knudsen, J. M.; Gunnlaugsson, H. P.; Hviid, S. F.; Madsen, M. B.

1996-09-01

319

Nondestructive testing and crack evaluation of ferromagnetic material by using the linearly integrated hall sensor array  

Microsoft Academic Search

Magnetic flux leakage testing (MFLT), which measures the distribution of a magnetic field on a magnetized specimen by using\\u000a a magnetic sensor such as a Hall sensor, is an effective nondestructive testing (NDT) method for detecting surface cracks\\u000a on magnetized ferromagnetic materials. A scan-type magnetic camera, based on the principle of MFLT, uses an inclined Hall\\u000a sensor array on a

Jinyi Lee; Jiseong Hwang; Jongwoo Jun; Seho Choi

2008-01-01

320

Coercivity dependence on periodicity of Co and Py antidot arrays  

NASA Astrophysics Data System (ADS)

An experimental study on the control of thin films magnetic coercivity through the change in geometry of antidot arrays has been performed on two different materials: cobalt and permalloy. Antidot arrays have been fabricated using a Focused Ion Beam, and magnetic hysteresis loops have been measured using Kerr effect microscopy. The coercivity dependence on the material and the array periodicity have been studied. A novel method to estimate the antidot diameter from MOKE data is presented. Results suggest a widening of the antidot effective diameter compared to the one measured from SEM images. This could be attributed to a damage of the magnetic material around the holes during the fabrication process, which leads to amorphization and concomitant reduction of the surrounding film magnetization.

Castán-Guerrero, Celia; Bartolomé, Juan; Bartolomé, Fernando; García, Luis Miguel; Sesé, Javier; Strichovanec, Pavel; Herrero-Albillos, Julia; Merazzo, Karla J.; Vázquez, Manuel; Vavassori, Paolo

2013-05-01

321

Early detection and monitoring of fatigue in high strength steels with MWM-Arrays  

Microsoft Academic Search

Fatigue monitoring of cyclically loaded shot peened high-strength steel components can be accomplished via magnetic permeability measurements during laboratory tests or in service. These measurements can be performed either continuously using permanently mounted Meandering Winding Magnetometer Arrays (MWM®-Arrays) or intermittently with scanning MWM-Arrays. The results obtained to date suggest that MWM-Array permeability measurements can provide early detection of fatigue damage

V. Zilberstein; D. Grundy; V. Weiss; N. Goldfine; E. Abramovici; J. Newman; T. Yentzer

2005-01-01

322

Nonreciprocal Effects in Magnetic Photonic Crystals  

Microsoft Academic Search

Magnetic photonic crystals are periodic arrays of lossless materials, at least one of which being magnetically polarized. Magnetization, either spontaneous or induced, is associated with nonreciprocal effects, such as Faraday rotation. In addition, magnetic photonic crystals of certain configuration can also display strong spectral asymmetry, implying that electromagnetic waves propagate in one direction much faster or slower than in the

Alex Figotin; Ilya Vitebskiy

2006-01-01

323

Antenna Array Element Study.  

National Technical Information Service (NTIS)

An investigation and analytical study of antenna array elements is being carried out to determine the influence of an individual element of specific characteristics on the performance of an array and, on the basis of element performance, to present data w...

M. B. Haslam

1966-01-01

324

The Square Kilometre Array  

Microsoft Academic Search

The Square Kilometre Array (SKA) is the future centimeter- and meter-wavelength telescope with a sensitivity about 50 times higher than present instruments. Its Key Science Projects are (a) Astrobiology including planetary formation within protoplanetary disks; (b) Testing theories of gravitation using an array of pulsars to search for gravitational waves and relativistic binaries to probe the strong-field regime; (c) The

Yervant Terzian; Joseph Lazio

2006-01-01

325

Active Element Array.  

National Technical Information Service (NTIS)

This technical report presents the findings and accomplishments of a 12 month study of active Van Atta arrays. The intent of the investigation was to determine the feasibility of constructing a lightweight 16-element planar Van Atta array which would act ...

P. Ver Planck W. Ku T. Glynn

1968-01-01

326

Pyroelectric Detector Arrays.  

National Technical Information Service (NTIS)

A pyroelectric detector array and the method for making it is described. A series of holes formed through a silicon dioxide layer on the surface of a silicon substrate forms the mounting fixture for the pyroelectric detector array. A series of nontouching...

A. L. Fripp

1980-01-01

327

Norwegian Seismic Array (NORSAR).  

National Technical Information Service (NTIS)

This report describes the operation and research activities at the Norwegian Seismic Array (NORSAR). The operation of the array in this period was dominated by the effects of the change from 22 to 7 subarrays. There have been 232 breaks in the operation o...

H. Bungum

1977-01-01

328

Integrated solar cell array  

Microsoft Academic Search

An integrated array of solar cells, each cell having a positive and a negative electrode, is disclosed. A first grid comprising a plurality of non-intersecting electrically conductive members is affixed to an insulating substrate. Each single individual member of this grid forms the negative electrode of an individual cell of the array. Overlying and affixed to the negative electrodes and

W. J. Biter; F. A. Shirland

1980-01-01

329

Tuned air gun array  

Microsoft Academic Search

The present invention provides a method for determining the spacing and size of air guns in a tuned air gun array. Volume ratios are calculated based upon a predetermined maximum volume for any individual air gun. The volumes are cross-referenced to spacings for optimum air gun interaction. The resulting air gun array operates as a broadband high-energy point source.

William H. Ruehle

1983-01-01

330

Optimal array pattern synthesis for broadband arrays.  

PubMed

Broadband beamformers with constant mainlobe response over the frequency of interest are desirable in many applications including underwater acoustics, ultrasonics, acoustic imaging and communications, and so on. Solutions to this problem have been presented for specific array geometry often requiring a larger number of sensors. And the array pattern synthesis error minimization is employed for the whole field of view, which leads to suboptimal designs. In this paper, a broadband array pattern synthesis approach to designing time-domain constant mainlobe response beamformer is proposed. By imposing constraints both on the mainlobe spatial response variation over frequency and on the sidelobes of the beamformer, several optimization criteria are presented and the corresponding convex second-order cone programming implementations are given. In this approach, no preliminary desired beampattern is required and the beam responses variation minimization is employed only in the mainlobe region and not in the sidelobe regions, which improves the beamformer mainlobe synthesis accuracy. Equally, one can obtain lower sidelobes at the same mainlobe synthesis accuracy. This approach is applicable to arrays with arbitrary geometry. Simulation and experimental results are presented to illustrate the effectiveness of this approach. Performance comparisons of the proposed beamformers and the existing beamformer are also provided. PMID:18189561

Yan, Shefeng; Ma, Yuanliang; Hou, Chaohuan

2007-11-01

331

Microfabricated ion trap array  

DOEpatents

A microfabricated ion trap array, comprising a plurality of ion traps having an inner radius of order one micron, can be fabricated using surface micromachining techniques and materials known to the integrated circuits manufacturing and microelectromechanical systems industries. Micromachining methods enable batch fabrication, reduced manufacturing costs, dimensional and positional precision, and monolithic integration of massive arrays of ion traps with microscale ion generation and detection devices. Massive arraying enables the microscale ion traps to retain the resolution, sensitivity, and mass range advantages necessary for high chemical selectivity. The reduced electrode voltage enables integration of the microfabricated ion trap array with on-chip circuit-based rf operation and detection electronics (i.e., cell phone electronics). Therefore, the full performance advantages of the microfabricated ion trap array can be realized in truly field portable, handheld microanalysis systems.

Blain, Matthew G. (Albuquerque, NM); Fleming, James G. (Albuquerque, NM)

2006-12-26

332

Results from a prototype permanent magnet dipole-quadrupole hybrid for the PEP-II B-factory  

SciTech Connect

We describe the construction of a prototype hybrid permanent magnet dipole and quadrupole. The magnet consists of two concentric rings of Sm{sub 2}Co{sub 17} magnetic material 5 cm in length. The outer ring is made of 16 uniformly magnetized blocks assembled as a Halbach dipole and the inner ring has 32 blocks oriented in a similar fashion so as to generate a quadrupole field. The resultant superimposed field is an offset quadrupole field which allows us to center the field on the high-energy beam in the interaction region of the PEP-II B-factory. The dipole blocks are glued to the inside surface of an outer support collar and the quadrupole blocks are held in a fixture that allows radial adjustment of the blocks prior to potting the entire assembly with epoxy. An extensive computer model of the magnet has been made and from this model we developed a tuning algorithm that allowed us to greatly reduce the n=3 17 harmonics of the magnet.

Sullivan, M.; Bowden, G.; Ecklund, S. [and others

1997-06-01

333

Gauge theories of Josephson junction arrays  

Microsoft Academic Search

We show that the zero-temperature physics of planar Josephson junction arrays in the self-dual approximation is governed by an Abelian gauge theory with a periodic mixed Chern-Simons term describing the charge-vortex coupling. The periodicity requires the existence of (Euclidean) topological excitations which determine the quantum phase structure of the model. The electric-magnetic duality leads to a quantum phase transition between

M. C. Diamantini; P. Sodano; C. A. Trugenberger

1996-01-01

334

A submillimeter VLBI array  

NASA Astrophysics Data System (ADS)

A VLBI array operating at ? 1.3 mm and 0.8 mm is being designed using existing submillimeter telescopes as ad-hoc stations. Initial three station ? = 1.3 mm observations of SgrA* and other AGN have produced remarkable results, which are reported by Doeleman elsewhere in this proceedings. Future observations are planned with an enhanced array which has longer baselines, more stations, and greater sensitivity. At ? = 0.8 mm and on the long baselines, the array will have about a 20 ?as angular resolution which equals the diameter of the event horizon of the massive black hole in SgrA*. Candidate single dish facilities include the Arizona Radio Observatory Submillimeter Telescope (SMT) in Arizona, the Caltech Submillimeter Observatory (CSO) and the James Clerk Maxwell telescope (JCMT) in Hawaii, the Large Millimeter Telescope (LMT) in Mexico, ASTE and APEX in Chile, and the IRAM 30 m in Spain; interferometers include the Submillimeter Array (SMA) in Hawaii, the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in California, IRAM PdB Interferometer in France, and the Atacama Large Millimeter Array (ALMA) in Chile. I will discuss the techniques we have developed for phasing interferometric arrays to act as single VLBI station. A strategy for detection of short (10s) time-scale source variability using VLBI closure phase will be described.

Weintroub, Jonathan

2008-10-01

335

Chaotic mixing and superdiffusion in a two-dimensional array of vortices  

NASA Astrophysics Data System (ADS)

We present experimental and numerical studies of mixing and long-range transport in an array of vortices forced by a magnetohydrodynamic technique. A current passing horizontally through a thin electrolytic solution interacts with a magnetic field produced by an array of magnets below the fluid. If the current is parallel to one of the primary directions of the magnet array, a square array of vortices is produced. If the current is tilted with respect to the magnet array, however, wavy channels form diagonally through the vortex pattern, allowing tracers in the flow to travel long distances in a short period of time. The addition of a time-dependent current results in a combination of chaotic and ordered vortex/jet regions that produces Levy flights and superdiffusive transport. If an AC current is applied in both cardinal directions, the resulting chaotic mixing is typically barrier-free.

Solomon, Tom; Winokur, Justin; O'Malley, Garrett; Paoletti, Matthew

2008-11-01

336

Arrays in Sisal  

SciTech Connect

Although Sisal (Streams and Iterations in a Single Assignment Language) is a general-purpose applicative language, its expected program domain is large-scale scientific applications. Since arrays are an indispensable data structure for such applications, the designers of Sisal included arrays and a robust set of array operations in the language definition. In this paper, we review and evaluate those design decisions in light of the first Sisal compilers and runtime systems for shared-memory multiprocessor systems. In general, array intensive applications written in Sisal 1.2 execute as fast as their Fortran equivalents. However, a number of design decisions have hurt expressiveness and performance. We discuss these flaws and describe how the new language definition (Sisal 2.0) corrects them. 14 refs., 2 figs.

Feo, J.T.

1990-09-01

337

Ultraviolet Array Detector Research.  

National Technical Information Service (NTIS)

Under this contract multiple tasks were performed in support of the development of Ultraviolet Array Detector Research. The Horizon Ultraviolet Program instrumentation was supported through a second Space shuttle launch. An Ebert-Fastie spectrometer was m...

M. Gangl M. Bullinger R. Cundiff J. McKay J. Middlestadt

1995-01-01

338

Systolic Array Adaptive Beamforming.  

National Technical Information Service (NTIS)

A computing architecture which reflects the specific requirements of an optimum adaptive space-time array processor is discussed. Specifically, a frequency domain implementation of the minimum variance distortionless response (MVDR) beamformer is describe...

N. L. Owsley

1987-01-01

339

Multiplication Series: Number Arrays  

NSDL National Science Digital Library

This one-page article describes and illustrates how arrays can be used to represent many number concepts, including building multiplication facts, commutativity, parity (odd/even), and exploring factors, prime numbers, and square numbers.

2002-10-01

340

Nanode Array Sensor Microchips.  

National Technical Information Service (NTIS)

The phase I SBIR grant had two primary objectives. The first objective was to demonstrate the fabrication of large arrays of individually addressable, nanometerscale ultramicroelectrodes (nanodes). The second objective was to develop model immunochemical ...

K. Dill

2000-01-01

341

Photon detection with high gain avalanche photodiode arrays  

Microsoft Academic Search

The detection of light emitted in fast scintillating fiber bundles and Cerenkov radiators used for fiber calorimetry and tracking applications requires fast detector arrays with high sensitivity to short-wavelength photons. Photomultiplier tube arrays, the traditional imaging detectors for short-wavelength optical radiation, have limited spatial resolution and require expensive anti-magnetic shielding. We report on short-wavelength sensitivity improvement and detection efficiency performance

S. Vasile; P. Gothoskar; D. Sdrulla; R. Farrell

1997-01-01

342

A Submillimeter VLBI Array  

NASA Astrophysics Data System (ADS)

A VLBI array operating at 1.3 mm and 0.8 mm wavelengths is being built using existing submillimeter telescopes as ad-hoc stations. Initial three station 1.3 mm observations of SgrA* and other AGN have produced remarkable results reported by Doeleman et al. in Nature (Vol 445, p 78) and also at this meeting. For SgrA*, the intrinsic size (angular diameter) is found to be 37 microarcseconds, or less than four Schwartzschild radii. Future observations are planned with an enhanced array which has longer baselines, more stations, and greater sensitivity. At 0.8 mm and on the long baselines, the array will have a 20 microarcsecond angular resolution which equals the diameter of the event horizon of the massive black hole in SgrA*. Candidate single dish facilities include the Arizona Radio Observatory Submillimeter Telescope (ARO/SMT) in Arizona, the Caltech Submillimeter Observatory (CSO) and the James Clerk Maxwell telescope (JCMT) in Hawaii, the Large Millimeter Telescope (LMT) in Mexico, ASTE and APEX in Chile, and the IRAM 30 m in Spain; interferometers include the Submillimeter Array (SMA) in Hawaii, the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in California, IRAM PdB Interferometer in France, and the Atacama Large Millimeter Array (ALMA) in Chile. We will discuss the challenges of converting existing submillimeter telescopes to act as VLBI stations at these short wavelengths. We will also describe techniques to improve the sensitivity of the array, which is crucial to discern the detailed structure of the source. In particular, we have developed a processor for phasing local interferometric arrays to contribute to VLBI observations with their full collecting area.

Weintroub, Jonathan; Primiani, R.; Moran, J.; Young, K.

2009-01-01

343

Photonic wideband array antennas  

Microsoft Academic Search

Presents an introduction to the optical control of array antennas by using fiber optic links for remote control and a photonic time shift network for wide instantaneous bandwidth. An overview of the development of a wideband conformal array designed for airborne surveillance radars is given. The paper covers the system design and the performance of an L-band (850-1400 MHz) M-element

J. J. Lee; R. Y. Loo; S. Livingston; V. I. Jones; J. B. Lewis; Huan-Wun Yen; G. L. Tangonan; M. Wechsberg

1995-01-01

344

Random array grid collimator  

DOEpatents

A hexagonally shaped quasi-random no-two-holes touching grid collimator. The quasi-random array grid collimator eliminates contamination from small angle off-axis rays by using a no-two-holes-touching pattern which simultaneously provides for a self-supporting array increasng throughput by elimination of a substrate. The presentation invention also provides maximum throughput using hexagonally shaped holes in a hexagonal lattice pattern for diffraction limited applications. Mosaicking is also disclosed for reducing fabrication effort.

Fenimore, E.E.

1980-08-22

345

The Telescope Array Experiment  

NASA Astrophysics Data System (ADS)

The Telescope Array (TA) is an ultra-high energy cosmic ray (UHECR) detector located in Millard County, Utah. The detector currently consists of a ground array of approximately 500 scintillator counters and three optical air-fluorescence stations. TA has now been fully operational for over two years and currently has the largest aperture for UHECRs in the Northern Hemisphere. Current analysis efforts will be discussed and recent findings will be presented.

Stokes, Benjamin

2010-10-01

346

VLSI Array processors  

Microsoft Academic Search

High speed signal processing depends critically on parallel processor technology. In most applications, general-purpose parallel computers cannot offer satisfactory real-time processing speed due to severe system overhead. Therefore, for real-time digital signal processing (DSP) systems, special-purpose array processors have become the only appealing alternative. In designing or using such array Processors, most signal processing algorithms share the critical attributes of

S. Kung

1985-01-01

347

Carbon nanotube array actuators  

NASA Astrophysics Data System (ADS)

Experimental investigations of highly vertically aligned carbon nanotubes (CNTs), also known as CNT-arrays, are the main focus of this paper. The free strain as result of an active material behavior is analyzed via a novel experimental setup. Previous test experiences of papers made of randomly oriented CNTs, also called Bucky-papers, reveal comparably low free strain. The anisotropy of aligned CNTs promises better performance. Via synthesis techniques like chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD), highly aligned arrays of multi-walled carbon nanotubes (MWCNTs) are synthesized. Two different types of CNT-arrays are analyzed, morphologically first, and optically tested for their active characteristics afterwards. One type of the analyzed arrays features tube lengths of 750–2000 ?m with a large variety of diameters between 20 and 50 nm and a wave-like CNT-shape. The second type features a maximum, almost uniform, length of 12 ?m and a constant diameter of 50 nm. Different CNT-lengths and array types are tested due to their active behavior. As result of the presented tests, it is reported that the quality of orientation is the most decisive property for excellent active behavior. Due to their alignment, CNT-arrays feature the opportunity to clarify the actuation mechanism of architectures made of CNTs.

Geier, S.; Mahrholz, T.; Wierach, P.; Sinapius, M.

2013-09-01

348

Tunable Magnetic Properties of Heterogeneous Nanobrush: From Nanowire to Nanofilm  

PubMed Central

With a bottom-up assemble technology, heterogeneous magnetic nanobrushes, consisting of Co nanowire arrays and ferromagnetic Fe70Co30 nanofilm, have been fabricated using an anodic aluminum oxide template method combining with sputtering technology. Magnetic measurement suggests that the magnetic anisotropy of nanobrush depends on the thickness of Fe70Co30 layer, and its total anisotropy originates from the competition between the shape anisotropy of nanowire arrays and nanofilm. Micromagnetic simulation result indicates that the switching field of nanobrush is 1900 Oe, while that of nanowire array is 2700 Oe. These suggest that the nanobrush film can promote the magnetization reversal processes of nanowire arrays in nanobrush.

2010-01-01

349

Photon detection with high gain avalanche photodiode arrays  

SciTech Connect

The detection of light emitted in fast scintillating fibers and Cerenkov radiators used for fiber calorimetry and tracking applications in high energy colliders, requires fast detector arrays with high sensitivity to short wavelength photons. Photomultiplier tubes, the traditional imaging detectors for short wavelength optical radiation, have limited spatial resolution and require expensive anti-magnetic shielding. The authors report on short wavelength sensitivity improvement and detection efficiency performance for a novel p-n junction planar structure silicon avalanche photodiode (APD) array, operated in Geiger mode. The APD array provides a high sensitivity detector for applications requiring the detection of light spatial distributions with single photon sensitivity.

Vasile, S.; Gothoskar, P.; Farrell, R. [Radiation Monitoring Devices, Inc., Watertown, MA (United States); Sdrulla, D. [Advanced Power Technology, Bend, OR (United States)

1998-06-01

350

Miniaturized Cassegrainian solar array development  

NASA Astrophysics Data System (ADS)

Viewgraphs on miniaturized Cassegrainian solar array development are presented. Topics covered include: miniature Cassegrainian concentrator (MCC) concept; folded box beam deployment of MCC array sub-wing; 100-kW MCC array system analysis summary; and array enables technology evolution.

Patterson, R.; Mills, M.

351

Design, Fabrication, and Integration Technology of Large-Scale Microlens Array for Infrared Charge Coupled Device Application  

Microsoft Academic Search

Infrared charge coupled device (IRCCD) integration with microlens array is an effective method for improving the detecting sensitivity of IRCCD sensors. In this paper, we present the diffractive microlens array (MLA), which is manufactured by the submicron photolithography technology and magnetically enhanced reactive ion etching (MERIE) on infrared quartz substrate. The integration procedure between microlens array and PtSi Schottky-barrier IRCCD

Caijun Ke; Xinjian Yi; Jianjun Lai; Sihai Chen; Miao He

2004-01-01

352

Sampled Longest Common Prefix Array  

NASA Astrophysics Data System (ADS)

When augmented with the longest common prefix (LCP) array and some other structures, the suffix array can solve many string processing problems in optimal time and space. A compressed representation of the LCP array is also one of the main building blocks in many compressed suffix tree proposals. In this paper, we describe a new compressed LCP representation: the sampled LCP array. We show that when used with a compressed suffix array (CSA), the sampled LCP array often offers better time/space trade-offs than the existing alternatives. We also show how to construct the compressed representations of the LCP array directly from a CSA.

Sirén, Jouni

353

A negative index of refraction metamaterial based on a wire array embedded in ferrite  

Microsoft Academic Search

A metamaterial exhibiting a negative index of refraction can be fabricated from an array of conducting wires cladded with non-magnetic dielectric and embedded in a magnetic host medium. The wires are responsible for the ? < 0 property and the magnetic medium for the mu < 0 property. A near exact calculation of the electromagnetic response of this metamaterial indicated

G. Dewar

2005-01-01

354

Scaling of the coercivity with the geometrical parameters in epitaxial Fe antidot arrays  

NASA Astrophysics Data System (ADS)

We studied a series of square lattice antidot arrays, with diameter and lattice parameter from hundreds of nanometers to some microns, fabricated using two lithography techniques in epitaxial Fe(001) films. The coercivity increase of each array with respect to its base film can be scaled to a simple geometric parameter, irrespective of the lithography technique employed. Magnetic transmission x-ray microscopy studies, in arrays fabricated on polycrystalline Fe films deposited on silicon nitride membranes, evidenced the propagation of reversed domains from the edges of the arrays, in agreement with the coercivity analysis of the epitaxial arrays and with micromagnetic models.

Paz, E.; Cebollada, F.; Palomares, F. J.; González, J. M.; Im, M.-Y.; Fischer, P.

2012-04-01

355

Microbial Cell Arrays  

NASA Astrophysics Data System (ADS)

The coming of age of whole-cell biosensors, combined with the continuing advances in array technologies, has prepared the ground for the next step in the evolution of both disciplines - the whole cell array. In the present chapter, we highlight the state-of-the-art in the different disciplines essential for a functional bacterial array. These include the genetic engineering of the biological components, their immobilization in different polymers, technologies for live cell deposition and patterning on different types of solid surfaces, and cellular viability maintenance. Also reviewed are the types of signals emitted by the reporter cell arrays, some of the transduction methodologies for reading these signals, and the mathematical approaches proposed for their analysis. Finally, we review some of the potential applications for bacterial cell arrays, and list the future needs for their maturation: a richer arsenal of high-performance reporter strains, better methodologies for their incorporation into hardware platforms, design of appropriate detection circuits, the continuing development of dedicated algorithms for multiplex signal analysis, and - most importantly - enhanced long term maintenance of viability and activity on the fabricated biochips.

Elad, Tal; Lee, Jin Hyung; Gu, Man Bock; Belkin, Shimshon

356

A 16-channel dual-row transmit array in combination with a 31-element receive array for human brain imaging at 9.4 T.  

PubMed

PURPOSE: Arranging transmit array elements in multiple rows provides an additional degree of freedom to correct B1 (+) field inhomogeneities and to achieve whole-brain excitation at ultrahigh field strengths. Receive arrays shaped to the contours of the anatomy increase the signal-to-noise ratio of the image. In this work, the advantages offered by the transmit and receive array techniques are combined for human brain imaging at 9.4 T. METHODS: A 16-element dual-row transmit array and a 31-element receive array were developed. Based on an accurate numerical model of the transmit array, the deposited power was calculated for different head sizes and positions. The influence of the receive array on the transmit field was characterized. Parallel imaging performance and signal-to-noise ratio of the receive array were evaluated. RESULTS: On average, a two fold increase in signal-to-noise ratio was observed in the whole-brain volume when compared with a 16-channel elliptic microstrip transceiver array. The benefits of combining the two arrays, B1 (+) shimming in three directions and high receive sensitivity, are demonstrated with high-resolution in vivo images. CONCLUSION: The dual-row transmit array provides whole-brain coverage at 9.4 T, which, in combination with the helmet-shaped receive array, is a valuable radio frequency configuration for ultra-high field magnetic resonance imaging of the human brain. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc. PMID:23483645

Shajan, G; Kozlov, Mikhail; Hoffmann, Jens; Turner, Robert; Scheffler, Klaus; Pohmann, Rolf

2013-03-11

357

GMR biosensor arrays: a system perspective.  

PubMed

Giant magnetoresistive biosensors are becoming more prevalent for sensitive, quantifiable biomolecular detection. However, in order for magnetic biosensing to become competitive with current optical protein microarray technology, there is a need to increase the number of sensors while maintaining the high sensitivity and fast readout time characteristic of smaller arrays (1-8 sensors). In this paper, we present a circuit architecture scalable for larger sensor arrays (64 individually addressable sensors) while maintaining a high readout rate (scanning the entire array in less than 4s). The system utilizes both time domain multiplexing and frequency domain multiplexing in order to achieve this scan rate. For the implementation, we propose a new circuit architecture that does not use a classical Wheatstone bridge to measure the small change in resistance of the sensor. Instead, an architecture designed around a transimpedance amplifier is employed. A detailed analysis of this architecture including the noise, distortion, and potential sources of errors is presented, followed by a global optimization strategy for the entire system comprising the magnetic tags, sensors, and interface electronics. To demonstrate the sensitivity, quantifiable detection of two blindly spiked samples of unknown concentrations has been performed at concentrations below the limit of detection for the enzyme-linked immunosorbent assay. Lastly, the multiplexing capability and reproducibility of the system was demonstrated by simultaneously monitoring sensors functionalized with three unique proteins at different concentrations in real-time. PMID:20207130

Hall, D A; Gaster, R S; Lin, T; Osterfeld, S J; Han, S; Murmann, B; Wang, S X

2010-02-06

358

GMR Biosensor Arrays: A System Perspective  

PubMed Central

Giant magnetoresistive biosensors are becoming more prevalent for sensitive, quantifiable biomolecular detection. However, in order for magnetic biosensing to become competitive with current optical protein microarray technology, there is a need to increase the number of sensors while maintaining the high sensitivity and fast readout time characteristic of smaller arrays (1 – 8 sensors). In this paper, we present a circuit architecture scalable for larger sensor arrays (64 individually addressable sensors) while maintaining a high readout rate (scanning the entire array in less than 4 seconds). The system utilizes both time domain multiplexing and frequency domain multiplexing in order to achieve this scan rate. For the implementation, we propose a new circuit architecture that does not use a classical Wheatstone bridge to measure the small change in resistance of the sensor. Instead, an architecture designed around a transimpedance amplifier is employed. A detailed analysis of this architecture including the noise, distortion, and potential sources of errors is presented, followed by a global optimization strategy for the entire system comprising the magnetic tags, sensors, and interface electronics. To demonstrate the sensitivity, quantifiable detection of two blindly spiked samples of unknown concentrations has been performed at concentrations below the limit of detection for the enzyme-linked immunosorbent assay. Lastly, the multipexability and reproducibility of the system was demonstrated by simultaneously monitoring sensors functionalized with three unique proteins at different concentrations in real-time.

Hall, D. A.; Gaster, R. S.; Lin, T.; Osterfeld, S. J.; Han, S.; Murmann, B.; Wang, S. X.

2010-01-01

359

Identification of antioxidants from Taraxacum mongolicum by high-performance liquid chromatography–diode array detection–radical-scavenging detection–electrospray ionization mass spectrometry and nuclear magnetic resonance experiments  

Microsoft Academic Search

Taraxacum mongolicum was a traditional Chinese medicine for the treatment of inflammatory disorders and viral infectious diseases. Furthermore, fresh leaves of T. mongolicum have been used by local people as vegetable food in Northern China. An on-line rapid screening method, high-performance liquid chromatography–diode array detection–radical-scavenging detection–electrospray ionization mass spectrometry (HPLC–DAD–RSD–ESI-MS) system, has been developed for the separation and identification of

Shuyun Shi; Yu Zhao; Honghao Zhou; Yuping Zhang; Xinyu Jiang; Kelong Huang

2008-01-01

360

Soldered solar arrays  

NASA Astrophysics Data System (ADS)

The ability of soldered interconnects to withstand a combination of long life and severe environmental conditions was investigated. Improvements in joint life from the use of solder mixes appropriate to low temperature conditons were studied. Solder samples were placed in a 150 C oven for 5 weeks (= 12 yr at 80 C, or 24 at 70 C according to Arrhenius's rule). Conventional and high solder melting point array samples underwent 1000 thermal cycles between -186 and 100 C. Results show that conventional and lead rich soldered arrays can survive 10 yr geostationary orbit missions.

Allen, H. C.

1982-06-01

361

Array signal processing  

SciTech Connect

This is the first book to be devoted completely to array signal processing, a subject that has become increasingly important in recent years. The book consists of six chapters. Chapter 1, which is introductory, reviews some basic concepts in wave propagation. The remaining five chapters deal with the theory and applications of array signal processing in (a) exploration seismology, (b) passive sonar, (c) radar, (d) radio astronomy, and (e) tomographic imaging. The various chapters of the book are self-contained. The book is written by a team of five active researchers, who are specialists in the individual fields covered by the pertinent chapters.

Haykin, S.; Justice, J.H.; Owsley, N.L.; Yen, J.L.; Kak, A.C.

1985-01-01

362

ALMA Extended Array  

NASA Astrophysics Data System (ADS)

We propose to append five 12-m antennas within 300-km from ALMA to realize high angular resolution of < 1 mas and sensitivity to detect Tb < 1000 K. This ALMA extended array offers a new parameter space of “Thermal universe with VLBI resolution”. Proposed science case includes black-hole formation in sub-mm galaxies, mass accretion processes onto protostars, imaging stellar photospheres, distance measurements of stars, and so on. The array also functions as a part of sub-mm VLBI that targets black-hole imaging.

Kameno, S.; Nakai, N.; Honma, M.

2013-10-01

363

Periodic nanowire array at the crystal interface.  

PubMed

A dislocation in a crystalline material has dangling bonds at its core and a strong strain field in its vicinity. Consequently, the dislocation attracts solute atoms and forms a so-called Cottrell atmosphere along the dislocation. A crystalline dislocation can be used as a template to produce nanowires by selectively doping foreign atoms along the dislocation. However, control of the configuration, spacing, and density of the formed periodic nanowire array has heretofore been extremely difficult. Here we show a method for fabricating ordered, electrically conductive nanowire arrays using periodic dislocations at crystal interfaces. As a demonstration, we fabricated arrays of titanium nanowires arranged at intervals of either 13 or 90 nm and then confirmed by scanning probe microscopy that they exhibit electrical conductivity inside an insulating aluminum oxide. Significantly, we were able to precisely control nanowire periodicity by the choice of crystal orientation and/or crystal planes at the crystal interface. This simple method for the fabrication of periodic nanowire arrays of highly controlled density should be widely applicable to electrical, magnetic, and optical devices. PMID:23876048

Nakamura, Atsutomo; Mizoguchi, Teruyasu; Matsunaga, Katsuyuki; Yamamoto, Takahisa; Shibata, Naoya; Ikuhara, Yuichi

2013-07-05

364

The implosion and stagnation of wire array z-pinches  

NASA Astrophysics Data System (ADS)

Experiments at all levels of current drive have demonstrated that the first 60-80 percent of the evolution of a wire array z- pinch is dominated by the gradual ablation of cold, dense wire cores into low density coronal plasma that is projected towards the axis of the array. Implosion of the array only begins when the wire cores start to break up, at which time a piston of current snowploughs up coronal plasma as it accelerates towards the axis. Here we present the detailed measurements of the snowplough process and the dynamics of the array during its stagnation on axis. The stability and width of the snowplough and the compression of the plasma at stagnation are related to X-ray emission, providing data on the mechanisms responsible for X-ray production.Several methods to alter the implosion of an array are explored. The interaction between the outer and inner of a nested array configuration is directly observed for the first time, highlighting how X-ray emission can be shaped. In a new type of array a ``coiled'' array the magnetic field topology is altered, resulting in large changes to the ablation dynamics and an implosion that snowploughs less mass to a higher velocity. With a relatively low number of wires, the use of coiled arrays can increase X-ray emission by ˜5x over that usually observed at stagnation. Using a radial array configuration, meanwhile, the scale of the stagnating plasma can be reduced without adversely affecting X-ray power. This may enable arrays to couple to far smaller hohlraums, significantly raising the available temperatures for HEDP experiments. This research was sponsored by Sandia National Labs and the NNSA under DOE Cooperative Agreement DE-F03-02NA00057.

Bland, Simon

2006-10-01

365

Zeeman slower based on magnetic dipoles  

Microsoft Academic Search

In this paper it is proposed to use a periodic array of very strong and compact neodymium magnets to create the desired magnetic field of the Zeeman slower. A model of the slower based on point-like magnetic dipoles has been introduced, which is a key element in designing of such type of a slower. The high precision of that simple

Yuri B. Ovchinnikov

2007-01-01

366

Flux creep in Josephson junction arrays  

SciTech Connect

This paper reports that, in order to analyze the diamagnetic properties of weakly coupled structures in high T{sub c} ceramic superconductors, the Josephson junction array model is used. The authors suppose that the coupling is strong enough to allow magnetic flux trappings inside non superconducting regions surrounded by superconducting loops closed by Josephson junctions. The authors remark that the presence of currents flowing through the junctions has to be taken explicitly into account in the Hamiltonian. This description leads to a creep model of the Josephson junction array. Indeed the authors have: pinning centers generated by non superconducting regions into the loops, pinning potentials determined by fluxon motion barriers due to the Josephson junctions, absence of degeneracy of the states corresponding to a different number of fluxons in the loops, a reduction of the barrier height due to measuring currents or to diamagnetic shielding currents.

Pace, S.; Saggese, A.; DeLuca, R. (Dept. of Physics, Univ. of Salerno, 84100 Salerno (IT)); Celani, F.; Liberatori, L. (INFN-LNF, 00044 Frascati (IT))

1991-03-01

367

Photovoltaic Cell Array.  

National Technical Information Service (NTIS)

A construction technique for making high density solar cell arrays at lowered costs is presented. Closely spaced filaments of silicon are prepared to have a continuous layer-type semiconductor junction formed by creating an internal P-type conductivity re...

J. T. Eliason

1975-01-01

368

The Askaryan Radio Array  

NASA Astrophysics Data System (ADS)

Ultra high energy cosmogenic neutrinos could be most efficiently detected in dense, radio frequency (RF) transparent media via the Askaryan effect. Building on the expertise gained by RICE, ANITA and IceCube's radio extension in the use of the Askaryan effect in cold Antarctic ice, we are currently developing an antenna array known as ARA (The Askaryan Radio Array) to be installed in boreholes extending 200 m below the surface of the ice near the geographic South Pole. The unprecedented scale of ARA, which will cover a fiducial area of ~ 100 square kilometers, was chosen to ensure the detection of the flux of neutrinos suggested by the observation of a drop in high energy cosmic ray flux consistent with the GZK cutoff by HiRes and the Pierre Auger Observatory. Funding to develop the instrumentation and install the first prototypes has been granted, and the first components of ARA were installed during the austral summer of 2010-2011. Within 3 years of commencing operation, the full ARA will exceed the sensitivity of any other instrument in the 0.1-10 EeV energy range by an order of magnitude. The primary goal of the ARA array is to establish the absolute cosmogenic neutrino flux through a modest number of events. This information would frame the performance requirements needed to expand the array in the future to measure a larger number of neutrinos with greater angular precision in order to study their spectrum and origins.

Hoffman, Kara D.

2013-01-01

369

Countermeasure Flexible Line Array.  

National Technical Information Service (NTIS)

A countermeasure buoy for use in an underwater environment includes a main body portion, a propulsion portion, a hull section, and an acoustical array. The main body portion includes a first end and a second end longitudinally opposed from the first end. ...

1998-01-01

370

Carbon nanotube arrays  

Microsoft Academic Search

Carbon nanotube arrays were prepared by chemical vapor deposition (CVD) of hydrocarbon gas on various substrates. The effect of substrates on the growth, morphology and structure of carbon nanotubes were investigated. Aligned carbon nanotubes with high density and purity were achieved by CVD on bulk silica substrate. On the film-like substrates, very long carbon nanotubes of length ~2 mm were produced,

S. S. Xie; W. Z. Li; Z. W. Pan; B. H. Chang; L. F. Sun

1999-01-01

371

Basic Photovoltaic Array Sizing  

NSDL National Science Digital Library

This learning activity from the Advanced Technology Environmental and Energy Center (ATEEC) allows students to conduct a photovoltaic array sizing assessment. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item.

2013-01-10

372

Array processors in chemistry  

SciTech Connect

The field of attached scientific processors (''array processors'') is surveyed, and an attempt is made to indicate their present and possible future use in computational chemistry. The current commercial products from Floating Point Systems, Inc., Datawest Corporation, and CSP, Inc. are discussed.

Ostlund, N.S.

1980-01-01

373

Biomimetic Tactile Sensor Array  

Microsoft Academic Search

The performance of robotic and prosthetic hands in unstructured environments is severely limited by their having little or no tactile information compared to the rich tactile feedback of the human hand. We are developing a novel, robust tactile sensor array that mimics the mechanical properties and distributed touch receptors of the human fingertip. It consists of a rigid core surrounded

Nicholas Wettels; Veronica J. Santos; Roland S. Johansson; Gerald E. Loeb

2008-01-01

374

Array Processing for FORTRAN.  

National Technical Information Service (NTIS)

The Special Task Force on Cray FORTRAN (STF) was chartered to consider ...new language features to exploit the vector hardware of the CRAY-1 that might also be applicable to other large scientific computers. The new array processing features in STF FORTRA...

C. Wetherell

1980-01-01

375

Graded reflectivity micromirror arrays  

Microsoft Academic Search

A technique for fabricating arrays of graded reflectivity micromirrors with diameters as small as 25 mum is reported. It is based on laser-induced physical vapor deposition through microholes on a thin free-standing noncontact mask, and it is suitable for applications in micro-optics and solid-state laser technology.

Pasquale Cusumano; Giuseppe Lullo; Angelo Mangione; Claudio Arnone

2002-01-01

376

Graded reflectivity micromirror arrays.  

PubMed

A technique for fabricating arrays of graded reflectivity micromirrors with diameters as small as 25 microm is reported. It is based on laser-induced physical vapor deposition through microholes on a thin free-standing noncontact mask, and it is suitable for applications in micro-optics and solid-state laser technology. PMID:11900430

Cusumano, Pasquale; Lullo, Giuseppe; Mangione, Angelo; Arnone, Claudio

2002-01-01

377

Norwegian Seismic Array (NORSAR).  

National Technical Information Service (NTIS)

This report describes the operation and research activities at the Norwegian Seismic Array (NORSAR) for the period from 1 October 1978 to 31 March 1979. The performance of the NORSAR online DP system has changed very little from the previous reporting per...

H. Gjoystdal

1979-01-01

378

Solar cell array  

Microsoft Academic Search

An array of photovoltaic cells in a back wall-type configuration supported by a rigid transparent vitreous substrate, such as glass, for admitting incident radiation to the cells is described. A plurality of cells are interconnected into a desired electrical configuration by one or more layers of electrically conducting materials which overlie the entire heterojunction of each cell to minimize the

J. F. Jordan; C. M. Lampkin

1982-01-01

379

Solar cell array  

Microsoft Academic Search

An array of photovoltaic cells in a back wall-type configuration supported by a rigid transparent vitreous substrate, such as glass, for admitting incident radiation to the cells is described. A plurality of cells are interconnected into a desired electrical configuration by one or more layers of electrically conducting materials which overlie substantially the entire heterojunction of each cell to minimize

J. F. Jordan; C. M. Lampkin

1981-01-01

380

Light Emitting Diode Array.  

National Technical Information Service (NTIS)

Four 15-element GaAsP light emitting diode arrays were fabricated and delivered to Night Vision Laboratory. Measured brightnesses of the emitting elements range higher than originally anticipated. The minimum brightness requirement at 10mA forward bias is...

G. A. Henderson

1973-01-01

381

DCA Using Suffix Arrays  

Microsoft Academic Search

DCA (Data Compression using Antidictionaries) is a novel lossless data compression method working on bit streams presented by Crochemore et al. DCA takes advantage of words that do not occur as factors in the text, i.e. that are forbidden. Due to these forbidden words (antiwords), some symbols in the text can be predicted. We build the antidictionary using suffix array

Martin Fiala; Jan Holub

2008-01-01

382

Optoelectronic Switch Array.  

National Technical Information Service (NTIS)

The report presents the second quarter work performed in the development of an optoelectronic switch array. The report is divided into three parts. Part I describes an improved light sensing circuit which has been included in the integrated design and des...

1968-01-01

383

Space Station Solar Arrays  

NASA Website

(3 April 2013) -- This close-up picture of a Zvezda Service Module array, reflecting bright rays of the sun, thus creating an artistic scene, was photographed on April 3 by one of the Expedition 35 crew members as part of an External Survey from ...

384

Thermal responsive microlens arrays  

Microsoft Academic Search

The authors developed a technique to encapsulate poly-N-isopropylacrylamide (PNIPAAm) for fabrication of monodisperse microcapsules, whose size, embedding efficiency, and wall thickness are controllable. The monodisperse microcapsules were hexagonally packed to form microlens array (MLA) via a self-assembly process. Due to the thermal respondence of PNIPAAm, the imaging capability and light transportation of the MLA were simply controlled by temperature.

Han Yang; Yong-Hao Han; Xiang-Wei Zhao; Keiji Nagai; Zhong-Ze Gu

2006-01-01

385

Polymer microlens arrays  

Microsoft Academic Search

The manufacture and study of micro-optics has developed into a major topic area as lasers have penetrated telecommunications, information technology and audio-visual services. Microlens arrays can be both high volume and high value articles. After reviewing the topic of microlenses made in both inorganic and plastic materials, this paper describes a new and inexpensive technique of hot pressing for converting

P. Pantelis; D. J. McCartney

1994-01-01

386

Electrode Array Electromagnetic Velocimeter.  

National Technical Information Service (NTIS)

A velocimeter for measuring the velocity field characteristics of a conductive fluid moving over a surface is provided. A magnet has a central axis that is aligned with a direction of fluid movement of interest such that a plurality of magnetic flux lines...

R. G. Kasper L. S. Langston

1993-01-01

387

Microwave transmission measurements through wire array photonic crystals  

NASA Astrophysics Data System (ADS)

We have measured the microwave transmission between 12.4 and 18.0 GHz through wire arrays formed into two dimensional square lattices. One array made of copper wire 0.16 mm in radius consisted of five rows by 21 columns having a lattice constant of 5.15 mm. This array exhibited a pass band above 15 GHz, in good agreement with the calculated plasma frequency found from an expression for the permittivity^1 derived in the long wavelength limit. A second array was made with wire of radius 18 microns and lattice constant 0.8 mm. This array was filled with dielectric loaded with powdered magnetite. A sample of this metamaterial 5.8 mm thick and with no externally applied magnetic field exhibited a pass band above 16 GHz. Implications for creating metamaterials with a negative index of refraction from wire arrays embedded in a magnetic host will be discussed. ^1G. Dewar, in Complex Mediums III: Beyond Linear Isotropic Dielectrics, Akhlesh Lakhtakai, Graeme Dewar, Martin W. McCall, Editors, Proceedings of SPIE Vol. 4806, 156-166 (2002).

Dewar, Graeme; Souther, Nathan; Johnson, Michael

2008-03-01

388

Spectrally narrowed external-cavity high-power stack of laser diode arrays  

PubMed Central

We describe an effective external cavity for narrowing the spectral linewidth of a multiarray stack of laser diode arrays. For a commercially available 279-W free-running five-array laser diode array operating at 60 A, we narrow the spectral linewidth to 0.40 nm at FWHM with 115 W of cw power output. This technique leads to the possibility of higher-efficiency, lower-cost production of hyperpolarized noble gases for magnetic resonance imaging.

Zhu, H.; Ruset, I. C.; Hersman, F. W.

2005-01-01

389

A method for array calibration in parametric sensor array processing  

Microsoft Academic Search

We present a method for calibrating the perturbations in the array manifold that resulted from the combined effects of mutual coupling, sensor gain and phase mismatch and sensor positioning error. The array calibration method proposed estimates the sensor positions and calibration matrix from a set of measured steering vectors. The calibration matrix is an array parameter that describes the combined

C. M. S. See

1994-01-01

390

Wave modes of collective vortex gyration in dipolar-coupled-dot-array magnonic crystals.  

PubMed

Lattice vibration modes are collective excitations in periodic arrays of atoms or molecules. These modes determine novel transport properties in solid crystals. Analogously, in periodical arrangements of magnetic vortex-state disks, collective vortex motions have been predicted. Here, we experimentally observe wave modes of collective vortex gyration in one-dimensional (1D) periodic arrays of magnetic disks using time-resolved scanning transmission x-ray microscopy. The observed modes are interpreted based on micromagnetic simulation and numerical calculation of coupled Thiele equations. Dispersion of the modes is found to be strongly affected by both vortex polarization and chirality ordering, as revealed by the explicit analytical form of 1D infinite arrays. A thorough understanding thereof is fundamental both for lattice vibrations and vortex dynamics, which we demonstrate for 1D magnonic crystals. Such magnetic disk arrays with vortex-state ordering, referred to as magnetic metastructure, offer potential implementation into information processing devices. PMID:23877284

Han, Dong-Soo; Vogel, Andreas; Jung, Hyunsung; Lee, Ki-Suk; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Fischer, Peter; Meier, Guido; Kim, Sang-Koog

2013-01-01

391

Processing and Display of Medical Three Dimensional Array of Numerical Data Using Octree Encoding.  

National Technical Information Service (NTIS)

Imaging modalities such as X-ray computerized tomography (CT), nuclear medicine and nuclear magnetic resonance can produce three-dimensional (3-D) array of numerical data of internal structure of medical objects. The OCTREE encoding technique, a related h...

J. L. Amans P. Darier

1985-01-01

392

Magnetic multilayers on nanospheres.  

NASA Astrophysics Data System (ADS)

In modern magnetic recording materials the `superparamagnetic effect' [1] has become increasingly important as new magnetic hard disk drive products are designed for higher storage densities. In this regard, nanoparticle media [2], where two-dimensional arrays of monodisperse nanoparticles with high magnetic anisotropy are used, is assumed to be the ideal future magnetic recording material. In this presentation a novel magnetic gradient nanomaterial, which has been created by depositing Co/Pd multilayers onto two-dimensional arrays of self-assembled nanoparticles [3] will be introduced. The magnetic nanostructures formed on top of the particles are in a magnetically exchange-isolated quasi-single-domain state. This nanoscale system is quite distinct from the classical geometries: Neither extrinsic properties nor the intrinsic properties are uniform in space. The film is extended over a wide region of the sphere and thus shows substantial curvature. The film thickness varies and so do the intrinsic magnetic properties most notable the magneto-crystalline anisotropy, which is a key factor affecting the fundamental nature of the reversal process. The specific magnetic characteristics of such a gradient nanomaterial and in particular its impact on the reversal mechanism will be discussed. Angle-dependent reversal studies were performed for different particle sizes and the experimental results were interpreted using micromagnetic simulations. The simulations account for the angular dependence of the hysteresis loops and provide a detailed picture of how the local magnetization evolves during reversal, offering new opportunities in the functionalization of magnetic nanostructures for storage applications. [1] A. Moser et al., J. Phys. D: Appl. Phys. 35, (2002) R157. [2] S. Sun et al., Science 87, (2000) 1989. [3] M. Albrecht et al., Nature Mater. 4, (2005) 203.

Albrecht, Manfred

2006-03-01

393

Superconducting bulk magnets for magnetic levitation systems  

NASA Astrophysics Data System (ADS)

The major applications of high-temperature superconductors have mostly been confined to products in the form of wires and thin films. However, recent developments show that rare-earth REBa2Cu3O7-x and light rare-earth LREBa2Cu3O7-x superconductors prepared by melt processes have a high critical-current density at 77 K and high magnetic fields. These superconductors will promote the application of bulk high-temperature superconductors in high magnetic fields; the superconducting bulk magnet for the Maglev train is one possible application. We investigated the possibility of using bulk magnets in the Maglev system, and examined flux-trapping characteristics of multi-superconducting bulks arranged in array.

Fujimoto, H.; Kamijo, H.

2000-06-01

394

Efficient Computation of Array Patterns.  

National Technical Information Service (NTIS)

The impact of a symmetrical array geometry, the use of quantized stored cosine function, the exploitation of digital Fourier transform algorithms, and the application of trigonometric interpolation in the computation of array patterns is discussed. Carefu...

V. C. Anderson

1976-01-01

395

Supporting dynamic parallel object arrays  

Microsoft Academic Search

ABSTRACT We present efficient support for generalized arrays of parallel data driven objects. Array elements are regular C++ objects, and are scattered across the parallel machine. An individual element is addressed by its \\

Orion Sky Lawlor; Laxmikant V. Kalé

2003-01-01

396

Stretchable Micro-Electrode Array.  

National Technical Information Service (NTIS)

This paper focuses on the design consideration, fabrication processes and preliminary testing of the stretchable micro-electrode array. We are developing an implantable, stretchable micro-electrode array using polymer-based microfabrication techniques. Th...

M. Maghribi J. Hamilton D. Polka K. Rose T. Wilson P. Krulevitch

2002-01-01

397

Large Retractable Solar Cell Array.  

National Technical Information Service (NTIS)

The main activities on the Large Retractable Solar Cell Array(LRSCA) program during the fifth quarterly reporting period consisted of completion of the detailed drawings of the solar array, drum mechanism, and control electronics unit (CEU). Circuit desig...

E. O. Felkel G. Wolff M. C. Olson W. N. Turner R. E. Daniel

1969-01-01

398

Lightweight Parameterized Suffix Array Construction  

NASA Astrophysics Data System (ADS)

We present a first algorithm for direct construction of parameterized suffix arrays and parameterized longest common prefix arrays for non-binary strings. Experimental results show that our algorithm is much faster than naïve methods.

Tomohiro, I.; Deguchi, Satoshi; Bannai, Hideo; Inenaga, Shunsuke; Takeda, Masayuki

399

The AGATA Demonstrator Array at Laboratori Nazionali di Legnaro: Status of the Project  

SciTech Connect

The AGATA Demonstrator Array is presently under installation at Laboratori Nazionali di Legnaro, Italy, where it will replace the CLARA array at the target position of the PRISMA magnetic spectrometer. In the present contribution, the details of the installation will be reviewed. Preliminary results from the first in-beam commissioning test will be given.

Farnea, E. [INFN Sezione di Padova, Padova (Italy)

2009-08-26

400

Very large array observations of solar active regions  

Microsoft Academic Search

Observations of solar active regions with the Very Large Array have led to a new understanding of the origin and prediction of the solar bursts which disrupt communication systems and interfere with high-flying aircraft. The detailed temperature, density and magnetic structure of coronal loops have been investigated by using observations at 20 cm wavelength. By studying loop evolution on time

K. R. Lang

1984-01-01

401

Application of field emitter arrays to microwave power amplifiers  

Microsoft Academic Search

This paper describes the operation of a field emitter array (FEA) as the electron source of a traveling-wave tube (TWT) amplifier. Issues of beam control and focus at high current density and low magnetic field are addressed as well as issues relating to the inherent high emittance of the FEA beam and cathode protection from ion bombardment. Large signal, nonlinear

David R. Whaley; Bartley M. Gannon; Carl R. Smith; Carter M. Armstrong; Capp A. Spindt

2000-01-01

402

A case for redundant arrays of inexpensive disks (RAID)  

Microsoft Academic Search

Increasing performance of CPUs and memories will be squandered if not matched by a similar performance increase in I\\/O. While the capacity of Single Large Expensive Disks (SLED) has grown rapidly, the performance improvement of SLED has been modest. Redundant Arrays of Inexpensive Disks (RAID), based on the magnetic disk technology developed for personal computers, offers an attractive alternative to

David A. Patterson; Garth A. Gibson; Randy H. Katz

1988-01-01

403

Dual dipole imaging array for MIR and ECE imaging  

Microsoft Academic Search

Two dual dipole antennas have been designed in the frequency range of 85-95 GHz and 100-135 GHz for use as imaging array elements for magnetic fusion plasma microwave imaging reflectometry (MIR) and electron cyclotron emission imaging (ECEI) diagnostics, respectively. The antenna pattern is of primary importance for these applications, with emphasis on clean antenna patterns and low sidelobe levels for

Z. Xia; C. W. Domier

2005-01-01

404

Construction of Chiral Metamaterial with a Helix Array  

Microsoft Academic Search

Here we report the designing of chiral metamaterial with metallic helix array. The effective electric and magnetic dipoles, which originate from the induced surface electric current upon illumination of incident light, are collinear at the resonant frequency. Consequently, for the circularly polarized incident light, negative refractive index is realized. Our design provides a unique approach to tune the optical properties

Xiang Xiong; Xiao-Chun Chen; Zhao-Wu Wang; Shang-Chi Jiang; Mu Wang; Ru-Wen Peng; Xi-Ping Hao; Cheng Sun

2011-01-01

405

Photodetector arrays for optical processing  

Microsoft Academic Search

The present discussion of design and performance issues emerging from the dynamic range requirements placed by optical processors on photodetector arrays emphasizes time-integrating photodetector arrays. The two most common photodetector element types used in time-integrating arrays are the N+\\/P and photogate detector types. Attention is given to detector array developments for optical processing which have yielded 1-2 orders-of-magnitude improvements, relative

Paul P. Suni

1989-01-01

406

A superconducting quadrupole array for transport of multiple high current beams  

SciTech Connect

We present a conceptual design of a superconducting quadrupole magnet array for the side-by-side transport of multiple high current particle beams in induction linear accelerators. The magnetic design uses a modified cosine 20 current distribution inside a square cell boundary. Each interior magnet's neighbors serve as the return flux paths and the poles are placed as close as possible to each other to facilitate this. No iron is present in the basic 2-D magnetic design; it will work at any current level without correction windings. Special 1/8th quadrupoles are used along the transverse periphery of the array to contain and channel flux back into the array, making every channel look as part of an infinite array. This design provides a fixed dimension array boundary equal to the quadrupole radius that can be used for arrays of any number of quadrupole channels, at any field level. More importantly, the design provides magnetic field separation between the array and the induction cores which may be surrounding it. Flux linkage between these two components can seriously affect the operation of both of them.

Faltens, A.; Shuman, D.

1999-11-01

407

High sensitivity, low noise Mirnov coil array on Prairie View rotamak.  

PubMed

An array of 32 Mirnov coils with novel features of high sensitivity and low noise has been installed on the outside chamber surface of Prairie View rotamak. This B(R)-oriented coil array has proven to be very reliable in the plasma driven by rotating magnetic field; it can resolve magnetic perturbation signals of 0.1 G. With this new diagnostic, the n = 1 tilt, radial shift, and kink modes are observed for the first time in rotamak plasmas. PMID:23126964

Yang, X; Houshmandyar, S; Dada, O; Reddic, E; Huang, T S

2012-10-01

408

Second harmonic generation in magnetic nanoparticles with vortex magnetic state  

NASA Astrophysics Data System (ADS)

Nonlinear optical properties of a regular array of triangular-shaped vortex magnetic nanoparticles is studied using the optical second harmonic generation (SHG) technique. We demonstrate that the SHG azimuthal anisotropy is consistent with the 3m symmetry of individual Co nanodots placed in a square surface lattice. Qualitatively different SHG magnetic hysteresis loops are obtained for circular and linear polarizations of the fundamental radiation. In the first case, a wide SHG hysteresis at zero DC magnetic field H is observed, which is attributed to a macroscopic magnetic toroid moment in Co nanodots induced by a noncentrosymmetric distribution of the magnetization. On the contrary, for the linear pump polarization the SHG loop is similar to observed commonly in linear magnetooptics for vortex magnetic structures and reveals a rather narrow width at H=0. A phenomenological SHG description based on the introduction of the SHG polarization induced by a magnetic toroid moment in vortex magnetic nanostructures is presented.

Krutyanskiy, V. L.; Kolmychek, I. A.; Gribkov, B. A.; Karashtin, E. A.; Skorohodov, E. V.; Murzina, T. V.

2013-09-01

409

Supporting dynamic parallel object arrays  

Microsoft Academic Search

We present efficient support for generalized arrays of parallel data driven objects. The “array elements” are scattered across a parallel machine. Each array element is an object that can be thought of as a virtual processor. The individual elements are addressed by their “index”, which can be an arbitrary object rather than a simple integer. For example, it can be

Orion Sky Lawlor; Laxmikant V. Kalé

2001-01-01

410

Flexible transceiver array for ultrahigh field human MR imaging.  

PubMed

A flexible transceiver array, capable of multiple-purpose imaging applications in vivo at ultrahigh magnetic fields was designed, implemented and tested on a 7 T MR scanner. By alternately placing coil elements with primary and secondary harmonics, improved decoupling among coil elements was accomplished without requiring decoupling circuitry between resonant elements, which is commonly required in high-frequency transceiver arrays to achieve sufficient element-isolation during radiofrequency excitation. This flexible array design is capable of maintaining the required decoupling among resonant elements in different array size and geometry and is scalable in coil size and number of resonant elements (i.e., number of channels), yielding improved filling factors for various body parts with different geometry and size. To investigate design feasibility, flexibility, and array performance, a multichannel, 16-element transceiver array was designed and constructed, and in vivo images of the human head, knee, and hand were acquired using a whole-body 7 T MR system. Seven Tesla parallel imaging with generalized autocalibrating partially parallel acquisitions (GRAPPA) performed using this flexible transceiver array was also presented. PMID:22246803

Wu, Bing; Zhang, Xiaoliang; Wang, Chunsheng; Li, Ye; Pang, Yong; Lu, Jonathan; Xu, Duan; Majumdar, Sharmila; Nelson, Sarah J; Vigneron, Daniel B

2012-01-13

411

Flexible Transceiver Array for Ultrahigh Field Human MR Imaging  

PubMed Central

A flexible transceiver array, capable of multiple-purpose imaging applications in vivo at ultrahigh magnetic fields was designed, implemented and tested on a 7 T MR scanner. By alternately placing coil elements with primary and secondary harmonics, improved decoupling among coil elements was accomplished without requiring decoupling circuitry between resonant elements, which is commonly required in high frequency transceiver arrays in order to achieve sufficient element-isolation during RF excitation. This flexible array design is capable of maintaining the required decoupling among resonant elements in different array size and geometry, and is scalable in coil size and number of resonant elements (i.e. number of channels), yielding improved filling factors for various body parts with different geometry and size. To investigate design feasibility, flexibility, and array performance, a multi-channel, 16-element transceiver array was designed and constructed, and in vivo images of the human head, knee, and hand were acquired using a whole-body 7T MR system. 7T parallel imaging with GRAPPA performed using this flexible transceiver array was also presented.

Wu, Bing; Zhang, Xiaoliang; Wang, Chunsheng; Li, Ye; Pang, Yong; Lu, Jonathan; Xu, Duan; Majumdar, Sharmila; Nelson, Sarah J.; Vigneron, Daniel B.

2012-01-01

412

Unified heliostat array project  

SciTech Connect

A set of diagrams and outlines describes a project to develop a unified heliostat array on an inclined structure. Project progress and performance is diagrammed. The proposed site is Barstow, California, and the soil properties, seismic zone, wind, temperature range, ice and snow for the area are given. For 1, 10, and 25 MWt unified heliostat arrays, aspect ratios are given for various plan views and elevations. Designs are sketched for three existing inclined structures. The relative advantages and disadvantages of concrete, steel, and timber are briefly outlined. Several design factors are presented, and the basic design concepts and some construction details are given. Possible changes in steel tonnage in the design, and cost estimates are presented. (LEW)

Not Available

1980-06-01

413

Detector array design  

SciTech Connect

Neutron scattering facility at Oak-Ridge National is used to measure residual stresses in many different materials. Neutron beam from the reactor can be used to penetrate the inner atomic distances of metals which then can be diffracted to a detector to measure the strain. The strain data later can be converted to stresses. The facility currently uses only one detector to carry the measurement. By designing an array of detectors data can be obtained at a much faster rate and or having a much better and improved resolution. The purpose of this report is to show design of such array of detectors and their movements (rotation) for possible maximum data collection at a faster rate.

Lari, S.

1996-02-01

414

Array processor supercomputers  

SciTech Connect

Array processor supercomputers achieve their supercomputer performance by connecting massive numbers (64K) of relatively simple processors together. Commercially available machines have computation rates of up to 4 billion operations per second. These large computation rates have generated a substantial body of research investigating their usefulness for computationally intensive tasks such as image processing. These machines, however, also hold promise of efficient execution of non-numerical algorithms because of their ability to perform massive searching in constant time, often eliminating the need for ordering and complex data structures such as those using pointers. This paper describes the range of hardware variations of array processors, comparing and contrasting the significant differences among them, as well as briefly illustrating the wide range of algorithms that can effectively utilize them.

Potter, J.L.; Meilander, W.C. (Kent State Univ., OH (USA). Dept. of Mathematical Sciences)

1989-12-01

415

Dynamic extended suffix arrays  

Microsoft Academic Search

The suffix tree data structure has been intensively described, studied and used in the eighties and nineties, its linear-time construction counterbalancing his space-consuming requirements. An equivalent data structure, the suffix array, has been described by Manber and Myers in 1990. This space-economical structure has been neglected during more than a decade, its construction being too slow. Since 2003, several linear-time

Mikaël Salson; Thierry Lecroq; Martine Léonard; Laurent Mouchard

2010-01-01

416

Suffix Arrays on Words  

Microsoft Academic Search

Surprisingly enough, it is not yet known how to build directly a suffix array that indexes just the k positions at word-boundaries of a text T (1 ,n ), taking O(n )t ime andO(k) space in addition to T.W e pro- pose a class-note solution to this problem that achieves such optimal time and space bounds. Word-based versions of indexes

Paolo Ferragina; Johannes Fischer

2007-01-01

417

Live mammalian cell arrays.  

PubMed

High-content assays have the potential to drastically increase throughput in cell biology and drug discovery, but handling and culturing large libraries of cells such as primary tumor or cancer cell lines requires expensive, dedicated robotic equipment. We developed a simple yet powerful method that uses contact spotting to generate high-density nanowell arrays of live mammalian cells for the culture and interrogation of cell libraries. PMID:23644546

Woodruff, Kristina; Fidalgo, Luis M; Gobaa, Samy; Lutolf, Matthias P; Maerkl, Sebastian J

2013-05-05

418

Fluorescence Based Sensor Arrays  

Microsoft Academic Search

\\u000a Fluorescence-based cross reactive sensor arrays have experienced significant development in the last decade because of the\\u000a advantages that they can offer with respect to other transduction mechanisms, in terms of the usual performance parameters\\u000a such as sensitivity, selectivity and so on. From this point of view, a great impulse to this development has been due to the\\u000a realization of novel

Roberto Paolesse; Donato Monti; Francesca Dini; Corrado Di Natale

419

Fiber laser hydrophone array  

NASA Astrophysics Data System (ADS)

In recent years growing interest has surrounded the development of fiber laser sensors (FLS). This is due to their ultra high sensitivity to temperature and strain as well as their ability to be multiplexed along a single fiber using WDM techniques. It is their extreme sensitivity that has led to them being considered as acoustic pressure sensors rather than standard fiber Bragg gratings. The work presented here describes the development of an array of FLS configured as hydrophones. We discuss the design of the single mode fiber laser used throughout our system; comparing examples based upon distributed Bragg reflectors (DBR) and distributed feedback (DFB). In addition we discuss both the theoretical and experimental acoustic sensitivity enhancements obtained by the application of an elasto-plastic coating to the FLS. The array configuration is described, as is the heterodyne interrogation scheme using an unbalanced Mach-Zehnder interferometer with WDM channel selection. Results from the measurement of the minimal detectable acoustic signal of a bare fiber laser are shown to be -69 dB re.Pa/(root)Hz at 1 kHz when using a 200 m path imbalanced readout interferometer. Further gains in the sensitivity due to the application of various coatings are reported, as is a full characterization of an array of fiber laser hydrophones. Finally we discuss the future research of the FLS, and the areas in which the technology is particularly applicable.

Hill, David J.; Nash, Phillip J.; Jackson, David A.; Webb, David J.; O'Neill, S. F.; Bennion, Ian; Zhang, Lin

1999-12-01

420

High-density peptide arrays.  

PubMed

Arrays promise to advance biology by allowing parallel screening for many different binding partners. Meanwhile, lithographic methods enable combinatorial synthesis of > 50,000 oligonucleotides per cm(2), an advance that has revolutionized the whole field of genomics. A similar development is expected for the field of proteomics, provided that affordable, very high-density peptide arrays are available. However, peptide arrays lag behind oligonucleotide arrays. This review discusses recent developments in the field with an emphasis on methods that lead to very high-density peptide arrays. PMID:19225611

Breitling, Frank; Nesterov, Alexander; Stadler, Volker; Felgenhauer, Thomas; Bischoff, F Ralf

2009-01-16

421

Optical magnetometer array for fetal magnetocardiography  

PubMed Central

We describe an array of spin-exchange-relaxation-free optical magnetometers designed for detection of fetal magnetocardiography (fMCG). The individual magnetometers are configured with a small volume with intense optical pumping, surrounded by a large pump-free region. Spin-polarized atoms that diffuse out of the optical pumping region precess in the ambient magnetic field and are detected by a probe laser. Four such magnetometers, at the corners of a 7 cm square, are configured for gradiometry by feeding back the output of one magnetometer to a field coil to null uniform magnetic field noise at frequencies up to 200 Hz. We present the first measurements of fMCG signals using an atomic magnetometer.

Wyllie, Robert; Kauer, Matthew; Wakai, Ronald T.; Walker, Thad G.

2012-01-01

422

Theoretical calculation of magneto-optical properties in cobalt nanotube array with hexagonal symmetry  

NASA Astrophysics Data System (ADS)

The extended Fourier components and effective electric dipole model allowing for the proper treatment of magneto-optical (MO) activity are presented. The scattering-matrix approach is employed to analyze the MO properties of hexagonal array of magnetic metallic nanotubes embedded in a dielectric medium in the presence of magnetic field. It is found the MO properties of the nanotube array are more prominent than those of the nanodisk array for the same value of the cobalt filling ratio in specific wavelength range. The spectral position of the Kerr maxima can be tuned by the nanotube's length, wall thickness, separation of the neighboring nanotubes and the filling medium.

Zhang, Shaoyin; Tang, Shaolong; Gao, Jinlong; Luo, Xiaojing; Xia, Wenbin; Du, Youwei

2013-09-01

423

Fabrication of magnetic microfiltration systems using soft lithography  

NASA Astrophysics Data System (ADS)

Arrays of nickel posts were used as magnetic elements in a microfiltration device that is compatible with microfluidic systems. The combination of microtransfer molding-a soft lithography technique-and electrodeposition generated nickel posts ~7 ?m in height and ~15 ?m in diameter inside a microfluidic channel. Once magnetized by a magnetic field from an external, permanent, neodymium-iron-boron magnet, these nickel posts generated strong magnetic field gradients and efficiently trapped superparamagnetic beads moving past them in a flowing stream of water. These nickel post arrays were also used to separate magnetic beads from nonmagnetic beads.

Deng, Tao; Prentiss, Mara; Whitesides, George M.

2002-01-01

424

ICE decoupling technique for RF coil array designs  

PubMed Central

Purpose: Parallel magnetic resonance imaging (MRI) requires an array of RF coil elements with different sensitivity distributions and with minimal electromagnetic coupling. The goal of this project was to develop a new method based on induced current compensation or elimination (ICE) for improved coil element decoupling and to investigate its performance in phantom MR images. Methods: An electromagnetic decoupling method based on induced current compensation or elimination for nonoverlapping RF coil arrays was developed with the design criteria of high efficiency, easy implementation, and no physical connection to RF array elements. An eigenvalue/eigenvector approach was employed to analyze the decoupling mechanism and condition. A two-channel microstrip array and an eight-channel coil array were built to test the performance of the method. Following workbench tests, MR imaging experiments were performed on a 7T MR scanner. Results: The bench tests showed that both arrays achieved sufficient decoupling with a S21 less than ?25 dB among the coil elements at 298 MHz. The MR phantom images demonstrated well-defined sensitivity distributions from each coil element and the unique decoupling capability of the proposed ICE decoupling technique. B1 distributions of the individual elements were also measured and calculated. Conclusions: The theoretical analysis and experiments demonstrated the feasibility of the decoupling method for high field RF coil array designs without overlapping or direct physical connections between coil elements, which provide more flexibility for coil array design and optimization. The method offers a new approach to address the RF array decoupling issue, which is a major challenge in implementing parallel imaging.

Li, Ye; Xie, Zhentian; Pang, Yong; Vigneron, Daniel; Zhang, Xiaoliang

2011-01-01

425

Field Directed Ordering in Magnetic Nanocrystal Structures  

NASA Astrophysics Data System (ADS)

Iron oxide nanocrystals (NCs) have been the focus of intense research owing to the observation of tunable magnetic properties which could lead to advances in many fields including magnetic storage devices and medicine. We have been targeting the use of iron oxide NCs as magnetoresistance (MR) based sensors using ordered NC arrays. In this work, we will present our efforts toward using external magnetic fields to induce intraparticle ordering in iron oxide NC drop cast films. We use x-ray diffraction to analyze effects of the external fields on the NC array structure, while using SQUID magnetometry to probe the effects of NC interactions on the magnetic properties of iron oxide NCs ranging from 5 - 20 nm in diameter. MR measurements suggest large changes in the MR ratio can be achieved using the directed ordering approach for NC arrays. Our work could provide new avenues towards the fabrication of new magnetic devices.

Lawson, Stuart; Meulenberg, Robert

2013-03-01

426

Storage array reflection considerations  

SciTech Connect

The assumptions used for reflection conditions of single containers are fairly well established and consistently applied throughout the industry in nuclear criticality safety evaluations. Containers are usually considered to be either fully water-reflected (i.e. surrounded by 6 to 12 in. of water) for safety calculations or reflected by 1 in. of water for nominal (structural material and air) conditions. Tables and figures are usually available for performing comparative evaluations of containers under various loading conditions. Reflection considerations used for evaluating the safety of storage arrays of fissile material are not as well established.

Haire, M.J.; Jordan, W.C. [Oak Ridge National Lab., TN (United States); Taylor, R.G. [Oak Ridge Y-12 Plant, TN (United States)

1997-08-01

427

Pulsar Timing Arrays  

NASA Astrophysics Data System (ADS)

In the last decade, the use of an ensemble of radio pulsars to constrain the characteristic strain caused by a stochastic gravitational wave background has advanced the cause of detection of very low frequency gravitational waves (GWs) significantly. This electromagnetic means of GW detection, called Pulsar Timing Array (PTA), is reviewed in this paper. The principle of operation of PTA, the current operating PTAs and their status are presented along with a discussion of the main challenges in the detection of GWs using PTA.

Joshi, Bhal Chandra

2013-01-01

428

Phased array ghost elimination.  

PubMed

Parallel imaging may be applied to cancel ghosts caused by a variety of distortion mechanisms, including distortions such as off-resonance or local flow, which are space variant. Phased array combining coefficients may be calculated that null ghost artifacts at known locations based on a constrained optimization, which optimizes SNR subject to the nulling constraint. The resultant phased array ghost elimination (PAGE) technique is similar to the method known as sensitivity encoding (SENSE) used for accelerated imaging; however, in this formulation is applied to full field-of-view (FOV) images. The phased array method for ghost elimination may result in greater flexibility in designing acquisition strategies. For example, in multi-shot EPI applications ghosts are typically mitigated by the use of an interleaved phase encode acquisition order. An alternative strategy is to use a sequential, non-interleaved phase encode order and cancel the resultant ghosts using PAGE parallel imaging. Cancellation of ghosts by means of phased array processing makes sequential, non-interleaved phase encode acquisition order practical, and permits a reduction in repetition time, TR, by eliminating the need for echo-shifting. Sequential, non-interleaved phase encode order has benefits of reduced distortion due to off-resonance, in-plane flow and EPI delay misalignment. Furthermore, the use of EPI with PAGE has inherent fat-water separation and has been used to provide off-resonance correction using a technique referred to as lipid elimination with an echo-shifting N/2-ghost acquisition (LEENA), and may further generalized using the multi-point Dixon method. Other applications of PAGE include cancelling ghosts which arise due to amplitude or phase variation during the approach to steady state. Parallel imaging requires estimates of the complex coil sensitivities. In vivo estimates may be derived by temporally varying the phase encode ordering to obtain a full k-space dataset in a scheme similar to the autocalibrating TSENSE method. This scheme is a generalization of the UNFOLD method used for removing aliasing in undersampled acquisitions. The more general scheme may be used to modulate each EPI ghost image to a separate temporal frequency as described in this paper. PMID:16705636

Kellman, Peter; McVeigh, Elliot R

2006-05-01

429

Magnetic levitation transport of mining products. Report of investigations/1995  

SciTech Connect

U.S. Bureau of Mines researchers have developed innovative magnetic levitation (mag-lev) technology that allows for noncontact, frictionless conveyance of materials within a dedicated transit corridor. A transport system incorporating this technology could improve the safety and reduce the cost of underground mining and materials handling. The mag-lev transport technology uses two types of permanent magnets. An array of neodymium-iron-boron magnets is contained in the base of each levitated materials container, and an array of ceramic-5 magnets lines the bottom of the transit corridor. The orientation of the magnets is such that the two arrays repel each other. An electronic position control system, located on the levitated materials containers, overcomes the inherent lateral instability of the repelling magnet arrays.

Geraghty, J.J.; Wright, W.E.; Lombardi, J.A.

1995-07-01

430

Target localization techniques for vehicle-based electromagnetic induction array applications  

NASA Astrophysics Data System (ADS)

State-of-the-art electromagnetic induction (EMI) arrays provide significant capability enhancement to landmine, unexploded ordnance (UXO), and buried explosives detection applications. Arrays that are easily configured for integration with a variety of mobile platforms offer improved safety and efficiency to personnel conducting detection operations including site remediation, explosive ordnance disposal, and humanitarian demining missions. We present results from an evaluation of two vehicle-based frequency domain EMI arrays. Our research includes implementation of a simple circuit model to estimate target location from sensor measurements of the scattered vertical magnetic field component. Specifically, we characterize any conductive or magnetic target using a set of parameters that describe the eddy current and magnetic polarizations induced about a set of orthogonal axes. Parameter estimations are based on the fundamental resonance mode of a series inductance and resistance circuit. This technique can be adapted to a variety of EMI array configurations, and thus offers target localization capabilities to a number of applications.

Miller, Jonathan S.; Schultz, Gregory M.; Shubitidze, Fridon; Marble, Jay A.

2010-04-01

431

Giant magnetoresistance in nanogranular magnets.  

SciTech Connect

We study the giant magnetoresistance of nanogranular magnets in the presence of an external magnetic field and finite temperature. We show that the magnetization of arrays of nanogranular magnets has hysteretic behavior at low temperatures leading to a double peak in the magnetoresistance which coalesces at high temperatures into a single peak. We numerically calculate the magnetization of magnetic domains and the motion of domain walls in this system using a combined mean-field approach and a model for an elastic membrane moving in a random medium, respectively. From the obtained results, we calculate the electric resistivity as a function of magnetic field and temperature. Our findings show excellent agreement with various experimental data.

Glatz, A.; Beloborodov, I. S.; Vinokur, V. M.; Materials Science Division; Univ. of Chicago

2008-05-01

432

Beamforming with collocated microphone arrays  

NASA Astrophysics Data System (ADS)

A collocated microphone array, including three gradient microphones with different orientations and one omnidirectional microphone, was used to acquire data in a sound-treated room and in an outdoor environment. This arrangement of gradient microphones represents an acoustic vector sensor used in air. Beamforming techniques traditionally associated with much larger uniformly spaced arrays of omnidirectional sensors are extended to this compact array (1 cm3) with encouraging results. A frequency-domain minimum-variance beamformer was developed to work with this array. After a calibration of the array, the recovery of sources from any direction is achieved with high fidelity, even in the presence of multiple interferers. SNR gains of 5-12 dB with up to four speech sources were obtained with both indoor and outdoor recordings. This algorithm has been developed for new MEMS-type microphones that further reduce the size of the sensor array.

Lockwood, Michael E.; Jones, Douglas L.; Su, Quang; Miles, Ronald N.

2003-10-01

433

A facile and universal way to fabricate superlattice nanowire arrays.  

PubMed

A facile and universal synthetic approach for preparing superlattice nanowire (SLNW) arrays is developed. In this method, two kinds of elements are alternately electrodeposited into the holes of the anodic alumina oxide (AAO) template, automatically in separate electrolytes by a programmed device. This method is not restricted by the relative values of the reduction potentials of the elements, and the deposition of each element can be controlled independently. Three kinds of representative SLNW arrays containing noble-metal material (Ag/Ni), thermoelectric material (Bi/Sb) and magnetic material (Ni/Cu) with adjustable segment length are fabricated successfully. PMID:21576782

Xu, Shao Hui; Fei, Guang Tao; Zhu, Xiao Guang; Wang, Biao; Wu, Bing; De Zhang, Li

2011-05-17

434

The Mileura Widefield Array  

NASA Astrophysics Data System (ADS)

The Mileura Widefield Array will be built in a superbly radio quiet environment at the Mileura Station in western Australia. It will consist of 500 tile antennas, each consisting of 16 dual-polarization dipoles operating in the 80-300 MHz range, distributed over a region 1.5km in diameter. The design has been optimized for epoch of reionization (EoR) studies, and in particular the field of view has been maximized in order to optimize sensitivity for EoR power spectrum detection and characterization. Many other design features are motivated by the need to control systematic errors of various kinds for this demanding spectroscopic measurement. The goal is to begin collecting EoR data at the start of 2008. The end-to-end array design will be described, with emphasis on capabilities relevant to the EoR measurements. Results from prototype hardware deployed at Mileura will be presented, and the current status of the project will be summarized.

Lonsdale, C. J.

2005-12-01

435

The Askaryan radio array  

NASA Astrophysics Data System (ADS)

The Askar'yan Radio Array (ARA), a neutrino detector to be situated at the South Pole next to the IceCube detector, will be sensitive to ultrahigh-energy cosmic neutrinos above 0.1 EeV and will have the greatest sensitivity within the favored energy range from 0.1 EeV up to 10 EeV. Neutrinos of this energy are guaranteed by current observations of the GZK-cutoff by the HiRes and Pierre Auger Observatories. The detection method is based on Cherenkov emission by a neutrino induced cascade in the ice, coherent at radio wavelengths, which was predicted by Askar'yan in 1962 and verified in beam tests at SLAC in 2006. The detector is planned to consist of 37 stations with 16 antennas each, deployed at depths of up to 200 m under the ice surface. During the last two polar seasons (2010 - 2011, 2011 - 2012), a prototype station and a first detector station were successfully deployed and are taking data. These data have been and are currently being analyzed to study the ambient noise background and the radio frequency properties of the South Pole ice sheet. A worldwide collaboration is working on the planning, construction and data analysis of the detector array. This article will give a short report on the status of the ARA detector and show recent results from the recorded data.

Meures, Thomas; ARA Collaboration

2013-05-01

436

Metamaterial Insulator Enabled Superdirective Array  

Microsoft Academic Search

Metamaterial EM insulators are shown to suppress mutual coupling between densely packed array elements. This technique allows for array element design in isolation, without consideration of adjacent elements and mutual coupling effects. Suppressing mutual coupling allows for denser packing and enhanced directivity in antenna arrays approaching the superdirective theoretical maximums. Metamaterial isolation walls 0.05lambda0 thick exhibit 20 dB peak isolations

Kevin Buell; Hossein Mosallaei; Kamal Sarabandi

2007-01-01

437

Linear work suffix array construction  

Microsoft Academic Search

Abstract Sux,trees and sux,arrays are widely used and largely interchangeable index structures on strings and sequences. Practitioners prefer sux,arrays due to their simplicity and space eciency,while theoreticians use sux,trees due to linear-time construction algorithms and more explicit structure. We narrow this gap between theory and practice with a simple linear-time construction algorithm for sux,arrays. The simplicity is demonstrated with a

Juha Kärkkäinen; Peter Sanders; Stefan Burkhardt

2006-01-01

438

Modeling and analysis of a magnetically levitated synchronous permanent magnet planar motor  

NASA Astrophysics Data System (ADS)

In this paper, a new magnetically levitated synchronous permanent magnet planar motor (MLSPMPM) driven by composite-current is proposed, of which the mover is made of a copper coil array and the stator are magnets and magnetic conductor. The coil pitch ?t and permanent magnet pole pitch ?p satisfy the following relationship 3n?t = (3n +/- 1)?p. Firstly, an analytical model of the planar motor is established, flux density distribution of the two-dimensional magnet array is obtained by solving the equations of the scalar magnetic potential. Secondly, the expressions of the electromagnetic forces induced by magnetic field and composite current are derived. To verify the analytical model and the electromagnetic forces, finite element method (FEM) is used for calculating the flux density and electromagnetic forces of the MLSPMPM. And the results from FEM are in good agreement with the results from the analytical equations. This indicates that the analytical model is reasonable.

Kou, Baoquan; Zhang, Lu; Li, Liyi; Zhang, Hailin

2012-04-01

439

Array radars - An update. II  

NASA Astrophysics Data System (ADS)

Research aimed at improving array radars is reviewed. Advances in MMICs, the use of HEMT low noise amplifiers for analog and digital circuitry, the application of VHSIC chips to the programmable signal processor of the F-16 airborne fire control radar, Si compiler language, memory chips, and GHz and GaAs logic are discussed. Consideration is given to CMOS gate arrays, floating point chips, a single-chip digital signal processor, systolic array architectures, radiation hardened chips, digital beamforming, distributed beamsteering computers, fiber optics, flat low voltage displays, and adaptive-adaptive array processing.

Brookner, Eli

1987-03-01

440

Efficient array design for sonotherapy  

NASA Astrophysics Data System (ADS)

New linear multi-row, multi-frequency arrays have been designed, constructed and tested as fully operational ultrasound probes to produce confocal imaging and therapeutic acoustic intensities with a standard commercial ultrasound imaging system. The triple-array probes and imaging system produce high quality B-mode images with a center row imaging array at 5.3 MHz and sufficient acoustic power with dual therapeutic arrays to produce mild hyperthermia at 1.54 MHz. The therapeutic array pair in the first probe design (termed G3) utilizes a high bandwidth and peak pressure, suitable for mechanical therapies. The second multi-array design (termed G4) has a redesigned therapeutic array pair which is optimized for a high time-averaged power output suitable for mild hyperthermia applications. The 'thermal therapy' design produces more than 4 W of acoustic power from the low-frequency arrays with only a 10.5 °C internal rise in temperature after 100 s of continuous use with an unmodified conventional imaging system or substantially longer operation at lower acoustic power. The low-frequency arrays in both probe designs were examined and contrasted for real power transfer efficiency with a KLM model which includes all lossy contributions in the power delivery path from system transmitters to the tissue load. Laboratory verification was successfully performed for the KLM-derived estimates of transducer parallel model acoustic resistance and dissipation resistance, which are the critical design factors for acoustic power output and undesired internal heating, respectively.

Stephens, Douglas N.; Kruse, Dustin E.; Ergun, Arif S.; Barnes, Stephen; Lu, X. Ming; Ferrara, Katherine W.

2008-07-01

441

Magnetic QCA systems  

Microsoft Academic Search

Abstract The field-coupled QCA architecture has emerged as a candidate for providing local interconnectivity for nanodevices, and offers the possibility to perform very dense, high speed, and low power computing in an altogether new paradigm. Magnetic interactions between nanomagnets,are sufficiently strong to allow room-temperature,operation. We are investigating the fabrication and testing of arrays of nanomagnets for this purpose, and have

Gary H. Bernstein; Alexandra Imre; V. Metlushko; Alexei O. Orlov; L. Zhou; L. Ji; György Csaba; Wolfgang Porod

2005-01-01

442

Finite size effect on spread of resonance frequencies in arrays of coupled vortices  

SciTech Connect

Dynamical properties of magnetic vortices in arrays of magnetostatically coupled ferromagnetic disks are studied by means of a broadband ferromagnetic-resonance (FMR) setup. Magnetic force microscopy and magnetic transmission soft X-ray microscopy are used to image the core polarizations and the chiralities which are both found to be randomly distributed. The resonance frequency of vortex-core motion strongly depends on the magnetostatic coupling between the disks. The parameter describing the relative broadening of the absorption peak observed in the FMR transmission spectra for a given normalized center-to-center distance between the elements is shown to depend on the size of the array.

Vogel, Andreas; Drews, André; Im, Mi-Young; Fischer, Peter; Meier, Guido

2011-01-25

443

A 32-Channel Lattice Transmission Line Array for Parallel Transmit and Receive MRI at 7 Tesla  

PubMed Central

Transmit and receive RF coil arrays have proven to be particularly beneficial for ultra-high-field MR. Transmit coil arrays enable such techniques as B1+ shimming to substantially improve transmit B1 homogeneity compared to conventional volume coil designs, and receive coil arrays offer enhanced parallel imaging performance and SNR. Concentric coil arrangements hold promise for developing transceiver arrays incorporating large numbers of coil elements. At magnetic field strengths of 7 tesla and higher where the Larmor frequencies of interest can exceed 300 MHz, the coil array design must also overcome the problem of the coil conductor length approaching the RF wavelength. In this study, a novel concentric arrangement of resonance elements built from capacitively-shortened half-wavelength transmission lines is presented. This approach was utilized to construct an array with whole-brain coverage using 16 transceiver elements and 16 receive-only elements, resulting in a coil with a total of 16 transmit and 32 receive channels.

Adriany, Gregor; Auerbach, Edward J.; Snyder, Carl J.; Gozubuyuk, Ark; Moeller, Steen; Ritter, Johannes; van de Moortele, Pierre-Francois; Vaughan, Tommy; Ugurbil, Kamil

2010-01-01

444

Scripps Orbit and Permanent Array Center: Permanent GPS Array Sites  

NSDL National Science Digital Library

This portal provides access to an extensive selection of Global Positioning Systems (GPS) arrays worldwide, totaling hundreds of sites. Each array link contains a listing of sites, a dynamic map, and contact information (when available). Data from the stations can be downloaded from an anonymous ftp site, and there are also links for data processing.

445

Phase diagrams of magnetic nanotubes  

NASA Astrophysics Data System (ADS)

Analytical expressions for the total magnetic energy of two characteristic internal configurations of nanometric tubes are calculated. A magnetic phase diagram with respect to the aspect ratio of the tubes is obtained which allows a discussion about the possibility of getting ensembles of nanotubes with low coercive fields. A comparison with recently reported coercive fields of three different cobalt nanotube arrays agrees well with the phase diagram derived here.

Escrig, J.; Landeros, P.; Altbir, D.; Vogel, E. E.; Vargas, P.

2007-01-01

446

Light harvesting arrays  

DOEpatents

A light harvesting array useful for the manufacture of devices such as solar cells comprises: (a) a first substrate comprising a first electrode; and (b) a layer of light harvesting rods electrically coupled to the first electrode, each of the light harvesting rods comprising a polymer of Formula I: X.sup.1.paren open-st.X.sup.m+1).sub.m (I) wherein m is at least 1, and may be from two, three or four to 20 or more; X.sup.1 is a charge separation group (and preferably a porphyrinic macrocycle, which may be one ligand of a double-decker sandwich compound) having an excited-state of energy equal to or lower than that of X.sup.2, and X.sup.2 through X.sup.m+1 are chromophores (and again are preferably porphyrinic macrocycles).

Lindsey, Jonathan S. (Raleigh, NC)

2002-01-01

447

Networked Sensor Arrays  

SciTech Connect

A set of independent radiation sensors, coupled with real-time data telemetry, offers the opportunity to run correlation algorithms for the sensor array as well as to incorporate non-radiological data into the system. This may enhance the overall sensitivity of the sensors and provide an opportunity to project the location of a source within the array. In collaboration with Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories (SNL), we have conducted field experiments to test a prototype system. Combining the outputs of a set of distributed sensors permits the correlation that the independent sensor outputs. Combined with additional information such as traffic patterns and velocities, this can reduce random/false detections and enhance detection capability. The principle components of such a system include: (1) A set of radiation sensors. These may be of varying type and complexity, including gamma and/or neutron detectors, gross count and spectral-capable sensors, and low to high energy-resolution sensors. (2) A set of non-radiation sensors. These may include sensors such as vehicle presence and imaging sensors. (3) A communications architecture for near real-time telemetry. Depending upon existing infrastructure and bandwidth requirements, this may be a radio or hard-wire based system. (4) A central command console to pole the sensors, correlate their output, and display the data in a meaningful form to the system operator. Both sensitivity and selectivity are important considerations when evaluating the performance of a detection system. Depending on the application, the optimization of sensitivity as well as the rejection of ''nuisance'' radioactive sources may or may not be critical.

R. J. Tighe

2002-10-01

448

A Zeeman slower based on magnetic dipoles  

Microsoft Academic Search

A transverse Zeeman slower composed of an array of compact discrete neodymium magnets is considered. A simple and precise model of such a slower based on magnetic dipoles is developed. The theory of a general Zeeman slower is modified to include spatial nonuniformity of the slowing laser beam intensity due to its convergence and absorption by slowed atoms. The slower

Yuri B. Ovchinnikov

2007-01-01

449

Dynamics of magnetic nano-particle assembly  

Microsoft Academic Search

Ferromagnetically coupled nano-particle assembly is analyzed accounting for inter- and intra- particle electronic structures within the randomly jumping interacting moments model including quantum fluctuations due to the discrete levels and disorder. At the magnetic jump anomalies caused by quantization the magnetic state equation and phase diagram are found to indicate an existence of spinodal regions and critical points. Arrays of

V. N. Kondratyev

2010-01-01