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Shim coils are essential components to improve the accuracy of finger blood glucose detection in magnetic resonance image (MRI). Halbach magnet is popular in the field of portable MRI due to the magnetic concentration effect, but shim coils are needed to improve its poor magnetic field uniformity in the region of interest (ROI). Based on the harmonic analysis method, the high linearity of shim coils are considered as the objective function and the power consumption of coils are taken as the penalty function. The appropriate current density coefficient is determined by adjusting the penalty factor and minimizing the objective function. The stream function is applied to the current density, and the specific winding pattern on the cylindrical-surface is obtained by using MATLAB. In order to verify the accuracy of the method, the finite element software COMSOL was used to calculate the magnetic field distribution in the ROI The results illustrate that eight shim coils (x, y, z, (z2−(x2+y2)/2), xz, yz, xy, (x2−y2)) well meet the linearity requirements and the performance requirements of the human finger blood glucose MRI detection apparatus. Finally, the y and z directions of the first-order shim coils are fabricated with flexible PCB.

Designing shimming parts in the aircraft manufacturing process is a common task that needs to be solved. In fact, whenever two or more composite parts need to be coupled, a shim could be designed to absorb any assembly tolerance. This process can be effectively improved with an automated analysis of multimodal data (2D and 3D) directly acquired on the field during an assembly process. In this paper, a comparative analysis of SIFT and SURF feature detectors for the automatic registration and subsequent stitching of dense 3D point clouds in the aeronautic field are presented. Results on real data acquired on the field demonstrate the feasibility of the proposed approach and can be seen as a first step towards the automation of the shimming process.

In a magnetic resonance imaging system, the magnetic field homogeneity plays a decisive role on the image quality. As an effective technique, passive shimming (PS) uses ferromagnetic material (shim pieces) to eliminate the field impurity in the imaging area. In existing PS algorithms, most attempt to efficiently find continuous solutions using standard linear programming (LP). However, discrete solution has to be used in shimming practice. Direct rounding off of the continuous solution may lead to an unacceptable homogeneity loss. In theory, integer programming (IP) can be used to find discrete solution, however, it usually requires a huge amount of computing time, and the optimization procedure can hardly to converge. In this work, a mixed integer programming scheme was proposed, which combines the LP and IP algorithms to find the practical shimming solution. In the hybrid optimization algorithms, the first step is to obtain the initial continuous solution using an improved linear programming model, which not only minimize the peak-peak field error, but also seek the optimal target magnetic field. The second step is to re-optimize those shim pieces having a significant influence on the field homogeneity using an integer linear programming model. In the established optimization model (step 1), the LP algorithm guarantees a global minimum solution for the given problem, without extra computational parameters involved in the transition from first-step to second-step optimization. Compared with other integer programming strategies, the hybrid algorithm can greatly save the computing time and maintain excellent shimming results achieved by continuous solution. This has been demonstrated by a shimming study for the 1.5 T superconducting magnets.

Pencil beam scanning nozzle as a key component in superconducting proton therapy facility, which Iaterally extends proton beam with a pair of scanning magnets so that the irradiation field can be consistent with the tumor section. The paper first introduce the nozzle layout principle. Second, based on the deflection theory and geometrical relationship about proton beam within magnetic field to figure out the mapping relation between scanning of magnetic field intensity and irradiation field (deflection distance), and preliminarily predicts about the $\displaystyle \max $ field intensity of scanning magnets X (SMX) and Y (SMY). Then designs the outline of the scanning magnet, modifies the scanning magnetic field by using a trapezoidal shim. The poles of the SMX have a taper to accommodate the deflection envelope of the SMY. The calculation results indicate that the integral fields' uniformity of SMX and SMY is below $2\times 10^{-3},$ which can well guarantee the deflection precision of the proton beam.

This paper describes a method for filling individual joining gaps in the automated assembly of large aircraft primary structures in the factory of the future. High manufacturing tolerances lead to unique gaps between large Carbon Fibre Reinforced Polymer (CFRP) parts. These gaps must be filled with liquid or solid materials, which are called shim materials in the aircraft industry. Under a specific threshold gap size defined by aviation certifications of the utilized materials, liquid shim is applied. Above this value solid shim must be used and therefore individually manufactured. Until now in industry all steps are done manually by workers, within the last years research has shown that these processes can be automated with the use of smart manufacturing processes. This paper shows that an extension of processes like joining surface scanning, virtual assembly of scanned parts and 3D gap calculation between parts with processes like shim decision and shim application leads to a significant reduction of process time. The algorithm for deciding which type of shim must be applied and the process flows for liquid and solid shim application are described. The method is evaluated and tested in a one-to-one scale assembly cell for large CFRP primary structures.

The objective of this study is to model a neutronic beam at Pakistan Research Reactor-II in order to obtain neutrons of epithermal energy for the therapy of deep seated tumors like glioblastoma multiforme etc. which have no other best alternative cure so far. The modeling of PARR-II was performed using Monte Carlo based open source simulation program called OpenMC. The core modeling was validated with reference values taken from final safety analysis report of Pakistan Research Reactor-II. The calculated value of excess reactivity is 4.14mk with an error of about 3.5% and beryllium shim worth is 19.95mk with an error of 6% and these values were found in good agreement to the reference values. For neutronic beam modeling of beam tube using different materials were done and validated by comparing with beam parametric values found in literature. The selection of reflector, moderator and filters of definite thicknesses for beam tube is based on the required energy and magnitude of the neutron flux required at the exit of tube. The variation of the total and epithermal flux was studied and found that both fluxes decrease with the increase in thickness of both reflector and moderator. In this way an optimum value of moderator thickness 11cm selected according to values of flux (108 neutrons/cm2.s) and energy of neutrons required for therapy as provided by international atomic energy commission (IAEA).

High-quality magnetic resonance imaging and spectroscopic measurements require a highly homogeneous magnetic field. Different from global shimming, localized off-resonance can be corrected by using multi-coil shimming. Previously, integrated RF and shimming coils have been used to implement multi-coil shimming. Such coils share the same conductor for RF signal reception and shim field generation. Here we propose a new design of the integrated RF-shim coil at 3-tesla, where two independent shim current paths are allowed in each coil. This coil permits a higher degree of freedom in shim current distribution design. We use both phantom experiments and simulations to demonstrate the feasibility of this new design.

In this paper we propose a method to characterize waveguide shims, which are being used in almost all calibration kits for waveguide connectors and also used as impedance standard in Thru-Reflect-Line (TRL) calibration, for their length and aperture width and height. Also given are preliminary uncertainty analyses for the electrical characterization of the length, actually the phase shift through the shim, for two calibration methods for the Vector Network Analyzer (VNA).

An efficient design method of shim coils for an open bipanar superconducting magnetic resonance imaging (MRI) system is proposed, using an inverse boundary element method (IBEM). This design method first discretizes the shim coil space into some small flat triangular elements. By formulating the magnetization distribution by discrete current density, an objective function is constructed to evaluate the minimum error between axial magnetic field and desired magnetic field. In particular, the self-induction is added into the objective function which is used to adjust the deviation from the ideal target field. Finally, the well-known stream function method is commonly used to map the current density into wires. The algorithm details have been exemplified through biplanar shim coil design examples in this paper. This method can be used for coils on arbitrary surface shapes.

This paper proposes an efficient design method for designing MRI gradient coils on a cylindrical surface geometry, using an inverse boundary element method (IBEM). Based on the approximate current density over the whole coils space, the magnetic field distribution can be obtained in the discrete form. An objective function is found to evaluate the minimum error between actual magnetic field that coils generate and desired magnetic field. Finally, the current distribution is transformed to the winding pattern of gradients via the relationship between current and stream function. This method can be used for coils on arbitrary surface shapes. The design examples of x-gradient coil, z-gradient are shown to demonstrate such method is more efficient and versatile to apply to the design of coils. Such method can also be used to design shim coils.

A waveguide embedded 250 GHz HBV-varactor quasi-optical multiplier array is presented. The module utilizes a mechanically compact and simple shim system, combining the large array power handling capability with the convenience of waveguide interfaced circuits. At the same time this approach offers excellent power and frequency scalability. The current tripler prototype produces a non saturated output power of 8 mW at 248 GHz during initial measurements at medium pump power.

IEEE Joint International Symposium on the Applications of Ferroelectrics / International Workshop on Acoustic Transduction Materials and Devices / Workshop on Piezoresponse Force Microscopy (ISAF/IWATMD/PFM) -- MAY 12-16, 2014 -- State College, PA, WOS: 000363973100019, Some of the piezoelectric devices work more efficiently around the resonance frequencies. Piezoelectric structures have the highest displacement and charge generation closer to the resonance conditions. In this study, a wide band energy harvester with a spiral metal plate was designed. Metal shim with various length were integrated with piezo ceramic rings in a spiral form. Each metal shim has its own resonance frequencies. Neighboring metal shim has also its own resonance frequency. Intriguingly, resonance frequency of each shim is close to each other to trigger each other vibration. With such a structure it will be possible to scavenge energy in vibrating structure with a wider frequency range. Resonance frequency of piezoelectric structures is depend on mass of piezoelectric ceramics and clamped metal shim geometry. Parametric studies were performed to investigate the optimal condition of such a structure., IEEE

It has been shown that Electrical Properties d(EPs) of biological tissues can be derived from MR-based B1 measurement. A strong appeal for these `Electrical Property Tomography' (EPT) methods is to estimate real-time and subject-specific local specific absorption rate (SAR) induced by RF transmission. In order to investigate the feasibility of EPT-based local SAR estimation, following previously proposed EPT protocols, induced local SAR has been firstly estimated under one B1 shim setting for a heating sequence at 7T; whereas with the same acquired B1 information, induced local SAR under a different B1 shim setting has been further predicted. Both of the SAR results have been compared to measured temperature changes using MRI Thermometry based on the proton chemical shift.

A set of external coils is designed to eliminate the induced voltage in shim coils caused by the changing current in the gradient coils. By placing the external coil near the line which supplies the current for the gradient coil in a certain way and inserting it into the circuit of shim coils, a induced voltage which has the same wave form with the induced voltage in the shim coil is generated and consequently the coupling between the shim coil and the gradient coil is eliminated. Moreover, the induced voltages of various shim coils are simulated and the parameter of one external coil is determined by the result of the simulation.

This paper describes the scattering parameters magnitude measurement and uncertainty comparison using different vector network analyzer (VNA) calibration algorithms at millimeter frequencies with WR10 (75 to 110 GHz) waveguides. The state of the art two port calibration algorithms Thru-Reflect-Line (TRL) and Quick Short-Open-Load-Thru (QSOLT) are considered in this comparison. The dimensional measurements for Shim WR10 are also carried out.

Target Field (TF) method is very important for design of shim and gradient coils. Many works based on TF have been proposed. To restrict the current distribution on a rectangular plane with finite size, the current density is expanded by Fourier series and the unknown coefficients are estimated based on the standard Least Square (LS) with L2 norm regularization (LS-L2). Then the winding pattern of the coils can be obtained by the stream function method. In this paper, the proposed method was employed to design a transverse gradient coil for a magnetic resonance imaging (MRI) system. The size of the two planes is 500 mm × 150 mm, the distance of which is 50 mm, and the region of interest is a cylinder with radius of 4 mm and length of 8 mm. The simulation results demonstrate that the proposed method is practical in biplanar MRI system.

When designing scientific workflows, users often face the so-called shimming problem when connecting two related but incompatible components. The problem is addressed by inserting a special kind of adaptors, called shims, that perform appropriate data transformations to resolve data type inconsistencies. However, existing shimming techniques provide limited automation and burden users with having to define ontological mappings, generate data transformations, and even manually write shimming code. In addition, these approaches insert many visible shims that clutter workflow design and distract user's attention from functional components of the workflow. To address these issues, we 1) reduce the shimming problem to a runtime coercion problem in the theory of type systems, 2) propose a scientific workflow model and define the notion of well-typed workflows, 3) develop three algorithms to typecheck workflows by first translating them into equivalent lambda expressions, 4) design two functions that together insert "invisible shims", or runtime coercions into workflows, thereby solving the shimming problem for any well-typed workflow, 5) implement our automated shimming technique, including all the proposed algorithms, lambda calculus, type system, and translation functions in our VIEW system and present a case study to validate the proposed approach.

There is often a requirement to interface a new model to a legacy implementation by creating a shim between them to make the legacy appear as close to the new model as possible. This is a common exercise, usually fraught with frustrations, but here we find the exercise reveals fundamental aspects about nature of layers that were previously not well understood. Here we will be primarily concerned with creating a shim between RINA and IEEE 802.1q (VLANs). The Recursive InterNet Architecture (RINA) proposes a network architecture derived from the fundamentals of InterProcess Communication (IPC). This yields a recursively layered architecture of Distributed IPC Facilities (DIFs).

An innovative waveguide flange offers superior alignment based on a concentric mating mechanism consisting of a boss and jack interface. Above 100 GHz, this flange interface improves repeatability and precision of S-parameters measurements by eliminating the mechanical tolerance build-up associated with separate alignment pins. By simplifying the build-up of tolerance to only the boss and jack interface, the alignment improves match, precision, repeatability and residual calibration performance for mm-wave and sub-mm-wave S-parameter measurements. This flange is entirely compatible with the MIL-DTL-3922/67D standard. This paper presents connection repeatability for 220–325 GHz (WR-03 band). This flange is awaiting standardization in the P1785 working group of IEEE.

Two competing delay-short calibration standard designs for WM-380/WR-1.5 rectangular waveguide (500–750GHz) are evaluated. Quantitative estimates of the connector uncertainty are made and it is shown that an end-milled design out-performs the shim design. The effect of each standard's repeatability on calibration uncertainty is used to determine corrected measurement uncertainty for an eighth wavelength verification standard.

With the current increase of energy resources prices and environmental concerns intelligent load management systems are gaining more and more importance. This paper concerns a SCADA House Intelligent Management (SHIM) system that includes an optimization module using deterministic and genetic algorithm approaches. SHIM undertakes contextual load management based on the characterization of each situation. SHIM considers available generation resources, load demand, supplier/market electricity price, and consumers' constraints and preferences. The paper focus on the recently developed learning module which is based on artificial neural networks (ANN). The learning module allows the adjustment of users' profiles along SHIM lifetime. A case study considering a system with fourteen discrete and four variable loads managed by a SHIM system during five consecutive similar weekends is presented.

Waveguide flange design makes major impact to measurement reproducibility in the range of millimeter and sub-millimeter-wave frequencies, e.g. above 110 GHz. Original concept of flange design, so-call “Oshima” flange, was established in the early 2000s. Its flange alignment is ensured using ring with tight tolerance, however, it is not compatible to MIL-DTL-3922/67C (UG-387) flange. This paper describes a modification of “Oshima” flange in order to establishing a compatibility with UG-387 flange design, and evaluation result of its capability of connection repeatability in the WR-3 (220 GHz–330 GHz) frequency band. Furthermore, the quarter wave length shim, as a TRL “through” line standard, is specially modified to fit with a new design of “Oshima” flange, then, its capability of connection repeatability is also measured and discussed.

High-generation FPD (Flat Panel Display) glass substrates need to be carried by large clean transfer robot. Due to the space of the deposited glass box is limited, the distance between the two substrates is very small, this requires the sag amount of the robot fork must be controlled within a certain range. The traditional design is completed only in robot manufacturing stage by adding a shim to compensate for this distortion, but this method can only make the fork be compensated at a determined location, deformation at other locations may not be considered. A new solution to the dynamic compensation for the robot fork is proposed. By establishing the robot FEA model and mechanism accuracy model respectively, the synthetic dynamic error is then obtained. One can just change the mechanism accuracy through rational allocation of design tolerances of the robot links to minimize the dynamic error.

Echo planar imaging (EPI) is used widely for neurological fMRI studies. However, in regions of magnetic field inhomogeneity—particularly near the nasal sinuses—EPI suffers from signal dropout. Z-shim methods are one approach to recover this lost signal, where a z gradient is employed prior to the EPI readout echo train to counter phase accumulation in the signal dropout region. Typically, two separate images of the same region are acquired under different z-shim gradient strengths, and then combined into a composite image. Single-shot z-shim methods give improved temporal resolution, but with a cost of longer echo trains, which increases geometric distortion. Here, we combine parallel MR imaging (pMRI) with a single-shot z-shim method to achieve short echo train lengths. We also employ temporal encoding to counter Nyquist ghost effects, which improves the pMRI calibration. We demonstrate the method with phantom images, and evaluate its suitability for fMRI applications.

This paper describes a complete dimensional evaluation technique andelectrical characterization of waveguide shims as primary standards suitable for vector network analyzer (VNA) calibration at millimeter-wave and sub-millimeter wave frequencies. The NMIJ has established techniques for dimensional measurements of aperture size and for evaluating aperture corner radii and flange misalignment. Scattering parameters for the waveguide shim were calculated both from basic electromagnetic theory and by computer simulation. Surface roughness was also evaluated as it affects the transmission loss of a waveguide shim. In this paper we summarize the evaluation and calculation of waveguide shim standards, discuss the reproducibility in VNA measurements and consider extensions of the method to waveguide shims with smaller aperture sizes.

Existing waveguide flanges impose a major limitation on measurement precision above ≃100 GHz. A ring-centered waveguide flange was proposed in [1, 2] and its electrical performance characterized in the WR-5 band. This paper explores an improved ring-centered waveguide flange which is backward compatible with the original UG-387 flange and with all its known variants, and facilitates standard TRL VNA calibration using a properly aligned "through" waveguide shim. The modifications to the ring-centered waveguide flange are discussed and measurements in the WR-2.2 (330–500 GHz) band presented.

Using the application of bulk data transfer, we investigate the performance of existing TCP-to-SCTP Translation shim scheme under the scenario of shim rules-table is static (i.e., manual). We find that a potential problem named stale shim rules-table value caused by shim rules-table static configuration, which induces TCP-to-SCTP Translation does not startup in time. Based on this, we present a suggestion called Dynamic Rules-Table (DRT) for TCP-to-SCTP Translation to implement the real-time startup and to improve the throughput of SCTP association. A demonstrate using simulation is provided showing how application performance in terms of responsiveness and throughput using the shim and SCTP is equivalent to or better than performance when application operate using TCP-to-SCTP translation shim as originally designed.

Previously, we found that an asymmetric microfabricated surface can feed microparts along using simple planar symmetric vibrations. Microparts move forward because they adhere to the asymmetric surface asymmetrically. To feed along 0402-type capacitors (size, 0.4 × 0.2 × 0.2 mm; weight, 0.1 mg), we used a slight stainless shim tape microfabricated by a femtosecond laser processing tool, specifically the double-pulsed femtosecond laser irradiation technique, to generate an asymmetric profile surface. We then evaluated the characteristics of the microfabricated surface, including the effects of decreased adhesion, the differences in profiles of the two inclined surfaces, the coefficients of friction in both the forward and backward directions, and the friction angle of the 0402-type capacitors in both directions. Using the results of feeding of these capacitors, we assessed the relationship between driving frequency and feeding velocity. We also assessed two other microfabricated surfaces generated by the single beam femtosecond laser diagonal irradiation technique. We evaluated the asymmetry of these microfabricated surfaces based on measurements using an atomic force microscope (AFM) system. We then performed feeding experiments of 0402-type capacitors with the same driving conditions using newly and previously generated surfaces. Experimental results were compared to assess the surface most appropriate for feeding 0402-type capacitors.

Nuclear magnetic resonance (NMR) plays an important role in the fields of physics, chemistry, biology and medicine. The homogeneity of the magnetic field is very significant for NMR experiment. Based on the principle of field mapping, gradient shimming is an efficient method to achieve a homogeneous magnetic field. Reflecting accurately the spatial magnetic field distribution produced by every shim coil, gradient shimming can optimize the homogeneity efficiently and quickly. In this paper, one-dimensional gradient shimming method was studied, and the corresponding computational process was improved. Experiments were done on the NMR spectrometer, and the results show that the improved algorithm operates more efficiently and still works in a great inhomogeneous magnetic field.

This work is an initial evaluation of the performance of a microPET Focus-Fl20 system modified to fit in the split in a 1 Tesla MR imaging system to create a rodent scanner capable of simultaneous PET and MR acquisition. The MR imager is a novel design with a split in the magnet former, cryostat and gradient coils and with sufficient self-shielding to radically reduce the stray field at the cryostat edge. This permits the Focus-F120 detector geometry to be maintained with the addition of longer fibre bundles coupling the crystals to the PMT’s, which consequently are situated in a low magnetic field region outside the cryostat. Baseline PET performance was measured with gradient and shim coils in place but without RF coils in the PET FOV. Misalignment of the crystal blocks has decreased the PET spatial resolution, from 1.7 mm to 2.2 mm at 5 mm radial distance, compared to the Focus-F120. The peak absolute sensitivity is reduced to 5.3% compared to 6.8% for a 250-750 keV energy window and 6 ns coincidence window. The noise equivalent count rate (NECR-1R) peaks at about 215 kcps at 112 MBq for a NEMA rat phantom compared to 300 kcps for the Focus-F120 at 140 MBq. Magnetic field homogeneity was assessed as +/− 6 hertz over a 10 cm long and 8 cm diameter cylindrical space and a pulsed gradient strength of 200 mT/m, with a rise time of less than 100 microseconds, demonstrated on all three axes. Separate PET and MR imaging capability has been demonstrated as well as continuous, simultaneous acquisition with no detectable interference between the two imaging systems.

The article relates to a method for shimming a main magnetic field in a magnetic resonance device. The method comprises the steps of generating at least one spatially selective radio frequency pulse (RF) for exciting nuclear spin magnetization that is sensitive to the homogeneity of the main magnetic field, and applying electric currents (DX, DY, DZ) to a shim coil arrangement of the magnetic resonance device such that the main magnetic field is adjusted in accordance to the properties of the acquired magnetic resonance signal (ES). In order to provide a shimming method, in which it is avoided that the shape or size of the selected volume is influenced by the adjustment of the magnetic field distribution generated by the shim coils, the article proposes that the electric currents (DX, DY, DZ) applied to the shim coil arrangement are at least partially switched off during the generation of the spatially selective radio frequency pulse (RF) and switched on during the acquisition of the magnetic resonance signal (ES).

The dynamic multipoles of the BESSY APPLE undulator UE112 have successfully been shimmed for the elliptical mode using Fe-shims. In the inclined mode the multipoles have to be minimized actively. This can be accomplished either with an array of flat current wires or with rotating permanent magnets. Both methods are compared with respect to accuracy, flexibility and complexity. For both strategies the dynamic properties of the device have been studied in tracking simulations which are based on a generating function formalism using an analytic description of the undulator and the shim field integrals.

The uniform field region (magnetic field roll-off) of the distributions of horizontal and vertical fields in the elliptically polarized undulator (EPU) of the APPLE-II structure is too short. Hence magnet block arrangements such as (1) the magnet block magnetized with a tilt angle, (2) a step shim of thickness 0.5 mm placed at the magnet edge, and (3) shortening the transverse dimension of the magnet block have been investigated to enlarge the uniform field region. The advantages and disadvantages of these block arrangements are discussed. The pure and hybrid structure of the EPU with an optimized end-pole design and the merit of flux as a function of varied phase have also been studied.

A new passive shim design method is presented which is based on a magnetization mapping approach. Well defined regions with similar magnetization values define the optimal number of passive shims, their shape and position. The new design method is applied in a shimming process without prior-axial shim localization; this reduces the possibility of introducing new errors. The new shim design methodology reduces the number of iterations and the quantity of material required to shim a magnet. Only a few iterations (1-5) are required to shim a whole body horizontal bore magnet with a manufacturing error tolerance larger than 0.1 mm and smaller than 0.5 mm. One numerical example is presented.

Wiggler field errors may significantly degrade free-electron-laser gain and extraction. A new technique has been developed by Spectra Technology, Inc., for significantly reducing field errors. Shims placed on magnets have been to shunt flux away from high-field regions, thereby controlling trajectory and phase-shift errors induced by magnetic-field deviations. A general-purpose, constrained minimization algorithm has been used to determine the optimum shim thicknesses. We have shimmed a 50 cm test fixture. The rms kick errors were reduced from 1.3 to 0.1%. Initial shimming tests on the Near-Infrared Scalable Undulator System 10 m wiggler have demonstrated 0.09% deviations between predicted and measured shim fields. Rms errors were 0.4 to 0.5% due to shim placement limitations imposed by modularity constraints. Experiments indicate that improved shimming is possible with shims placed on poles. Transverse magnetic field shimming is discussed, as well as several methods for improving higher-order moment field errors. A general field-error measure based on the spatial frequency of trajectory and taper errors (induced by phase-shift deviations) is proposed.

Magnetic source imaging is the reconstruction of the current distribution inside an inaccessible volume from magnetic field measurements made outside the volume. If the unknown current distribution is expressed as a linear combination of elementary current distributions in fixed positions, then the magnetic field measurements are linear in the unknown source amplitudes and both the least square and minimum mean square reconstructions are linear problems. This offers several advantages: The problem is well understood theoretically and there is only a single, global minimum. Efficient and reliable software for numerical linear algebra is readily available. If the sources are localized and statistically uncorrelated, then a map of expected power dissipation is equivalent to the source covariance matrix. Prior geological or physiological knowledge can be used to determine such an expected power map and thus the source covariance matrix. The optimal constrained linear inverse method (OCLIM) derived in this paper uses this prior knowledge to obtain a minimum mean square error estimate of the current distribution. OCLIM can be efficiently computed using the Cholesky decomposition, taking about a second on a workstation-class computer for a problem with 64 sources and 144 detectors. Any source and detector configuration is allowed as long asmore » their positions are fixed a priori. Correlations among source and noise amplitudes are permitted. OCLIM reduces to the optimally weighted pseudoinverse method of Shim and Cho if the source amplitudes are independent and identically distributed and to the minimum-norm least squares estimate in the limit of no measurement noise or no prior knowledge of the source amplitudes. In the general case, OCLIM has better mean square error than either previous method. OCLIM appears well suited to magnetic imaging, since it exploits prior information, provides the minimum reconstruction error, and is inexpensive to compute.« less

As more high-power wide-bandgap devices are being utilized, the thermal management issues associated with these devices need to be resolved. High power devices dissipate excessive heat that must be cooled, but traditional cooling methods are insufficient to provide such a cooling means. Although using SiC allows higher operating temperatures, an upper temperature threshold still exists for high frequency devices. The package under study consists of a SiC high frequency power device whose junction temperature must not exceed a specified temperature, such as 150/spl deg/C, 175/spl deg/C, or 200/spl deg/C, set by the particular device technology. The technical goal is to develop an innovative cooling concept providing less than 100/spl deg/C temperature rise relative to the base plate. In the baseline configuration, a high power SiC device is mounted onto a shim or thermal spacer that is then mounted onto a cold plate. This paper evaluates a SiC microcapillary pumped loop thermal management system that is incorporated into the shim of the device, taking advantage of phase-change to increase the thermal conductivity of the system. The results of the modeling, fabrication, and testing of the thermal management system are discussed.

A traditional scanning acoustic microscope (SAM) has been modified to operate in the near-field mode. A pinhole in a thin shim of brass defines the resolution of the instrument, which can be as small as 0.1 lambda . In an edge scan experiment, a 125- mu m-thick brass shim with a pinhole size of 125 mu m, a SAM operating at 3 MHz, and a transducer with an F-number of 0.7 are used. The improvement in resolution corresponds to using a transducer with an F-number of 0.2. The results of measurements of the line response of the system, using steel pinholes of several thicknesses and diameters at different linewidths and operating frequencies and showing the details of the design of the instrument, are presented. >

The linearly tapered slot antenna (LTSA) is an endfire radiator formed by a tapered slotline that is usually supported on a thin, low- epsilon /sub r/ substrate. K.S. Yngvesson et al. (1985) have studied the radiation characteristics of LTSAs that are optimized for use in the focal plane of imaging/multiple-beam systems having f/D in the range of 1 to 2. In the present work, the author presents the results of an experimental investigation of the radiation properties of antennas with wider beamwidths. Some data on narrow-beamwidth antennas are included. Particular emphasis is placed on polarization in the intercardinal planes, where high levels of cross-polarization are observed. The study was conducted by fabricating four antennas on 30-mil Duroid ( epsilon /sub r/=2.2). In addition, two antennas were fabricated from 3-mil shim stock and supported by a styrofoam bridge to create antennas with air dielectric. It is concluded that the LTSA has many advantageous characteristics, and it is compatible with printed-circuit feed networks. However, designers should be aware of its polarization properties, which could adversely affect system performance. >

The superconducting coils of LHC prototype dipole magnets wound from a Nb-Ti cable of the Rutherford type are assembled in an aluminium clamping structure, the so called collars. The coils have to be prestressed in order to avoid movements of the superconductor during operation, which may cause quenches. The exact value of the prestress and the uniformity of the prestress over the length are adjusted by the thickness of inserted shims. The basis for prestressing the dipole coils is the precise measurement of the size and the Young's modulus of the winding. Based on the measurements shims are calculated ensuring the specified prestress of the coil. During shim calculation several corrections of the shim thickness have to be taken into account e.g. corrections due to the deformation of collars. The measurement of Young's modulus and the shim calculation are presented.

A novel pulse septum magnet for the injection system of NSRL storage ring which is a dedicated synchrotron radiation facility was described in this paper. The main parameters and measured results of the septum including its magnetic field distribution and its vacuum characteristic were given also. After making a shim the stray field near current strip to gap magnetic field was reduced to 0.1%, and the pressure of the vacuum chamber, in which the septum magnet was installed, is less than 5/spl times/10/sup -10/ mbar after baking. Now the septum magnet is playing an important part in getting a high injection efficiency and high accumulating current in the NSRL storage ring during the machine running.

The Recycler Ring Gradient Magnets were designed with end shims which correct the field shape (harmonic components up to 10-pole). A standard correction was employed at one end to correct the average properties. A variable correction was used at the other end to correct individual magnet variations during the fabrication process. An initial Recycler operation revealed that the quadrupole fields did not produce the desired tune. In part, this was due to the sextupole of the end-shim interacting with the curved orbit through the straight magnet. The standard end-shim was replaced on all regular cell gradient magnets. Details of these end corrections and the resulting successful modification of the lattice are described.