Asymmetric MRI magnet design using a hybrid numerical method

This paper describes a hybrid numerical method for the design of asymmetric magnetic resonance imaging magnet systems. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to the desired current density. The field calculations are performed using a semi-analytical method. A new type of asymmetric magnet is proposed in this work. The asymmetric MRI magnet allows the diameter spherical imaging volume to be positioned close to one end of the magnet. The main advantages of making the magnet asymmetric include the potential to reduce the perception of claustrophobia for the patient, better access to the patient by attending physicians, and the potential for reduced peripheral nerve stimulation due to the gradient coil configuration. The results highlight that the method can be used to obtain an asymmetric MRI magnet structure and a very homogeneous magnetic field over the central imaging volume in clinical systems of approximately 1.2 m in length. Unshielded designs are the focus of this work. This method is flexible and may be applied to magnets of other geometries. (C) 1999 Academic Press.

A hybrid, inverse approach to the design of magnetic resonance imaging magnets

This paper describes a hybrid numerical method of an inverse approach to the design of compact magnetic resonance imaging magnets. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first, kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to the desired current density. The field calculations are performed using a semi-analytical method. The emphasis of this work is on the optimal design of short MRI magnets. Details of the hybrid numerical model are presented, and the model is used to investigate compact, symmetric MRI magnets as well as asymmetric magnets. The results highlight that the method can be used to obtain a compact MRI magnet structure and a very homogeneous magnetic field over the central imaging volume in clinical systems of approximately 1 m in length, significantly shorter than current designs. Viable asymmetric magnet designs, in which the edge of the homogeneous region is very close to one end of the magnet system are also presented. Unshielded designs are the focus of this work. This method is flexible and may be applied to magnets of other geometries. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)00303-5].

Does maintaining green leaf area in sorghum improve yield under drought? I. Leaf growth and senescence

Production of sorghum [Sorghum bicolor (L.) Moench], an important cereal crop in semiarid regions of the world, is often limited by drought. When water is limiting during the grain-filling period, hybrids possessing the stay-green trait maintain more photosynthetically active leaves than hybrids not possessing this trait. To improve yield under drought, knowledge of the extent of genetic variation in green leaf area retention is required. Field studies were undertaken in north-eastern Australia on a cracking and self-mulching gray clay to determine the effects of water regime and hybrid on the components of green leaf area at maturity (GLAM). Nine hybrids varying in stay-green were grown under a fully irrigated control, postflowering water deficit, and terminal (pre- and postflowering) water deficit. Water deficit reduced GLAM by 67% in the terminal drought treatment compared with the fully irrigated control. Under terminal water deficit, hybrids possessing the B35 and KS19 sources of stay-green retained more GLAM (1260 cm(2) plant(-1)) compared with intermediate (780 cm(2) plant(-1)) and senescent (670 cm(2) plant(-1)) hybrids. RQL12 hybrids (KS19 source of stay-green) displayed delayed onset and reduced rate of senescence; A35 hybrids displayed only delayed onset. Visual rating of green leaf retention was highly correlated with measured GLAM, although this procedure is constrained by an inability to distinguish among the functional mechanisms determining the phenotype. Linking functional rather than phenotypic differences to molecular markers may improve the efficiency of selecting for traits such as stay-green.

Hybrid modelling of coupled pore fluid-solid deformation problems

A hybrid formulation for coupled pore fluid-solid deformation problems is proposed. The scheme is a hybrid in the sense that we use a vertex centered finite volume formulation for the analysis of the pore fluid and a particle method for the solid in our model. The pore fluid formally occupies the same space as the solid particles. The size of the particles is not necessarily equal to the physical size of materials. A finite volume mesh for the pore fluid flow is generated by Delaunay triangulation. Each triangle possesses an initial porosity. Changes of the porosity are specified by the translations of the mass centers of particles. Net pore pressure gradients are applied to the particle centers and are considered in the particle momentum balance. The potential of our model is illustrated by means of a simulation of coupled fracture and fluid flow developed in porous rock under biaxial compression condition.

Hybrid auctions

In this paper we analyze a hybrid auction that combines a first-price and a Vickrey auction. We show that this auction may generate more expected revenue than a standard first-price auction. (C) 2002 Elsevier Science B.V. All rights reserved.

Synthesis and characterization of ternary hybrid material based on poly-o-methoxyaniline and poly(ethylene oxide) in mesostructured V(2)O(5)

New hybrid composites based on mesostructured V(2)O(5) containing intercalated poly(ethylene oxide), poly-o-methoxyaniline and poly(ethylene oxide)/poly-o-methoxyaniline were prepared. The results suggest that the polymers were intercalated into the layers of the mesostructured V(2)O(5). Electrochemical studies showed that the presence of both polymers in the mesostructured V(2)O(5) (ternary hybrid) leads to an increase in total charge and stability after several cycles compared with binary hybrid composites. This fact makes this material a potential component as cathode for lithium ion intercalation and further, a promising candidate for applications in batteries.

Calcium Carbonate Particle Growth Depending on Coupling among Adjacent Layers in Hybrid LB/LbL Films

There are practical and academic situations that justify the study of calcium carbonate crystallization and especially of systems that are associated with organic matrices and a confined medium. Despite the fact that many different matrices have been studied, the use of well-behaved, thin organic films may provide new knowledge about this system. In this work, we have studied the growth of calcium carbonate particles on well-defined organic matrices that were formed by layer-by-layer (LbL) polyelectrolyte films deposited on phospholipid Langmuir-Blodgett films (LB). We were able to change the surface electrical charge density of the LB films by changing the proportions of a negatively charged lipid, the sodium salt of dimyristoyl-sn-glycero-phosphatidyl acid (DMPA), and a zwitterionic lipid. dimyristoyl-sn-glycero-phosphatidylethanolamine (DMPE). This affects the subsequent polyelectrolyte LbL film deposition, which also changes the the nature of the bonding (electrostatic interaction or hydrogen bonding). This approach allowed for the formation of calcium carbonate particles of different final shapes, roughnesses, and sizes. The masses of deposited lipids, polyelectrolytes, and calcium cabonate were quantified by the quartz crystal microbalance technique. The structures of obtained particles were analyzed by scanning electron microscopy.

Synthesis, characterization and electrochemical behavior of the vanadium pentoxide/cetyl pyridinium chloride hybrid material

In situ and ex situ studies concerning the new hybrid material vanadium pentoxide xerogel in the presence of the cationic surfactant cetyl pyridinium chloride (V(2)O(5)/CPC) are presented. The in situ characterization studies revealed the presence of a lamellar structure for the V(2)O(5)/CPC hybrid material. The intercalation reaction was evidenced on the basis of the increase in the d-spacing as well as the displacement of the infrared bands toward lower energy levels. Electrochemical studies comprising the cyclic voltammetry and the electrochemical impedance spectroscopy techniques showed that the behavior of the hybrid material is considerably influenced by the electrolyte composition. The ion insertion/de-insertion into the V(2)O(5) xerogel structure accompanying the charge transfer process is influenced by the solid-state diffusion process modeled by using the finite-space Warburg element.

Synthesis and electrochemical properties of vanadyl phosphate di-hydrate/polyaniline derivatives hybrid films

Vanadyl phosphate and its hybrid compounds have proven to undergo electrochemical intercalation and de-intercalation of lithium ions, which enables its use as cathode material for Li ion rechargeable batteries. In this context, vanadyl phosphate di-hydrate/polyaniline derivatives hybrid films were synthesized via the exfoliation and reconstruction approach in order to evaluate their potential use as cathode in ion lithium batteries. X-ray diffraction patterns indicate that the lamellar structure of the inorganic matrix is maintained, consistent with the topotactic process. In the scanning electron micrographs, hybrid films exhibit rough surface consisting of warped and cracked crystallites, quite different from vanadyl phosphate di-hydrate square platelets crystallites. Electrochemical evaluation using cyclic voltammetry and charge-discharge galvanostatic techniques shows small differences between the charge and the discharge curves, indicating an irreversibility of the hybrid systems. (C) 2009 Elsevier B.V. All rights reserved.

Quantification of orientation of pore patterns in X-ray images of deformed clay

The use of X-ray imaging to assess variability in ceramic fabrication is common in archaeological studies aimed at examining ancient pottery technologies. In this paper, a method based on the measurement of individual pores orientation is presented. This method is successfully applied to ceramic specimens of known origin whose structure signified different deformation histories.

In familial hyperaldosteronism type I, hybrid gene-induced aldosterone production dominates that induced by wild-type genes

We compared the aldosterone-producing potency of the angiotensin II-sensitive wild-type aldosterone synthase genes and the ACTH-sensitive hybrid 11 beta-hydroxylase/aldosterone synthase gene by examining aldosterone, PRA, and cortisol day-curves (2-hourly levels over 24 h) in patients with familial hyperaldosteronism type I, before and during long-term (0.8-13.5 yr) glucocorticoid treatment. In 8 untreated patients, PRA levels were usually suppressed, and aldosterone correlated strongly with cortisol (r = 0.69-0.99). Fourteen studies were performed on 10 patients receiving glucocorticoid treatment that corrected hypertension, hypokalemia, and PRA suppression in all. ACTH was markedly and continuously suppressed in 6 studies, 3 of which demonstrated strong correlations between aldosterone and PRA (r = 0.77-0.92), ACTH was only partially suppressed in the remaining 8 studies; aldosterone correlated strongly: 1) with cortisol alone in 5 (r = 0.71-0.98); 2) with cortisol (r = 0.90) and PRA (r = 0.74) in one; 3) with PRA only in one (r = 0.80); and 4) with neither PRA nor cortisol in one. Unless ACTH is markedly and continuously suppressed, aldosterone is more responsive to ACTH than to renin/angiotensin II, despite the latter being unsuppressed. This is consistent with the hybrid gene being more powerfully expressed than the wild-type aldosterone synthase genes in familial hyperaldosteronism type I.

Occurrence of TRGV-BJ hybrid gene in SV40-transformed fibroblast cell lines

Illegitimate V(D)J-recombination in lymphoid malignancies involves rearrangements in immunoglobulin or T-cell receptor genes, and these rearrangements may play a role in oncogenic events. High frequencies of TRGV-BJ hybrid gene (rearrangement between the TRB and TRG loci at 7q35 and 7p14-15, respectively) have been detected in lymphocytes from patients with ataxia telangiectasia (AT), and also in patients with lymphoid malignancies. Although the TRGV-BJ gene has been described only in T-lymphocytes, we previously detected the presence of TRGV-BJ hybrid gene in the genomic DNA extracted from SV40-transformed AT5BIVA fibroblasts from an AT patient. Aiming to determine whether the AT phenotype or the SV40 transformation could be responsible for the production of the hybrid gene by illegitimate V(D)J-recombination, DNA samples were extracted from primary and SV40-transformed (normal and AT) cell lines, following Nested-PCR with TRGV- and TRBJ-specific primers. The hybrid gene was only detected in SV40-transformed fibroblasts (AT-5BIVA and MRC-5). Sequence alignment of the cloned PCR products using the BLAST program confirmed that the fragments corresponded to the TRGV-BJ hybrid gene. The present results indicate that the rearrangement can be produced in nonlymphoid cells, probably as a consequence of the genomic instability caused by the SV40-transformation, and independently of ATM gene mutation.

Micro-hardness evaluation of a micro-hybrid composite resin light cured with halogen light, light-emitting diode and argon ion laser

This in vitro study aimed to determine whether the micro-hardness of a composite resin is modified by the light units or by the thickness of the increment. Composite resin disks were divided into 15 groups (n = 5), according to the factors under study: composite resin thickness (0 mm, 1 mm, 2 mm , 3 mm and 4 mm) and light units. The light activation was performed with halogen light (HL) (40 s, 500 mW/cm(2)), argon ion laser (AL) (30 s, 600 mW/cm(2)) or light-emitting diode (LED) (30 s, 400 mW/cm(2)). Vickers micro-hardness tests were performed after 1 week and were carried out on the top surface (0 mm-control) and at different depths of the samples. Analysis of variance (ANOVA) and Tukey tests (P a parts per thousand currency signaEuro parts per thousand 0.05) revealed no statistically significant difference among the light units for the groups of 0 mm and 1 mm thickness. At 2 mm depth, the AL was not statistically different from the HL, but the latter showed higher micro-hardness values than the LED. In groups with 3 mm and 4 mm thickness, the HL also showed higher micro-hardness values than the groups activated by the AL and the LED. Only the HL presented satisfactory polymerization with 3 mm of thickness. With a 4 mm increment no light unit was able to promote satisfactory polymerization.

Effects of Nd:YAG Laser Irradiation on the Hybrid Layer of Different Adhesive Systems

Purpose: The aim of this in vitro study was to evaluate the microtensile bond strength (mu TBS) and hybrid layer morphology of different adhesive systems, either followed by treatment with Nd:YAG laser irradiation or not. Previous studies have shown the effects of Nd:YAG laser irradiation on the dentin surface at restoration margins, but there are few reports about the significance of the irradiation on the hybrid layer. Materials and Methods: The flattened coronal and root dentin samples of 24 bovine teeth were randomly divided into 8 groups, according to the adhesive system used - Scotchbond Multi Purpose (SBMP) or Clearfil SE Bond (CSEB) - and were either irradiated with Nd:YAG or not, with different parameters: 0.8 W/10 Hz, 0.8 W/20 Hz, 1.2 W/10 Hz, 1.2 W/20 Hz. The left sides of specimens were the control groups, and right sides were irradiated. A composite crown was built over bonded surfaces and stored in water (24 h at 37 degrees C). Specimens were sectioned vertically into slabs that were subjected to mu TBS testing and observed by SEM. Results: Control groups (27.81 +/- 1.38) showed statistically higher values than lased groups (21.37 +/- 0.99), and CSEB control group values (31.26 +/- 15.71) were statistically higher than those of SBMP (24.3 +/- 10.66). There were no significant differences between CSEB (20.34 +/- 10.01) and SBMP (22.43 +/- 9.82) lased groups. Among parameters tested, 0.8 W/10 Hz showed the highest value (25.54 +/- 11.74). Nd:YAG laser irradiation caused dentin to melt under the adhesive layer of both adhesive systems tested. Conclusion: With the parameters used in this study, Nd:YAG laser irradiation of the hybrid layer promoted morphological changes in dentin and negatively influenced the bond strength of both adhesive systems.

A study of the vacuum gamma-radiolysis of two aromatic polyimide fluoropolymers containing phenylphosphine oxide

The vacuum gamma -radiolysis of two fluorinated polyimides containing phenylphosphine oxide units, TOR-RC and TOR-RC ODPA, have been studied at 77 K and 300 K. The phenyl phosphine oxide units provide protection of the polymers towards oxidation by oxygen atoms and the bulky fluoromethyl groups reduce the colouration of the polymers by limiting donor-acceptor complex formation through the aromatic units. At 77 K the radicals formed were identified to be a mixture of neutral radicals (60%) and anion radicals. At 300 K only neutral radicals were found. The G-values for radical formation were found to be 0.50 and 0.42 at 77 K and 0.051 and 0.052 at 300 K for TOR-RC and TOR-RC ODPA, respectively. Little change was observed in the visible spectra of the polyimides following vacuum radiolysis at 300 K up to a dose of 3.3 MGy, and the polymers were shown to undergo net cross linking with a gel dose of 0.45 MGy.