Diffusion effects in eddy current nondestructive evaluation

Transducer response in nondestructive evaluation (NDE) requires fundamental knowledge of the field interaction with the material under test. Specifically, in eddy current NDE the transducer is an inductive coil or some combination of coils with an electromagnetic induction field surrounding the coil. The coil is used predominantly for surface or near-surface inspection of electrical conductors (metals). The change of impedance of the coil at its terminals is used as the criterion for defect detection. The impedance change due to a defect depends upon the relative disruption of the steady state field configuration in a given testing situation. A spatially smaller defect relative to the coil dimensions usually causes a smaller impedance change, therefore, it is more difficult to detect. The eddy currents induced in the metal by the exciting coil decay with distance into the metal due to energy loss in the form of Ohmic heating. Consequently, a defect easily detected at the surface with a given coil becomes undetectable at some distance beneath the metal surface. The distance at which a given defect becomes invisible is directly related to the rate of decay of the induced currents and their spatial distribution. The classical skin depth, δδ= √2/ωμσ, is the usual measure of the decay rate of currents in metals, but it is derived assuming a source field of infinite spatial extent and no inhomogeneity. In contrast, coils are often very small relative to the metal object under test and their useful fields are confined to a finite region surrounding the coil; therefore, assuming the classical skin depth in place of the actual skin depth may lead to erroneous conclusions about a coil\u27s ability to detect and size the defect. This thesis compares the actual decay of induced time-harmonic, steady-state current densities in conductors to the classical skin depth for an air-core coil over a conductor of both infinite (half-space) and finite thickness and for a pair of differential coils inside a conducting tube of infinite and finite thickness. In each case the finite element method (FEM) in its axisymmetric form is used to solve for the magnetic vector potential, A, from which all relevant quantities such as coil impedance and eddy current density are computed. For the coil over a half-space, the FEM is compared to an exact integral solution to confirm the validity of the FEM, while the FEM alone is used to compute quantities for coils in a tube. Actual current densities are computed and their rate of decay versus depth in the conductor, distance from exciting coil, and variations in coil and material parameters are investigated. The normalized coil impedance is computed versus coil proximity to the conductor (liftoff) and changing dimensionless parameter RS /δS (RS = coil mean radius). For the coil over a half-space, experimental measurements of coil impedance were performed and compared with the computed analytical solution and the FEM. In general, the experimental measurements show the range of validity of the analytical and FEM solutions. The experiments and computer simulations show the actual eddy current density distribution and decay is significantly different from the classical exponential decay in regions of operation where the coil is most useful for NDE but does approach the classical solution in the extreme region RS / δS\u3e\u3e 1. Caution should therefore be used when applying the classical skin depth approximation when RS /δS ~ 1. This study also shows the validity and usefulness of the axisymmetric FEM for modelling field/material interaction in spite of inherent simplifying assumptions. The analytical solution, while elegant and important in its own right, cannot model complex defects or material inhomogeneities in general, yet the FEM handles these situations with relative ease

Biophysical Characterization of Fluorotyrosine Probes Site-Specifically Incorporated into Enzymes:

Fluorinated tyrosines (F[subscript n]Y's, n = 2 and 3) have been site-specifically incorporated into E. coli class Ia ribonucleotide reductase (RNR) using the recently evolved M. jannaschii Y-tRNA synthetase/tRNA pair. Class Ia RNRs require four redox active Y's, a stable Y radical (Y·) in the β subunit (position 122 in E. coli), and three transiently oxidized Y's (356 in β and 731 and 730 in α) to initiate the radical-dependent nucleotide reduction process. F[subscript n]Y (3,5; 2,3; 2,3,5; and 2,3,6) incorporation in place of Y₁₂₂-β and the X-ray structures of each resulting β with a diferric cluster are reported and compared with wt-β2 crystallized under the same conditions. The essential diferric-F[subscript n]Y· cofactor is self-assembled from apo F[subscript n]Y-β2, Fe ²⁺, and O₂ to produce ∼1 Y·/β2 and ∼3 Fe ³⁺ /β2. The F[subscript n]Y· are stable and active in nucleotide reduction with activities that vary from 5% to 85% that of wt-β2. Each F[subscript n] Y·-β2 has been characterized by 9 and 130 GHz electron paramagnetic resonance and high-field electron nuclear double resonance spectroscopies. The hyperfine interactions associated with the 19 F nucleus provide unique signatures of each F[subscript n]Y· that are readily distinguishable from unlabeled Y·'s. The variability of the abiotic F[subscript n]Y pK a 's (6.4 to 7.8) and reduction potentials (-30 to +130 mV relative to Y at pH 7.5) provide probes of enzymatic reactions proposed to involve Y·'s in catalysis and to investigate the importance and identity of hopping Y·'s within redox active proteins proposed to protect them from uncoupled radical chemistry.National Institutes of Health (U.S.) (Grant GM29595)National Science Foundation (U.S.) (Grant 0645960

The factor structure of the Forms of Self-Criticising/Attacking & Self-Reassuring Scale in thirteen distinct populations

There is considerable evidence that self-criticism plays a major role in the vulnerability to and recovery from psychopathology. Methods to measure this process, and its change over time, are therefore important for research in psychopathology and well-being. This study examined the factor structure of a widely used measure, the Forms of Self-Criticising/Attacking & Self-Reassuring Scale in thirteen nonclinical samples (N = 7510) from twelve different countries: Australia (N = 319), Canada (N = 383), Switzerland (N = 230), Israel (N = 476), Italy (N = 389), Japan (N = 264), the Netherlands (N = 360), Portugal (N = 764), Slovakia (N = 1326), Taiwan (N = 417), the United Kingdom 1 (N = 1570), the United Kingdom 2 (N = 883), and USA (N = 331). This study used more advanced analyses than prior reports: a bifactor item-response theory model, a two-tier item-response theory model, and a non-parametric item-response theory (Mokken) scale analysis. Although the original three-factor solution for the FSCRS (distinguishing between Inadequate-Self, Hated-Self, and Reassured-Self) had an acceptable fit, two-tier models, with two general factors (Self-criticism and Self-reassurance) demonstrated the best fit across all samples. This study provides preliminary evidence suggesting that this two-factor structure can be used in a range of nonclinical contexts across countries and cultures. Inadequate-Self and Hated-Self might not by distinct factors in nonclinical samples. Future work may benefit from distinguishing between self-correction versus shame-based self-criticism.Peer reviewe

Biophysical Characterization of Fluorotyrosine Probes Site-Specifically Incorporated into Enzymes: E. coli Ribonucleotide Reductase As an Example.

Fluorinated tyrosines (FnY's, n = 2 and 3) have been site-specifically incorporated into E. coli class Ia ribonucleotide reductase (RNR) using the recently evolved M. jannaschii Y-tRNA synthetase/tRNA pair. Class Ia RNRs require four redox active Y's, a stable Y radical (Y·) in the β subunit (position 122 in E. coli), and three transiently oxidized Y's (356 in β and 731 and 730 in α) to initiate the radical-dependent nucleotide reduction process. FnY (3,5; 2,3; 2,3,5; and 2,3,6) incorporation in place of Y122-β and the X-ray structures of each resulting β with a diferric cluster are reported and compared with wt-β2 crystallized under the same conditions. The essential diferric-FnY· cofactor is self-assembled from apo FnY-β2, Fe(2+), and O2 to produce ∼1 Y·/β2 and ∼3 Fe(3+)/β2. The FnY· are stable and active in nucleotide reduction with activities that vary from 5% to 85% that of wt-β2. Each FnY·-β2 has been characterized by 9 and 130 GHz electron paramagnetic resonance and high-field electron nuclear double resonance spectroscopies. The hyperfine interactions associated with the (19)F nucleus provide unique signatures of each FnY· that are readily distinguishable from unlabeled Y·'s. The variability of the abiotic FnY pKa's (6.4 to 7.8) and reduction potentials (-30 to +130 mV relative to Y at pH 7.5) provide probes of enzymatic reactions proposed to involve Y·'s in catalysis and to investigate the importance and identity of hopping Y·'s within redox active proteins proposed to protect them from uncoupled radical chemistry

Biophysical Characterization of Fluorotyrosine Probes Site-Specifically Incorporated into Enzymes: E. coli Ribonucleotide Reductase As an Example

[Image: see text] Fluorinated tyrosines (F(n)Y’s, n = 2 and 3) have been site-specifically incorporated into E. coli class Ia ribonucleotide reductase (RNR) using the recently evolved M. jannaschii Y-tRNA synthetase/tRNA pair. Class Ia RNRs require four redox active Y’s, a stable Y radical (Y·) in the β subunit (position 122 in E. coli), and three transiently oxidized Y’s (356 in β and 731 and 730 in α) to initiate the radical-dependent nucleotide reduction process. F(n)Y (3,5; 2,3; 2,3,5; and 2,3,6) incorporation in place of Y(122)-β and the X-ray structures of each resulting β with a diferric cluster are reported and compared with wt-β2 crystallized under the same conditions. The essential diferric-F(n)Y· cofactor is self-assembled from apo F(n)Y-β2, Fe(2+), and O(2) to produce ∼1 Y·/β2 and ∼3 Fe(3+)/β2. The F(n)Y· are stable and active in nucleotide reduction with activities that vary from 5% to 85% that of wt-β2. Each F(n)Y·-β2 has been characterized by 9 and 130 GHz electron paramagnetic resonance and high-field electron nuclear double resonance spectroscopies. The hyperfine interactions associated with the (19)F nucleus provide unique signatures of each F(n)Y· that are readily distinguishable from unlabeled Y·’s. The variability of the abiotic F(n)Y pK(a)’s (6.4 to 7.8) and reduction potentials (−30 to +130 mV relative to Y at pH 7.5) provide probes of enzymatic reactions proposed to involve Y·’s in catalysis and to investigate the importance and identity of hopping Y·’s within redox active proteins proposed to protect them from uncoupled radical chemistry

Biophysical Characterization of Fluorotyrosine Probes Site-Specifically Incorporated into Enzymes: <i>E. coli</i> Ribonucleotide Reductase As an Example

Fluorinated tyrosines (F_<i>n</i>Y’s, <i>n</i> = 2 and 3) have been site-specifically incorporated into <i>E. coli</i> class Ia ribonucleotide reductase (RNR) using the recently evolved <i>M. jannaschii</i> Y-tRNA synthetase/tRNA pair. Class Ia RNRs require four redox active Y’s, a stable Y radical (Y·) in the β subunit (position 122 in <i>E. coli</i>), and three transiently oxidized Y’s (356 in β and 731 and 730 in α) to initiate the radical-dependent nucleotide reduction process. F_<i>n</i>Y (3,5; 2,3; 2,3,5; and 2,3,6) incorporation in place of Y₁₂₂-β and the X-ray structures of each resulting β with a diferric cluster are reported and compared with wt-β2 crystallized under the same conditions. The essential diferric-F_<i>n</i>Y· cofactor is self-assembled from apo F_<i>n</i>Y-β2, Fe²⁺, and O₂ to produce ∼1 Y·/β2 and ∼3 Fe³⁺/β2. The F_<i>n</i>Y· are stable and active in nucleotide reduction with activities that vary from 5% to 85% that of wt-β2. Each F_<i>n</i>Y·-β2 has been characterized by 9 and 130 GHz electron paramagnetic resonance and high-field electron nuclear double resonance spectroscopies. The hyperfine interactions associated with the ¹⁹F nucleus provide unique signatures of each F_<i>n</i>Y· that are readily distinguishable from unlabeled Y·’s. The variability of the abiotic F_<i>n</i>Y p<i>K</i>_a’s (6.4 to 7.8) and reduction potentials (−30 to +130 mV relative to Y at pH 7.5) provide probes of enzymatic reactions proposed to involve Y·’s in catalysis and to investigate the importance and identity of hopping Y·’s within redox active proteins proposed to protect them from uncoupled radical chemistry

Mind and Memory: Explorations of Creativity in the Arts and Sciences

Lectures by: Roald Hoffmann (chemist and poet); Paul West (novelist); Kenneth McClane (poet and essayist); Timothy DeVoogd (research psychologist); Diane Ackerman (poet and naturalist); Persis Drell (physicist); Vinay Ambegaokar (physicist); Steven Stucky (composer); Francis Moon (mechanical and aerospace engineer and sculptor); Byron Suber (dancer and choreographer); Victor Kord (artist); A.R. Ammons (poet) and James McConkey (writer); Thomas Eisner (chemical ecologist).English 301, "Mind and Memory: Explorations of Creativity in the Arts and Sciences," Spring 1996, M-W 2:55-4:10 p.m. (Lectures on Monday, 2:55-4:10 p.m.) Creativity is the attribute of the mind that enables us to make new combinations from often-familiar information, to perceive analogies and other linkages in seemingly unlike elements, to seek for syntheses. As is true of all learning, creativity is dependent upon memory—a memory that is genetic and social as well as personal and experiential. This course will explore the nature of creativity in science and art, indicating the differing requirements for discovery in the disparate disciplines while demonstrating the commonality that underlies the creative process and binds (say) physicist or mathematician to poet, composer, visual artist The opening sessions will be concerned with the crucial role of memory in learning, discovery, and spiritual insight for all humans, and will make reference to recent scientific research into the complex nature of the human brain, including its intimate connections with the rest of the body. Following this introduction, the course will rely on weekly guests from as many disciplines in the arts and sciences as possible, faculty members who will discuss (for interested undergraduates, whatever field they may be preparing to enter) the process underlying their research, or their work as creative or performing artists. The guests will be asked to speak of their goals, the problems they have faced, and what they have learned from their disappointments as well as their achievements. Members of the course are encouraged to enroll in another course or to be engaged in an activity (research or artistic production or performance) in which the insights gained in this class can be applied or tested. To further abet the active participation so necessary to learning, students will be asked to keep a journal, one that summarizes their understanding of, and response to, each presentation by a guest lecturer—a journal that will serve as a continuing record of their experiences as members of the course, and that will become the basic resource for an essay, to be submitted at the semester’s end, that will give their carefully considered assessment of the applicability of what they have learned in this course to that second course or activity, to their own mental processes, and to the future they propose for themselves.1_uasek62

Hypoalgesia and altered inflammatory responses in mice lacking kinin B1 receptors

Kinins are important mediators in cardiovascular homeostasis, inflammation, and nociception. Two kinin receptors have been described, B1 and B2. The B2 receptor is constitutively expressed, and its targeted disruption leads to salt-sensitive hypertension and altered nociception. The B1 receptor is a heptahelical receptor distinct from the B2 receptor in that it is highly inducible by inflammatory mediators such as bacterial lipopolysaccharide and interleukins. To clarify its physiological function, we have generated mice with a targeted deletion of the gene for the B1 receptor. B1 receptor-deficient animals are healthy, fertile, and normotensive. In these mice, bacterial lipopolysaccharide-induced hypotension is blunted, and there is a reduced accumulation of polymorphonuclear leukocytes in inflamed tissue. Moreover, under normal noninflamed conditions, they are analgesic in behavioral tests of chemical and thermal nociception. Using whole-cell patch-clamp recordings, we show that the B1 receptor was not necessary for regulating the noxious heat sensitivity of isolated nociceptors. However, by using an in vitro preparation, we could show that functional B1 receptors are present in the spinal cord, and their activation can facilitate a nociceptive reflex. Furthermore, in B1 receptor-deficient mice, we observed a reduction in the activity-dependent facilitation (wind-up) of a nociceptive spinal reflex. Thus, the kinin B1 receptor plays an essential physiological role in the initiation of inflammatory responses and the modulation of spinal cord plasticity that underlies the central component of pain. The B1 receptor therefore represents a useful pharmacological target especially for the treatment of inflammatory disorders and pain

Does abalone nacre form by heteroepitaxial nucleation or by growth through mineral bridges?

We present experimental support for a model of abalone nacre growth that is based on mineral bridges between successive aragonite tablets rather than on heteroepitaxial nucleation. Interlamellar sheets of organic polymers delineate the aragonite tablets but allow the tablets to grow mineral bridges through pores in the sheets. Atomic force microscope images of interlamellar organic sheets from flat pearls made by Haliotis rufescens (red abalone; marine gastropod mollusk) reveal a fibrous core and holes of 5-50 nm in diameter. Scanning ion conductance microscopy shows that these holes are actually pores through the interlamellar sheets. With the help of statistical analysis we can associate the pore-to-pore spacings in the interlamellar sheets with the observed offsets of successive nacre tablets. These results, supplemented by AFM, SEM, and TEM images, support and extend the model of biofabrication of gastropod nacre which is based on mineral bridges between the aragonite tablets.Godkänd; 1997; Bibliografisk uppgift: För övriga författare: Se artikeln; 20070410 (ysko)</p