Prototypical Transition Research Articles

Validation of a 1-mm Transit Time Flow Probe and the Potential for Use in Microsurgery

The objective of this study was to validate a prototype transit time ultrasound flow probe (Medi-Stim Butterfly Flowmeter BF 2004) of only 1 mm and to evaluate its potential for use in microsurgery. Knowledge of the ability of this kind of system to measure flow in small vessels and at small flow rates did not previously exist. The experimental design was an in vitro study using the median artery of 15-kg pigs. The vessel was perfused by the pigs' own heparinated blood, at a known flow rate, using a Gemini infusion pump. The infusion rate was increased stepwise, starting at 1 ml/min until 16 ml/min. Transit time flow was measured continuously. The results showed very accurate flow measurements at all flow rates when compared to the known infusion rate of the Gemini pump. However, at flow rates below 4 ml/min, variation became a problem.

Numerical Analysis of Coupling Between Dielectric Image Guide and Microstrip

An integral equation method of moments formulation of the coupling between dielectric image guide and microstrip is studied. The formulation implements a surface equivalence using rooftop and traveling wave basis functions. The specific structure under consideration is the aperture coupled microstrip image guide transition. Analysis of the structure and typical results are compared to measurements on a simple prototype transition.

Performance of diffusion Monte Carlo for the first dissociation energies of transition metal carbonyls

Fixed node diffusion Monte Carlo (FNDMC) calculations are carried out for the first ligand dissociation energies of the prototype transition metal carbonyls Cr(CO)6, Fe(CO)5, Ni(CO)4, and Fe(CO)4N2. Since Hartree-Fock theory performs particularly badly for these type of compounds they are difficult to treat with conventional ab initio methods. We find that a Kohn-Sham determinant from a standard density functional provides a balanced description of the fermionic nodal hyper surfaces of all compounds involved in the dissociation reaction. With one exception, the experimental dissociation enthalpies are reproduced by FNDMC within the statistical accuracy of the method.

Competition between C-C and C-H insertion in prototype transition metal-hydrocarbon reactions.

The competition between C-C and C-H insertion in model transition-metal reactions with cyclopropane and propene (C3H6) was studied as a function of total energy. Insertion of neutral transition metal atoms M (= Y, Zr, Nb, and Mo*) into the C-C bonds of cyclopropane led to formation of MCH2 + C2H4, whereas C-H insertion produced MC3H4 + H2. The measured product branching ratios verify the relative potential energy barrier heights for C-C and C-H insertion predicted by ab initio calculations.

Ingenuity and initiative in Australian radio astronomy: the Dover Heights 'hole-in-the ground' antenna

During the 1950s staff from the CSIRO's Division of Radiophysics based at the Dover Heights field station employed ingenuity and initiative in response to a lack of funding and support for a new radio telescope. In order to obtain the requisite aperture for the resolution sought they spent their own time excavating a 21.9-m parabolic depression in the sand at the field station, and when the viability of this prototype transit instrument was established its diameter was increased to 24.4 m, making this the largest radio telescope in Australia at the time. Operating at 400 MHz, this instrument was employed to map the galactic centre region and in a search for new discrete sources. It also was used to investigate polarization in the plane of the Galaxy, and in an unsuccessful search for the newly-proposed deuterium line. Today the Dover Heights hole-in-the-ground antenna lies buried beneath Rodney Reserve, and there is little at this public playing field to remind visitors of the important contributions made by this radio telescope, and others at this site, during the formative years of Australian radio astronomy.

CPW to waveguide transition with tapered slotline probe

A new CPW to waveguide transition is developed based on the concept of tapered slot antenna and E-plane probe coupling. The transition consists of a tapered slotline probe and a slotline to CPW matching section. The current design has the advantages of broad bandwidth, compact size, low fabrication cost, and high reliability. The characteristics of a prototype transition are investigated by numerical simulation on Duroid substrate and WR-90 waveguide. The back-to-back combination is measured to verify the agreement with the simulated results and realization of this design.

Change from sixfold to fivefold coordination of silicate polyhedra: Insights from first-principles calculations ofCaSi2O5

Recent x-ray-diffraction observations found a triclinic phase of ${\mathrm{CaSi}}_{2}{\mathrm{O}}_{5}$ stable under ambient conditions, related to a monoclinic phase with the titanite structure. It differs from the titanite structure by the elongation and loss of a Si-O bond within a ${\mathrm{SiO}}_{6}$ octahedron, thus having ${\mathrm{SiO}}_{5}$ polyhedra. We have studied both these phases using density-functional theory in the generalized gradients approximation, to investigate the relative stability and chemical changes between the phases. Mulliken analysis is used to calculate covalent bond populations and atomic charges. A series of intermediate structures are studied to approximate a prototype transition pathway.

Multiple-Epoch Monitoring of the Lobe-dominated Superluminal Quasar 3C 245

We report confirmation of superluminal motion in the nucleus of the lobe-dominated quasar 3C 245, based on three new 10.7 GHz epochs and a consistent reanalysis of older 10.7 GHz data; the total time spanned is a decade. In the inner 2 mas, we have tracked two components that have consistent motions in a position angle of 2900 3000, well fitted with constant apparent transverse velocities of flapp = (2.4 t 0.1) h-^{1 }and = (3.1 + 1.7) h ^{1 }(H_{0 }= 100 h km S-^{1 }Mpc <SUP>1</SUP>, q_{0 }= 0.5). We also present a new 8.4 GHz VLBI observation with superior short-baseline (u, v)-coverage that has yielded the best highresolution image to date of a faint, steep-spectrum extension of the one-sided jet, reaching out to &gt;40 mas from the VLBI core and having a brightness peak at 25 mas. We relate our findings to other properties of 3C 245 and interpret them in the context of relativistic beaming models and unification scenarios. We conclude that 3C 245 is in many ways a prototypical transition object between core- and lobe-dominated quasars.

Membrane binding properties of the factor IX gamma-carboxyglutamic acid-rich domain prepared by chemical synthesis.

The fully gamma-carboxylated peptides based upon the complete and truncated Gla/aromatic amino acid stack domains of human Factor IX were prepared by solid phase peptide synthesis using Fmoc (N-(9-fluorenyl)methoxycarbonyl) chemistry. A 47-residue peptide Factor IX-(1-47) and a 42-residue peptide Factor IX-(1-42), both containing 12 residues of L-gamma-carboxyglutamic acid, were purified by high performance liquid chromatography and oxidized to form the disulfide bond. Quantitative gamma-carboxyglutamic acid analysis of Factor IX-(1-47) and Factor IX-(1-42) indicated the presence of 12.1 and 11.2 gamma-carboxyglutamic acid residues/mol of peptide, respectively; no glutamic acid was detected. As monitored by fluorescence quenching, calcium ions induced the prototypical conformational transition in Factor IX-(1-47), but not in Factor IX-(1-42), that is observed with Factor IX. Half-maximal quenching of the intrinsic fluorescence of Factor IX-(1-47) was observed at Ca(II) concentrations of about 50 microM. Factor IX-(1-47) bound to the conformation-specific antibodies, anti-Factor IX:Mg(II) and anti-Factor IX:Ca(II)-specific in the presence of metal ions. Factor IX-(1-47) bound to phospholipid membranes, as monitored by energy transfer from intrinsic fluorophores to dansyl (5-dimethylaminonaphthalene-1-sulfonyl)-phosphatidylethanolamine incorporated into a lipid bilayer composed of phosphatidylserine:phosphatidylcholine. In contrast, Factor IX-(1-42) bound poorly to these same membranes. Factor IX-(1-47) did not inhibit Factor XIa activation of Factor IX but did inhibit the activation of Factor X by Factor IXa bound to Factor VIII in the presence of calcium ions and phospholipid. These results show that phospholipid membrane binding is a property of the Gla/aromatic amino acid stack domain and that the Factor IX-(1-47) peptide, prepared by chemical synthesis, preserves the membrane binding properties and the metal-induced conformational transitions observed in native Factor IX. These results indicate that Factor IX-(1-47) but not Factor IX-(1-42) is a suitable model for structural studies of Factor IX-membrane interaction.

Evidences of transitory metastable phases in refractory metals solidified from highly undercooled liquids in a drop tube.

Brightness traces of the solidification of highly undercooled Ta and Re droplets processed in an ultrahigh vacuum drop tube give evidences of two successive phase transformations. First-principles calculations of the structural stability of these metals are developed in order to appreciate the possibilities of obtaining alternative phases. Some prototype transition metal crystal structures were examined and the fcc phase for Re and the A 15 phase for Ta are possible candidates for the observed metastable phases

Extraction of linguistically relevant referential properties through language learning

In order to identify the role of language in extracting a particular referential property which was involved in a reference situation but which was not expressed as relevant, in the linguistic structure of the subjects' native language, three experiments were performed. Forty subjects were exposed to the same referential situations but to different linguistic structures, each encoding a particular referential property that was, relevant. Miniature artificial languages were used. The referential properties examined were prototypical transitivity as defined by Slobin (1980) and plurality. The results showed that prototypical transitivity was extracted more readily than plurality, even though the subjects were more familiar with the latter property. The discussion emphasized how language serves to promote, the extraction and encoding of linguistically relevant properties that underlie referential situations.

Richness of Input Data as a Condition of the Acquisition of Prototypical Transitivity in Language

An attempt was made to explore the nature of input data in the acquisition of a morphological rule having an intricate semantic property, prototypical transitivity, in which a person acts on objects with a resulting effect. The rule was acquired only by subjects given referential contexts, and rule acquisition did not occur for subjects given no referential contexts. The results were interpreted as suggesting that for the rule in question to be induced, the input data should contain a sufficient number and adequate type of exemplars that reveal the relation between linguistic structure and semantic or referential context. Language acquisition, at least in its beginning, can be construed as the process by which children or adult learners become aware of the invariant relations between referential meanings and linguistic structures. These relations are not always transparent for learners, since a great deal of irrelevant information may be involved both in the linguistic and referential aspects of experiencing contexts. There may be false starts, grammatical errors, and other noise information in the linguistic input, while referential situations include a great many irrelevant situations that are not immediately related to the particular linguistic descriptions. Learners exposed to such opaque input situations have to differentiate what is relevant from what is irrelevant for a given relation. Studies on miniature artificial languages (MALs) as a laboratory analog to the acquisition of linguistic structures have shown the mapping relation to be acquired under two conditions. The first type of study presents, along with regular forms, some irregular forms that are inconsistent with the underlying rule structure and examines the quantitative aspect of the mapping relation (Mori, 1980b, 1981;

Linear induction motor-equivalent-circuit model

An equivalent-circuit model of a linear induction motor is developed, using the rotary-motor model as a basis. The rotary-motor model is modified to account for the so-called `end effect´ and is used to predict output thrust, vertical forces and couples. These predictions are checked against test results of a practical motor used on a prototype transit vehicle.

The effects of chemical modification on the refolding transition of alpha-chymotrypsin.

The role of several active site residues of alpha-chymotrypsin in the prototypical refolding transition between active and inactive forms of this enzyme is examined using chemical modification. Oxidation of Met-192 to the sulfoxide results in a derivative which remains entirely in an active state from pH 6 to 9. The derivative becomes inactive only at high pH with pKa = 10.3, delta H0 = 9.5 kcal and delta S0 = -15 eu., indicating the sulfoxide group supplies about 2.1 kcal of active state stabilization relative to the unoxidized methionine side chain. The refolding transition of N-methyl-His-57-alpha-chymotrypsin, in which a nitrogen of the "charge relay" histidine is methylated, displays one ionization process with an apparent pKa of 9.45. The absence of an additional ionization process with a pKa near 7 provides evidence that one of the ionizations in the six state mechanism which describes this transition in alpha-chymotrypsin is linked to the charge relay system. We also demonstrate, using alpha-chymotrypsin, Met-192-sulfoxide-alpha-chymotrypsin and N-methyl-His-57-alpha-chymotrypsin, that the 230 nm circular dichroism band is a quantitative probe of the active-inactive equilibrium, although the chromophore or chromophores responsible for this and another very large negative band at 202 nm have not been identified. Circular dichroism was used to observe the active-inactive equilibrium in methan sulfonyl-alpha-chymotrypsin and phenylmethane sulfonyl-alpha-chymotrypsin. The enhanced stability of the active state of these derivatives relative to alpha-chymotrypsin can be rationalized in terms of steric effects in the substrate side chain binding site.