bluuebunny/crossref_metadata_2025 huggingface dataset:
G-actin conformational change and polymerization induced by paraquat
Authors: DalleDonne Isabella , Milzani Aldo , Colombo Roberto
Published: April 2011

Paraquat (1,1´-dimethyl-4,4´-bipyridilium dichloride) is a broad-spectrum herbicide that is highly toxic to animals (including man), the major lesion being in the lung. In mammalian cells, paraquat causes deep alterations in the organization of the cytoskeleton, marked decreases in cytoskeletal protein synthesis, and alterations in cytoskeletal protein composition; therefore, the involvement of the cytoskeleton in cell injury by paraquat was suggested. We previously demonstrated that monomeric actin binds paraquat; moreover, prolonged actin exposure to paraquat, in depolymerizing medium, induces the formation of actin aggregates, which are built up by F-actin. In this work we have shown that the addition of paraquat to monomeric actin results in a strong quenching of Trp-79 and Trp-86 fluorescence. Trypsin digestion experiments demonstrated that the sequence 61-69 on actin subdomain 2 undergoes paraquat-dependent conformational changes. These paraquat-induced structural changes render actin unable to completely inhibit DNase I. By using intermolecular cross-linking to characterize oligomeric species formed during paraquat-induced actin assembly, we found that the herbicide causes the formation of actin oligomers characterized by subunit-subunit contacts like those occurring in oligomers induced by polymerizing salts (i.e., between subdomain 1 on one actin subunit and subdomain 4 on the adjacent subunit). Furthermore, the oligomerization of G-actin induced by paraquat is paralleled by ATP hydrolysis.Key words: actin, paraquat, subdomain 2, DNase I, ATP hydrolysis.
Structure-function relationships of antimicrobial peptides
Authors: Hwang Peter M , Vogel Hans J
Published: April 2011

Antimicrobial peptides are ubiquitously produced throughout nature. Many of these relatively short peptides (6-50 residues) are lethal towards bacteria and fungi, yet they display minimal toxicity towards mammalian cells. All of the peptides are highly cationic and hydrophobic. It is widely believed that they act through nonspecific binding to biological membranes, even though the exact nature of these interactions is presently unclear. High-resolution nuclear magnetic resonance (NMR) has contributed greatly to knowledge in this field, providing insight about peptide structure in aqueous solution, in organic cosolvents, and in micellar systems. Solid-state NMR can provide additional information about peptide-membrane binding. Here we review our current knowledge about the structure of antimicrobial peptides. We also discuss studies pertaining to the mechanism of action. Despite the different three-dimensional structural motifs of the various classes, they all have similar amphiphilic surfaces that are well-suited for membrane binding. Many antimicrobial peptides bind in a membrane-parallel orientation, interacting only with one face of the bilayer. This may be sufficient for antimicrobial action. At higher concentrations, peptides and phospholipids translocate to form multimeric transmembrane channels that seem to contribute to the peptide's hemolytic activity. An understanding of the key features of the secondary and tertiary structures of the antimicrobial peptides and their effects on bactericidal and hemolytic activity can aid the rational design of improved analogs for clinical use.Key words: structure, antimicrobial peptide, NMR, membrane, hemolytic.
Magnetic resonance imaging of regenerating and dystrophic mouse muscle
Authors: McIntosh Laura M , Baker Ross E , Anderson Judy E
Published: April 2011

Magnetic resonance imaging allows serial visualization of living muscle. Clinically magnetic resonance imaging would be the first step in selecting a region of interest for assessment of muscle disease state and treatment effects by magnetic resonance spectroscopy. In this study, magnetic resonance imaging was used to follow dystrophy and regeneration in the mdx mouse, a genetic homologue to human Duchenne muscular dystrophy. It was hypothesized that images would distinguish normal control from mdx muscle and that regenerating areas (spontaneous and after an imposed injury) would be evident and evolve over time. T2-weighted images of hind-limb muscles were obtained on anaesthetized mice in a horizontal bore 7.1-T experimental magnet. Magnetic resonance images of mdx muscle appeared heterogeneous in comparison to homogeneous images of control muscle. Foci of high intensity in mdx images corresponded to dystrophic lesions observed in the histologic sections of the same muscles. In addition, it was possible to follow chronologically the extent of injury and repair after an imposed crush injury to mdx muscle. These results should make it possible to obtain meaningful magnetic resonance spectra from particular regions of interest in muscle as viewed in magnetic resonance images (i.e., regenerating, degenerating, normal muscle) acquired during neuromuscular diseases and treatment regimens.Key words: MRI, MRS, spectroscopy, muscular dystrophy, muscle regeneration, mdx mouse.
Diagnosis of cancer in humans by 1H NMR of tissue biopsies
Authors: Smith Ian CP , Blandford Dorothea E
Published: April 2011

We describe methodology for the diagnosis of human cancer, at high levels of accuracy, sensitivity, and specificity, by 1H NMR of tissue biopsies. This method is made robust and accurate by careful specimen preparation, and by multivariate analysis of spectral data. Examples are presented for the diagnosis of cancer of the prostate gland and the ovary. The potential for use of these methods noninvasively, in vivo, is shown to be very positive.Key words: methodology, prostate gland, ovary.
Na+/H+ exchanger: proton modifier site regulation of activity
Authors: Kinsella James L , Heller Phillip , Froehlich Jeffrey P
Published: April 2011

The Na+/H+ exchangers (NHE1-6) are integral plasma membrane proteins that catalyze the exchange of extracellular Na+ for intracellular H+. In addition to Na+ and H+ transport sites, NHE has an intracellular allosteric H+ modifier site that increases exchange activity when occupied by H+. NHE activity is also subject to control by a variety of extrinsic factors including hormones, growth factors, cytokines, and pharmacological agents. Many of these factors, working through second messenger pathways acting directly or indirectly on NHE, regulate NHE activity by shifting the apparent affinity of the H+ modifier site to more alkaline or more acid pH. The underlying molecular mechanisms involved in the activation of NHE by the H+ modifier site are poorly understood at this time, but likely involve slow protein conformational changes within a NHE oligomer. In this paper, we present initial experiments measuring intracellular pH-dependent transition rates between active and inactive oligomeric conformations and describe how these transition rates may be important for overall regulation of NHE activity.Key words: Na+/H+ exchangers, oligomers, hysteresis.
Regulation of Rho protein binding to membranes by rhoGDI: inhibition of releasing activity by physiological ionic conditions
Authors: Bilodeau Diane , Lamy Sylvie , Desrosiers Richard R , Gingras Denis , Béliveau Richard
Published: April 2011

The Rho GDP dissociation inhibitor (GDI) is an ubiquitously expressed regulatory protein involved in the cycling of Rho proteins between membrane-bound and soluble forms. Here, we characterized the Rho solubilization activity of a glutathione S-transferase (GST) - GDI fusion protein in a cell-free system derived from rat kidney. Addition of GST-GDI to kidney brush border membranes resulted in the specific release of Cdc42 and RhoA from the membranes, while RhoB and Ras were not extracted. The release of Cdc42 and RhoA by GST-GDI was dose dependent and saturable with about 50% of both RhoA and Cdc42 extracted. The unextracted Rho proteins were tightly bound to membranes and could not be solubilized by repeated GST-GDI treatment. These results demonstrated that kidney brush border membranes contained two populations of RhoA and Cdc42. Furthermore, the GST-GDI solubilizing activity on membrane-bound Cdc42 and RhoA was abolished at physiological conditions of salt and temperature in all tissues examined. When using bead-immobilized GST-GDI, KCl did not reduced the binding of Rho proteins. However, washing brush border membranes with KCl prior treatment by GST-GDI inhibited the extraction of Rho proteins. Taken together, these results suggest that the binding of GDI to membrane-bound Cdc42 and RhoA occurs easily under physiological ionic strength conditions, but a complementary factor is required to extract these proteins from membranes. These observations suggest that the shuttling activity of GDI upon Rho proteins could be normally downregulated under physiological conditions.Key words: rhoGDI, rho proteins, ionic strength, kidney.
Myoid cell density in the thymus is reduced duringmdxdystrophy and after muscle crush
Authors: Wong Annyue , Garrett Kerryn L , Anderson Judy E
Published: April 2011

Thymic myoid cells share structural and behavioural features with cells of the skeletal muscle lineage: they express regulatory genes and contractile proteins, and they can form myofibers in culture. Historically, those features suggested that myoid cells could be precursors for muscle repair in addition to the satellite cells in muscle that are typically designated as the only muscle precursors. Muscles of the mutant mdx dystrophic mouse strain have a large demand for precursors, which is greatest at a young age. In the present study, immunostaining for troponin T was used to localize myoid cells. We tested the hypothesis that the myoid cell population changes when there is a demand for muscle precursors and that these changes would be anticipated if myoid cells have a role as myogenic precursors or stem cells in muscle. Chronic demands for muscle precursors in mdx dystrophic mice were accompanied by lower myoid cell density in comparison with density in two normal strains (C57BL10/ScSn and Swiss Webster). Acute demand for precursors was accompanied by a sharp decline in thymic myoid cell density within 2 days after a crush injury to one tibialis anterior muscle in normal but not dystrophic animals. To standardize the developmental age of the thymus, density was determined in all animals at 28 days of age. Given the current interest in nonmuscle sources of myogenic stem cells, these data suggest that changes in the density of thymic myoid cells may accompany acute and chronic demands for muscle precursors. Further experiments are required to determine whether thymic myoid cells are participants in distant muscle cell proliferation, new fiber formation, or the establishment of new stem cells in regenerated muscle.Key words: thymus, myoid cells, troponin T, MyoD, tissue repair, myoblasts, mdx dystrophy.
Structure-function studies of the sodium pump
Authors: Blostein Rhoda
Published: April 2011

The Na+,K+-ATPase is an ubiquitous plasma membrane protein complex that belongs to the P-type family of ion motive ATPases. Under normal conditons, it couples the hydrolysis of one molecule of ATP to the exchange of three Na+for two K+ions, thus maintaining the normal gradient of these cations in animal cells. Despite decades of investigation of its structure and function, the structural basis for its cation specificity and for conformational coupling of the scalar energy of ATP hydrolysis to the vectorial movement of Na+and K+have remained a major unresolved issue. This paper summarizes our recent studies concerned with these issues. The findings indicate that regions(s) of the amino terminus and first cytoplasmic (M2/M3) loop act synergisticaly to affect the steady-state conformational equilibrium of the enzyme. Although carboxyl- or hydroxyl-bearing amino acids comprise the cation-binding and occlusion sites, our experiments also suggest that these interactions may be modulated by juxtapositioned cytoplasmic regions.Key words: sodium, potassium, ATPase, Na+,K+-ATPase, sodium pump.
Evidence for mitochondrial localization of betaine aldehyde dehydrogenase in rat liver: purification, characterization, and comparison with human cytoplasmic E3 isozyme
Authors: Chern Ming -Kai , Pietruszko Regina
Published: April 2011

Betaine aldehyde dehydrogenase has been purified to homogeneity from rat liver mitochondria. The properties of betaine aldehyde dehydrogenase were similar to those of human cytoplasmic E3 isozyme in substrate specificity and kinetic constants for substrates. The primary structure of four tryptic peptides was also similar; only two substitutions, at most, per peptide were observed. Thus, betaine aldehyde dehydrogenase is not a specific enzyme, as formerly believed; activity with betaine aldehyde is a property of aldehyde dehydrogenase (EC 1.2.1.3), which has broad substrate specificity. Up to the present time the enzyme was thought to be cytoplasmic in mammals. This report establishes, for the first time, mitochondrial subcellular localization for aldehyde dehydrogenase, which dehydrogenates betaine aldehyde, and its colocalization with choline dehydrogenase. Betaine aldehyde dehydrogenation is an important function in the metabolism of choline to betaine, a major osmolyte. Betaine is also important in mammalian organisms as a major methyl group donor and nitrogen source. This is the first purification and characterization of mitochondrial betaine aldehyde dehydrogenase from any mammalian species.Key words: betaine, aldehyde, dehydrogenase, mitochondria, rat liver.
Function and assembly of nuclear pore complex proteins
Authors: Bodoor Khaldon , Shaikh Sarah , Enarson Paul , Chowdhury Sharmin , Salina Davide , Raharjo Wahyu Hendrati , Burke Brian
Published: April 2011

Nuclear pore complexes (NPCs) are extremely elaborate structures that mediate the bidirectional movement of macromolecules between the nucleus and cytoplasm. The current view of NPC organization features a massive symmetrical framework that is embedded in the double membranes of the nuclear envelope. It embraces a central channel of as yet ill-defined structure but which may accommodate particles with diameters up to 26 nm provided that they bear specific import/export signals. Attached to both faces of the central framework are peripheral structures, short cytoplasmic filaments, and a nuclear basket assembly, which interact with molecules transiting the NPC. The mechanisms of assembly and the nature of NPC structural intermediates are still poorly understood. However, mutagenesis and expression studies have revealed discrete sequences within certain NPC proteins that are necessary and sufficient for their appropriate targeting. In addition, some details are emerging from observations on cells undergoing mitosis where the nuclear envelope is disassembled and its components, including NPC subunits, are dispersed throughout the mitotic cytoplasm. At the end of mitosis, all of these components are reutilized to form nuclear envelopes in the two daughter cells. To date, it has been possible to define a time course of postmitotic assembly for a group of NPC components (CAN/Nup214, Nup153, POM121, p62 and Tpr) relative to the integral inner nuclear membrane protein LAP2 and the NPC membrane glycoprotein gp210. Nup153, a dynamic component of the nuclear basket, associates with chromatin towards the end of anaphase coincident with, although independent of, the inner nuclear membrane protein, LAP2. Assembly of the remaining proteins follows that of the nuclear membranes and occurs in the sequence POM121, p62, CAN/Nup214 and gp210/Tpr. Since p62 remains as a complex with three other NPC proteins (p58, p54, p45) during mitosis, and CAN/Nup214 maintains a similar interaction with its partner, Nup84, the relative timing of assembly of these additional four proteins may also be inferred. These observations suggest that there is a sequential association of NPC proteins with chromosomes during nuclear envelope reformation and the recruitment of at least eight of these precedes that of gp210. These findings support a model in which it is POM121 rather than gp210 that defines initial membrane-associated NPC assembly intermediates and which may therefore represent an essential component of the central framework of the NPC. Key words: nuclear pore complex, nucleoporin, mitosis, nuclear transport
Differences in phosphatase modulation of α4 β1 and α5 β1 integrin-mediated adhesion and migration of B16F1 cells
Authors: Hangan-Steinman Dolores , Ho Wai-chi , Shenoy Priti , Chan Bosco MC , Morris Vincent L
Published: April 2011

It is well established that a biphasic relationship exists between the adhesive strength of β1 integrins and their ability to mediate cell movement. Thus, cell movement increases progressively with adhesive strength, but beyond a certain point of optimal interaction, cell movement is reduced with further increases in adhesive function. The interplay between the various kinase and phosphatase activities provides the balance in β1 integrin-mediated cell adhesion and migration. In the present study, the significance of protein tyrosine phosphatases (PTP) and ser/thr protein phosphatases (PP) in α4β1 and α5β1 integrin-mediated mouse melanoma B16F1 cell anchorage and migration on fibronectin was characterized using phosphatase inhibitors. At low fibronectin concentration, α5β1 functioned as the predominant receptor for cell movement; a role for α4β1 in B16F1 cell migration increased progressively with fibronectin concentration. Treatment of B16F1 cells with PTP inhibitors, sodium orthovanadate (Na3VO4) and phenylarsine oxide (PAO), or PP-1/2A inhibitor, okadaic acid (OA), abolished cell movement. Inhibition of cell movement by PAO and OA was associated by a reduction in the adhesive strength of α4β1 and α5β1. In contrast, treatment of B16F1 cells with Na3VO4 resulted in selective stimulation of the adhesive function of α5β1, but not α4β1. Therefore, our results demonstrate that (i) both PTP and PP-1/2A have roles in cell movement, (ii) modulation of cell movement by PTP and PP-1/2A may involve either a stimulation or reduction of β1 integrin adhesive strength, and (iii) distinct phosphatase-mediated signaling pathways for differential regulation of the various β1 integrins exist. Key words: phosphatases, integrins, cell movement, cell adhesion.
An NH2-terminal deleted plasma membrane H+-ATPase is a dominant negative mutant and is sequestered in endoplasmic reticulum derived structures
Authors: Masuda Claudio Akio , Montero-Lomelí Mónica
Published: April 2011

The NH2-terminus of the plasma membrane H+-ATPase is one of the least conserved segments of this protein among fungi. We constructed and expressed a mutant H+-ATPase from Saccharomyces cerevisiae deleted at an internal peptide within the cytoplasmic NH2-terminus (D44-F116). When the enzyme was subjected to limited trypsinolysis it was digested more rapidly than wild type H+-ATPase. Membrane fractionation experiments and immunofluorescence microscopy, using antibodies against H+-ATPase showed that the mutant ATPase is retained in the endoplasmic reticulum. The pattern observed in the immunofluorescence microscopy resembled structures similar to Russell bodies (modifications of the endoplasmic reticulum membranes) recently described in yeast. When the wild type H+-ATPase was co-expressed with the mutant, wild type H+-ATPase was also retained in the endoplasmic reticulum. Co-expression of both ATPases in a wild type yeast strain was lethal, demonstrating that this is a dominant negative mutant.
The role of amino acid neurotransmitters in the regulation of pituitary gonadotropin release in fish
Authors: Trudeau V L , Spanswick D , Fraser E J , Larivière K , Crump D , Chiu S , MacMillan M , Schulz R W
Published: April 2011

Both glutamate and γ-aminobutyric acid (GABA) are involved in pituitary hormone release in fish. Glutamate serves 2 purposes, both as a neurotransmitter and as a precursor for GABA synthesis. Glutamate can be catabolized to GABA by the actions of 2 distinct but related enzymes, glutamate decarboxylase 65 (GAD65) and GAD67. They derive from 2 different genes that likely arose from an early gene duplication prior to the emergence of teleosts more than 400 million years ago. There is good evidence for the involvement of GABA in luteinizing hormone (LH) release in fish. The mechanism of GABA action to stimulate LH release appears to be a combination of effects on GnRH release, potentiation of gonadotropin hormone-releasing hormone (GnRH) action, and in some cases directly at the LH cell. These actions appear to be dependent on such factors as sex or sex steroid levels, and there may also be species differences. Nevertheless, the stimulatory effects of GABA on LH are present in at least 4 fish species. In contrast, convincing data for the inhibitory effects of GABA on LH release have only been observed in 1 fish species. The sites and mechanisms of action of amino acid neurotransmitters on LH release have yet to be fully characterized. Both N-methyl-D-aspartic acid (NMDA) and S-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamate receptors are likely to have important roles. We suggest that it is a receptor similar to the GABAA type which mediates the effects of GABA on LH release in fish, at least partially acting on the GnRH neuron, but likely directly acting at the gonadotroph as well. GABA may also be involved in regulating the release of other pituitary hormones in fish, namely follicle stimulating hormone (FSH = GTH-I), prolactin, and growth hormone. Based on the findings described in this review, a working model for the involvement of glutamate and GABA in the regulation of LH release in teleost fish is proposed.

Key words: glutamate, GABA, luteinizing hormone, muscimol, patch clamp electrophysiology, reproduction, fish.
NOTE ON THE RELATION BETWEEN FEYNMAN'S FORMULATION OF SCATTERING PROBLEMS AND THE BORN APPROXIMATION
Authors: Dempster J. R. H.
Published: April 2011

Feynman's formulation of scattering problems is described briefly, and is compared with Born's approximation. The two procedures are shown to be equivalent and to be valid under the same conditions. Feynman's formulas are used to calculate the first and second order terms of the scattered particle wave function, with an arbitrary scattering potential.
A METHOD OF MEASURING GAMMA-RAY ABSORPTION COEFFICIENTS AT 0.51 Mev
Authors: Argyle P. E. , Griffiths G. M. , Warren J. B.
Published: April 2011

The coincidence method described makes use of the angular correlation between pairs of annihilation quanta to eliminate the effect of scattered radiation usually present in absorption measurements. Mass absorption coefficients in (gm./cm.2)−1 found by this method are as follows:[Formula: see text]
SELECTIVE REFLECTION FROM THE VAPORS OF THE ALKALI METALS
Authors: Lauriston A. C. , Welsh H. L.
Published: April 2011

Selective reflection from sodium, potassium, rubidium, and caesium vapors in the neighborhood of the resonance lines was observed for vapor pressures between 10 mm. and 1 atm., using a steel tube with a window of transparent magnesium oxide. Reflecting power as a function of frequency was measured by using incident light of continuous spectral distribution. The reflection contour for pressures up to ½ atm. is in good agreement with the theory of reflection from an absorbing medium. For each line the damping constant in the dispersion equations varies as the square root of the number of atoms per cubic centimeter, as was found previously for mercury and cadmium. For the two members of the resonance doublet the damping constants are proportional to the square roots of the oscillator strengths. In a region about 5 cm.−1 wide about each resonance frequency the reflected intensity measured experimentally is greater than that calculated. These lines of residual intensity may be due to a second kind of selective reflection. At pressures above ½ atm. the observed reflection contour cannot be explained by the simple anomalous dispersion theory.
ABSORPTION CORRECTIONS FOR RADIUM STANDARDIZATION
Authors: Keyser G. M.
Published: April 2011

The absorption corrections necessary for radium standardization have been redetermined. The measuring equipment and technique have been investigated to find the conditions necessary for minimum error. A lead filtered, aluminum walled chamber was found to have the best characteristics. The electronic absorption coefficients measured with this chamber fit an empirical formula depending only on the atomic number. This formula gives a value for the absorption coefficient of radium salts which was compared with a direct experimental value.
SOME RESULTS ON THE ELECTRICAL BREAKDOWN OF LIQUIDS USING PULSE TECHNIQUES
Authors: Edwards W. D.
Published: April 2011

Polar and nonpolar organic liquids of relatively simple structure have been used as test liquids. To obtain reproducible results and to avoid the considerable errors due to minute solid particles an apparatus has been constructed in which the liquid may be distilled and the breakdown measurements made within a completely enclosed system and at pressures less than atmospheric when desired. Single, rectangular pulses of voltage were applied to a pair of highly polished, metal spheres immersed in the test liquids. Time delays in breakdown of the order of one microsecond, the exact value depending on the gap width, have been found for the liquids used. In the liquid state hexane and ethyl alcohol were found to have negative temperature coefficients of breakdown strength. The breakdown strength of benzene was found to depend on the cathode metal but was independent of the anode metal. A reduction in gap width gave rise to an increase in breakdown strength for benzene and n-hexane.
ANGULAR CORRELATION OF ANNIHILATION RADIATION FROM POSITRONS DECAYING IN SEVERAL SUBSTANCES
Authors: Warren J. B. , Griffiths G. M.
Published: April 2011

Using anthracene scintillation counters in coincidence, the angular correlation between annihilation quanta produced by the decay of positrons in the following materials has been measured: the pure elements Mg, S, Cu, Sn, Pt, and Hg, and the chemical compounds LiCl, KCl, CsCl, KF, and KI.Calculations were performed to determine the effect of the geometry on the shape of the angular correlation curves, and the effects of scattering were investigated.The curves for copper, platinum, and possibly mercury could be approximated to by the expression[Formula: see text], where C(θ) is the coincidence counting rate as a function of θ, the angular departure of the two quanta from collinearity, and K and θ0 are constants. The curves for the other materials are more complicated and suggest that there is a relation between the shape of the curves and the outer electronic structure of the atoms with which the positrons annihilate. In alkali halides the positrons appear to annihilate only against the outer electrons of the negatively charged halogen ions.
SPECTROSCOPIC STUDY OF SMALL SAMPLES IN A HOLLOW CATHODE DISCHARGE
Authors: Newbound K. B. , Fish F. H.
Published: April 2011

Operating characteristics of the hollow cathode discharge have been investigated qualitatively. A sample of less than 10 μgm. of an element may be used to study the hyperfine structure of the principal lines in an exposure of a few hours. The useful lifetime of the sample in the discharge is about 10 hr., and up to 80% of the sample can be recovered after use.
THE MACROMOSAIC STRUCTURE OF TIN SINGLE CRYSTALS
Authors: Teghtsoonian E. , Chalmers Bruce
Published: April 2011

Single crystals of high purity tin grown from the melt by a modified Bridgman method are shown to be partitioned into bands, or striations. A difference of orientation exists between the striations such that the lattice of one striation may be brought into coincidence with the lattice of its neighbor by a pure rotation about an axis parallel to the specimen axis. The properties of the striations have been shown to be dependent on both the rate of growth and the crystallographic orientation relative to the direction of heat flow. A tentative explanation of the origin of this effect is advanced in terms of the formation of edge type dislocations from the condensation of vacant lattice sites.
DENDRITIC GROWTH IN LEAD
Authors: Weinberg F. , Chalmers Bruce
Published: April 2011

Dendritic growth of large single crystals of lead is revealed by decanting the remaining liquid at any required stage of the process of solidification. The direction of dendritic growth was determined as a function of crystallographic orientation and direction of solidification. It was found that all the dendritic rows in a single crystal were not quite parallel, owing to a crystal substructure. An explanation is advanced for the presence of the substructure in terms of dendritic growth based on their observed properties. Temperature measurements during solidification showed that the region of the liquid where dendrites were formed was supercooled by several degrees. No supercooling was observed in the portions not showing dendritic growth.
ROTATIONAL WINGS OF RAMAN BANDS AND FREE ROTATION IN LIQUID OXYGEN, NITROGEN, AND METHANE
Authors: Crawford M. F. , Welsh H. L. , Harrold J. H.
Published: April 2011

Rotation-vibrational Raman bands have been observed in liquid oxygen, nitrogen, and methane, and in solid methane. In every case the Q branches associated with isotropic Raman scattering are sharp lines; but the Q branches and rotational wings associated with anisotropic scattering form broad continuous bands, with extent and intensity distribution consistent with free molecular rotation. The lack of discrete structure in the broad bands is attributed to a removal of the m degeneracy of the rotational energy levels in the intermolecular force fields. Removal of the m degeneracy broadens those transitions for which the transition probability depends on the anisotropic part of the rate of change of the polarizability, but not those for which J and m are unchanged and for which the transition probability depends only on the isotropic part. The Raman spectrum of liquid oxygen yields no evidence for O4 aggregates. The Raman spectrum of liquid methane displays all fundamental vibrations of the molecule and two overtones, with Raman shifts (in cm.−1): 1300, band (ν4); 1535, band (ν2); 2570, line, and 2600, band (2ν4); 2906, line (ν1); 3020, band (ν3); 3053, line (2ν2).
FLUORESCENT SPECTRA OF SOME ORGANIC SOLID SOLUTIONS
Authors: Dekker A. J. , Lipsett F. R.
Published: April 2011

A method to measure the spectral distribution of the luminescence of solids is described. Use is made of a spectrophotometer in combination with a photo-multiplier tube. Spectra have been investigated and discussed for solid solutions of naphthacene and 1,2,5,6–dibenzanthracene in naphthalene and anthracene as functions of concentration.
FORBIDDEN TRANSITIONS IN DIATOMIC MOLECULES: II. THE ABSORPTION BANDS OF THE OXYGEN MOLECULE
Authors: Herzberg G.
Published: April 2011

The forbidden [Formula: see text] absorption bands of O2 in the near ultraviolet have been obtained under high resolution with absorbing paths up to 800 m. A detailed fine structure analysis has been carried out. It confirms the identification of the band system as a [Formula: see text] transition. Precise values of the rotational constants Bν and Dν as well as of the vibrational quanta [Formula: see text] in the upper state have been derived. Each of the "lines" of the Q branches observed under low dispersion is resolved into six components whose spacing yields the triplet splitting in the upper state. This splitting is more than twice as large as in the [Formula: see text] ground state and is of opposite sign. The splitting constants λ and γ have been determined and their variation with the vibrational quantum number observed. In addition to the Q-form branches weak O- and S-form branches have been found in agreement with the prediction of Present which is based on the assumption that spin–orbit coupling is the main cause for the occurrence of this forbidden transition. However, the relative intensities of the different branches deviate strongly from Present's prediction. The dissociation limit obtained from the convergence limit of the bands (without extrapolation) is at 41219 ± 40 cm.−1 This value is higher by about 220 cm.−1 than the value of the dissociation energy of O2 derived from the Schumann–Runge bands. It is possible that the limit of the Schumann–Runge bands, which is based on a short extrapolation, and therefore the value of the dissociation energy of O2 has to be slightly revised. The electron configurations and dissociation products of the various electronic states of O2 are briefly discussed.
THE MEASUREMENT OF PHOTONUCLEAR CROSS SECTIONS IN ISOTOPES LEADING TO SHORT-LIVED DECAY PRODUCTS
Authors: Haslam R. N. H. , Summers-Gill R. G. , Crosby E. H.
Published: April 2011

A dropping apparatus, including a new means of dosage rate monitoring, has been designed to allow the observation of short-lived activities produced by betatron irradiation of various parent materials. The photonuclear cross section for the reaction S32(γ, n)S31 has been measured by this means. The cross section has a peak value of 24.6 millibarns at 20.1 ± 0.5 Mev., a half width of 4.5 Mev., and an integrated cross section of 0.12 Mev-barns. The reaction threshold was found to be 15.0 ± 0.1 Mev. The experiment has also yielded a new half life for S31 − 2.66 ± 0.03 sec.
MODIFIED BRIDGE METHOD FOR ABSOLUTE DETERMINATION OF OHM
Authors: Romanowski M.
Published: April 2011

The principal characteristics of Campbell's original bridge for the determination of the ohm (in terms of mutual inductance and time) and of Picard's modification to the bridge are examined. Two other networks for the same measurement are found possible by rearranging components. One arrangement in particular offers advantages over previous methods and was built in an experimental form. In it all important circuit elements are constructed of manganin, rendering the bridge less subject to temperature effects, and no determination of self-inductance is necessary. The new bridge does require a mutual inductance equal to twice the value of the standard. A brief outline of the method for resolving this point is given as part of a more general work under way on the scale of inductance.
BOUNDARY CONDITIONS IN THE MECHANICS OF FIELDS
Authors: Neamtan S. M. , Vogt E.
Published: April 2011

A variational principle has been set up for the description of relativistic fields with the aid of Lagrangians involving second order derivatives of the field functions. This constitutes a generalization of the usual formulation in that, besides the boundary conditions usually imposed, it admits also linear homogeneous boundary conditions. The formulation has been developed for the complex scalar and complex vector fields. The variational principle then yields not only the wave equations but also the allowed boundary conditions. A Hamiltonian and equations of motion in canonical form can be set up. A symmetric stress–energy tensor and a charge–current vector are defined, yielding the usual conservation equations. For the vector field, π4 is not identically zero; also the Lorentz condition arises out of the variational principle and does not have to be separately imposed. For the Dirac field an extension to Lagrangians with second order derivatives is not possible, but for this field also the variational principle yields the allowed boundary conditions.
COINCIDENCE STUDIES OF THE DECAY OF INDIUM 114
Authors: Johns M. W. , McMullen C. C. , Donnelly R. J. , Nablo S. V.
Published: April 2011

A coincidence circuit of resolving time 3 × 10−9 sec. has been used to examine the decay of In114. Coincidence experiments are described to show that of the five gamma-rays which follow the K-capture process the 0.722 and 1.300 Mev. radiations are both in cascade with the 0.556 Mev. gamma-ray and that the spins and parities of the excited levels of energy 0.556, 1.278, and 1.856 Mev. in Cd114 are 2 +, 2 +, and 0 +, respectively. The observed beta–gamma coincidences may be ascribed to a combination of inner bremsstrahlung associated with the strong 2 Mev. β− transition and a weak β− group of intensity less than 1 × 10−3 beta per disintegration and end point about 0.8 Mev. The positron spectrum has a branching ratio of 4 ± 1 × 10−5 and an end point between 1.0 and 1.4 Mev.
ELECTRON CAPTURE BY SLOW SINGLY CHARGED HELIUM IONS IN HELIUM
Authors: Jackson J. David
Published: April 2011

The capture of electrons by slow singly charged helium ions passing through helium gas is discussed theoretically. Calculations of the capture cross section for incident ion energies from 200 ev. to 100 kev. are made using an impact parameter method due to Kohn. In this energy interval the computed cross section is found to be fitted very closely by the empirical expression (σ/πa02) = 7.94 – 2.35 log10E(kev.). The results are compared with recent experimental data. The agreement between theory and experiment is good, except for the data of Keene.
AN ATOMIC MASS STUDY OF NUCLEAR SHELL STRUCTURE IN THE REGION 82 < n < 126
Authors: Hogg Benjamin G. , Duckworth Henry E.
Published: April 2011

A number of new atomic masses are reported in the region 82 < n < 126 and are used to study nuclear stability in this region. No stability effects associated with a particular neutron number are noticed but rather there is a broad general increase in stability between the 82 and 126 neutron shells.
ON INVERTING LAPLACE TRANSFORMS OF THE FORM h(s)/(p(s) + q(s)e−τ s)
Authors: Hull T. E. , Wolfe W. A.
Published: April 2011

Some appeal is made to the theory of integral equations to construct a general and practical successive approximation procedure for inverting transforms of the form given in the title, where p(s) and q(s) are polynomials in s, the degree of p(s) being greater than the degree of q(s), and h(s) is any function which does not greatly complicate the transform. The approximations converge rapidly when τ is relatively small. In some cases upper and lower bounds and asymptotic expressions for the inverse are produced. Problems from the theory of counters and the theory of heat transfer are used to illustrate the method.
COUNTING SLOW ELECTRONS WITH AN ELECTRON MULTIPLIER
Authors: Cowan J. A.
Published: April 2011

The efficiency of counting slow velocity electrons by a 12-stage activated beryllium-copper electron multiplier was investigated. The total electron current in the incident beam was measured using an electrometer tube circuit. The number of pulses produced in the multiplier by the whole beam was counted using high speed scaling circuits. The efficiency of counting was thus determined without depending on calibrated slits to divide the beam.Efficiency curves for primary energies between 200 and 900 ev. are shown for freshly activated surfaces and also for surfaces which had been exposed to still air for five months. The curves were similar in shape, the former being a few per cent above the latter. A maximum of 63% was obtained for 300 ev. input energies.
FINE STRUCTURE OF THE SCHUMANN-RUNGE BANDS NEAR THE CONVERGENCE LIMIT AND THE DISSOCIATION ENERGY OF THE OXYGEN MOLECULE
Authors: Brix P. , Herzberg G.
Published: April 2011

The Schumann-Runge absorption bands of O2[Formula: see text] have been photographed in the fourth order of a 3 m. vacuum spectrograph with a resolution of 160,000. Some spectra were taken with the O2 at liquid air temperature. A detailed line structure analysis has been carried out for all bands with ν′ > 11. In addition to the six main branches (with ΔJ = ΔN = ± 1), for low values of the quantum number N (total angular momentum apart from spin), several lines of the six satellite branches [Formula: see text] as well as of the two "forbidden" branches (with ΔN = ± 3, ΔJ = ± 1) have been identified. Values of the rotational constants and the vibrational quanta in the upper state have been derived up to ν′ = 21. The triplet splitting increases rapidly with N and with ν′; it cannot be described accurately by the known theoretical formulae.The origin of the 21–0 band is at 57115 cm−1. A very short extrapolation gives the convergence limit at 57128 ± 5 cm−1. This limit agrees excellently with the one derived from the near ultraviolet [Formula: see text] bands if it is assumed that at both limits those O atoms that are produced in the 3P state are in the lowest component level of this state, viz. 3P2. A discrepancy pointed out earlier by Herzberg is thus removed. The convergence limit just mentioned and certain other data derived from the spectrum lead to very precise information about the dissociation energy of O2. Without any extrapolation the dissociation energy into normal atoms can be given as 41260 ± 15 cm−1 (or 5.1148 ± 0.002 ev. or 117.96 ± 0.04 kcal./mole), which is 0.63% higher than the old value.
DISINTEGRATION OF Au198
Authors: Elliott L. G. , Wolfson J. L. , Preston M. A.
Published: April 2011

In addition to the 411.77 kev. γ-ray transition, two γ-ray transitions of energies 676.5 ± 0.8 kev. and 1088.9 ± 0.9 kev. have been observed in Hg198 following the disintegration of Au198. The intensities of these transitions were found to be (8.20 ± 0.56) × 10−3 and (1.63 ± 0.12) × 10−3 per disintegration respectively. The K conversion coefficient of the 676.5 kev. transition was measured as 0.0224 ± 0.0019, identifying the radiation as a mixture of magnetic dipole and electric quadrupole. The K conversion coefficient of the 1088.9 kev. transition was measured as 0.00450 ± 0.00034, identifying this radiation as electric quadrupole.A β-transition to the ground state of Hg198, of energy 1371 kev. and intensity (2.5 ± 0.5) × 10−4 per disintegration, has been observed and identified as a third order forbidden, transition. The shape of this spectrum has been studied above the end point of the intense 959 kev. β-transition. Of the four combinations considered for the β-decay interaction form, viz. SA, VA, ST, VT, it was found that the experimental shape can be fitted by any one of VA, ST, or VT, but not by SA. The log f0 t value for the transition is 11.7.A disintegration scheme is proposed in which the excited states of Hg198 at 412 and 1089 kev. are each assigned spin 2 and even parity and the ground state of Au198 spin 3 and odd parity.
AN EXPERIMENTAL INVESTIGATION OF THE HEAT TRANSFER TO TURBULENTLY FLOWING PRESSURIZED AIR
Authors: Marris A. W.
Published: April 2011

Employing a counter-flow figure-of-eight heat exchanger, direct measurements are made of the Nusselt modulus for radial heat transfer to air pressurized up to 20 atmospheres for Reynolds numbers up to 1.20 × 105. For each heat transfer determination a simultaneous friction factor measurement is made and it is found that the latter is independent of heat transfer.Results in reasonable agreement with the momentum transfer theory are obtained for Reynolds numbers less than 0.75 × 105, provided the ratio of the eddy diffusivities for heat and momentum is taken as unity. For such values of the Reynolds number, the same value of the heat transfer coefficient was obtained irrespective of whether the Reynolds number was obtained by having high pressure (density) and low velocity, or high velocity and low pressure. For higher values of the Reynolds number, however, the value of the heat transfer coefficient appeared to become dependent on the over-all heat transfer rate.
THE IMPEDANCE OF AN ANTENNA ABOVE A CIRCULAR GROUND PLATE LAID UPON A PLANE EARTH
Authors: Bekefi G.
Published: April 2011

Recent theoretical work by Storer, concerning the impedance of a vertical antenna in contact with a circular metal disk, is extended to include the case when the system is laid upon an imperfectly conducting plane earth. The expression for the impedance of the antenna is cast into a form which is stationary with respect to small variations (about the true value) of the unknown radial electric field over the surface of the earth. Numerical results are given for the case when the ground plate is sufficiently large as compared to the wave length of the radiation; the effect of variations in dielectric constant of the earth upon the impedance is shown. These calculations are compared to those obtained from the approximate theory of Monteath.A second variational formula for the antenna impedance is developed in terms of surface currents flowing in the metal ground plate. The application of this method becomes useful when the ground plate is not too large in comparison with the wave length.
REFRACTIVE INDEX NOMOGRAM FOR DRY AND HUMID AIR
Authors: Bricout P. A.
Published: April 2011

The refractive index of humid air is the sum of unity plus a term depending on pressure and temperature (dry air refractivity) plus another term dependent on temperature and relative humidity (vapor refractivity). Two alignment nomograms give the values of both refractivities within a range of 300 to 1100 mb. for pressure, +45 °C. to −40 °C. for temperature, 0 to 100% for relative humidity. Relative errors do not exceed 1% of (n – 1).
FAST NEGATIVE HYDROGEN IONS
Authors: Whittier A. Charles
Published: April 2011

A proton beam was directed through hydrogen gas at low pressure and magnetic analysis of the emergent beam showed that an appreciable fraction of the beam was transformed into negative hydrogen ions. After the beam had traversed a sufficient layer of gas, the ratio of negative hydrogen ions to protons reached an equilibrium value which was a maximum of 22.2% at 8.5 kev. The proton energy interval investigated extended from 4 to 70 kev.In this interval the electron loss cross section for negative hydrogen ions was measured and found to vary from 6.3 × 10−16 sq. cm. at 4.2 kev. to 2.5 × 10−10 sq. cm. at 70.3 kev. The electron capture cross section for protons in hydrogen was measured over the same interval and the results agreed substantially with those of other workers. The electron capture cross section for neutral atoms was also determined by combining present results for the negative ion loss cross section and for the equilibrium ratio of H− to H+ with the values of Bartels and of Montague and Ribe for the ratio of neutral atom loss cross section to the proton capture cross section.
HIGH RESOLUTION RAMAN SPECTROSCOPY OF GASES: II. ROTATIONAL SPECTRA OF C6H6 AND C6D6, AND INTERNUCLEAR DISTANCES IN THE BENZENE MOLECULE
Authors: Stoicheff B. P.
Published: April 2011

The pure rotational Raman spectra of benzene and benzene–d6 at a pressure of [Formula: see text] atm. were photographed in the second order of a 21 ft. grating. Both spectra were resolved and analyzed, yielding for the rotational constants the values B0(C6H6) = 0.18960 ± 0.00005 cm.−1, B0(C6D6) = 0.15681 ± 0.00008 cm.−1and, therefore, for the moments of inertia about an axis perpendicular to the figure axis[Formula: see text]If it is assumed that the benzene molecule has the planar hexagonal structure, the moments of inertia just given yield for the internuclear distances in benzene the values[Formula: see text]
ELECTRON CAPTURE CROSS SECTIONS
Authors: Schiff Harry
Published: April 2011

Electron capture cross sections are calculated in the first Born approximation for alpha particles passing through hydrogen and singly charged helium ions passing through helium using the complete interaction Hamiltonian. Estimations of captures into excited states are made with the help of the partial cross sections obtained in a simple closed form using only the (incident ion)−(electron) interaction. The results indicate that the first Born approximation, using the complete interaction, is quite adequate in the velocity range given by [Formula: see text]. An impact parameter calculation for protons in hydrogen shows that the cross section obtained using only the (incident ion)–(electron) interaction gives unphysical results at low velocities [Formula: see text], and that most of the contribution to the cross section arises from impact parameters p > a0, where a0 is the radius of the first Bohr orbit in hydrogen.