Search Results - (Author, Cooperation:M. A. Carpenter)

2018-03-13

American Physical Society (APS)

1098-0121

1095-3795

Physics

Magnetism

2015-08-14

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2013-02-08

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Base Sequence ; Biocatalysis ; Breast Neoplasms/*enzymology/*genetics/pathology ; Cell Death ; Cell Line, Tumor ; Cytidine Deaminase/genetics/*metabolism ; DNA Damage/genetics ; DNA Fragmentation ; DNA, Neoplasm/genetics/metabolism ; Deamination ; Gene Expression Regulation, Enzymologic ; Gene Expression Regulation, Neoplastic ; Histones/metabolism ; Humans ; *Mutagenesis/genetics ; Phenotype ; *Point Mutation/genetics ; Tumor Suppressor Protein p53/genetics/metabolism ; Up-Regulation ; Uracil/metabolism

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

We present the angular and kinetic energy distributions for the products of the proton transfer reaction O−+HF→OH+F− at a center of mass collision energy of 40.5 kJ mol−1 (0.42 eV). The angular distribution shows clear forward–backward symmetry for the formation of products, indicating that the reaction proceeds through a transient [OHF]− complex living several rotational periods. This is the first direct experimental evidence for the participation of a complex in this reaction. The product kinetic energy distributions show clear structure that we attribute to the formation of OH in vibrational states with quantum numbers v'=0, 1, and 2. Approximately 40% of the OH reaction products are formed in v'=1. This value is consistent with drift tube studies at lower collision energies in which increasing reagent translational energy transforms preferentially into product vibration. Such energy partitioning is consistent with the argument that mixed energy release in the Heavy+Light–Heavy mass combination is induced by the strong electrostatic attraction of the reactants.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Energy and angular distributions for the hydrogen abstraction reaction O−+CH4→OH−+CH3, exothermic by 0.26 eV, and a prototype ionic pathway for methane oxidation in hydrocarbon flames have been studied in a crossed molecular beam experiment at collision energies of 0.34, 0.44, and 0.64 eV. At the two lower collision energies, two mechanisms contribute to the differential cross section: In the first, low impact parameter rebound collisions form sharply backward-scattered products, while in the second, larger impact parameter collisions produce a broad distribution of forward scattered products. We suggest that the first group of products is formed by collisions with hydrogen atoms oriented essentially along the relative velocity vector and proceeding through a near-collinear O(centered ellipsis)H(centered ellipsis)CH3 geometry, while the second group corresponds to collisions with one of the three off-axis hydrogens. The products are formed on average with 65% of the total available energy in product internal excitation. The product kinetic energy distribution shows structure that correlates with excitation of the ν2 umbrella bending mode of CH3. At the highest collision energy, the product angular distribution shifts entirely to the forward direction, suggesting that the low impact parameter collisions are no longer important in the reactive process. At this energy, the average product internal excitation corresponds to 59% of the total available energy. The data suggest that the majority of product internal excitation resides in the ν2 umbrella bending mode of CH3, with OH in its ground vibrational state. © 1997 American Institute of Physics.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] In principle, sillimanite should show an Al/Si disordering transformation at high temperature8'9. To study such a transformation experimentally, however, high pressures must be applied to suppress the breakdown reaction sillimanite -" mullite + SiO2 and incongruent melting10'11. The disordering ...

Electronic Resource

1432-2021

Key words Phase transition ; Anorthite ; Ising-Model ; BaAl2Ge2O8

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Geosciences

Physics

Abstract  BaAl2Ge2O8-Feldspar undergoes an order-disorder phase transition I2/c↔C2/m at T tr ≈1690 K. The thermodynamics of the Al,Ge cation ordering process is described in terms of the compressible Ising model in mean field approximation. The mean field potential predicts a first order character of the phase transition. This is compared to antiferromagnetic ordering in a two-dimensional square Ising model with NN-pair interactions and four-spin interactions on alternating squares. Calculated order parameters and short range ordering are in good agreement with the corresponding properties observed in BaAl2Ge2O8-feldspar by means of X-ray diffraction, hard mode infrared spectroscopy and TEM. Using known calorimetric data a similar model is postulated for Al,Si ordering in anorthite, CaAl2Si2O8, for which the derived potential describes a transition with slightly stronger first order character at T tr ≈1928 K.

Electronic Resource

1432-2021

Key words Aluminosilicate garnets ; Solid solution ; IR spectroscopy

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Geosciences

Physics

Abstract Local heterogeneities in pyrope-almandine, almandine-grossular and pyrope-grossular solid solutions have been investigated using IR-powder absorption spectroscopy. Correlations of the wavenumber shifts and line broadening systematics with the thermodynamic mixing properties were found. Wavenumber shifts of the highest energy modes correlate closely with the Si-O bond distances and give an indirect view of the average distortions across the three solid solutions. They have a linear behaviour for Py-Alm, but show positive variations from linearity for Alm-Gr and Py-Gr systems. An effective line width (Δcorr) of the absorption bands over a given wavenumber interval was obtained using the autocorrelation function. Line broadening is associated with local heterogeneities arising from cation substitution in the structure of samples at intermediate compositions. Non-linearities of the line broadening were found for Alm-Gr and Py-Gr and have a shape similar to the enthalpy of mixing, ΔHmix. An empirical analysis was therefore carried out to compare ΔHmix and Δcorr quantitatively. Low-temperature far-IR spectra were recorded for the end-members pyrope, almandine and grossular and far-IR and mid-IR low-temperature spectra for Py60Gr40 in the temperature range 292–44 K. Softening of the lowest energy band with decreasing temperature was observed in the spectrum of pyrope and more enhanced in the spectrum of Py60Gr40. The same softening occurs by substitution of grossular component into pyrope. High energy modes of Py60Gr40 show the effect of saturation below 110–130 K, which correlates with the volume saturation at low temperature. This could provide an alternative explanation for the heat capacity anomaly found for Py-Gr solid solution at low-temperatures.

Electronic Resource

1432-2021

Key words Nepheline ; Incommensurate ; Rigid unit mode

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Geosciences

Physics

Abstract  Calculations of the Rigid Unit Modes (RUMs) allowed in the nepheline structure are used to explain the diffuse scattering previously seen in electron diffraction experiments. The RUM calculations also show that the modulation wavelength for incommensurate nephelines is essentially determined by the framework topology. X-ray diffraction is used to measure the intensity of the diffuse scattering as a function of temperature. The diffuse intensity increases sharply at 308 K. This effect is interpreted as being due to the softening of a phonon mode, indicating a phase transition. Measurements of this phase transition below the transition temperature are made using hard mode infrared spectroscopy.

Electronic Resource

1432-2021

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Geosciences

Physics

Abstract Pigeonites in coarse grained dolerites from the Whin Sill have been examined by transmission electron microscopy. The observed micro-structures involve coarse, heterogeneous (001) augite lamellae and antiphase boundaries (APB's), some of which have nucleated fine (001) plates of augite. APB's approximately parallel to (211) and $$(\bar 211)$$ are Ca enriched and those approximately parallel to (120) are not (or at least are less so), the former changing their orientation according to the local Ca content of the pigeonite and providing suitable sites for the heterogeneous nucleation of augite. Simple structural models show how (211) and $$(\bar 211)$$ APB's provide more suitable sites for Ca2+ ions that those parallel to (120). The development of the antiphase domains is discussed. Concentrating Ca2+ ions onto a restricted number of sites is not favoured by entropy and therefore possibly does not occur at high temperatures. The final antiphase domain scale is a complex function of the Ca content and cooling rate of the pigeonite.

Electronic Resource

1432-0967

Springer Online Journal Archives 1860-2000

Geosciences

Abstract New single crystal diffraction data for natural and heat-treated anorthite crystals (Angel et al. 1990) allow the determination of their states of Al/Si order in terms of a macroscopic order parameter,Q OD , for the transition. Numerical values ofQ OD obtained from estimates of site occupancies are shown to vary with the scalar spontaneous strain, ε s , as ε s ∝Q OD 2 , and with the ratio of the sums of typeb (superlattice) reflections and typea (sublattice) reflections asΣI b/ΣI a ∝Q OD 2 . An empirical calibration for pure anorthite is obtained giving $$Q_{OD} = 10.1\left( 5 \right)\sqrt {\varepsilon _s } $$ varies between ∼ 0.92 and ∼ 0.87 in samples equilibrated at T≤1300° C, but then falls off relatively rapidly with increasing temperature, reaching ∼ 0.7 near the melting point (∼ 1557° C). The observed temperature dependence does not conform to the predictions of the simplest single order parameter models; coupling ofQ OD withQ of the transition is suspeeted.

Electronic Resource

1432-0967

Springer Online Journal Archives 1860-2000

Geosciences

Abstract Omphacites with a range of compositions from the blueschist rocks of Syros, Greece and from included blocks in serpentinite from the Motagua fault zone, Guatemala, have been examined by transmission electron microscopy. The complex microstructures observed are all on a fine scale and are composed of exsolution and antiphase features. At least three different assemblages have been identified: (a) a single ordered phase with antiphase domains, (b) two exsolved phases, one ordered and the other disordered and (c) two exsolved phases, both apparently ordered. Selected area electron diffraction patterns provide evidence for P2/n, P2/c, and P2 space groups in different parts of the ordered crystals. The microstructures cannot all be readily explained in terms of a simple equilibrium phase diagram and some are attributed to alternative and metastable transformations. It is suggested that under the low temperature conditions of blueschist metamorphism, omphacite crystallised metastably below its ordering temperature with imperfect cation order. Subsequent development by cation ordering and exsolution was controlled by kinetics, the fastest available transformation being used to give reductions in free energy. Ordering preceded exsolution and may have occurred in a series of steps as predicted by the Ostwald step rule. Slight differences in composition and initial state of order locally influenced which reaction pathway was embarked upon and many of the products may be metastable. Such behaviour is apparently sensitive to thermal history.

Electronic Resource

1432-2021

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Geosciences

Physics

Abstract Variations in the equilibrium degree of Al/Si order in anorthite have been investigated experimentally over the temperature range 800-1535° C. Spontaneous strain measurements give the temperature dependence of the macroscopic order parameter, Q, defined with respect to the $$C\bar 1 \rightleftharpoons I\bar 1$$ phase transition, while high temperature solution calorimetric data allow the relationship between Q and excess enthalpy, H, to be determined. The thermodynamic behaviour can be described by a Landau expansion in one order parameter if the transition is first order in character, with an equilibrium transition temperature, T tr, of ∼2595 K and a jump in Q from 0 to ∼0.65 at Ttr. The coefficients in this Landau expansion have been allowed to vary with composition, using Q=1 at 0 K for pure anorthite as a reference point for the order parameter. Published data for H and Q at different compositions allow the calibration of the additional parameters such that the free energy due to the $$C\bar 1 \rightleftharpoons I\bar 1$$ transition in anorthite-rich plagioclase feldspars may be expressed (in cal. mole-1) as: $$\begin{gathered}G = \tfrac{1}{2} \cdot 9(T - 2283 + 2525X_{Ab} )Q^2 \hfill \\ {\text{ + }}\tfrac{1}{4}( - 26642 + 121100X_{Ab} )Q^4 \hfill \\ {\text{ + }}\tfrac{1}{6}(47395 - 98663X_{Ab} )Q^6 \hfill \\ \end{gathered}$$ where X Ab is the mole fraction of albite component. The nature of the transition changes from first order in pure anorthite through tricritical at ∼An78 to second order, with increasing albite content. The magnitude of the free energy of $$)$$ ordering reduces markedly as X Ab increases. At ∼700° C incommensurate ordering in crystals with compositions ∼An50–An70 needs to have an associated free energy reduction of only a few hundred calories to provide a more stable structure. These results, together with a simple mixing model for the disordered ( $$)$$ ) solid solution, an assumed tricritical model for the incommensurate ordering and published data for ordering in albite have been used to calculate a set of possible free energy relations for the plagioclase system. The incommensurate structure should appear on the equilibrium phase diagram, but its apparent stability with respect to the assemblage albite plus anorthite at low temperatures depends on the values assigned to the mixing parameters of the $$$$ solid solution.

Electronic Resource

1432-2021

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Geosciences

Physics

Abstract The temperature dependence of the infrared active modes of meteoritic and synthetic tridymite have been investigated between 23 K and 1073 K in IR absorption and IR emission experiments. At room temperature both tridymite samples consist of a mixture of low temperature forms, in different proportions, due to the grinding. The sequence of phase transitions in Steinbach tridymite deduced from the IR data agrees well with recent X-ray and calorimetry studies using identical samples (Cellai et al. 1994). The previously suspected structural phase transition P6322⇔P63/mmc is confirmed by the disappearance of the 470 cm-1 mode and a temperature anomaly of the spectral shift of the 790 cm-1 mode. Changes in the infrared spectra of synthetic tridymite give a different sequence of phase transitions from those of the meteoritic sample, consistent with the structural phase transitions observed in a 29Si MAS NMR investigation using the same sample (Xiao et al. 1993).

Electronic Resource

1573-0662

soot aerosol ; nitric acid

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Geosciences

Abstract Long-pathlength infrared absorption spectroscopy wasused to investigate nitric acid-soot aerosol chemistryat 298 K and 0.5% relative humidity. Experimentswere performed by introducing nitric acid vapor(PHNO 3 ∼ 3 Pa, Ptotal ∼ 40 kPa) intoateflon-coated chamber and initiating acquisition ofinfrared spectra at 3 minute time intervals. After 36minutes of data collection, soot powder was rapidlyexpanded into nitric acid contained in the chamber togenerate a soot-HNO3 aerosol. Infrared spectracollected before, and after, soot introduction to thechamber were used to characterize chamber wallreaction processes and soot aerosol chemistry,respectively. Three soot types were investigated(Degussa FW2, Cabot Monarch 1000, and crystallinegraphite), each yielding similar chemistry. Upon sootintroduction to the chamber both HNO3 uptake andNO2 production occurred, with the molar ratio ofHNO3 uptake to NO2 production varying from1.2 to 2.9 for the three soot types studied. Unreacted HNO3 was present at the conclusion ofeach of the aerosol experiments, indicating incompleteconversion of HNO3 into NO2. Thisobservation suggested that `active' sites at the sootsurface responsible for the reduction of HNO3 arenot regenerated (i.e., formed) in the reactionprocess. In essence, a titration occurred betweenthese active sites and HNO3. The NO2concentrations produced, the soot mass concentrationsused, and the BET measured specific surface area ofthe powders allowed computation of the surface densityof active sites of ∼4.0 × 10-18 m2/active site(describing all three powders studied). This is thefirst reported measurement of surface density ofactive sites for nitric acid chemistry on soot. Sinceatmospheric heterogeneous reactions that exhibitsurface deactivation may, in principle, affect tracegas concentration, we perform an assessment in thisregard.

Electronic Resource

1432-1777

Springer Online Journal Archives 1860-2000

Biology

Medicine

Abstract Sheep x hamster cell hybrids containing sheep metacentric Chromosome (Chr) 2 were produced by fusing blood leukocytes from normal sheep with hamster auxotrophic Ade F-minus mutants. Cell clones that were isocitrate dehydrogenase 1 (IDH1) positive were cytogenetically characterized, confirming that they contained sheep Chr 2. The following loci were newly assigned by Southern hybridization to sheep Chr 2: lipoprotein lipase (LPL), glycoprotein-4-beta galactosyltransferase 2 (GGTB2), neurofilament light polypeptide (68 kDa; NEFL), surfactant-associated protein 2 (SFTP2), lymphocyte-specific protein tyrosine kinase (LCK), and nebulin (NEB). These new assignments and the in situ localization of gelsolin (GSN) to sheep Chr 2pter-p24 are consistent with the predicted homology of cattle Chr 8 (U18) with sheep Chr 2p, and of cattle Chr 2 (U17) with sheep 2q. In addition, the assignment by cell hybrid analysis of loci previously mapped to Chr 2 in sheep, viz., cholinergic receptor, nicotinic, delta polypeptide (CHRND), collagen type III alpha 1 (COL3A1), fibronectin 1 (FN1), isocitrate dehydrogenase (IDH1), and villin 1 (VIL1), confirmed the localization of sheep syntenic group U11 to this chromosome. By nutritional selection and complementation of the hamster auxotrophic Ade F mutation, the multifunctional enzyme locus phosphoribosylaminoimidazolecarboxamide formyltransferase (AICAR transformylase)/IMP cyclohydrolase (inosinicase) (provisionally given the symbol PRACFT) has also been newly assigned to sheep Chr 2. This report significantly extends the number of loci physically mapped to sheep Chr 2 and confirms its close homology with cattle Chrs 2 and 8.

Electronic Resource

1432-1777

Springer Online Journal Archives 1860-2000

Biology

Medicine

Electronic Resource