High-resolution X-ray Study Research Articles

Crystallization of phaseolin from Phaseolus vulgaris.

Three different types of crystals were grown from phaseolin, the major storage body protein from French bean. Type I crystals are cubes with space group symmetry P432, a = 67 A. Type II crystals are bipyramids with a rounded basal plane and belong to space group P2(1)2(1)2, a = 128 A, b = 136 A, and c = 162 A. Type III crystals are rhombs grown from phytic acid-free protein. The space group symmetry is P2(1)2(1)2(1), a = 113 A, b = 136 A, and c = 89 A. Both Type II and III crystals are suitable for high resolution x-ray study.

High resolution X-ray studies of monolayer krypton on varied forms of graphite

Monolayer krypton on graphite provides examples of two-dimensional lattice gas melting, continuous symmetry melting and commensurate-incommensurate transitions. We review recent X-ray studies of commensurate melting and the commensurate-incommensurate transition in this system. We present new results on the X-ray profiles for monolayer krypton physisorbed onto a variety of different forms of exfoliated graphite. The relative merits of these different forms of graphite for varied experiments are discussed.

High resolution X-ray studies of monolayer krypton on varied forms of graphite

High resolution X-ray studies of monolayer krypton on varied forms of graphite

Critical behavior near the nematic—smectic-Atransition in butyloxybenzylidene octylaniline (40.8)

We report a high-resolution heat-capacity and x-ray study of the nematic---smectic-$A$ transition in the single-layer smectic material butyloxybenzylidene octylaniline (40.8). We find that the transition is second order to within 3 mK, with critical behavior closely similar to that observed previously in bilayer smectic materials such as octyloxycyanobiphenyl (8OCB). For the critical exponents we measure $\ensuremath{\gamma}=1.31\ifmmode\pm\else\textpm\fi{}0.02$, ${\ensuremath{\nu}}_{\ensuremath{\parallel}}=0.70\ifmmode\pm\else\textpm\fi{}0.01$, ${\ensuremath{\nu}}_{\ensuremath{\perp}}=0.57\ifmmode\pm\else\textpm\fi{}0.01$, and $\ensuremath{\alpha}={\ensuremath{\alpha}}^{\ensuremath{'}}=0.15\ifmmode\pm\else\textpm\fi{}0.05$. These exponents are consistent with the anisotropic hyperscaling relation ${\ensuremath{\nu}}_{\ensuremath{\parallel}}+2{\ensuremath{\nu}}_{\ensuremath{\perp}}=2\ensuremath{-}\ensuremath{\alpha}$. In addition, we find that the ratio of the amplitudes of the critical heat capacities in 40.8 and 8OCB is inversely proportional to the ratio of the correlated volumes as measured with x rays. The smectic longitudinal correlation length measured directly with x rays agrees quantitatively with that deduced by von K\anel and Litster from the director fluctuations. Substantial disagreements with the superconducting analog model remain unexplained.

High resolution x-ray study of microstructural changes in semiconductors and insulators subject to high electric fields

Using a high-resolution X-ray diffractometer, microstructural changes have been observed in Si-, LiF- and CdS-crystals subject to high d.c. and a.c. fields. At high fields the diffraction peaks are unstable due to inhomogeneous distribution of the electric current in the specimen. The inhomogeneous regions have been directly observed in high-resolution topographs. A correlation between current fluctuations and the diffracted beam intensity has been observed. Changes in peak shapes as a result of field have been observed.

Six polymorphic crystal forms of alpha-cobratoxin.

Six different crystal forms of the long neurotoxin alpha-cobratoxin isolated from the venom of Naja naja siamensis have been obtained and the conditions for their crystallisation are described. Heavy atom derivatives for two of these forms have been prepared and have proven suitable for high-resolution X-ray studies and, with one of them, a 0.28-nm resolution structure has been determined. All but one of the crystal forms were grown between pH 2 and pH 3. Two novel suggestions are made which may be applicable to other protein crystallisation studies. One involves cocrystallisation with mercurous iodide and the other describes a two-step microdialysis procedure, first against salt solution, followed by dialysis against poly(ethylene glycol).

Critical Fluctuations near a Nematic-Smectic-A-Smectic-CMulticritical Point

We report a high-resolution x-ray study of the fluctuations in a system exhibiting nematic, smectic-$A$, and smectic-$C$ phases, with emphasis on the NAC multicritical region. We find that the transverse mass density fluctuations are always Lorentzian in character in explicit disagreement with the Lifshitz model for this system. Unexpectedly, both the mass density fluctuations and the tilt order parameter exhibit isotropic heliumlike critical exponents near the NAC point.

High-resolution X-ray studies of 2H-TaSe2: observation of the striped CDW phase

High-resolution X-ray studies of 2H-TaSe₂: observation of the striped CDW phase

High-resolution X-ray studies of the evolution, specificity and catalytic mechanism of acid proteinases

High-resolution X-ray studies of the evolution, specificity and catalytic mechanism of acid proteinases

High-resolution X-ray studies of microstructural changes associated with conduction at high electric fields in semiconductors and insulators

High-resolution X-ray studies of microstructural changes associated with conduction at high electric fields in semiconductors and insulators

High-Resolution X-ray Study of the Smectic A-Smectic B Phase Transition and the Smectic B Phase in Butyloxybenzylidene Octylaniline

Abstract We have carried out a high resolution X-ray study of the smectic phases of Butyloxybenzylidene Octylaniline. We find that the phase previously identified as Smectic-B in this material is crystalline with in-plane order extending over at least 1.4 μm. The in-plane Bragg peaks are accompanied by anomalously strong diffuse scattering that can be described by a form 1/(q 2⊥ + γ2 q 2 z). Unless the elastic constant C44 is more than an order of magnitude smaller than previously reported values of ∼ 108 ergs/cm3 the diffuse scattering can not be due to acoustic phonons. The crystalline-B to Smectic-A melting transition is strongly first order with no observable pre-transition effects on either side of the transition.

High-resolution x-ray study of a smectic-A—smectic-Cphase transition

We report measurements of the tilt angle $\ensuremath{\Phi}$ and the planar spacing ${d}_{C}$ near the second-order $\mathrm{Sm}C\ensuremath{-}\mathrm{Sm}A$ transition in $4\ensuremath{-}n\ensuremath{-}\mathrm{pentyl}\ensuremath{-}\mathrm{phenylthiol}\ensuremath{-}{4}^{\ensuremath{'}}\ensuremath{-}n\ensuremath{-}\mathrm{octyloxybenzoate} (8\overline{S}5)$. We find that the ratio $\frac{\ensuremath{\Phi}}{invcos}(\frac{{d}_{C}}{{d}_{A}})$ is constant (1.2 \ifmmode\pm\else\textpm\fi{} 0.1) through the $C$ phase, supporting a simple molecular-tilt model for the transition. For $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}>1\ensuremath{-}\frac{T}{{T}_{c}}>3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, $\ensuremath{\Phi}$ exhibits mean-field behavior. A simple Ginzburg-criterion argument indicates that the true critical region should be unobservably small for most $A\ensuremath{-}C$ transitions.

Observations of Three Radio Galaxies with The Einstein X-Ray Observatory

We would like to present early results from the EINSTEIN X-ray Observatory on three radio galaxies: Centaurus A, NGC 315 = DW0055+30, and Cygnus A = 3C405. We hope to demonstrate that imaging X-ray astronomy can provide important insights into the physics and environment of radio galaxies and their extended radio components.NGC 5128, the parent galaxy of the double-double radio source Centaurus A, is the nearest radio galaxy, providing the best testing ground for high resolution X-ray studies. The X-ray morphology has proved to be rich and varied. We detect four distinct components to the X-ray emission: (1) the strong, compact nucleus detected by earlier satellites; (2) extended emission around the nucleus; (3) emission from the inner radio lobes; and (4) a unique X-ray jet between the nucleus and the NE radio lobe. A detailed presentation of these observations can be found in Schreier et al. (1979).

High-resolution x-ray and light-scattering study of critical behavior associated with the nematic—smectic-Atransition in 4-cyano-4′-octylbiphenyl

We have carried out a high-resolution x-ray study of the mass-density fluctuations and a light-scattering study of the bend-mode-director fluctuations associated with the nematic-smectic-$A$ phase transition in 4-cyano-4\ensuremath{'}-octylbiphenyl (8CB). This phase transition is found to be nearly second order with a first-order temperature jump of less than 10 mK. The peak scattering intensity, $\ensuremath{\sigma}({\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}}_{0})$, with ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}}_{0}=(0, 0, \frac{2\ensuremath{\pi}}{d})$, where $d$ is the layer spacing, and the longitudinal correlation length, ${\ensuremath{\xi}}_{\ensuremath{\parallel}}$, exhibit single power-law divergences for $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}l|1\ensuremath{-}\frac{T}{{T}_{c}}|l2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ with critical exponents of $\ensuremath{\gamma}=1.26\ifmmode\pm\else\textpm\fi{}0.06$ and ${\ensuremath{\nu}}_{\ensuremath{\parallel}}=0.67\ifmmode\pm\else\textpm\fi{}0.02$, respectively. These exponents agree within the errors with the predicted $d=3$, $n=2$ values appropriate to de Gennes' superconductor analogue model. The ratio of the longitudinal to transverse correlation lengths, $\frac{{\ensuremath{\xi}}_{\ensuremath{\parallel}}}{{\ensuremath{\xi}}_{\ensuremath{\perp}}}$, increases gradually with decreasing reduced temperature, changing by a factor of 2.6 over the above temperature range. This corresponds to an effective exponent difference $\sqrt{\ensuremath{\parallel}}\ensuremath{-}\ensuremath{\surd}\mathit{\ifmmode\dagger\else\textdagger\fi{}}=0.16$. The bend mode elastic constant ${K}_{3}$, which is predicted to have a divergent contribution ${(\frac{{k}_{B}T{q}_{o}^{2}}{24\ensuremath{\pi}})}^{2}{\ensuremath{\xi}}_{\ensuremath{\parallel}}$, exhibits single power law behavior for ${10}^{\ensuremath{-}4}\ensuremath{\le}1\ensuremath{-}\frac{T}{{T}_{c}}l{10}^{\ensuremath{-}2}$, with ${\ensuremath{\nu}}_{\ensuremath{\parallel}}=0.62\ifmmode\pm\else\textpm\fi{}0.03$ in reasonable agreement with the x-ray results. The predicted amplitude is, however, wrong by a factor of four. Measurements of $B$, the layer compressibility coefficient in the smectic-$A$ phase, yield $\frac{B}{{K}_{1}}\ensuremath{\sim}{({T}_{c}\ensuremath{-}T)}^{\ensuremath{\varphi}}$ with $\ensuremath{\varphi}=0.26\ifmmode\pm\else\textpm\fi{}0.06$, in agreement with previous experiments in N-$p$-cyanobenzylidene-$p$-octyloxyanilene (CBOOA) and octyloxycyanobenzylidene (80CB), but in marked disagreement with the superconducting analogue model which predicts $\ensuremath{\varphi}={\ensuremath{\nu}}_{\ensuremath{\parallel}}^{1}=0.67$.

High resolution electron microscopic and X-ray studies of non-random disorder in an unusual layered silicate (chloritoid)

The power of high resolution electron microscopy as a technique for the direct study of non-random disorder in layered minerals is illustrated by the discovery, reported herein, of two new polytypes (one of monoclinic, the other of trigonal symmetry) in the orthosilicate chloritoid. These new variants had hitherto escaped detection in previous X-ray studies of chloritoid. Several specimens of this layered mineral, which cleaves on {110} as well as the expected {001} planes, were also analysed in parallel by X-ray diffraction, the limitations of which are demonstrated by these investigations. The X-ray diffraction procedures, unlike the real-space electron microscopic approach, yield no information concerning the inhomogeneity of intergrowths of one polytype within others. Apart from the existence of new polytypes, unexpected structural faults, in which one polytypic variant terminates within another, have also been identified by electron microscopy. A plausible structural model, which describes the atomic reorganization and the implied change in chemical composition, is proposed for this fault.

High resolution X-ray studies of the smectic A-nematic transition

High resolution X-ray studies of the smectic A-nematic transition

The X-ray Spectrum of Cygnus-A

The X-ray source 2U 1957 + 40 is shown from observations with the Copernicus X-ray instrument to be associated with the powerful radiogalaxy Cygnus A. The angular size of the source is found to be less than 10' arc, the resolution of the telescopes for these observations. The spectrum can be fitted by a power law of slope 1.3 ± 0.6 or by thermal bremsstrahlung at a temperature ≽ 5 keV. The low energy cut-off corresponds to a neutral hydrogen column density of (5.5 ± 1.6) × 1021 cm−2 which may arise from absorption within the Galaxy. The total emission taking a Hubble constant of 50 km s−1 Mpc−1 is found to be (2.3 ± 0.8) × 1045 erg s−1, which is similar to the emission in the radio or optical bands. Various emission mechanisms are considered, and it is shown that synchrotron or inverse Compton radiation from the radio components or a hypothetical halo can be excluded. Thermal bremsstrahlung from a cloud of intergalactic gas is a possible process, which would make 2U 1957 + 40 similar to the other X-ray cluster sources. The kinetic pressure of this gas is sufficient to contain the radio components. Processes occurring in the nucleus of the galaxy are an alternative possibility, however, and it appears that a final determination of the emission process requires high resolution X-ray studies of the structure of the source.