Sharp Component Research Articles

Supersonic Jet Studies on the Photophysics of Substituted Benzenes and Naphthalenes

Laser-induced fluorescence (LIF) studies of seven substituted benzene and naphthalene derivatives seeded in a supersonic jet are reported. Dual fluorescence has been observed in aniline, 4-aminobenzonitrile, 1-aminonaphthalene, and 1-cyano-4-aminonaphthalene. The dual fluorescence is comprised of sharp features from a locally excited state and an unstructured, red-shifted background from a state that may be a mixed La/CT state. In aniline and 4-aminobenzonitrile the unstructured background is absent when low vibronic levels are excited but appears when higher levels are excited. In 1-aminonaphthalene and 1-cyano-4-aminonaphthalene, the background is observable upon excitation of all vibronic levels including the zero-point level. In all of the molecules, the intensity of the background increases with respect to that of the sharp component as the excitation energy is increased. The background becomes the only observable feature in the spectra at high excess energy. The broadening and red shift of the band ...

Influence of defects on the critical behavior at the 105 K structural phase transition ofSrTiO3:On the origin of the two length scale critical fluctuations

The temperature dependence of the sharp and the broad component of the critical scattering above the cubic-to-tetragonal phase transition of ${\mathrm{SrTiO}}_{3}$ has been studied by means of high-resolution triple-crystal diffractometry using 100--200 keV synchrotron radiation in five samples differing with respect to growth technique and oxygen vacancy concentrations. Emphasis is on changes in the critical behavior, the critical temperature, and the strain fields at the transition from bulk to surface. The sharp component was observed only in surface near regions of highly perfect crystals and is coupled to the occurrence of a long-range strain gradient that was identified by an exponential increase of mosaicity, lattice parameter fluctuations, and Bragg-peak intensity when approaching the surface from the bulk of the sample. Vanishing of the sharp component was observed at the polished/etched surface of a platelet cut off the large perfect crystal after release of strain due to free bending of the platelet. The values of the critical temperature observed in the bulk of the different samples vary between $98.7l~{T}_{c}l~105.8 \mathrm{K}.$ In the surface near regions of a highly perfect float-zone grown crystal a variation of ${T}_{c}$ of about 0.5 K has been found. Concerning the broad component the critical exponent describing the temperature dependence of the inverse correlation length ${\ensuremath{\kappa}}_{b}$ varies between $0.73l~{\ensuremath{\nu}}_{b}l~1.19,$ the exponent for the susceptibility between $1.49l~{\ensuremath{\chi}}_{b}l~2.9,$ however, the ratio of the two exponents is almost sample independent and equal to ${\ensuremath{\chi}}_{b}/{\ensuremath{\nu}}_{b}=2.1$ with a variance of 0.2, in good agreement with the theoretical value of 1.97 obtained by LeGouillou and Zinn-Justin [Phys. Rev. B 21, 3976 (1980)]. The occurrence of the sharp component did not affect significantly the critical exponents for the underlying broad component of the critical scattering. The exponents for the sharp component observed in surface near layers of about 100 $\ensuremath{\mu}\mathrm{m}$ thickness at the highly perfect float zone and flux grown crystals varied between $0.58l~{\ensuremath{\nu}}_{s}l~1.30,$ the values for the ratio varied between $3.3l~{\ensuremath{\chi}}_{s}/{\ensuremath{\nu}}_{s}l~4.6.$ The average value of ${\ensuremath{\chi}}_{s}/{\ensuremath{\nu}}_{s}$ is 3.9 with a variance of 0.5, and is about twice the ratio ${\ensuremath{\chi}}_{b}/{\ensuremath{\nu}}_{b}$ for the broad component as suggested by Harris et al. [Phys. Rev. B 52, 14 420 (1995)].

Human embryonic stem cells can differentiate into myocytes with structural and functional properties of cardiomyocytes

The study of human cardiac tissue development is hampered by the lack of a suitable in vitro model. We describe the phenotypic properties of cardiomyocytes derived from human embryonic stem (ES) cells. Human ES cells were cultivated in suspension and plated to form aggregates termed embryoid bodies (EBs). Spontaneously contracting areas appeared in 8.1% of the EBs. Cells from the spontaneously contracting areas within EBs were stained positively with anti-cardiac myosin heavy chain, anti--alpha-actinin, anti-desmin, anti--cardiac troponin I (anti-cTnI), and anti-ANP antibodies. Electron microscopy revealed varying degrees of myofibrillar organization, consistent with early-stage cardiomyocytes. RT-PCR studies demonstrated the expression of several cardiac-specific genes and transcription factors. Extracellular electrograms were characterized by a sharp component lasting 30 +/- 25 milliseconds, followed by a slow component of 347 +/- 120 milliseconds. Intracellular Ca(2+) transients displayed a sharp rise lasting 130 +/- 27 milliseconds and a relaxation component lasting 200--300 milliseconds. Positive and negative chronotropic effects were induced by application of isoproterenol and carbamylcholine, respectively. In conclusion, the human ES cell--derived cardiomyocytes displayed structural and functional properties of early-stage cardiomyocytes. Establishment of this unique differentiation system may have significant impact on the study of early human cardiac differentiation, functional genomics, pharmacological testing, cell therapy, and tissue engineering.

Human embryonic stem cells can differentiate into myocytes with structural and functional properties of cardiomyocytes

The study of human cardiac tissue development is hampered by the lack of a suitable in vitro model. We describe the phenotypic properties of cardiomyocytes derived from human embryonic stem (ES) cells. Human ES cells were cultivated in suspension and plated to form aggregates termed embryoid bodies (EBs). Spontaneously contracting areas appeared in 8.1% of the EBs. Cells from the spontaneously contracting areas within EBs were stained positively with anti–cardiac myosin heavy chain, anti–α-actinin, anti-desmin, anti–cardiac troponin I (anti-cTnI), and anti-ANP antibodies. Electron microscopy revealed varying degrees of myofibrillar organization, consistent with early-stage cardiomyocytes. RT-PCR studies demonstrated the expression of several cardiac-specific genes and transcription factors. Extracellular electrograms were characterized by a sharp component lasting 30 ± 25 milliseconds, followed by a slow component of 347 ± 120 milliseconds. Intracellular Ca2+ transients displayed a sharp rise lasting 130 ± 27 milliseconds and a relaxation component lasting 200–300 milliseconds. Positive and negative chronotropic effects were induced by application of isoproterenol and carbamylcholine, respectively. In conclusion, the human ES cell–derived cardiomyocytes displayed structural and functional properties of early-stage cardiomyocytes. Establishment of this unique differentiation system may have significant impact on the study of early human cardiac differentiation, functional genomics, pharmacological testing, cell therapy, and tissue engineering.

ADP Ribosylation Factor 6 Binding to Phosphatidylinositol 4,5-Bisphosphate-Containing Vesicles Creates Defects in theBilayer Structure: An Electron Spin Resonance Study

The effects of binding of myristoylated ADP ribosylation factor 6 (myr-ARF6), an activator of phospholipase D (PLD), to a model membrane were investigated using an electron spin resonance (ESR) labeling technique. Initial studies were conducted in vesicles composed of 1-palmitoyl-2-oleoyl phosphatidylethanolamine, dipalmitoylphosphatidylcholine, phosphatidylinositol 4,5-biphosphate (PIP 2), and cholesterol. Recombinant ARF6 binding significantly enhances defects in both the headgroup and acyl-chain regions of the membrane, which are revealed by the emergence of sharp components in the spectra from a headgroup label, 1,2-dipalmitoylphosphatidyl-2,2,6,6-tetramethyl-1-piperidinyloxy-choline (DPPTC), and a chain label, 10PC, after myr-ARF6 binding. Binding of non-myristoylated ARF6 (non-ARF6) shows markedly reduced effects. Interestingly, no change in spectra from DPPTC was observed upon myr-ARF6 binding when PIP 2 in the vesicles was replaced by other negatively charged lipids, including phosphatidylinositol, phosphatidylserine, and phosphatidylglycerol, even when normalized for charge. The production of the sharp peak appears to be a specific event, because another GTP binding protein, CDC42, which binds PIP 2 and activates PLD, fails to induce changes in vesicle structure. These results suggest a previously unappreciated role for ARF in mediating a protein/lipid interaction that produces defects in lipid bilayers. This function may serve as an initial event in destabilizing membrane structure for subsequent membrane fusion or biogenesis of vesicles.

Rheological and microstructural evolution of Carrara marble with high shear strain: results from high temperature torsion experiments

This study investigated the rheological and microstructural evolution of Carrara marble deformed to large shear strain to understand how dynamic recrystallization and lattice-preferred orientation (LPO) are related to strain softening processes. Solid cylinders of Carrara marble were deformed in torsion up to a shear strain of γ=11 at constant twist rates, which correspond to a shear strain rate of 3×10−4s−1 at the outer surface, and at temperatures of 1000 and 1200K (727 and 927°C, respectively). For the initial grain size of 150μm, these conditions are within the dislocation creep regime.Substantial changes in both rheology and microstructure were observed as the marble deformed to high shear strain at 1000K (1200K). A peak stress was reached at about γ=1 (γ=0.5) followed by moderate strain weakening. An apparent steady-state flow stress was obtained at high shear strain of γ>5 (γ>2). The stress exponent n decreased slowly with strain from 10 (γ=1) to 6 (γ=9) at 1000K, but it remained approximately constant at 1200K (n around 10). At the maximum reached shear strain of γ=11 (γ=8.5), the marble had almost completely recrystallized to a fine grain size of about 10μm (20μm). A secondary foliation developed in the recrystallized matrix, which is at a large oblique angle to the shear zone boundary (SZB). LPO was measured by electron backscatter diffraction (EBSD). For both temperatures, the LPO evolved from an oblique deformation texture to a very sharp and symmetric single orientation component with r{101̄4} parallel to the shear plane and a〈1̄21̄0〉 parallel to the shear direction. It is concluded that strain weakening was associated with the development of a strong LPO during dynamic recrystallization to a finer grain size. Mechanical and microstructural steady-state is only reached at large shear strain. The steady-state lattice and grain shape fabrics can hardly be used as shear sense indicators in such recrystallized calcite mylonites.

Observations of the Interstellar Medium in the Magellanic Bridge

We present ultraviolet and optical spectra of DI1388, a young star in the Magellanic Bridge, a region of gas between the Small and Large Magellanic Clouds. The data have signal-to-noise ratios of 20–45 and a spectral resolution of 6.5 kms −1 . Interstellar absorption by the Magellanic Bridge at vLSR ≈ 200 kms −1 is visible in the lines of C I, C II, C II*, C IV, N I, O I, Al II, Si II, Si III, Si IV, S II, Ca II, Fe II, and Ni II. The relative gas-phase abundances of C II, N I, O I, Al II, Si II, Fe II, and Ni II with respect to S II are similar to those found in Galactic halo clouds, despite a significantly lower metallicity in the Magellanic Bridge. The higher ionization species in the cloud have a column density ratio N(C +3 )/N(Si +3 ) ∼ 1.9, similar to that inferred for collisionally ionized Galactic cloud interfaces at temperatures ∼ 10 5 K. We identify sub-structure in the stronger interstellar lines, with a broad component (FWHM ∼ 20 kms −1 ) at ∼ 179 kms −1 and a sharp component (FWHM ∼ 11 kms −1 ) at 198 kms −1 . The abundance analysis for these clouds indicates that the feature at 198 kms −1 consists of a low electron density, mainly neutral gas that may be associated with an interface responsible for the highly ionized gas. The 179 kms −1 cloud consists of warmer, lower density gas that is partially ionized. Subject headings: Galaxies: abundances — ISM: abundances — Magellanic Bridge — ISM: structure

Antiferromagnetic order and phase transitions in GdS as studied with X-ray resonance-exchange scattering

We report on X-ray resonance exchange and neutron scattering of metallic GdS. At the LII and L III absorption edges of Gd, resonance enhancements of more than two orders of magnitude over the non-resonant magnetic scattering are observed. Polarisation analysis proves that these enhancements are due to dipolar transitions from the 2p to the 5d states. The branching ratio between the LII and L III edges of 2.5 suggests a polarisation of the 5d electrons in the ground state. The antiferromagnetic order is of type II in the fcc lattice. Single crystal diffraction of hot neutrons suggests that the spin direction lies within the (111) planes with a value for the sublattice magnetisation of 6.51(3) . The critical exponent for the sublattice magnetisation has a value of β = 0.38(2) in agreement with a pure Heisenberg model. Above T N, a sharp component persists in the critical diffuse scattering. Lattice distortions give indications for two additional low-temperature phase transitions at about 49 K and 32 K. We argue that these transitions are not connected to spin reorientations and discuss the possible influence of fourth-order exchange interactions.

Texture development of calcite by deformation and dynamic recrystallization at 1000 K during torsion experiments of marble to large strains

Torsion deformation experiments were performed on solid cylinders of Carrara marble at high temperature (1000K) and constant twist rate (about 4×10−4rads−1) to large twist angles (between 80° and 840°). These conditions correspond to simple shear deformation at constant shear strain rate (3×10−4s−1) and variable amounts of shear strain γ of 1, 2, 5 and 11 at the outer mantle of the sample cylinders. Lattice preferred orientations (LPO) were measured on polished thin sections using automated electron backscatter diffraction (EBSD) to analyze the microtextures in orientation imaging micrographs (OIM).Shear deformation produced first a microstructure of elongated grains with shape and orientation close to the finite strain ellipse of the imposed shear strain (γ=1 and 2). A deformation texture developed with monoclinic sample symmetry and an oblique c-axis distribution relative to the shear plane. With increasing shear, the marble recrystallized by subgrain rotation and nucleation of small grains, starting along grain boundaries, which ultimately replaced the whole deformation microstructure. A steady-state recrystallization microstructure evolved with nearly equant grains of about 10μm in size (γ=5 and 11). The LPO changed completely from the monoclinic deformation texture into a distribution with a sharp single orientation component with r{101̄4} parallel to the shear plane and a〈1̄21̄0〉 parallel to the shear direction. This recrystallization texture has orthorhombic symmetry with respect to shear plane and shear direction. During the transition, the applied flow stress decreased.Simple shear deformation of calcite was modeled with the self-consistent polycrystal plasticity theory. It included a model for dynamic recrystallization based on a balance between growth and nucleation. Model results agree with experimental data if slip on r{101̄4}a〈1̄21̄0〉 is introduced as a potential slip system for calcite. In that case, the steady-state recrystallization texture has an “easy slip” preferred orientation. The hypothesis remains speculative until this slip system is actually confirmed by direct observation.

On the Multielectron Dissociative Ionization of Some Cyclic Aromatic Molecules Induced by Strong Laser Fields

The interaction of strong laser fields (4 × 1016 W/cm2) with cyclic aromatic molecules (furan, pyrrole, pyridine, and pyrazine) has been studied at λ = 790 nm. The fragmentation processes of multiply charged transient molecular ions were analyzed by means of a time-of-flight (TOF) spectrometer. Most ion peaks consisted of one broad and one sharp component. From the analysis of the peak profiles the kinetic energies of the molecular and atomic fragment ions have bean measured. On the basis of these energy values and the estimated charge separation distances, it is concluded that, for furan, it is probable that Coulomb explosion takes place in multiple charged parent ions with deformed molecular structure. The doubly charged parent ions of furan and pyrrole fragments through charge separation processes. At higher charged transient parent ions the fragmentation proceeds through direct (instantaneous) process. Moreover, there is evidence that, at least for furan, the ionization process takes place via a direct field ionization mechanism. Pyridine and pyrazine multiple charged ions seem to follow different dissociation routes. The abundance ratios C+/A+ (A = N, O) for the singly charged atoms were found to be equal to the stoichiometric ratio for all the molecules studied, while a divergence has been observed for the C2,3+/A2,3+ (A = N, O) ratios.

Strong narrow-band electron cyclotron emission from a mirror plasma heated by electron cyclotron waves

Strong electromagnetic radiation is observed in a narrow band slightly above the frequency of a heating wave that is absorbed by electrons near the electron cyclotron resonance layer in a magnetic beach. The frequency spectrum consists of a sharp component and a broad background, which is enhanced by more than 30 dB and 10 dB, respectively, above the radiation of thermal electrons. This observation is explained in terms of cyclotron radiation emitted by electrons, localized in a magnetic mirror, that are resonantly heated and bunched by a strong monochromatic wave.

Characterization of SOI wafers by X-ray CTR scattering

The CTR scattering around the 1 1 1 Bragg point was observed from two kinds of SOI wafers, SIMOX and UNIBOND ® wafers. The intensity profile of the CTR scattering from the UNIBOND wafer showed that the top Si layer had a good crystal quality and its interfaces were very flat. The profile from the SIMOX wafer consisted of sharp and broad components, indicating that the crystalline quality around the interfaces were poor for both the top Si layer and the substrate. It was also influenced by an ordered SiO 2 in the buried oxide layer.

Cholesterol Superlattice Model Is Compatible with the Calorimetric Behavior of Cholesterol/Phosphatidylcholine Bilayers

Previous studies have demonstrated that addition of cholesterol to bilayers of saturated phosphatidylcholine (PC) has dramatic effects on the gel-to-liquid phase-transition characteristics of the bilayer. In particular, the enthalpy of the original sharp transition diminishes strongly with increasing cholesterol concentration and a new, broad transition component appears. The enthalpy of the sharp component becomes essentially zero close to the cholesterol mole fraction of 0.25, while the enthalpy of the broad component achieves a maximum near this mole fraction. The broad component typically becomes undetectable when the cholesterol mole fraction is increased to 0.5. In this study we show that these previous experimental findings are fully compatible with a simple model proposing that (i) the cholesterol molecules tend to adopt a regular, superlattice-like lateral distribution within the PC matrix and (ii) the contribution of an acyl chain to the sharp and broad components is critically dependent on its ...

Temperature Dependence of the Yb 4f Spectra in Yb4Bi3Probed by Photoemission Spectroscopy

We have performed a photoemission study of Yb 4 Bi 3 . The valence band spectra have shown no multiplet structures associated with the trivalent Yb and revealed that the mean valence of the Yb ion is very close to 2.0. The divalent Yb 4f spectra have shown strong surface components besides weak but sharp bulk components. The surface 4f level shift is about 0.45 eV (300 K), 0.48 eV (150 K) and 0.54 eV (20 K). A clear energy shift of the bulk Yb 4f peaks toward EF with decreasing temperature has been observed, although Yb 4 Bi 3 shows neither phase transition nor crossover. Such an unusual peak shift of the bulk component may originate from a change of the lattice constant with decreasing temperature. The observed narrowing of the bulk 4f peaks is thought to be due to a phonon broadening (∼7 k B T ).

Cardiac- and noncardiac-related coherence between sympathetic drives to muscles of different human limbs.

Partial coherence analysis was used to evaluate the extent to which coherence between resting muscle sympathetic activity (MSA) in different pairs of limbs in humans is explained by the common baroreceptor input and by other noncardiac-related factors. Multiunit MSA in two or three nerves, arterial blood pressure, and electrocardiogram were recorded simultaneously. Correlated MSA consisted of a sharp periodic component at the heart rate and a wideband component of relatively low power distributed between 0 and 2-2.5 Hz. Quantitative analysis revealed stronger coupling between MSAs in close limbs than in distant limbs (peak coherence leg-leg, 0. 94 +/- 0.03; arm-leg, 0.76 +/- 0.11). Furthermore, the wideband component, unaffected by partialization with circulatory signals, was significantly stronger between leg-leg (0.67 +/- 0.10) than between arm-leg pairs (0.29 +/- 0.10), i.e., noncardiac-related components explained 71% of leg-leg and 38% of arm-leg coherences at the frequency of the heart. Our results indicate that nonuniform relationship exists between resting sympathetic outflow to muscles in close and distant extremities which is, however, partially masked by the effect of the common rhythmic baroreceptor input.

<I>In-Situ</I> Micro-Raman Scattering Investigation of LaNi<SUB>3.4</SUB>Co<SUB>1.2</SUB>Mn<SUB>0.1</SUB>Al<SUB>0.3</SUB> Metal Hydride under Hydrogen Atmosphere

In-situ micro-Raman scattering spectra of LaNi 3.4 Co 1.2 Mn 0.1 Al 0.3 metal hydride were observed in a hydrogen atmosphere at pressures up to 1 MPa using a specially designed micro-pressure cell. For the fresh surface created by cracking, broad components near 1600 cm -1 and 2900 cm -1 appear and grow in the depolarized Raman spectra as the pressure increases to the β phase region. In addition to this, sharp components appear near 3000 cm -1 in the polarized spectra in both α and β phases. The sharp and broad components are assigned to oxides and vibration of hydrogen atoms in the metal hydride, respectively. On the other hand, characteristic Raman spectra rarely appear for the polished flat surface. These results indicate that the catalytic fresh surface area created by cracking plays an important role in the hydride formation.

Two Length Scales and Crossover Behavior in the Critical Diffuse Scattering fromV2H

We have observed two length scales in a ${\mathrm{V}}_{2}\mathrm{H}$ crystal above the ${\ensuremath{\beta}}_{1}\ensuremath{-}{\ensuremath{\beta}}_{2}$ phase transition. A sharp Lorentzian profile in the critical diffuse scattering was superimposed on a broader one for a low-energy x-ray experiment in reflection, while no sharp component appeared in transmission at high energy. For the sharp component, we extracted tricritical exponents ${\ensuremath{\nu}}_{1}$ and ${\ensuremath{\gamma}}_{1}$ at small reduced temperatures $t$, where fluctuations are coherent over large distances. For larger $t$, where the correlation length is comparable to an effective defect size, there is a crossover to altered exponents.

Multiple-overtone resonance Raman scattering and fluorescence from I2 species adsorbed on silver surfaces

A detailed excitation profile of a Raman progression consisting of up to six overtones and a fundamental band at 123 cm−1 observed from iodide adsorbed on an electrochemically roughened silver surface at 20 K is analyzed. The excitation profile was constructed from 77 spectra obtained by tuning the laser wavelength in ∼0.25 nm steps through the spectral range 409 nm–433 nm. The shift between resonances in the excitation profile, corresponding to the spacing between vibronic levels in the excited state, is also equal to 123 cm−1 indicating that the ground state and excited state potential energy surfaces have the same shape. Only two distinct resonances spaced three vibrational quanta apart were evident in the profile for each band in the progression. Curve fitting of the Raman band shapes indicates that each overtone is composed of one sharp and one broad band, whereas the fundamental contains only one sharp component. The measured width of the fundamental was less than 2.5 cm−1 FWHM, limited by the instrument function. It is proposed that the sharp Raman bands represent a normal vibrational mode of a surface-adsorbed I2-like species with the width determined by the intrinsic vibrational dephasing in the ground state. On the other hand, the broad Raman bands reflect vibronic coupling between different I2-like species adsorbed on the same Ag cluster. The broad bandwidths result from both dephasing associated with the vibronic coupling and the intrinsic vibrational dephasing. Other weak emission bands are attributed to resonance fluorescence corresponding to direct transitions from higher vibronic levels of the excited state to the ground state. An emission at 429.9 nm is assigned to exciton recombination in small silver iodide clusters which are formed after spontaneous oxidation of the iodide-modified silver surface.

Texture and secondary extinction measurements in Al\\Ti stratified films by X-ray diffraction

In the present work the effects of secondary extinction has been studied using standard X-ray diffractometer and texture diffractometer techniques. For this purpose the texture of Al\\Ti stratified films have been measured and evaluated. It is shown that these films have a very sharp single component texture. Therefore the evaluation and the interpretation of the measurement data is only possible when secondary extinction correction is carried out. The effect of secondary extinction is evaluated on the 111 pole figures of the stratified films with different layer pair numbers. The volume fraction of the main texture component is calculated from pole figures and it is shown that the grains of the films are practically completely oriented with 〈111〉 crystallographic direction parallel to the film surface normal. Moreover in the case of pole density measurements the secondary extinction values themselves are simultaneously calculated.

Texture development of deep drawn aluminum cups

The differently heat-treated aluminum sheets (fully recrystallized or partially recrystallized) of 1 mm thick were deep drawn from a round shape with 60 mm diameter to a drawing ratio of 1.8. The initial texture of the fully recrystallized Al-sheet can be described by a very strong {001} cube texture and a weak beta-fiber component. The initial texture of the partially recrystallized Al-sheet consisted of the cube and the beta-fiber components with same amount of fraction. Ears with 2 mm height formed at 0° and 90° to the initial rolling direction in the drawn cup of the fully recrystallized sheet. And by partially recrystallized sheet the ears were found at 0° 45° and 90° After deep drawing, the maximum intensity of ODF was reduced to ca. 25% of the initial one by the fully recrystallized sheet and ca. 50% by the partially recrystallized sheet. The spread ranges of the orientation components were expanded. The sharp cube component of initial texture remained after deep drawing but the weak beta-fiber disappeared by the fully recrystallized sheet and some other components are formed by the partially recrystallized sheet.