Unusual Fine Structure Research Articles

Thin yttrium iron garnet films grown by pulsed laser deposition: Crystal structure, static, and dynamic magnetic properties

Pulsed laser deposition has been used to grow thin (10–84 nm) epitaxial layers of Yttrium Iron Garnet Y3Fe5O12 (YIG) on (111)–oriented Gadolinium Gallium Garnet substrates at different growth conditions. Atomic force microscopy showed flat surface morphology both on micrometer and nanometer scales. X-ray diffraction measurements revealed that the films are coherent with the substrate in the interface plane. The interplane distance in the [111] direction was found to be by 1.2% larger than expected for YIG stoichiometric pseudomorphic film indicating presence of rhombohedral distortion in this direction. Polar Kerr effect and ferromagnetic resonance measurements showed existence of additional magnetic anisotropy, which adds to the demagnetizing field to keep magnetization vector in the film plane. The origin of the magnetic anisotropy is related to the strain in YIG films observed by XRD. Magneto-optical Kerr effect measurements revealed important role of magnetization rotation during magnetization reversal. An unusual fine structure of microwave magnetic resonance spectra has been observed in the film grown at reduced (0.5 mTorr) oxygen pressure. Surface spin wave propagation has been demonstrated in the in-plane magnetized films.

Microtwinning in highly nonstoichiometric VO x thin films

Both pulsed-DC biased and commercial ion-beam sputtered VO x thin films maintain a face-centered-cubic nanocrystalline phase, even for stoichiometries of x > 1.5, which is well outside the bulk equilibrium solubility range for cubic VO x . Many of these highly nonstoichiometric films exhibit a high density of microtwins, which give rise to unusual fine structure in the selected-area electron diffraction patterns, namely: an additional defect ring; a significant broadening of the {2 0 0} ring; pairs of parallel rod features which are tangent to the additional defect ring; and additional fine-structure features between the {2 0 0} and {2 2 0} rings. The formation of the microtwins is correlated with the coalescence of vanadium vacancies along the {1 1 1} twin planes in the crystalline lattice.

Fine structure of decametric type II radio bursts

We have performed a comparative analysis of the fine structure of two decametric type II bursts observed on July 17 and August 16, 2002, with the 1024-channel spectrograph of the UTR-2 radio telescope in the frequency range 18.5-29.5 MHz and with the IZMIRAN spectrograph in the frequency range 25-270 MHz. The August 16 burst was weak, ∼ 2-5 s.f.u., but exhibited an unusual fine structure in the form of broadband fibers (∆fe > 250-500 kHz) that drifted at a rate characteristic of type II bursts and consisted of regular narrow-band fibers (∆fe > 50-90 kHz at 24 MHz) resembling a fiber bundle. The July 17 burst was three orders of magnitude more intense (up to 4500 s.f.u. at 20 MHz) and included a similar fiber structure. The narrow fibers were irregular and shorter in duration. They differed from an ordinary fiber bundle by the absence of absorption from the low-frequency edge and by slow frequency drift (slower than that of a type II burst). Both type II bursts were also observed in interplanetary space in the WIND/WAVES RAD2 spectra, but without any direct continuation. Analysis of the corresponding coronal mass ejections (CMEs) based on SOHO/LASCO C2 data has shown that the radio source of the type II burst detected on August 16 with UTR-2 was located between the narrow CME and the shock front trailing behind that was catching up with the CME. The July 17 type II fiber burst also occurred at the time when the shock front was catching up with the CME. Under such conditions, it would be natural to assume that the emission from large fibers is related to the passage of the shock front through narrow inhomogeneities in the CME tail. Resonant transition radiation may be the main radio emission mechanism. Both events are characterized by the possible generation of whistlers between the leading CME edge and the shock front. The whistlers excited at shock fronts manifest themselves only against the background of enhanced emission from large fibers (similar to the continuum modulation in type IV bursts). The reduction in whistler group velocity inside inhomogeneities to 760 km s −1 may be responsible for the unusually low drift rate of the narrow fibers. The magnetic field inside inhomogeneities determined from fiber parameters at 24 MHz is ∼0.9 G, while the density should be increased by at least a factor of 2.

Ultrastructural organization of Alicyclobacillus tolerans strain K1T cells

Electron microscopy examinations of thin sections and freeze-fracture replicas revealed the specific ultrastructural features of Alicyclobacillus tolerans strain K1(T). In particular, the cell wall displayed an ultrastructure typical of gram-positive bacteria and consisted of a thin murein layer (50-60 A in thickness); cells exhibited a surface S-layer constituted by large hexagonally packed (p6-symmetry) rod-shaped subunits of 150-160 A in diameter and 200 A in height. In the cytoplasmic membrane, there were intramembrane vesicular structures that sometimes appeared as large leaflets in the central part. The cytoplasm contained numerous vesicular inclusions covered with a monolayered wall, dissimilar to bilamellar lipid membranes. Endospore coats displayed an intricate structure and consisted of three thick layers; the outer layer had an unusual fine structure; the exosporium was also found.

MODE-LOCKING IN QUASIPERIODICALLY FORCED SYSTEMS WITH VERY SMALL DRIVING FREQUENCY

In this paper we consider the dynamics of the sine circle map with quasiperiodic forcing and very small forcing frequency. One of our goals is to compare the dynamics of our system with those of the system with larger values of the frequency. In particular we discovered an unusual fine structure of the mode-locking regions which disappears with increase in the forcing frequency. We investigated how this fine structure depends on the system parameters and described the bifurcations which occur on the boundaries of the mode-locking regions.

High-Resolution Survey of the Visible Spectrum of NiF by Fourier Transform Spectroscopy

High-resolution spectra of NiF have been recorded in emission by Fourier transform spectroscopy using a very stable discharge source. The 0–0 bands of 14 electronic transitions have been studied, 6 of them for the first time. This work confirms the presence of 5 low-lying spin components X2Π3/2, [0.25]2Σ+, [0.83]A2Δ5/2, [1.5]B2Σ+, and [2.2]A2Δ3/2 as known from previous laser-induced fluorescence experiments. Eight electronic states are now identified in the 18 000–24 000 cm−1 range above the ground X2Π3/2 state. Electronic assignments for these excited states are not always obvious because of violations of the selection rules and unusual fine structure parameters. We think that some of the upper states are spin components of quartet states. In such a congested spectrum, high-resolution spectra are best analyzed in conjunction with an energy level diagram constructed mainly by dispersed low resolution laser-induced fluorescence.

Huge longitudinal resistance maxima at fractional filling factors

Very large resistance maxima can be observed in the longitudinal magnetoresistance of a narrow single quantum well. They exist only at certain fractional filling factors and are clearly related to the coupling of the electron to the nuclear spin system. In resistively detected NMR experiments, which are possible in this system, a very unusual fine structure of the resonance lines is observed, which hints towards an unusual coupling between the electron and nuclear system.

Investigation of the role of a surface patch in the self-association of Chromatium vinosum high potential iron-sulfur protein

The role of a flattened, relatively hydrophobic surface patch in the self-association of Chromatium vinosum HiPIP was assessed by substituting phenylalanine 48 with lysine. The reduction potential of the F48K variant was 26 mV higher than that of the wild-type (WT) recombinant (rc) HiPIP, consistent with the introduction of a positive charge close to the cluster. Nuclear magnetic resonance spectroscopy (NMR) revealed that the electronic structure of the oxidized cluster in these two proteins is very similar at 295 K. In contrast, the electron transfer self-exchange rate constant of F48K was at least 15-fold lower than that of the WT rcHiPIP, indicating that the introduction of a positive charge at position 48 diminishes self-association of the HiPIP in solution. Moreover, the substitution at position 48 abolished the fine structure in the g z region of the electron paramagnetic resonance (EPR) spectrum of oxidized C. vinosum rcHiPIP recorded in the presence of 1 M sodium chloride. These results support the hypothesis that the flattened, relatively hydrophobic patch mediates interaction between two molecules of HiPIP and that freezing-induced dimerization of the HiPIP mediated by this patch is responsible for the unusual fine structure observed in the EPR spectrum of the oxidized C. vinosum HiPIP.

Light and electron microscope observations onNephroselmis gaoae sp. nov. (Prasinophyceae)

Nephroselmis gaoae sp. nov. is described on the basis of light and electron microscope observations of cultured material originally collected and isolated from seawater of Jiaozhou Bay, Qingdao, China. The periplasts on the cell body and flagella are covered by five types of scales, two types on the flagella and three on the body. Among these, the morphology and the number of spines of large stellate body scales differ remarkably from those of previously described species ofNephroselmis. Apart from these, the unusual fine structure of the eyespot (stigma) is very characteristic. As in the other species ofNephroselmis, the eyespot lies immediately under the two-membraned chloroplast envelope; unlike the others, however, it is not composed of a number of osmiophilic globules, but consists of about 14 curved rod-shaped osmiophilic bodies arranged loosely and randomly. This feature distinguishes the present new species not only from the other species ofNephroselmis but also from the other motile algal species, the eyespots structure of which had been previously described.

Spectroscopic properties of conducting Langmuir–Blodgett films obtained by the ‘‘homodoping strategy’’

Experimental IR properties of conducting (ODS-TCNQ)ξ(TCNQC18)1−ξ Langmuir–Blodgett (LB) films are presented and discussed within the frame of the electron-vibration coupling model of Rice, extended to take into account the modifications induced by grafting an alkyl chain to the TCNQ molecule. The quite good theoretical fit of experimental spectra (including unusual fine structure of agν5 vibronic band) indicates that (i) optical as well as electrical properties of the films can be accounted for by the existence of dimers the type of which depends on ξ; and (ii) inside the layer, an energy transfer takes place between the electroactive part and the alkyl chain via a two step coupling process.

Unusual fine structure of ν5 vibronic band in absorbance of conducting TCNQ LB films obtained by the “homodoping” strategy

Experimental IR properties of conducting (ODS-TCNQ) 0,33(TCNQC 18) 0,66.LB films are presented and discussed within the frame of the electron-vibration coupling model of Rice, extended to take into account the modifications induced by grafting an alkyl chain to TCNQ molecule. Quite good theoretical fit of experimental spectra (including unusual fine structure of a g ν 5 vibronic band) indicates that, inside the layer, an energy transfer takes place between the electroactive part and the alkyl chain via a two step coupling process.

A barrage of relativistic solar particle events

During a 4‐month period beginning July 25, 1989, the Sun released an unprecedented barrage of seven relativistic solar particle events detectable with ground‐based instrumentation. These “ground level enhancements” (GLE) are the first to occur in the present sunspot cycle, and they include the largest event observed since 1956. The seven new events bring to 44 the number of GLE observed since systematic observations began 50 years ago. Several events are distinguished by unusual fine structure in their time profiles, and one event exhibits an extraordinary spike‐like feature at event onset.

Life on a regular polygon: Maps induced by spatially extended prey-predator equations

We explore the time evolution of a set of integro-differential equations that describes a spatially inhomogenious prey-predator system. These equations are reduced to a set of nonlinearly coupled maps, which, when iterated, converge to spatial modes that undergo 2 n -cycles in time. The average density of the predator population is used as a collective coordinate. Using it as the independent variable and the reproduction rate of the predator as the bifurcation parameter, a bifurcation portrait that exhibits unusual fine structure is produced. The portrait also shows bifurcations that are not signaled by jacobian eigenvalues exceeding unity in magnitude. The various branches are identified with different spatial modes. Eigenportraits are also calculated. These are diagrams of all the jacobian eigenvalues plotted as a function of the bifurcation parameter and can be useful in identifying families of spatial modes. It is found that the degree of degeneracy of the eigenvalues whose magnitude is unity is predictive of the number of branches that emanate from each bifurcation.

Spin-orbit interactions and dynamical Jahn–Teller effect in the 4E states of Mn2+ in cubic and nearly cubic symmetry

A very detailed analysis of the fine structure of the 4E(G) state of Mn2+ in cubic and nearly cubic clusters is presented to account for the unusual fine structure observed in ZnSe:Mn. First, experimental results are reported which show that the spin-orbit interaction in the 4E(G) state of Mn2+ in ZnSe is about one half of that previously observed in cubic or nearly cubic clusters as MnS4, MnBr4, and MnCl4 and that the state Γ8 is neatly shifted with respect to the Kramers doublets Γ6 and Γ7. Second, a model is elaborated which shows that second-order spin-orbit interactions reduced by a Jahn–Teller coupling to E vibrational modes accounts well for the observed overall splitting of the 4E(G) state in the studied clusters and that fourth-order spin-orbit interactions correctly describe the shifts of the Γ8 state. The validity of the perturbation schemes is discussed and the results are compared to those obtained from a complete diagonalization in the d5 configuration.

Ultrastructure of the zoospore of Blastocladia ramosa (Blastocladiales)

Species of Blastocladia, unlike other members of the order Blastocladiales, have an obligately fermentative metabolism. The ultrastructure of the zoospores of Blastocladia ramosa is described and compared with that of zoospores of aerobic members of the Blastocladiales. Zoospores of Blastocladia ramosa are structurally similar to other blastocladialean zoospores in that they have (i) a nuclear cap composed of aggregated ribosomes delimited by an envelope of endoplasmic reticulum; (ii) a posteriorly located nucleus; (iii) nine sets of microtubules that surround the nucleus and nuclear cap; and (iv) a striated rootlet associated with the kinetosome. Zoospores of Blastocladia ramosa differ by having mitochondria with unusual fine structure and by lacking microbodies and microbody – lipid globule complexes. As shown by enzymatic digestion and staining, glycogen appears to be the primary storage material in the zoospore. Structures which resemble water expulsion vacuoles are present. The morphological differences between zoospores of Blastocladia ramosa and other zoospores of the Blastocladiales appear to be related to physiological differences.

Further studies on Nephroselmis and its allies (Prasinophyceae). I. The question of the genus Bipedinomonas

Based on a series of collections made in New Zealand it is concluded that Nephroselmis longifilis and Bipedinomonas pyriformis are identical species, for which the correct name is Nephroselmis pyriformis (N. Carter) comb. nov. A detailed examination by light and electron microscopy is given, using material from geographically widely separated areas, including Greenland, the North Sea, a shallow Danish Fiord, Thailand and New Zealand. N. pyriformis is a temperature– and halotolerant species, as shown by its known range of occurrence at temperatures from 2.3°C (West Greenland) to ca. 28°C (Thailand) and at salinities between 3 and 36%o. Features of fine structural interest include details of the scaly covering on the flagellar and cell surfaces, the former very similar to those on the flagella of Tetraselmis cordiformis, a quadriflagellate prasinophyte. Within the cell, the pyrenoid shows an unusual fine structure, being penetrated by a number of membrane–lined pockets, in which the membranes are continuous with thylakoids. N. pyriformis is compared with other members of the genus, and a list of the few known species is included.

The single-crystal electron spin resonance spectra of dichloro- and dibromo-oxobis(N,N,N′,N′-tetramethylurea)vanadium(IV); weak two-dimensional exchanging systems

The single-crystal e.s.r. spectra of [VOX2(tmu)2], where X = Cl or Br and tmu =N,N,N′,N′-tetramethylurea, at Q-band frequencies and over the temperature range 300–4.2 K are reported. Unusual fine structure, which does not correlate with the presence of an integral number of strongly interacting vanadium centres, was observed in the range ca.170–120 K. The spectra have been successfully simulated on the basis of a weak isotropic electronic exchange interaction, J0, within a two-dimensional layer. Parameters used were g∥= 1.941 ± 0.002, g⊥= 1.979 ± 0.002, A∥=–203 ± 2 G, A⊥=–69 ± 2 G, and J0= 130 ± 2 G (antiferromagnetic).

ON THE UNUSUAL SPECTROSCOPIC BEHAVIORS OF 3-METHYL-10-DODECYLISOALLOXAZINE(AMPHIPHILIC FLAVIN ANALOGUE)

Abstract At room temperature in aqueous solution, the visible absorption peak of the title isoalloxazine (III) gives a three-banded fine structure, which has been believed to appear only in enzymatic hydrophobic region, in nonpolar solvents, or at extremely low temperature. On the other hand, another amphiphilic flavin 3-hexadecyl-10-butylisoalloxazine (II) has not such a fine structure. Thus, the unusual fine structure in (III) was attributed to aggregative “stacking” of the isoalloxazine heads, and the difference in the stacking mode between (II) and (III) was discussed.

Effect of neutron irradiation on single-crystalV3Si: Sound velocity, magnetic susceptibility, and upper critical field

We have measured the sound velocity, magnetic susceptibility, and upper superconducting critical field ${H}_{c2}$ of a single crystal of V $_{3}\mathrm{Si}$ as a function of neutron irradiation up to a fluence of 22.2 \ifmmode\times\else\texttimes\fi{} ${10}^{18}$ n/${\mathrm{cm}}^{2}$. Very small doses affect the structural transormation, while leaving the superconducting transition temperature ${T}_{c}$, the soft acoustic shear mode, the susceptibility $\ensuremath{\chi}$, and ${H}_{c2}$ essentially unaltered. At higher defect concentrations, the strong anomalous temperature dependences of $\ensuremath{\chi}$ and the elastic modulus ${c}_{s}$ are considerably reduced, although significant anomalies remain for the highest fluence (which lowers ${T}_{c}$ from 17.2 to 7.4 K). Within models which assume unusual fine structure in the electronic density of states near the Fermi level, our results imply that defects produce broadening and smearing of the density-of-states function.

Fine structure due to magnetic dipole coupling in the low temperature EPR spectrum of Rb2Cu(SO4)2⋅6H2O

A study of the EPR spectrum of single crystals of Rb2Cu(SO4)2⋅6H2O over the temperature range 290 to 115 K is reported. Below ∼240 K unusual fine structure occurs for certain orientations of the magnetic field H, consisting of eight equally spaced lines when H is approximately along the z molecular axis and five equally spaced lines when H lies along the y molecular axis of the Cu(H2O)62+ ion. The fine structure may be explained largely in terms of a magnetic dipole coupling with four neighboring copper (II) ions, each of which produces an approximately equal splitting of the EPR lines at the central copper (II) ion; the five line pattern occurs when the hyperfine interaction with the copper nucleus is small, while the eight line pattern results from a hyperfine interaction which is essentially equal to the magnetic dipole interactions (these each being ∼120 G). Spectra were simulated by considering the point magnetic-dipole interactions with the ten nearest Cu(H2O)62+ ions using the expression K̂=g1g2β2 (1–3 cos2ϑ)/r3, where g1 and g2 are the g values of the two interacting ions, r is the distance between them, ϑ is the angle between the internuclear vector and the magnetic field, and β is the Bohr magneton. The resulting line shapes are in reasonable agreement with experiment for most orientations of the magnetic field in the (001) and (010) crystal planes. The agreement is significantly improved if the interaction with the two nearest copper (II) ions is ∼20% greater than that calculated using the simple magnetic dipole model, and it is shown that this is consistent with the unpaired electron density being represented as a quadrupole, as is required by the shape of the dx2y2 ground state orbital, rather than as a point charge. Further improvement occurs if a weak exchange coupling of J=+30 and J=−15 G takes place with the nearest and next-nearest copper ions, respectively, and if an anisotropic component to the background half-width is introduced.