Singular Peak Research Articles

Linear and nonlinear magnetic responses of weakly sintered YBa 2Cu 4O 8 ceramics of sub-micron scale grains

Weakly sintered ceramic samples of YBa 2Cu 4O 8 (124) are prepared as systems of Josephson-coupled sub-micron grains, with varying sintering time. The obtained ceramic systems are studied by observing fundamental and harmonic magnetic responses. Each specimen shows characteristic temperature dependence of the responses caused by intergrain ordering. The ordering temperature estimated by singular peak of the nonlinear response changes consistently with the sintering time, indicating that the coupling strength is systematically changed. Furthermore, dual anomalies of the nonlinear response are found. The results suggest that two different origins of nonlinear response inhere in the intergrain ordering.

UV–VIS–NIR spectroscopy study of sensitivity of single-wall carbon nanotubes to chemical processing and Van-der-Waals SWNT/SWNT interaction. Verification of the SWNT content measurements by absorption spectroscopy

Spectrophotometric measurements of a large number of suspensions of SWNTs-containing soots in aqueous solutions of a surfactant with known weight/volume ratio have been carried out. SWNTs were purified by two methods, by gas-phase oxidation and by centrifugation of suspension. In contrast with gas-phase oxidation, centrifugation does not lead to chemical modification of SWNTs and to irreversible waste of substance. It was shown that gas-phase oxidation, as compared with centrifugation, weakly (by 5%) enriches samples (in which more than 60% of SWNTs were burned) by SWNTs with large diameters. Gas-phase oxidation of nanotubes produces no shift of the van Hove singularity peak positions of solitary nanotubes. It increases relative height of the van Hove bands of solitary nanotubes due to predominant combustion of defective nanotubes. The red shift of the van Hove singularity peaks can be used as a qualitative measure of agglomeration. Comparison of suspension spectra after powerful centrifugation at 160 000g (spectra of solitary nanotubes) shows that different catalysts of the arc discharge synthesis (Ni/Co, Ni/Y, Ni/La, Ni/Ce, Ni/Gd, Ni/Pr) produce almost the same diameter set of SWNTs, but with different distribution. A careful examination of the spectrophotometric method of determination of the abundance of SWNTs in aqueous surfactant suspensions with known weight/volume ratio was carried out.

Reconstruction of electron spectra using singular component decomposition.

Reconstruction of electron spectra of medical accelerators from measured depth dose distributions is an attractive tool for commissioning of a Monte Carlo treatment planning system. However, the reconstruction method is an inverse radiation transport problem which is poorly conditioned, in the sense it may become unstable due to small perturbations in the input data. Predicting the sharp (delta-like) peak in the electron spectrum provides an additional challenge for the numerical reconstruction technique. To improve efficiency and robustness of the reconstruction technique, we developed an algorithm based on a separation of the electron spectrum into singular and regular components. We approximate the singular peak of the spectrum by a narrow weighted Gaussian function. The parameters of this Gaussian function are sought using only the fall-off and toe regions of the depth-dose curve. Analytical representation of the spectral peak by a Gaussian has benefit since only one weight and the mean and variance must be derived from the depth-dose curve instead of multiple spectra weights. The regular part of the spectrum is reconstructed from the residual depth-dose distribution using a variational method combined with a regularization technique to avoid the nonphysical oscillations. The effectiveness of the method is demonstrated by comparing predictions to "benchmark" spectra and depth-dose distributions from Monte Carlo simulation of medical accelerators.

Forced Convection Heat Transfer and Temperature Fluctuations of Lithium under Transverse Magnetic Fields

The MHD effects on a heat transfer of liquid lithium flowing in an annular channel were studied, using a newly constructed comparatively large-scale lithium loop. The data on the heat transfer characteristics were arranged in Nu-St diagrams where St=Ha2/Re. The diagrams indicate that Nu decreases as St increases as a whole trend. However, singular peaks of Nu were observed at about St=13, corresponding to the singular increments of temperature fluctuations, whereas the peaks occurred at St=1.5 in the previous experiment with a smaller channel. In considering a predominant MHD effect due to conductive wall duct, the current load factor KP for external circuit was taken into account. And Miyazaki number Mi=KPSt, which means the effective electromagnetic interaction, was adopted in substitution for St and the heater pin diameter was taken as the characteristic length in place of the conventional hydraulic equivalent diameter. Thus, an appreciably good agreement was obtained concerning the peaks at Mi=0.13 in the previous and at Mi=0.14 in the present experiments. Generation of vortex series in the singular phenomena was suggested from both the periodicity of temperature fluctuations in their PSD analysis and the proportionality between peak frequency and mean flow velocity, resulting in a 32 mm interval length of series.

Switching behavior and its strain dependence in epitaxial CrO/sub 2/ thin films

Chromium dioxide thin films grown epitaxially on TiO/sub 2/ substrates exhibited a strong in-plane uniaxial anisotropy. Field dependence of high frequency (10/sup 6/ Hz) transverse susceptibility (/spl chi//sub T/) measurements were used to probe the magnetic anisotropy and switching in CrO/sub 2/ films for varying temperature (10 to 300 K) and different orientations of the applied field with respect to the magnetic easy axis. Singular peaks in /spl chi//sub T/ were observed and are associated with the anisotropy and switching fields. The /spl chi//sub T/ data at low temperatures reveal an unusual variation of the singular peaks. This can be described by including magnetoelastic contributions resulting from the in-plane tensile strain in the film due to lattice mismatch with the substrate.

Mathematical quasicrystals with toric internal spaces, diffraction and rarefaction

Aperiodic crystals viewed as Delone sets of points on the real line, having an average lattice, are studied as congruence model λ-sets (physical space is Euclidean and the equivalent of the internal space is toric) in the context of cut-and-congruence λ-schemes, a new concept. When windows are finite point sets, the fractal rates of occupancy, at infinity, of the affine lattices associated with such Delone sets are shown to be simply related to the scaling exponents of the Fourier transform of the autocorrelation measure, completing results of Hof. These fractal rates of occupancy are named rarefaction laws. The case of the Thue–Morse quasicrystal, as a Meyer set, is explicitly developed. We present the arithmetics of 3-rarefaction phenomenon, the fractality of the Fourier transform of the autocorrelation measure. This new approach provides explicit formulae for singular continuous peaks and allows to discuss their possible extinction. In particular, this gives a possible sieve among Delone sets to be crystals in the new definition of a crystal by the IUCr in 1992. Ponctual scaling laws and the Bombieri–Taylor argument are considered.

Probing magnetic anisotropy effects in epitaxialCrO2thin films

The magnetic anisotropy in ferromagnetic chromium dioxide thin films ${(T}_{c}\ensuremath{\sim}393\mathrm{K})$ grown epitaxially on (100) ${\mathrm{TiO}}_{2}$ substrates, is probed using precise rf transverse susceptibility $({\ensuremath{\chi}}_{T})$ measurements. Singular peaks in ${\ensuremath{\chi}}_{T}$ are observed that are associated with the anisotropy $(\ifmmode\pm\else\textpm\fi{}{H}_{K})$ and switching $(\ifmmode\pm\else\textpm\fi{}{H}_{s})$ fields in ${\mathrm{CrO}}_{2}.$ Theoretical calculations of ${\ensuremath{\chi}}_{T}$ based on a simple coherent rotation model display remarkable agreement with the experimental data, indicating that these thin films behave like single-domain magnetic particles. Magnetoelastic contributions to the total anisotropy energy are needed to describe the evolution of ${\ensuremath{\chi}}_{T}$ peaks at lower temperatures.

Strain dependence and magnetic anisotropy in chromium dioxide thin films

AbstractField-dependent transverse susceptibility measurements based on a novel tunnel-diode oscillator (TDO) method were used to probe the magnetic anisotropy and switching in epitaxially grown CrO2 films on TiO2 substrates. The static field was applied in three different orientations (0°, 45° and 90° ) with respect to the magnetic easy axis. Singular peaks in the transverse susceptibility were observed that are associated with the anisotropy and switching fields in CrO2. Theoretical calculations based on a coherent rotation model display remarkable agreement with the experimental data. A new peak emerges at low temperatures and is identified to be a consequence of temperature-dependent magnetoelastic contributions resulting from the in-plane tensile strain in the films due to varying coefficients of thermal expansion in the film and the substrate.

Fluctuation-induced broadening of Mn2+ EPR lines in the incommensurate phase of Rb2ZnCl4 crystals

The EPR spectra of Mn2+ ions in Rb2ZnCl4 crystals is investigated in the vicinity of the transition from the paraelectric phase to an incommensurate modulated phase. When these crystals are cooled below the transition temperature Ti=304 K, a splitting of the resonance lines is observed in the singular spectrum. A one-harmonic model is used to discuss the contributions that fluctuations in the amplitude and phase of the incommensurate displacement wave make to the local width of the singular spectra. It is shown that anomalies in the local width of the low-temperature singular peaks observed in the vicinity of Ti are caused by amplitude fluctuations.

Comment on “Thermal conductivity ofYBa2(Cu1−xZnx)3O7−δ:Relation betweenxand δ ”

The interpretation of thermal conductivity measurements on ${\mathrm{YBa}}_{2}({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{)}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ by Houssa, Ausloos, and Cloots [Phys. Rev. B 56, 6226 (1997)] in terms of Zn substitution leading to electron doping and a concomitant shift in the Fermi level away from a van Hove singularity peak in the density of states is shown to be inconsistent with the wider body of experimental data.

Structure and properties of rapid thermal chemical vapor deposited polycrystalline silicon–germanium films on SiO2 using Si2H6, GeH4, and B2H6 gases

Deposition of undoped and in situ boron-doped polycrystalline silicon-germanium (poly-Si1−xGex) films on oxide has been investigated at temperatures below 625 °C and a pressure of 4 Torr in a rapid thermal chemical vapor deposition system. The influences of reactant gases such as Si2H6, SiH4, GeH4, and B2H6 on the nucleation behavior, and structural properties of poly-Si1−xGex films formed on oxide were studied. The experimental results showed that in situ boron-doped or undoped poly-Si1−xGex films can be directly deposited on oxide without an initial Si predeposition layer to provide the necessary nucleation sites on the surface when using Si2H6 as the Si source gas. However, when SiH4 was used as the Si source gas, only in situ boron-doped films can be deposited nonselectively on the oxide without the initial Si predeposition layer, and to deposit undoped poly-Si1−xGex films, Si predeposition is needed, otherwise Si1−xGex islands are formed on the oxide. X-ray diffraction analysis showed that poly-Si1−xGex films deposited using Si2H6, GeH4, and B2H6 gas mixture have three singular peaks corresponding to {311}, {220}, and {111} planes, thus indicating the Si1−xGex alloy is formed. In addition, we found that B2H6 gas has a minor effect on the Ge incorporation into the films but reduces the overall deposition rate.

Chiral-like spin ordering in Ni(Pt, Pd)Mn

Temperature dependence of nonlinear susceptibility of Ni 75.3Pt 1.3Mn 23.4 shows a singular peak irrelevant to the spin freezing and ferromagnetic transitions. The peak is more pronounced than that observed in Ni 76.6Mn 23.4, while it is not observed in the Pd-doped sample Ni 75.3Pd 1.6Mn 23.1. The difference in magnetic singularity correlates with the magnitude of magnetic anisotropy. This characteristic feature can be interpreted in terms of a possible chiral spin ordering appearing in Ni(Pt, Pd)Mn.

Application of computer-assisted morphometry to the analysis of prenatal development of human lung.

Morphometry is well-established in tumour pathology. To evaluate is potential usefulness for description of developmental processes, histological slides from paraffin-embedded specimens of 67 human fetal lungs were Feulgen-stained, and morphometric characteristics of nuclei of epithelial pulmonary cells were analysed with an automated image analysis system. The measured cytometric features comprised of integrated optical density (IOD), S-phase-related IOD fraction, IOD entropy and nuclear area. Histometric features of the specimens were based upon the minimum spanning tree (MST) and included distances between neighboring epithelial cells, between epithelial cells and neighboring lymphocytes, and assessment of MST entropy. Notably, certain parameters revealed a non-uniform level during prenatal development S-phase-related IOD fraction increased from 5% to 8% between 14 and 16 weeks of gestation, then declined to 6% until birth. The IOD entropy steadily increased during development, whereas the extent of nuclear area remained constant. In accordance with an increase of the S-phase-related fraction the MST entropy displayed a singular peak between 14 and 16 weeks of gestation, which is probably associated with development of glandular structures in the lung. Correlation of expression of binding sites for markers, presumably involved in functional aspects of development, with such alterations, is shown for binding capacities of biotinylated fucoidan and the S-phase-related fraction. This may be helpful to infer immuno- or ligando histochemically defined tissue sites with potential physiological significance in morphometrically distinguished periods of development.

The spin susceptibility of singlet correlated oxygen band in La2?x Sr x CuO4

We have shown that the unconventional temperature dependence of the static susceptibilityϰ(T) of the perovskite high-Tc superconductors above the superconducting transition temperatureTc can be explained in terms of two relevant band models containing the singlet-correlated oxygen band and the copper character band. The usual copper-oxygen Hamiltonian containing hopping and Coulomb repulsion terms has been reduced to an effective Hubbard-liket-t′-t″-Ueff model to describe the low-energy properties. The unusual behaviour of the susceptibility is due to thermally activated oxygen holes coming into the hybridization singularity peak in the density of states. A possible physical origin ofTmax in the temperature dependence of the susceptibility is discussed.

Insect thin films as solar collectors

A numerical method for simulation of microscale radiation effects in insect thin-film structures is described. Accounting for solar beam and diffuse radiation, the model calculates the reflectivity and emissivity of such structures. A case study examines microscale radiation effects in butterfuly wings, and results reveal a new function of these multilayer thin films: thermal regulation. For film thicknesses of the order of 0.10 µm, solar absorption levels vary by as much as 25% with small changes in film thickness; for certain existing structures, absorption levels reach 96%., This is attributed to the spectral distribution of the reflected radiation, which consists of a singular reflectance peak within the solar spectrum.

Electronic structure of Ni-based superconducting quaternary compounds: YNi2B2X (X=B, C, N, and O).

In order to explore a correlation between superconductivity and the electronic structure of Ni-based superconducting quaternary compounds, a systematic investigation of the electronic structures for ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$X (X=B, C, N, and O) is carried out, by employing the linearized muffin-tin orbital band method. It is found that the Ni 3d density of states (DOS) in ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C is broader than in fcc Ni metal, and so N(${\mathit{E}}_{\mathit{F}}$) becomes small enough to make the system nonferromagnetic and then superconducting. A rigid-band-like shift of the Fermi level is observed as atom X varies. In the case of ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C, the Fermi level is located right at the van Hove--like singular DOS peak, which originates from saddle-point extremal band crossing \ensuremath{\Gamma}. This singular DOS peak at ${\mathit{E}}_{\mathit{F}}$ is expected to be related to the superconductivity observed in ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C. A crude estimate within the framework of the simple rigid-ion approximation indicates that the superconductivity in ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C can be properly described by the conventional phonon mechanism.

Phase-conjugated wave and localized-delocalized transition of an exciton

An exciton in impure bulk crystals is expected to show a localized-delocalized transition with varying an excitation frequency. Around this mobility edge, phase-conjugated wave generation is theoretically shown to be singularly enhanced. It is proposed that the exciton mobility edge, which is insensitive to the linear optical response, will be clearly observed as a singular peak in this four-wave mixing spectroscopy.

Dynamics at the ferroelectric to dipolar glass transition

Abstract We review our measurements on the polarization dynamics near the dipolar glass transition in KTN, at low niobium concentration (0.9-1.2%). Measurements over a wide range of characteristic times, including Raman and Neutron scattering, Brillouin scattering, ac dielectric response, and polarization decay, have revealed the presence of relaxation processes which vary over a very wide time range as the low concentration sample is cooled. At the higher concentration (1.2%) this behavior changes somewhat, showing evidence for the development of two transitions, at temperatures of about 15 K and 19-20 K, respectively. The dynamic signatures of the two transitions are different. The upper transition is characterized by a low frequency soft mode which exhibits a minimum in frequency as a function of temperature, but no evidence has been found for development of long-range ferroelectric order. The lower transition exhibits a divergent and singular central peak phenomenon. We speculate as to the origin of this pair of transitions.

Cell‐cycle‐dependent, differential prenylation of proteins

Isoprenylated proteins related to cell growth have been detected during proliferation. Since cholesterogenesis (isoprenoid synthesis) is mandatory for cell proliferation, the observation of a temporally coordinated protein prenylation during the cell division cycle might constitute obligatory processes in the signalling pathway for initiating DNA replication and/or in maintaining the growing state. We have found such a definitive cell-cycle-phase-dependent pattern of prenylation for various classes of cytosolic and nuclear matrix proteins in synchronized HepG2 cells. Characteristic [3H]mevalonate incorporation began to increase during mid-to-late G1, just after cholesterol synthesis reached its apex, and peaked just prior to or coincident with mid S. Incorporation then declined subsequent to S (during G2) as cells approached mitosis. Prior to the rise in mevalonate incorporation into proteins, during early-to-mid G1, steady-state [14C]acetate incorporation into chromatographically resolved cholesterogenic lipid intermediates displayed a maximum only into cholesterol. However, during the late-G1/S interval, a singular peak of 14C incorporation was found for the farnesyl moiety (farnesol/nerolidol plus farnesyl diphosphate). Except for the farnesyl moiety, none of the other polyisoprenoids detected by our procedures showed any fluctuation in 14C incorporation subsequent to mid G1. These results support the proposal that subsequent to peak cholesterol synthesis in early-to-mid G1, the generation of a cholesterol-pathway-dependent set of post-translationally modified, polyisoprenylated proteins could constitute an obligatory step leading to the duplication of the cellular genome, thereby impelling transit through the cell cycle. The well known high flux through cholesterogenesis in tumors, which manifests an intrinsic lack of sensitivity to feedback inhibition and operates continuously, is consonant with this proposal.

HREELS studies of formamide on Pt(111): hydrogen bonding interactions between adsorbates

The adsorption properties of formamide, HCONH 2, on Pt(111) have been studied using high-resolution electron energy loss spectroscopy (HREELS). At low dosages, dissociative adsorption of formamide at 170 K results in the formation of coadsorbed NH 3 and CO. The onset of molecular adsorption occurs just prior to formation of a monolayer. At saturation monolayer coverages, hydrogen-bonding interactions between the chemisorbed molecules result in red-shifting of the ν(NH 2) vibrational frequency from the gas phase value of 3570 to 3307 cm −1. The linewidths of the ν s(NH 2) and ν a(NH 2) modes are broadened into a singular peak due to enhanced coupling with NH 2 modes of lower frequency. In the case of HCOND 2, the ν s(ND 2) and ν a(ND 2) peaks are distinctly resolved. Upon heating multilayer coverages of formamide, the hydrogen-bonding interactions lead to autocatalytic desorption of formamide at 223 K.