How universal are Fibonacci patterns?

Pattern patterns, or phyllotaxis, the arrangements of phylla (flowers, leaves, bracts, florets) in the neighborhood of growth tips, have intrigued natural scientists for over four hundred years. Prominent amongst the observed features is the fact that phylla lie on families of alternately oriented spirals and that the numbers in these families belong to subsets  {m _j } of the integers defined by the Fibonacci rule m _j + 1 = m _j  + m _j − 1. The corresponding patterns, which we call Fibonacci patterns, are widespread and universal on plants. Our goal in this paper is to ask if they may also be seen in other physical structures and to try to quantify the circumstances under which one may expect Fibonacci patterns to occur.     

Low frequency elastic properties of glasses at low temperatures—implications on the tunneling model

We have measured the low frequency elastic properties of dielectric, normal conducting and superconducting metallic glasses at audio-frequencies (f1 kHz) and temperatures down to 10 mK. Our results are discussed in the framework of the tunneling model of glasses. The major assumption of the tunneling model regarding the tunneling states with long relaxation time has been verified, but discrepancies to high frequency measurements have been found. In addition, our experiments on superconducting metallic glasses seem to indicate that the present treatment of the electron-tunneling state interaction is not sufficient.     

Effect of MAE on the properties of phosphate edge-cladding glasses

Edge-cladding is a key factor in improving saturated small signal gain coefficientβ_S of large laser disc glass.In this paper,the glasses were melted with traditional method.The influences of mixed alkali effect (MAE)on refractive index,thermal expansion coefficientα,glass transition temperature T_g,dilatometer softening temperature T_d,and relative chemical durability of phosphate edge-cladding glasses were studied. The results reveal that when Li/(Na Li)=0.5,T_g,T_d,and dissolution rate(DR)reach a minimal value. These results are preferred in phosphate edge-cladding glasses.     

How random are matrix elements of the nuclear shell model Hamiltonian?

In this paper we study the general behavior of matrix elements of the nuclear shell model Hamiltonian.We find that nonzero off-diagonal elements exhibit a regular pattern,if one sorts the diagonal matrix elements from smaller to larger values.The correlation between eigenvalues and diagonal matrix elements for the shell model Hamiltonian is more remarkable than that for random matrices with the same distribution unless the dimension is small.     

On the Anderson localization and “universal degradation” of the critical temperature in superconductors

We give an analytical formula for the critical temperature of a superconductor taking into account the enhanced Coulomb repulsion which will be considered as frequency dependent.     

Effects of installations on the low frequency vibration response of specimens in acoustic fatigue tests

The low frequency vibration response of a specimen in acousticfatigue tests depends not only on the dynamic characteristics and theboundary conditions of the specimen itself,but also on the test unit whichcouples the specimen to a given sound field.Further,the latter can even bedominant instead the former in some circumstances.This fact is shown in thepaper by using the experimental results and the theoretical analysis of theacoustic-induced vibration of a boundary clamped rectangular thin plate.Inanalysing the systems of acoustic fatigue test,an approach ofelectro-mechano-acoustical analogous circuit is used.The application of theapproach can give an estimation of the effcts on the low frequency vibrationmodes of various parameters in a system quantitatively.This supplies a theo-retical basis and a means for the rational layout of acoustic fatigue tests.     

Optical properties of Ce–Ti-containing silicate glasses

Silicate glasses doped with ceria and titania have been studied. Such co-doping determines the specific coloration of the glasses with adjustable absorption in the visible spectral region. Based on measurements of optical transmittance and photoluminescence and studies of electron paramagnetic resonance, it was established that the features of their optical properties are due to the formation of chromophore centers incorporating cerium and titanium ions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 202–208, March–April, 2009.     

Effects of sediment parameters on the low frequency acoustic wave propagation in shallow water

1IntroductionInoceanacousticsoneofveryimportantproblemsistheinteractionbetweentheacousticwavesand.eabedll--4)twhiChiscloselyassociatedtosoundcavepropagationinakindoflayerydmedium(air-seawater--scabedsediment).Itiswellknownthatacousticfarfieldinshallowwatercanbeexpressedasasumofnormalmodesusingnormalmodetheory[']5andsomeparameterssuchassoundspeedandattenuationofthesedimelltcanbeinverselydeduced[1'2].However,thenormalmodetheoryisdifficultlyusedwhentheshearwavespeedinthesedimentislessthanthatofwa…     

Low temperature acoustic properties in YBa2Cu3O7−δ

Temperature dependencies of acoustic lossesQ ^–1 and of relative sound velocity change v/v in YBa₂Cu₃O_7– up to 60 K are calculated by the tunneling model theory. The tunneling systems are related to the off-centered positions of the apical oxygen atoms O(A) and are described through the pseudo-Jahn-Teller effect. Tunneling systems' parameters are distributed in narrow range of values and are in correspondence with the experimentally observed infrared phonon spectra and thermal ellipsoids of O(A). Respective relaxation times are calculated by the adapted reaction rate method. The calculatedQ ^–1(T) and v(T)/v dependencies are in good agreement with the experimental data, which is an additional support to the conclusion about the existence of tunneling systems in YBa₂Cu₃O_7– due to the pseudo Jahn-Teller effect.     

How universal are hydrogen bond correlations? A density functional study of intramolecular hydrogen bonding in low-energy conformers of α-amino acids

Hydrogen bonding is one of the most important and ubiquitous interactions present in Nature. Several studies have attempted to characterise and understand the nature of this very basic interaction. These include both experimental and theoretical investigations of different types of chemical compounds, as well as systems subjected to high pressure. The O–H..O bond is of course the best studied hydrogen bond, and most studies have concentrated on intermolecular hydrogen bonding in solids and liquids. In this paper, we analyse and characterise normal hydrogen bonding of the general type, D–H...A, in intramolecular hydrogen bonding interactions. Using a first-principles density functional theory approach, we investigate low energy conformers of the twenty α-amino acids. Within these conformers, several different types of intramolecular hydrogen bonds are identified. The hydrogen bond within a given conformer occurs between two molecular groups, either both within the backbone itself, or one in the backbone and one in the side chain. In a few conformers, more than one (type of) hydrogen bond is seen to occur.

Interestingly, the strength of the hydrogen bonds in the amino acids spans quite a large range, from weak to strong. The signature of hydrogen bonding in these molecules, as reflected in their theoretical vibrational spectra, is analysed. With the new first-principles data from 51 hydrogen bonds, various parameters relating to the hydrogen bond, such as hydrogen bond length, hydrogen bond angle, bond length and vibrational frequencies are studied. Interestingly, the correlation between these parameters in these bonds is found to be in consonance with those obtained in earlier experimental studies of normal hydrogen bonds on vastly different systems. Our study provides some of the most detailed first-principles support, and the first involving vibrational frequencies, for the universality of hydrogen bond correlations in materials.     

What are the relative roles of heating and cooling in generating solar wind temperature anisotropies?

Temperature anisotropy in the solar wind results from a combination of mechanisms of anisotropic heating (e.g., cyclotron-resonant heating and dissipation of kinetic Alfvén waves) and cooling (e.g., Chew-Goldberger-Low double-adiabatic expansion). In contrast, anisotropy-driven instabilities such as the cyclotron, mirror, and firehose instabilities limit the allowable departure of the plasma from isotropy. This study used data from the Faraday cups on the Wind spacecraft to examine scalar temperature and temperature components of protons. Plasma unstable to the mirror or firehose instability was found to be about 3-4 times hotter than stable plasma. Since anisotropy-driven instabilities are not understood to heat the plasma, these results suggest that heating processes are more effective than cooling processes at creating and maintaining proton temperature anisotropy in the solar wind.     

Novel photosensitive properties of gadolinium–lead germanate glasses

Glasses of the system xGd₂O₃ · (100 ? x)[7GeO₂ · 3PbO] with 0 ≤ x ≤ 40 mol% were prepared using the melt quenching method. Lead germanate glasses are particularly interesting in the context of the germanate anomaly. In this paper, we investigate changes in the coordination number of germanium in gadolinium–lead germanate glasses using molar volume analysis, density measurements, FTIR and UV–VIS spectroscopy, and density functional theory (DFT). Despite some inconsistencies, the coordination change model remains the currently accepted model for the anomalous behaviour of lead germanate glasses. Based on these experimental results, we propose the following mechanism for the germanate anomaly. (i) The low thermodynamic stability of the [GeO₆] structural unit and the occupation of interstices of larger dimensions (the six-coordinated interstices of the [PbO₆] structural units) in the lead germanate network yield [GeO₅] structural units with higher thermodynamic stability and larger ionic radii. (ii) Not linked to the terminal oxygens of the [GeO₅] structural units and with the formation of smaller network cavities of the lead germanate glass, links are required with [GeO₄] tetrahedra for stabilization, generating the formation of three-membered rings of [GeO₄] tetrahedral structural units.     

How the Outliers Influence the Quality of Clustering?

In this article, we evaluate the efficiency and performance of two clustering algorithms: AHC (Agglomerative Hierarchical Clustering) and K−Means. We are aware that there are various linkage options and distance measures that influence the clustering results. We assess the quality of clustering using the Davies–Bouldin and Dunn cluster validity indexes. The main contribution of this research is to verify whether the quality of clusters without outliers is higher than those with outliers in the data. To do this, we compare and analyze outlier detection algorithms depending on the applied clustering algorithm. In our research, we use and compare the LOF (Local Outlier Factor) and COF (Connectivity-based Outlier Factor) algorithms for detecting outliers before and after removing 1%, 5%, and 10% of outliers. Next, we analyze how the quality of clustering has improved. In the experiments, three real data sets were used with a different number of instances.     

Effect of B2O3 on the structure and properties of tungsten–tellurite glasses

The elastic properties and Debye temperatures of xB₂O₃–70TeO₂–(30–x)WO₃, (0 ≤ x ≤ 30 mol%) glasses have been investigated using sound velocity measurements at 4 MHz. Ultrasonic and thermal parameters, combined with the results of IR spectroscopic analyses, were employed to explore the effect of B₂O₃ on the structure of tungsten–tellurite glasses. According to IR analysis, there is competition between WO₆ and TeO₄ units to form BO₄ units, and the vibrations of the tellurite structural units are shifted towards lower wavenumbers on the formation of non-bridging oxygens. It is assumed that B₂O₃ acts as a modifier by decreasing the glass-transition temperature T _g and increasing both the thermal stability and glass formation range of the tellurite glasses. The change in density and molar volume with B₂O₃ content reveals that the borate units are less dense than the tellurite structural units. The observed compositional dependence of elastic moduli is interpreted in terms of the effect of B₂O₃ on the coordination number of the tellurite units. A good correlation was observed between experimentally determined elastic moduli and those computed with the Makishima–Mackenzie model.