Peculiar lunar echoes at 13.866 MHz

Summary Peculiar lunar echoes obtained with a radar operating at 13.866 MHz are presented and discussed. Some of their features are reconduced to a total or to a partial guidance by ionospheric and magnetospheric irregularities aligned with the geomagnetic lines of force. Precisely, such irregularities are intervening as natural wave guides or as leaky-wave antennas. In the latter case they are characterized by very high gains so that one can speak of a sort of focusing. This focusing could be used for the observation of magnetospheric turbulence, could explain some of the solar bursts and could suggest a practical utilization of the round-the-world propagation.

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Riassunto Insoliti echi lunari ottenuti con un radar operante su una frequenza di 13.866 MHz sono presentati e discussi. Alcune loro caratteristiche sono ricollegate a una totale oppure a una parziale azione di guida da parte di irregolarità ionosferiche e magnetosferiche allineate con le linee di forza del campo geomagnetico. Precisamente dette irregolarità intervengono in qualità di guide d’onda naturali o di antenne a perdita d’onda. Queste ultime sono caratterizzate da altissimi guadagni, così che si può in un certo senso parlare di focalizzazione. Questa focalizzazione potrebbe essere usata per l’osservazione della turbolenza magnetosferica, potrebbe spiegare alcuni degli scoppi solari (solar bursts) e potrebbe suggerire una pratica utilizzazione della propagazione orbitale.

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Резюме Анализируется характерное лунное эхо, полученное с помощью радара, действующего на частоте 13.866 Мгц. Некоторые из особенностей эхо предопределяют ионосферные и магнитосферные иррегулярности, ориентированные вдоль геомагнитных силовых линий. Такие иррегулярности мешают распространению волн. Иррегулярности характеризуются очень большими усилениями, так что можно говорить о некотором виде фокусировки. Эта фокусировка может быть использована для наблюдения магнитосферической турбулентности, может объяснить некоторые солнечные вспышки и может служить для практического использования при распространении вокруг земного шара.

     

Generalizations of spectrally multiplicative surjections between uniform algebras

Let $ A $ A and ℬ be unital semisimple commutative Banach algebras. It is shown that if surjections S,T: $ A $ A → ℬ with S(1)=T(1)= 1 and α ∈ ℂ \ {0} satisfy r(S(a)T(b) − α)= r(ab− α) for all a,b ∈ $ A $ A , then S=T and S is a real algebra isomorphism, where r(a) is the spectral radius of a. Let I be a nonempty set, A and B be uniform algebras. Let ρ, τ: I → A and S,T: I → B be maps satisfying σ _π (S(p)T(q)) ⊂ σ _π (ρ(p) τ(q)) for all p,q ∈ I, where σ _π (f) is the peripheral spectrum of f. Suppose that the ranges ρ(I), τ(I) ⊂ A and S(I),T(I) ⊂ B are closed under multiplication in a sense, and contain peaking functions “enough”. There exists a homeomorphism ϕ: Ch(B)→Ch(A) such that S(p)(y)= ρ(p)(ϕ(y)) and T(p)(y)= τ(p)(ϕ(y)) for every p ∈ I and y ∈ Ch(B), where Ch(A) is the Choquet boundary of A.     

Variation of the Crystal Structure on Si(111) Surface Induced by Ion Bombardment and Subsequent Annealing

Technical Physics - Modification of Si(111) surface due to ion bombardment and subsequent annealing has been studied. It has been found that annealing following bombardment with 0.3- to 1.0-keV...     

Conformational indeterminism in protein misfolding: chiral amplification on amyloidogenic pathway of insulin

Unlike folding, protein aggregation is a multipathway, kinetically controlled process yielding different conformations of fibrils. The dynamics and determinism/indeterminism boundaries of misfolded conformations remain obscure. Here we show that, upon vortexing, insulin forms two distinct types of fibrils with opposite local chiral preferences, which manifest in the opposite twists of bound dye, thioflavin T. Occurrence of either type of fibrils in a test tube is only stochastically determined. By acting through an autocatalytic, "chiral amplification"-like mechanism, a random conformational fluctuation triggers conversion of the macroscopic amount of insulin into aggregates with uniformly biased chiral moieties, which bind and twist likewise the achiral dye. Although a convection-driven chiral amplification in achiral systems, which results in randomly distributed excesses of optically active forms, is known, observation of such a phenomenon in misfolded protein built of l-amino acids is unprecedented. The two optical variants of insulin fibrils show distinct morphologies and can propagate their chiral biases upon seeding to nonagitated insulin solutions. Our findings point to a new aspect of topological complexity of protein fibrils: a chiral feature of hierarchically assembled polypeptides, which is partly emancipated from the innate left-handedness of amino acids. Because altering chirality of a molecule changes dramatically its biological activity, the finding may have important ramifications in the context of the structural basis of "amyloid strains".     

Growth Curve Model with Hierarchical Within-Individuals Design Matrices

This paper deals with some inferential problems under an extended growth curve model with several hierarchical within-individuals design matrices. The model includes the one whose mean structure consists of polynomial growth curves with different degrees. First we consider the case when the covariance matrix is unknown positive definite. We derive a LR test for examining the hierarchical structure for within individuals design matrices and a model selection criterion. Next we consider the case when a random coefficients covariance structure is assumed, under certain assumption of between-individual design matrices. Similar inferential problems are also considered. The dental measurement data (see, e.g., Potthoff and Roy (1964, Biometrika, 51, 313-326)) is reexamined, based on extended growth curve models.     

Infrared Spectroscopy and X-Ray Diffraction Studies of C?H…O Hydrogen Bonding and Thermal Behavior of Biodegradable Poly(hydroxyalkanoate)

Infrared (IR) spectra and wide-angle X-ray diffraction (WAXD) patterns of poly(3-hydroxybutyrate) (PHB) and its copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), P(HB-co-HHx) (HHx = 12 mol%) were measured over a temperature range of 20 °C to higher temperatures (PHB, 185 °C, HHx = 12 mol%, 140 °C) to explore their structure change and thermal behavior and molecular interaction. The WAXD measurements revealed that the a lattice parameter increases significantly with temperature, while the b lattice parameter varies a little in the crystalline PHB and P(HB-co-HHx). It seems that the intermolecular interaction between the CO group of one helical structure and the CH₃ group of the other helical structure decreases along the a axis of crystalline PHB and P(HB-co-HHx) with temperature. The temperature-dependent IR spectral variations were analyzed for the CH stretching, CO stretching, CH₃ deformation, and C O C stretching variation regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It was found from the anomalous frequencies of the CH₃ asymmetric stretching and CO stretching bands of PHB and P(HB-co-HHx) and the X-ray crystallographic structure of PHB that there is an intermolecular interaction (C H…OC hydrogen bond) between the CO group and the CH₃ group combining two helical structures in PHB and P(HB-co-HHx). In this review paper we discuss the role of the C H…OC hydrogen bonding and the crystal and lamella structure of PHB and P(HB-co-HHx) (HHx = 12 mol %) in comparison with the structure of Nylon.     

Specific crystal structure of poly(3-hydroxybutyrate) thin films studied by infrared reflection–absorption spectroscopy

Infrared reflection–absorption (IR-RAS) and transmission spectra were measured for poly(3-hydroxybutyrate) (PHB) thin films to explore its specific crystal structure in the surface region. As IR-RAS is sensitive to the vibration mode of perpendicular orientation of the surface, differences between IR-RAS and transmission spectra indicate an orientation of the lamella structure in the surface of PHB thin films. The relative intensity of the crystalline CO stretching band in the IR-RAS spectrum is significantly weaker than that in the transmission spectrum. It may be concluded that the transient dipole moment of the CO stretching mode of the crystalline state is not oriented perpendicular but nearly parallel to the substrate surface. On the other hand, the relative intensity of the band at 3009 cm⁻¹ due to the C–H stretching mode of the C–HOC hydrogen bonding is similar between the IR-RAS and transmission spectra, suggesting that the C–H bond is oriented neither perpendicular nor parallel to the substrate surface but in an intermediate direction. Since the CO group of the C–HOC hydrogen bonding is oriented nearly parallel to the surface and its C–H group is in the intermediate direction, it is very likely that the C–HOC hydrogen bonding has a somewhat bent structure. These results are in good agreement with our previous conclusion that the C–HOC hydrogen bonding of PHB exists along the a-axis (not the b-axis) between the CH₃ group of one helix and the CO group of another helix.     

Predicting experimental yields as an index to rank synthesis routes II: application to the Curtius rearrangement

Synthesis yields of organic reactions are one of the most important factors in ranking synthesis routes created by synthesis route design systems such as Transform‐Oriented Synthesis Planning and Knowledge base‐Oriented Synthesis Planning. If it is possible to predict the yields of synthesis reactions before starting experiments, one can easily determine an order of synthesis routes for experimental works. In the present study, the reaction profiles of the Curtius rearrangement with different substituents were calculated to generate an equation predicting experimental yields of this reaction. Reactions followed by the formation of isocyanates were also analyzed to consider the relationship between reaction times and experimental yields. A partial least squares (PLS) regression was used to correlate the experimental yields with the calculated activation energies, E_a(calc), together with experimental conditions such as dielectric constants of solvents, reaction times, and reaction temperatures as explanatory variables. Although the PLS regression using all the data gave very poor results, we succeeded in making a model equation with R² = 0.887 using a modified data set. However, there is a conflict between the predictability and the interpretability on the reaction time. This discrepancy mainly comes from unnecessarily long reaction times in the experiments for azides with calculated E_a values of less than 33 kcal mol^–1. To construct a good model equation for the experimental yields of the Curtius reaction, we have to use data sets obtained from within 90 min of the reaction for the PLS regression. Copyright © 2011 John Wiley & Sons, Ltd.     

Rotational Spectra of XeH and Its Isotopic Species

Frequencies of rotational transitions of XeH⁺ and its isotopic species were measured in the 1–5 THz region with a highprecision far-infrared spectrometer using a tunable radiation source. Measured frequencies were analyzed together with previous microwave and infrared measurements to refine mass-independent Dunham parameters.     

Corrected versions of cross-validation criteria for selecting multivariate regression and growth curve models

This paper is concerned with cross-validation (CV) criteria for choice of models, which can be regarded as approximately unbiased estimators for two types of risk functions. One is AIC type of risk or equivalently the expected Kullback-Leibler distance between the distributions of observations under a candidate model and the true model. The other is based on the expected mean squared error of prediction. In this paper we study asymptotic properties of CV criteria for selecting multivariate regression models and growth curve models under the assumption that a candidate model includes the true model. Based on the results, we propose their corrected versions which are more nearly unbiased for their risks. Through numerical experiments, some tendency of the CV criteria will be also pointed.