Spectral Quantities Research Articles

Seasonal Variations of the 40-50 Day Oscillation in the Tropics

Abstract Daily rawinsonde data from 19 near-equatorial stations are examined to learn more about annual variations of the 40–50 day oscillations. Lengths of the available time series range from 5 to 28 years. A technique is devised to isolate spectral and cross-spectral quantities as a function of season. It is determined that a variance of the zonal wind in a relatively broad band centered on 47-day periods generally exceeds that in adjacent lower and higher frequency bands by the largest amount during December January and February (DJF) and at stations in the Indian and western Pacific Oceans during all seasons. The coherence between lower-and upper-tropospheric zonal winds tends to be largest in the summer hemisphere for stations in the Indian and western Pacific Oceans. Upper tropospheric zonal and meridional winds are coherent and out of (in) phase at several stations there during DJF [June, July and August (JJA) These results. coupled with composited wind and outgoing longwave radiation data, lead u...

Strongly driven Stark coupled three-level systems and transitions at the Rabi frequency

Calculations based on a full master equation approach have been made of the absorption spectrum for a certain three-level system in which two states mod 2), mod 1) are strongly driven by a near resonant monochromatic laser field whose Rabi frequency is large compared with the natural lifetime width of mod 2). A third state mod 3) is coupled to the nearby state mod 2) by a static electric field. As the static field coupling increases the spectrum in the neighbourhood of the laser frequency changes from the partly emissive, partly absorptive Mollow form to an absorptive spectrum with two strong peaks. Also, the spectrum in the neighbourhood of the upper level transition frequency changes from an Autler-Townes doublet to a spectrum where a new emissive line appears at the Rabi frequency. In terms of the dressed atom model, this transition corresponds to an intradoublet transition previously forbidden in two-level atoms, though predicted to occur in certain two-level molecular systems. The spectrum is interpreted in terms of a dressed atom model. In general terms not only do the dressed atom transition frequencies correlate well with the spectral features, but there is also good agreement between the heights and widths of the spectral features and those obtained from the full master equation approach. The importance of using the full dipole operator in the basic definitions of the spectral quantities is also demonstrated.

On-shell improved lattice gauge theories

By means of a spectrum conserving transformation, we show that one of the 3 coefficients in Symanzik’s improved action can be chosen freely, if only spectral quantities (masses of stable particles, heavy quark potential etc.) are to be improved. In perturbation theory, the other 2 coefficients are however completely determined and their values are obtained to lowest order.

Self-Tuning of a Wave Generator

Abstract In this paper the problem of sel-tuning of a random water generator of a laboratory canal is considered. The canal behaves as a frequency dependent gain, between wave generator movement and wave amplitude, and frequency dependent wave propagation delays. Reflection at the far end of the canal or on a model is considered. The objective is to control the incident spectrum, so that it follows a given form. The algorithm involved is of non-parametric nature in the logarithm of power spectral quantities. The study of convergence of the algorithm is addressed and the design of a proportional plus integral controller is considered. Finally, simulations results are shown and conclusions are drawn.

On-shell improved lattice gauge theories

By means of a spectrum conserving transformation, we show that one of the 3 coefficients in Symanzik’s improved action can be chosen freely, if only spectral quantities (masses of stable particles, heavy quark potential etc.) are to be improved. In perturbation theory, the other 2 coefficients are however completely determined and their values are obtained to lowest order.

Measurement of total reflectance, transmittance and emissivity over the thermal IR spectrum

A diffuse reflectometer/transmissometer has been designed to determine a complete set of absolute spectral radiometric quantities for any kind of sample, whether or not it has a regular component of reflectance or transmittance. The device uses a hemispherical Cu mirror in a gimbal mounting to focus radiation from an Opperman ceramic source onto the sample. Errors are caused by radiometric non-linearity arising from interreflection effects and by temperature changes of the source arising from interreflection and purge draught effects. Correction procedures are discussed and future developments to make these standards fully independent of other results are indicated. Measurements have been made over the whole thermal IR spectrum from 2.5 to 55 μm. Results are described and evaluated for radome materials developed to minimize energy transfer, and also for a number of black coatings for radiometry detectors where a low reflectance is needed independent of wavelength.

Nonstationary pandom vibpation analysis of linear elastic structures with finite element method

At present, the finite element method is an efficient method for analyzing structural dynamic problems. When the physical quantities such as displacements and stresses are resolved in the spectra and the dynamic matrices are obtained in spectral resolving form, the relative equations cannot be solved by the vibration mode resolving method as usual. For solving such problems, a general method is put forward in this paper. The excitations considered with respect to nonstationary processes are as follows: $$P(t) = \left\{ {P_1 (t)} \right\},{\text{ }}P_1 (t) = a_1 (t)P_1^0 (t),$$ a1(t) is a time function already known. We make Fourier transformation for the discretized equations obtained by finite element method, and by utilizing the behaviour of orthogonal increment of spectral quantities in random process[1], some formula of relations about the spectra of excitation and response are derived. The cross power spectral denisty matrices of responses can be found by these formulas, then the structrual safety analysis can be made. When a(1)=1 (i=1.2, ...,n), the method stated in this paper will be reduced to that which is used in the special case of stationary process.

Spectral transfer and velocity derivative skewness equation for a turbulent velocity field

A derivation of the high wavenumber spectral transfer equation is given which indicates the wavenumber range of validity for this equation in terms of Reλ. A similar treatment is given for the commonly used spectral approximation for the velocity derivative skewness and the analogous scalar spectral quantities.

Optical Radiation Measurements and Instrumentation

Accurate measurement of optical radiation is required when sources of optical radiation are used in biological research. Such measurement of broad-band noncoherent optical radiations usually must be performed by a highly trained specialist using sophisticated, complex, and expensive instruments. Presentation of the results of such measurement requires correct use of quantities and units with which many biological researchers are unfamiliar. The measurement process, quantities, units, measurement systems and instruments, and uncertainties associated with optical radiation measurements are reviewed in this paper. A conventional technique for evaluating the potential hazards associated with broad-band sources of optical radiation and a spectroradiometer developed to measure spectral quantities is described. A new prototype ultraviolet radiation hazard monitor which has recently been developed is also presented. This new instrument utilizes a spectrograph and a spectral weighting mechanical mask and provides a direct reading of the effective irradiance for wavelengths less than 315 nm.

ChemInform Abstract: COMMENTS ON THE ELECTRONIC PROPERTIES OF CYCLOPROPANE, CYCLOBUTANE, AND CYCLOHEXANE

Spectral quantities of cyclopropane, cyclobutane, cyclohexane, and of several derivatives, have been calculated by a semiempirical all-valence electron SCF-CI MO method. In cyclopropane, HOMO is practically localized in the carbon-frame, and LVMO is purely so. In cyclobutane, these two MO's are based on C-H bonds, while cyclohexane holds an intermediate position. Despite the overall similarity-experimental and computed-of the spectra of these molecules, assignments are non-parallel. Like cyclopropane, cyclobutane can extend conjugation, but to a diminished degree; cyclohexane behaves in this respect like an acyclic alkane. An interpretation of this gradation, in terms of the nature of high-lying MO's, is proposed.

Linear combination of hybrid orbitals: Acyclic alkanes

A LCHO SCF-CI semiempirical scheme is formulated for compounds of carbon and hydrogen, and far-UV transition energies computed for a number of acyclic alkanes. The type of spectral bands (CH → CH*, etc.) and symmetries of subbands are assigned, and their dependence on conformation and branching discussed. It is argued that, for pentanes and higher alkanes, spectral quantities can be estimated from data on the lower alkanes.

Comments on the electronic properties of cyclopropane, cyclobutane, and cyclohexane

Spectral quantities of cyclopropane, cyclobutane, cyclohexane, and of several derivatives, have been calculated by a semiempirical all-valence electron SCF-CI MO method. In cyclopropane, HOMO is practically localized in the carbon-frame, and LVMO is purely so. In cyclobutane, these two MO's are based on C-H bonds, while cyclohexane holds an intermediate position. Despite the overall similarity-experimental and computed-of the spectra of these molecules, assignments are non-parallel. Like cyclopropane, cyclobutane can extend conjugation, but to a diminished degree; cyclohexane behaves in this respect like an acyclic alkane. An interpretation of this gradation, in terms of the nature of high-lying MO's, is proposed.

Spectrum analysis of the electroencephalogram

Digital Auto- and Cross-spectral Analysis has become an important method for quantifying and analyzing electroencephalographic data. This paper presents a set of four procedures written in ALGOL, which perform spectrum analysis of up to 14 simultaneously recorded EEG channels on a medium to large size computer. The first procedure reduces the data after smoothing by a digital low pass filter with variable cutoff frequency. By the elimination of the higher frequency components of no interest, aliasing is prevented. The reduced but due to multiplexing still interleaved data are then rearranged by channels. The third procedure performs the Fast Fourier Transformation. Finally, the spectral quantities as power spectrum, cross-spectral amplitude, phase, coherence and gain are computed for preselected channel combinations. Smoothing in the frequency domain is performed either by a rectangular or a truncated normal spectral window of variable width.

Spectral Parameters of the VLF Radio Noise Observed as Functions of the Azimuth

The actions of a new atmospherics analyzer, which determines for every incoming atmospheric the apparent angle of arrival together with certain characteristics of the VLF spectrum, are briefly explained. Then the physical significance of the observable spectral quantities are considered by use of a simplified version of the VLF waveguide mode theory. Finally, spectral observations of a 4‐ week period are presented in such a way that the influence of daytime and azimuth are evident and comparison with theoretical propagation computations is enabled.

Photochemistry of the model phototropic system involving flavins and indoles. I. Fluorescence polarization and MO calculations of the direction of the electronic transition moments in flavins.

Abstract— The fluorescence polarization spectra of riboflavin, lumiflavin, and alloxazine under different conditions have been obtained. It has been shown that the polarization spectrum of riboflavin is not affected significantly by media such as D2O‐glycerol (50: 50) and castor oil. Our data do not indicate the anomalous spectral shift of riboflavin in castor oil, in contrast to the previous finding described by Thomas. The electronic structures of lumiflavin and alloxazine are similar to that of riboflavin, as revealed by the fluorescence polarization measurements and the molecular orbital calculations. The Pariser‐Parr‐Pople semiempirical SCF ASMO CI computations have been performed to compare the calculated transition moments with the polarization data. The theory predicts an angle of 42° between the 450 and 365 nm transition oscillators, in reasonable agreement with the experimental angle of about 49°. It has been shown, from the comparison of the calculated and observed spectral quantities, that the pseudo‐heteroatom model for treating methyl groups in the flavin molecule is not adequate. The group orbital and inductive approximations appear to be satisfactory. Finally, the implication of the present findings has been briefly discussed in connection with phototropism.

Non self-consistent field theory ? A new approach in quantum mechanical calculations

An R o-independent electronic repulsion matrix is constructed, replacing the R o-dependent Hamiltonian matrix (R o is the density matrix). A non-SCF theory is developed to solve the eigenequation without using an iterative procedure. Three methods are proposed to solve for the eigenvectors and eigenvalues. Illustrative calculations are reported comparing the non-SCF and SCF theories. The calculated results are as expected: the ground state energies are nearly unchanged while the orbital energies are nearer to the experimental results. Other physical properties and spectral quantities are also compared. It is found that the ZDO assumption is applicable in the non-SCF theory if it is applicable in SCF theory.

Calculation of the ?-electronic structures of vinyl boron compounds by the free-electron Method

The free-electron model has been used to investigate the π-electronic structures and spectra of two vinylboranes. It is concluded that none of the simple F. E. methods is satisfactory alone and agreement between calculated and observed spectral quantities is only obtained when electron interaction is explicitly included in the calculations.

Physical Equivalents of Spectral Notions

The notion of a Fourier spectral equivalent of an arbitrary function has been known for a long time in its basic mathematical form. Calculations of these spectral quantities are conventionally based on the Fourier integral. It is not so well known that the Laplace transformation also yields a spectral notion of which the Fourier form is a special case. In addition, vibration engineers have made extensive use in recent years of the concept of a shock spectrum. Simple physical experiments are described which yield direct quantitative spectral values at specified frequencies for any of the three spectra mentioned in the foregoing. These equivalents are useful in assigning physical significance to the quantities under discussion.

On Physical Equivalents to Spectra Notions

The notion of a Fourier spectral equivalent of an arbitrary function has been known for a long time in its basic mathematical form. Calculations of these spectral quantities are conventionally based on the Fourier integral. It is not so well known that the Laplace transformation also yields a spectral notion of which the Fourier form is a special case. In addition, vibration engineers have made extensive use in recent years of the concept of a shock spectrum. Simple physical experiments are described which yield direct quantitative spectral values at specified frequencies for any of the three spectra mentioned in the foregoing. These equivalents are useful in assigning physical significance to the quantities under discussion.