Beating Effect Research Articles

Graftability of beaten pulps and acetylated pulps

AbstractCe(IV)‐induced polymerization of acrylonitrile with acetylated bagasse and wood pulps, having different acetyl contents, has been investigated. The graft yield is dependent on the acetyl content as well as the origin of the pulp. Increasing the acetyl content of pulps caused a significant decrease in the polymer loading. However, the rate of polymerization of acetylated wood pulp is much higher than that of acetylated bagasse pulp. The ceric consumption during grafting decreases as the acetyl content of the pulp increases. The effect of beating of the pulps, to various degrees of freeness, on their reactivity toward grafting process has also been studied. Generally, the state of cellulose, as defined by its degree of beating, and the origin of the pulp strongly influenced the graft yield. In creasing the beating degree of bagasse pulp resulted in a decrease in graft yield, while beating of wood pulp, to a definite degree, inhibits the polymerization reaction. The consumption of Ce(IV) by the beaten pulps during oxidation is somewhat greater than that consumed by the unbeaten pulps, whereas the consumption during grafting of acrylonitrile onto beaten pulps depends on the initial concentration of ceric solution. Also, the effect of grafting of acrylonitrile onto acetylated wood and bagasse pulps on their strength properties as well as the effect of grafting onto beaten pulps on their properties has been investigated. Grafting of acrylonitrile onto acetylated bagasse pulp decreased its strength properties, but improved its beatability comparatively to those of original pulp (0 acetyl content). On the other hand, grafting of acrylonitrile onto acetylated wood pulp resulted in a great improvement in its strength properties compared to those of grafted unacetylated pulp. Grafted unbeaten pulps gave thinner and weaker paper than the original pulp (without grafting). Beating of bagasse pulp before grafting gave pulp which possessed a higher strength properties, at low °SR, than those of pulp beaten after grafting. Raising the °SR by rebeating the pulp after reaction up to the original value had an adverse effect on the strength. Beating of bagasse pulp before grafting did not accelerate the reaction rate, but it saved some power consumption, since the time required for beating of grafted pulp to a given °SR was lower than that of ungrafted pulp.

High resolution fluorescence excitation and quantum beat spectroscopy of the first electronically allowed transition of perdeuteromethylglyoxal

Laser induced fluorescence excitation spectra of supersonic nozzle beam cooled methylglyoxal-d4 reveal that a deformation occurs during the radiative electronic transition that destroys the planarity of the carbonyls. Consistent with the expectation that deuteration results in an increased number of low frequency vibrations, the number of observed vibronic lines increased and the energy of the breakoff of sharp vibronic structure above the O–O band decreased compared to the protonated molecule. As for the protonated molecule, the observed vibronic structure can be almost completely assigned on the basis of two fundamentals and a repeating pattern of lines that involves the methyl internal rotation and the cis–trans internal rotation of the carbonyls. Systematic anharmonicities involving the pattern and only one of the two fundamentals suggests which molecular motions correspond to the observed fundamentals. Quantum beat and Zeeman effect experiments unambiguously show the triplet states that are responsible for the radiationless dynamics that are known to occur in these molecules. All quantum beat data were analyzable using our previously published perturbation theory method and yield triplet densities which are intermediate compared to methylglyoxal-h4 and biacetyl-h6 and in good agreement with an estimate obtained by direct state coupling. The density of effectively coupled triplet states increases with the energy of the initially prepared singlet state and the intramolecular coupling is 2–15 MHz independent of the amount of vibrational-rotational excitation present. Radiationless transitions in these highly excited molecules are evidently not subject to any overriding selection rules other than spatial symmetry and conservation of total energy, total angular momentum, and nuclear spin. Zeeman experiments indicate extensive coupling of all molecular angular momenta which initially decouple at only ∼10 G. In this low field regime complicated splittings are observed which correspond roughly to g values of about 67% that of a free electron. At larger fields of about 50–60 G, the microsecond fluorescence is nearly completely quenched, and although we cannot completely explain this effect at present, we suspect both intra- and intermolecular processes are possible.

Interference effects in luminescence studies of thin films

Interference effects, including multiple-beam and wide-angle, associated with luminescence from within a thin film are described. A simple geometrical model is used to calculate the s- and p-polarized luminescent light assuming electric-dipole radiation. The luminescence exhibits fringes when measured both as a function of the film thickness and as a function of the wavelength of the light. In the latter case the fringes can also show a beating effect. The model is applied to several experimental examples of cathodoluminescence in SiO(2) and an example of photoluminescence in a-Si.

A wave theory for sandwaves in shelf-seas

Sea-waves are understood more easily if they are considered to move with constant velocity and without changing shape. A convenient mathematical technique is to imagine that these waves can be arrested in space and analysed as for flowing streams with a steady wave-like surface deformation. Hitherto, this technique has been used almost exclusively to study progressive surface waves. For depths as great as 45 m, such wave-like deformations occur on the sea surface as a weakly coupled mirror-image of sandwaves on the seabed. By assuming that these surface deformations are real arrested progressive waves and not merely analogous, we now show that sand-dunes are related empirically by a small-amplitude surface wave dispersion equation. Furthermore, finite-amplitude wave theory (that is, steepest wave theory) is related to the steepest dunes on a stream bed where previously, for want of a better theory, steepest dune wavelengths have been explained in terms of fluid turbulence. In particular, if the dune wavelengths associated here with Gerstner's finite amplitude theory are combined in a manner similar to a beat effect, the predicted wavelengths are in good agreement with the lengths of marine sandwaves.

Effect of Current Cycling on Contact Resistance, Force, and Temperature of Bolted Aluminium-to-Aluminium Connectors of High Ampacity

The effect of current cycling on the contact 10ad, resistance, and temperature of bolted aluminum-to-aluminum joints of high ampacity has been studied. The results show that current cycling causes significant changes in the contact load, resulting in a drastic loss of contact force. Contact resistance is less affected by current cycling, and connector temperature shows a normal beating effect produced by the cycling current. A new accelerated current cycling test has been proposed. The test is based on the passage of relatively high current for short periods of time followed by longer cooling times. The results obtained from the new test indicate that this testing procedure is a valid alternative to those presently in use, and that it can be used as a method for detecting the deterioration of electrical connections. The results also show that the use of Belleville washers, plating, and lubrication i lnproves the performance of the bolted joints under current cycling conditions.

Statistical analysis of polyatomic quantum beats using the properties of random matrices

We have devised a numerical method of analyzing polyatomic quantum beats for the case when so many states are coherently excited that the properties of individual states are inaccessible. The method involves ensemble averaging singlet character distributions obtained by diagonalization of random matrices and using these distributions in simulations of observable quantum beats. By ensemble averaging the simulated quantum beats, we can correlate the average parameters which describe the observable fluorescence decays to the molecular parameters that determine the form of the random matrices. We have found that when very complicated quantum beat effects are observed, extra information is available which relates the overall width of the singlet character distribution to a third observable parameter beyond the two parameters that have traditionally been employed to characterize biexponential fluorescence. In the absence of hyperfine structure this method allows the determination of the width of the singlet character distribution even when that width is greater than the width of the excitation source. This is important since our numerical studies also show that the density of nonradiatively coupled states and the root mean square interaction energy determine the width of the distribution of singlet character in a very simple and general fashion. We believe this method can be easily modified to describe other quantum beat phenomena and can presently be used to specify conditions for specific molecules under which quantum beats are observable.

Inversion layers in silicon on insulating substrates

Magnetoconductance oscillations in silicon MOSFETs on sapphire and spinel substrates were studied in magnetic fields up to 20 Tesla. For (100) n-type inversion layers the cyclotron mass and the effective Landé g-factor were determined from a measurement of the temperature dependence and the variation of the oscillatory structure in a tilted magnetic field. Apart from the unexplained valley degeneracy factor of two the results are in good agreement with the conception that due to the built-in stress the E′ 0 subband is occupied. The Landé g-factor obtained is about the same as in MOSFETs grown on bulk material. The occurrence of a beat effect in the oscillations above about 12 Tesla in silicon on sapphire samples can be explained by a splitting of the ground subband of about 1 meV. This effect was not observed on silicon on spinel samples which favours an explanation based on the stress anisotropy in silicon on sapphire.

Recent results of high magnetic field experiments on MOSFETS in Grenoble

A brief review is given about recent work on silicon inversion layers at the high magnetic field facility in Grenoble. Shubnikov-De Haas oscillations in SOS devices in fields up to 20 Tesla showed a beating effect which presumably arises from anisotropic internal stress. Cyclotron resonance experiments under uniaxial pressure on (100) MOSFETs revealed the occupation of the higher subband system with increasing pressure, which did not show-up in SdH oscillations. In (111) devices with 6-fold valley degeneracy structure has been observed in the SdH effect at high magnetic fields around 20 Tesla, which is interpreted as valley splitting. New data are reported about energy losses of electrons and holes in the non-ohmic regime.

Recent results of high magnetic field experiments on mosfets in Grenoble

Abstract A brief review is given about recent work on silicon inversion layers at the high magnetic field facility in Grenoble. Shubnikov-De Haas oscillations in SOS devices in fields up to 20 Tesla showed a beating effect which presumably arises from anisotropic internal stress. Cyclotron resonance experiments under uniaxial pressure on (100) MOSFETs revealed the occupation of the higher subband system with increasing pressure, which did not show-up in SdH oscillations. In (111) devices with 6-fold valley degeneracy structure has been observed in the SdH effect at high magnetic fields around 20 Tesla, which is interpreted as valley splitting. New data are reported about energy losses of electrons and holes in the non-ohmic regime.

Neutron diffraction studies of tetrachloride liquids

Neutron diffraction measurements of mixtures of TiCl4/SiCl4 and TiCl4/SnCl4 liquids have been made using the total scattering spectrometer of the Harwell Electron Linac. The high Q-value (5–20 Å-1) data exhibit a beat effect and have been analysed in terms of summed molecular form factors. The bond-length parameters are found to be in good agreement with other values and confirm the treatment adopted in the analysis of the data for the pure liquids.

Quantum beats observed in photoionization

Quantum beats of the hyperfine levels of the 3 2P 3 2 state of sodium have been observed in photoionization. The atoms are ionized stepwise with two pulsed lasers. The photoelectron angular distribution, measured as a function of the delay between the two laser pulses, exhibits a periodic variation due to the quantum beat effect. The hyperfine splitting of the intermediate state estimated from these measurements is in good agreement with literature values.

Post-extrasystolic left ventricular peak pressure with and without left ventricular failure.

18 patients without valvular pathology, coronary artery disease, or idiopathic hypertrophic subaortic stenosis were haemodynamically and angiographically investigated in order to analyse the effects of a ventricular extrasystolic beat upon the post-extrasystolic left ventricular peak pressure. In eight normal patients (group I), the post-extrasystolic peak pressure (P.ES.P.P.) was lower than that of the pre-extrasystolic beat; in 10 patients with symptoms of left ventricular failure (group II) the P.ES.P.P. significantly increased. The reasons are: 1) cardiac origin: stroke volume increased more in group II; 2) arterial origin. a) aortic compliance was lower in group II (this is probably related to the older age of patients in group II), and by decrease in end-diastolic aortic pressure was smaller in group II. Part of this arterial effect (2b) may probably be explained from the fact that post-extrasystolic compensatory pauses are equal in both groups, but the decay time of arterial pressure during diastole (assuming an exponential decay) is larger in group II. At the same age and with the identical aortic compliance only the two factors 1 and 2b play a part in the changes in P.ES.P.P.

Possible beat effect of specific heat due to impurities in semi-metal in external magnetic field

The simple model of a single-band semi-metal or degenerate semiconductor with impurities in an external quantizing magnetic field is discussed. The susceptibility and specific heat are studied in their dependence on the field-induced quasi-local levels, due to the impurities. These levels are shown to cause additional oscillations in the thermodynamical quantities as functions of the magnetic field. Their contribution to the susceptibility and specific heat is comparable to the values for the undoped system if the impurity concentration c i fulfils the condition c i = (c e/4√π)( h ̷ ω/ε F) 3 2 , with c e the electron concentration.

Optical fiber hydrophone

Recent studies [J.A. Bucaro, H.D. Dardy, and E.F. Carome, Appl. Opt. 16, 1761 (1977); J.H. Cole, R.L. Johnson, and P.G. Bhuta, J. Acoust. Soc. Am. to be published] have shown the viability of obtaining sensitive, versatile acoustic sensors utilizing long, low-loss optical fibers. In such devices an optical beam propagating in a length of optical fiber which is immersed in a fluid is modulated by the presence of a sound field in that fluid. We have studied such effects in a variety of fiber systems and have quantified various coupling mechanisms which lead to the optical modulation. Examples include phase retardation, acoustically induced birefringence, and intermode beating effects. These results will be discussed and future directions will be indicated. [This work has been supported in part by the Office of Naval Research.]

ASPECTS OF THE BEHAVIOUR AND ECOLOGY OF MIXED‐SPECIES BIRD FLOCKS IN KASHMIR

SummaryMixed‐species flocks of birds were observed between the end of July and late August, principally at Daksum, Kashmir, 2250 m. The species composition and the numbers of individuals in flocks changed during this period; these changes are attributed to resident territory holders and migrant birds joining the flocks. Within the flock different species showed some differences in foraging stations, but nevertheless often appeared to be taking the same type of food. Participant species had different roles in the flock organization. Behaviours involving the entire mixed‐flock acting as a unit included path reversal after encounters with avian predators and a tendency to follow set routes. The mixed‐ species flock exerted an attractive influence on aggregations of species not normally participant.Similarities between the flocks described in this study and those recorded by other workers are discussed. While different species may derive different benefits from joining these flocks, advantages that could benefit some or all participants include the receipt of information on good feeding areas in an unfamiliar locality, the avoidance of time wasted on feeding on substrates which have been very recently harvested, the beating effect to increase prey availability, and enhanced safety from predators, perhaps through differential alertness of different species and specialized anti‐predator behaviour.

Inversion-asymmetry splitting of the conduction band in InSb

The Shubnikov-de Haas (SdH) effect was used to study the strain dependence of the inversion-asymmetry splitting of the conduction band in InSb. This splitting is small and hence has been difficult to observe by any technique other than the one presented in this paper. At zero stress, studies in InSb have shown no indication of beating effects in the SdH oscillations. With the application of uniaxial stress, however, stress-induced beating effects appear in the SdH oscillations. These beating effects, which depend on the magnetic field direction and the electron concentration, are shown to be caused by the stress-induced band splitting. The strain theory developed by Bir and Pikus, along with a simple, classical beating-effects model, enables the evaluation of the band-splitting parameter $|{B}_{3}|=3.3(\frac{{\ensuremath{\hbar}}^{2}}{2{m}_{0}})$ and the deformation potential $|{C}_{2}|=2.0$ eV.

Support for the astronomical theory of climatic change

The quasi-periods of climatic variation found by Hays et al. (Science, vol.194, p.1121 (1976)) from deep-sea cores are examined. It is shown that these periods are very close to those predicted from the variations of the various `Milankovitch' parameters: the 24000 yr and 19500 yr periods from the core samples are not significantly different from the periods associated with the largest amplitude terms in the series expansion of the precessional parameters; the periods around 42000 yr are identical with the most important term in the expansion of the obliquity; and the peaks in the range of 106000 yr may be either a contribution from the eccentricity or a beat effect of precessional periods. Other periods that could be found in the geological record are identified.

Ultrafast coherent excitation and probing of molecular vibrations with isotopic substructure

Adjacent vibrational modes of different isotope species are coherently excited by an intense ultrashort light pulse. The free decay of the vibrational system is observed by coherent probe scattering of a second delayed interrogating pulse. Coherent superposition of the excited vibrational states gives rise to a beating effect of the collectively vibrating isotope components. The phenomenon is observed for the first time in several tetrahalides on a time scale of several ${10}^{\ensuremath{-}12}$ sec. The experimental information obtained by the probing technique depends on the wave-vector geometry of the material excitation and the interrogating pulse: One individual vibrational component is studied under a selective $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ condition while coherent superposition of the vibrational components is observed for nonselective $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ matching. Our technique provides new information on the vibrational system which is not obtained by other experimental methods.

Demodulation and detection of correlations in a beam by a scattering detector

The demodulation and the detection of correlations in a beam using a detector that scatters the beam is discussed employing a localized wave packet description of the beam. It is shown that a simple very general formula for the spectral excitation function of the detector can be given; by spectral excitation function we mean the rate of excitation of the detector to a given level. The formula is derived without making specific assumptions on the nature of the detector. The spectral excitation function is naturally decomposed as a sum of four terms: Two of these (the B terms in what follows) depend only on the wavefunction and stochastic distribution of the incident beam; they are proportional to the square (and higher powers) of the flux and contain all the information on the self-beat, Forrester-type effects and demodulation. More precisely, one of these B terms contains the information on the demodulation and the other on the beat effects. The remaining two terms (to be called the A terms) describe the conventional inelastic scattering (proportional to the flux) and some coherent corrections to it (proportional to higher powers of the flux): These A terms behave as noise if the signal of interest is that described by the B terms. The theory is illustrated with many examples to known situations; particular attention is given to some conceptual questions involved.

SIMULTANEOUS SPECTROSCOPIC AND PHOTOMETRIC OBSERVATIONS OF THE BETA CEPHEI STAR HR 6684.

ABSTRACT We have obtained simultaneous radial velocity observations and differential magnitude observations of the Cep star HR 6684. The full amplitude of the velocity curve is 18 km sec-1 and the range in blue light is . The ratio of these values is 550 km sec-1 mag-1 and maximum light falls at minimum radius. In these respects, HR 6684 is similar to other P Cep stars. There is some evidence for a beat effect. The spectral lines are sharp (v sin i = 110 km sec-1) and appear to vary in their profiles. Key words: P Cephei star - photometry - radial velocities