Plant delta(15)N associated with arbuscular mycorrhization, drought and nitrogen deficiency

It has long been evident that plant (15)N chiefly reflects the processes which fractionate (15)N/(14)N rather than the (15)N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant (15)N is the presence/absence, type or species of mycorrhiza, especially when interacting with nutrient deficiency. Ecto- and ericoid mycorrhizas are frequently associated with (15)N-depleted foliar (15)N, commonly as low as -12 per thousand. As shown by the present study, plants having no mycorrhiza, or those infected with various species of arbuscular mycorrhiza (AM)-forming fungi, interact with varying concentrations of soil nitrogen [N] and moisture to enrich plant (15)N by as much as 3.5 per thousand. Hence the lack of a mycorrhiza, or variation in the species of AM-forming fungal associations, can account for about 25% of the usually reported variations of foliar (15)N found in field situations and do so by (15)N enrichment rather than depletion. Copyright 1999 John Wiley & Sons, Ltd.     

Shakedown and limit analysis of periodic composites

The optimization of fiber distribution is analyzed in order to improve the strength performance of metal-matrix composite material, which is submitted to two variable independent loads by coupling homogenization and shakedown theories. Numerical Direct Methods are applied to acquire the shakedown domain of three-dimensional heterogeneous elastic-perfectly plastic fiber-reinforced composite for optimal design. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Einfaches Gerät zur Messung sehr kleiner Druckdifferenzen

A quadratic plate moves with very small clearance in an annular duct with a width of 1 cm². This plate is connected to a turnable spindle in the axis of the duct and can move with it against a thin spiral spring. On both sides of this plate pressures are applied, the difference of which is to be measured. Its amount can be read with a pointer on a scale. In measuring a small loss of gas will occur through the narrow slit between plate and annular duct. If this loss is not admissable, it can be avoided by using two equal instruments, of which one works as zero-instrument in a kind of compensation method. The loss of the second instrument is supplied from an additional source of gas. The instrument permits measurements with an accuracy of fractions of thousandth of a mm water column.

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Einfaches Gerät zur Messung sehr kleiner Druckdifferenzen

Zusammenfassung Eine quadratische Platte bewegt sich mit seht geringem Spiel in einem ringförmigen Kanal von l cm² Querschnitt, sie ist mit einer drehbaren Welle verbunden, die in der Achse des Kanals liegt und kann sich mit dieser gegen eine dünne Spiralfeder bewegen. Auf die beiden Seiten dieser Platte wirkt die zu messende Druckdifferenz und ihre Größe kann mit Hilfe eines Zeigers abgelesen werden. Die Messung ist mit einer geringen Menge überströmenden Gases durch den Spalt zwischen Platte und Ringkanal verbunden. Ist diese Überströmung nicht zulässig, so kann man sie durch Verwenden von zwei Geräten gleicher Art vermeiden, von denen das eine als Nullinstrument nach einer Art von Kompensationsverfahren arbeitet und der Gasverlust des anderen von einer zusätzlichen Gasquelle geliefert wird. Das Gerät erlaubt Messungen mit einer Genauigkeit von Bruchteilen eines Tausendstel mm Wassersäule.

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Prof. Dr.-Ing. U. Grigull zum 60. Geburtstag.     

Bandwidth of spectral resolution for two-formant synthetic vowels and two-tone complex signals

Spectral integration refers to the summation of activity beyond the bandwidth of the peripheral auditory filter. Several experimental lines have sought to determine the bandwidth of this "supracritical" band phenomenon. This paper reports on two experiments which tested the limit on spectral integration in the same listeners. Experiment I verified the critical separation of 3.5 bark in two-formant synthetic vowels as advocated by the center-of-gravity (COG) hypothesis. According to the COG effect, two formants are integrated into a single perceived peak if their separation does not exceed approximately 3.5 bark. With several modifications to the methods of a classic COG matching task, the present listeners responded to changes in pitch in two-formant synthetic vowels, not estimating their phonetic quality. By changing the amplitude ratio of the formants, the frequency of the perceived peak was closer to that of the stronger formant. This COG effect disappeared with larger formant separation. In a second experiment, auditory spectral resolution bandwidths were measured for the same listeners using common-envelope, two-tone complex signals. Results showed that the limits of spectral averaging in two-formant vowels and two-tone spectral resolution bandwidth were related for two of the three listeners. The third failed to perform the discrimination task. For the two subjects who completed both tasks, the results suggest that the critical region in vowel task and the complex-tone discriminability estimates are linked to a common mechanism, i.e., to an auditory spectral resolving power. A signal-processing model is proposed to predict the COG effect in two-formant synthetic vowels. The model introduces two modifications to Hermansky's [J. Acoust. Soc. Am. 87, 1738-1752 (1990)] perceptual linear predictive (PLP) model. The model predictions are generally compatible with the present experimental results and with the predictions of several earlier models accounting for the COG effect.     

Effects of normal and pathologic eardrum impedance on sound pressure in the aided ear canal: a computer simulation

Reported herein are results of computer simulations of aided sound spectra in ears with normal and pathologic eardrum impedance. The computer technique used in this study has been reported elsewhere [D. P. Egolf, D. R. Tree, and L. L. Feth, J. Acoust. Soc. Am. 63, 264-271 (1978)]. Consequently, to develop reader confidence in the computer scheme, its application to real ears was first tested. This was accomplished by (1) comparing computed spectral data with in-the-ear measurements and (2) comparing real ear minus 2-cc coupler data-both computer generated--with an idealized difference curve published elsewhere [R. M. Sachs and M. D. Burkhard, unpublished rep. no. 20022-1, Industrial Research Products, Inc., Elk Grove Village, IL (1972)]. Results indicate that the wide variation in eardrum impedance among normals evidenced in other studies produces a corresponding wide variation in aided spectrum shape. Likewise, simulations utilizing two sets of pathologic eardrum impedance data obtained from the literature show that aided sound spectra in such ears are likely to be significantly different from those occurring in normal ears. These findings suggest, as others have concluded, that there may be a substantial variation in spectrum shape among individuals wearing identically the same hearing aid--even if those individuals have normal hearing. In conclusion, questions are raised about the use of real-ear simulators and the need for a comprehensive computer-based model of an entire hearing aid.     

Upon electric charge systems moving without acceleration and associated with charge creation

A discussion is given of certain electromagnetic fields associated with charges moving with zero acceleration. These fields involve zero magnetic field and the creation of charge.     

Mathematical predictions of electroacoustic frequency response of in situ hearing aids

The amplitude spectrum of an acoustic signal presented to the microphone of a hearing aid is altered drastically before it finally reaches the user's eardrum. A major part of this alteration is due to the interaction of various mechanical and acoustic resonances which are characteristic of the hearing-aid receiver and the sound transmission system linking the receiver with the eardrum. Because of the complexity of this phenomenon, there is yet no means for predicting, a priori, the true shape of the sound spectrum that will occur at the user's eardrum. This paper reports on the development and testing of just such a scheme. The accuracy of this scheme--a computer-aided mathematical technique--is measured in the laboratory on real and artificial ears. The results of those measurements show good agreement between experimental and computer-generated data below 5000 Hz.     

Second-harmonic optical spectroscopy on split-ring-resonator arrays

Previous second-harmonic-generation experiments on metallic split-ring-resonator arrays have been performed at fixed fundamental laser center frequency. Here, we perform nonlinear optical spectroscopy on a first set of samples, revealing pronounced resonances. Furthermore, to clarify the role of higher-order split-ring resonances, we perform additional experiments on a second set of samples in which the fundamental split-ring-resonator resonance frequencies are lithographically tuned, whereas the higher-order resonances are fixed. We find that the higher-order resonances merely reabsorb the second-harmonic generation, revealing the fundamental split-ring resonance as the nonlinear source.