Tailoring the dynamics of multisection lasers for 40 Gb/s direct modulation
We demonstrate theoretically how a proper tailoring of the longitudinal structure of multisection semiconductor laser help to achieve the required device performance when modulating current with 40 Gbit/s PRBS signal. For this reason we simulate and analyze the longitudinal dynamics with the software package LDSL-tool.
Anderson lattice behavior in Yb1-xLuxAl3
Measurements of magnetic susceptibility x(T), specific heatC(T), Hall coefficient RH(T), and Yb valence n521n f @ f -occupation number n f (T) determined from Yb LIII x-ray absorption measurements# were carried out on single crystals of Yb12xLuxAl3. The low-temperature anomalies observed in x(T) and C(T) corresponding to an energy scale Tcoh;40 K in the intermediate valence, Kondo lattice compound YbAl3 are suppressed by Lu concentrations as small as 5% suggesting these low-T anomalies are extremely sensitive to disorder and, therefore, are a true coherence effect. By comparing the temperature dependence of various physical quantities to the predictions of the Anderson impurity model, the slow crossover behavior observed in YbAl3, in which the data evolve from a low-temperature coherent, Fermi-liquid regime to a high-temperature local moment regime more gradually than predicted by the Anderson impurity model, appears to evolve to fast crossover behavior at x;0.7 where the evolution is more rapid than predicted. These two phenomena found in Yb12xLuxAl3, i.e., the low-T anomalies and the slow/fast crossover behavior are discussed in relation to recent theories of the Anderson lattice.
VLA stereoscopy of solar active regions. 2: Altitude, relative motion, and center-to-limb darkening of 20 centimeter emission
A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of q(sub A) approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin(exp 2)B)). 5. We find a statistical limb darkening, which can be described by the relation (T(sub B)(alpha))/T(sub B)(0)) = 0.4 + ((0.6(cos(exp 2) alpha)) for sources with T(sub B) greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance.