Hot phonon decay in supported and suspended exfoliated graphene

Near infrared pump-probe spectroscopy has been used to measure the ultrafast dynamics of photoexcited charge carriers in monolayer and multilayer graphene. We observe two decay processes occurring on 100 fs and 2 ps timescales. The first is attributed to the rapid electron-phonon thermalisation in the system. The second timescale is found to be due to the slow decay of hot phonons. Using a simple theoretical model we calculate the hot phonon decay rate and show that it is significantly faster in monolayer flakes than in multilayer ones. In contrast to recent claims, we show that this enhanced decay rate is not due to the coupling to substrate phonons, since we have also seen the same effect in suspended flakes. Possible intrinsic decay mechanisms that could cause such an effect are discussed.Comment: 4 pages, 3 figure

Complete chaotic synchronization in mutually coupled time-delay systems

Complete chaotic synchronization of end lasers has been observed in a line of mutually coupled, time-delayed system of three lasers, with no direct communication between the end lasers. The present paper uses ideas from generalized synchronization to explain the complete synchronization in the presence of long coupling delays, applied to a model of mutually coupled semiconductor lasers in a line. These ideas significantly simplify the analysis by casting the stability in terms of the local dynamics of each laser. The variational equations near the synchronization manifold are analyzed, and used to derive the synchronization condition that is a function of the parameters. The results explain and predict the dependence of synchronization on various parameters, such as time-delays, strength of coupling and dissipation. The ideas can be applied to understand complete synchronization in other chaotic systems with coupling delays and no direct communication between synchronized sub-systems.Comment: 22 pages, 6 figure

A subsonic D-region probe-theory and instrumentation Scientific report no. 247

D-layer, subsonic, ion and electron probe operational mobility theory and instrumentation descriptio

Evolution of the Pairwise Peculiar Velocity Distribution Function in Lagrangian Perturbation Theory

The statistical distribution of the radial pairwise peculiar velocity of galaxies is known to have an exponential form as implied by observations and explicitly shown in N-body simulations. Here we calculate its statistical distribution function using the Zel'dovich approximation assuming that the primordial density fluctuations are Gaussian distributed. We show that the exponential distribution is realized as a transient phenomena on megaparsec scales in the standard cold-dark-matter model.Comment: 19 pages, 8 Postscript figures, AAS LaTe

The Effect of Diethylstilbestrol on the Digestibility of Dry Matter and Nitrogen and on Nitrogen Retention in Lambs

Although the usefulness of orally administered diethylstilbestrol (stilbestrol) in increasing weight gains and feed efficiency of fattening cattle has been established, little is known concerning the mechanism by which it exerts its beneficial effect. Two possible modes of action may exist. First, the stilbestrol may have some effect on the rumen microorganisms which might cause an increased digestion of feed in the rumen. Brooks et al. (1954) have shown that stilbestrol increased the digestibility of cellulose in the artificial rumen. They also obtained increased cellulose and protein digestion in sheep when stilbestrol was fed. However the levels fed the sheep were considerably above the mg. per lamb per day reported to be effective with lambs (Hale et al. 1955). Sykes et al. (1956) reported an increase in crude fiber digestibility and a decrease in protein digestibility with lactating cows when stilbestrol was fed. Digestibility of the dry matter of the ration tended to be improved but the differences were not statistically significant. Erwin et al. (1956) reported stilbestroI had no effect on digestibility of dry matter, crude fiber, crude protein or ether extract with steers. Secondly, the orally fed stilbestrol may exert some action on the metabolism of the animal\u27s tissue which is thought to occur when the stilbestrol is implanted (Clegg and Cole, 19 54). It has been shown that implanted stilbestrol increased nitrogen retention but had no effect on ration digestibility (Jordan 1953: Whitehair et al. 1953). Bell et al. (1955) found that orally fed stilbestrol increased nitrogen retention in lambs. Presumably this action is brought about by the absorbed stilbestrol acting similar to that on the implanted stilbestrol. The objectives of this report were to study the effects of different levels of stilbestrol upon the digestibility of dry matter and crude protein and on nitrogen retention with wether lambs

Measurements at low energies of the polarization-transfer coefficient Kyy' for the reaction 3H(p,n)3He at 0 degrees

Measurements of the transverse polarization coefficient Kyy' for the reaction 3H(p,n)3He are reported for outgoing neutron energies of 1.94, 5.21, and 5.81 MeV. This reaction is important both as a source of polarized neutrons for nuclear physics experiments, and as a test of theoretical descriptions of the nuclear four-body system. Comparison is made to previous measurements, confirming the 3H(p,n)3He reaction can be used as a polarized neutron source with the polarization known to an accuracy of approximately 5%. Comparison to R-matrix theory suggests that the sign of the 3F3 phase-shift parameter is incorrect. Changing the sign of this parameter dramatically improves the agreement between theory and experiment.Comment: 12 pages, RevTeX, 5 eps figures, submitted to Phys. Rev.

Control of unstable steady states by time-delayed feedback methods

We show that time-delayed feedback methods, which have successfully been used to control unstable periodic ortbits, provide a tool to stabilize unstable steady states. We present an analytical investigation of the feedback scheme using the Lambert function and discuss effects of both a low-pass filter included in the control loop and non-zero latency times associated with the generation and injection of the feedback signal.Comment: 8 pages, 11 figure