Ultrafast electroabsorption dynamics in an InAs quantum dot saturable absorber at 1.3 mu m

The authors report a direct measurement of the absorption dynamics in an InAs p-i-n ridge waveguide quantum dot modulator. The carrier escape mechanisms are investigated via subpicosecond pump-probe measurements at room temperature, under reverse bias conditions. The optical pulses employed are degenerate in wavelength with the quantum dot ground state transition at 1.28 mu m. The absorption change recovers with characteristic times ranging from 62 ps (0 V) to similar to 700 fs (-10 V), showing a decrease of nearly two orders of magnitude. The authors show that at low applied fields, this recovery is attributed to thermionic emission while for higher applied fields, tunneling becomes the dominant mechanism. (c) 2006 American Institute of Physics.</p

Kemampuan Pemahaman Matematis Siswa Melalui Model Pembelajaran Auditory Intellectualy Repetition Dan Problem Based Learning

Tujuan dari penelitian ini adalah: (1) Untuk mengetahui perbedaan kemampuan pemahaman matematis antara siswa yang mendapatkan model pembelajaran Auditory Intellectualy Repetition (AIR) dengan Problem Based Learning (PBL)?, (2) Untuk mengetahui sikap siswa terhadap mata pelajaran matematika dengan menerapkan model pembelajaran Auditory Intellectualy Repetition (AIR)?, (3) Untuk mengetahui sikap siswa terhadap mata pelajaran matematika dengan menerapkanProblem Based Learning (PBL)?.Penelitian ini merupakan penelitian kuasi eksperimen dengan desain penelitianPretest-Posttest ControlDesign. Populasi pada penelitian ini adalah seluruh kelas VII SMP Negeri 1 Cisurupan dengan mengambil sampelsebanyak dua kelas yaitu kelas VII-A sebagai kelas eksperimen Idan kelas VII-B sebagai kelas eksperimen II.Instrumen penelitian yang digunakan adalah tes kemampuan pemahaman matematis dan angket siswa.Berdasarkan hasil penelitian,diketahui bahwa: (1) Terdapat perbedaan kemampuan pemahaman matematis antara siswa yang mendapatkan model pembelajaran AIR dengan PBL. (2) Sikap siswa yang mendapatkan model pembelajaran AIR menunjukkan sikap dengan interpretasi sangat baik. (3) Sikap siswa yang mendapatkan PBL menunjukkan sikap dengan interpretasi baik

3C 48: Stellar Populations and the Kinematics of Stars and Gas in the Host Galaxy

We present deep Keck LRIS spectroscopy of the host galaxy of 3C 48. Our observations at various slit positions sample the different luminous components near the quasar, including the apparent tidal tail to the NW and several strong emission line regions. By fitting Bruzual & Charlot (1996) population synthesis models to our spectra, we obtain ages for the most recent major episodes of star formation in various parts of the host galaxy covered by our slits. There is vigorous current star formation in regions just NE and SE of the quasar and post-starburst regions with ages up to ~10^8 years in other parts of the host galaxy, but most of the NW tidal tail shows no sign of significant recent star formation. We use these model fits, together with the kinematics of the stars and gas, to outline a plausible evolutionary history for the host galaxy, its recent starburst activity, the triggering of the quasar, and the interaction of the radio jet with the ambient gas. There is strong evidence that the 3C 48 host is an ongoing merger, and that it is probably near the peak of its starburst activity. Nevertheless, the quasar itself seems to suffer little extinction, perhaps because we are viewing it along a particularly favorable line-of-sight.Comment: 27 pages plus 11 figures (7 postscript, 4 gif). Postscript version including figures (1840 kb) available at http://www.ifa.hawaii.edu/~canaguby/preprints.html . Accepted for publication in Ap

Chemical abundances in bright giants of the globular cluster M62 (NGC 6266)

With the exception of Terzan 5, all the Galactic globular clusters that possess significant metallicity spreads, such as omega Cen and M22, are preferentially the more luminous clusters with extended horizontal branches. Here we present radial velocities and chemical abundances for seven bright giants in the globular cluster M62, a previously little-studied cluster. With M_V = -9.18, M62 is the ninth most luminous Galactic globular cluster and has an extended horizontal branch. Within our sample, we find (i) no evidence for a dispersion in metallicity, [Fe/H], beyond the measurement uncertainties, (ii) star-to-star abundance variations for C, O, Na and Al with the usual correlations between these elements as seen in other globular clusters, and (iii) a global enrichment for the elements Zr, Ba and La at the level [X/Fe] = +0.4 dex. For elements heavier than La, the abundance ratios are consistent with the scaled-solar $r$-process distribution. Below La, the abundances are anomalous when compared to the scaled-solar s-process or r-process distributions. For these elements, the abundance signature in M62 is in agreement with predictions of the s-process from fast-rotating massive stars, although the high [Rb/Y] ratio we measure may be a challenge to this scenario.Comment: Accepted for publication in MNRA

Global existence of classical solutions to the Vlasov-Poisson system in a three dimensional, cosmological setting

The initial value problem for the Vlasov-Poisson system is by now well understood in the case of an isolated system where, by definition, the distribution function of the particles as well as the gravitational potential vanish at spatial infinity. Here we start with homogeneous solutions, which have a spatially constant, non-zero mass density and which describe the mass distribution in a Newtonian model of the universe. These homogeneous states can be constructed explicitly, and we consider deviations from such homogeneous states, which then satisfy a modified version of the Vlasov-Poisson system. We prove global existence and uniqueness of classical solutions to the corresponding initial value problem for initial data which represent spatially periodic deviations from homogeneous states.Comment: 23 pages, Latex, report #

The 2011 Eruption of the Recurrent Nova T Pyxidis; the Discovery, the Pre-eruption Rise, the Pre-eruption Orbital Period, and the Reason for the Long Delay

We report the discovery by M. Linnolt on JD 2455665.7931 (UT 2011 April 14.29) of the sixth eruption of the recurrent nova T Pyxidis. This discovery was made just as the initial fast rise was starting, so with fast notification and response by observers worldwide, the entire initial rise was covered (the first for any nova), and with high time resolution in three filters. The speed of the rise peaked at 9 mag/day, while the light curve is well fit over only the first two days by a model with a uniformly expanding sphere. We also report the discovery by R. Stubbings of a pre-eruption rise starting 18 days before the eruption, peaking 1.1 mag brighter than its long-time average, and then fading back towards quiescence 4 days before the eruption. This unique and mysterious behavior is only the fourth known anticipatory rise closely spaced before a nova eruption. We present 19 timings of photometric minima from 1986 to February 2011, where the orbital period is fast increasing with P/dot{P}=313,000 yrs. From 2008-2011, T Pyx had a small change in this rate of increase, so that the orbital period at the time of eruption was 0.07622950+-0.00000008 days. This strong and steady increase of the orbital period can only come from mass transfer, for which we calculate a rate of 1.7-3.5x10^-7 Mo/yr. We report 6116 magnitudes between 1890 and 2011, for an average B=15.59+-0.01 from 1967-2011, which allows for an eruption in 2011 if the blue flux is nearly proportional to the accretion rate. The ultraviolet-optical-infrared spectral energy distribution is well fit by a power law with flux proportional to nu^1.0, although the narrow ultraviolet region has a tilt with a fit of \nu^{1/3}. We prove that most of the T Pyx light is not coming from a disk, or any superposition of blackbodies, but rather is coming from some nonthermal source.Comment: ApJ submitted, 62 pages, 8 figures; much added data, updated analysi

Karhunen-Loeve eigenvalue problems in cosmology: how should we tackle large data sets?

Since cosmology is no longer "the data-starved science", the problem of how to best analyze large data sets has recently received considerable attention, and Karhunen-Loeve eigenvalue methods have been applied to both galaxy redshift surveys and Cosmic Microwave Background (CMB) maps. We present a comprehensive discussion of methods for estimating cosmological parameters from large data sets, which includes the previously published techniques as special cases. We show that both the problem of estimating several parameters jointly and the problem of not knowing the parameters a priori can be readily solved by adding an extra singular value decomposition step. It has recently been argued that the information content in a sky map from a next generation CMB satellite is sufficient to measure key cosmological parameters (h, Omega, Lambda, etc) to an accuracy of a few percent or better - in principle. In practice, the data set is so large that both a brute force likelihood analysis and a direct expansion in signal-to-noise eigenmodes will be computationally unfeasible. We argue that it is likely that a Karhunen-Loeve approach can nonetheless measure the parameters with close to maximal accuracy, if preceded by an appropriate form of quadratic "pre-compression". We also discuss practical issues regarding parameter estimation from present and future galaxy redshift surveys, and illustrate this with a generalized eigenmode analysis of the IRAS 1.2 Jy survey optimized for measuring beta=Omega^{0.6}/b using redshift space distortions.Comment: 15 pages, with 5 figures included. Substantially expanded with worked COBE examples for e.g. the multiparameter case. Available from http://www.sns.ias.edu/~max/karhunen.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/karhunen.html (faster from Europe) or from [email protected]

Travelling waves in a drifting flux lattice

Starting from the time-dependent Ginzburg-Landau (TDGL) equations for a type II superconductor, we derive the equations of motion for the displacement field of a moving vortex lattice without inertia or pinning. We show that it is linearly stable and, surprisingly, that it supports wavelike long-wavelength excitations arising not from inertia or elasticity but from the strain-dependent mobility of the moving lattice. It should be possible to image these waves, whose speeds are a few \mu m/s, using fast scanning tunnelling microscopy.Comment: 4 pages, revtex, 2 .eps figures imbedded in paper, title shortened, minor textual change

Geologic and Hydrogeologic Framework of Regional Aquifers in the Twin Mountains, Paluxy, and Woodbine Formations Near the SSC Site, North-Central Texas

Water-utility districts and many municipalities in North-Central Texas recently obtained as much as 100 percent of their water supply from deep regional aquifers in Cretaceous formations. Use of groundwater from the aquifers during the past century has resulted in water-level declines of as much as 850 ft (259 m), especially in Dallas and Tarrant Counties. Future water-level changes will depend on the amount of groundwater produced to help meet growing water-supply needs for municipalities, industries, and agriculture throughout North-Central Texas. It is probable that a significant part of the increased water demand will be met by groundwater although at less than historic rates. The objective of this study was to develop a predictive tool for studying the effect of future groundwater production from regional aquifers in North-Central Texas. To do this, we reviewed the history of groundwater development, hydrogeology of the regional aquifers, and constructed numerical models of groundwater flow. A cross-sectional model of both aquifers and confining layers was used to evaluate model boundary conditions and the vertical hydrologic properties of the confining layers. Results and insights from the cross-sectional model were used in a three-dimensional simulation of groundwater flow in the deep aquifers. The layers of the regional confining system were not explicitly included in the three-dimensional model. Hydrogeologic properties were assigned on the basis of aquifer test results and stratigraphic mapping of sandstone distribution in the aquifer units.Bureau of Economic Geolog

Phenolic Compounds And Anticancer Activity Of Commercial Sugarcane Cultivated In Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The cultivation of sugarcane hybrids (X Saccharum officinarum L.) is an important revenue source for the Brazilian economy. Herein it is reported the evaluation of the cytotoxic activity of mid-polarity sugarcane extracts against human cancer cell lines, as well as the isolation of steroids sitosterol, stigmasterol and campesterol, phenolic acids p-hydroxybenzoic, p-hydroxycinnamic, vanillic and ferulic acid, terpenoids alpha-tocopherol and beta-carotene and a novel substance in sugarcane, the flavonoid aglycone tricin (5,7,4-trihydroxy-3,5-dimethoxyflavone). The presence of large amounts of phenolic acids and the flavonoid tricin may explain the cytostatic activity observed for the mid-polarity crude extract and filtrates.88312011209Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)Fundacao AraucariaConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES