Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History

We model the star formation history (SFH) and the chemical evolution of the Galactic disk by combining an infall model and a limit-cycle model of the interstellar medium (ISM). Recent observations have shown that the SFH of the Galactic disk violently variates or oscillates. We model the oscillatory SFH based on the limit-cycle behavior of the fractional masses of three components of the ISM. The observed period of the oscillation ($\sim 1$ Gyr) is reproduced within the natural parameter range. This means that we can interpret the oscillatory SFH as the limit-cycle behavior of the ISM. We then test the chemical evolution of stars and gas in the framework of the limit-cycle model, since the oscillatory behavior of the SFH may cause an oscillatory evolution of the metallicity. We find however that the oscillatory behavior of metallicity is not prominent because the metallicity reflects the past integrated SFH. This indicates that the metallicity cannot be used to distinguish an oscillatory SFH from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap

In vitro propagation of Cordia verbenaceae L. (Boraginaceae).

Clonal propagation by tissue culture is useful to regenerate large populations of plants with similar characteristics. There are no previous reports of micropropagation of Cordia verbenacea. In this study, in vitro techniques were applied multiply this important Brazilian medicinal plant. Apical and nodal segments were cultured on Murashige and Skoog solid (0,6%) medium (MS) supplemented with 0.1, 1.0, 5.0 and 10.0 µM kinetin and 0.01µM naphthaleneacetic acid (NAA). Segments apical yielded more propagules than nodal segments. The number and length of propagules increased with in kinetin levels at 5 µM kinetin, decrease with more concentration. The treatment containing 5 µM kinetin and 0.01µM NAA yielded 2.7 propagules per explant. Propagules rooted on MS medium without growth regulators. Finally, 90-95% of the micropropagated plants survived when transferred to greenhouse conditions

Genetic diversity in a jaborandi ( Pilocarpus microphyllus Stapf.) germplasm bank assessed by RAPD markers.

Diversidade genética em banco de germoplasma de jaborandi ( Pilocarpus microphyllus Stapf .) por meio de marcadores RAPD. O objetivo deste trabalho é avaliar a presença de variabilidade genética no banco de germoplasma de P. microphyllus da Embrapa Amazônia Oriental por meio de marcadores RAPD. Foi extraído o DNA de 93 indivíduos, pertencentes a 12 áreas de coleta presentes no banco de germoplasma. Foram construídos dendrogramas entre indivíduos e entre áreas de coleta, usando os coeficientes de similaridade de Nei & Li por meio do programa NTSYS-pc. Para verificar a distribuição da variabilidade, foi realizada a análise de variância molecular (AMOVA), sendo obtidas as variâncias entre e dentro de áreas de coleta. Foi usado o índice de diversidade de Shannon, para medir a diversidade de cada área. Foi verificada uma boa amplitude de similaridades entre os indivíduos, sendo que o dendrograma não agrupou por completo os indivíduos de acordo com sua origem. A AMOVA obteve 24,16% de variação entre áreas e 75,84% dentro de áreas

Schwinger's Method for the Massive Casimir Effect

We apply to the massive scalar field a method recently proposed by Schwinger to calculate the Casimir effect. The method is applied with two different regularization schemes: the Schwinger original one by means of Poisson formula and another one by means of analytical continuation.Comment: plain TeX, 6 pages, DFTUZ-93-2

Reconstructing Deconstruction: High-Velocity Cloud Distance Through Disruption Morphology

We present Arecibo L-band Feed Array 21-cm observations of a sub-complex of HVCs at the tip of the Anti-Center Complex. These observations show morphological details that point to interaction with the ambient halo medium and differential drag within the cloud sub-complex. We develop a new technique for measuring cloud distances, which relies upon these observed morphological and kinematic characteristics, and show that it is consistent with H-alpha distances. These results are consistent with distances to HVCs and halo densities derived from models in which HVCs are formed from cooling halo gas.Comment: 8 pages, 2 figures, 1 tabe, Accepted to Ap

Ongoing Galactic Accretion: Simulations and Observations of Condensed Gas in Hot Halos

Ongoing accretion onto galactic disks has been recently theorized to progress via the unstable cooling of the baryonic halo into condensed clouds. These clouds have been identified as analogous to the High-Velocity Clouds (HVCs) observed in HI in our Galaxy. Here we compare the distribution of HVCs observed around our own Galaxy and extra-planar gas around the Andromeda galaxy to these possible HVC analogs in a simulation of galaxy formation that naturally generates these condensed clouds. We find a very good correspondence between these observations and the simulation, in terms of number, angular size, velocity distribution, overall flux and flux distribution of the clouds. We show that condensed cloud accretion only accounts for ~ 0.2 M_solar / year of the current overall Galactic accretion in the simulations. We also find that the simulated halo clouds accelerate and become more massive as they fall toward the disk. The parameter space of the simulated clouds is consistent with all of the observed HVC complexes that have distance constraints, except the Magellanic Stream which is known to have a different origin. We also find that nearly half of these simulated halo clouds would be indistinguishable from lower-velocity gas and that this effect is strongest further from the disk of the galaxy, thus indicating a possible missing population of HVCs. These results indicate that the majority of HVCs are consistent with being infalling, condensed clouds that are a remnant of Galaxy formation.Comment: 10 pages, 6 figures, ApJ Accepted. Some changes to techniqu

Review of two decades of progress in the development of successful drip irrigation for onions.

The irrigation needs of long day onion (Allium cepa) have been extensively studied at Ontario, Oregon, over the past 22 years. Drip irrigation has compared favorably with furrow and sprinkler irrigation systems. Onions were found to have very narrow soil moisture requirements. Drier soil than optima led to yield loss and wetter soil promoted bulb decomposition. Short term water stress at the three- to six-leaf stages of plant growth promoted multiple centers in long day onion varieties. Irrigation was successfully scheduled using soil water tension or evapotranspiration. Nitrogen fertilization and plant populations have been optimized. Drip system design must carefully consider the hydraulic conductivity of the soil in the placement of tape and onion rows since the soil moisture must wick over from the drip tape to the onion plant. The drip irrigation system design uniformity, operation, and maintenance are essential given onion?s low tolerance to water stress

Caby Photometry of the Hyades: Comparisons to the Field Stars

Intermediate-band photometry of the Hyades cluster on the Caby system is presented for dwarf stars ranging from spectral type A through late K. A mean hk, b-y relation is constructed using only single stars without anomalous atmospheres and compared to the field stars of the solar neighborhood. For the F dwarfs, the Hyades relation defines an approximate LOWER bound in the two-color diagram, consistent with an [Fe/H] between +0.10 and +0.15. These index-color diagrams follow the common convention of presenting stars with highest abundance at the bottom of the plot although the index values for the metal-rich stars are numerically larger. For field F dwarfs in the range [Fe/H] between +0.4 and -1.0, [Fe/H] = -5.6 delta-hk + 0.125, with no evidence for a color dependence in the slope. For the G and K dwarfs, the Hyades mean relation crosses the field star distribution in the two-color diagram, defining an approximate UPPER bound for the local disk stars. Stars found above the Hyades stars fall in at least one of three categories: [Fe/H] below -0.7, [Fe/H] above that of the Hyades, or chromospherically active. It is concluded that, contrary to the predictions of model atmospheres, the hk index for cool dwarfs at a given color hits a maximum value for stars below solar composition and, with increasing [Fe/H] above some critical value, declines. This trend is consistent, however, with the predictions from synthetic indices based upon much narrower Ca filters where the crossover is caused by the metallicity sensitivity of b-y.Comment: 13 pages, 9 eps figures, 1 tex table, 1 ascii tabl