Evidence for a 304-day Orbital Period for GX 1+4

In this paper we report strong evidence for a ~304-day periodicity in the spin history of the accretion-powered pulsar GX 1+4 that is very likely to be a signature of the orbital period of the system. Using BATSE public-domain data, we show a highly-significant periodic modulation of the pulsar frequency from 1991 to date which is in excellent agreement with the ephemeris proposed by Cutler, Dennis & Dolan in 1986, which were based on a few events of enhanced spin-up that occurred during the pulsar's spin-up era in the 1970s. Our results indicate that the orbital period of GX 1+4 is 303.8+-1.1 days, making it by far the widest low-mass X-ray binary system known. A likely scenario for this system is an elliptical orbit in which the neutron star decreases its spin-down rate (or even exhibits a momentary spin-up behavior) at periastron passages due to the higher torque exerted by the accretion disk onto the magnetosphere of the neutron star.Comment: 5 pages, 2 figures, 1 single PS file, to appear in "Proceedings of the 5th Compton Symposium on Gamma-Ray Astrophysics", AI

Performance of Nellore steers in Panicum maximum pastures.

O objetivo do trabalho foi avaliar o ganho de peso médio diário (GMD) de novilhos Nelore, a taxa de lotação(TL) e o ganho de peso por área (GA) em pastagens de três cultivares de Panicum maximum. O experimento foi conduzido em Planaltina, Distrito Federal, Brasil, durante 248 dias, divididos em período chuvoso (140 dias) e período seco (108 dias). Os tratamentos experimentais foram as cultivares Zuri, Tamani e Massai manejadas em lotação rotacionada em ciclos de pastejo de 28 dias (21 dias de descanso e 7 dias de pastejo) na estação chuvosa e 56 dias (42 dias de descanso e 14 dias de pastejo) na estação seca. Os ajustes na taxa de lotação foram conduzidos considerando a mesma oferta de forragem entre tratamentos. O GMD (novilhos desmamados de 216 kg de peso vivo) foi de 0,352, 0,391 e 0,254kg/cabeça para as cultivares Zuri, Tamani e Massai, respectivamente. O GMD diminuiu no período seco, mas permaneceu maior para Zuri e Tamani. O maior desempenho individual foi associado a valores mais elevados de proteína bruta e digestibilidade da forragem, especialmente para a cultivar Tamani. A TL foi mais elevada para Massai e Zuri em ambas as estações do ano, enquanto o GA foi semelhante entre os trata-mentos. Embora a cultivar Tamani tenha proporcionado lotação mais baixa, o GA foi parcialmente compensado por valores ele-vados de GMD. A cultivar Zuri conseguiu aliar maior desempenho individual com alta lotação

Optical and Near-Infrared UBVRIJHK Photometry for the RR Lyrae stars in the Nearby Globular Cluster M4 (NGC 6121)

We present optical and near-infrared UBVRIJHK photometry of stars in the Galactic globular cluster M4 (NGC 6121) based upon a large corpus of observations obtained mainly from public astronomical archives. We concentrate on the RR Lyrae variable stars in the cluster, and make a particular effort to accurately reidentify the previously discovered variables. We have also discovered two new probable RR Lyrae variables in the M4 field: one of them by its position on the sky and its photometric properties is a probable member of the cluster, and the second is a probable background (bulge?) object. We provide accurate equatorial coordinates for all 47 stars identified as RR Lyraes, new photometric measurements for 46 of them, and new period estimates for 45. We have also derived accurate positions and mean photometry for 34 more stars previously identified as variable stars of other types, and for an additional five non-RR Lyrae variable stars identified for the first time here. We present optical and near-infrared color-magnitude diagrams for the cluster and show the locations of the variable stars in them. We present the Bailey (period-amplitude) diagrams and the period-frequency histogram for the RR Lyrae stars in M4 and compare them to the corresponding diagrams for M5 (NGC 5904). We conclude that the RR Lyrae populations in the two clusters are quite similar in all the relevant properties that we have considered. The mean periods, pulsation-mode ratios, and Bailey diagrams of these two clusters show support for the recently proposed "Oosterhoff-neutral" classification.Comment: 33 pages, 16 figures, 7 table

Discovery of optical pulsations in V2116 Ophiuchi/GX 1+4

We report the detection of pulsations with $\sim 124$ s period in V2116 Oph, the optical counterpart of the low-mass X-ray binary GX 1+4. The pulsations are sinusoidal with modulation amplitude of up to 4% in blue light and were observed in ten different observing sessions during 1996 April-August using a CCD photometer at the 1.6-m and 0.6-m telescopes of Laborat\'orio Nacional de Astrof\'{\i}sica, in Brazil. The pulsations were also observed with the $UBVRI$ fast photometer. With only one exception the observed optical periods are consistent with those observed by the BATSE instrument on board the Compton Gamma Ray Observatory at the same epoch. There is a definite correlation between the observability of pulsations and the optical brightness of the system: V2116~Oph had $R$ magnitude in the range $15.3-15.5$ when the pulsed signal was detected, and $R = 16.0-17.7$ when no pulsations were present. The discovery makes GX 1+4 only the third of $\sim 35$ accretion-powered X-ray pulsars to be firmly detected as a pulsating source in the optical. The presence of flickering and pulsations in V2116 Oph adds strong evidence for an accretion disk scenario in this system. The absolute magnitude of the pulsed component on 1996 May 27 is estimated to be $M_V \sim -1.5$. The implied dimensions for the emitting region are 1.1 R_{\sun}, 3.2 R_{\sun}, and 7.0 R_{\sun}, for black-body spectral distributions with $T = 10^5$ K, $2 \times 10^4$ K, and $1 \times 10^4$ K, respectively.Comment: 9 pages, 3 figures in PostScript, latex, accepted for publication on the Astrophysical Journal Letter

Configurational temperature control for atomic and molecular systems

A new configurational temperature thermostat suitable for molecules with holonomic constraints is derived. This thermostat has a simple set of motion equations, can generate the canonical ensemble in both position and momentum space, acts homogeneously through the spatial coordinates, and does not intrinsically violate the constraints. Our new configurational thermostat is closely related to the kinetic temperature Nosé-Hoover thermostat with feedback coupled to the position variables via a term proportional to the net molecular force. We validate the thermostat by comparing equilibrium static and dynamic quantities for a fluid of n-decane molecules under configurational and kinetic temperature control. Practical aspects concerning the implementation of the new thermostat in a molecular dynamics code and the potential applications are discussed

Polar distortions in hydrogen bonded organic ferroelectrics

Although ferroelectric compounds containing hydrogen bonds were among the first to be discovered, organic ferroelectrics are relatively rare. The discovery of high polarization at room temperature in croconic acid [Nature \textbf{463}, 789 (2010)] has led to a renewed interest in organic ferroelectrics. We present an ab-initio study of two ferroelectric organic molecular crystals, 1-cyclobutene-1,2-dicarboxylic acid (CBDC) and 2-phenylmalondialdehyde (PhMDA). By using a distortion-mode analysis we shed light on the microscopic mechanisms contributing to the polarization, which we find to be as large as 14.3 and 7.0\,$\mu$C/cm$^{2}$ for CBDC and PhMDA respectively. These results suggest that it may be fruitful to search among known but poorly characterized organic compounds for organic ferroelectrics with enhanced polar properties suitable for device applications.Comment: Submitte

Viabilidade de pupas de Thelosia camina schaus coletadas em plantios de erva-mate.

Resumo

Influência da adubação fosfatada e calagem sobre a absorção do zinco, em dois solos de Minas.

Two experiments were installed in the greenhouse to study the relationships between phosphate fertilization, liming and zinc fertilization. One experiment used a red latosol soil while the other used a dark brown acid soil. Hybrid corn AG 206 was used to plant both experiments. The data collected consisted of dry matter productions level of zinc in the leaves, stems and tootes of the corn as well as the P/Zn and Ca/Zn rations in the leaves. Phosphate fertilization and liming lowed the level of zinc in the corn leaves to a point equal to or lower than 14 ppm. These leves were below 80% of the maximum yields of the experiments. The application of 4,5 ppm of zinc to the soil was adequate to raise the level of zinc in the leaves above the critical level. It also increase the production was limited by a zinc deficiency. The phosphorus and zinc interaction, which ocurred primarily in the roots of the plant, reduced the translocation of zinc to the leaves. The interaction between liming and zinc ocurred prior to the absorption of zinc by the plant. It aprears that there are ratios between phosphorus and zinc between calcium and zinc in the leaves which are critical to good plant growth. The critical P/Zn ratio is betwee 300 and 470 and the critical Ca/Zn ratio between 455-640