X-Ray Timing, Spectroscopy and Photometry of the Anomalous X-Ray Pulsar Candidate CXOU J010043.1-721134

We present new X-ray timing and spectral results on the 8.0-second X-ray pulsar CXOU J010043.1-721134 from a series of observations using the Chandra X-ray Observatory. We find a spin period in 2004 January of 8.020392pm0.000009 seconds. Comparison of this to 2001 Chandra observations implies a period derivative dot{P} = (1.88 pm 0.08) times 10^{-11} s s^{-1}, leading to an inferred dipole surface magnetic field of 3.9 times 10^{14} G. The spectrum is well fit to an absorbed blackbody of temperature kT = 0.38pm0.02 keV with a power law tail of photon index Gamma = 2.0pm0.6. We find that the source has an unabsorbed X-ray flux (0.5-10 keV) of 4(+2-1) times 10^{-13} erg cm^{-2} s^{-1} and a corresponding X-ray luminosity of ~2 times 10^{35} erg s^{-1} for a distance of 60 kpc. These properties support classification of CXOU J010043.1-721134 as the seventh confirmed anomalous X-ray pulsar,the eleventh confirmed magnetar, and the first magnetar to be identified in the Small Magellanic Cloud.Comment: 5 pages, plus 1 embedded eps figure. Refined coordinates of source, including typo in declination. ApJ Letters, in pres

Interaction with Nitric Oxide of the Nitrosomonas Europaea Tetraheme Protein Cytochrome C554, and Two of Its Variants, in Increasingly Reducing Environments

A re-investigation of the interaction with NO of the small tetraheme protein cytochrome c554 (C554) from Nitrosomonas europaea has shown that the 5-coordinate heme II of the 2-electron or 4-electron reduced protein will nitrosylate reversibly. The nitrosylation process was found to be first order in C554, first-order in NO, and second-order overall. The rate constant for NO binding to the heme was determined to be 3000 ± 140 M-1s-1, while the rate constant for dissociation was 0.034 ± 0.009 s-1; the degree of protein reduction does not appear to significantly influence the nitrosylation rate. In contrast to a previous report, [ Upadhyay, A. K., et al. (2006), J. Am. Chem. Soc. 128, 4330-4337] this study turned up no evidence of C554-catalyzed NO reduction, either with C55422- or with C55442-. Some sub-stoichiometric oxidation of the lowest potential heme IV was detected when C55444- was exposed to an excess of NO, and this could in principle be part of a process that yields N2O, though alternative explanations are equally plausible. The vacant heme II site of C554 is sterically crowded by three non-bonding hydrophobic amino acids, Thr 154, Pro 155 and Phe 156. Replacing Phe156 with a protonatable but still bulky histidine residue did not significantly alter the reactivity of the F156H mutant with NO, though the NO binding rate appeared to increase 10-fold. On the other hand, when Phe156 was replaced with the smaller but still hydrophobic alanine, the 6-coordinate low-spin hemes of the 4-electron reduced mutant oxidized over the course of several minutes after exposure to NO. Two-electron reduced F156A2 nitrosylated, but did not oxidize, upon exposure to NO. Notably, the nitrosylation rate for F156A2-and F156A4- was about 400x faster than for the wild type or for the F156H mutant, though the rate of the reverse denitrosylation process was almost the same for the three C554 variants. The midpoint potentials of C554, and of the F156A and F156H variants, were determined for all the hemes in these tetraheme proteins, using spectropotentiometric analysis. The heme II midpoint potential of F156H was profoundly altered from the wild type value, shifting about 170 mV to the negative. This is taken as evidence that the histidine ligand in the variant binds to the erstwhile vacant ferric heme II axial site, thus stabilizing the oxidized state. Consistent with this interpretation, the UV/Visible spectrum of fully oxidized F156H exhibited increased absorbance at 409 nm relative to the wild type, which suggests that the mutant protein has 4 low-spin ferrihemes, rather than three low-spin and one high-spin as seen in the wild type. Upon reduction of heme II though, the spectrum of F156H exhibited a band at 430 nm characteristic of high-spin ferrohemes, which suggests that His156 dissociates from the heme when this reduces. In contrast to the case with F156H, the midpoint potentials of hemes I and II in F156A were only slightly shifted relative to the wild type. On the other hand, the midpoint potentials of the low-potential hemes III and IV were shifted about 100 mV to the negative by mutating Phe156 to Ala, whereas mutation of Phe156 to His had minimal impact on these hemes. It appears that the substitution of bulky Phe by the small Ala significantly alters the conformation of the protein backbone, which in turn affects the environment of distant hemes enough to substantially alter their midpoint potentials. The lower heme III and IV midpoint potentials of F156A, together with the increased solvent access to the heme II vacant site in this variant, may work together in changing its reactivity to bound NO. The more strongly reducing hemes could more readily reduce bound NO, while increased solvent access could now allow protonation to accompany reduction of the bound nitrogen moiety

An approach to software cost estimation

A general procedure for software cost estimation in any environment is outlined. The basic concepts of work and effort estimation are explained, some popular resource estimation models are reviewed, and the accuracy of source estimates is discussed. A software cost prediction procedure based on the experiences of the Software Engineering Laboratory in the flight dynamics area and incorporating management expertise, cost models, and historical data is described. The sources of information and relevant parameters available during each phase of the software life cycle are identified. The methodology suggested incorporates these elements into a customized management tool for software cost prediction. Detailed guidelines for estimation in the flight dynamics environment developed using this methodology are presented

Sheep crutching technique

To obtain the best results and achieve the maximum returns from wool-growing, it is essential that the sheep should be efficiently cared for. Correct crutching, systematically performed as often as is necessary is a definite step towards ensuring the comfort and welfare of the sheep. A large proportion of the sheep in the agricultural areas are crutched either too early or too late, and many flocks are not crutched at all. This state of affairs is mainly due to the shortage of professional crutchers so that there are obvious advantages in farmers and their sons being able to crutch their flocks themselves at the right times of the year. Article is only available directly from the library through a request via email