Effect of surface roughness on friction behaviour of steel under boundary lubrication

The friction behaviour of grinded and polished surfaces was evaluated by using a reciprocal sliding tester under lubrication with PAO, PAO + ZnDTP and PAO + ZnDTP + MoDTC. Friction coefficients on the smooth surfaces showed higher values compared to those on the rough surfaces. For lubrication incorporating PAO and PAO + ZnDTP + MoDTC, friction coefficients on both the smoothest and the roughest surfaces decreased with sliding time. On the other hand, friction coefficients between these extremes decreased with sliding time. In this paper, the effects of surface roughness on friction behaviour are discussed

Coronal X-ray emission from an intermediate-age brown dwarf

We report the X-ray detection of the brown dwarf (BD) companion TWA 5B in a $\simeq 12$ Myr old pre-main sequence binary system. We clearly resolve the faint companion (35 photons) separated from the X-ray luminous primary by 2 arcsec in a {\it Chandra} ACIS image. TWA 5B shows a soft X-ray spectrum with a low plasma temperature of only 0.3 keV and a constant flux during the 3 hour observation, of which the characteristics are commonly seen in the solar corona. The X-ray luminosity is 4$\times10^{27}$ erg s$^{-1}$ (0.1--10 keV band) or $\log L_X/L_{bol} = -3.4$. Comparing these properties to both younger and older BDs, we discuss the evolution of the X-ray emission in BDs. During their first few Myr, they exhibit high levels of X-ray activity as seen in higher mass pre-main sequence stars. The level in TWA 5B is still high at $t \simeq 12$ Myr in $\log L_X/L_{bol}$ while $kT$ has already substantially cooled

The “maternal effect” on epilepsy risk: Analysis of familial epilepsies and reassessment of prior evidence

Objective: Previous studies have observed that epilepsy risk is higher among offspring of affected women thanoffspring of affected men. We tested whether this “maternal effect” was present in familial epilepsies, which areenriched for genetic factors that contribute to epilepsy risk.Methods: We assessed evidence of a maternal effect in a cohort of families containing ≥3 persons with epilepsyusing three methods: (1) “downward-looking” analysis, comparing the rate of epilepsy in offspring of affectedwomen versus men; (2) “upward-looking” analysis, comparing the rate of the epilepsy among mothers versusfathers of affected individuals; (3) lineage analysis, comparing the the proportion of affected individuals withfamily history of epilepsy on the maternal versus paternal side.Results: Downward-looking analysis revealed no difference in epilepsy rates among offspring of affectedmothers versus fathers (prevalence ratio 1.0, 95% CI 0.8, 1.2). Upward-looking analysis revealed more affectedmothers than affected fathers; this effect was similar for affected and unaffected sibships (odds ratio 0.8, 95%CI 0.5, 1.2) and was explained by a combination of differential fertility and participation rates. Lineage analysisrevealed no significant difference in the likelihood of maternal versus paternal family history of epilepsy.Interpretation: We found no evidence of a maternal effect on epilepsy risk in this familial epilepsy cohort.Confounding sex imbalances can create the appearance of a maternal effect in upward-looking analyses andmay have impacted prior studies. We discuss possible explanations for the lack of evidence, in familialepilepsies, of the maternal effect observed in population-based studie

Radio Synchrotron Emission from Secondary Leptons in the Vicinity of Sgr A*

A point-like source of ~TeV gamma-rays has recently been seen towards the Galactic center by HESS and other air Cerenkov telescopes. In recent work (Ballantyne et al. 2007), we demonstrated that these gamma-rays can be attributed to high-energy protons that (i) are accelerated close to the event horizon of the central black hole, Sgr A*, (ii) diffuse out to ~pc scales, and (iii) finally interact to produce gamma-rays. The same hadronic collision processes will necessarily lead to the creation of electrons and positrons. Here we calculate the synchrotron emissivity of these secondary leptons in the same magnetic field configuration through which the initiating protons have been propagated in our model. We compare this emission with the observed ~GHz radio spectrum of the inner few pc region which we have assembled from archival data and new measurements we have made with the Australia Telescope Compact Array. We find that our model predicts secondary synchrotron emission with a steep slope consistent with the observations but with an overall normalization that is too large by a factor of ~ 2. If we further constrain our theoretical gamma-ray curve to obey the implicit EGRET upper limit on emission from this region we predict radio emission that is consistent with observations, i.e., the hadronic model of gamma ray emission can, simultaneously and without fine-tuning, also explain essentially all the diffuse radio emission detected from the inner few pc of the Galaxy.Comment: 11 pages, 2 figures. Two references missing from published version added and acknowledgements extende

Deep Near-Infrared Observations and Identifications of Chandra Sources in the Orion Molecular Cloud 2 and 3

We conducted deep NIR imaging observations of the Orion molecular cloud 2 and 3 using QUIRC on the 88-inch telescope of the University of Hawaii. Our purposes are 1) to generate a comprehensive NIR source catalog of these star forming clouds, and 2) to identify the NIR counterpart of the Chandra X-ray sources that have no counterpart in the 2MASS catalog. Our J-, H-, and K-band observations are about 2 mag deeper than those of 2MASS, and well match the current Chandra observation. We detected 1448 NIR sources, for which we derived the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart. Using this catalog, we identified the NIR counterpart for about 42% of the 2MASS-unIDed Chandra sources. The nature of these Chandra sources are discussed using their NIR colors and spatial distributions, and a dozen protostar and brown dwarf candidates are identified.Comment: 39 pages, 9 postscript figures, accepted for publication in A

Discovery of X rays from Class 0 protostar candidates in OMC-3

We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with the Chandra X-ray Observatory (CXO). The northern part of OMC-3 is found to be particularly rich in new X-ray features; four hard X-ray sources are located in and along the filament of cloud cores. Two sources coincide positionally with the sub$mm$-$mm$ dust condensations of MMS 2 and 3 or an outflow radio source VLA 1, which are in a very early phase of star formation. The X-ray spectra of these sources show an absorption column of (1-3) x 10^23 H cm-2. Assuming a moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is estimated to be ~10^30 erg s^-1 at a distance of 450 pc. From the large absorption, positional coincidence and moderate luminosity, we infer that the hard X-rays are coming from very young stellar objects embedded in the molecular cloud cores. We found another hard X-ray source near the edge of the dust filament. The extremely high absorption of 3 x 10^23 H cm^-2 indicates that the source must be surrounded by dense gas, suggesting that it is either a YSO in an early accretion phase or a Type II AGN (e.g. a Seyfert 2), although no counterpart is found at any other wavelength. In contrast to the hard X-ray sources, soft X-ray sources are found spread around the dust filaments, most of which are identified with IR sources in the T Tauri phase.Comment: 9 pages, To be appeared in ApJ v554 n2 Jun 20, 2001 issue, related press release is available at http://science.psu.edu/alert/Tsuboi11-2000.htm, Figure 1 and figure 2 with the best resolution is available at ftp.astro.psu.edu/pub/tsuboi/OMC/010205

X-ray Line Emission from the Hot Stellar Wind of theta 1 Ori C

We present a first emission line analysis of a high resolution X-ray spectrum of the stellar wind of theta 1 Ori C obtained with the High Energy Transmission grating Spectrometer onboard the Chandra X-ray Observatory. The spectra are resolved into a large number of emission lines from H- and He-like O, Ne, Mg, Si, S, Ar and Fe ions. The He-like Fe XXV and Li-like Fe XXIV appear quite strong indicating very hot emitting regions. From H/He flux ratios, as well as from Fe He/Li emission measure ratios we deduce temperatures ranging from 0.5 to 6.1 x 10^7 K. The He-triplets are very sensitive to density as well. At these temperatures the relative strengths of the intercombination and forbidden lines indicate electron densities well above 10^12 cm^-3. The lines appear significantly broadened from which we deduce a mean velocity of 770 km/s with a spread between 400 and 2000 km/s. Along with results of the deduced emission measure we conclude that the X-ray emission could originate in dense and hot regions with a characteristic size of less then 4 x 10^10 cm.Comment: 4 pages, 3 figure