A rational approach to the use of Prandtl's mixing length model in free turbulent shear flow calculations

Prandtl's basic mixing length model was used to compute 22 test cases on free turbulent shear flows. The calculations employed appropriate algebraic length scale equations and single values of mixing length constant for planar and axisymmetric flows, respectively. Good agreement with data was obtained except for flows, such as supersonic free shear layers, where large sustained sensitivity changes occur. The inability to predict the more gradual mixing in these flows is tentatively ascribed to the presence of a significant turbulence-induced transverse static pressure gradient which is neglected in conventional solution procedures. Some type of an equation for length scale development was found to be necessary for successful computation of highly nonsimilar flow regions such as jet or wake development from thick wall flows

Near-infrared Observations of Nova V574 Puppis (2004)

We present results obtained from extensive near-infrared spectroscopic and photometric observations of nova V574 Pup during its 2004 outburst. The observations were obtained over four months, starting from 2004 November 25 (four days after the nova outburst) to 2005 March 20. The near-IR JHK light curve is presented - no evidence is seen from it for dust formation to have occurred during our observations. In the early decline phase, the JHK spectra of the nova are dominated by emission lines of hydrogen Brackett and Paschen series, OI, CI and HeI. We also detect the fairly uncommon Fe II line at 1.6872 micron in the early part of our observations. The strengths of the HeI lines at 1.0830 micron and 2.0585 micron are found to become very strong towards the end of the observations indicating a progression towards higher excitation conditions in the nova ejecta. The width of the emission lines do not show any significant change during the course of our observations. The slope of the continuum spectrum was found to have a lambda^{-2.75} dependence in the early stages which gradually becomes flatter with time and changes to a free-free spectral dependence towards the later stages. Recombination analysis of the HI lines shows deviations from Case B conditions during the initial stages. However, towards the end of our observations, the line strengths are well simulated with case B model values with electron density n_e = 10^{9-10} cm^{-3} and a temperature equal to 10^4 K. Based on our distance estimate to the nova of 5.5 kpc and the observed free-free continuum emission in the later part of the observations, we estimate the ionized mass of the ejecta to be between 10^{-5} and 10^{-6} solar-mass.Comment: 10 pages, 8 figures, Accepted for publication in MNRA

The new X-ray transient SAX J1711.6-3808: decoupling between its 3-20 keV luminosity and its state transitions

We present a study of the correlated spectral and timing behavior of the new X-ray transient SAX J1711.6-3808 during its 2001 outburst using data obtained with the RXTE. We also investigate the correlations between those source properties and the 3-20 keV X-ray luminosity. The behavior of the source during the observations can be divided into two distinct state types. During the hard state, the energy spectra are relatively hard and can be described by only a power-law component, and the characteristic frequencies (i.e., the frequency of the 1-7 Hz QPOs observed for the first time in this source) in the power spectra are low. However, during the ``soft'' state, the spectra are considerably softer (in addition to the power-law component, a soft component is necessary to fit the spectra) and the frequencies are the highest observed. Remarkably, this distinction into two separate states cannot be extrapolated to also include the 3-20 keV X-ray luminosity. Except for one observation, this luminosity steadily decreased but the hard state was observed both at the highest and lowest observed luminosities. In contrast, the soft state occurred only at intermediate luminosities. This clearly demonstrates that the state behavior of SAX J1711.6-3808 is decoupled from its X-ray luminosity and that if the X-ray luminosity traces the accretion rate in SAX J1711.6-3808, then the state transitions are not good accretion rate indicators, or vice versa. The data of SAX J1711.6-3808 does not allow us to conclusively determine its exact nature. The source resembles both neutron star and black hole systems when they have low luminosities. We discuss our results with respect to the correlated timing and spectral behavior observed in other LMXBs and the implications of our results on the modeling of the outburst light curves of X-ray transients.Comment: Accepted for publication in ApJ Main Journal, 13 September 200

Near-Infrared H and K band studies of the 2006 outburst of the recurrent nova RS Ophiuchi

We present near-IR photo-spectroscopy in the H and K bands of the 2006 outburst of the recurrent nova RS Ophiuchi (RS Oph). The observations cover the period between 1 to 94 days after the eruption. The near IR light curve and an extensive set of spectra are presented, lines identified and the general characteristics of the spectra discussed. Analysis of the HI line profiles show the presence of broad wings on both flanks of a strong central component indicating the presence of a bipolar velocity flow in the ejecta. Such a flow is kinematically consistent with the bipolar structure that the object displays in high-resolution spatial images. We discuss the behaviour and origin of the Fe II lines at 1.6872 and 1.7414 micron and show that Lyman alpha and Lyman continuum fluorescence are viable mechanisms to excite these lines. We draw upon the result, that collisional excitation can also contribute in exciting and significantly enhancing the strength of these Fe II lines, to propose that these lines originate from a site of high particle density. Such a likely site could be the high-density, low temperature contact surface that should exist in the shockfront in between the shocked ejecta and red giant wind. Recombination analysis of the HI lines indicate deviations from Case B conditions during most of the span of our observations indicating optical depth effects. It appears likely that the breakout of the shockfront had not yet occured till the end of our observations. An analysis is made of the temporal evolution of the [Si VI] 1.9641 micron coronal line and another coronal line at 2.0894 micron which is attributed to [Mn XIV]. Assuming collisional effects to dominate in the hot coronal gas, estimates are made of the ion temperature in the gas.Comment: Accepted in MNRAS. Accepted version with inclusion of additional analysi

Pengaruh Suplementasi Hidrolisat Bulu Ayam Dan Mineral Organik Terhadap Kadar Vfa Serta Nh3 Pada Cairan Rumen Sapi

This study aimed: 1) to optimalize the using of agroindustry by product through the hidrolyzedpoultry feather and organic mineral supplementation in ration to increase the digestion of cows; 2) todetermine the best effect of hidrolyzed poultry feather and organic mineral supplementation level toVFA and NH3 value in rumen liquid of cows.This study was conducted in August until October 2013 located in the Stall of Animal HusbandryDepartment, Faculty of Agriculture Lampung University. The analysis of feed stuff, VFA and NH3was conducted in Laboratory of Animal Feed, Animal Husbandry Department. This study used LatinSquare Design with 3 treatments and 3 replications. R0 = Bassal Ration, R1 = Bassal Ration + 3%hidrolyzed poultry feather, R2 = R1 + macro-organic Mineral (0,5% organic Ca, 0,04% organic Mg)and micro-organic Mineral (40 ppm organic Zn, 10 ppm organic Cu, 0,10 ppm organic Se, dan 0,30organic Cr).The data obtained were tested by analysis of variance ( ANOVA ) and was continued by usingLeast Significant Different (LSD) on significant level 5% and or 1%. The result of this study showedthat: the hidrolyzed poultry feather and macro-organic mineral supplementation (0,5% organic Ca,0,04% organic Mg) and micro-organic Mineral (40 ppm organic Zn, 10 ppm organic Cu, 0,10 ppmorganic Se, dan 0,30 organic Cr) were not significantly different (P>0,05) to VFA and NH3 value inrumen liquid of cows

Nonlinear coherent transport of waves in disordered media

We present a diagrammatic theory for coherent backscattering from disordered dilute media in the nonlinear regime. The approach is non-perturbative in the strength of the nonlinearity. We show that the coherent backscattering enhancement factor is strongly affected by the nonlinearity, and corroborate these results by numerical simulations. Our theory can be applied to several physical scenarios like scattering of light in nonlinear Kerr media, or propagation of matter waves in disordered potentials.Comment: 4 pages, 3 figure

Spectral evidence for jets from Accreting Millisecond X-ray Pulsars

Transient radio emission from X-ray binaries is associated with synchrotron emission from collimated jets that escape the system, and accreting millisecond X-ray pulsars (AMXPs) are no exception. Although jets from black hole X-ray binaries are well-studied, those from neutron star systems appear much fainter, for reasons yet uncertain. Jets are usually undetectable at higher frequencies because of the relative brightness of other components such as the accretion disc. AMXPs generally have small orbital separations compared with other X-ray binaries and as such their discs are relatively faint. Here, I present data that imply jets in fact dominate the radio-to-optical spectrum of outbursting AMXPs. They therefore may provide the best opportunity to study the behaviour of jets produced by accreting neutron stars, and compare them to those produced by black hole systems.Comment: 4 pages, 2 figures, to appear in the proceedings of "A Decade of Accreting Millisecond X-ray Pulsars", Amsterdam, April 2008, eds. R. Wijnands et al. (AIP Conf. Proc.

Evolution from protoplanetary to debris discs: The transition disc around HD 166191

HD 166191 has been identified by several studies as hosting a rare and extremely bright warm debris disc with an additional outer cool disc component. However, an alternative interpretation is that the star hosts a disc that is currently in transition between a full gas disc and a largely gas-free debris disc. With the help of new optical to mid-IR spectra and Herschel imaging, we argue that the latter interpretation is supported in several ways: i) we show that HD 166191 is co-moving with the ~4 Myr-old Herbig Ae star HD 163296, suggesting that the two have the same age, ii) the disc spectrum of HD 166191 is well matched by a standard radiative transfer model of a gaseous protoplanetary disc with an inner hole, and iii) the HD 166191 mid-IR silicate feature is more consistent with similarly primordial objects. We note some potential issues with the debris disc interpretation that should be considered for such extreme objects, whose lifetime at the current brightness is mush shorter than the stellar age, or in the case of the outer component requires a mass comparable to the solid component of the Solar nebula. These aspects individually and collectively argue that HD 166191 is a 4-5 Myr old star that hosts a gaseous transition disc. Though it does not argue in favour of either scenario, we find strong evidence for 3-5 um disc variability. We place HD 166191 in context with discs at different evolutionary stages, showing that it is a potentially important object for understanding the protoplanetary to debris disc transition.Comment: accepted to MNRAS, fixed typos in abstract and axis labe