21,193 research outputs found
Separation of gas from liquid in a two-phase flow system
Separation system causes jets which leave two-phase nozzles to impinge on each other, so that liquid from jets tends to coalesce in center of combined jet streams while gas phase is forced to outer periphery. Thus, because liquid coalescence is achieved without resort to separation with solid surfaces, cycle efficiency is improved
A Search for Intrinsic Polarization in O Stars with Variable Winds
New observations of 9 of the brightest northern O stars have been made with
the Breger polarimeter on the 0.9~m telescope at McDonald Observatory and the
AnyPol polarimeter on the 0.4~m telescope at Limber Observatory, using the
Johnson-Cousins UBVRI broadband filter system. Comparison with earlier
measurements shows no clearly defined long-term polarization variability. For
all 9 stars the wavelength dependence of the degree of polarization in the
optical range can be fit by a normal interstellar polarization law. The
polarization position angles are practically constant with wavelength and are
consistent with those of neighboring stars. Thus the simplest conclusion is
that the polarization of all the program stars is primarily interstellar.
The O stars chosen for this study are generally known from ultraviolet and
optical spectroscopy to have substantial mass loss rates and variable winds, as
well as occasional circumstellar emission. Their lack of intrinsic polarization
in comparison with the similar Be stars may be explained by the dominance of
radiation as a wind driving force due to higher luminosity, which results in
lower density and less rotational flattening in the electron scattering inner
envelopes where the polarization is produced. However, time series of
polarization measurements taken simultaneously with H-alpha and UV spectroscopy
during several coordinated multiwavelength campaigns suggest two cases of
possible small-amplitude, periodic short-term polarization variability, and
therefore intrinsic polarization, which may be correlated with the more widely
recognized spectroscopic variations.Comment: LaTeX2e, 22 pages including 11 tables; 12 separate gif figures; uses
aastex.cls preprint package; accepted by The Astronomical Journa
The fate of ethane in Titan's hydrocarbon lakes and seas
Ethane is expected to be the dominant photochemical product on Titan's
surface and, in the absence of a process that sequesters it from exposed
surface reservoirs, a major constituent of its lakes and seas. Absorption of
Cassini's 2.2 cm radar by Ligeia Mare however suggests that this north polar
sea is dominated by methane. In order to explain this apparent ethane
deficiency, we explore the possibility that Ligeia Mare is the visible part of
an alkanofer that interacted with an underlying clathrate layer and investigate
the influence of this interaction on an assumed initial ethane-methane mixture
in the liquid phase. We find that progressive liquid entrapment in clathrate
allows the surface liquid reservoir to become methane-dominated for any initial
ethane mole fraction below 0.75. If interactions between alkanofers and
clathrates are common on Titan, this should lead to the emergence of many
methane-dominated seas or lakes.Comment: Accepted for publication in Icaru
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Towards omnicompetence: the need for effective school-based preparation for primary headship
Teachers are entering deputy headship and then deciding not to become headteachers. This is a double problem for the profession. Firstly, potential headteachers are being lost to that role, and secondly, career deputies block the route to headship and prevent ambitious deputies from getting that essential management experience that will effectively prepare them for headship.
In Bromley, where this study was carried out, some deputies are getting good advice and support from their headteachers, are given real leadership development opportunities and are going on to become effective headteachers. However, some deputies are given low grade tasks and do not receive the support and encouragement from their headteachers that will lead them towards headship. Finally, there are some deputies who, although in a supportive environment, have decided that headship is not for them.
Initially, a short survey of all primary schools in Bromley was conducted to gain an overall picture of deputy headship in Bromley. All schools were contacted to find out whether the deputy at the school was interested in becoming a headteacher at some stage in the future.
During a period of twelve weeks, eleven primary headteachers were interviewed together with a senior Local Authority adviser. The aim of the work was to gain a picture of the state of deputy headship in one London Borough and establish what experiences and opportunities were given to deputy headteacher to prepare them for headship.
This inquiry found that the majority of deputies in Bromley did not want to be headteachers and that their preparation experiences differs greatly from school to school. The study suggests that deputies should be given the opportunities and experiences that will prepare them for headship. Information from the literature review, the survey and interviews are analysed to construct a model for effective preparation for headship and to make recommendations for improved practice
Programmed schedule holds for improving launch vehicle holds
Baseline definition and system optimization are used for the analysis of programmed holds developed through prelaunch system analysis. Identification of design specifications for ground support equipment and maintenance concepts, and design specifications are used to describe the functional utilization of the overall flow process
Liquid filled canyons on Titan
In May 2013 the Cassini RADAR altimeter observed channels in Vid Flumina, a drainage network
connected to Titanâs second largest hydrocarbon sea, Ligeia Mare. Analysis of these altimeter echoes shows
that the channels are located in deep (up to ~570 m), steep-sided, canyons and have strong specular surface
reflections that indicate they are currently liquid filled. Elevations of the liquid in these channels are at the
same level as Ligeia Mare to within a vertical precision of about 0.7 m, consistent with the interpretation of
drowned river valleys. Specular reflections are also observed in lower order tributaries elevated above the
level of Ligeia Mare, consistent with drainage feeding into the main channel system
Raman frequency shift in oxygen functionalized carbon nanotubes
In terms of lattice dynamics theory, we study the vibrational properties of
the oxygen-functionalized single wall carbon nanotubes (O-SWCNs). Due to the
C-O and O-O interactions, many degenerate phonon modes are split and even some
new phonon modes are obtained, different from the bare SWCNs. A distinct Raman
shift is found in both the radial breathing mode and G modes, depending not
only on the tube diameter and chirality but also on oxygen coverage and
adsorption configurations. With the oxygen coverage increasing, interesting, a
nonmonotonic up- and down-shift is observed in G modes, which is contributed to
the competition between the bond expansion and contraction, there coexisting in
the functionalized carbon nanotube.Comment: 4 pages, 3 figures, 1 tabl
Multiwavelength analysis of the Lyman alpha emitting galaxy Haro 2: relation between the diffuse Lyman alpha and soft X-ray emissions
In order to use Lyman alpha (Lya) emission as star formation tracer in
cosmological studies, we must understand how the resonant scattering affects
the escape fraction of the Lya photons. Thus, high spatial resolution
multiwavelength studies of nearby Lya emitters, like Haro 2, are highly needed.
For that purpose, we have used Chandra X-ray and HST (UV, optical and NIR)
images of Haro 2, and STIS and ground-based spectral images along its major and
minor axes, to characterize the Lya emission and the properties of the stellar
population. The UV, Ha (Halpha) and FIR luminosities of the Haro 2 nuclear
starburst are reproduced using evolutionary synthesis models assuming a young
stellar population with ages ~3.5-5.0 Myr, affected by differential
interstellar extinctions. The observed X-ray emission is attributed to gas
heated by the mechanical energy released by the starburst (soft component) and
a Ultra-Luminous X-ray source candidate (hard). Both compact and diffuse Lya
components are observed. Whereas Lya is spatially decoupled from Balmer lines
emission, Balmer decrement and UV continuum, the diffuse Lya component is
spatially correlated with the diffuse soft X-ray emission. Moreover, unlike the
compact one, diffuse Lya shows luminosities larger than predicted from Ha,
assuming case B recombination and dust extinction as derived from Ha/Hbeta. We
propose that, whereas the compact Lya emission is associated to the massive
stellar clusters and is affected by outflows and dust extinction, the diffuse
Lya originates in gas ionized by the hot plasma responsible for the soft X-ray
radiation, as suggested by their spatial correlation and by the measured
L(Ha)/LsoftX ratios. Calibration of Lya as star formation rate tracer should
therefore include both effects (destruction vs. enhancement) to avoid biases in
the study of galaxies at cosmological distances.Comment: Accepted for publication in A&A, 18 pages, 8 figures, 9 tables. If
problems with quality of images, see
http://www.cab.inta-csic.es/users/otih/haro2-v63.clean.pd
Physical properties and evolutionary state of the Lyman alpha emitting starburst galaxy IRAS 08339+6517
Though Lyman alpha emission (Lya) is one of the most used tracers of massive
star formation at high redshift, a correct understanding of radiation transfer
effects by neutral gas is required to properly quantify the star formation rate
along the history of the Universe. We are embarked in a program to study the
properties of the Lya emission (spectral profile, spatial distribution,
relation to Balmer lines intensity,...) in several local starburst galaxies. We
present here the results obtained for IRAS 08339+6517.
Using evolutionary population synthesis models, we have characterized the
properties of the starburst (UV continuum, Halpha, total infrared and X-ray
emissions, etc.), which transformed 1.4e+8 Mo of gas into stars around 5-6 Myr
ago. In addition to the central compact emission blob, we have identified a
diffuse Lya emission component smoothly distributed over the whole central area
of IRAS 08339+6517. This diffuse emission is spatially decoupled from the UV
continuum, the Halpha emission or the Halpha/Hbeta ratio. Both locally and
globally, the Lya/Halpha ratio is lower than the Case B predictions, even after
reddening correction, with an overall Lya escape fraction of only 4%.
We conclude that in IRAS 08339+6517 the resonant scattering of Lya photons by
an outflowing shell of neutral gas causes their highly-efficient destruction by
dust, which explains the low Lya escape fraction measured. These results stress
again the importance of a proper correction of scattering and transfer effects
when using Lya to derive the star formation rate in high-redshift galaxies.Comment: Accepted for publication in A&A, 17 pages, 13 figures, 8 tables. If
problems with quality of images, see
https://cloud.cab.inta-csic.es/public.php?service=files&file=%2Fotih%2Ffiles%2Foti_mas%2Firas%2Firas-v53.ack_referee.pd
Mount St. Helens aerosol evolution
Stratospheric aerosol samples were collected using a wire impactor during the year following the eruption of Mount St. Helens. Analysis of samples shows that aerosol volume increased for 6 months due to gas-to-particle conversion and then decreased to background levels in the following 6 months
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