18,854 research outputs found
Shock-induced separation of adiabatic turbulent boundary layers in supersonic axially symmetric internal flow
An experimental investigation at Mach 4 of shock-induced turbulent boundary layer separation at the walls of axially symmetric flow passages is discussed, with particular emphasis placed on determining the shock strengths required for incipient separation. The shock waves were produced by interchangeable sting-mounted cones placed on the axes of the flow passages and aligned with the freestream flow. The interactions under study simulate those encountered in axially symmetric engine inlets of supersonic aircraft. Knowledges of the shock strengths required for boundary layer separation in inlets is important since for shocks of somewhat greater strength rather drastic alterations in the inlet flow field may occur
A new solid-state logarithmic radiometer
Combination of temperature-compensated logarithmic amplifiers and p-i-n photodiodes operating in zero-bias mode provides lightweight radiometer for detecting spectral intensities encompassing more than three decades over a range of at least 300 to 800 nanometers at low power levels
XMM-Newton observations of the Seyfert 1 AGN H0557-385
We present XMM-Newton observations of the Seyfert 1 AGN H0557-385. We have
conducted a study into the warm absorber present in this source, and using
high-resolution RGS data we find that the absorption can be characterised by
two phases: a phase with log ionisation parameter xi of 0.50 (where xi is in
units of ergs cm/s) and a column of 0.2e21 cm^-2, and a phase with log xi of
1.62 and a column of 1.3e22 cm^-2. An iron K alpha line is detected. Neutral
absorption is also present in the source, and we discuss possible origins for
this. On the assumption that the ionised absorbers originate as an outflow from
the inner edge of the torus, we use a new method for finding the volume filling
factor. Both phases of H0557-385 have small volume filling factors (< 1%). We
also derive the volume filling factors for a sample of 23 AGN using this
assumption and for the absorbers with log xi > 0.7 we find reasonable agreement
with the filling factors obtained through the alternative method of equating
the momentum flow of the absorbers to the momentum loss of the radiation field.
By comparing the filling factors obtained by the two methods, we infer that
some absorbers with log xi < 0.7 occur at significantly larger distances from
the nucleus than the inner edge of the torus.Comment: Accepted for publication in MNRA
Control of rotordynamic instability in a typical gas turbine's power system
The effect of rotor internal friction on the system's stability was studied when operated above the first critical speed. This internal friction is commonly caused by sliding press fits or sliding splines. Under conditions of high speed and low bearing damping, these systems will occassionally whirl at a frequency less than the shaft's rotational speed. This subsynchronous precession is a self excited phenomenon and stress reversals are created. This phenomenon was observed during engine testing. The reduction of spline friction and/or the inclusion of squeeze film damping have controlled the instability. Case history and the detail design of the squeeze film dampers is discussed
Software Engineering Laboratory (SEL). Data base organization and user's guide, revision 1
The structure of the Software Engineering Laboratory (SEL) data base is described. It defines each data base file in detail and provides information about how to access and use the data for programmers and other users. Several data base reporting programs are described also
âThe Pandemic is Just Happening on Top of a Pandemic for Usâ. Unpaid Carersâ Experiences of Lockdown in the UK: A Thematic Analysis
Context: With reduced access to medical and social support during the COVID-19 pandemic, the level of support provided by unpaid carers over the lockdown period in the UK was higher than ever. However, the experience of unpaid carers during this period is often overlooked.
Objective: The aim of this study was to explore the question âwhat has been the experience of unpaid carers during lockdown?â.
Method: Eighteen unpaid carers, caring for a family member(s) with physical, learning, mental health, or behavioral disabilities, were interviewed about their experience of lockdown in the UK. Thematic analysis was utilized.
Findings: Three overarching themes created: (a) The value of support, (b) Non-stop care, and (c) Risk to health. A central theme of mental health was also created and discussed across the three overarching themes, rather than individually, due to its extensivity. Support for unpaid carers during the lockdown became more important than ever due to the higher risk to physical and mental health (of both the carer and dependent) and the lack of respite available.
Limitations: Due to volunteer sampling, the evidence in this report is largely based on the perspectives of female carersâ, with all but two participants being female.
Implications: Findings raise implications for prioritizing the return of in-person medical appointments post-pandemic and ensuring the continuation of support services for unpaid carers during a pandemic
Recommended approach to sofware development
A set of guideline for an organized, disciplined approach to software development, based on data collected and studied for 46 flight dynamics software development projects. Methods and practices for each phase of a software development life cycle that starts with requirements analysis and ends with acceptance testing are described; maintenance and operation is not addressed. For each defined life cycle phase, guidelines for the development process and its management, and the products produced and their reviews are presented
Magneto-elastic oscillations of neutron stars: exploring different magnetic field configurations
We study magneto-elastic oscillations of highly magnetized neutron stars
(magnetars) which have been proposed as an explanation for the quasi-periodic
oscillations (QPOs) appearing in the decaying tail of the giant flares of soft
gamma-ray repeaters (SGRs). We extend previous studies by investigating various
magnetic field configurations, computing the Alfv\'en spectrum in each case and
performing magneto-elastic simulations for a selected number of models. By
identifying the observed frequencies of 28 Hz (SGR 1900+14) and 30 Hz (SGR
1806-20) with the fundamental Alfv\'en QPOs, we estimate the required surface
magnetic field strength. For the magnetic field configurations investigated
(dipole-like poloidal, mixed toroidal-poloidal with a dipole-like poloidal
component and a toroidal field confined to the region of field lines closing
inside the star, and for poloidal fields with an additional quadrupole-like
component) the estimated dipole spin-down magnetic fields are between 8x10^14 G
and 4x10^15 G, in broad agreement with spin-down estimates for the SGR sources
producing giant flares. A number of these models exhibit a rich Alfv\'en
continuum revealing new turning points which can produce QPOs. This allows one
to explain most of the observed QPO frequencies as associated with
magneto-elastic QPOs. In particular, we construct a possible configuration with
two turning points in the spectrum which can explain all observed QPOs of SGR
1900+14. Finally, we find that magnetic field configurations which are entirely
confined in the crust (if the core is assumed to be a type I superconductor)
are not favoured, due to difficulties in explaining the lowest observed QPO
frequencies (f<30 Hz).Comment: 21 pages, 16 figures, 6 tables, matched to version accepted by MNRAS
with extended comparison/discussion to previous wor
Superbursts from Strange Stars
Recent models of carbon ignition on accreting neutron stars predict
superburst ignition depths that are an order of magnitude larger than observed.
We explore a possible solution to this problem, that the compact stars in low
mass X-ray binaries that have shown superbursts are in fact strange stars with
a crust of normal matter. We calculate the properties of superbursts on strange
stars, and the resulting constraints on the properties of strange quark matter.
We show that the observed ignition conditions exclude fast neutrino emission in
the quark core, for example by the direct Urca process, which implies that
strange quark matter at stellar densities should be in a color superconducting
state. For slow neutrino emission in the quark matter core, we find that
reproducing superburst properties requires a definite relation between three
poorly constrained properties of strange quark matter: its thermal
conductivity, its slow neutrino emissivity and the energy released by
converting a nucleon into strange quark matter.Comment: 4 pages, submitted to Ap. J. Let
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