3,930 research outputs found
Application of calibration masks to TV vidicon tube
Photographic application method devised for overlaying test pattern masks on TV camera vidicon tubes prints the mask within 0.0076 cm of the vertical and horizontal center lines of the tube face. Entire process, including mask fabrication and alignment procedure, requires less than 10 minutes
Epitaxial Growth of an n-type Ferromagnetic Semiconductor CdCr2Se4 on GaAs(001) and GaP(001)
We report the epitaxial growth of CdCr2Se4, an n-type ferromagnetic
semiconductor, on both GaAs and GaP(001) substrates, and describe the
structural, magnetic and electronic properties. Magnetometry data confirm
ferromagnetic order with a Curie temperature of 130 K, as in the bulk material.
The magnetization exhibits hysteretic behavior with significant remanence, and
an in-plane easy axis with a coercive field of ~125 Oe. Temperature dependent
transport data show that the films are semiconducting in character and n-type
as grown, with room temperature carrier concentrations of n ~ 1 x 10^18 cm-3.Comment: 12 pages, 3 figure
Further Constraints on Thermal Quiescent X-ray Emission from SAX J1808.4-3658
We observed SAX J1808.4-3658 (1808), the first accreting millisecond pulsar,
in deep quiescence with XMM-Newton and (near-simultaneously) Gemini-South. The
X-ray spectrum of 1808 is similar to that observed in quiescence in 2001 and
2006, describable by an absorbed power-law with photon index 1.74+-0.11 and
unabsorbed X-ray luminosity L_X=7.9+-0.7*10^{31} ergs/s, for N_H=1.3*10^{21}
cm^{-2}. Fitting all the quiescent XMM-Newton X-ray spectra with a power-law,
we constrain any thermally emitting neutron star with a hydrogen atmosphere to
have a temperature less than 30 eV and L_{NS}(0.01-10 keV)<6.2*10^{30} ergs/s.
A thermal plasma model also gives an acceptable fit to the continuum. Adding a
neutron star component to the plasma model produces less stringent constraints
on the neutron star; a temperature of 36^{+4}_{-8} eV and L_{NS}(0.01-10
keV)=1.3^{+0.6}_{-0.8}*10^{31} ergs/s. In the framework of the current theory
of neutron star heating and cooling, the constraints on the thermal luminosity
of 1808 and 1H 1905+000 require strongly enhanced cooling in the cores of these
neutron stars.
We compile data from the literature on the mass transfer rates and quiescent
thermal flux of the largest possible sample of transient neutron star LMXBs. We
identify a thermal component in the quiescent spectrum of the accreting
millisecond pulsar IGR J00291+5934, which is consistent with the standard
cooling model. The contrast between the cooling rates of IGR J00291+5934 and
1808 suggests that 1808 may have a significantly larger mass. This can be
interpreted as arising from differences in the binary evolution history or
initial neutron star mass in these otherwise similar systems.Comment: ApJ in press, 7 pages, 2 color figure
LOFT as a discovery machine for jetted Tidal Disruption Events
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of jetted tidal disruption events.
For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timin
The neutron star soft X-ray transient 1H1905+000 in quiescence
In this Paper we report on our analysis of a ~25 ksec. Chandra X-ray
observation of the neutron star soft X-ray transient (SXT) 1H1905+000 in
quiescence. Furthermore, we discuss our findings of the analysis of optical
photometric observations which we obtained using the Magellan telescope and
photometric and spectroscopic observations which we obtained using the Very
Large Telescope at Paranal. The X-ray counterpart of 1H1905+000 was not
detected in our Chandra data, with a 95 per cent confidence limit to the source
count rate of 1.2x10^-4 counts s^-1. For different spectral models this yields
an upper limit on the luminosity of 1.8x10^31 erg s^-1 (for an upper limit on
the distance of 10 kpc.) This luminosity limit makes 1H1905+000 the faintest
neutron star SXT in quiescence observed to date. The neutron star luminosity is
so low that it is similar to the lowest luminosities derived for black hole
SXTs in quiescence. This low luminosity for a neutron star SXT challanges the
hypothesis presented in the literature that black hole SXTs in quiescence have
lower luminosities than neutron star SXTs as a result of the presence of a
black hole event horizon. Furthermore, the limit on the neutron star luminosity
obtained less than 20 years after the outburst has ceased, constrains the
thermal conductivity of the neutron star crust. Finally, the neutron star core
must be so cold that unless the time averaged mass accretion rate is lower than
2x10^-12 M_sun yr^-1, core cooling has to proceed via enhanced neutrino
emission processes. We derive a limit on the absolute I-band magnitude of the
quiescent counterpart of M_I>7.8 assuming the source is at 10 kpc. This is in
line with 1H1905+000 being an ultra-compact X-ray binary, as has been proposed
based on the low outburst V-band absolute magnitude.Comment: 10 pages, 5 figures, accepted for publication in MNRA
Constraints on Thermal X-ray Radiation from SAX J1808.4-3658 and Implications for Neutron Star Neutrino Emission
Thermal X-ray radiation from neutron star soft X-ray transients in quiescence
provides the strongest constraints on the cooling rates of neutron stars, and
thus on the interior composition and properties of matter in the cores of
neutron stars. We analyze new (2006) and archival (2001) XMM-Newton
observations of the accreting millisecond pulsar SAX J1808.4-3658 in
quiescence, which provide the most stringent constraints to date. The X-ray
spectrum of SAX J1808.4-3658 in the 2006 observation is consistent with a
power-law of photon index 1.83\pm0.17, without requiring the presence of a
blackbody-like component from a neutron star atmosphere. Our 2006 observation
shows a slightly lower 0.5-10 keV X-ray luminosity, at a level of
68^{+15}_{-13}% that inferred from the 2001 observation. Simultaneous fitting
of all available XMM data allows a constraint on the quiescent neutron star
(0.01-10 keV) luminosity of L_{NS}<1.1*10^{31} erg/s. This limit excludes some
current models of neutrino emission mediated by pion condensates, and provides
further evidence for additional cooling processes, such as neutrino emission
via direct Urca processes involving nucleons and/or hyperons, in the cores of
massive neutron stars.Comment: 5 pages, 2 figures; slight revisions, accepted by Ap
The Role of Social Identity Inclusiveness and Structure in Intergroup Relations: Individual and Contextual Differences in Ethnic and Religious Minority Group Members
This thesis proposes a conceptual and operational framework to examine how minority group members subjectively construe their ingroup. Four community studies were devised to test this framework, and to examine individual versus contextual differences in ingroup construals. Chapter 1 provides a critical analysis of existing models of multiple social identities. Subsequently, a new conceptual framework is proposed to assess how minority group members construe their ingroup in the context of multiple, cross-cutting group memberships. The subjective combination of multiple ingroups is described in terms of Social Identity Structure (SIS) and Inclusiveness (SII). Chapter 2 introduces a method, the Triple-Crossed Categorisation Task, to measure both constructs. The validity of SII and SIS is assessed in a sample of Turkish Australian Muslim adults (Chapter 3), and adolescents (Chapter 4). Both studies showed SII to be a valid construct, distinct from measures of identification, and positively related to outgroup contact. Moreover, eight different SIS’s were replicated across both studies, further attesting to the validity of the conceptual model. Importantly, across both studies, SII uniquely predicted attitudes toward a range of outgroups. The following chapters examine whether and how Turkish Australian Muslims alter their ingroup construals after exposure to a religious identity threat versus reassurance (Chapter 5), or to a religious versus ethnic identity threat (Chapter 6). In both experiments, SII was not affected by threat. The distribution of SIS’s did show some effects of threat, but the pattern was not consistent across studies. Finally, Chapter 7 discusses these findings in light of the individual and contextual factors surrounding minority members’ ingroup construals. The contributions to the study of multiple social identities, practical implications, limitations, and future directions are discussed as well
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