2,471 research outputs found
Measurement of Gilbert damping parameters in nanoscale CPP-GMR spin-valves
In-situ, device level measurement of thermal mag-noise spectral linewidths in
60nm diameter CPP-GMR spin-valve stacks of IrMn/ref/Cu/free, with reference and
free layer of similar CoFe/CoFeGe alloy, are used to simultaneously determine
the intrinsic Gilbert damping for both magnetic layers. It is shown that
careful alignment at a "magic-angle" between free and reference layer static
equilibrium magnetization can allow direct measurement of the broadband
intrinsic thermal spectra in the virtual absence of spin-torque effects which
otherwise grossly distort the spectral line shapes and require linewidth
extrapolations to zero current (which are nonetheless also shown to agree well
with the direct method). The experimental magic-angle spectra are shown to be
in good qualitative and quantitative agreement with both macrospin calculations
and micromagnetic eigenmode analysis. Despite similar composition and
thickness, it is repeatedly found that the IrMn exchange pinned reference layer
has ten times larger intrinsic Gilbert damping (alpha ~ 0.1) than that of the
free-layer (alpha ~ 0.01). It is argued that the large reference layer damping
results from strong, off -resonant coupling to to lossy modes of an IrMn/ref
couple, rather than commonly invoked two-magnon processes.Comment: 11 pages (2-column format), 12 figures. This work was presented at
the 2010 Joint MMM-Intermag Conference (Washington, DC) as paper AB-01
(invited
Spitzer/IRAC Observations of the Variability of Sgr A* and the Object G2 at 4.5 microns
We present the first detection from the Spitzer Space Telescope of 4.5 micron
variability from Sgr A*, the emitting source associated with the Milky Way's
central black hole. The >23 hour continuous light curve was obtained with the
IRAC instrument in 2013 December. The result characterizes the variability of
Sgr A* prior to the closest approach of the G2 object, a putative infalling gas
cloud that orbits close to Sgr A*. The high stellar density at the location of
Sgr A* produces a background of ~250 mJy at 4.5 microns in each pixel with a
large pixel-to-pixel gradient, but the light curve for the highly variable Sgr
A* source was successfully measured by modeling and removing the variations due
to pointing wobble. The observed flux densities range from the noise level of
~0.7 mJy rms in a 6.4-s measurement to ~10 mJy. Emission was seen above the
noise level ~34% of the time. The light curve characteristics, including the
flux density distribution and structure function, are consistent with those
previously derived at shorter infrared wavelengths. We see no evidence in the
light curve for activity attributable to the G2 interaction at the observing
epoch, ~100 days before the expected G2 periapsis passage. The IRAC light curve
is more than a factor of two longer than any previous infrared observation,
improving constraints on the timescale of the break in the power spectral
distribution of Sgr A* flux densities. The data favor the longer of the two
previously published values for the timescale.Comment: 13 pages, 10 figures, 2 tables, accepted for publication in the Ap
Spitzer Observations of Interstellar Object 1I/`Oumuamua
1I/`Oumuamua is the first confirmed interstellar body in our Solar System.
Here we report on observations of `Oumuamua made with the Spitzer Space
Telescope on 2017 November 21--22 (UT). We integrated for 30.2~hours at 4.5
micron (IRAC channel 2). We did not detect the object and place an upper limit
on the flux of 0.3 uJy (3sigma). This implies an effective spherical diameter
less than [98, 140, 440] meters and albedo greater than [0.2, 0.1, 0.01] under
the assumption of low, middle, or high thermal beaming parameter eta,
respectively. With an aspect ratio for `Oumuamua of 6:1, these results
correspond to dimensions of [240:40, 341:57, 1080:180] meters, respectively. We
place upper limits on the amount of dust, CO, and CO2 coming from this object
that are lower than previous results; we are unable to constrain the production
of other gas species. Both our size and outgassing limits are important because
`Oumuamua's trajectory shows non-gravitational accelerations that are sensitive
to size and mass and presumably caused by gas emission. We suggest that
`Oumuamua may have experienced low-level post-perihelion volatile emission that
produced a fresh, bright, icy mantle. This model is consistent with the
expected eta value and implied high albedo value for this solution, but, given
our strict limits on CO and CO2, requires another gas species --- probably H2O
--- to explain the observed non-gravitational acceleration. Our results extend
the mystery of `Oumuamua's origin and evolution
Lorentz Invariant Superluminal Tunneling
It is shown that superluminal optical signalling is possible without
violating Lorentz invariance and causality via tunneling through photonic band
gaps in inhomogeneous dielectrics of a special kind.Comment: 10 pages revtex, no figure, more discussions added, submitted to
Phys. Rev.
The infrared dust bubble N22: an expanding HII region and the star formation around it
Aims. To increase the observational samples of star formation around
expanding Hii regions, we analyzed the interstellar medium and star formation
around N22.
Methods. We used data extracted from the seven large-scale surveys from
infrared to radio wavelengths. In addition we used the JCMT observations of the
J = 3-2 line of 12CO emission data released on CADC and the 12CO J = 2-1 and J
=3-2 lines observed by the KOSMA 3 m telescope. We performed a multiwavelength
study of bubble N22.
Results. A molecular shell composed of several clumps agrees very well with
the border of N22, suggesting that its expansion is collecting the surrounding
material. The high integrated 12CO line intensity ratio (ranging from 0.7 to
1.14) implies that shocks have driven into the molecular clouds. We identify
eleven possible O-type stars inside the Hii region, five of which are located
in projection inside the cavity of the 20 cm radio continuum emission and are
probably the exciting-star candidates of N22. Twenty-nine YSOs (young stellar
objects) are distributed close to the dense cores of N22. We conclude that star
formation is indeed active around N22; the formation of most of YSOs may have
been triggered by the expanding of the Hii region. After comparing the
dynamical age of N22 and the fragmentation time of the molecular shell, we
suggest that radiation-driven compression of pre-existing dense clumps may be
ongoing.Comment: accepted in A&A 30/05/2012. arXiv admin note: text overlap with
arXiv:1010.5430 by other author
The Challenge Non-Typhoidal Salmonella (CHANTS) Consortium: Development of a non-typhoidal Salmonella controlled human infection model: Report from a consultation group workshop, 05 July 2022, London, UK [version 2; peer review: 2 approved]
Invasive non-typhoidal Salmonella disease (iNTS) is a major cause of morbidity and mortality globally, particularly as a cause of bloodstream infection in children and immunocompromised adults in sub-Saharan Africa. Vaccines to prevent non-typhoidal Salmonella (NTS) would represent a valuable public health tool in this setting to avert cases and prevent expansion of antimicrobial resistance. Several NTS and combination typhoidal-NTS vaccine candidates are in early-stage development, although the pathway to licensure is unclear due to challenges in conducting large phase III field trials. Controlled human infection models (CHIM) present an opportunity to accelerate vaccine development for a range of enteric pathogens. Several recent typhoidal Salmonella CHIMs have been conducted safely and have played pivotal roles in progressing vaccine candidates to pre-qualification and licensure. The Challenge Non-Typhoidal Salmonella (CHANTS) consortium has been formed with funding from the Wellcome Trust, to deliver the first NTS CHIM, which can act as a platform for future vaccine evaluation. This paper reports the conclusions of a consultation group workshop convened with key stakeholders. The aims of this meeting were to: (1) define the rationale for an NTS CHIM (2) map the NTS vaccine pipeline (3) refine study design and (4) establish potential future use cases
Re-analysis of the radio luminosity function of Galactic HII regions
We have re-analyzed continuum and recombination lines radio data available in
the literature in order to derive the luminosity function (LF) of Galactic HII
regions. The study is performed by considering the first and fourth Galactic
quadrants independently. We estimate the completeness level of the sample in
the fourth quadrant at 5 Jy, and the one in the first quadrant at 2 Jy. We show
that the two samples (fourth or first quadrant) include, as well as giant and
super-giant HII regions, a significant number of sub-giant sources. The LF is
obtained, in each Galactic quadrant, with a generalized Schmidt's estimator
using an effective volume derived from the observed spatial distribution of the
considered HII regions. The re-analysis also takes advantage of recently
published ancillary absorption data allowing to solve the distance ambiguity
for several objects. A single power-law fit to the LFs retrieves a slope equal
to -2.23+/-0.07 (fourth quadrant) and to -1.85+/-0.11 (first quadrant). We also
find marginal evidence of a luminosity break at L_knee = 10^23.45 erg s^(-1)
Hz^(-1) for the LF in the fourth quadrant. We convert radio luminosities into
equivalent H_alpha and Lyman continuum luminosities to facilitate comparisons
with extra-galactic studies. We obtain an average total HII regions Lyman
continuum luminosity of 0.89 +/- 0.23 * 10^(53) sec^(-1), corresponding to 30%
of the total ionizing luminosity of the Galaxy.Comment: accepted for publication in Ap
A Wide-field Near- and Mid-Infrared Census of Young Stars in NGC 6334
This paper presents a study of the rate and efficiency of star formation in the NGC 6334 star-forming region. We obtained observations at J, H, and K_s taken with the NOAO Extremely Wide-Field Infrared Imager and combined them with observations taken with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope at wavelengths = 3.6, 4.5, 5.8, and 8.0 μm. We also analyzed previous observations taken at 24 μm using the Spitzer MIPS camera as part of the MIPSGAL survey. We have produced a point source catalog with >700, 000 entries. We have identified 2283 young stellar object (YSO) candidates, 375 Class I YSOs, and 1908 Class II YSOs using a combination of existing IRAC-based color classification schemes that we have extended and validated to the near-IR for use with warm Spitzer data. We have identified multiple new sites of ongoing star formation activity along filamentary structures extending tens of parsecs beyond the central molecular ridge of NGC 6334. By mapping the extinction, we derived an estimate for the gas mass, 2.2 × 10^5 M_☉. The heavy concentration of protostars along the dense filamentary structures indicates that NGC 6334 may be undergoing a "mini-starburst" event with Σ_(SFR) > 8.2 M_☉ Myr^(–1) pc^(–2) and SFE > 0.10. We have used these estimates to place NGC 6334 in the Kennicutt-Schmidt diagram to help bridge the gap between observations of local low-mass star-forming regions and star formation in other galaxies
Rethinking the social impacts of the arts
The paper presents a critical discussion of the current debate over the social impacts of the arts in the UK. It argues that the accepted understanding of the terms of the debate is rooted in a number of assumptions and beliefs that are rarely questioned. The paper goes on to present the interim findings of a three‐year research project, which aims to rethink the social impact of the arts, with a view to determining how these impacts might be better understood. The desirability of a historical approach is articulated, and a classification of the claims made within the Western intellectual tradition for what the arts “do” to people is presented and discussed
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