1,412 research outputs found
The cyclo-synchrotron process and particle heating through the absorption of photons
We propose a new approximation for the cyclo-synchrotron emissivity of a
single electron. In the second part of this work, we discuss a simple
application for our approximation, and investigate the heating of electrons
through the self-absorption process. Finally, we investigate the self-absorbed
part of the spectrum produced by a power-law population of electrons. In
comparison to earlier approximations, our formula provides a few significant
advantages. Integration of the emissivity over the whole frequency range,
starting from the proper minimal emitting frequency, gives the correct cooling
rate for any energy particle. Further, the spectrum of the emission is well
approximated over the whole frequency range, even for relatively low particle
energies (beta << 0.1), where most of the power is emitted in the first
harmonic. In order to test our continuous approximation, we compare it with a
recently derived approximation of the first ten harmonics. Finally, our formula
connects relatively smooth to the synchrotron emission at beta=0.9. We show
that the self-absorption is a very efficient heating mechanism for low energy
particles, independent of the shape of the particle distribution responsible
for the self-absorbed synchrotron emission. We find that the energy gains for
low energy particles are always higher than energy losses by cyclo-synchrotron
emission. We show also that the spectral index of the self-absorbed part of the
spectrum at very low frequencies differs significantly from the well known
standard relation I(nu) ~ nu^(5/2).Comment: 9 pages, 4 figures, accepted for publication in A&
Percolation model for structural phase transitions in LiHIO mixed crystals
A percolation model is proposed to explain the structural phase transitions
found in LiHIO mixed crystals as a function of the
concentration parameter . The percolation thresholds are obtained from Monte
Carlo simulations on the specific lattices occupied by lithium atoms and
hydrogen bonds. The theoretical results strongly suggest that percolating
lithium vacancies and hydrogen bonds are indeed responsible for the solid
solution observed in the experimental range .Comment: 4 pages, 2 figure
The first Infrared study of the close environment of a long Gamma-Ray Burst
We present a characterization of the close environment of GRB980425 based on
5-160mic spectro-imaging obtained with Spitzer. The Gamma-Ray Burst GRB980425
occurred in a nearby (z=0.0085) SBc-type dwarf galaxy, at a projected distance
of 900pc from an HII region with strong signatures of Wolf-Rayet (WR) stars.
While this "WR region" produces less than 5% of the B-band emission of the
host, we find that it is responsible for 45+/-10% of the total infrared
luminosity, with a maximum contribution reaching 75% at 25-30mic. This atypical
property is rarely observed among morphologically-relaxed dwarves, suggesting a
strong causal link with the GRB event. The luminosity of the WR region
(L_8-1000mic=4.6x10^8 Lsol), the peak of its spectral energy distribution at
<~100mic and the presence of highly-ionized emission lines (e.g., [NeIII]) also
reveal extremely young (<5Myr) star-forming activity, with a typical time-scale
of only 47Myr to double the stellar mass already built. Finally, the mid-IR
over B-band luminosity ratio in this region is substantially higher than in
star-forming galaxies with similar L_IR, but it is lower than in young
dust-enshrouded stellar clusters. Considering the modest obscuration measured
from the silicate features (tau_9.7mic ~ 0.015), this suggests that the WR
region is dominated by one or several star clusters that have either partly
escaped or cleared out their parent molecular cloud. Combined with the
properties characterizing the whole population of GRB hosts, our results
reinforce the idea that long GRBs mostly happen within or in the vicinity of
relatively unobscured galactic regions harboring very recent star formation.Comment: ApJ in press, 14 pages, 2 tables, 7 figure
Optimal Software Patching Plan for PMUs
Phasor measurement units (PMUs) deployed to monitor the state of an electrical grid need to be patched from time to time to prevent attacks that exploit vulnerabilities in the software. Applying some of these patches requires a PMU reboot, which takes the PMU offline for some time. If the PMU placement provides enough redundancy, it is possible to patch a set of PMUs at a time while maintaining full system observability. The challenge is then to find a patching plan that guarantees that the patch is rolled out to all PMUs in the smallest number of rounds possible while full system observability is maintained at all times. We show that this problem can be formulated as a sensor patching problem, which we demonstrate to be NP-complete. However, if the grid forms a tree, we show that the minimum number of rounds is two and we provide a polynomial-time algorithm that finds an optimal patching plan. For the non-tree case, we formulate the problem as a binary integer linear programming problem (BILP) and solve it using an ILP-solver. We also propose a heuristic algorithm to find an approximate solution to the patching problem for grids that are too large to be solved by an ILP-solver. Through simulation, we compare the performance of the ILP-solver and the heuristic algorithm over different bus systems
Waveforms for sub-THz 6G: Design Guidelines
The projected sub-THz (100 - 300 GHz) part of the upcoming 6G standard will
require a careful design of the waveform and choice of slot structure. Not only
that the design of the physical layer for 6G will be driven by ambitious system
performance requirements, but also hardware limitations, specific to sub-THz
frequencies, pose a fundamental design constraint for the waveform. In this
contribution, general guidelines for the waveform design are given, together
with a non-exhaustive list of exemplary waveforms that can be used to meet the
design requirements.Comment: Paper presented at EuCNC 2023, June 6-9 2023, Gothenburg, Swede
The dark GRB080207 in an extremely red host and the implications for GRBs in highly obscured environments
[Abridged] We present comprehensive X-ray, optical, near- and mid-infrared,
and sub-mm observations of GRB 080207 and its host galaxy. The afterglow was
undetected in the optical and near-IR, implying an optical to X-ray index <0.3,
identifying GRB 080207 as a dark burst. Swift X-ray observations show extreme
absorption in the host, which is confirmed by the unusually large optical
extinction found by modelling the X-ray to nIR afterglow spectral energy
distribution. Our Chandra observations obtained 8 days post-burst allow us to
place the afterglow on the sky to sub-arcsec accuracy, enabling us to pinpoint
an extremely red galaxy (ERO). Follow-up host observations with HST, Spitzer,
Gemini, Keck and the James Clerk Maxwell Telescope (JCMT) provide a photometric
redshift solution of z ~1.74 (+0.05,-0.06) (1 sigma), 1.56 < z < 2.08 at 2
sigma) for the ERO host, and suggest that it is a massive and morphologically
disturbed ultra-luminous infrared galaxy (ULIRG) system, with L_FIR ~ 2.4 x
10^12 L_solar. These results add to the growing evidence that GRBs originating
in very red hosts always show some evidence of dust extinction in their
afterglows (though the converse is not true -- some extinguished afterglows are
found in blue hosts). This indicates that a poorly constrained fraction of GRBs
occur in very dusty environments. By comparing the inferred stellar masses, and
estimates of the gas phase metallicity in both GRB hosts and sub-mm galaxies we
suggest that many GRB hosts, even at z>2 are at lower metallicity than the
sub-mm galaxy population, offering a likely explanation for the dearth of
sub-mm detected GRB hosts. However, we also show that the dark GRB hosts are
systematically more massive than those hosting optically bright events, perhaps
implying that previous host samples are severely biased by the exclusion of
dark events.Comment: 13 pages, 6 figures, accepted for publication in MNRA
Unexpected Consequences: Women’s experiences of a self-hypnosis intervention to help with pain relief during labour.
Background
Self-hypnosis is becoming increasingly popular as a means of labour pain management. Previous studies have produced mixed results. There are very few data on women’s views and experiences of using hypnosis in this context. As part of a randomized controlled trial of self-hypnosis for intra-partum pain relief (the SHIP Trial) we conducted qualitative interviews with women randomized to the intervention arm to explore their views and experiences of using self-hypnosis during labour and birth.
Methods
Participants were randomly selected from the intervention arm of the study, which consisted of two antenatal self-hypnosis training sessions and a supporting CD that women were encouraged to listen to daily from 32 weeks gestation until the birth of their baby. Those who consented were interviewed in their own homes 8-12 weeks after birth. Following transcription, the interviews were analysed iteratively and emerging concepts were discussed amongst the authors to generate organizing themes. These were then used to develop a principal organizing metaphor or global theme, in a process known as thematic networks analysis.
Results
Of the 343 women in the intervention group, 48 were invited to interview, and 16 were interviewed over a 12 month period from February 2012 to January 2013.
Coding of the data and subsequent analysis revealed a global theme of ‘unexpected consequences’, supported by 5 organising themes, ‘calmness in a climate of fear’, ‘from sceptic to believer’, ‘finding my space’, ‘delays and disappointments’ and ‘personal preferences’. Most respondents reported positive experiences of self-hypnosis and highlighted feelings of calmness, confidence and empowerment. They found the intervention to be beneficial and used a range of novel strategies to personalize their self-hypnosis practice. Occasionally women reported feeling frustrated or disappointed when their relaxed state was misinterpreted by midwives on admission or when their labour and birth experiences did not match their expectations.
Conclusion
The women in this study generally appreciated antenatal self-hypnosis training and found it to be beneficial during labour and birth. The state of focused relaxation experienced by women using the technique needs to be recognized by providers if the intervention is to be implemented into the maternity service
Innate immunity, assessed by plasma NO measurements, is not suppressed during the incubation fast in eiders
Immunity is hypothesized to share limited resources with other physiological
functions and may mediate life history trade-offs, for example between
reproduction and survival. However, vertebrate immune defense is a complex
system that consists of three components. To date, no study has assessed all of
these components for the same animal model and within a given situation.
Previous studies have determined that the acquired immunity of common eiders
(Somateria mollissima) is suppressed during incubation. The present paper aims
to assess the innate immune response in fasting eiders in relation to their
initial body condition. Innate immunity was assessed by measuring plasma nitric
oxide (NO) levels, prior to and after injection of lipopolysaccharides (LPS), a
method which is easily applicable to many wild animals. Body condition index
and corticosterone levels were subsequently determined as indicators of body
condition and stress level prior to LPS injection. The innate immune response
in eiders did not vary significantly throughout the incubation period. The
innate immune response of eiders did not vary significantly in relation to
their initial body condition but decreased significantly when corticosterone
levels increased. However, NO levels after LPS injection were significantly and
positively related to initial body condition, while there was a significant
negative relationship with plasma corticosterone levels. Our study suggests
that female eiders preserve an effective innate immune response during
incubation and this response might be partially determined by the initial body
condition
Use of STATCOM in wind farms with fixed-speed generators for grid code compliance
The increasing penetration of wind energy into power systems has pushed grid operators to set new requirements for this kind of generating plants in order to keep acceptable and reliable operation of the system. In addition to the low voltage ride through capability, wind farms are required to participate in voltage support, stability enhancement and power quality improvement. This paper presents a solution for wind farms with fixed-speed generators based on the use of STATCOM with braking resistor and additional series impedances, with an adequate control strategy. The focus is put on guaranteeing the grid code compliance when the wind farm faces an extensive series of grid disturbances
A deep search for the host galaxies of GRBs with no detected optical afterglow
Gamma-Ray Bursts can provide information about star formation at high
redshifts. Even in the absence of a optical/near-infrared/radio afterglow, the
high detection rate of X-ray afterglows by swift/XRT and its localization
precision of 2-3 arcsec facilitates the identification and study of GRB host
galaxies. We focus on the search for the host galaxies of a sample of 17 bursts
with XRT error circles but no detected long-wavelength afterglow. Three of
these events can also be classified as truly dark bursts: the observed upper
limit on the optical flux of the afterglow was less than expected based on the
X-ray flux. Our study is based on deep R and K-band observations performed with
ESO/VLT instruments, supported by GROND and NEWFIRM. To be conservative, we
searched for host galaxies in an area with a radius twice the 90% swift/XRT
error circle. For 15 of the 17 bursts we find at least one galaxy inside the
doubled XRT error circle. In seven cases we discover extremely red objects in
the error circles. The most remarkable case is the host of GRB 080207 which as
a colour of R-K~4.7 mag (AB), one of the reddest galaxies ever associated with
a GRB. As a by-product of our study we identify the optical afterglow of GRB
070517A. Optically dim afterglows result from cosmological Lyman drop out and
dust extinction, but the former process is only equired for a minority of cases
(<1/3). Extinction by dust in the host galaxies might explain all other events.
Thereby, a seemingly non-negligible fraction of these hosts are globally
dust-enshrouded, extremely red galaxies. This suggests that bursts with
optically dim afterglows trace a subpopulation of massive starburst galaxies,
which are markedly different from the main body of the GRB host galaxy
population, namely the blue, subluminous, compact galaxies.Comment: 29 pages, 31 figures, accepted for publication in A&
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