1,031 research outputs found
Integrated photonic building blocks for next-generation astronomical instrumentation II: the multimode to single mode transition
There are numerous advantages to exploiting diffraction-limited
instrumentation at astronomical observatories, which include smaller
footprints, less mechanical and thermal instabilities and high levels of
performance. To realize such instrumentation it is imperative to convert the
atmospheric seeing-limited signal that is captured by the telescope into a
diffraction-limited signal. This process can be achieved photonically by using
a mode reformatting device known as a photonic lantern that performs a
multimode to single-mode transition. With the aim of developing an optimized
integrated photonic lantern, we undertook a systematic parameter scan of
devices fabricated by the femtosecond laser direct-write technique. The devices
were designed for operation around 1.55 {\mu}m. The devices showed (coupling
and transition) losses of less than 5% for F/# 12 injection and the
total device throughput (including substrate absorption) as high as 75-80%.
Such devices show great promise for future use in astronomy.Comment: 12 pages, 9 figure
The shock process and light element production in supernovae envelopes
Detailed hydrodynamic modeling of the passage of supernova shocks through the hydrogen envelopes of blue and red progenitor stars was carried out to explore the sensitivity to model conditions of light element production (specifically Li-7 and B-11) which was noted by Dearborn, Schramm, Steigman and Truran (1989) (DSST). It is found that, for stellar models with M is less than or approximately 100 M solar mass, current state of the art supernova shocks do not produce significant light element yields by hydrodynamic processes alone. The dependence of this conclusion on stellar models and on shock strengths is explored. Preliminary implications for Galactic evolution of lithium are discussed, and it is suspected that intermediate mass red giant stars may be the most consistent production site for lithium
Multiband processing of multimode light: combining 3D photonic lanterns with waveguide Bragg gratings
The first demonstration of narrowband spectral filtering of multimode light
on a 3D integrated photonic chip using photonic lanterns and waveguide Bragg
gratings is reported. The photonic lanterns with multi-notch waveguide Bragg
gratings were fabricated using the femtosecond direct-write technique in
boro-aluminosilicate glass (Corning, Eagle 2000). Transmission dips of up to 5
dB were measured in both photonic lanterns and reference single-mode waveguides
with 10.4-mm-long gratings. The result demonstrates efficient and symmetrical
performance of each of the gratings in the photonic lantern. Such devices will
be beneficial to space-division multiplexed communication systems as well as
for units for astronomical instrumentation for suppression of the atmospheric
telluric emission from OH lines.Comment: 5 pages, 4 figures, accepted to Laser & Photonics Review
High-performance 3D waveguide architecture for astronomical pupil-remapping interferometry
The detection and characterisation of extra-solar planets is a major theme
driving modern astronomy, with the vast majority of such measurements being
achieved by Doppler radial-velocity and transit observations. Another technique
-- direct imaging -- can access a parameter space that complements these
methods, and paves the way for future technologies capable of detailed
characterization of exoplanetary atmospheres and surfaces. However achieving
the required levels of performance with direct imaging, particularly from
ground-based telescopes which must contend with the Earth's turbulent
atmosphere, requires considerable sophistication in the instrument and
detection strategy. Here we demonstrate a new generation of photonic
pupil-remapping devices which build upon the interferometric framework
developed for the {\it Dragonfly} instrument: a high contrast waveguide-based
device which recovers robust complex visibility observables. New generation
Dragonfly devices overcome problems caused by interference from unguided light
and low throughput, promising unprecedented on-sky performance. Closure phase
measurement scatter of only has been achieved, with waveguide
throughputs of . This translates to a maximum contrast-ratio
sensitivity (between the host star and its orbiting planet) at
(1 detection) of (when a conventional
adaptive-optics (AO) system is used) or (for typical
`extreme-AO' performance), improving even further when random error is
minimised by averaging over multiple exposures. This is an order of magnitude
beyond conventional pupil-segmenting interferometry techniques (such as
aperture masking), allowing a previously inaccessible part of the star to
planet contrast-separation parameter space to be explored
Where is the best site on Earth? Domes A, B, C and F, and Ridges A and B
The Antarctic plateau contains the best sites on earth for many forms of
astronomy, but none of the existing bases was selected with astronomy as the
primary motivation. In this article, we try to systematically compare the
merits of potential observatory sites.We include South Pole, Domes A, C, and F,
and also Ridge B (running northeast from Dome A), and what we call "Ridge A"
(running southwest from Dome A). Our analysis combines satellite data,
published results, and atmospheric models, to compare the boundary layer,
weather, aurorae, airglow, precipitable water vapor, thermal sky emission,
surface temperature, and the free atmosphere, at each site. We find that all
Antarctic sites are likely to be compromised for optical work by airglow and
aurorae. Of the sites with existing bases, Dome A is easily the best overall;
but we find that Ridge A offers an even better site. We also find that Dome F
is a remarkably good site. Dome C is less good as a thermal infrared or
terahertz site, but would be able to take advantage of a predicted "OH hole"
over Antarctica during spring.Comment: Revised version. 16 pages, 21 figures (22 in first version).
Submitted to PASP 16/05/09, accepted 13/07/09; published 20/08/0
Tin Whisker Electrical Short Circuit Characteristics Part 2
Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has a currently unknown probability associated with it. Due to contact resistance electrical shorts may not occur at lower voltage levels. In this experiment, we study the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From this data we can estimate the probability of an electrical short, as a function of voltage, given that a free tin whisker has bridged two adjacent exposed electrical conductors. In addition, three tin whiskers grown from the same Space Shuttle Orbiter card guide used in the aforementioned experiment were cross-sectioned and studied using a focused ion beam (FIB)
Gender Specific Disruptions in Emotion Processing in Younger Adults with Depression
Background: One of the principal theories regarding the biological basis of major depressive disorder (MDD) implicates a dysregulation of emotion-processing circuitry. Gender differences in how emotions are processed and relative experience with emotion processing might help to explain some of the disparities in the prevalence of MDD between women and men. This study sought to explore how gender and depression status relate to emotion processing. Methods: This study employed a 2 (MDD status) × 2 (gender) factorial design to explore differences in classifications of posed facial emotional expressions (N=151). Results: For errors, there was an interaction between gender and depression status. Women with MDD made more errors than did nondepressed women and men with MDD, particularly for fearful and sad stimuli (Ps Ps P=.01). Men with MDD, conversely, performed similarly to control men (P=.61). Conclusions: These results provide novel and intriguing evidence that depression in younger adults (years) differentially disrupts emotion processing in women as compared to men. This interaction could be driven by neurobiological and social learning mechanisms, or interactions between them, and may underlie differences in the prevalence of depression in women and men. Depression and Anxiety, 2009. Published 2008 Wiley-Liss, Inc
Olfactory groove meningioma: Discussion of clinical presentation and surgical outcomes following excision via the subcranial approach
Objectives/Hypothesis: To describe surgical outcomes and radiographic features of olfactory groove meningiomas treated by excision through the subcranial approach. Special emphasis is placed on paranasal sinus and orbit involvement. Study Design: Retrospective review of a series of patients. Methods: Nineteen patients underwent excision of olfactory groove meningioma (OGM) via the transglabellar/subcranial approach between December 1995 and November 2009. Nine patients had previously undergone prior resection at outside institutions, and four had prior radiotherapy in addition to a prior excision. Transglabellar/subcranial surgical approach to the anterior skull base was performed. Results: Tumor histology included three World Health Organization (WHO) grade III lesions, one WHO grade II lesion, and 15 WHO grade I lesions. Fourteen patients had evidence of extension into the paranasal sinuses, with the ethmoid sinus being most commonly involved. Kaplan‐Meier estimates of mean overall and disease‐free survival were 121.45 months and 93.03 months, respectively. The mean follow‐up interval was 41.0 months, and at the time of data analysis three patients had recurrent tumors. Seven (36.8%) patients experienced a major complication in the perioperative period; there were no perioperative mortalities. Orbit invasion was observed in four patients, with optic nerve impingement in 11 patients. Of these, three patients had long‐term diplopia. No patients experienced worsening of preoperative visual acuity. Conclusions: Olfactory groove meningiomas demonstrate a propensity to spread into the paranasal sinuses, particularly in recurrent cases. Given a tendency for infiltrative recurrence along the skull base, this disease represents an important area of collaboration between neurosurgery and otolaryngology. The subcranial approach offers excellent surgical access for excision, particularly for recurrences that involve the paranasal sinuses and optic apparatus.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87044/1/22174_ftp.pd
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