405 research outputs found
Laser Guide Stars for Extremely Large Telescopes: Efficient Shack-Hartmann Wavefront Sensor Design using Weighted center-of-gravity algorithm
Over the last few years increasing consideration has been given to the study
of Laser Guide Stars (LGS) for the measurement of the disturbance introduced by
the atmosphere in optical and near-infrared astronomical observations from the
ground. A possible method for the generation of a LGS is the excitation of the
Sodium layer in the upper atmosphere at approximately 90 km of altitude. Since
the Sodium layer is approximately 10 km thick, the artificial reference source
looks elongated, especially when observed from the edge of a large aperture.
The spot elongation strongly limits the performance of the most common
wavefront sensors. The centroiding accuracy in a Shack-Hartmann wavefront
sensor, for instance, decreases proportionally to the elongation (in a photon
noise dominated regime). To compensate for this effect a straightforward
solution is to increase the laser power, i.e. to increase the number of
detected photons per subaperture. The scope of the work presented in this paper
is twofold: an analysis of the performance of the Weighted Center of Gravity
algorithm for centroiding with elongated spots and the determination of the
required number of photons to achieve a certain average wavefront error over
the telescope aperture.Comment: 10 pages, 14 figure
Solid-state laser system for laser cooling of Sodium
We demonstrate a frequency-stabilized, all-solid laser source at 589 nm with
up to 800 mW output power. The laser relies on sum-frequency generation from
two laser sources at 1064 nm and 1319 nm through a PPKTP crystal in a
doubly-resonant cavity. We obtain conversion efficiency as high as 2 W/W^2
after optimization of the cavity parameters. The output wavelength is tunable
over 60 GHz, which is sufficient to lock on the Sodium D2 line. The robustness,
beam quality, spectral narrowness and tunability of our source make it an
alternative to dye lasers for atomic physics experiments with Sodium atoms
Cisplatin-induced posterior reversible encephalopathy syndrome and successful re-treatment in a patient with non-seminomatous germ cell tumor: a case report
UNLABELLED: Introduction: Cisplatin is a platinum compound that has revolutionized the treatment of various solid organ tumors. Cisplatin is associated with a variety of side effects and has recently been indicted in the development of posterior reversible encephalopathy syndrome. Posterior reversible encephalopathy syndrome is a potentially reversible condition, with the mainstay of therapy being correction of the underlying cause and withdrawal of the offending drug. However, there are no clear guidelines regarding the possibility of subsequent re-treatment with the causative agent.CASE PRESENTATION: A 23-year-old Asian man presented to our Emergency Department with a four-month history of concomitant abdominal pain and backache and a two-week history of left-sided leg swelling. Diagnostic investigations revealed bilateral pulmonary embolism, extensive deep venous thrombosis and widespread lung and liver metastatic deposits with abdomino-pelvic lymphadenopathy. His biopsy and tumor markers were consistent with non-seminomatous germ cell tumor and he was subsequently started on an initial cycle of cisplatin and etoposide chemotherapy. On the second day of treatment he developed posterior reversible encephalopathy syndrome clinically and radiologically. Cisplatin was stopped for the next two days while etoposide was continued, resulting in complete resolution of his symptoms. He was re-challenged with cisplatin on day five of chemotherapy because a platin-based chemotherapy regimen was his only hope of potential cure. He tolerated it well, with no recurrence of his neurological symptoms and the remainder of his in-patient stay remained uneventful. He was discharged on day eight. He has since then completed treatment and is currently in remission.CONCLUSIONS: The occurrence of posterior reversible encephalopathy syndrome after cisplatin use has been well reported in the literature. We strongly believe that our patient also developed posterior reversible encephalopathy syndrome secondary to cisplatin. The uniqueness of our patient\u27s case lies in the successful re-treatment of our patient with the offending drug. To the best of our knowledge, this is the first instance where a patient was successfully re-treated with cisplatin after having developed posterior reversible encephalopathy syndrome as a result of cisplatin use. The excellent response to re-treatment without recurrence of neurological symptoms in our patient\u27s case provides insight into re-treatment as an option in scenarios where treatment options are limited
Impact of age norms and stereotypes on managers' hiring decisions of retirees
Purpose -Our study investigates the role of managers in the re-employment of early retirees and asks what the effect is of managersâ age norms and stereotypes on managersâ employment decisions.
Design/methodology/approach- A combination of a factorial study and a survey was conducted. First, information on the age norms and stereotypes was collected. Secondly, profiles of hypothetical retired job applicants were presented to the employers, who were asked to make a specific hiring decision. The information collected during both studies was combined in the analysis and multilevel models were estimated.
Findings -The results indicate that higher age norms result in a higher propensity to hire an early retiree. Stereotypes, by contrast, do not influence managersâ decisions. Early retireesâ chances for re-employment are also related to their own circumstances (physical appearance and relevant experience) and organisational forces, as they are hired when organisations face labour force shortages.
Research limitation / implications â with the use of vignettes study we deal with hypothetical hiring situation.
Originality value- Although the effect of age norms and age stereotypes has been often suggested, not much empirical evidence was presented to support this notion. Our study estimates the effect of age norms and stereotypes on hiring decision.
key words: bridge employment; early retirees; age norms; age stereotypes; multilevel models.
Should Failure to Protect Laws Include Physical and Emotional Sibling Violence?
Physical and emotional sibling violence is a problematic occurrence for many children, adults, and families, yet this form of violence rarely falls within the purview of state laws and policies. Failure to protect laws offer one avenue through which sibling violence can be addressed by holding parents and caregivers accountable for harm that occurs to a child in their custody. This article provides background information on physical and emotional sibling violence as well as a general overview of failure to protect laws in the context of intimate partner violence with particular consideration of these laws in addressing sibling violence. In addition, the role social work practitioners can play in intervening and addressing sibling violence through psychoeducation leading to policy (i.e., failure to act laws) is presented
Starfire Optical Range 3.5-m telescope adaptive optical system
A 941 channel, 1500 Hertz frame rate adaptive optical (AO) system has been installed and tested in the coude path of the 3.5m telescope at the USAF Research Laboratory Starfire Optical Range. This paper describes the design and measured performance of the principal components comprising this system and present sample results from the first closed-loop test of the system on stars and an artificial source simulator
Modern optical astronomy: technology and impact of interferometry
The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics,
2002, to appear in April issu
Predictive value of neurological examination for early cortical responses to somatosensory evoked potentials in patients with postanoxic coma
Bilateral absence of cortical N20 responses of median nerve somatosensory evoked potentials (SEP) predicts poor neurological outcome in postanoxic coma after cardiopulmonary resuscitation (CPR). Although SEP is easy to perform and available in most hospitals, it is worthwhile to know how neurological signs are associated with SEP results. The aim of this study was to investigate whether specific clinical neurological signs are associated with either an absent or a present median nerve SEP in patients after CPR. Data from the previously published multicenter prospective cohort study PROPAC (prognosis in postanoxic coma, 2000â2003) were used. Neurological examination, consisting of Glasgow Coma Score (GCS) and brain stem reflexes, and SEP were performed 24, 48, and 72Â h after CPR. Positive predictive values for predicting absent and present SEP, as well as diagnostic accuracy were calculated. Data of 407 patients were included. Of the 781 SEPs performed, N20Â s were present in 401, bilaterally absent in 299, and 81 SEPs were technically undeterminable. The highest positive predictive values (0.63â0.91) for an absent SEP were found for absent pupillary light responses. The highest positive predictive values (0.71â0.83) for a present SEP were found for motor scores of withdrawal to painful stimuli or better. Multivariate analyses showed a fair diagnostic accuracy (0.78) for neurological examination in predicting an absent or present SEP at 48 or 72Â h after CPR. This study shows that neurological examination cannot reliably predict absent or present cortical N20 responses in median nerve SEPs in patients after CPR
Does proactive personality matter in leadership transitions? Effects of proactive personality on new leader identification and responses to new leaders and their change agendas
Despite the growing frequency of leadership transitions and their significant impact on team and organizational performance, little research has examined why and how teams develop an identification with a new leader or their subsequent receptiveness to the new leaderâs change initiatives. Drawing from the contrast and congruence effects and the theoretical perspectives of leader identification, this study empirically tests a model in which the congruence of new leadersâ and their teamsâ proactive personalities foster new leader identification, as well as the teamâs behavioral responses to the new leaderâs change agenda. This effect is strongest when the new leaderâs proactive personality is higher than that of the former leaderâs proactive personality (positive contrast). Our findings of a four-wave âbefore-and-afterâ transition survey of 155 hotel employees and 51 new leaders, achieved through polynomial regression analyses, proved very insightful. Essentially, we found that the congruence between a new leaderâs and his/her teamâs proactive personalities and the positive contrast between a former leaderâs and the new leaderâs proactive personalities enhanced new leader identification and the teamâs shared identification with the new leaderâs change agenda, and, thereby led the team to exhibit more behavioral engagement with, and voice behavior about, the new leaderâs change agenda
Starfire Optical Range 3.5-m telescope adaptive optical system
A 941 channel, 1500 Hertz frame rate adaptive optical (AO) system has been installed and tested in the coude path of the 3.5m telescope at the USAF Research Laboratory Starfire Optical Range. This paper describes the design and measured performance of the principal components comprising this system and present sample results from the first closed-loop test of the system on stars and an artificial source simulator
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