1,686 research outputs found
Rounding up the wanderers: optimizing coronagraphic searches for extrasolar planets
I derive analytic scalings for coronagraphic imaging searches for extrasolar
planets. I compute the efficiency of detecting planets about any given star,
and from this compute dimensionless distribution functions for the detected
planets as a function of planet-star distance and distance to the host stars. I
find the following for blind planet surveys: (1) the optimum wavelength is
between 4000-5000 Angstroms for Earth-like planets and 4200-5800 Angstroms for
Jovian planets; (2) between 21-32% of the number of planets per decade of
radius can be detected with an optimized survey; (3) target stars should be
ranked from greatest to least by their luminosity divided by distance to the
sixth or eighth power, depending on the dominant source of noise for the
survey; (4) surveys targeting all main sequence stars will detect ~3 times as
many planets as surveys only targeting G-type stars; and (5) stellar
populations with different metallicities should have exposure times that vary
with the cube of the metallicity. I apply these results to the current suite of
proposed coronagraphic satellite telescopes, of which TPF-C is the most
powerful, but a much smaller telescope, TOPS, may have a significant chance of
detecting Earth-sized planets due to its small inner working angle and high
throughput. The most significant uncertainty in these results is the noise
contribution of Exo-zodiacal light. These results can be applied to designing
coronagraphs, comparing proposed telescope designs, optimizing the observing
strategies, determining the properties of detected planet populations, and
selecting target stars.Comment: 21 pages, 7 figures, accepted for publication in MNRA
Testing a model of global citizenship in higher education institutions in the SADC region
Higher Education Institutions (HEIs) equip the labour force with the necessary skills and knowledge to engage effectively as global citizens. The aim of this study was to test the Reysen and Katzarska-Miller (2013) model of global citizenship identity in the context of HEIs in the SADC region. This study approaches global citizenship from a social identity perspective in which identification as a global citizen is at the center. Identification as a global citizen is theorised to follow a Normative Environment and Global Awareness as antecedents. In turn global citizen identification (GCI) produces six prosocial outcomes. This model proposes nine domains of Global Citizenship including two antecedents, an identification as a global citizen and six prosocial outcomes. Participants included 242 students and staff from universities across seven countries participating in the UNESCO #OpenUpYourThinking Researchers Challenge. Participants completed an online version of the Global Citizenship Scale. In this study, the antecedents and outcomes of GC were all positively and significantly correlated demonstrating a linear relationship between all domains. The results provided empirical support for this model in the context of HEIs in the SADC region. GCI was significantly predicted by normative environment and global awareness. In turn, GCI significantly predicted the six prosocial outcomes. Indirect prediction effects between normative environment, global awareness and GCI significantly predicted the six prosocial outcomes
Dreaming after trauma: exploring the relationship of replicative and recurrent posttraumatic nightmares to insomnia, nightmare distress, and posttraumatic stress disorder among survivors of intimate partner violence
Intimate partner violence (IPV) is a widespread problem with significant negative effects. A common result of IPV is the development of posttraumatic stress disorder (PTSD), a disorder that occurs when psychological recovery from a traumatic experience is impaired or arrested. There are a variety of approaches for treating PTSD, but one of the most prevalent symptoms of PTSD, posttraumatic nightmares (PTNMs), frequently does not resolve even when other PTSD symptoms have been significantly reduced or eliminated (Bradley, Greene, & Russ, 2005). In addition, PTNMs of IPV survivors often contain horrific content that is emotionally disturbing (Rasmussen, 2007), and PTNM frequency is linked to increased risk of suicide attempts, with several studies showing this increased risk is independent of depressive symptoms and insomnia (Nadorff et al., 2014; Sjostrom et al., 2007; Tanskanen et al., 2001). Due to the difficulty in resolving PTNMs and their negative effect on IPV survivors, this study sought to increase understanding of the function of PTNMs by examining elements of the Contemporary Theory of Dreaming (CTD) suggesting that nightmares help to integrate the emotion from trauma into the experience of the dreamer. The study also examined Levin and Nielsen's (2009) idea put forth in their (A)mygdala, (M)edial (P)refrontal Cortex, (H)ippocampus, (A)nterior (C)ingulate Cortex/(A)ffective (N)etwork (D)ysfunction (AMPHAC/AND) neurocognitive dreaming model that nightmares allow for fear-memory extinction. Both CTD and the AMPHAC/AND model suggest that when nightmares repeat the dreamer is not formulating new associations, which is an impairment of the normal function of nightmares, namely, to aid trauma recovery. Therefore, this study examined two forms of repeating nightmares that are linked with PTSD and with difficulty recovering from PTSD, and for which there is a dearth of research describing the relationship between these dream types and PTSD. These two types of repeating nightmares are replicative nightmares (nightmares that repeat the trauma exactly) and recurrent nightmares (nightmares that do not repeat the trauma but occur in the same form repeatedly). CTD suggests that insomnia is the likely cause of repeating nightmares, while the AMPHAC/AND model attributes affective distress (as measured through nightmare distress) as the cause. The current study evaluated these competing proposals for the cause of repeating nightmares as well as the relationship between repeating nightmares and PTSD using a cross-sectional correlation design to discover if the reported relationships of repeating nightmares, PTSD, insomnia, and nightmares distress among IPV survivors was consistent with the models (CTD and AMPHAC/AND). Analyses revealed that PTSD and repeating nightmares were strongly correlated among the sample of IPV survivors who participated in the study. In addition, nightmare distress had a strong significant correlation with repeating nightmares and PTSD, while insomnia had a moderate correlation with PTSD and only the replicative type of repeating nightmares. These findings were consistent with the propositions made in the AMPHAC/AND model, however, the CTD proposal that insomnia leads to repeating nightmares was not supported by the findings. There are implications from the research findings. The presence of repeating nightmares in clients should indicate the need for trauma assessment due to the strong relationship between repeating nightmares and PTSD symptom severity. IPV survivors should be assessed for repeating nightmares, and, based on the strong relationship between repeating nightmares, nightmare distress, and PTSD symptom severity, the nightmares of survivors experiencing repeating nightmares should be addressed in counseling to alleviate distress related to the experience of those repeating nightmares. In addition, further research is needed. Longitudinal studies to evaluate whether dreams and nightmares that generate new associations lead to improvements in PTSD symptoms among IPV survivors would provide valuable information towards evaluating the role of dreams and nightmares put forward in the AMPHAC/AND model. Additionally, due to the lack of research on IPV survivorsâ dreams and nightmares over time, qualitative research of IPV survivorsâ experiences with dreams and nightmares in the maintenance of PTSD and recovery from PTSD is needed
Ensemble evaluation of hydrological model hypotheses
It is demonstrated for the first time how model parameter, structural and data uncertainties can be accounted for explicitly and simultaneously within the Generalized Likelihood Uncertainty Estimation (GLUE) methodology. As an example application, 72 variants of a single soil moisture accounting store are tested as simplified hypotheses of runoff generation at six experimental grassland field-scale lysimeters through model rejection and a novel diagnostic scheme. The fields, designed as replicates, exhibit different hydrological behaviors which yield different model performances. For fields with low initial discharge levels at the beginning of events, the conceptual stores considered reach their limit of applicability. Conversely, one of the fields yielding more discharge than the others, but having larger data gaps, allows for greater flexibility in the choice of model structures. As a model learning exercise, the study points to a âleakingâ of the fields not evident from previous field experiments. It is discussed how understanding observational uncertainties and incorporating these into model diagnostics can help appreciate the scale of model structural error
Quantifying Parameter Sensitivity, Interaction and Transferability in Hydrologically Enhanced Versions of Noah-LSM over Transition Zones
We use sensitivity analysis to identify the parameters that are most responsible for shaping land surface model (LSM) simulations and to understand the complex interactions in three versions of the Noah LSM: the standard version (STD), a version enhanced with a simple groundwater module (GW), and version augmented by a dynamic phenology module (DV). We use warm season, high-frequency, near-surface states and turbulent fluxes collected over nine sites in the US Southern Great Plains. We quantify changes in the pattern of sensitive parameters, the amount and nature of the interaction between parameters, and the covariance structure of the distribution of behavioral parameter sets. Using Sobol s total and first-order sensitivity indexes, we show that very few parameters directly control the variance of the model output. Significant parameter interaction occurs so that not only the optimal parameter values differ between models, but the relationships between parameters change. GW decreases parameter interaction and appears to improve model realism, especially at wetter sites. DV increases parameter interaction and decreases identifiability, implying it is overparameterized and/or underconstrained. A case study at a wet site shows GW has two functional modes: one that mimics STD and a second in which GW improves model function by decoupling direct evaporation and baseflow. Unsupervised classification of the posterior distributions of behavioral parameter sets cannot group similar sites based solely on soil or vegetation type, helping to explain why transferability between sites and models is not straightforward. This evidence suggests a priori assignment of parameters should also consider climatic differences
Strong enhancement of spin fluctuations in the low-temperature-tetragonal phase of antiferromagnetically ordered La_{2-x-y}Eu_ySr_xCuO_4
Measurements of the static magnetization, susceptibility and ESR of Gd spin
probes have been performed to study the properties of antiferromagnetically
ordered La_{2-x-y}Eu_ySr_xCuO_4 (x less or equal 0.02) with the low temperature
tetragonal structure. According to the static magnetic measurements the CuO_2
planes are magnetically decoupled in this structural phase. The ESR study
reveals strong magnetic fluctuations at the ESR frequency which are not present
in the orthorhombic phase. It is argued that this drastic enhancement of the
spin fluctuations is due to a considerable weakening of the interlayer exchange
and a pronounced influence of hole motion on the antiferromagnetic properties
of lightly hole doped La_2CuO_4. No evidence for the stripe phase formation at
small hole doping is obtained in the present study.Comment: 10 pages, LaTeX, 3 EPS figures; to be published in Journal of
Physics: Condensed Matte
Automatic generation of alignments for 3D QSAR analyses
Many 3D QSAR methods require the alignment of the molecules in a dataset, which can require a fair amount of manual effort in deciding upon a rational basis for the superposition. This paper describes the use of FBSS, a pro-ram for field-based similarity searching in chemical databases, for generating such alignments automatically. The CoMFA and CoMSIA experiments with several literature datasets show that the QSAR models resulting from the FBSS alignments are broadly comparable in predictive performance with the models resulting from manual alignments
Exploratory laparotomy in the management of confirmed necrotizing enterocolitis
Introduction: Necrotizing enterocolitis (NEC) is a serious gastrointestinal emergency in newborn infants. Surgical management includes primary peritoneal drainage and/or exploratory laparotomy with bowel resection. This study describes obstetric complications, postnatal comorbidities, surgical care and intermediate postoperative outcomes in all infants with surgically and/or histologically proven NEC, who underwent exploratory laparotomy at our tertiary referral centre.Materials and methods: We conducted a retrospective review between January 2005 and December 2010. Results are reported as median (range). Fisherâs exact test (two tailed) was used for statistical analysis. A P-value of 0.05 or less was considered statistically significant.Results: A total of 71 infants had suspected (Bellâs stageZ1) NEC. Of them, 32 infants underwent laparotomy for stage 2â3 NEC. We excluded 11 infants with surgically and/or histologically proven spontaneous intestinal perforation. In the remaining 21 infants with confirmed NEC, median gestational age was 27 weeks (23â39 weeks) and median birth weight was 720 g (440â3510 g). NEC was suspected after a median 14 days of life (1â49 days of life). Fifteen patients (71%) were initially managed medically for a median total of 8 days (1â25 days). Laparotomy was performed after a median of 7 days (<1â35 days) from the suspicion of NEC. Eleven infants (52%) underwent bowel resection and enterostomy, four infants (19%) underwent bowel resection with primary anastomosis and one infant (5%) underwent proximal diverting jejunostomy. Bowel perforation was seen in seven patients (33%). Necrosis totalis was evident in five patients (24%). There were 12 postoperative deaths (57% mortality), and seven deaths (58%) occurred during the first 30 days. Infants who died were more likely to have had absent/reversed enddiastolic flow (n=5, P= 0.64), intrauterine growth retardation (n=5, P = 0.18) or a gestational birth weight between 501 and 750 g (n=9, P = 0.08). In the surviving children (n= 9), the median length of hospital stay was 134 days (87â190 days) and postoperative sequelae were frequently seen.Conclusion: The morbidity and mortality for infants with confirmed NEC who undergo laparotomy remain high in infants despite optimal medical and surgical care. Keywords: exploratory laparotomy, necrotizing enterocolitis, surger
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