878 research outputs found
Equilibrium temperatures of mass transfer cooled walls in high-speed flow of an absorbing-emitting gas
Equilibrium temperatures of mass transfer cooled walls in high speed flow of absorbing-emitting ga
Modified permittivity observed in bulk Gallium Arsenide and Gallium Phosphide samples at 50 K using the Whispering Gallery mode method
Whispering Gallery modes in bulk cylindrical Gallium Arsenide and Gallium
Phosphide samples have been examined both in darkness and under white light at
50 K. In both samples we observed change in permittivity under light and dark
conditions. This results from a change in the polarization state of the
semiconductor, which is consistent with a free electron-hole
creation/recombination process. The permittivity of the semiconductor is
modified by free photocarriers in the surface layers of the sample which is the
region sampled by Whispering Gallery modes.Comment: 8 pages, 3 figure
Belowground Meristem Populations as Regulators of Grassland Dynamics
Studies of plant populations are critical for linking organism to ecosystem-level phenomena and for understanding mechanisms driving responses to global change. In perennial grasslands, the below-ground population of meristems (the bud bank) plays a fundamental role in local plant population recruitment, persistence and dynamics. We explore two aspects of the bud bank in North American grasslands. It has been hypothesized that low variability in arid biomes is explained by meristem limitation, which constrains responses to pulses of high resource availability. Our research tests this hypothesis by comparing bud-bank populations across six sites in the United States that vary 3-fold in precipitation and 4.5-fold in productivity. In addition, we are examining the effects of management practices, such as fire and grazing, on bud-bank populations using replicated long-term treatments at Konza Prairie LTER site located in north-central Kansas
Inter-specific variation in bud banks and flowering effort among semi-arid African savanna grasses
Population viability and productivity of grasses in southern African savannas are dependent upon both successful seed production and tiller recruitment from the belowground bud bank. Relative recruitment rates from buds versus seeds influence population dynamics, genetic diversity, and patterns of vegetation productivity. We assessed patterns in bud bank size and flowering effort in fourteen semi-arid savanna grass species in the Kalahari region of Botswana. There was high inter-specific variability and between-year variability in flowering effort (percentage of tillers flowering). Bud production (number of buds per tiller) exhibited high inter-specific variability, but was more consistent between-years than flowering effort. Relative allocation to flowering versus bud production varied with life history, with longer-lived perennial grasses showing higher bud production and lower flowering effort relative to shorter-lived grasses. Several species showed higher bud production and lower flowering effort in a wet year compared to a dry year, and grass species that are regularly grazed maintained significantly larger bud banks than non-grazed species. These differential demographic responses among co-occurring species suggest that environmental change in semi-arid savannas may alter the composition, relative abundances and diversity of grasses, and that the maintenance of a belowground bud bank is an important factor influencing their resiliency, their capacity to recover from grazing and/or drought, and their persistence and sustainability under changing environmental conditions. Meristem-limitation in species that maintain few viable buds may constrain their population viability under changing conditions in semi-arid savannas. (C) 2012 SAAB. Published by Elsevier B.V. All rights reserved
Biographical learning: a process for promoting person-centredness in nursing
Background: This paper explores biographical approaches to nurses’ learning. It builds on previous PhD research to consider the effects of such approaches, drawing on the experiences of learners who have recently completed biographical study, in their own words.
Aims and objectives: The aim of the paper is to make sense of different forms of learning. The objectives are to identify how autobiographical approaches that involve people learning from their life stories can engage people to exert agency, or ownership, in their own lives by taking control of their learning plans.
Design: This longitudinal study started with the first group of learners undertaking a biographical preparation module on an Applied BSc Health and Social Care programme.
Methods: Research relating to nurses’ learning is considered, including a Swiss perspective, as well as the validity of the biographical approach to developing knowledge. The learners share stories of their learning in order to develop understanding and new insights into their own lives and those of others. Results: Different dimensions of learning including learning about self, learning to make a difference and processes of repair are revealed through the learners’ narrations.
Conclusions: Engaging biographically, to make sense of different forms of learning, appears to be beneficial to more person-centred working.
Implications for practice:
•Introducing biographical elements into courses of study can benefit learners by helping them to make sense of who they are as learners and practitioners
•Co-creating compelling spaces of learning can facilitate learners to exert agency within their own lives as well as help others to learn. By exerting agency we mean taking ownership of the learning revealed through the biographical work and taking it forward in positive ways to enhance person-centred care
Perceptions and understanding of research situations as a function of consent form characteristics and experimenter instructions
Two studies examined how research methodology affected participant behaviors. Study 1 tested (a) consent form perspective (1st, 2nd, or 3rd person) and (b) information on participants’ right to sue upon perceptions of coercion, ability to recall consent information, and performance on experimental tasks. Unexpectedly, participants who received instructions without the right to sue information had significantly better recall of their research rights. Study 2 manipulated (a) consent form complexity (presence or absence of jargon) and (b) the detail of verbal instructions (simple, elaborate); participants who received a consent form with simpler language spent more time on a difficult task, and participants in the elaborate instruction condition recalled more details. Together, these studies suggest (a) explaining the right to sue may actually be counterproductive; (b) providing a more detailed explanation may help participants remember procedural details; and (c) using jargon may decrease task performance
Colloquium: Comparison of Astrophysical and Terrestrial Frequency Standards
We have re-analyzed the stability of pulse arrival times from pulsars and
white dwarfs using several analysis tools for measuring the noise
characteristics of sampled time and frequency data. We show that the best
terrestrial artificial clocks substantially exceed the performance of
astronomical sources as time-keepers in terms of accuracy (as defined by cesium
primary frequency standards) and stability. This superiority in stability can
be directly demonstrated over time periods up to two years, where there is high
quality data for both. Beyond 2 years there is a deficiency of data for
clock/clock comparisons and both terrestrial and astronomical clocks show equal
performance being equally limited by the quality of the reference timescales
used to make the comparisons. Nonetheless, we show that detailed accuracy
evaluations of modern terrestrial clocks imply that these new clocks are likely
to have a stability better than any astronomical source up to comparison times
of at least hundreds of years. This article is intended to provide a correct
appreciation of the relative merits of natural and artificial clocks. The use
of natural clocks as tests of physics under the most extreme conditions is
entirely appropriate; however, the contention that these natural clocks,
particularly white dwarfs, can compete as timekeepers against devices
constructed by mankind is shown to be doubtful.Comment: 9 pages, 2 figures; presented at the International Frequency Control
Symposium, Newport Beach, Calif., June, 2010; presented at Pulsar Conference
2010, October 12th, Sardinia; accepted 13th September 2010 for publication in
Reviews of Modern Physic
Limits on GNSS Performance at High Latitudes
As climate change will likely lead to more of a human presence in the higher latitudes, it is important to consider how well our safety-critical positioning systems work near the poles. The orbits of the GPS (and other GNSS) preclude satellites with high elevation in these regions; hence, it is clear that at least vertical accuracy is impacted. This paper characterizes this positioning performance loss by developing lower bounds on GDOP as a function of receiver latitude. Examples with actual ephemeris data are included for comparison to the bounds
Spectral and picosecond temporal properties of flared guide Y‐coupled phase‐locked laser arrays
Spatio‐spectral and spatio‐temporal properties of flared waveguide ‘‘Y’’‐coupled laser arrays are investigated in both cw and pulsed operation. In each case, regular sustained self‐pulsations are exhibited. Destabilization of phase locking, caused by amplitude phase coupling, is thought to be the origin of the pulsations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70525/2/APPLAB-53-24-2380-1.pd
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