3,421 research outputs found
Identifying Student Difficulties with Entropy, Heat Engines, and the Carnot Cycle
We report on several specific student difficulties regarding the Second Law
of Thermodynamics in the context of heat engines within upper-division
undergraduates thermal physics courses. Data come from ungraded written
surveys, graded homework assignments, and videotaped classroom observations of
tutorial activities. Written data show that students in these courses do not
clearly articulate the connection between the Carnot cycle and the Second Law
after lecture instruction. This result is consistent both within and across
student populations. Observation data provide evidence for myriad difficulties
related to entropy and heat engines, including students' struggles in reasoning
about situations that are physically impossible and failures to differentiate
between differential and net changes of state properties of a system. Results
herein may be seen as the application of previously documented difficulties in
the context of heat engines, but others are novel and emphasize the subtle and
complex nature of cyclic processes and heat engines, which are central to the
teaching and learning of thermodynamics and its applications. Moreover, the
sophistication of these difficulties is indicative of the more advanced
thinking required of students at the upper division, whose developing knowledge
and understanding give rise to questions and struggles that are inaccessible to
novices
Unseen and unheard? women managers and organizational learning
Purpose
This paper uses (in)visibility as a lens to understand the lived experience of 6 women managers in the U.K. HQ of a large multinational organization, in order to identify how ‘gender’ is expressed in the context of organizational learning
Design/methodology/approach
The researchers take a phenomenological approach via qualitative data collection with a purposeful sample –the six female managers in a group of 24. Data was collected through quarterly semi structured interviews over 12 months with the themes - knowledge, interaction and gender.
Findings
Organisations seek to build advantage in order to gain and retain competitive leadership. Their resilience in a changing task environment depends on their ability to recognize, gain and use knowledge likely to deliver these capabilities. Here gender was a barrier to effective organizational learning with women's knowledge and experience often unseen and unheard.
Research limitations/implications
This is a piece of research limited to exploration of gender as other but ethnicity, age, social class, disability and sexual preference, alone or in combination may be equally subject to invisibility in knowledge terms, further research would be needed to test this however.
Practical implications
Practical applications relate to the need for organizations to examine and address their operations for exclusion based on perceived ‘otherness’. Gendered organizations cause problems for their female members but they also exclude the experience and knowledge of key individuals as seen here, where gender impacted on effective knowledge sharing and cocreation of knowledge.
Originality/value
This exploration of gender and organisational learning offers new insights to help explain the way in which organisational learning occurs – or fails to occur - with visibility/invisibility of one group shaped by gendered attitudes and processes. It shows that organizational learning is not gender neutral (as it appears in mainstream organizational learning research) and calls for researchers to include this as a factor in future research
Linear-time nearest point algorithms for Coxeter lattices
The Coxeter lattices, which we denote , are a family of lattices
containing many of the important lattices in low dimensions. This includes
, , and their duals , and . We consider
the problem of finding a nearest point in a Coxeter lattice. We describe two
new algorithms, one with worst case arithmetic complexity and the
other with worst case complexity O(n) where is the dimension of the
lattice. We show that for the particular lattices and the
algorithms reduce to simple nearest point algorithms that already exist in the
literature.Comment: submitted to IEEE Transactions on Information Theor
Identifying Student Difficulties with Heat Engines, Entropy, and the Carnot Cycle
We report on several specific student difficulties regarding the second law of thermodynamics in the context of heat engines within upper-division undergraduate thermal physics courses. Data come from ungraded written surveys, graded homework assignments, and videotaped classroom observations of tutorial activities. Written data show that students in these courses do not clearly articulate the connection between the Carnot cycle and the second law after lecture instruction. This result is consistent both within and across student populations. Observation data provide evidence for myriad difficulties related to entropy and heat engines, including students’ struggles in reasoning about situations that are physically impossible and failures to differentiate between differential and net changes of state properties of a system. Results herein may be seen as the application of previously documented difficulties in the context of heat engines, but others are novel and emphasize the subtle and complex nature of cyclic processes and heat engines, which are central to the teaching and learning of thermodynamics and its applications. Moreover, the sophistication of these difficulties is indicative of the more advanced thinking required of students at the upper division, whose developing knowledge and understanding give rise to questions and struggles that are inaccessible to novices
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Sonic hedgehog signalling mediates astrocyte crosstalk with neurons to confer neuroprotection
Sonic hedgehog (SHH) is a glycoprotein associated with development that is also expressed in the adult CNS and released after brain injury. Since the SHH receptors patched homolog-1 and Smoothened are highly expressed on astrocytes, we hypothesized that SHH regulates astrocyte function. Primary mouse cortical astrocytes derived from embryonic Swiss mouse cortices, were treated with two chemically distinct agonists of the SHH pathway, which caused astrocytes to elongate and proliferate. These changes are accompanied by decreases in the major astrocyte glutamate transporter-1 and the astrocyte intermediate filament protein glial fibrillary acidic protein. Multisite electrophysiological recordings revealed that the SHH agonist, smoothened agonist suppressed neuronal firing in astrocyte-neuron co-cultures and this was abolished by the astrocyte metabolic inhibitor ethylfluoroacetate, revealing that SHH stimulation of metabolically active astrocytes influences neuronal firing. Using three-dimensional co-culture, MAP2 western blotting and immunohistochemistry, we show that SHH-stimulated astrocytes protect neurons from kainate-induced cell death. Altogether the results show that SHH regulation of astrocyte function represents an endogenous neuroprotective mechanism
Harnessing the power of complex light propagation in multimode fibers for spatially resolved sensing
The propagation of coherent light in multimode optical fibers results in a
speckled output that is both complex and sensitive to environmental effects.
These properties can be a powerful tool for sensing, as small perturbations
lead to significant changes in the output of the fiber. However, the mechanism
to encode spatially resolved sensing information into the speckle pattern and
the ability to extract this information is thus far unclear. In this paper, we
demonstrate that spatially dependent mode coupling is crucial to achieving
spatially resolved measurements. We leverage machine learning to quantitatively
extract this spatially resolved sensing information from three fiber types with
dramatically different characteristics and demonstrate that the fiber with the
highest degree of spatially dependent mode coupling provides the greatest
accuracy.Comment: 17 pages and 7 figure
Aging and ultra-slow equilibration in concentrated colloidal hard spheres
We study the dynamic behaviour of concentrated colloidal hard spheres using
Time Resolved Correlation, a light scattering technique that can detect the
slow evolution of the dynamics in out-of-equilibrium systems. Surprisingly,
equilibrium is reached a very long time after sample initialization, the
non-stationary regime lasting up to three orders of magnitude more than the
relaxation time of the system. Before reaching equilibrium, the system displays
unusual aging behaviour. The intermediate scattering function decays faster
than exponentially and its relaxation time evolves non-monotonically with
sample age.Comment: Submitted to the proceedings of the 6th EPS Liquid Matter Conference,
Utrecht 2-6 July 200
The extinction law in high redshift galaxies
We estimate the dust extinction laws in two intermediate redshift galaxies.
The dust in the lens galaxy of LBQS1009-0252, which has an estimated lens
redshift of zl~0.88, appears to be similar to that of the SMC with no
significant feature at 2175 A. Only if the lens galaxy is at a redshift of
zl~0.3, completely inconsistent with the galaxy colors, luminosity or location
on the fundamental plane, can the data be fit with a normal Galactic extinction
curve. The dust in the zl=0.68 lens galaxy for B0218+357, whose reddened image
lies behind a molecular cloud, requires a very flat ultraviolet extinction
curve with (formally) R(V)=12 +- 2. Both lens systems seem to have unusual
extinction curves by Galactic standards.Comment: 15 pages, 3 figures. ApJ in pres
Identifying Lenses with Small-Scale Structure. I. Cusp Lenses
The inability of standard models to explain the flux ratios in many 4-image
gravitational lenses has been cited as evidence for significant small-scale
structure in lens galaxies. That claim has generally relied on detailed lens
modeling, so it is both model dependent and somewhat difficult to interpret. We
present a more robust and generic method for identifying lenses with
small-scale structure. For a close triplet of images associated with a source
near a cusp caustic, the sum of the signed magnifications should approximately
vanish. We derive realistic upper bounds on the sum, and argue that lenses with
flux ratios that significiantly violate the bounds can be said to have
structure in the lens potential on scales smaller than the image separation.
Five observed lenses have such flux ratio ``anomalies'': B2045+265, 1RXS
J1131-1231, and SDSS J0924+0219 have strong anomalies; B0712+472 has a strong
anomaly at optical/near-IR wavelengths and a marginal anomaly at radio
wavelengths; and RX J0911+0551 appears to have an anomaly, but this conclusion
is subject to uncertainties about octopole modes in early-type galaxies.
Analysis of the cusp relation does not identify the known anomaly in B1422+231,
so methods that are more sophisticated (and less generic) than the cusp
relation may be necessary to uncover flux ratio anomalies in some systems.
Although these flux ratio anomalies might represent milli- or micro-lensing, we
cannot identify the cause; we can only conclude that the lenses have
significant structure in the potential on scales smaller than the separation
between the images. Additional arguments must be invoked to specify the nature
of this small-scale structure. [Abridged]Comment: significant revisions to extend analysis and strengthen conclusions;
low-res version of Fig. 5 here, for high-res version see
http://astro.uchicago.edu/~ckeeton/Papers/cuspreln.ps.g
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