3,810 research outputs found
First year student experience
The application was made on behalf of the undergraduate courses team who sought to enhance the first year experience by engaging students in the practice of business. The intention was to develop and signpost enterprising qualities and characteristics in first year learners and develop confidence as well as competence.
The undergraduate review for FBL commenced in September 2009. This offered an opportunity to innovate and build good practice in enterprise learning as a pilot to inform the undergraduate review. The team sought to provide a coherent and relevant set of learning experiences that could be achieved outside structured curriculum that would enable learning through live projects
Nuclear Spirals in the inner Milky Way
We use hydrodynamical simulations to construct a new coherent picture for the
gas flow in the Central Molecular Zone (CMZ), the region of our Galaxy within
. We relate connected structures observed in
data cubes of molecular tracers to nuclear spiral arms. These arise naturally
in hydrodynamical simulations of barred galaxies, and are similar to those that
can be seen in external galaxies such as NGC4303 or NGC1097. We discuss a
face-on view of the CMZ including the position of several prominent molecular
clouds, such as Sgr B2, the and
clouds, the polar arc, Bania Clump 2 and Sgr C. Our model is also consistent
with the larger scale gas flow, up to , thus providing a
consistent picture of the entire Galactic bar region.Comment: Accepted for publication in MNRAS, 12 pages, 12 figure
Applications of a Venus thermospheric circulation model
A variety of Pioneer Venus observations suggest a global scale, day-to-night Venus thermospheric circulation. Model studies of the dynamics and energetics of the Venus thermosphere are presented in order to address new driving, mixing and cooling mechanisms for an improved model simulation. The adopted approach was to reexamine the circulation by first using a previous two dimensional code to quantify those physical processes which can be inferred from the Pioneer Venus observations. Specifically, the model was used to perform sensitivity studies to determine the degree to which eddy cooling, eddy or wave drag, eddy diffusion and 15 micrometer radiational cooling are necessary to bring the model temperature and composition fields into agreement with observations. Three EUV heating cases were isolated for study. Global temperature and composition fields in good agreement with Pioneer data were obtained. Large scale horizontal winds 220 m/s were found to be consistent with the observed cold nightside temperatures and dayside bulges of O, CO and CO2. Observed dayside temperatures were obtained by using a 7 to 19% EUV heating efficiency profile. The enhanced 15 micrometer cooling needed for thermal balance is obtained using the best rate coefficient available for atomic O collisional excitation of CO2(0,1,0). Eddy conduction was not found to be a viable cooling mechanism due to the weakened global circulation. The strong 15 micrometer damping and low EUV efficiency imply a very weak dependence of the general circulation to solar cycle variability. The NCAR terrestrial thermospheric general circulation model was adapted for Venus inputs using the above two dimensional model parameters, to give a three dimensional benchmark for future Venus modelling work
Sub-linear radiation power dependence of photo-excited resistance oscillations in two-dimensional electron systems
We find that the amplitude of the radiation-induced
magnetoresistance oscillations in GaAs/AlGaAs system grows nonlinearly as where is the amplitude and the exponent .
%, with in %the low temperature limit. This striking
result can be explained with the radiation-driven electron orbits model, which
suggests that the amplitude of resistance oscillations depends linearly on the
radiation electric field, and therefore on the square root of the power, .
We also study how this sub-linear power law varies with lattice temperature and
radiation frequency.Comment: 5 pages, 3 figure
A theoretical explanation for the Central Molecular Zone asymmetry
It has been known for more than thirty years that the distribution of
molecular gas in the innermost 300 parsecs of the Milky Way, the Central
Molecular Zone, is strongly asymmetric. Indeed, approximately three quarters of
molecular emission comes from positive longitudes, and only one quarter from
negative longitudes. However, despite much theoretical effort, the origin of
this asymmetry has remained a mystery. Here we show that the asymmetry can be
neatly explained by unsteady flow of gas in a barred potential. We use
high-resolution 3D hydrodynamical simulations coupled to a state-of-the-art
chemical network. Despite the initial conditions and the bar potential being
point-symmetric with respect to the Galactic Centre, asymmetries develop
spontaneously due to the combination of a hydrodynamical instability known as
the "wiggle instability" and the thermal instability. The observed asymmetry
must be transient: observations made tens of megayears in the past or in the
future would often show an asymmetry in the opposite sense. Fluctuations of
amplitude comparable to the observed asymmetry occur for a large fraction of
the time in our simulations, and suggest that the present is not an exceptional
moment in the life of our Galaxy.Comment: Accepted for publication in MNRAS. Videos of the simulations are
available at http://www.ita.uni-heidelberg.de/~mattia/download.htm
Minimum Thermal Conductivity of Superlattices
The phonon thermal conductivity of a multilayer is calculated for transport
perpendicular to the layers. There is a cross over between particle transport
for thick layers to wave transport for thin layers. The calculations shows that
the conductivity has a minimum value for a layer thickness somewhat smaller
then the mean free path of the phonons.Comment: new results added, to appear in PR
Long-term production of greenhouse gases from exposed continental shelves and oceanic islands during Quaternary glacial periods
The EPICA Dome C ice core in Antarctica has yielded an 800,000-year record of atmospheric carbon dioxide and methane composition from the Middle Pleistocene climatic transition to the present. In this record, there is a sharp increase in both carbon dioxide and methane immediately following the glacial maxima during the glacial periods which to date remains difficult to explain. We will present evidence to show that the exposed continental shelves and ...published_or_final_versio
The mineralogic evolution of the Martian surface through time: Implications from chemical reaction path modeling studies
Chemical reaction path calculations were used to model the minerals that might have formed at or near the Martian surface as a result of volcano or meteorite impact driven hydrothermal systems; weathering at the Martian surface during an early warm, wet climate; and near-zero or sub-zero C brine-regolith reactions in the current cold climate. Although the chemical reaction path calculations carried out do not define the exact mineralogical evolution of the Martian surface over time, they do place valuable geochemical constraints on the types of minerals that formed from an aqueous phase under various surficial and geochemically complex conditions
Incorporating Redispersal Microsites into Myrmecochory in Eastern North American Forests
Studies addressing the benefits of “directed dispersal” in ant seed dispersal systems have highlighted the beneficial soil properties of the nests of ants that disperse their seeds. No studies, however, have explored the properties of soils nearby exemplary seed-dispersing ant nests, where recent work indicates that seeds are quickly “redispersed” in eastern North America. To address this, we focused on a forested ecosystem in eastern United States where a keystone seed-dispersing ant, Aphaenogaster rudis, commonly disperses the seeds of numerous understory herbs, including Jeffersonia diphylla. We collected soil cores beneath J. diphylla, around A. rudis nests where seeds are dispersed, and from other forest locations. We analyzed the collected soils for microbial activity using potential soil enzyme activity as a proxy, as well as a number of environmental parameters. We followed this with a glasshouse experiment testing whether the soils collected from near nests, beneath J. diphylla, and from other forested areas altered seedling emergence. We found that microbial activities were higher in near-nest microsites than elsewhere. Specifically, the potential enzyme activities of a carbon-degrading enzyme (β-glucosidase), a phosphorus-acquiring enzyme (phosphatase), and a sulfur-acquiring enzyme (sulfatase) were all significantly higher in areas near ant nests than elsewhere; this same pattern, although not significant, was found for the nitrogen-acquiring enzyme NAGase. No differences were found in other environmental variables we investigated (e.g., soil temperature, soil moisture, soil pH). Our field results indicate that soil biological processes are significantly different in near-nest soils, where the seeds are ultimately dispersed. However, our glasshouse germination trials revealed no enhanced germination in near-nest soils, thereby refuting any near-term advantages of directed dispersal to near-nest locations. Future work should be directed toward addressing whether areas near ant nests provide biologically meaningful escape from seed predation and enhanced establishment, and further characterization of soil microbial communities in such settings
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