3,936 research outputs found
Enigmatic Sea Floor Mounds in Antarctica--analysis of bathymetry data from geophysical cruise NBP04-01
As part of the 2004 Nathaniel B. Palmer-0401
geophysical cruise, a structural geology enigma was identified on the Ross Sea floor off the Antarctica coast. Using multibeam bathymetry, a series of eight mysterious, âpepperoni-shapedâ
mounds were identified on the sea floor. My
research entails the morphological study of these
structures and the determination of their
relationship to either nearby volcanism or subglacial features.
Through the use of the IVS-Fledermaus©
software program, bathymetric data obtained
from the cruise was projected in a 3-dimensional model. Morphological data from the seafloor hills is compared to the attributes of glacial drumlins and volcanic tuya. Future work will include adding seismic and magnetic profiles of
the area to the 3D model to constrain their
composition and the internal subsurface structure associated with the hills. Once the origin of these features has been determined, a search for their existence in similar environments worldwide can be conducted in order to determine their uniqueness.Shell Oil Corp
Aerosol physical properties in the stratosphere (APPS) radiometer design
The measurement concepts and radiometer design developed to obtain earth-limb spectral radiance measurements for the Aerosol Physical Properties in the Stratosphere (APPS) measurement program are presented. The measurements made by a radiometer of this design can be inverted to yield vertical profiles of Rayleigh scatterers, ozone, nitrogen dioxide, aerosol extinction, and aerosol physical properties, including a Junge size-distribution parameter, and a real and imaginary index of refraction. The radiometer design provides the capacity for remote sensing of stratospheric constituents from space on platforms such as the space shuttle and satellites, and therefore provides for global measurements on a daily basis
Fluent temporal logic for discrete-time event-based models
Fluent model checking is an automated technique for verifying that an event-based operational model satisfies some state-based declarative properties. The link between the event-based and state-based formalisms is defined through fluents which are state predicates whose value are determined by the occurrences of initiating and terminating events that make the fluents values become true or false, respectively. The existing fluent temporal logic is convenient for reasoning about untimed event-based models but difficult to use for timed models. The paper extends fluent temporal logic with temporal operators for modelling timed properties of discrete-time event-based models. It presents two approaches that differ on whether the properties model the system state after the occurrence of each event or at a fixed time rate. Model checking of timed properties is made possible by translating them into the existing untimed framework. Copyright 2005 ACM
The resistance ratchet: theoretical implications of cyclic selection pressure
Objectives: To investigate the effects of cyclic antibiotic selection pressure on resistance in a simple mathematical model. Methods: The model assumed that resistance in microbial ecologies changes slowly with changing selection pressure, at a rate proportional to the difference between the current resistance level and the resistance level that would be in equilibrium with current selection pressure. The maximum rate of increase in resistance during periods of increasing selection was assumed to be greater than the maximum rate of decrease during decreased selection. Results: Under a simulated annual cyclic selection pressure variation of 40%, with maximum resistance rise and fall rates of 10 and 0.5%, respectively, resistance rose above the level expected from the mean selection pressure by small ratchet-like increments. Over 50 simulated years, resistance increased to 62%, rather than the 50% expected from the mean level of selection. Welsh community prescribing for a selection of antibiotics showed a seasonal cyclic variation of 13-45%. Conclusions: The intuitive assumption that cyclic selective pressure would produce resistance levels commensurate with the mean selection pressure was contradicted; rather resistance drifted towards a level commensurate with maximum selection pressure. If the ratchet effect exists in reality, it may produce unexpected excess resistance, particularly in the community for antibiotics used in respiratory infection, where cycling is pronounced, or in ITU antibiotic rotation. It should be most pronounced for resistance systems with strong asymmetry between rates of adaptation under rising and falling selection pressure. Non-linear dynamic systems in physics and ecology are notorious for producing counter-intuitive effects; resistance epidemiology may be similar
The Lennard-Jones-Devonshire cell model revisited
We reanalyse the cell theory of Lennard-Jones and Devonshire and find that in
addition to the critical point originally reported for the 12-6 potential (and
widely quoted in standard textbooks), the model exhibits a further critical
point. We show that the latter is actually a more appropriate candidate for
liquid-gas criticality than the original critical point.Comment: 5 pages, 3 figures, submitted to Mol. Phy
Inductive learning spatial attention
This paper investigates the automatic induction of spatial attention
from the visual observation of objects manipulated
on a table top. In this work, space is represented in terms of
a novel observer-object relative reference system, named Local
Cardinal System, defined upon the local neighbourhood
of objects on the table. We present results of applying the
proposed methodology on five distinct scenarios involving
the construction of spatial patterns of coloured blocks
The abundance of zâł10 galaxy candidates in the HUDF using deep JWST NIRCam medium-band imaging
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