13,412 research outputs found
Strain patterns and strain accumulation along plate margins
Observations of strain accumulation along plate margins in Japan, New Zealand, and the United States indicate that: (1) a typical maximum rate of secular strain accumulation is on the order of 0.3 ppm/a, (2) a substantial part of the strain accumulation process can be attributed to slip at depth on the major plate boundary faults, and (3) some plastic deformation in a zone 100 km or more in width is apparently involved in the strain accumulation process
The Relativity Concept Inventory: development, analysis and results
We report on a concept inventory for special relativity: the development
process, data analysis methods, and results from an introductory relativity
class. The Relativity Concept Inventory tests understanding of kinematic
relativistic concepts. An unusual feature is confidence testing for each
question. This can provide additional information; for example high confidence
correlated with incorrect answers suggests a misconception. A novel aspect of
our data analysis is the use of Monte Carlo simulations to determine the
significance of correlations. This approach is particularly useful for small
sample sizes, such as ours. Our results include a gender bias that was not
present in other assessment, similar to that reported for the Force Concept
Inventory
The Born and Markov approximations for atom lasers
We discuss the use of the Born and Markov approximations in describing the
dynamics of an atom laser. In particular, we investigate the applicability of
the quantum optical Born-Markov master equation for describing output coupling.
We derive conditions based on the atomic reservoir, and atom dispersion
relations for when the Born-Markov approximations are valid and discuss
parameter regimes where these approximations fail in our atom laser model.
Differences between the standard optical laser model and the atom laser are due
to a combination of factors, including the parameter regimes in which a typical
atom laser would operate, the different reservoir state which is appropriate
for atoms, and the different dispersion relations between atoms and photons. We
present results based on an exact method in the regimes in which the
Born-Markov approximation fails. The exact solutions in some experimentally
relavent parameter regimes give non-exponential loss of atoms from a cavity.Comment: 10 pages, 3 figures. (2 new figues). Exact solutions have been
included in section II. Sections IV and V have been expanded. A new section
discussing the effects of gravity has been include
Limits to the analogue Hawking temperature in a Bose-Einstein condensate
Quasi-one dimensional outflow from a dilute gas Bose-Einstein condensate
reservoir is a promising system for the creation of analogue Hawking radiation.
We use numerical modeling to show that stable sonic horizons exist in such a
system under realistic conditions, taking into account the transverse
dimensions and three-body loss. We find that loss limits the analogue Hawking
temperatures achievable in the hydrodynamic regime, with sodium condensates
allowing the highest temperatures. A condensate of 30,000 atoms, with
transverse confinement frequency omega_perp=6800*2*pi Hz, yields horizon
temperatures of about 20 nK over a period of 50 ms. This is at least four times
higher than for other atoms commonly used for Bose-Einstein condensates.Comment: 9 pages, 4 figures, replaced with published versio
Reliability model for planetary gear
A reliability model is presented for planetary gear trains in which the ring gear is fixed, the Sun gear is the input, and the planet arm is the output. The input and output shafts are coaxial and the input and output torques are assumed to be coaxial with these shafts. Thrust and side loading are neglected. This type of gear train is commonly used in main rotor transmissions for helicopters and in other applications which require high reductions in speed. The reliability model is based on the Weibull distribution of the individual reliabilities of the transmission components. The transmission's basic dynamic capacity is defined as the input torque which may be applied for one million input rotations of the Sun gear. Load and life are related by a power law. The load life exponent and basic dynamic capacity are developed as functions of the component capacities
The mechanical design of a vapor compressor for a heat pump to be used in space
A heat pump developed for use in Spacelab as a stand-alone refrigeration unit as well as within a fluid loop system is discussed. It will provide an active thermal control for payloads. Specifications for the heat pump were established: (1) heat removal rates at the source; (2) heat source temperatures from room temperature; (3) heat-sink fluid temperatures at condenser inlet; and (4) minimum power consumption. A reversed Carnot cycle heat pump using Freon 12 as working fluid incorporating a one-cylinder reciprocating compressor was selected. The maximum crankshaft speed was fixed relatively high at 100 rpm. The specified cooling rates then made it necessary to select a cylinder volume of 10 cu cm, which was obtained with a bore of 40 mm and a stroke of 8 mm
Stability of continuously pumped atom lasers
A multimode model of a continuously pumped atom laser is shown to be unstable
below a critical value of the scattering length. Above the critical scattering
length, the atom laser reaches a steady state, the stability of which increases
with pumping. Below this limit the laser does not reach a steady state. This
instability results from the competition between gain and loss for the excited
states of the lasing mode. It will determine a fundamental limit for the
linewidth of an atom laser beam.Comment: 4 page
Seismic response to evolving injection at the Rotokawa geothermal field, New Zealand
Catalogs of microseismicity are routinely compiled at geothermal reservoirs and provide valuable insights into reservoir structure and fluid movement. Hypocentral locations are typically used to infer the orientations of structures and constrain the extent of the permeable reservoir. However, frequency-magnitude distributions may contain additional, and underused, information about the distribution of pressure. Here, we present a four-year catalog of seismicity for the Rotokawa geothermal field in the central Taupō Volcanic Zone, New Zealand starting two years after the commissioning of the 140 MWe Nga Awa Purua power station. Using waveform-correlation-based signal detection we double the size of the previous earthquake catalog, refine the location and orientation of two reservoir faults and identify a new structure. We find the rate of seismicity to be insensitive to major changes in injection strategy during the study period, including the injectivity decline and shift of injection away from the dominant injector, RK24. We also map the spatial distribution of the earthquake frequency-magnitude distribution, or b-value, and show that it increases from ∼1.0 to ∼1.5 with increasing depth below the reservoir. As has been proposed at other reservoirs, we infer that these spatial variations reflect the distribution of pressure in the reservoir, where areas of high b-value correspond to areas of high pore-fluid pressure and a broad distribution of activated fractures. This analysis is not routinely conducted by geothermal operators but shows promise for using earthquake b-value as an additional tool for reservoir monitoring and management
- …