127,665 research outputs found
Inflating and Deflating Hot Jupiters: Coupled Tidal and Thermal Evolution of Known Transiting Planets
We examine the radius evolution of close-in giant planets with a planet
evolution model that couples the orbital-tidal and thermal evolution. For 45
transiting systems, we compute a large grid of cooling/contraction paths
forward in time, starting from a large phase space of initial semi-major axes
and eccentricities. Given observational constraints at the current time for a
given planet (semi-major axis, eccentricity, and system age) we find possible
evolutionary paths that match these constraints, and compare the calculated
radii to observations. We find that tidal evolution has two effects. First,
planets start their evolution at larger semi-major axis, allowing them to
contract more efficiently at earlier times. Second, tidal heating can
significantly inflate the radius when the orbit is being circularized, but this
effect on the radius is short-lived thereafter. Often circularization of the
orbit is proceeded by a long period while the semi-major axis slowly decreases.
Some systems with previously unexplained large radii that we can reproduce with
our coupled model are HAT-P-7, HAT-P-9, WASP-10, and XO-4. This increases the
number of planets for which we can match the radius from 24 (of 45) to as many
as 35 for our standard case, but for some of these systems we are required to
be viewing them at a special time around the era of current radius inflation.
This is a concern for the viability of tidal inflation as a general mechanism
to explain most inflated radii. Also, large initial eccentricities would have
to be common. We also investigate the evolution of models that have a floor on
the eccentricity, as may be due to a perturber. In this scenario we match the
extremely large radius of WASP-12b. (Abridged)Comment: 18 pages, 14 figures, 2 tables, Accepted for publication in Ap
A two-degree Kelvin refrigerator
Open-cycle cryogenic refrigerator maintains temperature as low as 2K for periods up to six months. Designed to cool an infrared detector, refrigerator can be used in cooling Josephson-junction devices, magnetic bubble domains, and superconducting devices
Secondary reflectors for economical sun-tracking energy collection system: A concept
Mechanism is simpler and lower in cost because it moves heat-collector pipe to stay in focus with sun, instead of moving heavy reflectors
Low-cost solar tracking system
Smaller heat-collector is moved to stay in focus with the sun, instead of moving reflector. Tracking can be controlled by storing data of predicted solar positions or by applying conventional sun-sensing devices to follow solar movement
Underground mineral extraction
A method was developed for extracting underground minerals such as coal, which avoids the need for sending personnel underground and which enables the mining of steeply pitched seams of the mineral. The method includes the use of a narrow vehicle which moves underground along the mineral seam and which is connected by pipes or hoses to water pumps at the surface of the Earth. The vehicle hydraulically drills pilot holes during its entrances into the seam, and then directs sideward jets at the seam during its withdrawal from each pilot hole to comminute the mineral surrounding the pilot hole and combine it with water into a slurry, so that the slurried mineral can flow to a location where a pump raises the slurry to the surface
Solar energy collection system
A fixed, linear, ground-based primary reflector having an extended curved sawtooth-contoured surface covered with a metalized polymeric reflecting material, reflects solar energy to a movably supported collector that is kept at the concentrated line focus reflector primary. The primary reflector may be constructed by a process utilizing well known freeway paving machinery. The solar energy absorber is preferably a fluid transporting pipe. Efficient utilization leading to high temperatures from the reflected solar energy is obtained by cylindrical shaped secondary reflectors that direct off-angle energy to the absorber pipe. A seriatim arrangement of cylindrical secondary reflector stages and spot-forming reflector stages produces a high temperature solar energy collection system of greater efficiency
Solar pond
Shallow pools of liquid to collect low-temperature solar generated thermal energy are described. Narrow elongated trenches, grouped together over a wide area, are lined with a heat-absorbing black liner. The heat-absorbing liquid is kept separate from the thermal energy removing fluid by means such as clear polyethylene material. The covering for the pond may be a fluid or solid. If the covering is a fluid, fire fighting foam, continuously generated, or siloons are used to keep the surface covering clean and insulated. If the thermal energy removing fluid is a gas, a fluid insulation layer contained in a flat polyethlene tubing is used to cover the pond. The side of the tube directed towards the sun is treated to block out ultraviolet radiation and trap in infrared radiation
The design and development of a solar tracking unit
The solar tracking unit was developed to support the Laser Heterodyne Spectrometer (LHS) airborne instrument, but has application to a general class of airborne solar occultation research instruments. The unit consists of a mirror mounted on two gimbals, one of which is hollow. The mirror reflects a 7.6 cm (3.0 in.) diameter beam of sunlight through the hollow gimbal into the research instrument optical axis. A portion of the reflected sunlight is directed into a tracking telescope which uses a four quadrant silicon detector to produce the servo error signals. The colinearity of the tracker output beam and the research instrument optical axis is maintained to better than + or - 1 arc-minute. The unit is microcomputer controlled and is capable of stand alone operation, including automatic Sun acquisition or operation under the control of the research instrument
Sampler of gas borne particles
An atmosphere sample is described which includes a very thin filter element with straight-through holes on the order of 1 micron. A sample of air with particles to be examined is driven by means of a pressurized low molecular weight gas, e.g., He to the filter element front side. A partial vacuum may be present at the back side of the filter element. The pressure differential across the filter element is just below the rupture point of the filter element. Particles smaller than filter holes are deposited on the filter element. When using a filter element of plastic material of a thickness on the order of 10 microns, a stainless steel back-up plate and a diffusion member are used to support the filter element when subjected to a pressure differential on the order of a few hundred atmospheres
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