8,939 research outputs found
Surveying the solar system by measuring angles and times: from the solar density to the gravitational constant
A surprisingly large amount of information on our solar system can be gained
from simple measurements of the apparent angular diameters of the sun and the
moon. This information includes the average density of the sun, the distance
between earth and moon, the radius of the moon, and the gravitational constant.
In this note it is described how these and other quantities can be obtained by
simple earthbound measurements of angles and times only, without using any
explicit information on distances between celestial bodies. The pedagogical and
historical aspects of these results are also discussed briefly.Comment: 12 pges, one figur
Comment on "On Mach's critique of Newton and Copernicus"
Hartman and Nissim-Sabat have argued that Mach's idea of the relativity of
rotational motion suffers from internal inconsistencies and leads to a
contradiction that there cannot be a stationary bucket in a rotating universe.
They also claimed that non-inertial electromagnetic and stellar aberration
observations can distinguish between a rotating and a stationary universe,
whereas according to Mach there cannot be any observable way to distinguish
these two cases. We contest these objections.Comment: Six pages, to appear in AJ
Microwave soil moisture measurements and analysis
An effort to develop a model that simulates the distribution of water content and of temperature in bare soil is documented. The field experimental set up designed to acquire the data to test this model is described. The microwave signature acquisition system (MSAS) field measurements acquired in Colby, Kansas during the summer of 1978 are pesented
Terminal velocity and drag reduction measurements on superhydrophobic spheres
Super water-repellent surfaces occur naturally on plants and aquatic insects and are created in the laboratory by combining micro- or nanoscale surface topographic features with hydrophobic surface chemistry. When such types of water-repellent surfaces are submerged they can retain a film of air (a plastron). In this work, we report measurements of the terminal velocity of solid acrylic spheres with various surface treatments settling under the action of gravity in water. We observed increases in terminal velocity corresponding to drag reduction of between 5% and 15% for superhydrophobic surfaces that carry plastrons
Self-organization of hydrophobic soil and granular surfaces
Soil can become extremely water repellent following forest fires or oil spillages, thus preventing penetration of water and increasing runoff and soil erosion. Here the authors show that evaporation of a droplet from the surface of a hydrophobic granular material can be an active process, lifting, self-coating, and selectively concentrating small solid grains. Droplet evaporation leads to the formation of temporary liquid marbles and, as droplet volume reduces, particles of different wettabilities compete for water-air interfacial surface area. This can result in a sorting effect with self-organization of a mixed hydrophobic-hydrophilic aggregate into a hydrophobic shell surrounding a hydrophilic core
The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23
The 11-year cycle of solar activity follows Hale's law by reversing the
magnetic polarity of leading and following sunspots in bipolar regions during
the minima of activity. In the 1996-97 solar minimum, most solar activity
emerged in narrow longitudinal zones - `active longitudes' but over a range in
latitude. Investigating the distribution of solar magnetic flux, we have found
that the Hale sunspot polarity reversal first occurred in these active zones.
We have estimated the rotation rates of the magnetic flux in the active zones
before and after the polarity reversal. Comparing these rotation rates with the
internal rotation inferred by helioseismology, we suggest that both `old' and
`new' magnetic fluxes were probably generated in a low-latitude zone near the
base of the solar convection zone. The reversal of active region polarity
observed in certain longitudes at the beginning of a new solar cycle suggests
that the phenomenon of active longitudes may give fundamental information about
the mechanism of the solar cycle. The non-random distribution of old-cycle and
new-cycle fluxes presents a challenge for dynamo theories, most of which assume
a uniform longitudinal distribution of solar magnetic fields.Comment: 4 pages, 5 figures; accepted for publication in ApJ Letter
The Late Quaternary geology of the Housatonic River basin in southwestern Massachusetts and adjacent Connecticut
Guidebook for field trips in western Massachusetts, northern Connecticut and adjacent areas of New York: 67th annual meeting October 10, 11, and 12, 1975: Trip B-7; C-
Investigation of remote sensing techniques of measuring soil moisture
Major activities described include development and evaluation of theoretical models that describe both active and passive microwave sensing of soil moisture, the evaluation of these models for their applicability, the execution of a controlled field experiment during which passive microwave measurements were acquired to validate these models, and evaluation of previously acquired aircraft microwave measurements. The development of a root zone soil water and soil temperature profile model and the calibration and evaluation of gamma ray attenuation probes for measuring soil moisture profiles are considered. The analysis of spatial variability of soil information as related to remote sensing is discussed as well as the implementation of an instrumented field site for acquisition of soil moisture and meteorologic information for use in validating the soil water profile and soil temperature profile models
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