125,227 research outputs found
Technique for producing bipolar and MOS field effect transistors on a single chip
Several cycles of photoetching, dopant deposition, and drive-in produce selectively-doped regions and semiconductor junctions within a single chip
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Ultraviolet protection on a snowball Earth
Habitats in the Antarctic provide an insight into habitats available on snowball earth. Physical UV protection on snowball earth would have been dominated by the manifestations of ice and snow in different habitats. The snowball period was a golden age of UV protection
The color of sea level: importance of spatial variations in spectral shape for assessing the significance of trends
We investigate spatial variations in the shape of the spectrum of sea level variability, based on a homogeneously-sampled 12-year gridded altimeter dataset. We present a method of plotting spectral information as color, focusing on periods between 2 and 24 weeks, which shows that significant spatial variations in the spectral shape exist,
and contain useful dynamical information. Using the Bayesian Information Criterion, we determine that, typically, a 5th order autoregressive model is needed to capture the structure in the spectrum. Using this model, we show that statistical errors in fitted local trends range between less than 1 and more than 5 times what would be calculated assuming “white” noise, and the time needed to detect a 1 mm/yr trend ranges between about 5 years and many decades. For global-mean sea level, the statistical error reduces to 0.1 mm/yr over 12 years, with only 2 years needed to detect a 1 mm/yr trend. We find significant regional differences in trend from the global mean. The
patterns of these regional differences are indicative of a sea level trend dominated by dynamical ocean processes, over this perio
Monolayers of 3He on the Surface of Bulk Superfluid 4He
We have used quantum evaporation to investigate the two-dimensional fermion
system that forms at the free surface of (initially isotopically pure) 4He when
small quantities of 3He are added to it. By measuring the first-arrival times
of the evaporated atoms, we have determined that the 3He-3He potential in this
system is V_3S/k_B=(0.23+/-0.02) K nm^2 (repulsive) and estimated a value of
m_3S=(1.53+/-0.02)m_3 for the zero-coverage effective mass. We have also
observed the predicted second layer-state which becomes occupied once the first
layer-state density exceeds about 0.6 monolayers.Comment: 2 pages, 3 figures. Submitted to Proc. LT-22 (1999) to appear in
Physica
Relative Evaporation Probabilities of 3He and 4He from the Surface of Superfluid 4He
We report a preliminary experiment which demonstrates that 3He atoms in
Andreev states are evaporated by high-energy (E/k_B ~ 10.2 K) phonons in a
quantum evaporation process similar to that which occurs in pure 4He. Under
conditions of low 3He coverage, high-energy phonons appear to evaporate 3He and
4He atoms with equal probability. However, we have not managed to detect any
3He atoms that have been evaporated by rotons, and conclude that the
probability of a roton evaporating a 3He atom is less than 2% of the
probability that it evaporates a 4He atom.Comment: 2 pages, 3 figures. Submitted to Proc. LT-22 (1999) Physica
Extended plasticity in commercial-purity zinc
90% rolling-reduction of annealed commercial-purity zinc sheet
(grain size 100 - 150 μ) results in the fragmentation of the large grains
into, finally, stable micro-grains, 1 - 211 in diameter. The stability of
the micro-grains is due to the presence of soluble and insoluble impurities
which prevent recrystallization.
This micro-grain material is strain-rate sensitive, and elongations of
200% have been obtained at room temperature.
Although this as-rolled, 90% reduction zinc sheet is not super-plastic
according to the current definition, its behaviour has led to the coining of
the phase 'extended plasticity'.
Evidence of grain-boundary sliding is found on examination of the surface
by scanning electron microscopy, while the examination of thin foils and
activation energy measurements support the dynamic softening (recovery) theory;
thus, both these mechanisms must be operating, to a greater or less extent,
to confer on this material the observe mechanical behaviour.
It is finally concluded that it is dangerous to draw conclusions regarding
the mechanism of plastic deformation from surface observations alone
Revealing the Secrets of the Temple: The Value of Publishing Central Bank Interest Rate Projections
The modern view of monetary policy stresses its role in shaping the entire yield curve of interest rates in order to achieve various macroeconomic objectives. A crucial element of this process involves guiding financial market expectations of future central bank actions. Recently, a few central banks have started to explicitly signal their future policy intentions to the public, and two of these banks have even begun publishing their internal interest rate projections. We examine the macroeconomic effects of direct revelation of a central bank's expectations about the future path of the policy rate. We show that, in an economy where private agents have imperfect information about the determination of monetary policy, central bank communication of interest rate projections can help shape financial market expectations and may improve macroeconomic performance.
Utilization of LANDSAT imagery for mapping vegetation on the millionth scale
A series of test sites were examined to determine if the information content of the LANDSAT imagery that may be obtained of these sites is sufficient to permit their mapping according to the vegetation classification system recently published by Unesco. These sites include examples from the humid tropics, arid and semi-arid subtropics and temperature zones: Western Highlands of Papua New Guinea, Mindoro Island in the Philippines, Great Smoky Mountains of the southeastern United States, East Tennessee Valley, interior of Western Australia, northeastern Uganda, and south-central Kansas. The results of the experiment were presented in the form of vegetation maps and annotated images which serve to illustrate the detectability of various formations. It was concluded that, for the test sites examined, the formations of the Unesco vegetation classification can be satisfactorily distinguished on LANDSAT MSS images, especially when used as color composites and judiciously chosen as to season
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