24,713 research outputs found
Rehabilitation of Cut-over Pine Stands in the Southwest
In the relatively near future, cut-over forests must become the main source of saw timber in the United States. Whether these forests will prove equal to the demands placed on them depends on what is done now toward increasing their productivity. That only a small proportion of all cut-over stands, even where “selective logging” has been practiced, are in condition to produce timber crops commensurate with site capacity is too well known to require confirmation. This statement leaves devastated lands out of consideration; it refers to lands already restocked or in the process of restocking and bearing more or less commercial timber, national forest lands included
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Did organic compounds in the Tagish Lake meteorite form via catalytic processes in the solar nebula and within parent bodies?
Surface spin flip probability of mesoscopic Ag wires
Spin relaxation in mesoscopic Ag wires in the diffusive transport regime is
studied via nonlocal spin valve and Hanle effect measurements performed on
permalloy/Ag lateral spin valves. The ratio between momentum and spin
relaxation times is not constant at low temperatures. This can be explained
with the Elliott-Yafet spin relaxation mechanism by considering the momentum
surface relaxation time as being temperature dependent. We present a model to
separately determine spin flip probabilities for phonon, impurity and surface
scattering and find that the spin flip probability is highest for surface
scattering.Comment: 5 pages, 4 figure
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Production of high molecular weight organic compounds on the surfaces of amorphous iron silicate catalysts: Implications for organic synthesis in the solar nebula
The high molecular weight organic products of Fischer-Tropsch/Haber-Bosch syntheses on the surfaces of Fe-silicate catalysts have been studied by GCMS
Pressure Induced Changes in the Antiferromagnetic Superconductor YbPd2Sn
Low temperature ac magnetic susceptibility measurements of the coexistent
antiferromagnetic superconductor YbPd2Sn have been made in hydrostatic
pressures < 74 kbar in moissanite anvil cells. The superconducting transition
temperature is forced to T(SC) = 0 K at a pressure of 58 kbar. The initial
suppression of the superconducting transition temperature is corroborated by
lower hydrostatic pressure (p < 16 kbar) four point resisitivity measurements,
made in a piston cylinder pressure cell. At ambient pressure, in a modest
magnetic field of ~ 500 G, this compound displays reentrant superconducting
behaviour. This reentrant superconductivity is suppressed to lower temperature
and lower magnetic field as pressure is increased. The antiferromagnetic
ordering temperature, which was measured at T(N) = 0.12 K at ambient pressure
is enhanced, to reach T(N) = 0.58 K at p = 74 kbar. The reasons for the
coexistence of superconductivity and antiferromagnetism is discussed in the
light of these and previous findings. Also considered is why superconductivity
on the border of long range magnetic order is so much rarer in Yb compounds
than in Ce compounds. The presence of a new transition visible by ac magnetic
susceptibility under pressure and in magnetic fields greater than 1.5 kG is
suggested.Comment: 5 pages, 6 figure
Effects of jamming on non-equilibrium transport times in nano-channels
Many biological channels perform highly selective transport without direct
input of metabolic energy and without transitions from a 'closed' to an 'open'
state during transport. Mechanisms of selectivity of such channels serve as an
inspiration for creation of artificial nano-molecular sorting devices and
bio-sensors. To elucidate the transport mechanisms, it is important to
understand the transport on the single molecule level in the experimentally
relevant regime when multiple particles are crowded in the channel. In this
paper we analyze the effects of inter-particle crowding on the non-equilibrium
transport times through a finite-length channel by means of analytical theory
and computer simulations
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