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Notes: Critical points and lines in magnetic field space define the boundaries of different magnetization states between which the magnetization may "jump," leading to hysteresis. We calculate the changes in these boundaries due to magnetoelastic coupling to applied stresses, and obtain the critical stresses required to eliminate jumping in specific cases. These results may provide a way of reducing or eliminating hysteresis in large magnetostriction materials. © 1997 American Institute of Physics.

Notes: The temperature dependence of Young's modulus has been measured for a series of Tb1−xDyxZn pseudobinary compounds with x ranging from 0 to 1. From the sharp dips in the modulus vs temperature data, the reorientation transition temperatures have been determined, and the magnetic phase diagram deduced. Magnetization measurements taken on the same samples show less pronounced features at the corresponding temperatures. © 1996 American Institute of Physics.

Notes: Magnetization, magnetostriction, and elastic modulus measurements were made on single crystal specimens of Tb1−xDyxZn. Easy axis magnetization rotation as much as 26° were observed in the (001) plane of Tb0.75Dy0.25Zn below 33 K. From these measurements, values of the K4/K8 anisotropy ratios were calculated. No easy axis magnetization rotation was observed in the x=0.6 and x=0.8 single crystals. Magnetostriction and modulus measurements at 77 K in Tb0.4Dy0.6Zn showed a saturation magnetostriction of ∼5×10−3 and a maximum magnetomechanical coupling factor of 0.96. © 1999 American Institute of Physics.

Notes: Electronic structure and hyperfine fields are calculated for antiferromagnetic YFe6Sn6 using the linear muffin-tin orbital method. The results show that Fe atoms have a strong ferromagnetic character with a full majority-spin band. The Fe moment is 2.2 μB while the Fermi contact term contributes a hyperfine field of 20 T at the natural lattice parameters. The hyperfine field is close to the experimental value of 22 T measured at low temperature. The calculation shows that the core s electrons contribute 24 T to the hyperfine field, but the 4s electron contributes 4 T in the opposite direction. Calculations using different unit cell volumes reveal that only the core electron contributions to the hyperfine field are proportional to the Fe magnetic moment with a conversion factor of 11.8 T/μB; the 4s contribution is not. The large local Fe moment and small hyperfine field are similar to those found in Fe2P and FeO. © 1998 American Institute of Physics.

Notes: Abstract In the Gulf of St. Lawrence, Canada, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the water column. The eggs and larvae of several commercially important marine invertebrates and fishes (e.g. Gadus morhua L.) are found in this layer. Measurements of the diffuse attenuation coefficients for ultraviolet-B radiation (280 to 320 nm, UV-B) at various locations in this geographic region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates at a given wavelength) of 3 to 4 m at a wavelength of 310 nm. This represents a significant percentage of the summer mixed-layer water column: organisms residing in this layer are exposed to UV-B radiation. Laboratory experiments using a Xenon-arc-lamp based solar simulator revealed that cod embryos exposed to UV-B exhibited high wavelength-dependent mortality. The strongest effects occurred under exposures to wavelengths below 312 nm. This susceptibility was also dependent upon developmental stage; mortality was particularly high during gastrulation. At the shorter wavelengths (〈305 nm) UV-B-induced mortality was strongly dose-dependent, and not significantly influenced by dose-rate. The biological weighting function (BWF) derived for UV-B-induced mortality in cod eggs is similar to that reported for naked DNA – suggesting that the mortality is a direct result of DNA damage. There was no evidence of a detrimental effect of ultraviolet-A radiation (320 to 400 nm). Calculations based upon the BWF indicate that, under current noon surface irradiance, 50% of cod eggs located at or very near (within 10 cm) the ocean surface will be dead after 42 h of exposure. Under solar spectral irradiance simulating a 20% decrease in ozone layer thickness, this time drops to 32 h. These are first-order estimates based upon surface irradiance taken at a time of day during which the values would be maximal. Nonetheless, they illustrate the relative changes in UV-B impacts that will result from ozone layer depletions expected over the coming decades. It is also important to point out that variability in cloud cover, water quality, and vertical distribution and displacement of cod eggs and larvae within the mixed layer, can all have a greater effect on the flux of UV-B radiation to which fish eggs are exposed than will ozone layer depletion at these latitudes.

Notes: Abstract The copepod Calanus finmarchicus Gunnerus is a key component of the planktonic food web in the Gulf of St. Lawrence, Canada. In this region, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the water column. The eggs and nauplii of C. finmarchicus are found in this layer. Measurements of the diffuse attenuation coefficients for solar ultraviolet-B radiation (280 to 320 nm, UV-B) at various locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates) of 3 to 4 m at a wavelength of 310 nm. This represents a significant percentage of the summer mixed-layer water column: organisms residing in this layer are exposed to UV-B radiation. Laboratory experiments using a Xenon-arc-lamp based solar simulator revealed that C. finmarchicus embryos exposed to UV-B exhibited high wavelength-dependent mortality. The strongest effects occurred under exposures to wavelengths below 312 nm. A significant percentage of nauplii hatched from eggs exposed to these wavelengths exhibited malformations indicative of errors in pattern formation during embryogenesis. At the shorter wavelengths (〈305 nm), UV-B-induced mortality was strongly dependent on cumulative exposure. The biological weighting function (BWF) derived for UV-B-induced mortality in C. finmarchicus eggs is similar to that reported for naked DNA. This suggests that the UV-B-induced mortality effect on C. finmarchicus embryos is a direct result of DNA damage. There was no evidence of a detrimental effect of ultraviolet-A radiation (320 to 400 nm). Calculations based upon the BWF indicate that, under current noon surface irradiance, 50% of C. finmarchicus eggs located at or very near (within 10 cm) the ocean surface will be dead after 2.5 h of exposure. Under solar spectral irradiance simulating a 20% decrease in ozone layer thickness, this time drops to 2.2 h. These are first-order estimates based upon irradiance taken at a time of day during which the values would be maximal. Nonetheless, they illustrate the relative changes in UV-B effects that will result from ozone layer depletions expected over the coming decades. It is also important to point out that variability in cloud cover, water quality, and vertical distribution and displacement within the mixed layer, can all have a greater effect on the flux of UV-B radiation to which C. finmarchicus eggs are exposed than will ozone layer depletion at these latitudes.