13,933 research outputs found
Large magnetoresistance in the magnetically ordered state as well as in the paramagnetic state near 300 K in an intermetallic compound,Gd7Rh3
We report the response of electrical resistivity to the application of
magnetic fields (H) up to 140 kOe in the temperature interval 1.8-300 K for the
compound, Gd7Rh3, ordering antiferromagnetically below 150 K. We find that
there is an unusually large decrease of for moderate values of H in the
close vicinity of room temperature uncharacteristic of paramagnets, with the
magnitude of the magnetoresistance increasing with decreasing temperature as
though the spin-order contribution to is temperature dependent. In
addition, this compound exhibits giant magnetoresistance behaviour at rather
high temperatures (above 77 K) in the magnetically ordered state due to a
metamagnetic transition.Comment: Europhyics Letters, in pres
A Radon Progeny Deposition Model
The next generation low-background detectors operating underground aim for
unprecedented low levels of radioactive backgrounds. Although the radioactive
decays of airborne radon (particularly Rn-222) and its subsequent progeny
present in an experiment are potential backgrounds, also problematic is the
deposition of radon progeny on detector materials. Exposure to radon at any
stage of assembly of an experiment can result in surface contamination by
progeny supported by the long half life (22 y) of Pb-210 on sensitive locations
of a detector. An understanding of the potential surface contamination from
deposition will enable requirements of radon-reduced air and clean room
environments for the assembly of low background experiments. It is known that
there are a number of environmental factors that govern the deposition of
progeny onto surfaces. However, existing models have not explored the impact of
some environmental factors important for low background experiments. A test
stand has been constructed to deposit radon progeny on various surfaces under a
controlled environment in order to develop a deposition model. Results from
this test stand and the resulting deposition model are presented.Comment: Proceedings of the Topical Workshop in Low Radioactivity Techniques,
(Sudbury, Canada) August 28-29, 201
Fast-Neutron Activation of Long-Lived Isotopes in Enriched Ge
We measured the production of \nuc{57}{Co}, \nuc{54}{Mn}, \nuc{68}{Ge},
\nuc{65}{Zn}, and \nuc{60}{Co} in a sample of Ge enriched in isotope 76 due to
high-energy neutron interactions. These isotopes, especially \nuc{68}{Ge}, are
critical in understanding background in Ge detectors used for double-beta decay
experiments. They are produced by cosmogenic-neutron interactions in the
detectors while they reside on the Earth's surface. These production rates were
measured at neutron energies of a few hundred MeV. We compared the measured
production to that predicted by cross-section calculations based on CEM03.02.
The cross section calculations over-predict our measurements by approximately a
factor of three depending on isotope. We then use the measured cosmic-ray
neutron flux, our measurements, and the CEM03.02 cross sections to predict the
cosmogenic production rate of these isotopes. The uncertainty in extrapolating
the cross section model to higher energies dominates the total uncertainty in
the cosmogenic production rate.Comment: Revised after feedback and further work on extrapolating cross
sections to higher energies in order to estimate cosmic production rates.
Also a numerical error was found and fixed in the estimate of the Co-57
production rat
Stimuli Responsive Shape Memory Microarchitectures
Shape memory polymers (SMPs) respond to heat by generating programmable movement in devices that require substantial deformation and operate at transient temperatures, including stents and embolization coils. To enable their use in small‐scale applications like retinal vasculature stenting, shape transformations must occur in SMPs with complex 3D geometries with nanoscale features. This work describes the synthesis and sculpting of a benzyl methacrylate‐based SMP into 3D structures with <800 nm characteristic critical dimensions via two photon lithography. Dynamic nanomechanical analysis of 8 µm‐diameter cylindrical pillars reveal the initiation of this SMP's glass transition at 60 °C. Shape memory programming of the characterized pillars as well as complex 3D architectures, including flowers with 500 nm thick petals and cubic lattices with 2.5 µm unit cells and overall dimensions of 4.5 µm × 4.5 µm × 10 µm, demonstrate an 86 +/− 4% characteristic shape recovery ratio. These results reveal a pathway toward SMP devices with nanoscale features and arbitrary 3D geometries changing shape in response to temperature
Atomic levels in superstrong magnetic fields and D=2 QED of massive electrons: screening
The photon polarization operator in superstrong magnetic fields induces the
dynamical photon "mass" which leads to screening of Coulomb potential at small
distances , is the mass of an electron. We demonstrate that this
behaviour is qualitatively different from the case of D=2 QED, where the same
formula for a polarization operator leads to screening at large distances as
well. Because of screening the ground state energy of the hydrogen atom at the
magnetic fields has the finite value .Comment: 12 pages, 2 figure
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