389 research outputs found
Hysteresis in a magnetic bead and its applications
We study hysteresis in a micron-sized bead: a non-magnetic matrix embedded
with super- paramagnetic nanoparticles. These hold tremendous promise in
therapeutic applications as heat generating machines. The theoretical
formulation uses a mean-field theory to account for dipolar interactions
between the supermoments. The study enables manipulation of heat dissipation by
a compatible selection of commercially available beads and the frequency f and
amplitude ho of the applied oscillating field in the labortory. We also
introduce the possibility of utilizing return point memory for gradual heating
of a local region.Comment: 8 pages, 4 figure
Measurement of the half-life of 198Au in a non-metal: High-precision measurement shows no host-material dependence
We have measured the half-life of the beta decay of 198Au to be 2.6948(9) d,
with the nuclide sited in an insulating environment. Comparing this result with
the half-life we measured previously with a metallic environment, we find the
half-lives in both environments to be the same within 0.04%, thus contradicting
a prediction that screening from a "plasma" of quasi-free electrons in a metal
increases the half-life by as much as 7%
Half-life of the electron-capture decay of 97Ru: Precision measurement shows no temperature dependence
We have measured the half-life of the electron-capture (ec) decay of 97Ru in
a metallic environment, both at low temperature (19K), and also at room
temperature. We find the half-lives at both temperatures to be the same within
0.1%. This demonstrates that a recent claim that the ec decay half-life for 7Be
changes by $0.9% +/- 0.2% under similar circumstances certainly cannot be
generalized to other ec decays. Our results for the half-life of 97Ru,
2.8370(14)d at room temperature and 2.8382(14)d at 19K, are consistent with,
but much more precise than, previous room-temperature measurements. In
addition, we have also measured the half-lives of the beta-emitters 103Ru and
105Rh at both temperatures, and found them also to be unchanged.Comment: 6 pages, 6 figure
Electron Transfer Control in Soluble Methane Monooxygenase
The hydroxylation or epoxidation of hydrocarbons by bacterial multicomponent monooxygenases (BMMs) requires the interplay of three or four protein components. How component protein interactions control catalysis, however, is not well understood. In particular, the binding sites of the reductase components on the surface of their cognate hydroxylases and the role(s) that the regulatory proteins play during intermolecular electron transfer leading to the hydroxylase reduction have been enigmatic. Here we determine the reductase binding site on the hydroxylase of a BMM enzyme, soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bath). We present evidence that the ferredoxin domain of the reductase binds to the canyon region of the hydroxylase, previously determined to be the regulatory protein binding site as well. The latter thus inhibits reductase binding to the hydroxylase and, consequently, intermolecular electron transfer from the reductase to the hydroxylase diiron active site. The binding competition between the regulatory protein and the reductase may serve as a control mechanism for regulating electron transfer, and other BMM enzymes are likely to adopt the same mechanism.National Institutes of Health (U.S.) (Grant GM032134)Waters Corporatio
Experimental Validation of the Largest Calculated Isospin-Symmetry-Breaking Effect in a Superallowed Fermi Decay
A precision measurement of the gamma yields following the beta decay of 32Cl
has determined its isobaric analogue branch to be (22.47^{+0.21}_{-0.19})%.
Since it is an almost pure Fermi decay, we can also determine the amount of
isospin-symmetry breaking in this superallowed transition. We find a very large
value, delta_C=5.3(9)%, in agreement with a shell-model calculation. This
result sets a benchmark for isospin-symmetry-breaking calculations and lends
support for similarly-calculated, yet smaller, corrections that are currently
applied to 0+ -> 0+ transitions for tests of the Standard Model
Branching ratios for the beta decay of 21Na
We have measured the beta-decay branching ratio for the transition from 21Na
to the first excited state of 21Ne. A recently published test of the standard
model, which was based on a measurement of the beta-nu correlation in the decay
of 21Na, depended on this branching ratio. However, until now only relatively
imprecise (and, in some cases, contradictory) values existed for it. Our new
result, 4.74(4)%, reduces but does not remove the reported discrepancy with the
standard model.Comment: Revtex4, 2 fig
Attention Patterns Detection using Brain Computer Interfaces
The human brain provides a range of functions such as expressing emotions,
controlling the rate of breathing, etc., and its study has attracted the
interest of scientists for many years. As machine learning models become more
sophisticated, and bio-metric data becomes more readily available through new
non-invasive technologies, it becomes increasingly possible to gain access to
interesting biometric data that could revolutionize Human-Computer Interaction.
In this research, we propose a method to assess and quantify human attention
levels and their effects on learning. In our study, we employ a brain computer
interface (BCI) capable of detecting brain wave activity and displaying the
corresponding electroencephalograms (EEG). We train recurrent neural networks
(RNNS) to identify the type of activity an individual is performing
Precise Half-Life Measurement of the Superallowed Beta+ Emitter 46V
The half-life of 46V has been measured to be 422.66(6) ms, which is a factor
of two more precise than the best previous measurement. Our result is also
consistent with the previous measurements, with no repeat of the disagreement
recently encountered with Q_{EC} values measured for the same transition. The
Ft value for the 46V superallowed transition, incorporating all world data, is
determined to be 3074.1(26) s, a result consistent with the average Ft value of
3072.08(79) s established from the 13 best-known superallowed transitions.Comment: 6 pages, 6 figure
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