3,398 research outputs found
Electron paramagnetic resonance and photochromism of in diamond
The defect in diamond formed by a vacancy surrounded by three
nearest-neighbor nitrogen atoms and one carbon atom,
, is found in of natural diamonds.
Despite being the earliest electron paramagnetic
resonance spectrum observed in diamond, to date no satisfactory simulation of
the spectrum for an arbitrary magnetic field direction has been produced due to
its complexity. In this work, is identified in
-doped synthetic diamond following irradiation and annealing.
The spin Hamiltonian parameters are revised
and used to refine the parameters for ,
enabling the latter to be accurately simulated and fitted for an arbitrary
magnetic field direction. Study of under
excitation with green light indicates charge transfer between
and . It is argued that this charge
transfer is facilitated by direct ionization of ,
an as-yet unobserved charge state of
Sit Back and Wait Till Sunrise
A thesis presented to the faculty of the College of Arts and Sciences at Morehead State University in partial fulfillment of the requirements for the Degree of Master of Arts by L. Michael Breeze in May of 1991
Continuous-wave room-temperature diamond maser
The maser, older sibling of the laser, has been confined to relative
obscurity due to its reliance on cryogenic refrigeration and high-vacuum
systems. Despite this it has found application in deep-space communications and
radio astronomy due to its unparalleled performance as a low-noise amplifier
and oscillator. The recent demonstration of a room-temperature solid- state
maser exploiting photo-excited triplet states in organic pentacene molecules
paves the way for a new class of maser that could find applications in
medicine, security and sensing, taking advantage of its sensitivity and low
noise. However, to date, only pulsed operation has been observed in this
system. Furthermore, organic maser molecules have poor thermal and mechanical
properties, and their triplet sub-level decay rates make continuous emission
challenging: alternative materials are therefore required. Therefore, inorganic
materials containing spin-defects such as diamond and silicon carbide have been
proposed. Here we report a continuous-wave (CW) room-temperature maser
oscillator using optically pumped charged nitrogen-vacancy (NV) defect centres
in diamond. This demonstration unlocks the potential of room-temperature
solid-state masers for use in a new generation of microwave devices.Comment: 7 pages, 4 figure
Magnon-photon coupling in the noncollinear magnetic insulator Cu 2 OSeO 3
Anticrossing behavior between magnons in the noncollinear chiral magnet Cu2OSeO3 and a two-mode X-band microwave resonator was studied in the temperature range 5–100 K. In the field-induced ferrimagnetic phase, we observed a strong-coupling regime between magnons and two microwave cavity modes with a cooperativity reaching 3600. In the conical phase, cavity modes are dispersively coupled to a fundamental helimagnon mode, and we demonstrate that the magnetic phase diagram of Cu2OSeO3 can be reconstructed from the measurements of the cavity resonance frequency. In the helical phase, a hybridized state of a higher-order helimagnon mode and a cavity mode—a helimagnon polariton—was found. Our results reveal a class of magnetic systems where strong coupling of microwave photons to nontrivial spin textures can be observed
All-optical hyperpolarization of electron and nuclear spins in diamond
Low thermal polarization of nuclear spins is a primary sensitivity limitation
for nuclear magnetic resonance. Here we demonstrate optically pumped
(microwave-free) nuclear spin polarization of and
in -doped diamond.
polarization enhancements up to above thermal equilibrium are observed
in the paramagnetic system . Nuclear spin polarization is
shown to diffuse to bulk with NMR enhancements of at
room temperature and at , enabling a route to
microwave-free high-sensitivity NMR study of biological samples in ambient
conditions.Comment: 5 pages, 5 figure
Phosphorescence and donor-acceptor pair recombination in laboratory-grown diamonds
Intense "blue-green" phosphorescence is commonly observed in near colourless
lab-grown high-pressure high-temperature (HPHT) diamonds following optical
excitation at or above the indirect bandgap. We have employed a holistic
combination of optically-excited time-resolved techniques (in addition to
standard spectroscopic characterisation techniques) to study the physics of
this long-lived phosphorescence and understand luminescence-related charge
transfer processes.
It is shown that the properties of the broad "blue-green" luminescence and
phosphorescence band can be fully explained by emission from neutral
substitutional nitrogen-boron donor-acceptor pairs
(...) , once the configurational
change between charge states is considered, and both tunneling between defects
and thermal ionization of donors and acceptors is considered. Significant
concentrations of metastable , are identified after
optical excitation at or above the indirect bandgap. is
much shallower (0.2 eV) than previously thought and plays a key role in
resetting the ... donor-acceptor
pairs.Comment: 15 pages, 13 figure
Mechanisms of Action in a Behavioral Weight-Management Program: Latent Growth Curve Analysis.
BACKGROUND: A greater understanding of the mechanisms of action of weight-management interventions is needed to inform the design of effective interventions. PURPOSE: To investigate whether dietary restraint, habit strength, or diet self-regulation mediated the impact of a behavioral weight-management intervention on weight loss and weight loss maintenance. METHODS: Latent growth curve analysis (LGCA) was conducted on trial data in which adults (N = 1,267) with a body mass index (BMI) ≥28 kg/m2 were randomized to either a brief intervention (booklet on losing weight), a 12 week weight-management program or the same program for 52 weeks. LGCA estimated the trajectory of the variables over four time points (baseline and 3, 12 and 24 months) to assess whether potential mechanisms of action mediated the impact of the weight-management program on BMI. RESULTS: Participants randomized to the 12 and 52 week programs had a significantly greater decrease in BMI than the brief intervention. This direct effect became nonsignificant when dietary restraint, habit strength, and autonomous diet self-regulation were controlled for. The total indirect effect was significant for both the 12 (estimate = -1.33, standard error [SE] = 0.41, p = .001) and 52 week (estimate = -2.13, SE = 0.52, p < .001) program. Only the individual indirect effect for dietary restraint was significant for the 12 week intervention, whereas all three indirect effects were significant for the 52 week intervention. CONCLUSIONS: Behavior change techniques that target dietary restraint, habit strength, and autonomous diet self-regulation should be considered when designing weight loss and weight loss maintenance interventions. Longer interventions may need to target both deliberative and automatic control processes to support successful weight management
Measurements of permittivity, dieletric loss tangent, and resistivity of float-zone silicon at microwave frequencies
Published versio
Metformin for weight control in pediatric patients on atypical antipsychotic medication
OBJECTIVE: Metformin was assessed as an interventional medication for weight gain in children and adolescents taking atypical antipsychotic agents.
METHOD: A 12-week open-label trial was conducted to evaluate metformin\u27s effectiveness and safety for weight management. Eleven subjects, ages 10-18 years, participated in the study. Each subject received metformin orally up to 2000 mg/day. Primary outcome measures included weight, body mass index (BMI), and waist circumference. Secondary outcome measures included serum glucose, insulin, and fasting lipid profile. Changes in weight, BMI, waist, and metabolic profile were obtained by using repeated measures of covariance.
RESULTS: The mean reduction in weight, waist, BMI, serum glucose, and serum insulin was not statistically significant. However, 5 out of 11 patients lost weight (mean, -2.82 kg +/- 7.25), and overall the sample did not continue to gain weight. There was a significant decrease in triglyceride levels. Metformin was fairly well tolerated.
CONCLUSION: Preliminary data suggests that metformin may safely and effectively improve the triglyceride profile. However, contrary to study hypotheses, weight, waist, and BMI reduction were not statistically significant. Future double-blind studies with larger sample sizes and of longer duration are warranted to assess more fully the safety and efficacy of this intervention
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