4,712 research outputs found
Conversion of neutral nitrogen-vacancy centers to negatively-charged nitrogen-vacancy centers through selective oxidation
The conversion of neutral nitrogen-vacancy centers to negatively charged
nitrogen-vacancy centers is demonstrated for centers created by ion
implantation and annealing in high-purity diamond. Conversion occurs with
surface exposure to an oxygen atmosphere at 465 C. The spectral properties of
the charge-converted centers are investigated. Charge state control of
nitrogen-vacancy centers close to the diamond surface is an important step
toward the integration of these centers into devices for quantum information
and magnetic sensing applications.Comment: 4 pages, 3 figure
KIC 10449976: discovery of an extreme-helium subdwarf in the Kepler field
Optical spectroscopy of the blue star KIC 10449976 shows that it is an
extremely helium-rich subdwarf with effective temperature T=40000+/-300 K and
surface gravity log g=5.3+/-0.1. Radial-velocity measurements over a five-day
timescale show an upper variability limit of ~50+/-20 km/s. Kepler photometry
of KIC 10449976 in both long and short cadence modes shows evidence for a
periodic modulation on a timescale of ~3.9 days. We have examined the
possibility that this modulation is not astrophysical but conclude it is most
likely real. We discuss whether the modulation could be caused by a low-mass
companion, by stellar pulsations, or by spots. The identification of any one of
these as cause has important consequences for understanding the origin of
helium-rich subdwarfs.Comment: Accepted by MNRA
Properties of implanted and CVD incorporated nitrogen-vacancy centers: preferential charge state and preferential orientation
The combination of the long electron state spin coherence time and the optical coupling of the ground electronic states to an excited state manifold makes the nitrogen-vacancy (NV) center in diamond an attractive candidate for quantum information processing. To date the best spin and optical properties have been found in centers deep within the diamond crystal. For useful devices it will be necessary to engineer NVs with similar properties close to the diamond surface. We report on properties including charge state control and preferential orientation for near surface NVs formed either in CVD growth or through implantation and annealing
Coupling of nitrogen-vacancy centers in diamond to a GaP waveguide
The optical coupling of guided modes in a GaP waveguide to nitrogen-vacancy
(NV) centers in diamond is demonstrated. The electric field penetration into
diamond and the loss of the guided mode are measured. The results indicate that
the GaP-diamond system could be useful for realizing coupled microcavity-NV
devices for quantum information processing in diamond.Comment: 4 pages 4 figure
Nanoscale Torsional Optomechanics
Optomechanical transduction is demonstrated for nanoscale torsional
resonators evanescently coupled to optical microdisk whispering gallery mode
resonators. The on-chip, integrated devices are measured using a fully
fiber-based system, including a tapered and dimpled optical fiber probe. With a
thermomechanically calibrated optomechanical noise floor down to 7 fm/sqrt(Hz),
these devices open the door for a wide range of physical measurements involving
extremely small torques, as little as 4x10^-20 N*m.Comment: 4 pages, 4 figures - Accepted to APL Oct 22nd, 2012. To appear in
February 4th issue - as cover articl
Seatbelt Usage in Kentucky [Nov. 1978]
In this report, the effectiveness and usage of seatbelts in Kentucky and factors affecting usage are examined and identified. Data were obtained from three sources: field observations, accident reports, and a questionnaire.
Kentucky drivers and passengers were found to have lower seatbelt usage rates (slightly under 10 percent) than drivers and passengers in other states. The accident data showed that the chances of being killed or severely injured is greatly reduced by wearing a seatbelt. Seatbelts reduced the chance of being killed by a factor of six and the chance of being severely injured by a factor of two. Several factors were found to have significant effects on seatbelt usage. Among other factors, usage was higher among drivers over 25 years of age, in newer cars, on interstates and parkways, in large cities, in out-of-state cars, and among drivers with a college education. Records of drivers who wear seatbelts were found to be better than records of those who do not wear seatbelts. It was found that approximately one-third of the drivers were in favor, one-third were neutral, and one-third were against a mandatory seatbelt usage law
Low-temperature tapered-fiber probing of diamond NV ensembles coupled to GaP microcavities
In this work we present a platform for testing the device performance of a
cavity-emitter system, using an ensemble of emitters and a tapered optical
fiber. This method provides high-contrast spectra of the cavity modes,
selective detection of emitters coupled to the cavity, and an estimate of the
device performance in the single- emitter case. Using nitrogen-vacancy (NV)
centers in diamond and a GaP optical microcavity, we are able to tune the
cavity onto the NV resonance at 10 K, couple the cavity-coupled emission to a
tapered fiber, and measure the fiber-coupled NV spontaneous emission decay.
Theoretically we show that the fiber-coupled average Purcell factor is 2-3
times greater than that of free-space collection; although due to ensemble
averaging it is still a factor of 3 less than the Purcell factor of a single,
ideally placed center.Comment: 15 pages, 6 figure
Erratum to 'The management of chronic hepatitis B in the immunocompromised patient: recommendations from a single topic meeting' [J. Clin. Virol. 41 (4) 2008 243-254]
Quaternary Geology and Seismic Hazard of the Sierra Madre and Associated Faults, Western San Gabriel Mountains
This detailed study of a 40-km-long section of the Sierra Madre and
associated fault zones in the central transverse Ranges, along the south
side of the San Gabriel Mountains, is aimed at providing information
for evaluating the seismic hazard that these faults pose to the heavily
populated area immediately to the south. Evidence on the location of
fault strands and the style and timing of fault movements during the
Quaternary was obtained from detailed geologic mapping, aerial-photograph
interpretation, alluvial stratigraphy, structural and stratigraphic
relations in some 33 trench excavations at critical localities, and subsurface
data.
We present a time-stratigraphic classification for the Quaternary
deposits in the study area, based on soil development, geomorphology,
and contact relations among the alluvial units. We distinguish four units,
with approximate ages, as follows: unit 4, about 200,000 yr to middle
Quaternary; unit 3: about 11,000 to 200,000 yr; unit 2; about 1,000 to
11,000 yr; and unit 1; younger than about 1,000 yr. We use this classification
to evaluate on a semi-quantitative basis the evidence for fault activity
in the study area and to infer the relative seismicity of different
segments of the Sierra Madre fault zone during the Quaternary. Alluvial-fan
development (particularly fanhead incision and the ages of alluvial-fan
deposits) also gives clues as to relative seismicity.
The most active segment of the Sierra Madre fault zone within the
study area is the westernmost section, adjacent to the faults that broke
during the 1971 San Fernando, Calif., earthquake. The age of activity,
as indicated by the occurrence of Holocene faulting, decreases toward
the east. Along the Sierra Madre fault, through La Canada, Altadena,
Sierra Madre, and Duarte, is abundant evidence of late Pleistocene
faulting. Total vertical displacement is more than 600 m, but there is
no evidence for Holocene fault movement. These observations suggest
that the presently applicable recurrence interval between major earthquakes
in the central and eastern sections of the Sierra Madre fault zone
is longer than about 5,000 yr. The local magnitude (M_L) of the largest
credible earthquake that could occur on the Sierra Madre fault zone in
the study area is estimated at 7, on the grounds that the fault zone is
probably limited mechanically by subdivision into separate arcuate
segments about 15 km long.
The Raymond fault, which branches southwestward from the Sierra
Madre fault in the eastern part of the study area, shows well-defined
evidence of a late Quaternary history of repeated fault movements.
Displacements of alluvial strata observed in trench excavations across
the fault give evidence of five major seismic events, whose times of occurrence
can be estimated from radiometric dating at approximately
36,000, 25,000, 10,000-2,200 (two events), and 2,200-1,500 yr B.P. Further
evidence suggests at least three more faulting events in the past 29,000 yr, for which specific dates cannot be determined. Because some
additional events probably remain undetected, we infer that an average
recurrence interval of about 3,000 yr, with an average vertical displacement
of 0.4 m per event, is applicable to the Raymond fault in its present
state, as indicated by its history of movement over the past 36,000
yr. This level of activity is distinctly higher than that found for the Sierra
Madre fault zone in the central and eastern parts of the study area. If
the entire 15-km length of the Raymond fault would rupture in a single
event, as seems likely, a maximum credible earthquake of M_L 6 3/4 can
reasonably be assumed
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