1,681 research outputs found
Three approaches to the classification of inland wetlands
In the Dismal Swamp project, seasonal, color-infrared aerial photographs and LANDSAT digital data were interpreted for a detailed analysis of the vegetative communities in a large, highly altered wetland. In Western Tennessee, seasonal high altitude color-infrared aerial photographs provided the hydrologic and vegetative information needed to map inland wetlands, using a classification system developed for the Tennessee Valley Region. In Florida, color-infrared aerial photographs were analyzed to produce wetland maps using three existing classification systems to evaluate the information content and mappability of each system. The methods used in each of the three projects can be extended or modified for use in the mapping of inland wetlands in other parts of the United States
Fine structure and optical pumping of spins in individual semiconductor quantum dots
We review spin properties of semiconductor quantum dots and their effect on
optical spectra. Photoluminescence and other types of spectroscopy are used to
probe neutral and charged excitons in individual quantum dots with high
spectral and spatial resolution. Spectral fine structure and polarization
reveal how quantum dot spins interact with each other and with their
environment. By taking advantage of the selectivity of optical selection rules
and spin relaxation, optical spin pumping of the ground state electron and
nuclear spins is achieved. Through such mechanisms, light can be used to
process spins for use as a carrier of information
Tunable lasers for water vapor measurements and other lidar applications
A tunable dye laser suitable for differential absorption (DIAL) measurements of water vapor in the troposphere was constructed. A multi-pass absorption cell for calibration was also constructed for use in atmospheric DIAL measurements of water vapor
Mockingbird morphing music: Structured transitions in a complex bird song
The song of the northern mockingbird, Mimus polyglottos, is notable for its extensive length and inclusion of numerous imitations of several common North American bird species. Because of its complexity, it is not widely studied by birdsong scientists. When they do study it, the specific imitations are often noted, and the total number of varying phrases. What is rarely noted is the systematic way the bird changes from one syllable to the next, often with a subtle transition where one sound is gradually transformed into a related sound, revealing an audible and specific compositional mode. It resembles a common strategy in human composing, which can be described as variation of a theme. In this paper, we present our initial attempts to describe the specific compositional rules behind the mockingbird song, focusing on the way the bird transitions from one syllable type to the next. We find that more often than chance, syllables before and after the transition are spectrally related, i.e., transitions are gradual, which we describe as morphing. In our paper, we categorize four common modes of morphing: timbre change, pitch change, squeeze (shortening in time), and stretch (lengthening in time). This is the first time such transition rules in any complex birdsong have been specifically articulated
Raman Scattering Spectra of Elementary Electronic Excitations in Coupled Double-Quantum Well Structures
Using the time-dependent-local-density-approximation (TDLDA) within a
self-consistent linear response theory, we calculate the elementary excitation
energies and the associated inelastic light-scattering spectra of a strongly
coupled two-component plasma in a double-quantum well system with electron
occupation of symmetric and antisymmetric subbands. We find, consistent with
the results of a recent experimental Raman scattering study, that the
intersubband spin density excitations tend to merge with the single particle
excitations (i.e. the excitonic shift decreases monotonically) as the Fermi
energy increases beyond the symmetric-antisymmetric energy gap
. However, our TDLDA calculation does not show the abrupt
suppresion of the excitonic shift seen experimentally at a finite value of the
subband occupancy parameter .Comment: 9 pages, RevTeX, 5 figures available upon request, PIT-SDS-00
Assessing the short-term outcomes of a community-based intervention for overweight and obese children: The MEND 5-7 programme
Objective The aim of this study was to report outcomes of the UK service level delivery of MEND (Mind,Exercise,Nutrition...Do it!) 5-7, a multicomponent, community-based, healthy lifestyle intervention designed for overweight and obese children aged 5–7 years and their families.
Design Repeated measures.
Setting Community venues at 37 locations across the UK.
Participants 440 overweight or obese children (42% boys; mean age 6.1 years; body mass index (BMI) z-score 2.86) and their parents/carers participated in the intervention.
Intervention MEND 5-7 is a 10-week, family-based, child weight-management intervention consisting of weekly group sessions. It includes positive parenting, active play, nutrition education and behaviour change strategies. The intervention is designed to be scalable and delivered by a range of health and social care professionals.
Primary and secondary outcome measures The primary outcome was BMI z-score. Secondary outcome measures included BMI, waist circumference, waist circumference z-score, children's psychological symptoms, parenting self-efficacy, physical activity and sedentary behaviours and the proportion of parents and children eating five or more portions of fruit and vegetables.
Results 274 (62%) children were measured preintervention and post-intervention (baseline; 10-weeks). Post-intervention, mean BMI and waist circumference decreased by 0.5 kg/m2 and 0.9 cm, while z-scores decreased by 0.20 and 0.20, respectively (p<0.0001). Improvements were found in children's psychological symptoms (−1.6 units, p<0.0001), parent self-efficacy (p<0.0001), physical activity (+2.9 h/week, p<0.01), sedentary activities (−4.1 h/week, p<0.0001) and the proportion of parents and children eating five or more portions of fruit and vegetables per day (both p<0.0001). Attendance at the 10 sessions was 73% with a 70% retention rate.
Conclusions Participation in the MEND 5-7 programme was associated with beneficial changes in physical, behavioural and psychological outcomes for children with complete sets of measurement data, when implemented in UK community settings under service level conditions. Further investigation is warranted to establish if these findings are replicable under controlled conditions
Fast spin rotations by optically controlled geometric phases in a quantum dot
We demonstrate optical control of the geometric phase acquired by one of the
spin states of an electron confined in a charge-tunable InAs quantum dot via
cyclic 2pi excitations of an optical transition in the dot. In the presence of
a constant in-plane magnetic field, these optically induced geometric phases
result in the effective rotation of the spin about the magnetic field axis and
manifest as phase shifts in the spin quantum beat signal generated by two
time-delayed circularly polarized optical pulses. The geometric phases
generated in this manner more generally perform the role of a spin phase gate,
proving potentially useful for quantum information applications.Comment: 4 pages, 3 figures, resubmitted to Physical Review Letter
Stimulated and spontaneous optical generation of electron spin coherence in charged GaAs quantum dots
We report on the coherent optical excitation of electron spin polarization in
the ground state of charged GaAs quantum dots via an intermediate charged
exciton (trion) state. Coherent optical fields are used for the creation and
detection of the Raman spin coherence between the spin ground states of the
charged quantum dot. The measured spin decoherence time, which is likely
limited by the nature of the spin ensemble, approaches 10 ns at zero field. We
also show that the Raman spin coherence in the quantum beats is caused not only
by the usual stimulated Raman interaction but also by simultaneous spontaneous
radiative decay of either excited trion state to a coherent combination of the
two spin states.Comment: 4 pages, 3 figures. Minor modification
All-Optical Ultrafast Control and Read-Out of a Single Negatively Charged Self-Assembled InAs Quantum Dot
We demonstrate the all-optical ultrafast manipulation and read-out of optical
transitions in a single negatively charged self-assembled InAs quantum dot, an
important step towards ultrafast control of the resident spin. Experiments
performed at zero magnetic field show the excitation and decay of the trion
(negatively charged exciton) as well as Rabi oscillations between the electron
and trion states. Application of a DC magnetic field perpendicular to the
growth axis of the dot enables observation of a complex quantum beat structure
produced by independent precession of the ground state electron and the excited
state heavy hole spins
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