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

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

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 $\bigtriangleup_{SAS}$. 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 $\eta \equiv \bigtriangleup_{\text{SAS}} / E_{\text{F}}$.Comment: 9 pages, RevTeX, 5 figures available upon request, PIT-SDS-00

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

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

Temperature dependence of polarization relaxation in semiconductor quantum dots

The decay time of the linear polarization degree of the luminescence in strongly confined semiconductor quantum dots with asymmetrical shape is calculated in the frame of second-order quasielastic interaction between quantum dot charge carriers and LO phonons. The phonon bottleneck does not prevent significantly the relaxation processes and the calculated decay times can be of the order of a few tens picoseconds at temperature $T \simeq 100$K, consistent with recent experiments by Paillard et al. [Phys. Rev. Lett. {\bf86}, 1634 (2001)].Comment: 4 pages, 4 figure

Stimulated Raman spin coherence and spin-flip induced hole burning in charged GaAs quantum dots

High-resolution spectral hole burning (SHB) in coherent nondegenerate differential transmission spectroscopy discloses spin-trion dynamics in an ensemble of negatively charged quantum dots. In the Voigt geometry, stimulated Raman spin coherence gives rise to Stokes and anti-Stokes sidebands on top of the trion spectral hole. The prominent feature of an extremely narrow spike at zero detuning arises from spin population pulsation dynamics. These SHB features confirm coherent electron spin dynamics in charged dots, and the linewidths reveal spin spectral diffusion processes.Comment: 5 pages, 5 figure

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

Hole Spin Mixing in InAs Quantum Dot Molecules

Holes confined in single InAs quantum dots have recently emerged as a promising system for the storage or manipulation of quantum information. These holes are often assumed to have only heavy-hole character and further assumed to have no mixing between orthogonal heavy hole spin projections (in the absence of a transverse magnetic field). The same assumption has been applied to InAs quantum dot molecules formed by two stacked InAs quantum dots that are coupled by coherent tunneling of the hole between the two dots. We present experimental evidence of the existence of a hole spin mixing term obtained with magneto-photoluminescence spectroscopy on such InAs quantum dot molecules. We use a Luttinger spinor model to explain the physical origin of this hole spin mixing term: misalignment of the dots along the stacking direction breaks the angular symmetry and allows mixing through the light-hole component of the spinor. We discuss how this novel spin mixing mechanism may offer new spin manipulation opportunities that are unique to holes.Comment: 13 pages, 9 figure