Exciton-optical phonon coupling in II-VI semiconductor nanocrystals.

This perspective reviews the topic of exciton-phonon coupling (EPC) in II-VI semiconductor nanocrystals. First, EPC is defined and its relevance is discussed, both as it influences the properties of the materials relevant to applications and as a probe of electronic structure. Different experimental and theoretical methods for probing EPC are outlined. Results for several different classes of II-VI nanocrystals are summarized. Finally, possible future directions are outlined

The economic value of viewing migratory shorebirds on the Delaware Bay: An application of the single site travel cost model using on-site data

We estimated a count data model of recreation demand using data from an on-site survey of recreational birders who had visited southern Delaware during the month–long annual horseshoe crab/shorebird spring migration in 2008. We analyzed daytrips only. Our estimates from the models ranged from $32 to$142/trip/household or about $131 to$582/season/household (2008$). The variation was due to differences in the value of time. The average household size was 1.66. We found that the valuation results were sensitive to the inclusion of covariates in the model. Our results are useful for damage assessments and benefit–cost analyses where birdwatching is affected.recreational birding, economic value, shorebird migration, onsite sampling, endogenous stratification

Measuring the Recreational Use Value of Migratory Shorebirds on the Delaware Bay

In this article we estimate the recreational use value of household trips to view shorebirds during the annual horseshoe crab/shorebird migration on the Delaware Bay. We use contingent valuation to estimate the value of day and overnight trips separately and use a discrete choice question followed by a payment-card question to generate our valuation data. Our best estimates for the value of a day trip are about $66–$90/household and for an overnight trip about $200–$425/household (2008$). Our data are from the 2008 season, and our average household size is 1.66. For some context, estimates from four other studies report values that vary from$63/trip/person to $442/trip/person. These studies vary in method and specific birding populations studied and mix day and overnight trips.Contingent valuation, discrete choice, bird watching, use value, Environmental Economics and Policy, Public Economics, Research Methods/ Statistical Methods, Q5,

Measuring the recreational use value of migratory shorebirds on the Delaware Bay

In this article we estimate the recreational use value of household trips to view shorebirds during the annual horseshoe crab/shorebird migration on the Delaware Bay. We use contingent valuation to estimate the value of day and overnight trips separately and use a discrete choice question followed by a payment-card question to generate our valuation data. Our best estimates for the value of a day trip are about $66–$90/household and for an overnight trip about $200–$425/household (2008$). Our data are from the 2008 season, and our average household size is 1.66. For some context, estimates from four other studies report values that vary from$63/trip/person to $442/trip/person. These studies vary in method and specific birding populations studied and mix day and overnight trips.Contingent valuation, discrete choice, bird watching, use value

"The Economic Value of Viewing Migratory Shorebirds on the Delaware Bay: An Application of the Single Site Travel Cost Model Using On-Site Data"

Using data from an on-site survey of recreational birders in southern Delaware during the annual horseshoe crab/shorebird spring migration, we estimated four truncated count data models of recreation demand accounting for endogenous stratification due to onsite sampling. We analyzed day-trips only and conducted sensitivity analysis on measurement of the value of time and inclusion of covariates. Our estimates from the models using all covariates were in the range of $40 to$178/trip/household (2008$). The variation is due to differences in the value of time. The average household size is 1.66.Travel-Cost Model, Shorebirds, Valuation

Weak Exciton-Phonon Coupling in CdSe Nanoplatelets from Quantitative Resonance Raman Intensity Analysis

Resonance Raman spectra, cross sections, and depolarization ratios have been measured for 4.5 monolayer thick CdSe nanoplatelets dispersed in chloroform. Five excitation wavelengths between 514.5 and 476.5 nm were employed. The resonance Raman spectra are dominated by the longitudinal optical (LO) phonon near 201 cm–1 and its overtone, as in CdSe quantum dots. The absolute scattering intensity is much higher for excitation on resonance with the sharp, lowest-energy heavy-hole to conduction band transition than with higher energy transitions, decreasing by about a factor of 30 between 514.5 and 496.5 nm excitation. The LO phonon overtone is weak directly on resonance with the heavy-hole transition but much stronger at higher excitation energies, a result that is reproduced by simulations of the spectra using standard resonance Raman intensity theory. The absolute Raman cross sections imply a Huang–Rhys parameter for the LO phonon of about 0.08 on resonance with the lowest heavy-hole transition. This is a factor of 2–3 lower than found previously for CdSe quantum dots. The depolarization ratios on resonance with the lowest heavy-hole excitonic transition are slightly higher than expected for a degenerate, plane-polarized transition even when the local field factors are taken into account

Comparison of three empirical force fields for phonon calculations in CdSe quantum dots

Three empirical interatomic force fields are parametrized using structural, elastic, and phonon dispersion data for bulk CdSe and their predictions are then compared for the structures and phonons of CdSe quantum dots having average diameters of ˜2.8 and ˜5.2 nm (˜410 and ˜2630 atoms, respectively). The three force fields include one that contains only two-body interactions (Lennard-Jones plus Coulomb), a Tersoff-type force field that contains both two-body and three-body interactions but no Coulombic terms, and a Stillinger-Weber type force field that contains Coulombic interactions plus two-body and three-body terms. While all three force fields predict nearly identical peak frequencies for the strongly Raman-active "longitudinal optical" phonon in the quantum dots, the predictions for the width of the Raman peak, the peak frequency and width of the infrared absorption peak, and the degree of disorder in the structure are very different. The three force fields also give very different predictions for the variation in phonon frequency with radial position (core versus surface). The Stillinger-Weber plus Coulomb type force field gives the best overall agreement with available experimental data

Learning Agility: Many Questions, a Few Answers, and a Path Forward

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92383/1/j.1754-9434.2012.01465.x.pd