Comment on "Quantum Confinement and Optical Gaps in Si Nanocrystals"

We show that the method used by Ogut, Chelikowsky and Louie (Phys. Rev. Lett. 79, 1770 (1997)) to calculate the optical gap of Si nanocrystals omits an electron-hole polarization energy. When this contribution is taken into account, the corrected optical gap is in excellent agreement with semi-empirical pseudopotential calculations.Comment: 3 pages, 1 figur

A new species of frog (Strabomantidae: Pristimantis) from Peru with comments on its ectoparasites (Acari: Trombiculidae)

In South America, frogs of the genus Pristimantis are diverse and can be found from lowland forests to elevations of about 4000 m in the Andes. The 444 known species of Pristimantis belong to 16 species groups. One of these groups is the Pristimantis orestes Group, the 14 members of which inhabit the páramo, puna, and upper montane forests in southern Ecuador (3 species) and Peru (11 species). Species of the Pristimantis orestes Group are characterized by having snout-vent lengths ranging from 18.0 to 29.4 mm, short robust bodies, relatively short snouts, narrow digital discs, and areolate ventral skin. Some species have variously colored pale spots in the groin. Herein, I describe a new, diminutive species of Pristimantis from the Andes of northern Peru that I assign to the Pristimantis orestes Group. The new species, denoted Prsitimantis sp. 1, has a snout-vent length of 17.35–29.08 mm (n = 47) in adult females, and 14.39–22.97 mm (n = 40) in adult males, and it differs from all other members of the Pristimantis orestes Group in having prominent scapular tubercles. Ectoparasitic mites (Trombiculidae) of the new species were studied to determine any relation between the degree of infestations and body regions, size, sex, and age. No relationships were found among sexes or ages of frogs. Larger females were 3.85 times more likely to be infested than small females, but no difference was seen between different sized males. The throat had significantly more mites than other body regions and the legs had significantly fewer mites than other regions. Mites were examined using scanning electron microscopy and their morphology was compared to drawings of a previously described mite. The mite on Pristimantis sp. 1 was not Hannimania sp., the genus commonly reported to infest frogs

Graphene Oxidation: Thickness Dependent Etching and Strong Chemical Doping

Patterned graphene shows substantial potential for applications in future molecular-scale integrated electronics. Environmental effects are a critical issue in a single layer material where every atom is on the surface. Especially intriguing is the variety of rich chemical interactions shown by molecular oxygen with aromatic molecules. We find that O2 etching kinetics vary strongly with the number of graphene layers in the sample. Three-layer-thick samples show etching similar to bulk natural graphite. Single-layer graphene reacts faster and shows random etch pits in contrast to natural graphite where nucleation occurs at point defects. In addition, basal plane oxygen species strongly hole dope graphene, with a Fermi level shift of ~0.5 eV. These oxygen species partially desorb in an Ar gas flow, or under irradiation by far UV light, and readsorb again in an O2 atmosphere at room temperature. This strongly doped graphene is very different than graphene oxide made by mineral acid attack.Comment: 15 pages, 5 figure

Risico's van bodemverontreiniging in het landelijk gebied; bodemkwaliteitskaarten, risico's voor de voedselveiligheid, actief bodembeheer en beslissingsondersteunende systemen

Dit rapport bevat achtergrondinformatie over de aanpak en resultaten van onderzoek naar bodemkwaliteitskaarten met daarop de gehalten en de risico's van zware metalen; de risico's van bodemverontreiniging voor gewaskwaliteit en diergezondheid; de effecten van veranderend landgebruik op bodemkwaliteit, bodemleven en hogere flora en fauna; de mogelijkheden van fytoremediëring voor het beheersen en terugdringen van risico's van bodemverontreiniging; verificatieonderzoek in verband met de toepassing van actief bodembeheer in de Krimpenerwaard; en ontwikkeling en toepassing van een beslissingondersteunend systeem voor inrichting en beheer van gronden voor natuurontwikkeling. De informatie in dit rapport is gebaseerd op artikelen die reeds toegestuurd zijn dan wel spoedig toegestuurd worden naar populair-wetenschappelijke tijdschriften

Can we gain precision by sampling with probabilities proportional to size in surveying recent landscape changes in the Netherlands?

Seventy-two squares of 100 ha were selected by stratified random sampling with probabilities proportional to size (pps) to survey landscape changes in the period 1996-2003. The area of the plots times the urbanization pressure was used as a size measure. The central question of this study is whether the sampling with probabilities proportional to size leads to gain in precision compared to equal probability sampling. On average 1.03 isolated buildings per 100 ha have been built, while 0.90 buildings per 100 ha have been removed, leading to a net change of 0.13 building per 100 ha. The area with unspoiled natural relief has been reduced by 2.3 ha per 100 ha, and the length of linear relicts by 137 m per 100 ha. On average 74 m of linear green elements have been planted per 100 ha, while 106 m have been removed, leading to a net change of -31 m per 100 ha. For the state variables 'unspoiled natural relief', 'linear relicts', 'removed linear green elements', and 'new - removed linear green elements' there is a gain in precision due to the pps-sampling. For the remaining state variables there is no gain or even a loss of precision (`new buildings', 'removed buildings', 'new - removed buildings', 'new linear green elements'). Therefore, if many state variables must be monitored or when interest is not only in the change but also in the current totals, we recommend to keep things simple, and to select plots with equal probability

Multiband theory of quantum-dot quantum wells: Dark excitons, bright excitons, and charge separation in heteronanostructures

Electron, hole, and exciton states of multishell CdS/HgS/CdS quantum-dot quantum well nanocrystals are determined by use of a multiband theory that includes valence-band mixing, modeled with a 6-band Luttinger-Kohn Hamiltonian, and nonparabolicity of the conduction band. The multiband theory correctly describes the recently observed dark-exciton ground state and the lowest, optically active, bright-exciton states. Charge separation in pair states is identified. Previous single-band theories could not describe these states or account for charge separation.Comment: 10 pages of ReVTex, 6 ps figures, submitted to Phys. Rev.

Magnetic phase transition in V2O3 nanocrystals

V2O3 nanocrystals can be synthesized through hydrothermal reduction of VO(OH)2 using hydrazine as a reducing agent. Addition of different ligands to the reaction produces nanoparticles, nanorods and nanoplatelets of different sizes. Small nanoparticles synthesized in this manner show suppression of the magnetic phase transition to lower temperatures. Using muon spin relaxation spectroscopy and synchrotron x-ray diffraction, it is determined that the volume fraction of the high-temperature phase, characterized by a rhombohedral structure and paramagnetism, gradually declines with decreasing temperature, in contrast to the sharp transition observed in bulk V2O3.Comment: 6 pages, 6 figure

Increased susceptibility to proactive interference in adults with dyslexia?

Recent findings show that people with dyslexia have an impairment in serial-order memory. Based on these findings, the present study aimed to test the hypothesis that people with dyslexia have difficulties dealing with proactive interference (PI) in recognition memory. A group of 25 adults with dyslexia and a group of matched controls were subjected to a 2-back recognition task, which required participants to indicate whether an item (mis)matched the item that had been presented 2 trials before. PI was elicited using lure trials in which the item matched the item in the 3-back position instead of the targeted 2-back position. Our results demonstrate that the introduction of lure trials affected 2-back recognition performance more severely in the dyslexic group than in the control group, suggesting greater difficulty in resisting PI in dyslexia.Peer reviewedFinal Accepted Versio

Atmospheric Oxygen Binding and Hole Doping in Deformed Graphene on a SiO2 Substrate

Using micro-Raman spectroscopy and scanning tunneling microscopy, we study the relationship between structural distortion and electrical hole doping of graphene on a silicon dioxide substrate. The observed upshift of the Raman G band represents charge doping and not compressive strain. Two independent factors control the doping: (1) the degree of graphene coupling to the substrate, and (2) exposure to oxygen and moisture. Thermal annealing induces a pronounced structural distortion due to close coupling to SiO2 and activates the ability of diatomic oxygen to accept charge from graphene. Gas flow experiments show that dry oxygen reversibly dopes graphene; doping becomes stronger and more irreversible in the presence of moisture and over long periods of time. We propose that oxygen molecular anions are stabilized by water solvation and electrostatic binding to the silicon dioxide surface.Comment: 17 pages, 5 figure