Inviscid flow field induced by a rotor in ground effect

Integral equations for inviscid flow field induced by rotor in ground effec

The size and polydispersity of silica nanoparticles under simulated hot spring conditions

The nucleation and growth of silica nanoparticles in supersaturated geothermal waters was simulated using a flow-through geothermal simulator system. The effect of silica concentration ([SiO2]), ionic strength (IS), temperature (T) and organic additives on the size and polydispersity of the forming silica nanoparticles was quantified. A decrease in temperature (58 to 33°C) and the addition of glucose restricted particle growth to sizes <20 nm, while varying [SiO2] or ISdid not affect the size (30-35 nm) and polydispersity (±9 nm) observed at 58°C. Conversely, the addition of xanthan gum induced the development of thin films that enhanced silica aggregation

Entanglement and statistics in Hong-Ou-Mandel interferometry

Hong-Ou-Mandel interferometry allows one to detect the presence of entanglement in two-photon input states. The same result holds for two-particles input states which obey to Fermionic statistics. In the latter case however anti-bouncing introduces qualitative differences in the interferometer response. This effect is analyzed in a Gedankenexperiment where the particles entering the interferometer are assumed to belong to a one-parameter family of quons which continuously interpolate between the Bosonic and Fermionic statistics.Comment: 7 pages, 3 figures; minor editorial changes and new references adde

Search for exchange-antisymmetric two-photon states

Atomic two-photon J=0 $\leftrightarrow$J'=1 transitions are forbidden for photons of the same energy. This selection rule is related to the fact that photons obey Bose-Einstein statistics. We have searched for small violations of this selection rule by studying transitions in atomic Ba. We set a limit on the probability $v$ that photons are in exchange-antisymmetric states: $v<1.2\cdot10^{-7}$.Comment: 5 pages, 4 figures, ReVTeX and .eps. Submitted to Phys. Rev. Lett. Revised version 9/25/9

Tuning Nanocrystal Surface Depletion by Controlling Dopant Distribution as a Route Toward Enhanced Film Conductivity

Electron conduction through bare metal oxide nanocrystal (NC) films is hindered by surface depletion regions resulting from the presence of surface states. We control the radial dopant distribution in tin-doped indium oxide (ITO) NCs as a means to manipulate the NC depletion width. We find in films of ITO NCs of equal overall dopant concentration that those with dopant-enriched surfaces show decreased depletion width and increased conductivity. Variable temperature conductivity data shows electron localization length increases and associated depletion width decreases monotonically with increased density of dopants near the NC surface. We calculate band profiles for NCs of differing radial dopant distributions and, in agreement with variable temperature conductivity fits, find NCs with dopant-enriched surfaces have narrower depletion widths and longer localization lengths than those with dopant-enriched cores. Following amelioration of NC surface depletion by atomic layer deposition of alumina, all films of equal overall dopant concentration have similar conductivity. Variable temperature conductivity measurements on alumina-capped films indicate all films behave as granular metals. Herein, we conclude that dopant-enriched surfaces decrease the near-surface depletion region, which directly increases the electron localization length and conductivity of NC films

MDMA (‘ecstasy’) use, and its association with high risk behaviors, mental health, and other factors among gay/bisexual men in New York City

This study assesses patterns of use of methylenedioxymethamphetamine (MDMA or ‘ecstasy’), and the characteristics of users, in a sample of 733 men who have sex with men (MSM) in New York City. Among respondents, 13.7% reported using MDMA in the past 6 months, with mean frequency of use of 6.24 times in that period. MDMA users were found to be younger, less educated, to have had more male partners, more one night stands with men, more visits to bars or clubs and sex clubs or bathhouses, to have unprotected anal sex with a male, to be likely to have been the victim of physical domestic violence, to have more gay/bisexual friends, to have disclosed their sexual orientation to more friends, family members, and coworkers, and to have higher levels of gay community participation and affiliation. Among MDMA users, higher frequency of MDMA use was associated with being younger, having more visits to bars or clubs, more gay/bisexual friends, and having an HIV negative test result or never having been tested. MDMA users thus constitute a group at risk for sexually transmitted diseases, including HIV, and other problems. The data suggest that MDMA use is associated with being more ‘out’, which may be advantageous in helping gay men deal with harmful psychological effects of stigma, but may place individuals in settings that expose them to MDMA. These men have also presumably already been well exposed to safer sex messages within the gay community, thus raising challenges for interventions aimed at prevention, as well as opportunities (e.g. MSM and community specific interventions) that need to be further explored

Youth equity pathways in informal science learning

This infographic reports findings from the Youth Access & Equity in Informal Science Learning (ISL) project, a UK-US researcher-practitioner partnership funded by the Science Learning+ Phase 1 scheme. Our project focuses on young people aged 11-14 primarily from under-served and non-dominant communities and includes researchers and practitioners from a range of ISL settings: designed spaces (eg museums, zoos), community-based (eg afterschool clubs) and everyday science spaces (eg science media)

Lorentz-Invariant "Elements of Reality" and the Question of Joint Measurability of Commuting Observables

It is shown that the joint measurements of some physical variables corresponding to commuting operators performed on pre- and post-selected quantum systems invariably disturb each other. The significance of this result for recent proofs of the impossibility of realistic Lorentz invariant interpretation of quantum theory (without assumption of locality) is discussed.Comment: 15 page

Pathways in informal science learning: a practice-research brief

This briefing paper reports findings from the Youth Access & Equity in Informal Science Learning (ISL) project, a UK-US researcher-practitioner partnership funded by the Science Learning+ Phase 1 scheme. Our project focuses on young people aged 11-14 primarily from under-served and non-dominant communities and includes researchers and practitioners from a range of ISL settings, including designed spaces (eg museums, zoos), community based (eg afterschool clubs) and everyday science spaces (eg science media)

Synchrotron X-ray Diffraction Study of BaFe2As2 and CaFe2As2 at High Pressures up to 56 GPa: Ambient and Low-Temperatures Down to 33 K

We report high pressure powder synchrotron x-ray diffraction studies on MFe2As2 (M=Ba, Ca) over a range of temperatures and pressures up to about 56 GPa using a membrane diamond anvil cell. A phase transition to a collapsed tetragonal phase is observed in both compounds upon compression. However, at 300 (33) K in the Ba-compound the transition occurs at 26 (29) GPa, which is a much higher pressure than 1.7 (0.3) GPa at 300 (40) K in the Ca-compound, due to its larger volume. It is important to note that the transition in both compounds occurs when they are compressed to almost the same value of the unit cell volume and attain similar ct/at ratios. We also show that the FeAs4 tetrahedra are much less compressible and more distorted in the collapsed tetragonal phase than their nearly regular shape in the ambient pressure phase. We present a detailed analysis of the pressure dependence of the structures as well as equation of states in these important BaFe2As2 and CaFe2As2 compounds.Comment: 26 pages, 12 figure