72,896 research outputs found
Defect chemistry of Ti and Fe impurities and aggregates in Al2O3
We report a theoretical evaluation of the properties of iron and titanium impurities in sapphire (corundum structured α-Al2O3). Calculations using analytical force fields have been performed on the defect structure with the metals present in isolated, co-doped and tri-cluster configurations. Crystal field parameters have been calculated with good agreement to available experimental data. When titanium and iron are present in neighbouring face and edge-sharing orientations, the overlap of the d-orbitals facilitates an intervalence charge transfer (FeIII/TiIII → FeII/TiIV) with an associated optical excitation energy of 1.85 eV and 1.76 eV in the respective configurations. Electronic structure calculations based on density functional theory confirm that FeIII/TiIII is the ground-state configuration for the nearest-neighbour pairs, in contrast to the often considered FeII/TiIV pair. Homonuclear intervalence charge transfer energies between both FeIII/FeII and TiIV/TiIII species have also been calculated, with the energy lying in the infra-red region. Investigation of multiple tri-clusters of iron and titanium identified one stable configuration, TiIII–(TiIV/FeII), with the energy of electron transfer remaining unchanged
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Gyne and drone production in bombus atratus (Hymenoptera: Apidae)
For over a decade, our research group has studied the biology of the native bumblebee, Bombus atratus, to investigate the feasibility of using it to pollinate crops such as tomato, strawberry, blackberry and peppers. Traditionally, captive breeding has depended on the use of captured wild queens to initiate the colonies. The goal of the current work is to investigate conditions required to produce new queens and drones in captivity. In this study, 31 colonies were evaluated under either greenhouse or open field conditions over a 15 month period. A total of 1492 drones (D) and 737 gynes (G, i.e., virgin queens) were produced by all colonies, with 16 colonies producing both drones and gynes (D&G), 11 producing only drones (D) and 4 producing neither. Some of the D&G colonies had more than one sexual phase, but no colonies produced exclusively gynes. More drones and fewer gynes were produced per colony under greenhouse conditions with the highest number of drones produced by D&G colonies. The numbers of immature stages per cell declined in colonies as increasingly more resources were allocated to the production of gynes and the maintenance of increased nest temperature
HST and ground-based eclipse observations of V2051 Ophiuchi: Binary parameters
We report on high-speed eclipse photometry of the dwarf nova V2051 Oph while
it was in a low brightness state, at B ~ 16.2 mag. In comparison to the average
IUE spectra, the ultraviolet continuum and emission lines appear reduced by
factors of, respectively, ~4 and ~5. Flickering activity is mostly suppressed
and the lightcurve shows the eclipse of a compact white dwarf at disc centre
which contributes ~60 per cent of the total light at 3900--4300 A. We use
measurements of contact phases in the eclipse lightcurve to derive the binary
geometry and to estimate masses and relevant dimensions. We find a mass ratio
of q= 0.19+/-0.03 and an inclination of i= 83+/-2 degrees. The masses of the
component stars are M_1 = 0.78+/-0.06 M_dot and M_2 = 0.15+/-0.03 M_dot. Our
photometric model predicts K_1 = 83+/-12 km/s and K_2= 435+/-11 km/s. The
predicted value of K_1 is in accordance with the velocity amplitude obtained
from the emission lines after a correction for asymmetric line emission in the
disc is made (Watts et al. 1986). The secondary of V2051 Oph is significantly
more massive than the secondaries of the other ultra-short period dwarf novae.
V2051 Oph is probably a relatively young system, whose secondary star had not
enough time to evolve out of thermal equilibrium.Comment: 16 pages, 7 postscript figures, coded using MNRAS latex style. To
appear in Monthly Notices of the Royal Astronomical Society. Revised version
with changes in section 4.3. For related papers and files see
ftp://fsc01.fsc.ufsc.br/pub/bap and http://www.fsc.ufsc.br/~astr
No influence of one right-sided prefrontal HF-rTMS session on alcohol craving in recently detoxified alcohol-dependent patients: results of a naturalistic study
Evaluation of Workload in High Complexity Work Place: an Experiment During a Real Situation
Some workplace have been widely changed with regard to their automation process, which has promoted a more complex environment concerning the task performance, demanding to the operator the introducing of new abilities. In the aeronautic activity the workload also has been diversified, as the mental demand has been enhanced. The needs of determining the impact of the workload on the operator due to such work place, evidencing a more complex nature, shows to be more important, mainly when looking at the certification requirements for new aircraft development. Such certification process is responsible for determining the minimum aircrew necessary, based on the distribution of the cabin workload, as well as keeping the situation awareness during the different phases of the flight. This study uses psychological and physiological methods of measurements to evaluate the workload in real situation during the end of the certification process of an aircraft, aiming at to identify potential methods to be implemented during the whole certification process. A protocol of workload evaluation was implemented based on the use of interview, NASA-TLX scale, heart rate (HR) and heart rate variability (HRV). Two pilots participated in the study. The measurements and interviews were conducted during flights performed in the final certification process of an aircraft produced in Brazil. A total of six take-off and six landings performed during three consecutive days were evaluated. Each route was previously determined, which involved some abnormal situations according to an established program for the evaluation of the aircraft in terms of human factor requirements. The data analysis was performed in a descriptive and qualitative basis due to the peculiarity of each task. Preliminary results indicate the landing to be more stressful than take-off, and for such situations, the pilot flying (PF) had the more workload during the tasks than the pilot monitoring (PM). When comparing all flights and their tasks, no important difference between the HR and HRV was observed, but, again, the landing showed a little higher stressful than take-off for the PF, as evidenced by the HR. However, the general results, including those from NASA-TLX, suggested a low workload for all tasks. With regards to the interviews, the more pronounced mental demands reported by the pilots in managing any fault of the aircraft were in those tasks that required anticipation, attention and monitoring procedures. Future studies should be conducted with the whole certification process and other scenarios in order to test the applicability of the methodology employed in the present study
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SUMMERTIME DISTRIBUTION OF PAN AND OTHER REACTIVE NITROGEN SPECIES IN THE NORTHERN HIGH-LATITUDE ATMOSPHERE OF EASTERN CANADA
Chromatic, Photometric and Thermal Modeling of LED Systems with Nonidentical LED Devices
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Reactive nitrogen over the tropical western Pacific: Influence from lightning and biomass burning during BIBLE A
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