2,982 research outputs found
Erfassung gasförmiger Emissionen vom Auslauf eines Jungviehstalles mittels aktiver Probenahmehaube
Open stable systems with outdoor yards are used in organic cattle farming. Until now there are no emission factors in Germany for outdoor yards of dairy barns or of cattle
barns generally. The measuring of the emission potential of gaseous substances (NH3, CO2, N2O and CH4) is difficult because of the size of the outdoor yards and the direct access by climate. One possibility to measure those emissions is the use of an active sampling hood. The sampling hood provides defined laminar exhaust airflow.
The product of flow rate and concentration results in the emission mass flow. In a preliminary study six cattle in calf with a total of 7.19 GV had access to an outdoor
yard. This was divided virtually in a 9 x 11 à 1 m² grid. To each m² a dirt level (clean, slightly, medium and heavily soiled) has been assigned. The grid area was sampled
randomly. The influence of a scraper was investigated, too. The levels of dirtiness were allocated to the NH3 emission mass flows. Based on the rating the results of the
random samples were transferred on the partial area of the entire outdoor yard. The outcome of this is an emission factor for NH3 of 3.02 kg/GV*a for the outdoor yard
before the scraper was used and 2.79 kg/GV*a afterwards. The preliminary results show that measuring NH3 emissions by an active sampling hood is practicable for the use at outdoor yards of cattle barns
Optimizing the performance of thermionic devices using energy filtering
Conventional thermionic power generators and refrigerators utilize a barrier
in the direction of transport to selectively transmit high-energy electrons.
Here we show that the energy spectrum of electrons transmitted in this way is
not optimal, and we derive the ideal energy spectrum for operation in the
maximum power regime. By using suitable energy filters, such as resonances in
quantum dots, the power of thermionic devices can, in principle, be improved by
an order of magnitude.Comment: 3 pages, 2 figure
Optimizing Stimulation and Analysis Protocols for Neonatal fMRI
The development of brain function in young infants is poorly understood. The core challenge is that infants have a limited behavioral repertoire through which brain function can be expressed. Neuroimaging with fMRI has great potential as a way of characterizing typical development, and detecting abnormal development early. But, a number of methodological challenges must first be tackled to improve the robustness and sensitivity of neonatal fMRI. A critical one of these, addressed here, is that the hemodynamic response function (HRF) in pre-term and term neonates differs from that in adults, which has a number of implications for fMRI. We created a realistic model of noise in fMRI data, using resting-state fMRI data from infants and adults, and then conducted simulations to assess the effect of HRF of the power of different stimulation protocols and analysis assumptions (HRF modeling). We found that neonatal fMRI is most powerful if block-durations are kept at the lower range of those typically used in adults (full on/off cycle duration 25-30s). Furthermore, we show that it is important to use the age-appropriate HRF during analysis, as mismatches can lead to reduced power or even inverted signal. Where the appropriate HRF is not known (for example due to potential developmental delay), a flexible basis set performs well, and allows accurate post-hoc estimation of the HRF
Transverse rectification of disorder-induced fluctuations in a driven system
We study numerically the overdamped motion of particles driven in a two
dimensional ratchet potential. In the proposed design, of the so-called
geometrical-ratchet type, the mean velocity of a single particle in response to
a constant force has a transverse component that can be induced by the presence
of thermal or other unbiased fluctuations. We find that additional quenched
disorder can strongly enhance the transverse drift at low temperatures, in
spite of reducing the transverse mobility. We show that, under general
conditions, the rectified transverse velocity of a driven particle fluid is
equivalent to the response of a one dimensional flashing ratchet working at a
drive-dependent effective temperature, defined through generalized Einstein
relations.Comment: 4.5 pages, 3 fig
High-fidelity quantum logic gates using trapped-ion hyperfine qubits
We demonstrate laser-driven two-qubit and single-qubit logic gates with
fidelities 99.9(1)% and 99.9934(3)% respectively, significantly above the
approximately 99% minimum threshold level required for fault-tolerant quantum
computation, using qubits stored in hyperfine ground states of calcium-43 ions
held in a room-temperature trap. We study the speed/fidelity trade-off for the
two-qubit gate, for gate times between 3.8s and 520s, and develop a
theoretical error model which is consistent with the data and which allows us
to identify the principal technical sources of infidelity.Comment: 1 trap, 2 ions, 3 nines. Detailed write-up of arXiv:1406.5473
including single-qubit gate data als
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The effect of supported MoOX structures on the reaction pathways of propene formation in the metathesis of ethylene and 2-butene
The kind of surface MoOX structures on Al2O3–SiO2 was found to determine propene selectivity in the metathesis of ethylene and 2-butene. Compared to isolated tetrahedral MoOX species, their polymerized octahedral counterparts show significantly lower activity for isomerisation of 2- to 1-butene thus hindering non-selective metathesis of these butenes. In addition, they reveal higher ability to engage ethylene in propene formation
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