1,349 research outputs found
Demagnetization factor for a powder of randomly packed spherical particles
The demagnetization factors for randomly packed spherical particle powders
with different porosities, sample aspect ratios and monodisperse, normal and
log-normal particle size distributions have been calculated using a numerical
model. For a relative permeability of 2, comparable to room temperature Gd, the
calculated demagnetization factor is close to the theoretical value. The
normalized standard deviation of the magnetization in the powder was 6.0%-6.7%.
The demagnetization factor decreased significantly, while the standard
deviation of the magnetization increased, for increasing relative permeability.Comment: 4 pages, 4 figure
Elliptical double corrugated tubes for enhanced heat transfer
The thermal performance at constant pumping power conditions was numerically investigated in ellipse and super ellipse-based double corrugated tubes. A significant increase in thermal efficiency in double corrugated tubes is accompanied with a reasonable penalty in flow reduction for the cases modelled. An ellipse and a super ellipse-based double corrugated tubes were modelled at laminar fully hydraulically developed incompressible flow. Each base geometry was analysed holding either hydraulic diameter constant or the cross-sectional area constant. The pressure drop was normalized to the length of each modelled tube in order to maintain the pumping power. Thermal analysis was conducted under constant wall temperature boundary condition. The governing equations for non-isothermal flow were solved using the finite element method, and the results of the simulations were normalized to an equivalent straight tube. Numerical results predict a thermal efficiency enhanced by 400% maintaining 4.2 times lower volumetric flow rate in double corrugated tubes at the same pressure drop. The global performance evaluation criterion increases up to 14% for the double corrugated tubes with an ellipse-base and up to 11% for the tubes with super ellipse-base
Dynamic rotor mode in antiferromagnetic nanoparticles
We present experimental, numerical, and theoretical evidence for a new mode
of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering
experiments on 8 nm particles of hematite display a loss of diffraction
intensity with temperature, the intensity vanishing around 150 K. However, the
signal from inelastic neutron scattering remains above that temperature,
indicating a magnetic system in constant motion. In addition, the precession
frequency of the inelastic magnetic signal shows an increase above 100 K.
Numerical Langevin simulations of spin dynamics reproduce all measured neutron
data and reveal that thermally activated spin canting gives rise to a new type
of coherent magnetic precession mode. This "rotor" mode can be seen as a
high-temperature version of superparamagnetism and is driven by exchange
interactions between the two magnetic sublattices. The frequency of the rotor
mode behaves in fair agreement with a simple analytical model, based on a high
temperature approximation of the generally accepted Hamiltonian of the system.
The extracted model parameters, as the magnetic interaction and the axial
anisotropy, are in excellent agreement with results from Mossbauer
spectroscopy
FSL-BM: Fuzzy Supervised Learning with Binary Meta-Feature for Classification
This paper introduces a novel real-time Fuzzy Supervised Learning with Binary
Meta-Feature (FSL-BM) for big data classification task. The study of real-time
algorithms addresses several major concerns, which are namely: accuracy, memory
consumption, and ability to stretch assumptions and time complexity. Attaining
a fast computational model providing fuzzy logic and supervised learning is one
of the main challenges in the machine learning. In this research paper, we
present FSL-BM algorithm as an efficient solution of supervised learning with
fuzzy logic processing using binary meta-feature representation using Hamming
Distance and Hash function to relax assumptions. While many studies focused on
reducing time complexity and increasing accuracy during the last decade, the
novel contribution of this proposed solution comes through integration of
Hamming Distance, Hash function, binary meta-features, binary classification to
provide real time supervised method. Hash Tables (HT) component gives a fast
access to existing indices; and therefore, the generation of new indices in a
constant time complexity, which supersedes existing fuzzy supervised algorithms
with better or comparable results. To summarize, the main contribution of this
technique for real-time Fuzzy Supervised Learning is to represent hypothesis
through binary input as meta-feature space and creating the Fuzzy Supervised
Hash table to train and validate model.Comment: FICC201
Observation of Spontaneous Brillouin Cooling
While radiation-pressure cooling is well known, the Brillouin scattering of
light from sound is considered an acousto-optical amplification-only process.
It was suggested that cooling could be possible in multi-resonance Brillouin
systems when phonons experience lower damping than light. However, this regime
was not accessible in traditional Brillouin systems since backscattering
enforces high acoustical frequencies associated with high mechanical damping.
Recently, forward Brillouin scattering in microcavities has allowed access to
low-frequency acoustical modes where mechanical dissipation is lower than
optical dissipation, in accordance with the requirements for cooling. Here we
experimentally demonstrate cooling via such a forward Brillouin process in a
microresonator. We show two regimes of operation for the Brillouin process:
acoustical amplification as is traditional, but also for the first time, a
Brillouin cooling regime. Cooling is mediated by an optical pump, and scattered
light, that beat and electrostrictively attenuate the Brownian motion of the
mechanical mode.Comment: Supplementary material include
Treibhausgasbilanz nachwachsender Rohstoffe : eine wissenschaftliche Kurzdarstellung. (KIT Scientific Reports ; 7556)
Die Untersuchung zeigt, dass insbesondere die mit dem Anbau verbundenen Lachgas-Emissionen und die Änderung des in der Vegetation und im Boden gespeicherten organischen Kohlenstoffs darüber entscheiden, ob nachwachsende Rohstoffe (NaWaRo) zur Ent- oder gar zur Belastung des Treibhausklimas beitragen. Bestehende Unsicherheiten und Verbesserungsmöglichkeiten in der Datenlage und methodischen Vorgehensweise werden aufgezeigt, einschließlich der zu präferierenden Nutzungsstrategien bei NaWaRo
Weight gain and enteric methane production of cattle fed on tropical grasses
Context: Planted grasses are becoming an increasingly important feed resource for tropical smallholder ruminant production; yet, limited research has been conducted to quantify productivity or enteric methane (CH) production of animals consuming these grasses.
Aim: An experiment was conducted to assess yields and nutritional attributes of the following three tropical grasses: Cenchrus purpureus var. Kakamega 1 (Napier), Chloris gayana var. Boma (Rhodes) and Urochloa brizantha var. Xaeres (Brachiaria), and quantify enteric CH production of cattle fed on them.
Methods: Yearling Boran steers (n:18; initial liveweight 216 ± 5.8 kg (mean ± s.e.m.) were allocated to one of three grasses, in a completely randomised design and fed ad libitum for two feeding periods, each period lasting for 70 days. Intake, liveweight (LW), apparent total-tract digestibility and enteric CH production were assessed. The grasses used were grown on site and biomass yields were monitored over a 2-year period. Animal growth was also simulated to a final weight of 350 kg, and the amount of feed and size of land required to produce, and days to reach final weight, were estimated.
Key results: Mean voluntary dry-matter intake (DMI) and ADG were higher (P 0.05) within period. Methane yield (MY; CH g/DMI kg) was similar among treatments (26.7–28.5, P = 0.26) but Napier had a higher CH conversion factor [Ym; CH (MJ)/gross energy intake (MJ)] than did Rhodes and Brachiaria (0.0987 vs 0.0873 and 0.0903 respectively; P = 0.013). Our modelling indicated that steers consuming Rhodes took at least 30 more days to reach the target LW, required larger land area for feed production and produced more enteric CH than did the other two diets.
Conclusion: Even though animal performance and MY among treatments did not differ, the animals had higher MY and Y than currently estimated by the Intergovernmental Panel on Climate Change.
Implication: The three grasses supported similar animal growth rate, implying that growing of higher-yielding grasses such as Napier offers an opportunity to optimise land productivity in the tropics. However, suitable feeding practices such as protein supplementation need to be explored to enhance ruminant production and reduce enteric CH production
Identifying landscape hot and cold spots of soil greenhouse gas fluxes by combining field measurements and remote sensing data
Upscaling chamber measurements of soil greenhouse gas (GHG) fluxes from point scale to landscape scale remain challenging due to the high variability in the fluxes in space and time. This study measured GHG fluxes and soil parameters at selected point locations (n=268), thereby implementing a stratified sampling approach on a mixed-land-use landscape (∼5.8 km2). Based on these field-based measurements and remotely sensed data on landscape and vegetation properties, we used random forest (RF) models to predict GHG fluxes at a landscape scale (1 m resolution) in summer and autumn. The RF models, combining field-measured soil parameters and remotely sensed data, outperformed those with field-measured predictors or remotely sensed data alone. Available satellite data products from Sentinel-2 on vegetation cover and water content played a more significant role than those attributes derived from a digital elevation model, possibly due to their ability to capture both spatial and seasonal changes in the ecosystem parameters within the landscape. Similar seasonal patterns of higher soil/ecosystem respiration (SR/ER–CO2) and nitrous oxide (N2O) fluxes in summer and higher methane (CH4) uptake in autumn were observed in both the measured and predicted landscape fluxes. Based on the upscaled fluxes, we also assessed the contribution of hot spots to the total landscape fluxes. The identified emission hot spots occupied a small landscape area (7 % to 16 %) but accounted for up to 42 % of the landscape GHG fluxes. Our study showed that combining remotely sensed data with chamber measurements and soil properties is a promising approach for identifying spatial patterns and hot spots of GHG fluxes across heterogeneous landscapes. Such information may be used to inform targeted mitigation strategies at the landscape scale.</p
Assessment of hydrological pathways in East African montane catchments under different land use
Conversion of natural forest (NF) to other land uses could lead to significant
changes in catchment hydrology, but the nature of these changes has been
insufficiently investigated in tropical montane catchments, especially in
Africa. To address this knowledge gap, we aimed to identify stream water
(RV) sources and flow paths in three tropical montane sub-catchments (27–36 km2)
with different land use (natural forest, NF; smallholder agriculture,
SHA; and commercial tea and tree plantations, TTP) within a 1021 km2 catchment
in the Mau Forest complex, Kenya. Weekly samples were collected from stream
water, precipitation (PC) and mobile soil water for 75Â weeks and analysed for
stable isotopes of water (δ2H and δ18O) for mean transit
time (MTT) estimation with two lumped parameter models (gamma model, GM; and exponential
piston flow model, EPM) and for the calculation of the young water fraction.
Weekly samples from stream water and potential endmembers were collected
over a period of 55Â weeks and analysed for Li, Na, Mg, K, Rb, Sr and Ba for
endmember mixing analysis (EMMA). Solute concentrations in precipitation were lower
than in stream water in all catchments (p < 0.05), whereas
concentrations in springs, shallow wells and wetlands were generally more
similar to stream water. The stream water isotope signal was considerably
damped compared to the isotope signal in precipitation. Mean transit time
analysis suggested long transit times for stream water (up to 4Â years) in the
three sub-catchments, but model efficiencies were very low. The young water
fraction ranged from 13 % in the smallholder agriculture sub-catchment to
15 % in the tea plantation sub-catchment. Mean transit times of mobile
soil water ranged from 3.2–3.3 weeks in forest soils and 4.5–7.9 weeks in
pasture soils at 15 cm depth to 10.4–10.8 weeks in pasture soils at 50 cm
depth. The contribution of springs and wetlands to stream discharge increased
from a median of 16.5 (95 % confidence interval: 11.3–22.9), 2.1
(−3.0–24.2) and 50.2 (30.5–65.5) % during low flow to 20.7
(15.2–34.7), 53.0 (23.0–91.3) and 69.4 (43.0–123.9) % during high flow
in the natural forest, smallholder agriculture and tea plantation
sub-catchments, respectively. Our results indicate that groundwater is an
important component of stream water, irrespective of land use. The results
further suggest that the selected transit time models and tracers might not
be appropriate in tropical catchments with highly damped stream water isotope
signatures. A more in-depth investigation of the discharge dependence of the
young water fraction and transit time estimation using other tracers, such as
tritium, could therefore shed more light on potential land use effects on the
hydrological behaviour of tropical montane catchments.</p
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