915 research outputs found
Development of a window correlation matching method for improved radar rainfall estimation
International audienceThe present study develops a method called window correlation matching method (WCMM) to reduce collocation and timing errors in matching pairs of radar measured reflectivity, Ze, and gauge measured rainfall intensity, R, for improving the accuracy of the estimation of Ze?R relationships. This method was compared with the traditional matching method (TMM), the probability matching method (PMM) and the window probability matching method (WPMM). The calibrated relationship Ze=18.05 R1.45 obtained from 7Ă—7 km of space window and both present and 5 min previous time of radar observation for time window (S77T5) produces the best results for radar rainfall estimates for orographic rain over the Mae Chaem Watershed in the north of Thailand. The comparison shows that the Ze?R relationship obtained from WCMM provide more accuracy in radar rainfall estimates as compared with the other three methods. The Ze?R relationships estimated using TMM and PMM provide large overestimation and underestimation, respectively, of mean areal rainfall whereas WPMM slightly underestimated the mean areal rainfall. Based on the overall results, it can be concluded that WCMM can reduce collocation and timing errors in Ze?R pairs matching and improve the estimation of Ze?R relationships for radar rainfall. WCMM is therefore a promising method for improved radar-measured rainfall, which is an important input for hydrological and environmental modeling and water resources management
An artificial neural network model for rainfall forecasting in Bangkok, Thailand
This paper presents a new approach using an Artificial Neural Network technique to improve rainfall forecast performance. A real world case study was set up in Bangkok; 4 years of hourly data from 75 rain gauge stations in the area were used to develop the ANN model. The developed ANN model is being applied for real time rainfall forecasting and flood management in Bangkok, Thailand. Aimed at providing forecasts in a near real time schedule, different network types were tested with different kinds of input information. Preliminary tests showed that a generalized feedforward ANN model using hyperbolic tangent transfer function achieved the best generalization of rainfall. Especially, the use of a combination of meteorological parameters (relative humidity, air pressure, wet bulb temperature and cloudiness), the rainfall at the point of forecasting and rainfall at the surrounding stations, as an input data, advanced ANN model to apply with continuous data containing rainy and non-rainy period, allowed model to issue forecast at any moment. Additionally, forecasts by ANN model were compared to the convenient approach namely simple persistent method. Results show that ANN forecasts have superiority over the ones obtained by the persistent model. Rainfall forecasts for Bangkok from 1 to 3 h ahead were highly satisfactory. Sensitivity analysis indicated that the most important input parameter besides rainfall itself is the wet bulb temperature in forecasting rainfall
Soft coronal X-rays from \beta{} Pictoris
A type stars are expected to be X-ray dark, yet weak emission has been
detected from several objects in this class. We present new Chandra/HRC-I
observations of the A5 V star \beta{} Pictoris. It is clearly detected with a
flux of 9+-2 10^{-4} counts/s. In comparison with previous data this constrains
the emission mechanism and we find that the most likely explanation is an
optically thin, collisionally dominated, thermal emission component with a
temperature around 1.1 MK. We interpret this component as a very cool and dim
corona, with \log L_X/L_{bol}=-8.2 (0.2-2.0 keV). Thus, it seems that \beta{}
Pictoris shares more characteristics with cool stars than previously thought.Comment: accepted by ApJ, 5 pages, 2 figure
Design of Multistep Aging Treatments of 2099 (C458) Al-Li Alloy
Multistep artificial aging treatments coupled with various natural aging times for aluminum lithium 2099 alloy (previously called C458) are discussed to obtain mechanical tensile properties in the T6 condition that match those in the T861 condition, having a yield strength in the range of 414-490 MPa (60-71 ksi), an ultimate strength in the range of 496-538 MPa (72-78 ksi), and 10-13% elongation. Yield and ultimate tensile strengths from 90-100% of the strength of the as-received material (in the T861 condition) were obtained. The highest tensile strengths were consistently obtained with two-step, low-to-high temperature artificial aging treatments consisting of a first step at 120 degrees C (248 degrees F) for 12-24 h followed by a second step between 165 and 180 degrees C (329-356 degrees F) for 48-100 h. These T6-type heat treatments produced average yield and ultimate strengths in the longitudinal direction in the range of 428-472 MPa (62.1-68.5 ksi) and 487-523 MPa (70.6-75.9 ksi), respectively, as well as lower yield strength anisotropy when compared with the as-received material in the T861 condition
Focusing by blocking: repeatedly generating central density peaks in self-propelled particle systems by exploiting diffusive processes
Over the past few years the displacement statistics of self-propelled
particles has been intensely studied, revealing their long-time diffusive
behavior. Here, we demonstrate that a concerted combination of boundary
conditions and switching on and off the self-propelling drive can generate and
afterwards arbitrarily often restore a non-stationary centered peak in their
spatial distribution. This corresponds to a partial reversibility of their
statistical behavior, in opposition to the above-mentioned long-time diffusive
nature. Interestingly, it is a diffusive process that mediates and makes
possible this procedure. It should be straightforward to verify our predictions
in a real experimental system.Comment: 6 pages, 6 figure
The effect of magnetic dipolar interactions on the interchain spin wave dispersion in CsNiF_3
Inelastic neutron scattering measurements were performed on the ferromagnetic
chain system CsNiF_3 in the collinear antiferromagnetic ordered state below T_N
= 2.67K. The measured spin wave dispersion was found to be in good agreement
with linear spin wave theory including dipolar interactions. The additional
dipole tensor in the Hamiltonian was essential to explain some striking
phenomena in the measured spin wave spectrum: a peculiar feature of the
dispersion relation is a jump at the zone center, caused by strong dipolar
interactions in this system. The interchain exchange coupling constant and the
planar anisotropy energy were determined within the present model to be J'/k_B
= -0.0247(12)K and A/k_B = 3.3(1)K. This gives a ratio J/J' \approx 500, using
the previously determined intrachain coupling constant J/k_B = 11.8$. The small
exchange energy J' is of the same order as the dipolar energy, which implies a
strong competition between the both interactions.Comment: 18 pages, TeX type, 7 Postscript figures included. To be published in
Phys. Rev.
Comparison of Two Hydrological Models, HEC-HMS and SWAT in Runoff Estimation: Application to Huai Bang Sai Tropical Watershed, Thailand
In the present study, the streamflow simulation capacities between the Soil and Water Assessment Tool (SWAT) and the Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS) were compared for the Huai Bang Sai (HBS) watershed in northeastern Thailand. During calibration (2007–2010) and validation (2011–2014), the SWAT model demonstrated a Coefficient of Determination (R2) and a Nash Sutcliffe Efficiency (NSE) of 0.83 and 0.82, and 0.78 and 0.77, respectively. During the same periods, the HEC-HMS model demonstrated values of 0.80 and 0.79, and 0.84 and 0.82. The exceedance probabilities at 10%, 40%, and 90% were 144.5, 14.5, and 0.9 mm in the flow duration curves (FDCs) obtained for observed flow. From the HEC-HMS and SWAT models, these indices yielded 109.0, 15.0, and 0.02 mm, and 123.5, 16.95, and 0.02 mm. These results inferred those high flows were captured well by the SWAT model, while medium flows were captured well by the HEC-HMS model. It is noteworthy that the low flows were accurately simulated by both models. Furthermore, dry and wet seasonal flows were simulated reasonably well by the SWAT model with slight under-predictions of 2.12% and 13.52% compared to the observed values. The HEC-HMS model under-predicted the dry and wet seasonal flows by 10.76% and 18.54% compared to observed flows. The results of the present study will provide valuable recommendations for the stakeholders of the HBS watershed to improve water usage policies. In addition, the present study will be helpful to select the most appropriate hydrologic model for humid tropical watersheds in Thailand and elsewhere in the world.Comparison of Two Hydrological Models, HEC-HMS and SWAT in Runoff Estimation: Application to Huai Bang Sai Tropical Watershed, ThailandpublishedVersio
X-ray Variability in the Young Massive Triple theta2 Ori A
Massive stars rarely show intrinsic X-ray variability. The only O-stars
credited to be intrinsically variable are theta1 Ori C due to effects from
magnetic confinement of its wind, and theta2 Ori A suspected of similar
activity. Early Chandra observations have shown that the most massive star
system in the Orion Trapezium Cluster, theta2 Ori A, shows rapid variability on
time scales of hours. We determine X-ray fluxes and find that the star shows
very strong variability over the last 5 years. We observed a second large X-ray
outburst in November 2004 with the high resolution transmission grating
spectrometer on-board Chandra. In the low state X-ray emissivities indicate
temperatures well above 25 MK. In the high state we find an extended emissivity
distribution with high emissivities in the range from 3 MK to over 100 MK. The
outburst event in stellar terms is one of the most powerful ever observed and
the most energetic one in the ONC with a lower total energy limit of 1.5x10^37
ergs. The line diagnostics show that under the assumption that the line
emitting regions in the low states are as close as within 1 -- 2 stellar radii
from the O-star's photosphere, whereas the hard states suggest a distance of 3
-- 5 stellar radii. The two outbursts are very close to the periastron passage
of the stars. We argue that the high X-ray states are possibly the result of
reconnection events from magnetic interactions of the primary and secondary
stars of the spectroscopic binary. Effects from wind collisions seem unlikely
for this system. The low state emissivity and R-ratios strengthen the
predicament that the X-ray emission is enhanced by magnetic confinement of the
primary wind. We also detect Fe fluorescence indicative of the existence of
substantial amounts of neutral Fe in the vicinity of the X-ray emission.Comment: 11 pages, 8 figures, accepted for publication in The Astrophysical
Main Journa
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