303 research outputs found
Infiltration characteristics of furrow irrigation in a heavy-textured soil
The objective of this thesis is to study the rate and pattern of infiltration of soil water, under the conditions of heavy texture and shallow depth in a tropical furrow- irrigated soil. The analysis is the result of a series of field-experiments and is supported by theories that has been proposed by others.The experiments were carried out in the Cojedes-Sarare Irrigation Project, Portuguesa State, Venezuela. Furrows with a length of 200 m, spaced at w = 0.70 m, and with an average slope of 0. 18 % were used. Three series of experiments were set out: (i) First series with variable inflow and surface roughness; (ii) Second series with variable initial soil moisture content; (iii) Third series with variable furrow length. Replicates of the treatments were distributed at random.Five irrigations were applied to the land during the period from January to March, 1970. Subsequently in the first series of experiments, first, third and fourth irrigations for three roughness conditions and four sizes of flow were tested. The second irrigation was used for the second series of experiments. The fifth irrigation served for the third series of experiments.During the first series of experiments, the following measurements were taken: (i) rate of advance of the water front (distance x in m at time t in min); (ii) furrow section parameters (top width T and depth h ); (iii) furrow inflow Q and outflow Q out . During the second and the third series of experiments, only the simultaneous inflow and outflow were recorded.Advance and infiltration functions were obtained for the period of advance of the water front (first stage), and infiltration functions for the period of wetting the root zone (second stage). Exponential equations were obtained by computer analysis for single furrow trials. Then, by averaging coefficients and exponents of the equations of the replicates, general equations for each treatment were found.The data of x as a function of t showed a good fit with the equation x = p t r . The coefficient p increased significantly with the flow size Q and the exponent r showed a trend to decrease although not significantly, with increasing Q . The coefficients of variation of p and r were rather high. Therefore a single furrow advance trial may not suffice to express the average field advance of the water front under the given conditions.The advance curves showed that the differences in roughness were great between the first irrigation with loose furrows and those irrigations after two or three applications have taken place. The roughness conditions appeared to be identical for third and fourth irrigations.With distance-averages of the furrow section parameters h and T , for three water front advance stages ( x = 87.5 m, x = 137,5 m and x = 175.0 m), the average section a f , and the average wetted perimeter P were obtained for a parabolic section of the furrows. The surface volume V f = a f p t r , and the area of infiltration A i (net area A in = P pt r and gross area A ig = w pt r ) were then arrived at.The infiltration functions were found for each treatment during the first stage, as V i= f(t) by using single furrow data of V i = Q t - V s ,. As the average infiltration depth I cum = V i / A i , the equations for I cum= f(t) were obtained. Equating these functions with the equation I cum = F at b+1/( b + 1) ( b + 2), the parameters a and b of the Kostiakov equation ( I = a t b ) were derived. For the second stage (when x = L = 175.0 m), the infiltration function was obtained by simultaneous measurements of the inflow and outflow, as infiltration flow: Q i = Q - Q out , from which the parameters of the infiltration equations, were found.The increase of infiltration with inflow size was clearly shown from the data analysis of both stages as being the effect of a larger volume of water. The parameters of the infiltration equation for the first stage altered in successive irrigations.Some emphasis was put on the unit inflow function q0 to relate flow sizes for both stages with length of run and infiltration. Equations for the unit inflow q0 = Q / A i and for unit infiltration flow q i = Q i / A i per unit area, were obtained for each treatment. Then a generalized type of equation was introduced which relates the unit inflow function with the average depth of water infiltrated during the advance time at the furrow intake. An equation to predict the length of advance is included x = Ï( Q ) t 0.927, for the surface roughness and soil conditions under which the experiments were carried out. The representation of q0= f(t) and q i = f(t) for both stages, in a composite figure with the advance function as a function of time, provides an illustration of the infiltration process, usable for the design and management of furrow irrigation under the conditions of the experiments.The relationship between the exponent of time in the advance equation and the exponent of time in the infiltration equation was analysed with the data from the experiments. This analysis confirmed that r increases when ( b + 1) decreases. This agrees with findings in the literature, such as the relationship proposed by FOK and BISHOP (1965) Values for the surface storage coefficient C 1 = D / D0 , and infiltration coefficient C 2 = I cum / I cum0 to solve the balance equation for predicting advance were also obtained.The second series of experiments, in which infiltration rate was measured during the second stage, as a function of the initial moisture content, showed that the value of the coefficient a of the Kostiakov equation increased not significantly as the initial content of soil moisture decreases.The third series of experiments - measurements taken during the second stage - showed that upon the increase of furrow length, the coefficient a of the infiltration equation decreases and the exponent b increases.Water losses by deep percolation and by run-off at the end of the run, were finally analysed on the bases of the equations found and the data available. The analysis was made for the case of constant inflow for both stages (third irrigation), and for the case of reduced inflow during the second stage (fourth irrigation).The data analysis showed that infiltration is a very variable factor affected by the conditions of the soil and the surface of the channel bed, as well as by the size of the flow, furrow length and stage of irrigation. Soil cracking upon drying was found to be a relevant factor in the entry of water into the soil. Because deep percolation losses are certainly very small under the indicated physical conditions, irrigation efficiency will be rather high if provisions are made to use a cut-back stream, during the second stage, in order to lose a minimum of water by run-off at the end of the run
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius . Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.Comment: Matches published versio
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory
The advent of the Auger Engineering Radio Array (AERA) necessitates the
development of a powerful framework for the analysis of radio measurements of
cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air
shower radio emission in coincidence with the surface particle detectors and
fluorescence telescopes of the Pierre Auger Observatory, the radio analysis
functionality had to be incorporated in the existing hybrid analysis solutions
for fluoresence and surface detector data. This goal has been achieved in a
natural way by extending the existing Auger Offline software framework with
radio functionality. In this article, we lay out the design, highlights and
features of the radio extension implemented in the Auger Offline framework. Its
functionality has achieved a high degree of sophistication and offers advanced
features such as vectorial reconstruction of the electric field, advanced
signal processing algorithms, a transparent and efficient handling of FFTs, a
very detailed simulation of detector effects, and the read-in of multiple data
formats including data from various radio simulation codes. The source code of
this radio functionality can be made available to interested parties on
request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to
author list and references in v
Search for First Harmonic Modulation in the Right Ascension Distribution of Cosmic Rays Detected at the Pierre Auger Observatory
We present the results of searches for dipolar-type anisotropies in different
energy ranges above eV with the surface detector array of
the Pierre Auger Observatory, reporting on both the phase and the amplitude
measurements of the first harmonic modulation in the right-ascension
distribution. Upper limits on the amplitudes are obtained, which provide the
most stringent bounds at present, being below 2% at 99% for EeV
energies. We also compare our results to those of previous experiments as well
as with some theoretical expectations.Comment: 28 pages, 11 figure
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS
We present the results of a search for new, heavy particles that decay at a
significant distance from their production point into a final state containing
charged hadrons in association with a high-momentum muon. The search is
conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV
and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS
detector operating at the Large Hadron Collider. Production of such particles
is expected in various scenarios of physics beyond the standard model. We
observe no signal and place limits on the production cross-section of
supersymmetric particles in an R-parity-violating scenario as a function of the
neutralino lifetime. Limits are presented for different squark and neutralino
masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final
version to appear in Physics Letters
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
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