294 research outputs found
The minimum quantity of lubricant technique in grinding of steel using a wheel cleaning system
The application of minimum quantity of lubricant (MQL) for metal cutting has emerged
as an alternative for reducing the abundant flow of cutting fluids, thus achieving cleaner
production. Although considered an innovative technique in grinding operations, the
widespread application is hindered mainly due to the high heat generation and the
clogging of wheel pores caused by machined chips, harming the final product quality
and increasing tool wear. This study sought to improve MQL use in grinding. Thus,
besides the conventional MQL injected at the wheel/workpiece interface, a
compressed air jet was also added, in order to clean the clogged wheel pores from the
mixture of MQL oil and machined chips. Experiments were conducted using external
cylindrical plunge grinding on AISI 4340 quenched and tempered steel, and a vitrified
cubic boron nitrite (CBN) wheel. The lubri-refrigeration methods employed were the
conventional with abundant flow, conventional MQL (both without any cleaning air jets)
and MQL with the cleaning jet, directed at the surface at different angles of incidence.
The main goal of these experiments was to verify the viability of replacing traditional
abundance flow with MQL with wheel cleaning. The analyses were conducted by
measuring the following output variables of the process: workpiece surface roughness,
roundness, diametrical wear of the wheel. Results show the possibility of implementing
the cleaning jet technique as a technological improvement of the minimum quantity of
and grinding, in order to reduce the usage of cutting fluids. The MQL technique with
cleaning compressed air jet, for a specific angle of incidence (30°) proved to be
extremely efficient to obtain improved surface quality and accurate workpiece shape,
as well as to reduce wear wheel and to prevent thermal damage, when compared to
the other lubri-refrigeration methods tested (without cleaning jet).Special thanks to FAPESP (State of São Paulo Research Assistance Foundation)
(process 2009/51440-5 (Research Assistance) and 2009/51439-7 (Scientific
Initiation)) for the financial resources made available for this study, and to the Schaeffler Group (INA brand) for the support offered in conducting metallographic
analyses
Mass Renormalization in the Su-Schrieffer-Heeger Model
This study of the one dimensional Su-Schrieffer-Heeger model in a weak
coupling perturbative regime points out the effective mass behavior as a
function of the adiabatic parameter , is the
zone boundary phonon energy and is the electron band hopping integral.
Computation of low order diagrams shows that two phonons scattering processes
become appreciable in the intermediate regime in which zone boundary phonons
energetically compete with band electrons. Consistently, in the intermediate
(and also moderately antiadiabatic) range the relevant mass renormalization
signals the onset of a polaronic crossover whereas the electrons are
essentially undressed in the fully adiabatic and antiadiabatic systems. The
effective mass is roughly twice as much the bare band value in the intermediate
regime while an abrupt increase (mainly related to the peculiar 1D dispersion
relations) is obtained at .Comment: To be published in Phys.Rev.B - 3 figure
Open Spinning Strings and AdS/dCFT Duality
We consider open spinning string solutions on an AdS_4 x S^2-brane (D5-brane)
in the bulk AdS_5 x S^5 background. By taking account of the breaking of
SO(6)_R to SO(3)_H x SO(3)_V due to the presence of the AdS-brane, the open
rotating string ansatz is discussed. We construct the elliptic folded/circular
open string solutions in the SU(2) and the SL(2) sectors, so that they satisfy
the appropriate boundary conditions. On the other hand, in the SU(2) sector of
the gauge theory, we compute the matrix of anomalous dimension of the defect
operator, which turns out to be the Hamiltonian of an open integrable spin
chain. Then we consider the coordinate Bethe ansatz with arbitrary number of
impurities, and compare the boundary condition of the Bethe wavefunction with
that of the corresponding open string solution. We also discuss the Bethe
ansatz for the open SL(2) spin chain with several supports from the string
theory side. Then, in both SU(2) and SL(2) sectors, we analyze the Bethe
equations in the thermodynamic limit and formulate the `doubling trick' on the
Riemann surface associated with the gauge theory.Comment: 1+50 pages, 7 figures, JHEP style, references adde
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
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
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays.
It consists of a surface array to measure secondary particles at ground level
and a fluorescence detector to measure the development of air showers in the
atmosphere above the array. The "hybrid" detection mode combines the
information from the two subsystems. We describe the determination of the
hybrid exposure for events observed by the fluorescence telescopes in
coincidence with at least one water-Cherenkov detector of the surface array. A
detailed knowledge of the time dependence of the detection operations is
crucial for an accurate evaluation of the exposure. We discuss the relevance of
monitoring data collected during operations, such as the status of the
fluorescence detector, background light and atmospheric conditions, that are
used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic
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
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
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