2,832 research outputs found
Prediction of performance parameters in Wire EDM of HcHcr steel using Artificial Neural Network
Electrical discharge machining has been extensively used for cutting intricate contours or delicate cavities that would be difficult to produce with a conventional machining methods or tools. Wire EDM is in use for a long time for cutting punches and dies, shaped pockets and other complex shaped parts. Performance of the process is mainly depends on many parameters used during process. Machining input parameters provided by the machine tool builder cannot always meet the operator’s requirements. So, artificial neural network is introduced as an efficient approach to predict the values of performance parameters. In the present research, experimental investigations have been conducted to develop predictive models for the effect of input parameters on the responses such as Material Removal Rate, surface finish and kerf width. Material tested was HcHcr steel material. Molybdenum wires of diameters 0.18 mm were used for the WEDM machine. A feed forward back propagation artificial neural network (ANN) is used to model the influence of current, pulse-ON and pulse-OFF time on material removal rate, kerf width & surface roughness. Multilayer perception model has been constructed with feed forward back propagation algorithm using peak current, pulse-ON and pulse-OFF time as input parameters and MRR and surface roughness and kerf width as the output parameters. The predicted results based on the ANN model are found to be in very close agreement with the unexposed experimental data set. The modeling results confirm the feasibility of the ANN and its good correlation with the experimental results
Process Parameters Optimization of Resistance Spot Welding of Galvanized Steel Using Taguchi Method
Spot welding is a resistance welding process for joining metal sheets by directly applying opposite forces with pointed tips. The current and the heat generation are localized by the form of electrode. The amount of heat produced is a function of current, time and resistance between the work pieces. The present work attempts experimental investigations to study influence of important process parameters of resistance spot welding on weld strength, current and cycle time are varied at three different levels for different thickness and manufactured specimens are tested for weld strength.. Experiment have been conducted as per Taguchi method and fixed the levels for the parameters Analysis of variance (ANOVA) and F-test has been used for determining most significant parameters affecting the spot weld parameters
BeppoSAX LECS background subtraction techniques
We present 3 methods for the subtraction of non-cosmic and unresolved cosmic
backgrounds observed by the Low-Energy Concentrator Spectrometer (LECS)
on-board BeppoSAX. Removal of these backgrounds allows a more accurate modeling
of the spectral data from point and small-scale extended sources. At high
(>|25| degree) galactic latitudes, subtraction using a standard background
spectrum works well. At low galactic latitudes, or in complex regions of the
X-ray sky, two alternative methods are presented. The first uses counts
obtained from two semi-annuli near the outside of the LECS field of view to
estimate the background at the source location. The second method uses ROSAT
Position Sensitive Proportional Counter (PSPC) all-sky survey data to estimate
the LECS background spectrum for a given pointing position. A comparison of the
results from these methods provides an estimate of the systematic
uncertainties. For high galactic latitude fields, all 3 methods give 3 sigma
confidence uncertainties of <0.9 10^-3 count/s (0.1-10 keV), or <1.5 10^-3
count/s (0.1-2 keV). These correspond to 0.1-2.0 keV fluxes of 0.7-1.8 and
0.5-1.1 10^-13 erg/cm2/s for a power-law spectrum with a photon index of 2 and
photoelectric absorption of 3 10^20 and 3 10^21 atom/cm2, respectively. At low
galactic latitudes, or in complex regions of the X-ray sky, the uncertainties
are a factor ~2.5 higher.Comment: 13 pages. Accepted for publication in A&A
Strongly absorbed quiescent X-ray emission from the X-ray transient XTE J0421+56 (CI Cam) observed with XMM-Newton
We have observed the X-ray transient XTE J0421+56 in quiescence with
XMM-Newton. The observed spectrum is highly unusual being dominated by an
emission feature at ~6.5 keV. The spectrum can be fit using a partially covered
power-law and Gaussian line model, in which the emission is almost completely
covered (covering fraction of 0.98_{-0.06}^{+0.02}) by neutral material and is
strongly absorbed with an N_H of (5_{-2}^{+3}) x 10^{23} atom cm^{-2}. This
absorption is local and not interstellar. The Gaussian has a centroid energy of
6.4 +/- 0.1 keV, a width < 0.28 keV and an equivalent width of 940
^{+650}_{-460} eV. It can be interpreted as fluorescent emission line from
iron. Using this model and assuming XTE J0421+56 is at a distance of 5 kpc, its
0.5-10 keV luminosity is 3.5 x 10^{33} erg s^{-1}. The Optical Monitor onboard
XMM-Newton indicates a V magnitude of 11.86 +/- 0.03. The spectra of X-ray
transients in quiescence are normally modeled using advection dominated
accretion flows, power-laws, or by the thermal emission from a neutron star
surface. The strongly locally absorbed X-ray emission from XTE J0421+56 is
therefore highly unusual and could result from the compact object being
embedded within a dense circumstellar wind emitted from the supergiant B[e]
companion star. The uncovered and unabsorbed component observed below 5 keV
could be due either to X-ray emission from the supergiant B[e] star itself, or
to the scattering of high-energy X-ray photons in a wind or ionized corona,
such as observed in some low-mass X-ray binary systems.Comment: 8 pages, 4 postscript figures, accepted for publication in Astronomy
and Astrophysic
A BeppoSAX observation of the super-soft source CAL87
We report on a BeppoSAX Concentrator Spectrometer observation of the
super-soft source (SSS) CAL87. The X-ray emission in SSS is believed to arise
from nuclear burning of accreted material on the surface of a white dwarf (WD).
An absorbed blackbody spectral model gives a chi^2_v of 1.18 and a temperature
of 42 +/- ^13 _11 eV. However, the derived luminosity and radius are greater
than the Eddington limit and radius of a WD. Including an O viii edge at 0.871
keV gives a significantly better fit (at > 95% confidence) and results in more
realistic values of the source luminosity and radius. We also fit WD atmosphere
models to the CAL87 spectrum. These also give reasonable bolometric
luminosities and radii in the ranges 2.7-4.8 10^{36} erg/s and 8-20 10^7 cm,
respectively. These results support the view that the X-ray emission from CAL87
results from nuclear burning in the atmosphere of a WD.Comment: 4 pages. Accepted for publication in A&A (Letters
SNODGRASS Procedure A Versatile Technique for Various Types of Hypospadias Repair
There are about 156 operations described forhypospadias. The sheer number of proceduresindicates that no single procedure is standardfor hypospadias. We report our series of 20patients operated for hypospadias by Snodgrassprocedure. The technical details of the proce-dure and post-operative management protocolis discussed
- …