398 research outputs found
Computation and verification of workpiece shape in electrochemical machining
This investigation was motivated by the need for accurate prediction of electrochemical machined surfaces relative to corresponding tool geometries for given sets of machining parameters. A mathematical model was formulated which simulates the electrochemical erosion achieved by primary current distribution under steady tool feed rate, but with correction for variable efficiency. The equations comprising the mathematical model were programmed for solution by a digital computer, using discrete steps and a quasi-steady approach. The model was not completely analytical; it utilised an empirical values for specific metal removal rates. The efficiency of machining with NaNO₃ electrolyte was estimated from experimental results of other investigators. To assess the validity of the model, drilling test runs were performed with tubular electrodes having two geometries at the leading edge of the tool. Work specimens were made out of EN58J stainless steel, both NaC1 and NaNO₃ electrolytes were used. The correlation between experimentally obtained drilled surfaces and the computer predicted surfaces were satisfactory, justifying the assumptions made during the development of the model and the numerical methods of the solution used. This investigation has provided a method which could be successfully employed to predict the electrochemically machined profiles relative to tool geometries. This undoubtedly helps the production engineer in achieving the desired tolerances of the finished component eliminating the high cost of trial and error techniques.This investigation was motivated by the need for accurate prediction of electrochemical machined surfaces relative to corresponding tool geometries for given sets of machining parameters. A mathematical model was formulated which simulates the electrochemical erosion achieved by primary current distribution under steady tool feed rate, but with correction for variable efficiency. The equations comprising the mathematical model were programmed for solution by a digital computer, using discrete steps and a quasi-steady approach. The model was not completely analytical; it utilised an empirical values for specific metal removal rates. The efficiency of machining with NaNO₃ electrolyte was estimated from experimental results of other investigators. To assess the validity of the model, drilling test runs were performed with tubular electrodes having two geometries at the leading edge of the tool. Work specimens were made out of EN58J stainless steel, both NaC1 and NaNO₃ electrolytes were used. The correlation between experimentally obtained drilled surfaces and the computer predicted surfaces were satisfactory, justifying the assumptions made during the development of the model and the numerical methods of the solution used. This investigation has provided a method which could be successfully employed to predict the electrochemically machined profiles relative to tool geometries. This undoubtedly helps the production engineer in achieving the desired tolerances of the finished component eliminating the high cost of trial and error techniques
Investigation of the agricultural resources in Sri Lanka
The author has identified the following significant results. Several in-house capabilities were developed. The facilities to prepare color composites of excellent quality were developed, using bulk B/W 70 mm transparencies or 1:1,000,000 positive transparencies. These color composites were studied through optical devices on light tables. A zoom transfer scope was also added, enabling direct transfer of LANDSAT composite data on to base maps
The Outstanding Decisions of the United States Supreme Court in 1954
We perform a kinematic and morphological analysis of 44 star-forming galaxies at z ̃ 2 in the COSMOS legacy field using near-infrared spectroscopy from Keck/MOSFIRE and F160W imaging from CANDELS/3D-HST as part of the ZFIRE survey. Our sample consists of cluster and field galaxies from 2.0 < z < 2.5 with K-band multi-object slit spectroscopic measurements of their Hα emission lines. Hα rotational velocities and gas velocity dispersions are measured using the Heidelberg Emission Line Algorithm (HELA), which compares directly to simulated 3D data cubes. Using a suite of simulated emission lines, we determine that HELA reliably recovers input S 0.5 and angular momentum at small offsets, but V 2.2/σ g values are offset and highly scattered. We examine the role of regular and irregular morphology in the stellar mass kinematic scaling relations, deriving the kinematic measurement S 0.5, and finding {log}({S}0.5)=(0.38+/- 0.07){log}(M/{M}☉ -10)+(2.04+/- 0.03) with no significant offset between morphological populations and similar levels of scatter (̃0.16 dex). Additionally, we identify a correlation between M ⋆ and V 2.2/σ g for the total sample, showing an increasing level of rotation dominance with increasing M ⋆, and a high level of scatter for both regular and irregular galaxies. We estimate the specific angular momenta (j disk) of these galaxies and find a slope of 0.36 ± 0.12, shallower than predicted without mass-dependent disk growth, but this result is possibly due to measurement uncertainty at M ⋆ < 9.5 However, through a Kolmogorov-Smirnov test we find irregular galaxies to have marginally higher j disk values than regular galaxies, and high scatter at low masses in both populations
Does the complex deformation of the Riemann equation exhibit shocks?
The Riemann equation , which describes a one-dimensional
accelerationless perfect fluid, possesses solutions that typically develop
shocks in a finite time. This equation is \cP\cT symmetric. A one-parameter
\cP\cT-invariant complex deformation of this equation,
( real), is solved exactly using the
method of characteristic strips, and it is shown that for real initial
conditions, shocks cannot develop unless is an odd integer.Comment: latex, 8 page
The MUSE-Wide Survey: Survey Description and First Data Release
We present the MUSE-Wide survey, a blind, 3D spectroscopic survey in the
CANDELS/GOODS-S and CANDELS/COSMOS regions. Each MUSE-Wide pointing has a depth
of 1 hour and hence targets more extreme and more luminous objects over 10
times the area of the MUSE-Deep fields (Bacon et al. 2017). The legacy value of
MUSE-Wide lies in providing "spectroscopy of everything" without photometric
pre-selection. We describe the data reduction, post-processing and PSF
characterization of the first 44 CANDELS/GOODS-S MUSE-Wide pointings released
with this publication. Using a 3D matched filtering approach we detected 1,602
emission line sources, including 479 Lyman- (Lya) emitting galaxies
with redshifts . We cross-match the emission line
sources to existing photometric catalogs, finding almost complete agreement in
redshifts and stellar masses for our low redshift (z < 1.5) emitters. At high
redshift, we only find ~55% matches to photometric catalogs. We encounter a
higher outlier rate and a systematic offset of z0.2 when
comparing our MUSE redshifts with photometric redshifts. Cross-matching the
emission line sources with X-ray catalogs from the Chandra Deep Field South, we
find 127 matches, including 10 objects with no prior spectroscopic
identification. Stacking X-ray images centered on our Lya emitters yielded no
signal; the Lya population is not dominated by even low luminosity AGN. A total
of 9,205 photometrically selected objects from the CANDELS survey lie in the
MUSE-Wide footprint, which we provide optimally extracted 1D spectra of. We are
able to determine the spectroscopic redshift of 98% of 772 photometrically
selected galaxies brighter than 24th F775W magnitude. All the data in the first
data release - datacubes, catalogs, extracted spectra, maps - are available on
the website https://musewide.aip.de. [abridged]Comment: 25 pages 15+1 figures. Accepted, A&A. Comments welcom
PT-symmetry breaking in complex nonlinear wave equations and their deformations
We investigate complex versions of the Korteweg-deVries equations and an Ito
type nonlinear system with two coupled nonlinear fields. We systematically
construct rational, trigonometric/hyperbolic, elliptic and soliton solutions
for these models and focus in particular on physically feasible systems, that
is those with real energies. The reality of the energy is usually attributed to
different realisations of an antilinear symmetry, as for instance PT-symmetry.
It is shown that the symmetry can be spontaneously broken in two alternative
ways either by specific choices of the domain or by manipulating the parameters
in the solutions of the model, thus leading to complex energies. Surprisingly
the reality of the energies can be regained in some cases by a further breaking
of the symmetry on the level of the Hamiltonian. In many examples some of the
fixed points in the complex solution for the field undergo a Hopf bifurcation
in the PT-symmetry breaking process. By employing several different variants of
the symmetries we propose many classes of new invariant extensions of these
models and study their properties. The reduction of some of these models yields
complex quantum mechanical models previously studied.Comment: 50 pages, 39 figures (compressed in order to comply with arXiv
policy; higher resolutions maybe obtained from the authors upon request
A study of lipid profile and glycemic status in patients with chronic kidney disease of unknown etiology in Sri Lanka
Background: Dyslipidemia and impaired glucose tolerance are common complications of chronic kidney disease (CKD) and are responsible for increased cardiovascular risk. Studies on lipid profile and glycemic status in CKD of unknown origin (CKDu) are scarce. The objective of this study was to evaluate the lipid profile and glycemic status of the patients with CKDu and to aid in preventing morbidity and mortality.Methods: The descriptive, cross sectional study was conducted in a rural CKDu endemic area, Girandurukotte. Data was collected from February 2018 to June 2019. For the diagnosis of CKDu, history and clinical features with supportive biochemical, renal biopsy and radiological evidence were taken as criteria. Blood samples were taken for serum creatinine, lipid profile and HbA1C. Already diagnosed patients with diabetes mellitus and dyslipidemia were excluded.Results: A total of 168 patients within the age range of 32-66 years (mean 50.3±7.7) were participated. There were 106 males (63%) 46.4% were farmers. Majority of the patients (65.5%) had normal body mass index (BMI) (mean 22.9 kg/m2, normal range 18.5-23.5%) followed by overweight (23.5-30 kg/m2) in 55 (32.7%) patients. The prevalence of dyslipidemia in CKDu was found to be 55.9%. Majority of the abnormality was seen in the HDL group with 68 (40.5%) patients having low HDL cholesterol (mean 44.7 mg/dl, SD=12.3). There was a significant rise in the serum triglyceride concentration (>150 mg/dl) in 53 (31.5%) (mean 152.4 mg/dl, SD=73.5) and total cholesterol (>200 mg/dl) in 30 (18%) patients (mean 182 mg/dl, SD=36.9). LDL cholesterol abnormality (>130 mg/dl) was seen in only 9 patients (mean 88.7 7658mg/dl, SD=25.4). From the total, 144 (85.7%) patients had abnormal HbA1C levels; 27 (16.1%) patients had HbA1C levels between 5.7% and 6.4% (pre-diabetes), and 117 (69.6%) patients had HbA1C level more than 6.5% (diabetes mellitus). There was no statistically significant association between HbA1C levels and BMI (p=0.29) or HbA1C and lipid abnormalities (p=0.32)Conclusions: The high prevalence of dyslipidemia, pre-diabetes and diabetes mellitus in patients with CKDu may accelerate the progression of chronic kidney disease and increase the risk of cardiovascular disease. Early detection, initiation of appropriate medication and early referral to the expertise will ameliorate morbidity and mortality.
Solvable simulation of a double-well problem in PT symmetric quantum mechanics
Within quantum mechanics which works with parity-pseudo-Hermitian
Hamiltonians we study the tunneling in a symmetric double well formed by two
delta functions with complex conjugate strengths. The model is exactly solvable
and exhibits several interesting features. Besides an amazingly robust absence
of any PT symmetry breaking, we observe a quasi-degeneracy of the levels which
occurs all over the energy range including the high-energy domain. This pattern
is interpreted as a manifestation of certain "quantum beats".Comment: 12 pages incl. 7 figure
A massive, quiescent galaxy at redshift of z=3.717
In the early Universe finding massive galaxies that have stopped forming
stars present an observational challenge as their rest-frame ultraviolet
emission is negligible and they can only be reliably identified by extremely
deep near-infrared surveys. These have revealed the presence of massive,
quiescent early-type galaxies appearing in the universe as early as z2,
an epoch 3 Gyr after the Big Bang. Their age and formation processes have now
been explained by an improved generation of galaxy formation models where they
form rapidly at z3-4, consistent with the typical masses and ages derived
from their observations. Deeper surveys have now reported evidence for
populations of massive, quiescent galaxies at even higher redshifts and earlier
times, however the evidence for their existence, and redshift, has relied
entirely on coarsely sampled photometry. These early massive, quiescent
galaxies are not predicted by the latest generation of theoretical models.
Here, we report the spectroscopic confirmation of one of these galaxies at
redshift z=3.717 with a stellar mass of 1.710 M whose
absorption line spectrum shows no current star-formation and which has a
derived age of nearly half the age of the Universe at this redshift. The
observations demonstrates that the galaxy must have quickly formed the majority
of its stars within the first billion years of cosmic history in an extreme and
short starburst. This ancestral event is similar to those starting to be found
by sub-mm wavelength surveys pointing to a possible connection between these
two populations. Early formation of such massive systems is likely to require
significant revisions to our picture of early galaxy assembly.Comment: 6 pages, 7 figures. This is the final preprint corresponding closely
to the published version. Uploaded 6 months after publication in accordance
with Nature polic
TMTDyn: A Matlab package for modeling and control of hybrid rigid–continuum robots based on discretized lumped systems and reduced-order models
A reliable, accurate, and yet simple dynamic model is important to analyzing, designing, and controlling hybrid rigid–continuum robots. Such models should be fast, as simple as possible, and user-friendly to be widely accepted by the evergrowing robotics research community. In this study, we introduce two new modeling methods for continuum manipulators: a general reduced-order model (ROM) and a discretized model with absolute states and Euler–Bernoulli beam segments (EBA). In addition, a new formulation is presented for a recently introduced discretized model based on Euler–Bernoulli beam segments and relative states (EBR). We implement these models in a Matlab software package, named TMTDyn, to develop a modeling tool for hybrid rigid–continuum systems. The package features a new high-level language (HLL)
text-based interface, a CAD-file import module, automatic formation of the system equation of motion (EOM) for different modeling and control tasks, implementing Matlab C-mex functionality for improved performance, and modules for static and linear modal analysis of a hybrid system. The underlying theory and software package are validated for modeling experimental results for (i) dynamics of a continuum appendage, and (ii) general deformation of a fabric sleeve worn by a rigid link pendulum. A comparison shows higher simulation accuracy (8–14% normalized error) and numerical robustness of the ROM model for a system with a small number of states, and computational efficiency of the EBA model with
near real-time performances that makes it suitable for large systems. The challenges and necessary modules to further automate the design and analysis of hybrid systems with a large number of states are briefly discussed
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