20 research outputs found
Optimization of production parameters in sms plant, welspun
Welspun Steel Limited produces steel billets of various dimensions 30% of which are sent to produce Re-bars. WSL’s TMT is presently the second best TMT available for business and industry based constructions in the market after JINDAL’s. As per the Welspun Fellowship Program, the student has undergone a training period alongside doing the project in optimizing the production of the WSL plant in Anjar, Gujarat. The thesis details the findings and discusses the current issues that a typical secondary steel industry, namely WSL, is facing along with some theoretical suggestions. DRI + Scrap is the raw material in the secondary steel production in WSL. A conclusive study is conducted to check the tap times, just by melting DRI without the steel scrap. The results indicate a success and so a new method, posing a new set of problems though, to be experimented and researched on. Finally, sets of loopholes, neglected zones and bottlenecks have been identified all through the process of steel making and casting. Suggestions have been insisted and some of them were effectively implemented
NanoprismMosaic
The picture here represents a false-colored scanning electron microscope image of gold nanoprisms, each only a few nanometers thick, but sub-micron sized in lateral dimensions. The nanoprisms, each colored differently, look like chards of painted glass in a mosaic. Ideally, a successful synthesis would yield nanoprisms that are identical in shape and size, but a “bad” day in lab can occasionally result in something truly beautiful.Ope
GaAs on Si epitaxy by aspect ratio trapping: analysis and reduction of defects propagating along the trench direction
The Aspect Ratio Trapping technique has been extensively evaluated for improving the quality of III-V heteroepitaxial films grown on Si, due to the potential for terminating defects at the sidewalls of SiO2 patterned trenches that enclose the growth region. However, defects propagating along the trench direction cannot be effectively confined with this technique. We studied the effect of the trench bottom geometry on the density of defects of GaAs fins, grown by metal-organic chemical vapor deposition on 300 mm Si (001) wafers inside narrow (<90 nm wide) trenches. Plan view and cross sectional Scanning Electron Microscopy and Transmission Electron Microscopy, together with High Resolution X-Ray Diffraction, were used to evaluate the crystal quality of GaAs. The prevalent defects that reach the top surface of GaAs fins are {111} twin planes propagating along the trench direction. The lowest density of twin planes, 8 108 cm 2, was achieved on “V” shaped bottom trenches, where GaAs nucleation occurs only on {111} Si planes, minimizing the interfacial energy and preventing the formation of antiphase boundaries
Chemical Mechanical Planarization for Ta-based Superconducting Quantum Devices
We report on the development of a chemical mechanical planarization (CMP)
process for thick damascene Ta structures with pattern feature sizes down to
100 nm. This CMP process is the core of the fabrication sequence for scalable
superconducting integrated circuits at 300 mm wafer scale. This work has
established the elements of the various CMP-related design rules that can be
followed by a designer for the layout of circuits that include Ta-based
coplanar waveguide resonators, capacitors, and interconnects for tantalum-based
qubits and single flux quantum (SFQ) circuits. The fabrication of these
structures utilizes 193 nm optical lithography, along with 300 mm process tools
for dielectric deposition, reactive ion etch, wet-clean, CMP and in-line
metrology, all tools typical for a 300 mm wafer CMOS foundry. Process
development was guided by measurements of physical and electrical
characteristics of the planarized structures. Physical characterization such as
atomic force microscopy across the 300 mm wafer surface showed local topography
was less than 5 nm. Electrical characterization confirmed low leakage at room
temperature, and less than 12% within wafer sheet resistance variation, for
damascene Ta line-widths ranging from 100 nm to 3 {\mu}m. Run-to-run
reproducibility was also evaluated. Effects of process integration choices
including deposited thickness of Ta are discussed.Comment: 31 pages, 16 figure
Engineering of Niobium Surfaces Through Accelerated Neutral Atom Beam Technology For Quantum Applications
A major roadblock to scalable quantum computing is phase decoherence and
energy relaxation caused by qubits interacting with defect-related two-level
systems (TLS). Native oxides present on the surfaces of superconducting metals
used in quantum devices are acknowledged to be a source of TLS that decrease
qubit coherence times. Reducing microwave loss by surface engineering (i.e.,
replacing uncontrolled native oxide of superconducting metals with a thin,
stable surface with predictable characteristics) can be a key enabler for
pushing performance forward with devices of higher quality factor. In this
work, we present a novel approach to replace the native oxide of niobium
(typically formed in an uncontrolled fashion when its pristine surface is
exposed to air) with an engineered oxide, using a room-temperature process that
leverages Accelerated Neutral Atom Beam (ANAB) technology at 300 mm wafer
scale. This ANAB beam is composed of a mixture of argon and oxygen, with
tunable energy per atom, which is rastered across the wafer surface. The
ANAB-engineered Nb-oxide thickness was found to vary from 2 nm to 6 nm
depending on ANAB process parameters. Modeling of variable-energy XPS data
confirm thickness and compositional control of the Nb surface oxide by the ANAB
process. These results correlate well with those from transmission electron
microscopy and X-ray reflectometry. Since ANAB is broadly applicable to
material surfaces, the present study indicates its promise for modification of
the surfaces of superconducting quantum circuits to achieve longer coherence
times.Comment: 22 pages, 7 figures, will be submitted to Superconductor Science and
Technology Special Focus Issue Journa
XQR-30: Black Hole Masses and Accretion Rates of 42 z>6 Quasars
We present bolometric luminosities, black hole masses and Eddington ratios
for 42 luminous quasars at z>6 using high signal-to-noise ratio VLT/X-Shooter
spectra, acquired in the enlarged ESO Large Programme XQR-30. In particular, we
derive bolometric luminosities from the rest-frame 3000 A, luminosities using a
bolometric correction from the literature, and the black hole masses by
modelling the spectral regions around the CIV 1549A and the MgII 2798A emission
lines, with scaling relations calibrated in the local universe. We find that
the black hole masses derived from both emission lines are in the same range,
and the scatter of the measurements agrees with expectations from the scaling
relations. The MgII-derived masses are between ~(0.8-12) x 10^9 Msun, and the
derived Eddington ratios are within ~0.13-1.73, with a mean (median) of 0.84
(0.72). By comparing the total sample of quasars at z>5.8, from this work and
from the literature, to a bolometric luminosity distribution-matched sample at
z~1.5, we find that quasars at high redshift host slightly less massive black
holes which accrete slightly more rapidly than at lower-z, with a difference in
the mean Eddington ratios of the two samples of ~0.27, in agreement with recent
literature work.Comment: 9 pages; 5 figures; accepted for publication in A&
XQR-30: The ultimate XSHOOTER quasar sample at the reionization epoch
The final phase of the reionization process can be probed by rest-frame UV absorption spectra of quasars at z ≳ 6, shedding light on the properties of the diffuse intergalactic medium within the first Gyr of the Universe. The ESO Large Programme 'XQR-30: the ultimate XSHOOTER legacy survey of quasars at z ≃ 5.8-6.6' dedicated ∼250 h of observations at the VLT to create a homogeneous and high-quality sample of spectra of 30 luminous quasars at z ∼6, covering the rest wavelength range from the Lyman limit to beyond the Mg ii emission. Twelve quasar spectra of similar quality from the XSHOOTER archive were added to form the enlarged XQR-30 sample, corresponding to a total of ∼350 h of on-source exposure time. The median effective resolving power of the 42 spectra is R ≃ 11 400 and 9800 in the VIS and NIR arm, respectively. The signal-to-noise ratio per 10 km s-1 pixel ranges from ∼11 to 114 at λ ≃ 1285 Å rest frame, with a median value of ∼29. We describe the observations, data reduction, and analysis of the spectra, together with some first results based on the E-XQR-30 sample. New photometry in the H and K bands are provided for the XQR-30 quasars, together with composite spectra whose characteristics reflect the large absolute magnitudes of the sample. The composite and the reduced spectra are released to the community through a public repository, and will enable a range of studies addressing outstanding questions regarding the first Gyr of the Universe
XQR-30: the ultimate XSHOOTER quasar sample at the reionization epoch
The final phase of the reionization process can be probed by rest-frame UV
absorption spectra of quasars at z>6, shedding light on the properties of the
diffuse intergalactic medium within the first Gyr of the Universe. The ESO
Large Programme "XQR-30: the ultimate XSHOOTER legacy survey of quasars at
z~5.8-6.6" dedicated ~250 hours of observations at the VLT to create a
homogeneous and high-quality sample of spectra of 30 luminous quasars at z~6,
covering the rest wavelength range from the Lyman limit to beyond the MgII
emission. Twelve quasar spectra of similar quality from the XSHOOTER archive
were added to form the enlarged XQR-30 sample, corresponding to a total of ~350
hours of on-source exposure time. The median effective resolving power of the
42 spectra is R~11400 and 9800 in the VIS and NIR arm, respectively. The
signal-to-noise ratio per 10 km/s pixel ranges from ~11 to 114 at \AA rest frame, with a median value of ~29. We describe the
observations, data reduction and analysis of the spectra, together with some
first results based on the E-XQR-30 sample. New photometry in the H and K bands
are provided for the XQR-30 quasars, together with composite spectra whose
characteristics reflect the large absolute magnitudes of the sample. The
composite and the reduced spectra are released to the community through a
public repository, and will enable a range of studies addressing outstanding
questions regarding the first Gyr of the Universe.Comment: 21 pages, 10 figures. Revised version resubmitted to MNRAS after
minor referee repor