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Structural, optical and Carrier dynamics of self-assembled InGaN nanocolumns on Si(111)
No full textWe investigated the morphological, structural, optical, electrical and carrier relaxation dynamic changes on the self-assembled grown InGaN nanocolumns (NCs) directly on pSi(111) substrate at two different substrate temperature, namely 580 degrees C (A) and 500 C (B). The emission wavelength of comparably low temperature (LT) grown NCs was red-shifted from 3.2eV to 2.4eV. First observations on the charge carrier dynamics of these directly grown NCs show comparable broad excited state absorption (ESA) for LT gown NCs, which manifest bi-exponential decay due to the radiative defects generated during the coalescence of these NCs
Core-Shell Nanostructured Mixed Ligand Directed ZnO Nanoparticles with Excellent Structural, Optical and Electronic Properties for Application in Light Emitting Devices
No full textIn the present study, three salicylaldehyde based surface directing agents (L1, L2, L3) were synthesized from the same amine, but different aldehydes using condensation reaction for their employment as capping layer. Surface decorated zinc oxide (ZnO) nanoparticles (N1, N2 and N3) were then synthesized by wet chemical precipitation. The optical studies of mixed ligand directed ZnO nanoparticles were carried out using ultraviolet-visible (UV-Vis) absorption spectroscopy and photoluminescence techniques. The capping with ligand resulted in the successful amendment of surface of ZnO nanoparticles as it reduced the surface defects and controlled the defect-related emissions. The photoluminescence studies of surface modified ZnO nanoparticles N1, N2 and N3 were further carried out to check their binding ability. N2 and N3 exhibited selective behavior towards Al(III) and Cu(II) respectively with change in the fluorescence emission profile; however, no such change was noticed for other metal ions. An increased fluorescence intensity together with narrow spectrum is observed in N2 with the addition of Al(III) ion. The surface modified ZnO nanoparticles demonstrated semiconducting behavior when incorporated in Light emitting diode (LED) structure with steady-state current densities of up to 1.9A/cm(2)
Source apportionment of PM10 in Delhi, India using PCA/APCS, UNMIX and PMF
No full textSource apportionment of particulate matter (PM10) measurements taken in Delhi, India between January 2013 and June 2014 was carried out using two receptor models, principal component analysis with absolute principal component scores (PCA/APCS) and UNMIX. The results were compared with previous estimates generated using the positive matrix factorization (PMF) receptor model to investigate each model's source-apportioning capability. All models used the P-10 chemical composition (organic carbon (OC), elemental carbon (EC), water soluble inorganic ions (WSIC), and trace elements) for source apportionment. The average PM10 concentration during the study period was 249.7 +/- 103.9 mu g/m(3) (range: 61.4-584.8 mu g/m(3)). The UNMIX model resolved five sources (soil dust (SD), vehicular emissions (VE), secondary aerosols (SA), a mixed source of biomass burning (BB) and sea salt (SS), and industrial emissions (IE)). The PCA/APCS model also resolved five sources, two of which also included mixed sources (SD, VE, SD+SS, (SA+BB+SS) and 1E). The PMF analysis differentiated seven individual sources (SD, VE, SA, BB, SS, IE, and fossil fuel combustion (FFC)). All models identified the main sources contributing to PM10 emissions and reconfirmed that VE, SA, BB, and SD were the dominant contributors in Delhi
Grid Computing Research from India: A Bibliometric Assessment of Publications during 2008-2017
Get PDFThe paper examines quality and quantity of scientific research in India as reflected in publications output on grid computing on a series of bibliometric indicators. Data
were extracted from Scopus database consisting of 1340 publications in grid computing research from India in 10 years during 2008-17 citation impact of 4.33 citations per paper and international collaborative publication share of 12.16%. The paper profiles global publication output and share of 10 most productive countries in grid computing research, 15 most productive Indian organizations and 15 most productive authors on a series of indicators including publications output, number of citations, the relative citation index, citations per paper, h-index and share of
international collaborative papers during 2008-17. Computer science, among top 3 subjects, accounted for the largest publication share (90.15%), followed by engineering (26.79%) and mathematics (13.66%). The 15 most leading organizations
and authors together contributed 31.57% and 14.25% as their share of Indian publication output and 44.93% and 16.17% as their share of Indian citation output respectively during 2008-17. The most productive Indian organizations were Anna
University, Chennai (74 papers) and Thapar University, Patiala (48 papers) The most productive authors were I. Chana of Thapar University, Patiala (21 papers) and N.
Mukherjee of Jadavpur University, Kolkata (18 papers). The 15 most productive journals contributed 43.92% share to the Indian journal publication output during 2008-17. The most productive journals were Applied Engineering Research (16
publications), Journal of Grid Computing (14 publications) and Future Generation Computer Systems (13 publication
'Constitution of India': Preservation of original
No full textthe ‘Constitution of India’ was adopted
by the ‘Constituent Assembly’ on 26
November 1949 and came into force on
26 January 1950. It is the longest consti-
tution of any sovereign country in the
world written under the chairmanship of
B. R. Ambedkar. The original English
version of the ‘Cons
titution of India’ was
calligraphed by Prem Behari Narain Rai-
zada, which weighs ~13 kg and consists
of 221 calligraphed sheets of hand-made
parchment paper of size 45.7 cm ×
58.4 cm size. The calligraphed sheets
were decorated and illuminated by Nand
Lal Bose, depicting a journey from the
Mohen-jo-Daro and Vedic periods to the
Indian freedom movement. The Hindi
version of the ‘Constitution of India’–
comprising of 252 calligraphed sheets
and
weighing
about
14 kg – was
calligraphed by Basantrao Vaidya.
Interestingly, the Hindi version was cal-
ligraphed exactly as its English counter-
part which had been calligraphed by
Nand Lal Bose. Both documents have
been bound in first-class Morocco leather
embossed in gold. Both the original cal-
ligraphed copies of the ‘Constitution of
India’ are with the Parliament Library,
and have great autographic and historical
value as they contain the signatures of
the founding fathers of the Constitution.
In the mid-1980s, it was felt that these
historic volumes need to be preserved for
long periods, and therefore, require
appropriate preservation solutions. The
Parliament Library based on the scienti-
fic report – consisting the results of opti-
cal testing, brightness of the paper, and
gloss of the gold on the document –
Figure 1.
The original ‘Constitution of
India’ (Hindi and English versions) at Par-
liament Library, preserved in hermetically
sealed glass cases jointly developed by
CSIR-National Physical Laboratory, New
Delhi and Getty Conservation Institute,
USA.
obtained from the National Research
Laboratory for Conservation of Cultural
Property at Lucknow, concluded that
both volumes were in fairly sound condi-
tion. The Parliament Library then began
discussions with the National Physical
Laboratory (NPL), New Delhi for deve-
loping a case for preserving these docu-
ments. NPL developed the concept of
‘hermetically sealed glass cases’ for dis-
playing and storing these documents
under inert-gas atmospheres, so that the
Constitution can be prevented from oxi-
dation, microbiological deterioration and
air-pollution damages. The challenging
aspects of constructing such a display
case were to produce a hermetical seal
with (i) mechanical strength so as to
withstand changes in temperature and
atmospheric pressure, and (ii) durability
over several decades. After an extensive
literature search on the subject, the fol-
lowing three available methods for pro-
ducing hermetic seals were identified and
evaluated: silver-lead soldering, organic
sealants and mechanical seals using O-
rings. During 1988–89, NPL fabricated
cases using tempered glass and appropri-
ate sealants; however, these cases were
not accepted as the durability of the seal
over many years could not be assured.
In parallel, NPL al
so made efforts to
collaborate with various national and
international institutions for the deve-
lopment of hermetically sealed glass
cases. In 1992–93, NPL scientist Hari
Kishan visited Saint-Gobain Company,
Paris, France to develop hermetically
sealed glass cases. He was able to fabri-
cate two display cases – one sealed by
the soldering process and another sealed
with O-rings; however, they were also
not found suitable as long-term preserva-
tion of the Constitution could not be as-
sured.
In France, Hari Kishan also discussed
the issue with Georges Amsel (a special-
ist in conservation aspects in the famous
Louvre Museum, Paris) who suggested to
contact the Getty Conservation Institute
(GCI), USA, as in 1989 they had devel-
oped nearly similar cases for the storage
and display of the 27 Royal Mummies at
the Egyptian Museum in Cairo. In
November 1992, NPL contacted M. A.
Corzo (Director GCI) who readily agreed
to sign an agreement to jointly develop
‘hermetically sealed glass cases’ – a task
that was highly significant and challeng-
ing. The following are edited portions of
the agreement signed between NPL and
GCI in July 1993 regarding the fabrica-
tion of the display cases for the Constitu-
tion of India. ‘Two identical display
cases will be fabricated, one for the Eng-
lish and the other for the Hindi version of
the document. The internal volume of
each case will be 96,250 cm
3
, and the
dimensions of each case will be 55 cm
wide, 70 cm long, and 25 cm high. The
documents will be stored and maintained
at a relative humidity of 40–50% in a ni-
trogen atmosphere with an oxygen con-
centration of less than 1% by volume. A
special protective vault like room,
180 cm wide, 180 cm deep, and 305 cm
high will be constructed in the Parlia-
ment Library at the Parliament House for
display and storage of the documents.
The room will be climate controlled to
maintain a temperature of 20
±
2
°
C and a
30
±
5% relative humidity throughout the
year. It was also agreed that the cases
would be constructed at the GCI in the
United States and transported to the Par-
liament Library in New Delhi, where
they would be installed and jointly tested
by the GCI and the NPL.’
In March 1994, these cases were
installed successfully at the Parliament
Library (Figure 1). The cases were indi-
vidually mounted on polished stainless-
steel stands (approximately 1 m in
height) with varnished teak cabinet-work
that covers the metal frames of the cases.
The stands and cabinets were constructed
at NPL. A trace-oxygen analyser con-
nected to a data logger was installed in
each nitrogen filled case for monitoring
oxygen leakage into it during perfor-
mance evaluation. The cases were initial-
ly flushed with dry nitrogen, and oxygen
content was reduced to below 1000 ppm.
The performance of the cases was
accepted by both NPL and GCI. The per-
formance of these display cases is
annually evaluated by a team of NPL
scientists
Enhancement in thermoelectric performance of bulk CrSi2 dispersed with nanostructured SiGe nanoinclusions
No full textCrSi2 is recognized as potential thermoelectric material for mid-temperature energy generation applications owing to its high temperature chemical stability coupled with its cost-effective and non-toxic constituent elements. However, its thermoelectric performance has been reported to be limited owing to its high thermal conductivity, which is reported to dominate by its lattice counterpart. In the present studies, we realize a state-of-the-art (ZT)(max )similar to 0.32 at 673 K in an optimized nanocomposite composition of CrSi2/7.5 wt%SiGe, synthesized using spark plasma sintering of bulk CrSi2 dispersed with SiGe nanoparticles (crystallite size similar to 12 nm). The incorporation SiGe nanoparticles in bulk CrSi2 resulted in a significant reduction in its thermal conductivity owing to enhanced scattering of heat-carrying phonons by a high density of nanoscale interfaces. Concurrently, the power factor of the nanocomposite was also found to increase due to an increase its carrier concentration and mobility on dispersion of SiGe nanoparticles in the CrSi2 matrix. Thus, the favorable tuning of the electrical and thermal transport properties led to a ZT similar to 0.32 which is similar to 125% higher than its pristine counterpart. The as-synthesized pristine and nanocomposites were characterized employing X-ray diffraction and field emission scanning electron microscopy, based on which the enhancement in their thermoelectric properties has been discussed
Structural, magnetic and dielectric properties of Gd3+ substituted NiFe2O4 nanoparticles
No full textNiGdxFe2-xO4 nanoparticles with x = 0.0, 0.03, 0.05, 0.07, and 0.10 were synthesized by co-precipitation method and effect of Gd3+ substitution on various properties of nanocrystalline NiFe2O4 has been studied. Formation of single phase cubic mixed spinel structure is confirmed by X-ray diffraction and Raman spectroscopy and cations distribution has also been proposed from Rietveld refined data. Room temperature Mossbauer spectra showed two ferrimagnetic Zeeman sextets with one superparamagnetic doublet. Octahedral site occupancy of Gd3+ ions in these nanoparticles is suggested by Mossbauer parameters. Within the framework of X-ray photoelectron spectroscopy analysis, the ratio of cation concentration at tetrahedral and octahedral sites has been found to be consistent with proposed cation distribution. Magnetic measurements at room temperature exhibit the reduction in the saturation magnetization from 36 emu/gm to 4.9 emu/gm for x = 0.0 to 0.10 samples. The discrepancy in measured and calculated magnetic moment may be ascribed to the nonzero Yafet-Kittel angles of B site spins, which weaken A-B interaction. The coercivity decreases from 121 Oe to 48 Oe for x = 0.0 to 0.07 samples and again increases to 153 Oe for x = 0.10 sample. The degree of inversion calculated by Raman analysis varies with Gd3+ concentration which is supported by the variation of coercivity. The calculated spin numbers from electron spin resonance spectra decreases with Gd3+ doping which confirms the reduction in magnetization. Both dielectric constant and dielectric loss are found to decrease with the Gd3+ substitution because of the reduced hopping rate for Fe3+ at the octahedral sites in doped nanoparticles. Lower values of dielectric loss suggest that Gd3+ doped NiFe2O4 nanoparticles are suitable for high frequency microwave device applications
Facile Synthesis of Semiconducting Ultrathin Layer of Molybdenum Disulfide
No full textIn this paper, we have reported a simple and efficient method for the synthesis of uniform, highly conducting single or few layer molybdenum disulfide (MoS2) on large scale. Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM) have been used for the confirmation of mono or few layered nature of the as-synthesized MoS2 sheets. X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and Raman Spectroscopy have also been used to study the elemental, phase, and molecular composition of the sample. Optical properties of as-synthesized sample have been probed by measuring absorption and photoluminescence spectra which also compliment the formation of mono and few layers MoS2 Current-voltage (I-V) characteristics of as-synthesized sample in the pellet form reveal that MoS2 sheets have an ohmic character and found to be highly conducting. Besides characterizing the as-synthesized sample, we have also proposed the mechanism and factors which play a decisive role in formation of high quality MoS2 sheets
Temperature dependent Raman investigation of multiwall carbon nanotubes
No full textWe report anomalous observations in our investigations of the temperature dependent Raman spectroscopic measurement of multiwall carbon nanotubes. The Micro-Raman spectra were recorded with the laser source having 514.5 nm wavelength and within the temperature range of 80-440 K. The major Raman bands, the G and D band, are observed at 1584 and 1348 cm(-1), respectively, at ambient. The absence of the radial breathing mode confirms the multiwall nature of carbon nanotubes. It has been observed that with an increase in the temperature above 120 K, there is a shift in Raman bands towards the higher wave-number region. However, a drop in the G and D bands is observed from 80 to 120 K which was not observed for the second order band. Thereafter, all Raman modes exhibited mode hardening up to about 320 K followed by mild softening of the phonon modes. Linear temperature coefficients were found to have higher contribution to mode hardening as compared to higher order terms. Total anharmonicity estimation shows a predominant effect of the quasi-harmonic term as compared to the true anharmonic term
Swift heavy ion induced material modifications in Ba1-xSrxTiO3 ceramics as probed by temperature-dependent Raman spectroscopy
No full textEffect of 100MeV O8+ swift heavy ion (SHI) irradiation on phonon properties of Ba1-xSrxTiO3 (x=0.10, 0.15) ceramics are probed using Raman spectroscopy. Temperature-dependent Raman spectra in the range (100 degrees C to -190 degrees C) have been investigated, and deconvoluted Raman modes parameters are used in pristine and irradiated ceramics to understand the effect of ion irradiation on phonon modes. Raman bands are successfully identified that discern changes in band parameters during transition from cubic tetragonal orthorhombic rhombohedral phases. Raman spectral analysis reveals that the phase transition sequence remains almost unaffected after SHI irradiation; however, band parameters (band positions, band intensity, and line widths) of some phonon modes show changes after SHI irradiation. Results are interpreted in terms of grain reorientation and oxygen vacancies annihilation due to irradiation. Comparisons of ferroelectric properties in pristine and irradiated ceramics unambiguously reveal that surface or near surface material modifications influence the bulk properties of these polar materials