Effect of gamma irradiation on Schottky-contacted vertically aligned ZnO nanorod-based hydrogen sensorSapana Ranwa
, Surendra Singh Barala
, Mattia Fanetti
, Mahesh Kumar
, 2016, original scientific article
Abstract: We report the impact of gamma irradiation on the performance of a gold Schottky-contacted ZnO nanorod-based hydrogen sensor. RF-sputtered vertically aligned highly c-axis-oriented ZnO NRs were grown on Si(100) substrate. X-ray diffraction shows no significant change in crystal structure at low gamma doses from 1 to 5 kGy. As gamma irradiation doses increase to 10 kGy, the single crystalline ZnO structure converts to polycrystalline. The photoluminescence spectra also shows suppression of the near-band emission peak and the huge wide-band spectrum indicates the generation of structural defects at high gamma doses. At 1 kGy, the hydrogen sensor response was enhanced from 67% to 77% for 1% hydrogen in pure argon at a 150 °C operating temperature. However, at 10 kGy, the relative response decreases to 33.5%. High gamma irradiation causes displacement damage and defects in ZnO NRs, and as a result, degrades the sensor's performance as a result. Low gamma irradiation doses activate the ZnO NR surface through ionization, which enhances the sensor performance. The relative response of the hydrogen sensor was enhanced by ∼14.9% with respect to pristine ZnO using 1 kGy gamma ray treatment. © 2016 IOP Publishing Ltd.
Found in: osebi
Keywords: ZnO, nanorods, gamma irradiation, sensor
Published: 12.01.2017; Views: 3006; Downloads: 0
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Circadian rhythm of exhaled biomarkers in health and asthmaStephen Fowler
, Royston Goodacre
, David Ray
, Dave Singh
, Iain White
, John Blaikley
, Andrew Loudon
, Robert Maidstone
, Max Wilkinson
, Hannah Durrington
, 2019, original scientific article
Abstract: Circadian rhythms control many biological processes in the body in both health and disease. Greater understanding of diurnal variability in disease related biomarkers is crucial for their application in clinical practice and biomarkers of circadian rhythm are required to facilitate further research into disturbed chronicity. To determine if fractional exhaled nitric oxide and breath volatile biomarkers vary rhythmically during the day in healthy and asthmatic individuals.
Ten individuals with moderate, atopic asthma (on regular inhaled corticosteroids) and 10 healthy volunteers (all non-smokers) completed an overnight visit where their exhaled breath volatiles and forced exhaled nitric oxide levels were collected every 6 h. Breath volatiles were analysed using gas chromatography mass spectrometry, after trapping these volatiles on sorbent materials for thermal desorption.
Nine breath volatiles (including acetone and isoprene) exhibit diurnal variation across all individuals. Furthermore the circadian pattern of several VOCs is altered in individuals with asthma and fractional exhaled nitric oxide is rhythmic in asthma but not in healthy controls.
Markers of circadian rhythm can be identified in breath and may offer insight into circadian profiling to help treat disease. Additionally this work suggests that time of day must be controlled when designing future biomarker discovery studies. Further work is required with larger cohorts to validate and extend these findings.
Found in: osebi
Keywords: VOCs, breath, asthma, circadian
Published: 21.10.2019; Views: 2122; Downloads: 0
Fulltext (479,14 KB)
Chemical characterization of PM2.5 and source apportionment of organic aerosol in New Delhi, IndiaUrs Baltensperger
, Griša Močnik
, Surender Singh
, Suresh Tiwari
, Deewan Bisht
, Atul Srivastava
, Suneeti Mishra
, Navaneeth Thamban
, Ashutosh Shukla
, Vipul Lalchandani
, Francesco Canonaco
, Deepika Bhattu
, Anna Tobler
, Sachchida Tripathi
, J. G. Slowik
, André S. H. Prévôt
, 2020, original scientific article
Abstract: Delhi is one of the most polluted cities worldwide and a comprehensive understanding and deeper insight into the air pollution and its sources is of high importance. We report 5 months of highly time-resolved measurements of non-refractory PM2.5 and black carbon (BC). Additionally, source apportionment based on positive matrix factorization (PMF) of the organic aerosol (OA) fraction is presented. The highest pollution levels are observed during winter in December/January. During that time, also uniquely high chloride concentrations are measured, which are sometimes even the most dominant NR-species in the morning hours. With increasing temperature, the total PM2.5 concentration decreases steadily, whereas the chloride concentrations decrease sharply. The concentrations measured in May are roughly 6 times lower than in December/January. PMF analysis resolves two primary factors, namely hydrocarbon-like (traffic-related) OA (HOA) and solid fuel combustion OA (SFC-OA), and one or two secondary factors depending on the season. The uncertainties of the PMF analysis are assessed by combining the random a-value approach and the bootstrap resampling technique of the PMF input. The uncertainties for the resolved factors range from ±18% to ±19% for HOA, ±7% to ±19% for SFC-OA and ±6 % to ±11% for the OOAs. The average correlation of HOA with eBCtr is R2 = 0.40, while SFC-OA has a correlation of R2 = 0.78 with eBCsf. Anthracene (m/z 178) and pyrene (m/z 202) (PAHs) are mostly explained by SFC-OA and follow its diurnal trend (R2 = 0.98 and R2 = 0.97). The secondary oxygenated aerosols are dominant during daytime. The average contribution during the afternoon hours (1 pm–5 pm) is 59% to the total OA mass, with contributions up to 96% in May. In contrast, the primary sources are more important during nighttime: the mean nightly contribution (22 pm–3 am) to the total OA mass is 48%, with contributions up to 88% during some episodes in April.
Found in: osebi
Keywords: New Delhi, PM2.5, Source apportionment, PMF
Published: 20.07.2020; Views: 1440; Downloads: 0
Fulltext (4,71 MB)
A survey of communication systems and modulation schemes for spectrum sensing by cognitive radioRajan Gupta
, Mrinal Sharma
, Gagandeep Singh
, 2014, original scientific article
Abstract: The growth of wireless applications and spectral limitations are grave anxiety for the military service and for civilian communities. A particular spectrum task force set up by Federal Communications Commission discloses that in many bands spectrum access is a more important problem than physical scarcity of the
spectrum. This is in part because present systems use a procedure draw up in the1920s where different frequency bands are allocated to users or service providers, and licenses are needed to operate with those bands. To avail unused spectrum more efficiently in dynamic environments, we desire a communication system that
adapts to rapidly changing environmental conditions while ensuring that minimal or at least manageable interference is introduced to existing users. Such a technology is known as cognitive radio (CR) technology. Transform domain communication system (TDCS) and wavelet domain communication system (WDCS) have
been reported to have interference avoiding capability under hostile environmental conditions. Conventionally, the Pseudo Random phase vectors in TDCS and WDCS were generated by a maximum length binary Pseudo Random sequence, which allows only a relatively small amount of users in the systems. This paper reports a method of Digital modulations schemes (FSK, PSK, CSK) and communications systems (TDCS,WDCS) for efficient utilization of the spectrum in Cognitive radio.
Found in: osebi
Keywords: cognitive radio, TDCS, WDCS, spectrum sensing
Published: 02.04.2021; Views: 806; Downloads: 4
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Atmospheric peroxyacetyl nitrate (PAN)H. B. Singh
, A. Roiger
, Katja Džepina
, D. B. Millet
, Jiandong Mao
, F. Paulot
, R. M. Yantosca
, M. P. Sulprizio
, E. V. Fischer
, D. J. Jacob
, 2014, original scientific article
Abstract: Peroxyacetyl nitrate (PAN) formed in the atmospheric oxidation of non-methane volatile organic compounds (NMVOCs) is the principal tropospheric reservoir for nitrogen oxide radicals (NOx = NO + NO2). PAN enables the transport and release of NOx to the remote troposphere with major implications for the global distributions of ozone and OH, the main tropospheric oxidants. Simulation of PAN is a challenge for global models because of the dependence
of PAN on vertical transport as well as complex and uncertain NMVOC sources and chemistry. Here we use an improved representation of NMVOCs in a global 3-D chemical
transport model (GEOS-Chem) and show that it can simulate PAN observations from aircraft campaigns worldwide.
The immediate carbonyl precursors for PAN formation include acetaldehyde (44 % of the global source), methylglyoxal (30 %), acetone (7 %), and a suite of other isoprene and
terpene oxidation products (19 %). A diversity of NMVOC
emissions is responsible for PAN formation globally including isoprene (37 %) and alkanes (14 %). Anthropogenic
sources are dominant in the extratropical Northern Hemisphere outside the growing season. Open fires appear to play
little role except at high northern latitudes in spring, although
results are very sensitive to plume chemistry and plume rise.
Lightning NOx is the dominant contributor to the observed
PAN maximum in the free troposphere over the South Atlantic.
Found in: osebi
Keywords: peroxyacetyl nitrate, non-methane volatile organic compounds, global 3-D chemical transport model, GEOS-chem
Published: 11.04.2021; Views: 1060; Downloads: 0
Fulltext (4,98 MB)