A cosmological model with a specific form of the Hubble parameter is constructed in a flat homogeneous, and isotropic background in the framework of f(R,T) gravity, where R is the scalar curvature ...and T is the trace of the stress-energy-momentum tensor. The proposed functional form of the Hubble parameter is taken in such a way that it fulfills the successful bouncing criteria to find the solution of the gravitational field equations provided the Universe is free from initial singularity. The various constraints on the parameters are involved in the functional form of the Hubble parameter which are analyzed in detail. In addition, we explore physical and geometrical consequences of the model based on the imposed constraints. Furthermore, we demonstrate the bouncing scenario which is realized in our model with some particular values of the model parameters. As a result, we find that all of the necessary conditions are satisfied for a successful bouncing model.
We investigate the magnetic field and temperature dependence of the single-electron spin lifetime in silicon quantum dots and find a lifetime of 2.8 ms at a temperature of 1.1 K. We develop a model ...based on spin-valley mixing and find that Johnson noise and two-phonon processes limit relaxation at low and high temperature, respectively. We also investigate the effect of temperature on charge noise and find a linear dependence up to 4 K. These results contribute to the understanding of relaxation in silicon quantum dots and are promising for qubit operation at elevated temperatures.
In the present paper, transparent and non-toxic Bi2O3-B2O3 glasses doped with BaO have been prepared by the authors which may replace the standard radiation shielding concretes and lead based ...commercial glasses for gamma ray shielding applications. The effects of BaO on the structural and optical properties of the prepared glass system have been investigated by Raman, FTIR and UV–Visible techniques. It has been observed that barium plays the role of a modifier and it is responsible for conversion of triangular BO3 units to tetrahedral BO4 units along with formation of non-bridging oxygen and increase in ionic character. It also improves the radiation shielding abilities of the glass system. The mass attenuation coefficients for gamma-ray photons at 662 keV energy by using 137Cs radioactive source have been measured by employing narrow beam transmission geometry. This was accompanied by theoretical computation of mass attenuation coefficients in the wide photon energy range varying from 1 keV to 100 GeV. It has been found that values of mean free path and tenth value layer decrease whereas, density and effective atomic number increase with the increase of barium oxide content. As compared with barite concrete and commercial shielding glass RS-360, our prepared Bi2O3 - BaO - B2O3 glasses have shown better gamma ray shielding properties. This implies that the prepared glass system is a better gamma ray absorber and it has the potential for use in gamma-ray shielding applications.
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•Glass samples of the composition 65Bi2O3-xBaO-(35-x)B2O3 where x = 0 to 10 wt% have been prepared by melt-quenching technique.•The addition of BaO in the glass system improves the gamma radiation shielding properties.•Transparent and environmental friendly nature of glasses system make them practical solution for gamma ray shielding applications.
► LAS rebars corrode 2–3 times slower than PCS in concrete pore solution and mortars. ► Raman and XRD studies show that goethite and maghemite phases of rusts formed on LAS. ► On PCS unstable phases ...of lepidocrocite and akaganite are formed. ► EIS confirms more stable rust on LAS than on PCS. ► A model is proposed to explain formation of passive film on surface of steels.
Correlation of corrosion characteristics and nature of rusts on low alloy (LA) and plain carbon (PC) steels exposed in simulated concrete pore solution of different pH is studied. Rusts formed under wet/dry conditions are examined by Raman spectroscopy and X-ray diffraction. LA rust is more adherent compared to PC as confirmed by measurement of weight in gain and electrochemical studies. EIS results show improvement in protective properties of steels with passage of time. Both steels are found prone to pitting attack in chloride contaminated pore solution. Rebars embedded in concrete exhibit same trend as recorded in solution exposure tests.
The present work is aimed at incorporating the heavy metal oxide ‘bismuth oxide’ in lithium-borate glass system and studying its effect on the glass structure, durability, gamma-ray and neutron ...shielding ability. The density, XRD, Raman, FTIR, and UV–Visible spectroscopic techniques assisted in understanding the structure of ternary bismuth‑lithium-borate glass system. It has been found that the glass samples are of amorphous nature and structure is mainly built up of BO4, BO3, BiO6, BiO3 units and non-bridging oxygens (NBOs). Bismuth-incorporated glasses possess improved water resistance ability. The gamma-ray shielding ability was evaluated from mass attenuation coefficient, mean free path, tenth value layer and effective atomic number and it was found to be improved with the addition of bismuth oxide content. The exposure build up factor was also computed to account for the secondary photons and multiple Compton scattering. The removal cross section for fast neutrons (∑R) was also evaluated to study the neutron shielding ability of our prepared glasses. The glasses were also compared with barite concrete and commercial shielding glass RS 360 for gamma-rays and, with H2O, graphite, ordinary and hematite-serpentine concrete for checking neutrons shielding ability. It was observed that our glasses have better radiation shielding properties than the compared materials. In the light of these obtained results, it was concluded that the prepared bismuth‑lithium-borate glass system can be utilised for radiation shielding applications.
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•Bi2O3-Li2O-B2O3 glasses have good gamma and neutron shielding properties which make them practical solutions for radiation shielding applications.•Bismuth changes its role from modifier to former which results in increase of glass network stability and durability.•EBF was computed to study the effect of multiple scattering of photons due to Compton scattering.
We report a new synthesis of best estimates of the inputs of fixed nitrogen to the world ocean via atmospheric deposition and compare this to fluvial inputs and dinitrogen fixation. We evaluate the ...scale of human perturbation of these fluxes. Fluvial inputs dominate inputs to the continental shelf, and we estimate that about 75% of this fluvial nitrogen escapes from the shelf to the open ocean. Biological dinitrogen fixation is the main external source of nitrogen to the open ocean, i.e., beyond the continental shelf. Atmospheric deposition is the primary mechanism by which land‐based nitrogen inputs, and hence human perturbations of the nitrogen cycle, reach the open ocean. We estimate that anthropogenic inputs are currently leading to an increase in overall ocean carbon sequestration of ~0.4% (equivalent to an uptake of 0.15 Pg C yr−1 and less than the Duce et al. (2008) estimate). The resulting reduction in climate change forcing from this ocean CO2 uptake is offset to a small extent by an increase in ocean N2O emissions. We identify four important feedbacks in the ocean atmosphere nitrogen system that need to be better quantified to improve our understanding of the perturbation of ocean biogeochemistry by atmospheric nitrogen inputs. These feedbacks are recycling of (1) ammonia and (2) organic nitrogen from the ocean to the atmosphere and back, (3) the suppression of nitrogen fixation by increased nitrogen concentrations in surface waters from atmospheric deposition, and (4) increased loss of nitrogen from the ocean by denitrification due to increased productivity stimulated by atmospheric inputs.
Key Points
A new estimate of total atmospheric fixed nitrogen inputs to the ocean (39 Tg N yr−1) and its spatial distribution is presented
The effects of atmospheric deposition on the oceans are estimated as an increase of productivity equivalent to 0.15 Pg C yr−1
Four key uncertainties in these estimates are identified
FLRW cosmology with EDSFD parametrization Singh, J. K.; Nagpal, Ritika
European physical journal. C, Particles and fields,
04/2020, Letnik:
80, Številka:
4
Journal Article
Recenzirano
Odprti dostop
In this paper, we study a cosmological model in the background of Friedmann–Lemaitre–Robertson–Walker (FLRW) space time by assuming an appropriate parametrization in the form of a differential ...equation in terms of energy density of scalar field
ρ
ϕ
, which is defined as Energy Density Scalar Field Differential equation (EDSFD) parametrization. The EDSFD parametrization leads to a required phase transition from early deceleration to present cosmic acceleration. This parametrization is used to reconstruct the equation of state parameter
ω
ϕ
in terms of redshift
z
i.e.
ω
ϕ
(
z
)
to examine the evolutionary history of the universe in a flat FLRW space time. Here, we constrain the model parameter using the various observational datasets of Hubble parameter
H
(
z
) , latest Union 2.1 compilation dataset
SNeIa
,
BAO
, joint dataset
H
(
z
)
+
S
N
e
I
a
and
H
(
z
)
+
S
N
e
I
a
+
B
A
O
for detail analysis of the behavior of physical parameters and we find its best fit present value. Also, we discuss the dynamics of reheating phase after inflation, analyse the behaviors of the physical features using some diagnostic tools, and examine the viability of our parametric model.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This paper reviews dissimilatory nitrate reduction to ammonium (DNRA) in soils - a newly appreciated pathway of nitrogen (N) cycling in the terrestrial ecosystems. The reduction of NO3− occurs in two ...steps; in the first step, NO3− is reduced to NO2−; and in the second, unlike denitrification, NO2− is reduced to NH4+ without intermediates. There are two sets of NO3−/NO2− reductase enzymes, i.e., Nap/Nrf and Nar/Nir; the former occurs on the periplasmic-membrane and energy conservation is respiratory via electron-transport-chain, whereas the latter is cytoplasmic and energy conservation is both respiratory and fermentative (Nir, substrate-phosphorylation). Since, Nir catalyzes both assimilatory- and dissimilatory-nitrate reduction, the nrfA gene, which transcribes the NrfA protein, is treated as a molecular-marker of DNRA; and a high nrfA/nosZ (N2O-reductase) ratio favours DNRA. Recently, several crystal structures of NrfA have been presumed to producee N2O as a byproduct of DNRA via the NO (nitric-oxide) pathway. Meta-analyses of about 200 publications have revealed that DNRA is regulated by oxidation state of soils and sediments, carbon (C)/N and NO2−/NO3− ratio, and concentrations of ferrous iron (Fe2+) and sulfide (S2−). Under low-redox conditions, a high C/NO3− ratio selects for DNRA while a low ratio selects for denitrification. When the proportion of both C and NO3− are equal, the NO2−/NO3− ratio modulates partitioning of NO3−, and a high NO2−/NO3− ratio favours DNRA. A high S2−/NO3− ratio also promotes DNRA in coastal-ecosystems and saline sediments. Soil pH, temperature, and fine soil particles are other factors known to influence DNRA. Since, DNRA reduces NO3− to NH4+, it is essential for protecting NO3− from leaching and gaseous (N2O) losses and enriches soils with readily available NH4+-N to primary producers and heterotrophic microorganisms. Therefore, DNRA may be treated as a tool to reduce ground-water NO3− pollution, enhance soil health and improve environmental quality.
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•DNRA is a novel and shortest biological pathway of N-cycling in terrestrial ecosystems where NO3- is reduced to NH4+ in soils•This pathway has potential to reduce N2O emissions and protect NO3- from leaching losses•It outcompetes the denitrification process under limited NO3- availability in the system•It enriches soil with NH4+-N and make available to primary producers as N-fertilizer•Meta-analyse revealed that DNRA is mainly regulated by C/N ratio, NO2- / NO3- ratio and S2-
This investigation addresses the effect of surface nanostructure developed through ultrasonic shot peening (USSP) on corrosion behavior of 7075 aluminum alloy. USSP develops surface nanostructure, ...induces severe plastic deformation, refines grain size up to certain depth and imparts compressive residual stress in the surface region. The sample USSPed for 15 s (USSP 15) exhibited lower current density (0.564 μA/cm2) and higher corrosion potential (−0.695 V) as compared with that of the un-USSP specimen with 1.269 μA/cm2 and -0.839 V respectively. The enhancement in corrosion resistance of USSPed sample is due to rapid development of uniform, homogeneous and effective passive layer on the nano-structured surface coupled with refinement of the coarse precipitates. Also, there is optimum combination of surface roughness, compressive residual stress, and dislocation density in the surface region to produce highest corrosion resistance in the USSP 15 condition.
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•Ultrasonic shot peening successfully induces nanostructure layer in surface region.•Refinement of second phase reduced the galvanic coupling.•Nanostructure causes uniform, homogeneous and effective passive layer formation.•Increased surface roughness leads to deterioration in corrosion resistance.•Combination of several factors governs the corrosion behavior.
•We evaluated best management practices to improve crop productivity.•Zero-till based cropping most energy efficient and water saving.•Substituting wheat with maize-potato in winter more productive ...and remunerative.•Higher cropping intensity with diversification is important for sustainability.
Cereal production systems in the Eastern Indo-Gangetic Plains (E-IGP) are traditional, with low yield and low farm income, and they have largely missed out on the benefits of the Green Revolution. To enhance productivity, alleviate environmental and management constraints, and enhance farmers’ income in the rice–wheat cropping system of the E-IGP, new approaches that are more productive and sustainable need to be developed. Conservation agriculture (CA) together with best management practices (BMP) used in other parts of the IGP offer potential to be extended in the E-IGP. A study was conducted during 2009–2011 with the objective of evaluating a range of approaches for enhancing the productivity and economic returns of rice-wheat-based cropping systems in the E-IGP. Four scenarios (S) involving a range of crop and resource management practices with crop rotations (including legumesθ) were compared with one another, of which Scenario 1 represented farmers practice. The lowest yields of wheat (2.78–3.07tha−1) and rice (4.38–6.52tha−1) were recorded with the current farmers’ practices (S1), consisting of intensive tillage (wet tillage or puddling in rice and dry tillage in wheat) followed by inefficient crop establishment practices (transplanting in rice and broadcasting in wheat) with complete removal of crop residues. Avoiding tillage in wheat (S2) and including mungbean increased the yields of wheat and the succeeding rice crop by 21–31% and 5–10%, respectively. The yields of wheat and rice increased further by 46–54% and by 10–24%, respectively, with the inclusion of more CA components (S3). In S4, which was designed to include higher cropping intensity and diversification (potato and maize–rice–cowpea rotation) with CA components, 144–163% higher rice equivalent system productivity was attained. Irrigation water productivity in the winter season increased by 39–48% in S2, by 72–84% in S3, and by 137–138% in S4 when compared to S1 while in the rainy season it increased by 14–18% in S2, by 46–56% in S3, and by 71–88% in S4. S4 had the highest net returns ($2855–4193ha−1), followed by S3 ($1883–3246ha−1). However, the system’s highest benefit–cost ratio was recorded with S3 due to its lower cost of crop cultivation. The results of this study showed that there is enormous untapped potential to improve overall system performance through the adoption of CA in integration with BMP in the intensive system of the E-IGP of India.
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