8,165 research outputs found
Irradiation of benzene molecules by ion-induced and light-induced intense fields
Benzene, with its sea of delocalized -electrons in the valence orbitals,
is identified as an example of a class of molecules that enable establishment
of the correspondence between intense ion-induced and laser-light-induced
fields in experiments that probe ionization dynamics in temporal regimes
spanning the attosecond and picosecond ranges.Comment: 4 ps figure
Forbidden oxygen lines at various nucleocentric distances in comets
To study the formation of the [OI] lines - i.e., 5577 A (the green line),
6300 A and 6364 A (the two red lines) - in the coma of comets and to determine
the parent species of the oxygen atoms using the green to red-doublet emission
intensity ratio (G/R ratio) and the lines velocity widths. We acquired at the
ESO VLT high-resolution spectroscopic observations of comets C/2002 T7
(LINEAR), 73P-C/Schwassmann-Wachmann 3, 8P/Tuttle, and, 103P/Hartley 2 when
they were close to the Earth (< 0.6 au). Using the observed spectra, we
determined the intensities and the widths of the three [OI] lines. We have
spatially extracted the spectra in order to achieve the best possible
resolution of about 1-2", i.e., nucleocentric projected distances of 100 to 400
km depending on the geocentric distance of the comet. We have decontaminated
the [OI] green line from C2 lines blends. It is found that the observed G/R
ratio on all four comets varies as a function of nucleocentric projected
distance. This is mainly due to the collisional quenching of O(1S) and O(1D) by
water molecules in the inner coma. The observed green emission line width is
about 2.5 km/s and decreases as the distance from the nucleus increases which
can be explained by the varying contribution of CO2 to the O(1S) production in
the innermost coma. The photodissociation of CO2 molecules seems to produce
O(1S) closer to the nucleus while the water molecule forms all the O(1S) and
O(1D) atoms beyond 1000 km. Thus we conclude that the main parent species
producing O(1S) and O(1D) in the inner coma is not always the same. The
observations have been interpreted in the framework of the
coupled-chemistry-emission model of Bhardwaj & Raghuram (2012) and the upper
limits of CO2 relative abundances are derived from the observed G/R ratios.
Measuring the [OI] lines could indeed provide a new way to determine the CO2
relative abundance in comets.Comment: accepted for publication in A&A, the abstract is shortene
The effect of fly ash, β-cyclodextrin and fly ash-β-cyclodextrin composites on concrete workability and strength
Abstract: To increase the use of fly ash (FA) as a pozzolanic material in concrete, a composite was formed with an interaction of FA with β-cyclodextrin (β-CD). Further research was carried out in this article to study the effects of replacing cement with FA (30% and 50% by mass), β-CD (0.025%, 0.05% and 0.1%) and FA-β-CD composite on the workability and strength of concrete. Workability was assessed by means of the slump test and strengths were assessed using the compressive and split tensile strength tests. Higher combined contents of FA and β- CD resulted in increased workability of concrete of up to approximately 550 %. Furthermore, the inclusion of β-CD generally increased both the compressive and tensile strengths of the concretes not containing FA by up to 10 %. When combined with FA, the β-CD resulted in increased compressive strengths of up to 63 % and tensile strengths of up to 28 %, compared to the relevant pozzolanic concretes which did not include β-CD. The study contributed to the knowledge of FA performance using cyclodextrin and promoted the continued inclusion of FA in concrete, which in turn should reduce the environmental pollution resulting from FA
Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study
An efficient way to precisely pattern particles on solid surfaces is to
dispense and evaporate colloidal drops, as for bioassays. The dried deposits
often exhibit complex structures exemplified by the coffee ring pattern, where
most particles have accumulated at the periphery of the deposit. In this work,
the formation of deposits during the drying of nanoliter colloidal drops on a
flat substrate is investigated numerically and experimentally. A finite-element
numerical model is developed that solves the Navier-Stokes, heat and mass
transport equations in a Lagrangian framework. The diffusion of vapor in the
atmosphere is solved numerically, providing an exact boundary condition for the
evaporative flux at the droplet-air interface. Laplace stresses and thermal
Marangoni stresses are accounted for. The particle concentration is tracked by
solving a continuum advection-diffusion equation. Wetting line motion and the
interaction of the free surface of the drop with the growing deposit are
modeled based on criteria on wetting angles. Numerical results for evaporation
times and flow field are in very good agreement with published experimental and
theoretical results. We also performed transient visualization experiments of
water and isopropanol drops loaded with polystyrene microsphere evaporating on
respectively glass and polydimethylsiloxane substrates. Measured evaporation
times, deposit shape and sizes, and flow fields are in very good agreement with
the numerical results. Different flow patterns caused by the competition of
Marangoni loops and radial flow are shown to determine the deposit shape to be
either a ring-like pattern or a homogeneous bump
Graphene boosts thermoelectric performance of a Zintl phase compound
The concept of nanocomposites derived by incorporating a second minor phase in bulk thermoelectric materials has established itself as an effective paradigm for optimizing high thermoelectric performance. In this work, this paradigm is for the first time extended to bulk Zintl phase Mg3Sb2 and its isoelectronically Bi-doped derivative Mg3Sb1.8Bi0.2 system. Herein, we report the synthesis, microstructural details, electronic structure and thermoelectric properties of (Mg3Sb2, Mg3Sb1.8Bi0.2)/ graphene nanosheet (GNS) nanocomposites with different mass ratios. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) investigation reveals that Mg3Sb2 nanoparticles are homogenously anchored on the surface of GNS. We demonstrate that Mg3Sb2-based materials incorporated with a small content of graphene outperform optimally, resulting in potential p-type thermoelectric materials. The present nanocomposite additive of GNS deriving such a novel nanocomposite of (Mg3Sb2, Mg3Sb1.8Bi0.2)/GNS, enhances the electrical conductivity significantly, thereby resulting in a substantially large increase in the power factor. The enhanced electrical conductivity of these nanocomposites is attributed to the increase in the carrier concentration and high carrier mobility owing to the ultra high mobility of graphene. X-ray photoelectron spectroscopy (XPS) core level spectra confirm weak bonding between GNS and Mg3Sb2. Increase in carrier concentration is reflected in XPS valence band spectra and change in spectral weight near valence band maxima is indicative of increased electrical conductivity in the nanocomposite material. The thermal conductivity of these nanocomposites is noted to be reduced at high temperature. These favorable conditions lead to enhanced thermoelectric figure-of-merit (ZT) = 0.71 at 773 K for Mg3Sb2/GNS and a ZT = 1.35 at 773 K for Mg3Sb1.8Bi0.2/GNS nanocomposites with the mass ratio of 80 : 1 which are similar to 170% and similar to 125% higher values compared to bare Mg3Sb2 and bare Mg3Sb1.8Bi0.2 respectively. We strongly believe that the present novel strategy of fabricating such a nanocomposite of a Zintl compound by utilizing GNS as a nanocomposite additive, may provide an emerging path for improving thermoelectric properties of various Zintl phase compounds
Galactic Bulge Population II Cepheids in the VVV Survey: Period-Luminosity Relations and a Distance to the Galactic Center
We present the near-infrared observations of population II Cepheids in the
Galactic bulge from VVV survey. We identify 340 population II Cepheids in the
Galactic bulge from VVV survey based on their match with OGLE-III Catalogue.
The single-epoch and multi-epoch observations complement the
accurate periods and optical mean-magnitudes from OGLE. The sample
consisting of BL Herculis and W Virginis subtypes is used to derive
period-luminosity relations after correcting mean-magnitudes for the
extinction. Our -band period-luminosity relation, , is consistent with published work
for BL Herculis and W Virginis variables in the Large Magellanic Cloud. We
present a combined OGLE-III and VVV catalogue with periods, classification,
mean magnitudes and extinction for 264 Galactic bulge population II Cepheids
having good-quality -band light curves. The absolute magnitudes for
population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space
Telescope parallaxes, together with calibrated magnitudes for Large Magellanic
Cloud population II Cepheids, are used to obtain a distance to the Galactic
center, , which
changes by with different extinction laws. While noting the
limitation of small number statistics, we find that the present sample of
population II Cepheids in the Galactic bulge shows a nearly spheroidal spatial
distribution, similar to metal-poor RR Lyrae variables. We do not find evidence
of the inclined bar as traced by the metal-rich red-clump stars. The number
density for population II Cepheids is more limited as compared to abundant RR
Lyraes but they are bright and exhibit a wide range in period that provides a
robust period-luminosity relation for an accurate estimate of the distance to
the Galactic center.Comment: 9 pages, 8 figures, Accepted for publication in A&
Soil Quality Under Forest Compared to Other Land Uses
Abstract. Present research was undertaken to examine the impact of land use on soil fertility in an Alfisol, at Dharamshala district of north western Himalayan region, India. Soil samples were collected from 0-15, 15-30, 30-45 and 45 -60 cm soil depths of five land uses viz. natural forest of Pinus roxburghii, grassland, horticulture, agriculture and wasteland. Soil was examined for pH, organic carbon (OC), electrical conductivity (EC), cation exchange capacity (CEC), available nitrogen (N), phosphorus (P), exchangeable calcium (Ca), magnesium (Mg), potassium (K), aluminium (Al), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), acid phosphatase activity (APHA) and dehydrogenase activity (DHA). Soil pH varied from 5.22 in forest and 5.72 in grassland. OC content was higher in forest (3.01%), followed by grassland (2.16%) and was least (0.36%) in deeper layers of agriculture. Highest N content was found under forest (699, 654, 623 and 597 kg/ha, at 0-15, 15-30, 30-45 and 45-60 cm depth, respectively), followed by grassland, horticulture and agriculture and least in wasteland. Maximum exchangeable Ca and Mg were found in grassland (0.801 c mol kg -1 and 0.402 c mol kg -1 , respectively). Exchangeable K and Al were higher under forest (0.231 c mol kg -1 and 1.89 c mol kg -1 , respectively) least in wasteland. Soil biological properties were highest under surface soil of forest (576 mg kg -1 , 31.24 mg kg -1 , 6.55 mg kg -1 , 29.6 mg PNP g -1 h -1 and 35.65 μg TPF 24 h -1 g -1 dry soil, respectively for MBC, MBN, MBP, APHA and DHA) and least in 45-60 cm layer, under wasteland. The forest had a higher fertility index and soil evaluation factor followed by grassland, horticulture, agriculture as compared to wasteland
The propensity of molecules to spatially align in intense light fields
The propensity of molecules to spatially align along the polarization vector
of intense, pulsed light fields is related to readily-accessible parameters
(molecular polarizabilities, moment of inertia, peak intensity of the light and
its pulse duration). Predictions can now be made of which molecules can be
spatially aligned, and under what circumstances, upon irradiation by intense
light. Accounting for both enhanced ionization and hyperpolarizability, it is
shown that {\it all} molecules can be aligned, even those with the smallest
static polarizability, when subjected to the shortest available laser pulses
(of sufficient intensity).Comment: 8 pages, 4 figures, to be submitted to PR
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