1,464 research outputs found
New Superhard Phases for 3D C60-based Fullerites
We have explored new possible phases of 3D C60-based fullerites using
semiempirical potentials and ab-initio density functional methods. We have
found three closely related structures - two body centered orthorhombic and one
body centered cubic - having 52, 56 and 60 tetracoordinated atoms per molecule.
These 3D polymers result in semiconductors with bulk moduli near 300 GPa, and
shear moduli around 240 GPa, which make them good candidates for new low
density superhard materials.Comment: To be published in Physical Review Letter
Efectos del cloruro de cloro colina y el paclobutrazol sobre el crecimiento de plantas y la calidad de raíces tuberosas de mandioca (Manihot esculenta Crantz cv. Rocha)
The effects of chlorocholine chloride (CCC) and paclobutrazol (PBZ) foliar application on shoot and root parameters of cassava field-grown plants were studied (0, 45 and 90 mg active ingredient per plant). CCC and PBZ reduced total plant and first branch height, aerial fresh mass and tuberous root number. PBZ delayed branching and significantly decreased tuberous root fresh mass, while CCC caused no modifications in these parameters. In addition, CCC and PBZ treatments did not modify tuberous root diameter, while PBZ reduced tuberous root length significantly. Starch content was increased by both growth regulators at the lower dose, whereas dry matter content was increased only by CCC. In conclusion, CCC suppresses excessive vegetative growth, favours quality attributes and does not alter yield, hence improving harvest index. Although PBZ at a low dose increases the starch content and harvest index, its effects on other parameters are undesirable.Fil: Medina, Ricardo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Burgos, A.. Universidad Nacional del Nordeste; ArgentinaFil: Difranco, V.. Universidad Nacional del Nordeste; ArgentinaFil: Mroginski, Luis Amado. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Cenóz, P.. Universidad Nacional del Nordeste; Argentin
Random Sequential Adsorption: From Continuum to Lattice and Pre-Patterned Substrates
The random sequential adsorption (RSA) model has served as a paradigm for
diverse phenomena in physical chemistry, as well as in other areas such as
biology, ecology, and sociology. In the present work, we survey aspects of the
RSA model with emphasis on the approach to and properties of jammed states
obtained for large times in continuum deposition versus that on lattice
substrates, and on pre-patterned surfaces. The latter model has been of recent
interest in the context of efforts to use pre-patterning as a tool to improve
selfassembly in micro- and nanoscale surface structure engineering
Detection of optical emission from the supernova remnant G7.7-3.7
We present the first optical study of the supernova remnant (SNR) G7.7-3.7,
with the aim of determining its evolutionary phase since it has been suggested
to be the remnant of SN 386 AD. We obtained narrow-band images in the filters
H + [NII], H, [OIII], [SII] that revealed faint optical emission
in the southern region of the SNR consisting of two filaments elongated in the
east-west direction aligned with the X-ray emitting region of the remnant. The
filaments were seen in H + [NII], [OIII] images and marginally in the
[SII] images, with a non-detection in H. Long-slit spectroscopy of three
regions along one filament revealed large ratios of [SII] / H =
(1.6-2.5), consistent with that expected for a shock-heated SNR. The [SII]
doublet ratio observed in two of the regions implies an upper limit for the
electron density of the gas, with estimates falling below 400 cm and 600
cm in the respective areas. We discuss potential physical mechanisms
that formed the observed optical filaments and we suggest that most likely they
resulted by a collision of the SNR with a dense circumstellar shell lying at
the southern region of the remnant.Comment: 10 pages, 5 figures, accepted in MNRA
Detection of optical emission from the supernova remnant G7.7–3.7
The work of VD is supported by a grant from NWO graduate programme/GRAPPA-PhD programme. VD also acknowledges support from the LKBF, subsidy no. 19.2.027. JVHS acknowledges support from STFC grant ST/R000824/1. PZ acknowledges the support from the NWO Veni Fellowship, grant no. 639.041.647 and NSFC grant 11590781. SA thanks the support under the grant 5077 financed by IAASARS/NOA. AdB thanks the support from the Spanish Government Ministerio de Ciencia e Innovación through grants PGC-2018-091, 3741-B-C22, and SEV 2015-0548, from the Canarian Agency for Research, Innovation and Information Society (ACIISI) of the Canary Islands Government, and from the European Regional Development Fund (ERDF), under grant with reference ProID2017010115.We present the first optical study of the supernova remnant (SNR) G7.7–3.7, with the aim of determining its evolutionary phase since it has been suggested to be the remnant of SN 386 AD. We obtained narrow-band images in the filters H α + [N ii], H β, [O iii], [S ii] that revealed faint optical emission in the southern region of the SNR consisting of two filaments elongated in the east–west direction aligned with the X-ray emitting region of the remnant. The filaments were seen in H α + [N ii], [O iii] images and marginally in the [S ii] images, with a non-detection in H β. Long-slit spectroscopy of the three regions along one filament revealed large ratios of [S ii]/H α = (1.6–2.5), consistent with that expected for a shock-heated SNR. The [S ii] doublet ratio observed in two of the regions implies an upper limit for the electron density of the gas, with estimates falling below 400 cm−3 and 600 cm−3 in the respective areas. We discuss potential physical mechanisms that formed the observed optical filaments and we suggest that most likely they resulted by a collision of the SNR with a dense circumstellar shell lying at the southern region of the remnant.Publisher PDFPeer reviewe
Fe-substituted mullite powders for the in situ synthesis of carbon nanotubes by catalytic chemical vapor deposition
Powders of iron-substituted mullite were prepared by combustion and further calcination in air at different temperatures. A detailed study involving notably Mo¨ssbauer spectroscopy showed that the Fe3+ ions are distributed between the mullite phase and a corundum phase that progressively dissolves into mullite upon the increase in calcination temperature. Carbon nanotube-Fe-mullite nanocomposites were prepared for the first time by a direct method involving a reduction of these powders in H2-CH4 and without any mechanical mixing step. The carbon nanotubes formed by the catalytic decomposition of CH4 on the smallest metal particles are mostly double-walled and multiwalled, although some carbon nanofibers are also observed
Multiparticle Reactions with Spatial Anisotropy
We study the effect of anisotropic diffusion on the one-dimensional
annihilation reaction kA->inert with partial reaction probabilities when
hard-core particles meet in groups of k nearest neighbors. Based on scaling
arguments, mean field approaches and random walk considerations we argue that
the spatial anisotropy introduces no appreciable changes as compared to the
isotropic case. Our conjectures are supported by numerical simulations for slow
reaction rates, for k=2 and 4.Comment: nine pages, plain Te
Distinct Biochemical Pools of Golgi Phosphoprotein 3 in the Human Breast Cancer Cell Lines MCF7 and MDA-MB-231
Golgi phosphoprotein 3 (GOLPH3) has been implicated in the development of carcinomas in many human tissues, and is currently considered a bona fide oncoprotein. Importantly, several tumor types show overexpression of GOLPH3, which is associated with tumor progress and poor prognosis. However, the underlying molecular mechanisms that connect GOLPH3 function with tumorigenicity are poorly understood. Experimental evidence shows that depletion of GOLPH3 abolishes transformation and proliferation of tumor cells in GOLPH3-overexpressing cell lines. Conversely, GOLPH3 overexpression drives transformation of primary cell lines and enhances mouse xenograft tumor growth in vivo. This evidence suggests that overexpression of GOLPH3 could result in distinct features of GOLPH3 in tumor cells compared to that of non-tumorigenic cells. GOLPH3 is a peripheral membrane protein mostly localized at the trans-Golgi network, and its association with Golgi membranes depends on binding to phosphatidylinositol-4-phosphate. GOLPH3 is also contained in a large cytosolic pool that rapidly exchanges with Golgi-associated pools. GOLPH3 has also been observed associated with vesicles and tubules arising from the Golgi, as well as other cellular compartments, and hence it has been implicated in several membrane trafficking events. Whether these and other features are typical to all different types of cells is unknown. Moreover, it remains undetermined how GOLPH3 acts as an oncoprotein at the Golgi. Therefore, to better understand the roles of GOLPH3 in cancer cells, we sought to compare some of its biochemical and cellular properties in the human breast cancer cell lines MCF7 and MDA-MB-231 with that of the non-tumorigenic breast human cell line MCF 10A. We found unexpected differences that support the notion that in different cancer cells, overexpression of GOLPH3 functions in diverse fashions, which may influence specific tumorigenic phenotypes
First measurement of the Head-Tail directional nuclear recoil signature at energies relevant to WIMP dark matter searches
We present first evidence for the so-called Head-Tail asymmetry signature of
neutron-induced nuclear recoil tracks at energies down to 1.5 keV/amu using the
1m^3 DRIFT-IIc dark matter detector. This regime is appropriate for recoils
induced by Weakly Interacting Massive Particle (WIMPs) but one where the
differential ionization is poorly understood. We show that the distribution of
recoil energies and directions induced here by Cf-252 neutrons matches well
that expected from massive WIMPs. The results open a powerful new means of
searching for a galactic signature from WIMPs.Comment: 4 pages, 6 figures, 1 tabl
Low Energy Electron and Nuclear Recoil Thresholds in the DRIFT-II Negative Ion TPC for Dark Matter Searches
Understanding the ability to measure and discriminate particle events at the
lowest possible energy is an essential requirement in developing new
experiments to search for weakly interacting massive particle (WIMP) dark
matter. In this paper we detail an assessment of the potential sensitivity
below 10 keV in the 1 m^3 DRIFT-II directionally sensitive, low pressure,
negative ion time projection chamber (NITPC), based on event-by-event track
reconstruction and calorimetry in the multiwire proportional chamber (MWPC)
readout. By application of a digital smoothing polynomial it is shown that the
detector is sensitive to sulfur and carbon recoils down to 2.9 and 1.9 keV
respectively, and 1.2 keV for electron induced events. The energy sensitivity
is demonstrated through the 5.9 keV gamma spectrum of 55Fe, where the energy
resolution is sufficient to identify the escape peak. The effect a lower energy
sensitivity on the WIMP exclusion limit is demonstrated. In addition to recoil
direction reconstruction for WIMP searches this sensitivity suggests new
prospects for applications also in KK axion searches
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