6,744 research outputs found
Disorder-induced double resonant Raman process in graphene
An analytical study is presented of the double resonant Raman scattering
process in graphene, responsible for the D and D features in the
Raman spectra. This work yields analytical expressions for the D and
D integrated Raman intensities that explicitly show the dependencies
on laser energy, defect concentration, and electronic lifetime. Good agreement
is obtained between the analytical results and experimental measurements on
samples with increasing defect concentrations and at various laser excitation
energies. The use of Raman spectroscopy to identify the nature of defects is
discussed. Comparison between the models for the edge-induced and the
disorder-induced D band intensity suggests that edges or grain boundaries can
be distinguished from disorder by the different dependence of their Raman
intensity on laser excitation energy. Similarly, the type of disorder can
potentially be identified not only by the intensity ratio
, but also by its laser energy
dependence. Also discussed is a quantitative analysis of quantum interference
effects of the graphene wavefunctions, which determine the most important
phonon wavevectors and scattering processes responsible for the D and
D bands.Comment: 10 pages, 4 figure
The two-echelon capacitated vehicle routing problem: models and math-based heuristics
Multiechelon distribution systems are quite common in supply-chain and logistics. They are used by public administrations in their transportation and traffic planning strategies, as well as by companies, to model own distribution systems. In the literature, most of the studies address issues relating to the movement of flows throughout the system from their origins to their final destinations. Another recent trend is to focus on the management of the vehicle fleets required to provide transportation among different echelons. The aim of this paper is twofold. First, it introduces the family of two-echelon vehicle routing problems (VRPs), a term that broadly covers such settings, where the delivery from one or more depots to customers is managed by routing and consolidating freight through intermediate depots. Second, it considers in detail the basic version of two-echelon VRPs, the two-echelon capacitated VRP, which is an extension of the classical VRP in which the delivery is compulsorily delivered through intermediate depots, named satellites. A mathematical model for two-echelon capacitated VRP, some valid inequalities, and two math-heuristics based on the model are presented. Computational results of up to 50 customers and four satellites show the effectiveness of the methods developed
Oviposição, desenvolvimento e reprodução de Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) em diferentes hospedeiros de importância econômica.
The host selection for oviposition by Spodoptera frugiperda (J.E. Smith) among corn, millet, cotton and soybean, and its relationship with the biological characteristics were investigated. Free and non-choice tests for oviposition using plots containing fi ve plants each, from each host in plastic greenhouse, resulted in similar oviposition preference among the host plants. In addition, selected biological characteristics of S. frugiperda were determined in the laboratory with larvae feeding on host leaves, and the combination of leaf and cotton boll. Neonate larvae exhibited low success of colonization on cotton boll compared to the leaves of all other hosts. Spodoptera frugiperda fed only on cotton bolls exhibited longer larval and pupal development, and longer adult life span; however with similar egg production. Larvae fed cotton leaves during six days and then transferred to cotton bolls, however, exhibited development and reproduction similar to those reared on corn or only on cotton leaves. Therefore, the variations on immature stages of S. frugiperda were not related with host selection for oviposition which was similar among the studied hosts. Based on our data, the millet as a winter, rotational, and cover crop is a potential host for S. frugiperda, while leaves and cotton bolls were diets of intermediate suitability as compared to corn and soybean leaves
Aspectos agronômicos e de qualidade do pequi.
Caracterização botânica; características agronômicas; características químicas do fruto; utilização; considerações finais.bitstream/CNPAT-2010/10884/1/Dc-113.pd
Group Theory analysis of phonons in two-dimensional Transition Metal Dichalcogenides
Transition metal dichalcogenides (TMDCs) have emerged as a new two
dimensional materials field since the monolayer and few-layer limits show
different properties when compared to each other and to their respective bulk
materials. For example, in some cases when the bulk material is exfoliated down
to a monolayer, an indirect-to-direct band gap in the visible range is
observed. The number of layers ( even or odd) drives changes in space
group symmetry that are reflected in the optical properties. The understanding
of the space group symmetry as a function of the number of layers is therefore
important for the correct interpretation of the experimental data. Here we
present a thorough group theory study of the symmetry aspects relevant to
optical and spectroscopic analysis, for the most common polytypes of TMDCs,
i.e. , and , as a function of the number of layers. Real space
symmetries, the group of the wave vectors, the relevance of inversion symmetry,
irreducible representations of the vibrational modes, optical selection rules
and Raman tensors are discussed.Comment: 32 pages, 4 figure
Peering through the holes: the far UV color of star-forming galaxies at z~3-4 and the escaping fraction of ionizing radiation
We aim to investigate the effect of the escaping ionizing radiation on the
color selection of high redshift galaxies and identify candidate Lyman
continuum (LyC) emitters. The intergalactic medium prescription of Inoue et
al.(2014) and galaxy synthesis models of Bruzual&Charlot (2003) have been used
to properly treat the ultraviolet stellar emission, the stochasticity of the
intergalactic transmission and mean free path in the ionizing regime. Color
tracks are computed by turning on/off the escape fraction of ionizing
radiation. At variance with recent studies, a careful treatment of IGM
transmission leads to no significant effects on the high-redshift broad-band
color selection. The decreasing mean free path of ionizing photons with
increasing redshift further diminishes the contribution of the LyC to
broad-band colors. We also demonstrate that prominent LyC sources can be
selected under suitable conditions by calculating the probability of a null
escaping ionizing radiation. The method is applied to a sample of galaxies
extracted from the GOODS-S field. A known LyC source at z=3.795 is successfully
recovered as a LyC emitter candidate and another convincing candidate at
z=3.212 is reported. A detailed analysis of the two sources (including their
variability and morphology) suggests a possible mixture of stellar and
non-stellar (AGN) contribution in the ultraviolet. Conclusions: Classical
broad-band color selection of 2.5<z<4.5 galaxies does not prevent the inclusion
of LyC emitters in the selected samples. Large fesc in relatively bright
galaxies (L>0.1L*) could be favored by the presence of a faint AGN not easily
detected at any wavelength. A hybrid stellar and non-stellar (AGN) ionizing
emission could coexist in these systems and explain the tensions found among
the UV excess and the stellar population synthesis models reported in
literature.Comment: Accepted for publication in Astronomy & Astrophysics. 13 pages, 7
figure
Local cosmic string in generalised scalar tensor theory
A recent investigation shows that a local gauge string with a
phenomenological energy momentum tensor, as prescribed by Vilenkin, is
inconsistent in Brans-Dicke theory. In this work it has been shown that such a
string is consistent in a more general scalar tensor theory where is
function of the scalar field.A set of solutions of full nonlinear Einstein's
equations for interior region of such a string are presented.Comment: 7 pages, latex format, minor changes according to referee's
suggestions, revised version submitted in Phys.Rev.
Torsional strengthening of tubular type RC beams with NSM technique: structural performance and cracking process using DIC
Despite the key role of thin-walled tubular reinforced concrete (RC) members in major critical infrastructure projects, for example, bridges, their torsional performance is still not well understood and the effectiveness of strengthening systems cannot be easily assessed, especially when using innovative strengthening materials. With a large part of critical infrastructure approaching its design service life, these issues are becoming more and more important. This paper examines the torsional behavior of thin-walled tubular RC beams and evaluates the contribution of different strengthening configurations using carbon fiber reinforced polymer (CFRP) reinforcement applied according to the near surface mounted (NSM) technique. Six strengthened specimens are tested with different amounts of CFRP laminates in the longitudinal and transverse direction. Digital image correlation (DIC) is used to gain a deeper understanding of the contribution of the NSM CFRP laminates to the fracture process and overall deformation behavior of the RC elements. The crack mouth opening displacement (CMOD) of the critical crack is compared to those of the other cracks, and the torsional crack evolution is assessed against the strain evolution in the CFRP laminates. The results confirm the effectiveness of NSM CFRP strengthening solutions for thin-walled RC members, and provide clear evidence that torsional performance can be improved in terms of torsional moment carrying capacity, torsional stiffness, torsional angle of rotation and limiting the crack width propagation, which improves the aggregate interlock shear resisting mechanism.Foundation of Science and Technology:FCT, Grant/Award Numbers: SFRH/BD/129472/2017, PTDC/ECM-EST/1882/2014; Marie Curie InitialTraining Network: ENDURE, Grant/Award Number: MC-ITN-2013-60785
Limits on the LyC signal from z~3 sources with secure redshift and HST coverage in the E-CDFS field
Aim: We aim to measure the LyC signal from a sample of sources in the Chandra
deep field south. We collect star-forming galaxies (SFGs) and active galactic
nuclei (AGN) with accurate spectroscopic redshifts, for which Hubble Space
Telescope (HST) coverage and multi-wavelength photometry are available. Method:
We selected a sample of about 200 sources at z~3. Taking advantage of HST
resolution, we applied a careful cleaning procedure and rejected sources
showing nearby clumps with different colours, which could be lower-z
interlopers. Our clean sample consisted of 86 SFGs (including 19 narrow-band
selected Lya emitters) and 8 AGN (including 6 detected in X-rays). We measured
the LyC flux from aperture photometry in four narrow-band filters covering
wavelengths below a 912 A rest frame (3.11<z<3.53). We estimated the ratio
between ionizing (LyC flux) and 1400 A non-ionizing emissions for AGN and
galaxies. Results: By running population synthesis models, we assume an average
intrinsic L(1400 A)/L(900 A) ratio of 5 as the representative value for our
sample. With this value and an average treatment of the lines of sight of the
inter-galactic medium, we estimate the LyC escape fraction relative to the
intrinsic value (fesc_rel(LyC)). We do not directly detect ionizing radiation
from any individual SFG, but we are able to set a 1(2)sigma upper limit of
fesc_rel(LyC)<12(24)%. This result is consistent with other non-detections
published in the literature. No meaningful limits can be calculated for the
sub-sample of Lya emitters. We obtain one significant direct detection for an
AGN at z=3.46, with fesc_rel(LyC) = (72+/-18)%. Conclusions: Our upper limit on
fescrel(LyC) implies that the SFGs studied here do not present either the
physical properties or the geometric conditions suitable for efficient
LyC-photon escape.Comment: Accepted for publication in A&A on Jan 5th, 201
An extreme [OIII] emitter at : a low metallicity Lyman continuum source
[Abridged] We investigate the physical properties of a Lyman continuum
emitter candidate at with photometric coverage from to MIPS
24m band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. Investigation of the
UV spectrum confirms a direct spectroscopic detection of the Lyman continuum
emission with . Non-zero Ly flux at the systemic redshift and
high Lyman- escape fraction suggest a low HI column density. The weak C
and Si low-ionization absorption lines are also consistent with a low covering
fraction along the line of sight. The
[OIII] equivalent width is one of the
largest reported for a galaxy at
(, rest-frame) and the NIR spectrum shows that this is mainly due to an
extremely strong [OIII] emission. The large observed [OIII]/[OII] ratio ()
and high ionization parameter are consistent with prediction from
photoionization models in case of a density-bounded nebula scenario.
Furthermore, the
is
comparable to recent measurements reported at , in the reionization
epoch. We also investigate the possibility of an AGN contribution to explain
the ionizing emission but most of the AGN identification diagnostics suggest
that stellar emission dominates instead. This source is currently the first
high- example of a Lyman continuum emitter exhibiting indirect and direct
evidences of a Lyman continuum leakage and having physical properties
consistent with theoretical expectation from Lyman continuum emission from a
density-bounded nebula.Comment: 14 pages, 11 figures, accepted for publication in A&A. Minor
modifications, Figure 2 updated, Figure 9 adde
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