13,834 research outputs found
Classification of scale-free networks
While the emergence of a power law degree distribution in complex networks is
intriguing, the degree exponent is not universal. Here we show that the
betweenness centrality displays a power-law distribution with an exponent \eta
which is robust and use it to classify the scale-free networks. We have
observed two universality classes with \eta \approx 2.2(1) and 2.0,
respectively. Real world networks for the former are the protein interaction
networks, the metabolic networks for eukaryotes and bacteria, and the
co-authorship network, and those for the latter one are the Internet, the
world-wide web, and the metabolic networks for archaea. Distinct features of
the mass-distance relation, generic topology of geodesics and resilience under
attack of the two classes are identified. Various model networks also belong to
either of the two classes while their degree exponents are tunable.Comment: 6 Pages, 6 Figures, 1 tabl
Anisotropic strains and magnetoresistance of La_{0.7}Ca_{0.3}MnO_{3}
Thin films of perovskite manganite La_{0.7}Ca_{0.3}MnO_{3} were grown
epitaxially on SrTiO_3(100), MgO(100) and LaAlO_3(100) substrates by the pulsed
laser deposition method. Microscopic structures of these thin film samples as
well as a bulk sample were fully determined by x-ray diffraction measurements.
The unit cells of the three films have different shapes, i.e., contracted
tetragonal, cubic, and elongated tetragonal for SrTiO_3, MgO, and LaAlO_3
cases, respectively, while the unit cell of the bulk is cubic. It is found that
the samples with cubic unit cell show smaller peak magnetoresistance than the
noncubic ones do. The present result demonstrates that the magnetoresistance of
La_{0.7}Ca_{0.3}MnO_{3} can be controlled by lattice distortion via externally
imposed strains.Comment: Revtex, 10 pages, 2 figure
Frustrated H-Induced Instability of Mo(110)
Using helium atom scattering Hulpke and L"udecke recently observed a giant
phonon anomaly for the hydrogen covered W(110) and Mo(110) surfaces. An
explanation which is able to account for this and other experiments is still
lacking. Below we present density-functional theory calculations of the atomic
and electronic structure of the clean and hydrogen-covered Mo(110) surfaces.
For the full adsorbate monolayer the calculations provide evidence for a strong
Fermi surface nesting instability. This explains the observed anomalies and
resolves the apparent inconsistencies of different experiments.Comment: 4 pages, 2 figures, submitted to PR
Oxidation States of Graphene: Insights from Computational Spectroscopy
When it is oxidized, graphite can be easily exfoliated forming graphene oxide
(GO). GO is a critical intermediate for massive production of graphene, and it
is also an important material with various application potentials. With many
different oxidation species randomly distributed on the basal plane, GO has a
complicated nonstoichiometric atomic structure that is still not well
understood in spite of of intensive studies involving many experimental
techniques. Controversies often exist in experimental data interpretation. We
report here a first principles study on binding energy of carbon 1s orbital in
GO. The calculated results can be well used to interpret experimental X-ray
photoelectron spectroscopy (XPS) data and provide a unified spectral
assignment. Based on the first principles understanding of XPS, a GO structure
model containing new oxidation species epoxy pair and epoxy-hydroxy pair is
proposed. Our results demonstrate that first principles computational
spectroscopy provides a powerful means to investigate GO structure.Comment: accepted by J. Chem. Phy
Elastic Moduli of Silicon Carbide Particulate Reinforced Aluminum Metal Matrix Composites
The mechanical properties of metal matrix composites (MMCs) reinforced by discontinuous silicon carbides are governed by the properties of the reinforcing phase, as well as their morphology (whisker vs. particulate), orientation and volume fraction. The morphology of SiC particles and their orientation are major variables affecting the anisotropic properties of these composites. SiC whisker (SiCW) reinforced aluminum MMCs tend to have higher strengths and moduli in the extrusion direction due to the high degree of whisker alignment in that direction, and these values are higher than those for SiC particulate (SiCp) reinforced composites at a given reinforcement level [1]. SiCpreinforced MMCs are known to be more isotropic in the extrusion plane. In situations requiring multidirectional reinforcement, particulate reinforced composites can outperform whisker reinforced composites. Thus, it is important to characterize the mechanical properties of these composites in order to develop the criteria for selecting microstructural design variables
Purification and detection of entangled coherent states
In [J. C. Howell and J. A. Yeazell, Phys. Rev. A 62, 012102 (2000)], a
proposal is made to generate entangled macroscopically distinguishable states
of two spatially separated traveling optical modes. We model the decoherence
due to light scattering during the propagation along an optical transmission
line and propose a setup allowing an entanglement purification from a number of
preparations which are partially decohered due to transmission. A purification
is achieved even without any manual intervention. We consider a nondemolition
configuration to measure the purity of the state as contrast of interference
fringes in a double-slit setup. Regarding the entangled coherent states as a
state of a bipartite quantum system, a close relationship between purity and
entanglement of formation can be obtained. In this way, the contrast of
interference fringes provides a direct means to measure entanglement.Comment: 9 pages, 6 figures, using Revtex
Nearest pattern interaction and global pattern formation
We studied the effect of nearest pattern interaction on a globally pattern
formation in a 2-dimensional space, where patterns are to grow initially from a
noise in the presence of periodic supply of energy. Although our approach is
general, we found that this study is relevant in particular to the pattern
formation on a periodically vibrated granular layer, as it gives a unified
perspective of the experimentally observed pattern dynamics such as oscillon
and stripe formations, skew-varicose and crossroll instabilities, and also a
kink formation and decoration
Quickest Paths in Simulations of Pedestrians
This contribution proposes a method to make agents in a microscopic
simulation of pedestrian traffic walk approximately along a path of estimated
minimal remaining travel time to their destination. Usually models of
pedestrian dynamics are (implicitly) built on the assumption that pedestrians
walk along the shortest path. Model elements formulated to make pedestrians
locally avoid collisions and intrusion into personal space do not produce
motion on quickest paths. Therefore a special model element is needed, if one
wants to model and simulate pedestrians for whom travel time matters most (e.g.
travelers in a station hall who are late for a train). Here such a model
element is proposed, discussed and used within the Social Force Model.Comment: revised version submitte
Жаростойкий сорт перца демонстрирует высокие показатели хлорофилла, фотосинтеза, устьичной проводимости и транспирации в режиме теплового стресса на стадии развития плодов
Relevance. Abiotic stress, as heat, significantly affect plant and floral organs growth and development, fruit set, productivity, the quality, and survival of crops. Heat injury occurs when plants are exposed to these temperatures for a long period of time. Depending on the intensity and duration of exposure to the high temperatures, photosynthesis, respiration, membrane integrity, water relations and the hormone balance of the plants may affected.Material and methods. In this study used the commercial pepper cultivar “NW Bigarim” (HT37) released in South Korea and accessions “Kobra” (HT1) and “Samchukjaere” (HT7) selected as heat tolerant and susceptible, respectively. Total chlorophyll index and photosynthetic activities measured using a SPAD meter (Konica, Japan) and portable photosynthesis measurement system (LI-6400, LI-COR Bioscience, Lincoln, NE, USA), respectively.Results. To evaluate the positive effects of high temperature regime (40/28°C day/night, 14/10-h light/dark cycle) on the response of photosynthetic parameters in pepper plants with different heat susceptibility, we measured the total chlorophyll content (CHL) and photosynthetic activities such as photosynthesis (Pn), stomatal conductance to H2O (Gs) and transpiration rate (Tr) in a heat-tolerant (HT1) and -susceptible cultivars (HT7) in comparison with released cultivar (HT37) at fruit development stage. Heat-tolerant cultivars showed higher and more stable index of the CHL, Pn, Gs and Tr than those in heat-sensitive cultivars for 14 days of heat treatment (HT) period. However, the initial index of Pn, Gs and Tr showed significant alteration among pepper plants regardless of thermotolerance rate before HT on day 0 and day 7 after recovery at normal treatment condition (NT) except for CHL, meaning that plants response to high temperature regime is different from that in normal condition. These results suggest that constant high rates of Pn, Gs and Tr as well as of CHL in heat stress condition periods confer to avoid from heat injury during reproductive growth stages.Актуальность. Абиотический стресс, такой как высокая температура, существенно влияет на рост и развитие репродуктивных органов растений, завязываемость плодов, продуктивность, качество и выживание. При длительном воздействия высоких температур у растений наблюдаются повреждения, и в зависимости от продолжительности и интенсивности высоких температур нарушается фотосинтез, транспирация, целостность мембраны, водный и гормональный баланс.Материал и методика. В данной работе использовали районированный в Южной Корее сорт перца «NW Bigarim» (HT37), а также сортообразцы «Kobra» (HT1) и «Samchukjaere» (HT7) выделенные как устойчивый и восприимчивый к высоким температурам, соответственно. Фотосинтез и общее содержание хлорофилла в листьях определяли при помощи портативного системы (LI-6400, LI-COR Bioscience, Lincoln, NE, USA) и спадметера (Konica Japan), соответственно.Результаты. Изучено и выявлено положительное влияние высокотемпературного режима (40/28°C день/ночь, 14/10-часовой цикл свет/темнота) на реакцию фотосинтетических параметров у растений перца с различной тепловой восприимчивостью, измерено общее содержание хлорофилла (CHL) и фотосинтетической активности, таких параметров, как фотосинтез (Pn), устьичная проводимость в H2O (Gs) и скорость транспирации (Tr) у листьев термостойкого (HT1) и чувствительного сортов (HT7) в сравнении с районированным сортом (HT37) на стадии развития плода. Термостойкий сорт показал более высокие и более стабильные показатели CHL, Pn, Gs и Tr, чем термочувствительный сорт HT7 в течение 14 дней термической обработки (HT). Однако исходные показатели Pn, Gs и Tr показали значительную вариабельность среди растений перца независимо от степени термотолерантности перед обработкой высокой температурой на 0 день и на день 7 после восстановления при нормальных условиях выращивание (NT), за исключением CHL, что означает, что растения реагируют на высокотемпературный режим, отличающийся от условий роста в NT. Эти результаты предполагают, что постоянное высокое снижение Pn, Gs и Tr, а также CHL в периоды теплового стресса позволяет избежать теплового повреждения на стадиях репродуктивного роста растений
Semimetalic antiferromagnetism in the half-Heusler compound CuMnSb
The half-Heusler compound CuMnSb, the first antiferromagnet (AFM) in the
Mn-based class of Heuslers and half-Heuslers that contains several conventional
and half metallic ferromagnets, shows a peculiar stability of its magnetic
order in high magnetic fields. Density functional based studies reveal an
unusual nature of its unstable (and therefore unseen) paramagnetic state, which
for one electron less (CuMnSn, for example) would be a zero gap semiconductor
(accidentally so) between two sets of very narrow, topologically separate bands
of Mn 3d character. The extremely flat Mn 3d bands result from the environment:
Mn has four tetrahedrally coordinated Cu atoms whose 3d states lie well below
the Fermi level, and the other four tetrahedrally coordinated sites are empty,
leaving chemically isolated Mn 3d states. The AFM phase can be pictured
heuristically as a self-doped CuMnSb compensated semimetal
with heavy mass electrons and light mass holes, with magnetic coupling
proceeding through Kondo and/or antiKondo coupling separately through the two
carrier types. The ratio of the linear specific heat coefficient and the
calculated Fermi level density of states indicates a large mass enhancement
, or larger if a correlated band structure is taken as the
reference
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