On time-varying collaboration networks

The patterns of scientific collaboration have been frequently investigated in terms of complex networks without reference to time evolution. In the present work, we derive collaborative networks (from the arXiv repository) parameterized along time. By defining the concept of affine group, we identify several interesting trends in scientific collaboration, including the fact that the average size of the affine groups grows exponentially, while the number of authors increases as a power law. We were therefore able to identify, through extrapolation, the possible date when a single affine group is expected to emerge. Characteristic collaboration patterns were identified for each researcher, and their analysis revealed that larger affine groups tend to be less stable

Can the X(3872) be a 1^{++} four-quark state?

We use QCD spectral sum rules to test the nature of the meson X(3872), assumed to be an exotic four-quark (c\bar{c}q\bar{q}) state with J^{PC}=1^{++}. For definiteness, we work with the current proposed recently by Maiani et al [1], at leading order in \alpha_s, consider the contributions of higher dimension condensates and keep terms which are linear in the light quark mass m_q. We find M_X=(3925+- 127) MeV which is compatible, within the errors, with he experimental candidate X(3872), while the SU(3) breaking-terms lead to an unusual mass-splitting M_{X^{s}}-M_X=- (61+-30) MeV. The mass-difference between the neutral states due to isospin violation of about (2.6-3.9) MeV is much smaller than the value (8+-3) MeV proposed in [1]. For the b-quark, we predict M_{X_b}= (10144+-106) MeV for the X_b(b\bar{b}q \bar{q}), which is much below the {\bar B}B* threshold in contrast to the {\bar B}B* molecule prediction [2], and for the X_b^s(b\bar{b}s \bar{s}), a mass-splitting M_{X^s_{b}}-M_{X_b}=-(121+-182) MeV. Our analysis also indicates that the mass-splitting between the ground state and the radial excitation of about (225~250) MeV is much smaller than in the case of ordinary mesons and is (within the errors) flavour-independent. We also extract the decay constants, analogous to f_\pi, of such mesons, which are useful for further studies of their leptonic and hadronic decay widths. The uncertainties of our estimates are mainly due to the ones from the c and b quark masses.Comment: 16 pages, 10 figures. Version to appear in Phys. Rev.

Kajian Peranan Tanaman Hedgerow Dalam Sistem USAhatani Konservasi Di Lahan Kering Terhadap Sifat Fisik Tanah

Study the Role of Hedgerow Plants in Conservation of Dryland Farming Systems on Soil Physical Properties. To determine the effect of infiltration rate and soil physical properties, a study was conducted in the village Oebola, Fatuleu, Kupang district, from November 2008 to June 2009. The experiment was designed in Randomized Block Design (RBD), with four treatments and three replications. The treatments were three types of fencing plants in alley cropping systems i.e. white leadtree (Leucaena leucocephala), hummingbird tree (Sesbania grandiflora syn. Aeschynomene grandiflora), gliricidia (Gliricidia sepium), and the treatment without fencing plants as the control. The parameters observed were organic matter content, bulk density, field water content, maximum water content, aggregate stability, and infiltration rate. Data were analyzed statistically using the F-test and was continued with Duncan test if there was a difference among the treatments tested. The result showed that in the three fencing plants tested, gliricidia gave the best effect in the terms of organic matter content, field water content, maximum water content, and infiltration rate while bulk density of these three plants relatively performed the similar influence

Rancang Bangun Model USAhatani Konservasi Sebagai Upaya Peningkatan Produktivitas Lahan Kering

Model Plan Usahatani Conservation As Dry Farming ProductivityEnhanced Efforts. In the effort erosion trouble-shooting and the low of dry farming productivity, has been executed serangkian research which in focussed in area of Praktek Politani Kupang having location in Oesao Kabupaten Kupang. Research aim to study specific USAhatani model of dry farming. Three kinds of model USAhatani conservation has been checked, yakti bench terrace, terrace;core gulud and without terrace;core. Measurement of level of erosion is done in emperis with method USLE. To evaluate farm productivity also is done cultivation of green peanut crop Result of research indicates that technically, model USAhatani conservation of bench terrace and terrace;core gulud gives repair impact to degradation of erosion speed and improvement of farm productivity. Bench terrace earns effectively lessens erosion until under admissible erosion boundary, however memerlukn technical clauses in its(the making in order not to harm plant growth. Terrace;core gulud is one of alternative of conservation that need to be considered, especially at soil;land;grounds having [shallow/ superficial] solum, because cost in its(the making is cheap and doesn\u27t require many labours, and top layer soil is not annoyed

Mimicking Nanoribbon Behavior Using a Graphene Layer on SiC

We propose a natural way to create quantum-confined regions in graphene in a system that allows large-scale device integration. We show, using first-principles calculations, that a single graphene layer on a trenched region of $[000\bar{1}]$ $SiC$ mimics i)the energy bands around the Fermi level and ii) the magnetic properties of free-standing graphene nanoribbons. Depending on the trench direction, either zigzag or armchair nanoribbons are mimicked. This behavior occurs because a single graphene layer over a $SiC$ surface loses the graphene-like properties, which are restored solely over the trenches, providing in this way a confined strip region.Comment: 4 pages, 4 figure