12,329 research outputs found

    Catalyst-free synthesis of single crystalline ZnO nanonails with ultra-thin caps

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    Arrays of single-crystalline ZnO nanonails with tapering diameters and ultra-thin caps have been successfully synthesized on a silicon substrate via a simple catalyst-free thermal evaporation method. Each of the ZnO nanonails consists a nanowire (stem) on the bottom and an ultra-thin symmetrical hexagonal cap on the top. Structural characterization reveals that the synthesized ZnO nanonail has a wurtzite (WZ) structure with a preferred growth direction of [0001] in the stem and in the cap. Remarkably, the ultra-thin cap shows a diameter-to-thickness ratio of over 20:1, which is much higher in magnitude than those reported in previous works. Based on the systematic morphological characterization and structural analysis, a self-catalyzed vapor–liquid–solid (VLS) mechanism followed by a vapor–solid (VS) process is proposed to explain the growth of the nanonails. Optical properties are also investigated with Raman and photoluminescence (PL) techniques, which show good crystal quality of the synthesized nanonails

    Note on a new fundamental length scale ll instead of the Newtonian constant GG

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    The newly proposed entropic gravity suggests gravity as an emergent force rather than a fundamental one. In this approach, the Newtonian constant GG does not play a fundamental role any more, and a new fundamental constant is required to replace its position. This request also arises from some philosophical considerations to contemplate the physical foundations for the unification of theories. We here consider the suggestion to derive GG from more fundamental quantities in the presence of a new fundamental length scale ll, which is suspected to originate from the structure of quantum space-time, and can be measured directly from Lorentz-violating observations. Our results are relevant to the fundamental understanding of physics, and more practically, of natural units, as well as explanations of experimental constraints in searching for Lorentz violation.Comment: 10 latex pages, final version for journal publicatio

    Hadron-quark phase transition in asymmetric matter with dynamical quark masses

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    The two-Equation of State (EoS) model is used to describe the hadron-quark phase transition in asymmetric matter formed at high density in heavy-ion collisions. For the quark phase, the three-flavor Nambu--Jona-Lasinio (NJL) effective theory is used to investigate the influence of dynamical quark mass effects on the phase transition. At variance to the MIT-Bag results, with fixed current quark masses, the main important effect of the chiral dynamics is the appearance of an End-Point for the coexistence zone. We show that a first order hadron-quark phase transition may take place in the region T=(50-80)MeV and \rho_B=(2-4)\rho_0, which is possible to be probed in the new planned facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From isospin properties of the mixed phase somepossible signals are suggested. The importance of chiral symmetry and dynamical quark mass on the hadron-quark phase transition is stressed. The difficulty of an exact location of Critical-End-Point comes from its appearance in a region of competition between chiral symmetry breaking and confinement, where our knowledge of effective QCD theories is still rather uncertain.Comment: 13 pages, 16 figures (revtex

    Early-type Stars: Most Favorable Targets for Astrometrically Detectable Planets in the Habitable Zone

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    Early-type stars appear to be a difficult place to look for planets astrometrically. First, they are relatively heavy, and for fixed planetary mass the astrometric signal falls inversely as the stellar mass. Second, they are relatively rare (and so tend to be more distant), and for fixed orbital separation the astrometric signal falls inversely as the distance. Nevertheless, because early-type stars are relatively more luminous, their habitable zones are at larger semi-major axis. Since astrometric signal scales directly as orbital size, this gives early-type stars a strong advantage, which more than compensates for the other two factors. Using the Hipparcos catalog, we show that early-type stars constitute the majority of viable targets for astrometric searches for planets in the habitable zone. We contrast this characteristic to transit searches, which are primarily sensitive to habitable planets around late-type stars.Comment: Submitted to ApJ Letters, 8 pages including 2 figure

    A novel explicit-implicit coupled solution method of SWE for long-term river meandering process induced by dam break

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    YesLarge amount of sediment deposits in the reservoir area can cause dam break, which not only leads to an immeasurable loss to the society, but also the sediments from the reservoir can be transported to generate further problems in the downstream catchment. This study aims to investigate the short-to-long term sediment transport and channel meandering process under such a situation. A coupled explicit-implicit technique based on the Euler-Lagrangian method (ELM) is used to solve the hydrodynamic equations, in which both the small and large time steps are used separately for the fluid and sediment marching. The main feature of the model is the use of the Characteristic-Based Split (CBS) method for the local time step iteration to correct the ELM traced lines. Based on the solved flow field, a standard Total Variation Diminishing (TVD) finite volume scheme is applied to solve the sediment transportation equation. The proposed model is first validated by a benchmark dambreak water flow experiment to validate the efficiency and accuracy of ELM modelling capability. Then an idealized engineering dambreak flow is used to investigate the long-term downstream channel meandering process with nonuniform sediment transport. The results showed that both the hydrodynamic and morphologic features have been well predicted by the proposed coupled model.This research work is supported by Sichuan Science and Technology Support Plan (2014SZ0163), Start-up Grant for the Young Teachers of Sichuan University (2014SCU11056), and Open Research Fund of the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKLH 1409; 1512)
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