6,955 research outputs found
Streamline topology and dilute particle dynamics in a Karman vortex street flow
Three types of streamline topology in a Karman vortex street flow are shown
under the variation of spatial parameters. For the motion of dilute particles
in the K\'arm\'an vortex street flow, there exist a route of bifurcation to a
chaotic orbit and more attractors in a bifurcation diagram for the proportion
of particle density to fluid density. Along with the increase of spatial
parameters in the flow filed, the bifurcation process is suspended, as well as
more and more attractors emerge. In the motion of dilute particles, a drag term
and gravity term dominate and result in the bifurcation phenomenon.Comment: 16 pages, 9 figure
Rotation numbers of invariant manifolds around unstable periodic orbits for the diamagnetic Kepler problem
In this paper, a method to construct topological template in terms of
symbolic dynamics for the diamagnetic Kepler problem is proposed. To confirm
the topological template, rotation numbers of invariant manifolds around
unstable periodic orbits in a phase space are taken as an object of comparison.
The rotation numbers are determined from the definition and connected with
symbolic sequences encoding the periodic orbits in a reduced Poincar\'e
section. Only symbolic codes with inverse ordering in the forward mapping can
contribute to the rotation of invariant manifolds around the periodic orbits.
By using symbolic ordering, the reduced Poincar\'e section is constricted along
stable manifolds and a topological template, which preserves the ordering of
forward sequences and can be used to extract the rotation numbers, is
established. The rotation numbers computed from the topological template are
the same as those computed from their original definition.Comment: 8 figures, 1 tabl
Harnessing optical micro-combs for microwave photonics
In the past decade, optical frequency combs generated by high-Q
micro-resonators, or micro-combs, which feature compact device footprints, high
energy efficiency, and high-repetition-rates in broad optical bandwidths, have
led to a revolution in a wide range of fields including metrology, mode-locked
lasers, telecommunications, RF photonics, spectroscopy, sensing, and quantum
optics. Among these, an application that has attracted great interest is the
use of micro-combs for RF photonics, where they offer enhanced functionalities
as well as reduced size and power consumption over other approaches. This
article reviews the recent advances in this emerging field. We provide an
overview of the main achievements that have been obtained to date, and
highlight the strong potential of micro-combs for RF photonics applications. We
also discuss some of the open challenges and limitations that need to be met
for practical applications.Comment: 32 Pages, 13 Figures, 172 Reference
Microwave and RF Applications for Micro-resonator based Frequency Combs
Photonic integrated circuits that exploit nonlinear optics in order to
generate and process signals all-optically have achieved performance far
superior to that possible electronically - particularly with respect to speed.
We review the recent achievements based in new CMOS-compatible platforms that
are better suited than SOI for nonlinear optics, focusing on radio frequency
(RF) and microwave based applications that exploit micro-resonator based
frequency combs. We highlight their potential as well as the challenges to
achieving practical solutions for many key applications. These material systems
have opened up many new capabilities such as on-chip optical frequency comb
generation and ultrafast optical pulse generation and measurement. We review
recent work on a photonic RF Hilbert transformer for broadband microwave
in-phase and quadrature-phase generation based on an integrated frequency
optical comb. The comb is generated using a nonlinear microring resonator based
on a CMOS compatible, high-index contrast, doped-silica glass platform. The
high quality and large frequency spacing of the comb enables filters with up to
20 taps, allowing us to demonstrate a quadrature filter with more than a
5-octave (3 dB) bandwidth and an almost uniform phase response.Comment: 10 pages, 6 figures, 68 references. arXiv admin note: substantial
text overlap with arXiv:1512.0174
Thiol-Functionalized Mesoporous Silica for Effective Trap of Mercury in Rats
The chance of exposure to heavy metal for human being rises severely today due to the increasing water contamination and air pollution. Here, we prepared a series of thiol-functionalized mesoporous silica as oral formulation for the prevention and treatment of heavy metal poisoning. The successful incorporation of thiol was verified by the FTIR spectra. SBA15-SH-10 was used for the study as it is of uniform mesopores and fine water dispersibility. In simulated gastrointestinal fluid, the thiol-functionalized mesoporous silica can selectively capture heavy metal, showing a very high affinity for inorganic mercury (II). The blood and urine mercury levels of rats fed with a diet containing Hg (II) and material were significantly lower than those of rats fed with the metal-rich diet only. On the contrary, the mercury content in fecal excretion of the treatment group increased more than twice as much as that of the control group. This result indicated that SBA15-SH-10 could effectively remove mercury (II) in vivo and the mercury loaded on SBA15-SH-10 would be excreted out. Hence, SBA15-SH-10 has potential application in preventing and treating heavy metal poisoning via digestive system
Bending modes and transition criteria for a flexible fiber in viscous flows
The present paper follows our previous work in which a coupling approach of smoothed particle hydrodynamics (SPH) and element bending group (EBG) was developed for modeling the interaction of viscous incompressible flows with flexible fibers. It was also shown that a flexible object may experience drag reduction because of its reconfiguration due to fluid force on it. However, the reconfiguration of deformable bodies does not always result in drag reduction as different deformation patterns can result in different drag scales. In the present work, we studied the bending modes of a flexible fiber in viscous flows using the presented SPH and EBG coupling approach. The flexible fiber is immersed in a fluid and is tethered at its center point, while the two ends of the fiber are free to move. We showed that the fiber undergoes four different bending modes: stable U-shape, slight swing, violent flapping, and stable closure modes. We found there is a transition criterion for the flexible fiber from slight swing, suddenly to violent flapping. We defined a bending number to characterize the bending dynamics of the interaction of flexible fiber with viscous fluid and revealed that this bending number is relevant to the non-dimensional fiber length. We also identified the critical bending number from slight swing mode to violent flapping mode
Plasticity performance of Al0.5CoCrCuFeNi high-entropy alloys under nanoindentation
The statistical and dynamic behaviors of the displacement-load curves of a high-entropy alloy Al0.3CoCrCuFeNi were analyzed for the nanoindentation performed at two temperatures. Critical behavior of serrations at room temperature and chaotic flows at 200 degrees C were detected. These results are attributed to the interaction among a large number of slip hands. For the nanoindentation at room temperature recurrent partial events between slip hands introduce a hierarchy of length scales leading to a critical state. For the nanoindentation at 200 degrees C there is no spatial interference between two slip hands which is corresponding to the evolution of separated trajectory of chaotic behavior
Accumulation capacity of ions in cabbage (Brassica oleracea L.) supplied with sea water
Cabbage seedlings were grown hydroponically to study the effects of different concentrations of seawater on the seedling growth, ion content under one-fourth strength Hoagland's nutrient solution in the greenhouse. The biomass of various organs of cabbage seedlings as well as the whole plants was significantly higher in the treatments with 1 g and 2 g sea salt/L than the no-salt control, but the treatments with 4, 5 or 6 g sea salt/L caused a decrease in growth. Root/shoot ratio remained at the level of control regardless of the sea salt treatment. Na+ and Cl- concentration in different parts of cabbage seedlings increased significantly, whereas K+ and Ca2+ concentration generally increased at low concentrations of sea salt and then decreased with increasing seawater concentration. Sodium and K+ concentrations were significantly higher in the stems than roots and leaves regardless of the sea salt treatment. The sea salt treatment increased Mg2+ concentration in stems and leaves of cabbage seedlings. An increase in Na+ and Cl- concentration in roots, stems and leaves of cabbage seedlings was the main contributor to declining ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+. The obtained data suggest that cabbage seedlings have strong ability to sustain seawater stress by the regulation of transport and distribution of ions
An inhomogeneous and anisotropic constitutive model of human dentin
Dentin constitutes the major part of human tooth. It is composed of a large number of tubules with both variational radii and
radially parallel pattern. In addition, peritubular dentin surrounds each tubule lumen and has a higher elastic modulus than the
matrix of dentin, i.e. intertubular dentin. Considering the above microstructural characteristics, a micromechanics model is used in
this paper to evaluate the overall elastic properties of dentin. Five independent effective elastic parameters in transverse isotropic
elasticity matrix can be expressed analytically by the material parameters of peri- and intertubular dentin and the volume fraction of
tubules. To determine the effectivity of this theoretical model, a finite element (FE) model simulating a longitudinal tooth slice in
moir!e fringe testing of Wang and Weiner (J. Biomech. 31 (1998) 135) was performed. Furthermore, the FE model was developed
incorporate modeling of variation of tubule’s diameter and softer characteristic of intertubular dentin near the dentin–enamel
junction and around the pulp chamber. It turned out that the isoline figure of longitudinal displacement by FE calculation has very
similar patterns to the moir!e fringe results. However, the FE results of displacement by traditional stress–strain models which regard
dentin as a homogeneous and isotropic material show an obviously different strain distributions as compared to published moir!e
fringes results. Thus the inhomogeneous and anisotropic model developed in this paper more accurately reflects the true physical
nature of human dentin
The asymptotic near-tip solution for mode-iii crack in steady growth in power hardening media
Two local solutions, one perpendicular and one parallel to the direction of solar gravitational field, are discussed. The influence of gravity on the gas-dynamical process driven by the piston is discussed in terms of characteristic theory, and the flow field is given quantitatively. For a typical piston trajectory similar to the one for an eruptive prominence, the velocity of the shock front which locates ahead the transient front is nearly constant or slightly accelerated, and the width of the compressed flow region may be kept nearly constant or increased linearly, depending on the velocity distribution of the piston. Based on these results, the major features of the transient may be explained. Some of the fine structure of the transient is also shown, which may be compared in detail with observations
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