13,864 research outputs found
Numerical simulation of stress wave interaction in short-delay blasting with a single free surface
It is generally believed that stress wave superposition does occur and plays an important role in cutting blasting with a single free surface, in which explosive columns of several blast holes with short spacing are simultaneously initiated. However, considering the large scatter of pyrotechnic delay detonators that are used in most underground metal mines in China, the existence of stress wave superposition and the influence of this effect on rock fragmentation are questionable. In the present study, the stress wave interaction in short-delay blasting with a single free surface was studied through the use of the LS-DYNA code. Stress waves induced by two blast holes blasting with different delays were compared with the single blast hole case, and the effects of delay time, detonating location and spacing on stress wave superposition were investigated. The numerical results showed that for blast holes with a 1 m spacing, stress wave interaction only occurs when the delay time is 0 ms and does not occur for blasting with delays of more than 1 ms. An increase in the duration of a stress wave via optimizing the detonation location does not improve the stress wave interaction. For a 1 ms delay, stress wave superposition only occurs when the spacing is more than 4 m, which is a rare case in practice. The results indicated that the occurrence of stress wave superposition for blasting with a single free surface is strictly limited to conditions that would be difficult to achieve under the existing delay accuracy of detonators. Therefore, it is unrealistic to improve fragmentation via the stress wave interaction in field blasting. Furthermore, the numerical results of the stress wave interaction also show that there would be a great potential to reduce the hazardous vibrations induced by short-delay blasting by using electronic detonators with better control of delays in an order of several milliseconds
Testing mechanisms of compensatory fitness of dioecy in a cosexual world
Questions: All else being equal, populations of dioecious species with a 50:50 sex ratio have only half the effective reproductive population size of bisexual species of equal abundance. Consequently, there is a need to explain how dioecious and bisexual species coexist. Increased mean individual seed mass, fecundity, and population density have all been proposed as attributes of unisexual individuals or populations that may contribute to the persistence or resilience of dioecious species. To date, no studies have compared sympatric dioecious and cosexual species with respect to all three components of fitness. In this study, we sought evidence for these compensatory advantages (higher seed mass, greater seed production per unit basal area, and higher population density) in dioecious species. Location: Five 20–25 ha forest dynamic plots spanning a latitudinal gradient in China, including two temperate, two subtropical, and one tropical forest. Methods: We used a phylogenetically corrected generalized linear modelling approach to assess the phylogenetic dependence and joint evolution of sexual system, seed mass and production, and ecological abundances among 48–333 species and 32,568–136,237 individuals per forest. Results: Across all five forests, we detected no consistent advantage for dioecious relative to sympatric cosexual species with respect to mean individual seed mass, seed production or the density of stems in any size class. Conclusions: Our study suggests that seed traits may provide compensatory mechanisms in some forests, but most often the coexistence of sexual systems cannot be explained by advantages of dioecy related to seed quality and demographic parameters. Future investigations of the factors that promote coexistence may increase our understanding by expanding the search to include attributes such as lifespan and tolerance or resistance to herbivores
Understanding the white-light flare on 2012 March 9 : Evidence of a two-step magnetic reconnection
We attempt to understand the white-light flare (WLF) that was observed on
2012 March 9 with a newly constructed multi-wavelength solar telescope called
the Optical and Near-infrared Solar Eruption Tracer (ONSET). We analyzed WLF
observations in radio, H-alpha, white-light, ultraviolet, and X-ray bands. We
also studied the magnetic configuration of the flare via the nonlinear
force-free field (NLFFF) extrapolation and the vector magnetic field observed
by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO). Continuum emission enhancement clearly appeared at the 3600
angstrom and 4250 angstrom bands, with peak contrasts of 25% and 12%,
respectively. The continuum emission enhancement closely coincided with the
impulsive increase in the hard X-ray emission and a microwave type III burst at
03:40 UT. We find that the WLF appeared at one end of either the sheared or
twisted field lines or both. There was also a long-lasting phase in the H-alpha
and soft X-ray bands after the white-light emission peak. In particular, a
second, yet stronger, peak appeared at 03:56 UT in the microwave band. This
event shows clear evidence that the white-light emission was caused by
energetic particles bombarding the lower solar atmosphere. A two-step magnetic
reconnection scenario is proposed to explain the entire process of flare
evolution, i.e., the first-step magnetic reconnection between the field lines
that are highly sheared or twisted or both, and the second-step one in the
current sheet, which is stretched by the erupting flux rope. The WLF is
supposed to be triggered in the first-step magnetic reconnection at a
relatively low altitude.Comment: 4 pages, 4 figures, published in A&A Lette
Damage Assessment of Two-Way RC Slab Subjected to Blast Load using Mode Approximation Approach
Significant research efforts have been invested on studying the response and damage of structures subjected to blast loads for better life and property protections. The single-degree-of-freedom (SDOF) approach has been widely adopted to simplify the structural response analysis for engineering design purpose. However, such an approach under certain circumstances oversimplifies the structural behavior and might not give reliable predictions of structural responses to blast loads. On the other hand, although detailed high fidelity finite element (FE) approach is able to give relatively accurate predictions of structural response, it is unfortunately not straightforward for application and very time-consuming, which impedes its application among engineers. Therefore, a method that can assure not only reliability but also efficiency is highly needed for design practice. In the present study, mode approximation method with Pressure–Impulse (P-I) diagrams is applied to analyze response and damage of RC slab due to blast load. Slab under analysis is assumed rigid-plastic and simply supported. Shear failure, bending failure and combined failure modes are considered based on different failure modes. Critical equations for structural shear and bending failures are derived respectively with appropriate failure criteria. P–I diagrams are then developed for quick damage assessments. The analytical results are verified by comparing with high fidelity numerical simulations. The reliability and efficiency of using this approach for design and analyzing RC slab response under blast loads are demonstrated
Bidirectional optimization of the melting spinning process
This is the author's accepted manuscript (under the provisional title "Bi-directional optimization of the melting spinning process with an immune-enhanced neural network"). The final published article is available from the link below. Copyright 2014 @ IEEE.A bidirectional optimizing approach for the melting spinning process based on an immune-enhanced neural network is proposed. The proposed bidirectional model can not only reveal the internal nonlinear relationship between the process configuration and the quality indices of the fibers as final product, but also provide a tool for engineers to develop new fiber products with expected quality specifications. A neural network is taken as the basis for the bidirectional model, and an immune component is introduced to enlarge the searching scope of the solution field so that the neural network has a larger possibility to find the appropriate and reasonable solution, and the error of prediction can therefore be eliminated. The proposed intelligent model can also help to determine what kind of process configuration should be made in order to produce satisfactory fiber products. To make the proposed model practical to the manufacturing, a software platform is developed. Simulation results show that the proposed model can eliminate the approximation error raised by the neural network-based optimizing model, which is due to the extension of focusing scope by the artificial immune mechanism. Meanwhile, the proposed model with the corresponding software can conduct optimization in two directions, namely, the process optimization and category development, and the corresponding results outperform those with an ordinary neural network-based intelligent model. It is also proved that the proposed model has the potential to act as a valuable tool from which the engineers and decision makers of the spinning process could benefit.National Nature Science Foundation of China, Ministry of Education of China, the Shanghai Committee of Science and Technology), and the Fundamental Research Funds for the Central Universities
Photometric properties and luminosity function of nearby massive early-type galaxies
We perform photometric analyses for a bright early-type galaxy (ETG) sample
with 2949 galaxies ( mag) in the redshift range of 0.05 to
0.15, drawn from the SDSS DR7 with morphological classification from Galaxy Zoo
1. We measure the Petrosian and isophotal magnitudes, as well as the
corresponding half-light radius for each galaxy. We find that for brightest
galaxies ( mag), our Petrosian magnitudes, and isophotal
magnitudes to 25 and 1\% of the sky brightness are on
average 0.16 mag, 0.20 mag, and 0.26 mag brighter than the SDSS Petrosian
values, respectively. In the first case the underestimations are caused by
overestimations in the sky background by the SDSS PHOTO algorithm, while the
latter two are also due to deeper photometry. Similarly, the typical half-light
radii () measured by the SDSS algorithm are smaller than our
measurements. As a result, the bright-end of the -band luminosity function
is found to decline more slowly than previous works. Our measured luminosity
densities at the bright end are more than one order of magnitude higher than
those of Blanton et al. (2003), and the stellar mass densities at and are a few tenths
and a factor of few higher than those of Bernardi et al. (2010). These results
may significantly alleviate the tension in the assembly of massive galaxies
between observations and predictions of the hierarchical structure formation
model.Comment: 43 pages, 14 figures, version accepted for publication in the
Astrophysical Journa
Accurate Modelling of Left-Handed Metamaterials Using Finite-Difference Time-Domain Method with Spatial Averaging at the Boundaries
The accuracy of finite-difference time-domain (FDTD) modelling of left-handed
metamaterials (LHMs) is dramatically improved by using an averaging technique
along the boundaries of LHM slabs. The material frequency dispersion of LHMs is
taken into account using auxiliary differential equation (ADE) based dispersive
FDTD methods. The dispersive FDTD method with averaged permittivity along the
material boundaries is implemented for a two-dimensional (2-D) transverse
electric (TE) case. A mismatch between analytical and numerical material
parameters (e.g. permittivity and permeability) introduced by the time
discretisation in FDTD is demonstrated. The expression of numerical
permittivity is formulated and it is suggested to use corrected permittivity in
FDTD simulations in order to model LHM slabs with their desired parameters. The
influence of switching time of source on the oscillation of field intensity is
analysed. It is shown that there exists an optimum value which leads to fast
convergence in simulations.Comment: 17 pages, 7 figures, submitted to Journal of Optics A Nanometa
special issu
Effect of propionate on the production of natamycin with Streptomyces gilvosporeus XM-172
This study described the influence of feeding short-chain fatty acids and alcohols on natamycin production in the glucose basal medium, produced by Streptomyces gilvosporeus XM-172. The highest natamycin production was obtained with feeding propionate as compared to other precursors. The optimal propionate concentration and feeding time were 6 g L-1 and early log phase, respectively. This optimal propionate feeding strategy led to a natamycin production of 6.72 g L-1, which was nearly 85% higher than that of the control. It was firstly revealed that propionate could greatly promote natamycin biosynthesis by S. gilvosporeus.Key words: Precursor, propionate, natamycin production, Streptomyces gilvosporeus XM-172
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