17,098 research outputs found
Work Function of Single-wall Silicon Carbide Nanotube
Using first-principles calculations, we study the work function of single
wall silicon carbide nanotube (SiCNT). The work function is found to be highly
dependent on the tube chirality and diameter. It increases with decreasing the
tube diameter. The work function of zigzag SiCNT is always larger than that of
armchair SiCNT. We reveal that the difference between the work function of
zigzag and armchair SiCNT comes from their different intrinsic electronic
structures, for which the singly degenerate energy band above the Fermi level
of zigzag SiCNT is specifically responsible. Our finding offers potential
usages of SiCNT in field-emission devices.Comment: 3 pages, 3 figure
Critical Current Density and Resistivity of MgB2 Films
The high resistivity of many bulk and film samples of MgB2 is most readily
explained by the suggestion that only a fraction of the cross-sectional area of
the samples is effectively carrying current. Hence the supercurrent (Jc) in
such samples will be limited by the same area factor, arising for example from
porosity or from insulating oxides present at the grain boundaries. We suggest
that a correlation should exist, Jc ~ 1/{Rho(300K) - Rho(50K)}, where Rho(300K)
- Rho(50K) is the change in the apparent resistivity from 300 K to 50 K. We
report measurements of Rho(T) and Jc for a number of films made by hybrid
physical-chemical vapor deposition which demonstrate this correlation, although
the "reduced effective area" argument alone is not sufficient. We suggest that
this argument can also apply to many polycrystalline bulk and wire samples of
MgB2.Comment: 11 pages, 3 figure
Morphological characterization of shocked porous material
Morphological measures are introduced to probe the complex procedure of shock
wave reaction on porous material. They characterize the geometry and topology
of the pixelized map of a state variable like the temperature. Relevance of
them to thermodynamical properties of material is revealed and various
experimental conditions are simulated. Numerical results indicate that, the
shock wave reaction results in a complicated sequence of compressions and
rarefactions in porous material. The increasing rate of the total fractional
white area roughly gives the velocity of a compressive-wave-series.
When a velocity is mentioned, the corresponding threshold contour-level of
the state variable, like the temperature, should also be stated. When the
threshold contour-level increases, becomes smaller. The area increases
parabolically with time during the initial period. The curve goes
back to be linear in the following three cases: (i) when the porosity
approaches 1, (ii) when the initial shock becomes stronger, (iii) when the
contour-level approaches the minimum value of the state variable. The area with
high-temperature may continue to increase even after the early
compressive-waves have arrived at the downstream free surface and some
rarefactive-waves have come back into the target body. In the case of energetic
material ... (see the full text)Comment: 3 figures in JPG forma
Comparison of Proanthocyanidins with Different Polymerisation Degrees among Berry Skins of ‘Shiraz’, ‘Cabernet Sauvignon’, and ‘Marselan’
Proanthocyanidins in grape berries are synthesised mainly before véraison, and very little attention ispaid to the evolution of proanthocyanidins (PAs) in grapes from véraison to harvest. The present studyfocused on the changes of flavan-3-ols with different degrees of polymerisation in grape skins and thedifference in proanthocyandin composition of ‘Shiraz’, ‘Cabernet Sauvignon’ and ‘Marselan’ grapes (Vitisvinifera L.). The results show that the content of flavan-3-ols, the percentage of prodelphinidins (%P)and mean degree polymerisation (mDP) found in ‘Cabernet Sauvignon’ berry skins at post-véraison werehigher than those in ‘Shiraz’ and ‘Marselan’ skins. Only monomeric, dimeric, trimeric and polymericflavan-3-ols were detected in the three grape cultivars. Polymers with more than tenfold flavan-3-ol unitsaccounted for a relatively high proportion in grape berry skins, and the content in the three cultivarsdeclined continuously during ripening. Principal component analysis showed that proanthocyanidincontent, composition and mDP at grape harvest stage depended strongly on grape cultivar. This studyprovides some useful information for understanding the accumulation of PAs during berry maturationand this information can be used to improve wine quality
The Friedmann equation in modified entropy-area relation from entropy force
According to the formal holographic principle, a modification to the
assumption of holographic principle in Verlinder's investigation of entropy
force is obtained. A more precise relation between entropy and area in the
holographic system is proposed. With the entropy corrections to the
area-relation, we derivate Newton's laws and Einstein equation with a static
spherically symmetric holographic screen. Furthermore we derived the correction
terms to the modified Friedmann equation of the FRW universe starting from the
holographic principle and the Debye model.Comment: Mod. Phys. Lett. A26, 489-500 (2011
Soft Clay Ground Improvement of Ningbo International Airport
Ningbo International Airport is built on the soft clay ground first in China. It has a runway 3,000m in length and 45m in width. The thickness of soft clay is greater than 32m. The calculating consolidation settlement is 0. 48m, far beyond to allowable limit. The soft clay ground is improved by wick drain and surcharge precompression. The airport has been put in service since July, 1990. The process and the results of a full scale embankment test, the ground improvement and the settlement observation are described. The influence of the smear and the well resistance of the wick drain on the consolidation rate are discussed
An empirical study on mutation testing of WS-BPEL programs
Nowadays, applications are increasingly deployed as Web services in the globally distributed cloud computing environment. Multiple services are normally composed to fulfill complex functionalities. Business Process Execution Language for Web Services (WS-BPEL) is an XML-based service composition language that is used to define a complex business process by orchestrating multiple services. Compared with traditional applications, WS-BPEL programs pose many new challenges to the quality assurance, especially testing, of service compositions. A number of techniques have been proposed for testing WS-BPEL programs, but only a few studies have been conducted to systematically evaluate the effectiveness of these techniques. Mutation testing has been widely acknowledged as not only a testing method in its own right but also a popular technique for measuring the fault-detection effectiveness of other testing methods. Several previous studies have proposed a family of mutation operators for generating mutants by seeding various faults into WS-BPEL programs. In this study, we conduct a series of empirical studies to evaluate the applicability and effectiveness of various mutation operators for WS-BPEL programs. The experimental results provide insightful and comprehensive guidance for mutation testing of WS-BPEL programs in practice. In particular, our work is the systematic study in the selection of effective mutation operators specifically for WS-BPEL programs
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