28,087 research outputs found
Development of a novel virtual coordinate measuring machine
Existing VCMMs (virtual coordinate measuring machine) have been mainly developed to either simulate the measurement process hence enabling the off-line programming, or to perform error analysis and uncertainty evaluation. Their capability and performance could be greatly improved if there is a complete solution to cover the whole process and provide an integrated environment. The aim of this study is to develop such a VCMM that not only supports measurement process simulation, but also performs uncertainty evaluation. It makes use of virtual reality techniques to provide an accurate model of a physical CMM, together with uncertainty evaluation. An interface is also provided to communicate with CMM controller, allowing the measuring programs generated and simulated in the VCMM to be executed or tested on the physical CMM afterwards. This paper discusses the proposal of a novel VCMM design and the preliminary results
The structural, mechanical, electronic, optical and thermodynamic properties of t-XAs (X Si, Ge and Sn) by first-principles calculations
The structural, mechanical, electronic, optical and thermodynamic properties
of the t-XAs (X Si, Ge and Sn) with
tetragonal structure have been investigated by first principles calculations.
Our calculated results show that these compounds are mechanically and
dynamically stable. By the study of elastic anisotropy, it is found that the
anisotropic of the t-SnAs is stronger than that
of t-SiAs and
t-GeAs. The band structures and density of states
show that the t-XAs (Si, Ge and Sn) are
semiconductors with narrow band gaps. Based on the analyses of electron density
difference, in t-XAs As atoms get electrons, X
atoms lose electrons. The calculated static dielectric constants,
, are 15.5, 20.0 and 15.1 eV for
t-XAs (X Si, Ge and Sn), respectively. The
Dulong-Petit limit of t-XAs is about 10 J
molK. The thermodynamic stability successively
decreases from t-SiAs to
t-GeAs to t-SnAs.Comment: 14 pages, 10 figures, 6 table
Caching and Auditing in the RPPM Model
Crampton and Sellwood recently introduced a variant of relationship-based
access control based on the concepts of relationships, paths and principal
matching, to which we will refer as the RPPM model. In this paper, we show that
the RPPM model can be extended to provide support for caching of authorization
decisions and enforcement of separation of duty policies. We show that these
extensions are natural and powerful. Indeed, caching provides far greater
advantages in RPPM than it does in most other access control models and we are
able to support a wide range of separation of duty policies.Comment: Accepted for publication at STM 2014 (without proofs, which are
included in this longer version
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Applying semantic web services to enterprise web
Enterprise Web provides a convenient, extendable, integrated platform for information sharing and knowledge management. However, it still has many drawbacks due to complexity and increasing information glut, as well as the heterogeneity of the information processed. Research in the field of Semantic Web Services has shown the possibility of adding higher level of semantic functionality onto the top of current Enterprise Web, enhancing usability and usefulness of resource, enabling decision support and automation. This paper aims to explore the use of Semantic Web Services in Enterprise Web and discuss the Semantic Web Services (SWS) approach for designing Enterprise Web applications. A Semantic Web Service oriented model is presented, in which resources and services are described by ontology, and processed through Semantic Web Service, allowing integrated administration, interoperability and automated reasoning
Morphological evolution of a 3D CME cloud reconstructed from three viewpoints
The propagation properties of coronal mass ejections (CMEs) are crucial to
predict its geomagnetic effect. A newly developed three dimensional (3D) mask
fitting reconstruction method using coronagraph images from three viewpoints
has been described and applied to the CME ejected on August 7, 2010. The CME's
3D localisation, real shape and morphological evolution are presented. Due to
its interaction with the ambient solar wind, the morphology of this CME changed
significantly in the early phase of evolution. Two hours after its initiation,
it was expanding almost self-similarly. CME's 3D localisation is quite helpful
to link remote sensing observations to in situ measurements. The investigated
CME was propagating to Venus with its flank just touching STEREO B. Its
corresponding ICME in the interplanetary space shows a possible signature of a
magnetic cloud with a preceding shock in VEX observations, while from STEREO B
only a shock is observed. We have calculated three principle axes for the
reconstructed 3D CME cloud. The orientation of the major axis is in general
consistent with the orientation of a filament (polarity inversion line)
observed by SDO/AIA and SDO/HMI. The flux rope axis derived by the MVA analysis
from VEX indicates a radial-directed axis orientation. It might be that locally
only the leg of the flux rope passed through VEX. The height and speed profiles
from the Sun to Venus are obtained. We find that the CME speed possibly had
been adjusted to the speed of the ambient solar wind flow after leaving COR2
field of view and before arriving Venus. A southward deflection of the CME from
the source region is found from the trajectory of the CME geometric center. We
attribute it to the influence of the coronal hole where the fast solar wind
emanated from.Comment: ApJ, accepte
Charmed Baryon Weak Decays with SU(3) Flavor Symmetry
We study the semileptonic and non-leptonic charmed baryon decays with
flavor symmetry, where the charmed baryons can be , , , or . With denoted as the baryon
octet (decuplet), we find that the
decays are forbidden, while the ,
, and decays are the only existing Cabibbo-allowed modes
for , , and , respectively. We predict the rarely studied
decays, such as and . For the observation, the doubly and triply charmed baryon decays of
, ,
, and are the favored Cabibbo-allowed decays,
which are accessible to the BESIII and LHCb experiments.Comment: 29 pages, no figure, a typo in the table correcte
Carbon and Nitrogen Pools in Soil Aggregates Were Affected by Grazing Component ---- Results from Dry and Wet Sieving Methods
Grazing intensity can affect soil carbon (C) sequestration in semiarid grassland, but less is known about the effects of grazing component (defoliation, trampling, excreta return and their combinations) on the C and Nitrogen (N) in soil aggregates. In this study, a simulated grazing experiment was established in a typical steppe of Inner Mongolia, and we investigated the impacts of different grazing component treatments on the different size of aggregates distribution and their C and N content from dry and wet physical separations. Different soil C fractions were showed in different sieving method. The C content of different aggregate size showed microaggregates (250-53μm, 7-17%)\u3emacroaggregates (\u3e250μm, 4-12%) \u3efine fraction (\u3c53μm, 0.4-3%) when dry sieving method was performed, but wet sieving resulted in the higher C content in microaggregates (6-14%) and fine fraction (5-11%) than macroaggregates (1-5%). N content of different size of aggregates showed similar trend with C content. The results revealed that grazing component had a marked impact on soil fraction and C and N content with the significant decreasing percentage of macroaggregates and their C and N storage under defoliation. Our result indicated that both dry-sieved aggregates and water-stable aggregates should be concerned to evaluate the short-term grazing disturbance on C and N distribution in soil aggregates. Furthermore, we suggest that trampling is critical for the soil compaction, but defoliation may play a more important role in soil aggregation and C storage in grazing grassland
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