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71.
T
c data are reported for powders of cation-stoichiometric Bi2Sr2CaCu2O and for nonstoichiometric samples based on the three mechanisms BiSr, SrCa and Sr vacancy. For each, the T
c values depend critically on the final oxygen contents, which were varied by heating samples in either O2 or N2 at different temperatures. Stoichiometric Bi2Sr2CaCu2O has the highest T
c, 92 K, obtained after heating in O2 at 820 °C. Heating in O2 at lower temperatures gives rise to overdoping and T
c decreases to 60 K. The other cation compositions show a smaller maximum T
c but also less reduction in T
c on overdoping. Under-doped samples, with reduced T
c values were obtained on heating in N2. These data, together with selected literature results, lead to a unified picture of the variation of T
c with cation composition and oxygen content. 相似文献
72.
Nima Taghipour Mariona Dalmases Guy L. Whitworth Miguel Dosil Andreas Othonos Sotirios Christodoulou Shanti Maria Liga Gerasimos Konstantatos 《Advanced materials (Deerfield Beach, Fla.)》2023,35(1):2207678
The use of colloidal quantum dots (CQDs) as a gain medium in infrared laser devices has been underpinned by the need for high pumping intensities, very short gain lifetimes, and low gain coefficients. Here, PbS/PbSSe core/alloyed-shell CQDs are employed as an infrared gain medium that results in highly suppressed Auger recombination with a lifetime of 485 ps, lowering the amplified spontaneous emission (ASE) threshold down to 300 µJ cm−2, and showing a record high net modal gain coefficient of 2180 cm−1. By doping these engineered core/shell CQDs up to nearly filling the first excited state, a significant reduction of optical gain threshold is demonstrated, measured by transient absorption, to an average-exciton population-per-dot 〈Nth〉g of 0.45 due to bleaching of the ground state absorption. This in turn have led to a fivefold reduction in ASE threshold at 〈Nth〉ASE = 0.70 excitons-per-dot, associated with a gain lifetime of 280 ps. Finally, these heterostructured QDs are used to achieve near-infrared lasing at 1670 nm at a pump fluences corresponding to sub-single-exciton-per-dot threshold (〈Nth〉Las = 0.87). This work brings infrared CQD lasing thresholds on par to their visible counterparts, and paves the way toward solution-processed infrared laser diodes. 相似文献
73.
Selecting the incorrect control during the operation of underground bolting and drilling equipment causes serious injuries. Shape coding and the layout of dual control banks are two aspects of control design which require further examination. The aims of this research were: (i) to determine whether arbitrary shape coding was effective in reducing selection error rates in a virtual analogy of roof-bolting; and (ii) to determine whether any advantages exist for mirror or place layouts for dual control situations in this situation. Two experiments were conducted to address these questions. No benefits of arbitrary shape coding were evident while control location remained constant. When control location was altered, shape coding did provide a significant reduction in selection error rate. No differences between mirror or place arrangements were detected and this question remains open. 相似文献
74.
A real time control strategy for fuel cell hybrid vehicles is proposed. The objective is to reduce the hydrogen consumption by using an efficient power sharing strategy between the fuel cell system (FCS) and the energy buffer (EB). The energy buffer (battery or supercapacitor) is charge-sustained (no plug-in capabilities). The real time control strategy is derived from a non-causal optimization algorithm based on optimal control theory. The strategy is validated experimentally with a hardware-in-the-loop (HiL) test bench based on a 600 W fuel cell system. 相似文献
75.
Daniel F. Macedo Aldri L. dos Santos Luiz H.A. Correia José M. Nogueira Guy Pujolle 《Computer Networks》2010,54(17):2979-2990
Wireless networks can vary both the transmission power and modulation of links. Existing routing protocols do not take transmission power control (TPC) and modulation adaptation (also known as rate adaptation – RA) into account at the same time, even though the performance of wireless networks can be significantly improved when routing algorithms use link characteristics to build their routes. This article proposes and evaluates extensions to routing protocols to cope with TPC and RA. The enhancements can be applied to any link state or distance vector routing protocols. An evaluation considering node density, node mobility and link error show that TPC- and RA-aware routing algorithms improve the average latency and the end-to-end throughput, while consuming less energy than traditional protocols. 相似文献
76.
Jordi Cabot Robert Clarisó Esther Guerra Juan de Lara 《Software and Systems Modeling》2010,9(3):335-357
In this paper we present an approach for the analysis of graph transformation rules based on an intermediate OCL representation.
We translate different rule semantics into OCL, together with the properties of interest (like rule applicability, conflicts
or independence). The intermediate representation serves three purposes: (1) it allows the seamless integration of graph transformation
rules with the MOF and OCL standards, and enables taking the meta-model and its OCL constraints (i.e. well-formedness rules)
into account when verifying the correctness of the rules; (2) it permits the interoperability of graph transformation concepts
with a number of standards-based model-driven development tools; and (3) it makes available a plethora of OCL tools to actually
perform the rule analysis. This approach is especially useful to analyse the operational semantics of Domain Specific Visual
Languages. We have automated these ideas by providing designers with tools for the graphical specification and analysis of
graph transformation rules, including a back-annotation mechanism that presents the analysis results in terms of the original
language notation. 相似文献
77.
78.
Guy Redding Marlon Dumas Arthur H. M. ter Hofstede Adrian Iordachescu 《Service Oriented Computing and Applications》2010,4(3):191-201
Mainstream business process modelling techniques often promote a design paradigm wherein the activities that may be performed
within a case, together with their usual execution order, form the backbone on top of which other aspects are anchored. This
Fordist paradigm, while effective in standardised and production-oriented domains, breaks when confronted with processes in
which case-by-case variations and exceptions are the norm. We contend that the effective design of flexible processes calls
for a substantially different modelling paradigm. Motivated by requirements from the human services domain, we explore the
hypothesis that a framework consisting of a small set of coordination concepts, combined with established object-oriented
modelling principles, provides a suitable foundation for designing highly flexible processes. Several human service delivery
processes have been designed using this framework, and the resulting models have been used to realise a system to support
these processes in a pilot environment. 相似文献
79.
80.
Guy Serbin Craig S.T. Daughtry James B. Reeves III 《Remote sensing of environment》2009,113(1):224-1836
The management of crop residues (non-photosynthetic vegetation) in agricultural fields influences soil erosion and soil carbon sequestration. Remote sensing methods can efficiently assess crop residue cover and related tillage intensity over many fields in a region. Although the reflectance spectra of soils and crop residues are often similar in the visible, near infrared, and the lower part of the shortwave infrared (400-1900 nm) wavelength region, specific diagnostic chemical absorption features are evident in the upper shortwave infrared (1900-2500 nm) region. Two reflectance band height indices used for estimating residue cover are the Cellulose Absorption Index (CAI) and the Lignin-Cellulose Absorption (LCA) index, both of which use reflectances in the upper shortwave infrared (SWIR). Soil mineralogy and composition will affect soil spectral properties and may limit the usefulness of these spectral indices in certain areas. Our objectives were to (1) identify minerals and soil components with absorption features in the 2000 nm to 2400 nm wavelength region that would affect CAI and LCA and (2) assess their potential impact on remote sensing estimates of crop residue cover. Most common soil minerals had CAI values ≤ 0.5, whereas crop residues were always > 0.5, allowing for good contrast between soils and residues. However, a number of common soil minerals had LCA values > 0.5, and, in some cases, the mineral LCA values were greater than those of the crop residues, which could limit the effectiveness of LCA for residue cover estimation. The LCA of some dry residues and live corn canopies were similar in value, unlike CAI. Thus, the Normalized Difference Vegetation Index (NDVI) or similar method should be used to separate out green vegetation pixels. Mineral groups, such as garnets and chlorites, often have wide ranges of CAI and LCA values, and thus, mineralogical analyses often do not identify individual mineral species required for precise CAI estimation. However, these methods are still useful for identifying mineral soils requiring additional scrutiny. Future advanced multi- and hyperspectral remote sensing platforms should include CAI bands to allow for crop residue cover estimation. 相似文献