457 research outputs found
Hydrogen sorption mechanisms in lithium amide and metal hydride reactive systems.
PhDConsiderable effort has been devoted to the M-N-H system for solid-state hydrogen
storage. However, the desorption mechanism is still unclear and the desorption
temperature is too high for practical considerations. Here, the desorption characteristics
of LiNH2 and a mixture of (LiNH2+LiH) were firstly comparatively studied by
simultaneous then-nogravimetry, differential scanning calorimetry and mass
spectrometry for further understanding of H2 desorption in the (LiNH2+LiH) system.
Mass spectrometry and thermal analysis of (LiNH2+LiH) mixtures indicate that
approximately 5 mass % of H2 is released at 180*C after four hours of milling without
any apparent release of NH3, whereas insufficient mixing of the two compounds cannot
stop the escaping of NH3 from the mixture. Non-unifon-ri mixing can lead to the escape
of NH3 from the mixture. The evidence further supports the notion that NH3
intermediated reaction is a possible reaction path within the thermal desorption of the
(LiNH2+ LiH) mixture. BN additive, among selected nitrides shows the best effect on
desorption from (LiNH2+ LiH). (LiNH2+MgH2)materials with different molar ratios
(4: 3,4: 2 and 4: 1) were also studied for their sorption properties and mechanisms.
Results show that more than 6 mass% H2 is desorbed from 1500C for the (4LiNH2
+3MgH2)mixture, with two H2peaks at 200 and 320'C. Meanwhile, there is only -5
mass% for (4LiNH2 +2MgH2) mixture with one H2 peak at 200 T. Reversibility
measurements suggest that LiNH2 and MgH2 cannot be recovered after absorption;
instead, Li2NH and Mg(NH2)2 (or MgNH) take over to perform the H2 storage functions.
The (4LiNH2+3MgH2 ) mixture possess a greater H2 capacity in first desorption, but
shows less than 2 mass% reversible capacity in subsequent cycles. However, there is
only about I mass% capacity loss during the reversibility measurement for the (4LiNH2
+2MgH2)mixture. Other M-N-H systems, mainly NaH, KH, AlH3 and CaH2, were also
investigated, and only CaH2 shows the capability of reacting with LiNH2 to produce H2
among these candidates
The Implications Of Accounting Conservatism For The Relation Between Earnings And Stock Returns
Characterizing accounting conservatism as the accountants’ tendency to require a higher degree of verification for recognizing good news than bad news, Basu (1997) predicts that the slope coefficient and R2 in a regression of earnings on concurrent stock returns will be higher for bad news (negative stock returns) than for good news (positive stock returns). However, standard econometric analysis indicates that the R2 is a function of the sensitivity of earnings to returns and the noise ratio, which is defined as the ratio of the variance of noise in earnings to the variance of noise in returns. I show that the R2 from the regression of earnings on stock returns is not necessarily higher for bad news than for good news. So the test of R2 is not a robust test of accounting conservatism. Consistent with the prediction, I find that the slope coefficient is higher for bad news firms reporting losses than for good news firms reporting profits, but R2 is lower for bad news firms reporting losses than for good news firms reporting profits
Dynamic multivariable optimization for routing in high-density manufacturing transportation systems
How Different Apology Components Drive Trust Repair: The Moderating Effect of Social Value Orientation
Trust is commonly recognized as a significant part in social life. Exploring how to repair violated trust is necessary because trust transgressions occur frequently. Apologizing is one of the methods commonly used to repair trust. Rather than simply regarding it as a dichotomous phenomenon in most extant researches, additional details on the effect mechanisms of apology components for trust repair must be investigated. Thus this study explores how three apology components drive trust repair through forgiveness, considering the moderating effect of social value orientation. Forgiveness mediates the effect of compensation, empathy, and acknowledgment on trust repair, and that prosocials react more positively to the effect of acknowledgment on trust repair in forgiveness than proselfs. This study can contribute to promoting understanding on how apology really works and how to apology in accordance with people’s tendencies. Keywords:Apology components, Forgiveness, Social value orientation, Trust repai
Amortising the Cost of Mutation Based Fault Localisation using Statistical Inference
Mutation analysis can effectively capture the dependency between source code
and test results. This has been exploited by Mutation Based Fault Localisation
(MBFL) techniques. However, MBFL techniques suffer from the need to expend the
high cost of mutation analysis after the observation of failures, which may
present a challenge for its practical adoption. We introduce SIMFL (Statistical
Inference for Mutation-based Fault Localisation), an MBFL technique that allows
users to perform the mutation analysis in advance against an earlier version of
the system. SIMFL uses mutants as artificial faults and aims to learn the
failure patterns among test cases against different locations of mutations.
Once a failure is observed, SIMFL requires either almost no or very small
additional cost for analysis, depending on the used inference model. An
empirical evaluation of SIMFL using 355 faults in Defects4J shows that SIMFL
can successfully localise up to 103 faults at the top, and 152 faults within
the top five, on par with state-of-the-art alternatives. The cost of mutation
analysis can be further reduced by mutation sampling: SIMFL retains over 80% of
its localisation accuracy at the top rank when using only 10% of generated
mutants, compared to results obtained without sampling
J-model: an open and social ensemble learning architecture for classification
Ensemble learning is a promising direction of research in machine learning, in which an ensemble
classifier gives better predictive and more robust performance for classification problems
by combining other learners. Meanwhile agent-based systems provide frameworks to
share knowledge from multiple agents in an open context. This thesis combines multi-agent
knowledge sharing with ensemble methods to produce a new style of learning system for open
environments.
We now are surrounded by many smart objects such as wireless sensors, ambient communication
devices, mobile medical devices and even information supplied via other humans. When
we coordinate smart objects properly, we can produce a form of collective intelligence from
their collaboration. Traditional ensemble methods and agent-based systems have complementary
advantages and disadvantages in this context. Traditional ensemble methods show better
classification performance, while agent-based systems might not guarantee their performance
for classification. Traditional ensemble methods work as closed and centralised systems
(so they cannot handle classifiers in an open context), while agent-based systems are natural
vehicles for classifiers in an open context.
We designed an open and social ensemble learning architecture, named J-model, to merge the
conflicting benefits of the two research domains. The J-model architecture is based on a service
choreography approach for coordinating classifiers. Coordination protocols are defined by
interaction models that describe how classifiers will interact with one another in a peer-to-peer
manner. The peer ranking algorithm recommends more appropriate classifiers to participate in
an interaction model to boost the success rate of results of their interactions. Coordinated participant
classifiers who are recommended by the peer ranking algorithm become an ensemble
classifier within J-model.
We evaluated J-model’s classification performance with 13 UCI machine learning benchmark
data sets and a virtual screening problem as a realistic classification problem. J-model showed
better performance of accuracy, for 9 benchmark sets out of 13 data sets, than 8 other representative
traditional ensemble methods. J-model gave better results of specificity for 7 benchmark
sets. In the virtual screening problem, J-model gave better results for 12 out of 16 bioassays
than already published results. We defined different interaction models for each specific classification
task and the peer ranking algorithm was used across all the interaction models.
Our research contributions to knowledge are as follows. First, we showed that service choreography
can be an effective ensemble coordination method for classifiers in an open context. Second, we used interaction models that implement task specific coordinations of classifiers to
solve a variety of representative classification problems. Third, we designed the peer ranking
algorithm which is generally and independently applicable to the task of recommending appropriate
member classifiers from a classifier pool based on an open pool of interaction models
and classifiers
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