215,892 research outputs found
Origin of Crashes in 3 US stock markets: Shocks and Bubbles
This paper presents an exclusive classification of the largest crashes in Dow
Jones Industrial Average (DJIA), SP500 and NASDAQ in the past century. Crashes
are objectively defined as the top-rank filtered drawdowns (loss from the last
local maximum to the next local minimum disregarding noise fluctuations), where
the size of the filter is determined by the historical volatility of the index.
It is shown that {\it all} crashes can be linked to either an external shock,
{\it e.g.}, outbreak of war, {\it or} a log-periodic power law (LPPL) bubble
with an empirically well-defined complex value of the exponent. Conversely,
with one sole exception {\it all} previously identified LPPL bubbles are
followed by a top-rank drawdown. As a consequence, the analysis presented
suggest a one-to-one correspondence between market crashes defined as top-rank
filtered drawdowns on one hand and surprising news and LPPL bubbles on the
other. We attribute this correspondence to the Efficient Market Hypothesis
effective on two quite different time scales depending on whether the market
instability the crash represent is internally or externally generated.Comment: 7 pages including 3 tables and 3 figures. Subm. for Proceeding of
Frontier Science 200
Probing spin dynamics and quantum relaxation in LiY0.998Ho0.002F4 via 19F NMR
We report measurements of 19F nuclear spin-lattice relaxation 1/T1 as a
function of temperature and external magnetic field in LiY0.998Ho0.002F4 single
crystal, a single-ion magnet exhibiting interesting quantum effects. The 19F
1/T1 is found to depend on the coupling with the diluted rare-earth (RE)
moments. Depending on the temperature range, a fast spin diffusion regime or a
diffusion limited regime is encountered. In both cases we find it possible to
use the 19F nucleus as a probe of the rare-earth spin dynamics. The results for
1/T1 show a behavior similar to that observed in molecular nanomagnets, a
result which we attribute to the discreteness of the energy levels in both
cases. At intermediate temperatures the lifetime broadening of the crystal
field split RE magnetic levels follows a T3 power law. At low temperature the
field dependence of 1/T1 shows peaks in correspondence to the critical magnetic
fields for energy level crossings (LC). The results can be explained by
inelastic scattering between the fluorine nuclear spins and the RE magnetic
levels. A key result of this study is that the broadening of the levels at LC
is found to be become extremely small at low temperatures, about 1.7 mT, a
value which is comparable to the weak dipolar fields at the RE lattice
positions. Thus, unlike the molecular magnets, decoherence effects are strongly
suppressed, and it may be possible to measure directly the level repulsions at
avoided level crossings.Comment: 21 pages, 5 figure
Assessing brand image through communalitites and asymmetries brand-to-attribute and attribute-to-brand associations.
Brand image is a key component of customer-based brand equity, and refers to the associations a consumer holds in memory. Such associations are often directional; one should distinguish between brand-to-attribute and attribute-to-brand associations. Information on these associations arise from two ways of collecting data respectively: brand-by-brand evaluations of all attributes and attribute-by-attribute evaluations of all brands. In this paper, the authors present a methodological approach, namely correspondence analysis of matched matrices, to assess the communalitites as well as asymmetries between brand-to-attribute and attribute-to-brand associations. The methodology results in perceptual maps visualizing brand image. The approach is illustrated in an empirical market research project in which two samples of consumers evaluated ten brands of deodorants and eleven attributes
Validation in the Software Metric Development Process
In this paper the validation of software metrics will be examined. Two approaches will be combined: representational measurement theory and a validation network scheme. The development process of a software metric will be described, together with validities for the three phases of the metric development process. Representation axioms from measurement theory are used both for the formal and empirical validation. The differentiation of validities according to these phases unifies several validation approaches found in the software metric's literature
A comparison between correspondence analysis and categorical conjoint measurement
We show the equivalence of using correspondence analysis of concatenated tables and a particular algorithm of conjoint analysis named categorical conjoint measurement. The connection is made using canonical correlation. However, although we have proved that equivalence, the standard practice of conjoint analyses to focus in one dimension (the optimal solution) has some shortcomings once we introduce interaction effects. In that case, the use of visual techniques, like correspondence analysis, provides a faster and easier way to compile the preference structure. Finally, we provide an application of our setting making use of an experiment of perfumes where interaction effects between type of essences and strength of essences are shown
Multilingual Schema Matching for Wikipedia Infoboxes
Recent research has taken advantage of Wikipedia's multilingualism as a
resource for cross-language information retrieval and machine translation, as
well as proposed techniques for enriching its cross-language structure. The
availability of documents in multiple languages also opens up new opportunities
for querying structured Wikipedia content, and in particular, to enable answers
that straddle different languages. As a step towards supporting such queries,
in this paper, we propose a method for identifying mappings between attributes
from infoboxes that come from pages in different languages. Our approach finds
mappings in a completely automated fashion. Because it does not require
training data, it is scalable: not only can it be used to find mappings between
many language pairs, but it is also effective for languages that are
under-represented and lack sufficient training samples. Another important
benefit of our approach is that it does not depend on syntactic similarity
between attribute names, and thus, it can be applied to language pairs that
have distinct morphologies. We have performed an extensive experimental
evaluation using a corpus consisting of pages in Portuguese, Vietnamese, and
English. The results show that not only does our approach obtain high precision
and recall, but it also outperforms state-of-the-art techniques. We also
present a case study which demonstrates that the multilingual mappings we
derive lead to substantial improvements in answer quality and coverage for
structured queries over Wikipedia content.Comment: VLDB201
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