4,449 research outputs found
Unboxing Cluster Heatmaps
Background: Cluster heatmaps are commonly used in biology and related fields to reveal hierarchical clusters in data matrices. This visualization technique has high data density and reveal clusters better than unordered heatmaps alone. However, cluster heatmaps have known issues making them both time consuming to use and prone to error. We hypothesize that visualization techniques without the rigid grid constraint of cluster heatmaps will perform better at clustering-related tasks.
Results: We developed an approach to “unbox” the heatmap values and embed them directly in the hierarchical clustering results, allowing us to use standard hierarchical visualization techniques as alternatives to cluster heatmaps. We then tested our hypothesis by conducting a survey of 45 practitioners to determine how cluster heatmaps are used, prototyping alternatives to cluster heatmaps using pair analytics with a computational biologist, and evaluating those alternatives with hour-long interviews of 5 practitioners and an Amazon Mechanical Turk user study with approximately 200 participants. We found statistically significant performance differences for most clustering-related tasks, and in the number of perceived visual clusters. Visit git.io/vw0t3 for our results.
Conclusions: The optimal technique varied by task. However, gapmaps were preferred by the interviewed practitioners and outperformed or performed as well as cluster heatmaps for clustering-related tasks. Gapmaps are similar to cluster heatmaps, but relax the heatmap grid constraints by introducing gaps between rows and/or columns that are not closely clustered. Based on these results, we recommend users adopt gapmaps as an alternative to cluster heatmaps
Entropy of generic quantum isolated horizons
We review our recent proposal of a method to extend the quantization of
spherically symmetric isolated horizons, a seminal result of loop quantum
gravity, to a phase space containing horizons of arbitrary geometry. Although
the details of the quantization remain formally unchanged, the physical
interpretation of the results can be quite different. We highlight several such
differences, with particular emphasis on the physical interpretation of black
hole entropy in loop quantum gravity.Comment: 4 pages, contribution to loops '11 conference proceedings; 2
references added, a sentence remove
Savory Grazing System: A Research Update
Livestock performance, forage use and soil compaction were studied in Repeated Seasonal (RSG) and High Performance Short Duration Grazing (HPSDG) systems on mixed prairie in good to excellent condition in western South Dakota. In May 1981 and 1982, yearling ewes were allocated to six RSG and six HPSDG pastures and removed in October of each year. Stocking rates in both systems were periodically adjusted to result in 40 to 50% terminal use of shortgrasses. In both years, the stocking rates in HPSDG were approximately twice those in RSG. Livestock performance was the same in both systems. Forage use was more uniform and higher proportions of midgrasses were grazed in HPSDG than in RSG. Soil compaction increased with grazing intensity in RSG but was constant at a value equivalent to moderate grazing intensity in HPSDG
Coherent states, constraint classes, and area operators in the new spin-foam models
Recently, two new spin-foam models have appeared in the literature, both
motivated by a desire to modify the Barrett-Crane model in such a way that the
imposition of certain second class constraints, called cross-simplicity
constraints, are weakened. We refer to these two models as the FKLS model, and
the flipped model. Both of these models are based on a reformulation of the
cross-simplicity constraints. This paper has two main parts. First, we clarify
the structure of the reformulated cross-simplicity constraints and the nature
of their quantum imposition in the new models. In particular we show that in
the FKLS model, quantum cross-simplicity implies no restriction on states. The
deeper reason for this is that, with the symplectic structure relevant for
FKLS, the reformulated cross-simplicity constraints, in a certain relevant
sense, are now \emph{first class}, and this causes the coherent state method of
imposing the constraints, key in the FKLS model, to fail to give any
restriction on states. Nevertheless, the cross-simplicity can still be seen as
implemented via suppression of intertwiner degrees of freedom in the dynamical
propagation. In the second part of the paper, we investigate area spectra in
the models. The results of these two investigations will highlight how, in the
flipped model, the Hilbert space of states, as well as the spectra of area
operators exactly match those of loop quantum gravity, whereas in the FKLS (and
Barrett-Crane) models, the boundary Hilbert spaces and area spectra are
different.Comment: 21 pages; statements about gamma limits made more precise, and minor
phrasing change
Value at Risk models with long memory features and their economic performance
We study alternative dynamics for Value at Risk (VaR) that incorporate a slow moving component and information on recent aggregate returns in established quantile (auto) regression models. These models are compared on their economic performance, and also on metrics of first-order importance such as violation ratios. By better economic performance, we mean that changes in the VaR forecasts should have a lower variance to reduce transaction costs and should lead to lower exceedance sizes without raising the average level of the VaR. We find that, in combination with a targeted estimation strategy, our proposed models lead to improved performance in both statistical and economic terms
Complex Ashtekar variables and reality conditions for Holst's action
From the Holst action in terms of complex valued Ashtekar variables
additional reality conditions mimicking the linear simplicity constraints of
spin foam gravity are found. In quantum theory with the results of You and
Rovelli we are able to implement these constraints weakly, that is in the sense
of Gupta and Bleuler. The resulting kinematical Hilbert space matches the
original one of loop quantum gravity, that is for real valued Ashtekar
connection. Our result perfectly fit with recent developments of Rovelli and
Speziale concerning Lorentz covariance within spin-form gravity.Comment: 24 pages, 2 picture
Generic isolated horizons in loop quantum gravity
Isolated horizons model equilibrium states of classical black holes. A
detailed quantization, starting from a classical phase space restricted to
spherically symmetric horizons, exists in the literature and has since been
extended to axisymmetry. This paper extends the quantum theory to horizons of
arbitrary shape. Surprisingly, the Hilbert space obtained by quantizing the
full phase space of \textit{all} generic horizons with a fixed area is
identical to that originally found in spherical symmetry. The entropy of a
large horizon remains one quarter its area, with the Barbero-Immirzi parameter
retaining its value from symmetric analyses. These results suggest a
reinterpretation of the intrinsic quantum geometry of the horizon surface.Comment: 13 page
The Gibbs paradox, Black hole entropy and the thermodynamics of isolated horizons
This letter presents a new, solely thermodynamical argument for considering
the states of the quantum isolated horizon of a black hole as distinguishable.
We claim that only if the states are distinguishable, the thermodynamic entropy
is an extensive quantity and can be well-defined. To show this, we make a
comparison with a classical ideal gas system whose statistical description
makes only sense if an additional 1/N!-factor is included in the state counting
in order to cure the Gibbs paradox. The case of the statistical description of
a quantum isolated horizon is elaborated, to make the claim evident.Comment: 8 pages, closest to the published version; taken from the author's
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A Multivariate Analysis of United States and Global Real Estate Investment Trusts
Using daily data for the period February 2006 to July 2013 we examine the return and volatility linkages between the two main United States REIT sub-sectors and global linkages between the Americas, Europe and the Asia Pacific regions using the BEKK-GARCH and the DCC-GARCH models. We find that there is no evidence of any volatility spillovers between the US sub-sectors. By contrast, we find evidence of volatility spillovers between the Asia Pacific and the Americas, the Asia Pacific and Europe but no spillovers between the United States and Europe. Our results suggest that the REIT market is becoming increasingly globalized and that investors need to consider time varying volatility and correlations across different regions of the world when forming their optimal portfolio-allocations
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