8,885 research outputs found
The Stability of Large External Imbalances: The Role of Returns Differentials
Were the U.S. to persistently earn substantially more on its foreign investments ("U.S. claims") than foreigners earn on their U.S. investments ("U.S. liabilities"), the likelihood that the current environment of sizeable global imbalances will evolve in a benign manner increases. However, utilizing data on the actual foreign equity and bond portfolios of U.S. investors and the U.S. equity and bond portfolios of foreign investors, we find that the returns differential of U.S. claims over U.S. liabilities is essentially zero. Ending our sample in 2005, the differential is positive, whereas through 2004 it is negative; in both cases the differential is statistically indecipherable from zero. Moreover, were it not for the poor timing of investors from developed countries, who tend to shift their U.S. portfolios toward (or away from) equities prior to the subsequent underperformance (or strong performance) of equities, the returns differential would be even lower. Thus, in the context of equity and bond portfolios we find no evidence that the U.S. can count on earning more on its claims than it pays on its liabilities.
Surveying the SO(10) Model Landscape: The Left-Right Symmetric Case
Grand Unified Theories (GUTs) are a very well motivated extensions of the
Standard Model (SM), but the landscape of models and possibilities is
overwhelming, and different patterns can lead to rather distinct
phenomenologies. In this work we present a way to automatise the model building
process, by considering a top to bottom approach that constructs viable and
sensible theories from a small and controllable set of inputs at the high
scale. By providing a GUT scale symmetry group and the field content, possible
symmetry breaking paths are generated and checked for consistency, ensuring
anomaly cancellation, SM embedding and gauge coupling unification. We emphasise
the usefulness of this approach for the particular case of a non-supersymmetric
SO(10) model with an intermediate left-right symmetry and we analyse how
low-energy observables such as proton decay and lepton flavour violation might
affect the generated model landscape.Comment: 36 pages, 6 figure
Compressed and Split Spectra in Minimal SUSY SO(10)
The non-observation of supersymmetric signatures in searches at the Large
Hadron Collider strongly constrains minimal supersymmetric models like the
CMSSM. We explore the consequences on the SUSY particle spectrum in a minimal
SO(10) with large D-terms and non-universal gaugino masses at the GUT scale.
This changes the sparticle spectrum in a testable way and for example can
sufficiently split the coloured and non-coloured sectors. The splitting
provided by use of the SO(10) D-terms can be exploited to obtain light first
generation sleptons or third generation squarks, the latter corresponding to a
compressed spectrum scenario.Comment: 35 pages, 10 figures, published versio
Spatial Filtering Pipeline Evaluation of Cortically Coupled Computer Vision System for Rapid Serial Visual Presentation
Rapid Serial Visual Presentation (RSVP) is a paradigm that supports the
application of cortically coupled computer vision to rapid image search. In
RSVP, images are presented to participants in a rapid serial sequence which can
evoke Event-related Potentials (ERPs) detectable in their Electroencephalogram
(EEG). The contemporary approach to this problem involves supervised spatial
filtering techniques which are applied for the purposes of enhancing the
discriminative information in the EEG data. In this paper we make two primary
contributions to that field: 1) We propose a novel spatial filtering method
which we call the Multiple Time Window LDA Beamformer (MTWLB) method; 2) we
provide a comprehensive comparison of nine spatial filtering pipelines using
three spatial filtering schemes namely, MTWLB, xDAWN, Common Spatial Pattern
(CSP) and three linear classification methods Linear Discriminant Analysis
(LDA), Bayesian Linear Regression (BLR) and Logistic Regression (LR). Three
pipelines without spatial filtering are used as baseline comparison. The Area
Under Curve (AUC) is used as an evaluation metric in this paper. The results
reveal that MTWLB and xDAWN spatial filtering techniques enhance the
classification performance of the pipeline but CSP does not. The results also
support the conclusion that LR can be effective for RSVP based BCI if
discriminative features are available
Scalable RDF Data Compression using X10
The Semantic Web comprises enormous volumes of semi-structured data elements.
For interoperability, these elements are represented by long strings. Such
representations are not efficient for the purposes of Semantic Web applications
that perform computations over large volumes of information. A typical method
for alleviating the impact of this problem is through the use of compression
methods that produce more compact representations of the data. The use of
dictionary encoding for this purpose is particularly prevalent in Semantic Web
database systems. However, centralized implementations present performance
bottlenecks, giving rise to the need for scalable, efficient distributed
encoding schemes. In this paper, we describe an encoding implementation based
on the asynchronous partitioned global address space (APGAS) parallel
programming model. We evaluate performance on a cluster of up to 384 cores and
datasets of up to 11 billion triples (1.9 TB). Compared to the state-of-art
MapReduce algorithm, we demonstrate a speedup of 2.6-7.4x and excellent
scalability. These results illustrate the strong potential of the APGAS model
for efficient implementation of dictionary encoding and contributes to the
engineering of larger scale Semantic Web applications
Structures and transitions in bcc tungsten grain boundaries and their role in the absorption of point defects
We use atomistic simulations to investigate grain boundary (GB) phase
transitions in el- emental body-centered cubic (bcc) metal tungsten. Motivated
by recent modeling study of grain boundary phase transitions in [100] symmetric
tilt boundaries in face-centered cu- bic (fcc) copper, we perform a systematic
investigation of [100] and [110] symmetric tilt high-angle and low-angle
boundaries in bcc tungsten. The structures of these boundaries have been
investigated previously by atomistic simulations in several different bcc
metals including tungsten using the the {\gamma}-surface method, which has
limitations. In this work we use a recently developed computational tool based
on the USPEX structure prediction code to perform an evolutionary grand
canonical search of GB structure at 0 K. For high-angle [100] tilt boundaries
the ground states generated by the evolutionary algorithm agree with the
predictions of the {\gamma}-surface method. For the [110] tilt boundaries, the
search predicts novel high-density low-energy grain boundary structures and
multiple grain boundary phases within the entire misorientation range.
Molecular dynamics simulation demonstrate that the new structures are more
stable at high temperature. We observe first-order grain boundary phase
transitions and investigate how the structural multiplicity affects the
mechanisms of the point defect absorption. Specifically, we demonstrate a
two-step nucleation process, when initially the point defects are absorbed
through a formation of a metastable GB structure with higher density, followed
by a transformation of this structure into a GB interstitial loop or a
different GB phase.Comment: 40 pages, 19 figure
Hedging in Field Theory Models of the Term Structure
We use path integrals to calculate hedge parameters and efficacy of hedging
in a quantum field theory generalization of the Heath, Jarrow and Morton (HJM)
term structure model which parsimoniously describes the evolution of
imperfectly correlated forward rates. We also calculate, within the model
specification, the effectiveness of hedging over finite periods of time. We use
empirical estimates for the parameters of the model to show that a low
dimensional hedge portfolio is quite effective.Comment: 18 figures, Invited Talk, International Econophysics Conference,
Bali, 28-31 August 200
Nonstationary Stochastic Resonance in a Reduced-Order Hodgkin-Huxley Neuron
In this work a physiologically realistic neural
system model is shown to be able to detect a weak
nonstationary signal through the addition of noise. It is
shown that the signal transduction performance is
optimised for a nonzero value of noise intenSity in a
manner suggestive of stochastic resonance
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