542 research outputs found
Multiscaled Cross-Correlation Dynamics in Financial Time-Series
The cross correlation matrix between equities comprises multiple interactions
between traders with varying strategies and time horizons. In this paper, we
use the Maximum Overlap Discrete Wavelet Transform to calculate correlation
matrices over different timescales and then explore the eigenvalue spectrum
over sliding time windows. The dynamics of the eigenvalue spectrum at different
times and scales provides insight into the interactions between the numerous
constituents involved.
Eigenvalue dynamics are examined for both medium and high-frequency equity
returns, with the associated correlation structure shown to be dependent on
both time and scale. Additionally, the Epps effect is established using this
multivariate method and analyzed at longer scales than previously studied. A
partition of the eigenvalue time-series demonstrates, at very short scales, the
emergence of negative returns when the largest eigenvalue is greatest. Finally,
a portfolio optimization shows the importance of timescale information in the
context of risk management
NICMOS Imaging of the Nuclei of Arp 220
We report high resolution imaging of the ultraluminous infrared galaxy Arp
220 at 1.1, 1.6, and 2.22 microns with NICMOS on the HST. The
diffraction-limited images at 0.1--0.2 arcsecond resolution clearly resolve
both nuclei of the merging galaxy system and reveal for the first time a number
of luminous star clusters in the circumnuclear envelope. The morphologies of
both nuclei are strongly affected by dust obscuration, even at 2.2 microns :
the primary nucleus (west) presents a crescent shape, concave to the south and
the secondary (eastern) nucleus is bifurcated by a dust lane with the southern
component being very reddened. In the western nucleus, the morphology of the
2.2 micron emission is most likely the result of obscuration by an opaque disk
embedded within the nuclear star cluster. The morphology of the central
starburst-cluster in the western nucleus is consistent with either a
circumnuclear ring of star formation or a spherical cluster with the bottom
half obscured by the embedded dust disk. Comparison of cm-wave radio continuum
maps with the near-infrared images suggests that the radio nuclei lie in the
dust disk on the west and near the highly reddened southern component of the
eastern complex. The radio nuclei are separated by 0.98 arcseconds
(corresponding to 364 pc at 77 Mpc) and the half-widths of the infrared nuclei
are approximately 0.2-0.5 arcseconds. At least 8, unresolved infrared sources
-- probably globular clusters -- are also seen in the circumnuclear envelope at
radii 2-7 arcseconds . Their near-infrared colors do not significantly
constrain their ages.Comment: LaTex, 15 pages with 1 gif figure and 5 postscript figures. ApJL
accepte
GYES, a multifibre spectrograph for the CFHT
We have chosen the name of GYES, one of the mythological giants with one
hundred arms, offspring of Gaia and Uranus, for our instrument study of a
multifibre spectrograph for the prime focus of the Canada-France-Hawaii
Telescope. Such an instrument could provide an excellent ground-based
complement for the Gaia mission and a northern complement to the HERMES project
on the AAT. The CFHT is well known for providing a stable prime focus
environment, with a large field of view, which has hosted several imaging
instruments, but has never hosted a multifibre spectrograph. Building upon the
experience gained at GEPI with FLAMES-Giraffe and X-Shooter, we are
investigating the feasibility of a high multiplex spectrograph (about 500
fibres) over a field of view 1 degree in diameter. We are investigating an
instrument with resolution in the range 15000 to 30000, which should provide
accurate chemical abundances for stars down to 16th magnitude and radial
velocities, accurate to 1 km/s for fainter stars. The study is led by
GEPI-Observatoire de Paris with a contribution from Oxford for the study of the
positioner. The financing for the study comes from INSU CSAA and Observatoire
de Paris. The conceptual study will be delivered to CFHT for review by October
1st 2010.Comment: Contributed talk at the Gaia ELSA conference 2010, S\`evres 7-11 June
2010, to be published on the EAS Series, Editors: C. Turon, F. Arenou & F.
Meynadie
The Palomar Testbed Interferometer Calibrator Catalog
The Palomar Testbed Interferometer (PTI) archive of observations between 1998
and 2005 is examined for objects appropriate for calibration of optical
long-baseline interferometer observations - stars that are predictably
point-like and single. Approximately 1,400 nights of data on 1,800 objects were
examined for this investigation. We compare those observations to an
intensively studied object that is a suitable calibrator, HD217014, and
statistically compare each candidate calibrator to that object by computing
both a Mahalanobis distance and a Principal Component Analysis. Our hypothesis
is that the frequency distribution of visibility data associated with
calibrator stars differs from non-calibrator stars such as binary stars.
Spectroscopic binaries resolved by PTI, objects known to be unsuitable for
calibrator use, are similarly tested to establish detection limits of this
approach. From this investigation, we find more than 350 observed stars
suitable for use as calibrators (with an additional being
rejected), corresponding to sky coverage for PTI. This approach
is noteworthy in that it rigorously establishes calibration sources through a
traceable, empirical methodology, leveraging the predictions of spectral energy
distribution modeling but also verifying it with the rich body of PTI's on-sky
observations.Comment: 100 pages, 7 figures, 7 tables; to appear in the May 2008ApJS, v176n
Protonation-Induced Microphase Separation in Thin Films of a Polyelectrolyte-Hydrophilic Diblock Copolymer
Block copolymers composed of poly(oligo ethylene glycol methyl ether methacrylate) and poly(2-vinylpyridine) are disordered in the neat state but can be induced to order by protonation of the P2VP block, demonstrating a tunable and responsive method for triggering assembly in thin films. Comparison of protonation with the addition of salts shows that microphase separation is due to selective protonation of the P2VP block. Increasing acid incorporation and increasing 2-vinylpyridine content for P2VP minority copolymers both promote increasingly phase-separated morphologies, consistent with protonation increasing the effective strength of segregation between the two blocks. The self-assembled nanostructures formed after casting from acidic solutions may be tuned based on the amount and type of acid incorporation as well as the annealing treatment applied after casting, where both aqueous and polar organic solvents are shown to be effective. Therefore, POEGMA-b-P2VP is a novel ion-containing block copolymer whose morphologies can be facilely tuned during casting and processing by controlling its exposure to acid.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001088)National Science Foundation (U.S.) (Award CMMI-1246740
Analytic philosophy for biomedical research: the imperative of applying yesterday's timeless messages to today's impasses
The mantra that "the best way to predict the future is to invent it" (attributed to the computer scientist Alan Kay) exemplifies some of the expectations from the technical and innovative sides of biomedical research at present. However, for technical advancements to make real impacts both on patient health and genuine scientific understanding, quite a number of lingering challenges facing the entire spectrum from protein biology all the way to randomized controlled trials should start to be overcome. The proposal in this chapter is that philosophy is essential in this process. By reviewing select examples from the history of science and philosophy, disciplines which were indistinguishable until the mid-nineteenth century, I argue that progress toward the many impasses in biomedicine can be achieved by emphasizing theoretical work (in the true sense of the word 'theory') as a vital foundation for experimental biology. Furthermore, a philosophical biology program that could provide a framework for theoretical investigations is outlined
Highly Differentiated, Resting Gn-Specific Memory CD8+ T Cells Persist Years after Infection by Andes Hantavirus
In man, infection with South American Andes virus (ANDV) causes hantavirus cardiopulmonary syndrome (HCPS). HCPS due to ANDV is endemic in Southern Chile and much of Argentina and increasing numbers of cases are reported all over South America. A case-fatality rate of about 36% together with the absence of successful antiviral therapies urge the development of a vaccine. Although T-cell responses were shown to be critically involved in immunity to hantaviruses in mouse models, no data are available on the magnitude, specificity and longevity of ANDV-specific memory T-cell responses in patients. Using sets of overlapping peptides in IFN-γ ELISPOT assays, we herein show in 78 Chilean convalescent patients that Gn-derived epitopes were immunodominant as compared to those from the N- and Gc-proteins. Furthermore, while the relative contribution of the N-specific response significantly declined over time, Gn-specific responses remained readily detectable ex vivo up to 13 years after the acute infection. Tetramer analysis further showed that up to 16.8% of all circulating CD3+CD8+ T cells were specific for the single HLA-B*3501-restricted epitope Gn465–473 years after the acute infection. Remarkably, Gn465–473–specific cells readily secreted IFN-γ, granzyme B and TNF-α but not IL-2 upon stimulation and showed a ‘revertant’ CD45RA+CD27−CD28−CCR7−CD127− effector memory phenotype, thereby resembling a phenotype seen in other latent virus infections. Most intriguingly, titers of neutralizing antibodies increased over time in 10/17 individuals months to years after the acute infection and independently of whether they were residents of endemic areas or not. Thus, our data suggest intrinsic, latent antigenic stimulation of Gn-specific T-cells. However, it remains a major task for future studies to proof this hypothesis by determination of viral antigen in convalescent patients. Furthermore, it remains to be seen whether Gn-specific T cells are critical for viral control and protective immunity. If so, Gn-derived immunodominant epitopes could be of high value for future ANDV vaccines
SHANK3 mutations identified in autism lead to modification of dendritic spine morphology via an actin-dependent mechanism
Genetic mutations of SHANK3 have been reported in patients with intellectual disability, autism spectrum disorder (ASD) and schizophrenia. At the synapse, Shank3/ProSAP2 is a scaffolding protein that connects glutamate receptors to the actin cytoskeleton via a chain of intermediary elements. Although genetic studies have repeatedly confirmed the association of SHANK3 mutations with susceptibility to psychiatric disorders, very little is known about the neuronal consequences of these mutations. Here, we report the functional effects of two de novo mutations (STOP and Q321R) and two inherited variations (R12C and R300C) identified in patients with ASD. We show that Shank3 is located at the tip of actin filaments and enhances its polymerization. Shank3 also participates in growth cone motility in developing neurons. The truncating mutation (STOP) strongly affects the development and morphology of dendritic spines, reduces synaptic transmission in mature neurons and also inhibits the effect of Shank3 on growth cone motility. The de novo mutation in the ankyrin domain (Q321R) modifies the roles of Shank3 in spine induction and morphology, and actin accumulation in spines and affects growth cone motility. Finally, the two inherited mutations (R12C and R300C) have intermediate effects on spine density and synaptic transmission. Therefore, although inherited by healthy parents, the functional effects of these mutations strongly suggest that they could represent risk factors for ASD. Altogether, these data provide new insights into the synaptic alterations caused by SHANK3 mutations in humans and provide a robust cellular readout for the development of knowledge-based therapies
The Impact of Error-Management Climate, Error Type and Error Originator on Auditors’ Reporting Errors Discovered on Audit Work Papers
We examine factors affecting the auditor’s willingness to report their own or their peers’ self-discovered errors in working papers subsequent to detailed working paper review. Prior research has shown that errors in working papers are detected in the review process; however, such detection rates only rarely exceed 50% of the seeded errors. Hence, measures that encourage auditors to be alert to their own (or their peers’) potential errors any time they revisit the audit working papers may be valuable in detecting such residual errors and potentially correcting them before damage occurs to the audit firm or its client. We hypothesize that three factors affect the auditor’s willingness to report post detailed review discovered errors: the local office error-management climate (open versus blame), the type of error (mechanical versus conceptual) and who committed the error (the individual who committed the error (self) or a peer). Local office error-management climate is said to be open and supportive where errors and mistakes are accepted as part of everyday life as long as they are learned from and not repeated. In alternative, a blame error-management climate focuses on a “get it right the first time” culture where mistakes are not tolerated and blame gets attached to those admitting to or found committing such errors. We find that error-management climate has a significant overall effect on auditor willingness to report errors, as does who committed the error originally. We find both predicted and unpredicted significant interactions among the three factors that qualify these observed significant main effects. We discuss implications for audit practice and further research
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