3,248 research outputs found
Electron beam welder X-rays its own welds
Beam of an electron beam welder X rays its own welds, enabling rapid weld quality checks to be made without removing the work from the vacuum chamber. A tungsten target produces X rays when hit by the beam. They are directed at the weld specimen and recorded on polaroid film
Anomalous strong exchange narrowing in excitonic systems
We investigate theoretically the phenomenon of exchange narrowing in the
absorption spectrum of a chain of monomers, which are coupled via resonant
dipole-dipole interaction. The individual (uncoupled) monomers exhibit a broad
absorption line shape due to the coupling to an environment consisting of a
continuum of vibrational modes. Upon increasing the interaction between the
monomers, the absorption spectrum of the chain narrows. For a non-Markovian
environment with a Lorentzian spectral density, we find a narrowing of the peak
width (full width at half maximum (FWHM)) by a factor 1/N, where N is the
number of monomers. This is much stronger than the usual 1/sqrt{N} narrowing.
Furthermore it turns out that for a Markovian environment no exchange narrowing
at all occurs. The relation of different measures of the width (FWHM, standard
deviation) is discussed
Continuous Measurement of a Non-Markovian Open Quantum System
Continuous quantum measurement is the backbone of various methods in quantum
control, quantum metrology, and quantum information. Here, we present a
generalized formulation of dispersive measurement of a complex quantum systems.
We describe the complex system as an open quantum system that is strongly
coupled to a non-Markovian environment, enabling the treatment of a broad
variety of natural or engineered complex systems. The system is monitored via a
probe resonator coupled to a broadband (Markovian) reservoir. Based on this
model, we derive a formalism of Stochastic Hierarchy Equations of Motion (SHEM)
describing the decoherence dynamics of the system conditioned on the
measurement record. Furthermore, we demonstrate a spectroscopy method based on
weak quantum measurement to reveal the non-Markovian nature of the environment,
which we term weak spectroscopy.Comment: Published version, the section on continuous state tomography will be
published in a separate manuscrip
Reduced neurosteroid potentiation of GABAA receptors in epilepsy and depolarized hippocampal neurons
OBJECTIVE: Neurosteroids regulate neuronal excitability by potentiating γ-aminobutyric acid type-A receptors (GABARs). In animal models of temporal lobe epilepsy, the neurosteroid sensitivity of GABARs is diminished and GABAR subunit composition is altered. We tested whether similar changes occur in patients with epilepsy and if depolarization-induced increases in neuronal activity can replicate this effect.
METHODS: We determined GABAR α4 subunit expression in cortical tissue resected from pediatric epilepsy patients. Modulation of human GABARs by allopregnanolone and Ro15-4513 was measured in Xenopus oocytes using whole-cell patch clamp. To extend the findings obtained using tissue from epilepsy patients, we evaluated GABAR expression and modulation by allopregnanolone and Ro15-4513 in cultured rat hippocampal neurons exposed to high extracellular potassium (HK) to increase neuronal activity.
RESULTS: Expression of α4 subunits was increased in pediatric cortical epilepsy specimens encompassing multiple pathologies. The potentiation of GABA-evoked currents by the neurosteroid allopregnanolone was decreased in Xenopus oocytes expressing GABARs isolated from epilepsy patients. Furthermore, receptors isolated from epilepsy but not control tissue were sensitive to potentiation by Ro15-4513, indicating higher expression of α
INTERPRETATION: These findings suggest that seizure activity-induced upregulation of
Non-Markovian quantum state diffusion for absorption spectra of molecular aggregates
In many molecular systems one encounters the situation where electronic
excitations couple to a quasi-continuum of phonon modes. That continuum may be
highly structured e.g. due to some weakly damped high frequency modes. To
handle such a situation, an approach combining the non-Markovian quantum state
diffusion (NMQSD) description of open quantum systems with an efficient but
abstract approximation was recently applied to calculate energy transfer and
absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL
103 (2009) 058301]. To explore the validity of the used approximation for such
complicated systems, in the present work we compare the calculated
(approximative) absorption spectra with exact results. These are obtained from
the method of pseudomodes, which we show to be capable of determining the exact
spectra for small aggregates and a few pseudomodes. It turns out that in the
cases considered, the results of the two approaches mostly agree quite well.
The advantages and disadvantages of the two approaches are discussed
Data-Mining a Large Digital Sky Survey: From the Challenges to the Scientific Results
The analysis and an efficient scientific exploration of the Digital Palomar
Observatory Sky Survey (DPOSS) represents a major technical challenge. The
input data set consists of 3 Terabytes of pixel information, and contains a few
billion sources. We describe some of the specific scientific problems posed by
the data, including searches for distant quasars and clusters of galaxies, and
the data-mining techniques we are exploring in addressing them.
Machine-assisted discovery methods may become essential for the analysis of
such multi-Terabyte data sets. New and future approaches involve unsupervised
classification and clustering analysis in the Giga-object data space, including
various Bayesian techniques. In addition to the searches for known types of
objects in this data base, these techniques may also offer the possibility of
discovering previously unknown, rare types of astronomical objects.Comment: Invited paper, to appear in Applications of Digital Image Processing
XX, ed. A. Tescher, Proc. S.P.I.E. vol. 3164, in press; 10 pages, a
self-contained TeX file, and 3 separate postscript figure
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Big Data and the Transformation of Operations Models: A Framework and A New Research Agenda
Big Data has been hailed as the ‘next big thing’ to drive business value, transform organisations and industries, and “reveal secrets to those with the humility, willingness and tools to listen” (Mayer-Schönberger and Cukier, 2013: 5). However, despite growing interest from organisations across industry sectors, Big Data applications appear to have concentrated on delivering incremental change and operational efficiency improvements, with little evidence on using Big Data to facilitate strategic, transformational change. In this paper, we explore how Big Data is actually being can be used across different sectors in leading organisations and examine the ways in which it is fostering change in the core operations models of organisations. A definition of ‘operations model’ is developed and the core components dimensions of an operations model are then examined, namely capacity, supply network, process and technology, and people development and organisation. Through a series of case studies, we examine the role of Big Data in affecting some, or all, of these components dimensions in order to generate value for the organisation by optimising, adapting or radically transforming the operations model. Following our analysis, we develop a tentative framework which can be used both for understanding how Big Data affects operations models, and for planning changes in operations models through Big Data. We set out a new research agenda to systematically understand the full potential of Big Data in transforming operations models
Suppression of quantum oscillations and the dependence on site energies in electronic excitation transfer in the Fenna-Matthews-Olson trimer
Energy transfer in the photosynthetic complex of the Green Sulfur Bacteria
known as the Fenna-Matthews-Olson (FMO) complex is studied theoretically taking
all three subunits (monomers) of the FMO trimer and the recently found eighth
bacteriochlorophyll (BChl) molecule into account. We find that in all
considered cases there is very little transfer between the monomers. Since it
is believed that the eighth BChl is located near the main light harvesting
antenna we look at the differences in transfer between the situation when BChl
8 is initially excited and the usually considered case when BChl 1 or 6 is
initially excited. We find strong differences in the transfer dynamics, both
qualitatively and quantitatively. When the excited state dynamics is
initialized at site eight of the FMO complex, we see a slow exponential-like
decay of the excitation. This is in contrast to the oscillations and a
relatively fast transfer that occurs when only seven sites or initialization at
sites 1 and 6 is considered. Additionally we show that differences in the
values of the electronic transition energies found in the literature lead to a
large difference in the transfer dynamics
The Role of Insider Influence in Mutual-to-Stock Conversions
Using a sample of 347 demutualizing thrifts from 1991 to 2004, we show that the level of inside participation is not a traditional signal of firm performance. We conclude that unanticipated inside participation reflects the incentives of insiders to reduce the size of the offer to influence the level of expected IPO returns. We find unanticipated inside participation is related to lower offer size and higher initial returns, but we do not find a relationship between inside participation and post-IPO performance
Mutual Holding Companies: Evidence of Conflicts of Interest through Disparate Dividends
The mutual holding company (MHC) structure establishes a dual-class stock that creates a unique opportunity to transfer wealth from thrift depositor-owners to new minority shareholders through the disparate payment of dividends. We show that MHCs are priced higher than comparable non-MHCs and dividend policy is a significant component of this valuation. We also show that MHC thrifts pay significantly higher dividends than non-MHC thrifts and that an Office of Thrift Supervision (OTS) ruling reducing the potential for disparate dividends between the two classes of shareholders resulted in lower dividends. These results have policy implications of special significance given that the OTS reversed its position in 2000 and because of the current controversy over the use of the MHC structure in the financial service industry
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