21,392 research outputs found
Macroeconomic implications of changes in micro volatility
We review evidence on the Great Moderation in conjunction with evidence about volatility trends at the micro level. We combine the two types of evidence to develop a tentative story for important components of the aggregate volatility decline and its consequences. The key ingredients of the story are declines in firm-level volatility and aggregate volatility – most dramatically in the durable goods sector – but the absence of a decline in the volatility of household consumption and individual earnings. Our explanation for volatility reduction stresses improved supply chain management, particularly in the durable goods sector, and a shift in production and employment from goods to services. We also provide some evidence for a specific mechanism, namely shorter lead times for materials orders. The tentative conclusion we draw is that, although better supply chain management involves potentially large efficiency gains with first-order effects on welfare, it does not imply (nor is there much evidence for) a reduction in uncertainty faced by individuals.
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When users control the algorithms: Values expressed in practices on the twitter platform
Recent interest in ethical AI has brought a slew of values, including fairness, into conversations about technology design. Research in the area of algorithmic fairness tends to be rooted in questions of distribution that can be subject to precise formalism and technical implementation. We seek to expand this conversation to include the experiences of people subject to algorithmic classification and decision-making. By examining tweets about the “Twitter algorithm” we consider the wide range of concerns and desires Twitter users express. We find a concern with fairness (narrowly construed) is present, particularly in the ways users complain that the platform enacts a political bias against conservatives. However, we find another important category of concern, evident in attempts to exert control over the algorithm. Twitter users who seek control do so for a variety of reasons, many well justified. We argue for the need for better and clearer definitions of what constitutes legitimate and illegitimate control over algorithmic processes and to consider support for users who wish to enact their own collective choices
Toward a better understanding of the doping mechanism involved in Mo(tfd-COCF doped PBDTTT-c
In this study, we aim to improve our understanding of the doping mechanism
involved in the polymer PBDTTT-c doped with(Mo(tfd-COCF3)3. We follow the
evolution of the hole density with dopant concentration to highlight the limits
of organic semiconductor doping. To enable the use of doping to enhance the
performance of organic electronic devices, doping efficiency must be understood
and improved. We report here a study using complementary optical and electrical
characterization techniques, which sheds some light on the origin of this
limited doping efficiency at high dopant concentration. Two doping mechanisms
are considered, the direct charge transfer (DCT) and the charge transfer
complex (CTC). We discuss the validity of the model involved as well as its
impact on the doping efficiency.Comment: Accepted manuscript, J. Appl. Phy
A DMRG Study of Low-Energy Excitations and Low-Temperature Properties of Alternating Spin Systems
We use the density matrix renormalization group (DMRG) method to study the
ground and low-lying excited states of three kinds of uniform and dimerized
alternating spin chains. The DMRG procedure is also employed to obtain
low-temperature thermodynamic properties of these systems. We consider a 2N
site system with spins and alternating from site to site and
interacting via a Heisenberg antiferromagnetic exchange. The three systems
studied correspond to being equal to and
; all of them have very similar properties. The ground state is found
to be ferrimagnetic with total spin . We find that there is
a gapless excitation to a state with spin , and a gapped excitation to
a state with spin . Surprisingly, the correlation length in the ground
state is found to be very small for this gapless system. The DMRG analysis
shows that the chain is susceptible to a conditional spin-Peierls instability.
Furthermore, our studies of the magnetization, magnetic susceptibility
and specific heat show strong magnetic-field dependences. The product
shows a minimum as a function of temperature T at low magnetic fields; the
minimum vanishes at high magnetic fields. This low-field behavior is in
agreement with earlier experimental observations. The specific heat shows a
maximum as a function of temperature, and the height of the maximum increases
sharply at high magnetic fields. Although all the three systems show
qualitatively similar behavior, there are some notable quantitative differences
between the systems in which the site spin difference, , is large
and small respectively.Comment: 16 LaTeX pages, 13 postscript figure
Cross-modal cue effects in motion processing
The everyday environment brings to our sensory systems competing inputs from different modalities. The ability to filter these multisensory inputs in order to identify and efficiently utilize useful spatial cues is necessary to detect and process the relevant information. In the present study, we investigate how feature-based attention affects the detection of motion across sensory modalities. We were interested to determine how subjects use intramodal, cross-modal auditory, and combined audiovisual motion cues to attend to specific visual motion signals. The results showed that in most cases, both the visual and the auditory cues enhance feature-based orienting to a transparent visual motion pattern presented among distractor motion patterns. Whereas previous studies have shown cross-modal effects of spatial attention, our results demonstrate a spread of cross-modal feature-based attention cues, which have been matched for the detection threshold of the visual target. These effects were very robust in comparisons of the effects of valid vs. invalid cues, as well as in comparisons between cued and uncued valid trials. The effect of intramodal visual, cross-modal auditory, and bimodal cues also increased as a function of motion-cue salience. Our results suggest that orienting to visual motion patterns among distracters can be facilitated not only by intramodal priors, but also by feature-based cross-modal information from the auditory system.First author draf
Predictor Aided Tracking in a System with Time Delay - Performance Involving Flat Surface, Roll, and Pitch Conditions
Predictor aided human tracking performance with time delay control under flat surface, roll, pitch, and roll and pitch condition
Matrix product states approach to the Heisenberg ferrimagnetic spin chains
We propose a new version of the matrix product (MP) states approach to the
description of quantum spin chains, which allows one to construct MP states
with certain total spin and its z-projection. We show that previously known MP
wavefunctions for integer-spin antiferromagnetic chains and ladders correspond
to some particular cases of our general ansatz. Our method allows to describe
systems with spontaneously broken rotational symmetry, like quantum
ferrimagnetic chains whose ground state has nonzero total spin. We apply this
approach to describe the ground state properties of the isotropic ferrimagnetic
Heisenberg chain with alternating spins 1 and 1/2 and compare our variational
results with the high-precision numerical data obtained by means of the quantum
Monte Carlo (QMC) method. For both the ground state energy and the correlation
functions we obtain very good agreement between the variational results and the
QMC data.Comment: 4 pages, RevTeX, uses psfig.sty, submitted to Phys. Rev.
Glycosylation of hyperthermostable designer cellulosome components yields enhanced stability and cellulose hydrolysis
Biomass deconstruction remains integral for enabling second‐generation biofuel production at scale. However, several steps necessary to achieve significant solubilization of biomass, notably harsh pretreatment conditions, impose economic barriers to commercialization. By employing hyperthermostable cellulase machinery, biomass deconstruction can be made more efficient, leading to milder pretreatment conditions and ultimately lower production costs. The hyperthermophilic bacterium Caldicellulosiruptor bescii produces extremely active hyperthermostable cellulases, including the hyperactive multifunctional cellulase CbCel9A/Cel48A. Recombinant CbCel9A/Cel48A components have been previously produced in Escherichia coli and integrated into synthetic hyperthermophilic designer cellulosome complexes. Since then, glycosylation has been shown to be vital for the high activity and stability of CbCel9A/Cel48A. Here, we studied the impact of glycosylation on a hyperthermostable designer cellulosome system in which two of the cellulosomal components, the scaffoldin and the GH9 domain of CbCel9A/Cel48A, were glycosylated as a consequence of employing Ca. bescii as an expression host. Inclusion of the glycosylated components yielded an active cellulosome system that exhibited long‐term stability at 75 °C. The resulting glycosylated designer cellulosomes showed significantly greater synergistic activity compared to the enzymatic components alone, as well as higher thermostability than the analogous nonglycosylated designer cellulosomes. These results indicate that glycosylation can be used as an essential engineering tool to improve the properties of designer cellulosomes. Additionally, Ca. bescii was shown to be an attractive candidate for production of glycosylated designer cellulosome components, which may further promote the viability of this bacterium both as a cellulase expression host and as a potential consolidated bioprocessing platform organism
Phase diagram of a frustrated mixed-spin ladder with diagonal exchange bonds
Using exact numerical diagonalization and the conformal field theory
approach, we study the effect of magnetic frustrations due to diagonal exchange
bonds in a system of two coupled mixed-spin Heisenberg chains. It
is established that relatively moderate frustrations are able to destroy the
ferrimagnetic state and to stabilize the critical spin-liquid phase typical for
half-integer-spin antiferromagnetic Heisenberg chains. Both phases are
separated by a narrow but finite region occupied by a critical
partially-polarized ferromagnetic phase.Comment: 5 PRB pages, 7 eps figures, to appear in Phys. Rev.
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