243 research outputs found
Assessing Researcher Publication Productivity in the Leading Information Systems Journals: A 2005–2009 Update
This study is an update of a previous scientometric study that examined the leading Information Systems (IS) researchers, their university affiliations, and the universities that supply them. We provide geographical comparisons of researcher affiliations for the AIS regions and for North American versus global institutions, along with a comparison of prior and current results. Our analysis shows that coauthorship is increasing in the top three IS journals and that most of the leading researchers continue to affiliate with institutions in North America. However, the proportion of publications from North American researchers in the top three journals has decreased slightly over time This research contributes to the scientometric literature by identifying a more broad and inclusive set of leading IS publications and by providing benchmarks for the productivity of IS scholars. These results can be valuable for deans and department chairs making tenure and promotion decisions. Prospective students and faculty can use these results to identify universities which match their personal research goals. This study also helps to define and expand the boundaries of the IS discipline due to its use of a broader set of leading journals
The Stochastic Dynamics of Tethered Microcantilevers in a Viscous Fluid
We explore and quantify the coupled dynamics of a pair of micron scale cantilevers immersed in a viscous fluid that are also directly tethered to one another at their tips by a spring force. The spring force, for example, could represent the molecular stiffness or elasticity of a biomolecule or material tethered between the cantilevers. We use deterministic numerical simulations with the fluctuation-dissipation theorem to compute the stochastic dynamics of the cantilever pair for the conditions of experiment when driven only by Brownian motion. We validate our approach by comparing directly with experimental measurements in the absence of the tether which shows excellent agreement. Using numerical simulations, we quantify the correlated dynamics of the cantilever pair over a range of tether stiffness. Our results quantify the sensitivity of the auto- and cross-correlations of equilibrium fluctuations in cantilever displacement to the stiffness of the tether. We show that the tether affects the magnitude of the correlations which can be used in a measurement to probe the properties of an attached tethering substance. For the configurations of current interest using micron scale cantilevers in water, we show that the magnitude of the fluid coupling between the cantilevers is sufficiently small such that the influence of the tether can be significant. Our results show that the cross-correlation is more sensitive to tether stiffness than the auto-correlation indicating that a two-cantilever measurement has improved sensitivity when compared with a measurement using a single cantilever
Electrically-driven phase transition in magnetite nanostructures
Magnetite (FeO), an archetypal transition metal oxide, has been
used for thousands of years, from lodestones in primitive compasses[1] to a
candidate material for magnetoelectronic devices.[2] In 1939 Verwey[3] found
that bulk magnetite undergoes a transition at T 120 K from a
high temperature "bad metal" conducting phase to a low-temperature insulating
phase. He suggested[4] that high temperature conduction is via the fluctuating
and correlated valences of the octahedral iron atoms, and that the transition
is the onset of charge ordering upon cooling. The Verwey transition mechanism
and the question of charge ordering remain highly controversial.[5-11] Here we
show that magnetite nanocrystals and single-crystal thin films exhibit an
electrically driven phase transition below the Verwey temperature. The
signature of this transition is the onset of sharp conductance switching in
high electric fields, hysteretic in voltage. We demonstrate that this
transition is not due to local heating, but instead is due to the breakdown of
the correlated insulating state when driven out of equilibrium by electrical
bias. We anticipate that further studies of this newly observed transition and
its low-temperature conducting phase will shed light on how charge ordering and
vibrational degrees of freedom determine the ground state of this important
compound.Comment: 17 pages, 4 figure
The native architecture of a photosynthetic membrane
In photosynthesis, the harvesting of solar energy and its subsequent conversion into a stable charge separation are dependent upon an interconnected macromolecular network of membrane-associated chlorophyll–protein complexes. Although the detailed structure of each complex has been determined, the size and organization of this network are unknown. Here we show the use of atomic force microscopy to directly reveal a native bacterial photosynthetic membrane. This first view of any multi-component membrane shows the relative positions and associations of the photosynthetic complexes and reveals crucial new features of the organization of the network: we found that the membrane is divided into specialized domains each with a different network organization and in which one type of complex predominates. Two types of organization were found for the peripheral light-harvesting LH2 complex. In the first, groups of 10–20 molecules of LH2 form light-capture domains that interconnect linear arrays of dimers of core reaction centre (RC)–light-harvesting 1 (RC–LH1–PufX) complexes; in the second they were found outside these arrays in larger clusters. The LH1 complex is ideally positioned to function as an energy collection hub, temporarily storing it before transfer to the RC where photochemistry occurs: the elegant economy of the photosynthetic membrane is demonstrated by the close packing of these linear arrays, which are often only separated by narrow 'energy conduits' of LH2 just two or three complexes wide
Production and characterization of astrocyte-derived human apolipoprotein E isoforms from immortalized astrocytes and their interactions with amyloid-beta
The apolipoprotein E (apoE) genotype is an important genetic risk factor for Alzheimer's disease (AD). In the central nervous system (CNS), most apoE is produced by astrocytes and is present in unique high-density lipoprotein (HDL)-like particles that have distinct properties from apoE derived from other sources. To develop an efficient system to produce astrocyte-derived apoE in large quantities, we produced and characterized immortalized cell lines from primary astrocyte cultures derived from human APOE knock-in mice. APOE2, APOE3, and APOE4 expressing cell lines were established that secrete apoE in HDL-like particles at similar levels, cholesterol composition, and size as those produced by primary astrocytes. In physiological buffers, astrocyte-secreted apoE3 and E4 associated equally well with amyloid-beta. Under the same conditions, only a small fraction of A beta formed sodium dodecyl sulfate (SDS)-stable complexes with apoE (E3 > E4). These immortalized astrocytes will be useful for studying mechanisms underlying the isoform-specific effects of apoE in the CNS
Measurement of the cosmic ray spectrum above eV using inclined events detected with the Pierre Auger Observatory
A measurement of the cosmic-ray spectrum for energies exceeding
eV is presented, which is based on the analysis of showers
with zenith angles greater than detected with the Pierre Auger
Observatory between 1 January 2004 and 31 December 2013. The measured spectrum
confirms a flux suppression at the highest energies. Above
eV, the "ankle", the flux can be described by a power law with
index followed by
a smooth suppression region. For the energy () at which the
spectral flux has fallen to one-half of its extrapolated value in the absence
of suppression, we find
eV.Comment: Replaced with published version. Added journal reference and DO
Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger
Observatory and is used to detect the radio emission of cosmic-ray air showers.
These observations are compared to the data of the surface detector stations of
the Observatory, which provide well-calibrated information on the cosmic-ray
energies and arrival directions. The response of the radio stations in the 30
to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of
the incoming electric field. For the latter, the energy deposit per area is
determined from the radio pulses at each observer position and is interpolated
using a two-dimensional function that takes into account signal asymmetries due
to interference between the geomagnetic and charge-excess emission components.
The spatial integral over the signal distribution gives a direct measurement of
the energy transferred from the primary cosmic ray into radio emission in the
AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air
shower arriving perpendicularly to the geomagnetic field. This radiation energy
-- corrected for geometrical effects -- is used as a cosmic-ray energy
estimator. Performing an absolute energy calibration against the
surface-detector information, we observe that this radio-energy estimator
scales quadratically with the cosmic-ray energy as expected for coherent
emission. We find an energy resolution of the radio reconstruction of 22% for
the data set and 17% for a high-quality subset containing only events with at
least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO
Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy
We measure the energy emitted by extensive air showers in the form of radio
emission in the frequency range from 30 to 80 MHz. Exploiting the accurate
energy scale of the Pierre Auger Observatory, we obtain a radiation energy of
15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV
arriving perpendicularly to a geomagnetic field of 0.24 G, scaling
quadratically with the cosmic-ray energy. A comparison with predictions from
state-of-the-art first-principle calculations shows agreement with our
measurement. The radiation energy provides direct access to the calorimetric
energy in the electromagnetic cascade of extensive air showers. Comparison with
our result thus allows the direct calibration of any cosmic-ray radio detector
against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI.
Supplemental material in the ancillary file
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