299 research outputs found
A modern-day requirement for co-ordinated covert action
Covert action can be an important weapon in a state’s arsenal. It is, however, inherently controversial and risky. Rory Cormac, Michael S Goodman and Tom Holman argue that when considering covert action, Whitehall should look to lessons from the recent past. The UK has long used covert action, and how best to manage and co-ordinate such sensitive activity was for many decades a key preoccupation of its policy-makers and politicians. Given the secrecy involved, these lessons, and the machinery created, have been lost to history. Yet with covert action seemingly now back on the agenda, previous experience and hard-learnt lessons have assumed renewed importance
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A survey of routing techniques in store-and-forward and wormhole interconnects.
This paper presents an overview of algorithms for directing messages through networks of varying topology. These are commonly referred to as routing algorithms in the literature that is presented. In addition to providing background on networking terminology and router basics, the paper explains the issues of deadlock and livelock as they apply to routing. After this, there is a discussion of routing algorithms for both store-and-forward and wormhole-switched networks. The paper covers both algorithms that do and do not adapt to conditions in the network. Techniques targeting structured as well as irregular topologies are discussed. Following this, strategies for routing in the presence of faulty nodes and links in the network are described
Inflation at the Electroweak Scale
We present a simple model for slow-rollover inflation where the vacuum energy
that drives inflation is of the order of ; unlike most models, the
conversion of vacuum energy to radiation (``reheating'') is moderately
efficient. The scalar field responsible for inflation is a standard-model
singlet, develops a vacuum expectation value of the order of 4\times
10^6\GeV, has a mass of order 1\GeV, and can play a role in electroweak
phenomena.Comment: 14 page
Type Ia Supernova Light Curve Inference: Hierarchical Bayesian Analysis in the Near Infrared
We present a comprehensive statistical analysis of the properties of Type Ia
SN light curves in the near infrared using recent data from PAIRITEL and the
literature. We construct a hierarchical Bayesian framework, incorporating
several uncertainties including photometric error, peculiar velocities, dust
extinction and intrinsic variations, for coherent statistical inference. SN Ia
light curve inferences are drawn from the global posterior probability of
parameters describing both individual supernovae and the population conditioned
on the entire SN Ia NIR dataset. The logical structure of the hierarchical
model is represented by a directed acyclic graph. Fully Bayesian analysis of
the model and data is enabled by an efficient MCMC algorithm exploiting the
conditional structure using Gibbs sampling. We apply this framework to the
JHK_s SN Ia light curve data. A new light curve model captures the observed
J-band light curve shape variations. The intrinsic variances in peak absolute
magnitudes are: sigma(M_J) = 0.17 +/- 0.03, sigma(M_H) = 0.11 +/- 0.03, and
sigma(M_Ks) = 0.19 +/- 0.04. We describe the first quantitative evidence for
correlations between the NIR absolute magnitudes and J-band light curve shapes,
and demonstrate their utility for distance estimation. The average residual in
the Hubble diagram for the training set SN at cz > 2000 km/s is 0.10 mag. The
new application of bootstrap cross-validation to SN Ia light curve inference
tests the sensitivity of the model fit to the finite sample and estimates the
prediction error at 0.15 mag. These results demonstrate that SN Ia NIR light
curves are as effective as optical light curves, and, because they are less
vulnerable to dust absorption, they have great potential as precise and
accurate cosmological distance indicators.Comment: 24 pages, 15 figures, 4 tables. Accepted for publication in ApJ.
Corrected typo, added references, minor edit
CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells
© 2018 Author(s). As single-junction silicon solar cells approach their theoretical limits, tandems provide the primary path to higher efficiencies. CdTe alloys can be tuned with magnesium (CdMgTe) or zinc (CdZnTe) for ideal tandem pairing with silicon. A II-VI/Si tandem holds the greatest promise for inexpensive, high-efficiency top cells that can be quickly deployed in the market using existing polycrystalline CdTe manufacturing lines combined with mature silicon production lines. Currently, all high efficiency polycrystalline CdTe cells require a chloride-based passivation process to passivate grain boundaries and bulk defects. This research examines the rich chemistry and physics that has historically limited performance when extending Cl treatments to polycrystalline 1.7-eV CdMgTe and CdZnTe absorbers. A combination of transmittance, quantum efficiency, photoluminescence, transmission electron microscopy, and energy-dispersive X-ray spectroscopy clearly reveals that during passivation, Mg segregates and out-diffuses, initially at the grain boundaries but eventually throughout the bulk. CdZnTe exhibits similar Zn segregation behavior; however, the onset and progression is localized to the back of the device. After passivation, CdMgTe and CdZnTe can render a layer that is reduced to predominantly CdTe electro-optical behavior. Contact instabilities caused by inter-diffusion between the layers create additional complications. The results outline critical issues and paths for these materials to be successfully implemented in Si-based tandems and other applications
Sputtered aluminum oxide and p+ amorphous silicon back-contact for improved hole extraction in polycrystalline CdSexTe1-x and CdTe photovoltaics
A thin layer of Al2O3 at the back of CdSexTe1-x/CdTe
devices is shown to passivate the back interface and drastically
improve surface recombination lifetimes and photoluminescent
response. Despite this, such devices do not show an improvement
in open-circuit voltage (VOC.) Adding a p
+
amorphous silicon layer
behind the Al2O3 bends the conduction band upward, reducing the
barrier to hole extraction and improving collection. Further
optimization of the Al2O3, amorphous silicon (a-Si), and indiumdoped tin oxide (ITO) layers, as well as their interaction with the
CdCl2 passivation process, are necessary to translate these electrooptical improvements into gains in voltag
Large Synoptic Survey Telescope Solar System Science Roadmap
The Large Synoptic Survey Telescope (LSST) is uniquely equipped to search for
Solar System bodies due to its unprecedented combination of depth and wide
field coverage. Over a ten-year period starting in 2022, LSST will generate the
largest catalog of Solar System objects to date. The main goal of the LSST
Solar System Science Collaboration (SSSC) is to facilitate the efforts of the
planetary community to study the planets and small body populations residing
within our Solar System using LSST data. To prepare for future survey cadence
decisions and ensure that interesting and novel Solar System science is
achievable with LSST, the SSSC has identified and prioritized key Solar System
research areas for investigation with LSST in this roadmap. The ranked science
priorities highlighted in this living document will inform LSST survey cadence
decisions and aid in identifying software tools and pipelines needed to be
developed by the planetary community as added value products and resources
before the planned start of LSST science operations.Comment: 7 pages; Feedback welcom
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