2,462 research outputs found
Approximating Higher-Order Derivative Tensors Using Secant Updates
Quasi-Newton methods employ an update rule that gradually improves the
Hessian approximation using the already available gradient evaluations. We
propose higher-order secant updates which generalize this idea to higher-order
derivatives, approximating for example third derivatives (which are tensors)
from given Hessian evaluations. Our generalization is based on the observation
that quasi-Newton updates are least-change updates satisfying the secant
equation, with different methods using different norms to measure the size of
the change. We present a full characterization for least-change updates in
weighted Frobenius norms (satisfying an analogue of the secant equation) for
derivatives of arbitrary order. Moreover, we establish convergence of the
approximations to the true derivative under standard assumptions and explore
the quality of the generated approximations in numerical experiments
On the relevance of the neurobiological analogue of the finite-state architecture
We present two simple arguments for the potential relevance of a neurobiological analogue of the finite-state architecture. The first assumes the classical cognitive framework, is well-known, and is based on the assumption that the brain is finite with respect to its memory organization. The second is formulated within a general dynamical systems framework and is based on the assumption that the brain sustains some level of noise and/or does not utilize infinite precision processing. We briefly review the classical cognitive framework based on Church-Turing computability and non-classical approaches based on analog processing in dynamical systems. We conclude that the dynamical neurobiological analogue of the finite-state architecture appears to be relevant, at least at an implementational level, for cognitive brain systems
North Atlantic 2001 - Part 4 Cruise No. 50, Leg 4 16 July – 12 August 2001, Reykjavik – Hamburg
Characterization of Passive CMOS Strip Sensors
Recent advances in CMOS imaging sensor technology , e.g. in CMOS pixel
sensors, have proven that the CMOS process is radiation tolerant enough to cope
with certain radiation levels required for tracking layers in hadron collider
experiments. With the ever-increasing area covered by silicon tracking
detectors cost effective alternatives to the current silicon sensors and more
integrated designs are desirable. This article describes results obtained from
laboratory measurements of silicon strip sensors produced in a passive p-CMOS
process. Electrical characterization and charge collection measurements with a
90Sr source and a laser with infrared wavelength showed no effect of the
stitching process on the performance of the sensor.Comment: 6 pages, 16 figure
Mechanisms of Thermal Adaptation Revealed From the Genomes of the Antarctic Archaea Methanogenium frigidum and Methanococcoides burtonii
We generated draft genome sequences for two cold-adapted Archaea, Methanogenium frigidum and Methanococcoides burtonii, to identify genotypic characteristics that distinguish them from Archaea with a higher optimal growth temperature (OGT). Comparative genomics revealed trends in amino acid and tRNA composition, and structural features of proteins. Proteins from the cold-adapted Archaea are characterized by a higher content of noncharged polar amino acids, particularly Gin and Thr and a lower content of hydrophobic amino acids, particularly Leu. Sequence data from nine methanogen genomes (OGT 15degrees-98degreesC) were used to generate IIII modeled protein structures. Analysis of the models from the cold-adapted Archaea showed a strong tendency in the solvent-accessible area for more Gin, Thr, and hydrophobic residues and fewer charged residues. A cold shock domain (CSD) protein (CspA homolog) was identified in M. frigidum, two hypothetical proteins with CSD-folds in M. burtonii, and a unique winged helix DNA-binding domain protein in M. burtonii. This suggests that these types of nucleic acid binding proteins have a critical role in cold-adapted Archaea. Structural analysis of tRNA sequences from the Archaea indicated that GC content is the major factor influencing tRNA stability in hyperthermophiles, but not in the psychrophiles, mesophiles or moderate thermophiles. Below an OGT of 60degreesC, the GC content in tRNA was largely unchanged, indicating that any requirement for flexibility of tRNA in psychrophiles is mediated by other means. This is the first time that comparisons have been performed with genome data from Archaea spanning the growth temperature extremes. from psychrophiles to hyperthermophile
RNA interference in Lepidoptera: an overview of successful and unsuccessful studies and implications for experimental design
A
Nuclear Level Density and the Determination of Thermonuclear Rates for Astrophysics
The prediction of cross sections for nuclei far off stability is crucial in
the field of nuclear astrophysics. We discuss the model mostly employed for
such calculations: the statistical model (Hauser-Feshbach). Special emphasis is
put on the uncertainties arising from nuclear level density descriptions and an
improved global description is presented. Furthermore, criteria for the
applicability of the statistical model are investigated and a "map" for the
applicability of the model to reactions of stable and unstable nuclei with
neutral and charged particles is given.Comment: REVTeX paper + 7 B/W figures + 2 color figures; PRC, in press. Also
available at http://quasar.physik.unibas.ch/preps.htm
Search for supersymmetry in events with b-quark jets and missing transverse energy in pp collisions at 7 TeV
Results are presented from a search for physics beyond the standard model
based on events with large missing transverse energy, at least three jets, and
at least one, two, or three b-quark jets. The study is performed using a sample
of proton-proton collision data collected at sqrt(s) = 7 TeV with the CMS
detector at the LHC in 2011. The integrated luminosity of the sample is 4.98
inverse femtobarns. The observed number of events is found to be consistent
with the standard model expectation, which is evaluated using control samples
in the data. The results are used to constrain cross sections for the
production of supersymmetric particles decaying to b-quark-enriched final
states in the context of simplified model spectra.Comment: Submitted to Physical Review
The evolution and nomenclature of GnRH-type and corazonin-type neuropeptide signaling systems
The work of the authors reported in this review was supported by grants from the BBSRC (BB/M001644/1; BB/M001032/1), the Leverhulme Trust (RGP-2013-351) and the China Scholarship Council
Sustainable Development
The emergence of a global and technological world and the accelerating dissemination of technology does not only give rise to technological, economic, social, environmental, political and educational tasks. Significant philosophical questions, epistemic reflections and cultural debates result and have to be pushed forward. To move sustainable development from a political mission statement and scientific challenge into everyday life we have to shift our focus of attention to those who are driving a non-sustainable development: human beings and their societal and cultural conditions and interactions. Ultimately not the ecological footprint is the core challenge, but we and those who are leaving this footprint. The idea of the present volume of Sustainable Development - Relationships to Culture, Knowledge and Ethics was developed in the course of the international conference “Sustainability 2010: The Cultural Dimension”, which took place in July 2010 in Berlin. The aim of this book is to provide discussions about cultural, epistemic and ethical implications of contemporary changes and emerging challenges on an interdisciplinary and international level
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