808,796 research outputs found
On Closed Einstein-de Sitter Universes
We briefly summarize the idea of cosmological models with compact, flat
spatial sections. It has been suggested that, because of the COBE satellite's
maps of the microwave background, such models cannot be small in the sense of
Ellis, and hence are no longer interesting. Here we use Lehoucq et al.'s method
of cosmic crystallography to show that these models are physically meaningful
even if the size of the spatial sections is of the same order of magnitude as
the radius of the observational horizon.Comment: 8 pages, 1 figure. Revision includes comment on "top-down" and
"bottom-up" pictures of structure formation. Figure is unmodifie
Formal Systems Architectures for Biology
When the word "systems" is used in systems biology, it invokes a variety of assumptions about what defines the subject under investigation, which in turn can lead to divergent research outcomes. We will take the position that systems are defined by their potential organizing and "control" mechanisms, 
which distinguishes complex, living systems from a primordial soup. This will be accomplished by defining and investigating three interesting control motifs in biological systems: dominoes and clocks, futile cycles, and complex feedforward regulation. Additional mechanisms that combine feedback and feedforward mechanisms will also be briefly elaborated upon. Throughout these examples, our focus will be on the connection between top-down control mechanisms and bottom-up self-organizing mechanisms
A Role for Bottom-Up Synthetic Cells in the Internet of Bio-Nano Things?
The potential role of bottom-up Synthetic Cells (SCs) in the Internet of Bio-Nano Things (IoBNT) is discussed. In particular, this perspective paper focuses on the growing interest in networks of biological and/or artificial objects at the micro- and nanoscale (cells and subcellular parts, microelectrodes, microvessels, etc.), whereby communication takes place in an unconventional manner, i.e., via chemical signaling. The resulting "molecular communication" (MC) scenario paves the way to the development of innovative technologies that have the potential to impact biotechnology, nanomedicine, and related fields. The scenario that relies on the interconnection of natural and artificial entities is briefly introduced, highlighting how Synthetic Biology (SB) plays a central role. SB allows the construction of various types of SCs that can be designed, tailored, and programmed according to specific predefined requirements. In particular, "bottom-up" SCs are briefly described by commenting on the principles of their design and fabrication and their features (in particular, the capacity to exchange chemicals with other SCs or with natural biological cells). Although bottom-up SCs still have low complexity and thus basic functionalities, here, we introduce their potential role in the IoBNT. This perspective paper aims to stimulate interest in and discussion on the presented topics. The article also includes commentaries on MC, semantic information, minimal cognition, wetware neuromorphic engineering, and chemical social robotics, with the specific potential they can bring to the IoBNT
A Role for Bottom-Up Synthetic Cells in the Internet of Bio-Nano Things?
he potential role of bottom-up Synthetic Cells (SCs) in the Internet of Bio-Nano Things (IoBNT) is discussed. In particular, this perspective paper focuses on the growing interest in networks of biological and/or artificial objects at the micro- and nanoscale (cells and subcellular parts, microelectrodes, microvessels, etc.), whereby communication takes place in an unconventional manner, i.e., via chemical signaling. The resulting “molecular communication” (MC) scenario paves the way to the development of innovative technologies that have the potential to impact biotechnology, nanomedicine, and related fields. The scenario that relies on the interconnection of natural and artificial entities is briefly introduced, highlighting how Synthetic Biology (SB) plays a central role. SB allows the construction of various types of SCs that can be designed, tailored, and programmed according to specific predefined requirements. In particular, “bottom-up” SCs are briefly described by commenting on the principles of their design and fabrication and their features (in particular, the capacity to exchange chemicals with other SCs or with natural biological cells). Although bottom-up SCs still have low complexity and thus basic functionalities, here, we introduce their potential role in the IoBNT. This perspective paper aims to stimulate interest in and discussion on the presented topics. The article also includes commentaries on MC, semantic information, minimal cognition, wetware neuromorphic engineering, and chemical social robotics, with the specific potential they can bring to the IoBNT
Bottom-up visual attention model for still image: a preliminary study
The philosophy of human visual attention is scientifically explained in the field of cognitive psychology and neuroscience then computationally modeled in the field of computer science and engineering. Visual attention models have been applied in computer vision systems such as object detection, object recognition, image segmentation, image and video compression, action recognition, visual tracking, and so on. This work studies bottom-up visual attention, namely human fixation prediction and salient object detection models. The preliminary study briefly covers from the biological perspective of visual attention, including visual pathway, the theory of visual attention, to the computational model of bottom-up visual attention that generates saliency map. The study compares some models at each stage and observes whether the stage is inspired by biological architecture, concept, or behavior of human visual attention. From the study, the use of low-level features, center-surround mechanism, sparse representation, and higher-level guidance with intrinsic cues dominate the bottom-up visual attention approaches. The study also highlights the correlation between bottom-up visual attention and curiosity
Three-jet production at LEP and the bottom quark mass
We consider the possibility of extracting the bottom quark mass from LEP
data. The inclusive decay rate for \zbb +\cdots is obtained at order \as by
summing up the one-loop two-parton decay rate to the tree-level three-parton
rate. We calculate the decay width of the -boson into two and three jets
containing the -quark including complete quark mass effects. In particular,
we give analytic results for a slight modification of the JADE clustering
algorithm. We also study the angular distribution with respect to the angle
formed between the gluon and the quark jets, which has a strong dependence on
the quark mass. The impact of higher order QCD corrections on these observables
is briefly discussed. Finally, we present numerical results for some popular
jet-clustering algorithms and show that, indeed, these three-jet observables
are very sensitive to the -quark mass and well suited for its determination
at LEP.Comment: 24 pages, CERN-TH.7419/94, LaTeX, full postscript version with 6
figures included is available as an additional compressed uuencoded fil
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