952 research outputs found
Aristotle on the Principles of Perceptible Body (Gen. Corr. 2.1-3)
With his clarification of the philosophical significance of the Pre- Socratic theories of elements Aristotle completes his discussion of the principles of perceptible bodies. He had embarked on this subject with the intent of explaining the first bodies and their role as principles of genesis and destruction. Jumping off from the theories of the Ionian philosophers who first proposed simple elemental bodies as principles of change, he probed behind these to discover even more fundamental principles, one of which was anticipated by another Ionian and by his teacher Plato. These ultimate principles will become for Aristotle the foundation of all explanations of material change in the natural world. In the end Aristotle’s exposition comes around full circle to those Ionians from which it began, to show them not so much as confused misadventurers in the quest for truth, but as successful explorers who, without realizing what they had really done, had caught a glimpse of the new world of imperceptible reality lying at the very foundations of the universe. By showing how even the errors of their incompatible and incorrect theories derived from the true structure of the natural world as he himself had come to understand it, Aristotle gained for his own theories the support of the wisest philosophers of the past and at the same time forged the first links with the phenomenal world that he proposed to explain
Aristotle\u27s De Philosophia and the Introduction of the Fifth Element
One of the most influential of Aristotle\u27s ideas, the idea that the heavenly bodies consist of a fifth element distinct from the four earthly elements (earth, water, air, and fire) is widely believed to have been introduced to the world for the first time in Aristotle\u27s lost dialogue De Philosophia. This assumption has created a host of problems which have not yet been solved
Origins of Stoic cosmology
(print) xix, 292 p. ; 24 cmPreface ix -- Abbreviations xi -- Introduction xiii -- I Corporealism 3 -- II Principles 29 -- III Cosmogony 57 -- IV Cosmology 91 -- V Cosmobiology 136 -- VI The Cosmic Cycle 185 -- VII Epilogue : The Definition of Nature and the Origins of Stoic Cosmology 200 -- Appendixes -- I. Influences on Stoicism According to the Biographical Tradition 219 -- II. The Contents of Book One of Chrysippus's Physics 238 -- III. Cleanthes' Cosmogony 240 -- IV. Accounts of the Stoic Proofs for the Immobility and Coherence of the Cosmos 249 -- V. Chrysippus's Statement on the Alleged Imperishability of the Cosmos 260 -- VI. Cleanthes' Proof for the Intelligence of the Cosmos 267 -- Indexes 27
Transcription-translation coupling: direct interactions of RNA polymerase with ribosomes and ribosomal subunits.
In prokaryotes, RNA polymerase and ribosomes can bind concurrently to the same RNA transcript, leading to the functional coupling of transcription and translation. The interactions between RNA polymerase and ribosomes are crucial for the coordination of transcription with translation. Here, we report that RNA polymerase directly binds ribosomes and isolated large and small ribosomal subunits. RNA polymerase and ribosomes form a one-to-one complex with a micromolar dissociation constant. The formation of the complex is modulated by the conformational and functional states of RNA polymerase and the ribosome. The binding interface on the large ribosomal subunit is buried by the small subunit during protein synthesis, whereas that on the small subunit remains solvent-accessible. The RNA polymerase binding site on the ribosome includes that of the isolated small ribosomal subunit. This direct interaction between RNA polymerase and ribosomes may contribute to the coupling of transcription to translation
Human prostate sphere-forming cells represent a subset of basal epithelial cells capable of glandular regeneration in vivo.
BackgroundProstate stem/progenitor cells function in glandular development and maintenance. They may be targets for tumor initiation, so characterization of these cells may have therapeutic implications. Cells from dissociated tissues that form spheres in vitro often represent stem/progenitor cells. A subset of human prostate cells that form prostaspheres were evaluated for self-renewal and tissue regeneration capability in the present study.MethodsProstaspheres were generated from 59 prostatectomy specimens. Lineage marker expression and TMPRSS-ERG status was determined via immunohistochemistry and fluorescence in situ hybridization (FISH). Subpopulations of prostate epithelial cells were isolated by cell sorting and interrogated for sphere-forming activity. Tissue regeneration potential was assessed by combining sphere-forming cells with rat urogenital sinus mesenchyme (rUGSM) subcutaneously in immunocompromised mice.ResultsProstate tissue specimens were heterogeneous, containing both benign and malignant (Gleason 3-5) glands. TMPRSS-ERG fusion was found in approximately 70% of cancers examined. Prostaspheres developed from single cells at a variable rate (0.5-4%) and could be serially passaged. A basal phenotype (CD44+CD49f+CK5+p63+CK8-AR-PSA-) was observed among sphere-forming cells. Subpopulations of prostate cells expressing tumor-associated calcium signal transducer 2 (Trop2), CD44, and CD49f preferentially formed spheres. In vivo implantation of sphere-forming cells and rUGSM regenerated tubular structures containing discreet basal and luminal layers. The TMPRSS-ERG fusion was absent in prostaspheres derived from fusion-positive tumor tissue, suggesting a survival/growth advantage of benign prostate epithelial cells.ConclusionHuman prostate sphere-forming cells self-renew, have tissue regeneration capability, and represent a subpopulation of basal cells
Electronic structure of crystalline binary and ternary Cd-Te-O compounds
The electronic structure of crystalline CdTe, CdO, -TeO,
CdTeO and CdTeO is studied by means of first principles
calculations. The band structure, total and partial density of states, and
charge densities are presented. For -TeO and CdTeO, Density
Functional Theory within the Local Density Approximation (LDA) correctly
describes the insulating character of these compounds. In the first four
compounds, LDA underestimates the optical bandgap by roughly 1 eV. Based on
this trend, we predict an optical bandgap of 1.7 eV for CdTeO. This
material shows an isolated conduction band with a low effective mass, thus
explaining its semiconducting character observed recently. In all these oxides,
the top valence bands are formed mainly from the O 2p electrons. On the other
hand, the binding energy of the Cd 4d band, relative to the valence band
maximum, in the ternary compounds is smaller than in CdTe and CdO.Comment: 13 pages, 15 figures, 2 tables. Accepted in Phys Rev
Shear-Flow Driven Current Filamentation: Two-Dimensional Magnetohydrodynamic Simulations
The process of current filamentation in permanently externally driven,
initially globally ideal plasmas is investigated by means of two-dimensional
Magnetohydrodynamic (MHD)-simulations. This situation is typical for
astrophysical systems like jets, the interstellar and intergalactic medium
where the dynamics is dominated by external forces. Two different cases are
studied. In one case, the system is ideal permanently and dissipative processes
are excluded. In the second case, a system with a current density dependent
resistivity is considered. This resistivity is switched on self-consistently in
current filaments and allows for local dissipation due to magnetic
reconnection. Thus one finds tearing of current filaments and, besides, merging
of filaments due to coalescence instabilities. Energy input and dissipation
finally balance each other and the system reaches a state of constant magnetic
energy in time.Comment: 32 Pages, 13 Figures. accepted, to appear in Physics of Plasmas
(049012
Automated Security Analysis of IoT Software Updates
IoT devices often operate unsupervised in ever-changing environments for several years. Therefore, they need to be updated on a regular basis. Current approaches for software updates on IoT, like the recent SUIT proposal, focus on granting integrity and confidentiality but do not analyze the content of the software update, especially the IoT application which is deployed to IoT devices. To this aim, in this paper, we present IoTAV, an automated software analysis framework for systematically verifying the security of the applications contained in software updates w.r.t. a given security policy. Our proposal can be adopted transparently by current IoT software updates workflows. We prove the viability of IoTAV by testing our methodology on a set of actual RIOT OS applications. Experimental results indicate that the approach is viable in terms of both reliability and performance, leading to the identification of 26 security policy violations in 31 real-world RIOT applications
GaN and InN nanowires grown by MBE: a comparison
Morphological, optical and transport properties of GaN and InN nanowires
grown by molecular beam epitaxy (MBE) have been studied. The differences
between the two materials in respect to growth parameters and optimization
procedure was stressed. The nanowires crystalline quality has been investigated
by means of their optical properties. A comparison of the transport
characteristics was given. For each material a band schema was shown, which
takes into account transport and optical features and is based on Fermi level
pinning at the surface.Comment: 5 pages, 5 figure
Two-dimensional turbulence in magnetised plasmas
In an inhomogeneous magnetised plasma the transport of energy and particles
perpendicular to the magnetic field is in general mainly caused by quasi
two-dimensional turbulent fluid mixing. The physics of turbulence and structure
formation is of ubiquitous importance to every magnetically confined laboratory
plasma for experimental or industrial application. Specifically, high
temperature plasmas for fusion energy research are also dominated by the
properties of this turbulent transport. Self-organisation of turbulent vortices
to mesoscopic structures like zonal flows is related to the formation of
transport barriers that can significantly enhance the confinement of a fusion
plasma. This subject of great importance in research is rarely touched on in
introductory plasma physics or continuum dynamics courses. Here a brief
tutorial on 2D fluid and plasma turbulence is presented as an introduction to
the field, appropriate for inclusion in undergraduate and graduate courses.Comment: This is an author-created, un-copyedited version of an article
published in European Journal of Physics. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher authenticated version
is available online at doi: 10.1088/0143-0807/29/5/00
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