127 research outputs found
Front Propagation with Rejuvenation in Flipping Processes
We study a directed flipping process that underlies the performance of the
random edge simplex algorithm. In this stochastic process, which takes place on
a one-dimensional lattice whose sites may be either occupied or vacant,
occupied sites become vacant at a constant rate and simultaneously cause all
sites to the right to change their state. This random process exhibits rich
phenomenology. First, there is a front, defined by the position of the
left-most occupied site, that propagates at a nontrivial velocity. Second, the
front involves a depletion zone with an excess of vacant sites. The total
excess D_k increases logarithmically, D_k ~ ln k, with the distance k from the
front. Third, the front exhibits rejuvenation -- young fronts are vigorous but
old fronts are sluggish. We investigate these phenomena using a quasi-static
approximation, direct solutions of small systems, and numerical simulations.Comment: 10 pages, 9 figures, 4 table
Eco-morphodynamic carbon pumping by the largest rivers in the Neotropics
AbstractThe eco-morphodynamic activity of large tropical rivers in South and Central America is analyzed to quantify the carbon flux from riparian vegetation to inland waters. We carried out a multi-temporal analysis of satellite data for all the largest rivers in the Neotropics (i.e, width > 200 m) in the period 2000–2019, at 30 m spatial resolution. We developed a quantification of a highly efficient Carbon Pump mechanism. River morphodynamics is shown to drive carbon export from the riparian zone and to promote net primary production by an integrated process through floodplain rejuvenation and colonization. This pumping mechanism alone is shown to account for 8.9 million tons/year of carbon mobilization in these tropical rivers. We identify signatures of the fluvial eco-morphological activity that provide proxies for the carbon mobilization capability associated with river activity. We discuss river migration—carbon mobilization nexus and effects on the carbon intensity of planned hydroelectric dams in the Neotropics. We recommend that future carbon-oriented water policies on these rivers include a similar analysis
Mathematics in Software Reliability and Quality Assurance
This monograph concerns the mathematical aspects of software reliability and quality assurance and consists of 11 technical papers in this emerging area. Included are the latest research results related to formal methods and design, automatic software testing, software verification and validation, coalgebra theory, automata theory, hybrid system and software reliability modeling and assessment
Non-equilibrium dynamics of spin facilitated glass models
We consider the dynamics of spin facilitated models of glasses in the
non-equilibrium aging regime following a sudden quench from high to low
temperatures. We briefly review known results obtained for the broad class of
kinetically constrained models, and then present new results for the behaviour
of the one-spin facilitated Fredrickson-Andersen and East models in various
spatial dimensions. The time evolution of one-time quantities, such as the
energy density, and the detailed properties of two-time correlation and
response functions are studied using a combination of theoretical approaches,
including exact mappings of master operators and reductions to integrable
quantum spin chains, field theory and renormalization group, and independent
interval and timescale separation methods. The resulting analytical predictions
are confirmed by means of detailed numerical simulations. The models we
consider are characterized by trivial static properties, with no finite
temperature singularities, but they nevertheless display a surprising variety
of dynamic behaviour during aging, which can be directly related to the
existence and growth in time of dynamic lengthscales. Well-behaved
fluctuation-dissipation ratios can be defined for these models, and we study
their properties in detail. We confirm in particular the existence of negative
fluctuation-dissipation ratios for a large number of observables. Our results
suggest that well-defined violations of fluctuation-dissipation relations, of a
purely dynamic origin and unrelated to the thermodynamic concept of effective
temperatures, could in general be present in non-equilibrium glassy materials.Comment: 72 pages, invited contribution to special issue of JSTAT on
"Principles of Dynamics of Nonequilibrium Systems" (Programme at Newton
Institute Cambridge). v2: New data added to Figs. 11, 23, 24, new Fig. 26 on
East model in d=3, minor improvements to tex
Mountain building in Taiwan: A thermokinematic model
The Taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening. However, a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge. We propose here a new thermokinematic model of the Taiwan mountain belt reconciling existing kinematic, thermometric and thermochronological constraints. In this model, shortening across the orogen is absorbed by slip on the most frontal faults of the foothills. Crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge (Tananao Complex, TC), where the uplift rate is estimated to ~6.3 mm a^(−1), and beneath the westernmost internal region of the orogen (Hsueshan Range units, HR), where the uplift rate is estimated to ~4.2 mm a^(−1). Our model suggests that the TC units experienced a synchronous evolution along strike despite the southward propagation of the collision. It also indicates that they have reached a steady state in terms of cooling ages but not in terms of peak metamorphic temperatures. Exhumation of the HR units increases northward but has not yet reached an exhumational steady state. Presently, frontal accretion accounts for less than ~10% of the incoming flux of material into the orogen, although there is indication that it was contributing substantially more (~80%) before 4 Ma. The incoming flux of material accreted beneath the TC significantly increased 1.5 Ma ago. Our results also suggest that the flux of material accreted to the orogen corresponds to the top ~7 km of the upper crust of the underthrust Chinese margin. This indicates that a significant amount (~76%) of the underthrust material has been subducted into the mantle, probably because of the increase in density associated with metamorphism. We also show that the density distribution resulting from metamorphism within the orogenic wedge explains well the topography and the gravity field. By combining available geological data on the thermal and kinematic evolution of the wedge, our study sheds new light onto mountain building processes in Taiwan and allows for reappraising the initial structural architecture of the passive margin
Recent tectonic reorganization of the Nubia-Eurasia convergent 2 boundary heading for the closure of the western Mediterranean
: In the western Mediterranean area, after a long period (late Paleogene-Neogene) of Nubian northward subduction beneath Eurasia, subduction is almost ceased as well as convergence accommodation in the subduction zone. With the progression of Nubia-Eurasia convergence, a tectonic reorganization is therefore necessary to accommodate future contraction. Previously-published tectonic, seismological, geodetic, tomographic, and seismic reflection data (integrated by some new GPS velocity data) are reviewed to understand the reorganization of the convergent boundary in the western Mediterranean. Between northern Morocco, to the west, and northern Sicily, to the east, contractional deformation has shifted from the former subduction zone to the margins of the two backarc oceanic basins (Algerian-Liguro-Provençal and Tyrrhenian basins) and it is now active in the south-Tyrrhenian (northern Sicily), northern Liguro-Provençal, Algerian, and Alboran (partly) margins. Compression and basin inversion has propagated in a scissor-like manner from the Alboran (c. 8 Ma) to the Tyrrhenian (younger than c. 2 Ma) basins following a similar propagation of the subduction cessation and slab breakoff, i.e., older to the west and younger to the east. It follows that basin inversion is rather advanced in the Algerian margin, where a new southward subduction seems to be in its very infant stage, while it has still to properly start in the Tyrrhenian margin, where contraction has resumed at the rear of the fold-thrust belt and may soon invert the Marsili oceanic basin. GPS-derived strain rates higher in the Tyrrhenian margin than in the Algerian boundary suggest that this latter manner of contraction accommodation (contraction resumption at the rear of the orogenic wedge) is more efficient than subduction inception and basin inversion along newly-generated reverse faults (Algeria), but the differential strain rates may also be explained with the heterogeneous distribution of GPS stations. Part of the contractional deformation may have shifted toward the north in the Liguro-Provençal basin possibly because of its weak rheological properties compared with the area between Tunisia and Sardinia, where no oceanic crust occurs and seismic deformation is absent or limited compared with the adjacent strands of the Nubia-Eurasia boundary. The tectonic reorganization of the Nubia-Eurasia boundary in the study area is still strongly controlled by the inherited tectonic fabric and rheological attributes, which are both discontinuous and non-cylindrical along the boundary. These features prevent, at present, the development of long and continuous thrust faults. In an extreme and approximate synthesis, the evolution of the western Mediterranean is inferred as being similar to a Wilson Cycle in the following main steps: (1) northward Nubian subduction with Mediterranean backarc extension (since ~35 Ma); (2) progressive cessation, from west to east, of Nubian main subduction (since ~15 Ma); (3) progressive compression, from west to east, in the former backarc domain and consequent basin inversion (since ~8-10 Ma); (4) possible future subduction of former backarc basins
Late Cenozoic metamorphic evolution and exhumation of Taiwan
The Taiwan mountain belt is composed of a Cenozoic slate belt (Hsuehshan Range units, HR, and Backbone Slates, BS) and of accreted polymetamorphic basement rocks (Tananao Complex, TC). Ongoing crustal shortening has resulted from the collision between the Chinese continental margin and the Luzon volcanic arc, which initiated ~6.5 Ma ago. The grade and age of metamorphism and exhumation are a key record of the development of the orogenic wedge. Because the Taiwan mountain belt is mostly composed by accreted sediments lacking metamorphic index minerals, quantitative constraints on metamorphism are sparse. By contrast, these rocks are rich in carbonaceaous material (CM) and are therefore particularly appropriate for RSCM (Raman Spectroscopy of CM) thermometry. We apply this technique in addition to (U-Th)/He thermochronology on detrital zircons to assess peak metamorphic temperatures (T) and the late exhumational history respectively, along different transects in central and southern Taiwan. In the case of the HR units, we find evidence for high metamorphic T of at least 340°–350°C and locally up to 475°C, and for relative rapid exhumation with zircon (U-Th)/He ages in the range of 1.5–2 Ma. Farther east, the BS were only slightly metamorphosed (T < 330 °C), and zircons are not reset for (U-Th)/He. From the eastern BS to the inner TC schists, T gradually increases from ~350°C up to ~500°C following an inverted metamorphic gradient. Available geochronological constraints and the continuous thermal gradient from the BS to the basement rocks of the TC suggest that the high RSCM T of the TC were most probably acquired during the last orogeny, and were not inherited from a previous thermal event. Zircons yield (U-Th)/He ages of ~0.5–1.2 Ma. Peak metamorphic T and the timing of exhumation do not show along-strike variations over the TC in the studied area. In contrast, exhumation is laterally diachronous and decreases southward in the case of the HR units. In particular, our data imply that the HR units have been exhumed by a minimum of 15 km over the last few Ma. In the case of the BS, they show far less cumulated exhumation and much slower cooling rates. We propose that most of the deformation and exhumation of the Taiwan mountain belt is sustained through two underplating windows located beneath the Hsuehshan Range and the TC. Our data show significant departures from the predictions of the prevailing model in Taiwan, which assumes a homogeneous critical wedge with dominant frontal accretion. Our study sheds new light on how the mountain belt has grown as a possible result of underplating mostly
Dependability Assessment of Android OS
In this brave new world of smartphone-dependent society, dependability is a strong requirement and needs to be addressed properly. Assessing the dependability of these mobile system is still an open issue, and companies should have the tools to improve their devices and beat the competition against other vendors.
The main objective of this dissertation is to provide the methods to assess the dependability of mobile OS, fundamental for further improvements.
Mobile OS are threatened mainly by traditional residual faults (when errors spread across components as failures), aging-related faults (when errors accumulate over time), and misuses by users and applications. This thesis faces these three aspects. First, it presents a qualitative method to define the fault model of a mobile OS, and an exhaustive fault model for Android. I designed and developed AndroFIT, a novel fault injection tool for Android smartphone, and performed an extensive fault injection campaign on three Android devices from different vendors to analyze the impact of component failure on the mobile OS. Second, it presents an experimental methodology to analyze the software aging phenomenon in mobile OS. I performed a software aging analysis campaign on Android devices to identify the impacting factors on performance degradation and resource consumption. Third, it presents the design and implementation of a novel fuzzing tool, namely Chizpurfle, able to automatically test Android vendor customizations by leveraging code coverage information at run-time
多細胞組織のメゾスコピックレベルでの分解と再構成 : 複雑適応系の非平衡相転移理論に向けて
学位の種別: 課程博士審査委員会委員 : (主査)東京大学准教授 陳 昱, 東京大学教授 飛原 英治, 東京大学教授 奥田 洋司, 東京大学教授 大橋 弘忠, 京都大学准教授 井上 康博University of Tokyo(東京大学
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