The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Catuscia Palamidessi - One of the best experts on this subject based on the ideXlab platform.
-
comparing the expressive power of the synchronous and asynchronous pi calculi
Mathematical Structures in Computer Science, 2003Co-Authors: Catuscia PalamidessiAbstract:The Asynchronous $\pi$-calculus, proposed in Honda and Tokoro (1991) and, independently, in Boudol (1992), is a subset of the $\pi$-calculus (Milner et al. 1992), which contains no explicit operators for choice and output Prefixing. The communication mechanism of this calculus, however, is powerful enough to simulate output Prefixing, as shown in Honda and Tokoro (1991) and Boudol (1992), and input-guarded choice, as shown in Nestmann and Pierce (2000). A natural question arises, then, as to whether or not it is as expressive as the full $\pi$-calculus. We show that this is not the case. More precisely, we show that there does not exist any uniform, fully distributed translation from the $\pi$-calculus into the asynchronous $\pi$-calculus, up to any ‘reasonable’ notion of equivalence. This result is based on the incapability of the asynchronous $\pi$-calculus to break certain symmetries that may be present in the initial communication graph. By similar arguments, we prove a separation result between the $\pi$-calculus and CCS, and between the $\pi$-calculus and the $\pi$-calculus with internal mobility, a subset of the $\pi$-calculus proposed by Sangiorgi where the output actions can only transmit private names.
-
Comparing the Expressive Power of the Synchronous and the Asynchronous pi-calculi
Mathematical Structures in Computer Science, 2003Co-Authors: Catuscia PalamidessiAbstract:The Asynchronous $\pi$-calculus, proposed by Honda and Tokoro (1991) and, independently, by Boudol (1992), is a subset of the $\pi$-calculus \cite{Milner:92:IC} which contains no explicit operators for choice and output-Prefixing. The communication mechanism of this calculus, however, is powerful enough to simulate output-Prefixing, as shown by Honda and Tokoro (1991) and by Boudol (1992), and input-guarded choice, as shown by Nestmann and Pierce (2000). A natural question arises, then, whether or not it is as expressive as the full $\pi$-calculus. We show that this is not the case. More precisely, we show that there does not exist any uniform, fully distributed translation from the $\pi$-calculus into the asynchronous $\pi$-calculus, up to any ''reasonable'' notion of equivalence. This result is based on the incapability of the asynchronous $\pi$-calculus to break certain symmetries possibly present in the initial communication graph. By similar arguments, we prove a separation result between the $\pi$-calculus and CCS, and between the $\pi$-calculus and the $\pi$-calculus with internal mobility, a subset of the $\pi$-calculus proposed by Sangiorgi where the output actions can only transmit private names.
-
comparing the expressive power of the synchronous and the asynchronous π calculus
Symposium on Principles of Programming Languages, 1997Co-Authors: Catuscia PalamidessiAbstract:The Asynchronous π-calculus, as recently proposed by Boudol and, independently, by Honda and Tokoro, is a subset of the π-calculus which contains no explicit operators for choice and output-Prefixing. The communication mechanism of this calculus, however, is powerful enough to simulate output-Prefixing, as shown by Boudol, and input-guarded choice, as shown recently by Nestmann and Pierce. A natural question arises, then, whether or not it is possible to embed in it the full π-calculus. We show that this is not possible, i.e. there does not exist any uniform, parallel-preserving, translation from the π-calculus into the asynchronous π-calculus, up to any "reasonable" notion of equivalence. This result is based on the incapablity of the asynchronous π-calculus of breaking certain symmetries possibly present in the initial communication graph. By similar arguments, we prove a separation result between the π-calculus and CCS.
Helge Kuster - One of the best experts on this subject based on the ideXlab platform.
-
the promoter of the vicia faba l gene vfenod12 encoding an early nodulin is active in cortical cells and nodule primordia of transgenic hairy roots of vicia hirsuta as well as in the Prefixing zone ii of mature transgenic v hirsuta root nodules
Plant Science, 2000Co-Authors: Martin Fruhling, Gerald Schroder, Natalija Hohnjec, Alfred Puhler, Andreas M Perlick, Helge KusterAbstract:A full-length cDNA encoding the Vicia faba L. early nodulin VfEnod12 was isolated. The deduced protein sequence specified a 90 amino acid protein with a MW of 10 206 and contained a putative signal peptide sequence followed by PPX3 repeats characteristic of Enod12 proteins. The VfEnod12 gene was found to be expressed specifically in root nodules as early as 3 days post inoculation with Rhizobium leguminosarum bv. viciae. In mature nodules, VfEnod12 transcripts were confined to the Prefixing zone II. A 3.3 kb genomic fragment carrying the complete VfEnod12 coding region was isolated. No intervening sequences were identified in the coding region. A promoter fragment carrying the -692/-41 region mediated reporter gene expression in root cortical cells, module primordia and the Prefixing zone II of transgenic Vicia hirsuta root nodules. This fragment contained a putative binding site for the transcription factor ENBP1. In contrast to the highly conserved terminal AATAA motif of the ENBP1 binding site of known Enod12 promoters, the VfEnod12 promoter was characterized by an altered terminal AATAT sequence. This alteration did not interfere with VfEnod12 promoter activity in transgenic roots and nodules of V. hirsuta. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.
Polis Stéphane - One of the best experts on this subject based on the ideXlab platform.
-
Swimming against the typological tide or paddling along with language change? Dispreferred structures and diachronic biases in affix ordering
'John Benjamins Publishing Company', 2018Co-Authors: Grossman Eitan, Polis StéphaneAbstract:peer reviewedaudience: researcherIt has repeatedly been observed that there is a worldwide preference for suffixes as opposed to prefixes. In this paper, we argue that universally dispreferred – or rare – structures can and do arise as the result of regular processes of language change, given the right background structures. Specifically, we show that Ancient Egyptian-Coptic shows a long-term diachronic macro-change from mixed suffixing-Prefixing to an overwhelming preference for Prefixing. The empirical basis for this study is a comparison of ten typologically significant parameters in which Prefixing or affixing is potentially at stake, based on Dryer’s (2013a) 969-language sample. With its extremely high Prefixing preference, Coptic belongs to the rare 6% or so of languages that are predominantly Prefixing. We argue that each of the micro-changes implicated in this macro-change are better understood in terms of changes at the level of individual constructions, rather than in terms of a broad structural ‘drift.’ Crucially, there is nothing unusual about the actual processes of change themselves
-
Swimming against the typological tide or paddling along with language change? Dispreferred structures and diachronic biases in affix ordering
2018Co-Authors: Grossman Eitan, Polis StéphaneAbstract:It has repeatedly been observed that there is a worldwide preference for suffixes as opposed to prefixes. In this paper, we argue that universally dispreferred – or rare – structures can and do arise as the result of regular processes of language change, given the right background structures. Specifically, we show that Ancient Egyptian-Coptic shows a long-term diachronic macro-change from mixed suffixing-Prefixing to an overwhelming preference for Prefixing. The empirical basis for this study is a comparison of ten typologically significant parameters in which Prefixing or affixing is potentially at stake, based on Dryer’s (2013a) 969-language sample. With its extremely high Prefixing preference, Coptic belongs to the rare 6% or so of languages that are predominantly Prefixing. We argue that each of the micro-changes implicated in this macro-change are better understood in terms of changes at the level of individual constructions, rather than in terms of a broad structural ‘drift.’ Crucially, there is nothing unusual about the actual processes of change themselves.Peer reviewe
-
Universally dispreferred structures through change. The diachrony of affix ordering in Egyptian-Coptic
2017Co-Authors: Grossman Eitan, Polis StéphaneAbstract:peer reviewedaudience: researcherIt has been repeatedly observed, on the basis of typological ‘big data,’ that there is a worldwide preference for suffixes as opposed to prefixes. This can be explained in several ways. A possible explanation is that this feature is a world-wide retention from Proto-World, or is prone to diffusion through language contact. Another possible explanation is that suffixes are preferred for some reason in Universal Grammar or for hitherto unclear general cognitive reasons (Caballero et al. 2008). Yet another explanation is that suffixes are more prone to be created through regular processes of language change, e.g., grammaticalization (Bybee 1985), perhaps due to online usage factors (Himmelmann 2014). The explanation of this preference is directly relevant to a question highlighted in Good (2008), namely, the relationship between language universals and language change: do synchronic structural universals constrain change, or do diachronic universals, ultimately motivated by synchronic usage factors, give rise to synchronic universals? Kiparsky (2008) argues that the form of synchronic grammars constrains change, i.e., languages should not be able to change in such a way that they flout Universal Grammar. On the other hand, for Bybee (2008), the most robust universals are in fact universals of language change, and synchronic states are in a sense epiphenoma. For this question, apparently ‘counter-directional’ changes are crucial: why should language change lead to universally dispreferred distributions of linguistic structures? n this paper, we argue that universally dispreferred structures can and do arise as the result of regular language change, given the right background structures as the particular ‘ecology’ in which change takes place. Specifically, we show that Ancient Egyptian-Coptic (Afroasiatic), shows a long-term diachronic macro-change from mixed suffixing-Prefixing to an overwhelming preference for Prefixing. The empirical basis for this study is a comparison of ten typologically-significant parameters in which Prefixing or affixing is at stake, based on Dryer’s (2013) 969-language sample. With its extremely high Prefixing preference, Coptic belongs to the rare 6% or so of languages that are predominantly Prefixing (Tables 1,2). Moreover, it has a higher Prefixing index (11) than any other language in Dryer’s 969-language sample. The closest competitor is Hunde (Bantu; Democratic Republic of Congo), with a Prefixing index of 9.5. In terms of areality, Coptic is an outlier: in mediterranean northern Africa, Coptic is the only language that is predominantly Prefixing. We argue that each of the micro-changes implicated in this macro-change are better understood in terms of changes at the level of individual constructions, via grammaticalization, rather than in terms of a broad structural ‘drift.’ Crucially, there is nothing unusual about the actual processes of change themselves; what may be unusual, from a cross-linguistic point of view, is the length of uninterrupted documentation of a single language, which allows us to observe long-term changes with abundant evidence. In short, we argue that Ancient Egyptian-Coptic looks as though it is swimming against the typological tide, although it is constantly paddling along with the usual tides of language change
-
Universally dispreferred structures through change. The diachrony of affix ordering in Egyptian-Coptic
2017Co-Authors: Grossman Eitan, Polis StéphaneAbstract:It has been repeatedly observed, on the basis of typological ‘big data,’ that there is a worldwide preference for suffixes as opposed to prefixes. This can be explained in several ways. A possible explanation is that this feature is a world-wide retention from Proto-World, or is prone to diffusion through language contact. Another possible explanation is that suffixes are preferred for some reason in Universal Grammar or for hitherto unclear general cognitive reasons (Caballero et al. 2008). Yet another explanation is that suffixes are more prone to be created through regular processes of language change, e.g., grammaticalization (Bybee 1985), perhaps due to online usage factors (Himmelmann 2014). The explanation of this preference is directly relevant to a question highlighted in Good (2008), namely, the relationship between language universals and language change: do synchronic structural universals constrain change, or do diachronic universals, ultimately motivated by synchronic usage factors, give rise to synchronic universals? Kiparsky (2008) argues that the form of synchronic grammars constrains change, i.e., languages should not be able to change in such a way that they flout Universal Grammar. On the other hand, for Bybee (2008), the most robust universals are in fact universals of language change, and synchronic states are in a sense epiphenoma. For this question, apparently ‘counter-directional’ changes are crucial: why should language change lead to universally dispreferred distributions of linguistic structures? n this paper, we argue that universally dispreferred structures can and do arise as the result of regular language change, given the right background structures as the particular ‘ecology’ in which change takes place. Specifically, we show that Ancient Egyptian-Coptic (Afroasiatic), shows a long-term diachronic macro-change from mixed suffixing-Prefixing to an overwhelming preference for Prefixing. The empirical basis for this study is a comparison of ten typologically-significant parameters in which Prefixing or affixing is at stake, based on Dryer’s (2013) 969-language sample. With its extremely high Prefixing preference, Coptic belongs to the rare 6% or so of languages that are predominantly Prefixing (Tables 1,2). Moreover, it has a higher Prefixing index (11) than any other language in Dryer’s 969-language sample. The closest competitor is Hunde (Bantu; Democratic Republic of Congo), with a Prefixing index of 9.5. In terms of areality, Coptic is an outlier: in mediterranean northern Africa, Coptic is the only language that is predominantly Prefixing. We argue that each of the micro-changes implicated in this macro-change are better understood in terms of changes at the level of individual constructions, via grammaticalization, rather than in terms of a broad structural ‘drift.’ Crucially, there is nothing unusual about the actual processes of change themselves; what may be unusual, from a cross-linguistic point of view, is the length of uninterrupted documentation of a single language, which allows us to observe long-term changes with abundant evidence. In short, we argue that Ancient Egyptian-Coptic looks as though it is swimming against the typological tide, although it is constantly paddling along with the usual tides of language change.Peer reviewe
Arvind Atreya - One of the best experts on this subject based on the ideXlab platform.
-
NO formation in counterflow partially premixed flames
Combustion and Flame, 2007Co-Authors: Hemant P. Mungekar, Arvind AtreyaAbstract:An experimental and computational study of NO formation in low-strain-rate partially premixed methane counterflow flames is reported. For progressive fuel-side partial premixing the peak NO concentration increased and the NO distribution along the stagnation streamline broadened. New temperature-dependent emissivity data for a SiO{sub 2}-coated Pt thermocouple was used to estimate the radiation correction for the thermocouple, thus improving the accuracy of the reported flame temperature. Flame structure computations with GRIMech 3.00 showed good agreement between measured and computed concentration distributions of NO and OH radical. With progressive partial premixing the contribution of the thermal NO pathway to NO formation increases. The emission index of NO (EINO) first increased and then decreased, reaching its peak value for the level of partial premixing that corresponds to location of the nonpremixed reaction zone at the stagnation plane. The observation of a maximum in EINO at a level of partial premixing corresponding to the nonpremixed reaction zone at the stagnation plane seems to be a consistent feature of low (
-
Effect of partial premixing on the sooting structure of methane flames
Combustion and Flame, 2005Co-Authors: Hemant P. Mungekar, Arvind AtreyaAbstract:Abstract An experimental investigation of the sooting structure of diluted methane–oxygen counterflow flames is reported for partial premixing in the following two nonpremixed flame configurations: Case 1: Nonpremixed flame on the oxidizer side of the stagnation plane, Case 2: Nonpremixed flame on the fuel side of the stagnation plane. Effects of both fuel-side and oxidizer-side partial premixing for Cases 1 and 2 were investigated in a low-strain-rate (∼6–8 s −1 ) counterflow flame. Computations using OPPDIF code were in excellent agreement with the measured concentrations of major species and [OH]. Distribution of measured soot volume fraction and particle sizes are presented along with measured distributions of C 2 hydrocarbon species. Soot loading can increase or decrease depending on (a) the level of partial premixing, (b) the side of partial premixing (fuel side or oxidizer side), and (c) the nonpremixed flame configuration. Of particular interest is the trend for fuel-side partial premixing of Case 1, where the peak soot loading, the peak soot particle diameter, and the thickness of the soot zone initially decrease and then increase with progressive partial premixing. The trends presented are discussed based on chemical, dilution, and flow-field effects of partial premixing on soot growth in counterflow flames. Unlike previous literature, which focused on soot inception, this work emphasizes the role of partial premixing on soot growth by taking into account the changes in the temperature–time history of soot particulates in addition to the previously reported “chemical” and “dilution” effects.
-
The effect of time-dependent partial premixing in radiating flamelets
Combustion and Flame, 2000Co-Authors: Tariq Shamim, Arvind AtreyaAbstract:An understanding of the effect of partial premixing on flame characteristics is important to improve the design of many practical applications. In this study, a numerical investigation is carried out to examine the effect of time-dependent partial premixing in counterflow diffusion flames. The objective is to help understand the effect of turbulent fluctuations on a flamelet embedded in the flow field. Premixing of both air with the fuel stream and of fuel with the air stream is considered. The equivalence ratio of the partially premixed reactants is varied as a function of time. As expected, unsteady partial premixing results in a fluctuating double-flame configuration: a premixed flame and a diffusion flame. The maximum flame temperature, heat release rate and radiative heat loss are used to describe the flame response to fluctuations in partial premixing. The increase in partial premixing raises the diffusion flame temperature. This increase in temperature is greater at higher strain rates due to closer proximity of the premixed flame. The flame dynamics to changes in partial premixing is influenced by similar physical processes as those responsible for flame dynamics of pure diffusion flames subjected to unsteady effects. At low fluctuation frequencies, the flame responds quasi-steadily to changes in partial premixing. However, the amplitude of the flame response decreases gradually with an increase in the fluctuation frequency. At large frequencies, the flame is effectively insensitive to changes in partial premixing. A modified Strouhal number (based on the ratio of imposed fluctuation frequency and strain rate) is defined to predict the flame response to imposed fluctuation in partial premixing and to identify a regime where transient effects are important.
Venkat Anantharam - One of the best experts on this subject based on the ideXlab platform.
-
repetition error correcting sets explicit constructions and Prefixing methods
SIAM Journal on Discrete Mathematics, 2009Co-Authors: Lara Dolecek, Venkat AnantharamAbstract:In this paper we study the problem of finding maximally sized subsets of binary strings (codes) of equal length that are immune to a given number $r$ of repetitions, in the sense that no two strings in the code can give rise to the same string after $r$ repetitions. We propose explicit number theoretic constructions of such subsets. In the case of $r=1$ repetition, the proposed construction is asymptotically optimal. For $r\geq1$, the proposed construction is within a constant factor of the best known upper bound on the cardinality of a set of strings immune to $r$ repetitions. Inspired by these constructions, we then develop a Prefixing method for correcting any prescribed number $r$ of repetition errors in an arbitrary binary linear block code. The proposed method constructs for each string in the given code a carefully chosen prefix such that the resulting strings are all of the same length and such that despite up to any $r$ repetitions in the concatenation of the prefix and the codeword, the original codeword can be recovered. In this construction, the prefix length is made to scale logarithmically with the length of strings in the original code. As a result, the guaranteed immunity to repetition errors is achieved while the added redundancy is asymptotically negligible.
-
Prefixing method for correcting repetition errors
International Symposium on Information Theory, 2008Co-Authors: Lara Dolecek, Venkat AnantharamAbstract:We develop a Prefixing method for correcting any prescribed number r of repetition errors in an arbitrary binary block code. The proposed method constructs a prefix for each codeword such that the resulting strings are all of the same length and despite any r repetitions in the concatenation of the prefix and the codeword, the original codeword can be recovered. Further, the prefix length scales logarithmically with the blocklength of the original code, so the added redundancy is asymptotically negligible.