274 research outputs found
Brief Announcement: Grassroots Distributed Systems: Concept, Examples, Implementation and Applications
No full textInformally, a distributed system is grassroots if it is permissionless and can have autonomous, independently-deployed instances - geographically and over time - that may interoperate voluntarily once interconnected. More formally, in a grassroots system the set of all correct behaviors of a set of agents P is strictly included in the set of the correct behaviors of P when they are embedded within a larger set of agents P' ⊃ P.
Grassroots systems are potentially important as they may allow communities to conduct their social, economic, civic, and political lives in the digital realm solely using their members' networked computing devices (e.g., smartphones), free of third-party control, surveillance, manipulation, coercion, or rent seeking (e.g., by global digital platforms such as Facebook or Bitcoin).
Client-server/cloud computing systems are not grassroots, and neither are systems designed to have a single global instance (Bitcoin/Ethereum with hardwired seed miners/bootnodes), and systems that rely on a single global data structure (IPFS, DHTs). An example grassroots system would be a serverless smartphone-based social network supporting multiple independently-budding communities that can merge when a member of one community becomes also a member of another.
Here, we formalize the notion of grassroots distributed systems; describe a grassroots dissemination protocol for the model of asynchrony and argue its safety, liveness, and being grassroots; extend the implementation to mobile (address-changing) devices that communicate via an unreliable network (e.g. smartphones using UDP); and discuss how grassroots dissemination can realize grassroots social networking and grassroots cryptocurrencies. The mathematical construction employs distributed multiagent transition systems to define the notions of grassroots protocols, to specify the grassroots dissemination protocols, and to prove their correctness. The protocols use the blocklace - a distributed, partially-ordered counterpart of the replicated, totally-ordered blockchain
Cordial Miners: Fast and Efficient Consensus for Every Eventuality
No full textCordial Miners are a family of efficient Byzantine Atomic Broadcast
protocols, with instances for asynchrony and eventual synchrony.
They improve the latency of state-of-the-art DAG-based protocols by almost 2X
and achieve optimal good-case complexity of O(n) by forgoing Reliable Broadcast
as a building block.
Rather, Cordial Miners use the blocklace -- a partially-ordered counterpart
of the totally-ordered blockchain data structure -- to implement the three
algorithmic components of consensus: Dissemination, equivocation-exclusion, and
ordering
An RNA interference knock-down of nitrate reductase enhances lipid biosynthesis in the diatom Phaeodactylum tricornutum
No full textWhen diatoms are stressed for inorganic nitrogen they remodel their intermediate metabolism and redirect carbon towards lipid biosynthesis. However, this response comes at a significant cost reflected in decreased photosynthetic energy conversion efficiency and growth. Here we explore a molecular genetics approach to restrict the assimilation of inorganic nitrogen by knocking down nitrate reductase (NR). The transformant strain, NR21, exhibited about 50% lower expression and activity of the enzyme but simultaneously accumulated over 40% more fatty acids. However, in contrast to nitrogen-stressed wild-type (WT) cells, which grow at about 20% of the rate of nitrogen-replete cells, growth of NR21 was only reduced by about 30%. Biophysical analyses revealed that the photosynthetic energy conversion efficiency of photosystem II was unaffected in NR21; nevertheless, the plastoquinone pool was reduced by 50% at the optimal growth irradiance while in the WT it was over 90% oxidized. Further analyses reveal a 12-fold increase in the glutamate/glutamine ratio and an increase NADPH and malonyl-CoA pool size. Transcriptomic analyses indicate that the knock down resulted in changes in the expression of genes for lipid biosynthesis, as well as the expression of specific transcription factors. Based on these observations, we hypothesize that the allocation of carbon and reductants in diatoms is controlled by a feedback mechanism between intermediate metabolites, the redox state of the plastid and the expression and binding of transcription factors related to stress responses.Peer reviewe
The Story of Ehud and Eglon in Judges 3:12-30. A Literary Pearl as a Theological Stumbling Block
No full textMaking use of numerous stylistic devices and playing with words, the author of Judg 3:12-30 has succeeded in creating a masterpiece of literature that challenges its reader. Moreover and simultaneously, this story, that narrates the brutal murder of king Eglon by the Israelite Ehud, is very problematic from a theological perspective. The present article offers firstly an analysis of Judg 3:12-20 and subsequently demonstrates how a specific and often-overlooked aspect of the violent nature of the text – after all, king Eglon has been utilized by YHWH to restore obedience among the Israelites – holds a key to unlocking the theological intention of this text
OR-parallel PROLOG in flat concurrent PROLOG
No full textAbstractWe describe a simple or-parallel execution algorithm for PROLOG that naturally collects all solutions to a goal. For a large class of programs the algorithm has O(log n) overhead and exhibits O(n/(log n)2) parallel speedup over the standard sequential algorithm. Its constituent parallel processes are independent, and hence the algorithm is suitable for implementation on non-shared-memory parallel computers. The algorithm can be implemented directly in Flat Concurrent PROLOG. We describe a simple interpreter-based fcp implementation of the algorithm, analyze its performance under Logix, and include initial measurements of its speedup on the parallel implementation of fcp. The implementation is easily extended. We show an extension that performs parallel demand-driven search. We define two parallel variants of cut, cut-clause and cut-goal, and describe their implementation. We discuss the execution of the algorithm on a parallel computer, and describe implementations of it that perform centralized and distributed dynamic load balancing. Since the fcp implementation of the algorithm relies on full test unification, the algorithm does not seem to have a similarly natural implementation in ghc or parlog
The genetic basis of persistence and recovery in stuttering
No full textThe purpose of this study was to elaborate on genetic perspectives of stuttering with reference to recovery and chronicity in children. Past research has provided evidence of a genetic factor in the transmission of susceptibility to stuttering, but factors governing persistence and recovery have not been as yet identified.Immediate and extended families of 66 stuttering probands were investigated to determine frequencies of persistent and recovered stuttering. Pedigree analysis and segregation analysis were utilized to examine patterns of heritability.The following questions were investigated: (1) Is there a sex effect in recovery from stuttering? This hypothesis examined the notion that females have a greater chance of recovery than do males, leading to the changing sex ratio from approximately 2:1 males to females close to onset of the disorder, to 4 or 5:1 in adulthood. A significant chi square indicated that recovery among females is significantly more frequent than among males, as shown by the sharply different sex ratios of persistent vs. recovered stutterers. (2) Is persistence or recovery from stuttering heritable? If recovery appears to be heritable, (a) are recovered and persistent stuttering a unitary disorder where recovered stuttering is a genetically milder form of persistent stuttering; (b) is recovery transmitted independent of stuttering; or (c) are recovered and persistent stuttering independent disorders? Results indicated that persistence or recovery are indeed heritable, and further, that recovery is not a milder form, nor do the two types of stuttering appear to be unrelated, independent disorders. Data are most consistent with the hypothesis that persistence is in part due to an additional genetic factor.Segregation analyses supported these conclusions and provided statistical evidence for both a single major locus and polygenic component for persistent and recovered stuttering.This study was supported by grant #R01-DC00459 from the National Institute of Deafness and Other Communication Disorders, National Institutes of Health, Principal Investigator: Ehud Yairi.Made available in DSpace on 2011-05-07T12:49:38Z (GMT). No. of bitstreams: 2
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