511 research outputs found
Wait-Free Solvability of Equality Negation Tasks
We introduce a family of tasks for n processes, as a generalization of the two process equality negation task of Lo and Hadzilacos (SICOMP 2000). Each process starts the computation with a private input value taken from a finite set of possible inputs. After communicating with the other processes using immediate snapshots, the process must decide on a binary output value, 0 or 1. The specification of the task is the following: in an execution, if the set of input values is large enough, the processes should agree on the same output; if the set of inputs is small enough, the processes should disagree; and in-between these two cases, any output is allowed. Formally, this specification depends on two threshold parameters k and l, with k<l, indicating when the cardinality of the set of inputs becomes "small" or "large", respectively. We study the solvability of this task depending on those two parameters. First, we show that the task is solvable whenever k+2 <= l. For the remaining cases (l = k+1), we use various combinatorial topology techniques to obtain two impossibility results: the task is unsolvable if either k <= n/2 or n-k is odd. The remaining cases are still open
The solvability of consensus in iterated models extended with safe-consensus
The safe-consensus task was introduced by Afek, Gafni and Lieber (DISC'09) as
a weakening of the classic consensus. When there is concurrency, the consensus
output can be arbitrary, not even the input of any process. They showed that
safe-consensus is equivalent to consensus, in a wait-free system. We study the
solvability of consensus in three shared memory iterated models extended with
the power of safe-consensus black boxes. In the first model, for the -th
iteration, processes write to the memory, invoke safe-consensus boxes and
finally they snapshot the memory. We show that in this model, any wait-free
implementation of consensus requires safe-consensus black-boxes
and this bound is tight. In a second iterated model, the processes write to
memory, then they snapshot it and finally they invoke safe-consensus boxes. We
prove that in this model, consensus cannot be implemented. In the last iterated
model, processes first invoke safe-consensus, then they write to memory and
finally they snapshot it. We show that this model is equivalent to the previous
model and thus consensus cannot be implemented.Comment: 49 pages, A preliminar version of the main results appeared in the
SIROCCO 2014 proceeding
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Expression of TRIM Genes in Different Immune Cells and Mechanism of Regulation of Their Expression: Implications for the Immune Response to Pathogens
The tripartite motif (TRIM) proteins are important in a variety of cellular functions including antiviral activity. We systematically analyzed mRNA expression of representative TRIMs in primary mouse macrophages, myeloid and plasmacytoid dendritic cells, and a selection of CD4+ T cell subsets. These cells have different effector functions in innate and adaptive immune responses, to a large extent due to the different patterns of cytokines that they produce. Here, we defined four clusters of TRIM genes based on their selective expression in these cell subsets. The first group of TRIMs was preferentially expressed in CD4+T cells and contained the COS-FN3 motif. Additional TRIMs were identified that showed up-regulation in macrophages and dendritic cells upon influenza virus infection in a type-I IFN dependent manner suggesting that they may play a role in anti-viral responses. However, stimulation of macrophages and mDC with LPS and double stranded RNA also led to type-I IFN dependent up-regulation of these TRIM genes, suggesting that their expression is not directly regulated by the virus, and that they may have broader functions in innate immune responses. In support of the proposed role of TRIMs in anti-viral responses, a subset of the type-I IFN dependent TRIMs mapped to mouse chromosome 7, syntenic to human chromosome 11 where TRIMs such as TRIM5, shown to have anti-viral activity, are localized. Consistent with these findings, up-regulation of the same TRIM genes in human macrophages was mainly observed under conditions which resulted in the induction of IFNβ (in this case by LPS and IFNγ stimulations), as observed by reanalysis of a previously published microarray study. Within the group of TRIMs induced by viruses in macrophages and dendritic cells via a type-I IFN dependent mechanism we distinguish two clusters on the basis of TRIM expression in CD4+ T cells. A fourth group of TRIMs was constitutively expressed in plasmacytoid dendritic cells independently of viral infection or signalling through the type-I IFN receptor. Our findings on expression and regulation of TRIMs may help to develop potential strategies for determining functions of this diverse family of molecules in immune cells
An Introduction to the Topological Theory of Distributed Computing with Safe-consensus
AbstractThe theory of distributed computing shares a deep and fascinating connection with combinatorial and algebraic topology. One of the key ideas that facilitates the development of the topological theory of distributed computing is the use of iterated shared memory models. In such a model processes communicate through a sequence of shared objects. Processes access the sequence of objects, one-by-one, in the same order and asynchronously. Each process accesses each shared object only once. In the most basic form of an iterated model, any number of processes can crash, and the shared objects are snapshot objects. A process can write a value to such an object, and gets back a snapshot of its contents.The purpose of this paper is to give an introduction to this research area, using an iterated model based on the safe-consensus task (Afek, Gafni and Lieber, DISCʼ09). In a safe-consensus task, the validity condition of consensus is weakened as follows. If the first process to invoke an object solving a safe-consensus task returns before any other process invokes it, then the process gets back its own input; otherwise the value returned by the task can be arbitrary. As with consensus, the agreement requirement is that always the same value is returned to all processes.A safe-consensus-based iterated model is described in detail. It is explained how its runs can be described with simplicial complexes. The usefulness of the iterated memory model for the topological theory of distributed computing is exhibited by presenting some new results (with very clean and well structured proofs) about the solvability of the (n,k)-set agreement task. Throughout the paper, the main ideas are explained with figures and intuitive examples
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