96 research outputs found
Prior-Independent Mechanisms for Scheduling
We study the makespan minimization problem with unrelated selfish machines
under the assumption that job sizes are stochastic. We design simple truthful
mechanisms that under various distributional assumptions provide constant and
sublogarithmic approximations to expected makespan. Our mechanisms are
prior-independent in that they do not rely on knowledge of the job size
distributions. Prior-independent approximation mechanisms have been previously
studied for the objective of revenue maximization [Dhangwatnotai, Roughgarden
and Yan'10, Devanur, Hartline, Karlin and Nguyen'11, Roughgarden, Talgam-Cohen
and Yan'12]. In contrast to our results, in prior-free settings no truthful
anonymous deterministic mechanism for the makespan objective can provide a
sublinear approximation [Ashlagi, Dobzinski and Lavi'09].Comment: This paper will appear in Proceedings of the ACM Symposium on Theory
of Computing 2013 (STOC'13
Principles of Carbon Catabolite Repression in the Rice Blast Fungus: Tps1, Nmr1-3, and a MATE–Family Pump Regulate Glucose Metabolism during Infection
Understanding the genetic pathways that regulate how pathogenic fungi respond to their environment is paramount to developing effective mitigation strategies against disease. Carbon catabolite repression (CCR) is a global regulatory mechanism found in a wide range of microbial organisms that ensures the preferential utilization of glucose over less favourable carbon sources, but little is known about the components of CCR in filamentous fungi. Here we report three new mediators of CCR in the devastating rice blast fungus Magnaporthe oryzae: the sugar sensor Tps1, the Nmr1-3 inhibitor proteins, and the multidrug and toxin extrusion (MATE)–family pump, Mdt1. Using simple plate tests coupled with transcriptional analysis, we show that Tps1, in response to glucose-6-phosphate sensing, triggers CCR via the inactivation of Nmr1-3. In addition, by dissecting the CCR pathway using Agrobacterium tumefaciens-mediated mutagenesis, we also show that Mdt1 is an additional and previously unknown regulator of glucose metabolism. Mdt1 regulates glucose assimilation downstream of Tps1 and is necessary for nutrient utilization, sporulation, and pathogenicity. This is the first functional characterization of a MATE–family protein in filamentous fungi and the first description of a MATE protein in genetic regulation or plant pathogenicity. Perturbing CCR in Δtps1 and MDT1 disruption strains thus results in physiological defects that impact pathogenesis, possibly through the early expression of cell wall–degrading enzymes. Taken together, the importance of discovering three new regulators of carbon metabolism lies in understanding how M. oryzae and other pathogenic fungi respond to nutrient availability and control development during infection
The \u3ci\u3eMagnaporthe oryzae\u3c/i\u3e nitrooxidative stress response suppresses rice innate immunity during blast disease
Understanding how microorganisms manipulate plant innate immunity and colonize host cells is a major goal of plant pathology. Here, we report that the fungal nitrooxidative stress response suppresses host defenses to facilitate the growth and development of the important rice pathogen Magnaporthe oryzae in leaf cells. Nitronate monooxygenases encoded by NMO genes catalyze the oxidative denitrification of nitroalkanes. We show that the M. oryzae NMO2 gene is required for mitigating damaging lipid nitration under nitrooxidative stress conditions and, consequently, for using nitrate and nitrite as nitrogen sources. On plants, the Δnmo2 mutant strain penetrated host cuticles like wild type, but invasive hyphal growth in rice cells was restricted and elicited plant immune responses that included the formation of cellular deposits and a host reactive oxygen species burst. Development of the M. oryzae effector-secreting biotrophic interfacial complex (BIC) was misregulated in the Δnmo2 mutant. Inhibiting or quenching host reactive oxygen species suppressed rice innate immune responses and allowed the Δnmo2 mutant to grow and develop normally in infected cells. NMO2 is thus essential for mitigating nitrooxidative cellular damage and, in rice cells, maintaining redox balance to avoid triggering plant defenses that impact M. oryzae growth and BIC development
Substrate Micropatterning as a New in Vitro Cell Culture System to Study Myelination
ArtÃculo de publicación ISIMyelination is a highly regulated developmental
process whereby oligodendrocytes in the central nervous system
and Schwann cells in the peripheral nervous system ensheathe axons
with a multilayered concentric membrane. Axonal myelination
increases the velocity of nerve impulse propagation. In this work,
we present a novel in vitro system for coculturing primary dorsal root
ganglia neurons along with myelinating cells on a highly restrictive
and micropatterned substrate. In this new coculture system, neurons
survive for several weeks, extending long axons on defined Matrigel
tracks. On these axons, myelinating cells can achieve robust myelination, as demonstrated by the distribution of compact myelin
and nodal markers. Under these conditions, neurites and associated myelinating cells are easily accessible for studies on the
mechanisms of myelin formation and on the effects of axonal damage on the myelin sheath.Regenerative Medicine and Nanomedicine Initiative of the Canadian Institutes of Health Research (CIHR)
RMF-7028
FONDECYT
1080252
CIHR
Ministry of Industry of Canada
Rio Tinto Alcan
Molson Foundatio
Sequential Posted Pricing and Multi-parameter Mechanism Design
We consider the classical mathematical economics problem of {\em Bayesian optimal mechanism design} where a principal aims to optimize expected revenue when allocating resources to self-interested agents with preferences drawn from a known distribution. In single-parameter settings (i.e., where each agent's preference is given by a single private value for being served and zero for not being served) this problem is solved [Myerson '81]. Unfortunately, these single parameter optimal mechanisms are impractical and rarely employed [Ausubel and Milgrom '06], and furthermore the underlying economic theory fails to generalize to the important, relevant, and unsolved multi-dimensional setting (i.e., where each agent's preference is given by multiple values for each of the multiple services available) [Manelli and Vincent '07]. In contrast to the theory of optimal mechanisms we develop a theory of sequential posted price mechanisms, where agents in sequence are offered take-it-or-leave-it prices. These mechanisms are approximately optimal in single-dimensional settings, and avoid many of the properties that make optimal mechanisms impractical. Furthermore, these mechanisms generalize naturally to give the first known approximations to the elusive optimal multi-dimensional mechanism design problem. In particular, we solve multi-dimensional multi-unit auction problems and generalizations to matroid feasibility constraints. The constant approximations we obtain range from 1.5 to 8. For all but one case, our posted price sequences can be computed in polynomial time.
Abstract On Profit-Maximizing Envy-free Pricing
We study the problem of pricing items for sale to consumers so as to maximize the seller’s revenue. We assume that for each consumer, we know the maximum amount he would be willing to pay for each bundle of items, and want to find pricings of the items with corresponding allocations that maximize seller profit and at the same time are envy-free, which is a natural fairness criterion requiring that consumers are maximally happy with the outcome they receive given the pricing. We study this problem for two important classes of inputs: unit demand consumers, who want to buy at most one item from among a selection they are interested in, and single-minded consumers, who want to buy one particular subset, but only if they can afford it. We show that computing envy-free prices to maximize the seller’s revenue is APX-hard in both of these cases, and give a logarithmic approximation algorithm for them. For several interesting special cases, we derive polynomial-time algorithms. Furthermore, we investigate some connections with the corresponding mechanism design problem, in which the consumer’s preferences are private values: for this case, we give a log-competitive truthful mechanism.
Four Mechanisms in the Reactions of 3‑Aminopyrrole with 1,3,5-Triazines: Inverse Electron Demand Diels–Alder Cycloadditions vs S<sub>N</sub>Ar Reactions via Uncatalyzed and Acid-Catalyzed Pathways
Reaction of 3-aminopyrrole with seven
1,3,5-triazines was studied
in a one-step reaction (in situ formation of 3-aminopyrrole) and a
two-step reaction (using the tetraphenylborate salt and an amine base).
An inverse-electron demand Diels–Alder reaction (IEDDA) was
observed with R<sub>1</sub> = CF<sub>3</sub>, CO<sub>2</sub>Et, and
H with the formation of 5<i>H</i>-pyrroloÂ[3,2-<i>d</i>]Âpyrimidine derivatives. S<sub>N</sub>Ar was observed when 2,4,6-trifluoro-
or 2,4,6-trichloro-1,3,5-triazine were usedî—¸1,3,5-triazines
that had leaving groups. If excess 1,3,5-triazine was present the
initial S<sub>N</sub>Ar product reacted further, in the presence of
acid and water, with another equivalent of 1,3,5-triazine to give
compounds containing three linked heterocyclic rings. No reaction
was observed with R<sub>1</sub> = C<sub>6</sub>H<sub>5</sub> and OCH<sub>3</sub>. Four mechanisms are proposed to explain the experimental
results: uncatalyzed and acid catalyzed inverse electron demand Diels–Alder
cascades leading to cycloaddition, and uncatalyzed and acid-catalyzed
S<sub>N</sub>Ar reactions leading, respectively, to single and double
substitution products. Acid catalysis was a factor when there was
reduced reactivity in either reactant
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