136 research outputs found
Improved Prophet Inequalities for Combinatorial Welfare Maximization with (Approximately) Subadditive Agents
m-1} measures the maximum number of items that complement each other, and (3) as a byproduct, an O(1)-competitive prophet inequality for submodular or fractionally subadditive (a.k.a. XOS) agents, matching the optimal ratio asymptotically. Our framework is computationally efficient given sample access to the prior and demand queries
Vasoprotection by Dietary Supplements and Exercise: Role of TNFα Signaling
Vascular dysfunction contributes to the pathogenesis of various cardiovascular diseases. Dietary supplements, including fish oil, dietary fibers, and various natural products, and exercise training exert vasoprotective effects. However, the mechanisms underlying the vasoprotective benefits of dietary supplements and physical activity demand extensive investigation. Accumulating evidence suggests that inflammatory cytokine tumor necrosis factor-alpha (TNFα) plays a pivotal role in the dysregulation of macrovascular and microvascular function. TNFα induces vascular inflammation, monocyte adhesion to endothelial cells, vascular oxidative stress, apoptosis, and atherogenic response and participates in the regulation of thrombosis and coagulation through multiple signaling pathways involving NFκB, Sp1, activator protein 1, JNK, p38, STAT3, and so forth. Dietary supplements and exercise training decrease TNFα production and ameliorate TNFα-mediated pathological changes in vasculature. Thus, the inhibitory effects of dietary supplements and physical exercise on TNFα production and TNFα signaling may contribute to their vasoprotective properties
An Improved Algorithm for Incremental DFS Tree in Undirected Graphs
Depth first search (DFS) tree is one of the most well-known data structures
for designing efficient graph algorithms. Given an undirected graph
with vertices and edges, the textbook algorithm takes time to
construct a DFS tree. In this paper, we study the problem of maintaining a DFS
tree when the graph is undergoing incremental updates. Formally, we show: Given
an arbitrary online sequence of edge or vertex insertions, there is an
algorithm that reports a DFS tree in worst case time per operation, and
requires preprocessing time.
Our result improves the previous worst case update time
algorithm by Baswana et al. and the time by Nakamura and
Sadakane, and matches the trivial lower bound when it is required
to explicitly output a DFS tree.
Our result builds on the framework introduced in the breakthrough work by
Baswana et al., together with a novel use of a tree-partition lemma by Duan and
Zhan, and the celebrated fractional cascading technique by Chazelle and Guibas
Automated Mechanism Design for Classification with Partial Verification
We study the problem of automated mechanism design with partial verification,
where each type can (mis)report only a restricted set of types (rather than any
other type), induced by the principal's limited verification power. We prove
hardness results when the revelation principle does not necessarily hold, as
well as when types have even minimally different preferences. In light of these
hardness results, we focus on truthful mechanisms in the setting where all
types share the same preference over outcomes, which is motivated by
applications in, e.g., strategic classification. We present a number of
algorithmic and structural results, including an efficient algorithm for
finding optimal deterministic truthful mechanisms, which also implies a faster
algorithm for finding optimal randomized truthful mechanisms via a
characterization based on convexity. We then consider a more general setting,
where the principal's cost is a function of the combination of outcomes
assigned to each type. In particular, we focus on the case where the cost
function is submodular, and give generalizations of essentially all our results
in the classical setting where the cost function is additive. Our results
provide a relatively complete picture for automated mechanism design with
partial verification.Comment: AAAI'2
Non-Excludable Bilateral Trade Between Groups
Bilateral trade is one of the most natural and important forms of economic
interaction: A seller has a single, indivisible item for sale, and a buyer is
potentially interested. The two parties typically have different, privately
known valuations for the item, and ideally, they would like to trade if the
buyer values the item more than the seller. The celebrated impossibility result
by Myerson and Satterthwaite shows that any mechanism for this setting must
violate at least one important desideratum. In this paper, we investigate a
richer paradigm of bilateral trade, with many self-interested buyers and
sellers on both sides of a single trade who cannot be excluded from the trade.
We show that this allows for more positive results. In fact, we establish a
dichotomy in the possibility of trading efficiently. If in expectation, the
buyers value the item more, we can achieve efficiency in the limit. If this is
not the case, then efficiency cannot be achieved in general. En route, we
characterize trading mechanisms that encourage truth-telling, which may be of
independent interest. We also evaluate our trading mechanisms experimentally,
and the experiments align with our theoretical results.Comment: 14 pages, 2 figures, 1 table, aaai 202
Carbonate-superstructured solid fuel cells with hydrocarbon fuels
A basic requirement for solid oxide fuel cells (SOFCs) is the sintering of electrolyte into a dense impermeable membrane to prevent the mixing of fuel and oxygen for a sufficiently high open-circuit voltage (OCV). However, herein, we demonstrate a different type of fuel cell, a carbonate-superstructured solid fuel cell (CSSFC), in which in situ generation of superstructured carbonate in the porous samarium-doped ceria layer creates a unique electrolyte with ultrahigh ionic conductivity of 0.17 S.cm21 at 550 °C. The CSSFC achieves unprecedented high OCVs (1.051 V at 500 °C and 1.041 V at 550 °C) with methane fuel. Furthermore, the CSSFC exhibits a high peak power density of 215 mW.cm22 with dry methane fuel at 550 °C, which is higher than all reported values of electrolyte-supported SOFCs. This provides a different approach for the development of efficient solid fuel cells
Capturing Complementarity in Set Functions by Going Beyond Submodularity/Subadditivity
We introduce two new "degree of complementarity" measures: supermodular width and superadditive width. Both are formulated based on natural witnesses of complementarity. We show that both measures are robust by proving that they, respectively, characterize the gap of monotone set functions from being submodular and subadditive. Thus, they define two new hierarchies over monotone set functions, which we will refer to as Supermodular Width (SMW) hierarchy and Superadditive Width (SAW) hierarchy, with foundations - i.e. level 0 of the hierarchies - resting exactly on submodular and subadditive functions, respectively.
We present a comprehensive comparative analysis of the SMW hierarchy and the Supermodular Degree (SD) hierarchy, defined by Feige and Izsak. We prove that the SMW hierarchy is strictly more expressive than the SD hierarchy: Every monotone set function of supermodular degree d has supermodular width at most d, and there exists a supermodular-width-1 function over a ground set of m elements whose supermodular degree is m-1. We show that previous results regarding approximation guarantees for welfare and constrained maximization as well as regarding the Price of Anarchy (PoA) of simple auctions can be extended without any loss from the supermodular degree to the supermodular width. We also establish almost matching information-theoretical lower bounds for these two well-studied fundamental maximization problems over set functions. The combination of these approximation and hardness results illustrate that the SMW hierarchy provides not only a natural notion of complementarity, but also an accurate characterization of "near submodularity" needed for maximization approximation. While SD and SMW hierarchies support nontrivial bounds on the PoA of simple auctions, we show that our SAW hierarchy seems to capture more intrinsic properties needed to realize the efficiency of simple auctions. So far, the SAW hierarchy provides the best dependency for the PoA of Single-bid Auction, and is nearly as competitive as the Maximum over Positive Hypergraphs (MPH) hierarchy for Simultaneous Item First Price Auction (SIA). We also provide almost tight lower bounds for the PoA of both auctions with respect to the SAW hierarchy
Nonbossy Mechanisms: Mechanism Design Robust to Secondary Goals
We study mechanism design when agents may have hidden secondary goals which
will manifest as non-trivial preferences among outcomes for which their primary
utility is the same. We show that in such cases, a mechanism is robust against
strategic manipulation if and only if it is not only incentive-compatible, but
also nonbossy -- a well-studied property in the context of matching and
allocation mechanisms. We give complete characterizations of
incentive-compatible and nonbossy mechanisms in various settings, including
auctions with single-parameter agents and public decision settings where all
agents share a common outcome. In particular, we show that in the single-item
setting, a mechanism is incentive-compatible, individually rational, and
nonbossy if and only if it is a sequential posted-price mechanism. In contrast,
we show that in more general single-parameter environments, there exist
mechanisms satisfying our characterization that significantly outperform
sequential posted-price mechanisms in terms of revenue or efficiency (sometimes
by an exponential factor)
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