1,638 research outputs found
Scalable Methods for Adaptively Seeding a Social Network
In recent years, social networking platforms have developed into
extraordinary channels for spreading and consuming information. Along with the
rise of such infrastructure, there is continuous progress on techniques for
spreading information effectively through influential users. In many
applications, one is restricted to select influencers from a set of users who
engaged with the topic being promoted, and due to the structure of social
networks, these users often rank low in terms of their influence potential. An
alternative approach one can consider is an adaptive method which selects users
in a manner which targets their influential neighbors. The advantage of such an
approach is that it leverages the friendship paradox in social networks: while
users are often not influential, they often know someone who is.
Despite the various complexities in such optimization problems, we show that
scalable adaptive seeding is achievable. In particular, we develop algorithms
for linear influence models with provable approximation guarantees that can be
gracefully parallelized. To show the effectiveness of our methods we collected
data from various verticals social network users follow. For each vertical, we
collected data on the users who responded to a certain post as well as their
neighbors, and applied our methods on this data. Our experiments show that
adaptive seeding is scalable, and importantly, that it obtains dramatic
improvements over standard approaches of information dissemination.Comment: Full version of the paper appearing in WWW 201
Online Admission Control and Embedding of Service Chains
The virtualization and softwarization of modern computer networks enables the
definition and fast deployment of novel network services called service chains:
sequences of virtualized network functions (e.g., firewalls, caches, traffic
optimizers) through which traffic is routed between source and destination.
This paper attends to the problem of admitting and embedding a maximum number
of service chains, i.e., a maximum number of source-destination pairs which are
routed via a sequence of to-be-allocated, capacitated network functions. We
consider an Online variant of this maximum Service Chain Embedding Problem,
short OSCEP, where requests arrive over time, in a worst-case manner. Our main
contribution is a deterministic O(log L)-competitive online algorithm, under
the assumption that capacities are at least logarithmic in L. We show that this
is asymptotically optimal within the class of deterministic and randomized
online algorithms. We also explore lower bounds for offline approximation
algorithms, and prove that the offline problem is APX-hard for unit capacities
and small L > 2, and even Poly-APX-hard in general, when there is no bound on
L. These approximation lower bounds may be of independent interest, as they
also extend to other problems such as Virtual Circuit Routing. Finally, we
present an exact algorithm based on 0-1 programming, implying that the general
offline SCEP is in NP and by the above hardness results it is NP-complete for
constant L.Comment: early version of SIROCCO 2015 pape
Root and tuber crops in Central Vietnam: an underestimated potential for food and income? Results of a scoping study.
Experimental observation of exceptional points in coupled pendulums
The concept of exceptional point (EP) is demonstrated experimentally in the
case of a simple mechanical system consisting of two coupled pendulums.
Exceptional points correspond to specific values of the system parameters that
yield defective eigenvalues. These spectral singularities which are typical of
non-Hermitian system means that both the eigenvalues and their associated
eigenvectors coalesce. The existence of an EP requires an adequate
parameterization of the dynamical system. For this aim, the experimental device
has been designed with two controllable parameters which are the length of one
pendulum and a viscous-like damping which is produced via electromagnetic
induction. Thanks to the observation of the free response of the coupled
pendulums, most EP properties are experimentally investigated, showing good
agreements with theoretical considerations. In contrast with many studies on
EPs, mainly in the field of physics, the novelty of the present work is that
controllable parameters are restricted to be real-valued, and this requires the
use of adequate search algorithms. Furthermore, it offers the possibility of
exploiting the existence of EPs in time-domain dynamic problems
Concurrent bandits and cognitive radio networks
We consider the problem of multiple users targeting the arms of a single
multi-armed stochastic bandit. The motivation for this problem comes from
cognitive radio networks, where selfish users need to coexist without any side
communication between them, implicit cooperation or common control. Even the
number of users may be unknown and can vary as users join or leave the network.
We propose an algorithm that combines an -greedy learning rule with a
collision avoidance mechanism. We analyze its regret with respect to the
system-wide optimum and show that sub-linear regret can be obtained in this
setting. Experiments show dramatic improvement compared to other algorithms for
this setting
Game-theoretic analysis of pay-as-bid mechanisms
Enterprises are facing a challenging dilemma. In order to be able to accommodate peak loads on their IT systems, they must maintain large computing clusters, which lie idle most of the time. At the same time, IT departments are under constant pressure to cut down on hard- and software expenses. Grid technology offers a promising way out of this dilemma by allowing the dynamic sharing both within enterprises as well as across organizational boundaries. This sharing approach, however, requires proper economic incentives. This paper is concerned with the determination of dynamic market-based prices. Due to their simplicity, so-called pay-as-bid mechanisms have become popular. This paper is novel as we provide an in-depth analysis of two such pay-as-bid mechanisms – Proportional Share and a discriminatory pay-as-bid mechanism – for the case of three users, thus extending previous work by Sanghavi and Hajek (2004) and Stößer et al. (2008). This analysis is important as we show that the nice results for two users cannot be retained once three or more users are present. Even worse, we show that these results can even be reversed if we move to games with more than two players
Pseudorandomness for Regular Branching Programs via Fourier Analysis
We present an explicit pseudorandom generator for oblivious, read-once,
permutation branching programs of constant width that can read their input bits
in any order. The seed length is , where is the length of the
branching program. The previous best seed length known for this model was
, which follows as a special case of a generator due to
Impagliazzo, Meka, and Zuckerman (FOCS 2012) (which gives a seed length of
for arbitrary branching programs of size ). Our techniques
also give seed length for general oblivious, read-once branching
programs of width , which is incomparable to the results of
Impagliazzo et al.Our pseudorandom generator is similar to the one used by
Gopalan et al. (FOCS 2012) for read-once CNFs, but the analysis is quite
different; ours is based on Fourier analysis of branching programs. In
particular, we show that an oblivious, read-once, regular branching program of
width has Fourier mass at most at level , independent of the
length of the program.Comment: RANDOM 201
Exploring Molecular Simulations of a Plausible Prebiotic Reduced Phospholipid Using Hyperchem Software
How the first cells emerged from the primordial milieu is one of the great questions in science. Biomolecular emergence scenarios abound in the literature, but the lack of bioaccessible phosphate and molecular oxygen on the primordial Earth has posed formidable challenges for deducing emergence pathways. One idea gaining wide acceptance invokes delivery of the phosphide mineral schreibersite ((Fe,Ni)3P) to Earth via meteorite impacts ca. 4.2 billion years ago, whereupon they were corroded to reduced phosphorous oxyacids and phosphonates in primordial aquatic environments. We previously proposed that these reduced phosphorus forms could readily combine with putative geochemical species in shallow mineral-rich alkaline hydrothermal systems to form reduced phospholipid analogs of contemporary phosphate-based phospholipids (Fitch, N.W., K.L. Even, L.J. Leinen and M.O. Gaylor. 2016. Plausible prebiotic assembly of a primitive reduced phospholipid from meteoritic phosphorus on the primordial earth. Proceedings of the South Dakota Academy of. Science 95:176.). Lacking resources to empirically validate this idea, we explored “water box” simulations of the proposed phospholipid structure using the HyperChem software package. Simulation results showed the hydrophobic tails migrating away from water molecules, while hydrophilic heads migrated towards them, resulting in quasistacking behaviors consistent with those of known amphiphiles in water. Inspired by these results, we are now investigating more complex primordial simulation scenarios
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