707 research outputs found
Duistermaat-Heckman measure and the mixture of quantum states
In this paper, we present a general framework to solve a fundamental problem
in Random Matrix Theory (RMT), i.e., the problem of describing the joint
distribution of eigenvalues of the sum \bsA+\bsB of two independent random
Hermitian matrices \bsA and \bsB. Some considerations about the mixture of
quantum states are basically subsumed into the above mathematical problem.
Instead, we focus on deriving the spectral density of the mixture of adjoint
orbits of quantum states in terms of Duistermaat-Heckman measure, originated
from the theory of symplectic geometry. Based on this method, we can obtain the
spectral density of the mixture of independent random states. In particular, we
obtain explicit formulas for the mixture of random qubits. We also find that,
in the two-level quantum system, the average entropy of the equiprobable
mixture of random density matrices chosen from a random state ensemble
(specified in the text) increases with the number . Hence, as a physical
application, our results quantitatively explain that the quantum coherence of
the mixture monotonously decreases statistically as the number of components
in the mixture. Besides, our method may be used to investigate some
statistical properties of a special subclass of unital qubit channels.Comment: 40 pages, 10 figures, LaTeX, the final version accepted for
publication in J. Phys.
Online Influence Maximization in Non-Stationary Social Networks
Social networks have been popular platforms for information propagation. An
important use case is viral marketing: given a promotion budget, an advertiser
can choose some influential users as the seed set and provide them free or
discounted sample products; in this way, the advertiser hopes to increase the
popularity of the product in the users' friend circles by the world-of-mouth
effect, and thus maximizes the number of users that information of the
production can reach. There has been a body of literature studying the
influence maximization problem. Nevertheless, the existing studies mostly
investigate the problem on a one-off basis, assuming fixed known influence
probabilities among users, or the knowledge of the exact social network
topology. In practice, the social network topology and the influence
probabilities are typically unknown to the advertiser, which can be varying
over time, i.e., in cases of newly established, strengthened or weakened social
ties. In this paper, we focus on a dynamic non-stationary social network and
design a randomized algorithm, RSB, based on multi-armed bandit optimization,
to maximize influence propagation over time. The algorithm produces a sequence
of online decisions and calibrates its explore-exploit strategy utilizing
outcomes of previous decisions. It is rigorously proven to achieve an
upper-bounded regret in reward and applicable to large-scale social networks.
Practical effectiveness of the algorithm is evaluated using both synthetic and
real-world datasets, which demonstrates that our algorithm outperforms previous
stationary methods under non-stationary conditions.Comment: 10 pages. To appear in IEEE/ACM IWQoS 2016. Full versio
The Faster the Better? Innovation Speed and User Interest in Open Source Software
It is often believed that for open source software (OSS) projects the faster the release, the better for attracting user interest in the software. Whether this is true, however, is still open to question. There is considerable information asymmetry between OSS projects and potential users as project quality is unobservable to users. We suggest that innovation speed of OSS project can signal the unobservable project quality and attract users’ interest in downloading and using the software. We contextualize innovation speed of OSS projects as initial release speed and update speed and examine their impacts on user interest. Drawing on the signaling theory, we propose a signaling effect through which a higher initial release speed or update speed increases user interest, while the effect diminishes as initial release or update speed increases. Using a large-scale panel data set from 7442 OSS projects on SourceForge between 2007 and 2010, our results corroborate the inverted U-shaped relationships between initial release speed and user downloads and between update speed and user downloads
A Churn for the Better: Localizing Censorship using Network-level Path Churn and Network Tomography
Recent years have seen the Internet become a key vehicle for citizens around
the globe to express political opinions and organize protests. This fact has
not gone unnoticed, with countries around the world repurposing network
management tools (e.g., URL filtering products) and protocols (e.g., BGP, DNS)
for censorship. However, repurposing these products can have unintended
international impact, which we refer to as "censorship leakage". While there
have been anecdotal reports of censorship leakage, there has yet to be a
systematic study of censorship leakage at a global scale. In this paper, we
combine a global censorship measurement platform (ICLab) with a general-purpose
technique -- boolean network tomography -- to identify which AS on a network
path is performing censorship. At a high-level, our approach exploits BGP churn
to narrow down the set of potential censoring ASes by over 95%. We exactly
identify 65 censoring ASes and find that the anomalies introduced by 24 of the
65 censoring ASes have an impact on users located in regions outside the
jurisdiction of the censoring AS, resulting in the leaking of regional
censorship policies
Online Job Scheduling in Distributed Machine Learning Clusters
Nowadays large-scale distributed machine learning systems have been deployed
to support various analytics and intelligence services in IT firms. To train a
large dataset and derive the prediction/inference model, e.g., a deep neural
network, multiple workers are run in parallel to train partitions of the input
dataset, and update shared model parameters. In a shared cluster handling
multiple training jobs, a fundamental issue is how to efficiently schedule jobs
and set the number of concurrent workers to run for each job, such that server
resources are maximally utilized and model training can be completed in time.
Targeting a distributed machine learning system using the parameter server
framework, we design an online algorithm for scheduling the arriving jobs and
deciding the adjusted numbers of concurrent workers and parameter servers for
each job over its course, to maximize overall utility of all jobs, contingent
on their completion times. Our online algorithm design utilizes a primal-dual
framework coupled with efficient dual subroutines, achieving good long-term
performance guarantees with polynomial time complexity. Practical effectiveness
of the online algorithm is evaluated using trace-driven simulation and testbed
experiments, which demonstrate its outperformance as compared to commonly
adopted scheduling algorithms in today's cloud systems
Dynamic Survival Transformers for Causal Inference with Electronic Health Records
In medicine, researchers often seek to infer the effects of a given treatment
on patients' outcomes. However, the standard methods for causal survival
analysis make simplistic assumptions about the data-generating process and
cannot capture complex interactions among patient covariates. We introduce the
Dynamic Survival Transformer (DynST), a deep survival model that trains on
electronic health records (EHRs). Unlike previous transformers used in survival
analysis, DynST can make use of time-varying information to predict evolving
survival probabilities. We derive a semi-synthetic EHR dataset from MIMIC-III
to show that DynST can accurately estimate the causal effect of a treatment
intervention on restricted mean survival time (RMST). We demonstrate that DynST
achieves better predictive and causal estimation than two alternative models.Comment: Accepted to the NeurIPS 2022 Workshop on Learning from Time Series
for Healt
Sequence-Level Certainty Reduces Hallucination In Knowledge-Grounded Dialogue Generation
Model hallucination has been a crucial interest of research in Natural
Language Generation (NLG). In this work, we propose sequence-level certainty as
a common theme over hallucination in NLG, and explore the correlation between
sequence-level certainty and the level of hallucination in model responses. We
categorize sequence-level certainty into two aspects: probabilistic certainty
and semantic certainty, and reveal through experiments on Knowledge-Grounded
Dialogue Generation (KGDG) task that both a higher level of probabilistic
certainty and a higher level of semantic certainty in model responses are
significantly correlated with a lower level of hallucination. What's more, we
provide theoretical proof and analysis to show that semantic certainty is a
good estimator of probabilistic certainty, and therefore has the potential as
an alternative to probability-based certainty estimation in black-box
scenarios. Based on the observation on the relationship between certainty and
hallucination, we further propose Certainty-based Response Ranking (CRR), a
decoding-time method for mitigating hallucination in NLG. Based on our
categorization of sequence-level certainty, we propose 2 types of CRR approach:
Probabilistic CRR (P-CRR) and Semantic CRR (S-CRR). P-CRR ranks individually
sampled model responses using their arithmetic mean log-probability of the
entire sequence. S-CRR approaches certainty estimation from meaning-space, and
ranks a number of model response candidates based on their semantic certainty
level, which is estimated by the entailment-based Agreement Score (AS). Through
extensive experiments across 3 KGDG datasets, 3 decoding methods, and on 4
different models, we validate the effectiveness of our 2 proposed CRR methods
to reduce model hallucination
Die Struktur und Funktion von mimischen Emotikons in Deutschland und in China
In den letzten zwei Jahrzehnten haben sich Emotikons zu einem der effizientesten Mittel für den Ausdruck von Emotionen in geschriebenen Texten entwickelt. Besonders beliebt sind Emotikons, in denen lachende und lächelnde Gesichter dargestellt werden. Der vorliegende Beitrag analysiert die Ergebnisse einer vergleichenden Studie von chinesischen und deutschen Emotikons unter besonderer Berücksichtigung der Beziehung zwischen Zeichen und Objekten.In the last two decades emoticons have become one of the most efficient means for the expression of emotions in written texts. Especially popular are emoticons with the facial traits of laughing and smiling persons. The present article analyzes the results of a comparative study of Chinese and German emoticons with special consideration of the relation between signs and objects
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